The review covers the knowledge on photoremovable protecting
groups and includes all relevant chromophores studied in the
time period of 2000–2012; the most relevant earlier works are
also discussed.

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Photoremovable Protecting Groups in Chemistry and Biology: Reaction Mechanisms and Efficacy

Curcumin, bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione, is a natural yellow-orange dye derived from the rhizome of Curcuma longa, an East Indian plant. In order to understand the photobiology of curcumin better we have studied the spectral and photochemical properties of both curcumin and 4-(4-hydroxy-3-methoxy-phenyl)-3-buten-2-one (hC, half curcumin) in different solvents. In toluene, the absorption spectrum of curcumin contains some structure, which disappears in more polar solvents, e.g. ethanol, acetonitrile. Curcumin fluorescence is a broad band in acetonitrile (lambda max = 524 nm), ethanol (lambda max = 549 nm) or micellar solution (lambda max = 557 nm) but has some structure in toluene (lambda max = 460, 488 nm). The fluorescence quantum yield of curcumin is low in sodium dodecyl sulfate (SDS) solution (phi = 0.011) but higher in acetonitrile (phi = 0.104). Curcumin produced singlet oxygen upon irradiation (lambda > 400 nm) in toluene or acetonitrile (phi = 0.11 for 50 microM curcumin); in acetonitrile curcumin also quenched 1O2 (kq = 7 x 10(6) M-1 s-1). Singlet oxygen production was about 10 times lower in alcohols and was hardly detectable when curcumin was solubilized in a D2O micellar solution of Triton X-100. In SDS micelles containing curcumin no singlet oxygen phosphorescence could be observed. Curcumin photogenerates superoxide in toluene and ethanol, which was detected using the electron paramagnetic resonance/spin-trapping technique with 5,5-dimethyl-pyrroline-N-oxide as a trapping agent. Unidentified carbon-centered radicals were also detected.(ABSTRACT TRUNCATED AT 250 WORDS)

Spectral and photochemical properties of curcumin

We report a facile template-free method for the large-area growth of freestanding hollow Co3O4 nanowire arrays on a variety of substrates including transparent conducting glass, Si wafer, and copper foil, et al. These nanowires have the interesting combined properties of mesoporosity and quasi-single-crystallinity. With their high surface area and crystallinity, and their direct growth on conductive substrate, these Co3O4 nanowire arrays will have promising applications in lithium-ion batteries, chemical sensing, and field-emission and electrochromic devices. Using the prepared nanowire arrays as electrode, an electrochemical sensor for hydrogen peroxide sensing has been demonstrated.

Freestanding mesoporous quasi-single-crystalline CO3O4 nanowire arrays.

Cyclobutarenes and Related Compounds

The long story of aromatic compounds has extended over almost two centuries, since the discovery by Faraday of "bicarburet of hydrogen", or C 6 H 6 , now called benzene. Since then, the chemistry of aromatic compounds has been developed extensively; this is reflected in the synthesis of novel classes of aromatic derivatives including charged species, nonclassical (Mobius, three-dimensional, homo-, metalla-) aromatics, and fullerenes. The theory of aromaticity has also undergone a spectacular evolution since the first definition of aromaticity by Huckel; the classification of aromaticity now requires the consideration of versatile criteria: energetic, structural, magnetic, among others. In this Review, we discuss the current state of affairs in the chemistry of aromatic compounds of the heavier Group 14 elements, the latest experimental achievements, as well as future prospects in the field.

Aromaticity of group 14 organometallics : Experimental aspects

The Aromaticity of the Stannole Dianion

The reversible redox behavior between the stannole dianion and the bistannole-1,2-dianion is demonstrated. Reaction of the stannole dianion with oxygen (1 eq) gives the 1,2-bistannole-1,2-dianion which is a tin-analogue of the cyclopentadienyl anion in 94% yield. Reaction of the stannole dianion with ferrocenium tetrafluoroborate (1 eq) also gives the 1,2-dianion. The 1,2-bistannole-1,2-dianion has a nonaromatic nature as evidenced by X-ray and NMR analysis. Reduction of the 1,2-dianion with lithium gives the starting dianion.

Reversible redox behavior between stannole dianion and bistannole-1,2-dianion.

Reaction of tert-butylchloride with the stannole dianion first and simply prepared by the reduction of 1,1,2,3,4,5-hexaphenylstannole with lithium in ether gave 1-tert-butylstannole anion which was characterized by 1H, 13C, 119Sn, and 7Li NMR spectra and whose reactivities were investigated.

Synthesis of Stannole Anion by Alkylation of Stannole Dianion

Synthesis of Stannaindenyl Anions and a Dianion

The reaction of 9,9-bis(p-methoxyphenyl)-9-stannafluorene with lithium or potassium gave the corresponding dimetallostannafluorene, as evidenced by NMR spectral analysis and a trapping experiment.

Michikazu Yoshioka

Papers

The Aromaticity of the Stannole Dianion

Reversible redox behavior between stannole dianion and bistannole-1,2-dianion.

Synthesis of Stannole Anion by Alkylation of Stannole Dianion

Synthesis of Stannaindenyl Anions and a Dianion

Synthesis and Characterization of Dimetallostannafluorenes