Application Of Quantum Mechanical Calculations Research Articles

Метод моделирования диэлектрической проницаемости анизотропного иерархически построенного нанокомпозита с периодической структурой

A method is proposed for modeling the complex dielectric constant of an anisotropic hierarchically constructed nanocomposite with a periodic structure, based on the complex application of quantum mechanical calculations, an effective medium model, and equivalent equivalent circuits. The dielectric constant of the TiO2 - Al2O3 nanocomposite under the action of external high-frequency electromagnetic radiation has been investigated. The wavelength ranges at which resonance bursts are observed are determined. The possibility of controlling the maxima of difference losses and resonance absorption maxima by changing the geometric parameters of the nanocomposite is shown.

Phytotoxins produced by Phoma chenopodiicola, a fungal pathogen of Chenopodium album

Two phytotoxins were isolated from the liquid culture of Phoma chenopodiicola, a fungal pathogen proposed for the biological control of Chenopodium album, a common worldwide weed of arable crops. The two phytotoxins appeared to be a new tetrasubstituted furopyran and a new ent-pimaradiene. From the same culture a new tetrasubstituted isocoumarin was also isolated. These compounds were characterized by using spectroscopic (essentially 1D and 2D NMR and HR ESI MS) and chemical methods as 3-(3-methoxy-2,6-dimethyl-7aH-furo[2,3-b]pyran-4-yl)-but-2-en-1-ol (chenopodolan D, 1) (1S,2S,3S,4S,5S,9R,10S,12S,13S)-1,3,12-triacetoxy-2,hydroxy-6-oxo-ent-pimara-7(8),15-dien-18-oic acid 2,18-lactone (chenopodolin B, 3), and, 4,5,7-trihydroxy-3-methyl-isochroman-1-one (chenisocoumarin, 2) The absolute configuration of chenisocoumarin was assigned by applying an advanced Mosher’s method through the derivatization of its secondary hydroxylated carbon C-4, while that of chenopodolan D by application of quantum mechanical calculations of chiroptical (ECD and ORD) properties. When assayed by leaf puncture against non-host weeds, chenopodolan D and chenopodolin B showed phytotoxicity while chenisocoumarin and the 9-O-acetyl derivative of chenopodolan D were inactive. These results confirm that the nature of the side chain at C-4 in chenopodolans, and in particular its hydroxylation, are important features for activity. The activity of chenopodolin B could also be explained by its possible hydrolysis to chenopodolin.