Optical anisotropy of synthetic polynucleotides. I. Flow birefringence and π-electron polarizabilily of bases

✍ Scribed by Shiro Takashima

• Publisher: Wiley (John Wiley & Sons)
• Year: 1968
• Tongue: English
• Weight: 719 KB
• Volume: 6
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.1968.360061007

✦ Synopsis

Birefringence of poly-A, poly-U, and double-stranded poly-AU are investigated experimentally as well as theoretirally. Single-stranded poly-A, a t low ionic strength, exhibits a strong negative birefringenre indicating that adenine molecules are stacked regularly with their planes along the transverse direction. On the addition of Mg or Mn ions, the birefringence decreases markedly. Poly-U has no noticeable birefringenre indicating that poly-U has a contracted configuration in solution. 0 1 1 mixing poly-A and poly-U with l W 3 N MgCl,, the l)irefri!igence increases markedly, but the change in the chain configuration seems less proiiounced. The polarizability of adenine and uracyl are claculated using the simple liuckel scheme. The calculation shows that the x-electron polarizability normal to the base plane is zero. Therefore, the negative birefringence is probably due to the lack of x-electron polarizability in the direction normal to the base plane and accordingly 110 x-electron polarizability along the major helix axis. Conversely, the negative birefringence is an indiactioii of base st,:ickiiig.