Exploring the molecular solvatochromism, stability, reactivity, and non-linear optical response of resveratrol.

CONTEXT: This work analyzes the isomerization effects and solvent contributions to the stability, electronic excitations, reactivity, and non-linear optical properties (NLO) of resveratrol molecules within the formalism of the Density Functional Theory. The findings suggest that resveratrol solvatochromism is significantly influenced by solvent polarization. The electronic and free energies (E and G) indicate that trans is the most stable conformer. The system is classified as a strong nucleophile. However, the analysis of the Fukui functions and the Mulliken charges indicate that cis-trans isomerization jointly affects the reactive indices of the carbon and hydrogen atoms. The results also suggest that solvent is relevant to solvatochromism and the NLO response. Both cis and trans conformers present strong π - π ∗ excitations that undergo a visible hypsochromic change when the polarity of the solvent increases. Once the absorption spectra are connected to the first hyperpolarization ( ß ) by the Oudar and Chemla relation, the hypsochromism of resveratrol is the reason for the drop in the generation of the second harmonic when the ambient polarity decreases. The CAM-B3LYP DFT results suggest that resveratrol is interesting for NLO applications. Depending on the choice of solvent, values ∼ 50 times those observed for urea ( ß = 0.34 × 10 - 34 esu), which is a standard NLO material. METHODS: The optimized geometries of cis and trans isomers of resveratrol in vacuum were obtained using Density Functional Theory (DFT) with the hybrid exchange-correlation function (CAM-B3LYP) and Pople basis set functions, specifically 6-311++G(d,p). The solvent effect on the geometries of both isomers was included using the polarizable continuum model (PCM) with the same level of QM calculation. Vibrational analysis was conducted to confirm that all optimized geometries correspond to the minimum energy. Various electronic properties, including dipole moments, molecular orbitals, transition energy, dipole polarizabilities, and global reactivity parameters, were calculated using both continuum and discrete solvation models based on the sequential QM/MM methodology. All QM calculations were performed with the Gaussian 09 program and the MC simulations with the DICE program. All NLO analysis was carried out using the Multiwfn code.

Exploration of Free Energy Surface of the Au10 Nanocluster at Finite Temperature.

The first step in comprehending the properties of Au10 clusters is understanding the lowest energy structure at low and high temperatures. Functional materials operate at finite temperatures; however, energy computations employing density functional theory (DFT) methodology are typically carried out at zero temperature, leaving many properties unexplored. This study explored the potential and free energy surface of the neutral Au10 nanocluster at a finite temperature, employing a genetic algorithm coupled with DFT and nanothermodynamics. Furthermore, we computed the thermal population and infrared Boltzmann spectrum at a finite temperature and compared it with the validated experimental data. Moreover, we performed the chemical bonding analysis using the quantum theory of atoms in molecules (QTAIM) approach and the adaptive natural density partitioning method (AdNDP) to shed light on the bonding of Au atoms in the low-energy structures. In the calculations, we take into consideration the relativistic effects through the zero-order regular approximation (ZORA), the dispersion through Grimme's dispersion with Becke-Johnson damping (D3BJ), and we employed nanothermodynamics to consider temperature contributions. Small Au clusters prefer the planar shape, and the transition from 2D to 3D could take place at atomic clusters consisting of ten atoms, which could be affected by temperature, relativistic effects, and dispersion. We analyzed the energetic ordering of structures calculated using DFT with ZORA and single-point energy calculation employing the DLPNO-CCSD(T) methodology. Our findings indicate that the planar lowest energy structure computed with DFT is not the lowest energy structure computed at the DLPN0-CCSD(T) level of theory. The computed thermal population indicates that the 2D elongated hexagon configuration strongly dominates at a temperature range of 50-800 K. Based on the thermal population, at a temperature of 100 K, the computed IR Boltzmann spectrum agrees with the experimental IR spectrum. The chemical bonding analysis on the lowest energy structure indicates that the cluster bond is due only to the electrons of the 6 s orbital, and the Au d orbitals do not participate in the bonding of this system.

