Exciton effects in dinucleotides and polynucleotides

The absorption, fluorescence emission and fluorescence excitation spectra of dinucleoside phosphates adenylyl (3′→5′) adenine (ApA), cytidylyl (3′→5′) cytidine (CpC), deoxythymidylyl (3′→5′) deoxythymidine (dTpdT) and guanylyl (3′→5′) guanine (GpG) and polynucleotides polyadenylic acid (poly-A) and polycytidylic acid (poly-C) at 77 K, and their fluorescence polarization spectra at 130 K, were studied in neutral ethylene glycol-water glasses (1:1, v/v). For ApA and CpC, the difference between the fluorescence excitation and absorption spectra of the corresponding monomers is suggested to be of exciton nature. The spectral manifestations of exciton interaction between the bases of dTpdT and GpG are weak. The fluorescence emission and excitation spectra of the polynucleotides are similar to those of the corresponding dinucleoside phosphates, which supports the conclusion that exciton interaction acts no further than two bases.