Reactivity hydrophobic interaction

Pairwise hydrophobic interactions can be used to alter the reactivity of organic molecules in water. For instance, the rate of hydrolysis reactions may be influenced significantly by the presence of hydrophobic cosolutes. The effect on reactivity has been analysed by comparirg the interactions between initial state and cosolute with those between transition state and cosolute. ... 

Besides the electrostatic potential effect on reactivity, functionalized polyelectrolytes have a variety of interesting features worthy of study. If a polyelectrolyte is covalently modified with highly hydrophobic functional groups, it provides an unusual opportunity to study the chemical reactions of normally otherwise water insoluble functional groups in aqueous solution. Furthermore, a structural organization via hydrophobic interactions may occur in aqueous solution [25 — 31], which is of general scientific importance and is worth studying for its own sake. 

The chemical adsorption of a relatively high molecular weight neutral polymer (poly(succinimide), M = 13000) on aminopropyl-Vydac 101 TP silica gel was applied by Alpert [47, 48] to prepare a reactive composite support for use in cation-exchange [47] and hydrophobic-interaction [48] chromatography of pro-... 

Water has physical hemical properties that are very different from those of other solvents [1] and its role in enhancing the reactivity and selectivity of some organic reactions is still a debated question. Recent experimental studies [3e, 9] and computer simulations [10] seem to indicate, at least with respect to the rate enhancement of aqueous Diels Alder reactions, that the main effects are due to the enforced hydrophobic interactions and hydrogen bond interactions. 

The R groups of the non-polar, alipathic amino acids (Gly, Ala, Val, Leu, lie and Pro) are devoid of chemically reactive functional groups. These R groups are noteworthy in that, when present in a polypeptide s backbone, they tend to interact with each other non-covalently (via hydrophobic interactions). These interactions have a significant stabilizing influence on protein conformation. 

The influence of metal ions on the aggregation of Cl Reactive Red 2 (3.14) in aqueous solution at various pH values has been examined in detail recently [18]. Sodium ions have a profound effect on these disulphonated dye anions, so that the enhancement of substantivity during the dyeing process is accompanied by aggregation attributable to hydrophobic interaction between the phenyl and s-triazine ring systems. Aggregation is much greater,... 

These results suggests that stronger hydrophobic interactions between the aromatic end-group of 27 and the P-CD cavity are favoring the 1 1 inclusion complex with the central double bond just under the reactive 0 = Ru = 0 center. In contrast, 1, 25 and 26 slide within the CD cavity exposing three double bonds rather than one to the reactive Ru = 0. Determination of the binding constant of 27 to the receptor 10 supports this interpretation, i.e., (27-10) — 5.0 x... 

Extrinsic fluorescence is used whenever the natural fluorescence of a macromolecule is inadequate for accurate fluorescence measurement. In this case, one can attach a fluorescent reporter group by using the reactive isocyanate or isothiocyanate derivatives of fluorescein or rhodamine, two intensely fluorescent molecules. One can covalently also label a protein s a- and e-amino groups with dansyl chloride (/.e., A,A-dimethylaminonaphtha-lenesulfonyl chloride). Another useful reagent is 8-ani-lino-l-naphthalenesulfonic acid (abbreviated ANS). This compound is bound noncovalently by hydrophobic interactions in aqueous solutions, ANS is only very fluorescent, but upon binding within an apolar environment, the quantum yield of ANS becomes about 100 times greater. 

PVP(DP 98)-Co(Ilf) > PVP(DP 19)-Co(III) > N-ethylimidazole-Co(III) - pyridine-Co(III), and this order agrees with that of the reactivity. The hydrophobic interaction between polymer ligands and Fe(II)(phen)3 is considered to account for the higher reactivity of the polymer complexes. 

Murakami et al. studied alternative pyridoxamine-surfactant systems [23]. These authors synthesized hydrophobic pyridoxamine derivatives (30 and 31) and peptide lipid molecules (32-35). Catalyst 30 or 31 and the peptide lipids formed bilayer membranes in water, which showed transamination reactivity in the presence of metal ions such as Cu(ii). It was proposed that the pyridoxamine moiety was placed in the so-called hydrogen-belt domain interposed between the polar surface region and the hydrophobic domain that is composed of double-chain segments within the bilayer assembly. The basic group (such as imidazole) in the peptide lipid molecules could catalyze the proton transfer involved in the transamination reaction. In addition, marked substrate discrimination by these bilayer membrane systems was performed through hydrophobic interactions between substrates and the catalytic site. 

There is another phenomenon, regarded as a deteriorative change in the protein of soy milk, caused also by the evaporation of water. This is a film formation on the surface of soy milk, which occurs when heated soy milk is kept open to the air. This phenomenon is observed not only in heated soy milk but also in heated cow s milk. Film formation of soy milk occurs only when the soy milk is heated above 60°C and there is evaporation of water from the surface of the soy milk. The mechanism of protein insolubilization is basically the same as that of soy milk powder produced from heated soy milk (10. When water is removed from the surface of heated soy milk by evaporation, the molecular concentration of protein near the surface increases locally and the exposed reactive groups of the denatured molecules come close enough to interact intermolecularly both by hydrophobic interactions and through the sulfhydryl/disulfide interchange reaction to form a polymerization (film) on the surface. The upper side of the film contains more hydrophobic amino acids because of orientation of the hydrophobic portions of the unfolded molecules to the atmosphere rather than into the aqueous solution. 

---