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Context: The intermolecular interactions of ethyl acetate (EtOAc)-water (H 2 O)/ethanol (EtOH) mixtures were investigated using a combination of Raman spectroscopy and quantum chemical calculations. The computational approach was used to analyze the structure of hydrogen-bonded complexes of ethyl acetate with water/ethanol molecules, based on density functional theory (DFT). The calculated frequencies closely matched the experimental Raman values, with differences being under 4%. Experimental data show that when the concentrations of ethyl acetate in the ethyl acetate/water/ethanol solutions were reduced, almost all Raman spectral bands are blue-shifted. The AIM analysis reveals that all the given complexes possess a positive energy density, indicating that the molecules interact electrostatically. The energy and bond length indicate that the methyl group forms relatively weak hydrogen bonds. Analysis indicates that EtOAc forms weak H-bonding C = O∙∙∙H and C-H∙∙∙O, which are recognized as van der Waals interactions. As the amount of ethyl acetate decreases in the complex, the interaction forces also decrease. This could also explain why the bands are blue-shifted. It was discovered that the title complexes' hydrogen bond energy decreased exponentially as bond length increased., Methods: The geometries of the molecular complexes were optimized using the Gaussian 09W program and the B3LYP/6-311 +  + G(d,p) set of functions. The potential energy distribution (PED) analysis was performed using VEDA 4.0 software. Raman spectra were drawn using the Origin 8.5 software. The Multiwfn 3.8 software was used to calculate topological parameters of electron density in molecular systems. GaussView 6.0 and Visual Molecular Dynamics (VMD) 1.9.3 tools were used to visualize all computational results., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Background: The influence of hybrid solvation models on the molecular structures and vibrational characteristics of g-aminobutyric acid (GABA) and a-aminoisobutyric acid (AIB) zwitterions was assessed by employing a variety of Density Functional Theory (DFT). The quantum chemical methods included the B3LYP and B3PW91 hybrid functionals and the 6‑311++G(d,p) basis set., Methods: The most stable conformation derived from the potential energy surface (PES) scans using the B3LYP/6-311++G(d,p) model chemistry for each studied molecule was predicted within a continuum environment represented by the COSMO and SMD solvation models. The stable structures were subsequently immersed in explicit/COSMO and explicit/SMD hybrid solvation models, where 10 and 8 water molecules were explicitly positioned around the functional groups of the GABA and AIB zwitterions, respectively. The number of water molecules chosen was sufficient to prevent proton transfer among the carboxylate group (COO-) and the ammonium group (NH3+) within each molecule under investigation. After optimizing the geometry of each hydrated complex, the normal vibrational modes were determined. The scaled theoretical frequencies obtained from the various model chemistries were then compared to available experimental data from infrared (IR) and Raman spectroscopy., Results: In the case of GABA and AIB molecules, the comparisons revealed that the B3LYP/6-311++G(d,p) model chemistry yielded wavenumber values that closely matched the experimental IR and Raman data, particularly when the explicit/SMD solvent was employed. The computed results indicate deviations of less than 4% when compared to the experimental data for the two molecules under investigation., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The present work investigates the infrared spectra and solvation free energies (SE) of PEHA ((E)-2-(Pyridin-2-yl) ethyl 3-(3,4-dihydroxyphenyl) acrylate) and their impact on the oxidation. The latter was examined through the ionization potential parameter (IP). These investigations were carried out by the DFT method at B3LYP/6-31G(d) for optimization and frequency calculations and corrected for BSSE. X3LYP/6-311++G(2d,2p) was employed for single-point energy calculations. Water and methanol cluster sizes were used for solvation through the explicit solvent model. Thus, the infrared spectra show that the overview frequencies of PEHA compare well with the experimental results. The intense infrared absorptions of complexes are due to the stretching of O-H bonds of solvent clusters in the range 2600-3850 cm -1 . The binding energy per solvent molecule of complexes was calculated and shows that water and methanol clusters mimic the liquid state as from 5 to 10 solvent molecules. The SE of PEHA increases with the increase of the cluster size of water and methanol in the direction of the limit. The latter was censured by the solvation done using the combined explicit-implicit solvent model. As for IP parameter, the results are largely above the IP limit and lower than the IP from gas phase. Thus, water and methanol media have an effect of lowering the IP of PEHA compound. Consequently, both media favour the oxidation of PEHA molecule, which facilitates its metabolism in human organism.

