Vibrational spectra and assignments of 2-amino-5-iodopyridine by ab initio Hartree-Fock and density functional methods

The effect of complex formation on the static and frequency-dependent nonlinear optical properties: A combined experimental and theoretical investigation

A novel mixed ligand Mn(II) complex of 6-Bromopyridine-2-carboxylic acid (6Brpca) and 4,4'-dimethyl-2,2'-dipyridyl has been prepared and structurally characterized using single-crystal X-ray diffraction. The spectroscopic properties were also analyzed by using FT-IR and UV-Vis spectral techniques. The coordination complexes having transition metal ions are known to have promising optical nonlinearity behavior. Therefore, B3LYP level density functional theory was used to investigate first- and second-order hyperpolarizabilities (β and γ) and provide a deep understanding of the relation between the structure and NLO properties. The calculations of frequency-dependent α, β, and γ at frequencies of ω = 0.0856252 and 0.0428126 au. for 6Brpca and Dmdpy ligands as well as Mn(II) complex have been also carried out using B3LYP/LanL2DZ level. Especially second harmonic generation (SHG) first and second hyperpolarizabilities (β(-2ω;ω,ω) and γ (-2ω;ω,ω,0)) parameters for Mn(II) complex have been calculated as 11448 × 10-30 and 680035 × 10-36 esu, respectively. It has been determined that there is a tremendous increase in β and γ parameters when 6Brpca and Dmdpy ligands coordinate to the high spin multiplicity Mn(II) ion. Theoretical calculations revealed that the large first- and second-order hyperpolarizabilities are caused by strong intramolecular charge transfer between the transition metal and the coordinated ligands. These results indicate that the the organometallic complex under investigation is valuable candidate for optoelectronic and photonic applications.

The spectroscopic (FT-IR, FT-Raman, dispersive Raman and NMR) study of ethyl-6-chloronicotinate molecule by combined density functional theory

In this study, ethyl-6-chloronicotinate (E-6-ClN) molecule is recorded in the region 4000-400 cm(-1) and 3500-100 cm(-1) (FT-IR, FT-Raman and dispersive Raman, respectively) in the solid phase. ((1))H and ((13))C nuclear magnetic resonance (NMR) spectra are recorded in DMSO solution. The structural and spectroscopic data of the molecule are obtained for two possible isomers (S1 and S2) from DFT (B3LYP) with 6-311++G(d,p) basis set calculations. The geometry of the molecule is fully optimized, vibrational spectra are calculated and fundamental vibrations are assigned on the basis of the potential energy distribution (PED) of the vibrational modes. ((1))H and ((13))C NMR chemical shifts are calculated by using the gauge-invariant atomic orbital (GIAO) method. The electronic properties, such as excitation energies, oscillator strengths, wavelengths, HOMO and LUMO energies, are performed by time-dependent density functional theory (TD-DFT). Total and partial density of state and overlap population density of state diagrams analysis are presented for E-6-ClN molecule. Furthermore, frontier molecular orbitals (FMO), molecular electrostatic potential, and thermodynamic features are performed. In addition to these, reduced density gradient of the molecule is performed and discussed. As a conclusion, the calculated results are compared with the experimental spectra of the title compound. The results of the calculations are applied to simulate the vibrational spectra of the molecule, which show excellent agreement with the observed ones. The theoretical and tentative results will give us a detailed description of the structural and physicochemical properties of the molecule. Natural bond orbital analysis is done to have more information stability of the molecule arising from charge delocalization, and to reveal the information regarding charge transfer within the molecules.

