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On the basis of first-principles electronic structure calculations, crystallographic parameters have been refined for calcium hydroxozincate (Qatranaite mineral), and the vibration properties (frequencies and eigenvectors) calculated. A detailed analysis of vibration modes is done, in the context of comparison with infrared and Raman spectra previously available. Special attention is paid to a posteriori symmetry analysis of vibration modes, discussing the latters' attribution to four irreducible representations of the P 2 1 / c space group, and to identifying stretchings and bendings of particular chemical bonds, pronounced in different vibrations. It turns out that high-frequency (> 700 cm−1) vibrations of hydroxyl groups bridging the Ca or Zn cations differ quite considerably for crystallographically distinct hydroxyl positions. It is shown that the vibrations involving hydroxyl groups and crystalline water typically come about in quadruplets at very close frequencies, whereby different irreducible representations reflect different combinations of similar "molecular" vibrations of four identical entities (of each hydroxyl or water) present in the unit cell. However, some vibrations show exceptions from this rule. In addition to interpretation of earlier experimental investigations, our study indicates that the low-frequency (< 700 cm−1) vibrations within the cation–hydroxyl connected skeleton are of more "solid-state-like" character and cannot be reasonably interpreted in terms of "molecular" vibrations within ZnO 4 or CaO 6 units. [Display omitted] • Projection of vibration eigenvectors according to different criteria is suggested. • Contributions from different stretchings and bendings are naturally identified. • Molecular-type vibrations make almost degenerate symmetry-constrained combinations. • Vibrations throughout metal-oxygen cages make a dense quasi-continuous spectrum. [ABSTRACT FROM AUTHOR]

[Display omitted] • Yttrium nitride YN in different forms was investigated by using DFT/B3LYP level of theory. • A variety of properties of the YN (n,0) single-walled square nanotubes was studied, where the trend toward the square monolayer in the limit of large nanotube is attained. • Scanning mode procedure confirms that larger YN (n,0) single-walled hexagonal nanotubes are slightly distorted compared to their corresponding central point. Through this contribution, we aim to highlight the structural stability of low dimensional YN structures ranging from the 3D bulk to the 2D square and hexagonal monolayers and their corresponding 1D zigzag single walled nanotubes. For all arrangements, geometry optimization is achieved at the DFT/B3LYP level of theory using a Gaussian basis set. Then, the coupled perturbed Kohn-Sham and Hartree-Fock (CPKS/HF) computational approach is used to simulate Raman and IR spectrum. Rolling, cohesive and relaxation energies, electronic and vibrational contributions to the polarizability and equilibrium lattice parameters are also reported. Insights into their structural stability are provided by combining optimized parameters and vibrational phonon spectra. For the optimized 3D bulks, 2D monolayers and 1D square nanotubes, no imaginary frequency has been recorded in their vibrational spectra which reveals a dynamic stability. Likewise, imaginary frequencies appeared only for relatively large YN (n,0) single walled hexagonal nanotubes (n > 6) indicating that the optimized structures are not a real global minimum and implying a dynamic instability. A scaning mode procedure along the largest imaginary vibrational mode has been adopted to obtain the equilibrium geometry of (22,0) YN hexagonal nanotube. Therefore, it must be emphasized that the obtained potential energy surface presents two minima between a saddle point. These minima corresponds to a stable structures slightly distorted compared to the initial one. The absence of imaginary phonon frequencies in the Raman and IR spectra of the optimized (22,0) YN hexagonal nanotube confirms its structural stability. [ABSTRACT FROM AUTHOR]

In this work, the structure–property relationship of push–pull chalcone derivative (3DPNP) has been studied through spectroscopic experiments and density functional theory calculations. The figure on the right side shows the non-linear absorption and non-linear refraction curves of 3DPNP. [Display omitted] • The structure–property relationship of a chalcone-based push–pull molecule (3DPNP) was explored using combined experimental and theoretical studies. • The vibrational and electronic contribution to NLO activity of 3DPNP was estimated. • Frequency-dependent NLO calculations shows abrupt changes when the incident frequency is doubled which confirms SHG efficiency of 3DPNP. • Z-scan studied indicated that the molecule 3DPNP is suitable for optical limiting application in CW laser regime. • The optical limiting threshold of 3DPNP is found to be 3.26 kJ/cm2. In this work, the optical limiting response of a highly π-conjugated push–pull chalcone derivative (2 E)-3-(2,3-dimethoxyphenyl)-1-(3-nitrophenyl)prop-2-en-1-one (abbreviated as 3DPNP) has been investigated. The structure–property relationship of 3DPNP was explored through spectroscopic investigation and quantum chemical computations. The existence of weak-non-covalent interactions and charge transfer species that responsible for the chemical stability of 3DPNP were studied by AIM and NBO analyses. The quantitative and qualitative analysis of vibrational and electronic contribution to non-linear optical (NLO) response of 3DPNP were discussed in detail. The normal vibrational modes associated with a change in the dipole moment, polarizability, first- and second-order hyperpolarizabilities of 3DPNP were identified using DFT calculations followed by potential energy distribution (PED) analysis using Gaussian 09 W software and Gar2ped program, respectively. The changes in the NLO parameters with respect to the varying frequencies and electric dipole fields were studied. The abrupt changes in the NLO properties were noticed when the frequency doubled, confirming the second harmonic generation (SHG) efficiency of 3DPNP. From the non-linear absorption and refraction studies through the z-scan experiment, the optical limiting threshold value of 3DPNP is determined to be 3.26 kJ/cm2, which shows the suitability of the material for optical limiting applications in the continuous wave (CW) laser regime. [ABSTRACT FROM AUTHOR]

The complex crystals of the family of the Tutton's salt have been investigated through the numerous experimental and theoretical studies to understand their physical properties and their potential technological applications. In spite of the more than 60 years of research, there are very few studies about the electronic properties of Tutton's salt. In our present work, we have calculated the stability, electronic properties and the first theoretical study of band structure of the three different crystals of the Tutton's salt, ammonium nickel sulfate hexahydrate ((NH 4) 2 Ni(SO 4) 2 ·6H 2 O), ammonium nickel‐copper sulfate hexahydrate ((NH 4) 2 Ni 0.5 Cu 0.5 (SO 4) 2 ·6H 2 O) and ammonium copper sulfate hexahydrate ((NH 4) 2 Ni(SO 4) 2 ·6H 2 O) with the help of periodic ab-initio calculations based on density functional theory (DFT). In addition to this, the internal Raman and FTIR modes of the ionic fragments [Ni(H 2 O) 6 ]2+, [Cu(H 2 O) 6 ]2+ NH 4 + and SO 4 2− of the sample crystals were obtained by employing the ab initio and the orientation of the molecular vibrations of the ionic fragments have been presented in picturized form. Furthermore, the Raman and FTIR spectroscopy of the sample crystals were measured in the range 100–4000 cm−1 and 400–4000 cm−1 respectively, and the internal vibrational modes obtained from experimental measurement have been compared with those obtained from DFT calculations. Unlabelled Image • Electronic properties and DFT band structure of Tutton's salt • Internal modes obtained from the ab initio and experimental study • Representations of the molecular vibrations of the ionic fragments [ABSTRACT FROM AUTHOR]

