WorldWideScience
 
 
1

Terrestrial and Meteorite Carbon Appear to Have the Same Isotopic Composition  

UK PubMed Central (United Kingdom)

The carbon-isotope ratio recently obtained for the carbon found in the Murchison meteorite, which has been shown (by the racemic nature of twelve component amino acids) to be free of terrestrial contamination,...Full Text Available

1971-02-01

2

Endocrine and Neurochemical Effects of 3,4-Methylenedioxymethamphetamine and Its Stereoisomers in Rhesus Monkeys  

UK PubMed Central (United Kingdom)

3,4-Methylenedioxymethamphetamine (MDMA) is an amphetamine derivative that elicits complex biological effects in humans. One plausible mechanism for this phenomenon is that racemic MDMA is composed...Full Text Available

2010-08-01

3

Some observations on amino acid racemization under pyrolytic temperatures and inorganic oxide-catalyzed intermolecular condensation.  

Science.gov (United States)

The problem of homochirality is of crucial importance for the origins of Life. While most laboratory studies are focused on the search of physical and chemical sources of handedness in the Universe, they reflect only one aspect of the problem: the origin of homochiral biomolecules. At the same time, any space environments where biomolecules are expected to form and where they have to pass through before the first primitive forms of Life emerge, include strong irradiation or/and high temperatures. This automatically implies the possibility of losing the optical activity, i.e. racemization. The simulation experiments performed by our group deal with the following two aspects of amino acid abiotic chemistry: (1) amino acid pyrolysis associated with their extraterrestrial delivery; and (2) peptide formation from amino acids catalyzed by inorganic oxides. According to our observations, the racemization phenomena are very common in the systems ...

2001-01-01

4

Preparation of radioactive lead complexes utilizing Chelex methodology  

Energy Technology Data Exchange (ETDEWEB)

The use of Chelex resin for the synthesis of radioactive lead complexes has been explored. The process involved immobilization of {sup 203}Pb on the resin and subsequent elution of complexed lead by chelating agents. {sup 203}Pb complexes derived from meso- and racemic dimercaptosuccinic acid (meso-DMSA, rac-DMSA) were prepared and assessed for stability in vitro.

1996-11-01

5

Preparation of radioactive lead complexes utilizing Chelex methodology  

International Nuclear Information System (INIS)

The use of Chelex resin for the synthesis of radioactive lead complexes has been explored. The process involved immobilization of "2"0"3Pb on the resin and subsequent elution of complexed lead by chelating agents. "2"0"3Pb complexes derived from meso- and racemic dimercaptosuccinic acid (meso-DMSA, rac-DMSA) were prepared and assessed for stability in vitro.

1996-11-01

6

Esterification of chiral secondary alcohols with fatty acid in organic solvents by polyethylene glycol-modified lipase.  

Science.gov (United States)

Lipase from Pseudomonas fragi 22.39B was modified with polyethylene glycol. The modified lipase (PEG-lipase) was soluble and active in organic solvents such as benzene and 1,1,1-trichloroethane. PEG-lipase catalyzed esterification of chiral secondary alcohols with fatty acids in benzene and exhibited preference for R isomers over S isomers. Km and Vmax values for each isomer of various alcohols were obtained by kinetic study of the esterification in benzene. PEG-lipase-catalyzed esterification leads to optical resolution of a racemic alcohol. PMID:2635854

1989-11-01

7

New b-amino-a-trifluoromethyl alcohols and their exploration in the synthesis of trifluoromethylated imidazole derivatives  

British Library Electronic Table of Contents (United Kingdom)

Racemic and enantiomerically pure b-amino-a-trifluoromethyl alcohols were obtained via sequential nucleophilic trifluoromethylation of selected a-imino ketones, derived from arylglyoxals, and subsequent removal of the MeO or Ph(Me)CH substituent, respectively, located at the N-atom. The obtained products, containing a primary amino group, were used for the synthesis of imidazole N-oxides bearing a trifluoromethyl group as a part of the N(1)-alkyl chain. Imidazole N-oxides with an electron-withdrawing ester group at C(4) underwent spontaneous isomerization under the reaction conditions, and the corresponding imidazol-2-ones derivatives were isolated as final products.

2011-01-01

8

Lipase catalyzed esterification of glycidol in organic solvents  

Science.gov (United States)

The authors studied the resolution of racemic glycidol through esterification with butyric acid catalyzed by porcine pancreatic lipase in organic media. A screening of seven solvents (log P values between 0.49 and 3.0, P being the n-octanol-water partition coefficient of the solvent) showed that neither log P nor the logarithm of the molar solubility of water in the solvent provides good correlations between enantioselectivity and the properties of the organic media. Chloroform was one of the best solvents as regards the enantiometic purity (e.p.) of the ester produced. In this solvent, the optimum temperature for the reaction was determined to be 35C. The enzyme exhibited maximum activity at a water content of 13 [plus minus] 2% (w/w). The enantiomeric purity obtained was 83 [plus minus] 2% of (S)-glycidol butyrate and did not depend on the alcohol concentration or the enzyme water content for values of these parameters up to 200 mM and 25% (w/w), respectively. ...

