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Momilactones A and B (MA and MB, respectively) are phytoalexins and plant growth inhibitors available in rice husks. However, to date, the isolation and purification of the two compounds have been complicated, laborious, and less effective. The present study was conducted to establish a protocol to simplify and optimize quantities of MA and MB by combinations of ethyl acetate (EtOAc), distilled water, methanol (MeOH), temperature, and pressure for extractions. At a temperature of 100 °C, combined with EtOAc and MeOH 100%, MA and MB were enriched in greater quantities than non-treated rice husks, of which MB was much augmented than MA. The EtOAc extract obtained from samples dried at 100 °C for 1 h, then placed in MeOH 100% for 1 week, provided maximum yields of MA [58.76 µg/g dry weight (DW)] and MB (104.43 µg/g DW). The use of pressure effectively enhanced yields of MA (17.90–26.26 µg/g DW) and MB (40.78–71.0 µg/g DW). The actual purified amounts of MA and MB increased by 5 and 15 folds, respectively. The use of either sole distilled water or MeOH ≤ 50% at any temperature did not successfully isolate both MA and MB. The yield optimization aids to easier and more productive purification of the two compounds, and thus extends researches on biological activities of MA and MB, including pharmaceutical and medicinal properties.
We present a study of the influence of disorder on the Mott metal-insulator transition for the organic charge-transfer salt κ -(BEDT-TTF) 2 Cu[N(CN) 2 ]Cl. To this end, disorder was introduced into the system in a controlled way by exposing the single crystals to X-ray irradiation. The crystals were then fine-tuned across the Mott transition by the application of continuously controllable He-gas pressure at low temperatures. Measurements of the thermal expansion and resistance show that the first-order character of the Mott transition prevails for low irradiation doses achieved by irradiation times up to 100 h. For these crystals with a moderate degree of disorder, we find a first-order transition line which ends in a second-order critical endpoint, akin to the pristine crystals. Compared to the latter, however, we observe a significant reduction of both, the critical pressure pc and the critical temperature Tc . This result is consistent with the theoretically-predicted formation of a soft Coulomb gap in the presence of strong correlations and small disorder. Furthermore, we demonstrate, similar to the observation for the pristine sample, that the Mott transition after 50 h of irradiation is accompanied by sizable lattice effects, the critical behavior of which can be well described by mean-field theory. Our results demonstrate that the character of the Mott transition remains essentially unchanged at a low disorder level. However, after an irradiation time of 150 h, no clear signatures of a discontinuous metal-insulator transition could be revealed anymore. These results suggest that, above a certain disorder level, the metal-insulator transition becomes a smeared first-order transition with some residual hysteresis.