Hydronium Ion Concentration Research Articles

Kinetic studies of reduction of nitrate ions at Sn-modified Pt electrodes using a quartz crystal microbalance

An electrochemical quartz crystal microbalance (EQCM) was used to determine the surface coverage of adsorbed nitrate during the reduction of nitrate on Sn-modified Pt electrodes. The rate equation was derived as a function of the surface coverage of nitrate, the concentration of hydronium ion and the electrode potential for an electrode with a tin coverage of ca. 0.35, which showed the highest activity of the electrodes reported so far. N 2 (30%) and NH 4 + ( 62 % ) were produced. From the Tafel slope at a constant surface coverage (−0.115 V decade −1) and the reaction orders (1.1 and 0.94 with respect to the surface coverage of the adsorbed nitrate and the concentration of hydronium ion, respectively), it is concluded that the rate-determining step is the reaction of the adsorbed nitrate with the hydronium ion and an electron.

In vitro hydrolysis of poly( l-lactide) crystalline residues as extended-chain crystallites : III. Effects of pH and enzyme

The effects of pH and an enzyme on the hydrolysis of poly( l-lactide) [i.e. poly( l-lactic acid) (PLLA)] crystalline residues or extended-chain crystallites containing a negligibly small amount of chains in an amorphous state were investigated in aqueous solutions at pH range from −0.9 to 12.8 and in Tris–HCl buffered solution with or without proteinase K by the use of gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). GPC results showed that the hydrolysis of the crystalline residues proceeded from their surface composed of very short chains with a free end along the chain direction, irrespective of pH, but that from their lateral surface could not be traced. GPC and DSC results indicated that the hydrolysis of the crystalline residues was accelerated with the pH deviation from 7, reflecting that the hydronium and hydroxide ions have catalytic effects on the hydrolysis of the crystalline residues. The dependence of hydrolysis rates estimated by GPC on the concentration of hydronium or hydroxide ions revealed that the catalytic effect of hydroxide ions on the hydrolysis is much higher than that of hydronium ions. The significant T m decrease at high and low pH means that there is a decrease in thickness of the crystalline residues by the hydrolysis. On the other hand, GPC and DSC results also showed that proteinase K has no catalytic effect on the hydrolysis of the crystalline residues, confirming the reported finding that the hydrolysis of very short chains with a free end is not accelerated by the presence of proteinase K.

The estimation of glutaminyl deamidation and aspartyl cleavage rates in glucagon

The major hydrolytic degradation pathways of glucagon under acidic conditions are cleavage at Asp-9, Asp-15, and Asp-21, and deamidation at Gln-3, Gln-20, Gln-24, and Asn-28. The rate constants for these pathways were determined in the pH range 1–2.4 at 60 °C by kinetic data analysis of substrate and degradation product concentration–time profiles. Deamidation kinetics were determined using penta-peptide fragments of glucagon containing the labile amide residue. The accurate determination of the cleavage rate constants was confounded by the complexity of the degradation scheme of glucagon. Peptide cleavage kinetics were determined by degradation of glucagon and its cleavage fragments under identical conditions and the use of area-under-the-curve (AUC) and nonlinear regression methods of analysis. Glucagon degradation was first-order with respect to time and concentration in the range of 31–00 μM. Glutaminyl deamidation rate constants were first-order with respect to hydronium ion concentration and were similar for all three residues indicating a lack of sequence effects. The rate constants for Asp cleavage were not first-order with respect to hydronium ion concentration and cleavage at Asp-21 was slower than cleavage at Asp-9 and Asp-15 over the studied pH range.

Electrochemical Properties of Poly-o-Phenylenediamine Films in Solutions with Variable Concentration of Hydronium Ions

Electrochemical behavior of poly-o-phenylenediamine (PoPhD) films in lithium perchlorate and perchloric acid solutions of different pH and constant ionic strength is studied using cyclic voltammetry, low-amplitude chronoamperometry, chronopotentiometry, and faradaic-impedance spectroscopy. The experimental results point to the diffusion–migration kinetics of charge transfer processes in redox-active PoPhD films and show that two such processes occur during oxidation–reduction of PoPhD. The processes are separated most fully at low concentrations of hydronium ions. Effect of the electrode potential and electrolyte composition on these processes is examined. Different methods yield similar results and permit their more reliable interpretation.

