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

Terminal Alkynes ◽

Isotopic Labelling ◽

Wide Range ◽

Boronic Esters ◽

9-Borabicyclo[3.3.1]nonane (H-B-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(sp3)-B / B-H transborylation reaction. Transition-state thermodynamic parameters and 10-boron-isotopic labelling experiments are indicative of an σ-bond metathesis exchange pathway.

Bis-NHC–Ag/Pd(OAc)2 Catalytic System Catalyzed Transfer Hydrogenation Reaction

Catalysts ◽

10.3390/catal11010008 ◽

2020 ◽

Vol 11 (1) ◽

pp. 8

Author(s):

Hui-Ju Chen ◽

Chien-Cheng Chiu ◽

Tsui Wang ◽

Dong-Sheng Lee ◽

Ta-Jung Lu

Keyword(s):

Functional Groups ◽

Catalytic System ◽

High Efficiency ◽

Aqueous Media ◽

Hydrogenation Reaction ◽

Transfer Hydrogenation ◽

Terminal Alkynes ◽

Wide Range ◽

Transfer Hydrogenation Reaction

The bis-NHC–Ag/Pd(OAc)2 catalytic system (NHC = N-heterocyclic carbene), a combination of bis-NHC–Ag complex and Pd(OAc)2, was found to be a smart catalyst in the Pd-catalyzed transfer hydrogenation of various functionalized arenes and internal/terminal alkynes. The catalytic system demonstrated high efficiency for the reduction of a wide range of various functional groups such as carbonyls, alkynes, olefins, and nitro groups in good to excellent yields and high chemoselectivity for the reduction of functional groups. In addition, the protocol was successfully exploited to stereoselectivity for the transformation of alkynes to alkenes in aqueous media under air. This methodology successfully provided an alternative useful protocol for reducing various functional groups and a simple operational protocol for transfer hydrogenation.

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

Organic & Biomolecular Chemistry ◽

10.1039/d1ob01769a ◽

2021 ◽

Author(s):

Houchao Xu ◽

Carsten Schotte ◽

Russell Cox ◽

Jeroen Dickschat

Keyword(s):

Isotopic Labelling ◽

Acremonium Strictum ◽

The Face ◽

Face Selectivity ◽

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...

Solvolysis of isopropyl bromide in ethanol–water mixtures. Dissection into initial state and transition state contributions

Canadian Journal of Chemistry ◽

10.1139/v76-565 ◽

1976 ◽

Vol 54 (24) ◽

pp. 3944-3948 ◽

Cited By ~ 1

Author(s):

Wiendelt Drenth ◽

Michael Cocivera

Keyword(s):

Vapor Pressure ◽

Transition State ◽

Activation Parameters ◽

Solvent Composition ◽

Initial State ◽

Partial Vapor Pressure ◽

State Variation

Rates were determined for the solvolysis of isopropyl bromide in ethanol–water mixtures (20 to 80% by volume of ethanol) at 50 and 75 °C and the corresponding activation parameters calculated. From the partial vapor pressure of isopropyl bromide over the various solutions at 50 and 75 °C, the variations in its initial state thermodynamic parameters were calculated. Thus, the variation in the activation parameters with solvent composition could be analyzed in terms of initial and transition state contributions. The initial state variation dominates according to a unimolecular as well as to a bimolecular treatment of data.

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

Organic & Biomolecular Chemistry ◽

10.1039/d0ob01470b ◽

2020 ◽

Vol 18 (31) ◽

pp. 6072-6076 ◽

Cited By ~ 3

Author(s):

Zhiyang Quan ◽

Jeroen S. Dickschat

Keyword(s):

Absolute Configuration ◽

Isotopic Labelling ◽

The Absolute ◽

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

Thermodynamic parameters ΔΔH# and ΔΔS# as probes for the transition state in the reaction of N-phenyltriazolinedione with alkenes in nucleophilic solvents

Tetrahedron Letters ◽

10.1016/j.tetlet.2006.02.099 ◽

2006 ◽

Vol 47 (17) ◽

pp. 2961-2964 ◽

Cited By ~ 8

Author(s):

Zois Syrgiannis ◽

Yiannis Elemes

Keyword(s):

Transition State ◽

Thermodynamic Parameters

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

Canadian Journal of Microbiology ◽

10.1139/w04-076 ◽

2004 ◽

Vol 50 (10) ◽

pp. 877-881 ◽

Cited By ~ 5

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 ◽

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.

