The conformation of polycytidylic acid, polyguanylic acid, polyinosinic acid, and their helical complexes in aqueous solution from laser Raman scattering

✍ Scribed by Kenneth G. Brown; Ernest J. Kiser; Warner L. Peticolas

• Publisher: Wiley (John Wiley & Sons)
• Year: 1972
• Tongue: English
• Weight: 797 KB
• Volume: 11
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.1972.360110907

✦ Synopsis

Abstract

The Raman spectra of the double helical complexes of poly C–poly G and poly I–poly C at neutral p^H^ are presented and compared with the spectra of the constituent homopolymers.

When a completely double‐helical structure is formed in solution a strong sharp band at 810–814 cm^−1^ appears which has previously been shown to be due to the A‐type conformation of the sugar–phosphate backbone chain. By taking the ratio of the intensity of the 810–814 cm^−1^ band to the intensity of the 1090–1100 cm^−1^ phosphate vibration, one can obtain an estimate of the fraction of the backbone chain in the A‐type conformation for both double‐stranded helices and self‐stacked single chains. This type of information can apparently only be obtained by Raman spectroscopy.

In addition, other significant changes in Raman intensities and frequencies have been observed and tabulated: (1) the Raman intensity of certain of the ring vibrations of guanine and hypoxanthine bases decrease as these bases become increasingly stacked (Raman hypochromism), (2) the Raman band at 1464 cm^−1^ in poly I is asigned to the amide II band of the cis‐amide group of the hypoxanthine base. It shifts in frequency upon base pairing to 1484 cm^−1^, thus permitting the determination of the fraction of I–C pairs formed.