Hydrolytic reactions of diadenosine 5′,5′-triphosphate

The hydrolysis of diadenosine 5',5'-triphosphate to AMP and ADP has been studied over a wide pH-range. Under acidic conditions the reaction shows a first-order dependence on the hydronium ion concentration. Below pH 3 the rate-increase begins to level off. From pH 6 to 9 the hydrolysis is slow and pH-independent. Base-catalysed hydrolysis is observed in NaOH-solutions. Under alkaline conditions an intramolecular nucleophilic attack on the phosphate producing 3',5'-cAMP is also observed, but it is slower than the intermolecular reaction. Depurination of the adenosine moieties competes with the hydrolysis both under acidic and alkaline conditions, but the mechanisms are different. The temperature-dependence of the hydrolysis of Ap(3)A and the depurination of adenosine moieties were studied under acidic conditions, and the activation parameters of the reactions were calculated. The results of the work reflect the fact that the negatively charged polyphosphate group is very resistant towards nucleophilic attack. An efficient catalysis is only observed under acidic conditions, where the phosphate group becomes protonated. General acids or bases did not catalyse the hydrolysis. Furthermore, hydroxide ion catalysed cleavage is only observed at high base concentrations and other negatively charged nucleophiles did not attack the phosphate groups of diadenosine polyphosphates.

Enzyme and Proton-Activated Prodrugs for a Selective Cancer Therapy

This review is a survey of two approaches for a selective anticancer therapy that are based on a specific cleavage of specially designed non-toxic prodrugs with the liberation of a cytotoxic compound either by antibody-enzyme conjugates targeted to tumor-associated antigens or by acid-catalyzed hydrolysis of the prodrugs due to the increased concentration of hydronium ions in malignant tissue under hyperglycemic conditions. Herein, the design, synthesis and the biological testing of prodrugs are described.

Determination of the Gibbs excess of H and OH adsorbed at a Pt(1 1 1) electrode surface using a thermodynamic method

The thermodynamics of the so-called perfectly polarized electrode were employed to analyze the total charge densities for a Pt(1 1 1) electrode in a series of solutions (0.1− x) M HClO 4+ x M KClO 4 with a constant ionic strength and a variable hydronium ion concentration. The total charge densities were calculated by integration of cyclic voltammetry curves. A complete thermodynamic analysis using charge and potential as independent variables has been performed. The Gibbs excesses of adsorbed hydrogen and OH were determined without the need to introduce an arbitrary correction for the so-called charging of the double layer and further assumptions about the charge number per adsorbed species. We found that the maximum surface concentration of H amounts to ∼11×10 14 ions cm −2 or to a coverage 0.73 monolayer (ML) in good agreement with previous estimates. The maximum surface coverage of OH is equal to ∼8×10 14 ions cm −2 or to a coverage ∼0.53 ML. Using the thermodynamic method, the charge numbers at a constant potential (electrosorption valency) and at a constant chemical potential (reciprocal of the Esin–Markov coefficient) for adsorbed H and OH were calculated using the Gibbs excess data. The charge numbers are equal to ∼1 for H and to ∼−1 for OH. These values suggest that the adsorbed species is hydrogen atom and discharged OH species.

Acid-Catalyzed Reactions in Carbon Dioxide-Enriched High-Temperature Liquid Water

We report, for the first time, the acceleration of acid-catalyzed reactions in high-temperature liquid water by the addition of carbon dioxide to the reaction medium. The reactions examined are the dehydration of cyclohexanol to form cyclohexene and the alkylation of p-cresol with tert-butyl alcohol to form 2-tert-butyl-4-methylphenol. In some cases, the mean product yield more than doubled when carbon dioxide was added to the aqueous medium. The basis of this rate enhancement is reaction between carbon dioxide and water to yield carbonic acid, which subsequently dissociates to increase the hydronium ion concentration above that of water alone. We also use the thermodynamics of the CO2−H2O system to estimate the pH of carbon dioxide-enriched high-temperature water. This analysis demonstrates that it is possible to lower the pH of high-temperature water by several units through the addition of carbon dioxide to the reaction medium. These results demonstrate the feasibility of using CO2−H2O mixtures as an e...

