The previously reported Ni(II) complex, Tp*Ni(?(3)-BH(4)) (Tp* = hydrotris(3,5-dimethylpyrazolyl)borate anion), which has an S = 1 spin ground state, was studied by high-frequency and -field electron paramagnetic resonance (HFEPR) spectroscopy as a solid powder at low temperature, by UV-vis-NIR spectroscopy in the solid state and in solution at room temperature, and by paramagnetic (11)B NMR. HFEPR provided its spin Hamiltonian parameters: D = 1.91(1) cm(-1), E = 0.285(8) cm(-1), g = [2.170(4), 2.161(3), 2.133(3)]. Similar, but not identical parameters were obtained for its borodeuteride analogue. The previously unreported complex, Tp*Zn(?(2)-BH(4)), was prepared, and IR and NMR spectroscopy allowed its comparison with analogous closed shell borohydride complexes. Ligand-field theory was used to model the electronic transitions in the Ni(II) complex successfully, although it was less successful at reproducing the zero-field splitting (zfs) parameters. Advanced computational methods, both density functional theory (DFT) and ab initio wave function based approaches, were applied to these Tp*MBH(4) complexes to better understand the interaction between these metals and borohydride ion. DFT successfully reproduced bonding geometries and vibrational behavior of the complexes, although it was less successful for the spin Hamiltonian parameters of the open shell Ni(II) complex. These were instead best described using ab initio methods. The origin of the zfs in Tp*Ni(?(3)-BH(4)) is described and shows that the relatively small magnitude of D results from several spin-orbit coupling (SOC) interactions of large magnitude, but with opposite sign. Spin-spin coupling (SSC) is also shown to be significant, a point that is not always appreciated in transition metal complexes. Overall, a picture of bonding and electronic structure in open and closed shell late transition metal borohydrides is provided, which has implications for the use of these complexes in catalysis and hydrogen storage. PMID:22335547

In the present work, we report on the modeling of the crystal field parameters (CFP) and spin-Hamiltonian parameters of ?-Zn2SiO4:Mn2+. The calculated CFP values were used for diagonalization of the manganese ion Hamiltonian in a complete basis set spanned by the all wave functions of the LS terms of the 3d5 electronic configuration. The scheme of the energy levels was obtained. The spin-Hamiltonian parameters of the ground state of manganese ion in willemite are theoretically evaluated using ab initio method for gx, gy, gz parameters. The theoretically obtained results are compared with the optical-spectral and electronic paramagnetic resonance experimental data (from literature) and a satisfactory agreement was obtained.

The spin-Hamiltonian parameters (g factor g//, g and hyperfine structure constants A//, A ) of the trigonal U^5^+ center in CaF2 crystal have been calculated from the complete diagonalization (of energy matrix) method (CDM) for 5f^1 ions in trigonal crystal field and under an external magnetic field. In the calculation, the crystal-field parameters are estimated from the superposition model. From the calculations, these spin-Hamiltonian parameters are reasonably explained, and the defect model (i.e., the trigonal U^5^+ center is attributed to U^5^+ substituting for Ca^2^+ in CaF2 with six F^- ions replaced by O^2^- and the other two F^- sites vacant because of charge compensation) given in the previous paper is confirmed. The results are discussed.

The spin Hamiltonian separation (SHS) method is employed to investigate the local environment around the orthorhombic Fe3+ centers in TlGaS2 single crystal. In this analysis, we employ the spin-Hamiltonian parameters measured by electron paramagnetic resonance (EPR) at 15 K and room temperature. On the basis of the SHS analysis and the comparison with the experimental values at 15 K and room temperature, some anomalies have been found in the ratios of the zero-field splitting (ZFS) parameters (ZFSPs) Formula Not Shown to the separated parameters B 2a(1). Such anomalies may be attributed to the effects of the nearby Tl ions located on the cavities among the GaS4 tetrahedrons.

The electron paramagnetic resonance spectrum of trigonal Fe sup 3 sup + centres has been investigated and parameters of the spin Hamiltonian obtained for nominally pure congruent LiTaO sub 3 crystals annealed at approx 1500 K under Li sub 2 O vapour pressure corresponding to the pressure over the stoichiometric lithium tantalate. The possibility of calculating the zero-field splitting of the ground state of the impurity ion on the basis of the superposition model is discussed.

The four optical band positions and six spin-Hamiltonian parameters (the g factors gi and the hyperfine structure constants Ai, i=x, y, z) for the rhombic Cu2+ center in ?-Ca3(PO4)2 are calculated by two theoretical methods: the complete diagonalization (of energy matrix) method and the perturbation theory method (PTM). Both methods are based on the cluster approach, in which the covalence due to admixture of ligands to the central metal ion is considered. The calculated results of the two methods are close to each other and agree with the experimental values. This suggests that both methods are effective in explaining the optical and electron paramagnetic resonance data for d9 ions in crystals. The calculations also show that although the admixture of |dz2rang to the ground state wave function is small, it should not be neglected in calculations of spin-Hamiltonian parameters. So, in PTM, the high-order perturbation formulae of spin-Hamiltonian parameters based on the cluster approach for d9 ion in rhombic symmetry should be derived by taking into account the admixture of the |dz2rang state to the |dx2-y2rang ground state.

Electron paramagnetic resonance (EPR) of Fe sup 3 sup + ions in Al sub 2 O sub 3 is studied in powder samples prepared by different routes and/or modified by thermal or mechanical treatments, with different doping levels and grain sizes. The measurements are performed in various frequency bands (S, X, K, Q and W) and with bimodal detection in X-band. Simulations of the spectra are achieved with a code designed for computing EPR powder spectra described by any spin Hamiltonian including second-, fourth-and sixth-order ZFS terms (S <= 7/2). The linewidths, intensities and lineshapes are accounted for. The lineshape is Gaussian at low Fe sup 3 sup + concentration whereas it is Lorentzian for higher concentration. The linewidths are interpreted as the superimposition of three main contributions: intrinsic linewidth, dipolar broadening and broadening due to lattice imperfections. The latter is tentatively interpreted in terms of quadrupolar spin Hamiltonian parameter distributions treated using first-order pert...

The triphosphanes RMe(2)SiCH(2)P(PR'(2))(2) (R = Me, Ph; R' = SiMe(3), Cy) are synthesised in good yield via metathesis of organodichlorophosphanes and LiPR'(2), while for R' = Ph a propensity to form (Ph(2)P)(2) precludes isolation of the in situ characterised triphosphanes. Where R = Me and R' = SiMe(3) the triphosphane has also been characterised by single crystal X-ray diffraction and exhibits a single geometric conformer in the solid state, though solution-phase NMR spectra are indicative of facile conformational exchange across a wide temperature range. All of the described triphosphanes exhibit comparable behaviour, with their respective (31)P{(1)H} NMR spectra manifesting anomalous 'second-order' characteristics, which are considered using full spin-Hamiltonian simulation. Preliminary studies of coordination chemistry and ancillary reactivity of the triphosphanes are described. PMID:22072299

Single-crystal and powder EPR studies of VO2+-doped lithium hydroxylammonium sulphate (LiNH3OHSO4) were carried out at room temperature. The results indicate the presence of two magnetically inequivalent VO2+ sites. The VO2+ ion takes up a substitutional position in the host lattice. The angular variation of EPR spectra in three mutually perpendicular planes were used to determine the spin Hamiltonian parameters, and the values obtained were the following: For Site 1, gx = 2.0249 ± 0.0002, gy = 1.9698 ± 0.0002, gz = 1.9552 ± 0.0002, Ax = (51 ± 2) × 10-4 cm-1, Ay = (93 ± 2) × 10-4 cm-1, and Az = (165 ± 2...

The magnetic susceptibility, and low-temperature magnetization curve, of the [3 x 3] grid [Mn(III)4Mn(II)5(2poap-2H)6](ClO4)10.10H2O is analyzed within a spin Hamiltonian approach. The Hilbert space is huge (4,860,000 states), but the consequent use of all symmetries and a two-step fitting procedure nevertheless allows the best-fit determination of the magnetic exchange parameters in this system from complete quantum mechanical calculations. The cluster exhibits a total spin S = 1/2 ground state; the implications are discussed.

Two theoretical methods, the perturbation theory method (PTM) and the complete diagonalization (of energy matrix) method (CDM), are applied to calculate the spin-Hamiltonian parameters (g-factors g{sub ||} , g{sub perpendicular} and hyperfine structure constants A{sub ||} , A{sub perpendicular} , obtained from electron paramagnetic resonance (EPR) spectra) and d-d transitions (obtained from optical spectra) for two tetragonal Cu{sup 2+} centers in Ba{sub 2}ZnF{sub 6}:Cu{sup 2+} crystals. The Cu{sup 2+}(I) ion replaces the Zn{sup 2+} ion at tetragonally compressed octahedral coordination and has the ground state {sup 2}A{sub 1}(|d{sub z}{sup 2}>), whereas the Cu{sup 2+}(II) ion is at an interstitial site with a square-planar F{sup -}coordination and has the ground state {sup 2}B{sub 2}(|d{sub x}{sup 2}{sub -y}{sup 2}>). The calculated spin-Hamiltonian parameters and d-d transitions from the PTM and CDM coincide and are in reasonable agreement with the experimental values. This suggests that both methods are effective for the theoretical studies of EPR and optical spectral data for 3d{sup 9} ions in tetragonal symmetry with different ground states. The defect structures of the two Cu{sup 2+} centers in Ba{sub 2}ZnF{sub 6}:Cu{sup 2+} are also estimated.

Double electron electron resonance (DEER) spectroscopy has been established as a valuable method to determine distances between spin labels bound to protein molecules. Caused by selective excitation of molecular orientations DEER primary data also depend on the mutual orientation of the spin labels. For a doubly spin labeled variant of the cytoskeletal protein vinculin tail strong orientation selection can be observed already at X-band frequencies, which allows us to reduce the problem to the relative orientation of two molecular axes and the spin-spin axis parameterized by three angles. A full grid search of parameter space reveals that the DEER experiment introduces parameter-space symmetry higher than the symmetry of the spin Hamiltonian. Thus, the number of equivalent parameter sets is...

The ESR study of the Cu^2^+ doped zinc glutamate dihydrate is carried out at room temperature. Two magnetically nonequivalent sites for Cu^2^+ are observed. The spin Hamiltonian parameters are determined with the fitting of spectra to rhombic symmetry crystalline field. The parameters are as follows: Cu^2^+(I): gx=2.0170+/-0.0002, gy=2.0768+/-0.0002, gz=2.2334+/-0.0002, Ax=(74+/-2)x10^-^4, Ay=(99+/-2)x10^-^4, Az=(134+/-2)x10^-^4cm^-^1and Cu^2^+(II): gx=2.0180+/-0.0002, gy=2.0550+/-0.0002, gz=2.1633+/-0.0002, Ax=(100+/-2)x10^-^4, Ay=(100+/-2)x10^-^4, Az=(115+/-2)x10^-^4cm^-^1. The ground state wave function is also determined. The g-anisotropy is evaluated and compared with the experimental value. Using the data of optical absorption study undertaken at room temperature the nature of bondin...

EPR measurements at X-band were performed in the temperature range 4.2-300K with angular dependence measurements at 77K for Cu2+ in KZnClSO43H2O. Rigid lattice spin - Hamiltonian parameters are: gz=2.4247, gy=2.0331, gx=2.1535, Az=-103x10-4cm-1, 63x10-4cm-1, and -31x10-4cm-1. The parameters were analyzed using MO-theory with the Formula Not Shown ground state containing admixture of the Formula Not Shown -state in the rhombic symmetry D2h. The analysis consistently explained unusual g-factor sequence and relatively small hyperfine splitting anisotropy as the consequence of the mixing and spin density delocalization via excited orbital states. We assigned that Cu2+ ions substituting host Zn2+ prefer one of the four structurally different zinc sites where they are coordinated by four water m...

Single crystal EPR studies of Cu(II) incorporated in magnesium rubidium sulphate hexahydrate are carried out at RT and 77 K. Since the hyperfine lines are not resolved at RT, single crystal rotations have been carried out at 77 K. The spin Hamiltonian parameters calculated from the 77 K spectra are: g11=2.133, g22=2.137, g33=2.327, A11=0.01, A22=1.44 and A33=10.80mT. The impurity ion occupies an interstitial position in this crystal lattice, which is not very common for copper ion. In addition, the low hyperfine coupling constant is explained by considering an admixture of dx-y ground state with dz excited state. Bonding parameters, ?=0.254, P=282.7×10cm, ?=0.706, ?=0.8406 have also been calculated. The present study has helped to understand the static nature of JT, for which the present system is an example.

Electron paramagnetic resonance (EPR) studies are carried out on vanadyl (VO{sup 2+}) ions in diammonium tricadmium tetrakis (sulfate) pentahydrate single crystals at room temperature. The EPR spectra of a single crystal exhibit resonance signals characteristic to VO{sup 2+} ions. The analysis of EPR spectra indicates that the VO{sup 2+} ions in single crystals show two magnetically inequivalent VO{sup 2+} sites in distinct orientations occupying substitutional positions in the lattice and showing very high angular dependence. They form in octahedral coordination with tetragonal compression with C{sub 4v} symmetry. The spin Hamiltonian parameters are determined, and these parameters have been used to estimate the bonding coefficients of the VO{sup 2+} ion in a diammonium tricadmium tetrakis (sulfate) pentahydrate lattice. The parallel and perpendicular components of axially symmetric g and hyperfine (A) tensors are evaluated and the results are discussed and compared with previous reports. (orig.)

Electron Paramagnetic Resonance (EPR) and optical absorption spectra of Cu2+ ions in sodium–lead borophosphate glasses doped with different concentrations of Cu2+ ions have been studied. EPR spectra of all the glass samples exhibit resonance signals characteristic of Cu2+ ions. The values of spin-Hamiltonian parameters indicate that the Cu2+ ions in sodium–lead borophosphate glasses are present in octahedral sites with tetragonal distortion. The optical absorption spectra of all the glass samples show a single broad band, which has been assigned to the 2B1g?2B2g transition of Cu2+ ions. The optical band gap energy (Eopt) and Urbach energy (?E) are calculated from their ultraviolet absorption edges. The emission bands o...

EPR studies of VO^2^+ doped diglycine calcium chloride tetrahydrate (DGCCT) single crystals are done at room temperature. The results indicate that the paramagnetic impurity takes up a substitutional site in the lattice. The spin Hamiltonian parameters are evaluated using the data of angular variation of EPR spectra in three mutually perpendicular planes and the values are: gx=1.9976+/-0.0002, gy=1.9631+/-0.0002, gz=1.9336+/-0.0002, Ax=(59+/-2)x10^-^4cm^-^1, Ay=(81+/-2)x10^-^4cm^-^1 and Az=(185+/-2)x10^-^4cm^-^1 for Site I and gx=1.9969+/-0.0002, gy=1.9689+/-0.0002, gz=1.9306+/-0.0002, Ax=(49+/-2)x10^-^4cm^-^1, Ay=(83+/-2)x10^-^4cm^-^1 and Az=(175+/-2)x10^-^4cm^-^1 for Site II. The optical absorption study is also done at room temperature. The analysis of the spectrum indicates that the fi...

An effective intra- and inter-ladder charge-spin hamiltonian for the quarter-filled ladder compound $\\alpha'$-NaV$_2$O$_5$ has been derived by using the standard canonical transformation method. In the derivation, it is clear that a finite inter-site Coulomb repulsion is needed to get a meaningful result otherwise the perturbation becomes ill-defined. Various limiting cases depending on the values of the model parameters have been analyzed in detail and the effective exchange couplings are estimated. We find that the effective intra-ladder exchange may become ferromagnetic for the case of zig-zag charge ordering in a purely electronic model. We estimate the magnitude of the effective inter-rung Coulomb repulsion in a ladder and find it to be about one-order of magnitude too small in order to stabilize charge-ordering.

A series of imidazolate-bridged trinuclear complexes [Cu(A)M(hfac)2Cu(A)] (M = Zn2+, Cu2+, Ni2+, Co2+, Mn2+) have been prepared, where H2A = 4-(6-methyl-8-hydroxy-2,5-diazanonane-1,5,7-trienyl)imidazole and Hhfac = hexafluoroacetylacetone. The magnetic susceptibility data (4.2–300 K) were well reproduced by the equation based on the spin-Hamiltonian H = ?2JCuM (SCu1·SM+SM·SCu2) to give the coupling parameters of JCuCu = ?52.5 cm?1 (SCu = 1?2), JCuNi = ?20.3 cm?1 (SNi = 1), JCuCo = ?13.2 cm?1 (SCo = 3?2), and JCuMn = ?4.5 cm?1 (SMn = 5?2).   

Single crystal EPR studies on Cu(II) doped Diaquamalonatozinc(II) are carried out at room temperature to identify the local structure of the host ion. Angular variation of copper hyperfine lines in the three orthogonal planes shows the presence of a single site in an interstitial position and the location has been identified. The spin-Hamiltonian parameters calculated from the spectra are: g11 = 2.077, g22 = 2.087, g33 = 2.442; A11 = 1.83, A22 = 2.88; A33 = 14.74 mT. A slightly lower parallel value noticed for copper nucleus has been explained by considering a small admixture of ground state with the excited state. The optical, infra-red and EPR data have been collaborated to obtain various admixture and molecular orbital coefficients.

By considering distance-regular graphs as spin networks, first we introduce some particular spin Hamiltonians which are extended version of those of Refs.\\cite{8,9''}. Then, by using spectral analysis techniques and algebraic combinatoric structure of distance-regular graphs such as stratification introduced in \\cite{obata, js} and Bose-Mesner algebra, we give a method for finding a set of coupling constants in the Hamiltonians so that a particular state initially encoded on one site of a network will evolve freely to the opposite site without any dynamical controls, i.e., we show that how to derive the parameters of the system so that perfect state transfer (PST) can be achieved. As examples, the cycle networks with even number of vertices and $d$-dimensional hypercube networks are considered in details and the method is applied for some important distance-regular networks in appendix.

The long-wavelength spin waves in Rb2CrCl4, a nearly two-dimensional ferromagnet, have been investigated at several temperatures below Tc=52.4K using neutron inelastic scattering techniques. The data have been analysed in terms of a Hartree-Fock theory using matching-matrix elements to give correctly the effects of anisotropy. Values for the parameters in the spin Hamiltonian have been found, and the theory accounts well for the energy renormalisation of the spin waves and for the transition temperature and variation of magnetic moment with temperature. Due to weak uniaxial anisotropy terms the spin wave spectrum has a small energy gap of approximately=1K at zero wavevector, which precludes true XY-type behaviour, and a canting of the spins of +or-1.1 degrees from (110) directions is predicted.

We performed high resolution diffraction and inelastic neutron scattering measurements of Mn_{12}-acetate. Using a very high energy resolution, we could separate the energy levels corresponding to the splitting of the lowest S multiplet. Data were analyzed within a single spin model (S=10 ground state), using a spin Hamiltonian with parameters up to 4^{th} order. The non regular spacing of the transition energies unambiguously shows the presence of high order terms in the anisotropy (D= -0.457(2) cm^{-1}, B_4^0 = -2.33(4) 10^{-5}cm^{-1}). The relative intensity of the lowest energy peaks is very sensitive to the small transverse term, supposed to be mainly responsible for quantum tunneling. This allows an accurate determination of this term in zero magnetic field (B_4^4 = \\pm 3.0(5) 10^{-5} cm^{-1}). The neutron results are discussed in view of recent experiments and theories.

