How green is green chemistry? Chlorophylls as a bioresource from biorefineries and their commercial potential in medicine and photovoltaics

Chlorophylls are the natural green pigments par excellence and offer potential as therapeutics and in energy generation. This perspective outlines the state-of-the-art, their possible applications and indicates future directions in the context of green chemistry and their production from biorefineries.

Organometallic chemistry on periodic mesoporous organosilicas: generation of surface-confined zinc and yttrium centres

Periodic mesoporous ethylenesilicas with hexagonal P6mm and cubic Fm3m/Pm3n symmetry were prepared by using divalent surfactant C(16-3-1) and binary surfactant mixtures C(18-3-1) and C18TABr as structure-directing agents, respectively, under basic conditions. A tetramethyldisilazane-based surface silylation was carried out under mild conditions affording hybrid materials SiHMe2@PMO[MCM-41], SiHMe2@PMO[KIT-5] and SiHMe2@PMO[SBA-1], corresponding to silanol group populations of ca. 1.46, 0.67 and 1.63 mmol g(-1), respectively. New molecular zinc precursor compounds Zn[N(SiHMe2)2]2 and EtZn(OSiHtBu2) were synthesized via salt metathesis and alkane elimination procedures from ZnCl2 and LiN[SiH(CH3)2]2, HOSiHtBu2 and ZnEt2, respectively. Organozinc and organoyttrium complexes were reacted with the surface silanol groups according to a heterogeneously performed silylamide route, aswell as an alkane elimination reaction, yielding Zn[N(SiHMe2)2]@PMO[MCM-41], Zn[N(SiHMe2)2]@PMO[KIT-5], Zn[N(SiHMe2)2]@PMO[SBA-1], Zn[N(SiMe3)2]@PMO[MCM-41], Zn[N(SiMe3)2]@PMO[KIT-5], Zn[N(SiMe3)2]@PMO[SBA-1], Y[N(SiHMe2)2]x(THF)y@PMO[MCM-41], Y[N(SiHMe2)2]x(THF)y@PMO[KIT-5], Y[N(SiHMe2)2]x(THF)y@PMO[SBA-1] and Zn(OSiHtBu2)@PMO[MCM-41]. The metal loading mainly depended on the surface silanol group population, size and shape of metal-coordinated ligand, and reaction time as shown for Zn contents in the range of 4.2 to 10.6 wt%. In addition, a preferred N(SiHMe2)2/OC6H2tBu2-2,6-Me-4 ligand exchangeability was found for the large yttrium surface centres. The parent and functionalized materials were characterized by powder X-ray diffraction, elemental analysis, N2 physisorption, FTIR, 13C CP and 1H MAS NMR spectroscopy.

Energy transfer between chlorophyll derivatives in silica mesostructured films and photocurrent generation

Layered silica/surfactant mesostructured thin films containing chlorophyllous pigments [C13(2)-demethoxycarbonyl-pheophytin b (pyroPheo b) or zinc C13(2)-demethoxycarbonyl-chlorophyll b (Zn-pyroChl b)] have been prepared on an indium tin oxide (ITO) electrode grafted with a chlorophyll derivative possessing a triethoxysilyl group (copper C13(2)-demethoxycarbonyl-chlorophyllide a 3-triethoxysilyl propylamide, Cu-APTES-Chl a) to achieve effective light harvesting and successive photocurrent generation by the mesostructured films. The incorporation of pyroPheo b and Zn-pyroChl b in the mesostructured film resulted in 1.2- and 1.6-fold increases of the photocurrent density, respectively, as compared to the case of an antenna pigment-free film also grafted to a surface-modified ITO electrode. The difference action spectra, between the electrodes with and without the antenna pigments, coincided well with the absorption spectra of the immobilized pigments. Because direct electron injection from the antenna pigments in the mesostructured films to the ITO electrode was scarcely observed, the energy transfer from the antenna pigments to Cu-APTES-Chl a plays an important role for the increase in photocurrent density. The usefulness of the mesostructured films as model systems is discussed in relation to the photosynthetic primary processes of higher plants.