Opposite effect of urea and some of its derivatives on water structure
01 May 1970-The Journal of Physical Chemistry (American Chemical Society)-Vol. 74, Iss: 10, pp 2230-2232
About: This article is published in The Journal of Physical Chemistry.The article was published on 1970-05-01. It has received 91 citations till now. The article focuses on the topics: Urea.
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TL;DR: 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 is proposed; this mechanism suggests a simple model for the behaviour of water at all interfaces, regardless of whether the non-aqueous component is neutral or charged, polar or non-polar.
Abstract: 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
1,468 citations
TL;DR: The mechanism of denaturation of proteins by urea is explored by using all-atom microseconds molecular dynamics simulations of hen lysozyme generated on BlueGene/L and shows that water molecules are expelled from the first hydration shell of the protein.
Abstract: The mechanism of denaturation of proteins by urea is explored by using all-atom microseconds molecular dynamics simulations of hen lysozyme generated on BlueGene/L Accumulation of urea around lysozyme shows that water molecules are expelled from the first hydration shell of the protein We observe a 2-stage penetration of the protein, with urea penetrating the hydrophobic core before water, forming a "dry globule" The direct dispersion interaction between urea and the protein backbone and side chains is stronger than for water, which gives rise to the intrusion of urea into the protein interior and to urea's preferential binding to all regions of the protein This is augmented by preferential hydrogen bond formation between the urea carbonyl and the backbone amides that contributes to the breaking of intrabackbone hydrogen bonds Our study supports the "direct interaction mechanism" whereby urea has a stronger dispersion interaction with protein than water
492 citations
TL;DR: It is shown by molecular dynamics simulations that a 7 M aqueous urea solution unfolds a chain of purely hydrophobic groups which otherwise adopts a compact structure in pure water, and that urea forms stronger attractive dispersion interactions with the protein side chains and backbone than does water and, therefore, is able to dissolve the core Hydrophobic region.
Abstract: For more than a century, urea has been commonly used as an agent for denaturing proteins. However, the mechanism behind its denaturing power is still not well understood. Here we show by molecular dynamics simulations that a 7 M aqueous urea solution unfolds a chain of purely hydrophobic groups which otherwise adopts a compact structure in pure water. The unfolding process arises due to a weakening of hydrophobic interactions between the polymer groups. We also show that the attraction between two model hydrophobic plates, and graphene sheets, is reduced when urea is added to the solution. The action of urea is found to be direct, through its preferential binding to the polymer or plates. It is, therefore, acting like a surfactant capable of forming hydrogen bonds with the solvent. The preferential binding and the consequent weakened hydrophobic interactions are driven by enthalpy and are related to the difference in the strength of the attractive dispersion interactions of urea and water with the polymer chain or plate. This relation scales with square root(epsilon(b)), where epsilon(b) is the Lennard Jones (LJ) energy parameter for each group on the chain. Larger values of epsilon(b) increase the preferential binding and result in a larger decrease of the hydrophobic interactions, with a crossover at very weak dispersions. We also show that the indirect mechanism, in which urea acts as a chaotrope, is not a likely cause of urea's action as a denaturant. These findings suggest that, in denaturing proteins, urea (and perhaps other denaturants) forms stronger attractive dispersion interactions with the protein side chains and backbone than does water and, therefore, is able to dissolve the core hydrophobic region.
304 citations
TL;DR: Surprisingly, even at high concentrations of urea (8 M), the orientational dynamics of most water molecules are the same as in pure liquid water, showing that urea has a negligible effect on the hydrogen-bond dynamics of these molecules.
Abstract: We use polarization-resolved mid-infrared pump-probe spectroscopy to study the effect of urea on the structure and dynamics of water. Surprisingly, we find that, even at high concentrations of urea (8 M), the orientational dynamics of most water molecules are the same as in pure liquid water, showing that urea has a negligible effect on the hydrogen-bond dynamics of these molecules. However, a small fraction of the water molecules (approximately one water molecule per urea molecule) turns out to be strongly immobilized by urea, displaying orientational dynamics that are more than six times slower than in bulk water. A likely explanation is that these water molecules are tightly associated with urea, forming specific urea–water complexes. We discuss these results in light of the protein denaturing ability of aqueous urea.
183 citations
TL;DR: In this article, the effect of binding and conformational changes induced by anionic surfactants such as sodium dodecyl sulfate (SDS) and SOS on bovine serum albumin (BSA) was studied using differential scanning calorimetry (DSC), circular dichroism (CD), fluorescence and UV spectroscopic methods.
Abstract: The effect of binding and conformational changes induced by anionic surfactants sodium dodecyl sulfate (SDS) and sodium octyl sulfate (SOS) on bovine serum albumin (BSA) have been studied using differential scanning calorimetry (DSC), circular dichroism (CD), fluorescence and UV spectroscopic methods. The denaturation temperature, van't Hoff enthalpy and calorimetric enthalpy of BSA in the presence of SDS and SOS and urea at pH 7 have been determined. The results indicate that SDS plays two opposite roles in the folding and stability of BSA. It acts as a structure stabiliser at a low molar concentration ratio of SDS/BSA and as a destabilizer at a higher concentration ratio as a result of binding of SDS to denatured BSA. The Brandts and Lin model has been used to simulate the results.
179 citations