We report continuous-wave electron-paramagnetic-resonance (EPR) spectra of the high-spin FeII complex Fe[(SPPh2)2N]2 at 275.7GHz, 94.1GHz and 9.5GHz. Combined analysis of these EPR spectra shows that the complex occurs in multiple conformations. For two main conformations the spin-Hamiltonian parameters, which reflect the electronic structure of the complex, are accurately determined: (1) Formula Not Shown (275GHz), Formula Not Shown and (2) Formula Not Shown (266GHz), Formula Not Shown . The EPR spectra obtained at 275.7GHz on single crystals of the complex are essential for the analysis and in addition they reveal that the two main conformations occur at two magnetically distinguishable sites.

Single-crystal electron paramagnetic resonance (EPR) spectra of a gem-quality jeremejevite, Al6B5O15(F, OH)3, from Cape Cross, Namibia, reveal an S?=?1/2 hole center characterized by an 27Al hyperfine structure arising from interaction with two equivalent Al nuclei. Spin-Hamiltonian parameters obtained from single-crystal EPR spectra at 295?K are as follows: g 1?=?2.02899(1), g 2?=?2.02011(2), g 3?=?2.00595(1); A 1/g e ? e ?=??0.881(1)?mT, A 2/g e ? e ?=??0.951(1)?mT, and A 3/g e ? e ?=??0.972(2)?mT, with the orientations of the g 3- and A 3-axes almost coaxial and perpendicular to the Al?O?Al plane; and those of the g 1- and A 1-axes approximately along the Al?Al and Al?OH directions, respectively. These results suggest that this aluminum-associated hole center represents hole trapping on...

The mineral monazite, a mixed lanthanide orthophosphate LnPO/sub 4/, is considered as a perfect host for geologic disposal of actinides, rare earths, and possibly other elements formed during nuclear-reactor operation. Synthetic monazite-type orthophosphates of all the elements of the first half of the lanthanide series (except Pm) have been prepared: single crystals were grown using a flux technique, and powders were precipitated in molten urea. The electron paramagnetic resonance (EPR) spectra of intentionally added Gd impurities show that the Gd/sup 3 +/ ions occupy predominantly substitutional rare-earth sites in both the flux-grown single crystals and the precipitated powders. Though these sites have a very low (triclinic C/sub 1/) symmetry, the spectra were successfully interpreted using an orthorhombic spin Hamiltonian. It has been found that, while the main spin-Hamiltonian parameter b/sup 0//sub 2/ is almost constant when going from the LaPO/sub 4/ to the EuPO/sub 4/ host (b/sup 0//sub 2/approx. =+830 x 10/sup -4/ cm/sup -1/), the parameter b/sup 2//sub 2/ decreases monotonically from +373 x 10/sup -4/ to +283 x 10/sup -4/ cm/sup -1/, respectively. The complete analysis (i.e., angular variations of the EPR lines and position of the principal electric-field axes relative to the crystallographic axes) of the EPR single-crystal spectra has been done for the two diamagnetic hosts LaPO/sub 4/ and EuPO/sub 4/, where the observed EPR lines are the sharpest. It is shown, in particular, that the two magnetically inequivalent EPR spectra (i.e., 14 lines) observed for the monazite-type single crystals are in fact equivalent when the magnetic field is applied parallel or perpendicular to the b axis of the monoclinic structure (i.e., for these directions, only seven degenerate lines are observed). These results are in perfect agreement with the description of the monazite structure.

A combined Monte Carlo-molecular dynamics simulation technique is used to study the dynamic structure factor on a square lattice for isotropic Heisenberg and planar classical ferromagnetic spin Hamiltonians.

The spin-Hamiltonian (SH) parameters (g -factors g {sub parallel}, g {sub perpendicular} {sub to} and hyperfine structure constants A {sub parallel}, A {sub perpendicular} {sub to}) of the tetragonal Cu(H{sub 2}O){sub 6}{sup 2+} centres (which are caused by the static Jahn-Teller effect) in trigonal ZnMF{sub 6}.6H{sub 2}O (M=Si,Ti,Zr) crystals are calculated from two theoretical methods, the perturbation theory method (PTM) and the complete diagonalization (of energy matrix) method (CDM). In the calculations, the required crystal-field parameters are estimated from the superposition model which enables correlation of the crystal-field parameters and hence the SH parameters with the tetragonal distortion (characterized by {delta}R=R {sub parallel} -R {sub perpendicular} {sub to}, where R {sub parallel} and R {sub perpendicular} {sub to} denote the metal-ligand distances parallel with and perpendicular to the tetragonal axis) of Cu(H{sub 2}O){sub 6}{sup 2+} centres. The calculated SH parameters from both methods are in reasonable agreement with the experimental values, suggesting that both PTM and CDM can explain satisfactorily the SH parameters of 3d{sup 9} ions in crystals. The tetragonal distortion of the Cu(H{sub 2}O){sub 6}{sup 2+} centres in ZnMF{sub 6}.6H{sub 2}O crystals are also obtained from the calculations. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

The spin-Hamiltonian (SH) parameters, g factors g{sub ||}, g{sub perpendicular} and zero-field splitting D, for Pd{sup 2+} (4d{sup 8}) ions in trigonal sites of CsMgCl{sub 3} crystals are calculated from the complete diagonalization (of energy matrix) method (CDM) and the perturbation theory method (PTM). The results from both CDM and PTM are not only close to each other, but also in agreement with the experimental values. The very small trigonal distortion of Pd{sup 2+} impurity center in CsMgCl{sub 3} crystal is acquired from the calculation. The reasons that the small differences between the calculated SH parameters, particularly, the zero-field splitting D, from PTM and CDM are discussed. On the basis of this, the PTM can be used for approximate estimations of SH parameters for Pd{sup 2+} (4d{sup 8}) centers in crystals with same trigonal distortion. However, it is unadvisable in the studies of SH parameters for 5d{sup 8} Pt{sup 2+} and Au{sup 3+} centers in crystals even with small trigonal distortion because of the very large spin-orbit coupling parameters {zeta}{sub 0} ({approx}4626 and 5640 cm{sup -1} for Pt{sup 2+} and Au{sup 3+}, respectively)

The Ni(II) sites of urease (from Klebsiella aerogenes and jack bean), coenzyme F[sub 430] (from Methanobacterium thermoautotrophicum), and several model compounds having octahedral symmetry have been studied using the saturation megnetization technique. Data were collected at four fixed fields over the temperature range from 2 - 200K. Theoretical curves calculated from the spin Hamiltonian were used to fit the experimentally obtained magnetization curves. The following parameters were determined: the spine state (S), the amount of the sample in this spin state ([S]), the gyromagnetic ratio (g), and the zero field splitting parameters (D, E/D). The amount of S=1 paramagnetism of the Ni(II) sites was found to depend on the pH of the buffer and on the concentration of the protein in D[sub 2]O (for coenzyme F[sub 430]). The relationship of the strength of the ligand field to the zero field splitting parameter was studied for the model compounds. There was no evidence for exchange coupling between the two Ni(II) ions at the active sites of either plant or bacterial urease.

Double electron electron resonance (DEER) spectroscopy has been established as a valuable method to determine distances between spin labels bound to protein molecules. Caused by selective excitation of molecular orientations DEER primary data also depend on the mutual orientation of the spin labels. For a doubly spin labeled variant of the cytoskeletal protein vinculin tail strong orientation selection can be observed already at X-band frequencies, which allows us to reduce the problem to the relative orientation of two molecular axes and the spin-spin axis parameterized by three angles. A full grid search of parameter space reveals that the DEER experiment introduces parameter-space symmetry higher than the symmetry of the spin Hamiltonian. Thus, the number of equivalent parameter sets is twice as large as expected and the relative orientation of the two spin labels is ambiguous. Except for this inherent ambiguity the most probable relative orientation of the two spin labels can be determined with good confidence and moderate uncertainty by global fitting of a set of five DEER experiments at different offsets between pump and observer frequency. The experiment provides restraints on the angles between the z axis of the nitroxide molecular frame and the spin-spin vector and on the dihedral between the two z axes. When using the same type of label at both sites, assignment of the angle restraints is ambiguous and the sign of the dihedral restraint is also ambiguous.

EPR study of the Cr3+ ion doped l-histidine hydrochloride monohydrate single crystal is done at room temperature. Two magnetically inequivalent interstitial sites are observed. The hyperfine structure for Cr53 isotope is also obtained. The zero field and spin Hamiltonian parameters are evaluated from the resonance lines obtained at different angular rotations and the parameters are: D=(300?2)?10?4 cm?1, E=(96?2)?10?4 cm?1, gx=1.9108?0.0002, gy=1.9791?0.0002, gz=2.0389?0.0002, Ax=(252?2)?10?4 cm?1, Ay=(254?2)?10?4 cm?1, Az=(304?2)?10?4 cm?1 for site I and D=(300?2)?10?4 cm?1, E=(96?2)?10?4 cm?1, gx=1.8543?0.0002, gy=1.9897?0.0002, gz=2.0793?0.0002, Ax=(251?2)?10?4 cm?1, Ay=(257?2)?10?4 cm?1, Az=(309?2)?10?4 cm?1 for site II, respectively. The optical absorption studies of single crystals ar...

The spin Hamiltonian parameters (zero-field splitting D, g factors and hyperfine structure constants) and local structure as well as their concentration dependences for Cd1-xMnxS quantum dots are theoretically investigated from the perturbation formulae of these parameters for a 3d5 ion under trigonally distorted tetrahedra. The impurity Mn2+ is found not to occupy exactly the host Cd2+ site in the CdS quantum dots but to experience an inward displacement 0.041 Å towards the ligand triangle along the C3-axis because of the size mismatching substitution and the internal stress. As compared with bulk CdS:Mn2+, the larger impurity displacement and stronger Mn2+ 3d-3s orbital admixture in the Cd1-xMnxS quantum dots suitably account for the higher zero-field splitting and hyperfine structure constant, respectively. The impurity axial displacement and the Mn2+ 3d-3s orbital admixture in the Cd1-xMnxS quantum dots may exhibit an approximately cubic increase with increasing the Mn concentration x from 0.001 to 0.15.

In this work the four-centre Jahn-Teller effect and its influence on the structure and magnetic properties of Cu4OX6L4 copper tetraclusters is investigated. The resulting adiabatic potential in the subspace of E vibrations is qualitatively similar in shape to the E-e problem. In the strong Jahn-Teller coupling limit, when the splitting of the degenerate electronic states of the Cu2+ ions is large enough, the Heisenberg spin hamiltonian is valid for the exchange interaction. The spin energy spectrum is determined, taking account of nuclear dynamics, and the temperature dependence of the effective magnetic moment ?eff is evaluated. The exchange and vibronic parameter values, producing different types of dependencies ?eff(T), including the anomalous, non-monotonic one, are discussed. The effect of the spin-orbit interaction on the temperature dependence of the ?eff values is determined. For a number of copper tetraclusters, good agreement is obtained between the theoretical curves ?eff(T), resulting from the vibronic model in the strong Jahn-Teller coupling case, with the experimental data. It is shown that the X-ray, E.P.R. and ?eff(T) experimental data for Cu4OCl6(TPPO)4 tetraclusters can be understood within the above vibronic approach with a given relation between the crystal field, tunnelling and exchange parameters.

Electron paramagnetic resonance (EPR) and optical studies of VO2+ ions in zinc ammonium phosphate hexahydrate ZnNH4PO4·6H2O (ZAPH) single crystals were carried out at room temperature. Analysis of EPR spectra indicates the presence of two distinct VO2+ sites. The angular variations of EPR spectra in three mutually perpendicular planes ab, bc and ca are used to determine the principal axes and values of the tensors g and A. The spin Hamiltonian (SH) parameters are obtained using Schonland's method as: gx = 1.9967, gy = 1.9767, gz = 1.9668, Ax = 62, Ay = 70, Az = 172(×10?4) cm?1 for site I, whereas gx = 1.9998, gy = 1.9820, gz = 1.9698, Ax = 54, Ay = 60, Az = 149(×10?4) cm?1 for site II. The optical absorption study at room temperature is also carried out and the absorption bands are assigned to various transitions. The theoretical band positions are calculated using approximate energy expressions. Good agreement is obtained between theoretical and experimental band positions. By correlating EPR and optical data, various molecular orbital coefficients of the vanadyl ion in the ZAPH lattice are evaluated and the nature of bonding in the crystal is discussed.

Electron paramagnetic resonance (EPR) study of Cu^2^+ doped bis (glycinato) Mg (II) monohydrate single crystals is carried out at room temperature. Copper enters the lattice substitutionally and is trapped at two magnetically inequivalent sites. The observed spectra are fitted to a spin-Hamiltonian of rhombic symmetry with the following values of the parameters: Cu^2^+ (I), gx=2.1577+/-0.0002, gy=2.2018+/-0.0002, gz=2.3259+/-0.0002, Ax=(87+/-2)x10^-^4cm^-^1, Ay=(107+/-2)x10^-^4cm^-^1, Az=(141+/-2)x10^-^4cm^-^1; Cu ^2^+ (II), gx=2.1108+/-0.0002, gy=2.1622+/-0.0002, gz=2.2971+/-0.0002, Ax=(69+/-2)x10^-^4cm^-^1, Ay=(117+/-2)x10^-^4cm^-^1and Az=(134+/-2)x10^-^4cm^-^1. The ground state wave function of the Cu^2^+ ion in this lattice is evaluated to be predominantly |x^2-y^2?. The g-factor aniso...

[(iC3H7)2NH2][Cr8NiF9(O2CCMe)18], or Cr8Ni, is a prominent example of an odd-membered antiferromagnetic “wheel.” A detailed characterization of the magnetic properties of Cr8Ni has been conducted. Inelastic neutron scattering (INS) is used to investigate the energy and momentum transfer dependence of the low-lying spin excitations, including excited states inaccessible by other experimental techniques. The richness of the INS data, in conjunction with microscopic spin Hamiltonian simulations, enables an accurate characterization of the magnetic properties of Cr8Ni. Nearest-neighbor exchange constants of JCrCr = 1.31 meV and JCrNi = 3.22 meV are determined, and clear evidence of axial single-ion anisotropy is found. The parameters determined by INS are shown to fit magnetic susceptibility. The spectroscopic identification of several successive S=1 excited total spin states and lowest spin band excitations show that the rotational band picture, valid for bipartite AFM wheels, breaks down for this odd-numbered wheel. The exchange constants determined here differ from previous efforts based on bulk measurements, and possible reasons are discussed. The large JCrNi/JCrCr ratio in Cr8Ni puts this wheel into a regime with strong quantum fluctuations in which the ground state can be described with a valence bond solid state picture.

The synthesis and crystal and molecular structure of the first zinc(II) mixed ligand chelate containing a dithiolene ligand (maleonitriledithiolate) and N,N-diethyldithiocarbamate are reported. The compound Ph/sub 4/As(Zn(mnt)(Et/sub 2/dtc) crystallizes monoclinic, space group P2/sub 1//c with four molecules in the unit cell; a = 17.834(3), b = 12.056(2), c = 16.171(4) A, ..beta.. = 93.73(2)/sup 0/. The coordination geometry of the ZnS/sub 4/ unit is nearly tetrahedral, with a dihedral angle of 87.6/sup 0/ between the chelate rings. The structure is compared with those of both the parent compounds (Ph/sub 4/As)/sub 2/(Zn(mnt)/sub 2/) and Zn/sub 2/(Et/sub 2/dtc)/sub 4/. Ph/sub 4/As(Zn(mnt)(Et/sub 2/dtc)) could be used as the host lattice in single-crystal ESR investigations of the planar Cu mixed ligand complex. The rhombic spin-Hamiltonian parameters g and A/sup Cu/ are indicative of a low symmetry of the incorporated (Cu(mnt)(Et/sub 2/dtc))/sup -/ complex anions. In order to substantiate the experimental findings about the actual structure of the copper molecules, the principal values of g and A/sup Cu/ were recalculated by means of Extended Hueckel MO calculations. However, the calculations performed for the dihedral angles between the ligand planes varying between 0/sup 0/ and 90/sup 0/ suggest that the rotation of the ligands is not larger than 10/sup 0/.

Free radicals produced in natural and tanned collagen by gamma-ray irradiation within 1-15 kGy absorbed dose ranges were investigated by EPR spectroscopy. Tanned collagen was prepared using formaldehyde as well as aluminum basic salts [Al(OH)SO{sub 4}] tanning processes. Both natural and formaldehyde-tanned irradiated collagen show the same kind of EPR spectrum consisting of a single broad, slightly asymmetric line. Irradiated collagen tanned by aluminum basic salts process displayed a complex EPR spectrum consisting of a superposition of broad and narrow lines. A computer simulation of this spectrum allowed to evidence the presence of seven different kinds of paramagnetic centers, including those observed in the irradiated natural collagen. Corresponding Spin Hamiltonian parameters (g-factor, hyperfine splitting constant) as well as relative concentrations of these centers were calculated. Experimentally determined relative concentrations display a positive correlation with the absorbed dose described by a linear-type dependence. After three weeks of storage at room temperature, the concentration of some centers diminished by about 50%. The possible nature of these centers is discussed in connection with the local structure of the tanned collagen.

Rare-earth ions in dielectric crystals are interesting candidates for storing quantum states of photons. A limiting factor on the optical density and thus the conversion efficiency is the distortion introduced in the crystal by doping elements of one type into a crystal matrix of another type. Here we investigate the system Pr3+:La2(WO4)3, where the similarity of the ionic radii of Pr and La minimizes distortions due to doping. We characterize the praseodymium hyperfine interaction of the ground-state (3H4) and one excited state (1D2) and determine the spin Hamiltonian parameters by numerical analysis of Raman-heterodyne spectra, which were collected for a range of static external magnetic-field strengths and orientations. On the basis of a crystal-field analysis, we discuss the physical origin of the experimentally determined quadrupole and Zeeman tensor characteristics. We show the potential for quantum memory applications by measuring the spin coherence lifetime in a magnetic field that is chosen such that additional magnetic fields do not shift the transition frequency in first order. Experimental results demonstrate a spin coherence lifetime of 158 ms — almost 3 orders of magnitude longer than in zero field.