Abstract A novel fluorescence molecule (2‑hydroxy‑4‑methoxyphenyl)(phenyl)‑methanone azine (HMPM) has been explored theoretically in this present work. Based on density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods, we investigate the excited state hydrogen bonding behaviors and excite state intramolecular proton transfer (ESIPT) process for HMPM molecule. Via simulating the reduced density gradient (RDG) versus sign(λ 2)ρ, we firstly verify the double intramolecular hydrogen bonds (O1 H2⋯N3 and O4 H5⋯N6) for HMPM system. Comparing with the changes about these two hydrogen bonds (i.e., bond distances, bond angles and infrared (IR) vibrational spectra), we find that they should be enhanced in the first excited state upon the photo-excitation. The shortened hydrogen bonding distance of H2⋯N3 and H5⋯N6 provide the possibility for ESIPT reaction. Given the photo-excitation process, we confirm the charge redistribution around the hydrogen bonding moieties plays an important role as a driving force for the ESIPT process. Further, via constructing S 0 -state and S 1 -state potential energy surfaces (PESs), we confirm the excited state double proton transfer (ESDPT) is excludable since the high optimized energy and high potential energy barrier. While the low potential barrier for excited state single proton transfer path results in the ultrafast ESIPT reaction, which explains why the initial HMPM fluorescence peak cannot be detected in previous experimental phenomenon. This work not only clarifies the excited state dynamical behavior for HMPM system, but also explains previous experimental phenomenon and attributions about steady state spectra. We hope this work can facilitate novel applications based on the novel HMPM system in future. Graphical Abstract Unlabelled Image Highlights • Hydrogen bond of HMPM should be strengthened in the first excited state. • Charge transfer facilitates the ESIPT process for HMPM molecule. • Only the excited state single proton transfer process occurs for HMPM molecule. [ABSTRACT FROM AUTHOR]

Abstract Hydrogen bonding is a weak chemical interaction widely existed in the variety of organic and biological molecules. As an important structural motif of pyrimidine bases, the solvent effect of the hydrogen bonding of 2-cyclohexen-1-one (CHO) and 3-methyl- 2-cyclohexen-1-one (3MCHO) and its effect on the frequency shift of the C O stretching mode were investigated by using the FT-Raman and UV absorption spectra and density functional theory calculations. The electronic transitions associated with the UV absorptions in different solvents were calculated at B3LYP-TD/6-31++G(d,p) level of theory and employing SCIPCM solvent model. The vibrational spectra of CHO and 3MCHO were assigned on the basis of the FT-Raman spectra in neat liquid and different solvents, the calculated vibrational spectra of monomer and CHO dimers, and the concentration dependent experiments of the band pair intensities. Hydrogen bonding energies of CHO-(H 2 O) n (n = 1,2) clusters were predicted. The results reveal that the CHO-(H 2 O) 2 cluster and CHO monomer are respectively the major source of spectral observation in water and cyclohexane, while CHO dimmer and CHO monomer coexist in acetonitrile. The difference in the frequency of the ν C=O stretching mode between 3MCHO monomer and CHO monomer in cyclohexane were explored. Graphical Abstract Solvent effects on the UV absorption and FT-Raman spectra of CHO and 3MCHO in solution phases were evaluated by using the UV and FT-Raman spectroscopies and B3LYP-TD/6-31++G(d, p) calculations employing SCIPCM solvent model in cyclohexane, acetonitrile and water solutions. The Raman intensity profiles in the ν C O region of CHO and 3MCHO were affected strongly by solvents of different polarity and hydrogen bonding capability. The results indicated that nonpolar solvents favored CHO monomer, while protic solvents favored CHO-(H 2 O) n (n = 1,2) clusters. The new band at 1653 cm−1 for CHO and at 1643 cm−1 for 3MCHO in water were assigned respectively to CHO-(H 2 O) n clusters and 3MCHO-(H 2 O) n clusters. The hydrogen bonding of solvents and the π-σ superconjugation or π-p conjugation between C C C O and the neighbouring groups (such as CH 3 and NH 2) made the frequency of the ν C O mode down-shift. The Raman spectra of CHO and 3MCHO were assigned. Unlabelled Image Highlights • The Raman spectra of 2-cyclohexen-1-one (CHO) and 3-methyl- 2-cyclohexen-1-one (3MCHO) were assigned. • Effect of the UV and Raman spectra of CHO and 3MCHO by different polarity solvents and hydrogen bonding were clarified. • Effect of the electronic transitions of CHO by functionals were evaluated employing PCM and SCIPCM solvent models. • New band at 1653 cm−1 for CHO and at 1643 cm−1 for 3MCHO in water were assigned to their water clusters respectively. [ABSTRACT FROM AUTHOR]

Abstract A new compound named 7-hydroxy-4-methyl-2-oxo- 2H -chromene-8-carbaldehyde oxime (7-Oxime) was synthesized and characterized by FT-IR, FT-Raman, 1H NMR and 13C NMR techniques. The conformer possibilities were studied to find the most stable conformer and its molecular geometry. Then, the dimer form of the most stable monomer was built and optimized. Density functional theory (DFT) B3LYP method with 6-311++G(d,p) basis set was applied to analyze the molecular electrostatic potential (MEP), HOMO and LUMO orbitals, the vibrational wavenumbers, the infrared intensities, the Raman scattering activities and several thermodynamic properties (at different temperatures). The stability of the molecule derived from hyperconjugative interactions and charge delocalization has been analyzed by using natural bond orbital (NBO) analysis. In order to find the possible inhibitory activity of 7-Oxime, an accurate molecular blind docking simulation was performed. The results indicated that the mentioned compound has a good binding affinity to interact with the active sites of human α-glucosidase and α-amylase. For the first time, our computational finding suggests that this compound has a potential to be used as a supplementary agent in the pre-management of diabetes mellitus. Graphical Abstract Unlabelled Image Highlights • 7-hydroxy-4-methyl-2-oxo-2 H -chromene-8-carbaldehyde oxime has been synthesized. • The complete vibrational assignments and spectroscopic analyses were performed. • The druglikeness of the title compound was investigated by following Lipinski's rule of five. • The electronic structures of ligand/receptors were investigated with the radius of 4 Å. [ABSTRACT FROM AUTHOR]

[Display omitted] • Purple bacterial reaction centers with phylloquinone incorporated into the Q A binding site were studied. • Vibrational properties of the phyllosemiquinone anion in the protein binding site were calculated. • Calculated and experimental spectra agree well. [Q A – – Q A ] Fourier transform infrared difference spectra have previously been obtained using purple bacterial reaction centers from Rhodobacter sphaeroides with unlabeled, 18O and 13C isotope labeled phylloquinone (PhQ, also known as vitamin K 1) incorporated into the Q A protein binding site (Breton, (1997), Proc. Natl. Acad. Sci. USA 94 11318–11323). The nature of the bands in these spectra and the isotope induced band shifts are poorly understood, especially for the phyllosemiquinone anion (PhQ–) state. To aid in the interpretation of the bands in these experimental spectra, ONIOM type QM/MM vibrational frequency calculations were undertaken. Calculations were also undertaken for PhQ– in solution. Surprisingly, both sets of calculated spectra are similar and agree well with the experimental spectra. This similarity suggests pigment-protein interactions do not perturb the electronic structure of the semiquinone in the Q A binding site. This is not found to be the case for the neutral PhQ species in the same protein binding site. PhQ also occupies the A 1 protein binding site in photosystem I, and the vibrational properties of PhQ– in the Q A and A 1 binding sites are compared and shown to exhibit considerable differences. These differences probably arise because of changes in the degree of asymmetry of hydrogen bonding of PhQ– in the A 1 and Q A binding sites. [ABSTRACT FROM AUTHOR]

