|
|
|
Novel allylic phosphonium salts in free radical accelerated cationic polymerization
2009-01-01
In the present study, the synthesis and evaluation of novel allylic phosphonium salts as addition fragmentation agents in combination of conventional (photo-/thermal) free radical source for cationic polymerization are described. The amide based allylic phosphonium salts, namely 2-(N, N-dimethylcaboxy-propenyl) triphenylphosphonium hexafluoroantimonate (DMTPH) and 2-(morpholinocarboxy-propenyl) triphenyl phosphonium hexafluoroantimonate (MTPH) were synthesized and characterized. The thermal and photo-latency of these salts was examined with and without free radical sources in bulk polymerization of cyclohexene oxide (CHO) salts at 70C and
2010-01-01
A rapid cationic polymerization of cyclohexene oxide that completed within a few minutes was achieved by a new initiation system that involves (1) a copper-catalyzed reduction of benzoyl peroxide by an ascorbic acid derivative that generates free radicals and (2) capture of the radicals by allyl sulfonium salt having hexafluoroantimonate (SbF6-) as a counter anion, followed by fragmentation of sulfonium radical cation, from which a super acid HSbF6 was produced to initiate the rapid polymerization. The key factor in designing an efficient allyl sulfonium salt was attachment of an electron withdrawing ester group at the allyl group, of which ability to stabilize the formed radical can enhance the efficiency in trapping radicals by the allylic salt. Copyright 2010 Wiley Periodicals, Inc. J P...
1987-01-01
The effect of quaternary ammonium salts on the decays of the radical cations of biphenyl, trans-stilbene, anthracene and pyrene generated by pulse radiolysis in chlorohydrocarbons has been investigated. The decays, which are due to neutralization reactions with Cl-, are retarded by the addition of salts having non-nucleophilic PF6-, BF4- and ClO4-, whereas the radical cations are rapidly quenched by salts having I- and BPh4-. The retarding effect of the salts is attributed to the formation of ion pairs between the reacting ions and the counter-ions from the salts. The rate constants for the neutralization reactions in 1,2-dichloroethane have been determined for the free-ion and ion-paired states. The latter state is attained by the addition of ...
Multi-tetrathiafulvalene system linked by 1,3- and 1,3,5-positions of aromatic rings
1995-03-15
New donors having two or three TTF units in the molecules have been synthesized, in order to examine the interaction of TTF radicals in diradical-dication and triradical-trication states. The molecular structure of two donors and a radical-cation salt and the conductivity of the CT complexes and the radical salts of new donors are presented. (orig.)
1999-01-01
Tetraalkyl and dialkyl derivatives, where alkyl=ethyl and propyl, of the organic electron donor molecule bis(ethylenedithio)tetrathiafulvalene, BEDT-TTF or ET, have been synthesized via the Diels-Alder approach. Several cation-radical salts of these new donors have been prepared and structurally characterized, and found to contain donor molecules in nominally higher oxidation states (+1, +1.5 and +2) than the typically observed oxidation state of +0.5 in BEDT-TTF salts. The higher solubility of the tetraalkyl and dialkyl derivatives in solvents used for crystal growth is proposed as the principal reason for this finding. Surprisingly, X-ray crystallographic studies reveal that the alkyl groups in the neutral tetraethyl-ET as well as the oxidized tetraethyl-ET and diethyl-ET molecules in their cation-radical salts adopt axial configurations, rather than the expected equatorial configurations. Electrical properties of the cation-radical salts have been found to be either insulating or semiconducting, consistent with the higher oxidation states of the donor molecules in the salts and the crystal structures.
Kinetics of the reduction of organic cations by cation radicals
It has been found that the reduction of substituted diazonium, iodonium, and tropylium salts by cation radicals of tetra-tert-butyl-bis-pyrylium, tetramethyl-p-phenylene diamine (I), tetraphenylbenzidine, and N-methylphenothiazine obey the kinetic equation of the second order and that it follows an electron transfer mechanism. The logarithms of the rate constants of these reactions decrease with increasing standard free energy of the electron transfer reaction. The rate of the reaction of C/sub 6/H/sub 5/N/sub 2//sup +/ BF/sub 4//sup -/ with I and the selectivity of the reactions of the substituted diazonium salts with I increases with the electron donor capacity of the solvent. The addition of crown-ethers accelerates the reaction. The reaction rate increases also with increasing ionic strength of the solution, whereby the Cl/sup -/ anions have a specifically accelerating effect. The observed rules governing the influence of the medium contradict those found earlier for the interaction of organic cations with neutral radicals and anion radicals. This is attributed to the fact that the electron transfer takes place in ternary complexes cation-solvent (crown ether, Cl/sup -/ ion)-cation radical.
Kinetics of the reduction of organic cations by cation radicals
1985-07-01
It has been found that the reduction of substituted diazonium, iodonium, and tropylium salts by cation radicals of tetra-tert-butyl-bis-pyrylium, tetramethyl-p-phenylene diamine (I), tetraphenylbenzidine, and N-methylphenothiazine obey the kinetic equation of the second order and that it follows an electron transfer mechanism. The logarithms of the rate constants of these reactions decrease with increasing standard free energy of the electron transfer reaction. The rate of the reaction of C/sub 6/H/sub 5/N/sub 2//sup +/ BF/sub 4//sup -/ with I and the selectivity of the reactions of the substituted diazonium salts with I increases with the electron donor capacity of the solvent. The addition of crown-ethers accelerates the reaction. The reaction rate increases also with increasing ionic strength of the solution, whereby the Cl/sup -/ anions have a specifically accelerating effect. The observed rules governing the influence of the medium contradict those found earlier for the interaction of organic cations with neutral radicals and anion radicals. This is attributed to the fact that the electron transfer takes place in ternary complexes cation-solvent (crown ether, Cl/sup -/ ion)-cation radical.
Reaction of radical cations with multilayers of tannic acid and polyelectrolytes
2007-01-01
Specific features of the reaction of radical cations of 2,2-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS+) with mono-and multialyers of a polyphenol (tannic acid) and polycations (polyallylamine hydrochloride or dimethyldiallylammonium chloride), formed by layer-by-layer deposition, were studied. The antioxidant properties of tannic acid are preserved in the multilayers, and the kinetic features of the reaction of ABTS+ with tannic acid depend on the film architecture.?
1987-06-01
The effect of quaternary ammonium salts on the decays of the radical cations of biphenyl, trans-stilbene, anthracene and pyrene generated by pulse radiolysis in chlorohydrocarbons has been investigated. The decays, which are due to neutralization reactions with Cl/sup -/, are retarded by the addition of salts having non-nucleophilic PF/sub 6//sup -/, BF/sub 4//sup -/ and ClO/sub 4//sup -/, whereas the radical cations are rapidly quenched by salts having I/sup -/ and BPh/sub 4//sup -/. The retarding effect of the salts is attributed to the formation of ion pairs between the reacting ions and the counter-ions from the salts. The rate constants for the neutralization reactions in 1,2-dichloroethane have been determined for the free-ion and ion-paired states; the latter state is attained by the addition of Bu/sub 4/NPF/sub 6/. The rate constant determined in the absence of the salt for Pysup(radical)/sup +/ is one order of magnitude smaller than those for the others. The salt effect is also smallest on the reaction of Pysup(radical)/sup +/. The charge delocalisation of the large aromatic radical cation may be responsible for the exceptional results for Pysup(radical)/sup +/. The largest salt effect was observed on the reaction of Ph/sub 2/CH/sup +/, a charge-localized carbenium ion investigated for comparison. The solvent effect on the neutralization reactions is also discussed.
Crystal structure of radical cation salt (BEDT-TTF)4(GaCl4)2 centre dot C6H5CH3
2001-01-01
A new radical cation salt based on bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) with the tetrahedral anion GaC1-4, namely, (BEDT-TTF)4(GaCl4)2 centre dot C6H5CH3 , has been synthesized. The crystal structure of this salt is determined by X-ray diffraction analysis [a = 31.757(2) A, b = 6.8063(3) A, c = 34.879(2) A, beta = 90.453(4) deg., V 7538.8(7) A3 , space group I2/c, and Z = 4]. In the structure, the radical cation layers alternate with the anion layers along the c-axis. The anion layers consist of the GaC1-4 tetrahedra and solvent molecules. The packing of BEDT-TTF molecules in the radical cation layer differs from that in the structure of the known salt (BEDT-TTF)2GaCl4 , ...
Tetrathiafulvalene-Based Conductors Containing Organometallic Components
Hundreds of cation radical salts containing tetrathiafulvalene (TTF) and its derivatives have been prepared and characterized over the past 50 years. After superconductivity was discovered in salts containing bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF), a tremendous international effort was undertaken to prepare cation radical salts containing nearly every imaginable type of anion in a search for new superconducting materials. Surprisingly, only a relatively small number of these salts contained organometallic anions. The use of tetrakis(trifluoromethyl)metallate anions as charge compensating components in BEDT-TTF salts resulted in the discovery of a diverse family of molecular superconductors. More recently, organometallic anions have been utilized as a means to introduce multiple properties into a single material. Halophenylene, metallocarborane and metallocene-type anions have been utilized as components of cation radical salts. Several covalent derivatives of the TTF molecule have also been reported that incorporate organometallic moieties. Due to the diverse nature of organometallic anions and contemporary interest in coupling redox active species to the TTF moiety, it is likely that this field will exhibit significant growth in the years ahead.
1986-01-01
Pulse radiolysis of trans-stilbene (St) in tetrahydrofuran (THF) solution was carried out in the presence of quaternary ammonium salts, such as Bu4NPF6, Bu4NI, Bu4NBPh4, CeMe3NPF6, PhMe3NPF6, and BzMe3NPF6 (Bu, butyl. Ce, cetyl. Me, methyl. Ph, phenyl. And Bz, benzyl). The absorption peak of the radical anions, St-., was shifted to shorter wavelengths in the presence of the salts. The magnitude of the shift depends on the substituent groups of the quaternary ammonium cations. It is suggested that St-. forms contact ion pairs with the quaternary ammonium cations. The decay rate of St-. decreases with increasing salt concentration and becomes steady. The rate constants for the neutralization ...
Study on radiation-induced cationic polymerization enhanced by pyridinium salts
2003-01-01
A study was carried out on radiation-induced cationic polymerization enhanced by the N-Alkoxypyridinium salt having relatively stable nonnucleophilic anion (PF6-). After investigations on the cationic inhibitors, different atmosphere conditions and the molecular weight and its distribution, it was proved that the cationic polymerization takes place in CHO/CH2Cl2 or C6H6/EMP+PF6- system on irradiation with the gamma-rays. The onium not only oxidated alpha-alkoxyalkyl radicals, produced from CHO in dichloromethane, to the corresponding cations, but also gave nonucleophilic anions PF6- for the polymerization system. A preliminary discussion is made on the effect of different polar solvents to ...
Coalification by clay-catalyzed oligomerization of plant monomers
1990-01-01
One of the main objectives is to explore the possibility that radical cation Diels-Alder reactions are involved in the biosynthesis of lignans in plants. Two of the most highly sought after classes of lignans are the dibenzocyclooctadienes represented by stegnol and the aryltetralins represented by podophyllotoxin. Both are powerful anticancer agents and have structures that might be assembled from C{sub 6}-C{sub 3} units via radical cation processes. A common feature of both of these molecules is the benzyllic hydroxyl group. The hydroxyl group is cis to the lactone carbonyl carbon. The hypothetical mechanism by which this hydroxyl group might be introduced into the aryltetralins is outlined. We have also begun to study the radical cation Diels-Alder chemistry of cinnamate salts. The preliminary results are described. In an extension of our previous work with tethered cinnamates, we have returned to the tethered molecule and are in the process of reexamining its radical cation Diels-Alder chemistry in the presence of Na{sub 2}CO{sub 3}. We have begun to investigate the radical cation chemistry of polycyclic aromatic hydrocarbons in an effort to find chemistry that will produce the coupling of these aromatic molecules. Our first effort has been to look at naphthalene treated with DBAHA. 2 refs.
2010-01-01
A novel hybrid photoinitiator for visible light photopolymerization, (^6-3-benzoyl-4-chlorodiphenylamine) (^5-cyclopentadienyl) iron hexafluorophosphate (Fc-NBP), was synthesized and studied. Its absorption in the UV and visible light regions showed much stronger activity than those of either the commercialized cationic photoinitiator I-261 or the conventional free radical photoinitiator benzophenone, especially above wavelengths of 350nm. When exposed to visible light, the photoinitiator under study initiates both cationic polymerization and radical polymerization. The photoinitiator's abilities in the photopolymerization of acrylates and epoxides were evaluated by near infrared (NIR) spectroscopy. The results from NIR clearly indicate that Fc-NBP exhibited high efficiency in photopolymer...
2002-01-01
This article reports preparation, structure, and conducting property of several cation radical salts of organic donors tetramethyltetrathiafulvalene (TMTTF), ethylenedithiotetrathiafulvalene (EDT-TTF), bis(ethylenedithio)tetrathiafulvalene (ET), bis(ethylenedithio)tetraselenafulvalene (BETS) and hexamethylenetetraselenafulvalene (HMTSF) with two novel planar Te-based dianions, TeI42- and Te2I62-. (ET)5Te2I6 1 and (BETS)5Te2I6 2 are isostructural. In these Te2I62- salts, intermolecular short Icentre dotcentre dotcentre dotI contacts form a supramolecular corrugated anion sheet. Donor arrangement is similar to the ...
2009-01-01
This article is focused on the description of the synthesis, spectroscopic, electrochemical properties, and the free radical photoinitiation abilities of new three-cationic carbocyanine dyes. A new synthestic strategy for preparation of symmetrical cyanine dyes has been developed based on the 2-methylbenzothiazole, 2-methylbenzoxazole and 2,3,3-trimethylindolinium quaternization by a-bromo--tertiary ammonium salts followed by the condensation of obtained product with triethyl ortho-formate. Resulted dyes possess in one molecule three quaternary nitrogen atoms, for example, they are three-cationic in character. Novel three-cationic symmetric carbocyanine dyes paired with n-butyltriphenylborate anions are very efficient photoinitiators of free radical polymerization of acrylate monomers, for...
2010-01-01
Nanocomposite materials prepared from radically photocurable hybrid sol-gel precursors have been widely developed within the last decade, especially to devise novel optical devices and coatings. For their synthesis, a preferential route has involved in the successive sol-gel process of acrylate trialkoxysilane precursors followed by radical photopolymerization. In contrast, this work presents an original one-step synthesis based on the association of two different photoinitiators (PIs) in the same formulation: the photolysis of a hydroxyphenylketone (radical PI) affords polyacrylate chains while that of a diaryl iodonium salt (cationic PI) generates powerful superacids catalyzing the sol-gel reactions of the alkoxy functions. The behavior of methacrylate and acrylate trimethoxysilane precu...
Radical arylation of thiobenzanilides by aryldiazonium salts in the presence of ferrocene
1985-05-20
The radical chain thiophilic arylation of thiobenzanilide and thiobenz-p-anisidide by phenyl- and p-methoxyphenyldiazonium tetrafluoroborides was carried out using ferrocene as the catalyst. The corresponding s-arylisothiobenzanilides were obtained in high yield. p-Nitrophenyldiazonium tetrafluoroboride arylates these thiobenzanilides in the absence of ferrocene, presumably also by a radical mechanism; the thioamide is the catalyst for decomposition of the aryldiazonium cation. s-Arylisothiobenzanilides containing electron-withdrawing substituents on the aniline ring undergo hydrolysis under the reaction conditions.
2010-01-01
The combination of radical-promoted cationic polymerization, atom transfer radical polymerization (ATRP) and click chemistry was employed for the efficient preparation of poly(cyclohexene oxide)-block-polystyrene (PCHO-b-PSt). Alkyne end-functionalized poly(cyclohexene oxide) (PCHO-alkyne) was prepared by radical-promoted cationic polymerization of cyclohexene oxide monomer in the presence of 1,2-diphenyl-2-(2-propynyloxy)-1-ethanone (B-alkyne) and an onium salt, namely 1-ethoxy-2-methylpyridinium hexafluorophosphate, as the initiating system. The B-alkyne compound was synthesized using benzoin photoinitiator and propargyl bromide. Well-defined bromine-terminated polystyrene (PSt-Br) was prepared by ATRP using 2-oxo-1,2-diphenylethyl-2-bromopropanoate as initiator. Subsequently, the bromin...
2008-01-01
In this communication, polyanionic poly(potassium 3-sulfopropyl methacrylate) (PSPM) brushes were switched from hydrophilic to hydrophobic by exchange of the counter cations. First, poly(potassium 3-sulfopropyl methacrylate) brushes were grown by means of atom transfer radical polymerization (ATRP) from thiol monolayers of initiating -mercaptoundecyl bromoisobutyrate and mixed monolayers of thiol initiator and 1-undecanothiol (blank thiol) attached to gold surfaces. The kinetics of the polymerization reaction were followed by means of the quartz microbalance technique with dissipation (QCM-D). The collapse of PSPM brushes in the presence of cationic surfactants like quaternary ammonium salts (tetraethylammonium bromide, hexadecyltrimethylammonium bromide) and imidazolium salts (1-dodecyl-3...
