No abstract

We have studied the interaction of a polymeric water soluble anthracenyl derivative () with salmon testes DNA. The results from UV-Vis, fluorescence, Fourier transform infrared (FT-IR) and circular dichroism spectroscopies indicate that the groove binding process regulates the interaction between and DNA. The binding constants, calculated by absorption spectroscopy at 298, 304 and 310 K, were equal to 3.2 × 10(5) M(-1), 4.7 × 10(5) M(-1), and 6.6 × 10(5) M(-1) respectively, proving a relatively high affinity of for salmon testes DNA. Results of Hoechst 33258 displacement assays strongly support the groove binding mode of to DNA. The association stoichiometry of the :DNA adduct was found to be 1 for every 5 base pairs. FT-IR spectra, recorded at different /DNA molar ratios, indicate the involvement of the phosphate groups and adenine and thymine DNA bases in the association process. Thermodynamic results suggest that hydrophobic forces regulate the binding of with DNA without excluding some extent of involvement of van der Waals forces and hydrogen bonding arising due to surface binding between the hydrophilic polymeric arms of the ligand and the functional groups positioned on the edge of the groove. The resulting composite biomaterial could constitute a valuable candidate for future biological and/or photonic applications.

Polarized Fourier transform-infrared (FT-IR) reflectance spectra and powder Raman spectra have been measured for 1,3-dinitrobenzene crystal in order to revise the assignments of bands by means of the oriented gas model reinforced with quantum chemical [density functional theory (DFT)] calculations. Longitudinal optical/transverse optical (LO-TO) splitting of some bands is observed indicating medium strong, long-range, dipole-dipole interactions. The analysis of overtones in the polarized FT-NIR spectra has allowed us to estimate the anharmonicity of vibrations in the crystal. The molecular motions of the nitro groups are analyzed on the basis of temperature-dependent polycrystalline IR spectra. Based on the values of the energy difference ( ν el ) between the forbidden A 1g →B 2u transition in the benzene molecule in the gas phase and the first electronic transition in 1,3-dinitrobenzene, it has been concluded that the intermolecular interactions are medium strong. The nitro group interactions are proposed to play the main role in the optical nonlinearity.

The Raman excitation profiles of solid 2-methyl-4-nitroaniline (MNA) reveal several band enhancements by intermolecular and intramolecular charge transfer states. Calculated excited- and ground-state molecular geometries and excited state distortions qualitatively determined from Raman spectra indicate multiple vibrations leading to MNA dissociation. Also, overtones and combination tones can generate charged polarons, as detected by electron paramagnetic resonance after the exposure to 980 and 1550 nm laser diodes. The MNA space group Ia (C(s)(4)) is nonchiral; however, the electronic circular dichroism (CD) spectra of solution, KBr pellet, and single crystal were recorded. The crystal chirality is elucidated by room-temperature dynamic disorder, possible helical superstructure along the [102] polar axis, and charged polarons presence. The CD spectra ab initio calculations for MNA neutral and negatively charged monomers, dimers, and trimers, lying along the helix, confirmed the chirality. The role of these findings toward efficient optical nonlinearity and electric conductivity failure is discussed.