Novel gas-phase ions. The radical cations [CH2XH]+• (X = F, Cl, Br, I, OH, NH2, SH) and [CH2CH2NH3]+•

1983 ◽  
Vol 61 (10) ◽  
pp. 2305-2309 ◽  
Author(s):  
John L. Holmes ◽  
F. P. Lossing ◽  
Johan K. Terlouw ◽  
Peter C. Burgers
Keyword(s):  
Energy Requirement ◽  
Radical Cations ◽  
Isotopic Labelling ◽  
Ionisation Mass Spectrometry ◽  
Gas Phase Ions ◽  
Conventional Structure ◽  
Precursor Molecules ◽  
Isotopic Labelling Experiments ◽  
Good Agreement ◽  
Abinitio Calculations

The title ions have been generated by dissociative ionisation of appropriate precursor molecules and have been unequivocally identified by collisional activation and collisional ionisation mass spectrometry. Their heats of formation, [Formula: see text], have been measured and were found to be similar to those for their ionic isomer of conventional structure, [CH3X]+•. The exception is [CH2NH3]+• whose [Formula: see text], is ca. 30 kcal mol−1 higher than that of [CH3NH2]+•. The shapes and appearance energies of metastable peaks in conjunction with isotopic labelling experiments, show that these novel ions do not interconvert with their conventional isomer at internal energies below the threshold for their fragmentation of lowest energy requirement, namely, loss of H•. However, unimolecular H• loss from all [CH2XH]+• ions is preceded by a rate determining isomerisation to [CH3X]+•, followed by fast dissociation. The results are generally in good agreement with recent abinitio calculations. Also described are the properties of the homologous ion [CH2CH2NH3]+•.

Stereochemical Characterisation of the Non-Canonical α-Humulene Synthase from Acremonium strictum

2021 ◽  
Author(s):  
Houchao Xu ◽  
Carsten Schotte ◽  
Russell Cox ◽  
Jeroen Dickschat
Keyword(s):  
Isotopic Labelling ◽  
Acremonium Strictum ◽  
The Face ◽  
Face Selectivity ◽  
Isotopic Labelling Experiments

The non-canonical fungal α-humulene synthase was investigated through isotopic labelling experiments for its stereochemical course regarding inversion or retention at C-1, the face selectivity at C-11, and the stereoselectivity of...

On the mechanism of ophiobolin F synthase and the absolute configuration of its product by isotopic labelling experiments

2020 ◽  
Vol 18 (31) ◽  
pp. 6072-6076 ◽  
Author(s):  
Zhiyang Quan ◽  
Jeroen S. Dickschat
Keyword(s):  
Absolute Configuration ◽  
Isotopic Labelling ◽  
The Absolute ◽  
Isotopic Labelling Experiments

The cyclisation mechanism of ophiobolin F synthase AcldOS and the absolute configuration of its product were investigated by isotopic labelling experiments.

Role of glutamine synthetase in phenazine antibiotic production by Pantoea agglomerans Eh1087

2004 ◽  
Vol 50 (10) ◽  
pp. 877-881 ◽  
Author(s):  
Matthew D Galbraith ◽  
Stephen R Giddens ◽  
H Khris Mahanty ◽  
Bruce Clark
Keyword(s):  
Glutamine Synthetase ◽  
Antibiotic Production ◽  
Amino Acid Sequences ◽  
Pantoea Agglomerans ◽  
Wild Type ◽  
Isotopic Labelling ◽  
High Degree ◽  
Degree Of Similarity ◽  
Isotopic Labelling Experiments

Pantoea agglomerans strain Eh1087 produces the phenazine antibiotic D-alanylgriseoluteic acid. A glutamine auxotroph harboring an insertion in a putative glnA gene was obtained by transposon-mutagenesis of Eh1087 that produced less D-alanylgriseoluteic acid than the parental strain (strain Eh7.1). Cosmids encoding the Eh1087 glnA were isolated by their ability to complement the mutant for prototrophy. The role of the Eh1087 glnA locus was functionally confirmed by complementation of an Escherichia coli glnA mutant. Analysis of the nucleotide and deduced amino acid sequences of the Eh1087 glnA gene indicated a high degree of similarity to the glnA genes and glutamine synthetase enzymes of other Enterobacteriaceae. Isotopic labelling experiments with 15N-labelled ammonium sulfate demonstrated that wild-type Eh1087 incorporated 15N into griseoluteic acid more readily than the glnA mutant Eh7.1. We conclude that the 2 nitrogens in the phenazine nucleus originate from glutamine and the intracellular glutamine synthesized by Eh1087 is a source of the phenazine nucleus nitrogens even in glutamine-rich environments.Key words: phenazine, Pantoea, Erwinia, glutamine synthetase, biosynthesis.

