Search Results (4)

A novel Schiff base, (E)-4-acetyl-N-(4-hydroxy-3-methoxybenzylidene)aniline (abbreviated as ANHMA), was synthesized and characterized using infrared and ¹H- and ¹³C-NMR spectroscopies. Optical properties in different solvents were evaluated using UV-vis absorption spectroscopy. The compound is shown to exhibit both positive and negative solvatochromism with reversal occurring for solvents with E_T(30)~45 (e.g., DMSO). The solvatochromic behavior of the compound was found to be strongly dependent on the hydrogen bond abilities and polarizability of the solvent, the observed reversal in solvatochromism being explained by the change in the dominant solvent effects in non-polar and polar–aprotic solvents (H-bond acceptor ability of the solvent and polarizability) compared to polar–protic solvents (H-bond donor ability), according to the developed Catalán multiparametric solvatochromic model. In all freshly prepared solutions studied, the (E)-enol-imine tautomer of the compound was found to strongly predominate over the keto-amine tautomeric forms, the latter increasing their populations over time in the presence of H-bond donor/acceptor species. Irradiation of ANHMA with UV light (λ ≥ 311 nm) was also investigated in several solvents and shown to follow a general pattern, with the conversion of the (E)-enol-imine tautomer into the keto-amine forms in a solvent-mediated enol-imine/keto-amine tautomerism, and (Z)→(E) C=C isomerization between the keto-imine forms. The experimental results received support from an extensive series of calculations on the structure and UV-vis spectra of the relevant tautomeric/isomeric forms of the compound performed at the DFT(B3LYP)/6-311++G(d,p) level of approximation (including time-dependent DFT calculations and solvent consideration). Full article

Relative equilibrium populations of the five lowest-energy isolated-pentagon-rule (IPR) isomeric structures of Pr@C${}_{82}$ under high-temperature fullerene synthesis conditions were calculated with the Gibbs energy terms based on molecular characteristics derived using density functional theory (DFT) treatments (B3LYP/6-31+G${}^{*}$∼SDD energetics and B3LYP/6-31G${}^{*}$∼SDD entropy). Two leading isomers were identified, major Pr@$C_{2v};9$-C${}_{82}$ and minor Pr@$C_s;6$-C${}_{82}$. The calculated isomeric relative equilibrium populations agreed with observations. Full article

Wild chervil (Anthriscus sylvestris) is a wild-growing plant from the Apiaceae family, used as a food in Europe and eastern Asia. Due to its high content of lignans known to possess anti-inflammatory, antiproliferative, antiviral and other activities, it represents a potential functional food. However, quantitative data on lignans are still scarce and limited to deoxypodophyllotoxin, nemerosin and yatein. In this paper, a newly developed and validated reverse-phase HPLC–UV method was used to evaluate the content of 14 lignans in both aerial parts and roots of A. sylvestris. The most abundant root components were found to be deoxypodophyllotoxin (2.0–42.8 mg/g), nemerosin (2.0–23.4 mg/g), yatein (1.1–18.5 mg/g), podophyllotoxone (0.7–20.5 mg/g), guaiadequiol (0.8–8.3 mg/g) and dimethylmatairesinol (0.1–5.2 mg/g). Despite the high intra-population variability, a general trend of an increased lignan content during plant development could be observed in the root samples, whereas an opposite trend was observed in the herb samples. A validation study indicated that some of the investigated compounds—7-oxoaryltetralins and dibenzylbutyrolactones—have low stability and require cold storage in the dark. Furthermore, dibenzylbutyrolactones were confirmed to undergo a fast cis–trans isomerization; therefore, only the total content of these isomers should be reported. Full article

The exo⇔endo isomerization of 2,5-dimethoxybenzaldehyde was theoretically studied by density functional theory (DFT) to examine its favored conformers via sp²–sp² single rotation. Both isomers were docked against 1BNA DNA to elucidate their binding ability, and the DFT-computed structural parameters results were matched with the X-ray diffraction (XRD) crystallographic parameters. XRD analysis showed that the exo-isomer was structurally favored and was also considered as the kinetically preferred isomer, while several hydrogen-bonding interactions detected in the crystal lattice by XRD were in good agreement with the Hirshfeld surface analysis calculations. The molecular electrostatic potential, Mulliken and natural population analysis charges, frontier molecular orbitals (HOMO/LUMO), and global reactivity descriptors quantum parameters were also determined at the B3LYP/6-311G(d,p) level of theory. The computed electronic calculations, i.e., TD-SCF/DFT, B3LYP-IR, NMR-DB, and GIAO-NMR, were compared to the experimental UV–Vis., optical energy gap, FTIR, and ¹H-NMR, respectively. The thermal behavior of 2,5-dimethoxybenzaldehyde was also evaluated in an open atmosphere by a thermogravimetric–derivative thermogravimetric analysis, indicating its stability up to 95 °C. Full article