Two new sesterterpenes, ophiobolin O (1) and 6-epi-ophiobolin O (2), together with the known ophiobolins G (3), H (4), and K (5), and 6-epi-ophiobolin K (6) were isolated from the marine derived fungus Aspergillus sp. The structures of these compounds were elucidated based on chemical and physicochemical evidence, including MS, UV, IR and NMR spectra. The stereochemistry of 1 was further confirmed by catalytic reaction of 5 with p-TsOH as a catalyst.
The adsorption properties of precious metal clusters such as Rh, Pd, Ag, Ir, Pt, and Au toward NO were systematically investigated using the density functional calculations. It was found that the most energetically stable adsorption state of NO on the tetrahedral M 4 clusters was found to be the NO/Ir 4 system. The ability of the precious metal clusters to activate the N-O bond was also discussed mainly from a geometric point of view. The entire linear behavior of the elongation of the N-O bond of NO molecules adsorbed on M 4 clusters was observed with increasing values of the molecular charge on the NO molecules, which suggests the back-donation of an electron to the 2π* orbital of the NO molecules. The substantial elongation of the N-O bond was found on the NO/Ir 4 system, which was nearly equal to that on the NO/Rh 4 systems. These results indicate that the Ir cluster has the best properties for the adsorption and activation of NO.
The phonon echo excited by radio-frequency pulses in superconducting MgB 2 in external magnetic field was studied. Using the echo technique two contributions to ultrasound attenuation are observed: low-temperature relaxation, which depends on the magnetic field, and a decay connected to the superconducting energy gap at temperatures close to Tc. The value of about 7kBTc for the energy gap was extracted from the experimental data.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.