AM1 study on the conformations and electronic properties of phenethicillin (original) (raw)
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AM1 study of the electronic structure of Methicillin
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The geometry, conformation and electronic structure of methicillin have been optimized and calculated in the gas phase, usually considering an isolated molecule surrounded in a vacuum by using semi-empirical molecular orbital AM1 method. Further, the mechanism of protonation in methicillin has been studied by comparison of the different positions of net charges on nitrogen atoms in the molecule. In this connection, the heats of formation (∆Hf o ), dipole moment (µ), ionization potential (IP), full atomic charges and energies of frontier molecular orbitals (EHOMO and ELUMO) have been performed and discussed. The conformational analyses of mono- and diprotonated species have also been performed for stable conformations.
AM1 study on the conformations and electronic properties of Phenoxymethylpenicillin
The geometry, conformation and electronic structure of phenoxymethylpenicillin have been optimized and calculated in the gas phase by semi-empirical molecular orbital AM1 method usually considering an isolated molecule surrounded by vacuum. Further, the mechanism of protonation in phenoxymethylpenicillin has been studied by comparison of the different positions of net charges on nitrogen atoms in the molecule. In this connection, the heats of formation (∆H f o), dipole moment (µ), ionization potential (IP), full atomic charges and energies of frontier molecular orbitals (E HOMO and E LUMO) have been performed and discussed. The conformational analyses of mono-and di-protonated species and their stable conformations have also been performed. Introduction Penicillin derivatives have been studied extensively because of their broad anti-microbial spectra, more favourable absorption patterns and reduced undesirable side effects 1 . Significance of β-Lactam ring of penicillin has been kno...
Pteridines, 1998
SummaryAb initio quantum chemical computations at the Hartree-Fock 6-31g** level of theory were performed on pterin, 7,8-dihydropterin and 5,6,7,8 -tetrahydropterin. The resulting electronic charge density functions and the electrostatic potential functions of the molecules are visualized by graphical software. The results demonstrate the profound changes in electronic properties among these structurally closely related compounds. Our contribution may serve as a basis for deeper insight into the molecular characteristics, also of other chemically or biologically important pterin derivatives of different oxidation state.
AM1 study on the conformations of keto-enol tautomerism in methicillin
The geometry, conformation and electronic structure of keto-enol tautomerism in methicillin have been optimized and calculated in the gas phase usually considering an isolated molecule surrounded by vacuum using semi-empirical molecular orbital AM1 method. The mechanism of protonation in enol tautomer of methicillin has been studied by comparison of the different positions of net charges at nitrogen atoms in the molecule. Further, the heats of formation (∆H f o ), dipole moment (µ), ionization potential (IP), full atomic charges and energies of frontier molecular orbitals (E HOMO and E LUMO ) have been performed and discussed. The conformational analyses of mono-and di-protonated enol tautomers have also been performed for their stable conformations.
Journal of Molecular Structure: THEOCHEM, 2010
The effect induced by introducing electron captor substituent, namely, fluorine in the arene rings of phenoxathiin on the structure of the phenoxathiin nucleus have been studied using the ab initio method at the B3LYP/(6-31+G)+d basis set level. The study predicts and analyses the configuration of several not yet synthesized fluorinated-phenoxathiin derivatives. Thus, the magnitude of change in the puckering angle U c of phenoxathiin was found to be dependent on the position of the fluorine atom with respect to the oxygen atom of the central heterocyclic ring. Substitution at the 1-position, meta to the oxygen did induce flattening of the nucleus i.e. increased U c , while substitutions at the 2-and 4-positions, para and ortho to the oxygen, respectively, induced further puckering on the nucleus i.e. decreased U c. Successive substitution at these positions enhanced these effects. Thus, 1,9-difluorophenoxathiin was found to be the most flattened, while 2,3,4,6,7,8-hexafluorophenoxathiin was found to be the most puckered fluorinated phenoxathiins. The predicted inversion barrier for all the studied compounds was very small; it did not exceed 1.67 kcal/mol for the most puckered isomer. Consequently, we anticipated these compounds to enjoy an easy butterfly interconversion.