Solvolysis of sulphonyl halides. V. Hydrolysis and deuterolysis of methanesulphonyl chloride

Australian Journal of Chemistry ◽

10.1071/ch9702427 ◽

1970 ◽

Vol 23 (12) ◽

pp. 2427

Author(s):

ML Tonnet ◽

AN Hambly

Keyword(s):

Transition State ◽

Isotope Effect ◽

Large Reduction ◽

Butyl Chloride ◽

Solvent Isotope Effect ◽

Initial State ◽

Solvent Isotope ◽

Hydrolysis Of

The values of the thermodynamic parameters of activation have been determined for the solvolysis of methanesulphonyl chloride in H2O and D2O and their mixtures with moderate amounts of dioxan. Some of the data are not in agreement with the postulate that the kinetic solvent isotope effect and the maximum in the rate of solvolysis produced by the addition of dioxan are due to changes in the initial state of the reacting system rather than to changes in the transition state. The addition of dioxan does not produce a large reduction in the solvent isotope effect as reported for the hydrolysis of t-butyl chloride and predicted to be general. The relative rates of solvolysis in mixtures of H2O and D2O are not in agreement with the analysis of such reactions by Swain and Thornton.

Intergenic suppression of the γM23K uncoupling mutation in F0F1 ATP synthase by βGlu-381 substitutions: the role of the β380DELSEED386 segment in energy coupling

Biochemical Journal ◽

10.1042/bj3300707 ◽

1998 ◽

Vol 330 (2) ◽

pp. 707-712 ◽

Cited By ~ 61

Author(s):

J. Christian KETCHUM ◽

Marwan K. AL-SHAWI ◽

K. Robert NAKAMOTO

Keyword(s):

Hydrogen Bond ◽

Transition State ◽

Atp Synthase ◽

Energy Coupling ◽

Crystallographic Structure ◽

Β Subunit ◽

Wild Type ◽

F0f1 Atp Synthase

We previously demonstrated that the Escherichia coli F0F1-ATP synthase mutation, γM23K, caused increased energy of interaction between γ- and β-subunits which was correlated to inefficient coupling between catalysis and transport [Al-Shawi, Ketchum and Nakamoto (1997) J. Biol. Chem. 272, 2300-2306]. Based on these results and the X-ray crystallographic structure of bovine F1-ATPase [Abrahams, Leslie, Lutter and Walker (1994) Nature (London) 370, 621-628] γM23K is believed to form an ionized hydrogen bond with βGlu-381 in the conserved β380DELSEED386 segment. In this report, we further test the role of γ-β-subunit interactions by introducing a series of substitutions for βGlu-381 and γArg-242, the residue which forms a hydrogen bond with βGlu-381 in the wild-type enzyme. βE381A, D, and Q were able to restore efficient coupling when co-expressed with γM23K. All three mutations reversed the increased transition state thermodynamic parameters for steady state ATP hydrolysis caused by γM23K. βE381K by itself caused inefficient coupling, but opposite from the effect of γM23K, the transition state thermodynamic parameters were lower than wild-type. These results suggest that the βE381K mutation perturbs the γ-β-subunit interaction and the local conformation of the β380DELSEED386 segment in a specific way that disrupts the communication of coupling information between transport and catalysis. βE381A, L, K, and R, and γR242L and E mutations perturbed enzyme assembly and stability to varying degrees. These results provide functional evidence that the β380DELSEED386 segment and its interactions with the γ-subunit are involved in the mechanism of coupling.

Machine Learning Enhanced Dynamic Response Modelling of Superelastic Shape Memory Alloy Wires

Materials ◽

10.3390/ma15010304 ◽

2022 ◽

Vol 15 (1) ◽

pp. 304

Author(s):

Niklas Lenzen ◽

Okyay Altay

Keyword(s):

Machine Learning ◽

Shape Memory Alloy ◽

Strain Rate ◽

Shape Memory ◽

Expert Knowledge ◽

Material Behavior ◽

Model Parameters ◽

Engineering Structures ◽

Wide Range

Superelastic shape memory alloy (SMA) wires exhibit superb hysteretic energy dissipation and deformation capabilities. Therefore, they are increasingly used for the vibration control of civil engineering structures. The efficient design of SMA-based control devices requires accurate material models. However, the thermodynamically coupled SMA behavior is highly sensitive to strain rate. For an accurate modelling of the material behavior, a wide range of parameters needs to be determined by experiments, where the identification of thermodynamic parameters is particularly challenging due to required technical instruments and expert knowledge. For an efficient identification of thermodynamic parameters, this study proposes a machine-learning-based approach, which was specifically designed considering the dynamic SMA behavior. For this purpose, a feedforward artificial neural network (ANN) architecture was developed. For the generation of training data, a macroscopic constitutive SMA model was adapted considering strain rate effects. After training, the ANN can identify the searched model parameters from cyclic tensile stress–strain tests. The proposed approach is applied on superelastic SMA wires and validated by experiments.