Magnetic nanocrystalline MnO particles have been synthesized in a silica glass matrix by the sol-gel method at calcination temperatures up to 1000 °C. EPR spectra of 0.1 mol% MnO doped silica gel and glasses studied in the temperature range 10-290 K show with the exception of those samples calcined at 900 and 1000 °C 6-line characteristic Mn(II) hyperfine (HF) lines. Additionally five spin-forbidden doublets have been observed at 100 K and below. Small spreads in spin Hamiltonian parameters (D and E) imply that the ligand field environments of Mn(II) ions embedded in the silica glass are nearly uniform. Monotonous decrease in HF linewidth in going from 120 °C gel to 800 °C calcined glass has been interpreted as the continuous decrease in population of isolated Mn2+ ions in silica glass matrix resulting in the decrease of magnetic dipolar interactions leading to the observed decrease in HF linewidth. XRD and TEM of sample calcined at 1000 °C shows the presence of nanocrystals of MnO having orthorhombic crystalline phase and sizes about 10 nm. The thermal behavior of magnetization (zero-field-cooled and field-cooled) and magnetic hysteresis of MnO nanocrystals in the 5-300 K temperature interval have demonstrated that the MnO nanocrystals display superparamagnetic-ferromagnetic transition at low temperatures. X-band EPR linewidth data plotted versus inverse of temperature (1/T) for samples calcined at 900 and 1000 °C (EPR recorded in the vicinity of 0.35 T applied field) depict similar transitions.

Time domain multiple-quantum (MQ) nuclear magnetic resonance (NMR) spectroscopy is a powerful tool for spectral simplification and for providing new information on molecular dynamics. In this thesis, applications of MQ NMR are presented and show distinctly the advantages of this method over the conventional single-quantum NMR. Chapter 1 introduces the spin Hamiltonians, the density matrix formalism and some basic concepts of MQ NMR spectroscopy. In chapter 2, {sup 14}N double-quantum coherence is observed with high sensitivity in isotropic solution, using only the magnetization of bound protons. Spin echoes are used to obtain the homogeneous double-quantum spectrum and to suppress a large H{sub 2}O solvent signal. Chapter 3 resolves the main difficulty in observing high MQ transitions in solids. Due to the profusion of spin transitions in a solid, individual lines are unresolved. Excitation and detection of high quantum transitions by normal schemes are thus difficult. To ensure that overlapping lines add constructively and thereby to enhance sensitivity, time-reversal pulse sequences are used to generate all lines in phase. Up to 22-quantum {sup 1}H absorption in solid adamantane is observed. A time dependence study shows an increase in spin correlations as the excitation time increased. In chapter 4, a statistical theory of MQ second moments is developed for coupled spins of spin I = 1/2. The model reveals that the ratio of the average dipolar coupling to the rms value largely determines the dependence of second moments on the number of quanta. The results of this model are checked against computer-calculated and experimental second moments, and show good agreement. A simple scheme is proposed in chapter 5 for sensitivity improvement in a MQ experiment. The scheme involves acquiring all of the signal energy available in the detection period by applying pulsed spinlocking and sampling between pulses. Using this technique on polycrystalline adamantane, a large increase in sensitivity is observed. Correlation of motion of two interacting methyl groups is the subject of chapter 6. This system serves as a model for the study of hindered internal motion. Because the spin system is small and the motions are well-defined, the calculations involved are tractable. Group theory appropriate for nonrigid molecules is used to treat the change in the Hamiltonian as the methyl groups transit from correlated to uncorrelated motion. Results show that the four-quantum order alone is sufficient to distinguish between the two motions.

The electronic and magnetic properties of polynuclear complexes, in particular the magnetic anisotropy (zero field splitting, ZFS), the leading term of the spin Hamiltonian (SH), are commonly analyzed in a global manner and no attempt is usually made to understand the various contributions to the anisotropy at the atomic scale. This is especially true in weakly magnetically coupled systems. The present study addresses this problem and investigates the local SH parameters using a methodology based on experimental measurements and theoretical calculations. This work focuses on the challenging mono ?-oxo bis ?-acetato dinuclear Mn(III) complex: [Mn(2)(III)(?-O)(?-OAc)(2)L(2)](PF(6))(2) (with L = trispyrrolidine-1,4,7-triazacyclononane) (), which is particularly difficult for EPR spectroscopy because of its large magnetic anisotropy and the weak ferromagnetic interaction between the two Mn(III) ions. High field (up to 12 T) and high frequency (190-345 GHz) EPR experiments have been recorded for between 5 and 50 K. These data have been analyzed by employing a complex Hamiltonian, which encompasses terms describing the local and inter-site interactions. Density functional theory and multireference correlated ab initio calculations have been used to estimate the ZFS of the Mn(III) ions (D(Mn) = +4.29 cm(-1), E(Mn)/D(Mn) = 0.19) and the Euler angles reflecting the relative orientation of the ZFS tensor for each Mn(III) (? = -52°, ? = 28°, ? = 3°). This analysis allowed the accurate determination of the local parameters: D(Mn) = +4.50 cm(-1), E(Mn)/D(Mn) = 0.07, ? = -35°, ? = 23°, ? = 2°. The spin ladder approach has also been applied, but only the parameters of the ground spin state of have been accurately determined (D(4) = +1.540 cm(-1), E(4)/D(4) = 0.107). This is not sufficient to allow for the determination of the local parameters. The validity and practical performance of both approaches have been discussed. PMID:23160651

The spin Hamiltonian that describes the molecular magnet Fe$_8$ has biaxial symmetry with mutually perpendicular easy, medium, and hard magnetic axes. Previous calculations of the ground state tunnel splittings in the presence of a magnetic field along the hard axis are extended, and the meaning of the previously discovered oscillation of this splitting is further clarified.

We derive an effective spin Hamiltonian for the one-dimensional half-filled alternating Hubbard model in the limit of strong on-site repulsion. We show that the effective Hamiltonian is a spin S = 1/2 Heisenberg chain with asymmetric next-nearest-neighbour (nnn) exchange.

An investigation of the orientation and temperature dependence of domain wall properties in FeP! is presented. We use a microscopic, atomic model for the magnetic interactions within an effective, classical spin Hamiltonian constructed on the basis of spin density functional theory. We find a signif...

MgAl{sub 2}O{sub 4}:Mn phosphors have been prepared at 500 deg. C by combustion route. Powder X-ray diffraction (XRD) indicated the presence of mono-MgAl{sub 2}O{sub 4} phase. Scanning electron microscopy showed that the powder particle crystallites are mostly angular. Fourier transform infrared spectroscopy confirmed the presence of AlO{sub 6} group which makes up the MgAl{sub 2}O{sub 4} spinel. Photoluminescence studies showed green/red emission indicating that two independent luminescence channels in this phosphor. The green emission at 518 nm is due to {sup 4} T {sub 1} {sup {yields}}{sup 6} A {sub 1} transition of Mn{sup 2+} ions. The emission at 650 nm is due to the charge-transfer deexcitation associated with the Mn ion. EPR spectrum exhibits allowed and forbidden hyperfine structure at g=2.003. The g{approx}2.00 is due to Mn{sup 2+} ion in an environment close to tetrahedral symmetry. It is observed that N and {chi} increase with decrease of temperature obeying the Boltzmann law. The variation of zero-field splitting parameter (D) with temperature is evaluated and discussed. - Graphical abstract: MgAl{sub 2}O{sub 4}:Mn phosphors have been prepared at 500 deg. C by combustion route and are well characterized by PXRD, SEM and FTIR. Photoluminescence studies showed green/red emission indicating two independent luminescence channels in this phosphor. EPR spectrum exhibits allowed and forbidden hyperfine structure at g=2.003. From EPR spectra the spin-Hamiltonian parameters have been evaluated and discussed.

EPR studies of Cu2+ and two free radicals formed by ?-radiation were performed for KHCO3 single crystal at room temperature. From the rotational EPR results we concluded that Cu2+ is chelated by two carbonate molecules in a square planar configuration with spin-Hamiltonian parameters g|| = 2.2349 and A|| = 18.2 mT. Free radicals were identified as neutral HOCO with unpaired electron localized on the carbon atom and a radical anion CO3·- with unpaired electron localized on two oxygen atoms. The hyperfine splitting of the EPR lines by an interaction with a single hydrogen atom of HOCO was observed with isotropic coupling constants ao = 0.31 mT. Two differently oriented radical sites were identified in the crystal unit cell. Electron spin-lattice relaxation measured by electron spin echo methods shows that both Cu2+ and free radicals relax via two-phonon Raman processes with almost the same relaxation rate. The temperature dependence of the relaxation rate 1/T1 is well described with the effective Debye temperature ?D = 175 K obtained from a fit to the Debye-type phonon spectrum. We calculated a more realistic Debye temperature value from available elastic constant values of the crystal as ?D = 246 K. This ?D-value and the Debye phonon spectrum approximation give a much worse fit to the experimental results. Possible contributions from a local mode or an optical mode are considered and it is suggested that the real phonon spectrum should be used for the relaxation data interpretation.It is unusual that free radicals in KHCO3 relax similarly to the well localized Cu2+ ions, which suggests a small destruction of the host crystal lattice by the ionizing irradiation allowing well coupling between radical and lattice dynamics.

We will present a solid-state 17O NMR study of ?-glycine and demonstrate that 17O NMR parameters are highly sensitive to the local molecular structures, in particular, hydrogen-bond environments, indicating that, potentially, solid-state 17O NMR is a powerful tool for investigating the polymorphs of drugs.   

The aim of this work was to obtain average molecular parameters by using some analytical techniques, namely NMR ({sup 1}H and {sup 13}C NMR), vapor pressure osmometry (VPO), and elemental analysis. NMR provided particular information on important molecular parameters such as aromatic carbon fraction, aliphatic carbons fraction, alkyl-substituted aromatic carbons, unsubstituted aromatic carbons, among others. Molecular modeling was employed to build the structure of asphaltenes using the experimental data. (author)

We have developed a method to systematically compute the form of Rashba- and Dresselhaus-like contributions to the spin Hamiltonian of heterostructures to an arbitrary order in the wavevector k. This is achieved by using the double group representations to construct general symmetry-allowed Hamiltonians with full spin-orbit effects within the tight-binding formalism. We have computed full-zone spin Hamiltonians for [001]-, [110]- and [111]-grown zinc blende heterostructures (D_{2d},C_{4v},C_{2v},C_{3v} point group symmetries), which are commonly used in spintronics. After an expansion of the Hamiltonian up to third order in k, we are able to obtain additional terms not found previously. The present method also provides the matrix elements for bulk zinc blendes (T_d) in the anion/cation and effective bond orbital model (EBOM) basis sets with full spin-orbit effects.

We explore feasibility of a quantum self-correcting memory based on 3D spin Hamiltonians with topological quantum order in which thermal diffusion of topological defects is suppressed by macroscopic energy barriers. To this end we characterize the energy landscape of stabilizer code Hamiltonians with local bounded-strength interactions which have a topologically ordered ground state but do not have string-like logical operators. We prove that any sequence of local errors mapping a ground state of such Hamiltonian to an orthogonal ground state must cross an energy barrier growing at least as a logarithm of the lattice size. Our bound on the energy barrier is shown to be tight up to a constant factor for one particular 3D spin Hamiltonian.

Optically detected magnetic resonance (ODMR) was applied to reveal the exchange interaction effects between Mn2+ ions and confined holes in (Cd,Mn)Te quantum wells with 2D hole gas. Two anisotropic ODMR signals with different angular variations were found and ascribed to isolated manganese ions and to exchange-coupled complexes consisting of manganese and holes. It is shown that calculations on the basis of spin Hamiltonian for these systems are in agreement with the experimental data.

A new Schiff base, [H(4)pydmedpt](2+)·2Cl(-), derived from one of the forms of vitamin B(6) has been synthesized by condensation of pyridoxal hydrochloride with N,N-bis[3-aminopropyl]-methylamine (medpt) and characterized by analytical and spectroscopic methods. The molecular structure is calculated by density functional theory (DFT) procedures, and the donor properties of each individual donor atom are evaluated by calculation of the Fukui function. One pot reaction of pyridoxal and medpt with vanadyl acetylacetonate yields the brown complex [V(IV)O(H(2)pydmedpt)](2+)·2Cl(-)1, which upon recrystallization from water crystallizes as [V(IV)O(pydmedpt)]·5H(2)O 2. The compounds are characterized by analytical and spectroscopic methods, 2 being also characterized by single crystal X-ray diffraction. It displays a slightly distorted octahedral geometry around the vanadium atom involving the coordination of N(amine), two N(imine), and O(phenolato) donors of the ligand. One of the phenolato oxygen donors is positioned trans to the terminal O-oxido atom with relatively short V-O(phenolate) {2.041(3) Å} and long V-O(oxido) {1.625(4) Å} bond distances when compared to other known compounds. The two different pK(a) values (6.0 and 7.9) obtained for 1 are due to protonation of the pyridine ring nitrogen atoms having different basic characters, this being also substantiated by theoretical calculation of the proton affinity of the O- and N- atoms of the molecule. The spin Hamiltonian parameters are obtained from the electron paramagnetic resonance (EPR) spectra, but the A(z) value (ca. 155 × 10(-4) cm(-1)) is lower than expected by applying the additivity rule for the present set of equatorial donor atoms (ca. 162-163 × 10(-4) cm(-1)), this being attributed to the strong trans V-O(phenolate) bond. The UV-vis transitions and EPR spectral parameters are calculated by DFT procedures, and both the calculated electronic transitions and the hyperfine coupling constants agree well with those experimentally observed. The inhibitory effect of 1 on FFA release and % glucose uptake determined with isolated rat adipocyte cells gave IC(50) and EC(50) values lower than for V(IV)OSO(4) and of the same order of magnitude of other reported insulin enhancing vanadium compounds. PMID:21495653

Zero field Mossbauer measurements on ('57)Fe-enriched reaction centers (RCs) differing in ubiquinone content, detergent, oxidation state, or the presence of o-phenanthroline all show a single quadrupole doublet of similar splitting (DELTA)E(,Q), center shift (delta), and temperature dependence. The results are indicative of high-spin ferrous iron (Fe('+2), S = 2) with an approximately invariant first coordination sphere consisting most likely of 6 (or 5) oxygens and nitrogens. The spectra show no evidence for either of the quinones or o-phenanthroline binding directly to the iron. High field (1.0T (LESSTHEQ) B (LESSTHEQ) 6.15T) variable temperature (4.2K (LESSTHEQ) T (LESSTHEQ) 211K) Mossbauer measurements on native (N) and dithionite reduced (R) RCs yield details concerning the electronic state of the iron. At low temperatures and fields the spectra of N and R differ; the former consists of a sharp quadrupole doublet, while the lines in the latter are magnetically broadened via the spin-spin interaction with the semiquinone free radical. In high field the spectra of N and R are similar, showing broad unresolved doublets at 4.2K, which resolve at higher temperatures. The width of the lower energy line has a minimum near 25K. Analysis of the magnetic data using an empirical model of the internal magnetic field shows that the largest component of the quadrupole tensor, V(,zz), is positive, the asymmetry parameter, (eta), is 0.3 at 4.2K and 0.6 at 211K, and the quadrupole tensor is rotated with respect to the internal magnetic field. The compounds of the internal field differ widely in magnitude and temperature dependence. Spin Hamiltonian simulations of the data suggest an unusually small A-tensor at 4.2K, (-9.41T,+1.72T,-10.3T), however, good simulations at other temperatures and fields are obtained if the A-tensor components are allowed to vary. Analysis using a crystal field model with strong electron delocalization can account for the temperature dependence of (DELTA)E(,Q), and indicates considerable "unquenched"(' ). Both the zero field and magnetic measurements suggest the ground state is primarily an (VBAR)xy> orbital and together they suggest that the symmetry at the iron site is lower than rhombic.

The authors conduct a full-scale analysis of the NMR, IR, and UV spectra of dicyandiamide-formaldehyde resins, including line behavior, chemical shifts, spin-spin coupling constants, and hyperfine splitting parameters. Molecular and compositional configurations are proposed. The NMR spectra was recorded in dueterated DMSO.

Thermodynamic parameters and the host-guest stoichiometry of inclusion complex cycluron with {beta}-cyclodextrin in aqueous solution have been determined. The supramolecular structure has been investigated by isothermal titration nanocalorimetry and {sup 1}H NMR spectroscopy at 298.15 K.

Four studies of the ^1H NMR spectrum for the aromatic protons of 4-fluoroaniline between 1958 and 1974 give three very different solutions to the second-order, AA'BB'X, spectrum. A re-evaluation of the second-order spectrum was done at 300MHz. Simultaneous simulations of the ^1H NMR spectrum and ^1^9F NMR spectrum for 4-fluoroaniline were done using WINDNMR-Pro, and a new set of parameters for the six coupling constants was obtained from the optimized simulations. This new set of parameters was used as a basis to evaluate the AA'BB'X spectrum for the aromatic protons in N^4-(4'-fluorophenyl)succinamic acid and in N^4-(4'-fluorophenyl)-3,3-difluorosuccinamic acid by simultaneous simulations of the ^1H NMR spectrum and ^1^9F NMR spectrum for each using WINDNMR-Pro. Formation of the amide bon...

Spin-phonon relaxation due to two-phonon processes of a spin cluster embedded in an elastic medium has been studied. For the case of uniaxial anisotropy, relaxation rates due to Raman processes and processes involving the emission of two phonons have been obtained. For a biaxial spin Hamiltonian, the rates of transitions between tunnel-split levels have been computed. By comparison with the rates of corresponding direct processes, we have established temperature ranges where the Raman mechanism dominates over the one-phonon decay mechanism.

A collection of trapped atomic ions represents one of the most attractive platforms for the quantum simulation of interacting spin networks and quantum magnetism. Spin-dependent optical dipole forces applied to an ion crystal create long-range effective spin–spin interactions and allow the simulation of spin Hamiltonians that possess nontrivial phases and dynamics. Here we show how the appropriate design of laser fields can provide for arbitrary multidimensional spin–spin interaction graphs even for the case of a linear spatial array of ions. This scheme uses currently available trap technology and is scalable to levels where the classical methods of simulation are intractable.

We report cold-neutron inelastic neutron scattering measurements on deuterated samples of the giant polyoxomolybdate magnetic molecule {Mo72Fe30}. The 30 s = 5/2 Fe+3 ions occupy the vertices of an icosidodecahedron, and interact via antiferromagnetic nearest neighbor coupling. The measurements reveal a band of magnetic excitations near E ~ 0.6 meV. The spectrum broadens and shifts to lower energy as the temperature is increased, and also is strongly affected by magnetic fields. The results can be interpreted within the context of an effective three-sublattice spin Hamiltonian.

In the framework of the spin-operator diagram technique, the processes of relaxation of lower branch magnons in a two-sublattice easy-plane antiferromagnet are investigated. The procedure of the spin Hamiltonian diagonalization allowing to obtain compact expressions for magnon interaction amplitudes is proposed. The relaxation frequencies due to three- and four-magnon processes, processes of elastic scattering and interbranch transformation by thermal and concentrational magnetization fluctuations as well as the three-magnon confluence processes with rescattering of thermal magnons by fluctuations are calculated. The results obtained are consistent with the experimental data on parametric excitation of spin waves in the low-temperature antiferromagnets MnCO3 and CsMnF3.

Magnetization measurements of a truly axial symmetry Mn12-tBuAc molecular nanomagnet with a spin ground state of S = 10 show resonance tunneling. This compound has the same magnetic anisotropy as Mn12-Ac but the molecules are better isolated and the crystals have less disorder and a higher symmetry. Hysteresis loop measurements at several temperatures reveal a well-resolved step fine-structure which is due to level crossings of excited states. All step positions can be modeled by a simple spin Hamiltonian. The crossover between thermally assisted and pure quantum tunneling can be investigated with unprecedented detail.

