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.

On the conformational stability of globular proteins - the effects of various electrolytes and nonelectrolytes on the thermal ribonuclease transition

Publisher Summary This chapter discusses the process of isolation, chromatography, structure, and molecular and catalytic properties of bovine pancreatic ribonuclease. At present there are three simple and widely used chromatographic procedures: (1) Hirs base their method on the carboxyl ion exchange resin IRC-50 with 0.2 M phosphate buffer pH 6.45 as the eluting medium. The principal active component of the enzyme preparation is well retarded and is universally referred to as ribonuclease-A. Several poorly resolved faster running peaks are usually seen, the area having the highest activity and running closest to A normally being called ribonuclease B. The ratio of A to B varies with the preparation but may be as high as 10 to 1. (2) Taborsky has described a system based on carboxymethyl cellulose as the exchanger operated in Tris buffer at pH 8 with a sodium chloride gradient. The excellent and adjustable resolution of this system is frequently useful. The principal peak, labeled D by Taborsky, is indistinguishable from ribonuclease-A in the IRC-50 system. (3) Crestfield found chromatography on sulfoethyl Sephadex valuable. Ribonuclease-A may develop heterogeneity during lyophilization and storage. Aggregation appears to occur. A careful study of the preparation problem has been made by Crestfield by using chromatography on Sephadex G-75, and sulfoethyl Sephadex C-25 as well as IRC-50. These authors recommended that RNase-A be stored as a solution in phosphate buffer at –20°C, that salts be exchanged by dialysis or pre-equilibrated Sephadex columns, and that concentration, if necessary, be effected by ultrafiltration. If lyophilization is necessary, it should be carried out from dilute salt-free solution to minimize aggregate formation. The aggregates can be converted to monomers by heating to 60° for a few minutes at neutral pH. The properties of the ribonuclease dimer are also discussed in the chapter.

24 Bovine Pancreatic Ribonuclease

The basis for toxicity of certain cryoprotectants: A hypothesis

According to chemical data, methanol raises the shrinkage temperature of collagen significantly more than ethanol (86° C versus 70° C). Since increase of shrinkage temperature appears desirable in tissues to be embedded in paraffin, methanol was substituted for ethanol in Carnoy's fluid. This methanol-Carnoy mixture is referred to as methacarn solution. The fixation-embedding procedure was similar to that described in the study of Carnoy fixation. Methacarn-fixed sections showed little or no shrinkage and compared well with material fixed in Carnoy's or Zenker's fluid. Myofibrils, especially in endothelial and epithelial cells, were more prominent in methacarn- than in Carnoy-fixed tissues.

Methacarn (methanol-Carnoy) fixation. Practical and theoretical considerations.

The effect of aqueous alcohol solutions on the thermal transition of ribonuclease.

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The effect of aqueous alcohol solutions on the thermal transition of ribonuclease.