Experimental and theoretical study of stabilization of delocalized forms of semibullvalenes and barbaralanes by dipolar and polarizable solvents. Observation of a delocalized structure that is lower in free energy than the localized form.

[reaction: see text] UV/vis spectra of thermochromic semibullvalenes 1 and barbaralanes 2, which undergo rapid degenerate Cope rearrangements, display temperature-dependent shoulders (1b, 1d, 1e) or absorption maxima (1c, 2c, 2f) at the low-energy side of their strong UV bands. These long-wavelength absorptions are ascribed to Franck-Condon transitions from delocalized structures 1(deloc) and 2(deloc). Gibbs free energy differences, DeltaG*, between delocalized and localized forms were calculated from the temperature dependence of the long-wavelength absorptions.

Online analysis of xestodecalactones A-C, novel bioactive metabolites from the fungus Penicillium cf. montanense and their subsequent isolation from the sponge Xestospongia exigua.

Fungal isolates of Penicillium cf. montanense were obtained from the marine sponge Xestospongia exiguacollected from the Bali Sea, Indonesia. Culture filtrates of the fungi yielded three novel decalactone metabolites, xestodecalactones A, B, and C (1, 2a, and 2b), consisting of 10-membered macrolides with a fused 1,3-dihydroxybenzene ring.