Complexation Thermodynamics of Cyclodextrins.

Starting from known properties of non-specific salt effects on the surface tension at an air–water interface, we propose the first general, detailed qualitative molecular mechanism for the origins of ion-specific (Hofmeister) effects on the surface potential difference at an air–water interface; this mechanism suggests a simple model for the behaviour of water at all interfaces (including water–solute interfaces), regardless of whether the non-aqueous component is neutral or charged, polar or non-polar Specifically, water near an isolated interface is conceptually divided into three layers, each layer being 1 water-molecule thick We propose that the solute determines the behaviour of the adjacent first interfacial water layer ( I 1 ); that the bulk solution determines the behaviour of the third interfacial water layer ( I 3 ), and that both I 1 and I 3 compete for hydrogen-bonding interactions with the intervening water layer ( I 2 ), which can be thought of as a transition layer The model requires that a polar kosmotrope (polar water-structure maker) interact with I 1 more strongly than would bulk water in its place; that a chaotrope (water-structure breaker) interact with I 1 somewhat less strongly than would bulk water in its place; and that a non-polar kosmotrope (non-polar water-structure maker) interact with I 1 much less strongly than would bulk water in its place We introduce two simple new postulates to describe the behaviour of I 1 water molecules in aqueous solution The first, the ‘relative competition’ postulate, states that an I 1 water molecule, in maximizing its free energy (—δG), will favour those of its highly directional polar (hydrogen-bonding) interactions with its immediate neighbours for which the maximum pairwise enthalpy of interaction (—δ H ) is greatest; that is, it will favour the strongest interactions We describe such behaviour as ‘compliant’, since an I 1 water molecule will continually adjust its position to maximize these strong interactions Its behaviour towards its remaining immediate neighbours, with whom it interacts relatively weakly (but still favourably), we describe as ‘recalcitrant’, since it will be unable to adjust its position to maximize simultaneously these interactions The second, the ‘charge transfer’ postulate, states that the strong polar kosmotrope–water interaction has at least a small amount of covalent character, resulting in significant transfer of charge from polar kosmotropes to water–especially of negative charge from Lewis bases (both neutral and anionic); and that the water-structuring effect of polar kosmotropes is caused not only by the tight binding (partial immobilization) of the immediately adjacent ( I 1 ) water molecules, but also by an attempt to distribute among several water molecules the charge transferred from the solute When extensive, cumulative charge transfer to solvent occurs, as with macromolecular polyphosphates, the solvation layer (the layer of solvent whose behaviour is determined by the solute) can become up to 5- or 6-water-molecules thick We then use the ‘relative competition’ postulate, which lends itself to simple diagramming, in conjunction with the ‘charge transfer’ postulate to provide a new, startlingly simple and direct qualitative explanation for the heat of dilution of neutral polar solutes and the temperature dependence of relative viscosity of neutral polar solutes in aqueous solution This explanation also requires the new and intriguing general conclusion that as the temperature of aqueous solutions is lowered towards o °C, solutes tend to acquire a non-uniform distribution in the solution, becoming increasingly likely to cluster 2 water molecules away from other solutes and surfaces (the driving force for this process being the conversion of transition layer water to bulk water) The implications of these conclusions for understanding the mechanism of action of general (gaseous) anaesthetics and other important interfacial phenomena are then addressed

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0033583500005369

The Hofmeister effect and the behaviour of water at interfaces.

In the presence of multivalent cations, high molecular weight DNA undergoes a dramatic condensation to a compact, usually highly ordered toroidal structure. This review begins with an overview of DNA condensation: condensing agents, morphology, kinetics, and reversibility, and the minimum size required to form orderly condensates. It then summarizes the statistical mechanics of the collapse of stiff polymers, which shows why DNA condensation is abrupt and why toroids are favored structures. Various ways to estimate or measure intermolecular forces in DNA condensation are discussed, all of them agreeing that the free energy change per base pair is very small, on the order of 1% of thermal energy. Experimental evidence is surveyed showing that DNA condensation occurs when about 90% of its charge is neutralized by counterions. The various intermolecular forces whose interplay gives rise to DNA condensation are then reviewed. The entropy loss upon collapse of the expanded wormlike coil costs free energy, and stiffness sets limits on tight curvature. However, the dominant contributions seem to come from ions and water. Electrostatic repulsions must be overcome by high salt concentrations or by the correlated fluctuations of territorially bound multivalent cations. Hydration must be adjusted to allow a cooperative accommodation of the water structure surrounding surface groups on the DNA helices as they approach. Undulations of the DNA in its confined surroundings extend the range of the electrostatic forces. The condensing ions may also subtly modify the local structure of the double helix.

