The Effects of Cobalt-Hexammine and Cobalt-Pentammine Cations on the Solution Structure of Calf-Thymus DNA. DNA Condensation and Structural Features Studied by FTIR Difference Spectroscopy

Abstract

The interaction of calf-thymus DNA with cobalt-hexammine and cobalt-pentammine cations was investigated, in aqueous solution at pH 6-7 with cation/DNA(phosphate) molar ratios r = 1/80, 1/40, 1/20, 1/10, 1/4, 1/2 and 1, using Fourier Transform infrared (FTIR) difference spectroscopy. Correlations between spectral changes, DNA condensation and helical stabilization due to the cation interaction as well as conformational features are established. At a very low cation concentration (r = 1/80), the binding of cobalt-hexammine cation with DNA is through the H-bond formation between cation NH3 groups and the PO2 groups of the backbone, resulting in duplex stability. As the cation concentration increases, hydrogen bonding expands towards guanine N-7 and O-6 atoms. At r > 1/20, DNA condensation occurs with major reduction in the intensity of several DNA in-plane vibrations and that of the phosphate group. The cobalt-pentammine cation binding is via the PO2 groups (directly) at very low metal cation concentration (r = 1/80) and the guanine N-7 and the O-6 groups (indirectly) at higher ratios. At r > 1/10, DNA condensation begins with some degree of direct cation-base binding. No major conformational changes from the B-family structure were observed before and after DNA collapse, in the presence of cobalt-ammine cations.

An FTIR Spectroscopic Study of Calf-thymus DNA Complexation with Al(III) and Ga(III) Cations

“…The aggregation of partially melted DNA by metal ions via cation cross-linking was observed for several divalent metal-DNA complexes ( 40). Similar structural changes were also observed for DNA, upon trivalent cation complexation (41)(42)(43). Since the spectra of the AI-DNA complexes with r= 112 could not be recorded in solution (due to solid gel formation), it is rather difficult to predict if similar structural changes occur by AI cation at r= 1/2.…”

Gold and colloidal gold surface influence on dna conformational change

“…Divalent transition metal causes deviation from the canonical B-form in the backbone and base vibrations [2933,36]. Essential change in DNA conformation has been registered by trivalent cations such as Eu, La, Tb, as well as cobalt hexamine and cobalt pentamine [34,35]. A partial conversion of the B-DNA form into Z-DNA form has been observed in some abovementioned cases [35,37].…”

“…Essential change in DNA conformation has been registered by trivalent cations such as Eu, La, Tb, as well as cobalt hexamine and cobalt pentamine [34,35]. A partial conversion of the B-DNA form into Z-DNA form has been observed in some abovementioned cases [35,37]. In our experiment, the DNA conformation induced by colloidal gold has showed the features of A and B-form with some amount of Z-conformation and its spectroscopic features are close to condensed DNA.…”

Attraction between DNA molecules mediated by multivalent ions

“…Experimental evidence of such an attraction is seen for deoxyribose nucleic acid (DNA) molecules [1][2][3][4], colloidal rods [5], charged clay particles [6], charged microspheres [7][8][9], and charged plates [10,11]. In particular, DNA molecules in solution are a paradigm for negatively charged polyelectrolytes due to ionization of its acidic phosphate groups [12].…”