DFT, FT-Raman and FT-IR investigations of 5-methoxysalicylic acid

FT-IR and FT-Raman spectra of 5-methoxysalicylic acid (5MeOSA) have been experimentally reported in the region of 4000–10 cm⁻¹ and 4000–50 cm⁻¹, respectively. The optimized geometric parameters, conformational equilibria, normal mode frequencies and corresponding vibrational assignments of 5MeOSA (C₈H₈O₄) are theoretically examined by means of B3LYP hybrid density functional theory (DFT) method together with 6-31++G(d,p) basis set. Furthermore, reliable vibrational assignments have made on the basis of potential energy distribution (PED) calculated and the thermodynamics functions, highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) of 5MeOSA have been predicted. Calculations are employed for different conformations of 5MeOSA, both in gas phase and in solution. Solvent effects are investigated using chloroform and dimethylsulfoxide. All results indicate that B3LYP method is able to provide satisfactory results for predicting vibrational frequencies and the structural parameters, vibrational frequencies and assignments, IR and Raman intensities of 5MeOSA are solvent dependent.     

Temperature-dependent vibrational spectroscopic studies of pure and gold nanoparticles dispersed 4-n-Hexyloxy-4’-cyanobiphenyls

Raman spectra of pure and 2 wt.% gold nanoparticles (GNPs) dispersed liquid crystalline compound 4-n-Hexyloxy-4?- cyanobiphenyls (6OCB) has been recorded as a function of temperature from room temperature (solid crystal) to 80°C (isotropic liquid) in the spectral region of 500–2500 cm^?1. The variation of Raman spectral parameters (peak positions and line width) with temperature is used to explain the changes in molecular alignment and its effect on inter-/intra-molecular interactions at crystal-Nematic (K-N) transition. To understand the change in molecular structure during phase transition and on account of dispersion of gold nanoparticles in pure liquid crystal more precisely, two spectral regions 1000–1500 cm^?1 and 1500–2400 cm^?1 have been selected separately. From the detailed study, it is concluded that increased orientational/vibrational freedom of the molecules as well as delocalisation of electron clouds results in the spectral anomalies at K-N transition. The geometrical structure of 6OCB was optimised using density functional theory (DFT) and theoretical Raman spectra have been obtained for comparison with experimental spectra. The tentative assignment of vibrational modes observed in our region of study was calculated based on potential energy distribution (PED) using vibrational energy distribution analysis (VEDA) calculation.     

Development and validation of an improved reversed‐phase liquid chromatographic method combined with pulsed electrochemical detection for the analysis of netilmicin

Netilmicin is one of the aminoglycoside antibiotics that lacks a strong UV absorbing chromophore. However, the application of pulsed electrochemical detection has been used successfully for the direct analysis of aminoglycoside antibiotics. This study describes an improved LC method combined with pulsed electrochemical detection for the analysis of netilmicin. Using a Zorbax SB C‐18 column (250 mm×4.6 mm id, 5 μm), isocratic elution was carried out with a mobile phase containing sodium sulfate (20 g/L), sodium octanesulfonate (0.3 g/L), THF (20 mL/L), and 0.2 M phosphate buffer pH 3.0 (50.0 mL/L). The robustness of the method was examined by means of an experimental design. The method proved to be sensitive, repeatable, linear, and robust. The method has also been used to analyze some commercial netilmicin samples.     

Molecular structure,vibrational spectra and potential energy distribution of protopine using <Emphasis Type="Italic">ab initio</Emphasis> and density functional theory

This work is devoted to theoretical study on molecular structure of protopine. The equilibrium geometry, harmonic vibrational frequencies and infrared intensities were calculated by ab initio Hartree-Fock and density functional B3LYP methods with the 6-31G(d) basis set and were interpreted in terms of potential energy distribution (PED) analysis. The internal coordinates were optimized repeatedly for many times to maximize the PED contributions. A detailed interpretation of the infrared spectra of protopine is reported. The calculations are in agreement with experiment. The thermodynamic functions of the title compound were also performed at HF/6-31G(d) and B3LYP/6-31G(d) level of theory. The FT-IR spectra of protopine were recorded in solid phase.     

Vibrational investigation of 1-cyclopentylpiperazine: A combined experimental and theoretical study

FT-IR and Raman spectra of 1-cyclopentylpiperazine(1cppp)have been experimentally examined in the region of 4000–200cm-1.The optimized geometric parameters,conformational equilibria,normal mode frequencies and corresponding vibrational assignments of 1cppp(C9H18N2)are theoretically examined by means of B3LYP hybrid density functional theory(DFT)method together with 6-31++G(d,p)basis set.On the basis of potential energy distribution(PED)reliable vibrational assignments have been made and the thermodynamics functions,highest occupied and lowest unoccupied molecular orbitals(HOMO and LUMO)of 1cppp have been predicted.Calculations are employed for four different conformations in C1 and Cs point groups of 1cppp in gas phase.Comparison between the experimental and theoretical results indicates that B3LYP method is able to provide satisfactory results for predicting vibrational frequencies and the structural parameters,vibrational frequencies and assignments.Furthermore,C1(equatorial-axial)point group has been found as the most stable conformer of 1cppp.     

Crystallographic, vibrational and theoretical studies of 2,3-diaminopyridinium selenate

The new organic–inorganic salt, 2,3-diaminopyridinium selenate, has been synthesized and characterized by means of single-crystal X-ray crystallography, FT-IR and FT-Raman spectroscopy. A diprotonated organic ligand, H₂^1,3L²⁺, existing in the crystal structure was theoretically shown to be the most stable cationic species of 2,3-diaminopyridine. The weak non-covalent forces of N–H?O type between the hydrogen atoms of the amino and ammonio groups of 2,3-diaminopyridinium cation and oxygen atoms of tetrahedral selenate anions determine three-dimensional arrangement with complex network of intermolecular interactions of hydrogen bond type (donor–acceptor distances from 2.697(3) Å to 3.088(3) Å). Vibrational spectra have been discussed in comparison with X-ray results. Juxtaposition of spectra of the complex with the pure organic ligand and deuterated analogue of the title compound allowed to give reliable assignments of most observed vibrational bands. Presented data can be useful in elucidation of molecular mechanism of uptake of tetrahedral SeO₄²⁻ anion by the living organisms.     

Temperature-dependent Raman study of pure and silver nanoparticles dispersed N-(4-n-heptyloxybenzylidene)-4’-n-butylaniline (7O.4)

Temperature-dependent micro-Raman study of C-H in-plane bending mode of aromatic rings, C-N and C=N stretching of linking group (-C(H)=N) and C=C stretching of rings of pure and silver nanoparticles dispersed (0.5% and 1% by weight) Schiff’s base liquid crystal (LC) compound, N-(4-n-heptyloxybenzylidene)-4’-n-butylaniline (7O.4) in 500–2250 cm^?1 region has been done. The change in Raman spectral parameters (peak position and linewidth) at crystal–smecticG (K–smG) and smecticG–smecticC (smG–smC) gives the evidence of charge shift at phase transition which is associated with changes in orientation and vibrational freedom of the molecules. The peak position of the Raman bands shows blue shift for 0.5 wt% dispersed sample, whereas it shows red shift for 1 wt% dispersed sample. The blue and red shifts of the Raman bands indicate an increase and decrease in the charge density, respectively. The optimised structure and theoretical room temperature Raman spectra of 7O.4 were obtained using density functional theory. The vibrational assignment using potential energy distribution is reported using vibrational energy distribution analysis (VEDA).