Raman spectroscopic study on low‐frequency collective modes in self‐associates of guanosine monophosphates

Abstract

Abstract Low‐frequency Raman spectra of the self‐associates of guanosine monophosphates (GMPs) Na 2 · 5′GMP, K 2 · 5′GMP, Na 2 · 3′GMP, and K 2 · 3′GMP, and polyribonucleic acid K · poly(rG), were obtained. In acidic gels and dried fibers, GMP molecules are known to form helical stacks of hydrogen‐bonded tetramers. Some low‐frequency collective modes specific to the helically stacked structures were observed. We examined the dependence of these modes on counterions and water content. The lowest frequency mode at ca. 20 cm −1 is sensitive to the water content of the sample and is clearly visible in solid‐state samples, so it works as a marker band of the environmental condition of the helices. The intensity and the peak frequency of this mode in solid‐state samples depend on the helical structure and counterions. The broad peaks in the vicinity of 100 cm −1 are influenced by cations and are independent of water content.