Investigation of structure, vibrational, electronic, NBO and NMR analyses of 2-chloro-4-nitropyridine (CNP), 2-chloro-4-methyl-5-nitropyridine (CMNP) and 3-amino-2-chloro-4-methylpyridine (ACMP) by experimental and theoretical approach

This study reports about the optimized molecular structures, vibrational wavenumbers, atomic charges, molecular electrostatic potentials, NBO, electronic properties, (1)H NMR and (13)C NMR chemical shifts for the molecules 2-chloro-4-nitropyridine (CNP), 2-chloro-4-methyl-5-nitropyridine (CMNP) and 3-amino-2-chloro-4-methylpyridine (ACMP). Theoretical calculations were performed by density functional theory (DFT)/B3LYP method using 6-311++G (d,p) basis set. The stability and charge delocalization of the title molecules were studied by natural bond orbital (NBO) analysis. Molecular electrostatic potential maps (MEP) were calculated to predict the reactive sites. The reactivity of the title compounds were investigated by HOMO-LUMO energies and global descriptors. The electronic properties of the compounds were also discussed and the transitions were found to be π→π(∗). In addition, the thermodynamic properties were studied for the title compounds and corresponding relations between the properties and temperature were also discussed. The hyperpolarizability values (βtot) were calculated for the title compounds. Hyperpolarizability value (βtot) of CMNP was found to be high and nineteen times greater than that of urea.

Molecular docking, spectroscopic studies and quantum calculations on nootropic drug

A systematic vibrational spectroscopic assignment and analysis of piracetam [(2-oxo-1-pyrrolidineacetamide)] have been carried out using FT-IR and FT-Raman spectral data. The vibrational analysis was aided by an electronic structure calculation based on the hybrid density functional method B3LYP using a 6-311G++(d,p) basis set. Molecular equilibrium geometries, electronic energies, IR and Raman intensities, and harmonic vibrational frequencies have been computed. The assignments are based on the experimental IR and Raman spectra, and a complete assignment of the observed spectra has been proposed. The UV-visible spectrum of the compound was recorded and the electronic properties, such as HOMO and LUMO energies and the maximum absorption wavelengths λmax were determined by the time-dependent DFT (TD-DFT) method. The geometrical parameters, vibrational frequencies and absorption wavelengths were compared with the experimental data. The complete vibrational assignments are performed on the basis of the potential energy distributions (PED) of the vibrational modes in terms of natural internal coordinates. The simulated FT-IR, FT-Raman, and UV spectra of the title compound have been constructed. Molecular docking studies have been carried out in the active site of piracetam by using Argus Lab. In addition, the potential energy surface, HOMO and LUMO energies, first-order hyperpolarizability and the molecular electrostatic potential have been computed.

FT-IR, FT-Raman, UV, NMR spectra, molecular structure, ESP, NBO and HOMO-LUMO investigation of 2-methylpyridine 1-oxide: a combined experimental and DFT study

In this paper, the equilibrium geometry, bonding features, vibrational frequencies, (1)H and (13)C chemical shift values, molecular electrostatic potential maps, HOMO-LUMO energies and several thermodynamic parameters of title compound in the ground state have been calculated by using the density functional method with 6-31G(d,p) and 6-311G(d,p) basis sets. A detailed interpretation of the infrared and Raman spectra of 2-methylpyridine 1-oxide was reported. Furthermore, natural bond orbitals were performed in this work. The theoretical results showed an excellent agreement with the experimental values.

Determination of structural and vibrational spectroscopic features of neutral and anion forms of dinicotinic acid by using NMR, infrared and Raman experimental methods combined with DFT and HF

In this study; the experimental (NMR, infrared and Raman) and theoretical (HF and DFT) analysis of dinicotinic acid were presented. (1)H and (13)C NMR spectra were recorded in DMSO solution and chemical shifts were calculated by using the gauge-invariant atomic orbital (GIAO) method. The vibrational spectra of dinicotinic acid were recorded by FT-Raman and FT-IR spectra in the range of 4000-10 cm(-1) and 4000-400 cm(-1), respectively. To determine the most stable neutral conformer of molecule, the selected torsion angle was changed every 10° and molecular energy profile was calculated from 0° to 360°. The geometrical parameters and energies were obtained for all conformers form from density functional theory (DFT/B3LYP) and HF with 6-311++G(d,p) basis set calculations. However, the results of the most stable neutral and two anion forms (anion(-1) and anion(-2) forms) of dinicotinic acid are reported here. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational wavenumbers, calculated with scaled quantum mechanics (SQM) method and PQS program.