Journal of Molecular Structure, 1999
The IR (4000-400 cm Ϫ1) and Raman (4000-50 cm Ϫ1) spectra of 3-methoxymethylene-2,4-pentanedione (H 3 CO -CHyC (COCH 3) 2) in the liquid and solute forms in various solvents of different polarity were recorded at ambient temperature. Additional IR and Raman spectra were obtained for amorphous and crystalline solid at low temperature. The vibrational spectra revealed that compound exists atleast in two dominant conformers with different polarity and that conformer present in the solid phase is less polar. NMR spectra in various solvents at different temperatures were also obtained.The compound can exist in several conformers as a result of rotation around O-Cy and both yC-C bonds with planar or nonplanar arrangement of the heavy atoms. Semiempirical (AM1, PM3, MNDO, MINDO3) and ab initio using TZP and 6-31G** basis sets calculations were carried out. According to ab initio calculations at least five conformational structures with the methoxy group oriented as anti or syn and carbonyl groups oriented as Z or E towards the CyC double bond were obtained at energy surface. The calculated ab initio and AM1 energies of all conformers suggest as the most stable anti-ZE conformer where Z and E regard of the trans and cis acetyl group, respectively. As the second most stable conformer with energy at least 10 kJ mol Ϫ1 higher was calculated anti-EZ conformer. Assignments of the vibrational spectra for the studied compound were made with the aid of normal coordinate calculations employing scaled ab initio force field constants. The scaled ab initio frequencies as well as calculated energies indicate that the conformer present in the solid phase is anti-ZE.
Journal of Atomic and Molecular Sciences, 2011
The molecular properties and harmonic wavenumbers of 3-(2-methoxyphenoxy) propane-1,2-diol have been calculated using ab initio and density functional theory. The polarizability and first static hyperpolarizability of the title molecule have been calculated at different basis sets. In general a good agreement between experimental and calculated normal modes has been observed. The frontier orbital and molecular electrostatic potential surface study has also been employed to understand the active sites of 3-(2methoxyphenoxy) propane-1,2-diol. PACS: 31.15.A, 31.15.es, 31.15.ap ½½ Key words: Density functional theory, frontier orbital energy gap, first static hyperpolarizability ½¾ ½¿ 1 Introduction ½ With the standard quantum chemical models (i.e., without the inclusion of parity violation), ½ there is no difference whatsoever in energetics, vibrational frequencies, polarizabilities, NMR ½ spectra, or any other non-chiral property for a given pair, i.e., (R) and (S) forms of enan-½ tiomers [1-4]. Differences in the properties of enantiomers arise either only within chiral en-½ vironments or interactions with other chiral compounds. The present investigation therefore ½ deals with the quantum chemical study of molecular structural, energetic and vibrational data ¾¼ of one of the pair i.e., (R) enantiomer of 3-(2-methoxyphenoxy) propane-1,2-diol [MPPD], in ¾½ gas phase, due to its biological and pharmaceutical importance. The drug MPPD, also known ¾¾ as guaifenesin, is an expectorant, used extensively in anti-tussive and is capable of increasing ¾¿ the excretion of phlegm from the respiratory tract. Bredikhin and others have carried out ¾ * Corresponding author. Email address: ÓÒ ÖÔÖ × ½ Ñ ÐºÓÑ (O. Prasad) http://www.global-sci.org/jams 212 c 2011 Global-Science Press L. Sinha, A. Kumar, V. Narayan, et al. / J. At. Mol. Sci. 2 (2011) 212-224 213 extensive studies on the structure, solid state properties and issues related to the effective ¾ resolution procedure for MPPD [5-7]. ¾ The vibrational spectroscopic analysis is known to provide immensely invaluable molecu-¾ lar structure elucidation in synergy with quantum chemical calculations. In order to obtain a ¾ complete description of molecular dynamics, vibrational wavenumber calculations along with ¾ the normal mode analysis have been carried out at the DFT level employing the basis set ¿¼ 6-311+G(2d,2p). The optimized geometry of molecule under investigation and its molecu-¿½ lar properties such as equilibrium energy, frontier orbital energy gap, molecular electrostatic ¿¾ potential energy map, dipole moment, polarizability, first static hyperpolarizability have also ¿¿ been used to understand the properties and active sites of the drug. ¿ 2 Experimental ¿ 2.1 Structure and Spectra ¿