ENERGETICS AND STRUCTURAL INSIGHTS OF MOLECULAR CONDUCTORS USING DENSITY FUNCTIONAL THEORY METHODS: 1,3-DITHIOLE-2-THIONE, 1,3-DITHIOLE-2-ONE, 1,3-DIOXOLE-2-ONE, AND 1,3-DIOXOLE-2-THIONE

2009 ◽  
Vol 08 (06) ◽  
pp. 1185-1195 ◽  
Author(s):  
R. L. PRASAD ◽  
A. KUSHWAHA ◽  
RAJENDRA PRASAD ◽  
S. JAISWAL ◽  
R. A. YADAV
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Energy Requirement ◽  
Radical Cations ◽  
Geometrical Parameters ◽  
Dft Methods ◽  
Molecular Conductors ◽  
Relaxation Energy ◽  
Functional Theory ◽  
Hartree Fock

Computations were carried out employing the restricted Hartree–Fock (RHF) and density functional theory (DFT) methods to investigate the geometries and energies for the 1,3-dithiole-2-thione (DTT), 1,3-dithiole-2-one (DTO), 1,3-dioxole-2-thione (DOT), and 1,3-dioxole-2-one (DOO) molecules and their radical cations. The geometrical parameters of all the four molecules suggest a finite extent of extended conjugation across the molecules. The radical cations of the DTT and DOT molecules exhibit increased extent of conjugation compared to their neutral analogues. However, on going from the neutral DOO and DTO molecules to their radical cations, the extent of conjugation across the ions decreases and two unsaturated sites become isolated from each other. Requirement of the relaxation energy for the formation of radical cation is much lower for the DTT and DOT molecules compared to that for the DOO and DTO molecules. Smaller relaxation energy requirement favors minimal resistance to charge transport along the molecular stacking. Therefore, it is speculated that the DTT and DOT molecules are better molecular conductors as compared to the DOO and DTO molecules.

The reaction of aluminum atoms with methane

1990 ◽  
Vol 68 (4) ◽  
pp. 633-639 ◽  
Author(s):  
Hengtai Yu ◽  
John D. Goddard
Keyword(s):  
Transition State ◽  
Energy Barrier ◽  
Energy Requirement ◽  
Basis Sets ◽  
Insertion Reaction ◽  
Reaction Coordinates ◽  
Abstraction Reaction ◽  
Level Transition ◽  
Split Valence ◽  
Good Agreement

Abinitio SCF and CISD calculations with split valence and larger basis sets have been carried out for several possible reactions of ground state (2P) aluminum atoms with methane. In particular, the barriers to insertion of Al into a CH bond to give a CH3AlH intermediate and the abstraction of a hydrogen by Al to give AlH and CH3 have been studied. At the SCF level, transition state structures have been located and verified by vibrational analyses. In addition, intrinsic reaction coordinates (IRC) have been followed from the transition state geometries down to reactants and to products. Calculated vibrational frequencies and lowest excitation energy for the CH3AlH intermediate are in good agreement with matrix isolation experimental results. As anticipated on the basis of MO natural correlation symmetry arguments, the energy barrier to the insertion reaction is high (~50 kcal mol−1 at the CI level). The energy requirement for the abstraction reaction is similar.[Formula: see text]Keywords: Al, CH4, HAlCH3, insertion and abstraction reactions.

scholarly journals A Boron-Boron Double Transborylation Strategy for the Synthesis of gem-Diborylalkanes

2020 ◽  
Author(s):  
Jamie Docherty ◽  
Kieran Nicholson ◽  
Andrew P Dominey ◽  
Stephen Thomas
Keyword(s):  
Transition State ◽  
Thermodynamic Parameters ◽  
Terminal Alkynes ◽  
Isotopic Labelling ◽  
Wide Range ◽  
Boronic Esters ◽  
Isotopic Labelling Experiments

9-Borabicyclo[3.3.1]nonane (H-<i>B</i>-9-BBN) has been used as a catalyst for the sequential double hydroboration of alkynes with pinacolborane (HBpin) to give alkyl gem-di-pinacol boronic esters. This strategy, which is effective for a wide range of terminal alkynes, is predicated upon a key C(<i>sp</i><sup>3</sup>)-B / B-H transborylation reaction. Transition-state thermodynamic parameters and 10-boron-isotopic labelling experiments are indicative of an <i>σ</i>-bond metathesis exchange pathway.

Isotopic Labelling Experiments and Enzymatic Preparation of Iso-Casbenes with Casbene Synthase from Ricinus communis

2022 ◽  
Author(s):  
Heng Li ◽  
Jeroen Dickschat
Keyword(s):  
Ricinus Communis ◽  
Enzyme Mechanism ◽  
Enzymatic Preparation ◽  
Isotopic Labelling ◽  
Isotopic Labelling Experiments

Isotopic labelling experiments gave insights into the enzyme mechanism of casbene synthase from Ricinus communis, showing a clear stereochemical course for the cyclisation reaction, in agreement with the reported absolute...

Abinitio Calculations of the Barriers to Rotation in Some Monosubstituted Benzenes

1986 ◽  
Vol 39 (7) ◽  
pp. 1157 ◽  
Author(s):  
S Marriott ◽  
RD Topsom
Keyword(s):  
Electron Transfer ◽  
Ab Initio ◽  
Benzene Ring ◽  
Theoretical Calculations ◽  
Geometry Optimization ◽  
Basis Set ◽  
Monosubstituted Benzenes ◽  
Split Valence ◽  
Good Agreement ◽  
Abinitio Calculations

Theoretical calculations at the ab initio level have been made of the twofold rotational barriers of some monosubstituted benzenes, and the effects both of basis set and of geometry optimization have been examined. Values at the STO-3G//STO-3G level are in good agreement with experiment. The use of split-valence sets, even with geometry optimization, is much less satisfactory, and this may be related to an overestimation of π-electron transfer between the substituent and the benzene ring.

Keto-enol tautomerism of gas-phase ions. Structure of reactive 1,3-cyclohexadien-5-one radical cations

1978 ◽  
Vol 100 (19) ◽  
pp. 6133-6137 ◽  
Author(s):  
D. H. Russell ◽  
M. L. Gross ◽  
N. M. M. Nibbering
Keyword(s):  
Gas Phase ◽  
Radical Cations ◽  
Gas Phase Ions
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