Photochemical and radiation-chemical aspects of matrix acidity effects on some organic systems
1992-05-01
The role of matrix effects in radiolysis and photolysis is illustrated using two systems: organosulphur compounds and benzenediazonium salts. Their intermediates as detected by low temperature ESR and optical spectroscopy or FAB-MS give evidence that the main reaction pathways depend strongly on these effects. Changes in matrix acidity can control the formation of neutral radical, ion-radical or ionic species which are crucial to the character of the final products of irradiation of organosulphur compounds, which are of great importance in medicine, biology, ecology and industry. Microenvironmental influences determine whether the triplet aryl cation or radical species are detected as the principal or sole intermediates in the decomposition of diazonium salts, a process leading to different stable products with industrial application. (Author).
Photochemical and radiation-chemical aspects of matrix acidity effects on some organic systems
1992-01-01
The role of matrix effects in radiolysis and photolysis is illustrated using two systems: organosulphur compounds and benzenediazonium salts. Their intermediates as detected by low temperature ESR and optical spectroscopy or FAB-MS give evidence that the main reaction pathways depend strongly on these effects. Changes in matrix acidity can control the formation of neutral radical, ion-radical or ionic species which are crucial to the character of the final products of irradiation of organosulphur compounds, which are of great importance in medicine, biology, ecology and industry. Microenvironmental influences determine whether the triplet aryl cation or radical species are detected as the principal or sole intermediates in the decomposition of diazonium salts, a process leading to different stable products with industrial application. (Author)
Controlling solubility of lithium salts in liquid sulfur dioxide
1984-11-13
The solubility of lithium salts in sulfur dioxide-based solvent systems is enhanced and controlled by the presence of a salt which contains a cation selected from the group consisting of metal cation complexes, quaternary ammonium cations and organic phosphonium cations.
An in situ colorimetric measurement study of electrochromism in the di-n-heptyl viologen system
2008-01-01
An in situ colorimetric method, based on the CIE (Commission Internationale de l'Eclairage) system of colorimetry, has been applied to the study of the electrochromic N,Nprime-bis(n-heptyl)-4,4prime-bipyridylium (di-n-heptyl viologen) system in aqueous solution on transmissive ITO/glass substrates. On electrochemical reduction of the di-n-heptyl viologen di-cation, the purple di-n-heptyl viologen radical cation salt deposits as a film and the changes in hue and saturation have been tracked using CIE 1931 xy chromaticity coordinates. The CIELAB 1976 colour space coordinates of the purple di-n-heptyl viologen radical cation salt were L*=76, a*=33, and b*=-20, with a complementary wavelength of 548nm. A sharp decrease in luminance was found on formation of the di-n-heptyl viologen radical cat...
Combination of transition metal carbonyls and silanes: New photoinitiating systems
2010-01-01
The recently developed silyl radical chemistry is used in combination with transition metal carbonyls MC (dimanganese(0) decacarbonyl; dirhenium decacarbonyl; cyclopentadienyl iron(II) dicarbonyl dimer) for both free radical promoted cationic photopolymerization (FRPCP) and free radical photopolymerization (FRP). The newly developed photoinitiating systems (MC/silane and MC/silane/iodonium salt) are highly efficient under air. Photopolymerization profiles obtained upon a visible light irradiation delivered by a xenon lamp show that high conversion can be easily achieved after a 400 s exposure. Sunlight irradiations under air can also lead to tack free coatings. The processes associated with the metal carbonyl radical/silane interactions are investigated by Laser Flash Photolysis (LFP) and ...
17.3.2 Radical cations of other cycloalkanes
This document is part of Subvolume E2 ?Phosphorus-Centered Radicals, Radicals Centered on Other Heteroatoms, Organic Radical Ions? of Volume 26 ?Magnetic Properties of Free Radicals? of Landolt-Brnstein Group II ?Molecules and Radicals?.
1986-01-01
ESR spectra of gamma-irradiated acetone and CH3COEt solutions (0.1-22%) in CFCl3 were studied. The yields of monomer and dimer radical cations of ketones and RCHCOCH3 radicals depend on ketone concentration in CFCl3. When exposed to light the dimeric radical cations are transformed into RCHCOMe, while the monomeric radical cations disappear without further radical production. Different types of solid phase ion-molecular reactions for monomer and dimer radical cations are discussed. (author)
The use of sodium dithionite as the reducing agent to produce the radical cation of methyl viologen cofactor for the nitrate reductase-catalyzed reduction of nitrate to nitrite causes a negative interference in the diazonium salt azo dye determination of nitrite. The interference results from bisulfite, a reaction product of dithionite, reacting with the diazonium salt formed from nitrite and sulfanilamide. Addition of formaldehyde before the diazotization reaction masks this interference but at low acidity introduces a nonlinearity in the nitrite calibration curve. This nonlinearity is due to a competing reaction of formaldehyde with sulfanilamide to yield a Schiff base and can be eliminated by increasing the HCl content of the sulfanilamide reagent.
1976-10-01
The use of sodium dithionite as the reducing agent to produce the radical cation of methyl viologen cofactor for the nitrate reductase-catalyzed reduction of nitrate to nitrite causes a negative interference in the diazonium salt azo dye determination of nitrite. The interference results from bisulfite, a reaction product of dithionite, reacting with the diazonium salt formed from nitrite and sulfanilamide. Addition of formaldehyde before the diazotization reaction masks this interference but at low acidity introduces a nonlinearity in the nitrite calibration curve. This nonlinearity is due to a competing reaction of formaldehyde with sulfanilamide to yield a Schiff base and can be eliminated by increasing the HCl content of the sulfanilamide reagent.
Transformations of toluene radical cation in ZSM-5 and Silicalite
1992-11-25
Toluene radical cations produced by {gamma} irradiation at 77 K in ZSM-5 and Silicalite (isomorphous with ZSM-5 but nonpolar) undergo a reversible transformation to the norbornadiene radical cation at temperatures {le}150K. The transformation occurs to a greater extent in the more polar zeolite (ZSM-5). The substrate concentration plays an important role. Toluene radical cations undergo ion-molecule reactions to give benzyl radicals at low substrate loading at temperatures >200 K. At higher concentration, different adsorption sites become populated which allow the transformation to norbornadiene radical cation to take place.
A fragmentation study of the Rhodamine 610 cation using visible-laser desorption ionization
2010-01-01
The fragmentation of a potential visible matrix-assisted laser desorption ionization: Rhodamine 610 was studied under 532 nm visible irradiation, as a function of anion counter ion. It was found that at a fixed fluence, the chloride salt produced fewer fragments than those formed with ClO4- or BF4-. Evidence presented suggests that the degree of fragmentation is inversely proportional to the strength of the contact ion pair in the solid state; that is, more energy is deposited into the radical cation which can lead to fragmentation when less energy is required to separate the ion pair. Similar results were found for salts of Rhodamine 6G. Copyright Copyright 2010 John Wiley & Sons, Ltd.
2008-01-01
The antioxidant properties of 15 honey samples from different floral sources and various Slovak regions were investigated by means of electron paramagnetic resonance spectroscopy. Cation radical of ABTS (2,2prime-azino-bis(3-ethylbenzothiazoline-6-sulfonate) diammonium salt), DPPH (1,1-diphenyl-2-picrylhydrazyl) and hydroxyl radicals generated by the photochemical decomposition of hydrogen peroxide were used as oxidants. The antioxidant activities found with ABTS+, expressed as trolox equivalent antioxidant capacity (TEAC), ranged from 0.15 to 1.14mmolkg-1, and those determined with DPPH, from 0.04 to 0.32mmolkg-1. TEAC values correlated well with results found by elimination of DPPH, and both values revealed a linear relationship with the concentration of phenolics obtained with the Folin...
Structure and spectral studies of the BEDO-TTF radical cation salt with isocyanuric acid anion
2006-01-01
A new radical cation salt based on bis(ethylenedioxy)tetrathiafulvalene (BEDO-TTF) and the isocyanuric acid anion (C3H2N3O3)- was synthesized and characterized by X-ray and spectral analysis. The unit cell of (BEDO-TTF)2(C3H2N3O3) is triclinic, space group P1-bar , a=3.974(1)A, b=5.429(2)A, c=18.720(7)A, alpha=86.26(3)o, beta=84.65(3)o, gamma=81.13(3)o. The crystal structure is layered one and the donor packing is beta-type. IR and Raman spectra of single crystals and UV-Vis-NIR absorption spectra of the sample dispersed in KBr pellet were analyzed. The normal mode vibrations and the intramolecular excitations of the neutral BEDO-TTF ...
Nanosecond laser flash photolysis studies of the radical cation of 4-hydroxy-3-methoxystyrene show that the radical cation reacts with neutral 4-hydroxy-3-methoxystyrene and non-phenolic styrenes with rate constants that range from 1 x 10(8) to 5 x 10(8) M(-1) s(-1). Similar 4-vinylphenol radical cations such as the radical cations of isoeugenol and coniferyl alcohol display reduced reactivity, presumably due to the presence of beta-alkyl substituents. Overall, the results show that the reactivity of 4-vinylphenol radical cations with neutral styrenes parallels the reactivity of non-phenolic styrene radical cations, which are known to undergo efficient radical cation mediated dimerization reactions to give lignan-like compounds. The possibility that the biosynthesis of some lignans may follow a radical cation mediated mechanism is discussed.
Arene-thioether mixed complex radical cations
1994-03-01
Studies of radiolytically generated radical cations in aromatic hydrocarbon solvents have led to the first direct characterization of monomeric thioether radical cations in liquid solution. Observation of these very reactive chemical intermediates is made possible by the great sensitivity of fluorescence-detected magnetic resonance (FDMR) and by solvent stabilization of the thioether radical cations via electron donation. Monomeric thioether radical cations in arene solvents such as toluene exist as arene-thioether mixed complex radical cations -- the first {pi}-lone pair mixed complex radical cations ever observed. Such orbital interactions are of fundamental importance for open-shell intermediates as they have consequences for both electronic structure and reactivity. Thioether radical cations provide a valuable test system to probe the chemical influence of orbital interactions that are generic to all {pi}-type and heteroatom-containing organic radical cations, and magnetic resonance provides unsurpassed structural resolution for condensed-phase paramagnetic intermediates.
Electrochemical oxidation of tertiary phosphines in the presence of camphene
2009-01-01
Anodic oxidation of tertiary phosphines (tripropyl-, tributyl-, and triphenylphosphine) in the presence of a bicyclic alkene (camphene) on a platinum and a glassy carbon electrodes was studied. For the first time the voltammetric characteristics of the process of camphene anodic oxidation were obtained. The electrochemical reactions with alkyl and aromatic phosphine were found to be dissimilar. The results of preparative electrooxidation of trialkylphosphines showed that in the course of electrolysis the tertiary phosphine cation-radicals generated on the anode enter into two concurrent reactions: (1) with the parent phosphine to form eventually trialkylphosphonium salts and trialkylphosphine oxides presumably as complex compounds and (2) with camphene to form trialkylcamphenylphosphonium ...
2010-01-01
A model study of the interaction between biologically active bisquaternary ammonium salts and their molecular targets in living systems is urgently needed to elucidate the molecular mechanisms involved in the interactions between these compounds. To address this need a combined experimental-computational study of the interaction of two tetramethylammonium cations (modeling two quaternary groups) with the chlorine anion and with the deprotonated 2,5-dihydroxybenzoic acid (modeling a carboxylic group and an aromatic ring of side radicals of proteins) has been performed. Fast atom bombardment mass spectrometry method and DFT/B3LYP/6-31++G** and MP2/6-31++G** calculations have been employed in the study. Stable noncovalent complexes with different ratios of the tetramethylammonium cations and ...
Levels of antioxidants and nutraceuticals in basil grown in hydroponics and soil
2010-01-01
Owing to the traditional phytotherapeutic use of basil and its importance as a basic component of the Mediterranean diet, this research aimed to study the nutraceutical properties of basil (Ocimum basilicum cv. Genova) grown in hydroponics in comparison with that grown in soil. The antioxidant activities of aqueous and lipid extracts of basil leaves were evaluated both by spectrophotometric detection with the 2,2prime-azinobis(3-ethylbenzothiazoline-6-sulphonic acid) radical cation (ABTS+) and by electron paramagnetic resonance (EPR) detection with the stable radicals peroxylamine disulphonate (Fremy's salt, hydrophilic) and 1,1-diphenyl-2-picrylhydrazyl (DPPH, lipophilic). From EPR decay kinetics analysis, it was possible to distinguish (in the lipid extract) a fast rate constant and a sl...
Toward crystal design in organic conductors and superconductors.
1999-04-23
We have seen that many different types of intermolecular interactions in organic conducting cation radical salts. Hydrogen bonding between the donor molecules and the anions is weak but not negligible. The ionic Madelung energy is insufficient to completely intersperse anions and cations, thus the layers favored by the van der Waals interactions remain intact. The search for new conducting and superconducting salts has been mainly by trial-and-error methods, even though simple substitutions have been employed in order to obtain isostructural analogs of successful (e.g., superconducting) salts. However, even seemingly minor substitutions sometimes destroy the packing type, and different crystal structures result. Simulations with the aim at predicting crystal structures have not succeeded, mainly because the different interaction types are of comparable energy, and the delocalized and partial charges render the calculations of the ionic terms extremely unreliable. Clearly, the development of suitable crystal modeling techniques with predictive capabilities is one of the great needs of the field.
Toward crystal design in organic conductors and superconductors.
We have seen that many different types of intermolecular interactions in organic conducting cation radical salts. Hydrogen bonding between the donor molecules and the anions is weak but not negligible. The ionic Madelung energy is insufficient to completely intersperse anions and cations, thus the layers favored by the van der Waals interactions remain intact. The search for new conducting and superconducting salts has been mainly by trial-and-error methods, even though simple substitutions have been employed in order to obtain isostructural analogs of successful (e.g., superconducting) salts. However, even seemingly minor substitutions sometimes destroy the packing type, and different crystal structures result. Simulations with the aim at predicting crystal structures have not succeeded, mainly because the different interaction types are of comparable energy, and the delocalized and partial charges render the calculations of the ionic terms extremely unreliable. Clearly, the development of suitable crystal modeling techniques with predictive capabilities is one of the great needs of the field.
Two new structures in the glycine-oxalic acid system
2010-01-01
Glycinium semi-oxalate-II, C2H6NO2+C2HO4-, (A), and diglycinium oxalate methanol disolvate, 2C2H6NO2+C2O42-2CH3OH, (B), are new examples in the glycine-oxalic acid family. (A) is a new polymorph of the known glycinium semi-oxalate salt, (C). Compounds (A) and (C) have a similar packing of the semi-oxalate monoanions with respect to the glycinium cations, but in (A) the two glycinium cations and the two semi-oxalate anions in the asymmetric unit are non-equivalent, and the binding of the glycinium cations to each other is radically different. Based on this difference, one can expect that, although the two forms grow concomitantly from the same batch, a transformation between (A) and (C) in the solid state should be difficult. In (B), two glycinium cations and an oxalate anion, which sits ac...
1994-01-01
Anion-exchange extraction of B10H102- anion by higher quaternary ammonium salts (QAS) has been studied, exchange constants (K), being ascertained. It is established that extractional affinity of B10H102-anions to anion-exchange device phase increases abruptly, when passing from acid solvents (hexanol) to inert ones. It is shown that the presence of one ethyl radical on QAS cation gives rise to insignificant increase in K. B10H102--selective electrode is suggested. 3 refs., 1 fig., 2 tabs
Studies of radiation-produced radicals and radical ions
The radiolytic oxidation of anti-5-methylbicyclo(2.1.0)pentane gives the 1-methylcyclopentene radical cation as the sole rearrangement product H migration whereas oxidation of its syn isomer results in the highly selective formation of the 3-methylcyclopentene radical cation by methyl group migration. Since exactly the same stereoselectivity of olefin formation was observed in corresponding PET (photosensitized electron transfer) studies in the liquid phase, it is concluded that the rearrangement in this case also occurs through the intermediacy of radical cations. Clearly, the radical cation rearrangement must occur very rapidly (10{sup {minus}8}--10{sup {minus}9}s) under liquid-phase conditions at room temperature to compete with back electron transfer, and therefore the hydrogen (or methyl) migration is a fast process under these conditions. An intramolecular cycloaddition reaction was demonstrated in the radical cation rearrangement of 4-vinylcyclohexene to bicyclo(3.2.1)oct-2-ene. ESR studies show that the radiolytic oxidation of quadricyclane in Freon matrices under conditions of high substrate dilution leads to the bicyclo(3.2.0)hepta-2,6-diene radical cation as well as the previously reported norbornadiene radical cation, the former species predominating at sufficiently low concentrations.
