Solvent effects on chemical reactivity. Evaluation of anion- and cation-solvation components

Swain, C. Gardner; Swain, Marguerite S.; Powell, Arnet L.; Alunni, Sergio

doi:10.1021/ja00341a033

Cited by 319 publications

(224 citation statements)

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“…The effective dielectric is used as a simplified parameter to describe the ability of the environment to stabilize isolated charges and dipoles: the better this stabilization is accomplished, the less the energetic consequences of charge development. The effective dielectric is distinct from the bulk dielectric constant; it can account for the impact of the molecular properties of the local environment on interactions between adjacent groups, such as H bonds (41)(42)(43)(44)(45).…”

Section: Origins Of the Larger Brønsted Slopes Of H Bonding Inmentioning

confidence: 99%

The change in hydrogen bond strength accompanying charge rearrangement: Implications for enzymatic catalysis

Shan

Herschlag²

1996

Proc. Natl. Acad. Sci. U.S.A.

186

197

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The equilibrium for formation of the intramolecular hydrogen bond (K HB ) in a series of substituted salicylate monoanions was investigated as a function of ⌬pK a , the difference between the pK a values of the hydrogen bond donor and acceptor, in both water and dimethyl sulfoxide. The dependence of log K HB upon ⌬pK a is linear in both solvents, but is steeper in dimethyl sulfoxide (slope ‫؍‬ 0.73) than in water (slope ‫؍‬ 0.05). Thus, hydrogen bond strength can undergo substantially larger increases in nonaqueous media than aqueous solutions as the charge density on the donor or acceptor atom increases. These results support a general mechanism for enzymatic catalysis, in which hydrogen bonding to a substrate is strengthened as charge rearranges in going from the ground state to the transition state; the strengthening of the hydrogen bond would be greater in a nonaqueous enzymatic active site than in water, thus providing a rate enhancement for an enzymatic reaction relative to the solution reaction. We suggest that binding energy of an enzyme is used to fix the substrate in the low-dielectric active site, where the strengthening of the hydrogen bond in the course of a reaction is increased.Electronic rearrangement typically occurs in the course of a reaction, resulting in changes in the charge density of functional groups on the reactant. This is shown in Scheme I for the example of the triosephosphate isomerase (TIM) reaction.As the reaction proceeds from the ground state to the transition state, negative charge accumulates on the carbonyl oxygen, as reflected by the Ϸ10-unit increase in the pK a of this group. [The pK a of the carbonyl oxygen in the ground state is estimated to be Ϫ2 to 0; the pK a of the enol hydroxyl in a fully enolic transition state is estimated to be Ϸ10 (1).] The hydrogen bond (H bond) from a histidine residue of TIM to the carbonyl oxygen can be strengthened by this charge buildup (depicted by the darker dots in Scheme I). However, to obtain a rate enhancement relative to the solution reaction, the strengthening of an H bond to an enzymatic group in the course of a reaction must be greater than the strengthening of the corresponding H bond to water.Could the environment of the enzyme active site increase the change in H bond strength accompanying charge rearrangements relative to that in water? To address this question, we used the aprotic organic solvent dimethyl sulfoxide (DMSO) as a crude mimic of the active site environment and investigated the energetics of the intramolecular H bond in a series of substituted salicylate monoanions in both DMSO and water. There is a larger increase in H bond strength in DMSO than in water as the pK a values of the H bonding groups are varied. We suggest that a substantial amount of catalysis can be obtained by enzymes from the greater strengthening of H bonds accompanying charge rearrangements in nonaqueous environments than in aqueous solutions. MATERIALS AND METHODS Materials.The indicators 2,6-di-tert-butyl-4-nitrophenol and 9-carboxym...

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Section: Origins Of the Larger Brønsted Slopes Of H Bonding Inmentioning

confidence: 99%

The change in hydrogen bond strength accompanying charge rearrangement: Implications for enzymatic catalysis

Shan

Herschlag²

1996

Proc. Natl. Acad. Sci. U.S.A.