[Display omitted] • Raman spectra and vibrational properties of five FOX-7 polymorphs were calculated. • Phases α' and β are intermediate phases with transitional properties. • NH2 anti-symmetry-stretching softening under pressure corresponds to H-transfer. FOX-7 (1,1-diamino-2,2-dinitroethene) as one of the widely studied insensitive high explosives exists five polymorphs (α, β, γ, α', ε) whose crystal structures have been determined by XRD (X-rays Diffraction) and which are investigated by a density functional theory (DFT) approach in this work. The calculation results show that the GGA PBE-D2 method can reproduce the experimental crystal structure of FOX-7 polymorphs better. The calculated Raman spectra of FOX-7 polymorphs were compared in detail and fully with the experimental Raman spectra data and it was found that the calculated Raman spectra frequencies have an overall red-shift in middle band (800–1700 cm−1), and that the maximum deviation does not exceed 4 % (The maximum point is the mode of C C in plane bending). The high-temperature phase transform path (α → β → γ) and the high-pressure phase transform path (α → α'→ε) can be well represented in the computational Raman spectra. In addition, crystal structure of ε-FOX-7 was performed up to 70 GPa to probe Raman spectra and vibrational properties. The results showed that the NH 2 Raman shift is jittering with pressure (not smooth compared to other vibrational modes) and NH 2 anti-symmetry-stretching appears red-shifted. The vibration of hydrogen mixes in all of other vibrational modes. This work shows that the dispersion-corrected GGA PBE method can reproduce the experimental structure, vibrational properties and Raman spectra very well. [ABSTRACT FROM AUTHOR]

Inelastic neutron scattering (INS) and infra-red (IR) spectroscopy methods were used for determination of dynamic structure of l -leucine – chloranilic acid complex. A theoretical dynamic pattern calculated by the density functional theory (DFT) method for periodic boundary conditions accompanied the experimental ones. Normal modes in the vibrational spectra were defined and described. The characteristic presence of the Hadži's trio enriched by numerous submaxima is observed in the wavenumber range 3200–800 cm −1 . Bands assigned to CH 3 torsion vibrations in the leucine cation were observed at 231 cm −1 and 258 cm −1 in the INS spectrum. Temperature-dependent far-infrared spectra in the temperature range 9 K–290 K were obtained. Vibrational bands were analyzed as a function of temperature. Activation energies for reorientational motion of CH 3 and CH 2 groups were determined by means of the band shape analysis performed for torsional and twisting vibrations of these groups. The estimated energy is equal to E a  = 2.7 ± 0.2 kJ/mol and E a  = 2.17 ± 0.12 kJ/mol for CH 3 and CH 2 groups, respectively. A phase transition at about 130 K in the l -leucine – chloranilic acid complex was observed. [ABSTRACT FROM AUTHOR]

The equilibrium geometry, nuclear magnetic resonance (NMR) and UV–Vis analysis, and vibrational frequencies for the azo and hydrazone isomers of 1,3-dimethyl-5-(phenylazo)-6-aminouracil have been performed using density functional theory (DFT/B3LYP) method with 6–311G(d,p) basis set. A detailed interpretation of the vibrational spectra has been made on the basis of the calculated potential energy distribution (PED) obtained from the Vibrational Energy Distribution Analysis (VEDA4) program. The 1 H NMR chemical shifts with respect to TMS were calculated by the gauge independent atomic orbital (GIAO) method and compared with the experimental data. Stability of the molecule arising from hyper conjugative interactions, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. Using the TD-DFT method, electronic absorption spectra in CHCl 3 solvent of the title compound have been predicted, and good agreement is determined with the experimental one. The NLO properties such as mean polarizability (⟨ α ⟩), the anisotropy of the polarizability (⟨Δ α ⟩) and the mean first-order hyperpolarizability (⟨ β ⟩) were computed by using finite field method. The computed values of μ , α and β for the azo and hydrazone forms of the title molecule are 5.4717 and 3.8905 D, 2.7773 × 10 − 23 and 2.7598 × 10 − 23 esu, and 3.4499 × 10– 30 and 6.8504 × 10– 30 esu, respectively. The high β values and non-zero values of μ indicate that the title compound might be a good candidate for NLO material. [ABSTRACT FROM AUTHOR]

The spectroscopy of amide-I vibrations has been widely utilized for the understanding of dynamical structure of polypeptides. For the modeling of amide-I spectra, two frequency maps were built for β-peptide analogue ( N -ethylpropionamide, NEPA) in a number of solvents within different schemes (molecular mechanics force field based, GM map; DFT calculation based, GD map), respectively. The electrostatic potentials on the amide unit that originated from solvents and peptide backbone were correlated to the amide-I frequency shift from gas phase to solution phase during map parameterization. GM map is easier to construct with negligible computational cost since the frequency calculations for the samples are purely based on force field, while GD map utilizes sophisticated DFT calculations on the representative solute-solvent clusters and brings insight into the electronic structures of solvated NEPA and its chemical environments. The results show that the maps' predicted amide-I frequencies present solvation environmental sensitivities and exhibit their specific characters with respect to the map protocols, and the obtained vibrational parameters are in satisfactory agreement with experimental amide-I spectra of NEPA in solution phase. Although different theoretical schemes based maps have their advantages and disadvantages, the present maps show their potentials in interpreting the amide-I spectra for β-peptides, respectively. [ABSTRACT FROM AUTHOR]

In the present work we systematically investigated the vibrationally-resolved absorption spectra of three core substituted naphthalenediimide cyclophane derivatives. It has been performed by time-dependent density functional theory calculations using three different exchange-correlation functionals, including the conventional B3LYP functional and two long-range corrected functionals: CAM-B3LYP and ω B97XD. The solvent effects were also considered with the polarizable continuum model. Calculation results showed that long range corrections are needed to correctly describe the optical properties of the three molecules because of the strong charge transfer characteristic of the excited states. The core substitution induced red shift to the first absorption band is nicely explained by the theoretical calculations. It is found that this band mainly involves the transitions within the core substituted naphthalenediimide chromophore. The high energy absorption band, on the other hand, is generated mainly from the un-substituted chromophore. These characters result in different substitution dependence for those two main absorption bands. Furthermore, the simulated vibrational profiles of the first two absorption bands nicely reproduce the observed vibrational features in the measured spectra. The accuracy of the calculated results from different functionals and basis sets has been discussed. [ABSTRACT FROM AUTHOR]

The polar organic 2-(α-methylbenzylamino)-5-nitropyridine crystal (MBANP) has been studied by Raman spectroscopy at low temperatures (from 300 to 10 K). The effect of temperature change on the vibrational spectrum is discussed with the aid of DFT calculations. The behavior of the Raman spectra indicates that MBANP molecules present a different conformation at low temperatures associated with the rotation of the phenyl and pyridine rings. Temperature-dependent X-ray measurements and differential scanning calorimetry (DSC) analysis were utilized as complementary techniques to investigate the structural stability of MBANP crystal. [ABSTRACT FROM AUTHOR]

[Display omitted] • Synthesis of 8 branched Isopropyl-Imidazolium-ILs with Br, BF 4 , PF 6 , NTf 2 anions. • Infrared and Raman spectra of the methylated and protonated ILs are reported. • Vibrational assignments performed and confirmed by DFT calculations. • Electronic structure and hydrogen bonding analyzed by employing DFT calculations and AIM analysis. • Good agreement between experiments and DFT calculations. In the present work, four branched methylated, 1,2-dimethyl-3-isopropyl-imidazolium (i-[C 3 Dmim+]) and protonated,1-methyl-3-isopropyl-imidazolium (i-[C 3 mim+])-based ionic liquids (ILs) with varying anion (Br–, BF 4 –, PF 6 –, and NTf 2 –) were synthesized and investigated by NMR, infrared (IR) and Raman spectroscopy. Based on infrared and Raman spectroscopy, complete vibrational assignments have been performed. The IR and Raman analysis revealed that the vibrational spectra are virtually unaffected upon methylation, while significant frequency changes were observed by changing anion. Furthermore, to determine the electronic structure, energetic stability, and vibrational properties of these i-[C 3 Dmim]Y, i-[C 3 mim]Y (Y = Br, BF 4 , PF 6 , and NTf 2) ion pairs, quantum chemical calculations including the dispersion correction method are performed both on single ions and on ionic couples. The calculated electron density was analyzed to expose non-covalent intra- and interionic interactions by the quantum theory of atoms in molecules (AIM) and interpreted in terms of both anion dependence and type of interaction. Computational results suggest that for all ionic couples the most energetically stable configuration is obtained with the anions located close to the C2 position of the imidazolium cation. However, in the case of i-[C 3 mim]NTf 2 and i-[C 3 Dmim]BF 4 , similar energies were obtained in configurations 2 and 3 where the anion is located above the imidazolium ring. For i-[C 3 mim]Br a stronger hydrogen bond is predicted than for other studied ILs. Calculations indicate that a red shift of the CH stretching bands should occur due to hydrogen bonding; indeed, such displacement of bands is experimentally observed. [ABSTRACT FROM AUTHOR]

