Interaction lyophobic

The four terms that need discussion are (1) "hydrophobic interactions", (2)"lyophobic interactions", (3)"hydrophilic interactions" and (4) "lyophilic interactions". 

The term lyophobic interactions is intended to generalize the expres sion hydrophobic interactions to other solvents than water. Hydro-phobic interactions have been prominently implicated in determining the native configuration of proteins in aqueous solution. These interactions are actually not of a single relatively well-defined character, as are electrostatic or hydrogen bond interactions, but are rather a set of interactions responsible for the immiscibility of nonpolar substances and water. Proteins contain a substantial proportion of amino acids such as phenylalanine, valine, leucine, etc., with nonpolar side-chain residues. These nonpolar groups should tend, therefore, other factors permitting, to cluster on the... 

The sum of these AF , S AF , taken over all the nonpolar residues found in typical protein molecules, can attain very large negative values. If the native conformation of a protein molecule in aqueous solution is indeed in considerable part stabilized by lyophobic interactions, it follows that this stabiUzation should be substantially if not completely lost on transferring the protein molecule to almost any pure nonaqueous solvent. This destabilization might be expected to be less extensive in those few weakly protic nonaqueous solvents with which hydrocarbons are only partially miscible, such as glycerol, ethylene and propylene glycols, and formamide, than in the other solvents with which hydrocarbons are completely miscible. Furthermore the latter solvents should be very little differentiated under these circumstances, since AFt is so similar for most of them. As is demonstrated subsequently, these expectations are closely realized in fact. 

It is an oversimplification, of course, to correlate lyophobic interactions in a solvent-protein system solely with the solubility of simple hydrocarbons in the solvent. There are many other kinds of groups besides hydrocarbon ones in protein molecules and the influence of altered solvent environment on such groups must also be considered. In this connection, systematic... 

In these relatively simple polypeptide systems, therefore, the experimental studies so far performed suggest at least a crude correlation between the capacity of a solvent to disrupt polypeptide helices and the capacity of a solvent to form strong hydrogen bonds, although in special cases electrostatic and lyophobic interactions also appear to be involved. There is little apparent correlation whth any other independent property of the solvents. 

While such lyophobic interactions must be weaker in ethylene glycol solution than in water, they should be considerably stronger in ethylene glycol, which is still only slightly miscible with hydrocarbons, than in nonaqueous solvents such as ethanol or dioxane, which are completely miscible with hydrocarbons at 25°C (see Section IV,B,3). It is therefore... 

A marked decrease, compared to water, in lyophobic interactions towards the nonpolar residues of the protein. Of the common strongly protic liquids, only hydrofluoric acid, formic acid, and hydrazine are not completely miscible with simple hydrocarbons, while the others, such as ethylenediamine, dichloroacetic and trifluoroacetic acids, are completely miscible with them. Even in the cases of hydrofluoric acid, formic acid, and hydrazine, the solubility of hydrocarbons is much greater than in water. Thus, a satmated solution of benzene in formic acid at 25°C contains 0.088 mole fraction of benzene, compared to 0.00035 mole fraction of benzene in water (see Section IV,B,3 and Table IV). 

Dispersion forces are those that occur between hydrocarbons and other substances that have either no permanent dipoles or can have no dipoles induced in them. In biotechnology and biochemistry, dispersive interactions are often referred to as hydrophobic or lyophobic interactions, apparently because dispersive substance such as the aliphatic hydrocarbons do not dissolve readily in water. To a first approximation, the interaction energy Ud) involved with dispersive forces has been deduced to be... 

In the case of appreciable specific adsorption, i.e., if the adsorption is due largely to metal-/ interactions rather than lyophobic interactions with the solvent, changes of solvent will mainly modify filb Better solvents for i will lower the energy filb and diminish the magnitude of the standard free energy of adsorption. In cases where the adsorption arises mainly from lyophobic interactions, better solvation of / in the bulk will usually have a similar effect, since at the interface it is coordinated only by about half the number of solvent molecules that coordinate / in the bulk phase. Since for a given pure solute (chemical potential fil) in saturation equilibrium with its saturated solution ... 

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