Experimental and theoretical investigation of the molecular and electronic structure of anticancer drug camptothecin

The Fourier Transform Infrared spectrum of (S)-4 ethyl-4-hydroxy-1H-pyrano [3',4':6,7]-indolizino-[1,2-b-quinoline-3,14-(4H,12H)-dione] [camptothecin] was recorded in the region 4000-400 cm(-1). The Fourier Transform Raman spectrum of camptothecin (CPT) was also recorded in the region 3500-50 cm(-1). Quantum chemical calculations of geometrical structural parameters and vibrational frequencies of CPT were carried out by MP2/6-31G(d,p) and density functional theory DFT/B3LYP/6-311++G(d,p) methods. The assignment of each normal mode has been made using the observed and calculated frequencies, their IR and Raman intensities. The harmonic vibrational frequencies were calculated and the scaled values have been compared with experimental FT-IR and FT-Raman spectra. Most of the computed frequencies were found to be in good agreement with the experimental observations. The isotropic chemical shifts computed by (13)C and (1)H NMR analysis also show good agreement with experimental observations. Comparison of calculated spectra with the experimental spectra provides important information about the ability of computational method to describe the vibrational modes of large sized organic molecule.     

Ab initio and DFT studies of the vibrational spectra of benzofuran and some of its derivatives

The vibrational spectra of benzofuran and some of its derivatives have been systematically investigated by ab initio and density functional B3LYP methods. The harmonic vibrational wavenumbers and intensity of vibrational bands were calculated at ab initio and DFT levels invoking different basis sets up to 6-311++g**. Vibrational assignments have been made and it has been found that the calculated DFT frequencies agree well in most cases with the observed frequencies for each molecule. Conformational studies have also been carried out and it is evident from ab initio calculations that 2(3H) benzofuranone is more stable than 3(2H) benzofuranone in support to our earlier semiempirical results.     

FT-IR, FT-Raman, NMR and UV-vis spectra, vibrational assignments and DFT calculations of 4-butyl benzoic acid

The solid phase FTIR and FT-Raman spectra of 4-butyl benzoic acid (4-BBA) have been recorded in the regions 400-4000 and 50-4000cm(-1), respectively. The spectra were interpreted in terms of fundamentals modes, combination and overtone bands. The structure of the molecule was optimized and the structural characteristics were determined by density functional theory (DFT) using B3LYP method with 6-311++G(d,p) as basis set. The vibrational frequencies were calculated for monomer and dimer by DFT method and were compared with the experimental frequencies, which yield good agreement between observed and calculated frequencies. The infrared and Raman spectra were also predicted from the calculated intensities. (13)C and (1)H NMR spectra were recorded and (13)C and (1)H nuclear magnetic resonance chemical shifts of the molecule were calculated using the gauge independent atomic orbital (GIAO) method. UV-visible spectrum of the compound was recorded in the region 200-400nm and the electronic properties HOMO and LUMO energies were measured by time-dependent TD-DFT approach. The geometric parameters, energies, harmonic vibrational frequencies, IR intensities, Raman intensities, chemical shifts and absorption wavelengths were compared with the available experimental data of the molecule.     

FT-IR and FT-Raman spectroscopic investigation, computed vibrational frequency analysis and IR intensity and Raman activity peak resemblance analysis on 2-nitroanisole using HF and DFT (B3LYP and B3PW91) calculations

Fourier-transform Raman and infrared spectra of 2-nitroanisole are recorded (4000-100 cm(-1)) and interpreted by comparison with respective theoretical spectra calculated using HF and DFT method. The geometrical parameters with C(S) symmetry, harmonic vibrational frequencies, infrared and Raman scattering intensities are determined using HF/6-311++G (d, p), B3LYP/6-311+G (d, p), B3LYP/6-311++G (d, p) and B3PW91/6-311++G (d, p) level of theories. A detailed vibrational spectral analysis has been carried out and assignments of the observed fundamental bands have been proposed on the basis of peak positions and relative intensities. The results of the calculations have been used to simulate IR and Raman spectra for the molecule that showed good agreement with the observed spectra. The SQM method, which implies multiple scaling of the DFT force fields has been shown superior to the uniform scaling approach. The vibrational frequencies and the infrared intensities of the C-H modes involved in back-donation and conjugation are also investigated.     

