Kinetic Medium Effects Research Articles

Reactivity in organised assemblies

This report reviews the 2009 literature on reactivity in organised assemblies, with virtually all examples taken from literature covering aqueous systems. The report is broadly organised along the lines that we set out last year,1 but with the addition of a “miscellaneous” section containing two papers that we did not want to leave out of this report. Nevertheless, as always, we cannot and will not claim that this report provides an exhaustive review. Several main themes covered by this report were reviewed in 2009; Prins and Scrimin reviewed covalent capture which they defined as relying on “the combined use of covalent and noncovalent synthesis by taking advantage of their complementarity”,2 Peyralans and Otto reviewed recent highlights in systems chemistry,3 metallomicellar catalysis was reviewed by Tecilla et al.4 and one of us reviewed kinetic medium effects on organic reactions in aqueous colloidal solutions.5

Hydrophobicity and Reactivity of Base Hydrolysis of Some Novel Low Spin Fe(II) Amino Acid Schiff Base Complexes in Some Binary Aqueous Solvent Mixtures

Rate constants for base hydrolysis of bis(naphthylidene isoleucinate)iron (II) (nili), bis(naphthylidene leucinate)iron(II) (nli), bis(naphthylidene serinate)iron(II) (nsi), bis(salicylidene isoleucinate)iron(II) (sili), (salicylidene leucinate)iron(II) (sli), bis(salic- ylidene methioninate)iron(II) (smi), and (salicylidene tryptophanate)iron(II) (sti) have been reported in different binary aqueous mixtures at 298 K. The observed reactivity trends are discussed in terms of the hydrophilic and hydrophobic forms of the complexes investigated, as well as the transfer chemical potentials of hydroxide ion and the complex. Both the solvent–solute and solvent–solvent interactions have been considered. The hydrophobic character of the complexes studied was manifested by enhancing the rate of base hydrolysis at the initial addition of the different cosolvents; further addition led mostly to a decrease in reactivity, but, in some cases, the greater destabilization of OH− ion by added DMSO and acetone increases the rate of base hydrolysis. The modified Savage–Wood equation, based on the principle of group additivity, was applied to estimate the observed kinetic medium effects.

Kinetic evidence for hydrophobically stabilized encounter complexes formed by hydrophobic esters in aqueous solutions containing monohydric alcohols.

The pH-independent hydrolysis of four esters, p-methoxyphenyl 2,2-dichloroethanoate (1a), p-methoxyphenyl 2,2-dichloropropanoate (1b), p-methoxyphenyl 2,2-dichlorobutanoate (1c), and p-methoxyphenyl 2,2-dichloropentanoate (1d), in dilute aqueous solution has been studied as a function of the molality of added cosolutes ethanol, 1-propanol, and 1-butanol. The rate constants for the neutral hydrolysis decrease with increasing cosolute concentration. These kinetic medium effects respond to both the hydrophobicity of the ester and of the monohydric alcohol. The observed rate effects were analyzed using both a thermodynamic and a kinetic model. The kinetic model suggests a molecular picture of a hydrophobically stabilized encounter complex, with equilibrium constants K(ec) often smaller than unity, in which the cosolute blocks the reaction center of the hydrolytic ester for attack by water. The formation of these encounter complexes leads to a dominant initial-state stabilization as follows from the thermodynamic model. Decreases in both apparent enthalpies and entropies of activation for these hydrolysis reactions correspond to unfavorable enthalpies and favorable entropies of complexation, which confirms that the encounter complexes are stabilized by hydrophobic interactions.

Pairwise gibbs energies of interaction involving N-alkyl-2-pyrrolidinones and related compounds in aqueous solution obtained from kinetic medium effects

