Salt-Bridge Transition State for the Charge Separation Co(H2O)42+→ CoOH(H2O)2++ H3O+

The rate of hydrolysis of bis (2-chloroethyl) sulfide (sulfur mustard) in aqueous mixtures of ethanol, acetone and dimethyl sulfoxide has been measured and compared with previously reported values. Rate constants in water at 25°C for the two consecutive hydrolysis reactions undergone by sulfur mustard were estimated to be (2.93�0.15)×10-3 and (3.87�0.14)×10-3 s-1. Charge separation of 0.42 in the transition states was indicated together with significant solvation of the positive end of the transition state dipoles.

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Unbiased Atomistic Insight in the Mechanisms and Solvent Role for Globular Protein Dimer Dissociation

10.1101/442889 ◽

2018 ◽

Author(s):

Faidon Z. Brotzakis ◽

Peter G. Bolhuis

Keyword(s):

Transition State ◽

Degrees Of Freedom ◽

Process Analysis ◽

Salt Bridge ◽

Underlying Mechanism ◽

Full Detail ◽

Hydration Water ◽

Native Contact ◽

Reorientation Dynamics

Association and dissociation of proteins are fundamental processes in nature. While this process is simple to understand conceptually, the details of the underlying mechanism and role of the solvent are poorly understood. Here we investigate the mechanism and solvent role for the dissociation of the hydrophilic β-lactoglobulin dimer by employing transition path sampling. Analysis of the sampled path ensembles indicates that dissociation (and association) occurs via a variety of mechanisms: 1) a direct aligned dissociation 2) a hopping and rebinding transition followed by unbinding 3) a sliding transition before unbinding. Reaction coordinate and transition state analysis predicts that, besides native contact and vicinity salt-bridge interactions, solvent degrees of freedom play an important role in the dissociation process. Analysis of the structure and dynamics of the solvent molecules reveals that the dry native interface induces enhanced populations of both disordered hydration water and hydration water with higher tetrahedrality, mainly nearby hydrophobic residues. Bridging waters, hydrogen bonded to both proteins, support contacts, and exhibit a faster decay and reorientation dynamics in the transition state than in the native state interface, which renders the proteins more mobile and assists in rebinding. While not exhaustive, our sampling of rare un-biased reactive molecular dynamics trajectories shows in full detail how proteins can dissociate via complex pathways including (multiple) rebinding events. The atomistic insight obtained assists in further understanding and control of the dynamics of protein-protein interaction including the role of solvent.PACS numbers:

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Thermolysis of 5,5-dimethyl-4-aryl-Δ1-1,2,4-triazolin-3-ones in solution. Products, kinetics, substituent effects, and solvent effects

Canadian Journal of Chemistry ◽

10.1139/v81-016 ◽

1981 ◽

Vol 59 (1) ◽

pp. 100-105 ◽

Cited By ~ 2

Author(s):

Lubomira M. Cabelkova-Taguchi ◽

John Warkentin

Keyword(s):

Transition State ◽

Solvent Effects ◽

Charge Separation ◽

Substituent Effects ◽

Activation Parameters ◽

Oxidative Cyclization ◽

First Order ◽

Temperature Range ◽

Aryl Amine ◽

First Order Kinetics

A series of 5,5-dimethyl-4-aryl-Δ1-1,2,4-triazolin-3-ones (Ar = C6H5, p-C6H4CH3, p-C6H4OCH3, p-C6H4Cl, and p-C6H4Br) were prepared from the corresponding 4-arylsemicarbazones of acetone by oxidative cyclization on alumina. The triazolinones decompose in solution to N2, CO, and isopropylidene aryl amine, with first order kinetics, in the temperature range 148–200 °C. Average activation parameters are ΔH≠ = 35 kcal mol−1 and ΔS≠ = 8 cal K−1 mol−1. Substituent effects are correlated through σ-constants but the thermolyses are relatively insensitive to substituents, with ρ = −0.17 at 172.5 °C. Solvent effects indicate a transition state that is less polar than the ground state.It is tentatively concluded that the triazolinone fragmentation, like the analogous thermolysis of a Δ3-1,3,4-oxadiazolin-2-one, may be a fully-concerted but nonsynchronous process with a transition state involving little, if any, charge separation. Other mechanisms, except for those involving highly polar (e.g. zwitterionic) transition states, have not been ruled out.

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The hydrolysis of substituted cyclopropyl bromides in water. IV. The effect of vinyl and methyl substitution on ΔCP≠

Canadian Journal of Chemistry ◽

10.1139/v77-357 ◽

1977 ◽

Vol 55 (13) ◽

pp. 2582-2588 ◽

Cited By ~ 3

Author(s):

Surendra Singh ◽

Ross Elmore Robertson

Keyword(s):

