Ultrafast intersystem crossing in xanthone from wavepacket dynamics

Most aromatic ketones containing first-row elements undergo unexpectedly fast intersystem crossing in few tens of picoseconds and a quantum yield close to unity. Among them, xanthone (9H-xanthen-9-one) possesses one of the fastest singlet-triplet rates of ~1.5 ps. The exact mechanism of this unusually fast transition is still under debate. Here, we perform the wavepacket dynamics of the photochemistry of xanthone in the gas phase and in polar solvents. We show that xanthone follows El-Sayed's rule for intersystem crossing. From the second singlet excited state, the mechanism is sequential: (i) an internal conversion between singlets 1pipi*-1npi* (85 fs), (ii) an intersystem crossing 1npi*-3pipi* (2.0 ps), and (iii) an internal conversion between triplets 3pipi*-3npi* (602 fs). Each transfer finds its origin in a barrierless access to electronic state intersections. These intersections are close to minimum energy structures, allowing for efficient transitions from the initial singlet state to the triplets.

Design, Synthesis and Antibacterial Activity of some 3,6-Dimethlyquinoxaline-2-Hydrazone Derivatives

Aims: This aims of this study was to continue the effort to synthesis new quinoxaline-based heterocycles and study its antibacterial properties. Objective: This study was designed to reacts 3,6-dimethylquinoxaline-2-hydrazine with some substituted aromatic ketones and study their antibacterial properties on some locally and clinically isolated bacterial strains. Materials and Methods: Five 3,6-dimethylquinoxaline-2-hydrazone derivatives were synthesized from the reactions of 3,6-dimethylquinoxaline-2-hydrazine with various substituted aromatic ketones. The products were then tested for their potential antibacterial properties. Results: All the synthesized compounds were found to be active against all the bacterial strains investigated in this study. It was observed that the zones of inhibition observed for the synthesized compounds against the test organisms ranged between 15 mm and 38 mm. The MIC observed for the synthesized compounds ranged between 0.0313mg/mL and 0.125 mg/mL, while that of the standard antibiotic, streptomycin, varied between 0.0313 mg/mL and 0.500 mg/mL and those observed for tetracycline falls between 0.0313 mg/mL and 0.500 mg/mL. The minimum bactericidal concentrations exhibited by the synthesized compounds ranged between 0.0625 mg/mL and 0.250 mg/mL Discussion and conclusion: The study concluded that all the compounds exhibited appreciable bactericidal effects against all the bacterial strains, which is an indication that such synthetic compounds possessed broad spectrum activities and such compounds could be useful in formulation of antibacterial compounds which could be used to mitigates infections caused by pathogens that are now developing resistance against the available antibiotics.

Study on the Characteristic Components of Distinguishing Dalbergia cochinchinensis from the Other Three Similar Dalbergia Species

Dalbergia cochinchinensis can be distinguished from Dalbergia retusa, Dalbergia bariensis, and Dalbergia oliveri quickly using infrared spectrum characteristic peaks as shown in a previous study. To investigate the components corresponding to the infrared characteristic peaks of Dalbergia cochinchinensis, petroleum ether, ethyl acetate, and butyl alcohol were sequentially used to extract the dispersion liquid of D. cochinchinensis. The petroleum ether extracts were further fractionated by column chromatography, using Fourier-transform infrared spectroscopy (FTIR) to track the characteristic components during separation. FTIR spectra of petroleum ether extractives indicated the presence of aromatic ketones and olefin compounds. The gas chromatography–mass spectrometry research showed some main components and gave possible structure. Furthermore, their detailed structures were characterized thorough a nuclear magnetic resonance approach, and then two possible components (3,5-dihydroxy-7-methoxy-2-phenylchroman-4-one and 3,5,7-trihydroxy-2-phenylchroman-4-one) were identified.