The effects of the interaction of the monovalent (Li + , Na + , K + ) and divalent (Mg 2+ ) counterions hexahydrated (6H 2 O), with the PO 2 - group, on the geometrical and vibrational characteristics of 3', 5'-dDCMP, were studied using the DFT/B3LYP/6-31++G(d) method. These calculations were performed using the explicit (6H 2 O) and hybrid (6H 2 O/Continuum) solvation models. The optimizations reveal that in the conformation g - g - and in the explicit model of solvation, the small ions (Li + , Na + ) deviate from the bisector plane of the angle O1-P-O2 and the large ions (K + and Mg 2+ ) remain in this plane, whereas in the hybrid model of solvation, the counterions deviate from this plane. However, when the conformer is g + g + , the monovalent counterions deviate and divide the remainder of the plane regardless of the type of solvation model. In addition, the g - g - conformer is the most stable in the presence of the explicit solvent, while the g + g + conformer is the most stable in the presence of the hybrid solvent. Finally, the normal modes of the conformers g - g - and g + g + in the presence of the counterions in the hybrid model show a better agreement with the available experimental data of the DNA forms A, B (g - g - ), and Z (g + g + ) relatively to the explicit model. This very good agreement is illustrated by the very small deviations ≤ 0.08% (g - g - ) and ≤ 0.41% (g + g + ) observed between the calculated and experimental data for the PO 2 - (asymmetric) stretching mode in the presence of the counterion K + in the hybrid model. Graphical abstract.

Natural and anthropogenic pressures are major concerns about the stability of vegetation in protected areas of the Sudano-Sahelian regions. This study aims to describe the woody flora of Mozogo-Gokoro National Park, submitted to these geographical area constraints in the Far North of Cameroon. Global inventory of this flora is carried out, through three collection units representing strata in vegetation that are previously identified by photo-interpretation, with analyses focusing on compositional diversity parameters. Results show a very rich woody flora (110 woody plant species, for 46 genera and 30 families), having a quasi-typical Sudano-Sahelian physiognomy. Vegetation is mainly a shrubby dry forest, dominated by species such as Senegalia ataxacantha, Anogeissus leiocarpa, Tamarindus indica, Psorospermum senegalense, Clerodendrum capitatum, Celtis toka, and the botanical families of Fabaceae and Combretaceae. The diversity indices, the woody density, and the basal area are high (4.32 bits for the Shannon-Weaver index, 2694.16 stems/ha and 43.89 m 2 /ha). Despite the dominance of Sahelian individuals, the importance of Sudanian and Guinean species (more than 22.68% of species) brings vegetation closer to those of much humid areas. In wooded savanna collection unit, several values of the evaluated parameters are lower in comparison with those obtained in the two others. However, these fluctuations related to the degradation of vegetation are insignificant, indicating a preserved resilience. The Mozogo-Gokoro National Park stands as a model of plant conservation in the Sudano-Sahelian zone in Cameroon, hence the major interest to be granted for its conservation and sustainable management.