The results of electron paramagnetic resonance (EPR) studies of Ce3+ impurity ions in single crystals of lead thiogallate PbGa2S4 have been reported. The Ce3+ ions substitute for Pb2+ ions in the crystal lattice of PbGa2S4. A number of paramagnetic cerium centers in lead thiogallate have been observed. The spectra are described by the spin Hamiltonian of rhombic symmetry with the effective spin S = 1/2. The g factors of the main cerium centers have been determined. A large number of paramagnetic centers are due to both nonequivalent positions of lead and local charge compensation under the substitution Ce3+ ? Pb2+.

The spin wave excitations of the ideal S=5/2 Kagome lattice antiferromagnet KFe3(OH)6(SO4)2 have been measured using high-resolution inelastic neutron scattering. We directly observe a flat mode which corresponds to a lifted "zero energy mode," verifying a fundamental prediction for the Kagome lattice. A simple Heisenberg spin Hamiltonian provides an excellent fit to our spin wave data. The antisymmetric Dzyaloshinskii-Moriya interaction is the primary source of anisotropy and explains the low temperature magnetization and spin structure.

The synthesis and crystallographic characterization of a new family of M(?-CN)Ln complexes are reported. Two structural series have been prepared by reacting in water rare earth nitrates (LnIII = La, Pr, Nd, Sm, Eu, Gd, Dy, Ho) with K3[M(CN)6] (MIII = Fe, Co) in the presence of hexamethylenetetramine (hmt). The first series consists of six isomorphous heterobinuclear complexes, [(CN)5M-CNLn(H2O)8]·2hmt ([FeLa] 1, [FePr] 2, [FeNd] 3, [FeSm] 4, [FeEu] 5, [FeGd] 6), while the second series consists of four isostructural ionic complexes, [Ln(H2O)8][M(CN)6]·hmt ([FeDy] 7, [FeHo] 8, [CoEu] 9, [CoGd] 10). The hexamethylenetetramine molecules contribute to the stabilization of the crystals by participating in an extended network of hydrogen bond interactions. In both series the aqua ligands are hydrogen bonded to the nitrogen atoms from both the terminal CN groups and the hmt molecules. The [FeGd] complex has been analyzed with 57Fe Mössbauer spectroscopy, EPR, and magnetic susceptibility measurements. We have also analyzed the [FeLa] complex, in which the paramagnetic GdIII is replaced by diamagnetic LaIII, to obtain information about the low-spin FeIII site that is not accessible in the presence of a paramagnetic ion at the complementary site. For the same reason, the [CoGd] complex, containing diamagnetic CoIII, was studied with EPR and magnetic susceptibility measurements, which confirmed the S = 7/2 spin of GdIII. Prior knowledge about the paramagnetic sites in [FeGd] allows a detailed analysis of the exchange interactions between them. In particular, the question of whether the exchange interaction in [FeGd] is isotropic or anisotropic has been addressed. Standard variable-temperature magnetic susceptibility measurements provide only the value for a linear combination of Jx, Jy, and Jz but contain no information about the values of the individual exchange parameters Jx, Jy, and Jz. In contrast, the spin-Hamiltonian analysis of the variable-field, variable-temperature Mössbauer spectra reveals an exquisite sensitivity on the anisotropic exchange parameters. Analysis of these dependencies in conjunction with adopting the g-values obtained for [FeLa], yielded the values Jx = ?1 · J · ?2 +0.11 cm?1, Jy = +0.33 cm?1, and Jz = +1.20 cm?1 (convention). The consistency of these results with magnetic susceptibility data is analyzed. The exchange anisotropy is rooted in the spatial anisotropy of the low-spin FeIII ion. The condition for anisotropic exchange is the presence of low-lying orbital excited states at the ferric site that (i) effectively interact through spin-orbit coupling with the orbital ground state and (ii) have an exchange parameter with the Gd site with a value different from that for the ground state. DFT calculations, without spin-orbit coupling, reveal that the unpaired electron of the t2g5 ground configuration of the FeIII ion occupies the xy orbital, i.e. the orbital along the plane perpendicular to the Fe?Gd vector. The exchange-coupling constants for this orbital, jxy, and the other t2g orbitals, jyz and jxz, have been determined using a theoretical model that relates them to the anisotropic exchange parameters and the g-values of FeIII. The resulting values, jyz = ?5.7 cm?1, jxz = ?4.9 cm?1, and jxy = +0.3 cm?1 are quite different. The origin of the difference is briefly discussed.

In this paper, we describe a grafting methodology associated to a quantitative ^1^9F NMR method (qNMR) for the conjugation of small molecules on a PEG building block aimed at click chemistry applications in the domain of drug delivery systems. Acetylenic PEG (PEG-yne) was first derivatized with a fluorinated benzyl amine (TagF6) by means of photografting of a trifluoromethylphenyl diazirine bifunctional linker (TPD-clip). The amount of TagF6 grafted on PEG-yne was calculated by NMR using an internal standard (trifluoroethanol) and adjusting of the acquisition and processing parameters. NMR is used as a valuable alternative to the complex procedures often employed for the quantification of functionalities on biomaterials. The accuracy of the qNMR methodology was attested by controlling its ...

The objective of this report is to characterize the fluid properties and fluid-rock interactions that are needed for formation evaluation by NMR well logging. The advances made in the understanding of NMR fluid properties are summarized in a chapter written for an AAPG book on NMR well logging. This includes live oils, viscous oils, natural gas mixtures, and the relation between relaxation time and diffusivity. Oil based drilling fluids can have an adverse effect on NMR well logging if it alters the wettability of the formation. The effect of various surfactants on wettability and surface relaxivity are evaluated for silica sand. The relation between the relaxation time and diffusivity distinguishes the response of brine, oil, and gas in a NMR well log. A new NMR pulse sequence in the presence of a field gradient and a new inversion technique enables the T{sub 2} and diffusivity distributions to be displayed as a two-dimensional map. The objectives of pore morphology and rock characterization are to identify vug connectivity by using X-ray CT scan, and to improve NMR permeability correlation. Improved estimation of permeability from NMR response is possible by using estimated tortuosity as a parameter to interpolate between two existing permeability models.

The 17O NMR spectra of glasses quenched from melts at high pressure are often difficult to interpret due to overlapping peaks and lack of crystalline model compounds. High-pressure aluminosilicate glasses often contain significant amounts of [5]Al and [6]Al, thus these high-pressure glasses must contain oxygen bonded to high-coordinated aluminum. The 17O NMR parameters for the minerals jadeite, pyrope, grossular, and mullite are presented to assist interpretation of glass spectra and to help test quantum chemical calculations. The 17O NMR parameters for jadeite and grossular support previous peak assignments of oxygen bonded to Si and high-coordinated Al in high-pressure glasses as well as quantum chemical calculations. The oxygen tricluster in mullite is very similar to the previously observed tricluster in grossite (CaAl4 O7) and suspected triclusters in glasses. We also present 27Al NMR spectra for pyrope, grossular, and mullite.

One of the main problems in coal utilization is the inability to properly characterize its complex pore structure. Coals typically have micro/ultra-micro pores but they also exhibit meso and macroporosity. We believe that measurement of the NMR parameters of various gas phase and adsorbed phase NMR active probes can provide the resolution to this problem. We will investigate the dependence of the common NMR parameters such as chemical shifts and relaxation times of several different nuclei and compounds on the pore structure of model microporous solids, carbons, and coals. In particular, we will study the interaction between several small molecules ({sup 129}Xe, {sup 3}He, {sup 2}H{sub 2}, {sup 14}N{sub 2}, {sup 14}NH{sub 3}, {sup 15}N{sub 2}, {sup 13}CH{sub 4}, {sup 13}CO{sub 2}) and the pore surfaces in coals. These molecules have been selected for their chemical and physical properties. A special NMR probe will be constructed which will allow the concurrent measurement of NMR properties and adsorption uptake at a variety of temperatures. All samples will be subjected to a suite of conventional'' pore structure analyses. These include nitrogen adsorption at 77 K with BET analysis, C0{sub 2} and CH{sub 4} adsorption at 273 K with D-R (Dubinin-Radushkevich) analysis, helium pycnometry, and small angle X-ray scattering as well as gas diffusion measurements. The project combines expertise at the UNM (pore structure, NMR), Los Alamos National Laboratory (NMR), and Air Products (porous materials).

La{sub 2}CuO{sub 4} undergoes a magnetic field induced transition in a field of {approx}5.7 Tesla at low temperatures. The origin of this transition is the Dzyaloshinskii-Moriya interaction which is present in effective spin Hamiltonians for systems of sufficiently low symmetry, and, which leads to weak ferromagnetism in the CuO planes in La{sub 2}CuO{sub 4}. It is shown here how this interaction depends on symmetry and how its form changes with structural phase transitions which occur in compounds closely related to La{sub 2}CuO{sub 4}. These different forms of the interaction lead to different properties in magnetic fields. I also discuss how the approach presented here of determining an effective spin Hamiltonian from symmetry is related to the determination of terms in the free expansion close to a second order phase transition. It is pointed out that the present approach may be extended to itinerant systems and 1 take UPt{sub 3} as an example. 28 refs., 4 figs.

Linear free energy relationships (LFER) were applied to the kinetic data and 13C NMR chemical shifts in 4-[[(substituted phenyl)imino]methyl]benzoic acids. The correlation analysis for the kinetic data and substituent-induced chemical shifts (SCS) with using single substituent parameter (SSP), as well as inductive (I) and various resonance (R) parameters using dual-substituent parameter (DSP), were carried out. The presented calculations account satisfactorily for the polar and resonance substituent effects having similar contributions at all carbons studied. Negative values were found for several correlations (reverse substituent effect). Exceptionally good Hammett correlation of 13C NMR chemical shifts of azomethine carbon with electrophilic substituent constants + indicates a significan...

NMR techniques for measurements of spatial distribution of material phase, velocity and velocity fluctuation are being developed and refined. Versions of these techniques which provide time average liquid fraction and fluid phase velocity have been applied to several concentrated suspension systems which will not be discussed extensively here. Technical developments required to further extend the use of NMR to the multi-phase flow arena and to provide measurements of previously unobtainable parameters are the focus of this report.

The potential of the approach combining nuclear magnetic resonance (NMR) spectroscopy, relaxed grid search (RGS), molecular dynamics (MD) simulations, and quantum mechanical (QM) calculations for the determination of diastereomer configurations is demonstrated using four diastereomers of a trisubstituted epoxide. Since the change in configuration of the chiral center is expected to change the distribution of conformer populations (including those of side-chain rotamers), changes in NMR parameters [chemical shifts, J couplings, and nuclear Overhauser effects (NOEs)] are expected. The method therefore relies on (1) identification of possible conformations in each diastereomer using relaxed grid search analysis and MD simulations; (2) geometry optimizations of conformers selected from step (1), followed by calculations of their relative energies (populations) using QM methods; (3) calculations of averaged NMR parameters using QM methods; (4) matching calculated and experimental values of NMR parameters of diastereomers. The diastereomer configurations are considered resolved, if three NMR parameters different in nature, chemical shifts, J couplings, and NOEs, are in agreement. A further advantage of this method is that full structural and dynamics characterization of each of the diastereomers is achieved based on the joint analysis of experimental and computational data. PMID:22734494

Protein internal motions influence observables of NMR experiments. The effect of internal motions occurring at the sub-nanosecond timescale can be described by NMR order parameters. Here, we report that the use of order parameters derived from Molecular Dynamics (MD) simulations of two holo-structures of Protein Kinase A increase the discrimination power of INPHARMA, an NMR based methodology that selects docked ligand orientations by maximizing the correlation of back-calculated to experimental data. By including internal motion in the back-calculation of the INPHARMA transfer, we obtain a more realistic description of the system, which better represents the experimental data. Furthermore, we propose a set of generic order parameters, derived from MD simulations of globular proteins, which...

The successful measurement of anisotropic NMR parameters like residual dipolar couplings (RDCs), residual quadrupolar couplings (RQCs), or residual chemical shift anisotropy (RCSA) involves the partial alignment of solute molecules in an alignment medium. To avoid any influence of the change of environment from the isotropic to the anisotropic sample, the measurement of both datasets with a single sample is highly desirable. Here, we introduce the scaling of alignment for mechanically stretched polymer gels by varying the angle of the director of alignment relative to the static magnetic field, which we call variable angle NMR spectroscopy (VA-NMR). The technique is closely related to variable angle sample spinning NMR spectroscopy (VASS-NMR) of liquid crystalline samples, but due to the mechanical fixation of the director of alignment no sample spinning is necessary. Also, in contrast to VASS-NMR, VA-NMR works for the full range of sample inclinations between 0° and 90°. Isotropic spectra are obtained at the magic angle. As a demonstration of the approach we measure 13C-RCSA values for strychnine in a stretched PDMS/CDCl3 gel and show their usefulness for assignment purposes. In this context special care has been taken with respect to the exact calibration of chemical shift data, for which three approaches have been derived and tested.

A general theory has been developed for the application of the maximum likelihood (ML) principle to the estimation of NMR parameters (frequency and amplitudes) from multidimensional time-domain NMR data. A computer program (ChiFit) has been written that carries out ML parameter estimation in the D-1 indirectly detected dimensions of a D-dimensional NMR data set. The performance of this algorithm has been tested with experimental three-dimensional (HNCO) and four-dimensional (HN(CO)-CAHA) data from a small protein labeled with 13C and 15N. These data sets, with different levels of digital resolution, were processed using ChiFit for ML analysis and employing conventional Fourier transform methods with prior extrapolation of the time-domain dimensions by linear prediction. Comparison of the results indicates that the ML approach provides superior frequency resolution compared to conventional methods, particularly under conditions of limited digital resolution in the time-domain input data, as is characteristic of D-dimensional NMR data of biomolecules. Close correspondence is demonstrated between the results of analyzing multidimensional time-domain NMR data by Fourier transformation, Bayesian probability theory [Chylla, R.A. and Markley, J.L. (1993) J. Biomol. NMR, 3, 515-533], and the ML principle. PMID:7787422

Nuclear magnetic resonance (NMR) is a tool used to probe the physical and chemical environments of specific atoms in molecules. This research explored small molecule analogues to biological materials to determine NMR parameters using ab initio computations, comparing the results with solid-state NMR measurements. Models, such as dimethyl phosphate (DMP) for oligonucleotides or CuCl for the active site of the protein azurin, represented computationally unwieldy macromolecules. 31P chemical shielding tensors were calculated for DMP as a function of torsion angles, as well as for the phosphate salts, ammonium dihydrogen phosphate (ADHP), diammonium hydrogen phosphate, and magnesium dihydrogen phosphate. The computational DMP work indicated a problem with the current standard 31P reference of 85% H3PO 4(aq.). Comparison of the calculations and experimental spectra for the phosphate salts indicated ADHP might be a preferable alternative as a solid state NMR reference for 31P. Experimental work included magic angle spinning experiments on powder samples using the UNL chemistry department's Bruker Avance 600 MHz NMR to collect data to determine chemical shielding anisotropies. For the quadrupolar nuclei of copper and scandium, the electric field gradient was calculated in diatomic univalent metal halides, allowing determination of the minimal level of theory necessary to compute NMR parameters for these nuclei.

In 2001, Mauri and Pickard introduced the gauge including projected augmented wave (GIPAW) method that enabled for the first time the calculation of all-electron NMR parameters in solids, i.e. accounting for periodic boundary conditions. The GIPAW method roots in the plane wave pseudopotential formalism of the density functional theory (DFT), and avoids the use of the cluster approximation. This method has undoubtedly revitalized the interest in quantum chemical calculations in the solid-state NMR community. It has quickly evolved and improved so that the calculation of the key components of NMR interactions, namely the shielding and electric field gradient tensors, has now become a routine for most of the common nuclei studied in NMR. Availability of reliable implementations in several so...

Nuclear Magnetic Resonance (NMR) is a medical diagnostic imaging technique that applies the atomic principles of magnetic spin to visualize and analyze disease states in bodily tissues. NMR differs from the radiological devices in that (a) it does not utilize potentially harmful ionizing radiation, and (b) it has the capacity to not only produce anatomical images but also to generate biochemical data. NMR devices are very versatile in the ways they can generate, process and present information; manufacturers are developing several kinds of units with different magnets, field strengths, and operational parameters. At this time there are no definitive guidelines on how NMR should be operated for optimal results, even for the most basic clinical applications.

The spatial and temporal analysis of the magnetic field of magnets used in NMR is realised by a NMR multi-probe magnetometer whose orders are managed by a PC. The interface between the PC and the magnetometer call fact to a general-purpose acquisition card piloted by a program developed under Labview. After excitation of the selected probe, a NMR signal is acquired by the card, treated by the PC, and characteristic parameters of the temporal evolution of the signal frequency are extracted by parametric identification. One deduces the temporal evolution of the field to the place of the probe. A line of the space is swept by selecting successively probes, whose totality can also displace inside the magnet to change the line to explore. The equipment has been developed to analyse the drift of the gradients of field in a cryogenic magnet at 2 Tesla used in experimental NMR. (authors)

The objective of the project was to develop an advanced imaging method, including pore scale imaging, to integrate nuclear magnetic resonance (NMR) techniques and acoustic measurements to improve predictability of the pay zone in hydrocarbon reservoirs. This will be accomplished by extracting the fluid property parameters using NMR laboratory measurements and the elastic parameters of the rock matrix from acoustic measurements to create poroelastic models of different parts of the reservoir. Laboratory measurement techniques and core imaging were linked with a balanced petrographical analysis of cores and theoretical modeling.

Basic data of four fractions, PM{sub 1}, PM{sub 6}, PM{sub 7} and PM{sub 8}, derived from Pinshuo bituminous coal were obtained by ultimate analyses, mean molecular weight measure, GC/MS, {sup 13}C-NMR, {sup 1}H-NMR and FTIR techniques. A method of calculating the average molecular parameters of the fractions is introduced. Based on the calculated parameters, the molecular structure models of the fractions of PM{sub 6}, PM{sub 7} and PM{sub 8} are constructed. Significant structural information about the saturated hydrocarbon and aromatic hydrocarbon with heteroatom groups is given also. 6 refs., 7 figs., 7 tabs.

