Millettia dubia De Wild. (Fabaceae): Structural analysis of the oleanane-type glycosides and stimulation of the sweet taste receptors TAS1R2/TAS1R3.

From the root barks of a Central African tree Millettia dubia De Wild. (Fabaceae), ten previously undescribed oleanane-type glycosides were isolated by various chromatographic protocols. Their structures were elucidated by spectroscopic methods, mainly 2D NMR experiments and mass spectrometry, as mono- and bidesmosidic glycosides of mesembryanthemoidigenic acid, hederagenin and oleanolic acid. The stimulation of the sweet taste receptor TAS1R2/TAS1R3 by these glycosides was evaluated, and structure/activity relationships were proposed. Two of them showed an agonist effect on TAS1R2/TAS1R3.

Visible-light hydrogen generation using as photocatalysts layered titanates incorporating in the intergallery space ruthenium tris(bipyridyl) and methyl viologen.

A series of layered titanates containing in the interlayer space tris(2,2'-bipyridyl)ruthenium(II) [Ru(bpy)(3)(2+)] or methyl viologen (MV(2+)) or both has been prepared and characterized by elemental analyses, XRD, and optical and vibrational spectroscopy. Incorporation of Ru(bpy)(3)(2+) and MV(2+) is confirmed by the increase of the distance between the titanate layers. The presence of Ru(bpy)(3)(2+) in the material is also revealed in optical spectroscopy where the ligand to metal charge transfer band appearing at λ(max) 460 nm is observed. Also incorporation of MV(2+) leads to the observation of the charge transfer complex band with the titanate host from 350 to 650 nm. These solids are active for the photocatalytic hydrogen generation from water when colloidal platinum as catalyst and EDTA as sacrificial electron donor are present in the solution. The maximum efficiency was obtained for a solid consisting of layered titanate containing a 10.2 wt.% loading of Ru(bpy)(3)(2+) incorporated in the titanate layers and MV(2+) and Pt nanoparticles in the aqueous solution. This heterogeneous system produced about one-half the hydrogen generated for the conventional homogeneous system where all the components [Ru(bpy)(3)(2+), MV(2+), Pt, and EDTA] are in solution, with the advantage that it can be used as film or recovered by filtration from the aqueous medium.

Layered double hydroxides as highly efficient photocatalysts for visible light oxygen generation from water.

Oxygen generation through photocatalytic water splitting under visible light irradiation is a challenging process. In this work we have synthesized a series of Zn/Ti, Zn/Ce, and Zn/Cr layered double hydroxides (LDH) at different Zn/metal atomic ratio (from 4:2 to 4:0.25) and tested them for the visible light photocatalytic oxygen generation. The most active material was found to be (Zn/Cr)LDH with an atomic ratio of 4:2 that exhibits two absorption bands in the visible region at lambda(max) of 410 and 570 nm. It was found that the efficiency of these chromium layered double oxides for oxygen generation increases asymptotically with the Cr content. Using iron oxalate as chemical actinometer we have determined that the apparent quantum yields for oxygen generation (Phi apparent = 4 x mol oxygen/mol incident photons) are of 60.9% and 12.2% at 410 and 570 nm, respectively. These quantum yields are among the highest values ever determined with visible light for solid materials in the absence of light harvesting dye. The overall efficiency of (Zn/Cr)LDH for visible light oxygen generation was found to be 1.6 times higher than that of WO(3) under the same conditions.