Contents Hydrophobic Interactions

Sutoh and Noda154 succeeded in proving, by synthesizing block copolymers of the structure (Gly-Pro-Pro)n(Gly-Ala-Pro)m-(Gly-Pro-Pro)n, that with increasing imino add content, AS° changes to higher positive values. They do, however, not relate this to lower entropy losses of conformation but to hydrophobic interactions of the proline residues in the helical state. 

CSPs has, overall, a hydrophobic character (very similar to RP phases with C4-C8 ligands) which stems from contributions of the chiral selectors itself and (capped) linker groups (only a portion of the linkers are utilized for selector attachment) which constitutes a kind of hydrophobic basic layer on the support surface. Hence under typical RP-conditions, hydrophobic interactions between lipophilic residues of the solute and hydrophobic patches of the sorbent may be active and thus a reversed-phase like partition mechanism may be superimposed upon the primary ion-exchange process k = A rp -I- A ix). This A Rp-retention contribution may be especially important for eluents with high aqueous content. 

When the leuconitrile content was 1.0 mole %, the 1 mass % aqueous polymer solution showed Tc at 29.2 °C. Upon UV irradiation, the polymer did not show any more clear phase separation. The transmittance decreased gradually with increasing temperature above 36 °C. The absence of the phase separation behavior indicates that the hydrophobic interaction of the main chain is not strong enough to overcome the hydrophilidty of the photogenerated triphenyl-methyl cations and the polymer chain cannot shrink any further even at a higher temperature. 

Partial data on the optical rotation (57) and optical rotatory dispersion (55) of native, denatured, and renatured /3-lactamases of B. cereus suggest fairly strong hydrophobic interactions and compact folding. An a-helix content of 30%> has been proposed for the native and renatured enzyme of B. cereus 569 (55). 

Soluble glutenins Insoluble glutenins 15-35 Extractable in dilute acid or alkali (e.g., 0.05 N acetic acid) High-MW (100,000-3,000,000) complexes containing low-MW (40,000-10,000) subunits linked by disulfide bonds extra stabilization by hydrogen and hydrophobic interactions Rich in Glu, Pro, and hydrophobic amino acids, and low content of basic amino acids Glu and Asp in primarily amide form low net charge... 

After adsorption one side of the protein molecule is oriented towards the sorbent surface, turned away from the aqueous solution. As a consequence, hydrophobic parts of the protein that are buried in the interior of the dissolved molecule may become exposed to the sorbent surface where they are still shielded from contact with water. Because hydrophobic interaction between apolar amino acid residues in the protein s interior support the formation of secondary structures as a-helices and P-sheets, a reduction of this interaction destabilizes such structures. Breakdown of the a-helices and/or P-sheets content is, indeed, expected to occur if peptide units released from these ordered structures can form hydrogen bonds with the sorbent surface. This is the case for polar surfaces such as oxides, e.g. silica and metal oxides, and with sorbent retaining residual water at their surfaces. Then the decrease in ordered secondary structures leads to an increased conformational entropy of the protein. This may favour the protein adsorption process considerably.13 It may be understood that proteins having an intrinsically low structural stability are more prone to undergo adsorption-induced structural changes. 

Ammonium sulfate is frequently used as lyotropic salt to promote hydrophobic interaction. It is also known that in the presence of this salt, antibodies tend to precipitate (see Section IV.D.i) and share their water content with the solid phase with consequent association. This is a dual mechanism where each phenomenon contributes for the adsorption of the antibody on an hydrophobic resin and has been frequently used for purification of antibodies from different sources.106-109... 

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