Molecular structure and vibrational analysis of 3-Ethylpyridine using ab initio HF and density functional theory (B3LYP) calculations

The FT-Raman and FT-IR spectra for 3-Ethylpyridine (3-EP) have been recorded in the region 4000-100 cm(-1) and compared with the harmonic vibrational frequencies calculated using HF/DFT (B3LYP) method by employing 6-31G(d,p) and 6-311++G(d,p) basis set with appropriate scale factors. IR intensities and Raman activities are also calculated by HF and DFT (B3LYP) methods. Optimized geometries of the molecule have been interpreted and compared with the reported experimental values of some substituted benzene. The experimental geometrical parameters show satisfactory agreement with the theoretical prediction from HF and DFT. The scaled vibrational frequencies at B3LYP/6-311++G(d,p) seem to coincide with the experimentally observed values with acceptable deviations. The theoretical spectrograms (IR and Raman) have been constructed and compared with the experimental FT-IR and FT-Raman spectra. Some of the vibrational frequencies of the pyridine are effected upon profusely with the C2H5 substitutions in comparison to pyridine and these differences are interpreted.     

Vibrational assignment of the normal modes of 2-phenyl-4-(4-methoxy benzylidene)-2-oxazolin-5-one via FTIR and Raman spectra, and ab inito calculations

Raman and FTIR spectra of 2-phenyl-4-(4-methoxy benzylidene)-2-oxazolin-5-one were recorded in the regions, 100-3300 and 400-4000 cm(-1), respectively. Vibrational frequencies and intensities of the fundamental modes of this hetrocyclic organic molecule were computed using ab initio as well as AM1 semiempirical molecular orbital methods. Ab initio calculations were carried out with basis set up to RHF/6-311G. Conformational studies regarding the effect of moving the methoxy group in the 2-phenyl-4-(4-methoxy benzylidene)-2-oxazolin-5-one molecule to a different position on the ring was also carried out. Observed vibrational wavenumbers were found to be mostly consistent with ab initio values. The most intense mode of vibration observed at 1250 cm(-1) in Raman spectra, also observed as a strong band in FTIR, was assigned as C-O stretching vibration in the methoxy group. Asymmetric stretching vibrations between CC and CN bonds was predicted as most intense mode by our ab initio calculation.     

Vibrational spectrum of glycine molecule

The infrared and Raman spectra of glycine molecule has been studied in spectral region 400-4000 cm(-1) in solid form as well as in water. The vibrational frequencies for the fundamental modes of the glycine in neutral and its zwitterionic form have also been calculated using AM1 semiempirical method as well as ab initio method with minimal basis set. The reliability of the minimal basis set and AM1 method with higher basis sets, for IR spectra of the neutral glycine conformers were examined. We find that the 6-21G basis set calculation yields structural parameters, rotational constant and dipole moment of glycine conformers, which are very similar to those obtained from extended basis set calculation as well as experimental values. IR frequencies for glycine conformer I are also calculated in water using SCRF=PCM model and compared with experimental values. A comparison between calculated frequencies for neutral glycine, and its zwitterionic form with observed IR and Raman bands have been made. The total energies for gas phase glycine and its zwitterionic form along with those of hydrated forms were also calculated. It is found from the calculations that in the gas phase neutral glycine is more stable as compared to its zwitterionic form.     

Fourier transform infrared and Raman spectral investigations of 5-aminoindole

Fourier transform infrared (FT-IR) and Raman (FT-Raman) spectra of 5-aminoindole has been recorded and analysed. The FT-IR spectrum of the compound was recorded in a BrukerIFS 66 V spectrometer in the range 4000-400 cm(-1) and the FT-Raman spectrum was also recorded in the same instrument in the region 3500-100 cm(-1). Observed frequencies for normal modes are compared with those calculated form normal co-ordinate analysis. The shift in the frequencies of the fundamental modes with the substituent amino group and the mixing of different normal modes are discussed with the help of potential energy distribution (PED) calculated through normal co-ordinate analysis.     