The vibrational spectra of 5-fluorocytosine, fumaric acid and their cocrystal were measured using terahertz time-domain spectroscopy (THz-TDS) and Raman spectroscopy at room temperature. Experimental THz results show that the cocrystal has distinct fingerprint spectra in terahertz region. The absorption peaks observed in the terahertz spectra of the cocrystal were at 0.61 and 0.91 THz. These are quite different from corresponding raw starting materials. Raman spectra also show similar results about differences between the cocrystal and corresponding raw starting materials. Density functional theory (DFT) was used to simulate the structure of the possible salt form and the cocrystal form between 5-fluorocytosine and fumaric acid. The theoretical terahertz result shows that the cocrystal form has absorption at 0.62 and 0.87 THz, which is in agreement with the experimental result. The theoretical Raman result also indicates that the cocrystal form has more possibilities than the salt form. So, it is more reasonable that the structure between 5-fluorocytosine and fumaric acid could be the corresponding cocrystal form. The characteristic bands of the cocrystal between 5-fluorocytosine and fumaric acid are also assigned based on the simulation results from the DFT calculation. [ABSTRACT FROM AUTHOR]

DFT and periodic-DFT (PAW-PBE method, code VASP) calculations have been performed to study the structural and vibrational characteristics of cis -diamminedichloroplatinum(II) (cisplatin) at molecular and outside molecular level. To estimate the effect of the intermolecular interactions in crystal on the structural and vibrational properties of cisplatin, three theoretical models are considered in the present study: monomer (isolated molecule), hydrogen bonded dimer and periodic solid state structures. The work focused on the role of the theoretical models for correct modeling and prediction of geometrical and vibrational parameters of cisplatin. It has been found that the elaborate three-dimensional intermolecular hydrogen bonding network in the crystalline cisplatin significantly influences the structural and vibrational pattern of cisplatin and therefore the isolated cisplatin molecule is not the correct computational model regardless of the theoretical level used. To account for the whole intermolecular hydrogen bonding network in direction of both a and c axis and for more reliable calculations of structural and vibrational parameters periodic DFT calculations were carried out in the full crystalline periodic environment with the known lattice parameters for each cisplatin polymorph phase. The model calculations performed both at molecular level and for the periodic structures of alpha and beta cisplatin polymorph forms revealed the decisive role of the extended theoretical model for reliable prediction of the structural and vibrational characteristics of cisplatin. The powder diffraction pattern and the calculated IR and Raman spectra predicted beta polymorph form of our cisplatin sample freshly synthesized for the purposes of the present study using the Dhara's method. The various rotamers realized in the polymorph forms of cisplatin were explained by the low population of the large number of rotamers in solution as well as with the high rotamer interconversion rate due to the low energy barrier. [ABSTRACT FROM AUTHOR]

A combined experimental and theoretical DFT study of the structural, vibrational and electronic properties of liriodenine is presented using B3LYP function with 6-311G (2d, p) basis set. The theoretical geometry optimization data were compared with the X-ray data for a similar structure in the associated literature, showing similar values. In addition, natural bond orbitals (NBOs), HOMO-LUMO energy gap, mapped molecular Electrostatic Potential (MEP) surface calculation, first and second order hyperpolarizabilities were also performed with the same calculation level. Theoretical UV spectrum agreed well with the measured experimental data, with transitions assigned. The molecular electrostatic potential map shows opposite potentials regions that forms hydrogen bonds that stabilize the dimeric form, which were confirmed by the close values related to the C O bond stretching between the dimeric form and the experimental IR spectra (1654 cm − 1 for the experimental, 1700 cm − 1 for the dimer form). Calculated HOMO/LUMO gaps shows the excitation energy for Liriodenine, justifying its stability and kinetics reaction. Molecular docking studies with Candida albicans dihydrofolate reductase (DHFR) and Candida albicans secreted aspartic protease (SAP) showed binding free energies values of − 8.5 and − 8.3 kcal/mol, suggesting good affinity between the liriodenine and the target macromolecules. [ABSTRACT FROM AUTHOR]

Polysilsesquioxanes (POSS) are molecules with the empirical formula (RSiO 1.5 ) n where R is a hydrogen atom or hydroxyl or an organic moiety such as an alkyl, alkene, acrylate or epoxide. The silicon atoms occupy the corners of a cube and oxygen atoms are located on the edges, the versatility of silsesquioxanes arises from the vacant fourth position of silicon. The choice of substituent enables a wide variety of properties to be engineered in a straightforward manner. The parent POSS is octasilsesquioxane, H 8 Si 8 O 12 , with R = H and n = 8. The present work employs periodic density functional theory calculations in conjunction with all the available vibrational (infrared, Raman and inelastic neutron scattering) spectra to generate a complete assignment of all the modes of the parent POSS octasilsesquioxane and some of its isotopomers for both the free, ( O h ), molecule and the solid state material ( C 3i site symmetry) including the forbidden and very weak modes. The latter are of interest because in less symmetrical silsesquioxanes, these modes will be activated. [ABSTRACT FROM AUTHOR]

Surface enhanced Raman spectroscopy (SERS) is a powerful vibrational spectroscopy technique that allows amplifying weak Raman signals by the excitation of localized surface plasmons. In this paper, we used nanoscale roughened silver surface to enhance Raman signals of melamine analyte. Silver nanoparticles were synthesized by wet-chemical method and employed for SERS measurement. Theoretically, optimized geometries and vibrational frequencies of melamine and melamine absorbed on silver-cluster surface were calculated by using the B3LYP/6-31G(d) method. Then, the predicted spectrograms are compared with the experimental Raman spectra. As a result, Raman signals of melamine were dramatically enhanced by using obtained silver nanoparticles as the substrate. Typical peaks of melamine at 676 and 983 cm − 1 were enhanced and could be obviously observed in experiments. The calculated vibrational frequencies seem to relatively coincide with the experimental values. SERS effect of melamine on nanoscale silver was also explained by analyzing molecular frontier orbitals (HOMO and LUMO) melamine–silver complexes. [ABSTRACT FROM AUTHOR]

The molecular structure of a new complex of copper (II) with (E)-9-ethyl-3-(2-(6-(4-methylpyridin-2-yl)pyridin-3-yl)vinyl)-9H-carbazole ([Cu 2 (emppc) 2 Cl 2 ]Cl 2 ) was optimized with B3LYP/LanL2DZ, PBE1PBE/LanL2DZ and M062X/LanL2DZ theoretical level. The ligand, (E)-9-ethyl-3-(2-(6-(4-methylpyridin-2-yl)pyridin-3-yl)vinyl)-9H-carbazole (emppc), binds to Cu(II) ions with a bi-dentate mode, two Cl − serve as bridging ligand, each Cu(II) ion has a highly distorted tetrahedron coordination geometry. With M062X/LanL2DZ theoretical level, the calculated interaction energies of Cu(II) with coordination atoms N are between 183.3–200.0 kJ mol − 1 for α spin and 319.4–324.9 kJ mol − 1 for β spin, and interaction energies of Cu(II) with coordination atoms Cl atom are 248.0–252.4 kJ mol − 1 for α spin and 332.6–333.6 kJ mol − 1 for β spin. The experimental Fourier transform infrared spectrum was assigned. The calculated IR based on B3LYP/LanL2DZ, PBE1PBE/LanL2DZ and M062X/LanL2DZ methods were performed and compared with experimental results. The UV–Vis experimental spectra of [Cu 2 (emppc) 2 Cl 2 ]Cl 2 was measured in methanol solution. The calculated electronic spectrum was performed with TD/M062X and PCM-TD/M062X methods with LanL2DZ basis set. The nature bond orbital analysis and temperature dependence of the thermodynamic properties were calculated with the same methods. [ABSTRACT FROM AUTHOR]