Transition State ◽

Trans Isomer ◽

Charge Separation ◽

Methyl Substitution ◽

A Value ◽

Low Degree ◽

Cis And Trans ◽

Hydrolysis Of ◽

Limiting Values

In this study of the effect of vinyl and methyl substitution on the rates of hydrolysis of cyclopropyl bromides in water, we examine the changes in ΔCP≠ with substitution and configuration. The unusual values of ΔCP≠ found by Ong and Robertson (Can. J. Chem. 52, 2660 (1974)) for the hydrolysis of 2-cis- and trans-vinylcyclopropyl bromide are shown to be characteristic of the vinyl substituent and reflect either a transition state which corresponds to a low degree of charge separation or to internal cancellation due to the formation of an extended dienylic cation. The 2,3-cis,cis-dimethylcyclopropyl bromide gave a value of ΔCP≠ = −145 cal mol−1 deg−1, comparable to limiting values obtained for hydrolysis of 1- and 2-adamantyl nitrate. The corresponding value of ΔCP≠ for 2,3-cis,trans-dimethylcyclopropyl bromide (−56 cal mol−1 deg−1) was less negative than for the 2,3-trans,trans isomer (−75 cal mol−1 deg−1). The mechanistic implications are discussed.

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Solvent effects in the solvolysis of aryldi-tert-butylcarbinyl-p-nitrobenzoates in aqueous acetic acid. Substituent effects on transition state charge separation

The Journal of Organic Chemistry ◽

10.1021/jo00910a039 ◽

1975 ◽

Vol 40 (22) ◽

pp. 3303-3304 ◽

Cited By ~ 15

Author(s):

John S. Lomas ◽

Jacques E. Dubois

Keyword(s):

Acetic Acid ◽

Transition State ◽

Solvent Effects ◽

Charge Separation ◽

Substituent Effects ◽

Aqueous Acetic Acid ◽

State Charge

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Dynamics and mechanism of dimer dissociation of photoreceptor UVR8

Nature Communications ◽

10.1038/s41467-021-27756-w ◽

2022 ◽

Vol 13 (1) ◽

Author(s):

Xiankun Li ◽

Zheyun Liu ◽

Haisheng Ren ◽

Mainak Kundu ◽

Frank W. Zhong ◽

...

Keyword(s):

Charge Separation ◽

Ultrafast Spectroscopy ◽

Salt Bridge ◽

Water Molecules ◽

Interfacial Water ◽

Biological Functions ◽

Domino Effect ◽

Light Sensing ◽

Computational Calculations ◽

Protective Processes

AbstractPhotoreceptors are a class of light-sensing proteins with critical biological functions. UVR8 is the only identified UV photoreceptor in plants and its dimer dissociation upon UV sensing activates UV-protective processes. However, the dissociation mechanism is still poorly understood. Here, by integrating extensive mutations, ultrafast spectroscopy, and computational calculations, we find that the funneled excitation energy in the interfacial tryptophan (Trp) pyramid center drives a directional Trp-Trp charge separation in 80 ps and produces a critical transient Trp anion, enabling its ultrafast charge neutralization with a nearby positive arginine residue in 17 ps to destroy a key salt bridge. A domino effect is then triggered to unzip the strong interfacial interactions, which is facilitated through flooding the interface by channel and interfacial water molecules. These detailed dynamics reveal a unique molecular mechanism of UV-induced dimer monomerization.

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Charge Separation in Transition States of Reactions Involving Neutral Molecules as Reactants

Australian Journal of Chemistry ◽

10.1071/ch9791183 ◽

1979 ◽

Vol 32 (6) ◽

pp. 1183

Author(s):

B Poh

Keyword(s):

Transition State ◽

Charge Separation ◽

Transition States ◽

Butyl Chloride

It is shown that the parameter m in the Grunwald-Winstein equation, log(k/k0) = mY, can be equated to z/z0 where z0 is the charge separation in the transition state of solvolysis of t-butyl chloride in a given pair of solvents and z is the charge separation in the transition state of a reaction in which only neutral molecules are involved as reactants in the same pair of solvents.

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Substituent Rate Effects in Sigmatropic Homodienyl [1,5]-Hydrogen Migrations

Australian Journal of Chemistry ◽

10.1071/ch9901357 ◽

1990 ◽

Vol 43 (8) ◽

pp. 1357 ◽

Cited By ~ 1

Author(s):

GG Pegg ◽

GV Meehan

Keyword(s):

Transition State ◽

Charge Separation ◽

Substituent Effect ◽

Substituent Effects ◽

Aryl Group ◽

Rate Enhancement ◽

Polar Substituent ◽

Rate Effects ◽

Electronic Perturbation

The small but systematic polar substituent effect on the rates of [1,5]- homodienyl hydrogen migrations previously observed for the series of alkenylcyclopropane substrates (1) has been further explored through two additional substrate series (4) and (6) bearing the aryl probe at C4 and at the migration origin C1 respectively. However, negligible substituent effects were apparent at these positions. It now seems that the substituent effect originally observed at C5 reflects electronic perturbation by the substituent, rather than an inherent charge separation in the transition state for homodienyl rearrangement. The aryl group at C1 of the series (6) does, however, afford a substantial rate enhancement relative to the parent cis-1-methyl-2-vinylcyclopropane. In addition, exclusive formation of (1E,4Z)-1-arylhexa-1,4-diene rearrangement products is observed. These kinetic and stereochemical observations are interpreted in terms of a stereoelectronically favoured equatorial conformation for the aryl group in the transition state for rearrangement.

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