Vibrational spectral analysis and first hyperpolarizability studies of 1-bromonaphthalene based on ab initio and DFT methods

In this work, the experimental and theoretical vibrational spectra of 1-bromonaphthalene (1-BN) were studied. FTIR and FT Raman spectra were recorded in the region 4000-400 cm(-1) and 3500-50 cm(-1), respectively. The structural and spectroscopic data of the molecule in the ground state were calculated by using ab initio Hartree-Fock and density functional method (B3LYP) with the 6-311++G(d,p) basis set. The vibrational frequencies were calculated and scaled values were compared with experimental FTIR and FT Raman spectra. The observed and calculated frequencies are found to be in good agreement. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. The optimized geometric parameters were calculated. The predicted first hyperpolarizability also shows that the molecule might have a reasonably good nonlinear optical (NLO) behaviour. The calculated HOMO-LUMO energy gap reveals that charge transfer occurs within the molecule.     

Vibrational spectroscopy [FTIR and FTRaman] investigation, computed vibrational frequency analysis and IR intensity and Raman activity peak resemblance analysis on 4-chloro 2-methylaniline using HF and DFT [LSDA, B3LYP and B3PW91] calculations

In the present study, the FT-IR and FT-Raman spectra of 4-chloro-2-methylaniline (4CH2MA) have been recorded in the range of 4000-100 cm(-1). The fundamental modes of vibrational frequencies of 4CH2MA are assigned. All the geometrical parameters have been calculated by HF and DFT (LSDA, B3LYP and B3PW91) methods with 6-31G (d, p) and 6-311G (d, p) basis sets. Optimized geometries of the molecule have been interpreted and compared with the reported experimental values for aniline and some substituted aniline. The harmonic and anharmonic vibrational wavenumbers, IR intensities and Raman activities are calculated at the same theory levels used in geometry optimization. The calculated frequencies are scaled and compared with experimental values. The scaled vibrational frequencies at LSDA/B3LYP/6-311G (d, p) seem to coincide with the experimentally observed values with acceptable deviations. The impact of substitutions on the benzene structure is investigated. The molecular interactions between the substitutions (Cl, CH(3) and NH(2)) are also analyzed.     

FT-IR, FT-Raman spectra, density functional computations of the vibrational spectra and molecular conformational analysis of 2,5-di-tert-butyl-hydroquinone

The purpose of finding conformer among six different possible conformers of 2,5-di-tert-butyl-hydroquinone (DTBHQ), its equilibrium geometry and harmonic wavenumbers were calculated by the B3LYP/6-31G(d,p) method. The infrared and Raman spectra of DTBHQ were recorded in the region 400-4000 cm(-1) and 50-3500 cm(-1), respectively. In addition, the IR spectra in CCl(4) at various concentrations of DTBHQ are also recorded. The computed vibrational wavenumbers were compared with the IR and Raman experimental data. Computational calculations at B3LYP level with two different basis sets 6-31G(d,p) and 6-311++G(d,p) are also employed in the study of the possible conformer of DTBHQ. The complete assignments were performed on the basis of the potential energy distribution (PED) of the vibrational modes, calculated using VEDA 4 program. The general agreement between the observed and calculated frequencies was established.     

Molecular structure, vibrational spectroscopic, first order hyperpolarizability and HOMO-LUMO studies of 7-amino-8-oxo-3-vinyl-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid

The FT-IR and FT-Raman spectra of 7-amino-8-oxo-3-vinyl-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid (7AVCA) were recorded in the region 4000-400 cm(-1) and 3500-10 cm(-1), respectively. Quantum chemical calculations of energies, geometrical structure and vibrational wavenumbers were carried out by ab initio HF and density functional theoretical methods invoking 6-311G(d,p) basis set. The differences between the observed and scaled wavenumber values of most of the fundamentals are very small. The electric dipole moment (μ) and the first order hyperpolarizability (β0) values have been computed quantum mechanically. The calculated results show that 7AVCA may have microscopic nonlinear optical (NLO) behavior with non-zero values. A detailed interpretation of the FT-IR and FT-Raman spectra of 7AVCA is reported. The theoretical IR and Raman spectra of 7AVCA have also been constructed. The calculated HOMO and LUMO energies show that the charge transfer occurs within the molecule.     

