Interactions self-association, molecular

A study of the effect of substitution patterns in oxadiazoles and isoxazoles and their effect on the UV spectra in the lO -lO M concentration range was performed. Hypso-chromic effects and deviations from Beer s law were observed and were believed to be associated with antiparallel, sandwich-type self-association via dipole-dipole interactions. Beer s law is followed when the molecular dipole moments are small or when self-association is sterically hindered. 

Coacervation occurs in tropoelastin solutions and is a precursor event in the assembly of elastin nanofibrils [42]. This phenomenon is thought to be mainly due to the interaction between hydro-phobic domains of tropoelastin. In scanning electron microscopy (SEM) picmres, nanofibril stmc-tures are visible in coacervate solutions of elastin-based peptides [37,43]. Indeed, Wright et al. [44] describe the self-association characteristics of multidomain proteins containing near-identical peptide repeat motifs. They suggest that this form of self-assembly occurs via specific intermolecular association, based on the repetition of identical or near-identical amino acid sequences. This specificity is consistent with the principle that ordered molecular assembhes are usually more stable than disordered ones, and with the idea that native-like interactions may be generally more favorable than nonnative ones in protein aggregates. 

In the case of the analytes able to participate in the self-associative lateral interactions (i.e., containing at least one AB functionality in their molecular structure), the negative impact of the interactions exerted on the separation performance depends on the number of the associated monomers per one H-bonded -meric unit, and the higher the number (n) of the self-associated analyte monomers in a given aggregate, the more crippled is the separation process. 

Theories or computer simulations used to calculate the potential of mean force W(r) are typically based on numerous simplifying assumptions and approximations (de Kruif, 1999 Bratko et al., 2002 Prausnitz, 2003 de Kruif and Tuinier, 2005 Home et al., 2007 Jonsson et al., 2007). Therefore they can provide only a qualitative or, at best, semi-quantitative description of the potential of mean force. Such calculations are nevertheless useful because they can serve as a guide for trends in the factors determining the interactions of both biopolymers and colloidal particles. Thus, an increase in the absolute value of the calculated negative depth of W(r) may be attributed to a predominant type of molecular feature favouring aggregation or self-association. To assist with such a theoretical analysis, expressions for some of the mean force potentials will be presented here in the discussion of specific kinds of interactions occurring between pairs of colloidal particles covered by biopolymers in food colloids. 

In an aqueous medium these wtermolecular attractive interactions make a strong contribution to biopolymer self-association and inclusion complex formation, as well as to the flocculation of biopolymer-coated colloidal particles. // //Y/molecular hydrophobic interactions commonly influence the level of folding/unfolding of macromolecules as well as their detailed conformations. 

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 ... 

Molecular Complexes. These species are formed by noncovalent interactions between the substrate and ligand. Among the kinds of complexspecies included in this class are small molecule-small molecule complexes, small molecule-macromolecule species, ion-pairs, dimers and other self-associated species, and inclusion complexes in which one ofthe molecules, the host, forms or possesses a cavity into which it can admit a guest molecule. 

As observed for the molecular clips reported above, the chiral scaffold is pivotal in promoting homo- or heterochiral self-discrimination. Amide hydrogen bonds were implemented on helicene chiral scaffolds as well, but in this case dimerization of the monomers was characterized by homochiral enantioselective self-recognition, that is self-association between molecules with the same helicity (Fig. 17B) [44], These species dimerized in solution with association constants of 207 M 1 by means of four non-covalent bonding interactions and, in combination with the peculiar helical shape of the monomers, forms only homochiral dimers. 

In this paper, a molecular thermodynamic approach is developed to predict the structural and compositional characteristics of microemulsions. The theory can be applied not only to oil-in-water and water-in-cil droplet-type microemulsions but also to bicontinuous microemulsions. This treatment constitutes an extension of our earlier approaches to micelles, mixed micelles, and solubilization but also takes into account the self-association of alcohol in the oil phase and the excluded-volume interactions among the droplets. Illustrative results are presented for an anionic surfactant (SDS) pentanol cyclohexane water NaCl system. Microstructur al features including the droplet radius, the thickness of the surfactant layer at the interface, the number of molecules of various species in a droplet, the size and composition dispersions of the droplets, and the distribution of the surfactant, oil, alcohol, and water molecules in the various microdomains are calculated. Further, the model allows the identification of the transition from a two-phase droplet-type microemulsion system to a three-phase microemulsion system involving a bicontinuous microemulsion. The persistence length of the bicontinuous microemulsion is also predicted by the model. Finally, the model permits the calculation of the interfacial tension between a microemulsion and the coexisting phase. 

In this paper, a predictive molecular thermodynamic approach is developed to calculate the structural and compositional characteristics of microemulsions. The theory applies not only to oil-in-water and water-in-oil droplet-type microemulsions but also to bicontinuous microemulsions. The treatment is an extension of our earlier theories for micelles, mixed micelles, and solubilization but also takes into account the self-association of alcohol in oil and the volume-excluded interactions among... 

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