Influence of Hofmeister Effects on Surface pH and Binding of Peptides to Membranes

An understanding of local surface pH and binding of peptides to membranes is of interest for a number of biological processes. Ionic dispersion forces that give rise to Hofmeister effects have not previously been taken into account by theories. It is demonstrated that pH-changes near surfaces (e.g. membrane and mica) and binding of peptides to membranes depend on the specific ionic species. Near mica surfaces, the effect can be especially large: some anions, for example, Br-, experience large attractive dispersion forces that can give rise to strong co-ion adsorption and enhanced pH-gradients. The concentration of hydronium ions at a model membrane surface is obtained from a modified nonlinear Poisson−Boltzmann equation that includes ionic dispersion potentials consistently. The fraction of ionizable surface groups is treated as a self-consistent functional of the electrostatic potential. We finally demonstrate that good agreement between theoretical and experimental binding energies of peptides to membr...

Effect of Dye-Bath pH on Photostability of Dyed Nylon 66

Nylon 66 films were dyed in aqueous dye-bath with C. I. Acid Blue 25 (1-amino-4-(aminophenyl)-2-anthraquinone sodium sulfonate) at various pH values ranging from 2.0 to 7.0. Films were exposed to polychromatic irradiation (λ ⪈ 290 nm) at 60°C in air. The extent of photo-oxidation was monitored by FT-IR spectroscopy. Fading of dye with polychromatic irradiation was monitored by UV spectroscopy. We observed a peculiar effect of dye-bath pH on the photostability of dyed nylon 66. Samples were more stable when dyed at pH 3 and above that (up to pH 7), whereas the samples dyed at pH < 3.0 showed sensitized photo-oxidative degradation in nylon 66. Formation of quaternary ammonium salt on dye-chromophore was considered responsible for the pH-controlled behavior of anthraquinone acid dyes. The dyeing pH significantly effects the photofading behavior of dyed samples. The effect of dye-bath pH on photofading of the dyed samples was more pronounced at lower dyeing pH and prevailed up to pH 4. The hydronium ion concentration was considered to be responsible for the enhanced fading of dye for the samples dyed at the lower pH.

Hydrolysis of tert-butyl methyl ether (MTBE) in dilute aqueous acid.

tert-Butyl methyl ether (MTBE) is generally considered to be resistant to chemical transformation in aqueous solution. This lack of reactivity has led to concerns of the long-term impacts of MTBE in groundwater. Although hydrolysis in the presence of strong acids has been recognized as a mechanism for MTBE transformation, it has been discounted as a significant reaction under environmental conditions. In this study, we have examined the fate of MTBE and other ether oxygenates under moderately acidic conditions (> or=pH 1). The results demonstrate that MTBE is sensitive to acid-catalyzed hydrolysis reaction that generates tert-butyl alcohol (TBA) and methanol as products. The reaction is first-order with respect to the concentration of MTBE and hydronium ion with a second-order rate constant of about 0.9 x 10(-2) M(-1) h(-1) at 26 degrees C. Commercially available acidic ion-exchange resins were also shown to catalyze the hydrolysis of MTBE at near neutral pH. Pseudo-first-order rate constants were observed to be as high as 0.03 h(-1) at 25 degrees C and 0.12 h(-1) at 35 degrees C. These findings are discussed in terms of their possible implications for the treatment and environmental fate of MTBE and other gasoline oxygenates.

Catalysis and inhibition of ligand substitution in palladium(II) square-planar complexes: effects of DNA.

The kinetics of substitution, by thiourea, of ethylenediamine (en) or N,N'-dimethylethylenediamine (Me(2)en) coordinated to palladium(II) in the complexes [Pd(4,4'-R(2)bpy)(en)](PF(6))(2) (bpy = 2,2'-bipyridine; R = H or Me), [Pd(en)(2)](PF(6))(2) and [Pd(Me(2)en)(2)](PF(6))(2) have been studied at 25 degrees C, pH 7 and various ionic strength values, in the presence of calf thymus DNA. The rate of the reaction in water depends on ionic strength, pH, and nucleophile concentration; at fixed pH and ionic strength the k(obsd) values are correlated to the square of the thiourea concentration. This rate law is not altered by the presence of DNA, but the rate of reaction is influenced, depending on the nature of ancillary ligand, L-L, bound to palladium. DNA inhibits the substitution process when L-L is bpy or 4,4'-Me(2)bpy and catalyzes the same reaction when L-L is en or Me(2)en. These opposite kinetic effects can be related to the noncovalent interactions of the various complexes with the DNA double helix. Inhibition of the reactivity of the complexes [Pd(4,4'-R(2)bpy)(en)](2+) is due to protection of the reaction center from nucleophile attack by DNA. Acceleration of the reaction when L-L is en or Me(2)en is related to the dependence of the rate of reaction on pH. If, due to the higher activity of water under the electric field of phosphate groups, hydronium ion concentration on DNA surface is higher than in the bulk solution, the enzyme-like dependence of the rate of reaction on [DNA] is due to progressive accumulation of the complexes around the double helix. Regardless of the complexes' nature, the rate constant values obtained in DNA at pH 7 correspond to values determined in water at pH 5. This pH value on the DNA surface, lower by about two units with respect to the bulk solution, is in good agreement with theoretical predictions. Acceleration of ethylenediamine substitution has been observed for all of the complexes studied in the presence of sodium polyvinylsulfonate.