The B3LYP/6-31++G* theoretical level was used to study the influence of various hexahydrated monovalent (Li + , Na + , K + ) and divalent (Mg 2+ ) metal counterions in interaction with the charged PO 2 - group, on the geometrical and vibrational characteristics of the DNA fragments of 3',5'-dDSMP, represented by four conformers (g + g + , g + t, g - g - and g - t). All complexes were optimized through two solvation models [the explicit model (6H 2 O) and the hybrid model (6H 2 O/Continuum)]. The results obtained established that, in the hybrid model, counterions (Li + , Na + , K + , Mg 2+ ) always remain in the bisector plane of the O1-P-O2 angle. When these counterions are explicitly hydrated, the smallest counterions (Li + , Na + ) deviate from the bisector plane, while the largest counterions (K + and Mg 2+ ) always remain in the same plane. On the other hand, the present calculations reveal that the g + g + conformer is the most stable in the presence of monovalent counterions, while conformers g + t and g - t are the most stable in the presence of the divalent counterion Mg 2+ . Finally, the hybrid solvation model seems to be in better agreement with the available crystallographic and spectroscopic (Raman) experiments than the explicit model. Indeed, the six conformational torsions of the C4'-C3'-O3'-PO - 2 -O5'-C5'-C4' segment of all complexes of the g - g - conformer in 6H 2 O/Continuum remain similar to the available experimental data of A- and B-DNA forms. The calculated wavenumbers of the g + g + conformer in the presence of the monovalent counterion and of g - t conformer in presence of the divalent counterion in the hybrid model are in good agreement with the Raman experimental data of A- and B-DNA forms. In addition, the maximum deviation between the calculated wavenumbers in the 6H 2 O/Continuum for the g + g + conformer and experimental value measured in an aqueous solution of the DMP-Na + complex, is <1.07% for the PO 2 - (asymmetric and symmetric) stretching modes and <2.03% for the O5'-C5' and O3'-C3' stretching modes. Graphical abstract dDSMP-(OO) - Mg 2+ /6W/Continuum.

Calculations were done by applying the B3LYP/6-31++G(d) method on the zwitterionic L-diglycine and L-dialanine to study the solvent effects on their structures and vibrational features. Three models of solvation (implicit, explicit, and explicit in implicit) were used and the subsequent resulting values compared. Even though both dipeptides surrounded by 12 water molecules seem sufficient to stabilize their zwitterionic characters, notably to avoid the proton transfer between the backbone (N t H[Formula: see text], COO (-)) groups, the hybrid model of solvation (explicit in implicit noted 12W/Continuum) appears to be in better agreement with available IR and Raman experiments than explicit and implicit models. The harmonic vibrational modes derived from geometry optimization of L-diglycine and L-dialanine in 12W/Continuum, agree with the available IR and Raman experimental values within 1 % for L-diglycine and 2 % for L-dialanine, and they appear more accurate than those found using the explicit model (12W). Graphical Abstract DFT/6-31++G∗ Optimized structures of L-diglycine (top) and L-dialanine (bottom) surrounded by 12 water molecules all embedded in a continuum.

H-atom transfer from caffeic acid phenethyl ester (CAPE), MBC (3-methyl-2-butenyl caffeate), BC (benzoic caffeate), P3HC (phenethyl-3-hydroxycinnamate), and P4HC (phenethyl-4-hydroxycinnamate) to the selected free radicals (·)HO2 and (·)O2(-) was studied. Such a transfer can proceed in three different ways: concerted proton-coupled electron transfer (CPCET), electron transfer followed by proton transfer (ET-PT), and proton transfer followed by electron transfer (PT-ET). The latter pathway is sometimes competitive with SPLET (sequential proton loss electron transfer) in polar media. Analyzing the thermodynamic descriptors of the reactions of CAPE and its derivatives with co-reactive species-in particular, the free energies of reactions, the activation barrier to the CPCET mechanism, and their rate constants-appears to be the most realistic method of investigating the H-atom transfers of interest. These analyses were performed via DFT calculations, which agree well with the data acquired from experimental studies (IC50) and from CBS calculations. The CPCM solvation model was used throughout the work, while the SMD model-employed as a reference-was used only for CAPE. The main conclusion drawn from the analysis was that SPLET is the mechanism that governs the reaction of phenolic acids with (·)HO2, while PT-ET governs the reaction of phenols with (·)O2(-). In kinetic investigations of the CPCET process, the rate constant decreases as the solvent polarity increases, so the reaction velocity slows down.