Protonation-Dependent Base Flipping at Neutral pH in the Catalytic Triad of a Self-Splicing Bacterial Group†II Intron.

NMR spectroscopy has revealed pH-dependent structural changes in the highly conserved catalytic domain 5 of a bacterial group II intron. Two adenines with pK(a) values close to neutral pH were identified in the catalytic triad and the bulge. Protonation of the adenine opposite to the catalytic triad is stabilized within a G(syn)-AH(+) (anti) base pair. The pH-dependent anti-to-syn flipping of this G in the catalytic triad modulates the known interaction with the linker region between domains 2 and 3 (J23) and simultaneously the binding of the catalytic Mg(2+) ion to its backbone. Hence, this here identified shifted pK(a) value controls the conformational change between the two steps of splicing.

Ozone-induced band bending on metal-oxide surfaces studied under environmental conditions.

Ozone adsorption and decomposition on metal oxides is of wide interest in technology and in atmospheric chemistry. Here, ozone-adsorption-induced band bending is observed on Ti- and Fe-oxide model surfaces under dry and humid conditions. Photoelectron spectroscopic studies indicate the effect of charge transfer to O3, which limits the surface coverage of the precursor to decomposition reactions. This is also consistent with the negative pressure dependence observed in previous studies. These results contribute to our fundamental understanding of ozone adsorption and decomposition mechanisms on metal oxides of environmental and technological relevance.

Constituents of Cypriol Oil (Cyperus scariosus R.Br.): N-Containing Molecules and Key Aroma Components.

Cypriol oil, the essential oil from Cyperus scariosus R.Br., has been investigated to reveal minor nitrogen-containing molecules and minor components responsible for the odor. A total of 21 nitrogenous components are reported, of which epi-guaipyridine (32 mg/kg), guaia-9,11-dienpyridine (9 mg/kg), and cananodine (10 mg/kg) were the most abundant. A new ketone, cyperen-8-one, with a significant woody, ambery odor could also be isolated and identified along with a novel lactone, cyperolactone, and an alcohol. Rotundone was found to have the highest odor-activity value of the measured compounds and, together with the other ketones, contributes to the woody-amber character of cypriol oil.