Flap dynamics of HIV-1 protease (HIV-pr) controls the entry of inhibitors and substrates to the active site. Dynamical models from previous simulations are not all consistent with each other and not all are supported by the NMR results. In the present work, the effect of force field on the dynamics of HIV-pr is investigated by MD simulations using three AMBER force fields ff99, ff99SB, and ff03. The generalized order parameters for amide backbone are calculated from the three force fields and compared with the NMR S2 values. We found that the ff99SB and ff03 force field calculated order parameters agree reasonably well with the NMR S2 values, whereas ff99 calculated values deviate most from the NMR order parameters. Stereochemical geometry of protein models from each force field also agrees well with the remarks from NMR S2 values. However, between ff99SB and ff03, there are several differences, most notably in the loop regions. It is found that these loops are, in general, more flexible in the ff03 force field. This results in a larger active site cavity in the simulation with the ff03 force field. The effect of this difference in computer-aided drug design against flexible receptors is discussed. PMID:22845837

Abstract The IDEM estimates the reactivity ratios of multiple-site-type catalysts used to make ethylene/-olefin copolymers. Analytical data from high-temperature GPC and 13C NMR are required in the estimation process. The CSLD information from the 13C NMR is a crucial step in the estimation method due to NMR sensitivity and probe efficiency. The effect of inter-laboratory analysis on IDEM parameter estimation and model predictions is studied. The copolymer samples are analyzed at the University of Waterloo and Dow Chemical Research Center at Freeport, Texas without standardization. The results prove that the IDEM is a robust parameter estimation model for ethylene/-olefin copolymers made with multiple-site-type catalysts, even when the copolymer samples are analyzed in different laboratori...

Borates consisting of diverse fundamental building blocks (FBB) formed from complex polymerization of planar triangular [B?3] groups and tetrahedral [B?4] groups, where ??=?O and OH, provide an excellent opportunity for investigation of correlations between the NMR parameters and local structures. However, previous studies suggested that the 11B NMR parameters in borates are insensitive to local structural environments other than the B coordination number, in contrast to those documented for 29Si, 23Na and 27Al in silicates, and no correlation between 11B chemical shifts and the sum of bond valences has been established for borate minerals with hydroxyl groups or molecular water in the structures. In this study, high-resolution NMR spectra have been acquired at the ultra high field of 21 T...

Formation of diastereomers of ?- and ?-[Co(en)3]3+ was investigated in aqueous chiral-electrolyte solutions using 59Co NMR spectroscopy. The chiral electrolytes used were alkali salts for L- and D-tartrates, bis(?-(?)589-tartrato)diantimonate(III), N-dodecanoyl-L-(and D-)alaninate, N-dodecanoyl-L-threoninate, and N-hexadecanoyl-L-prolinate. The 59Co NMR parameters for the [Co(en)3]3+ group were different between the enantiomers in most cases. The NMR parameters used for chiral discrimination were chemical shifts (in simple electrolyte and micellar solutions), relaxation rates (in simple electrolyte and micellar solutions), peak areas (in micellar solutions), and quadrupole splittings (in liquid crystalline solutions). The larger values of the relaxation rates suggest stronger interactions. On the other hand, the magnitude of the chemical shift change was not simply related to the extent of the interactions. For a chemical shift, the contribution of a geometrical factor seems to be dominant in systems having local anisotropy in the interaction.   

On-line measurement of the magnetic fields of electromagnets at GANIL (France) was studied and developed. This type of measurement is necessary for it allows the adjustment and the monitoring of the parameters which control the transport of particle beams from the accelerators to the experimental vaults. The developments were based on nuclear magnetic resonance (NMR) magnetometers and Hall-effect magnetometers. The limitations of operating NMR probes in inhomogeneous fields required particular solutions. Techniques of positioning and appropriate compensation for field gradients were put in place. NMR probes and Hall-effect probes are integrated into the electronics for monitoring and control according to the defined standards at GANIL. The unit comprises instrumentation which perfectly meets the needs, particularly from the point of view of the measurement and the monitoring of the magnetic parameters. (author)

Boron-11 and silicon-29 NMR spectra of xSiO(2)-(1-x)B(2)O(3) glasses (x=0.40, 0.80 and 0.83) have been calculated using a combination of molecular dynamics (MD) simulations with density functional theory (DFT) calculations of NMR parameters. Structure models of 200 atoms have been generated using classical force fields and subsequently relaxed at the PBE-GGAlevel of DFT theory. The gauge including projector augmented wave (GIPAW) method is then employed for computing the shielding and electric field gradient tensors for each silicon and boron atom. Silicon-29 MAS and boron-11 MQMAS NMR spectra of two glasses (x=0.40 and 0.80) have been acquired and theoretical spectra are found to well agree with the experimental data. For boron-11, the NMR parameter distributions have been analysed using a Kernel density estimation (KDE) approach which is shown to highlight its main features. Accordingly, a new analytical model that incorporates the observed correlations between the NMR parameters is introduced. It significantly improves the fit of the (11)B MQMAS spectra and yields, therefore, more reliable NMR parameter distributions. A new analytical model for a quantitative description of the dependence of the silicon-29 and boron-11 isotropic chemical shift upon the bond angles is proposed, which incorporates possibly the effect of SiO(2)-B(2)O(3) intermixing. Combining all the above procedures, we show how distributions of Si-O-T and B-O-T (T=Si, B) bond angles can be estimated from the distribution of isotropic chemical shift of silicon-29 and boron-11, respectively. PMID:20818801

The objective of this study was first to prove the concept of a low field pulsed nuclear magnetic resonance (NMR) process for assessing the cortical porosity and pore size distribution of human bone in vitro, and then to apply the technique to detect age-related changes of bone in these parameters. The Carr-Purcell-Meiboom-Gill NMR spin echo train method is used to determine the porosity, and an inversion NMR spin-spin relaxation (T(2)) spectrum is used to assess the pore size distribution in cortical bone. Using these techniques, cortical porosity and pore size distribution of 19 specimens of human cadaveric bone, ranging from 16 to 89 years of age, were assessed. The NMR results were compared with the histomorphometric data of the same bone samples to verify the efficacy of the NMR approach. Moreover, a coefficient (surface relaxivity) relating the pore size to the T(2) relaxation time was determined empirically for the Haversian canals and the osteocytic lacunae. The results of this study demonstrate that the in vitro NMR approach using T(2) relaxation techniques can directly assess the porosity and pore size distribution (Haversian canals and osteocytic lacunae) in human cortical bone. In addition, this study indicates that the age-related changes in cortical porosity relate predominantly to Haversian canals, whereas the porosity of osteocytic lacunae appears to be independent of age. PMID:12568964

Since hydrogen is the most abundant element in all living organisms, proton NMR lends itself well as a method of investigation in biology and medicine. NMR imaging has some special advantages as a diagnostic tool: no ionizing radiation is used, it is noninvasive; it provides a safer means of imaging than the use of x-rays, gamma rays, positrons, or heavy ions. In contrast with ultrasound, the radiation penetrates the bony structures without attenuation. In additional to morphological information, NMR imaging provides additional diagnostic insights through relaxation parameters, which are not available from other imaging methods. In the decade since the first primitive NMR images were obtained, the quality of images now obtained approaches those from CT x-ray scanners. Prototype instruments are being constructed for clinical evaluation and the first whole-body scanners are beginning to appear on the market at costs comparable to CT scanners. Primary differences in equipment for conventional NMR and NMR imaging are the much larger aperture magnets that are required for the examination of human subjects and the addition of coils to generate field gradients and facilities for manipulating the gradients. Early results from clinical trials in many parts of the world are encouraging, and in a few years, the usefuleness of this modality of medical imaging to the medical profession in diagnosis and treatment of disease will be defined. 10 figures.

Molecular nanomagnets are among the first examples of spin systems of finite size and have been test-beds for addressing a range of elusive but important phenomena in quantum dynamics. In fact, for short-enough timescales the spin wavefunctions evolve coherently according to the an appropriate cluster spin-Hamiltonian, whose structure can be tailored at the synthetic level to meet specific requirements. Unfortunately, to this point it has been impossible to determine the spin dynamics directly. If the molecule is sufficiently simple, the spin motion can be indirectly assessed by an approximate model Hamiltonian fitted to experimental measurements of various types. Here we show that recently-developed instrumentation yields the four-dimensional inelastic-neutron scattering function S(Q,E) in vast portions of reciprocal space and enables the spin dynamics to be determined with no need of any model Hamiltonian. We exploit the Cr8 antiferromagnetic ring as a benchmark to demonstrate the potential of this new appr...

We study theoretically the electromagnon and its optical spectrum (OS) of the terahertz-frequency regime in the magnetic-spiral-induced multiferroic phases of the rare-earth-metal (R) Mn perovskites, RMnO3, taking into account the spin-angle modulation or the higher harmonics of the spiral spin configuration, which has been missed so far. A realistic spin Hamiltonian, which gives phase diagrams in agreement with experiments, resolves a puzzle, i.e., the double-peak structure of the OS with a larger low-energy peak originating from magnon modes hybridized with the zone-edge state. We also predict the magnon branches associated with the electromagnon, which can be tested by neutron-scattering experiment. PMID:20482138

We present a theoretical method for the design and optimization of quantum corrals with specific electronic properties. Taking advantage that spins are subject to a RKKY interaction that is directly controlled by the scattering of the quantum corral, we design corral structures that reproduce spin Hamiltonians with coupling constants determined a priori. We solve exactly the two-dimensional electron gas scattering problem for each corral configuration within the effective mass approximation and s-wave scattering using a Green function method. Subsequently, the geometry of the quantum corral is optimized with an algorithm that combines simulated annealing and genetic approaches. We demonstrate that it is possible to automatically design quantum corrals with complicated target electronic properties, such as multiple mirages with predefined relative intensities at specific locations. In addition we design structures that are particularly sensitive to the phase shift of impurities at certain positions allowing th...

We study zero-temperature stability of topological phases of matter under weak time-independent perturbations. Our results apply to quantum spin Hamiltonians that can be written as a sum of geometrically local commuting projectors on a D-dimensional lattice with certain topological order conditions. Given such a Hamiltonian H_0 we prove that there exists a constant threshold \\epsilon>0 such that for any perturbation V representable as a sum of short-range bounded-norm interactions the perturbed Hamiltonian H=H_0+\\epsilon V has well-defined spectral bands originating from O(1) smallest eigenvalues of H_0. These bands are separated from the rest of the spectrum and from each other by a constant gap. The band originating from the smallest eigenvalue of H_0 has exponentially small width (as a function of the lattice size). Our proof exploits a discrete version of Hamiltonian flow equations, the theory of relatively bounded operators, and the Lieb-Robinson bound.

A dinuclear manganese(II) unit of the composition {[Na"2(H"2O)"4Mn"2(@m-pmtz)"4(NCS)"2].xH"2O}"n (1.xH"2O) (x=3 or 0.5), where pmtz=5-(pyrimidyl)tetrazolate(1-), involved in 1D ladder-like chains mediated through pmtz bridges, was prepared and characterized by elemental analysis, FT-IR spectroscopy, simultaneous thermogravimetric (TG) and differential thermal (DTA) analyses, single crystal X-ray analysis and magnetic measurements, accompanied by DFT calculations. The magnetic data, treated with the spin Hamiltonian formalism, revealed a weak antiferromagnetic exchange mediated via the @k^2N"1,N"7:@kN"2 chelating/bridging mode of pmtz. This finding was also supported by the DFT calculations performed on the experimentally determined geometry of the dinuclear manganese(II) unit at the B3LYP/...

The gadolinium complexes: [Gd(SiW{sub 11}O{sub 39}){sub 2}]{sup 13-} [I] and [GdP{sub 5}W{sub 30}O{sub 110}]{sup 12-} [II] have been chosen for EPR study. This study is a continuation of our recent investigation related to solid gadolinium complexes:{beta}-diketonates and aminopolycarboxylates. The EPR spectra of the Gd-polyoxometalates studied provide much better resolution than those recently studied. The EPR spectra obtained for the compounds I and II markedly differ from the U-spectrum characteristic of Gd(III) in glasses. Taking into account the spin-Hamiltonian calculations the existence of Gd(III) ion in two different surroundings: in a strong crystal field of rhombic symmetry and in weak crystal field, is observed. The differences observed between the case I and II seem to be related to a various hydration degree. (author) 16 refs, 3 figs, 1 tab

A study of silicon enriched in the 28Si isotope with a low oxygen content (N ? 2 × 1014 cm?3) at low temperatures (T = 3.8 K) has revealed a set of electron spin resonance (ESR) spectra with anisotropic g factors associated with an isolated Li donor center, whose lines are assigned to triplet and doublet states. The spectra were investigated without and with application of external load to the sample and their g factors were found to be smaller than 2 (g < 2.000), which distinguishes them from the previously obtained spectra. Based on theoretical and experimental estimates made within the spin-Hamiltonian analysis of the spectra, the states of donor electrons of lithium and their g factors are found to depend strongly on internal strains in the crystal and intervalley spin-orbit interactio...

Abstract Three new polynuclear cluster complexes were synthesized and characterized using single-crystal X-ray measurements, infrared spectroscopy, and elemental analyses. A Schiff-base, 2-{[(1-hydroxybutan-2-yl)imino]methyl}phenol (himpH2), synthesized in situ from the reaction of salicylaldehyde and ()-2-aminobutanol, was used as ligand. Reactions of the ligand with different MnII and NiII salts led to two homometallic complexes and a heterometallic complex with [MnIII4] (1), [NiII4] (2), and [MnIII2NiII2] (3) cores exhibiting square, cubane-type, or butterfly arrangement, respectively. Analysis of the temperature dependence of the magnetic susceptibility of compounds 1-3, using appropriate spin Hamiltonians, indicated that the [MnIII4] and [NiII4] compounds show dominant ferromagnetic c...

This paper offers an overview of the possibilities for the use of NMR techniques in solvent extraction studies for new extraction systems (monoamides, malonamides and picolinamides) and tri-n-butylphosphate (TBP) properties investigations. We have used NMR spectroscopy with monoamides to identify the structural parameters that control monoamide selectivity and efficiency. Distances between the carbon atoms of the monoamide ligands and the lanthanides(lII) or actinides(IV) metallic centres were determined through the analysis of the {sup 13}C T{sub 1} NMR relaxation time data. The conformational data obtained by NMR measurements related to lanthanide nitrate monoamide solvates were then compared with the corresponding distribution coefficients. Dynamic information on the extractant were also obtained and gave an indication of the time scale of different motions in liquid phases as well as the influence of a metal ion in the media. From {sup 1}H, {sup 2}H and {sup 13}C NMR spectra analyses, extractants in organic phases show some weak interactions such as malonamide dimer formations. These were observed for diluted benzenic solutions but for more concentrated solutions, micellar formation were observed. This may explain: decantation problems and the large amount of extracted water observed. Nitric acid extraction mechanisms can be also determined by NMR. The case of the picolinamide extractants, analysed from {sup 1}H and {sup 13}C NMR spectra is a good example. A relatively straightforward mechanism results of this and protonation sites are determined. {sup 31}P NMR was found useful for practical and basic research dealing with the hydrolytic and radiolytic degradations of the TBP : each organophosphorus TBP degradation product was identified and quantified. A chemical exchange between dibutylphosphoric acid (HDBP) and DBP:Zr(NO{sub 3}){sub 4} system was pointed out and allows us to understand the original Zr(IV) property that induces demixion of HDBP from aqueous nitric solutions. (authors) 3 refs., 2 tabs., 3 figs.

Local structures in denatured proteins may be important in guiding a polypeptide chain during the folding and misfolding processes. Existence of local structures in chemically denatured proteins is a highly controversial issue. NMR parameters [coupling constants 3 J(H?,HN) and chemical shifts] of ch...

Optimizing the surface-coil design and spectral-acquisition parameters has lead to the observation of the 13C NMR natural abundance glycogen signal in man at 2.1 T. Both the human muscle and hepatic glycogen signals can be detected definitively with a time resolution of approximately equal to 13 min...

Structural analysis of carbohydrates involves three parameters: composition, linkage, and conformation, and tends to rely on the various forms of two techniques; mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy. These techniques are enhanced and extended by the use of stable...

Biomedical imaging makes possible to see with nuclear magnetic resonance, with x rays, radioactive tracers, ultrasonics, or photons. All the different imaging methods (NMR, positron computed tomography) explore new ways of doing and new parameters. Imaging is become an essential tool in human medicine but also in the study of animal models for human pathologies. (N.C.)

500 MHz 1H, 67.89 MHz 13C and 80.97 MHz 31P-NMR studies are reported on the ribotrinucleoside diphosphate UpUpC, the triplet codon corresponding to the amino acid phenylalanine. Complete spectral assignments are given and conformational parameters for the backbone and the furanose rings are determin...

The nature of strontium binding by soil minerals directly affects the transport and sequestration/remediation of radioactive strontium species released from leaking high-level nuclear waste storage tanks. However, the molecular-level structure of strontium binding sites has seldom been explored in phyllosilicate minerals by direct spectroscopic means and is not well-understood. In this work, we use solid-state NMR to analyze strontium directly and indirectly in a fully strontium-exchanged synthetic mica of nominal composition Na(4)Mg(6)Al(4)Si(4)O(20)F(4). Thermogravimetric analysis, X-ray diffraction analysis, and NMR evidence supports that heat treatment at 500 degrees C for 4 h fully dehydrates the mica, creating a hydrogen-free interlayer. Analysis of the strontium NMR spectrum of the heat-treated mica shows a single strontium environment with a quadrupolar coupling constant of 9.02 MHz and a quadrupolar asymmetry parameter of 1.0. These quadrupolar parameters are consistent with a highly distorted and asymmetric coordination environment that would be produced by strontium cations without water in the coordination sphere bound deep within the ditrigonal holes. Evidence for at least one additional strontium environment, where proton-strontium couplings may occur, was found via a (1)H-(87)Sr transfer of populations by double resonance NMR experiment. We conclude that the strontium cations in the proton-free interlayer are observable by (87)Sr NMR and bound through electrostatic interactions as nine coordinate inner-sphere complexes sitting in the ditrigonal holes. Partially hydrated strontium cations invisible to direct (87)Sr NMR are also present and located on the external mica surfaces, which are known to hydrate upon exposure to atmospheric moisture. These results demonstrate that modern pulsed NMR techniques and high fields can be used effectively to provide structural details of strontium binding by phyllosilicate minerals. PMID:16599480

A novel multitopic, two-pocket ligand H, containing the nitronyl nitroxide radical, has been designed for a self-assembled [2 × 2] grid system. H is not stable in methanol and slowly undergoes a disproportionation, during which the nitronyl nitroxide radical converts to the diamagnetic amidino oxide. In situ reaction of H with Cu(BF(4))(2) in methanol depending on the reaction time affords self-assembled [2 × 2] grids ()(2)()(2)Cu(ii)(4)(BF(4))(4)·CH(3)OH () or ()(0.5)()(3.5)Cu(ii)(4)(BF(4))(4)·CH(3)OH (), in which contains an amidino oxide arising from a 3-electron reduction of the nitronyl nitroxide radical. The percentages of stable radical in grids and as determined by X-ray are 50 and 12.5%, respectively. Structures and contain a six-coordinated distorted Cu(ii) that is oxo-bridged at 140°. The nitronyl nitroxide radical coordinates via the oxo-atom of the N(+)-O(-) fragment in a chelating fashion and lies in the equatorial plane of the metal ion. The magnetic properties of could be fitted to a 5-spin Hamiltonian with J(Cu-Cu) = +3.1 cm(-1) and J(Cu-Nit) = -278 cm(-1), while those of to a 4-spin Hamiltonian with J(Cu-Cu) = +2.9 cm(-1). The Q-band EPR spectra of and recorded in solution at 20 K showed intricate anisotropic features of the Cu(ii) ion and a much weaker signal of the -NO? fragment, associated with a strong Cu(ii)-Nit antiferromagentic coupling. The DFT calculated (B3LYP/TZVP/6-31G*) magnetic coupling constants for the grid of were J(Cu-Cu) = +5 cm(-1) and J(Cu-Nit) = -282 cm(-1), which are in very good agreement with the experimentally obtained values. PMID:23073390

Two series of polyimides were synthesized based on different aromatic dianhydrides containing various flexible linkages and two aromatic diamines containing ether and nitrile groups. The structure of the polymers was confirmed by FTIR and 1H NMR spectroscopy. The correlation between some physical properties, such as solubility, thermal stability and glass transition temperature, and conformational rigidity parameters, such as Kuhn segment, characteristic ratio and rigidity parameter p, was studied.

