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.

F. Vinyl Sulfones and Other Michael Acceptors 4683 G. Azodicarboxamides 4695 IV. Acylating Agents 4695 A. Aza-peptides 4695 B. Carbamates 4699 C. Peptidyl Acyl Hydroxamates 4700 D. â-Lactams and Related Inhibitors 4704 E. Heterocyclic Inhibitors 4714 1. Isocoumarins 4715 2. Benzoxazinones 4722 3. Saccharins 4725 4. Miscellaneous Heterocyclic Inhibitors 4728 V. Phosphonylation Agents 4728 A. Peptide Phosphonates 4728 B. Phosphonyl Fluorides 4734 VI. Sulfonylating Agents 4735 A. Sulfonyl Fluorides 4735 VII. Miscellaneous Inhibitors 4736 VIII. Summary and Perspectives 4737 IX. Acknowledgments 4740 X. Note Added in Proof 4740 XI. References 4740

Irreversible inhibitors of serine, cysteine, and threonine proteases.

Cysteine Proteases and Their Inhibitors.

Preparation, characterization, solution properties and rheological behaviour of polyacrylamide

In polymer science and technology, linear, branched and crosslinked structures are usually distinguished. For crosslinked polymers, insolubility and lack of fusibility are considered as characteristic properties. However, insoluble polymers are not necessarily covalently crosslinked because insolubility and infusibility may be also caused by extremely high molecular masses,strong intermolecular interaction via secondary valency forces or by the lack of suitable solvents. For a long time, insolubility was the major obstacle for characterization of crosslinked polymers because it excluded analytical methods applicable to linear and branched macromolecules. In particular, the most important structural characteristic of crosslinked polymers, the crosslink density, could mostly be determined by indirect methods only [1],or was expressed relatively by the fraction of crosslinking monomers used in the synthesis.

Microgels-Intramolecularly Crossünked Macromolecules with a Globular Structure

Crosslinked poly(acryloylmorpholines) have been prepared in bead form by suspension polymerization of N-acryloylmorpholine and N,N′-methylenediacrylamide, respective molar ratios 10/1, in aqueous solution dispersed in liquid paraffin. The swelling properties of beads of two porosities, designated Enzacryl Gel K1 and Enzacryl Gel K2, were measured in a range of common solvents. Gels derived by swelling in both chloroform and tetrahydrofuran were evaluated as column packings for gel permeation chromatography. For Enzacryl Gel K1 and polystyrene solutes, molecular weight exclusion limits of approximately 4 × 103 and 6 × 102 were observed in chloroform and tetrahydrofuran, respectively. In the case of Enzacryl Gel K2, the corresponding exclusion limits were 104 and 5 × 103. Molecular weight fractionation ranges for both polystyrenes and polyethylene glycols are discussed in terms of gel structure.

Crosslinked poly(acryloylmorpholines) as matrices for gel permeation chromatography

1. Chymotrypsin is inactivated by N -acetyl-α-azaphenylalanine phenyl ester (phenyl N 2 -acetyl- N 1 -benzylcarbazate) in a stoicheiometric reaction. 2. The inactivation is reversible spontaneously (first-order rate constant is 1.2×10 -4 s -1 ) and accelerated by the presence of hydroxylamine. 3. Polymers based on polyacrylamide and carrying ligands containing the α-azaphenylalanine phenyl ester group were prepared. 4. Chymotrypsin reacts with these polymers and is removed by them from solution. Trypsin reacts less rapidly. 5. Chymotrypsin is slowly released from the polymer spontaneously and more rapidly on treatment with hydroxylamine. 6. The reaction of trypsin can be inhibited by competitive inhibitors. 7. Chymotrypsin was separated from trypsin by the selective bonding of chymotrypsin on to and its subsequent liberation from one of the polymers described.

J.V. McLaren

Papers

Crosslinked poly(acryloylmorpholines) as matrices for gel permeation chromatography

The reaction of an α-aza-amino acid derivative with chymotrypsin and its use as a ligand for covalent affinity purification

Water-insolubilisation of glycoside hydrolases with cross-linked poly(acryloylaminoacetaldehyde dimethyl acetal) (Enzacryl Polyacetal).

Phenolic poly(acryloyl morpholine)-based bead matrix for solid (gel) phase peptide synthesis

Synthesis and characterization of poly(acryloyl morpholine) xerogel networks suitable for the gel permeation chromatography of small molecules