The structure and several spectroscopic features along with reactivity parameters of the compound 4-(6-methoxy-2-naphthyl)-2-butanone (Nabumetone) have been studied using experimental techniques and tools derived from quantum chemical calculations. Structure optimization is followed by force field calculations based on density functional theory (DFT) at the B3LYP/6-311++G(d,p) level of theory. The vibrational spectra have been interpreted with the aid of normal coordinate analysis. UV–visible spectrum and the effect of solvent have been discussed. The electronic properties such as HOMO and LUMO energies have been determined by TD-DFT approach. In order to understand various aspects of pharmacological sciences several new chemical reactivity descriptors - chemical potential, global hardness and electrophilicity have been evaluated. Local reactivity descriptors - Fukui functions and local softnesses have also been calculated to find out the reactive sites within molecule. Aqueous solubility and lipophilicity have been calculated which are crucial for estimating transport properties of organic molecules in drug development. Estimation of biological effects, toxic/side effects has been made on the basis of prediction of activity spectra for substances (PASS) prediction results and their analysis by Pharma Expert software. Using the THz-TDS technique, the frequency-dependent absorptions of NBM have been measured in the frequency range up to 3 THz. [ABSTRACT FROM AUTHOR]

Molecular modeling and potential energy scanning of histamine molecule, which is an important neurotransmitter, with respect to the dihedral angle of methylamine side chain have done which prefer three different conformers of histamine monomer. We have calculated molecular structures and vibrational spectra with IR and Raman intensities of these conformers using Density Functional Theory (DFT) with the exchange functional B3LYP incorporated with the basis set 6-31 ++G(d,p) and Hartree-Fock (HF) with the same basis set. We have also employed normal coordinate analysis (NCA) to scale the theoretical frequencies and to calculate potential energy distributions (PEDs) for the conspicuous assignments. Normal modes assignments of some of the vibrational frequencies of all the three conformers are in good agreement with the earlier reported experimental frequencies of histamine whereas others have modified. The standard deviations between the theoretical and experimental frequencies fall in the region 13–20 cm − 1 for the three conformers. NBO analyses of histamine conformers were also performed. The net charge transfers from ethylamine side chain to the imidazole ring. The intensive interactions between bonding and anti-bonding orbitals are found in imidazole ring. The HOMO-LUMO energy gap is nearly 5.50 eV. [ABSTRACT FROM AUTHOR]

[Display omitted] • Interactions between pterin (Ptr) and Ag clusters have been explored using quantum chemistry. • It has been established that Ptr-Ag 3 2+ complex is the most favorable one. • Presence of Ag clusters significantly red-shifts the absorption spectrum of Ptr. • SERS detection has potential benefits in both acidic and alkaline pH. Metal nanoclusters (NCs) are widely present today in biosensing, bioimaging, and diagnostics due to their small size, great biocompatibility, and sensitivity to the biomolecular environment. Silver (Ag) NCs often possess intense fluorescence, photostability, and low photobleaching, which is in high demand during the detection of organic molecules. Pterins are small compounds, which are used in medicine as biomarkers of oxidative stress, cardiovascular diseases, neurotransmitter synthesis, inflammation and immune system activation. It is experimentally possible to detect pterin (Ptr) through the adsorption on Ag colloid. We optimized geometries and evaluated the binding energy in Ptr-Ag n q complexes (n = 1–6; q = 0, +1, +2) using quantum chemistry methods. Different Ptr atoms were preferential for silver attachment depending on NC charge and size. The highest E b was obtained for the complexes between the Ptr0 and Ag 3 2+ (-50.8 kcal mol−1), between Ptr-1 and Ag 3 2+ (-64.8 kcal mol−1), which means that these complexes should be formed preferably in aqueous solutions in acidic and alkaline media, respectively. The colorimetric detection of pterin with silver clusters does not seem to be promising. However, intense S 0→ S 1 transitions of Ag 5 + complexes look promising for luminescent Ptr detection. SERS detection of pterin is better to be done at pH > 8 since deprotonated pterin Raman undergo more dramatic changes upon addition of Ag than the neutral pterin. The characteristics of absorption and vibrational spectra of silver-pterin should be exploited during biosensor development. [ABSTRACT FROM AUTHOR]

Infrared and Raman spectral measurements in the region 4000–400 cm − 1 have been carried out for (R)-(+)-Methylsuccinic acid. The vibrational band structures near 3100–3040 cm − 1 in the IR and near 1650 cm − 1 in the Raman spectra have indicated the presence of an inter-molecular hydrogen bonding. A DFT dimer model has been proposed that involves O–H ⋯ OC type of hydrogen bonding. The proposed dimer model has been derived from the three stable monomers computed at RHF/3-21G and B3LYP/6-311 + G(d,p) levels of theory. A total of six dimer structures have been considered with a Boltzmann population of 38% for the most stable dimer and 62% for the remaining five dimer populations. A Boltzmann population weighted vibration spectrum has predicted bands, among others, for O–H ⋯ OC group that are in very good agreement with experiment. All the dimers have the same structure in that the two pairs of –O–H and –OC form a closed cyclic structure with a local center of inversion. This dimer geometry has given rise to one asymmetric mode at 1683 and one symmetric –CO mode at 1637 cm − 1 corresponding to mutually exclusive an experimental IR band at 1700 and a Raman band at 1651 cm − 1 . Further, the bond length, H ⋯ O, for the most stable dimer is 1.686 Å, being shorter than the sums of van der Waals radii, 2.72 Å and the angle between O–H and H ⋯ O is almost linear (179°) suggesting that the hydrogen bonding is fairly strong. [ABSTRACT FROM AUTHOR]

Bis(4-amino-5-mercapto-1,2,4-triazol-3-yl)propane (BAMTP) was synthesized and characterized by FT-IR and FT-Raman spectra. Gas phase structure of BAMTP was examined under density functional theory B3LYP/6-311 ++G(d, p) level of basis set, wherein the molecule was subjected to conformational analysis. Thus the identified stable structure utilized for the calculations such as geometry optimization, vibrational behavior, hyperpolarizability analysis, natural bond orbital analysis, band gap, chemical hard/softness and stability. Geometry of BAMTP has been discussed elaborately with related crystal data. The results found from experimental and theoretical methods were reported herewith. [ABSTRACT FROM AUTHOR]

Combined computational/FTIR spectroscopic analyses of 3-methyl-2-oxazolidinone (NMO) solutions with varying molar ratios of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) are reported. Based on the second derivative spectral profile, overlapping peaks are distinguished as well as assigned to the vibrational modes of implicitly and explicitly interacting NMO molecules. Thereby, the geometry of a monomeric, a dimeric and a simplified solvation structure [Li(NMO) 1 ] + are optimized with a polarizable continuum model at a B3LYP theoretical level. With increasing contents of LiTFSI, the formation of Li + solvation structures is scrutinized by semi-quantitative analysis of deconvoluted integral peak areas for three different ring-related vibrations and C O-stretch vibration. A discrepancy in the obtained data is observed implying the influence of the TFSI anion the ring-related vibrations are prone to. The solvation number of 4 is determined according to the C O-signal in diluted solution, which is proven by the computed Gibbs free energy for solvation of [Li(NMO) 4 ] + in a NMO medium (− 41.7 kcal mol − 1 ). [ABSTRACT FROM AUTHOR]

