Volume 7, Issue 6

A computational study of the chemical kinetics and thermodynamics study of the S N Ar between 3,5-dinitroethoxypyridine 1a and 3,5-dinitromethoxypyridine 1b with piperidine 2 in the gas phase is reported using hybrid density functional theory method B3PW91 and 6–31G(d,p) basis set. The reaction was modeled via both the catalyzed and base-catalyzed pathways which proceeded with the initial attack of the nucleophile 2 on the substrates 1 to yield the Meisenheimer complex intermediate that is stabilized with hydrogen bonding. Calculations show that the reaction goes via the formation and decomposition of a Meisenheimer complex, which was observed to be stabilized by hydrogen bonding. Along the uncatalyzed pathway, the decomposition of the Meisenheimer complex was the slow step and requires about 28 kcal/mol. This barrier was reduced to about 14.8 kcal/mol with the intervention of the base catalyst, thus making the formation of the Meisenheimer complex rate determining. All reactions were calculated to be exothermic, about −6.5 kcal/mol and −0.6 kcal/mol, respectively, for the reaction of 1a and 1b with 2 .

Graphene quantum dots (GQDs) belong to the vast and versatile family of carbon nanomaterials. Their unique position amongst versatile carbon nanoparticles (NPs) originates from the properties of quantum confinement and edge effects. GQDs are similar to conventional semiconductor QDs due to their tunable band gaps and high photoluminescence activity. However, GQDs have superior characteristics due to their excellent biocompatibility, low toxicity, good water dispersibility, large optical absorptivity, high fluorescence activity and photostability. These properties have generated significant interest in GQDs applications in various fields: nanosensor fabrication, drug delivery, photocatalysis, photovoltaics, and photodynamic therapy. Numerous GQD-based nanocomposites/nanohybrides have been synthesized and/or studied computationally. This review focuses on recent computational studies of various GQD-based nanocomposites/nanohybrides and systems which can be related to them.

Designing new van der Waals (vdW) heterostructures from various two-dimensional transition metal dichalcogenides (TMDs) materials shows outstanding properties, such as an ultrafast charge transfer process and strong interlayer interactions by combining the advantageous properties of the different TMD materials. In this study, using the density functional theory method, we systemically investigate the optical property, band alignment, electronic structures, interface charge transfer, mechanical properties and stability of MTe 2 /GaTe 2 (M = Mo and W) vdW heterostructures as promising photovoltaic solar cells materials. In this work, gallium telluride and MTe 2 were used as acceptors and donors in high-quality photovoltaic cells. The calculated binding energies suggest that they were energetically favourable and relatively easy to fabricate under suitable conditions. Moreover, the heterostructures possess exceptional characteristics of enhanced visible light absorption edge (∼10 4  cm −1 ), type-II band alignment and strong charge separation. The suitable band alignment leads to maximum power conversion efficiency (PCE) of 22.43 and 22.91%, respectively, which was quite promising for photovoltaic solar cells. The high PCE could be due to the internal built-in electric field at the MTe 2 /GaTe 2 interface, which induces efficient separation of charge carriers. This work offers theoretical support for the design and prediction of next-generation low-cost, highly efficient and promising materials for solar device applications.

Protein tyrosine phosphatases (PTP) regulate various cellular processes and represent important targets for therapeutic intervention in various diseases. Studies have shown that partial or total cessation of the PTP-1B gene in normal and diabetic mice has led to resistance to weight gain and improved insulin response. Also, a further study showed that inhibition of PTP-1B or a reduction in its cellular abundance in mice resulted in similar effects and, as such, provided a rationale for the treatment strategy for type 2 diabetes. Thiazolidinedione (TZD) derivatives have been identified as new PTP-1B inhibitors but the mechanism of interaction between TZD derivatives and PTP-1B is still elusive. In this study, a three-dimensional quantitative structure-activity relationship (3D-QSAR) analysis was performed, including multiple linear regression (MLR) and cross-validation, on a set of TZD derivatives as antidiabetic agents. MLR analysis was performed on 23 PTP-1B TZD derivatives to determine the relationships between physicochemical properties and antidiabetic properties of TZD derivatives. The training data set creates a QSAR model with a correlation coefficient ( R 2 ) of 0.8516, a Q 2 (Leave-One-Out) cross-validation factor of 0.6473, r 2 (correlation coefficient) for the external dataset is 0.8367 while r 2 of predicted dataset is 0.8934 by the MLR Method. The MLR model was also validated by the standardization approach. We observed a high correlation between predicted and observed activity (experimental values), thus confirming and proving the high quality of QSAR models. Finally, molecular docking analysis was performed to better understand the interactions between the PTP-1B target and TZD derivatives. The model proposed in this project can be used to design new TZD derivatives with specific PTP-1B inhibitory activity.

Conformers of 3-halogenobenzaldehydes (3HB, halogen atom: F [3FB], Cl [3CB] and Br [3BB]) in the gas phase and solutions were studied using density functional theory (DFT) and time dependent density functional theory (TDDFT), B3LYP functional and MP2 method with 6–311+G(3df,p) and aug-cc-pVDZ basis sets. The present study aims to investigate the halogen and medium effects on the conformational stability, structural parameter, dipole moment, carbonyl stretching frequency, frontier molecular orbitals, band gap, absorption band and density of states. Carbonyl stretching frequencies were evaluated with some solvent models. All results will be useful for further analysis of halogen-substituted benzaldehydes.

A large variety of molecules contain large amplitude motions (LAMs), inter alia internal rotation and inversion tunneling, resulting in tunneling splittings in their rotational spectrum. We will present the modern strategy to study LAMs using a combination of molecular jet Fourier transform microwave spectroscopy, spectral modeling, and quantum chemical calculations to characterize such systems by the analysis of their rotational spectra. This interplay is particularly successful in decoding complex spectra revealing LAMs and providing reference data for fundamental physics, astrochemistry, atmospheric/environmental chemistry and analytics, or fundamental researches in physical chemistry. Addressing experimental key aspects, a brief presentation on the two most popular types of state-of-the-art Fourier transform microwave spectrometer technology, i.e., pulsed supersonic jet expansion–based spectrometers employing narrow-band pulse or broad-band chirp excitation, will be given first. Secondly, the use of quantum chemistry as a supporting tool for rotational spectroscopy will be discussed with emphasis on conformational analysis. Several computer codes for fitting rotational spectra exhibiting fine structure arising from LAMs are discussed with their advantages and drawbacks. Furthermore, a number of examples will provide an overview on the wealth of information that can be drawn from the rotational spectra, leading to new insights into the molecular structure and dynamics. The focus will be on the interpretation of potential barriers and how LAMs can act as sensors within molecules to help us understand the molecular behavior in the laboratory and nature.