Design of chemically modified oligonucleotides for regulation of gene expression has attracted considerable attention over the last decades. One actively pursued approach involves antisense or antigene constructs carrying reactive groups, many of these based on transition metal complexes. The complexes of Co(II) with phthalocyanines are extremely good catalysts of oxidation of organic compounds with molecular oxygen and hydrogen peroxide. In this study, we have investigated the kinetics and thermodynamics of sequence-specific modification of DNA with deoxyribooligonucleotide linked to Co(II)-tetracarboxyphthalocyanine (PtcCo(II)) in the presence of H(2)O(2).