Concerning the standstill state of pervaporation desulfurization, development of new pervaporation desulfurization membranes is vital. The polymer selection can be based on solubility parameter theory. Using group contribution method, the solubility parameter of poly[bis(trifluoroethoxy) phosphazene] (PTFEP) was calculated. The differences in solubility parameters between thiophene and polymers including PTFEP were calculated and investigated for their potential application as pervaporation desulfurization membranes. PTFEP had the most similar solubility parameter to thiophene among the polymers calculated in this work. The results indicated superior possibility for its application in pervaporation desulfurization. PTFEP was thus synthesized and characterized by DSC, GPC, XPS, ^1H-NMR and ...

With the use of alicyclic diisocyanates, aliphatic alcohols and dibutyltin dilaurate as well as triethylamine as a catalysts internally-blocked polyisocyanate crosslinkers which contained allophanate bonds were synthesized. The chemical structure of those compounds were characterized by IR, 1H-NMR, and 13C-NMR spectroscopy. Their molecular weight distribution (MWD) parameters were determined by gel permeation chromatography (GPC). Those blocked polyisocyanates were used for the production of ecological lacquer compositions and coatings. The unblocking and curing reactions were investigated on the DTA, TG, and DSC thermograms. The resulting powder lacquers exhibit an excellent appearance; they are transparent, smooth, and nonyellowing. Copyright 2010 Wiley Periodicals, Inc. J Appl Polym Sci...

Asphaltenes are a major concern in production operations, due to their role in conversion of vacuum residues by processes such as coking, catalytic cracking and hydroconversion. Six Turkish asphaltenes were characterized by elemental content, proton NMR, carbon NMR, GPC, DSC. Differential scanning calorimetry (DSC) provides parameters for comparing the glass transition temperatures, endothermic behavior of asphaltene and a hypothetical melting temperature of the asphaltenes which is within the range of the pyrolysis temperature of asphaltenes. The glass transition temperatures points (Tg) of asphaltenes were determined using DSC. Hypothetical melting point temperature (Tm) of the asphaltenes was also calculated. Among all the asphaltenes tested, Bati Raman showed much higher glass transiti...

A variety of techniques and measurements on all NMR accessible nuclei allow one to obtain a complete and precise set of chemical shift and quadrupole coupling parameters for both boron and nitrogen in cubic and hexagonal boron nitride. For hexagonal boron nitride, 11B to 15N cross polarization under magic angle sample spinning conditions is demonstrated at natural isotope abundance. The presented approach for NMR characterization of the crystalline boron nitrides should also be applicable to structurally related composite materials, nanotubes, and amorphous ceramics. PMID:9808290

The benchmark set is proposed, which comprises 126 principal elements of chemical shielding tensors, and the respective isotropic chemical shielding values, of all 42 13C nuclei in crystalline Tyr-D-Ala-Phe and Tyr-Ala-Phe tripeptides with known, but highly dissimilar structures. These data are obtained by both the NMR measurements and the density functional theory in the pseudopotential plane-wave scheme. Using the CASTEP program, several computational strategies are employed, for which the level of agreement between calculations and experiment is established. This set is mainly intended for the validation of methods capable of predicting the 13C NMR parameters in solid-state systems.

The effects of a non-magnetic Zn impurity substituting an in-plane Cu are studied by solving the Bogoliubov-de Gennes equation self-consistently which is derived from the \\ttju Hamiltonian with all the allowed order parameters included. The Zn impurity, modeled in terms of a potential scatterer in unitary limit, induces local staggered magnetic moments around itself, and the calculated NMR shifts from the induced moments are in agreement with the experimental Cu NMR spectra. We also note that the experimentally observed negative slope of the tunneling conductance can result from the next-nearest hopping $t'$.

Abstract Noninvasive in vivo monitoring of tissue implants provides important correlations between construct function and the observed physiologic effects. As oxygen is a key parameter affecting cell and tissue function, we established a monitoring method that utilizes 19F nuclear magnetic resonance (NMR) spectroscopy, with perfluorocarbons (PFCs) as oxygen concentration markers, to noninvasively monitor dissolved oxygen concentration (DO) in tissue engineered implants. Specifically, we developed a dual PFC method capable of simultaneously measuring DO within a tissue construct and its surrounding environment, as the latter varies among animals and with physiologic conditions. In vitro studies using an NMR-compatible bioreactor demonstrated the feasibility of this method to monitor the DO ...

The need for sustainable management of fresh water resources is one of the great challenges of the 21st century. Since most of the planet's liquid fresh water exists as groundwater, it is essential to develop non-invasive geophysical techniques to characterize groundwater aquifers. A field experiment was conducted in the High Plains Aquifer, central United States, to explore the mechanisms governing the non-invasive Surface NMR (SNMR) technology. We acquired both SNMR data and logging NMR data at a field site, along with lithology information from drill cuttings. This allowed us to directly compare the NMR relaxation parameter measured during logging, T2, to the relaxation parameter T2* measured using the SNMR method. The latter can be affected by inhomogeneity in the magnetic field, thus obscuring the link between the NMR relaxation parameter and the hydraulic conductivity of the geologic material. When the logging T2 data were transformed to pseudo- T2* data, by accounting for inhomogeneity in the magnetic field and instrument dead time, we found good agreement with T2* obtained from the SNMR measurement. These results, combined with the additional information about lithology at the site, allowed us to delineate the physical mechanisms governing the SNMR measurement. Such understanding is a critical step in developing SNMR as a reliable geophysical method for the assessment of groundwater resources.

Borates consisting of diverse fundamental building blocks (FBB) formed from complex polymerization of planar triangular [B?3] groups and tetrahedral [B?4] groups, where ? = O and OH, provide an excellent opportunity for investigation of correlations between the NMR parameters and local structures. However, previous studies suggested that the 11B NMR parameters in borates are insensitive to local structural environments other than the B coordination number, in contrast to those documented for 29Si, 23Na and 27Al in silicates, and no correlation between 11B chemical shifts and the sum of bond valences has been established for borate minerals with hydroxyl groups or molecular water in the structures. In this study, high-resolution NMR spectra have been acquired at the ultra high field of 21 T as well as at 14 T for selected borate and borosilicate minerals, and have been used to extract high-precision NMR parameters by using combined ab initio theoretical calculations and spectral simulations. These new NMR parameters reveal subtle correlations with various structural characters, especially the effects of the 11B chemical shifts from the bridging oxygen atom(s), site symmetry, symmetry of FBB, the sum of bond valences, as well as the next-nearest-neighbor cations and hydrogen bonding. Also, these results provide new insights into the shielding mechanism for 11B in borate and borosilicate minerals. In particular, this study demonstrates that the small variation in 11B chemical shifts can still be used to probe the local structural environments and that the established correlations can be used to investigate the structural details in borates and amorphous materials.

Signal analysis in Nuclear Magnetic Resonance spectroscopy is among the most powerful methods to quantify reaction rates in aqueous solutions. To this end, the Swift-Connick approximations to the Bloch-McConnell equations have been used extensively to estimate rate parameters for elementary reactions. The method is primarily used for 17O NMR in aqueous solutions, but the list of geochemically relevant nuclei that can be used is long, and includes 29Si, 27Al, 19F, 13C and many others of particular interest to geochemists. Here we review the derivation of both the Swift-Connick and Bloch-McConnell equations and emphasize assumptions and quirks. For example, the equations were derived for CW-NMR, but are used with modern pulse FT-NMR and can be applied to systems that have exchange rates that...

Tris-diisobutyl-dithiophosphinate complexes of europium(III) with 2,2prime-Bipyridyl are of great interest as promising luminescent sensors for biology and medicine. 1H and 13C NMR measurements are reported for the CDCl3 solution of [Eu(2,2prime-Bipy)(i-DBDTPh)3] complex. The analysis of the structural parameters found by relaxation spectroscopy NMR testifies that the bipyridyl and i-DBDTPh anions are in the first coordination sphere of a Ln cation. The found experimental results indicate that the structure of these complexes in solution is similar to that one in the solid state (known from the X-ray crystal structure data). Paramagnetic complex investigated in the paper represents the new type of thermometric NMR sensors and lanthanide paramagnetic probes for in situ temperature control i...

In this work, we address the description of the dynamics of cyclodextrins in relation with nuclear magnetic resonance (NMR) relaxation data collected for hydroxymethyl groups. We define an integrated computational approach based on the definition and parametrization of a stochastic equation able to describe the relevant degrees of freedom affecting the NMR observables. The computational protocol merges molecular dynamics simulations and hydrodynamics approaches for the evaluation of most of the molecular parameters entering the stochastic description of the system. We apply the method to the interpretation of the (13)C NMR relaxation of the -CH(2)OH group of cyclodextrins. We use ?-cyclodextrin as a case study. Results are in agreement with quantitative and qualitative analyses performed in the past with simpler models and molecular dynamics simulations. The element of novelty in our approach is in the treatment of the coupling of the relevant internal (glucopyranose ring twisting/tilting and hydroxymethyl group jumps) and global (molecular tumbling) degrees of freedom. PMID:23057513

Summary We present a new, efficient and accurate forward modelling and inversion scheme for magnetic resonance sounding (MRS) data. MRS, also called surface-nuclear magnetic resonance (surface-NMR), is the only non-invasive geophysical technique that directly detects free water in the subsurface. Based on the physical principle of NMR, protons of the water molecules in the subsurface are excited at a specific frequency, and the superposition of signals from all protons within the excited earth volume is measured to estimate the subsurface water content and other hydrological parameters. In this paper, a new inversion scheme is presented in which the entire data set is used, and multi-exponential behaviour of the NMR signal is approximated by the simple stretched-exponential approach. Compa...

Low field Nuclear Magnetic Resonance (LF-NMR) relaxation time measurements were used to evaluate the effect of different pre-salting methods (brine injection of salt and/or phosphates followed by brining, solely brining, pickling and kench salting) on the protein denaturation and change in muscle properties during the production steps of dry salted cod fillets followed by rehydration. The NMR relaxation curves were affected by the salting method and represented well the structural differences between the salting methods at each processing step. Significant correlations were observed between the NMR relaxation parameters and all physicochemical quality properties measured, except the cooking yield, when samples from all processing stages were analyzed together. The longitudinal relaxation t...

The phase transition at T?=80 K in YbAl3C3 has been studied by 27Al nuclear quadrupole resonance (NQR) measurement and nuclear magnetic resonance (NMR) measurement up to 30 T. The NQR and NMR spectra reveal clear anomalies just below T?, which provides the first microscopic evidence for symmetry lowering in the low-temperature phase below T?. The transition is characterized by marked changes in the 27Al-NQR frequencies ?Q’s without significant changes in the lattice parameters. The field dependence of the transition is also investigated. The NMR line exhibits field-induced rapid broadening below T?, which almost vanishes in zero field. Moreover, we found that T? increases by 10 K at 30 T. These unique magnetic properties are consistent with the scheme that the microscopic mechanism underlying the phase transition involves Yb-4f electrons rather than the scheme of a simple structural phase transition.   

NMR based methods to screen for high-affinity ligands have become an indispensable tool for designing rationalized drugs, as these offer a combination of good experimental design of the screening process and data interpretation methods, which together provide unprecedented information on the complex nature of protein-ligand interactions. These methods rely on measuring direct changes in the spectral parameters, that are often simpler than the complex experimental procedures used to study structure and dynamics of proteins. The goal of this review article is to provide the basic details of NMR based ligand-screening methods, with particular focus on the saturation transfer difference (STD) experiment. In addition, we provide an overview of other NMR experimental methods and a practical guide on how to go about designing and implementing them.

9-Hydroxyphenalenone is a planar multicyclic [beta]-keto-enol, which is synthesized via a Friedel-Crafts acylation followed by acid-catalyzed intramolecular Michael addition with the loss of a phenyl group in a one-pot reaction during a four-hour lab period. Tautomerization of the [beta]-keto-enol results in C[subscript 2v] symmetry on the NMR time scale, which simplifies the spectra and provides a unique structure for teaching 2D NMR spectroscopy. The [to the first power]H and [to the thirteenth power]C assignments can be made using 1D and 2D NMR techniques and data collection can be reduced to less than twenty minutes with optimized parameters. (Contains 2 figures, 1 scheme, 1 table and 1 note.)

Due to its broken spin and orbit rotation symmetries, superfluid $^3$He plays a unique role for testing rotational quantum properties on a macroscopic scale. In this system the orbital momentum forms textures that provide an effective potential well for the creation of stationary spin waves. In the limit of the lowest temperatures presently attainable, we observe by NMR techniques a profound change in the spin dynamics. The NMR line shape becomes asymmetric, strongly hysteretic and displays substantial frequency shifts. This behavior, quantitatively described by an anharmonic oscillator model, indicates that the parameters of the potential well depend on the spin waves amplitude, and therefore that the orbital motion is not damped in this new regime, not considered by the standard Leggett-Takagi theory. This regime of non-linear stationary spin waves is shown to give rise to the pulsed NMR "Persistent Signals" reported recently.

Macroscopic magnetization, muon spin rotation (muSR), and NMR measurements were carried out to study magnetism in the Na1CoO2 cobaltate. Using SQUID measurements, Na1CoO2 is shown to have a bulk magnetic susceptibility much lower and flatter than NaxCoO2 with x=0.7-0.9. In fact, muSR yields a signal of mostly non-magnetic origin, which is attributed to the x=1 phase. The intrinsic cobalt spin susceptibility corresponding to this x=1 phase is measured using Na NMR. It is indeed found to be almost zero, in agreement with a low-spin 3+ charge-state of all cobalt atoms. This single state of Co ions in CoO2 planes is confirmed by Co NMR, whose determination of cobalt shift and quadrupolar parameters allows us to give a reference value of the Co3+ orbital shift in cobaltates.

The surface active and aggregation behavior of ionic liquids of type [C n mim][X] (1-alkyl-3-methylimidazolium (mim) halides), where n?=?4, 6, 8 and [X]?=?Cl?, Br? and I? was investigated by using three techniques: surface tension, 1H nuclear magnetic resonance (NMR) spectroscopy, small-angle neutron scattering (SANS). A series of parameters including critical aggregation concentrations (CAC), surface active parameters and thermodynamic parameters of aggregation were calculated. The 1H NMR chemical shifts and SANS measurements reveal no evidence of aggregates for the short-chain 1-butylmim halides in water and however small oblate ellipsoidal shaped aggregates are formed by ionic liquids with 1-hexyl and 1-octyl chains. Analysis of SANS data analysis at higher concentrations of [C8mim][Cl]...

The thermodynamic parameters viz. excess molar volume V{sup E} and speed of sound u, transport parameter viscosity {eta}, and spectroscopic parameters viz. IR, {sup 1}H, {sup 13}C NMR have been measured for the mixtures of isomeric butanediol (1,2-, 1,3-, 1,4-, and 2,3-butanediol) and N-methyl-2-pyrrolidinone over the whole composition range at 308.15 K. The partial molar quantities Q{sub i}{sup E}, isentropic compressibility K{sub S}{sup E}, viscosity deviation {delta}{eta}, deviation in Gibbs free energies of activation for viscous flow g(x), and excess NMR chemical shift {delta}{sup E} have been estimated and analyzed. Results show that the interaction between unlike molecules takes place through hydroxyl groups of isomeric butanediol and CO group of N-methyl-2-pyrrolidinone. Excellent agreement between thermodynamic and spectroscopic measurements is observed.

A molecular-level understanding of the function of a protein requires knowledge of both its structural and dynamic properties. NMR spectroscopy allows the measurement of generalized order parameters that provide an atomistic description of picosecond and nanosecond fluctuations in protein structure. Molecular dynamics (MD) simulation provides a complementary approach to the study of protein dynamics on similar time scales. Comparisons between NMR spectroscopy and MD simulations can be used to interpret experimental results and to improve the quality of simulation-related force fields and integration methods. However, apparent systematic discrepancies between order parameters extracted from simulations and experiments are common, particularly for elements of noncanonical secondary structure. In this paper, results from a 1.2 micros explicit solvent MD simulation of the protein ubiquitin are compared with previously determined backbone order parameters derived from NMR relaxation experiments [Tjandra, N.; Feller, S. E.; Pastor, R. W.; Bax, A. J. Am. Chem. Soc. 1995, 117, 12562-12566]. The simulation reveals fluctuations in three loop regions that occur on time scales comparable to or longer than that of the overall rotational diffusion of ubiquitin and whose effects would not be apparent in experimentally derived order parameters. A coupled analysis of internal and overall motion yields simulated order parameters substantially closer to the experimentally determined values than is the case for a conventional analysis of internal motion alone. Improved agreement between simulation and experiment also is encouraging from the viewpoint of assessing the accuracy of long MD simulations.

NMR is sensitive to many interactions that the nucleus experiences with its environment. Included among these interactions are two that were heavily exploited in this thesis. They are the electric quadrupole interaction and the chemical shift interaction. These interactions yield structural information on short-range order and atom coordinations, which are very valuable and important to the understanding of properties and microstructures of glasses. Both the static or MASS NMR at high field and low field CW NMR were utilized to obtain information concerning the coordinations and local environments of several oxide glasses. For some systems, other spectroscopic methods (thermal analysis, X-ray and IR spectroscopies) were also used to assist NMR studies. In Chapter I relevant NMR theory and detection techniques used for this work are introduced. In Chapters 2-4, some structural aspects of alkali borate, borosilicate or alkali boroaluminate glasses are studied. In particular, boron coordinations in these glasses are carefully reinvestigated. The relationship between the change in boron coordinations and the changes in macroscopic characteristics of the glasses (such as electric conductivity and the mixed alkali effects) are studied. In mixed alkali glasses, the postulated alkali -pairing model provides a reasonable explanation for the structural changes. Chapter 5 is dedicated to the ^{71}Ga and ^{69 }Ga NMR studies of alkali gallate glasses. The glassforming range is explored and the gallium atom coordinations are studied. A structural model for the glass systems is suggested based on the distribution of galliums of different coordinations and structural parameters (quadrupole coupling constants, asymmetry parameters, and isotropic chemical shifts, etc.). A study of ^{31} P spectra in lead-iron-phosphate nuclear waste glasses is presented in Chapter 6. By subjecting the samples to various magnetic field strengths and different temperatures, information on the local phosphorus networks is obtained.

