Theoretical insights into the reaction mechanism and kinetics of ampicillin degradation with hydroxyl radical

CONTEXT

Ampicillin (AMP) is a penicillin-class beta-lactam antibiotic widely used to treat infections caused by bacteria. Therefore, due to its widespread use, this antibiotic is found in wastewater, and it contains long-term risks such as toxicity to all living organisms.

METHOD

In this study, the degradation reaction of ampicillin with hydroxyl radical was investigated by the density functional theory (DFT) method. All the calculations were performed with B3LYP functional at 6-31G(d,p) basis set.

RESULTS

The thermodynamic energy values and reaction rates of all possible reaction paths were calculated. The addition of the hydroxyl radical to the carbonyl group of the beta-lactam ring is thermodynamically the most probable reaction path. The calculated overall reaction rate constant is 1.36 × 10¹¹ M^-1 s^-1. To determine the effect of temperature on the reaction rate, rate constants were calculated for all reaction paths at five different temperatures. The subsequent reaction kinetics of the most preferred primary route was also examined, and the toxicity values of the intermediates were estimated. The acute toxicity of AMP and its degradation product were calculated using the Ecological Structure Activity Relationships (ECOSAR) software. The degradation product was found to be more toxic than AMP.

Theoretical determination of half-wave potentials for phenanthroline-, bipyridine-, acetylacetonate-, and glycinate-containing copper (II) complexes

We report a protocol for the evaluation of theoretical half-wave potential (E_1/2) using a set of 22 mixed chelate copper (II) complexes containing 1,10-phenanthroline and 2,2'-bipyridine derivatives as primary ligands, and acetylacetonate or glycinate as secondary ligands (formally from the Casiopeínas® family) for which accurate experimental values were determined in a 2/5 mixture of ethanol/water. We have calibrated the BP86, PBE, PBE0, B3LYP, M06-2X, and ω-B97XD functionals, using the Los Alamos LANL2DZ and Stuttgart-Köln SDDAll effective core potentials for the Cu and Fe atoms and the 6-311+G* basis set for the C, H, O, and N atoms. To address the solvent effects, we have saturated the first solvation shell with up to 9 water molecules for the explicit model and compared it with the Continuum Like-Polarizable Continuum Model (CPCM) implicit solvent scheme. We found that the PBE/LANL2DZ-6-311+G* protocol (with the CPCM implicit solvent scheme with an effective dielectric constant ε = 64.9121 for the 2/5 mixture of ethanol/water) yields the overall best performance. The theoretical values are compared with experimental data, three of which are reported here for the first time. We find good correlations between the theoretical and experimental E_1/2 values for the 2,2'-bipyridine derivatives (R² = 0.987, MAE = 86 mV) and 1,10-phenanthroline derivatives (R² = 0.802, MAE = 58.4 mV). The correlation trends have been explained in terms of the copper atom's ability to be reduced in the presence of the ligands. The Gibbs free energy differences at 298 K obtained for the redox reactions show that the more flexible secondary ligands (acetylacetonate) lead to larger entropic contributions which, as expected, increase the average MAE values as compared with the more rigid ligands (glycine). The present protocol yields lower MAEs as compared with previous approaches for similar mixed and flexible Cu(II) complexes.

Determination of Specific Heat Capacity on Composite Shape-Stabilized Phase Change Materials and Asphalt Mixtures by Heat Exchange System

Previous research has shown that composite shape-stabilized phase change material (CPCM) has a remarkable capacity for thermal storage and stabilization, and it can be directly applied to highway construction without leakage. However, recent studies on temperature changing behaviors of CPCM and asphalt mixture cannot intuitively reflect the thermoregulation mechanism and efficiency of CPCM on asphalt mixture. The objective of this paper is to determine the specific heat capacity of CPCM and asphalt mixtures mixed with CPCM using the heat exchange system and the data acquisition system. Studies have shown that the temperature-rise curve of 5 °C CPCM has an obvious temperature plateau, while an asphalt mixture mixed with 5 °C CPCM does not; with increasing temperature, the specific heat capacities of both 5 °C CPCM and asphalt mixture first increase and then decrease, while the variation rate of 5 °C CPCM is larger than that of the asphalt mixture, and the maximum specific heat capacity of 5 °C CPCM appears around the initial phase change temperature. It is concluded that the temperature intervals of 5 °C CPCM are −18 °C–7 °C, 7 °C–25 °C and 25 °C–44 °C, respectively, and that of the asphalt mixture are −18 °C~10 °C, −10 °C~5 °C and 5 °C~28 °C. A low dosage of 5 °C CPCM has little influence on the specific heat capacity of asphalt mixture. Finally, the functions of specific heat capacities and temperature for CPCM and asphalt mixture mixed with CPCM were recommended by the sectional regression method.

