Hydrophobic interactions definition

Salt Effects. The definition of a capacity factor k in hydrophobic interaction chromatography is analogous to the distribution coefficient, in gel permeation chromatography ... 

Although the fact that the cycloamyloses include a variety of substrates is now universally accepted, the definition of the binding forces remains controversial. Van der Waals-London dispersion forces, hydrogen bonding, and hydrophobic interactions have been frequently proposed to explain the inclusion phenomenon. Although no definitive criteria exist to distinguish among these forces, several qualitative observations can be made. 

K generally varies only by factors of three to five for a given solute (12). K typically correlates well with physico-chemical properties of the sorbate, such as aqueous solubility (S) or the octanol-water partition coefficient (K ), again suggesting that hydrophobic interaction predominates. The correlation of Koc with K has led to the definition of linear free-energy relationships (LFER) of the form... 

The ICD of the dyes bound to saccharides through an ionic coupling or hydrophobic interaction may remain a conflicting problem. The side-chain chromophores covalently bound to saccharides permit CD bands in the far or near ultraviolet region. These side-chain chromophores can exhibit CD and thus provide more definitive information on the conformation of saccharide moieties. Thus, acetamide CD has been observed to reflect polymer secondary structure of glycosaminoglycans, which are the connective-tissue proteoglycans. 

The structure of living cells depends very much on the covalent bonds within individual molecules and on covalent crosslinks that sometimes form between molecules. However, weaker forces acting between molecules and between different parts of the same molecule are responsible for many of the most important properties of biochemical substances. These are described as van der Waals forces, electrostatic forces, hydrogen bonds, and hydrophobic interactions. In the discussion that follows the thermodynamic quantities AH, AS, and AG will be used. If necessary, please see Chapter 6 for definitions and a brief review. 

There are other novel media with characteristics similar to functionalized membranes. Some of the commercially available media are listed in Table 2. These materials in many cases are at the cross-lines of definitions and are frequently compared in the MA literature. Organic separations in the reserve-phase (RP) and hydrophobic interaction chromatography (HIC) mode are not very common on filtration-based MA materials. However, the methacrylate copolymers can be used for this purpose. Also rodlike monolithic materials enable greater flexibility in these types of chemistry.13,14 The method of Tennikova and Svec15-17 has been used to commercialize a novel disk type separation media, called CIM (Convective interaction media, BIA, Ljubljana, Slovenia).18-21 Analytical-scale separations can be performed on... 

Table VI shows a progression in the intramolecular hydrophobic interaction between two rings. In diphenyl, additivity holds. In di-phenylethane, which has some conformational freedom, there is a small but quite definite interaction. In the tricyclic Compound 3, the rings are held at a definite angle to one another, with no possibility for rotation. Adding log F values for N-methylaniline and toluene, and making a correction for cyclic methylene groups, we obtain an estimate far greater than the experimental log F value.

In RmL the analysis of the structural features of the lid is simplified by the availability of structures of both native and complexed molecules this allows for clear identification of the mobile fragments. The lid is created by a long surface loop made up by residues 80—109. This fragment defies a classical definition of an H loop (Leszczynski and Rose, 1986) in that it exhibits well-defined secondary structure in its central helical fragment. Residues 82-96 (which include a short helix) directly obscure the entrance to the active site in the native enzyme. It is notable that between Arg-80 and Val-95 this fragment is not involved in any hydrogen bonds with any other parts of the molecule. Thus, the lid interacts with the main body of the protein only through hydrophobic interactions. 

The appearance of CMC s for polysoaps bearing particularly short hydro-phobic tails [193] is rather a semantic problem as these examples do not match the original definition of polysoaps anymore. If the hydrophobe tails are too short, no intramolecular aggregation can take place as evident from viscosity measurements [24, 133, 193], and intermolecular aggregation is needed to reduce hydrophobic interactions. 

A simple example is one where the hydrophobic interactions result in < i for all > 1, but the packing constraints on the chains and heads result in a minimum energy for a finite value of N = M (i.e., m < for N Af). (Below, a curvature energy model is discussed this model can also be used to motivate, but not to calculate in detail, a study of micellar sizes and shapes.) If this minimum is deep n rises sharply compared to ksT around N = Af), the distribution of micelles will be nearly monodisperse. In this approximation, one can consider monomers and micelles of aggregation number Af only. At small values of 4>s (or equivalently, at small values of fi). Pi Pm (Af > 1) almost all the surfactant exists as monomers and the number of micelles is exponentially small. The requirement that all amphiphiles have the same chemical potential in equilibrium, Eq. (8.2) and the definition of the CMC (where Pi = Pi, Pm = Pmc ft = = c) allows us to calculate... 

Before this chapter is concluded, the question raised at the outset is to be answered. That is, whether or not one can reasonably attribute the nonpolar affinity of water-swollen hydrophilic gels to the hydrophobic interaction. The answer depends on the definition of the hydrophobic Interaction if it is defined as "any favorable nonpolar interaction in aqueous media", then the answer is "yes". It is further concluded that this nonpolar affinity stems from the intrinsic nonpolar affinity of the monomeric residues that is markedly enhanced in the gels by a cooperative mechanism involving the water/solute/gel matrix interactions. 

The perspectives provided by Lehn s supramolecular chemistry (3,7) and Cram s host/guest complexation (4) do indeed broaden the realm of coordination chemistry, but the focus still remains on a molecular coordination entity. On the other hand, the coordination polyhedron has lost its pivotal position in the broad definition of coordination chemistry. Furthermore, all manner of intermolecular interactions and interacting pairs are included, and the forces included range from van der Waals and subtle hydrophobic interactions through strong covalent bonds. Coordination chemistry demands only that the molecular entities that unite to form the complex still be recognizable substructures within the complex (6). It is particularly instructive, at this point, to examine examples of coordination entities formed by various modes of interaction that were not recognized in traditional coordination chemistry. 

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