SELF-RECOGNITION AND SELF-ASSEMBLY OF FOLIC-ACID SALTS - COLUMNAR LIQUID-CRYSTALLINE POLYMORPHISM AND THE COLUMN GROWTH-PROCESS

Alkaline folates in water, with or without added NaCl, form columnar m esophases; the columns are composed of a stacked array of folate tetra mers held together by Hoogsteen-type hydrogen bonds and stacking inter actions. There is a considerable difference in both the liquid crystal line polymorphism and the columnar characteristics in pure water and t hose in 1 mol L(-1) NaCl solutions. In pure water, the tetramer-tetram er interaction is weak, the columnar length changes slowly with the fo late concentration, and only the hexagonal mesophase is observed. In 1 mol L(-1) NaCl, the tetramer-tetramer interaction is stronger, a chol esteric mesophase is observed, and, even at relatively low folate conc entration, the length of the columns is significant (ca. 20 disks at t he isotropic-to-cholesteric transition). In both cases, the columns ar e finite at all concentrations investigated. The formation of a choles teric mesophase with a pitch of ca. 14 mu m indicates that the tetrame rs do not pile up in register but are rotated one with respect to the other to give a chiral column similar both to the four-stranded helix of poly(G) and to the columnar aggregates formed by homoguanylic oligo deoxynucleotides.