The stereochemistry of the incorporation of the methyl groups of ‘chiral methyl valine’ into methylene groups in cephalosporin C

1983 ◽  
pp. 723-724 ◽  
Author(s):  
Edward Abraham ◽  
Chi-Pui Pang ◽  
Robert L. White ◽  
David H. G. Crout ◽  
Max Lutstorf ◽  
...  
Keyword(s):  
Methyl Groups ◽  
Cephalosporin C ◽  
Methylene Groups

scholarly journals Stereochemistry of the incorporation of valine methyl groups into methylene groups in cephalosporin C.

1984 ◽  
Vol 222 (3) ◽  
pp. 777-788 ◽  
Author(s):  
C P Pang ◽  
R L White ◽  
E P Abraham ◽  
D H G Crout ◽  
M Lutstorf ◽  
...  
Keyword(s):  
Side Chain ◽  
Methyl Groups ◽  
Cephalosporin C ◽  
Cephalosporium Acremonium ◽  
Methyl Group ◽  
Methylene Groups ◽  
Methylene Group

‘Chiral methyl valines’, i.e. samples of valine labelled stereospecifically in the methyl groups with 2H and 3H, were incorporated into cephalosporin C by a suspension of washed cells of Cephalosporium acremonium. Analysis by 3H n.m.r. of the cephalosporin C produced showed that the conversion of the 3-pro-S-methyl group of valine into the acetoxymethyl side-chain was a highly stereospecific process. By contrast, conversion of the 3-pro-R-methyl group into the endocyclic methylene group of the dihydrothiazine ring was shown to proceed by a non-stereospecific process.

Ftir Studies Of Organometallic Surface Chemistry Relevant To Atomic Layer Epitaxy.

1991 ◽  
Vol 222 ◽  
Author(s):  
Ananth V. Annapragada ◽  
Sateria Salim ◽  
Klavs F. Jensen
Keyword(s):  
Critical Role ◽  
Atomic Layer ◽  
Atomic Layer Epitaxy ◽  
Growth Surface ◽  
Methyl Groups ◽  
Dissociative Chemisorption ◽  
Decomposition Products ◽  
General Assertion ◽  
Methylene Groups ◽  
Dehydrogenation Reactions

ABSTRACTThe adsorption and surface reactions of trimethylgallium and tertiarybutylarsine on GaAs(100) surfaces have been investigated by Fourier transform infrared spectroscopy. Adsorbed methyl groups resulting from the dissociative chemisorption of trimethylgallium on GaAs(100) are shown to form As-H and CH2 species on the surface. The CH2 groups are stable on the surface at temperatures as high as 550 °C. The surface coverage is low (∼0.2% of a monolayer) and is reduced by the presence of hydrogen on the surface. This dehydrogenation of surface methyl groups could be a possible route to carbon incorporation in GaAs grown by atomic layer epitaxy. Tertiarybutylarsine is shown to decompose primarily by homolysis to form a tertiary butylgroup and AsH2. At temperatures below 400°C on trimethylgallium dosed surfaces, the decomposition products appear to cause the hydrogenation of methylene groups remaining from prior surface dosing with trimethylaallium. At high temperatures, the tertiarybutyl radical appears to undergo dehydrogenation reactions to an unsaturated species which is stable on the surface. In contrast, the dehydrogenation does not appear to occur on surfaces treated with tertiarybutylarsine. The data for trimethylgallium and tertiarybutylarsine support the general assertion that surface As-H species play a critical role in the removal of hydrocarbon species from the growth surface.

THE INFRARED ABSORPTION SPECTRA OF DEUTERATED ESTERS: III. METHYL LAURATE

1962 ◽  
Vol 40 (2) ◽  
pp. 301-320 ◽  
Author(s):  
R. Norman Jones
Keyword(s):  
Absorption Spectrum ◽  
Infrared Absorption ◽  
Carbon Disulphide ◽  
Infrared Absorption Spectrum ◽  
Methyl Laurate ◽  
Methyl Groups ◽  
Acid Chlorides ◽  
Methyl Group ◽  
Methylene Groups ◽  
Infrared Absorption Spectra

The infrared absorption spectrum of methyl laurate in carbon tetrachloride and carbon disulphide solutions has been compared with the spectra of seven derivatives deuterated in the ω-methyl group, the α-methylene groups, the carbomethoxy group, and in binary and ternary combinations of these positions. The spectra of n-dodecanes deuterated in the terminal methyl groups and of methyl laurates chlorinated in the ω-methyl and α-methylene groups have also been measured.From an analysis of these spectra, all the bands and inflections between 3100 and 700 cm−1 in the spectrum of methyl laurate can be assigned to localized group vibrations. The spectra of some related acid chlorides, alcohols, and bromides are also briefly noted.

