And hydrophobic effect

The work by Hammett and Taft in the 1950s had been dedicated to the separation and quantification of steric and electronic influences on chemical reactivity. Building on this, from 1964 onwards Hansch started to quantify the steric, electrostatic, and hydrophobic effects and their influences on a variety of properties, not least on the biological activity of drugs. In 1964, the Free-Wilson analysis was introduced to relate biological activity to the presence or absence of certain substructures in a molecule. 

Aqueous SEC is widely used for the determination of MWDs of a variety of synthetic and naturally occurring water soluble polymers, as well as for separations of small molecules. The column requirements for aqueous SEC are very demanding to eliminate ionic and hydrophobic effects. 

The binding constants between the anionic substrates and cationic micelles are large because of the combination of coulombic and hydrophobic effects so rate enhancements may be large even with dilute surfactant. There is binding with non-ionic and zwitterionic micelles despite the absence of coulombic attraction (Bunton et al., 1975). 

N-Alkylhydroxamic acid hydrolysis Methyl Violet + OH" Cl C12H25S03Na + H30+, CTABr + OH". An attempt made to separate electronic and hydrophobic effects on the micellar reaction Anionic and cationic micelles. Effect of surfactant structure examined Berndt el at., 1984 Malaviya and Katiyar, 1984... 

In the Balaban MTD approach the additional influence of electronic and hydrophobic effects is accounting for by adding e.g. and a... 

By introducing fluorine atoms to the polyenic system of retinal, the geometry, electronic properties, hydrophobicity, and absorption properties of the molecule will be modified. Thus, fluoro derivatives of retinal are useful tools to understand the interactions between retinal and opsin, especially on the level of charge and hydrophobic effects at the protein site. Moreover, fluorine atoms are probes in NMR and allow studies on model molecules of visual pigments Consequently, syntheses of mono-, di-, and trifluoro derivatives of retinal have been the subject of many investigations. 

In a parallel development, structural effects on the chemical reactivity and physical properties of organic compounds were modelled quantitatively by the Hammett equation 8). The topic is well reviewed by Shorter 9>. Hansen 10) attempted to apply the Hammett equation to biological activities, while Zahradnik U) suggested an analogous equation applicable to biological activities. The major step forward is due to the work of Hansch and Fujita12), who showed that a correlation equation which accounted for both electrical and hydrophobic effects could successfully model bioactivities. In later work, steric parameters were included 13). 

The substrate specificities for these enzyme reactions were originally based only on electronic effects of substituents 12,13) the chemical mechanism of action depending on the electron-withdrawing ability of aromatic substituents has been postulated as being expressible by biphasic Hammett plots such as Fig. 1 for the reactions of Eq. 12. Eq. 9 and 10 clearly indicate the significance not only of electronic but also of steric and hydrophobic effects. 

We can draw schematically the interaction of ammonium ions with the anionic site of acetylcholinesterase in Fig. 5 based upon Eq. 36 since the informations for the steric and hydrophobic effects of substituents do not change practically even if la is used for the analysis 26). 

Leo et al. indicated that the van der Waals volume is linearly related to hydro-phobicity for non-polar compounds expressed in terms of log P (octanol/water)66). Moriguchi et al. showed that the log P value is generally factored into two components attributable to hydrophilic effect of polar group and hydrophobic effect due to the net molar volume 67). Thus, the van der Waals volume could be a parameter related to solute-solvent interactions and partition coefficient. 

Electrostatic forces contribute a major part to the hydrophilic and hydrophobic effects which are important in the discussion of Langmuir-Blodgett films and other topics dealt with in this book. Water is the... 

Interactions of polyelectrolytes in solution and at interfaces are of predominantly Coulombic nature [27,150]. However, other interactions including dipol-di-pol, charge-transfer, and hydrophobic effects also have to be considered [27,151, 152]. Table 13 demonstrates general characteristics of interactions of polycations with oppositely charged species which can be applied to PDADMAC. 

Simulations of Alkanes in Water Hydration Numbers and Hydrophobic Effect. 

When amphipathic molecules (i.e. molecules with distinct hydrophilic and hydrophobic sections) are dispersed in water, association colloids or micelles are formed above a certain critical concentration, the critical micelle concentration (CMC). The stability of these micelles depends on the nature of the hydrophilic and hydrophobic effects. A high CMC value indicates rapid exchange of the constitutive... 

The process of particle collision is governed by physical factors such as diffusion, temperature, fluid shear, particle and fluid density, and the size of particles and aggregates. Whether particles will adhere when they collide is considered to be a function of conditions at the interface between the two solid particles and the fluid medium. Chemical interactions at the solid-liquid interface are responsible for the development of surface charge and potential, the electric diffuse layer, and hydration and hydrophobic effects which determine the probability of particle attachment. 

Amphiphilic compounds — Compounds that possess both a hydrophilic and a hydrophobic part. Examples are carbonic acids, having a hydrophobic alkyl chain and a hydrophilic carboxyl group, lecithins, lipids, and many other organic compounds. See also -> hydrophilicity, and -> hydrophobic effect. 

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