Kinetics of Carbosulfan Degradation in the Aqueous Phase in the Presence of a Cosolvent

AbstractThe degradation of the carbamate pesticide carbosulfan (2,3‐dihydro‐2,2‐dimethyl‐7‐ben/ofuranyl [(dibutylamino)thio]methylcarbamate] was investigated in aqueous buffer solutions (pH 3.0–7.0) containing low (1%, v/v) and high (10–60%, v/v) concentrations of acetonitrile. The cleavage of the carbamyl N‐S bond yields carbofuran (2,3‐dihydro‐2,2‐dinicthyl‐7‐benzofuranol methylcarbamate). The rate of carbosulfan degradation depends on pH, the initial concentration of carbosulfan, acetonitrile concentration, shaking speed, ionic strength, and temperature. Carbosulfan was completely dissolved only in solutions with high acetonitrile concentrations. The concentration of acetonitrile needed for the complete dissolution of carbosulfan depended on the initial concentration of carbosulfan. In this case, the degradation is a pseudo‐second‐order reaction with respect to the concentration of carbosulfan and hydronium ion. The degradation reaction is promoted by the hydronium ion. In the case of low acetonitrile concentrations, where carbosulfan was not completely dissolved, the overall kinetics depend also on the slow dissolution process. The degradation of carbosulfan probably is not a pure hydrolysis reaction, but a protonation‐intermolecular rearrangement reaction. The results indicate that the abiotic degradation of carbosulfan in natural waters is a very slow process when organic solvents and minerals are absent or present in only minor concentrations.

Adsorption of atomic hydrogen on a polycrystalline Pt electrode surface studied by FT-IRAS: the influence of adsorbed carbon monoxide on the spectral feature

Abstract Adsorption of atomic hydrogen on a polycrystalline Pt electrode surface was studied by in situ infrared reflection absorption spectroscopy (IRAS). When the electrode potential was adjusted in a potential range where the underpotential-deposited (upd) hydrogen was formed, an absorption band assignable to the vibration of on-top CO (which would be formed by the reduction of a trace of CO2) appeared at ca. 2010 cm−1 even for highly purified 0.1 M (M=mol dm−3) H2SO4 solution. An absorption band due to the on-top H was observed at ca. 2070 cm−1 for a conventional acidic solution in a potential range as narrow as ca. 0.1 V just before the hydrogen evolution reaction (her) ascribable to the reduction of hydronium ions began. On the other hand, the on-top H band was observed unequivocally for a solution containing 1 mM H2SO4 and 99 mM Na2SO4 over a wide potential range where molecular hydrogen was formed by the reduction of hydronium ions. Even for a neutral solution such as 0.1 M KCl, the weak band ascribable to the on-top H was detected. The dependence of the spectral feature on the concentration of hydronium ions and the applied electrode potential strongly suggested that the on-top H is the intermediate in the electrochemical reduction of hydronium ions. We demonstrated that the adsorbed CO is readily formed by the reduction of CO2 in the 0.1 M H2SO4 solution.

Synthesis of resorcinol from meta-phenylenediamine in the presence of zeolites

Resorcinol can be produced in high yields starting from meta-phenylenediamine (MPDA) in the presence of homogeneous mineral acids. The synthesis in the presence of alumino-silicates (e.g., zeolites) offers a solution to the extremely corrosive properties of the mineral acids at reaction temperature (200–275°C). Environmental hazards associated with mineral acids will thus be eliminated. From studies using mineral acids, it was deduced that the rate of reaction is directly proportional to the hydronium ion concentration. The ionisation constants and thus hygroscopic property of the mineral acid determines the degree of resorcinol and MPDA polymerisation. As an alternative, the synthesis can be performed in the presence of alumino-silicates, albeit at higher temperatures. Zeolites H-USY, H-Beta, and amorphous silica-alumina gave good resorcinol yields. During the reaction, the crystal structure of zeolites H-Beta and H-USY is destroyed. H-ZSM-5 is stable under reaction conditions, but the resorcinol yield is rather poor. This can be ascribed to the low adsorption capacity for MPDA in comparison to zeolites H-USY and H-Beta. For all zeolites the dominant part of the reaction may occur on the external surface acid sites.