A general approach of size exclusion chromatography (SEC)-NMR is introduced for the determination of the classical molar mass parameters M(W), M(N), and M(P). It can be used for the determination of molar mass distributions of homopolymers and copolymers. The main advantage of SEC-NMR of copolymers is the possibility of detecting each monomer unit simultaneously with NMR as a quantitative concentration detector. Therefore, it is possible to provide the chemical compositions of copolymers at any elution volume without calibrations. In this respect, a new method will be presented for getting correct signal quantities of onflow data with sufficient NMR sensitivities. As the consequence, the chemical composition of copolymers can be correctly quantified under typical chromatographic conditions with respect to sample concentration and flow rate. Finally, the molar mass calibrations of the copolymers can be easily adjusted according to their chemical compositions. The methods were applied to polystyrene-b-poly(methyl methacrylate) block copolymers of different molar masses. The results of the molar mass distributions and the chemical composition distributions obtained by SEC-NMR are in very good agreement with the complex SEC multidetector analysis. PMID:20809564

One of the main problems in coal utilization is the inability to properly characterize its complex pore structure. Coals typically have micro/ultra-micro pores but they also exhibit meso and macroporosity. Conventional pore size techniques (adsorption/condensation, mercury porosimetry) are limited because of this broad pore size range, microporosity, reactive nature of coal, samples must be completely dried, and network/percolation effects. Small angle scattering is limited because it probes both open and dosed pores. Although one would not expect any single technique to provide a satisfactory description of a coal`s structure, it is apparent that better techniques are necessary. Small angle scattering could be improved by combining scattering and adsorption measurements. Also, the measurement of NMR parameters of various gas phase and adsorbed phase NMR active probes can provide pore structure information. We will investigate the dependence of the common NMR parameters such as chemical shifts and relaxation times of several different nuclei and compounds on the pore structure of model microporous solids, carbons, and coals. In particular, we will study the interaction between several small molecules ({sup 129}Xe, {sup 3}He, {sup 14}N{sub 2}, {sup 14}NH{sub 3}, {sup 15}N{sub 2}, {sup 13}CH{sub 4}, {sup 13}CO{sub 2}) and pore surface. Our current work may be divided into three areas: small-angle X-ray scattering (SAXS), adsorption, and NMR.

This work describes the development and applications to solids and liquid crystals of zero field nuclear magnetic resonance (NMR) experiments with pulsed dc magnetic fields. Zero field NMR experiments are one approach for obtaining high resolution spectra of amorphous and polycrystalline materials which normally (in high field) display broad featureless spectra. The behavior of the spin system can be coherently manipulated and probed in zero field with dc magnetic field pulses which are employed in a similar manner to radiofrequency pulses in high field NMR experiments. Nematic phases of liquid crystalline systems are studied in order to observe the effects of the removal of an applied magnetic field on sample alignment and molecular order parameters. In nematic phases with positive and negative magnetic susceptibility anisotropies, a comparison between the forms of the spin interactions in high and low fields is made. High resolution zero field NMR spectra of unaligned smectic samples are also obtained and reflect the symmetry of the liquid crystalline environment. These experiments are a sensitive measure of the motionally induced asymmetry in biaxial phases. Homonuclear and heteronuclear solute spin systems are compared in the nematic and smectic phases. Nonaxially symmetric dipolar couplings are reported for several systems. The effects of residual fields in the presence of a non-zero asymmetry parameter are discussed theoretically and presented experimentally. Computer programs for simulations of these and other experimental results are also reported. 179 refs., 75 figs.

The purpose of this study was to prepare nanocomposites of high-density polyethylene and montmorillonite organoclay by polymer melt intercalation, employing different processing parameters. Effective clay incorporation into polyethylene matrix was observed. The nanocomposites were structurally characterized. Intercalated nanocomposites were obtained from different process parameters, employing polyethylene resin and montmorillonite organoclays. The XRD results and other analysis showed that the processing parameters affect the organoclay delamination. The polyethylene nanocomposite presented the better performance using twin screw extruder, at 90 rpm. The purpose of characterization of polyethylene/organoclay nanocomposite by low-field NMR showed that this technique was important to understand changes in the molecular mobility of polyethylene when organoclay was incorporated. (author)

The conformation and interconversion dynamics of two derivatives of the 18-membered hexathia metacyclophane 1 and 2 were studied by (1)H NMR spectroscopy in isotropic solvents and by (2)H NMR in chiral liquid crystalline (CLC) solutions, as well as by molecular structure computations. For the analysis of the dynamic effects, we made use of the concepts of "average symmetry" and "isodynamic groups", introduced by Altmann (Altmann, Proc. R. Soc.1967, 184, A298). Compound 1, which is unsubstituted in the inner aromatic site, has, according to the NMR and molecular force field calculations, a boat shaped ground conformation with C(2) symmetry. It is highly flexible and in the NMR spectrum exhibits two successive dynamic processes. There is a low temperature (170-210 K, E(a) = 10.5 kcal/mol) alternate "wing flipping", which corresponds to interchange between pairs of enantiomers and results, in the fast exchange limit, in an average prochiral molecule with C(2v) symmetry. This process is followed, at higher temperatures (290-320 K, E(a) = 28.5 kcal/mol), by an umbrella flipping type inversion with an average structure of D(2h) symmetry. This second process involves averaging of effective enantiotopic into homotopic sites and can only be studied in chiral solvents. The origin of the chiral discrimination and of their stepwise averaging is discussed. Compound 2, which is substituted with methoxy groups at the inner sites of the benzene rings, is much less flexible and exhibits dynamic effects in the NMR spectrum only at temperatures above 370 K. We were able to study the kinetic parameters of this process in isotropic solvents (E(a) = 21.4 kcal/mol). As for 1, the detailed mechanism of this process can in principle be established using dynamic NMR in CLC; however, experimental limitation precluded us from doing so. Possible alternatives and their effect on the 1D and 2D exchange spectra in CLC are discussed in a concluding section. PMID:21894977

NMR-spin echo method has been used to study spin-lattice relaxation time of protons T1 in plant and animal cells ? muscle tissue of fish, the cells of which unlike plant cells have no developed system of vacuoles, plastids and a solid cell wall. According to the values of T1 time a new NMR parameter K, a coefficient of relaxation effectiveness of a cell structure, has been calculated. This parameter can be used for quantitative characterization of the influence of different cell structures, the tissue water interact with, for a time of spin-lattice relaxation of water protons. It has been ascertained that the values of K coefficient in animal tissue and in storing tissues of some plants differ little; it may be stipulated by permanent transmembrane water exchange which occurs at high rate ...

This study demonstrated the feasibility of using CP/MAS {sup 13}C-NMR spectroscopy for the chemical structural examination of distillation resid materials derived from direct coal liquefaction. A set of twelve carbon skeletal-structure parameters and eight molecular structural descriptors were derived from the NMR data. The technique was used previously to determine these parameters for coal and char, and in the construction of a coal pyrolysis model. The method was applied successfully to the tetrahydrofuran (THF)-soluble portion of eleven 850{degrees}F{sup +} distillation resids and one 850{degrees}F{sup +} distillation resid which contained ash and insoluble organic material (IOM). The results of this study demonstrate that this analytical method can provide data for construction of a model of direct coal liquefaction. Its further development and use is justified based on these results.

A new benzoxazine monomer based on aromatic diamine was synthesized. The influence of the reaction time on the bis[6-benziloxy-3,4-dihydro-2H-1,3-benzoxazinyl] diphenyl methane composition was investigated by ^1H NMR, ^1^3C NMR and GPC. Increasing of the reaction time leads to high closed ring content in the benzoxazine monomer. The polymerization behavior of the benzoxazine monomer synthesized at 6h reaction time was further investigated by FT-IR and differential scanning calorimetry (DSC). Non-isothermal DSC at four different heating rates was performed in order to determine the kinetic parameters and kinetic models of the curing process. Kissinger and Kissinger-Akahira-Sunose methods were used to determine the kinetic parameters. The DSC curves show an overlapping of the polymerization ...

Methodological foundations of a physical analysis of the structure of a crystallized binary system constituted by 5,6-(3?,4?-furazano)-1,2,3,4-tetrazine-1,3-dioxide and 2,4-dinitro-2,4-diazapentane by optical microscopy, NMR tomography, and X-ray diffraction analysis were developed. First results were obtained, which characterize specific features of the crystallization process and parameters of crystals being formed in a eutectic mixture and molecular compound.

A new approach is presented that treats NMR spin-spin relaxation as kinetics in spin phase space. The approach is applied to free induction decay (FID) in solids containing equivalent nuclear spins 1/2. The description obtained does not involve adjustable parameters. As an example, the calculation is performed for the fluorine FID in calcium fluoride, and the results are in good agreement with experiment.

High resolution optically pumped NMR (OPNMR) experiments are used to resolve fine features in the spin-dependent electronic structure of the valence bands in semi-insulating GaAs. By theoretically calculating oscillations in the OPNMR signal intensity with respect to the excitation energy, we have mapped out the conduction band electronic spin polarization under optical pumping. Comparison with a theoretical analysis of the oscillatory experimental features allows the extraction of semiconductor energy band parameters.

The effect of structural variations on bonding in acylated and diacylated amines (amides and imides) was studied using /sup 1/H and /sup 13/C N.M.R. spectoscopy. For benzamide derivatives, Ph-C(O)NYZ, polar and resonance substituent constants of the C(O)NYZ groups were derived by applying the dual-substituent parameter approach to the /sup 13/C chemical shifts of ring carbon atoms.

Accelerator magnets steer particle beams according to the field integrated along the trajectory over the magnet length. Purpose-wound coils measure these relevant parameters with high precision and complement efficiently point-like measurements performed with Hall plates or NMR probes. The rotating coil method gives a complete two-dimensional description of the magnetic field in a series of normal and skew multipoles. The more recent single stretched wire is a reference instrument to measure field integrals and to find the magnetic axis.

One of the main problems in coal utilization is the inability to properly characterize its complex pore structure. Coals typically have micro/ultra-micro pores but they also exhibit meso and macroporosity. Conventional pore size techniques (adsorption/condensation, mercury porosimetry) are limited because of this broad pore size range, microporosity, reactive nature of coal, samples must be completely dried, and network/percolation effects. Small angle scattering is limited because it probes both open and closed pores. Although one would not expect any single technique to provide a satisfactory description of a coal`s structure, it is apparent that better techniques are necessary. We believe that measurement of the NMR parameters of various gas phase and adsorbed phase NMR active probes can provide the resolution to this problem. We will investigate the dependence of the common NMR parameters such as chemical shifts and relaxation times of several different nuclei and compounds on the pore structure of model microporous solids, carbons, and coals. In particular, we will study the interaction between several small molecules and the pore surfaces in coals. These molecules have been selected for their chemical and physical properties. A special NMR probe will be constructed which will allow the concurrent measurement of NMR properties and adsorption uptake at a variety of temperatures. All samples will be subjected to a suite of ``conventional`` pore structure analyses. These include nitrogen adsorption at 77 K with BET analysis, CO{sub 2} and CH{sub 4} adsorption at 273 K with D-R (Dubinin-Radushkevich) analysis, helium pycnometry, and small angle X-ray scattering as well as gas diffusion measurements.

Solid-state (35)Cl NMR (SSNMR) spectroscopy is shown to be a useful probe of structure and polymorphism in HCl pharmaceuticals, which constitute ca. 50% of known pharmaceutical salts. Chlorine NMR spectra, single-crystal and powder X-ray diffraction data, and complementary ab initio calculations are presented for a series of HCl local anesthetic (LA) pharmaceuticals and some of their polymorphs. (35)Cl MAS SSNMR spectra acquired at 21.1 T and spectra of stationary samples at 9.4 and 21.1 T allow for extraction of chlorine electric field gradient (EFG) and chemical shift (CS) parameters. The sensitivity of the (35)Cl EFG and CS tensors to subtle changes in the chlorine environments is reflected in the (35)Cl SSNMR powder patterns. The (35)Cl SSNMR spectra are shown to serve as a rapid fingerprint for identifying and distinguishing polymorphs, as well as a useful tool for structural interpretation. First principles calculations of (35)Cl EFG and CS tensor parameters are in good agreement with the experimental values. The sensitivity of the chlorine NMR interaction tensor parameters to the chlorine chemical environment and the potential for modeling these sites with ab initio calculations hold much promise for application to polymorph screening for a wide variety of HCl pharmaceuticals. PMID:18656917

In this paper, equations are proposed which relate various NMR parameters of OHN hydrogen-bonded pyridine-acid complexes to their bond valences which are in turn correlated with their hydrogen-bond geometries. As the valence bond model is strictly valid only for weak hydrogen bonds appropriate empirical correction factors are proposed which take into account anharmonic zero-point energy vibrations. The correction factors are different for OHN and ODN hydrogen bonds and depend on whether a double or a single well potential is realized in the strong hydrogen-bond regime. One correction factor was determined from the known experimental structure of a very strong OHN hydrogen bond between pentachlorophenol and 4-methylpyridine, determined by the neutron diffraction method. The remaining correction factors which allow one also to describe H/D isotope effects on the NMR parameters and geometries of OHN hydrogen bond were determined by analysing the NMR parameters of the series of protonated and deuterated pyridine- and collidine-acid complexes. The method may be used in the future to establish hydrogen-bond geometries in biologically relevant functional OHN hydrogen bonds. PMID:15372662

The experiments conducted in this work demonstrate the efficiency and sensitivity of single-sided NMR for investigating macromolecular materials on large time and length scales. Elastomers can readily be characterized by unilateral NMR of protons in terms of a variety of parameters, which correlate with the overall molecular mobility. In this way information about the cross-link density, state of cure and strain, the effects of aging and product heterogeneity can obtained. For these purposes, the NMR-MOUSE was used to optimize product development and to monitor product and production quality on-line. The sensor is also suitable for nondestructive probing of the mechanical deformation in cross-linked elastomers. A special magnet design that fits a stress-strain device has been used for complementary investigation of a series of different rubber stripes during mechanical testing. The profile NMR-MOUSE was found to be a unique tool for the characterization of changes induced by the UV irradiation in natural rubber. The aging profiles were interpreted for the first time based on a novel model in which the radiation absorption coefficient depends on the depth in the sample. (orig.)

The fluorescent properties of a trinitrophenylated Meisenheimer complex of adenosine (TNP-Ado) in water were examined in the presence of alpha-, beta-, and gamma-cyclodextrins (CDs). The TNP-Ado complex exhibits minimal fluorescence in water, whereas addition of 10 mM alpha-CD, beta-CD, and gamma-CD enhances fluorescence by factors of 2, 7, and 110, respectively. The large enhancement by gamma-CD is attributed to its larger hydrophobic cavity, which is able to accommodate the TNP moiety of TNP-Ado. (1)H NMR spectra demonstrate 1:1 stoichiometry of the complex, which undergoes slow exchange on the NMR time scale. (1)H NMR and 2D ROESY spectra reveal substantial interaction of the TNP hydrogens with gamma-CD. Equilibrium constants were determined by fluorimetry from 10 to 20 degrees C by nonlinear curve fitting. Fluorescence is temperature dependent, with maximum fluorescence increasing with decreasing temperature. Complexation is exothermic with large negative entropy, consistent with formation of a tight complex between TNP-Ado and gamma-CD. Rate constants and activation parameters for both complexation and dissociation were determined by a combination of fluorimetry and 2D NMR exchange spectroscopy (EXSY). PMID:20499941

Site-specific isotopic values of methyl tertiary butyl ether (MTBE) were measured using quantitative site-specific (2)H nuclear magnetic resonance (NMR) spectroscopy for seven commercially available MTBE products. The delta(2)H values of the methoxy and tertiary butyl groups ranged from -103 per thousand to -171 per thousand, and from -76 per thousand to -104 per thousand, reflecting their production from methanol and isobutene, respectively. Several MTBE products whose whole-compound delta(13)C and delta(2)H MTBE values were within error of each other, as measured by isotope ratio mass spectrometry (IRMS), had demonstrably different delta(2)H values for their methoxy and tertiary butyl groups measured by (2)H NMR. Site-specific isotopic variations were large enough to provide proof of principle that quantitative site-specific (2)H NMR may provide an additional parameter for contaminant sourcing at field sites. Isotopic variations were small enough to not bias the comparability of degradation-associated isotopic enrichment factors determined using different MTBE products. Calculated delta(2)H values for MTBE, derived as weighted averages of (2)H NMR measurements of the two functional groups, showed good agreement with IRMS measurements. The ability to gain accurate information about the site-specific isotopic ratios of (2)H/(1)H within a molecule offers considerable promise as a new environmental tool to track the source and fate of environmental contaminants. PMID:20041709

NMR imaging, NMR spectroscopic, and histopathologic techniques were used to study the proton relaxation time and related biochemical changes in the central nervous system after helium beam in vivo irradiation of the rodent brain. The spectroscopic observations reported in this dissertation were made possible by development of methods for measuring the NMR parameters of the rodent brain in vivo and in vitro. The methods include (1) depth selective spectroscopy using an optimization of rf pulse energy based on a priori knowledge of N-acetyl aspartate and lipid spectra of the normal brain, (2) phase-encoded proton spectroscopy of the living rodent using a surface coil, and (3) dual aqueous and organic tissue extraction technique for spectroscopy. Radiation induced increases were observed in lipid and p-choline peaks of the proton spectrum, in vivo. Proton NMR spectroscopy measurements on brain extracts (aqueous and organic solvents) were made to observe chemical changes that could not be seen in vivo. Radiation-induced changes were observed in lactate, GABA, glutamate, and p-choline peak areas of the aqueous fraction spectra. In the organic fraction, decreases were observed in peak area ratios of the terminal-methyl peaks, the N-methyl groups of choline, and at a peak at 2.84 ppM (phosphatidyl ethanolamine and phosphatidyl serine resonances) relative to TMS. With histology and Evans blue injections, blood-brain barrier alternations were seen as early as 4 days after irradiation. 83 references, 53 figures.

The dynamics of interlayer H2O in VOPO4·2H2O have been studied by 1H and 2H NMR measurements. This compound contains two different kinds of water molecules. One of the two water molecules has a coordination bond to the V in the layer. The 2H NMR spectrum at 150 K was reproduced by one component with the quadrupole-coupling constant QCC = 220 kHz and the asymmetry parameter ? = 0.12. This result suggests that all H2O molecules are static at this temperature. In the temperature range of 160–240 K, both interlayer H2O molecules show 180°-flipping motion from the 2H NMR spectra. This motion of the two different H2O molecules suggests the hydrogen-bonding network between these interlayer H2O. The activation energies of this motion could be determined to be 30 kJ mol?1 from the 2H NMR spectrum simulation. Additionally, the diffusional component also appeared above 240 K. Above 270 K, two-dimensional diffusion of the interlayer species is suggested in this material.   