Kinetic solvent effects of N-alkyl-2-pyrrolidinones and structurally related compounds on the water-catalyzed hydrolysis reactions of p-methoxyphenyl dichloroacetate (MPDA), 1-benzoyl-3-phenyl-1,2, 4-triazole (BPhT), and 1-benzoyl-1,2,4-triazole (BT) in highly dilute aqueous solutions at pH 4 and 298.15 K have been determined by UV/vis spectroscopy. Using a thermodynamic description of solute-solute interactions in aqueous solutions, the kinetic results have been analyzed in terms of pairwise Gibbs energy interaction parameters: G(c) values. These are negative, indicating that hydrophobic interactions in the initial state dominate the medium effects. The interaction parameters increase in the order MPDA<BT<BPhT, suggesting increasing hydrophobic stabilization in the order of MPDA>BT>BPhT. However, when differences in reactivity and transition state effects are taken into account, it appears that BPhT is more successful in establishing hydrophobic interactions with the cosolutes than are MPDA and BT. Using the SWAG-approach for additivity of group interactions, additivity is observed for the first three consecutive CH(2) groups in the cosolute in all three hydrolysis reactions. Larger alkyl substituents cause larger retardations than anticipated on basis of this additivity. The results are explained by intramolecular destructive overlap of the polar hydration shell of the amide functionality and the apolar (hydrophobic) hydration shell of the alkyl group, which extends to the third CH(2) group in the N-alkyl group of the cosolute molecule. The inner apolar groups, therefore, have a reduced apparent hydrophobicity. More remote CH(2) groups develop independent hydrophobic hydration shells. The effect of the position of a CH(2) group in the cosolute molecule is also considered. Kinetic solvent effects with structurally related esters show that amide-amide, ester-ester, and amide-ester group interactions affect the transition state in different ways. Finally, the effects of PVP polymers on the three hydrolysis reactions have been examined. The data presented enhance the understanding of pairwise hydrophobic interactions in aqueous solutions. In addition the results provide insights into the interactions between hydrophobic and hydrophilic hydration shells as well as into the energetics of amide hydration and interactions involving amides in aqueous solution, both playing important roles in protein stabilization.

Quantitative comparison of the effect of methylD-glycopyranosides as cosolutes on the rates of base hydrolysis and aquation of some iron(II)-diimine Complexes

The kinetics of base hydrolysis and of aquation of some iron(II)–diimine complexes in the presence of stereoisomeric carbohydrates were monitored spectrophotometrically at 25.0°C. In basic aqueous solution dissociation of both Fe(1,10-phenanthroline)32+ and Fe(2,2\'-bipyridine)32+ is accelerated when methyl D-glycopyranosides are present. The aquation reaction of Fe(1,10-phenanthroline)32+ in an aqueous EDTA medium is also accelerated in the presence of carbohydrates, but that of Fe(5-nitro-1,10-phenanthroline)32+ is retarded. An equation obtained from a modification of the Savage–Wood additivity of groups principle applied to kinetics is used to quantify the kinetic medium effects observed. The magnitudes of these effects can be explained in terms of the hydration characteristics of the carbohydrates, which depend on their stereochemistry, and the change in the hydration environment of the iron(II)–diimine complexes during activation. Results and their interpretation for the aquation in acidic medium of the Fe(5-bromo-1,10-phenanthroline)32+ and Fe(4,7-dimethyl-1,10-phenanthroline)32+ complexes in highly aqueous methanol and ethanol solutions are also presented. The kinetic medium effects of the carbohydrates are consistent with those of simple alcohols.

1,3-Dipolar Cycloadditions of Benzonitrile Oxide with Various Dipolarophiles in Aqueous Solutions. A Kinetic Study

The second-order rate constants for the 1,3-dipolar cycloaddition of benzonitrile oxide (1) with various dipolarophiles (2a-e) were determined in aqueous media and in organic solvents to gain more insight into the influence of an aqueous medium on pericyclic reactions. 1,3-Dipolar cycloadditions with electron-poor dipolarophiles are accelerated in water and protic solvents, whereas an aqueous medium has no special effect when electron-poor dipolarophiles are involved. These observations can be explained using frontier molecular orbital theory. In all cases, enforced hydrophobic interactions promote the reaction. These results are supported by kinetic experiments in water-ethanol mixtures. Sodium dodecyl sulfate micelles accelerate the cycloaddition of 1 with both electron-rich and electron-poor dipolarophiles. More than for other systems, the present results show that hydrogen bonding and hydrophobic interactions can either cooperate or counteract each other in determining the kinetic medium effects in aqueous solutions.