1983-04-01
Diphenylamine and 4, 4'-dimethoxydiphenylamine in acetonitrile are oxidized monoelectronically by NOBF/sub 4/. On the 4, 4'-dimethoxydiphenylamine example a maximum current concentration of intermediate cation-radicals formed in this reaction is measured. Cation-radicals in acetonitrile get dimeric transforming into products of oxidizing condensation of amines, with no respective nitrozamines being observed. Nitrosamines production on through cation-radical-NO recombination is realized but in the presence of protonoacceptor solvents, in particular pyridine.
Radical Ions in Photochemistry. 44. The Photo-NOCAS Reaction with Acetonitrile as the Nucleophile.
Studies on the photoinduced electron transfer (PET) reactions of isobutylene (2-methylpropene, 1) in the absence of methanol have identified a new photochemical nucleophile-olefin combination, aromatic substitution (photo-NOCAS) reaction. Under these conditions acetonitrile was found to act as the nucleophile and to combine with the alkene radical cation. The resulting distonic radical cation then adds to the radical anion of 1,4-dicyanobenzene (2(-*)). The final product (6) results from cyclization into the ortho postion of the phenyl group. This product formation is rationalized on the basis of the relatively high oxidation potential of the alkene (i.e., one-electron oxidation yields a reactive radical cation), the fact that addition of the nucleophile (acetonitrile) to the radical cation is relatively unhindered, and the relatively low acidity of the radical cation due to the low radical stability of the allylic radical formed upon deprotonation. High-level ab initio molecular orbital calculations were used to determine the structures and relative energies of the possible intermediate distonic and bridged radical cations. The scope and mechanism of this type of photo-NOCAS reaction are discussed.
Electron transfer from ascorbic acid to various phenothiazine radicals
1979-11-07
The reaction of electron transfer from ascorbic acid to N-alkylphenothiazine radical cations was studied in the pH range 0 to 7.2. The radical cations were produced by oxidation with Br/sub 2//sup -/ or Cl/sub 2//sup -/ using the pulse radiolysis technique. The radical cations are reduced by the deprotonated form of ascorbic acid in the pH range 2.2 to 7.2. The product of this reaction has a spectrum which is identical with that of the ascorbate radical. It is concluded that, if a charge-transfer complex is formed upon the reaction of ascorbic acid with the phenothiazine radical cations, its lifetime is shorter than 7 x 10/sup -8/s. It is suggested that even at high acidities no long lived complex is formed and it is proposed that at very low pH the thermodynamically stable species in this reaction is the phenothiazine radical cation rather than the ascorbic acid radical. It is shown experimentally that at 1 M HCl the ascorbic acid radical oxidizes N-alkylphenothiazine to give the radical cation of the latter in reverse to the direction of the electron transfer at higher pH. 8 figures, 2 tables.
The intracomplex radical-cation chain oxidation of tryptophan photosensitized by uranyl ion
2010-01-01
Photooxidation of tryptophan (Trp) in complexes with the uranyl ion upon selective excitation was studied, and the quantum yields of amino acid oxidation ((O2)) were determined. It was shown that the photosensitized oxidation of Trp by the uranyl ion involves the chain reaction of Trp+ radical cations with O2, rather than follows the commonly accepted mechanism of interaction of the substrate radical cation with the superoxide ion Formula Not Shown .
Study on intermediate species of polystyrene by using pulse radiolysis
2000-03-01
The reaction mechanism of intermediates of polystyrene solutions in cyclohexane and chlorinated hydrocarbon solvents has been studied by using pulse radiolysis. Absorption peaks observed around 1250 {approx} 1350 nm in chlorinated hydrocarbon and cyclohexane solutions of polystyrene, were identified with the dimer cation radicals of polystyrene. The absorption intensities of polystyrene dimer cation radicals were enhanced with increasing of polarities of solvents. Because free ion yields of polystyrene cation radicals were increased with increasing of polarities. (author)
Fragmentation of alpha-Radical Cations of Arginine-Containing Peptides
Fragmentation pathways of peptide radical cations, M+, with well-defined initial location of the radical site were explored using collision-induced dissociation (CID) experiments. Peptide radical cations were produced by gas-phase fragmentation of CoIII(salen)-peptide complexes [salen = N,N-ethylenebis (salicylideneaminato)]. Subsequent hydrogen abstraction from the -carbon of the side chain followed by Ca-C bond cleavage results in the loss of a neutral side chain and formation of an a-radical cation with the radical site localized on the a-carbon of the backbone. Similar CID spectra dominated by radical-driven dissociation products were obtained for a number of a-radicals when the basic arginine side chain was present in the sequence. In contrast, proton-driven fragmentation dominates CID spectra of a-radicals produced via the loss of the arginine side chain. Our results suggest that in most cases radical migration precedes fragmentation of large peptide radical cations.
Fragmentation of alpha-Radical Cations of Arginine-Containing Peptides
2010-04-01
Fragmentation pathways of peptide radical cations, M+, with well-defined initial location of the radical site were explored using collision-induced dissociation (CID) experiments. Peptide radical cations were produced by gas-phase fragmentation of CoIII(salen)-peptide complexes [salen = N,N-ethylenebis (salicylideneaminato)]. Subsequent hydrogen abstraction from the -carbon of the side chain followed by Ca-C bond cleavage results in the loss of a neutral side chain and formation of an a-radical cation with the radical site localized on the a-carbon of the backbone. Similar CID spectra dominated by radical-driven dissociation products were obtained for a number of a-radicals when the basic arginine side chain was present in the sequence. In contrast, proton-driven fragmentation dominates CID spectra of a-radicals produced via the loss of the arginine side chain. Our results suggest that in most cases radical migration precedes fragmentation of large peptide radical cations.
1986-04-24
Pulse radiolysis of trans-stilbene (St) in tetrahydrofuran (THF) solution was carried out in the presence of quaternary ammonium salts, such as Bu/sub 4/NPF/sub 6/, Bu/sub 4/NI, Bu/sub 4/NBPh/sub 4/, CeMe/sub 3/NPF/sub 6/, PhMe/sub 3/NPF/sub 6/, and BzMe/sub 3/NPF/sub 6/ (Bu, butyl; Ce, cetyl; Me, methyl; Ph, phenyl; and Bz, benzyl). The absorption peak of the radical anions, St/sup -/., was shifted to shorter wavelengths in the presence of the salts. The magnitude of the shift depends on the substituent groups of the quaternary ammonium cations. It is suggested that St/sup -/. forms contact ion pairs with the quaternary ammonium cations. The decay rate of St/sup -/. decreases with increasing salt concentration and becomes steady. The rate constants for the neutralization reaction of St/sup -/. with the solvent counterions, THF(H/sup +/), have been determined in the absence and presence of Bu/sub 4/NPF/sub 6/; in the latter case, the reaction occurs between the ion pairs St/sup -/./Bu/sub 4/N/sup +/ and THF(H/sup +/)/PF/sub 6//sup 7/. The results for other aromatic compounds such as biphenyl, anthracene, and pyrene are also presented. Comparison was made with the effect of NaBPh/sub 4/. 17 references, 2 figures, 2 tables.
1989-11-07
A new series of isostructural cation-radical salts of bis(ethylene)dithiotetrathiafulvalene (BEDT-TTF) with the octahedral metal complex dianions PtCl{sub 6}{sup 2-}, PtBr{sub 6}{sup 2-}, TeCl{sub 6}{sup 2-} and SnCl{sub 6}{sup 2-} have been obtained. The crystal structure of the (BEDT-TTF){sub 4}PtCl{sub 6}C{sub 6}H{sub 5}CN salt has been determined. Although it should be attributed to the k-type of BEDT-TTF metallic salts due to the packing arrangement of the BEDT-TTF molecules, it undergoes a first-order transition into the insulating state at 250 K. Application of a pressure higher than 6 kbar results in a new conducting state. The complexes of (BEDT-TTF) with the anions PtBr{sub 6}{sup 2-}, TeCl{sub 6}{sup 2-} and SnCl{sub 6}{sup 2-} exhibit semiconducting properties. (orig.).
Absorption spectra of the radical ions of quinones: a pulse radiolysis study
1991-09-22
The formation of quinone radical ions was observed at room temperature using pulse radiolysis. The following quinones were investigated: p-benzoquinone, p-naphthoquinone, 5,8-dihydroxy-1,4-naphthoquinone, anthraquinone and 1,4-dihydroxyanthraquinone. The radial cations were produced in freon-113 solutions and the radical anions were produced in methanol solutions. The absorption spectra of the radical ions were found in the near-UV-VIS range. The spectra of the radical cations were blue shifted compared with the spectra of the corresponding radical anions. (author).
Optical absorption spectra of dications of carotenoids
1996-04-04
Quantitative optical absorption spectra of the cation radicals and the dications of canthaxanthin (I), {beta}carotene (II), 7`-cyano-7`-ethoxycarbonyl-7`-apo-{beta}-carotene (III), and 7`,7`-dimethyl-7`-apo-{beta}-carotene (IV) in dichloromethane solution are reported. Exclusive formation of dications occurs when the carotenoids are oxidized with ferric chloride. Addition of neutral carotenoid to the dications results in equilibrium formation of cation radicals. Oxidation with iodine in dichloromethane affords only cation radicals; electrochemical oxidation under suitable conditions yields both dications and cation radicals. Values of the optical parameters depend on the nature of the oxidative medium. The oscillator strengths calculated for gas phase cation radicals and dications of I-IV using the INDO/S method show the same trend as the experimental values. 31 refs., 4 figs., 2 tabs.
2009-01-01
The radical cation 2-(3-N-methylpyridinium)-4,4,5,5-tetramethyl-4, 5-dihydro-1H-imidazol-1-oxyl-3-N-oxide (abbreviated as m-MPYNN) is successfully intercalated into the layered host structure CdPS3. The reaction proceeds via an ion exchange reaction from methanol solutions containing the radical iodide salt, leading to materials described by the compositional formula Cd1-xPS3(metaMPYNN)2x. Detailed characterization of the intercalates by chemical analysis, X-ray powder diffraction, EPR, and NMR spectroscopy indicate that the maximum uptake corresponds to x=0.20. Attempts to produce higher intercalated materials result in the formation of a side product with inferred composition CdI4(metaMPYNN)2. Magnetic susceptibility measurements indicate CURIE-like behavior ...
2009-01-01
The radical cation 2-(3-N-methylpyridinium)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1- oxyl-3-N-oxide (abbreviated as m-MPYNN) is successfully intercalated into the layered host structure CdPS3. The reaction proceeds via an ion exchange reaction from methanol solutions containing the radical iodide salt, leading to materials described by the compositional formula Cd1−xPS3(metaMPYNN)2x. Detailed characterization of the intercalates by chemical analysis, X-ray powder diffraction, EPR, and NMR spectroscopy indicate that the maximum uptake corresponds to x=0.20; attempts to produce higher intercalated materials result in the formation of a side product with inferred composition CdI4(metaMPYNN)2. Magnetic susceptibility measurements indicate Curie-like behavior for x=0.13, while at ...
Coordinated cations in dipicolinato complexes of divalent metal ions
2010-01-01
Several salts of alkali, alkaline earth metal and organic ammonium cations of a complex anion [ML2]2- {Where L=dipicolinato dianion, M=copper(II), nickel(II) and zinc(II)} are prepared. The coordination effect of [ML2]2- with the cations such as sodium, potassium, calcium, magnesium, and organic cations namely diammonium cation of 1,5-pentanediamine, diammonium cation of 1,8-octyldiamine, mono ammonium cation of 4-aminobenzylamine are studied by determining their X-ray crystal structures. Depending on the nature of cations, four different types of structures are obtained. When calcium is the cation a polymeric structure with calcium ions bridging the [ML2]2- is observed. The salts having sodium and potassium cations form polymeric chain like structures by oxo and aqua bridges. In the case ...
Electron spin resonance spectroscopic studies of radical cation reactions
1990-01-01
A spin Hamiltonian suitable for theoretical analyses of ESR spectra is derived using the general effective Hamiltonian theory in the usual Schroedinger representation. The Permutation Indices method is extended to obtain the dynamic exchange equations used in ESR lineshape simulation. The correlation between [beta]-hydrogen coupling constants and their geometric orientations are derived using a perturbation method. The three electron bond model is extended to rationalize unimolecular rearrangements of radical cations. The ring-closed radical cations of 9,10-octalin oxide and synsesquinorbornene oxide have been characterized by ESR spectroscopy in the CFCl[sub 3] matrix at low temperature. The self-electron-transfer rate constants between the methyl viologen dication and cation have been determined by dynamic ESR lineshape simulations at room temperature in allyl alcohol, water, methanol and propargyl alcohol solvents. The radical cation formed by the radiolytic oxidation of allylamine in Freon matrices at 77 K is the 3-iminiopropyl distonic species(3-iminium-1-propyl radical). The nucleophilic endocylization of the but-3-en-1-ol radical cation to the protonated tetrahydrofuran-3-yl radical was observed in the radiolytic oxidation of but-3-en-1-ol in Freon matrices. ESR studies of the radiolytic oxidation of 1,5-hexdiyne have resulted in characterization the 1,5-hexadiyne radical cation isomerizing to the 1,2,4,5-hexatetraene radical cation. The symmetric (C[sub 2v]) bicyclo[3.3.0]-octa-2,6-diene-4,8-diyl(a bridged 1,4-bishomobenzene species) radical cation is produced by the radiolytic oxidation of semibullvalene in Freon matrices. The ring-opening 3,4-dimethylenecyclobutene radical cation to 1,2,4,5-hexatetraene radical cation was observed in the photolysis of 3,4-dimethylenecyclobutene radical cation. The cyclooctatetraene radical cation generated by radiolytic oxidation photoisomerizes to bicyclo[3.3.0]octa-2,6-diene-4,8-diyl radical cation.
Structure and spectral studies of the BEDO-TTF radical cation salt with isocyanuric acid anion
A new radical cation salt based on bis(ethylenedioxy)tetrathiafulvalene (BEDO-TTF) and the isocyanuric acid anion (C3H2N3O3)? was synthesized and characterized by X-ray and spectral analysis. The unit cell of (BEDO-TTF)2(C3H2N3O3) is triclinic, space group P1, a = 3.974(1) , b = 5.429(2) , c = 18.720(7) , ? = 86.26(3), ? = 84.65(3), ? = 81.13(3). The crystal structure is layered one and the donor packing is ?-type. IR and Raman spectra of single crystals and UV Vis-NIR absorption spectra of the sample dispersed in KBr pellet were analyzed. The normal mode vibrations and the intramolecular excitations of the neutral BEDO-TTF molecule, BEDO-TTF+ cation and (C3H2N3O3)? anion were calculated using the density functional theory. On the base of these calculations an assignment of the vibrational and electronic features in the experimental spectra was proposed. Moreover, analyzing the normal modes related to the CC vibrations it was found that the average charge on the donor molecule is equal +0.5 e.
1997-09-01
The radical cation of C{sub 60} is generated either via hole transfer from the radical cation of polar chlorinated methane to C{sub 60} or via electron transfer from the triplet of C{sub 60} to electrophilic polar chlorinated methane. The radical adducts {sup .}CHCl{sub 2} and {sup .}CH{sub 2}Cl of C{sub 60} were produced via a similar mechanism to the generation of the radical adduct {sup .}[C{sub 60}-CCl{sub 3}] in CCl{sub 4}. (author).
2007-01-01
The formation of radicals during the liquid-phase radiolysis of ethylamine, diethylamine, and triethylamine was studied by means of the spin trapping technique. The samples in question were exposed to X radiation (E=50 keV) with doses of 1-5 kGy. The radicals produced in ion-molecule reactions and in the rearrangement and fragmentation reactions of the primary radical cations of the amines were identified. The structure and reactions of the primary radical cations were studied in a low-temperature CFCl3 freon matrix in which amine radical cations were generated via charge transfer from matrix radical cations to amines during freon irradiation. The results of experiments in the liquid and solid phases are consistent with one another. The structure of neutral radicals and radical cations of the ethylamines was corroborated by quantum-chemical calculations
2000-01-01
Electron transfer from solutes to radiation-generated solvent parent radical cations shows some peculiarities as proceeding after a very low number of collisions of the partners and as exhibiting only a low solvent reorganization energy. This is observed for aromatic solutes substituted with phenol and thiophenol groups where the products of electron transfer were found to be radical cations as well as radicals. The phenomenon is interpreted in terms of a encounter geometry controlled product distributions of this free electron transfer process. (author)
ESR detection of the dimethyl ether radical cation. [Gamma radiation]
1981-11-18
The ESR spectra of the radical cation of dimethyl ether, (CH/sub 3/)/sub 2/O/sup +/, which is isoelectronic with the dimethyl aminyl radical, (CH/sub 3/)/sub 2/N, are reported. The first- and second-derivative spectra were obtained from a ..gamma..-irradiated solid solution of dimethyl ether in trichlorofluoromethane at 97/sup 0/K. Analysis of the spectrum is discussed, and assignment of the spectrum to the oxygen-centered radical cation of dimethyl ether is felt to be unambiguous. (BLM)
2010-01-01
Selecting nitrobenzene as a model compound, the assistance of magnesium cations on ozon ation of refractory organic pollutant was investigated in pure water background. It is interesting to find that the presence of magnesium cations with a level of tens of millimoles per liter can obviously increase the degradation and mineralization efficiency of nitrobenzene compared with the case of ozonation alone. At lower pH condition, the magnesium cations still effectively assisted the ozonation of nitrobenzene. Ozone decomposition was accelerated by the presence of magnesium cations. It was confirmed that the presence of magnesium cations promoted the generation of hydroxyl radicals. It was speculated that the formation of hydroxyl group by the deprotonation of the hexaqueous magnesium cations co...
