Forces solvophobic

The solvophobic model of Hquid-phase nonideaHty takes into account solute—solvent interactions on the molecular level. In this view, all dissolved molecules expose microsurface area to the surrounding solvent and are acted on by the so-called solvophobic forces (41). These forces, which involve both enthalpy and entropy effects, are described generally by a branch of solution thermodynamics known as solvophobic theory. This general solution interaction approach takes into account the effect of the solvent on partitioning by considering two hypothetical steps. Eirst, cavities in the solvent must be created to contain the partitioned species. Second, the partitioned species is placed in the cavities, where interactions can occur with the surrounding solvent. The idea of solvophobic forces has been used to estimate such diverse physical properties as absorbabiHty, Henry s constant, and aqueous solubiHty (41—44). A principal drawback is calculational complexity and difficulty of finding values for the model input parameters. 

Entropy-related adsorption, denoted hydrophobic sorption (or solvophobic interaction) is the partitioning of nonpolar organics out of the polar aqueous phase onto hydrophobic surfaces. Fig. 5.6 shows a schematic model of forces that contribute to the sorption of hydrophobic organics, relevant to the subsurface environment. 

All of these models predict that the hydrophobic effect provides a significant driving force for the exclusion of even highly polar, charged peptides from an aqueous environment to the nonpolar environment of the RPC sorbent. According to the solvophobic model, in order to place a peptide into a mobile phase, a cavity of the same molecular dimensions must first be created. The energy required to create this cavity is related to the cohesive energy density or the surface tension of the mobile phase. Conceptually, each solvent-accessible unit... 

LC Tan, PW Carr. Revisionist look at solvophobic driving forces in reversed-phase liquid chromatography. II. Partitioning vs. adsorption mechanism in monomeric alkyl bonded phase supports. J Chromat A 775 1-12, 1997. 

It is general considered that the driving force for the self-assembly of amphiphilic molecules is a solvophobic effect, more specific in an aqueous environment, this is referred to as the hydrophobic effect. The type of aggregate morphology formed can be predicted... 

Cram DJ et al (1992) Host-guest complexation 62. Solvophobic and entropic driving forces for forming velcraplexes, which are 4-fold, lock-key dimers in organic media. J Am Chem Soc 114 7748-7765... 

Secondary binding forces are mainly classified into Coulomb forces, hydro-gen-bonding forces, van der Waals forces, charge transfer forces, exchange repulsion and hydrophobic interactions (Table 1). Besides these forces, there are other interactions such as ion-dipole and solvophobic interactions. 

Similarly, attractive forces called solvophobic interaction"28 exist when the interaction forces between solvent molecules are stronger than those between solvent and solute molecules. 

When a selective solvent is used to solubilize block copolymers, a reversible assembly may occur in order to minimize energetically unfavorable solvophobic interactions. Micelle formation requires the presence of two opposing forces, i.e., an attractive force between the insoluble blocks which leads to aggregation, and a repulsive force between the soluble blocks which prevents unlimited growth of the micelle into a distinct macroscopic phase. Micelles are stabilized in the solution due to the interaction of the soluble blocks and the solvent [23]. 

Recently, Horvath and co-workers (B9, N1) introduced the concept of a dual binding mechanism to explain the atypical behavior of some solutes under reversed-phase conditions. In addition to solvophobic forces, it is possible for solutes to interact with the free surface silanols of the silica-based hydrocarbonaceous packing material. The term silanophilic interaction has been introduced to denote a reversible binding mechanism between solute molecules and silanol groups. 

This proposed mechanism for protein separations is supported by the recent theoretical studies of Horvath ef al. (29) and Horvath and Melander (28). In these studies, the hydrophobic effect in aqueous-organic systems (termed the solvophobic theory) was used to predict the retention of peptides on a nonpolar column. These authors found that the dominant interactions were between the mobile and stationary phases and between the mobile phase and the sample molecules. The driving force in both interactions was the shielding of a nonpolar region of either the column or sample molecule from the polar aqueous phase. 

In common with other polar solutes, peptide-nonpolar stationary phase interactions can be discussed in terms of a solvophobic model. In this treatment solute retention is considered to arise due to the exclusion of the solute molecules from a more polar mobile phase with concomitant adsorption to the hydrocarbonaceous bonded ligand, where they are held by relatively weak dispersion forces until an appropriate decrease in mobile-phase polarity occurs. This process can be regarded as being en-tropically driven and endothermic, i.e., both AS and AH are positive. 

P. W. Carr, J. Li, A. J. Dallas, D. I. Likens, and L. C. Tan, Revisionst look at solvophobic driving forces in versed-phased liquid chromatography, J. Chromatogr. A... 

The driving force for the formation of the hpid bilayer structure is the amphiphiUcity of the component molecules one part of the molecule is soluble in a particular solvent while the other has a low affinity to the solvent. If this concept is extended, the use of water as a medium is not a necessary condition of bilayer structure formation. Reversed micelles are formed in organic solvents. Are bilayer structures also formed in organic solvent This is an important question regarding the fundamental nature of amphiphilicity and the abihty to extend the applicability of amphiphile assembhes to various fields. The answer to this question is yes . Some compounds with a fluorocarbon part and a hydrocarbon part can form bilayer-like assemblies in organic solvent. The fluorocarbon part has a low affinity to the organic solvent and has a solvophobic nature, hi contrast, solvophilic characteristics are exhibited by the hydrocarbon parts. As shown in Fig. 4.30, these amphiphilic molecules assemble in order to expose the solvophilic part to the solvent and to hide the solvophobic part inside the assembly. If there is a good structural balance between the solvophilic part... 

In water, however, the above contribution from EDA interactions tends to be over-ridden by solvation effects. In this solvent, solvophobic forces (see below) can provide a very favourable contribution to the free energy of association of host and guest. 

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