Formations of bimolecular barbituric acid complexes through hydrogen bonding interactions: DFT analyses of structural and electronic features

Formations of bimolecular barbituric acid (BA) complexes through hydrogen-bonding (HB) interactions were investigated in this work. BA has been known as a starting compound of pharmaceutical compounds developments, in which the molecular and atomic features of parent BA in homo-paring with another BA molecule were investigated here. The models were optimized to reach the stabilized structures and their properties were evaluated at the molecular and atomic scales. Density functional theory (DFT) calculations were performed to provide required information for achieving the goal of this work. Six dimer models were obtained finally according to examining all possible starting dimers configurations for involving in optimization calculations. N-H . . . O and C-H . . . O interactions were also involved in dimers formations besides participation of the X-center of parent BA in interaction. Molecular and atomic scales features were evaluated for characterizing the dimers formations. As a consequence, several configurations of BA dimers were obtained showing the importance of performing such structural analyses for developing further compounds from BA.

A detailed kinetic study on the tautomerization reactions of barbituric acid: A combined DFT-QTAIM analysis

A detailed kinetic study on the tautomerization reactions of barbituric acid (BA) at elevated temperatures from 270 K up to 1000 K was performed in this work. The B3LYP/6-311 + G(3df,2p) density functional theory (DFT) calculations were performed to evaluate the rate constants of transition states (TS) conversions of the tautomerization reactions. The connections from a given TS to the corresponding local minima of the reactant and product sides were confirmed by means of employing the intrinsic reaction coordinate (IRC) method. Moreover, the quantum theory of atoms in molecules (QTAIM) approach was employed to analyze the molecular mechanisms of reactions. The effects of vibrational normal mode frequencies of the reactant and TS were investigated on the curvature of the corresponding Arrhenius plot in the presence and absence of the tunneling effect. For each tautomerization reaction, the investigated reaction was partitioned into three different stages and four zones. The obtained results were plotted along with the corresponding reaction coordinates for each reaction considering and comparing different factors in agreement with already affirmed concepts. As a consequence, details of performed kinetic study on the tautomerization reactions of BA were successfully provided in this work.

Investigating Functionalization Impacts on Structural Features of Barbituric Acid Derivatives: DFT Approach

Density functional theory (DFT) calculations were performed to investigate electronic and structural properties of barbituric acid (BA) and sixtheen of its derivatives to show impacts of structural functionalization on the features of parent BA. The models were optimized and the minimum energy structures were confirmed by frequency calculations. Molecular and atomic descriptors were evaluated for the optimized models, in which the results of formation binding strength and molecular orbital features indicated significance of such functionalization processes on the observed properties. The highest occupied and the lowest unoccupied molecular orbitals (HOMO and LUMO) and their related parameters all indicated magnitudes of changes from one molecule to another one. Furthermore, atomic scale quadrupole coupling constants (Cq) were evaluated for the nitrogen and oxygen atoms of BA compounds showing significance of structural functionalization impacts on the atomic properties of parent BA. As a consequence, such structural analyses of BA compounds could show their characteristic features for further developments especially for their efficient pharmaceutical applications.

Quantum processing of cytidine derivatives and evaluating their in silico interactions with the COVID-19 main protease

This work was performed by the importance of exploring possible medications for COVID-19 pandemic. In this regard, cytidine (Cyd) derivatives were investigated to reach a point to see their benefit of employing for the purpose. Each of halogenated models of Cyd including CydF, CydCl, CydBr, and CydI were investigated in addition to the original CydH model. Density functional theory (DFT) based quantum processing were performed to obtain stabilized structures in addition to evaluation of frontier molecular orbitals features. Next, molecular docking (MD) simulations were performed to reach a point of formations of interacting ligand-target complexes. Among the investigated models CydH and CydI were working better than other model for reaching the purpose of this work, in which the derived CydI model was indeed the ligand with the highest suitability for formation of ligand-target complexes. As a consequence, such ligands of original and halogenated Cyd models might work for inhibition of main protease (MPro) enzyme of COVID-19 based on the obtained meaningful vales for complex strengths in addition interacting with the amino acids of active site. More precisely, the CydI model could be proposed as promising ligand for showing the inhibitory effects towards the MPro target of COVID-19.

Identification of amphetamine as a stimulant drug by pristine and doped C70 fullerenes: a DFT/TDDFT investigation

The density functional theory (DFT) was used to examine the electronic reactivity and sensitivity of a pristine, Si, and Al-doped fullerene C₇₀ with AM drug. AM drug has been shown to be physically absorbed by its N-head on the pristine C₇₀ with an adsorption energy of about - 1.09 kcal/mol and to have no impact on the electric conductivity of that cluster. The atom substitution of Si and Al for C atoms at C₇₀ significantly increases C₇₀ fullerene reactivity, with adsorption energy predictions of approximately - 31.09 and - 45.59 kcal/mol, respectively. The energy difference of LUMO and HOMO, i.e., Eg from C₇₀ fullerene, significantly affects AM drug. Significant LUMO destabilization in Al-C₇₀ by adsorption of the drug AM boosts the electrical conductivity of Al-C₇₀ while generating electric signals that are related to the environmental presence of AM drug. Hence, Al-doped C₇₀ is demonstrated to be an effective electronic AM drug sensor. In contrast to Si-C₇₀ fullerene, significant AM-drug adsorption effects on Fermi and Si-C₇₀ work functions make Si-C₇₀ an Ф-type candidate for AM drug sensor applications. The time-dependent theory of the functional density shows that the AM/Al-C₇₀ complex is steadily situated at a maximum peak of 784.15 nm.