2009-01-01
This review deals with the synthesis, properties and applications of metal complexes of tetrathiafulvalene-based group XV (N, P, As, Sb) ligands. The different synthetic methods for the preparations of tetrathiafulvalenes (TTFs) incorporating coordination functions such as N atoms (essentially sp2 N atoms in pyridines, pyrazines, bipyridines, imines, etc.) and P atoms (essentially in tertiary phosphines) are reviewed, together with the redox properties of these free ligands, showing in most cases that the electron donating ability of the TTF core is only scarcely affected upon association with the coordinating group. Metal complexes of such ligands have been reported with a large variety of metal centers, from group 6 (Cr, Mo, W) to group 12 (Zn, Cd, Hg). Their structural and electronic an...
2006-01-01
The crystal structures of the family of low-dimensional molecular conductors based on radical cation salts of different organic pi donors with photochromic and magnetic metal complexes as anions have been considered. This class of supramolecular systems demonstrates a large variety of structural types and a wide range of transport properties. The specificity of the structure and properties of such hybrid materials is illustrated by several examples. The crystallochemical analysis of the conductors considered indicates the possibility of purposeful control of their transport properties via changing of the charge, sizes, shape, and symmetry of the anionic block components. The specificity of the crystal structure and properties of some organic conductors shows that such systems can be used as model systems in the study of new physical phenomena related to ...
2007-01-01
Poly(phenylene sulfide phenyleneamine), PPSA, is a soluble copolymer of poly(aniline) and poly(phenylene sulfide). Its electrochemical behavior has already been studied in both aqueous and organic media in the presence of different electrolytes, where it was observed the loss of electroactivity after few cycles. In this paper, the spectroelectrochemical characterization of PPSA films in a room temperature ionic liquid (RTIL), 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanes sulfonyl)imide (BMMITFSI), is shown. The electrochemical response of a PPSA modified electrode in BMMITFSI is different from that obtained in organic solvent/salt systems. In RTIL, two reversible redox processes were observed and they were assigned to the reversible radical cation/dication transition based on 'in situ' UV-vis and Raman spectroscopic studies. The stabilization ...
Magnetotransport properties of a new hybrid metal ?-(BEDT-TTF)2[Mn2Cl5(H2O)5]
The magnetotransport properties of the ?-(BEDT-TTF)2[Mn2Cl5(H2O)5] radical cation salt with a new type of magnetic polymeric complex anion, [Mn2Cl5(H2O)5]?-, are reported. The crystals exhibit metallic behavior down to 0.4 K. Shubnikov-de Haas oscillations, observed at B>10 T, are characterized by two fundamental frequencies, corresponding to cross-sections of the Fermi surface, in agreement with the electronic band structure calculations.
Magnetotransport properties of a new hybrid metal α-(BEDT-TTF)2[Mn2Cl5(H2O)5]
2010-01-01
The magnetotransport properties of the α-(BEDT-TTF)2[Mn2Cl5(H2O)5] radical cation salt with a new type of magnetic polymeric complex anion, [Mn2Cl5(H2O)5] Formula Not Shown , are reported. The crystals exhibit metallic behavior down to 0.4K. Shubnikov-de Haas oscillations, observed at B>10T, are characterized by two fundamental frequencies, corresponding to cross-sections of the Fermi surface, in agreement with the electronic band structure calculations.
2005-10-10
We have studied the crystal structure and magnetic properties of the organic radical cation salt, BBDTA-InCl4. This material formed a one-dimensional coordination polymer, whose structure was characteristic of inorganic spin-Peierls materials. Magnetic measurements indicated the spin-Peierls transition like behavior at 108 K, which was higher than those typically observed for the other organic spin-Peierls materials. The structural aspects of the lattice distortion from X-ray diffraction measurements at 50 K have been discussed.
1,8-diketone ring closure reaction to the synthesis of BEDT-TTF derivatives
2004-01-01
For the past 25 years there has been considerable interest in crystalline organic materials that possess unusual electronic and magnetic properties. This is due to metallic behaviour of its radical cation salts with mono anions and electron acceptors such as TCNQ, which exhibit semiconducting, and superconducting properties. The most widely studied derivative, bis(ethylenedithio) tetrathiafulvalene (BEDT-TTF or ET) which shows superconducting property, has the highest critical temperature, Tc=12.8K, with K-(BEDT-TTF)Cu(NCN2Br). The aim of this work is to synthesise new derivatives of bis(ethylenedithio) tetrathiafulvalene. Use of Lawesson's reagent (LR) and Phosphoruspentasulfide (P4S10) leads such a ring formation via chemical conversion of groups to thiocarbonyls, which is called 1,8 diketone ring ...
Full Text Available.SummaryTetrakis(dimethylamino)ethylene (TDAE 1), has been exploited for the first time as a mild reagent for the reduction of arenediazonium salts to aryl radical intermediates through a single electron transfer (SET) pathway. Cyclization of the aryl radicals produced in this way led, in appropriate substrates, to syntheses of indolines and indoles. Cascade radical cyclizations of aryl radicals derived from arenediazonium salts are also reported. The relative ease of removal of the oxidized by-products of TDAE from the reaction mixture makes the methodology synthetically attractive.
Free radicals in the perimidine series. 2-tert-Butylperimidyl radicals
1987-01-01
Electrochemical and EPR methods have been applied to a study of perimidyl free radicals containing a bulky tert-butyl substituent in the 2-position. A stepwise mechanism is proposed for the dehydrogenation of 1,3-dimethyl-2-tert-butyl-2,3-dihydroperimidine; the mechanism involves formation of a cation-radical from the substrate in the first step. Shielding of the nitrogen atoms seems to be an important factor in increasing the stability of free perimidyl radicals.
The π-Cation Radical of Chlorophyll a
1970-10-01
Full Text Available. Chlorophyll a undergoes reversible one-electron oxidation in dichloromethane and butyronitrile. Removal of the electron by controlled potential electrolysis or by stoichiometric charge transfer to a known cation radical yields a radical (epr line width = 9 gauss, g = 2.0025 ± 0.0001) whose optical spectrum is bleached relative to that of chlorophyll. Upon electrophoresis this bleached species behaves as a cation. By comparison with the known properties of π-cation radicals of porphyrins and chlorins, the chlorophyll radical is also identified as a π-cation. Further correlation of optical and epr properties with published studies on photosynthesis leads to the conclusion that oxidized P700, the first photochemical product of photosystem I in green plants, contains a π-cation radical of the chlorin component of chlorophyll a. This radical is the likely source of the rapidly-decaying, narrow epr signal of photosynthesis.
1990-01-01
Halogenated peroxyl radicals are found to oxidize thiazine and azine dyes to their radical cations. The bimolecular rate constants for the oxidation of these dyes by different halogenated peroxyl radicals have been measured from the rate of build-up of the absorbance of the radical cations by the pulse radiolysis technique. The oxidative power is observed to depend on the nature and number of halogen atoms and the structure of the substrate dye molecule. The bimolecular rate constant values are observed to depend directly on Taft's inductive parameter ({sigma}*) and the extent of relative oxidation of methylene blue. (author).
1990-01-01
Halogenated peroxyl radicals are found to oxidize thiazine and azine dyes to their radical cations. The bimolecular rate constants for the oxidation of these dyes by different halogenated peroxyl radicals have been measured from the rate of build-up of the absorbance of the radical cations by the pulse radiolysis technique. The oxidative power is observed to depend on the nature and number of halogen atoms and the structure of the substrate dye molecule. The bimolecular rate constant values are observed to depend directly on Taft's inductive parameter (sigma*) and the extent of relative oxidation of methylene blue. (author)
1985-11-01
The ESR spectra of el-irradiated solutions of acetic acid and acetic anhydride were studied depending on their concentrations in CFClsub(3). The structure of thus produced radical cations is confirmed with the deuterium substituted analogues. It is shown that the ion-molecular reaction of the radical cation CHsub(3) COOHsup(+) in the isolated dimer takes place for the dilute solutions of acetic acid in CFClsub(3) resulting in the formation of CHsub(3)COO followed by its decomposition to CHsub(3) + COsub(2) while the radicals CHsub(2)COOH are formed via secondary processes. The reactions of radical cations of acetic oxide were also studied.
Radiolysis of tetrazolium salts in polyvinyl alcohol
1992-01-01
The radiation chemical yields of formazans were measured in binary systems containing polyvinyl alcohol and tetrazolium salts as additives; it was established that they are more than half of the yields of radicals in pure polyvinyl alcohol. The ESR spectra of the indicated systems were measured at various temperatures, and the relative changes in the radical concentrations were determined. It was suggested that the increase in the concentration of single radicals at T > 400 K is due to the participation of radical pairs in the reaction. 15 refs., 4 figs., 1 tab.
Alkylbenzenesulfonate salts and their applications
1972-08-18
These alkyl benzene sulfonium salts have a formula where X is an alkyl radical with 1 to 4 C atoms, or the radical -C/sub 2/H/sub 4/-OH; R/sub 1/ is a linear or ramified alkyl radical with 4 to 18 C atoms, attached to the benzene ring in position 2 or 4; R/sub 2/ is hydrogen, a linear or ramified alkyl radical with 1 to 9 C atoms.
1979-01-01
Various N-heterosubstituted benzenes, naphthalenes, anthracenes, and phenanthrenes have been ionized to their ion radicals in frozen solutions through intermolecular charge transfer induced by gamma-ray irradiation. Cation and anion radicals have been produced selectively and studied by ESR and optical spectroscopy. The cations can be grouped into those in which the spin density is localized mainly on the in-plane lone-pair orbitals of nitrogen (n cations) and those in which the density is distributed over a pi-electron orbital (pi cations). They can be unambiguously distinguished by ESR and optical spectra. For the n cations the optical transition energies are in accord with photoelectron spectra. The spin density of the n cations substantiates significant interactions of lone-pair orbitals as elaborated previously in terms ...
Ion-exchange softening of Black Sea water
1980-09-01
Ion-exchange softening of Black Sea water under the conditions of fixed-bed filtration, by means of Na-cation exchange with strong-acid cation-exchanger and H-cation exchange with weak-acid cation-exchanger and by Na-cation exchange in the continuous countercurrent technique were investigated. The possibility for utilizing spent regeneration solutions for magnesium-salts production is evaluated.
Proton magnetic resonance spectra and constitution of salts of quaternary ammonium bases in solution
1986-06-20
In nonpolar solvents, broad, unstructured PMR signals of the cations of tertiary ammonium salts result from slow exchange between different forms of association in the salt. Increase of temperature, increase in the polarity of the solvent, and reduction in the salt concentration lead to rupture of the associations and the appearance of fine structure in the PMR signals. Structural peculiarities in trioctylbenzylammonium salts make it possible to record changes in the degree of association and in the constitution of the salts on the PMR spectrum.
New TTF-based ligands (TTF=tetrathiafulvalene) with Schiff base-type coordination sites have been synthesized: 4,5-bis(4-salicylideneiminophenyl)-4?,5?-ethylenedithio-TTF (1a), 4,5-bis(4-picolinideneiminophenyl)-4?,5?-ethylenedithio-TTF (1b), and 4-(2-salicylideneiminoethylthio)-5-methyl-4?,5?-ethylenedithio-TTF (Hsae-TTF). X-ray crystallography for 1a revealed that 1a has rigid structure around the coordination sites, which prevents it to form metal complexes. On the other hand, Hsae-TTF ligand has flexibility around its coordination sites due to alkyl chain spacer, and gave mononuclear complexes with Ni(II) and Cu(II) ions, [MII(saeTTF)2] (MII=Ni(II) and Cu(II)). The metal ions in [MII(saeTTF)2] have a square planar coordination structure with two TTF-based ligands, which was sandwiched by two neutral TTF moieties. The Cu(II) complex, [CuII(saeTTF)2], yielded charge transfer (CT) complexes with acceptors such as F4TCNQ, DDQ, and iodine. CT complexes with F4TCNQ and iodine were semiconductive, but that with DDQ was insulator. This is due to the difference of the degree of charge transfer; TTF moiety in F4TCNQ salt was partially oxidized but that of DDQ salt was completely oxidized. The radical cation salts of [CuII(saeTTF)2] with PF6- anion was also obtained in 1:1 donor and anion ratio by electrocrystallization. The donor and anion ratio indicates that the oxidation state of TTF moieties in the radical salt, [CuII(saeTTF)2]PF6, was partial oxidation state.
Fragmentation of protonated RVYIHPF and RVYIHPF-OMe and the corresponding radical cations was studied using time- and collision energy-resolved surface-induced dissociation (SID) in a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) specially equipped to perform SID experiments. Peptide radical cations were produced by gas-phase fragmentation of CoIII(salen)-peptide complexes. Both the energetics and mechanisms of dissociation of even-electron and odd-electron angiotensin III ions are quite different. Protonated molecules are much more stable towards fragmentation than the corresponding radical cations. RRKM modeling of the experimental data suggests that this stability is largely attributed to differences in threshold energies for dissociation while activation entropies are very similar. Detailed analysis of the experimental data obtained for radical cations demonstrated the presence of two distinct structures separated by a high free-energy barrier. The two families of structures were ascribed to the canonical and zwitterionic forms of the radical cations produced in our experiments.
2008-09-28
Fragmentation of protonated RVYIHPF and RVYIHPF-OMe and the corresponding radical cations was studied using time- and collision energy-resolved surface-induced dissociation (SID) in a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) specially equipped to perform SID experiments. Peptide radical cations were produced by gas-phase fragmentation of CoIII(salen)-peptide complexes. Both the energetics and mechanisms of dissociation of even-electron and odd-electron angiotensin III ions are quite different. Protonated molecules are much more stable towards fragmentation than the corresponding radical cations. RRKM modeling of the experimental data suggests that this stability is largely attributed to differences in threshold energies for dissociation while activation entropies are very similar. Detailed analysis of the experimental data obtained for radical cations demonstrated the presence of two distinct structures separated by a high free-energy barrier. The two families of structures were ascribed to the canonical and zwitterionic forms of the radical cations produced in our experiments.
Antioxidant Activity of Tannin Fractions Isolated from Buckwheat Seeds and Groats
2010-01-01
Phenolic compounds were extracted with 80% (v/v) aqueous acetone from buckwheat seeds and groats. Tannin fractions were obtained from the crude extracts by Sephadex LH-20 column chromatography. Total phenolic contents of isolated fractions from buckwheat seeds and groats were 477 and 371mg catechin equiv/g, respectively. The analyzed samples were characterized by electrophoretic separations using capillary zone electrophoresis. Both fractions exhibited strong antioxidant activity. The tannin fraction of buckwheat seeds reduced 1,1-diphenyl-2-picrylhydrazyl radicals (DPPH) and [2,2-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid)] diammonium salt radical cations (ABTS+) stronger than the fraction of buckwheat groats. The EC50 values amounted to 0.019 and 0.020mg while Trolox equ...
Pulse radiolysis studies of aminobenzenesulfonates: Formation of cation radicals
1991-01-01
Sulfanilic acid and anilinedisulfonic acids (ADS) react with OH radicals (k = 8.2 x 109 and 5.9 x 109 M-1s-1) to form the corresponding OH adducts. In acid solutions the adducts react with protons to yield cation radicals (k = 5.3 x 108 and 8.7 x 108 M-1s-1). N3 oxidizes sulfanilic acid directly to the cation radical by an electron-transfer reaction at a diffusion-controlled rate constant, k = 6.5 x 109M-1s-1, while the rate of oxidation of ADS by N3 is only 7.6 x 107 M-1s-1. SO4- on the other hand oxidizes ADS to the cation radical at a rate of 1.8 x 109M-1s-1. Both cation radicals deprotonate to the anilino-type radicals ...