Photosan-II loaded hollow silica nanoparticles: preparation and its effect in killing for QBC939 cells

BACKGROUND

Nanoparticles have been explored recently as an efficient means to deliver photosensitizers for photodynamic therapy. However, it is largely unknown if polyhematoporphyrin (C34H38N4NaO5, Photosan-II, PS) or other photosensitizers can be efficiently delivered by hollow silica nanoparticles (HSNP).

METHODS

Polyhematoporphyrin (C34H38N4NaO5, Photosan-II, PS) was loaded into hollow silica nanoparticles (HSNP) by one-step wet chemical-based synthetic route. Dynamic light scattering (DLS) and polydispersive index (PDI) were used for measurement of the particles size and size distribution. Transmission electron microscope and scanning electron microscopy were used for the microstructure, morphological and chemical composition analysis. Fourier transform infrared spectrometry spectra and fluorescence emission spectrum were obtained. The photobiological activity of the PS-loaded HSNP was evaluated on human cholangiocarcinoma QBC939 cells. The cellular viability was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. Apoptotic and necrotic cells were measured by flow cytometry.

RESULTS

DLS measurements showed that the size of the particles is in the range of 25-90 nm. PDI of the PS-loaded HSNP is 0.121 ± 0.01, indicating that samples have excellent quality with narrow size distribution to monomodal systems. In MTT assay, PS-loaded HSNP and free PS of the same concentration killed about 95.3% ± 2.0% and 55.7% ± 1.9% of QBC939 cells, respectively. The flow cytometry demonstrated that the laser induced cell death with PS-loaded HSNP was much more severe than that of free PS (P<0.05).

CONCLUSIONS

Photosan-II-loaded hollow silica nanoparticles not only can quickly deliver Photosan-II into cells but also can reach a more high concentration than free Photosan-II. HSNP is a desirable vehicle and the release system that shows promises for photodynamic therapy use, which not only improve the aqueous solubility, stability and transport efficiency of PS, but also increase its photodynamic efficacy compared to free PS.

Synthesis, spectroscopic characterization and quantum chemical computational studies of (S)-N-benzyl-1-phenyl-5-(pyridin-2-yl)-pent-4-yn-2-amine

The synthesis and characterization of a novel compound (S)-N-benzyl-1-phenyl-5-(pyridin-2-yl)-pent-4-yn-2-amine (abbreviated as BPPPYA) was presented in this study. The spectroscopic properties of the compound were investigated by FT-IR, NMR and UV spectroscopy experimentally and theoretically. The molecular geometry and vibrational frequencies of the BPPPYA in the ground state were calculated by using density functional theory (DFT) B3LYP method invoking 6-311++G(d,p) basis set. The geometry of the BPPPYA was fully optimized, vibrational spectra were calculated and fundamental vibrations were assigned on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method and PQS program. The results of the energy and oscillator strength calculated by time-dependent density functional theory (TD-DFT) and CIS approach complement with the experimental findings. Total and partial density of state (TDOS and PDOS) and also overlap population density of state (COOP or OPDOS) diagrams analysis were presented. The theoretical NMR chemical shifts ((1)H and (13)C) complement with experimentally measured ones. The dipole moment, linear polarizability and first hyperpolarizability values were also computed. The linear polarizabilities and first hyper polarizabilities of the studied molecule indicate that the compound is a good candidate of nonlinear optical materials. The calculated vibrational wavenumbers, absorption wavelengths and chemical shifts showed the best agreement with the experimental results.

