Complex, Dynamic Behavior of Extremely Asymmetric Di-n-Alkylphosphate-Anion Aggregates, the Long-Chain Effect and the Role of a Limiting Size: Cryo-TEM, SANS, and X-Ray Diffraction Studies.

For extremely asymmetric n-hexyl(n-decyl)phosphate (HDeP), n-hexyl(n-dodecyl)phosphate (HDoP), and n-hexyl(n-cetyl)phosphate (HCeP), the effect of the long-chains on the dynamic behavior of their aggregate structures in water was examined by cryo-TEM imaging, SANS, and X-ray diffraction techniques. The cryo-TEM images demonstrated the complex and dynamic behavior of the aggregates, and its dependence on the length of the long-chain. Application of the one-dimensional aggregate theory to the SANS results led to the conclusion that the existence of a limiting size also depended on the length of the main long-hydrocarbon chain and affected strongly the dynamic behavior of the aggregates, causing breakage of thread-like micelles or ribbon-like aggregates. The X-ray diffraction patterns of the lyotropic liquid crystalline samples of HDeP and HCeP were used to estimate the aggregate structures of this limited size.

The role of an L-leucine residue on the conformations of glycyl-L-leucine oligomers and its N- or C-terminal dependence: infrared absorption and Raman scattering studies.

The conformations of glycyl-L-leucine oligomers (GnL, residue number n = 3, 4, and 5) in the solid state were found to be similar to that of a polyglycine II (PGII). However, for L-leucyl-glycine oligomers (LGn; n = 3, 4, 5) in the solid state, LG3 and LG4 have already been confirmed to take a reverse-turn structure (LG3-type reverse-turn) while LG5 adopts a PGII-type helix. The present results provide evidence that the conformations of L-leucine-containing glycine oligomers depend strongly upon whether the L-leucine residue is placed in the N- or C-terminal position. For the aqueous G3L and G4L samples, we assumed that reverse-turn structures similar to the type II ß-turn, rather than the LG3-type reverse-turn, are stabilized in concentrated solution, probably as the result of aggregation. Models to explain the mechanism of these phenomena are presented.

Aggregate structures of asymmetric di-alkyl phosphate anions and the role of conformations about the polar region: SANS, cryo-TEM, Raman scattering, 13C NMR, and selective NOE studies.

The aggregate structures of two di-n-alkyl-phosphate anions (di-n-alkyl: n-butyl(n-dodecyl)(BDoP) and n-hexyl(n-dodecyl)(HDoP)) in water were studied by the use of SANS, cryo-TEM, Raman scattering, (13)C NMR, and selective NOE ((1)H{(1)H}) techniques. The results of SANS indicated that the different -CH(2)- lengths of the short chain led to a marked difference in the aggregational behavior of BDoP and HDoP. Cryo-TEM added direct images to support the average aggregation size and shape predicted by the SANS analyses. Raman scattering, (13)C NMR, and selective NOE results provided further evidence that variation of molecular conformations strongly contributed to variation in the shape of the aggregates. In particular, selective NOE was a powerful technique for investigating the dynamic structures of the hydrocarbon chains during growth of the micelles.

Concentration-resolved 2D correlation gel permeation chromatography study of aggregate-aggregate interactions in the polymerization products of triethoxysilyl-terminated polystyrene silane-coupling agent.

Concentration-resolved 2D correlation gel permeation chromatography (GPC) has been used to examine the intricate details of the HCl-catalyzed polymerization of a polymeric silane-coupling agent (SCA), triethoxysilyl-terminated polystyrene (TESiPS). The concentration-resolved 2D correlation GPC maps directly reflect the marked difference in the aggregate-aggregate interactions of dilute and concentrated monomeric units, which govern the differences in the polymerized products. There is an optimum concentration of SCA for the enhancement of interfacial strength and subsequent polymerization. Thus, the concentration-resolved 2D correlation GPC technique can be used as a powerful tool for elucidation of aggregate-aggregate interactions and reaction mechanisms in a surface- or interface-enhanced reaction system. It has been shown that the yield value of polymerization products can be improved to a marked extent by choosing a high initial monomer concentration, due to the increase in the production of oligomers. Multiple reaction processes are promoted by the self-assembly of the monomeric and oligomeric components.

Folded structures of L-leucylglycine oligopeptides and their aggregational behavior in aqueous solution: Raman scattering spectra and proton NMR spin-lattice relaxation studies.

The aggregational behavior of three L-leucylglycine oligopeptides (residue numbers of glycine are 3, 4, and 5) in aqueous solution was investigated by the use of Raman scattering and 1H NMR spin-lattice relaxation methods. The results indicate that their oligopeptides take up a folded structure to form dimeric aggregates above their critical aggregation concentration. The application of one-dimensional aggregate theory to these systems provides the following prediction. Elongation up to 6 glycine residues makes it possible to form dimeric aggregates, but further elongation (up to 7 glycine residues) makes the aggregates very unstable, and up to 8 or 9 glycine residues makes the formation of dimeric aggregates very difficult. The one-dimensional aggregate theory may be used to predict the existence of peptide aggregates through intermolecular hydrogen bonding.

Fourier transform IR study of aggregational behavior of N-acetyl-L- and N-butyloxycarbonyl-L-glutamic acid oligomeric benzyl esters in dioxane and benzene: beta-turn --> antiparallel beta-sheet transition.

Oligomeric N-acetyl-L-glutamic acid benzyl esters (AN(p)Z) with exact residue numbers (N(p) = 2, 3, 4, and 5) and N-butyloxycarbonyl-L-glutamic acid benzyl esters (BOCN(p)Z) with exact residue numbers (N(p) = 4, 5, 6, and 8) are synthesized by a stepwise procedure in a liquid phase. The aggregational behavior of these oligomeric molecules in dioxane and benzene is examined by Fourier transform IR spectra. In particular, the concentration dependence of the IR spectra for the AN(p)Z solutions with N(p) values of 4 (A4Z) and 5 (A5Z) shows that the predominant antiparallel beta-sheet structure is stabilized above the critical aggregation concentration (cac), while other conformations including beta-turns may coexist below the cac. This fact provides evidence that aggregation induces the conformational transition from other conformers (probably beta-turns) to an antiparallel beta-sheet form. The IR results for the A3Z and A2Z solutions indicate that specific conformers (beta-turns), which are different from the beta-sheet structure, may be preferentially stabilized upon aggregation. Thus, the critical residue number of the AN(p)Z oligopeptides, which is essential for formation of a rodlike aggregate in dioxane and benzene, is 4 or 5.