2010-01-01
Optically detected electron paramagnetic resonance technique has been applied to study the stability of sterically hindered amine radical cations with respect to the ionmolecule proton transfer reaction in liquid squalane solutions. The reaction has proved very sensitive to the steric effect of bulky tertiary substituents at the nitrogen atom. It has been established that steric hindrance is able to efficiently block the NH proton transfer reaction, while the H-bonding may stabilize the distonic intermediate complex of aminyl radical and cation of ammonium type.
The monoadducts (4a-d) of thianthrene cation radical perchlorate (1a) and isobutene, 2-methylbutene, 2-methyl-2-butene, and 2-methylpentene decompose spontaneously in acetonitrile (MeCN) solution, with the formation of thianthrene (Th). Decomposition of 4a (1,2-(5,10-thianthreniumdiyl)-2-methylpropane diperchlorate) and 4a', the corresponding dihexafluorophosphate, was studied in depth and extensively with (1)H and (13)C NMR spectroscopy. Decomposition of 4a was found to involve the solvent itself as well as water in the solvent, remaining from incomplete drying, and gave, apart from Th, successively, the perchlorate salts of 2,4,4-trimethyl-2-oxazoline (6) and 2-amino-2-methylpropyl acetate (7). These salts, 6-HClO(4) and 7-HClO(4), respectively, were prepared and used in understanding the reactions of 4a as well as the relationships among 6, 7, and 2-(acetylamino)-2-methyl propanol (8) in acidified MeCN solution. Decompositions of 4a-d in MeCN and other nitriles (RCN) containing an added alcohol (R'OH) led to new products, 5-[(1-alkoxyalkylidene)ammonio]alkylthianthrenium diperchlorates (5a-u). These compounds were identified with (1)H and (13)C NMR spectroscopy and, in part, with X-ray crystallography and elemental analysis. The mechanisms of formation of 5-7 are discussed.
We investigate the electronic absorption spectra of several maximally pericondensed polycyclic aromatic hydrocarbon radical cations with time dependent density functional theory calculations. We find interesting trends in ...
2010-09-01
RP-51Electron Transfer Dissociation (ETD) occurs when precursor cations are reacted with radical reagent anions to induce fragmentation. Electron transfer from anion to cation, promotes...Full Text Available
Ultraviolet-radiation-curable paints
1981-09-30
In product finishing lines, ultraviolet radiation curing of paints on prefabricated structures could be more energy efficient than curing by natural gas fired ovens, and could eliminate solvent emission. Diffuse ultraviolet light can cure paints on three dimensional metal parts. In the uv curing process, the spectral output of radiation sources must complement the absorption spectra of pigments and photoactive agents. Photosensitive compounds, such as thioxanthones, can photoinitiate unsaturated resins, such as acrylated polyurethanes, by a free radical mechanism. Newly developed cationic photoinitiators, such as sulfonium or iodonium salts (the so-called onium salts) of complex metal halide anions, can be used in polymerization of epoxy paints by ultraviolet light radiation. One-coat enamels, topcoats, and primers have been developed which can be photoinitiated to produce hard, adherent films. This process has been tested in a laboratory scale unit by spray coating these materials on three-dimensional objects and passing them through a tunnel containing uv lamps.
Method for foam drilling using a biodegradable foaming agent
1978-10-24
A method for conducting foam drilling and workover operations in a borehole, penetrating a subterranean reservoir, and employing an aqueous solution of a biodegradable foaming agent composition containing about 0.3 to 3 parts by weight of an N-fatty ethyl sulfonic acid salt having the formula: RNHCH/sub 2/CH/sub 2/SO/sub 2/OM and per part by weight of an N-fatty propionic acid salt having the formula R/sub 1/NHCH/sub 2/CH/sub 2/COOM/sub 1/ is described. The R and R/sub 1/ are straight chain alkyl radicals having from 10 to 16 carbon atoms, and M and M/sub 1/ are alkali metal or ammonium cations. A particularly preferred foaming agent composition contains sodium 2-(N-lauryl) ethyl sulfonic acid and sodium 2-(N-lauryl) propionic acid.
Redox Reactions of Atoms and Radicals with Ions in Solution
The reactions of hydrogen atoms and various radicals (HO, HO2, RO2, RO, R, diphenylpicrylhydrazyl) in solution with cations and complexes of metals of variable valency and also with anions are surveyed, and their mechanism is discussed. The rate constants of these reactions are tabulated. A list of 130 references is included.
Directions of the oxidative dimerization of diphenylamine compounds
The purpose of this work was a quantum chemical study of the directions of oxidative dimerization of diarylamines by calculating the spin density in the amine radical cations and diarylnitrogen radicals, as well as calculating the total energies of the molecules, dications, and dianions of the oxidation products of Ar/sub 2/NH.
Directions of the oxidative dimerization of diphenylamine compounds
1987-08-10
The purpose of this work was a quantum chemical study of the directions of oxidative dimerization of diarylamines by calculating the spin density in the amine radical cations and diarylnitrogen radicals, as well as calculating the total energies of the molecules, dications, and dianions of the oxidation products of Ar/sub 2/NH.
Directions of the oxidative dimerization of diphenylamine compounds
1987-01-01
The purpose of this work was a quantum chemical study of the directions of oxidative dimerization of diarylamines by calculating the spin density in the amine radical cations and diarylnitrogen radicals, as well as calculating the total energies of the molecules, dications, and dianions of the oxidation products of Ar2NH
The single electron chemistry of coals. [Quarterly], April 1--June 30, 1992
Depolymerization of coals at low temperatures may offer advantages over thermal bond cleavage. Because bond cleavage energies of radical cations are lower than the corresponding homolytic bond cleavage energies of the same bond, generation of radical cations in coal may make possible depolymerization at lower temperatures. We seek to investigate the above possibility using single molecules containing functional groups common in coals. Since the generation of a radical cation requires the removal of an electron from a neutral molecule, a primary focus of the study will be finding oxidants that will remove an electron from compounds with structural similarity to those typically found in coals. The study will also be concerned with the decomposition of radical cations and the products formed as a result of the decomposition.
The single electron chemistry of coals. [Quarterly], April 1--June 30, 1992
1992-10-01
Depolymerization of coals at low temperatures may offer advantages over thermal bond cleavage. Because bond cleavage energies of radical cations are lower than the corresponding homolytic bond cleavage energies of the same bond, generation of radical cations in coal may make possible depolymerization at lower temperatures. We seek to investigate the above possibility using single molecules containing functional groups common in coals. Since the generation of a radical cation requires the removal of an electron from a neutral molecule, a primary focus of the study will be finding oxidants that will remove an electron from compounds with structural similarity to those typically found in coals. The study will also be concerned with the decomposition of radical cations and the products formed as a result of the decomposition.
1989-01-01
Carotenoids are present in the chloroplasts of photosynthetic green plants and serve as photoprotect devices and antenna pigments, and active role in the photosynthetic electron-transport chain with the carotenoid cation radical as an integral part of the electron-transfer process. The research reported herein has confirmed that carotenoid cation radicals have a lifetime that is sensitive to solvent, being longest in CH2Cl2 and are best prepared electrochemically. Semiempirical AM1 and INDO calculations of the trans and cis isomers of beta-carotene, canthaxanthin and beta-apo-8'-carotenal cation radicals predicted the unresolved EPR line whose linewidth varies to a measurable degree with carotenoid, which subsequent experimental observations affirmed. Simultaneous electrochemical - electron spin ...
Radiation and photochemistry section
1991-01-01
The highlights of this past year in the Radiation and Photochemistry Section at Argonne include: (1) picosecond optical studies of radical cations and excited states produced in hydrocarbon radiolysis provided the first kinetic measurements of ion transformation and production of triplet and singlet excited states by ion recombination. (2) studies of radical cations of alkyl-substituted amines and sulfides provided insights into ion-molecule reactions of radical cations in the condensed phase. (3) studies of the behavior of strained alkane radical cations, such as cubane {sup +}{center dot}, revealed new rearrangements and remarkable, medium-dependent differences in their structures. (4) H{center dot}atom reactions yielding e{sub aq}{sup {minus}} provided the first reliable measurements of hydrated-electron enthalpy and entropy and forced the revision of some previous thinking about the driving force in {sub aq}{sup {minus}} reactions.
Molecular Structure of Silylene
Silylene is a very reactive gas that belongs to the divalent silicon species. Silicon-based anions, cations, and radicals are important intermediates in the reactions of silicon. Silylenes have been proposed as catalysts for olefin polymerization.
Redox initiated cationic polymerization: Silane-N-aryl heteroaromatic onium salt redox couples
2010-01-01
In this article, a new route for the synthesis of N-aryl heteroaromatic onium salts by the direct copper catalyzed arylation of pyridine, substituted pyridines, isoquinoline, and acridine with diaryliodonium salts is described. It was demonstrated that these N-aryl heteroaromatic onium salts undergo facile platinum or rhodium-catalyzed reduction by silanes bearing Si H groups. The reduction of N-aryl heteroaromatic onium salts generates Bronsted acids. When this redox reaction was carried out in situ in the presence of an appropriate monomer, cationic polymerization was observed. Using this approach, the cationic polymerizations of epoxides, oxetanes, 1,3,5-trioxane, styrene, and vinyl ethers were carried out. The use of optical pyrometry to monitor the redox initiated cationic polymerizat...
1980-07-01
A rate equation for reactions of transient radicals in radiation chemistry is presented where the radical recombination is a second-order process with a rate coefficient depending on the structure of the initially inhomogeneous distribution of the reactants. For a Gaussian distribution in spurs this rate coefficient can be reduced to the well-known rate coefficient of a homogeneous diffusion-controlled reaction corrected by the ratio of the local concentration in the sgurs to the average concentration. The derived formalism is used for interpreting the reactive behaviour of transient arenediazo radicals observed in the pulse radiolysis of arene diazonium salts in a mixture of tert.-butanol/water. Evidence for the inhomogeneous kinetics of the arenediazo radicals was obtained from the unusual behaviour of the half-life times of radical recombination in dependence on pulse dose and salt concentration.
Guanine as a major site of DNA damage involving the direct effects of ionising radiation
1996-12-31
Full text: Exposure of cells to ionising radiation results in DNA damage which is produced by either diffusible water radicals or direct effects of radiation. Although significant information is known as DNA damage by water radicals, far less is known about the chemical pathways leading to DNA damage by direct effects. Ionising radiation initially results in the formation of a radical cation and an electron in DNA. The electron is known to migrate in DNA whereas information is lacking about hole migration in DNA at ambient temperatures and its subsequent localisation. Since 193 nm light monophotonically ionises DNA at the nuclesbases, it has been possible to address the consequences of hole migration in DNA. Following photo-ionisation of DNA with 193 nm light, the majority of the oxidative damage migrates and becomes localised at guanine. The resulting guanine radical results in a low yield of single strand breaks through radical transfer from the guanine moiety to produce a sugar radical. That prompt single strand breaks occur predominantly at guanine was confirmed from sequencing gel analysis. One of the major consequences of hole migration in DNA is base modification at guanine. Using an enzyme sensitive probe, 8-oxoguanine is identified as a major base modification, presumably resulting from hydration of the radical cation of guanine in double stranded DNA. In contrast, hydration of the one electron oxidised guanine radical in the mononucleoside, guanosine, does not occur. Therefore, the chemical pathways involving the guanine radical cation in DNA may differ significantly to those reported for the radical cation of guanosine. Since the guanine radical hydrates in double stranded DNA, the question arises as to changes of the reaction pathways of the guanine radical in DNA with oxygen or other radiation modifiers, not observed with the mononucleoside radical cation of guanine.
Task specific onium salts (TSOSs) as efficient soluble supports for Zard radical addition to olefins
2007-01-01
Task specific onium salts (TSOSs), that is, functionalised ammonium salts, have been used as soluble supports to carry out intermolecular radical additions of xanthates to olefins and functional group interconversions. This methodology provides results by far superior to those reported with other soluble supports and allows for very easy purifications of reaction products.
Various N-heterosubstituted benzenes, naphthalenes, anthracenes, and phenanthrenes have been ionized to their ion radicals in frozen solutions through intermolecular charge transfer induced by ..gamma..-ray irradiation. Cation and anion radicals have been produced selectively and studied by ESR and optical spectroscopy. The cations can be grouped into those in which the spin density is localized mainly on the in-plane lone-pair orbitals of nitrogen (n cations) and those in which the density is distributed over a ..pi..-electron orbital (..pi.. cations). They can be unambiguously distinguished by ESR and optical spectra. For the n cations the optical transition energies are in accord with photoelectron spectra. The spin density of the n cations substantiates significant interactions of lone-pair orbitals as elaborated previously in terms of through-space and through-bond interactions. The ..pi.. cations and ..pi.. anions exhibit an approximate mirror image relation in the optical spectrum. Failure of CNDO/S calculations to account for the observed optical spectra of n cations suggests sigma-..pi.. interactions. 14 figures, 1 table.
1979-11-07
Various N-heterosubstituted benzenes, naphthalenes, anthracenes, and phenanthrenes have been ionized to their ion radicals in frozen solutions through intermolecular charge transfer induced by ..gamma..-ray irradiation. Cation and anion radicals have been produced selectively and studied by ESR and optical spectroscopy. The cations can be grouped into those in which the spin density is localized mainly on the in-plane lone-pair orbitals of nitrogen (n cations) and those in which the density is distributed over a ..pi..-electron orbital (..pi.. cations). They can be unambiguously distinguished by ESR and optical spectra. For the n cations the optical transition energies are in accord with photoelectron spectra. The spin density of the n cations substantiates significant interactions of lone-pair orbitals as elaborated previously in terms of through-space and through-bond interactions. The ..pi.. cations and ..pi.. anions exhibit an approximate mirror image relation in the optical spectrum. Failure of CNDO/S calculations to account for the observed optical spectra of n cations suggests sigma-..pi.. interactions. 14 figures, 1 table.
Measurement of exchangeable cations in saline soils
2004-01-01
The measurement of exchangeable cations in saline soils is limited by the difficulty in accurately separating soluble cations from exchangeable cations. A method is examined for saline soils in which exchangeable cations are calculated as the total extractable cations minus the concentration of soil solution (soluble) cations. In addition, a further two standard methods were investigated, one which assumes the total soil extractable cations are exchangeable, the other utilises a pretreatment to remove soluble salts prior to measurement of the remaining (exchangeable) cations. After equilibration with a range of sodium adsorption ratio (SAR) solutions at various ionic strengths, the exchangeable cation concentrations of two soils (Dermosol and Vertosol) were determined by these methods and compared to known values. The assumption that exchangeable cations can be estimated as the total soil extractable cations, although valid at low ionic strength, resulted in an overestimation of exchangeable Na and Ca concentrations at higher ionic strengths due to the presence of soluble salts. Pretreatment with ethanol and glycerol was found to effectively remove soluble salts thus allowing the accurate measurement of the effective cation exchange capacity (ECEC), however, dilution associated with the pretreatment process decreased concentrations of exchangeable Ca while simultaneously increasing exchangeable Na. Using the proposed method, good correlations were found between known and measured concentrations of exchangeable Na (Dermosol: y=0.873x and Vertosol: y=0.960x) and Ca (Dermosol: y=0.906x, and Vertosol: y=1.05x). Therefore, for soils with an ionic strength of approximately 50 mM (ECse 4 dS m-1) or greater (in which exchangeable cation concentrations are overestimated by assuming the total soil cations are exchangeable), concentrations can be calculated as difference between total extractable cations and soluble cations. Publisher: The Regionals Institute Contributor: B. Sing Coverage: 2004-01-01T00:00:00Z
2010-01-01
A combination of electrospray ionization (ESI), multistage, and high-resolution mass spectrometry experiments are used to examine the gas-phase fragmentation reactions of radical cations of cysteine containing di- and tripeptides. Two different chemical methods were used to form initial populations of radical cations in which the radical sites were located at different positions: (1) sulfur-centered cysteinyl radicals via bond homolysis of protonated S-nitrosocysteine containing peptides; and (2) α-carbon backbone-centered radicals via Siu's sequence of reactions (J. Am. Chem. Soc. 2008, 130, 7862). Comparison of the fragmentation reactions of these regiospecifically generated radicals suggests that hydrogen atom transfer (HAT) between the α C–H of adjacent residues an...
Photophysics of hole injection in liquid cycloalkanes.
1999-06-03
In liquid cycloalkanes, single-photon excitation of solute radical cations leads to rapid transfer of a valence band electron and formation of a free solvent hole ('hole injection'). Quantum yields for this process upon 2.3 and 5 eV laser excitation of several aromatic radical cations in trans-decalin are reported and the photophysics of the hole injection in cycloalkane liquids is discussed.