Kinetics and thermodynamics of ionization of 4,4′-dimethoxytrityl alcohol in acetonitrile–aqueous acids: determination of enthalpies and entropies of activation and of reaction

We have studied the equilibration shown in eqn. (2) of 4,4′-dimethoxytrityl alcohol in aqueous perchloric, nitric, and hydrochloric acids containing 20% acetonitrile at different temperatures using stopped-flow kinetics techniques. The observed overall pseudo first-order rate constant for equilibration, kobs, decreases with increasing electrolyte concentrations at constant hydronium ion concentration; kobs, has been resolved into forward and reverse components using the equilibrium UV absorbance and the temperature-independent molar absorptivity of the 4,4′-dimethoxytrityl carbenium ion. The forward reaction (rate constant kf) is first order in both the alcohol and the acid; the reverse reaction (rate constant kr) is pseudo first order with respect to the carbocation. At constant hydronium ion concentration, the forward rate constant increases with the concentration of electrolyte whereas the reverse rate constant decreases. Quantitative effects for perchlorate, nitrate, and chloride are different. Results are accommodated by a mechanism which involves pre-equilibrium protonation of the alcohol, heterolysis of the protonated alcohol to give a 4,4′-dimethoxytrityl carbenium ion–water ion–molecule pair, then conversion of this into the dissociated carbenium ion in equilibrium with ion pairs. There are additional parallel reaction channels from the protonated alcohol and electrolyte anions. Some of the elementary rate constants have been evaluated, and enthalpies and entropies of activation have been determined. Correspondingly, some equilibrium constants of the proposed mechanism have been evaluated, and associated enthalpies and entropies of reaction have been determined.

The 4,4'-dimethoxytrityl carbenium ion by ionization of 4,4'-dimethoxytrityl alcohol in acetonitrile - aqueous perchloric and nitric acids containing electrolytes: kinetics, equilibria, and ion-pair formation

We have studied the equilibration shown in eq. [3] of 4,4prime-dimethoxytrityl alcohol in aqueous perchloric and nitric acids containing low proportions of acetonitrile using stopped-flow kinetics techniques. The rate constants for the overall progress to equilibrium, kobs, have been resolved into forward and reverse components using the equilibrium UV absorbance and a value for the molar absorptivity of the 4,4prime-dimethoxytrityl carbenium ion determined in concentrated aqueous perchloric acid. The forward reaction (rate constant kf) is first order in both the alcohol and the acid concentrations; the reverse reaction (rate constant kr) is pseudo first order with respect to the carbocation. At constant hydronium ion concentration, the forward rate constant increases linearly with the concentration of electrolyte, whereas the reverse rate constant decreases. These effects depend upon the nature of the anion, but not the cation, and are not ionic strength effects. At constant anion concentrations, kf in both acids, and kr in perchloric acid, are independent of hydronium ion concentration; however, kr decreases with increasing hydronium ion concentration at constant nitrate concentration. At nonconstant ionic strength, changes in kf and kr observed in increasing concentrations of perchloric acid are attributable wholly to changes in perchlorate concentration. A mechanism is proposed which involves pre-equilibrium protonation of the alcohol, heterolysis of the protonated alcohol to give a 4,4prime-dimethoxytrityl carbenium ion - water ion-molecule pair, then conversion of this into a dissociated carbenium ion in equilibrium with ion pairs. To account for the strong effects of perchlorate and nitrate upon the forward rate constants, it is proposed that these anions provide additional reaction channels from the ion-molecule pair. However, we find no evidence of acid catalysis in the reaction of the ion-molecule pair (in contrast to our finding for the reaction of the corresponding ion-molecule pair formed from dimethoxytritylamine in acidic media). Some of the elementary rate and equilibrium constants of the proposed mechanism have been evaluated.Key words: trityl, carbenium ion, stopped-flow, ion pair, ion-molecule pair.