The present report documents the efforts to develop an impedance method for determining the distribution of the water saturation in a chalk core sample. Measurement of this distribution during a displacement process will make it possible to make numerical simulations of the process which may in turn reveal important rock parameters. The impedance method is one among other methods to determine saturation profiles in a research programme on rock parameters with participants from Danmarks Tekniske Universitet, DTU, and Danmarks og Groenlands Geologiske Undersoegelse, GEUS. The other methods investigated are nmr-scanning and {gamma}-logging. (au)

Abstract in english A series of forty Mannich bases of glutarimides with sulfonamides and secondary amines were synthesized and evaluated in vitro against six pathogenic Gram-positive and Gram-negative bacteria. The synthesized Mannich bases were characterized by elemental and spectral analysis. The modeling anti-bacterial activities of these newly synthesized Mannich bases against six bacteria was attempted employing ¹H NMR chemical shift, physicochemical properties and topological indices (more) as the correlating parameters. Our results, based on Quantitative Structure-Activity Relationships (QSARs), have indicated that statistically significant models are obtained for modeling the anti-bacterial activities The results are discussed critically using a variety of statistical parameters.

The determination of the average molecular parameters of bitumens represents an important step in describing the skeletons of asphalt cements. Knowledge of this seems to be an important step towards understanding ageing and oxidation mechanisms. A new investigation method is presented, based only on the analysis of {sup 13}C nuclear magnetic resonance (n.m.r.) data and molecular weights. This method is proved to be an efficient procedure to give independent parameters and to try to define a `fingerprint` of the bitumens. In particular, the aromatic part of these complex mixtures is described by comparison with an exhaustive list of possible models. 17 refs., 6 tabs., 3 figs.

The macromolecular structures of the three major macerals, vitrinite, exinite and fusinite, separated from a unique Pingshuo bituminous coal are probed and characterized using advanced analytical techniques including [sup 13]C-NMR, XPS, FTIR and XRD. Structural parameters of the individual macerals, for instance, aromaticity, carbon and hydrogen distribution, existing form of heteroatoms and functional groups are measured and investigated. The microcrystallite parameters are also calculated from XRD analysis. The results indicate that the differences in macromolecular structure of the three macerals are obvious and can be distinguished from each other. 7 refs., 5 figs., 7 tabs.

Li diffusion and transport parameters of binary lithium carbide Li{sub 2}C{sub 2} were complementarily investigated by {sup 7}Li (nuclear magnetic resonance) NMR and impedance spectroscopy. Long-range Li diffusion parameters were measured by using mixing-time-dependent and temperature-variable stimulated echo NMR spectroscopy. The method is sensitive to ultra-slow Li hopping processes which were probed from an atomic-scale point of view. Two-time phase correlation functions S{sub 2} obtained can be parameterized by stretched exponentials only. The corresponding echo decay rates {tau}{sup -1}, which were recorded at a resonance frequency of e.g. 155.5 MHz, show Arrhenius behaviour revealing an activation energy of 0.80(2) eV. This value is in very good agreement with that deduced from dc conductivity measurements (0.79(2) eV) probing Li transport processes on a macroscopic length scale. The comparison of impedance data with the measured NMR echo decay functions showed that both methods reflect diffusion processes being characterized by very similar motional correlation functions.

One of the main problems in coal utilization is the inability to properly characterize its complex pore structure. Coals typically have micro/ultramicro pores but they also exhibit meso and macroporosity. Conventional pore size techniques (adsorption/condensation, mercury porosimetry) are limited because of this broad pore size range, microporosity, reactive nature of coal, samples must be completely dried, and network/percolation effects. Small angle scattering is limited because it probes both open and closed pores. Although one would not expect any single technique to provide a satisfactory description of a coal`s structure, it is apparent that better techniques are necessary. Small angle scattering could be improved by combining scattering and adsorption measurements. Also, the measurement of NMR parameters of various gas phase and adsorbed phase NMR active probes can provide pore structure information. The dependence of the common NMR parameters such as chemical shifts and relaxation times of several different nuclei and compounds on the pore structure of model microporous solids, carbons, and coals is investigated. In particular, the interaction between several small molecules ({sup 129}Xe, {sup 3}He, {sup 14}N{sub 2},{sup 14}NH{sub 3},{sup 15}N{sub 2},{sup 13} CH{sub 4}, {sup 13}CO{sub 2}) and pore surface is studied.

One of the main problems in coal utilization is the inability to properly characterize its complex pore structure. Coals typically have micro/ultramicro pores but they also exhibit meso and macroporosity. Conventional pore size techniques (adsorption/condensation, mercury porosimetry) are limited because of this broad pore size range, microporosity, reactive nature of coal, samples must be completely dried, and network/percolation effects. Small angle scattering is limited because it probes both open and closed pores. Although one would not expect any single technique to provide a satisfactory description of a coal`s structure, it is apparent that better techniques are necessary. Small angle scattering could be improved by combining scattering and adsorption measurements. Also, the measurement of NMR parameters of various gas phase and adsorbed phase NMR active probes can provide pore structure information. We will investigate the dependence of the common NMR parameters such as chemical shifts and relaxation times of several different nuclei and compounds on the pore structure of model microporous solids, carbons, and coals. In particular, we will study the interaction between several small molecules ({sup 129}Xe, {sup 3}He, {sup 2}H{sub 2},{sup 14}N{sub 2}, {sup 14}NH{sub 3}, {sup 15}N{sub 2},{sup 13}CH{sub 4}, {sup 13}CO{sub 2}) and the pore surfaces in coals.

Hydrogen (1H) and carbon (13C) high resolution nuclear magnetic resonance (NMR) spectroscopy, gas chromatography-mass spectroscopy (GC-MS), and high pressure liquid chromatography (HPLC) were used to determine the relative amounts of molecular functional groups in a series of narrow boiling range distillates from two crude oils. San Andres formation and Tensleep black oils were characterized. Spinning band distillation was used to generate fractions centered approximately on each successive normal paraffin. Each fraction spanned a range of about three- to four carbon numbers from C7 to C35. The heavy C35+ distillate residue was also studied. Quantitative HPLC separations were performed on each distillate to provide paraffin-naphthene (PN), one-ring aromatic (A1), two-ring aromatic (A2) and three-plus-ring aromatic (A3+) weight percentages. The total aromatic weight percentage was also determined based on NMR data and was observed to agreed closely with the HPLC results. The aromatic character of the San Andres formation oil and the paraffinic character of the Tensleep are clearly indicated in the spectroscopic and chromatographic results. The NMR data also provided such unique structural parameters as the total weight fraction of aromatic ring carbons, aromatic hydrogenated ring carbons, bridgehead aromatic ring carbons, methyl substituted ring carbons, other alkyl substituted aromatic ring carbons, and aromatic side chain carbons. Differences in these parameters were observed between the two oils across their boiling ranges providing unique characterization fingerprinting.

We used V51 NMR to study magnetic ordering in the Ni3V2O8 single crystal with a Kagome staircase structure of Ni atoms. The NMR spectra were measured in the temperature range T=(3-300)K and magnetic fields H=(2-9.4)T directed along the main a,b,c axes of the orthorhombic (Cmca) crystal. The local magnetic field at the V51 NMR probe determines position and the shape of the corresponding NMR line. These parameters yield an unique information, respectively, on the uniform and the staggered spin components of the ordered Ni. The NMR data collected at H?2T are considered in line with predictions of the representation theory [A. Harris, Phys. Rev. B 76, 054447 (2007)] with a result that incommensurate amplitude-modulated structure of the spine Nis spins acquires in the high-temperature incommensurate (HTI) phase two prominent nearly equal spin components Sa?Sc?Sb instead of the longitudinal incommensurate spin-density wave (SDW) order with Sa?Sc,Sb as it was deduced from neutron-diffraction data [M. Kenzelmann , Phys. Rev. B 74, 014429 (2006)]. No noticeable variation of SDW polarization in the ab plane was detected below the HTI-low-temperature incommensurate (LTI) transition. In both the HTI and LTI phases two almost equal spin components of the Nis spins Sa?Sc?Sb exist at H<4.7T . Their phasing is still not determined. The bulk magnetization in these phases is explained by contribution of the cross-tie Nic spins which antiferromagnetic structure in the LTI phase is canted along H .

Exercise modulates the metabolome in urine or blood as demonstrated previously for humans and animal models. Using nuclear magnetic resonance (NMR) metabolomics, the present study compares the metabolic consequences of an exhaustive exercise at peak velocity (Vp) and at critical velocity (Vc) on mice. Since small-volume samples (blood and urine) were collected, dilution was necessary to acquire NMR spectra. Consequently, specific processing methods were applied before statistical analysis. According to the type of exercise (control group, Vp group and Vc group), 26 male mice were divided into three groups. Mice were sacrificed 2 h after the end of exercise, and urine and blood samples were drawn from each mouse. Proton NMR spectra were acquired with urine and deproteinized blood. The NMR data were aligned with the icoshift method and normalised using the probabilistic quotient method. Finally, data were analysed with the orthogonal projection of latent-structure analysis. The spectra obtained with deproteinized blood can neither discriminate the control mice from exercised mice nor discriminate according to the duration of the exercise. With urine samples, a significant statistical model can be estimated when comparing the control mice to both groups, Vc and Vp. The best model is obtained according to the exercise duration with all mice. Taking into account the spectral regions having the highest correlations, the discriminant metabolites are allantoin, inosine and branched-chain amino acids. In conclusion, metabolomic profiles assessed with NMR are highly dependent on the exercise. These results show that urine samples are more informative than blood samples and that the duration of the exercise is a more important parameter to influence the metabolomic status than the exercise velocity. PMID:22706325

MUC1 mucin is a breast cancer-associated transmembrane glycoprotein, of which the extracellular domain is formed by the repeating 20-amino acid sequence GVTSAPDTRPAPGSTAPPAH. In neoplastic breast tissue, the highly immunogenic sequence PDTRPAP (in bold above) is exposed. Antibodies raised directly against MUC1-expressing tumors offer unique access to this neoplastic state, as they represent immunologically relevant ''reverse templates'' of the tumor-associated mucin. In a previous study [Grinstead, J. S., et al. (2002) Biochemistry 41, 9946-9961], 1H NMR methods were used to correlate the effects of cryptic glycosylation outside of the PDTRPAP core epitope sequence on the recognition and binding of Mab B27.29, a monoclonal antibody raised against breast tumor cells. In the study presented here, isotope-edited NMR methods, including 15N and 13C relaxation measurements, were used to probe the recognition and binding of the PDTRPAP epitope sequence to Fab B27.29. Two peptides were studied: a one-repeat MUC1 16mer peptide of the sequence GVTSAPDTRPAPGSTA and a two-repeat MUC1 40mer peptide of the sequence (VTSAPDTRPAPGSTAPPAHG)2. 15N and 13C NMR relaxation parameters were measured for both peptides free in solution and bound to Fab B27.29. The 13CR T1 values best represent changes in the local correlation time of the peptide epitope upon binding antibody, and demonstrate that the PDTRPAP sequence is immobilized in the antibody-combining site. This result is also reflected in the appearance of the 15N- and 13C-edited HSQC spectra, where line broadening of the same peptide epitope resonances is observed. The PDTRPAP peptide epitope expands upon the peptide epitope identified previously in our group as PDTRP by homonuclear NMR experiments [Grinstead, J. S., et al. (2002) Biochemistry 41, 9946-9961], and illustrates the usefulness of the heteronuclear NMR experiments. The implications of these results are discussed within the context of MUC1 breast cancer vaccine design.

Accidental overexposures and radiotherapy treatment must be able to evaluate and to control the dose absorbed by a tissue. We propose in this work to employ nuclear magnetic resonance (NMR) technique to detect effects of ionizing radiations in a tissue-equivalent model. A Fricke solution formed with ammonium ferrous sulphate in acid environment was incorporated in an Agorose gelling substance. Exposed to ionizing radiations, an oxidation transforms ferrous ions to ferric ions. Both Fe{sup 2+} and Fe{sup 3+} are paramagnetic and the spin lattice relaxation process of protons (measured by NMR) is accelerated according to the amount of Fe{sup 2+} transformed into Fe{sup 3+}. Experiments were performed with {gamma} rays of {sup 197}Ir and {sup 60}Co sources with doses in the 0 - 100 Gy range. The concentrations of Fe{sup 2+} were 0.5, 1, 1,5 and 2 mM and these solutions were incorporated in a gelling substances of 1, 2, 3 and 4% agarose. NMR experiments performed in an imaging system operating at 2 Tesla, consisted to measure longitudinal relaxation times T1 and to acquire spin echo NMR images at different Fe{sup 2+} concentrations and doses. A linear relationship between absorbed doses and the NMR parameters (TI{sup -1} and relative image intensity) was obtained (Fig. 1 and 2). A marked decrease in longitudinal relaxation times was observed depending on the absorbed dose, on the [Fe{sup 2+}] concentration, and on the irradiating source. This work had permit one to verify the existence of a dose-effect relationship between the proton relaxation times and the irradiation dose and to extend previous results to an irradiation dose range corresponding to the conditions of accidental human exposure (i.e. doses higher than 60 Gy) involving {sup 60}Co or {sup 192}Ir {gamma} rays. (author)

Using first-principles calculations within the frame of the density functional theory, we analyze electronic properties of the boron fullerene B80, based on NMR, NQR parameters and NBO analysis. Our results show three typical ranges for boron chemical shielding parameters corresponding to each of the nonequivalent magnetic sites of the B atoms. These three sites are related to frame atoms and two sets of atoms capping hexagons, endohadral and exohedral caps. Calculating quadrupole coupling components confirm this conclusion with more sensitivity than chemical shielding parameters. In addition calculated asymmetry parameter shows that EFG tensor for boron atoms capping hexagons is axially symmetric, @h ~ 0, while this tensor becomes considerably asymmetric for frame atoms, @h = 0.95, as a r...

The local electric properties of ?-Ag0.33V2O5, a pressure-induced superconductor, were studied at ambient pressure using a nuclear magnetic resonance (NMR) technique. Three crystallographically inequivalent Vi sites (i=1, 2, and 3) were identified from 51V-NMR spectra. We determined the principal axes of the electric-field-gradient (EFG) tensor, electric quadrupole frequency, asymmetric parameter, and Knight shift for each Vi site in the metallic phase and the subsequent charge-ordering (CO) phase at low temperatures. The results suggest that the electric properties for the V1 sites are similar to those for the V3 sites, whereas those for the V2 sites are different from those for the V1 and V3 sites. The peculiarity in the metallic phase reflects the electric properties in the CO phase and is attributable to the diagonal structure of the Vi orbitals.   

^1H HRMAS NMR spectroscopy has been applied to investigate differences at a metabolic level between ''flavor varieties'' of high quality tomatoes marketed as Protected Geographical Indication from Almeria (Spain). The varieties studied include the non-hybrid Raf tomato, one of the most tasteful commercial tomatoes that is traditionally grown in this Spanish region, together with other two hybrid varieties of commercial names Rambo and Zayno. Standard quality parameters were poorly reliable for establishing specific correlations with a given variety. In contrast, ^1H HRMAS NMR spectroscopy, in combination with principal component analysis (PCA) and assigned signal analysis (ASA) provided a clear differentiation between varieties as a function of the ripening process and revealed the existen...

The metabolomic approach has been widely used in toxicology to investigate mechanisms of toxicity. To understand the mammalian system?s response to nickel exposure, we analysed the NiCl2 induced metabolomic changes in urine of rats using 1H nuclear magnetic resonance (1H NMR) spectroscopy together with clinically relevant biochemical parameters. Male Sprague?Dawley rats were administered intraperitoneally with NiCl2 at doses of 4, 10 and 20?mg/kg body weight. Urine samples were collected at 8, 16, 24, 72, 96 and 120?h post treatment. The metabolomic profile of rat urine showed prominent changes in citrate, dimethylamine, creatinine, choline, trimethylamine oxide (TMAO), phenyl alanine and hippurate at all doses. Principal component analysis of urine 1H NMR spectra demonstrated the dose and...

A series of X-type alkyl sulfonate Gemini surfactants (XCn, nÃ? =Ã? 6, 8, 10) was synthesized by a simple method. The chemical structures of the prepared compounds were confirmed by 1H NMR, 13C NMR, ESIââ?¬â??MS and Elementary analysis. The surface activity and thermodynamic properties of micellization of the X-type alkyl sulfonate Gemini surfactants were compared with sodium dodecylsulfate by means of surface tension. The properties of XCn are superior to those of SDS such as the Ã?³CMC and CMC of XC10 are 26.3Ã? mN/m and 0.2Ã? mmol/L respectively. The adsorption isotherms for XCn were established by fitting the pre-CMC surface tension data with a quadratic function. The thermodynamic parameters of micellization ( Formula Not Shown , Formula Not Shown , Formula Not Shown ) derived f...

Nuclear magnetic resonance imaging techniques were investigated for nondestructive evaluation of injection molded structural ceramics. Several injection-molded Si{sub 3}N{sub 4} test bars, fabricated using different mixing and molding parameters, were imaged by 2-D back-projection {sup 1}H NMR techniques. The gray scale intensities of the images were correlated with the data obtained by destructive testing. The correlation studies indicate that changes in the organic concentration to a level of {plus minus} 0.5 wt % can be detected with NMR. It is possible, with these techniques, to monitor the chemical changes that occur at various stages of ceramic processing and use this information to improve the ceramic processing and reliability. 8 refs., 1 tab.

In this study, we have applied two different spanning protocols for obtaining the molecular conformations of L-tryptophan in aqueous solution, namely a molecular dynamics simulation and a molecular mechanics conformational search with subsequent geometry re-optimization of the stable conformers using a quantum mechanically based method. These spanning protocols represent standard ways of obtaining a set of conformations on which NMR calculations may be performed. The results stemming from the solute–solvent configurations extracted from the MD simulation at 300 K are found to be inferior to the results stemming from the conformations extracted from the MM conformational search in terms of replicating an experimental reference as well as in achieving the correct sequence of the NMR relative chemical shifts of L-tryptophan in aqueous solution. We find this to be due to missing conformations visited during the molecular dynamics run as well as inaccuracies in geometrical parameters generated from the classical molecular dynamics simulations.

H3 ? 2x Nb x M2 ? x (PO4)3 (M = In, Fe) acid phosphates have been obtained by ion exchange from their lithium forms and X-ray powder diffraction, impedance measurements, and 7Li and 1H NMR spectroscopy. The parameters of the hexagonal unit cell of the proton-exchanged forms differ only slightly from those of the initial lithium compounds. According to 1H NMR data, the proton in the acid phosphates is not hydrated. The conductivity of the acid phosphates at high temperatures depends weakly on their composition and is ?1.7 ? 10?7 S cm?1 at 620 K. The activation energy of conduction is 30?33 kJ/mol (430?770 K).

Complexes of CrIII, MnII, ZnII & CdII with the polydentate carboxamide ligandN?, N??-bis(3-carboxy-1-oxoprop-2-enyl) 2-Amino-N-arylbenzamidine (H2L) have been synthesized and characterized by elemental analyses, spectroscopic studies (Vibrational, electronic, ESR and 1H-NMR), magnetic susceptibility measurements, thermal studies and powder diffraction studies. The vibrational spectral data are in agreement with coordination of amide and carboxylate oxygen of the ligands with the metal ions. The electronic spectra indicates octahedral or tetrahedral geometry around the metal ions, has been supported by magnetic susceptibility measurements. The results of electron spin resonance & 1H-NMR spectra have supported the results of other spectral techniques. Kinetic and thermodynamic parameters wer...