Mechanism of the oxidation of diphenylamine compounds
A spectrophotometric, radiospectroscopic, and quantum chemical study of the oxidation of compounds of the diphenylamine series in acid medium has made it possible to establish a common reaction scheme for amines with different types of substituents and to determine certain details of the reaction mechanism: the participation of protonated amine molecules in the interaction with the oxidizing agent; intermediate formation of radical cations of the type of diphenylamine and N,N'-diarylbenzidine; the concrete directions of the dimerization of radical cations of diarylamines with the participation of the para-carbon atoms of the aromatic rings.
Mechanism of the oxidation of diphenylamine compounds
1986-10-20
A spectrophotometric, radiospectroscopic, and quantum chemical study of the oxidation of compounds of the diphenylamine series in acid medium has made it possible to establish a common reaction scheme for amines with different types of substituents and to determine certain details of the reaction mechanism: the participation of protonated amine molecules in the interaction with the oxidizing agent; intermediate formation of radical cations of the type of diphenylamine and N,N'-diarylbenzidine; the concrete directions of the dimerization of radical cations of diarylamines with the participation of the para-carbon atoms of the aromatic rings.
Mechanism of the oxidation of diphenylamine compounds
1986-01-01
A spectrophotometric, radiospectroscopic, and quantum chemical study of the oxidation of compounds of the diphenylamine series in acid medium has made it possible to establish a common reaction scheme for amines with different types of substituents and to determine certain details of the reaction mechanism: the participation of protonated amine molecules in the interaction with the oxidizing agent. Intermediate formation of radical cations of the type of diphenylamine and N,N'-diarylbenzidine. The concrete directions of the dimerization of radical cations of diarylamines with the participation of the para-carbon atoms of the aromatic rings
Hyperfine coupling in chlorophyll radical cations. A nuclear magnetic resonance approach
Most of the relative proton hyperfine coupling constants in the radical cations of chlorophyll a, chlorophyll b, and bacteriochlorophyll a have been determined using electron transfer NMR line broadening in the fast exchange limit. The results have been used to confirm ENDOR assignments for some methyl groups and to give a detailed spin density distribution for many positions exhibiting no ENDOR signals. Agreement with ENDOR is qualitatively good for Chl a and Bchl a, but is poor for Chl b.
Hyperfine coupling in chlorophyll radical cations. A nuclear magnetic resonance approach
1978-06-07
Most of the relative proton hyperfine coupling constants in the radical cations of chlorophyll a, chlorophyll b, and bacteriochlorophyll a have been determined using electron transfer NMR line broadening in the fast exchange limit. The results have been used to confirm ENDOR assignments for some methyl groups and to give a detailed spin density distribution for many positions exhibiting no ENDOR signals. Agreement with ENDOR is qualitatively good for Chl a and Bchl a, but is poor for Chl b.
Hyperfine coupling in chlorophyll radical cations. A nuclear magnetic resonance approach
1978-01-01
Most of the relative proton hyperfine coupling constants in the radical cations of chlorophyll a, chlorophyll b, and bacteriochlorophyll a have been determined using electron transfer NMR line broadening in the fast exchange limit. The results have been used to confirm ENDOR assignments for some methyl groups and to give a detailed spin density distribution for many positions exhibiting no ENDOR signals. Agreement with ENDOR is qualitatively good for Chl a and Bchl a, but is poor for Chl b
The report describes the annual progress of a project directed towards determining the factors which govern the breaking of carbon-carbon bonds in coal-related aryl-alkyl molecules by radical cation pathways. Coal model compounds have been oxidized by Cop...
2004-01-01
Novel cyclopropyl containing fatty acids are good substrates for P450(BM3) catalysed hydroxylation and analysis of their oxidation products indicates the presence of a radical intermediate (maximum rebound rate 2.6x10(10) s(-1)) and the absence of any cationic intermediate. Publisher: Royal Society of Chemistry Coverage: 2004-03-07T00:00:00Z
Calorimetric study of cationic photopolymerization
1996-03-01
The photopolymerization of penta-erythritol tetra-glycidyl ether (initiator Degacure KI-85) was studied by a du Pont 910 type DSC. From our experimental results the following conclusions can be drawn: (1) During the cationic polymerization reaction the lifetime of the initiating centers are long compared to the lifetime of free radicals in case of radical polymerization. (2) The rate of deactivation of the initiating centers increases with increasing temperature. (author).
Calorimetric study of cationic photopolymerization
1996-01-01
The photopolymerization of penta-erythritol tetra-glycidyl ether (initiator Degacure KI-85) was studied by a du Pont 910 type DSC. From our experimental results the following conclusions can be drawn: (1) During the cationic polymerization reaction the lifetime of the initiating centers are long compared to the lifetime of free radicals in case of radical polymerization. (2) The rate of deactivation of the initiating centers increases with increasing temperature. (author)
The radiolytic oxidation of anti-5-methylbicyclo[2.1.0]pentane gives the 1-methylcyclopentene radical cation as the sole rearrangement product H migration whereas oxidation of its syn isomer results in the highly selective formation of the 3-methylcyclopentene radical cation by methyl group migration. Since exactly the same stereoselectivity of olefin formation was observed in corresponding PET (photosensitized electron transfer) studies in the liquid phase, it is concluded that the rearrangement in this case also occurs through the intermediacy of radical cations. Clearly, the radical cation rearrangement must occur very rapidly (10{sup {minus}8}--10{sup {minus}9}s) under liquid-phase conditions at room temperature to compete with back electron transfer, and therefore the hydrogen (or methyl) migration is a fast process under these conditions. An intramolecular cycloaddition reaction was demonstrated in the radical cation rearrangement of 4-vinylcyclohexene to bicyclo[3.2.1]oct-2-ene. ESR studies show that the radiolytic oxidation of quadricyclane in Freon matrices under conditions of high substrate dilution leads to the bicyclo[3.2.0]hepta-2,6-diene radical cation as well as the previously reported norbornadiene radical cation, the former species predominating at sufficiently low concentrations.
Pulse radiolysis studies of aminobenzenesulfonates: Formation of cation radicals. [7 MeV electrons]
1991-09-19
Sulfanilic acid and anilinedisulfonic acids (ADS) react with OH radicals (k = 8.2 {times} 10{sup 9} and 5.9 {times} 10{sup 9} M{sup {minus}1}s{sup {minus}1}) to form the corresponding OH adducts. In acid solutions the adducts react with protons to yield cation radicals (k = 5.3 {times} 10{sup 8} and 8.7 {times} 10{sup 8} M{sup {minus}1}s{sup {minus}1}). N{sub 3} oxidizes sulfanilic acid directly to the cation radical by an electron-transfer reaction at a diffusion-controlled rate constant, k = 6.5 {times} 10{sup 9}M{sup {minus}1}s{sup {minus}1}, while the rate of oxidation of ADS by N{sub 3} is only 7.6 {times} 10{sup 7} M{sup {minus}1}s{sup {minus}1}. SO{sub 4}{sup {minus}} on the other hand oxidizes ADS to the cation radical at a rate of 1.8 {times} 10{sup 9}M{sup {minus}1}s{sup {minus}1}. Both cation radicals deprotonate to the anilino-type radicals in acid-base equilibria. The pK{sub a} of deprotonation of the sulfanilic cation radical is 5.8 {plus minus} 0.05 and that of the ADS cation radical is 4.3 {plus minus} 0.05.
High efficiency removal of technetium values from a nuclear waste stream is achieved by addition to the waste stream of a precipitant contributing tetraphenylphosphonium cation, such that a substantial portion of the technetium values are precipitated as an insoluble pertechnetate salt.
High efficiency removal of technetium values from a nuclear waste stream is achieved by addition to the waste stream of a precipitant contributing tetraphenylphosphonium cation, such that a substantial portion of the technetium values are precipitated as an insoluble pertechnetate salt.
Role of ionic processes in the formation of free radicals in. gamma. -irradiated glassy toluene
1980-08-21
Spectrophotometric study has been made on the reaction intermediates generated by ..gamma..-irradiation in glassy toluene at 77 K. Benzyl and methylcyclohexadienyl radicals are generated roughly in equal amounts, and the total yield (G value) of the radicals is 0.19. The addition of biphenyl results in the formation of biphenyl anion and cation and depletes the radical yield by 40%. The results indicate that the excited-state toluene, the precursor of the radicals, is generated by recombination of ions as well as by the direct effect of the radiation on toluene.
...combined the basic radical sodium, potassium, aluminum, barium, calcium, strontium, or...with the basic radical sodium, potassium, aluminum, barium, calcium, strontium, or zirconium...chlorides and sulfates (as sodium salts), not...
...combined the basic radical sodium, potassium, aluminum, barium, calcium, strontium, or...with the basic radical sodium, potassium, aluminum, barium, calcium, strontium, or zirconium...chlorides and sulfates (as sodium salts), not...
2007-03-02
The radiation- and photo- chemistry of room temperature ionic liquids (ILs) composed of ammonium, phosphonium, pyrrolidinium, and imidazolium cations and bis(triflyl)amide, dicyanamide, and bis(oxalato)borate anions, have been studied using low-temperature Electron Paramagnetic Resonance (EPR). Several classes of radicals have been identified and related to reactions of the primary radiolytically generated electrons and holes. Large yields of terminal and penultimate C-centered radicals are observed in the aliphatic chains of the phosphonium, ammonium and pyrrolidinium cations, but not for imidazolium cation. This pattern can be accounted for by efficient deprotonation of a hole trapped on the cation (the radical dication) that competes with rapid charge transfer to a nearby anion. The latter leads to the formation of stable N- or O-centered radicals. The electrons either react with the protic impurity (for nonaromatic cations) yielding H atoms or the aromatic moiety (for imidazolium cations). Excitation of bis(triflyl)amide anion is shown to yield trifluoromethyl radical; the yield of this radical in radiolysis, though, is low (< 10% of the alkyl radical yield). In terms of their radiation chemistry, neat ILs appear to be intermediate between organic liquids and ionic solids. Addition of 10-40 wt% of trialkylphoshate (a common extraction agent for nuclear cycle separations) has relatively little effect on the fragmentation of the ILs. Radiation induced dealkylation of the phosphate is prominent, but the yield of the alkyl radical fragments derived from the phosphates is < 4% of the yield of the radical fragments drived from the solvent. We discuss the implication of these results for the radiation stability of nuclear cycle extraction systems based upon the IL diluents.
2007-07-20
Full Text Available.The Ce(IV) initiated oxidation of synthetically relevant β-diketones and β-keto silyl enol ethers were explored in three solvents: acetonitrile, methylene chloride, and methanol. The studies presented herein show that the rate of reaction between Ce(IV) and the substrates is dependent upon the polarity of the solvent. Thermochemical studies and analysis are interpreted to be consistent with transition state stabilization by solvent being primarily responsible for the rate of substrate oxidation. Kinetic investigation of radical cations obtained from oxidations of β-diketones reveal that a more ordered transition state for the radical cation decay is achieved through the direct involvement of methanol in the deprotonation of the intermediate. In the case of radical cations derived from β-keto silyl enol ethers, experimental data supports a mechanism involving unimolecular decay of the intermediate. Remarkably, radical cations derived from β-diketones and β-keto silyl enol ethers are surprisingly stable in methylene chloride.
Geometrical isomerization of carotenoids mediated by cation radical/dication formation
1996-03-28
Electrochemical oxidation of all-trans-canthaxanthin and {beta}-carotene in dichloromethane leads to significant trans-to-cis isomerization, with cis isomers accounting for about 40% of the products formed. The electrochemically generated isomers were separated by reverse-phase high-performance liquid chromatography and identified as 9-cis, 13-cis, 15-cis, and 9,13-di-cis isomers of the carotenoids by {sup 1}H-NMR spectroscopy and optical spectroscopy (Q ratio). The results of simultaneous bulk electrolysis and optical absorption spectroscopy indicate the following isomerization mechanism: the all-trans cation radicals and/or dications formed by electrochemical oxidation of all-trans-carotenoids can easily undergo geometrical isomerization to form cis cation radicals and/or dications. The latter are converted by the comproportionation equilibrium to cation radicals which are then transformed to neutral cis-carotenoids by exchanging one electron with neutral carotenoids. AM1 molecular orbital calculations, which show that the energy barriers of configurational transformation from trans to cis are much lower in the cation radical and dication species than in the neutral molecule, strongly support the first step of this mechanism. 36 refs., 5 figs., 2 tabs.
2003-01-01
Inductive, resonance and polarization effects of substituents (X) on ionization potential of n-orbitals of iodine atom in molecules of the series IX, ISnR3 and ICident toCX, as well as on the energy of charge transfer band in UV spectra of complexes of the first two series of molecules with tetracyanoethylene and iodine were considered. It is shown that cation-radicals formed during photoionization of individual molecules in gaseous phase, which are components of close ion-radical pairs (excited state of the complexes with charge transfer) in solution are similar in terms of electronic structure. For the first time resonance parameters sigmaR+ silicon-, germanium- and tin-organic substituents relating to cation-radical centers I+. and I+.Cident toC have been ...
Electron spin resonance study of radicals formed from tetrolic acid by radiolysis in a freon matrix
1989-06-01
In the present study, e.s.r. spectra have been observed following {gamma}-irradiation of dilute frozen solutions of tetrolic acid, MeCident toCCO{sub 2}H, in CFCl{sub 3} at 77 K. A typical spectrum is shown which we interpret in terms of an isotropic quartet from the parent radical cation. MeCident toCCo{sub 2}H{sup +center dot}, and an anisotropic triplet arising from the propargyl radical, center dotCH{sub 2}Cident toCCO{sub 2}H, formed by deprotonation of the parent cation. This appears to be the first example of an alkyne radical cation to be observed in a CFCl{sub 3} matrix. (author).
1989-01-01
In the present study, e.s.r. spectra have been observed following gamma-irradiation of dilute frozen solutions of tetrolic acid, MeCident toCCO2H, in CFCl3 at 77 K. A typical spectrum is shown which we interpret in terms of an isotropic quartet from the parent radical cation. MeCident toCCo2H+centre dot, and an anisotropic triplet arising from the propargyl radical, centre dotCH2Cident toCCO2H, formed by deprotonation of the parent cation. This appears to be the first example of an alkyne radical cation to be observed in a CFCl3 matrix. (author)
Pulse Radiolysis of Aqueous Solutions of Aniline and Substituted Anilines
1971-07-01
The primary reactions of hydrated electrons, hydrogen atoms and hydroxyl radicals with aniline and the aniline cation in aqueous solutions have been studied by the technique of pulse radiolysis and by determination of end products after y-radiolysis. Hydrogen atoms and hydrated electrons react with aniline under formation of the cyclohexadienyl type radical with absorption maximum at 355 nm and an extinction coefficient of 4100/M/cm. A similar radical formed by reaction of hydrogen atoms with the aniline cation has its absorption maximum at 31 0 nm and an extinction coefficient of 3200/M/cm. Hydrogen atoms react with the acid and neutral forms of aniline with rate constants of (1.3 +- 0.2 ) x 109/M/s and (2.9 +- 0.7) x 109/M/s, respectively. OH radicals react with aniline with a rate constant of (1.4 +- 0.3) x 1010/M/s under formation of the cyclohexadienyl radical with absorption maximum at 355 nm and the anilino radical with absorption maxima at 300 and 400 nm. The cyclohexadienyl radical decayed in a first order process with a rate constant of 1.4 x 105/s by elimination of NH{sub 3}, whereas the anilino radical disappeared in a second order reaction under formation of hydrazobenzene. O- radicals react with aniline at pH 13.3 with a rate constant of (3.1 +- 0.6) x 109 under formation of anilino radicals. The reaction of OH radicals with the aniline cation produced the anilino radical cation with a rate constant of (4.8 +- 0.8) x 109 . The absorption maximum was placed at 415 nm, The cyclohexadienyl type radical with absorption maximum at 350 nm was also found in aqueous solutions of 2-amino-1,3-dimethylbenzene but was not formed in solutions of N,N' -dimethylaniline
Photochemical reactions of disulphide radical anions in frozen water-salt matrix
1986-01-01
Photochemical reactions of disulfide radical anions CH3SSCH-3 induced by light with lambda=436, 405 and 365 nm in a water-salt matrix of 6M LiCl at 77 K were studied. It was shown that upon excitation disulfide radical anions may enter into electron photodetachment reaction and the S-S bond is cleft. Kinetical nonequivalence of disulfide radical anions in photochemical reactions was shown to manifest itself in different mechanisms of their transformations. (author)
On the use of hexacyanocobaltates in the separation of caesium from radioactive waste solutions
1999-01-01
This paper reviews our work on the use of hexacyanocobaltate salts in the chemical treatment of radioactive waste solutions. The divalent cations of the 3d-block elements together with the hexacyanocobaltate moiety form insoluble polymeric coordination compounds. These compounds have been used as chemical precipitants or ion exchangers for the separation of radiocesium from various simulated and actual waste solutions. Precipitation in situ has been performed by using various hexacyanocobaltate salts of the divalent cations of Mn, Fe, Co and Ni. The results showed that Co2+ and Ni2+ salts have high selectivity for caesium. The presence of monovalent cations and detergent has significant effect on the precipitation process. On the other hand Cd2+ salt has been found to be more stable than other salts in alkaline medium. As ion ...