The mean spherical approximation and medium effects in the kinetics of solution reactions involving ions

The mean spherical approximation has been applied to describe medium effects in the kinetics of reactions between ions in water. When the ionic strength of the medium is altered by the addition of an inert electrolyte, the rate of reaction can be accurately predicted with the inert electrolyte concentration up to 1 M. The theoretical rate constant at the limit of infinite dilution kr0, has been estimated for five earlier kinetics studies for which data are available in the literature. Keywords: kinetic medium effects, mean spherical approximation, activity coefficients.

Kinetic medium effects of cationic cosolutes in aqueous solution: the effects of alkylammonium bromides on the neutral hydrolysis of 1-benzoyl-1,2,4-triazole

We have investigated the kinetic effects of alkylammonium, alkyldimethylammonium, alkyltrimethylammonium and tetraalkylammonium bromides on the water-catalysed hydrolysis of 1-benzoyl-1,2,4-triazole at pH 4 and 25 °C. All cosolutes retard the reaction. The retardation is attributed to a dominant stabilisation of the initial state through hydrophobic interactions with the cosolute. The results are analysed in terms of pairwise Gibbs energy interaction parameters. These G(C) values show that alkyl groups shorter than propyl have no significant influence on the medium effect. The extensively hydrated ammonium groups prevent the formation of a well developed hydrophobic hydration shell by methylene moieties in its vicinity. We observe additivity of kinetic effects of methylene groups outside the ionic hydration sphere on the hydrolysis reaction. Pairwise group interaction parameters were obtained for the CH2-group of the different cosolutes; the contribution of the CH2-group to the overall cosolute effect is -94 J kg mol-2 for both alkylammonium bromides and alkyldimethylammonium bromides, and -110 J kg mol-2 for alkyltrimethylammonium bromides. Ammonium bromide, which is primarily hydrophilic, also retards the reaction. We suggest that competition between ammonium bromide and the transition state for water molecules results in the strict orientational requirements for the water molecules in the activated complex not being met. Hence the hydrolysis is retarded.

Kinetic medium effects of amphiphilic cosolutes below their critical micelle concentration: the effect of sodium n-alkyl sulfates on the neutral hydrolysis of 1-benzoyl-1,2,4-triazole

Kinetic medium effects are presented for sodium n-alkyl sulfates (R = methyl to n-octyl) on the neutral hydrolysis of 1-benzoyl-1,2,4-triazole at 298.15 K in highly aqueous solutions below the critical micellar concentration. The observed rate-decreasing effects are quantitatively analyzed in terms of pairwise solute-solute interactions. It is shown that the effect of the alkyl chains cannot be accounted for on the basis of additivity of pairwise group interactions involving individual methylene moieties. Apparently, the sulfate group shields methylene moieties in close proximity for intermolecular interactions. Methylene groups, further away from the ionic functionality, are shielded less effectively. At the critical micellar concentration of the longer-chain sodium n-alkyl sulfates, the observed medium effects change dramatically as expected on the basis of the onset of micellization. No clear indication for premicellar aggregation was found. The medium effect of the sulfate moiety is estimated by extrapolation of kinetic medium effects to zero methylene groups and appears to be rate-retarding as well.

Stereochemical aspects of hydration of carbohydrates in aqueous solutions. 2. Kinetic medium effects

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStereochemical aspects of hydration of carbohydrates in aqueous solutions. 2. Kinetic medium effectsSaskia A. Galema, Michael J. Blandamer, and Jan B. F. N. EngbertsCite this: J. Org. Chem. 1992, 57, 7, 1995–2001Publication Date (Print):March 1, 1992Publication History Published online1 May 2002Published inissue 1 March 1992https://doi.org/10.1021/jo00033a019RIGHTS & PERMISSIONSArticle Views313Altmetric-Citations72LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (922 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Stereochemical aspects of the hydration of carbohydrates. Kinetic medium effects of monosaccharides on a water-catalyzed hydrolysis reaction

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStereochemical aspects of the hydration of carbohydrates. Kinetic medium effects of monosaccharides on a water-catalyzed hydrolysis reactionSaskia A. Galema, Michael J. Blandamer, and Jan B. F. N. EngbertsCite this: J. Am. Chem. Soc. 1990, 112, 26, 9665–9666Publication Date (Print):December 1, 1990Publication History Published online1 May 2002Published inissue 1 December 1990https://doi.org/10.1021/ja00182a050RIGHTS & PERMISSIONSArticle Views245Altmetric-Citations85LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (275 KB) Get e-Alerts Get e-Alerts

