Molecular orientation of gel forming compounds and their effect on molecular-shape selectivity in liquid chromatography.

Double-alkylated glutamic acid and aminoadipic acid derived gel systems (G1 and G2) have been prepared and then grafted onto silica particles. Gel-forming compounds-grafted silica particles (Sil-G1 and Sil-G2) were then applied for the liquid chromatographic separation of shape-constrained isomers of polycyclic aromatic hydrocarbons (PAHs) and tocopherols as stationary phases. G1 and G2 were analyzed before and after immobilization onto silica. Elemental analysis and thermogravimentric analysis (TGA) results showed almost the same amounts of organic phases were grafted in Sil-G1 and Sil-G2 phases. However, chromatographic results showed large differences of molecular-shape selectivity between the stationary phases. Little change in the chemical structures of the gel-forming compounds can change the molecular orientation as well as drastic change in molecular recognition in liquid chromatography. Molecular orientation of the functional groups affected the interaction mechanism for the separation of shape-constrained isomers. Comparison of the shape selectivity of Sil-G1 and Sil-G2 phases with other commercial columns is also described.

Functionalization of methyl orange using cationic peptide amphiphile: colorimetric discrimination between ATP and ADP at pH 2.0.

A solvatochromic and non-fluorescent acid-base indicator, methyl orange (MO) was applied to colorimetric discrimination between adenosine triphosphate (ATP) and the corresponding diphosphate (ADP) at pH 2.0 in the presence of L-glutamic acid-derived cationic peptide amphiphile 1. This method is based on the fact that the amphiphile 1 can prevent MO from protonation even at pH 2.0. No similar colour change was observed when ADP was added instead of ATP under the same conditions. The effect of the molecular structure of several peptide amphiphiles and dyes was also investigated.

Molecular structural requirements, dye specificity, and application of anionic peptide amphiphiles that induce intense fluorescence in cationic dyes.

We have previously reported that a double-chain anionic amphiphile capable of intermolecular triple hydrogen bonds could form extremely hydrophobic sites in water and specifically incorporated stilbazolium-based compact hemicyanine dyes as monomeric species, resulting in induction of intense fluorescence emission in the dyes. In this paper, the structural requirements of the intense fluorescence-inducing amphiphiles were investigated. It is noted that the introduction of beta-Ala residues into two long-chain alkyl group moieties was most effective for the amphiphiles derived from L-glutamic acid with relatively shorter side-chain methylenes. The dye specificity in terms of induction of the intense fluorescence was also investigated using hemicyanines (stilbazolium etc.), cyanine, carbocyanine, thiacarbocyanines, and azo dye. The amphiphile with the shortest octanoyl-beta-alanyl double-chain alkyl groups, longer side-chain, and shorter spacer was found to show increased sensitivity to alkali metal ions, especially Li(+). This could be a potential OFF-ON type fluorescence sensor for Li(+).

Formation of specific dipolar microenvironments complementary to dipolar betaine dye by nonionic peptide lipids in nonpolar medium.

This paper describes the host-guest interaction between nonionic peptide lipids and solvatochromic dipolar betaine dyes in nonpolar aprotic organic solvent. We have serendipitously found that the colour of Reichardt's Dye (referred to as ET(30) hereafter, although the term ET(30) has been used as a polarity parameter) in chlorobenzene unusually blue-shifted in the presence of L-glutamic acid-derived peptide lipid 1 with a benzyloxycarbonylated Gly headgroup. Since it is widely accepted that ET(30) shows negative solvatochromism, i.e., the visible absorption band of this dye blue-shifts as the solvent polarity increases, the blue-shift indicates that ET(30) was in contact with the more polar microenvironment produced by the peptide lipid 1 rather than chlorobenzene under aggregate-free conditions. The binding site was assumed to be N-H(delta+) and CO(delta-) attached to both sides of the Gly residue, respectively, i.e., the O- and N+ of ET(30) complementarily bound to N-H(delta+) and CO(delta-) through hydrogen bonding and ion-dipole interaction, respectively. Since ET(30) is practically non-fluorescent, it was not feasible to use fluorescence spectrometry, which is a powerful method for the study of host-guest interactions, in order to specify the binding mode of ET(30). Therefore, a synthetic approach, although very laborious but reliable, has been used in conjunction with solvatochromic probing using visible absorption spectroscopy to specify the binding site on peptide lipid 1. The binding site has been found to be located on two dipoles, i.e., N-H(delta+) and CO(delta-) attached to both sides of the Gly residue, respectively, because introducing steric hindrance into the Gly moiety using several L-alpha-amino acids with bulky -substituents interfered with the binding of ET(30). Similar specific binding behaviour of ET(30) was observed by replacing the Gly residue of the lipid 1 with sarcosine (Sar). It was found that self-assembly of the peptide lipid was necessary for effective capture of ET(30). The molecular structural requirements of the peptide lipids that form such specific polar microenvironments complementary to dipolar betaine dyes have also been investigated.

Intense fluorescence-inducing amphiphile in cationic dyes and its applicability.

An anionic amphiphile has been found to form extremely hydrophobic sites in water and specifically incorporate stilbazolium-based compact hemicyanine dyes as monomeric species, resulting in induction of intense fluorescence emission.

Novel self-assembling organogelators by combination of a double chain-alkylated L-glutamide and a polymeric head group.

This communication introduces a new class of self-assembling organogelators composed of a double chain-alkylated L-glutamide with a polymeric head group.