Termoquímica computacional: en la búsqueda de la precisión química

Introducción: La termoquímica computacional es un campo de gran interés por sus diversas aplicaciones en diferentes campos de la química. En la actualidad, con el avance en el desarrollo de los supercomputadores se pueden emplear diversas metodologías que emplean cálculos de estructura electrónica para estimar valores termodinámicos con errores ~ 1,0 kcal/mol en comparación con los datos experimentales. Metodología: En este artículo se describen brevemente los principales métodos compuestos empleados en la termoquímica computacional como la serie de Petersson, los métodos Weizmann, el modelo HEAT y con especial énfasis en las teorías Gaussian-n. Aplicaciones: Diversas aplicaciones de la termoquímica computacional se presentan en este trabajo tales como el estudio de la reactividad y las estabilidades de nuevos derivados de compuestos químicos con potencialidades como fármacos, estudios de contaminantes en la química de la atmosfera donde se estiman valores importantes de entalpias de formación sobre compuestos derivados del gas de efecto invernadero SF6, estudios de compuestos derivados del petróleo de potencial importancia como nuevos combustibles y el desarrollo de explosivos con estimaciones energéticas de las entalpias de disociación de enlace y de combustión de nuevos compuestos orgánicos. Conclusiones: La termoquímica computacional es una herramienta actual para resolver problemas de la química donde la experimentación es difícil y con un alto costo económico. Se espera en un futuro que esta área desarrolle nuevos métodos y códigos computacionales que permitan estudiar sistemas moleculares de gran tamaño importantes en otras áreas de las ciencias como la física, la biología, ciencias de los materiales, entre otros.

Introdução: A termoquímica computacional é uma área de grande interesse devido às suas diversas aplicações em diferentes campos da química. Hoje em dia, com o avanço no desenvolvimento de supercomputadores, várias metodologias podem ser utilizadas que utilizam cálculos de estrutura eletrônica para estimar valores termodinâmicos com erros de ~ 1,0 kcal/mol em comparação com os dados experimentais. Metodologia: Este artigo descreve resumidamente os principais métodos compostos usados em termoquímica computacional, como a série Petersson, os métodos de Weizmann, o modelo HEAT e com especial ênfase nas teorias Gaussianas-n. Aplicações: Várias aplicações da termoquímica computacional são apresentadas neste trabalho tais como o estudo da reatividade e estabilidades de novos derivados de compostos químicos com potencial como drogas, estudos de poluentes em química atmosférica onde valores importantes de entalpias são estimados de treinamento em compostos derivados do gás de efeito estufa SF6, estudos de compostos derivados do petróleo com potencial importância como novos combustíveis e o desenvolvimento de explosivos com estimativas energéticas das entalpias de dissociação de ligações e combustão de novos compostos orgânicos. Conclusões: A termoquímica computacional é uma ferramenta atual para resolver problemas de química onde a experimentação é difícil e com alto custo econômico. Espera-se que no futuro esta área desenvolva novos métodos e códigos computacionais que permitam estudar grandes sistemas moleculares importantes em outras áreas da ciência como física, biologia, ciência dos materiais, entre outras.

SUMMARY Introductión: Computational thermochemistry is an area of great interest for its various applications in many different fields of chemistry. With the increase of the computational power readily available, it is currently possible to use various calculation based on the electronic structure methods for estimate thermodynamic properties with an error on the order of ~1.0 kcal/mol, which is comparable to experimental values. Methodology: In this work we briefly describe the main composite methods such as Petersson series, the Weizmann methods the HEAT model and with special focus on the Gaussian-n theories. Applications: Various applications of computational thermochemistry are presented in this work such as the study of reactivity and stabilities of new derivatives of chemical compounds with potential use as drugs, studies of pollutants in atmospheric chemistry where important values of enthalpies are estimated of training on compounds derived from the greenhouse gas SF6, studies of compounds derived from petroleum of potential importance as new fuels and the development of explosives with energy estimates of the enthalpies of bond dissociation and combustion of new organic compounds. Conclusions: Computational thermochemistry is a current tool to solve chemistry problems where experimentation is difficult and with a high economic cost. It is expected in the future that this area will develop new methods and computational codes that allow studying large molecular systems important in other areas of science such as physics, biology, materials science, among others.

Theoretical Prediction of Structures, Vibrational Circular Dichroism, and Infrared Spectra of Chiral Be4B8 Cluster at Different Temperatures.