DNA condensation by multivalent cations.

The role of hydroxyl radical reactions in ozonation processes in aqueous solutions

Mechanism of Fatty-Acid-Dependent UCP1 Uncoupling in Brown Fat Mitochondria

Complexes between DNA and polyamines: a molecular model

Diffusion coefficients for the binary system glycerol + water have been studied at 25 °C. Accurate mutual diffusion coefficients have been measured by the Taylor dispersion and Gouy interferometric techniques. Intradiffusion coefficients of both components have been measured by the pulsed gradient spin−echo−Fourier transform NMR technique. The collected diffusion coefficients have been combined with data of water excess chemical potential present in the literature to calculate the velocity correlation coefficients. The results have been interpreted in terms of molecular interactions.

Diffusion Coefficients for the Binary System Glycerol + Water at 25 °C. A Velocity Correlation Study

Opposite effect of urea and some of its derivatives on water structure

http://geo1.tcu.edu/annunziata/1999_JCIS_02.pdf

Transport Properties for Aqueous Sodium Sulfonate Surfactants.

Intradiffusion coefficients, D , of n -alkyltrimethylammonium bromides [CH 3 –(CH 2 ) n −1 –N(CH 3 ) 3 Br, C n TAB] ( n =6, 8, 10, 12) in mixtures with heavy water were measured by the PGSE–NMR technique at 25°C. The experimental data permitted evaluation of the influence of the alkyl chain length on the surfactant self-aggregation process. For all the surfactants considered, the D trend showed a slope change corresponding to the critical micellar composition (cmc). In the premicellar composition range, D decreased linearly with the square root of the surfactant molality. The D values extrapolated at infinite dilution were related to the limiting mutual diffusion coefficients, determined through the Taylor dispersion technique. In the micellar composition range, solubilized tetramethylsilane (TMS) molecules were used to determine the micelle intradiffusion coefficient, D M , from which the aggregate radii and the aggregation numbers were obtained. The decreasing trend of D M with increasing surfactant molality was interpreted in terms of interparticle electrostatic repulsion. D M values allowed evaluation of the Gouy–Chapman layer thickness. The solvent intradiffusion coefficient in the heavy water–C n TAB mixtures, D w , was also measured. It decreased with increasing surfactant molality. For n =8, 10, 12 the D w trend presented a slope change at the cmc, which could be ascribed to the strong decrease in hydration of surfactant molecules upon micellization. Because of its short hydrophobic tail, C 6 TAB exhibited peculiar aggregation behavior. Its cmc, which is poorly marked, is lower than the value predicted by extrapolating the cmc values obtained for the other terms of the series. The C 6 TAB aggregates do not solubilize TMS molecules; the estimated aggregation number is extremely low (∼3). Finally, no abrupt slope change in the solvent intradiffusion coefficient trend was detected. This evidence suggests that C 6 TAB molecules do not micellize in aqueous solution, but form trimers in which the surfactant hydrophobic tails are not hidden from contact with water molecules.

Vincenzo Vitagliano

Papers

Complexes between DNA and polyamines: a molecular model

Diffusion Coefficients for the Binary System Glycerol + Water at 25 °C. A Velocity Correlation Study

Opposite effect of urea and some of its derivatives on water structure

Transport Properties for Aqueous Sodium Sulfonate Surfactants.

Transport Properties of Aqueous Solutions of Alkyltrimethylammonium Bromide Surfactants at 25°C