1993-08-05

9

Histamine Molecule and Dianion Oxalate are Efficient Blocks for Building 2D Supramolecular Networks  

British Library Electronic Table of Contents (United Kingdom)

One salt and two Cu(II) complexes (H2hsm)(ox), 1, [Cu(hsm)(ox)], 2, and [Cu(hsm)(ox)H2O], 3, have been synthesized and X-ray characterized (hsm is histamine and ox2? is the oxalate dianion). Starting from the prochiral tetracoordinated complex 2, pentacoordinated complex 3 crystallizes as a racemic mixture of the enantiomeric ? and ? isomers, in space group P21/c. In all cases, the side chain of the hsm group is gauche, allowing the formation of strong hydrogen bonds in the salt 1, and to chelate the metal center in complexes 2 and 3. The combination hsm/ox seems to favor the formation of 2D supramolecular structures (planes or wavy planes), through efficient networks of N?H???O hydrogen bonds. Cell parameters: 1, P21/c, a?=?6.260 (2) ?, b?=?11.500 (4) ?, c?=?12.525 (4) ?, ??=?104.047 (17)...

2011-01-01

10

Dating techniques in fault investigations  

International Nuclear Information System (INIS)

Determining the time of most recent fault movement is an important part of assessing a possible site for a nuclear power plant. The purpose of this paper is not to present research information but to provide a practical guide to some of the dating techniques available to the engineering geologist working on nuclear power plant siting. Emphasis is placed on the practical aspects, such as usable minerals, conditions necessary for them to yield correct dates, degree of accuracy, sample collection, sample size, and sample packaging. In this paper, the usual geologic field techniques are taken for granted (such as those used in stratigraphy, paleontology, and structural analysis) for assessing fault history. Laboratory techniques used in conjunction with or supplemental to field methods are discussed. The specific radiometric methods discussed are "1"4C(carbon-14), fission track, K-Ar (potassium-argon), thermoluminescense, Rb-Sr (rubidium-strontium), and U-Th (uranium-thorium). ...

11

Chiral salicyloxazolines as auxiliaries for the asymmetric synthesis of ruthenium polypyridyl complexes.  

Science.gov (United States)

Chiral auxiliaries are promising emerging tools for the asymmetric synthesis of octahedral metal complexes. We recently introduced chiral salicyloxazolines as coordinating bidentate chiral ligands which provide excellent control over the metal-centered configuration in the course of ligand substitution reactions and can be removed afterward in an acid-induced fashion under complete retention of configuration (J. Am. Chem. Soc. 2009, 131, 9602-9603). Here reported is our detailed investigation of this sequence of reactions, affording virtually enantiopure ruthenium polypyridyl complexes. The control of the metal-centered chirality by the coordinated chiral salicyloxazolinate ligand was evaluated as a function of reaction conditions, the employed bidentate 2,2'-bipyridine and 1,10-phenanthroline ligands, and the substituent at the asymmetric 5-position of the oxazoline heterocycle. Most striking was the strong influence of the reaction solvent, with aprotic solvents of lower polarity ...

2010-09-01

12

(Phospinoalkyl)silyl complexes. 10. Formation of chelated bis[(diphenylphosphinoethyl)diorganosilyl]platinum(II) complexes. Precoordination through phosphorus, intermediacy of a platinum(IV) disilyl, and diastereoisomerism at planar platinum(II) in 'chelate-assisted' hydrosilylation  

Energy Technology Data Exchange (ETDEWEB)

Addition of the silane PPh[sub 2]CH[sub 2]CH[sub 2]SiMe[sub 2]H (chelH, 1a) to Pt(COD)[sub 2] (COD = cycloocta-1,5-diene) affords in high yield the cis-bis chelate Pt(chel)[sub 2] (2); formation of the same product from Pt(COD)(X)Y (X = Y = Me; X = Me, Y = Cl) has been shown by NMR spectroscopy ([sup 1]H, [sup 31]P, [sup 195]Pt) to proceed via prior coordination of chelH through P to afford Pt(chelH)[sub 2](X)(Y) (cis and trans isomers) and through intermediacy of PtH(chel)[sub 2]Cl (22) in which P trans to Si at Pt(IV) leads to an exceptionally low [sup 2]J(Pt-P) = 1084 Hz. Cleavage of Pt-Si bonds in 2 by HCl can be controlled to give the monochelate species Pt(chel)(chelH)Cl (7), from which chelH is displaced by PMe[sub 2]Ph, or trans-PtH(PPh[sub 2]CH[sub 2]SiMe[sub 2]Cl)[sub 2]Cl (9). Products related to 9 result from Pt-Si bond cleavage by I[sub 2] or MeI. Using the analogue PPh[sub 2]CH[sub 2]CH[sub 2]SiMe(Ph)H (1c) of 1a, the analogue Pt-[PPh[sub 2]CH[sub 2]CH[sub 2]SiMe(Ph)][sub ...

1991-08-21