Search

Doping nematic liquid crystals with nonracemic chiral compounds induces a twisted nematic (cholesteric) phase. The ability of solutes to twist the nematic phase may be related to the overall shape of the chiral dopant and consequently to its absolute configuration. The cholesteric induction is therefore a powerful tool complementary to chiroptical techniques to obtain stereochemical information on chiral molecules.

The lipophilic guanosine derivative 1 acts as a self-assembled ionophore and, in the presence of alkali metal ions, forms chiral polymeric structures in organic solvents. These polymeric columnar aggregates are comprised of G-quartets held together by alkali metal ions which are located inside the tubular structure; the quartets are surrounded by hydrocarbon chains. In hydrocarbon solvents, these columnar aggregates form lyomesophases of the cholesteric and hexagonal type. Chirality 13:7–12, 2001. © 2000 Wiley-Liss, Inc.

Temperature-dependent studies on the diastereoselective nucleophilic addition of n- BuLi to α-chiral aldehydes as (S)-O-(t-butyl-dimethylsilyl)lactal, (S)-O-(t-butyl-dimethylsilyl) mandelic aldehyde, and (R)-2-phenylpropanal in n-decane and n-dodecane reveal dynamic solvation phenomena with the presence of inversion temperatures (Tinv) in the Eyring plots of ln (anti/syn) vs. 1/ T. These dynamic solvent effects were disclosed by temperature-dependent studies of the 13C NMR, CD, and UV spectra of the starting aldehydes in solution of n-decane and n-dodecane. The concomitant presence of three peculiar temperatures TCD, TUV, and TNMR, whose values are identical and match Tinv, clearly confirms our earlier interpretation of the solvent-dependent nature of Tinv. The inversion temperature, as well as TCD, TUV, and TNMR represents the interconversion temperature of two different solvation clusters which act as two different supramolecules with different stereoselectivities. Chirality 16:50–56, 2004. © 2003 Wiley-Liss, Inc.

The lipophilic guanosine derivative 1 acts as a self-assembled ionophore and, in the presence of alkali metal ions, forms chiral polymeric structures in organic solvents. These polymeric columnar aggregates are comprised of G-quartets held together by alkali metal ions which are located inside the tubular structure; the quartets are surrounded by hydrocarbon chains. In hydrocarbon solvents, these columnar aggregates form lyomesophases of the cholesteric and hexagonal type. Copyright 2000 Wiley-Liss, Inc.