Interaction of metal ions with nucleic acids and related compounds. II. Studies on Au(III)‐nucleic acid system

Abstract

SynopsisThe nature of interaction of Au(II1) with nucleic acids was studied by using methods such as uv and ir spectrophotometry, viscometry, pH titrations, and melting-temperature measurements. Au(II1) is found to interact slowly with nucleic acids over a period of several hours. The uv spectra of native calf-thymus DNA (pH 5.6 acetate buffer containing 0.01M NaC104) showed a shift in X max to high wavelengths and an increase in optical density at 260 nm. There was a fourfold decrease in viscosity (expressed as 7jgp/c). The reaction was faster a t pH 4.0 and also with denatured DNA (pH 5.6) and whole yeast RNA (pH 5.6). The order of preference of Au(II1) (as deduced from the time of completion of reaction) for the nucleic acids in RNA > denatured DNA > DNA. The reaction was found to be completely reversible with respect to KCN. Infrared spectra of DNA-Au(II1) complexes showed binding to both the phosphate and bases of DNA. The same conclusions were also arrived a t by meltingtemperature studies of Au(II1)-DNA system. pH titrations showed liberation of two hydroxyl ions at r = 0.12 [r = moles of HAuC14 added per mole of DNA-(P)] and one hydrogen ion a t r = 0.5. The probable binding sites could be N(1)/N(7) of adenine, N(7) and/or C(6)O of guanine, N(3) of cytosine and N(3) of thymine. The results indicate that Au(II1) ions probably bind to the phosphate group in the initial stages of the reaction, particularly a t low values of r , and participation of the base interaction takes place with time. As the value of r increases, participation of the base interaction also increases. Cross-linking of the two strands by Au(II1) may take place, but a complete collapse of the double helix is not envisaged. It is probable that tilting of the bases or rotation of the bases around the glucosidic bond, resulting in a significant distortion of the double helix, might take place due to binding of Au(II1) to DNA.

DNA-Templated Preparation of Gold Nanoparticles

“…Earlier, we reported the dependence electrical conductance of a DNA-Au(III) complexes on the degree of complexation and also detailed electrical properties of a DNA-Au(III) complex fiber [ 19 ]. Complexation of DNA with Au (III) was thoroughly studied in the 1970s by Nandi and coworkers [ 20 , 21 , 22 ].…”

Nanojacketing and Dejacketing of ds-DNA: A Nondestructive Characterization of a Nanojacketed Sample by Impedance Spectroscopy

“…16,19 When the HAuCl 4 is added to the system, the AuCl 4 − ions immediately interact with the phosphate groups of DNA due to its stronger affinity than OMA, producing an intermediate complex (Scheme 2) and it is probably appropriate particularly for a short time period of reaction. 65 …”

“…65 AuCl 4 − ions interact with the phosphate group at the initial stage and then it can also interact with the base pairs of DNA after a long time interval. 65 In our synthetic procedure, the polymerization starts instantaneously just after the addition of HAuCl 4 solution with simultaneous formation of AuNPs. Thus, it is reasonable to think that AuCl 4 − interacts with the phosphate groups of DNA and the so formed negatively charged Au complex electrostatically interacts with the protonated OMA present near the periphery of DNA.…”

“…At first, the monomer molecules (OMA) interact with protonated DNA and become organized around the DNA surface through a weak electrostatic interaction. , When the HAuCl 4 is added to the system, the AuCl 4 – ions immediately interact with the phosphate groups of DNA due to its stronger affinity than OMA, producing an intermediate complex (Scheme ) and it is probably appropriate particularly for a short time period of reaction . According to Pillai et al, the AuCl 4 – ions interact with the phosphate group at the initial stage and then it can also interact with the base pairs of DNA after a long time interval .…”

“…At first, the monomer molecules (OMA) interact with protonated DNA and become organized around the DNA surface through a weak electrostatic interaction. , When the HAuCl 4 is added to the system, the AuCl 4 – ions immediately interact with the phosphate groups of DNA due to its stronger affinity than OMA, producing an intermediate complex (Scheme ) and it is probably appropriate particularly for a short time period of reaction . According to Pillai et al, the AuCl 4 – ions interact with the phosphate group at the initial stage and then it can also interact with the base pairs of DNA after a long time interval . In our synthetic procedure, the polymerization starts instantaneously just after the addition of HAuCl 4 solution with simultaneous formation of AuNPs.…”