Kinetic medium effects in N-cyclohexyl-2-pyrrolidone-water mixtures. Evidence for a low critical hydrophobic interaction concentration

Kinetic medium effects in N-cyclohexyl-2-pyrrolidone-water mixtures. Evidence for a low critical hydrophobic interaction concentration

Nematic—isotropic solution thermodynamics in di( p-methoxyphenyl)- trans-cyclohexane-1,4-dicarboxylate

Solution thermodynamic parameters of selected non-polar solutes have been determined in the nematic and isotropic fluid states of di( p-methoxyphenyl)- trans-cyclohexane-1,4-dicarboxylate. These states have been reported to exert no measurable differential in kinetic medium effects on the Claisen rearrangement 1. Partial molar enthalpies Δ H soln 2 and entropies Δ S soln 2 of solution of a series of substituted benzenes in the nematogenic solvent, determined by the gas—liquid chromatographic method of Martire, 2–4, are reported. Changes in solute excess Gibbs free energy Δ G E 2 over the nematic—isotropic transition of the solvent, corresponding to the changes in free energy of solution ΔΔ G soln 2, have been calculated for the series. The results show the nematic and isotropic states of the medium to exhibit distinctly different solvent characteristics and suggest that Claisen reaction kinetics in the nematogenic solvent reflect compensating medium effects on the reactant and its activated state.

Kinetic medium effects. IV. Transition state activity coefficients in mixed solvents

The kinetics of acid hydrolysis of a number of aliphatic acetals have been studied in dimethyl sulphoxide-water and dioxan-water mixtures. Where possible, experimentally measured medium activity coefficients for the acetals in the solvent systems have been used in order to calculate the transition state activity coefficients as a function of solvent composition. These activity coefficients are compared with those calculated for the transition states of other hydrolytic reactions, and with the known activity coefficients of some stable ions. The results show no features inconsistent with the assumptions of transition state theory.

Kinetic medium effects. IV. Hydrolysis of trimethyl phosphate in mixed solvents

The rate of hydrolysis of trimethyl phosphate (tmp) has been measured at 90.5� as a function of solvent composition in water-dimethyl sulphoxide and water-ethylene glycol mixtures. The rate constant of the "spontaneous" hydrolysis decreases with decreasing water content; an acid-catalysed reaction, whose rate constant increases with decreasing water content, becomes dominant at low water concentrations. Solvent isotope effects in D2O have been measured for both the spontaneous and acid-catalysed reactions, and are close to unity in each case. Salt effects have also been studied In aqueous sodium nitrate and perchlorate solutions, and are found to be small. Reaction mechanisms are discussed in the light of the results obtained.

Kinetic medium effects. III. Solvent effects on A1 and A2 Hydrolyses in water-dimethyl sulphoxide mixtures

The relative rates of the concurrent A1 and A2 hydrolyses of t-butyl acetate have been measured as a function of solvent composition in water-dimethyl sulphoxide (DMSO) mixtures. A large difference in solvent effect is observed, which correlates well with observed solvent effects on ethyl acetate (A2) and acetal (Al) hydrolyses in the same solvent system. Activity coefficients have been measured for t-butyl acetate, ethyl acetate, and acetal in various water-DMSO mixtures.

Kinetic medium effects. II. Hydrolysis of esters in electrolyte solutions

Rate constants have been measured for the acid-catalysed hydrolyses of t-butyl acetate and methyl chloroacetate in various aqueous electrolyte solutions; the activity coefficients of the esters in these electrolyte solutions have also been measured. The results are used to test a recently proposed method of determining transition state hydration numbers for reactions in aqueous media.

Kinetic Medium Effects in the Reaction between Bromoacetate and Thiosulfate Ions

Kinetic Medium Effects in the Reaction between Bromoacetate and Thiosulfate Ions

Kinetic Medium and Salt Effects in Reactions between Ions of Unlike Sign. Reaction between Ammonium Ion and Cyanate Ion

Kinetic Medium and Salt Effects in Reactions between Ions of Unlike Sign. Reaction between Ammonium Ion and Cyanate Ion