title: Electronic states of DNA and M-DNA studied by optical absorption.
abstract: To unveil the electronic states of divalent metal ion incorporated M-DNAs, where M is Mg, Mn, Ni, Co, or Fe, optical absorption spectra have been studied in aqueous solutions of single-stranded (SS) 30 mer DNA of poly(dA) (adenine), poly(dG) (guanine), poly(dT) (thymine), poly(dC) (cytosine), salmon-sperm DNA (B-DNA), and M-DNA. The absorption spectrum of the double-stranded (DS) B-DNA can be reproduced with the sum of the four absorption spectra of the SS oligo-DNAs in the ratio corresponding to the composition of B-DNA. This observation suggests that the interactions between complementary strands of DS DNA are negligibly weaker than the bandwidths of the optical spectra. In the metal-incorporated M-DNAs, except for Fe-DNA, the absorption spectra show no significant qualitative change from that of B-DNA. Quantitatively, however, the absorption intensity decreases by ≈ 15% uniquely in a DS poly(dA)-poly(dT) solution with adding MCl(2), while nothing happens quantitatively and qualitatively in any SS oligo-DNA and DS poly(dG)-poly(dC) solutions, suggesting some suppression of the electronic excitation only in the Adenine-M-Thymine complex. In contrast, remarkable differences have been observed in Fe-DNA, prepared with FeCl(2) and B-DNA. New absorption bands appear in the intragap energy of Fe-DNA, in addition to the suppression of the interband absorption peak of DNA at 4.8 eV. The intragap absorption is attributed to the appearance of Fe(3+) species with the same spectral feature as that of FeCl(3), that is, purely ionic Fe(3+) species. This observation suggests that FeCl(2) + B-DNA forms Fe-DNA with hydrated Fe(3+) ions with ionic bonds. Thus, it is concluded that the charge transfer from Fe(2+) to DNA has occurred in Fe-DNA and that the transferred charges are expected to be located in the nearby bases.
authors.affiliation: Department of Physics, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan.
authors.forename: Makoto
authors.initials: M
authors.lastname: Tsuburaya
authors.affiliation: Department of Physics, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan.
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Sakamoto
authors.affiliation: Department of Physics, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Mizoguchi
mesh_terms: D065638:Absorption, Radiation; D003198:Computer Simulation; D004247:DNA / Q000737:chemistry* / Q000648:ultrastructure*; D004579:Electron Transport; D008027:Light; D008670:Metals / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D013057:Spectrum Analysis / Q000379:methods*
chemical_list: D008670:Metals; D004247:DNA