Structures and vibrational frequencies of 2-naphthoic acid and 6-bromo-2-naphthoic acid based on density functional theory calculations

The solid phase mid FTIR and FT Raman spectra of 2-naphthoic acid (NA) and 6-bromo-2-naphthoic acid (BNA) have been recorded in the regions 4000-400 cm(-1) and 3500-100 cm(-1), respectively. The fundamental vibrational frequencies and intensities of the vibrational bands were evaluated using density functional theory (DFT) using standard B3LYP method and 6-311+G** basis set combinations. The vibrational spectra were interpreted, with the aid of normal coordinate analysis based on a scaled quantum mechanical force field. The infrared and Raman spectra were also predicted from the calculated intensities. Comparison of simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes.     

FT-IR and FT-Raman spectra and vibrational investigation of 4-chloro-2-fluoro toluene using ab initio HF and DFT (B3LYP/B3PW91) calculations

FT-IR (4000-100 cm(-1)) and FT-Raman (4000-100 cm(-1)) spectra of solid sample of 4-chloro-2-fluoro toluene (4Cl2FT) have been recorded using Bruker IFS 66 V spectrometer. Ab initio-HF (HF/6-311++G (d, p)) and DFT (B3LYP/6-311++G and B3PW91/6-311++G (d, p)) calculations have been performed giving energies, optimized structures, harmonic vibrational frequencies, depolarization ratios, IR intensities, Raman activities. The vibrational frequencies are calculated and scaled values are compared with FT-IR and FT-Raman experimental values. The isotropic HF and DFT analyses showed good agreement with experimental observations. The differences between the observed and scaled wave number values of most of the fundamentals are very small in B3LYP than HF. Comparison of the simulated spectra provides important information about the ability of the computational method (B3LYP) to describe the vibrational modes. The influences of substitutions on the geometry of molecule and its normal modes of vibrations have also been discussed. The changes made by substitutions on the benzene are much responsible for the non-linearity of the molecule. This is an attractive entity for the future studies of non-linear optics.     

FTIR and FT Raman, molecular geometry, vibrational assignments, ab initio and density functional theory calculations for 1,5-methylnaphthalene

The FTIR and FT Raman vibrational spectra of 1,5-methylnaphthalene (1,5-MN) have been recorded using Brunker IFS 66 V Spectrometer in the range 3600-10 cm(-1) in the solid phase. A detailed vibrational spectral analysis has been carried out and assignments of the observed fundamental bands have been proposed on the basis of peak positions and relative intensities. The Optimized molecular geometry, harmonic frequencies, electronic polarizability, atomic charges, dipole moment, rotational constants and several thermodynamic parameters in the ground state were calculated using ab initio Hartree Fock (HF) and density functional B3LYP methods (DFT) with 6-311++ G(d) basis set. With the help of different scaling factors, the observed vibrational wavenumbers in FTIR and FT Raman spectra were analyzed and assigned to different normal modes of the molecule. Most of the modes have wavenumbers in the expected range. The results of the calculations were applied to simulated infrared and Raman spectra of the title compound which showed excellent agreement with the observed spectra.     

Vibrational spectroscopic (FTIR and FTRaman) investigation using ab initio (HF) and DFT (LSDA and B3LYP) analysis on the structure of Toluic acid

The FTRaman and FTIR spectra for Toluic acid (TA) have been recorded in the region 4000-100 cm(-1) and compared with the harmonic vibrational frequencies calculated using HF/DFT (LSDA and B3LYP) method BY employing 6-311G (d, p) basis set with appropriate scale factors. IR intensities and Raman activities are also calculated by HF and DFT (LSDA/B3LYP) methods. Optimized geometries of the molecule have been interpreted and compared with the reported experimental values for benzoic acid and some substituted benzoic acids. The experimental geometrical parameters show satisfactory agreement with the theoretical prediction from HF and DFT. The scaled vibrational frequencies at B3LYP/6-311G (d, p) seem to coincide with the experimentally observed values with acceptable deviations. The theoretical spectrograms (IR and Raman) have been constructed and compared with the experimental FT-IR and FT-Raman spectra. Some of the vibrational frequencies of the TA are effected upon profusely with the methyl substitutions in comparison to benzoic acid and these differences are interpreted.     

