AM1 study of the electronic structure of 7-aminodeacetoxycephalosporanic acid (7-ADCA) (original) (raw)
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AM1 study on the conformations of 6-aminopenicillanic acid
Indian Journal of Chemistry Section B-organic Chemistry Including Medicinal Chemistry, 2002
The geometry and electronic structure of 6-aminopenicillanic acid (6-APA) molecule having various reaction centers have been fully optimized and calculated by semi-empirical molecular orbital AMI method. Furthermore, the effect of conformational changes on the electronic properties has been studied. In this connection, the heats of formation, dipole moments, ionization potentials, full atomic charges, and energies of frontier molecular orbital (E H O M O and E L U M O ) have been calculated and discussed. The mechanism of protonation in 6-APA has been studied by comparison of net charges on nitrogen atoms in the different positions of the molecule. The conformational analyses of mono- and di-protonated species have also been performed by AM1 and their stable conformations determined.
AM1 study on the conformations of zwitterions of 6-aminopenicillanic acid (6-APA)
Indian Journal of Chemistry Section B-organic Chemistry Including Medicinal Chemistry, 2006
The geometry and electronic Structure of zwitterions of 6-aminopenicillanic acid (6-APA) have been optimized and calculated by semi-empirical molecular orbital AMI method. The mechanism of formation of zwitterions of 6-APA 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 (ΔΗ° f ), dipole moments (μ), ionization potentials (IP), full atomic charges, and energies of frontier molecular orbital (E HOMO and E LUMO ) have been performed and discussed. The effect of conformational changes and electronic properties of stable conformations have been determined.
Calculations on the low energy conformers of N‐acetyl‐D‐alanyl‐D‐alanine
Biopolymers, 1998
In this article a conformational analysis of the D-alanyl-D-alanine dipeptide, both charged and neutral, has been carried out. The preferred conformations were determined by means of ab initio and semiempirical quantum, together with empirical force field calculations. The AMBER* force field and the 6-31 / G** and 6-31G** ab initio levels give rise to a coincident minimum energy structure, which, on the other hand, differs from that determined by AM1, 3-21 / G, and 3-21G. The solvent effect on the different charged and neutral conformations have been considered through the AMSOL semiempirical method. A quantification regarding the structural similarities between the different dipeptide conformations and the ampicillin has been performed. The results show that the best overlay is attained by the minimum structure energy obtained by using the 6-31
The Journal of Physical Chemistry A, 2005
A theoretical study on the origin of the common electronic excitations in amino acids is presented, focusing on the excited states of glycine, alanine and the related substructures formic acid, acetic acid, propionic acid, ammonia, methylamine, and ethylamine. Special attention is given to the valence excitation from the nonbonding lone-pair on the carboxylic oxygen atom to the antibonding π-orbital (n O f π CO /) and the first Rydberg excitation from the nonbonding lone-pair on the nitrogen atom (n N f 3s). From extensive calculations on formic acid and methylamine, different basis sets and electron correlation treatments are benchmarked using a hierarchy of coupled cluster (CC) methods, consisting of CCS, CC2, CCSD, CCSDR(3), and CC3, in combination with augmented correlation consistent basis sets. The dependence of the excitation energies on the size of the backbone structure in the two groups of molecules is investigated, and 0-0 transition energies for the n O f π CO / and n N f 3s transitions are calculated for the smallest molecules. Excellent agreement with experimental values is found where secure experimental assignments are available. A few outstanding problems in the experimental assignments found in the literature are described for both the carboxylic acids and the amines. Final predictions for vertical excitation energies are given for all molecules, including glycine and alanine where no gas-phase experimental results are available. Finally, calculations on protonated amino acids are presented showing an isolation of the n O f π CO / from higher lying states by as much as 1.9 eV for alanine.
AM1 study on the conformations and electronic properties of phenethicillin
The geometry, conformation and electronic structure of phenethicillin 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 phenethicillin 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 (∆Hfo), 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 di-protonated 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...
Journal of Molecular Structure, 2020
An efficient method has been developed for the synthesis of ((Phenylcarbamoylmethyl-phosphonomethyl-amino)-methyl)-phosphonic acid (PCMPA) under solvent free conditions using microwave irradiation. PCMPA was obtained in high yield under mild conditions by reaction of the 2-Amino-N-phenylacetamide (APA) with formaldehyde and phosphorous acid under microwave irradiation. Comparison between conventional and microwave-assisted synthesis was done by comparing total reaction time and percentage yield. The PCMPA was characterized by FTIR, Elemental analysis, 1 H, 13 C, 31 P NMR. Then, this molecule has been studied from a theoretical point of view in order to know the effects of the methylenephosphonic moiety, (eCH 2-P(O)(OH) 2), on their electronic, vibrational, thermodynamic and optical properties by means of Density Functional Theory (DFT) calculations, using the Gaussian09 program. The stable structure was optimized by using the hybrid B3LYP/6-31G method. In order to make comparative study between the started (APA) and obtained (PCMPA) molecules, different proprieties for this molecule were analyzed by means of the HOMO-LUMO proprieties, atomic. The global and local reactivity descriptors of the two molecules are calculated and discussed. Molecular electrostatic potential (MEP), Mulliken atomic charges and dipole moment were also performed by the DFT method.
Vibrational Analysis and MP2 Calculations of [(4-Hydroxyphenyl)amino] (oxo) Acetic Acid
International journal of engineering research and technology, 2019
Vibrational spectral analysis and quantum chemical computation of [(4-Hydroxyphenyl)amino] (oxo) acetic acid have been carried out by using MP2 level with 6-31G(d,) basis set. The equillibrium geometry, various bonding features and harmonic vibrational wavenumber of [(4Hydroxyphenyl)amino] (oxo) acetic acid have been computed by MP2 method. The calculated molecular geometry has been compared with the experimental data. Natural bond orbital analysis has been carried out to explain the charge transfer or delocalization of charge due to the intramolecular interactions. Energy of the highest occupied molecular orbital (HOMO) and lowest unoccupied (LUMO) molecular orbital have been predicted. The molecular electrostatic potential (MESP) were constructed. The absorption spectrum of the molecule was studied using time-dependent density functional theory (TDDFT) method.
Angewandte Chemie International Edition, 1999
X-ray diffraction experiments not only give atomic positions from which the geometry of a chemical structure can be determined, but the exact charge density distribution 1(r) can also be deduced, [1] which is an observable in contrast to the wave-function in the Schrödinger equation. To accomplish this the experiment has to be carried out up to high resolution (d 0.5 or sinq l À1 ! 1.0 À1 ) and at the lowest temperature possible. With conventional diffractometers and serial (scintillation) detection this required measurement periods of several weeks or even months, even for structures of moderate size (20 ± 30 atoms), so that the method, although known since the 1960s, [2] was hardly applied and led only to more qualitative results. In the meantime several developments have changed the situation drastically.
Synthesis and Quantum Chemical Calculations of 2,4-dioxopentanoic Acid Derivatives -Part I
In the section based on DFT calculations of this study, all calculations were carried out using DFT/B3LYP method with 6-311G(d,p) basis sets of Gaussian program . Optimization of synthesized molecules was performed with the help of 6-311G (d,p) basis set, because this basis set is known as one of the basis sets that gives more accurate results in terms of the determination of geometries and electronic properties for a wide range of organic compounds. Quantum chemical parameters such as the energy of the highest occupied molecular orbital (E HOMO ), the energy of the