2007-01-01
Paramagnetic products of gamma-radiolysis of 12-crown-4 and its solutions in CFCl3 and CFCl2CF2Cl at 77 K were studied by ESR spectroscopy. It was found that the ESR spectra of 12-crown-4 irradiated with gamma-rays at 77 K contained superimposing signals of at least two species, the radicals resulting from macrocycle opening -C radical H-C(H) = O and macrocyclic radicals -O-C radical H-CH2-, which are formed with nearly equal yields. It was shown that -O-C radical H-CH2- radicals rapidly decayed at temperatures above 140 K. However, the -C radical H-C(H)=O radicals are stable almost up to the matrix softening temperature. The radical cations of 12-crown-4 are not stabilized in the matrices of Freon 11 and Freon 113, since they undergo transformation to macrocyclic radicals O-C radical ...
Photoinduced isomerization and fragmentation of the pentane radical cation in condensed phase
1986-01-01
Isolated molecular cations of pentane were generated at 77 K by gamma ray irradiation of dilute solutions of pentane (1-5% molar) in solid CF3CCl3 and CF2ClCFCl2 matrices. Both unlabelled and pentanes specifically labelled with deuterium were used. After irradiation the samples were bleached at 77 K with filtered or unfiltered white light, heated to room temperature and analyzed by GC/MS or by GC. The main photolytic products from pentane solutions are: methane, 2-butene and methylbutane. Label retention in 2-butene, kinetics of the photolysis and cutoff energy dependence of the yields of these products are interpreted as following: the pentane radical cation isomerizes to methylbutane cation under the action of light of wavelength shorter than about 1000nm. The methylbutane cation can fragment to butene ...
1988-11-22
The invention relates to a rechargeable high temperature electrochemical cell having a molten sodium anode, a molten halide salt liquid electrolyte, a compatible cathode in contact with the liquid electrolyte, and a beta-alumina solid electrolyte between the anode and liquid electrolyte is non-acidic and contains sodium cations as its only alkali metal cations, aluminium cations, as its only alkali metal cations, aluminium cations, and chloride anions. The electrolyte is doped with fluoride anions to combat progressively increasing internal resistance of the cell associated with cyclic charging and discharging thereof.
...with the basic radical aluminum or calcium. (2) Specifications...chlorides and sulfates (as sodium salts), not more than...prepared by extending the aluminum salt prepared from FD...C Blue No. 1?Aluminum...
...with the basic radical aluminum or calcium. (2) Specifications...chlorides and sulfates (as sodium salts), not more than...prepared by extending the aluminum salt prepared from FD...C Blue No. 1?Aluminum...
21 CFR 82.2051 - Lakes (Ext. D&C).
...potassium, barium, or calcium; or (ii) a salt prepared...color with the basic radical sodium, potassium, aluminum, barium, calcium, strontium, or zirconium...chlorides and sulfates (as sodium salts), not more than...
21 CFR 82.2051 - Lakes (Ext. D&C).
...potassium, barium, or calcium; or (ii) a salt prepared...color with the basic radical sodium, potassium, aluminum, barium, calcium, strontium, or zirconium...chlorides and sulfates (as sodium salts), not more than...
Salts of alkali metal anions and process of preparing same
Compounds of alkali metal anion salts of alkali metal cations in bicyclic polyoxadiamines are disclosed. The salts are prepared by contacting an excess of alkali metal with an alkali metal dissolving solution consisting of a bicyclic polyoxadiamine in a suitable solvent, and recovered by precipitation. The salts have a gold-color crystalline appearance and are stable in a vacuum at -10.degree. C. and below.
Salts of alkali metal anions and process of preparing same
1978-08-15
Compounds of alkali metal anion salts of alkali metal cations in bicyclic polyoxadiamines are disclosed. The salts are prepared by contacting an excess of alkali metal with an alkali metal dissolving solution consisting of a bicyclic polyoxadiamine in a suitable solvent, and recovered by precipitation. The salts have a gold-color crystalline appearance and are stable in a vacuum at -10/sup 0/C and below.
Salts of alkali metal anions and process of preparing same
Compounds of alkali metal anion salts of alkali metal cations in bicyclic polyoxadiamines are disclosed. The salts are prepared by contacting an excess of alkali metal with an alkali metal dissolving solution consisting of a bicyclic polyoxadiamine in a suitable solvent, and recovered by precipitation. The salts have a gold-color crystalline appearance and are stable in a vacuum at -10.degree. C. and below.
Colour development and luminescence phenomena in epoxy glasses
1998-01-01
The process of colour development in aromatic-amine cured epoxy resin glasses following exposure to oxygen has been studied using electron spin resonance (ESR) and thermoluminescence (TL). Even short duration exposure to oxygen was found to produce species in glassy epoxy resins which gave rise to TL when heated from room temperature to a temperature just below the cure temperature. In some epoxy samples, oxygen exposure over longer periods was found to produce sample colouration. UV-visible spectrophotometry revealed chromophores which were believed to arise from the diaminodiphenylmethane structural unit found in epoxy systems containing the resin, N,N,N,N-tetraglycidyl-4,4-diaminodiphenylmethane (TGDDM) or the curing agent, 4,4-diaminodiphenylmethane (DDM). The chromophore produced in TGDDM-based resins appeared to be simlar to the "Wurster's salt'-type structure produced by photo-ionization of these systems. A distinctive ESR spectrum was also noted for samples exposed to oxygen. These results are indicative of both peroxide group formation on the methylene groups as well as the formation of amine centred radical cations, and are consistent with the oxidative sensitivity of these epoxy resins. The TL is believed to result from the thermally induced recombination of the 'Wurster's salt'-like cations with peroxy anions leading to the production of an electronically excited diaminobenzophenone structure Other identifier: Polymers for Advanced Technologies 9 (1), pp. 75-83, January 1998 Language: en_US
2010-01-01
Tris(p-carboxyltetrathiaaryl)methyl radicals (TAM) are good EPR probes for measurement of dioxygen concentration in biological systems and for EPR imaging. It has been previously reported that these radicals are efficiently oxidized by superoxide, O2-, or alkylperoxyl radicals, ROO, and by liver microsomes via an oxidative decarboxylation mechanism leading to the corresponding quinone-methides (QM). This article shows that peroxidases, such as horseradish peroxidase (HRP), lactoperoxidase (LPO) and prostaglandin synthase (PGHS), and other hemeproteins, such as methemoglobin (metHb), metmyoglobin (metMb) and catalase, also efficiently catalyze the oxidation of TAM radicals to QM by H2O2 or alkylhydroperoxides. These reactions involve the intermediate formation of the corresponding cations T...
On the dissociation of DNA enhanced by radical cations
2010-01-01
This concerns the heat of reaction, Formula Not Shown , accompanying the cleavage of deoxyribonucleosides (KL) to give sugar radicals (K) and (adenine or guanine) base radicals ( Formula Not Shown ) under the influence of radical cations Formula Not Shown and Formula Not Shown . (The cited Formula Not Shown 's are the appropriate standard enthalpies of formation at 298.15K.) Addition of R+ onto one or another nitrogen of the bases does indeed perturb the zero-point+heat-content energies Z, namely, Formula Not Shown , as well as the "reorganizational energies" Re, i.e., Formula Not Shown . (Re describes how a free radical differs from its hypothetical electroneutral counterpart found in a symmetrical molecule L-L.) Finally, the "Charge Neutralization Energy" CNE describes the energetics acc...
2009-01-01
Oxidation potentials of 40 enols, enolates and some selected a-carbonyl radicals are presented along with their characterization by various techniques as applicable (X-ray, EPR, ENDOR, general TRIPLE, magnetic susceptibility measurements, UV-vis, fast scan cyclic voltammetry, isotope effects). The model compounds comprise representatives of stable simple enols linked to a multitude of substituents (alkyl, alkenyl, alkynyl, aryl, heteroaryl, propargyl alcohols) and of stable simple enols of amides. The results allow to clarify the primary reaction pathway of enol radical cations as a rapid deprotonation and-if warranted by the redox potential and the strength of the oxidant-a follow-up oxidation of the resultant a-carbonyl radical to the a-carbonyl cation. Moreover, the experimental oxidati...
Time-resolved pulsed EPR: microwave and optical detection
1981-01-01
Time-resolved pulsed EPR spectrometers are described. EPR spectra, kinetic profiles, and relaxation studies are used to illustrate some capabilities of the pulsed EPR experiment. Optical detection of time-resolved EPR spectra of radical ion pairs is used to study radical-ion recombination kinetics, recombination pathways, and the structure of radical anions and cations. 17 figures.
Pulse radiolysis of doped polyethylene in molten state
1990-01-01
With pulse radiolysis and detection by optical absorption spectroscopy in transparent, molten and highly viscous polyethylene polymer radicals and alkene type radical cations were observed and characterized by their reactions with scavengers. In presence of additives as diphenylamine, benzophenone, sterically hindered phenols, styrene, etc. product radicals appear mainly in a very rapid reaction (
1994-01-01
The transient optical absorption band (lambdamax = 325 nm), formed on reaction of OH radicals in neutral aqueous solutions of bromobenzene is assigned to OH-adduct with benzene ring. In acidic solutions, transient bands with lambdamax = 320 and 540 nm are assigned to solute radical cation formed on electron transfer from benzene ring and Br respectively. (author). 1 ref., 2 figs
Organic metals: BVDT-TTF and BDVDT-TTF polyiodides
1987-01-01
In order to experimentally investigate the influence of the steric effects of the ethylene groups in BEDT-TTF on the structure and electroconducting properties of the salts, the authors synthesized polyiodides of two derivatives of BEDT-TTF: bis(vinylenedithio)tetrathiafulvalene (BVDT-TTF), and bis(dimethylvinylenedithio)tetrathiafulvalene (BDVDT-TTF). Comparison of the structure and properties of the (BVDT-TTF)(I/sub 3/)/sub 0.4/ and (BDVDT-TTF) (I/sub 3/)/sub 0.4/ crystals with the (BEDT-TTF)(I/sub 3/)/sub 0.5/ crystals shows that substitution in BEDT-TTF of ethylene bridges for the vinylene bridges, leading to a completely conjugated planar system, probably ensures the possibility of a denser packing of the cation-radicals in the stacks. This results in strong unidimensional anisotropy of the intermolecular interactions, which leads to dielectrization of the electronic system in BVDT-TTF and BDVDT-TTF polyiodides.
Fermiology and superconductivity at high magnetic fields in a completely organic cation radical salt
We report specialized interplane magnetoresistance (MR) measure-ments on the organic superconducting compound ?''-(BEDT-TTF)2SF5CH2CF2SO3 (where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene) in both the superconducting (Tc ~ 5 K) and normal states versus magnetic field direction. In the normal state, detailed angular-dependent magnetoresistance oscillation (AMRO) studies reveal peculiar features of the Fermi surface topology of this compound, and very high magnetic field studies further support the unusual nature of the electronic structure. In the superconducting state we investigate, through detailed AMRO measurements, the anomalous MR peak that appears within the superconducting field-temperature phase diagram. Our results reveal a direct connection between the superconducting state determined from purely in-plane field, and the vortex lattice produced by the inter-plane magnetic field. We also describe several unique sample rotation instruments used in these high field experiments, including the use of dysprosium pole pieces in combination with a 45 T hybrid magnet to carry out measurements at the highest steady-state resistive magnetic field (47.8 T) yet achieved.
1986-08-12
A composition is described for absorbing oil from oil-in-water emulsions comprising the reaction product of a cellulose-containing substance having cationic exchange properties and a fatty quaternary ammonium salt.
Cationic surfactants based on ferrocene
1988-07-20
Quaternary ammonium salts based on ferrocene were synthesized and their surface active properties were studied as potential cationic surfactants and for uses including antiknock compounds. The salts were halide and nitrate derivatives of dimethylferrocenylmethylammonium and were prepared by aminomethylation of ferrocene. Chemical reaction yields, melting points, surface tension isotherms, and other characteristics were assessed.
Electronic structure and photochemical interconversions of dihydropentalene radical cations
1995-08-02
Starting from the recently characterized radical cation of bicyclo[3,3,0]octa-2,6-diene-4,8-diyl, four additional dihydropentalene radical cations (DHP{sup -4}) can be formed by phototautomerization in Freon glasses and argon matrices where they can be characterized by optical (Freon, argon) and ESR spectroscopy (Freon). Two of these DHP isomers can be prepared independently, while the cations of the other two are identified by analogy of their spectra with those of related compounds. The electronic structure of 1,2-, 1,4-, and 1,5-DHP{sup +}, which have linear and cross-conjugated triene {pi}-systems is discussed on the basis of their photoelectron and optical spectra and INDO/S calculations. The part of the C{sub 8}H{sub 8}{sup +} potential surface comprising all ten possible DHP{sup +} tautomers and some related valence isomers is explored by high-level ab initio calculations. An FMO-based set of rules for sigmatropic rearrangements in radical cations is presented and serves to rationalize the observed H-shifts. 40 refs., 12 figs., 4 tabs.
Naphthoxy Bounded Ferrocenium Salts as Cationic Photo initiators for Epoxy Photo polymerization
2009-01-01
To improve the absorption and the bulk of arene ligands, two naphthoxy bounded ferrocenium salts as new cationic photo initiators, (6-a-naphth oxybenzene) (5-cyclopentadienyl) iron hexafluorophosphate (NOFC-1) and (6-beta-naphth oxybenzene) (5-cyclopentadienyl) iron hexafluorophosphate (NOFC-2), were synthesized, characterized, and studied. NOFC-1 and NOFC-2 were prepared by the reaction of nucleophilic substitution (SNAr) with naphthol and chlorobenzene-cyclopentadienyliron salt. Their activity as cationic photo initiators was studied using real-time infrared spectroscopy. The results obtained showed that NOFC-1 and NOFC-2 are capable of photo initiating the cationic polymerization of epoxy monomer directly on irradiation with long-wavelength UV light (365 nm). Comparative studies also demonstrated that they exhibited better ...
Infrared Spectroscopy of Water Cluster Radical Cations (H_2O)_n^+ (n = 3 to 11)
To obtain structural information about radical cationic hydrogen-bonded water networks, we have measured size-selected infrared spectra of the water cluster cations (H_2O)_n^+ (n = 3--11) in the OH stretching region. The spectra of smaller-sized clusters (n ? 6) show a free OH band associated with the OH radical. This band indicates that nominal water cluster cations (H_2O)_n^+ form H^+(H_2O)n-1OH type structures, and that the OH radical lies in the network terminal. For larger-sized clusters, the analyses of the hydrogen-bonded OH stretching bands aided by quantum chemical calculations evidence the existence of the OH radical in the clusters. Detailed cluster structures will be discussed on the basis of the experimental spectra.
2000-01-01
The radicals formed on gamma-radiolysis of oligopeptides containing methionine and glycine residues in the polycrystalline state at 77 k and subsequent warming over the temperature range 77-293 K were identified using the electron spin resonance (ESR) technique. In all oligopeptides studied, anion peptide radicals and monomeric sulfur radical cations over the temperature range 77-95 K and decarboxylation and deamination radicals over the temperature range 180-250 K were detected. In addition, in oligopeptides containing adjacent methionyl residues, three-electron-bonded dimeric sulfur radical cations (S:.S)+ were detected at 110 K. In oligopeptides containing N-terminal methionine residue, H-abstraction radicals in the side chain of methionine residue were observed over the temperature range of 180-250 K. H-abstraction radicals ...
Elastomeric binders for battery electrodes
1989-03-21
A battery is described, comprising: an anode comprising one or more particulate anode active materials selected from the group consisting of conjugated backbone polymers, alkali metals, alloys of alkali metals and alkali metal cation inserting materials dispersed in an elastomeric binder; an electrolyte comprising an organic solvent and an alkali metal salt, and a cathode. The alkali metal cations from the electrolyte are incorporated into the anode as a metal alloy as or as an inserted ion in the alkali metal cation inserting material or the conjugated polymer during the charging of the battery.
The intermediates formed by fast atom bombardment, radiolysis and photolysis of arenediazonium salts
1990-01-01
The possibility of the aryl cation formation from diazonium salts has been examined by fast atom bombardment and radiolysis, and the results have been compared with those obtained in photolysis. The ready loss of N{sub 2} due to the heterolytic decomposition pathway leading to the aryl cation formation has been observed under the types of radiation. The stabilization of the species depends strongly on matrix properties, especially under ionizing radiation. Ring substituents are crucial for ESR studies (for the triplet aryl cation stabilization) in solid matrices. They seem to not influence much the appearance of the aryl cation under fast atom bombardment and the three-substituent pattern seems not to favour the aryl cation formation as it does in photo- and radiolysis. (author).
