Computational study of some details of the cyclization reaction between 3,5-diacetyl-2,6-dimethylpyridine and salicylic aldehyde in an acidic medium was performed by the DFT RB3LYP/6-31G method using the Gaussian-2016 software package. It was shown that protonation of the pyridine nitrogen atom leads to a significant increase in the charge of the hydrogen atom of the 2-methyl group of pyridine and the methyl acetyl group. This leads to the growth of the methyl group CH-acidity and enolization of the acetyl group. It was also found that the protonated tautomeric enol form of 3,5-diacetyl-2,6-dimethylpyridine gives a stable pre-reaction complex with salicylic aldehyde due to the formation of three hydrogen bonds. The formation of this pre-reaction complex, apparently, leads to the implementation of the Knoevenagel reaction, instead of the alternative possible Claisen-Schmidt reaction of salicylic aldehyde at the acetyl group of pyridine. The possible biological activity of the previously obtained cyclization products was evaluated by molecular docking using the AutoDock Vina software. Some cyclization products showed higher values of the binding affinity with the selected target proteins in comparison with the known antiviral drugs Nevirapine and Favipiravir. The results obtained confirm the correctness of the proposed cyclization mechanism between 3,5-diacetyl-2,6-dimethylpyridine and salicylic aldehyde. This also makes it possible to assess the prospects of previously obtained derivatives of epoxybenzo [7,8]oxocino [4,3-b]pyridine as synthetic analogs of natural integrastatins A, B for further synthesis and study of their antiviral activity.
Investigation of intermolecular proton exchange of 3,6-di-tert-butyl-2-oxyphenoxyl with N-phenylanthranilic acid by ESR spectroscopy method In this work we studied the intermolecular proton exchange (IPE) reaction between the spin probe of 3,6-ditert-butyl-2-hydroxyphenoxyl (I) and the aromatic amino acid N-phenylanthranilic acid (N-PhAA). The experimental spectra of the 3,6-di-tert-butyl-2-hydroxyphenoxyl-N-phenylanthranilic acid system were recorded using dynamic EPR spectroscopy. The studies were carried out in a non-aqueous indifferent solvent toluene in a wide temperature range. The theoretical EPR spectra of the radical IN -PhAA system corresponding to various process rates were successfully simulated using the ESR-EXHANGE program. This program is written in the modern version of the algorithmic language Fortran 90. The general line-form equation for the four-jump model have been derived from the modified Bloch equations. The second-order rate constants for the intermolecular proton exchange process between radical I and N-PhAA were determined by comparison of the experimental and simulated EPR spectra. The iterative least squares procedure was used for computer analysis of the kinetic data of intermolecular proton exchange and for obtaining activation parameters of the reaction. From kinetic data it follows that N-phenylanthranilic acid has the lowest value of protolytic ability in comparison with aminobenzoic acids.
The encapsulation of the famous alkaloid, anabasine, with β-CD was studied to obtain a more stable and bioavailable inclusion complex. Various in silico and experimental studies of the obtained β-CD-anabasine complex are presented. Firstly, molecular docking studies were conducted against the α, β, and γ cyclodextrins to explore which subclass is the best for encapsulation. The obtained results that pointed at β-cyclodextrin were further confirmed by five MD simulations and MM-PBSA studies. Experimentally, the spectral properties of the anabasine β-cyclodextrin complex were determined by FT-IR, 1H, and 13C-NMR spectroscopic methods. Additionally, the surface morphology of the anabasine β-cyclodextrin was investigated using a scanning electron microscope. Furthermore, the outputs of the thermographic measurements utilizing a differential scanning calorimeter were displayed. The activation energy of the reaction of thermo-oxidative destruction of the clathrate complex was calculated, and the kinetic parameters of the thermal destruction processes were decided using the Freeman–Carroll, Sharpe–Wentworth, Achar, and Coates–Redfern methods. The kinetic parameters of the thermal decomposition of the anabasine β-cyclodextrin were in agreement and verified the reliability of the obtained results. The obtained computational, spectral, morphological, and thermogravimetric results verified the successful formation of the anabasine β-cyclodextrin complex.
Proton exchange in hydrogen-bounded complexes occupies an important place among dynamic processes taking place in molecular systems with hydrogen bond. However, despite numerous experimental and theoretical studies in this field, a single point of view on the mechanism of proton exchange has not yet been accepted by scientists. Ammonia, water and formic acid are small in size protolytes with widely differing acid-base properties. This makes them suitable and comfortable for theoretical modeling of proton exchange reaction. Quantum-chemical simulation of the proton exchange reaction in model dimers of ammonia, water and formic acid was carried out by AM1 and ab initio 6-31G, 6-31G++ methods of Gaussian-2009 program. The search of transition state structure was performed by using of QST2 procedure, the descent along the reaction coordinate was held by using of IRC procedure. The symmetrical structure of transition state in the case of formic acid dimer and the asymmetric structure of transition complex in the case of ammonia dimer were obtained for studied proton exchange reaction. A synchronous mechanism of proton exchange reaction is shown in the case of the formic acid dimer and a sequential mechanism is shown in the case of ammonia dimer. The dynamic shortening of the hydrogen bridge length was noted during proton exchange reaction in all model systems. It was suggested that the mechanism of proton exchange reaction is determined by the nature of the resulting transition state (symmetrical or asymmetrical). At the same time, the transition state structure is determined by the acid-base properties of reaction partners.
The results of the computational and the physicochemical studies of the encapsulation of resveratrol with β-cyclodextrin are presented here. At first, the molecular docking experiments predicted good binding. Several MD simulations and MM-PBSA experiments confirmed the reliable binding, showing optimal kinetics and energy. As an application, resveratrol inclusion complexes with β-cyclodextrin were obtained in an aqueous alcohol medium via microwave treatment. The results of thermographic measurements of the obtained clathrates using a differential scanning calorimeter are presented, and the obtained activation energy was calculated using the Ozawa–Flynn–Wall and Friedman methods, as well as nonparametric kinetics. The effect of complexation on the kinetic parameters of thermal destruction of the β-cyclodextrin–resveratrol inclusion complex was considered. The morphology of the surface of the obtained clathrate complexes was described using a scanning electron microscope. The spectral properties of the inclusion complex were characterized by FT-IR, 1H, and 13С NMR spectroscopic data. The obtained in silico, morphological, thermogravimetric, and spectral results confirmed the formation of the resveratrol–β-cyclodextrin complex. The antioxidant activities of the inclusion complex were determined to be 12.1 μg/mL, compared to 14.3 μg/mL for free resveratrol, indicating an improvement in the bioactivity.
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