ESR and photopolymerization study of polymerizable benzophenone photoinitiators containing functional maleimide groups

e-Polymers ◽  
2008 ◽  
Vol 8 (1) ◽  
Author(s):  
Jun Wei ◽  
Fang Liu
Keyword(s):  
Free Radical ◽  
Methyl Methacrylate ◽  
Esr Spectra ◽  
Methyl Groups ◽  
Vinyl Monomers ◽  
Initiation Mechanism ◽  
Excited Triplet ◽  
Trimethylolpropane Triacrylate ◽  
Methylene Groups

AbstractFour kinds of novel polymerizable benzophenone (BP) photoinitiators MBP, BMBP, MPBP, BMPBP containing functional maleimide groups, were used as free radical photoinitiators with N-methyldiethanolamine (MDEA) as coinitiator (H donor). Such photoredox systems were studied by means of ESR spectra. The results show that all the four photoinitiators possess the same initiation mechanism as BP/MDEA system; meanwhile, two kinds of radicals were observed as the excited triplet of the photoinitiators can abstract hydrogen from the methylene groups or the methyl groups of MDEA. The photopolymerization of three monomers with different functionality, methyl methacrylate (MMA), 1,6-hexanediol diacrylate (HDDA) and trimethylolpropane triacrylate (TMPTA), initiated by these four polymerizable photoinitiators, was studied through dilatometer and photo- DSC. The results show that different photoinitiators behave differently towards monomers: MPBP system is the most efficient for all the three monomers; BMPBP is the least efficient for MMA, and BMBP is the least efficient for HDDA and TMPTA. The efficiency of the photopolymerization is greatly affected by maleimide groups and different vinyl monomers.

Sulfur-free Penicillin Derivatives. II. Functionalization of the Methyl Groups

1972 ◽  
Vol 50 (17) ◽  
pp. 2898-2902 ◽  
Author(s):  
Saul Wolfe ◽  
Wha Suk Lee ◽  
Jean-Bernard Ducep ◽  
Gérard Kannengiesser
Keyword(s):  
Carbonyl Group ◽  
Ring Opening ◽  
Methyl Groups ◽  
Cephalosporin C ◽  
Lactam Carbonyl Group ◽  
Molar Equivalent ◽  
Lactam Carbonyl

Allylic bromination of anhydropenicillin chlorination products by N-bromosuccinimide (NBS) is described. With two molar-equivalents of NBS both methyl groups are functionalized; with one molar-equivalent of NBS a mixture of Z and E monobrominated isomers is obtained.Nitrogen and oxygen nucleophiles attack the dibrominated derivatives at the β-lactam carbonyl group, with concomitant ring-opening. However, the mono-brominated derivatives undergo ready displacement by azide and formate ions. The mechanism of these reactions, leading to preferred formation of Z-isomer, is discussed.Cyclization of the allylic formates yields sulfur-free derivatives corresponding to the cephalosporin Cc class of compounds.

The Normal Paraffins Revisited

1990 ◽  
Vol 5 (2) ◽  
pp. 93-100 ◽  
Author(s):  
R. D. Heyding ◽  
K. E. Russell ◽  
T. L. Varty ◽  
D. St-Cyr
Keyword(s):  
Nearest Neighbor ◽  
Methyl Groups ◽  
Monoclinic Symmetry ◽  
Crystal Forms ◽  
Hydrocarbon Chains ◽  
Chain Axis ◽  
Methylene Groups ◽  
In Trans ◽  
Methylene Group ◽  
Long Chain

The low temperature modifications of the normal paraffins n-CnH2n+2crystallize in three groups (Broadhurst, 1962). The structure is triclinic for n even, 6 < n < 26 (Muller and Lonsdale, 1948; Nyburg and Luth, 1972); orthorhombic for n odd, 11 < n < 39 (Smith, 1953; Teare, 1959); and monoclinic for n even, 28 < n < 36 (Shearer and Vand, 1956). In all of these structures the hydrocarbon chains are linear and in trans configuration. The chains are parallel to one another, the terminal methyl groups forming the surfaces of lamella which are more or less perpendicular to the chain axis. For n < ca.36, it is apparently the interlamellar interaction between end methyl groups which dictates the symmetry. For longer chains the structure is usually orthorhombic and comparable to the structure of highly crystalline polyethylenes. Chains do not fold (as they undoubtedly do in polyethylenes) unless n is greater than 102 (Bidd and Whiting, 1985; Ungar and Keller, 1986).The several crystal forms differ in the manner in which the nearest neighbor chains are related to one another. In the triclinic lattices the packing is such that a triclinic sublattice containing one methylene group is evident. In the other modifications the sublattice is orthorhombic and contains four methylene groups. If the overall symmetry is orthorhombic the long chain axes are perpendicular to the interlamellar surface; the x and y translations, perpendicular to the long axis, are common to both cells. If the nearest neighbor chains are displaced by two or four methylene groups along the chain axis, overall monoclinic symmetry results (Sullivan and Weeks (1970)).