Molecular structure and vibrational investigation of benzenesulfonic acid methyl ester using DFT (LSDA, B3LYP, B3PW91 and MPW1PW91) theory calculations

The FT-Raman and FT-IR spectra for benzenesulfonic acid methyl ester (BSAME) have been recorded in the region 4000-100 cm(-1) and compared with the harmonic vibrational frequencies calculated using DFT (LSDA, B3LYP, B3PW91 and MPW1PW91) method by employing 6-311G (d, p) basis set with appropriate scale factors. IR intensities and Raman activities are also calculated by DFT (LSDA, B3LYP, B3PW91 and MPW1PW91) methods. Optimized geometries of the molecule have been interpreted and compared with the reported experimental values for sulfonic acid and some substituted sulfonic acids. The experimental geometrical parameters show satisfactory agreement with the theoretical prediction from DFT. The scaled vibrational frequencies at LSDA/B3LYP/6-311G (d, p) seem to coincide with the experimentally observed values with acceptable deviations. The theoretical spectrograms (IR and Raman) have been constructed and compared with the experimental FT-IR and FT-Raman spectra. Some of the vibrational frequencies of the sulfonic acid are effected upon profusely with the methyl substitution in comparison to benzene sulfonamide and these differences are interpreted.     

Rotationally resolved infrared spectroscopy of adamantane

We present the first rotationally resolved spectra of adamantane (C(10)H(16)) applying gas-phase Fourier transform infrared (IR) absorption spectroscopy. High-resolution IR spectra are recorded in the 33-4500 cm(-1)range using as source of IR radiation both synchrotron radiation (at the AILES beamline of the SOLEIL synchrotron) as well as a classical globar. Adamantane is a spherical top molecule with tetrahedral symmetry (T(d) point group) and has no permanent dipole moment in its vibronic ground state. Of the 72 fundamental vibrational modes in adamantane, only 11 are IR active. Here we present rotationally resolved spectra for seven of them: ν(30), ν(28), ν(27), ν(26), ν(25), ν(24), and ν(23). The typical rotational structure of spherical tops is observed and analyzed using the STDS software developed in the Dijon group, which provides the first accurate energy levels and rotational constants for seven fundamental modes. Rotational levels with quantum numbers as high as J = 107 have been identified and included in the fit leading to a typical standard deviation of about 10(-3) cm(-1).     

Vibrational absorption and circular dichroism studies of trans-(3S,4S)-d6-cyclopentene in the gas phase

Vibrational absorption (IR) and circular dichroism (VCD) measurements of trans-(3S,4S)-d6-cyclopentene in the gas phase were performed in the C-H, C-D, and mid-infrared regions. In this study, we report the first VCD spectra recorded at high spectral resolution (up to 0.5 cm(-1)) with a very good signal-to-noise ratio (differential absorbance lower than 5 x 10(-6)). The quality of the experimental spectra allows us the observation of the vibration-rotation structure of the bands in both absorption and VCD spectra. Experimental spectra have been compared with the density functional theory (DFT) absorption and VCD spectra, calculated using B3LYP functional and cc-pVTZ basis set for the axial, equatorial, and planar conformers. Lorentzian and PQR band profiles have been used to convert the calculated dipolar and rotational strengths. In the mid-infrared (<2000 cm(-1)) region, predicted (population-weighted) spectra were in excellent agreement with experiment, allowing the determination of the absolute configuration of this molecule. Above 2000 cm(-1), a reasonable agreement was obtained even if anharmonicity was not considered and if Fermi resonance occurs in the C-D stretching region. Finally, a more precise analysis of the absorption spectrum has been achieved by taking into account anharmonicity of the C-H stretching and its coupling with the ring-puckering motion.     

Vibrational spectra and normal coordinate analysis of diazepam, phenytoin and phenobarbitone

Vibrational spectroscopy is an important tool for the structural investigation of the organic molecules. In the present investigation, a normal coordinate analysis has been carried out on some anti-epileptic drugs, viz. diazepam, phenytoin and phenobarbitone. Diazepam is a derivative of benzodiazepine, phenytoin is a derivative of hydanation and pheonobarbitone is a barbiturate. The infrared spectra of the compounds are recorded in the region 4000-400 cm(-1) and Raman spectra are recorded in the region 3500-50 cm(-1). From the structural point of view, diazepam, phenytoin and phenobarbitone have been assumed to C(s) point group. A systematic set of symmetry coordinates has been constructed for these compounds and Wilson's FG matrix method has been applied for the normal coordinate analysis using general quadratic valance force field. The potential energy distribution is also calculated to check the vibrational band assignments.