Bis-8-hydroxyquinoline-armed diazatrithia-15-crown-5 and diazatrithia-16-crown-5 ligands: possible fluorophoric metal ion sensors.

The synthesis and preliminary photophysical properties of a series of diazatrithia-15-crown-5 and diazatrithia-16-crown-5 ligands containing two 8-hydroxyquinoline sidearms are reported. The ligands were prepared by a two-step process. First, diazatrithiacrown ethers 11 and 12 were prepared by treating bis(alpha-chloroamide) 5 with various dimercaptans followed by reduction using a boron-THF complex. Hydroxymethyl-substituted macrocycle 12 was rearranged to hydroxy-substituted diazatrithia-16-crown-5 in refluxing aqueous HCl. Macrocyclic diamines 11-13 were converted to either 5-chloro-8-hydroxyquinolin-7-ylmethyl-substituted diazatrithiacrown ethers 14-16 by a Mannich aminomethylation reaction or to 8-hydroxyquinolin-2-ylmethyl-substituted diazatrithiacrown ethers 17-19 by reductive amination using 8-hydroxyquinoline-2-carboxaldehyde. Preliminary photophysical studies show that ligands 16 and 19 exhibit increased fluorescence in the presence of Zn(2+), indicating that these ligands could be chemical sensors for Zn(2+).

Reversed-phase liquid chromatography of proteins and peptides using multimodal copolymer-encapsulated silica.

Multimodal copolymer-encapsulated particles for liquid chromatography were prepared by bonding 1-octadecene and unsaturated carboxylic acids on silica particles (5 microm diameter, 300 A pores) for liquid chromatography of proteins. These multimodal copolymer-encapsulated particles can provide both hydrophobic and hydrogen bonding interactions with polar compounds. The chromatographic performance of these multimodal copolymer-encapsulated particles for peptide and protein separations was evaluated under reversed-phase conditions. Compared with typical C8-bonded silica, polymer-encapsulated particles were more stable in acidic mobile phases and provided better recoveries, especially for large proteins (Mr>0.5 x 10(6)). Totally hydrophobic polymer-encapsulated particles were found to produce broad peaks for proteins, and significant improvements were observed by introducing hydrophilic groups (-COOH) onto the polymer-encapsulated surface to form a multimodal phase. For the reversed-phase liquid chromatography of peptides and proteins, improved selectivity and increased solute retention were found using the multimodal polymer-encapsulated particles. More peaks were resolved for the separation of complex peptide mixtures such as protein digests using the multimodal polymer-encapsulated particles as compared to totally hydrophobic polymer-encapsulated particles.

Semipreparative scale enantioseparation of racemic amine and amino ester hydrogen perchlorate salts using a silica gel-bound optically active di-tert-butylpyridino-18-crown-6 ligand.

We report herein results on the enantioseparation of selected racemic amine and amino ester hydrogen perchlorate salts using a silica gel-bound optically pure chiral di-tert-butylpyridino-18-crown-6 ligand (R,R)-1. The effect of solvent composition was studied using appropriate binary and ternary solvent mixtures as eluents. We found that acetonitrile/ methanol/ dichloromethane (MeCN/MeOH/CH2 Cl2 ) ternary solvent mixtures gave better enantioseparations for the racemic salts using chiral stationary phase (R,R)-1 than any of the binary ones. In the present paper we also describe the studies of chromatographic parameters such as loading, flow rate and eluent polarity.

Characterization of chiral host-guest complexation in fast atom bombardment mass spectrometry.

A new method has been developed for the characterization of complexion between host and guest molecules. Adduct formation between chiral crown ethers 1 and 2 and enantiomeric ammonium ions 4 and 5 was examined. The reference compound 3 (achiral host) was chosen to be similar in structure to the chiral crown ethers for quantitative measurements. Our approach is based on a formalism assuming an equilibrium: [chiral host + H](+) + [achiral host + chiral guest](+) ⇌ [chiral host + chiral guest](+) + [achiral host + H](+). The equlibrium constant for this process was calculated using the relative peak intensities of the corresponding species in the FAB mass spectra. It was found that these provide significantly better reproducibility and more reliable results than the relative peak intensity method described before (Sawada, M.; et al. J. Am. Chem. Soc. 1992, 114, 4405; 1993, 115, 7381; Org. Mass Spectrom. 1993, 28, 1525).(1)(-)(3) In the examples studied, the equilibrium constants corresponding to the formation of heterochiral adducts (S,S-R or R,R-S) were higher than those for the formation of homochiral aggregates (S,S-S or R,R-R).