In this paper the Raman total half bandwidths of calf-thymus DNA vibrations have been measured as a function of Zn2+ions concentration, in the presence of a constant concentration of Na+ions, respectively. The dependencies of the total half bandwidths and of the global relaxation times, on DNA molecular subgroup structure and on Zn2+ions concentration, are reported. It is shown that changes in the subpicosecond dynamics of molecular subgroups in ZnDNA complexes can be monitored with Raman spectroscopy.Particularly, the Raman band parameters for the vibrations at 729 cm−1(dA), 792 cm−1(dC, dT and 5'-C–O–P–O–C-3' network), 1094 cm−1(DNA backbone PO2−symmetric stretching), 1377 cm−1(dA, dT, dC), 1489 cm−1(the guanine N-7 and adenine rings) and 1581 cm−1(dG, dA) of ZnDNA complexes, in the presence of Zn2+ions concentrations that varied between 0 and 250 mM, are presented. In our study, the full widths at half-maximum (FWHM) of the bands in calf-thymus DNA complexes are typically in the wavenumber range from 10 to 50 cm−1. It can be observed that the molecular relaxation processes studied in this work, have a global relaxation time smaller than 0.94 ps and larger than 0.21 ps. The limit values are characterizing the dA and dG residues, respectively (vibrations at 729 cm−1and 1489 cm−1).Binding of Zn2+ions to double helical calf-thymus DNA results for some vibrations in smaller global relaxation times and larger bandwidths, respectively, possible as a consequence of the increased interaction of the base moieties with the solvent molecules in unstacked structures.The fastest and the slowest dynamics for different DNA structural subgroups and different Zn2+ions concentrations, respectively, have been analyzed.A comparison between different time scales of the vibrational energy transfer processes, characterizing the ZnDNA structural subgroups has been given.We have found that metal ion's type and concentration are modulators for the (sub)picosecond dynamics of calf thymus DNA molecular subgroups.
The influence of Zn2+ions on the structure of natural calf thymus DNA was studied by Raman spectroscopy. Measurements were done at room temperature and pH 6.2±0.1, in the presence of 10 mM Na+, and of Zn2+in a concentration range varying between 0 and 250 mM, respectively. No condensation of DNA was observed.As judging from the marker bands near 681 cm−1(dG), 729 cm−1(dA), 752 cm−1(dT), and 787 cm−1(dC, dT) altered nucleoside conformations in these residues are supposed to occur, in different intervals of Zn2+ions concentration. Changes in the conformational marker centered around 835 cm−1, upon Zn2+binding to DNA, were detected. Binding of zinc(II) ions to the charged phosphate groups of DNA, stabilizing the double helical structure, is indicated in the spectra. We have found that binding of metal ions at N3 of cytosine takes place at zinc(II) concentrations between 150–250 mM and interaction of Zn2+ions with adenine is observed in a concentration range from 10 to 250 mM. Binding of zinc(II) ions to N7 of guanine and, possibly, in a lesser extent to adenine was also observed as indicated by the Raman marker bands near 1490 and 1581 cm−1. There is no intensity change of the band at 1668 cm−1, suggesting no change in their base pairing and no change induced in the structure of water by Zn2+cations. No evidence for DNA melting was identified.
Concerning several attacks using letter bombs within Europe in the last couple of years and the highly rising number of new drugs, there is a need for new kinds of detection devices for explosives and drugs. We present a postscanner on basis of Terahertz (THz) spectroscopy using novel chemometric methods for the evaluation of detected THz fingerprints
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