Stability self-association

A (macro)emulsion is formed when two immiscible Hquids, usually water and a hydrophobic organic solvent, an oil, are mechanically agitated (5) so that one Hquid forms droplets in the other one. A microemulsion, on the other hand, forms spontaneously because of the self-association of added amphiphilic molecules. During the emulsification agitation both Hquids form droplets, and with no stabilization, two emulsion layers are formed, one with oil droplets in water (o /w) and one of water in oil (w/o). However, if not stabilized the droplets separate into two phases when the agitation ceases. If an emulsifier (a stabilizing compound) is added to the two immiscible Hquids, one of them becomes continuous and the other one remains in droplet form. 

Stability of anthocyanins can be attained by self-association, that is, when two or more anthocyanin molecules are associated. This effect was verihed by increasing the concentration of the cyanidin 3,5-diglucoside solution from 10 M to 10 M with a consequent bathochromic shift in maximum wavelength absorption in the visible region. "... 

An anthocyanin occurs in solution as a mixture of different secondary structures, a quinonoidal base, a carbinol pseudobase, and a chalcone pseudobase. ° hi addition, different mechanisms for the stabilization of anthocyanins lead to the formation of tertiary structures such as self-association, inter-, and intra-molecular co-pigmentation. ... 

Leon, O. Rogel, E. Espidel, J., and Torres, G., Asphaltenes Structural Characterization, Self-Association, and Stability Behavior. Energy Fuels, 2000. 14 pp. 6-10. 

Buurman P, van Lagen B, Piccolo A. Increased in stability against thermal oxidation of soil humic substances as a result of self association. Org. Geochem. 2002 33 367-381. 

Physical properties of the protein structure should be considered in designing strategies to achieve stable formulations because they can often yield clues about which solution environment would be appropriate for stabilization. For example, the insulin molecule is known to self-associate via a nonspecific hydrophobic mechanism66 Stabilizers tested include phenol derivatives, nonionic and ionic surfactants, polypropylene glycol, glycerol, and carbohydrates. The choice of using stabilizers that are amphiphilic in nature to minimize interactions where protein hydrophobic surfaces instigate the instability is founded upon the hydro-phobic effect.19 It has already been mentioned that hydrophobic surfaces prefer... 

This reduction in self-aggregated AmB and the stability of the formulation suggested that LC-AmB could be a useful pharmaceutical formulation because it is generally accepted that the origin of toxicity toward mammalian cell membranes is free, self-associated AmB (2). 

One factor determining toxicity of AmB formulations is the form in which the antibiotic is released monomeric or aggregated because only self-associated AmB can complex cholesterol in eukaryote membranes (25). The differential toxicity of the lipid formulations toward macrophages could be related to their stability in the culture medium. For example, the Ampho-liposome formulation, which is destabilized in the presence of serum (24), has... 

The influences at work on these interactions have been discussed in two important papers (80JOC1347, 80JOC1354). It is found that influences of media can be expressed in terms of two effects, differential stabilization of the different dipoles of the two tautomeric species by the dielectric constant of the medium, the dipole reaction field and by differential hydrogen bonding. For self-association pyridin-4-one is shown to form oligomers, in contrast to the well-known dimerization of pyridin-2-ones. This self-association can shift the position of apparent tautomeric equilibrium (hence the warnings previously noted about effect of concentration on Kr). 

In biological recognition phenomena, protein-protein interactions are of primary importance. In an attempt to mimic these processes, LaBrenz and Kelly [51] synthesized the peptidic host 64. In this receptor, the dibenzofuran template separates the two peptide units by roughly 10 A and allows for the complexation of a guest peptide (65), as depicted in Fig. 21. The complex first forms a three-stranded, antiparallel /J-sheet that is stabilized by hydrogen bonds, electrostatic interactions, and aromatic-aromatic interactions between the dibenzofuran and the benzamide moieties. This complex can further self associate to form more complex structures. This example shows that structurally defined peptide nanostructures can interfere with biological recognition processes and potentially have therapeutic applications. 

Several laboratories have described systems by which synthetic linear peptide chains self-assemble into desirable secondary and tertiary structures. One self-assembly approach has been the creation of a peptide-amphiphile, whereby a peptide head group has the propensity to form a distinct structural element, while a lipophilic tail serves to align the peptide strands and induce secondary and tertiary structure formation, as well as providing a hydrophobic surface for self-association and/or interaction with other surfaces. The preparation of a dialkyl ester tail first involves the acid-catalyzed condensation of H-Glu-OH with the appropriate fatty acid alcohol to form the dialkyl ester of H-Glu-OH a typical example is shown in Scheme 7. The assembly of peptide-amphiphiles with mono- and dialkyl ester tails is shown in Scheme 8. A series of studies have demonstrated that triple-helical and a-helical protein-like molecular architecture is stabilized in the peptide-amphiphile 44,63-65 ... 

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