Lowest-energy structures, the distribution of isomers, and their molecular properties depend significantly on geometry and temperature. Total energy computations using DFT methodology are typically carried out at a temperature of zero K; thereby, entropic contributions to the total energy are neglected, even though functional materials work at finite temperatures. In the present study, the probability of the occurrence of one particular Be4B8 isomer at temperature T is estimated by employing Gibbs free energy computed within the framework of quantum statistical mechanics and nanothermodynamics. To identify a list of all possible low-energy chiral and achiral structures, an exhaustive and efficient exploration of the potential/free energy surfaces is carried out using a multi-level multistep global genetic algorithm search coupled with DFT. In addition, we discuss the energetic ordering of structures computed at the DFT level against single-point energy calculations at the CCSD(T) level of theory. The total VCD/IR spectra as a function of temperature are computed using each isomer's probability of occurrence in a Boltzmann-weighted superposition of each isomer's spectrum. Additionally, we present chemical bonding analysis using the adaptive natural density partitioning method in the chiral putative global minimum. The transition state structures and the enantiomer-enantiomer and enantiomer-achiral activation energies as a function of temperature evidence that a change from an endergonic to an exergonic type of reaction occurs at a temperature of 739 K.

Thermochemistry and kinetic analysis for the conversion of furfural to valuable added products.

Furfural is a valuable oxygenated compound derived from the thermal decomposition of biomass, and is one of the major problems of bio-oil upgrading. Due to its high reactivity, this compound requires further upgrading to more stable products such as furfuryl alcohol, 2-methylfuran (MF), furan, 2-methyltetrahydrofuran, and tetrahydrofuran. The thermochemical data and kinetic analysis of the reactions involved in the conversion of furfural were investigated by molecular modeling to guide experimental investigations in the process of designing efficient catalysts that allows the control of the reaction pathways in specific directions, towards the production of fuel precursors or chemicals. All calculations for reactants, intermediates, and products were performed using the long range corrected functional WB97XD, with the basis set 6-311+g(d,p), under the density functional theory framework. Thermochemistry results suggest that furfural hydrogenation to form furfuryl alcohol is spontaneous up to a temperature of 523 K, but beyond this temperature the reaction becomes a nonspontaneous process. By contrast, the decarbonylation of furfural was thermodynamically favored at temperatures greater than 523 K. Therefore, furan is a thermodynamically favored product, while furfuryl alcohol is kinetically preferred. Once furfuryl alcohol is formed, the hydrogenolysis path to produce methylfuran is favored kinetically and thermodynamically, compared to the ring-hydrogenation towards tetrahydrofurfuryl alcohol. Gas phase thermodynamic properties and rate constants of the reactions involved in the conversion of furfural were calculated and compared against existing experimental data. This study provides the basis for further vapor phase catalytic studies required for upgrading of furans/furfurals to value-added chemicals. Graphical abstract Furan is a thermodynamically favored product, while furfuryl alcohol is kinetically preferred.

How computational methods and relativistic effects influence the study of chemical reactions involving Ru-NO complexes?

Two treatments of relativistic effects, namely effective core potentials (ECP) and all-electron scalar relativistic effects (DKH2), are used to obtain geometries and chemical reaction energies for a series of ruthenium complexes in B3LYP/def2-TZVP calculations. Specifically, the reaction energies of reduction (A-F), isomerization (G-I), and Cl- negative trans influence in relation to NH3 (J-L) are considered. The ECP and DKH2 approaches provided geometric parameters close to experimental data and the same ordering for energy changes of reactions A-L. From geometries optimized with ECP, the electronic energies are also determined by means of the same ECP and basis set combined with the computational methods: MP2, M06, BP86, and its derivatives, so as B2PLYP, LC-wPBE, and CCSD(T) (reference method). For reactions A-I, B2PLYP provides the best agreement with CCSD(T) results. Additionally, B3LYP gave the smallest error for the energies of reactions J-L. © 2017 Wiley Periodicals, Inc.

Conformational and reactivity study of dithiophenyl-fucosyl ketals with theoretical chemical methods.

Carbohydrates can be used as substrates to synthesize new complex molecules; these molecules contain several chiral centers that can be used in organic synthesis. D-Fucose diphenyl thioacetal reacts differentially with acetone, and this paper describes a study of the mechanism of this reaction using theoretical chemistry methods. The conformer distribution was studied using a Monte Carlo method for the reaction products, and the obtained conformers were validated by calculating the hydrogen spin-spin coupling constants with the DFT/B3LYP/DGDZVP method. Results agreed with the experimental coupling constants with an adequate root mean squared deviation. The free energies and enthalpies of formation of the resulting global minimum conformers were calculated with the same method and with the thermochemical compound method CBS-4 M. This technique, combined with the conformational analysis, allowed comparison of the formation enthalpies of the compounds involved in this reaction, and, with this information, we can postulate the correct reaction pathway. Graphical abstract Reaction pathway.