Molecular structure, spectral analysis and hydrogen bonding analysis of ampicillin trihydrate: a combined DFT and AIM approach

Abstract

Ampicillin trihydrate chemically associated to C 16 H 19 N 3 O 4 S·3H 2 O empirical formula, is a semi-synthetic amino-penicillin derived from the elementary penicillin nucleus, 6aminopenicillanic acid. It is a very common antibiotic that is active against an extensive range of Gram-positive and Gram-negative organisms. It is used to treat certain varieties of bacterial infections, like gonorrhea and infections of the urinary, intestinal and respiratory tracts. In the present effort, quantum chemical calculations of molecular geometries (bond lengths and bond angles) and bonding features of monomer and dimer of ampicillin trihydrate in the ground state have been carried out due to its biological and industrial importance. The optimized geometry and wavenumber of the vibrational bands of the molecule have been calculated by ab-initio density functional theory (DFT) using Becke's three-parameters hybrid functional (B3LYP) with 6-311++G(d,p) basis set. Vibrational wavenumbers were compared with the observed FT-Raman and FT-IR spectra. Molecular electrostatic potential (MEP) has also been plotted for predicting the molecule reactivity towards positively or negatively charged reactants and it shows that electropositive potential is visualized in the vicinity of the -NH 3 group and electropositive region is found near the H 2 O molecule in both monomer and dimer. HOMO-LUMO analysis has been done to describe the way the molecule interacts with other species. Natural bond orbitals (NBO) analysis has been carried out to inspect the intra-and inter-molecular hydrogen-bonding, conjugative and hyperconjugative interactions and their second order stabilization energy E (2) . Nonlinear optical (NLO) analysis has also been performed to study the non-linear optical properties of the molecule by computing the first hyperpolarizability (β 0 ). The variation of thermodynamic properties with temperature has been studied. Topological parameters at bond critical points (BCP) have been evaluated by 'Quantum theory of atoms in molecules' (QTAIM).

Structural and Reactivity Analyses of Nitrofurantoin–4-dimethylaminopyridine Salt Using Spectroscopic and Density Functional Theory Calculations

“…A molecule having a lesser HOMO-LUMO gap is more polarizable and is usually related to low kinetic stability and high chemical reactivity [49,50]. Thus, the softness corresponds to the HOMO-LUMO gap.…”

“…These descriptors refer to the overall stability of the molecule. Contrariwise, the local equivalent refers to the site reactivity and selectivity [49,50]. The HOMO-LUMO energy gap, χ, µ, η, S and ω for API, coformer, salt using wB97X-D and B3LYP methods are listed in Table 2.…”

Structural Analysis, Molecular Docking and DFT Calculations of Bis(Pyrazolium Picrate) Monohydrate Interaction with Calf Thymus DNA and Microbes

“…The chemical reactivity and site selectivity of the molecular systems have been determined according to Koopman's theorem . Global reactivity descriptors of BPPMH are calculated using the energies of frontier molecular orbitals ϵ HOMO , ϵ LUMO with various reactivity descriptors such as chemical potential (μ), electronegativity (χ), global softness (η), global hardness (S) and electrophilicity index (ω) …”

“…[23] Global reactivity descriptors of BPPMH are calculated using the energies of frontier molecular orbitals e HOMO , e LUMO with various reactivity descriptors such as chemical potential (m), electronegativity (c), global softness (h), global hardness (S) and electrophilicity index (w). [24] Electrophilicity index (w) measures the energy stabilization when the system gains additional electronic charge from surroundings. [25] The higher the value of (w) electrophilicity index indicates the greater electrophilic behaviour of the system as well as lower chemical potential.…”

Crystal structure, Hirshfeld surface analysis and DFT studies of (E)-2-{[(3-chloro-4-methylphenyl)imino]methyl}-4-methylphenol

“…The highest-occupied molecular orbital (HOMO), acting as an electron donor, and the lowest-unoccupied molecular orbital (LUMO), acting as an electron acceptor, are very important parameters for quantum chemistry. When the energy gap is small, the molecule is highly polarizable and has high chemical reactivity (Fukui, 1982;Khan et al, 2015). The DFT calculations provide some important information on the reactivity and site selectivity of (a) The overall two-dimensional fingerprint plot for the title compound and (b)-(f) those delineated into HÁ Á ÁH, CÁ Á ÁH/HÁ Á ÁC, ClÁ Á ÁH/HÁ Á ÁCl, OÁ Á ÁH/HÁ Á ÁO and NÁ Á ÁH/HÁ Á ÁN contacts, respectively.…”