Self-association, prevention

In the linear konjac mannan, the degree of acetylation profoundly affects the solubility and flow properties of this hydrocolloid. The acetyl substitution prevents self-association of the mannan chains, but following deacetylation chain interactions become more energetically favorable [230]. 

The self-association and/or complex formation of organozinc componnds involves considerable rehybridization of the zinc valence orbitals. When only one coordinate bond is formed, the zinc atom becomes sp -hybridized and the resnlting complex is planar or nearly so with bond angles around the zinc of abont 120°. The zinc centre then still has one unoccupied valence orbital and remains coordinatively nnsatnrated. Three-coordinate zinc, however, is relatively rare and only occurs when steric crowding around the zinc prevents the approach of a fourth ligand. 

Due to the preference for a cis-amide bond[93] with the preceding residue of C2-substituted pseudoprolines, their incorporation results in a kink conformation of the peptide backbone, thus preventing peptide aggregation, self-association, or (3-structure formation. 

Polymeric micelle formation occurs as a result of two forces. One is an attractive force that leads to the association of molecules while the other one, is a repulsive force, preventing unlimited growth of the micelles to a distinct macroscopic phase (Price, 1983 AstaLeva et al., 1993 Jones and Leroux, 1999). Amphiphilic copolymers form micellar structures through self-association of the insoluble segments when placed in a solvent that is selective for the other monomer (Kataoka et al., 1993 Jones and Leroux, 1999). The process of micellization for amphiphilic copolymers is similar to the process described for conventional hydrocarbon chain-based surfactants as described in the Lrst part of this chapter. 

Prevents premature self association during diffusion from bacteria to host cells... 

Studies on host-guest peptides have shown that incorporation of a proline residue into peptides which have a high tendency to fold into ordered secondary structures disrupts the onset of helical as well as P-sheet conformations and increases solubility and coupling rates.f Based on this observation, serine- and threonine-derived oxazolidine, and cysteine-derived thiazolidine derivatives (pseudoprolines) were proposed as valuable tools for combining protection of their side-chain functions with the simultaneous solubilization of the peptide chain. Due to the induction of kink conformations in the peptide backbone, originating from the preference of these pseudoproline residues to adopt the cis-imide bond configuration, insertion of such derivatives into peptides prevents self-association and P-structure formation. 

Some proteins self-associate in aqueous solution to form oligomers. Insulin, for example, exists in several associated states the zinc hexamer of insulin is a complex of insulin and zinc which dissolves slowly into dimers and eventually monomers following its subcutaneous administration, so giving it long-acting properties. In most cases, however, it is desirable to prevent association such that only monomeric or dimeric forms are present in the formulations and a more rapid absorption is achieved. Recent studies have been directed towards engineering insulin molecules which are not prone to association, " or the prevention of association through the addition of surfactants. Protein self-association is a reversible process, i.e. alteration of the solvent properties can lead to the re-formation of the monomeric native protein. There is an important distinction between this association... 

The formation of solvent shells around molecules is essential to prevent self-association of the solute species and to allow solution to take place. Solvents other than water which have high dielectric constants, and including some of the dipolar aprotic solvents (defined below), dissolve ionic species by separating and solvating the ions. 

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