The chemical trapping toolbox: Exploring ion binding with a rigid gemini surfactant, investigating weak hydrogen bonding, and demonstrating amide bond cleavage.

摘要

The chemical trapping method, based on the heterolytic chemistry of 4-alkyl-2,6-dimethylbenzenediazoniurn ions, 16-ArN2+ (4-hexadecyl) and 1-ArN2 + (4-methyl), is used to probe: the relationship between micellar properties, head group structure and counterion in gemini surfactants with a rigid imidazolidinium head group; the ion binding properties of their short chain analogs and the distributions of halide ions around their short chain analogs in the solid state; and to develop a new method for analyzing one of the cleavage products from reaction of 16-ArN2+ with peptide bond models.; Chapter 2 describes the use of 16-ArN2+ to determine halide ion concentration at micellar interfaces composed of rigid cis-N,N'-dimethyldidodecylimidazolidinium gemini surfactants with Cl - and Br- counterions, 12-Im-12 2X (X = Cl, Br), to examine whether they also undergo a sphere-to-rod transition. This is compared with the flexible 12-2-12 2Br gemini surfactants which undergo the transition. Surprisingly, both imidazolidinium surfactants had interfacial counterion concentrations that are about 20 times below that of the gemini analog.; Chapter 3 describes the use of single crystal X-ray diffraction to solve for the structures of the short chained N,N,N',N'-tetramethylimidazolidinium dihalide salts, 1-Im-1 2X (X = Cl, Br, I). The crystal structures show that the dicationic imidazolidinium ring conformation and the positions of the halide ions around the 1-Im-1 ring are about the same for all three halide ions, but the arrangements of the ions in the unit cell are different. A number of halide ions are within the van der Waals radii sum of C-H bonds and X -, which is consistent with the presence of weak hydrogen bonds. The presence of weak hydrogen bonds is supported by IR signals of the crystals in fluorolube and in D2O solutions.; Chapter 4 shows that dediazoniation of 16-ArN2+ in micellar solutions of N-dodecanoyl phenylalanine gives products from trapping the amide carbonyl group followed by hydrolysis to give an ester and phenylalanine. A method was developed to monitor the formation of phenylalanine by derivatization with danzyl chloride. The approach is applicable to any amino acid product and to the analysis of the fragments from cleavage of peptide bonds in the interfacial regions of membrane mimetic aggregates.