The 4,4'-dimethoxytrityl carbenium ion by ionization of 4,4'-dimethoxytrityl alcohol in acetonitrile - aqueous perchloric and nitric acids containing electrolytes: kinetics, equilibria, and ion-pair formation

We have studied the equilibration shown in eq. [3] of 4,4prime-dimethoxytrityl alcohol in aqueous perchloric and nitric acids containing low proportions of acetonitrile using stopped-flow kinetics techniques. The rate constants for the overall progress to equilibrium, kobs, have been resolved into forward and reverse components using the equilibrium UV absorbance and a value for the molar absorptivity of the 4,4prime-dimethoxytrityl carbenium ion determined in concentrated aqueous perchloric acid. The forward reaction (rate constant kf) is first order in both the alcohol and the acid concentrations; the reverse reaction (rate constant kr) is pseudo first order with respect to the carbocation. At constant hydronium ion concentration, the forward rate constant increases linearly with the concentration of electrolyte, whereas the reverse rate constant decreases. These effects depend upon the nature of the anion, but not the cation, and are not ionic strength effects. At constant anion concentrations, kf in both acids, and kr in perchloric acid, are independent of hydronium ion concentration; however, kr decreases with increasing hydronium ion concentration at constant nitrate concentration. At nonconstant ionic strength, changes in kf and kr observed in increasing concentrations of perchloric acid are attributable wholly to changes in perchlorate concentration. A mechanism is proposed which involves pre-equilibrium protonation of the alcohol, heterolysis of the protonated alcohol to give a 4,4prime-dimethoxytrityl carbenium ion - water ion-molecule pair, then conversion of this into a dissociated carbenium ion in equilibrium with ion pairs. To account for the strong effects of perchlorate and nitrate upon the forward rate constants, it is proposed that these anions provide additional reaction channels from the ion-molecule pair. However, we find no evidence of acid catalysis in the reaction of the ion-molecule pair (in contrast to our finding for the reaction of the corresponding ion-molecule pair formed from dimethoxytritylamine in acidic media). Some of the elementary rate and equilibrium constants of the proposed mechanism have been evaluated.Key words: trityl, carbenium ion, stopped-flow, ion pair, ion-molecule pair.

Local dielectric constants and Poisson-Boltzmann calculations of DNA counterion distributions

Recent work by the authors on the calculation of local solvent dielectric constants around polyelectrolytes using the Poisson–Boltzmann approach is analyzed in terms of the effect on surface potentials and counterion concentrations. Polyelectrolyte surface geometry, local electric fields, and counterion distributions contribute to the self-consistent prediction of local solvent dielectric constants. For an all-atom cell model of DNA with added monovalent salt varying from 0 to 0.5M, the Poisson–Boltzmann-determined electrostatic potential increases (negatively) by 50–100% upon the inclusion of local dielectric constants. This, in turn, implies that hydronium ion concentrations in the major and minor grooves increase by about 0.65 and 0.35 pH units, respectively. While counterion concentrations in the major groove change only slightly, those in the minor groove increase by 60–90%. It is also noted that while the local dielectric constant in the major groove monotonically increases away from the surface toward the bulk value of water the dielectric constant in the minor groove has a minimum about 2 Å from the surface due primarily to the local electric field. Certain other properties, such as ionic and dipole first passage times, are affected little by local dielectric constants (less than about 3%). © 1997 John Wiley & Sons, Inc. Int J Quant Chem 65: 1087–1093, 1997

Local dielectric constants and Poisson–Boltzmann calculations of DNA counterion distributions

Recent work by the authors on the calculation of local solvent dielectric constants around polyelectrolytes using the Poisson–Boltzmann approach is analyzed in terms of the effect on surface potentials and counterion concentrations. Polyelectrolyte surface geometry, local electric fields, and counterion distributions contribute to the self-consistent prediction of local solvent dielectric constants. For an all-atom cell model of DNA with added monovalent salt varying from 0 to 0.5M, the Poisson–Boltzmann-determined electrostatic potential increases (negatively) by 50–100% upon the inclusion of local dielectric constants. This, in turn, implies that hydronium ion concentrations in the major and minor grooves increase by about 0.65 and 0.35 pH units, respectively. While counterion concentrations in the major groove change only slightly, those in the minor groove increase by 60–90%. It is also noted that while the local dielectric constant in the major groove monotonically increases away from the surface toward the bulk value of water the dielectric constant in the minor groove has a minimum about 2 Å from the surface due primarily to the local electric field. Certain other properties, such as ionic and dipole first passage times, are affected little by local dielectric constants (less than about 3%). © 1997 John Wiley & Sons, Inc. Int J Quant Chem 65: 1087–1093, 1997