Molecular structure and vibrational spectra of 3-and 4-amino-2-bromopyridine by density functional methods

In this work, experimental and theoretical study on the molecular structure and the vibrational spectra of 3-amino-2-bromopyridine (Compound I) and 4-amino-2-bromopyridine (Compound II) are presented. The vibrational frequencies of these compounds were obtained theoretically by DFT/B3LYP employing the 6-311G(2df,2p) basis set for optimized geometries and were compared with Fourier Transform Infrared solid phase spectra (FTIR) in the region of 400-4000 cm(-1), FT-Raman spectra in the region of 100-4000 cm(-1) and with solution phase spectra in the region of 400-4000 cm(-1). Complete vibrational assignment, analysis and correlation of the fundamental modes for these compounds have been carried based on the potential energy distribution (PED). The vibrational harmonic frequencies were scaled using scale factors, yielding a good agreement between the experimentally recorded and the theoretically calculated values. Finally the calculated HOMO and LUMO energies are localized on the entire ring and substituents.

Spectroscopic analysis of 2-(2,3-dihydro-1,5-dimethyl-3-oxo-2-phenyl-1H-pyrazol-4-ylimino)-2-(4-nitro-phenyl) acetonitrile

The optimized geometry and vibrational frequencies of 2-(2,3-dihydro-1,5-dimethyl-3-oxo-2-phenyl-1H-pyrazol-4-ylimino)-2-(4-nitro-phenyl) acetonitrile (DOPNA) were obtained by ab initio DFT/B3LYP level with complete relaxation in the potential energy surface using 6-31G and 6-311G basis sets. The Fourier-transform infrared (FT-IR) spectrum of DOPNA has been recorded in the region 4000-400 cm(-1). The harmonic vibrational frequencies were calculated and the scaled values have been compared with experimental FT-IR spectrum. The calculated frequencies are in comparable agreement with the experimental frequencies. The calculated energy span between the HOMO and the LUMO of DOPNA is 2.94 and 2.87eV by B3LYP/6-31G and B3LYP/6-311G, respectively.

Comparison of experimental and density functional study on the molecular structure, infrared and Raman spectra and vibrational assignments of 6-chloronicotinic acid

The experimental and theoretical study on the structures and vibrations of 6-chloronicotinic acid (6-CNA, C(6)H(4)ClNO(2)) are presented. The Fourier transform infrared spectra (4,000-50 cm(-1)) and the Fourier transform Raman spectra (3,500-50 cm(-1)) of the title molecule in solid phase have been recorded, for the first time. The geometrical parameters and energies have been obtained for all four conformers from DFT (B3LYP) with different basis sets calculations. There are four conformers, C1, C2, C3, and C4 for this molecule. The computational results diagnose the most stable conformer of 6-CNA as the C1 form. The vibrations of the two stable and two unstable conformers of 6-CNA are researched with the aid of quantum chemical calculations. The molecular structure, vibrational frequencies, infrared intensities and Raman scattering activities and theoretical vibrational spectra were calculated a pair of molecules linked by the intermolecular OH...O hydrogen bond. The spectroscopic and theoretical results are compared to the corresponding properties for 6-CNA stable monomers and dimer of C1 conformer.

Ab initio Hartree-Fock and density functional theory study on molecular structures, energies, and vibrational frequencies of conformations of 2-hydroxy-3-nitropyridine and 3-hydroxy-2-nitropyridine

The optimized molecular structures, vibrational frequencies and corresponding vibrational assignments of conformations of 2-hydroxy-3-nitropyridine and 3-hydroxy-2-nitropyridine molecules have been investigated using ab initio Hartree-Fock (HF) and density functional theory (B3LYP) methods with 6-311++G(d,p) basis set. The comparison of the experimental and calculated spectra of the molecules have shown that they exist in two conformations with the two OH bond angles (110 degrees and 250 degrees ) respective to the CO bond in the ground state and their energy curves having two minimums have been drawn.