The structure and harmonic vibrations of Li n F n ( n = 3–10) clusters have been investigated using density functional theory. All structures are found to be cumulenic D nh rings (equal bonds, alternating angles), with one intense out of plane mode and three infrared-active degenerate modes, of which the highest one is extremely intense and asymptotically increases to 1597 cm −1 for n = 10 at the B3LYP/6–311++G(2d,2p) level. Comparisons with C 2 n clusters, B n N n and Be n O n clusters, the structure and bonding type for the Li n F n clusters are consistent with those of the C 2 n ( n = 3,5,7,…) clusters, B n N n ( n = 3–10) and Be n O n ( n = 3–10) clusters. [ABSTRACT FROM AUTHOR]

FT-IR and FT-Raman spectra of bis[( E )-anthranyl-9-acrylic]anhydride were recorded and analyzed. The conformational behavior is also investigated. The vibrational wave numbers were calculated using density functional theory (DFT) quantum chemical calculations. The data obtained from wave number calculations are used to assign vibrational bands obtained in Infrared and Raman spectra. Potential energy distribution was done using GAR2PED program. The geometrical parameters are compared with related structures. The stability of the molecule arising from hyper-conjugative interaction and charge delocalization has been analyzed using Natural Bonding Orbital (NBO) analysis. The Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) analysis are used to determine the charge transfer within the molecule. Molecular Electrostatic Potential (MEP) was performed by the DFT method. The calculated first hyperpolarizability of the title compound is comparable with the reported values of similar derivatives and is 4.23 times that of the standard nonlinear optical (NLO) material urea and the title compound and its derivatives are an attractive object for future studies of nonlinear optical properties. To evaluate the in silico antitumor activity of the title compound molecular docking studies were carried out against protein Bcl-xL. The 1 H-NMR spectrum is also reported. [ABSTRACT FROM AUTHOR]

In a recently published paper [Spectrochim. Acta A: Mol. Biomol. Spect. 138 (2015) 711–722], Prabhaharan, Prabakaran, Srinivasan, and Gunasekaran presented a combined experimental and theoretical study on molecular structure, vibrational spectra and NBO analysis of cyanuric acid, and explain their findings using the tri-hydroxy tautomeric form of the compound. In reality, the compound adopts the tri-oxo tautomeric form, which is by over 100 kJ mol −1 more stable comparatively to the tri-hydroxy tautomer discussed and characterized by Prabhaharan et al. [ABSTRACT FROM AUTHOR]

Violacein is a bisindole pigment occurring as a biosynthetic product of Chromobacterium violaceum and Janthinobacterium lividum. It has some structural similarities to the cyanobacterial UV-protective pigment scytonemin, which has been the subject of comprehensive spectroscopic and structural studies. A detailed experimental Raman spectroscopic study with visible and near-infrared excitation of violacein produced by C. violaceum has been undertaken and supported using theoretical DFT calculations. Raman spectra with 514 and 785 nm excitation of cultivated cells as well as extracts and Gaussian (B3LYP/6-311++G(d,p)) calculations with proposed molecular vibrational assignments are reported here. [ABSTRACT FROM AUTHOR]

Bis(melaminium) sulphate dihydrate (BMSD), an interesting melaminium derivative for nonlinear optical activity, has been subjected to vibrational spectral analysis using FT IR and FT Raman spectra. The analysis has been aided by the Potential Energy Distribution (PED) of vibrational spectral bands, derived using density functional theory (DFT) at B3LYP/6-31G(d) level. The geometry is found to correlate well with the XRD structure and the band profiles for certain vibrations in the finger print region have been theoretically explained using Evans hole. The detailed Natural Bond Orbital (NBO) analysis of the hydrogen bonding in BMSD has also been carried out to understand the correlation between the stabilization energy of hyperconjugation of the lone pair of donor with the σ ∗ orbital of hydrogen-acceptor bond and the strength of hydrogen bond. The theoretical calculation shows that BMSD has NLO efficiency, 2.66 times that of urea. The frontier molecular orbital analysis points to a charge transfer, which contributes to NLO activity, through N–H…O intermolecular hydrogen bonding between the melaminium ring and the sulphate. The molecular electrostatic potential (MEP) mapping has also been performed for the detailed analysis of the mutual interactions between melaminium ring and sulphate ion. [ABSTRACT FROM AUTHOR]

In the present work, we have synthesized and reported a combined experimental and theoretical study on the molecular structure, vibrational spectra and HOMO–LUMO analysis of N,N′-diphenyl-6-piperidin-1-yl-[1,3,5]-triazine-2,4-diamine (C 20 N 6 H 22 ). The FT-IR and FT-Raman spectra of N,N′-diphenyl-6-piperidin-1-yl-[1,3,5]-triazine-2,4-diamine were recorded. The molecular geometry, harmonic vibrational wavenumbers and bonding features of the title molecule in the ground-state have been calculated by using the density functional B3LYP method with 6-31G(d) as basis set. Non-linear optical (NLO) behavior of the N,N′-diphenyl-6-piperidin-1-yl-[1,3,5]-triazine-2,4-diamine was investigated by determining the electric dipole moment μ , polarizability α , and hyperpolarizability β using the above mentioned basis set. The molecular properties such as ionization potential, electro-negativity, chemical potential, electrophilicity have been deduced from HOMO–LUMO analysis employing the same basis set. The calculated HOMO and LUMO energies showed that charge transfer occurs within the molecule. Stability of the molecule arising from hyper conjugative interaction and charge delocalization has been analyzed using natural bond orbital (NBO) analysis. Finally, the calculation results were applied to simulate infrared and Raman spectra of the title compound which showed good agreement with the observed spectra. [ABSTRACT FROM AUTHOR]

Spectroscopic and theoretical quantum chemical studies of 2,5-dihydrothiophene-1,1-dioxide and 3-methyl-2,5-dihydrothiophene-1,1-dioxide have been carried out by FTIR and FT-Raman spectral techniques along with B3LYP methods. The geometry of the compounds have been optimised by B3LYP method with 6-311++G ∗∗ and cc-pVTZ basis sets. The geometrical parameters obtained at B3LYP levels have been compared with the experimental values. Molecular electrostatic potential surface, total electron density distribution and frontier molecular orbital are constructed at B3LYP/cc-pVTZ level to understand the electronic properties. The charge density distribution and sites of chemical reactivity of the molecules have been obtained by mapping electron density isosurface with electrostatic potential surfaces. Natural bond orbital analysis of the molecules are carried out and the occupancies and the atomic hybrid contributions are calculated. [ABSTRACT FROM AUTHOR]

FT-IR and FT-Raman spectra of ethyl 3-( E )-(anthracen-9-yl)prop-2-enoate were recorded and analyzed. The conformational behavior of the molecule was also investigated. The vibrational wavenumbers were calculated using DFT quantum chemical calculations. The data obtained from the wavenumber calculations were used to assign vibrational bands obtained experimentally. The geometrical parameters are in agreement with XRD data. The stability of the molecule arising from hyper-conjugative interaction and charge delocalization has been analyzed using NBO analysis. The HOMO and LUMO analysis were used to determine the charge transfer within the molecule and quantum chemical parameters related to the title compound. From the MEP analysis, it is clear that the negative electrostatic potential regions are mainly localized over the carbonyl groups and anthracene ring and are possible sites for electrophilic attack and the positive regions are localized at all the hydrogen atoms as possible sites for nucleophilic attack. NLO and NMR studies are also reported. Molecular docking studies suggest that the title compound might exhibit inhibitory activity against IDE and may act as an insulysin inhibitor. Conformational analysis is also reported. [ABSTRACT FROM AUTHOR]

