Photoinduced Structural Phase Transitions in Polyacene

There exist two types of structural instability in polyacene: double bonds in a cis pattern and those in a trans pattern. They are isoenergetic but spectroscopically distinct. We demonstrate optical characterization and manipulation of Peierls-distorted polyacene employing both correlated and uncorrelated Hamiltonians. We clarify the phase boundaries of the cis- and trans-distorted isomers, elucidate their optical-conductivity spectra, and then explore their photoresponses. There occurs a photoinduced transformation in the polyacene structure, but it is one-way switching: The trans configuration is well convertible into the cis one, whereas the reverse conversion is much less feasible. Even the weakest light irradiation can cause a transition of uncorrelated electrons, while correlated electrons have a transition threshold against light irradiation.Comment: 14 pages with 15 figures embedde

In vitro and in vivo hepatoprotective effects of the total alkaloid fraction of Hygrophila auriculata leaves

Objective: To investigate the total alkaloid fraction of the methanol extract of leaves of Hygrophila auriculata for its hepatoprotective activity against CCl4-induced toxicity in freshly isolated rat hepatocytes, HepG2 cells, and animal models. Materials and Methods: Mature leaves of H. auriculata were collected, authenticated, and subjected to methanolic extraction followed by isolation of total alkaloid fraction. Freshly isolated rat hepatocytes were exposed to CCl4 (1%) along with/without various concentrations of the total alkaloid fraction (80-40 μg/ml). Protection of human liver-derived HepG2 cells against CCl4-induced damage was determined by the MTT assay. Twenty-four healthy Wistar albino rats (150-200 g) of either sex were used for the in vivo investigations. Liver damage was induced by administration of 30% CCl4 suspended in olive oil (1 ml/kg body weight, i.p). Results: The antihepatotoxic effect of the total alkaloid fraction was observed in freshly isolated rat hepatocytes at very low concentrations (80-40 μg/ml). A dose-dependent increase in the percentage viability was observed when CCl4-exposed HepG2 cells were treated with different concentrations of the total alkaloid fraction. Its in vivo hepatoprotective effect at 80 mg/kg body weight was comparable with that of the standard Silymarin at 250 mg/kg body weight. Conclusion: The total alkaloid fraction was able to normalize the biochemical levels which were altered due to CCl4 intoxication