Molecular interactions of 2'-deoxyguanosine 5'-monophosphate with glycine in aqueous media probed via concentration and pH dependent Raman spectroscopic investigations and DFT study

Protonation induces base rotation of purine nucleotides pdGuo and pGuo

Infrared multiple photon dissociation (IRMPD) action spectra of the protonated forms of 2'-deoxyguanosine-5'-monophosphate and guanosine-5'-monophosphate, [pdGuo+H](+) and [pGuo+H](+), are measured over the IR fingerprint and hydrogen-stretching regions using the FELIX free electron laser and an OPO/OPA laser system. Electronic structure calculations are performed to generate low-energy conformations of [pdGuo+H](+) and [pGuo+H](+) and determine their relative stabilities at the B3LYP/6-311+G(2d,2p)//B3LYP/6-311+G(d,p) and MP2(full)/6-311+G(2d,2p)//B3LYP/6-311+G(d,p) levels of theory. Comparative analyses of the measured IRMPD action spectra and B3LYP/6-311+G(d,p) linear IR spectra computed for the low-energy conformers are performed to determine the most favorable site of protonation and the conformers present in the experiments. These comparisons and the computed energetics find that N7 protonation is considerably preferred over O6 and N3, and the N7 protonated ground-state conformers of [pdGuo+H](+) and [pGuo+H](+) are populated in the experiments. The 2'-hydroxyl substituent does not significantly impact the stable low-energy conformers of [pdGuo+H](+)vs. those of [pGuo+H](+). The effect of the 2'-hydroxyl substituent is primarily reflected in the relative intensities of the measured IRMPD bands, as the IRMPD profiles of [pdGuo+H](+) and [pGuo+H](+) are quite similar. Comparisons to previous IRMPD spectroscopy investigations of the protonated forms of the guanine nucleosides, [dGuo+H](+) and [Guo+H](+), and deprotonated forms of the guanine nucleotides, [pdGuo-H](-) and [pGuo-H](-), provide insight into the effects of the phosphate moiety and protonation on the conformational features of the nucleobase and sugar moieties. Protonation is found to induce base rotation of the guanine residue to an anti orientation vs. the syn orientation found for the deprotonated forms of the guanine nucleotides.

Terahertz spectra of DNA nucleobase crystals: A joint experimental and computational study

Terahertz (THz) spectra of DNA nucleobase crystals were experimentally studied by terahertz time domain spectroscopy (THz-TDS), Fourier transform infrared spectroscopy (FTIR), and computationally studied by the generalized energy-based fragmentation approach under periodic boundary conditions (denoted as PBC-GEBF). We analyzed the vibrational spectra of solid-state DNA nucleobases and assigned the corresponding vibrational modes to the main peaks in the experimental spectra with the PBC-GEBF results. The computational results were verified to be in good accordance with the experimental data. Harmonic vibrational frequency results revealed that all the vibrational modes belong to collective vibrational modes, which involve complicated mixtures of inter- and intramolecular displacements, somewhere in the vicinity of 0.5-9THz.

Monitoring potential molecular interactions of adenine with other amino acids using Raman spectroscopy and DFT modeling

We report on the modes of inter-molecular interaction between adenine (Ade) and the amino acids: glycine (Gly), lysine (Lys) and arginine (Arg) using Raman spectroscopy of binary mixtures of adenine and each of the three amino acids at varying molar ratios in the spectral region 1550-550 cm(-1). We focused our attention on certain specific changes in the Raman bands of adenine arising due to its interaction with the amino acids. While the changes are less apparent in the Ade/Gly system, in the Ade/Lys or Ade/Arg systems, significant changes are observed, particularly in the Ade Raman bands that involve the amino group moiety and the N7 and N1 atoms of the purine ring. The ν(N1-C6), ν(N1-C2), δ(C8-H) and δ(N7-C8-N9) vibrations at 1486, 1332, 1253 and 948 cm(-1) show spectral changes on varying the Ade to amino acid molar ratio, the extent of variation being different for the three amino acids. This observation suggests a specific interaction mode between Ade and Lys or Arg, which is due to the hydrogen bonding. The measured spectral changes provide a clear indication that the interaction of Ade depends strongly on the structures of the amino acids, especially their side chains. Density functional theory (DFT) calculations were carried out to elucidate the most probable interaction modes of Ade with the different amino acids.