186

197

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“…9 One particularly useful set consists of complementary Lewis acid-base solvent parameters, now known for most common organic solvents. 10,11 It was found for example, by analysis of the variation of Kamlet-Taft's, β and α values, 12 for mixtures of methanol and other organic solvents, that one important factor influencing the basicity or acidity of solvent mixtures is due to an order/disorder process, particularly in binary mixtures of protic solvents with non-hydrogen bond donor (non-HBD) solvents. 12,13 Nucleotides play a key role in almost all kinds of metabolic processes.…”

Section: Introductionmentioning

confidence: 99%

Complexation of Thallium(I) with Adenosine 5′-Monophosphate in Aqueous Methanol Solutions

2005

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The development of various kinds of approaches to hydrophobic hydration is necessary for a better understanding of its key role in controlling biochemical processes in water. 1,2 In the last few years, several experimental and theoretical works dealing with the effect of solvent on many reactions have been published. [3][4][5] Most of these papers are concerned with the effect of solvent on reaction rates. There is surprisingly little work, involving the effect of solvent on the thermodynamics and complexation of some biologically important ligands. [6][7][8] Various empirical solvent polarity parameters have been used to describe the influence of solvents on physicochemical solute properties. 9One particularly useful set consists of complementary Lewis acid-base solvent parameters, now known for most common organic solvents.10,11 It was found for example, by analysis of the variation of Kamlet-Taft's, β and α values, 12 for mixtures of methanol and other organic solvents, that one important factor influencing the basicity or acidity of solvent mixtures is due to an order/disorder process, particularly in binary mixtures of protic solvents with non-hydrogen bond donor (non-HBD) solvents. 12,13 Nucleotides play a key role in almost all kinds of metabolic processes. Much effort was devoted to the complexes of AMP, adenosine 5′-monophosphate, with metal ions. The properties and structures of binary complexes of most metal ion-AMP systems in aqueous solution are now relatively well described.14,15 Depending on the kind of metal ion involved, coordination occurs not only to the phosphate chain but also to N-1, leading thus to macrochelates.Thallium has been recognized as a toxic element for many years. It produces a variety of adverse effects in human beings. This element acts on the central nervous system and induces an inflammatory response. 16,17 However, the metabolic action and mechanism and fate of thallium toxicity are still not well understood, though there is some experimental evidence that suggests sulfur-containing compounds have been the main detoxifying drug in the case of poisoning. 17,18 Since thallium(I) shows marked similarities to that of potassium cation, 19 its interaction with nucleotides, the monomeric units of DNA and RNA, would be of major biochemical interest.This work deals with the study of thallium(I) complexes by AMP and the determination their stability constants in different solutions of methanol + water to show how the solvent and their mixtures with various dielectric constants affect the complexation.Recently, more attention has been paid to binary solvent mixtures in this field. 20-22 Solute-solvent interactions are much more complex in mixed solvent systems than in pure solvents, due to the possibility of preferential solvation by any of the solvents present in the mixtures. Moreover, the solvent-solvent interactions produced in solvent mixtures can affect the solutesolvent interactions and therefore they can also affect preferential solvations. 23At present, there are two more imp...

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“…It was then kept in the dark for ca. [15][16][17][18][19][20] h to ensure completion of the reaction. It was rendered alkaline and evaporated to dryness under reduced pressure.…”

Section: Product Analysismentioning

confidence: 99%

Kinetics and Mechanism of the Oxidation of Aliphatic Aldehydes by Benzimidazolium Dichromate

Kumar¹,

Panday²,

Kothari³

2011

Croat. Chem. Acta

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Abstract. Kinetic and mechanistic studies of the oxidation of aliphatic aldehydes, (in organic non-aqueous solvents), were discussed with an emphasis of correlation of structure and reactivity. The reactions were of first order with respect to BIDC and hydrogen-ion. However, Michaelis-Menten type kinetics were observed with respect to aldehyde. The deuterium isotope effect for the oxidation of acetaldehyde (k H /k D = 6.36 at 298 K) indicated an α-C-H bond cleavage in the rate-determining step. Based on kinetic data, analyses of the solvent effect and results of structure-reactivity correlation along with some nonkinetic parameters suggested a mechanism involving rate-determining oxidative decomposition of a aldehyde-BIDC complex via a cyclic transition state to give a carbocationic species through hydride-ion transfer from the aldehyde to the oxidant. (doi: 10.5562/cca1694)

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Solvent effects on chemical reactivity. Evaluation of anion- and cation-solvation components

Cited by 319 publications

References 0 publications

The change in hydrogen bond strength accompanying charge rearrangement: Implications for enzymatic catalysis

The change in hydrogen bond strength accompanying charge rearrangement: Implications for enzymatic catalysis

Complexation of Thallium(I) with Adenosine 5′-Monophosphate in Aqueous Methanol Solutions

Kinetics and Mechanism of the Oxidation of Aliphatic Aldehydes by Benzimidazolium Dichromate

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