The intermediates formed by fast atom bombardment, radiolysis and photolysis of arenediazonium salts
1990-01-01
The possibility of the aryl cation formation from diazonium salts has been examined by fast atom bombardment and radiolysis, and the results have been compared with those obtained in photolysis. The ready loss of N2 due to the heterolytic decomposition pathway leading to the aryl cation formation has been observed under the types of radiation. The stabilization of the species depends strongly on matrix properties, especially under ionizing radiation. Ring substituents are crucial for ESR studies (for the triplet aryl cation stabilization) in solid matrices. They seem to not influence much the appearance of the aryl cation under fast atom bombardment and the three-substituent pattern seems not to favour the aryl cation formation as it does in photo- and radiolysis. (author)
1993-04-01
Dynamic fluorescence spectroscopy of micelle-solubilized pyrene was used to measure the size of the sodium dodecylsulfate (SDS) aggregate bound to polyethylene glycol (PEG). The measurements were carried out with very dilute PEG and SDS concentrations, to ensure that there were no free surfactant aggregates in solution and that all aggregates present were bound to the polymer. Effect of salts of sodium, cesium, lithium, and magnesium of varying concentrations on the size of the bound aggregate was determined. The affinity of the cation toward PEG controlled the size of the SDS aggregate bound to the polymer. The stronger the binding between the cation and PEG, the smaller was the bound SDS aggregate. There was no effect of either the anion or the salt concentration for a particular cation on the size of the bound SDS aggregate. As the ionic strength increased, the only parameter affected was the number of bound surfactant aggregates per polymer chain. Results are discussed in terms of simultaneous affinities of the cations toward the polymer and the micelle.
Cation exchange in a glacial till drumlin at a road salt storage facility
2009-01-01
We use laboratory and field data to calibrate existing geochemical and transport models of cation exchange induced by contamination of an unconfined aquifer at a road salt storage facility built upon a glacial till drumlin in eastern Massachusetts. A Gaines and Thomas selectivity coefficient K models the equilibrium sodium and divalent cation distribution in the groundwater and solid matrix, while an existing method of characteristics model describes the advective transport of total dissolved cations and sorbed sodium. Laboratory isotherms of split spoon soil samples from the drumlin calibrate K with an average value of 0.0048(L/g)1/2 for a measured cation exchange capacity of 0.057meq/g dry soil. Ten years of monitoring well data document groundwater flow and the advection of conserva...
Spin-frustrated antiferromagnets based on BEDT-TTF and manganese dicyanamide complexes
The magnetic properties of new radical cation salts ( BEDT-TTF)2[CuMn( dca)4] ( I) and ( BEDT-TTF)2[Mn( dca)3] ( II) [where BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene and dca = N(CN2)] are investigated using superconducting quantum interference device (SQUID) magnetometry and electron paramagnetic resonance (EPR) spectroscopy. It is established that, at temperatures below 25 K, both salts are characterized by antiferromagnetic deviations from the paramagnetic behavior. The Weiss constants for compounds I and II are determined to be ?5 and ?10 K, respectively. The corresponding correlations in the structure of compound I are short-range correlations and do not lead to a change in the effective spin equal to 5/2. It is found that the widths of the EPR lines attributed to the BEDT-TTF conducting sublattice correlate with the widths of the EPR lines associated with the magnetic sublattice of the Mn( dca){3/?} counterion in the structure of salt II. This correlation suggests that the antiferromagnetic ordering in the magnetic sublattice of compound II affects the spin-lattice relaxation in the BEDT-TTF sublattice. The dependence of the magnetic moment on the magnetic field for compound II at a temperature of 2 K is typical of weakly frustrated uniaxial antiferromagnets and exhibits a kink in a magnetic field of 20 kOe, which corresponds to spin-flop transitions.
The calculation of the rate constants for the processes in the reduction of diazonium, tropylium, verdazylium, and pyrylium cations by various organic electron donors, using the equations of the Marcus theory with allowance for the reorganization energy of only the outer coordination sphere, leads to values which are one to seven orders of magnitude higher than the experimental values. By quantum-chemical calculations it was shown that the reduction of diazonium and tropylium cations to the corresponding radicals is accompanied by a substantial change in the structure of the reagents. This leads to high values for the reorganization energy of the inner coordination sphere of the cations, which must be taken into account during calculation of the rate constants. The differences in the rate constants of the processes of direct electron transfer from the electron donors to the organic cations and the recombination of these reagents depend on the dissociation energy of the bond of the cation with the donor leading to the electron transfer products.
1987-09-01
The calculation of the rate constants for the processes in the reduction of diazonium, tropylium, verdazylium, and pyrylium cations by various organic electron donors, using the equations of the Marcus theory with allowance for the reorganization energy of only the outer coordination sphere, leads to values which are one to seven orders of magnitude higher than the experimental values. By quantum-chemical calculations it was shown that the reduction of diazonium and tropylium cations to the corresponding radicals is accompanied by a substantial change in the structure of the reagents. This leads to high values for the reorganization energy of the inner coordination sphere of the cations, which must be taken into account during calculation of the rate constants. The differences in the rate constants of the processes of direct electron transfer from the electron donors to the organic cations and the recombination of these reagents depend on the dissociation energy of the bond of the cation with the donor leading to the electron transfer products.
2004-11-01
Upon the addition of multivalent cations, a giant DNA chain exhibits a large discrete transition from an elongated coil into a folded compact state. We performed single-chain observation of long DNAs in the presence of a tetravalent cation (spermine), at various temperatures and monovalent salt concentrations. We confirmed that the compact state is preferred at higher temperatures and at lower monovalent salt concentrations. This result is interpreted in terms of an increase in the net translational entropy of small ions due to ionic exchange between higher and lower valence ions.
While ionization of some polyatomic molecular liquids (such as water and aliphatic alcohols) yields so-called "solvated electrons" in which the excess electron density is localized in the interstices between the solvent molecules, most organic and inorganic liquids yield radical anions and cations in which the electron and spin densities reside on the solvent molecule or, more commonly, a group of such molecules. The resulting multimer ions have many unusual properties, such as high rates of diffusive hopping. The "solvated electron" can be regarded as a variant of a multimer radical anion in which the charge, while perturbing the solvent molecules, mainly resides in the space between these molecules. We give several examples of less known modes for electron localization in liquids that yield multimer radical anions (such as C6F6, benzene, acetonitrile, carbon disulfide and dioxide, etc.) and holes localization in liquids that yield multimer radical cations (such as cycloalkanes). Current understanding of the reaction properties for these high-mobility solvent radical anions and cations is discussed.
1984-05-15
Photoproduced N,N,N',N'-tetramethylbenzidine cation radicals in sodium dodecyl sulfate micelles decay in a pseudo-first-order reaction with an apparent rate constant k(t) depending on time according to k(t) = Bt/sup alpha-1/ , where B and ..cap alpha..(0<..cap alpha..< or =1) are constants. At a given temperature the numerical value of B decreases with the storage time between preparation of the micellar solution and photoionization achieving a constant value for a storage time of a few days. The numerical value of ..cap alpha.. is essentially independent of the storage time and determines the distribution of cation radical lifetimes for a given value of B.
1989-01-01
The spectra of stabilized solvent holes were obtained by the method of optically detected ESR (OD ESR) in glassy matrices at 77 K. Using this technique we obtained the spectra for radical-cations of cis-decalin, squalane, 2-methylpentane, 3-methylpentane, 3,3-dimethylpentane, 3-methylheptane and 2,3-dimethylbutane. For all matrices except that of squalane, an hf-structure in the OD ESR spectra belonging to the radical-cations of matrices used is detected. Thus an unpaired electron is shown to be localized mainly on one molecule. The efficiency of hole transfer to acceptors with a lower ionization potential is studied in squalane and cis-decalin. It increases with difference in ionization DELTAI
Radical cations in radiation chemistry of liquid hydrocarbons
1996-07-01
The state of knowledge concerning radical cations in liquid alkanes is discussed with particular emphasis on those which exhibit high mobility. Uncertainty has existed in the interpretation of previous results with respect to the nature and reactivity of high mobility ions, especially for cyclohexane. Recent time-resolved studies on pulse radiolysis/transient absorption, photoconductivity, and magnetic resonance in these systems have led us to propose new mechanisms for the high mobility ions. In decalins, scavenging of these ions by solutes is a pseudo-first-order reaction. In cyclohexane, the behavior is more complex and is indicative of the involvement of two species. This bimodality is rationalized in terms of a dynamic equilibrium between two conformers of the solvent radical cation. Several experimental tests supporting these views include a recent study on two-color laser photoionization in cyclohexane.
1986-10-01
The report describes the annual progress of a pr,ject directed towards determining the factors that govern the breaking of carbon-carbon bonds in coal-related aryl-alkyl molecules by radical cation pathways. Coal model compounds were oxidized by copper (II)-peroxydisulfate in water/acetonitrile/acetic acid media, and the reactions of the intermediate radical cations have been inferred from product analyses. Results for 9-methyl-, 9-hydroxymethyl-, 9-benzyl, 9-styrl-, 9,10-dimethyl-, and 2-ethylanthracene, and benzyl phenyl sulfides are presented and discussed. A new synthesis of lepidopterene, an oxidation product of methylanthracene, is described.
Radical scavenging properties of nicotinamide and its metabolites
2008-03-15
By means of pulse radiolysis the reactivity of nicotinamide, its metabolites and selected pyridinium salts towards reactive oxygen species was tested and compared with the pharmacological efficacy of this group of compounds. It was found that pyridinium salts are poor radical scavengers but the positive charge distribution enhances their interactions with immobilized heparin. Thus, superior pharmacological efficacy of 1-methylnicotinamide may be related to its ability to interact with biological tissues rather than to its direct anti-oxidant properties.
Radical scavenging properties of nicotinamide and its metabolites
2008-01-01
By means of pulse radiolysis the reactivity of nicotinamide, its metabolites and selected pyridinium salts towards reactive oxygen species was tested and compared with the pharmacological efficacy of this group of compounds. It was found that pyridinium salts are poor radical scavengers but the positive charge distribution enhances their interactions with immobilized heparin. Thus, superior pharmacological efficacy of 1-methylnicotinamide may be related to its ability to interact with biological tissues rather than to its direct anti-oxidant properties
2010-01-01
Hydroperoxides, olefins, and arenediazonium salts selectively combine to give azo compounds via an iron(II)-mediated three-component reaction. Starting with a fragmentation liberating acetic acid, the hydroperoxides act as radical source and the diazonium ions as nitrogen-centered radical scavengers.
Oxidation intermediates of {alpha}-glucosyl rutin by pulse radiolysis
1997-11-01
Transient intermediates generated in the reaction of {alpha}-glucosyl rutin (G-rutin) with the OH radical or the azide radical were investigated by pulse radiolysis. The OH radical reacted with G-rutin to produce the OH-adduct radical, followed by deprotonation in neutral and acidic solutions. In alkaline solutions, the OH-adduct di-anion radical formed from the di-anions of G-rutin were dehydrated to the phenoxyl radical. On the other hand, G-rutin was oxidized to one-electron oxidized cation radical by the azide radical. The pK{sub a} values of the OH radical adduct were found to be 6.83 {+-} 0.10 and 8.87 {+-} 0.13. While, the pK{sub a} values of the phenoxyl radical of G-rutin were found to be 7.52 {+-} 0.11 and 9.95 {+-} 0.13. (author).
Oxidation intermediates of alpha-glucosyl rutin by pulse radiolysis
1997-01-01
Transient intermediates generated in the reaction of alpha-glucosyl rutin (G-rutin) with the OH radical or the azide radical were investigated by pulse radiolysis. The OH radical reacted with G-rutin to produce the OH-adduct radical, followed by deprotonation in neutral and acidic solutions. In alkaline solutions, the OH-adduct di-anion radical formed from the di-anions of G-rutin were dehydrated to the phenoxyl radical. On the other hand, G-rutin was oxidized to one-electron oxidized cation radical by the azide radical. The pKa values of the OH radical adduct were found to be 6.83 +- 0.10 and 8.87 +- 0.13. While, the pKa values of the phenoxyl radical of G-rutin were found to be 7.52 +- 0.11 and 9.95 +- 0.13. (author)
2010-01-01
Our previous mechanistic discussion of the free-radical crosslinking monoallyl/diallyl copolymerizations was extended to the cationic crosslinking monoepoxide/diepoxide copolymerizations, typically including 1,2-epoxycyclohexane (ECH) as a monoepoxide and bis[3,4-epoxycyclohexylmethyl] adipate (BECHMA) as a diepoxide crosslinker. In the cationic polymerization, oligomer is usually obtained because of the occurrence of characteristic chain-forming reactions. Therefore, cationic crosslinking monoepoxide/diepoxide copolymerizations could be in the category of the network formation through free-radical crosslinking monoallyl/diallyl copolymerizations. Thus, the gelation behavior was discussed by comparing the actual gel points with the theoretical ones; the greatly delayed gelation from theory...
The photophysics of the perylene radical cation (Pe?+) was studied using the molecular mechanics-valence bond (MMVB) hybrid force field. Potential energy surfaces of the first three electronic states were investigated. Geometry optimizations of critical points-including conical intersections between the relevant electronic states-were performed using the MMVB analytical energy gradient for cations. No accessible planar conical intersection between the D0 and D1 states of Pe?+ was found; this is consistent with the experimentally observed D1 lifetimes and the observation of D1 emission from this cation in the condensed phase. Benchmark RASSCF and TD-DFT calculations support the reliability of the MMVB results.
Antioxidant activity of flavone C-glucosides determined by updated analytical strategies
2011-01-01
The antioxidant activity of flavone C-glucosides, namely orientin (OR), homoorientin (hOR), vitexin (VT) and isovitexin (iVT) in comparison to quercetin (Q) was measured against 2,2prime-azinobis-(3-ethylbenzothiazoline-6-sulphonate) radical cation (ABTS+), 2,2-diphenyl-1-picrylhydrazyl radical (DPPH), superoxide anion radical Formula Not Shown whilst the reducing activity was determined by cyclic voltammetry (CV) method. The order of the antioxidant activity determined against ABTS+ and DPPH radicals was as follows: Formula Not Shown . Orientin (OR) and homoorientin (hOR) showed the highest ability to scavenge superoxide anion radicals whilst about threefold lower was found for VT and iVT. The order of the antioxidant activity determined against superoxide anion radicals was hOR
Isolation of transplutonium elements on ion exchangers from solutions of high salt concentration
1985-05-01
The behaviour of transplutonium elements (TPE) on cation and anion exchangers in aqueous alcoholic solutions of chlorides and nitrates of some alkali and alkaline earth metals depending on different factors: salt concentration, content of alcohol and of acid in the solution as well as the nature of a cation was studied. The data obtained were used to determine the optimal conditions of concentration of TPE on ion exchangers from solutions containing great quantities of salts. The advantages of the use of aqueous alcoholic solutions of nitric acid in the isolation of TPE are shown.
Isolation of transplutonium elements on ion exchangers from solutions of high salt concentration
1985-01-01
The behaviour of transplutonium elements (TPE) on cation and anion exchangers in aqueous alcoholic solutions of chlorides and nitrates of some alkali and alkaline earth metals depending on different factors: salt concentration, content of alcohol and of acid in the solution as well as the nature of a cation was studied. The data obtained were used to determine the optimal conditions of concentration of TPE on ion exchangers from solutions containing great quantities of salts. The advantages of the use of aqueous alcoholic solutions of nitric acid in the isolation of TPE are shown. (author)
2009-09-08
Full Text Available.SUMMARYThe in vitro photodynamic therapy activity of four imidazole-substituted metalloporphyrins has been studied using human (HeLa) and mouse (CT26) cancer cell lines: an anionic Zn porphyrin and a homologous series of three cationic Zn, Pd or InCl porphyrins. A dramatic difference in phototoxicity was found: Pd cationic > InCl cationic > Zn cationic > Zn anionic. HeLa cells were more susceptible than CT26 cells. Induction of apoptosis was demonstrated using a fluorescent caspase assay. The anionic Zn porphyrin localized in lysosomes while the cationic Zn porphyrin localized in lysosomes and mitochondria, as assessed by fluorescence microscopy. Studies using fluorescent probes suggested that the cationic Pd porphyrin produced more hydroxyl radicals as the reactive oxygen species. Thus, the cationic Pd porphyrin has high potential as a photosensitizer and gives insights into characteristics for improved molecular designs.
Website Policies and Important Links Comments
 |
 |
 |
WorldWideScience.org is maintained by the
U.S. Department of Energy's
Office of Scientific and Technical Information as the Operating Agent
for the WorldWideScience Alliance.