Correlation Effects in Trimeric Acylphloroglucinols

Trimeric acylphloroglucinols (T-ACPLs) are a subclass of the large class of acylphloroglucinols—derivatives of 1,3,5-trihydroxybenzene containing an R–C=O group. T-ACPL molecules contain three acylphloroglucinol moieties linked by methylene bridges. Many of them are present in natural sources and exhibit biological activities, often better than the corresponding activities of monomeric acylphloroglucinols. All the stable conformers of T-ACPLs contain seven intramolecular hydrogen bonds, which constitute the dominant stabilising factors. A total of 38 different T-ACPLs, including both naturally occurring and model molecules, have been calculated at the HF and DFT/B3LYP levels. The DFT/B3LYP calculations were carried out both without and with Grimme’s dispersion correction, to highlight the dispersion (and, therefore, also electron correlation) effects for these molecules. The roles of dispersion are evaluated considering the effects of Grimme’s correction on the estimation of the conformers’ energies, the description of the characteristics of the individual hydrogen bonds, the conformers’ geometries and other molecular properties. Overall, the results offer a comprehensive overview of the conformational preferences of T-ACPL molecules, their intramolecular hydrogen bond patterns, and the correlation effects on their properties.

Cis and trans linkage of spin frustrated copper triangles creating Cu6 clusters

Two C3-symmetric guanidine-based copper triangles bridged by acetates in a cis manner and by chloride anions in a trans manner, respectively gave rise to two antiferromagnetically coupled hexanuclear CuII compounds, namely [Cu6L2Cl(μ-OAc)(DMF)3]·DMF (Cu6) and [Cu6L2(μ-Cl)2(DMF)4] (Cu6Cl)(where L stands for fully deprotonated tris (2-hydroxybenzylidene) triaminoguanidinium chloride, H5L). The experimental magnetic data of the two compounds were analyzed theoretically. A relatively good agreement with the experimental data was obtained when using the wavefunction theory (CASSCF) in combination with DFT (B3LYP) calculations for the very strong antiferromagnetic coupling within the Cu3 triangles (Javg = − 300 cm−1 for Cu6 and Javg = − 250 cm−1 for Cu6Cl), leading to spin-frustrated systems. It is worth mentioning that the electronic structure of each CuII center remains very similar in each complex with a Kramers ground state well separated from the first excited state (over 12000 cm−1) and weakly anisotropic (g∥ ≈ 2.40 and g⊥ ≈ 2.10).

Structural, Vibrational, Electronic and Optical Properties of 3-methoxy-2,4,5-trifluorobenzoic Acid Using DFT Calculations

The molecular vibrations of 3-methoxy-2,4,5-trifluorobenzoic acid (MFBA) were studied by recording the FTIR and FT-Raman spectra and the vibrational frequencies have been compared with the DFT-B3LYP calculations. The optimized structural characteristics of the molecule have been studied by both calculated and experimental data. NBO analyses and the LUMO-HOMO energy gap of the molecule shows the intramolecular charge transfer interaction. Further, the nonlinear optical properties of MFBA have been investigated from the calculated values of first hyperpolarizability and total dipolemoment. The electrostatic potential and Mulliken charges of MFBA have also been performed.

Solvent Free Three-Component Synthesis of 2,4,5-trisubstituted-1H-pyrrol-3-ol-type Compounds from L-tryptophan: DFT-B3LYP Calculations for the Reaction Mechanism and 3H-pyrrol-3-one↔1H-pyrrol-3-ol Tautomeric Equilibrium

In this paper, we describe the solvent-free three-component synthesis of 2,4,5-trisubstituted-1H-pyrrol-3-ol-type compounds from L-tryptophan. The first step of the synthetic methodology involved the esterification of L-tryptophan in excellent yields (93–98%). Equimolar mixtures of alkyl 2-aminoesters, 1,3-dicarbonyl compounds, and potassium hydroxide (0.1 eq.) were heated under solvent-free conditions. The title compounds were obtained in moderate to good yields (45%–81%). Density functional theory using “Becke, 3-parameter, Lee–Yang–Parr” correlational functional (DFT-B3LYP) calculations were performed to understand the molecular stability of the synthesized compounds and the tautomeric equilibrium from 3H-pyrrol-3-one type intermediates to 1H-pyrrol-3-ol type aromatized rings.

Saturating ability of the borax melt

The work is devoted to the research of influence of the electrolysis on the saturating ability of the electrolyte, which is a borax melt. To establish regularity when the saturating medium activity changes, which influences the intensification of saturation process, the structure and properties of borax during electrolysis were investigated. The change in the saturating medium activity was estimated by a relative value equal to the ratio of the boride layer depth obtained by non-electrolysis borating to the layer depth obtained by electrolysis borating. When comparing the real and theoretical saturating abilities, their convergence was observed. It was found that the saturation ability of the borax melt increases with increasing electrolyte runtime, which is due to a change in the structural components of the borax melt. A quantum-chemical calculation of the borax molecule structure was carried out using the non-empirical method of molecular orbitals in the theory of the density functional (DFT) with the three-parameter exchange-correlation functional B3LYP. Calculations show that two main structures are characteristic of a borax molecule: non-coplanar, with two mutually perpendicular 4-membered boron-oxygen cycles and flat linear. An increase in the saturation ability of the borax melt during electrolysis allows the development of new low-energy borating processes.

Excited State Frequencies of Chlorophyll f and Chlorophyll a and Evaluation of Displacement through Franck-Condon Progression Calculations

We present ground and excited state frequency calculations of the recently discovered extremely red-shifted chlorophyll f. We discuss the experimentally available vibrational mode assignments of chlorophyll f and chlorophyll a which are characterised by particularly large downshifts of 131-keto mode in the excited state. The accuracy of excited state frequencies and their displacements are evaluated by the construction of Franck–Condon (FC) and Herzberg–Teller (HT) progressions at the CAM-B3LYP/6-31G(d) level. Results show that while CAM-B3LYP results are improved relative to B3LYP calculations, the displacements and downshifts of high-frequency modes are underestimated still, and that the progressions calculated for low temperature are dominated by low-frequency modes rather than fingerprint modes that are Resonant Raman active.

Reduction Potential Predictions for Some 3-Aryl-Quinoxaline-2-Carbonitrile 1,4-Di-N-Oxide Derivatives with Known Anti-Tumor Properties

The ability for DFT: B3LYP calculations using the 6-31g and lanl2dz basis sets to predict the electrochemical properties of twenty (20) 3-aryl-quinoxaline-2-carbonitrile 1,4-di-N-oxide derivatives with varying degrees of cytotoxic activity in dimethylformamide (DMF) was investigated. There was a strong correlation for the first reduction and moderate-to-low correlation of the second reduction of the diazine ring between the computational and the experimental data, with the exception of the derivative containing the nitro functionality. The four (4) nitro group derivatives are clear outliers in the overall data sets and the derivative E4 is ill-behaved. The remaining three (3) derivatives containing the nitro groups had a strong correlation between the computational and experimental data; however, the computational data falls substantially outside of the expected range.