Comparing vibrational spectra of free bumetanide and its solutions

Bumetanide, which is known as a potent diuretic, is currently under investigation for its potential anti-epileptic effects in neonatal seizures. The purpose of this study was to examine the molecular structure of bumetanide both in the free form and its solutions via vibrational spectra (FT-IR, FT-Raman spectroscopies) and quantum chemical calculations. FT-IR and FT-Raman spectra of the title compound were recorded for the solid phase and the solutions of DMSO and ethanol. Optimized molecular geometry and vibrational wavenumbers of bumetanide were calculated by DFT/B3LYP functional with 6-31G(d,p), 6-31G++(d,p) and 6-311++G(d,p) basis sets. The assignment of the vibrational modes were performed based on total energy distribution (TED). The same calculations were performed for the molecule in DMSO and ethanol solutions using the polarizable conductor continuum model (CPCM) method. Lastly, probable donor-acceptor interactions of the molecule were examined with NBO analysis in different media. In all forms of bumetanide (the free molecule and the other solvents), some significant changes were observed in the dihedral angles and the vibrational frequencies.

DFT analysis of P-nitrobenzotrifluoride--a combined study of experimental (FT-IR and FT-Raman) and theoretical calculations

In this, a combined experimental and theoretical study on molecular structure and vibrational analysis of P-nitrobenzotrifluoride (PNBTF) is reported. The Fourier transform infrared and FT-Raman was recorded in the solid phase. The molecular geometry and vibrational frequencies of PNBTF in the ground state have been calculated by using density functional method (B3LYP) with 6-311++G(d,p) as basis set. Comparison of the observed fundamental vibrational frequencies with calculated results by density functional methods indicates that B3LYP/6-311++G(d,p) is superior to other methods for molecular vibrational problems. The bioactivity of the compound is analyzed by the HOMO-LUMO analysis. The reactivity sites are identified by mapping of electron density into electrostatic potential surface (MEP). Besides, (13)C and (1)H nuclear magnetic resonance (NMR) chemical shifts are calculated by using the gauge-invariant atomic orbital (GIAO) method. Furthermore, the compound can be used as a good nonlinear optical material due to the higher value of first hyperpolarizability. Solventation effect of NMR spectra by CPCM model of P-nitrobenzotrifluoride has been analyzed.

Phytochemical profiling of Curcuma kwangsiensis rhizome extract, and identification of labdane diterpenoids as positive GABAA receptor modulators

An ethyl acetate extract of Curcuma kwangsiensis S.G. Lee & C.F. Liang (Zingiberaceae) rhizomes (100 μg/ml) enhanced the GABA-induced chloride current (IGABA) through GABAA receptors of the α1β2γ2S subtype by 79.0±7.0%. Potentiation of IGABA was measured using the two-microelectrode voltage-clamp technique and Xenopus laevis oocytes. HPLC-based activity profiling of the crude extract led to the identification of 11 structurally related labdane diterpenoids, including four new compounds. Structure elucidation was achieved by comprehensive analysis of on-line (LC-PDA-ESI-TOF-MS) and off-line (microprobe 1D and 2D NMR) spectroscopic data. The absolute configuration of the compounds was established by comparison of experimental and calculated ECD spectra. Labdane diterpenes represent a new class of plant secondary metabolites eliciting positive GABAA receptor modulation. The highest efficiency was observed for zerumin A (maximum potentiation of IGABA by 309.4±35.6%, and EC50 of 24.9±8.8 μM).

Aromatic Claisen Rearrangements of O-prenylated tyrosine and model prenyl aryl ethers: Computational study of the role of water on acceleration of Claisen rearrangements

LynF, an enzyme from the TruF family, O-prenylates tyrosines in proteins; subsequent Claisen rearrangements give C-prenylated tyrosine products. These reactions in tyrosines and model phenolic systems have been explored with DFT and SCS-MP2 calculations. Various ab initio benchmarks have been computed (CBS-QB3, MP2, SCS-MP2) to examine the accuracy of commonly used density functionals, such as B3LYP and M06-2X. Solvent effects from water were considered using implicit and explicit models. Studies of the ortho-C-prenylation and Claisen rearrangement of tyrosine, and the Claisen rearrangement of α,α-dimethylallyl (prenyl) coumaryl ether establish the energetics of these reactions in the gas phase and in aqueous solution.