FT-IR and FT-Raman spectra of 2-[( E )-2-phenylethenyl]quinoline-5-carboxylic acid were recorded and obtained and analyzed. The vibrational wavenumbers were computed using DFT quantum chemical calculations. The geometrical parameters (SDD) of the title compound are in agreement with that of similar derivatives. Stability of the molecule arising from the hyper conjugative interactions, charge delocalization has been analyzed using natural bond orbital analysis. From the natural and Mulliken charges, it can be concluded that electrophilic substitution of the quinoline scaffold is more preferred than nucleophilic substitution. From the MEP map it is evident that the negative regions are mainly localized over the carbonyl group and are possible sites for electrophilic attack. The title compound forms a stable complex with PknB as is evident from the binding affinity values and the molecular docking study suggests that the compound might exhibit inhibitory activity against PknB. [ABSTRACT FROM AUTHOR]

In the present work, the structural and vibrational properties of the sesquiterpene lactone onopordopicrin (OP) were studied by using infrared spectroscopy and density functional theory (DFT) calculations together with the 6-31G ∗ basis set. The harmonic vibrational wavenumbers for the optimized geometry were calculated at the same level of theory. The complete assignment of the observed bands in the infrared spectrum was performed by combining the DFT calculations with Pulay’s scaled quantum mechanical force field (SQMFF) methodology. The comparison between the theoretical and experimental infrared spectrum demonstrated good agreement. Then, the results were used to predict the Raman spectrum. Additionally, the structural properties of OP, such as atomic charges, bond orders, molecular electrostatic potentials, characteristics of electronic delocalization and topological properties of the electronic charge density were evaluated by natural bond orbital (NBO), atoms in molecules (AIM) and frontier orbitals studies. The calculated energy band gap and the chemical potential ( μ ), electronegativity ( χ ), global hardness ( η ), global softness ( S ) and global electrophilicity index ( ω ) descriptors predicted for OP low reactivity, higher stability and lower electrophilicity index as compared with the sesquiterpene lactone cnicin containing similar rings. [ABSTRACT FROM AUTHOR]

The Fourier-Transform Infrared and Fourier-Transform Raman spectra of 2,2-diphenyl-4-(piperidin-1-yl)butanamide were recorded in the region 4000–400 cm −1 and 4000–0 cm −1 . The vibrational wavenumbers are computed using HF and DFT methods. The complete vibrational assignments were performed on the basis of potential energy distribution using GAR2PED program. The geometrical parameters of the title compound are in agreement with the XRD data. From the MEP study, the negative electrostatic potential regions are mainly localized of carbonyl group and are possible sites for electrophilic attack and the positive regions are localized all the rings, indicating possible sites for nucleophilic attack. Stability of the molecule arising from hyper-conjugative interaction and charge delocalization has been analyzed using natural bond orbital analysis. The calculated HOMO and LUMO energies also confirm that charge transfer occurs within the molecule. PASS analysis of the title compound predicts among other activities, antidyskinetic activity. Molecular docking results draw us to the conclusion that the compound might exhibit inhibitory activity against adenosine A2A and may act as antidyskinetic agent. [ABSTRACT FROM AUTHOR]

In this study, FT-IR spectrum of 4-(imidazol-1-yl)phenol was recorded. Its vibrational frequencies and modes were determined. Vibrational assignments were proposed with the help of B3LYP/6-311++G(d,p) level of calculations. Three possible dimeric forms of the molecule were investigated theoretically. Besides, solvent effects on the structure, vibrational frequencies, and atomic charges were studied theoretically. Water, dimethyl sulfoxide, and ethanol were the solvents considered. Experimental FT-IR spectrum in DMSO solution was recorded and compared with solid phase experimental data. DFT B3LYP combined with polarized continuum model (PCM) was employed to characterize the solvent effects. [ABSTRACT FROM AUTHOR]

In this study based on vibrational spectroscopic measurements and Density Functional Theory (DFT), we aimed for a reliable interpretation of the IR and Raman spectra recorded for anserine in the solid phase and water (H 2 O) and heavy water (D 2 O) solutions. Initial DFT calculations at the B3LYP/6-31G(d) searched possible conformers of the anserine zwitterion using a systematic conformational search. The corresponding equilibrium geometrical parameters and vibrational spectral data were determined for each of the stable conformers (in water) by the geometry optimization and hessian calculations performed at the same level of theory using the polarized continuum model (PCM). The same calculations were repeated to determine the most energetically preferred dimer structure for the molecule and the associated geometry, force field and vibrational spectral data. The harmonic force constants obtained from these calculations were scaled by the Scaled Quantum Mechanical Force Field (SQM) method and then used in the calculation of the refined wavenumbers, potential energy distributions, IR and Raman intensities. These refined theoretical data, which confirm the zwitterion structure for anserine in the solid phase or aqueous solvents, revealed the remarkable effects of intermolecular hydrogen bonding on the structural properties and observed IR and Raman spectra of this molecule. [ABSTRACT FROM AUTHOR]

The vibrational properties of glutathione have been investigated by infrared absorption and Raman spectroscopic techniques, and density functional theory calculations at the B3LYP/6-31+G(d,p) level. Assignments of all the experimentally observed vibrational bands have been done with the help of simulated vibrational spectra and potential energy distribution calculations of glutathione water cluster, which includes the effect of hydrogen bonding. Optimized molecular parameters of energy minimized structure have been compared with the available experimental values. Calculated molecular parameters of glutathione–water cluster match well with the experimental values. Some of the calculated molecular parameters and vibrational frequencies of vapor phase glutathione–water cluster suggest participation of some atoms of glutathione in hydrogen bonding. Experimentally observed UV–Visible absorption spectrum of glutathione has also been reported. Observed band at 203 nm has been assigned to electronic transitions calculated with time dependent density functional theory. [ABSTRACT FROM AUTHOR]

Molecular structure and properties of 1-(2-hydroxy-4,5-dimethylphenyl)ethanone were experimentally investigated by X-ray diffraction technique and vibrational spectroscopy. Experimental results on the molecular structure of the reported compound were supported with computational studies using the density functional theory (DFT), with the Becke-3-Lee–Yang–Parr (B3LYP) functional and the 6-311+G(3df,p) basis set. Potential energy distribution (PED) and potential energy surface (PES) analyses were performed to identify characteristic frequencies and reliable conformational analysis correspondingly. The compound crystallizes in monoclinic space group C 2/ c with the CO up–OH down conformation. There is a good agreement between the experimentally determined geometrical parameters and vibrational frequencies of the compound to those predicted theoretically. [ABSTRACT FROM AUTHOR]

Amylamine constitutes an important class of organic compounds which exists in a variety of ammonia derivatives. In present study, a comparative analysis of amylamine and its two potential isomers, iso-amylamine and tert-amylamine, has been performed using density functional theory with B3LYP method and 6-311G(d,p) as the basis set. The equilibrium structures of amylamine as well as its iso and tert forms have been obtained. The vibrational spectroscopic analysis has been carried out for the three molecules and complete assignments to all possible modes have been offered. The HOMO, LUMO and MESP surfaces are analyzed to discuss the chemical reactivity patterns in the molecules. A number of reactivity parameters have been calculated to further explain their chemical reactivity. The thermodynamic and nonlinear optical parameters are also calculated and discussed. [ABSTRACT FROM AUTHOR]

