Formation of the Liquid Crystals of Polyribonucleotide Complexes
Double-stranded helices of poly(A) · poly(U), poly(G) · poly (C) and poly(C) · poly(I) and triple-stranded helices of poly(A) · 2poly (U) and poly(A) · 2poly(I) in concentrated solutions form nematic liquid crystals. Poly(C) · poly(I) also contains some spherulitic structures. The molecular assemblies of the two complexes of poly(A) and poly(U) are rod-like and align themselves with their long axes parallel to the direction of orientation. On standing for several weeks these two complexes are converted from the nematic to cholesteric type, which reverses to the oriented nematic crystals under shearing stresses. All the helical complexes show negative linear dichroism and strong negative birefringence. In a magnetic field the pitch of the cholesteric crystals changes with the field strength; this change also varies with the angle that the helicoidal axis of the cholesteric structure makes with respect to the magnetic field. The nematic liquid crystals of the two complexes of poly(A) and poly(U) appear to orient themselves perpendicular to the direction of a magnetic field of more than ten kilogausses.
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