On the Stereochemistry of Natural Irones,Dihydroirones, and their Precursors

Natural irones from the essential oil of Iris rhizomes develop by oxidative degradation of C₃₁-triterpenoids produced by the plant. Two enantiomeric forms of irones are found in Iris, oils of different origin. The optical properties and CD spectra of irones, dihydroirones and their C₃₁-precursors are reported and their absolute stereochemistry is determined.     

C-terminal processing of yeast Spt7 occurs in the absence of functional SAGA complex

Background  

Spt7 is an integral component of the multi-subunit SAGA complex that is required for the expression of ~10% of yeast genes. Two forms of Spt7 have been identified, the second of which is truncated at its C-terminus and found in the SAGA-like (SLIK) complex.     

NMR Studies on Hydrolysis and Condensation Reactions of Alkoxysilanes Containing Si—H Bonds

Hydrolysis and condensation reactions of four organically modified alkoxides, used for the preparation of silicon oxycarbide gel precursors, have been followed by 29Si NMR. Triethoxysilane (HSi(OEt)3) and methyldiethoxysilane (MeHSi(OEt)2) react extremely fast compared to methyltriethoxysilane (MeSi(OEt)3) and tetraethoxysilane (Si(OEt)4). Co-hydrolysis reactions between different pairs of precursors—MeSi(OEt)3/Si(OEt)4; MeSi(OEt)3/HSi(OEt)3; MeHSi(OEt)2/Si(OEt)4; and MeHSi(OEt)2/HSi(OEt)3—were investigated by solution state 29Si and 17O NMR. Despite significantly different reactivities between precursors, evidence for co-condensation reactions has been found for each system. Finally, two-dimensional 29Si-1H heteronuclear correlation MAS-NMR spectroscopy was used to probe the local environments of the various Si sites in the product hybrid networks.     

Fast photoreduction of a heme peptide encapsulated in nanostructured materials

Microperoxidase-11 has been immobilized on siliceous materials MCM-41 and SBA-15 and on amino-functionalized SBA-15. Resonance Raman spectroscopy has provided solid evidence that the exogenous species occupy the pores of the mesoporous silica materials. Photoreduction of the microperoxidase-11 Fe(III) center has been observed to occur in the immobilized samples and results in a long-lived stable reduced heme. Reoxidation of the heme occurs upon addition of oxygen, and the redox cycle can be repeated numerous times. The source of the electron resulting in reduction of the heme is proposed to originate from the silica matrix, and functionalization of silica surface is suggested to facilitate electron transfer to the heme.     

Improved hydrogen release from ammonia-borane with ZIF-8

The promotion for hydrogen release from ammonia-borane (AB) was observed in the presence of ZIF-8. Even at concentrations of ZIF-8 as low as 0.25 mol %, a reduction of the onset temperature for dehydrogenation accompanies an increase in both the rate and amount of hydrogen released from AB.     

Newly Applied Two-Dimensional Solid-State NMR Correlation Techniques for the Characterization of Organically Modified Silicates

This paper highlights the use of two-dimensional (2D) solid-state NMR correlation techniques to probe the chemical homogeneity of organically modified silicate networks. Specifically, ²⁹Si{¹H} heteronuclear correlation (HETCOR) NMR experiments have revealed the spatial proximity of the two types of Si units present in a gel obtained from co-hydrolysis of methyldiethoxysilane and triethoxysilane. Similar information has also been obtained by using 2D ¹H homonuclear correlation NMR spectroscopy. Such experiments were only possible by combining the use of high magnetic field (14.10 T) with fast MAS spinning rate (30 kHz).