Hydrogenolysis of nitrogen-containing compounds on a cobalt-molybdenum catalyst

1979 ◽  
Vol 44 (1) ◽  
pp. 85-98 ◽  
Author(s):  
Mirko Černý
Keyword(s):  
Nitrogen Atom ◽  
Methyl Groups ◽  
Molybdenum Catalyst ◽  
Methyl Group ◽  
Cobalt Molybdenum Catalyst ◽  
Methylene Groups ◽  
Methyl Derivatives ◽  
Nitrogen Containing Compounds

A sulphidized cobalt-molybdenum catalyst on Al2O3 has been used to study hydrogenolysis of pyridine, piperidine, quinoline and their methyl derivatives. In reaction mixtures were identified the compounds which contribute to the knowledge of the mechanism of hydrogenolysis. The cleavage of 2-methylpiperidine ring takes place between the nitrogen atom and the methylene groups and not between the nitrogen atom and the carbon substituted with the methyl group. The amount of hydrogenolysis products decreases in the series pyridine, 2-methylpyridine, 2,6-dimethylpyridine and 2,4,6-trimethylpyridine, i.e. with the increasing number of the methyl groups bonded to the ring.

Reduction of carbon impurities in aluminium nitride from time-resolved chemical vapour deposition using trimethylaluminum

2020 ◽  
Author(s):  
Polla Rouf ◽  
Pitsiri Sukkaew ◽  
Lars Ojamäe ◽  
Henrik Pedersen
Keyword(s):  
Chemical Vapour Deposition ◽  
Vapour Deposition ◽  
Chemical Vapour ◽  
Aluminium Nitride ◽  
Methyl Groups ◽  
Time Resolved ◽  
Thermally Induced ◽  
Light Emitting ◽  
Carbon Impurities ◽  
Wide Range

<p>Aluminium nitride (AlN) is a semiconductor with a wide range of applications from light emitting diodes to high frequency transistors. Electronic grade AlN is routinely deposited at 1000 °C by chemical vapour deposition (CVD) using trimethylaluminium (TMA) and NH<sub>3</sub> while low temperature CVD routes to high quality AlN are scarce and suffer from high levels of carbon impurities in the film. We report on an ALD-like CVD approach with time-resolved precursor supply where thermally induced desorption of methyl groups from the AlN surface is enhanced by the addition of an extra pulse, H<sub>2</sub>, N<sub>2</sub> or Ar between the TMA and NH<sub>3</sub> pulses. The enhanced desorption allowed deposition of AlN films with carbon content of 1 at. % at 480 °C. Kinetic- and quantum chemical modelling suggest that the extra pulse between TMA and NH<sub>3</sub> prevents re-adsorption of desorbing methyl groups terminating the AlN surface after the TMA pulse. </p>

Detection of Chemical Exchange in Methyl Groups of Macromolecules

2019 ◽  
Author(s):  
Michelle Gill ◽  
Andrew Hsu ◽  
Arthur G. Palmer, III
Keyword(s):  
Relaxation Rate ◽  
Chemical Exchange ◽  
Double Quantum ◽  
Methyl Groups ◽  
Multiple Quantum ◽  
Relaxation Data ◽  
E Coli ◽  
Methyl Trosy ◽  
Dynamics Simulations ◽  
Exchange Broadening

<div> <div> <div> <p>The zero- and double-quantum methyl TROSY Hahn-echo and the methyl <sup>1</sup>H-<sup>1</sup>H dipole- dipole cross-correlation nuclear magnetic resonance experiments enable estimation of multiple quantum chemical exchange broadening in methyl groups in proteins. The two relaxation rate constants are established to be linearly dependent using molecular dynamics simulations and empirical analysis of experimental data. This relationship allows chemical exchange broadening to be recognized as an increase in the Hahn-echo relaxation rate constant. The approach is illustrated by analyzing relaxation data collected at three temperatures for <i>E. coli </i>ribonuclease HI and by analyzing relaxation data collected for different cofactor and substrate complexes of <i>E. coli </i>AlkB. </p> </div> </div> </div>

The synthesis and stereochemistry of the ternary cobalt(III) complex with a stereospecific ligand derived from (S)-leucine

1986 ◽  
Vol 51 (2) ◽  
pp. 318-326 ◽  
Author(s):  
Milan Strašák ◽  
Pavol Novomeský
Keyword(s):  
Ir Spectroscopy ◽  
Aqueous Medium ◽  
Absorption Spectroscopy ◽  
Absolute Configuration ◽  
Nmr Spectra ◽  
Methyl Groups ◽  
Electron Absorption Spectroscopy ◽  
Electron Absorption ◽  
C Nmr

A new stereospecific ligand, ethylenediamine-N,N'-di(S)-α-isocapronic acid, was synthesized by condensation of (S)-leucine with 1,2-dibromoethane in alkaline aqueous medium. It follows from the 1H and 13C NMR spectra that the terminal methyl groups are chemically and magnetically nonequivalent. Of the four theoretically possible isomers of the ternary cobalt (III) complex with ethylenediamine, separation on catex yielded only one, whose absolute configuration was determined by a combination of 1H and 13C NMR, electron absorption spectroscopy and CD and IR spectroscopy.

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