Hydrophobic-polar

Each amino acid has atoms in common, and these form the main chain of the protein. The remaining atoms form side chains that can be hydrophobic, polar, or charged. 

Hydrophobic bonds, or, more accurately, interactions, form because nonpolar side chains of amino acids and other nonpolar solutes prefer to cluster in a nonpolar environment rather than to intercalate in a polar solvent such as water. The forming of hydrophobic bonds minimizes the interaction of nonpolar residues with water and is therefore highly favorable. Such clustering is entropically driven. The side chains of the amino acids in the interior or core of the protein structure are almost exclusively hydrophobic. Polar amino acids are almost never found in the interior of a protein, but the protein surface may consist of both polar and nonpolar residues. 

Factors that affect the accessibility of chemicals to plant roots include hydrophobicity, polarity, sorption properties and solubility. In order to apply phytoremediation techniques to soils polluted by organic contaminants, the contaminant must come into contact with the plant roots and be dissolved... 

Hydrophobic polar surfaces, adsorption of ionic surfactants on, 24 140-141 Hydrophobic precipitated silica, 22 399 Hydrophobic solvents, 16 413 Hydrophobic surfaces, 1 584-585... 

Homology modelling is not an exact technique. Especially, when the extent of sequence homology (exact matches and matches between amino acid residues of similar property, e.g. hydrophobic, polar, acidic, basic) is low, then more attention will be paid to structural rather than sequence similarities and to prediction of structure for unmatched sequences. In such cases, and always when there is no crystal structure of a member of the family to provide a template, then total reliance has to be placed on the experience of the investigator or in one of the many computer programs now available. The principal methods have been reviewed by Sternberg (1986) and Blundell et al. (1987a). 

A membrane is usually seen as a selective barrier that is able to be permeated by some species present into a feed while rejecting the others. This concept is the basis of all traditional membrane operations, such as microfiltration, ultrafiltration, nanofil-tration, reverse osmosis, pervaporation, gas separation. On the contrary, membrane contactors do not allow the achievement of a separation of species thanks to the selectivity of the membrane, and they use microporous membranes only as a mean for keeping in contact two phases. The interface is established at the pore mouths and the transport of species from/to a phase occurs by simple diffusion through the membrane pores. In order to work with a constant interfacial area, it is important to carefully control the operating pressures of the two phases. Usually, the phase that does not penetrate into the pores must be kept at higher pressure than the other phase (Figure 20.1a and b). When the membrane is hydrophobic, polar phases can not go into the pores, whereas, if it is hydrophilic, the nonpolar/gas phase remains blocked at the pores entrance [1, 2]. 

ProtScale tool of ExPASy computes amino acid scale (physicochemical properties/parameters) and presents the result in a profile plot. Perform ProtScale computations to compare the hydrophobicity/polarity profiles with %buried resi-dues/%accessible residues profiles for human serine protease with the following amino acid sequence. 

Just as for cubic phases, the rod description of the R phase is an approximation to a hyperbolic surface. The smooth surface that defines the hydrophobic-polar interfaces resembles mesh surfaces containing a hexagonal array of pores. The genesis of this phase can also be understood as a resolution of the requirement for quasi-homogeneous interface. 

Lipophilicity can be factorized in two main terms as [Carrupt et al, 1997] lipophilicity = hydrophobicity - polarity... 

Fig. (12). (A) Hydrophobic/polar surface. (B) Potential surface describing the average positive and negative surface charge. The C-terminus is at the bottom. The two images on the right side of panels A and B are obtained by 180° rotation around the axis indicated in the center of the figure. Reprinted with permission from [151]. Copyright (2006) American Chemical Society.

The adsorption of ionic surfactants onto hydrophobic polar surfaces resembles that for carbon black [24,25]. For example, Saleeb and Kitchener [24] found a similar limiting area for cetyltrimethyl ammonium bromide on Graphon and polystyrene ( 0.4nm ). As with carbon black, the area per molecule depended on the nature and amount of the added electrolyte. This can be accounted for in terms of the reduction in head group repulsion and/or counterion binging. 

The 20 amino acids capable of appearing in various microstructural combinations of sequence lengths, and total molecular lengths, allow assembly of an infinite number of distinct proteins [57]. The side chain R may be hydrophobic, polar, acidic, or basic. The structure of the amino acid is given in Fig. 5. 

The interactions between the amino acids and the solvent (electrostatic, hydrophilic, hydrophobic, S-S) determine the globular conformation. We can give some naive picture of the folded state in terms of a liquid-hydrocarbon model where the hydrophobic core stabilizes globular proteins. The hydrophilic (polar and charged) amino acids are exposed to the solvent and the hydrophobic (polar) amino acids are less exposed to the solvent and buried in the interior of the protein. 

To obtain reliable QSRR, appropriate input data and stringent statistical analysis must be conducted. An important point to be emphasized here is that when QSRR are built from MEKC data, a physicochemical model for the solute-micelle interaction must be established before any statistical processing takes place. Therefore, considering that the intermolecular interactions responsible for solute retention are hydrophobic, polar, and specific in character, only the descriptors able to account for these interactions must be preselected. 

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