DNA Complexes with Cobalt(II) Phthalocyanine Disodium Disulfonate

Nina A Kasyanenko; Roman A Tikhomirov; Vladimir M Bakulev; Viktor N Demidov; Elena V Chikhirzhina; Eugenia B Moroshkina

doi:10.1021/acsomega.9b02300

DNA Complexes with Cobalt(II) Phthalocyanine Disodium Disulfonate

ACS Omega. 2019 Oct 3;4(16):16935-16942. doi: 10.1021/acsomega.9b02300. eCollection 2019 Oct 15.

Authors

Nina A Kasyanenko¹, Roman A Tikhomirov¹, Vladimir M Bakulev¹, Viktor N Demidov², Elena V Chikhirzhina³, Eugenia B Moroshkina¹

Affiliations

¹ Faculty of Physics, Saint Petersburg State University, Universitetskaya emb., 7-9, Saint Petersburg 199034, Russia.
² Pro-Brite Company, 93, Sofiyskaya st., Saint Petersburg 192289, Russia.
³ Institute of Cytology RAS, Tikhoretsky avenue, 4, Saint Petersburg 194064, Russia.

Abstract

The interaction of cobalt phthalocyanine disodium disulfonate (CoPc) with calf thymus DNA in solutions was investigated by UV/vis spectrophotometry, circular dichroism (CD), and hydrodynamic methods (viscosity and flow birefringence). Two types of CoPc binding to DNA were observed. Fast CoPc interactions with DNA via external binding to phosphates were accompanied by the formation of stack-type phthalocyanine structures on the periphery of the DNA helix. The optical absorption spectra of such CoPc complexes with DNA were analyzed in order to obtain a binding constant K = (4.8 ± 0.4) × 10⁴ M^-1. CD spectra show the increasing optical activity of phthalocyanines bonded to DNA. DNA plays the role of a matrix, contributing to an increase in their stacking interactions. The CD spectrum of DNA varies slightly. The second type of cobalt-to-DNA binding manifests itself over a certain time. It can be associated with the reorganization of ligands in the cobalt coordination sphere by introducing DNA atoms. In our experiments, such binding was observed after storage of solutions for approximately 20 h at a temperature of 4 °C. It was shown that the minor groove of DNA remains free in CoPc-DNA complexes. CoPc does not bind with the most important group for metal coordinating to DNA in the major groove (N7 guanine). We completely excluded the intercalation binding model. The planes of phthalocyanines in CoPc-DNA complexes are oriented predominantly normal to the axis of the DNA helix. DNA rigidity (persistent length) does not change. This follows from the data on the measurement of the optical anisotropy and intrinsic viscosity of DNA in complexes.