In this work we present a study of the vibrational spectra of 4,5,6,8,9-pentachloropyrimido-[1,2-a][1,8]naphthyridin-10-one, C 11 H 2 Cl 5 N 3 O, a substance belonging to the important pharmacological class of 1,8-naphthyridine derivatives. The Fourier transform infrared and the Fourier transform Raman spectra of the crystal were recorded at room temperature in the regions 400–4000 and 50–4000 cm −1 , respectively. Vibrational wavenumbers were predicted using Density Functional Theory calculations with the B3LYP functional on 6-31G(d,p) and 6-311++G(d,p) basis sets. The descriptions of the normal modes were made after calculating the potential energy distribution. Additionally, potential reaction sites were evaluated through Mulliken population and Frontier Orbital analysis. [ABSTRACT FROM AUTHOR]

In this work, we reported a combined experimental and theoretical study on molecular structure, vibrational spectra and Homo–Lumo analysis of Purpurin and TiO 2 /Purpurin. The geometries, electronic structures, molecular orbital analysis of natural dye sensitizer Purpurin were studied based on density functional theory (DFT) using the hybrid functional B3LYP. Fourier transform infrared (FT-IR) and FT-Raman spectra have been recorded and extensive spectroscopic investigations have been carried out on Purpurin. The optimized geometries, wave number and intensity of the vibrational bands of Purpurin have been calculated using density functional level of theory (DFT/B3LYP) employing 6-311G (d, p) basis set. Based on the comparison between calculated and experimental results, assignments of the fundamental vibrational modes are examined. Features of the electronic absorption spectrum in the visible and near-UV regions were assigned based on TD-DFT calculations. The calculated results suggest that the three excited states with the lowest excited energies in 1,2,4, trihydroxy 9-10 anthraquinone was due to photo-induced electron transfer processes. Frontier molecular orbitals (FMO), LUMO, HOMO, and energy gap, of these dyes have been analyzed to show their effect on the process of electron injection and dye regeneration. Interaction between HOMO and LUMO of Purpurin are investigated to understand the recombination process and charge transfer process involving these dyes. We also performed analysis of I–V characteristics to investigate the role of charge transfer and the stability of the dye molecule. [ABSTRACT FROM AUTHOR]

The experimental and theoretical spectra of (S)-2-Oxopyrrolidin-1-yl Butanamide (S2OPB) were studied. FT-IR and FT-Raman spectra of S2OPB in the solid phase were recorded and analyzed in the range 4000–450 and 5000–50 cm −1 respectively. The structural and spectroscopic analyses of S2OPB were calculated using ab initio Hartree Fock (HF) and density functional theory calculations (B3PW91, B3LYP) with 6-31G(d,p) basis set. A complete vibrational interpretation has been made on the basis of the calculated Potential Energy Distribution (PED). The HF, B3LYP and B3PW91 methods based NMR calculation has been used to assign the 1 H NMR and 13 C NMR chemical shift of S2OPB. Comparative study on UV–Vis spectral analysis between the experimental and theoretical (B3PW91, B3LYP) methods and the global chemical parameters and local descriptor of reactivity through the Fukui function were performed. Finally the thermodynamic properties of S2OPB were calculated at different temperatures and the corresponding relations between the properties and temperature were also studied. [ABSTRACT FROM AUTHOR]

Experimental IR and solution phase spectra of (R)-(−)-2-Pyrrolidinemethanol showing evidence of hydrogen bonding have been interpreted by computing vibrational modes of monomers and dimers with the molecular species due to intra - and inter -molecular hydrogen bonding, at B3LYP/6-311+G(d,p) level density functional theoretical calculations. Computed vibrational frequencies of Boltzmann population-weighted dimers for stretching and bending of O H and N H modes associated with the inter -molecular N H⋯O and O H⋯O hydrogen bonding are in good agreement with the measured IR absorption, Raman and solution-phase IR values near 3289 cm −1 , 3450 cm −1 and 1400–1300 cm −1 . Further, the H⋯O length is shorter in O H⋯O than in N H⋯O by ∼10% suggesting that O H⋯O is a stronger bond. While the solution-phase IR spectral features suggest strong inter -molecular associations, it is short of demonstrating which type of bonding is dominant factor. We conclude that the measured IR, Raman and solution-phase IR spectral features indicate the presence of both types of hydrogen bonds. [ABSTRACT FROM AUTHOR]

A novel (2 E )-1-(5-chlorothiophen-2-yl)-3-{4-[( E )-2-phenylethenyl]phenyl}prop-2-en-1-one [C 21 H 15 ClOS] compound has been synthesized and its structure has been characterized by FT-IR, Raman and single-crystal X-ray diffraction techniques. The conformational isomers, optimized geometric parameters, normal mode frequencies and corresponding vibrational assignments of the compound have been examined by means of HF, MP2, BP86, BLYP, BMK, B3LYP, B3PW91, B3P86 and M06-2X functionals. Reliable vibrational assignments and molecular orbitals have been investigated by the potential energy distribution and natural bonding orbital analyses, respectively. The compound crystallizes in the triclinic space group P -1 with the cis – trans–trans form. There is a good agreement between the experimentally determined structural parameters and vibrational frequencies of the compound and those predicted theoretically using the density functional theory with the BLYP and BP86 functionals. [ABSTRACT FROM AUTHOR]

Combined experimental and theoretical studies were conducted on the molecular structure and vibrational spectra of 4-AminoPhthalhydrazide (APH). The FT-IR and FT-Raman spectra of APH were recorded in the solid phase. The molecular geometry and vibrational frequencies of APH in the ground state have been calculated by using the ab initio HF (Hartree–Fock) and density functional methods (B3LYP) invoking 6-311+G(d,p) basis set. The optimized geometric bond lengths and bond angles obtained by HF and B3LYP method show best agreement with the experimental values. Comparison of the observed fundamental vibrational frequencies of APH with calculated results by HF and density functional methods indicates that B3LYP is superior to the scaled Hartree–Fock approach for molecular vibrational problems. The difference between the observed and scaled wave number values of most of the fundamentals is very small. A detailed interpretation of the NMR spectra of APH was also reported. The theoretical spectrograms for infrared and Raman spectra of the title molecule have been constructed. UV–vis spectrum of the compound was recorded and the electronic properties, such as HOMO and LUMO energies, were performed by time dependent density functional theory (TD-DFT) approach. Finally the calculations results were applied to simulated infrared and Raman spectra of the title compound which show good agreement with observed spectra. And the temperature dependence of the thermodynamic properties of constant pressure ( C p ), entropy ( S ) and enthalpy change (Δ H 0 → T ) for APH were also determined. [ABSTRACT FROM AUTHOR]

In this study, in which the group vibrations of 3-aminophenylacetic acid were investigated by electronic structure calculations based on Density Functional Theory (DFT), the possible stable conformers of the molecule were searched through a relaxed “potential energy surface scan” carried out at B3LYP/6-31G(d) level of theory. The corresponding equilibrium geometrical and vibrational spectral data for each of the determined stable conformers and for their possible dimer structures were obtained through “geometry optimisation” and “frequency” calculations carried out at B3LYP/6-31G(d) and B3LYP/6-311G++(d,p) levels of theory. The obtained results confirmed that anharmonic wavenumbers calculated at B3LYP/6-311G++(d,p) level generally quite well agree with the experimental wavenumbers, however, harmonic wavenumbers calculated at both levels of theory need an efficient refinement for a satisfactory agreement with experiment. In particular, the harmonic wavenumbers, IR and Raman intensities refined within Scaled Quantum Mechanical Force Field (SQM FF) methodology constituted the primary data set in the interpretation of the experimental FT-IR, FT-Raman and dispersive Raman spectra of 3-aminophenylacetic acid. By the help of these refined spectral data, the effects of conformation and intermolecular hydrogen bonding on the fundamental bands observed in the experimental spectra could be correctly predicted. [ABSTRACT FROM AUTHOR]