Structural Chemistry, 2010
The crystal and molecular structures of an o-hydroxy Schiff base derivative, (E)-2-ethoxy-6-[(2methoxyphenylimino)methyl]phenol, have been determined by single crystal X-ray diffraction analyses at 296 and 100 K. The results from temperature-dependent structural analysis regarding the tautomeric equilibrium of the compound were interpreted with the aid of quantum chemical calculations. To clarify the tautomerization process and its effects on the molecular geometry, the gasphase geometry optimizations of two possible tautomers of the title molecule, its OH and NH form, were achieved using DFT calculations with B3LYP method by means of 6-31 ? G(d,p) basis set. In order to describe the potential barrier belonging to the phenolic proton transfer, nonadiabatic Potential Energy Surface (PES) scan was performed based on the optimized geometry of the OH tautomeric form by varying the redundant internal coordinate, O-H bond distance. The Harmonic Oscillator Model of Aromaticity (HOMA) indices were calculated in every step of the scan process so as to express the deformation in the aromaticities of principal molecular moieties of the compound. The results show that there is a dynamic equilibrium between the aromaticity level of phenol and chelate ring and furthermore p-electron coupling affecting overall molecule of the title compound. Charge transfer from phenol ring to pseudo-aromatic chelate ring increases with increasing temperature, whereas p-electron transfer from chelate ring to anisole ring is decreased as temperature increases. The most strength intramolecular H-bonds are observed for conformers close to transition state.
Materials Today: Proceedings, 2016
The Fourier Transform Infrared (FTIR) spectrum of 2-azido-1-phenylethanone (APE) has been recorded in the range 4000-400 cm-1 respectively. The optimized geometry of the molecule has been computed by evaluating the torsional potential energy as a function of angle of rotation about the interlinking bonds of APE using quantum chemical calculations. These calculations were carried out using density functional theory (DFT) employing B3LYP functional with 6-311++G(d,p) basis set. Stability of the molecule arising from hyper conjugative interactions, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The values of dipole moment, polarizability and hyperpolarizability were computed to determine the NLO behaviour of the molecule under study. The HOMO and LUMO energies were also evaluated for this molecule to demonstrate the chemical stability.
The main purpose of this study is to characterize a new organic material, (E)-5-methoxy-2-[(3,4-dimethylphenylimino)methyl]phenol, which was synthesized and grown as a single crystal. The molecular structure and spectroscopic properties of the ortho-hydroxy Schiff base compound were determined by X-ray diffraction analysis, Fourier-transform infrared (FT-IR), ultraviolet-visible (UV-Vis) and nuclear magnetic resonance (NMR) spectroscopy techniques, experimentally and computationally with density functional theory (DFT) calculations. X-ray and UV-Vis studies show that the compound exists in an OH tautomeric form in the solid and solvent media. The gas phase geometry optimizations of two possible forms of the title compound, resulting from the prototropic tautomerism, were obtained using DFT calculations at the B3LYP/6-311G+(d,p) level of theory. A relaxed potential energy surface (PES) scan was performed based on the optimized geometry of the OH tautomeric form by varying the redundant internal coordinate , the O-H bond distance. According to the PES scan process, the molecular geometry is strongly affected by the intramolecular proton transfer. The calculated first hyperpolarizability indicates that the compound could be a good material for non-linear optical applications.