The Stability of Seven-Coordinate Species of Earlier Members in the First Transition Series: Heptahydrated Ti(II), V(II), Cr(II), and Mn(II) Ions Relevant to Intermediate and Transition State in Water-Exchange Reaction

1998 ◽  
Vol 71 (1) ◽  
pp. 73-78 ◽  
Author(s):  
Yuko Tsutsui ◽  
Hiroaki Wasada ◽  
Shigenobu Funahashi
Keyword(s):  
Transition State ◽  
Exchange Reaction ◽  
Water Exchange ◽  
Transition Series ◽  
The Stability

Allowed and Forbidden Reaction Paths for the H2 + D2 Exchange Reaction

1975 ◽  
Vol 53 (4) ◽  
pp. 549-555 ◽  
Author(s):  
James S. Wright
Keyword(s):  
Transition Metal ◽  
Transition State ◽  
Exchange Reaction ◽  
Barrier Height ◽  
Dissociation Energy ◽  
Basis Set ◽  
Reaction Paths ◽  
Double Zeta ◽  
Double Zeta Basis

Symmetry arguments and abinitio s.c.f. calculations (double-zeta basis set) are used to show that the exchange reaction H2+ D2 → 2HD could proceed in a concerted fashion through a six-center transition state. The computed barrier height of 90 kcal/mol for this process lies below the experimental dissociation energy of H2 (but above the computed dissociation energy) and also below the energy required for exchange through a four-center transition state. Either the termolecular(2 + 2 + 2 ) or bimolecular(4 + 2 ) cycloadditions are thermally allowed. The presence of a transition metal would allow the reaction to proceed through a four-center geometry, leading to the formation of a possibly stable metal-H4 complex.

scholarly journals Monitoring the stabilities of a mixture of peptides by mass-spectrometry-based techniques

2019 ◽  
Vol 25 (1) ◽  
pp. 73-81 ◽  
Author(s):  
Daniel R Fuller ◽  
Christopher R Conant ◽  
Tarick J El-Baba ◽  
Zhichao Zhang ◽  
Kameron R Molloy ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Amino Acid ◽  
Transition State ◽  
Elevated Temperatures ◽  
Proteolytic Enzymes ◽  
Side Chain ◽  
Free Energies ◽  
Dissociation Kinetics ◽  
Penultimate Proline ◽  
The Stability

Biomolecular degradation plays a key role in proteostasis. Typically, proteolytic enzymes degrade proteins into smaller peptides by breaking amino acid bonds between specific residues. Cleavage around proline residues is often missed and requires highly specific enzymes for peptide processing due to the cyclic proline side-chain. However, degradation can occur spontaneously (i.e. in the absence of enzymes). In this study, the influence of the first residue on the stability of a series of penultimate proline containing peptides, with the sequence Xaa–Pro–Gly–Gly (where Xaa is any amino acid), is investigated with mass spectrometry techniques. Peptides were incubated as mixtures at various solution temperatures (70℃ to 90℃) and were periodically sampled over the duration of the experiment. At elevated temperatures, we observe dissociation after the Xaa–Pro motif for all sequences, but at different rates. Transition state thermochemistry was obtained by studying the temperature-dependent kinetics and although all peptides show relatively small differences in the transition state free energies (∼95 kJ/mol), there is significant variability in the transition state entropy and enthalpy. This demonstrates that the side-chain of the first amino acid has a significant influence on the stability of the Xaa–Pro sequence. From these data, we demonstrate the ability to simultaneously measure the dissociation kinetics and relative transition state thermochemistries for a mixture of peptides, which vary only in the identity of the N-terminal amino acid.

Laser catalysis and transition state spectra of the H+H2 exchange reaction

1988 ◽  
Vol 88 (9) ◽  
pp. 5525-5535 ◽  
Author(s):  
Tamar Seideman ◽  
Moshe Shapiro
Keyword(s):  
Transition State ◽  
Exchange Reaction
Sign in / Sign up

Export Citation Format

Share Document