Reversed photoresponse: Indium tin oxide (ITO)/Au nanoparticle (NP)/TiO(2) electrodes (see picture) exhibit cathodic photocurrents and positive photopotentials under visible light, whereas ITO/TiO(2)/Au NP electrodes show an inverted response. This behavior indicates that electron transfer occurs from the plasmon-excited Au NPs to the TiO(2) film. An enhanced O(2) photoreduction activity is found for ITO/Au NP/TiO(2)/Pt electrodes.

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Hyperbranched polysiloxanes were synthesized by polyhydrosilylation of silsesquioxane derivatives and vinyl derivatives in the presence of Karstedt's catalyst. The hyperbranched polymers (HBPs) with M n ¼5.2Â10 3 -9.8Â10 4 were soluble in common solvents and exhibited good thermal stability. HBPs based on double-decker-shaped silsesquioxane showed a large thermal-optical coefficient compared with the corresponding linear polymer. The refractive index values of the polymers obtained tended to decrease with the increasing structure size of the co-monomers.

Chemical modifications of histones, such as lysine acetylation and ubiquitination, play pivotal roles in epigenetic regulation of gene expression. Methods to alter the epigenome thus hold promise as tools for elucidating epigenetic mechanisms and as therapeutics. However, an entirely chemical method to introduce histone modifications in living cells without genetic manipulation is unprecedented. Here, we developed a chemical catalyst, PEG-LANA-DSSMe 11, that binds with nucleosome’s acidic patch and promotes regioselective, synthetic histone acetylation at H2BK120 in living cells. The size of polyethylene glycol in the catalyst was a critical determinant for its in-cell metabolic stability, binding affinity to histones, and high activity. The synthetic acetylation promoted by 11 without genetic manipulation competed with and suppressed physiological H2B ubiquitination, a mark regulating chromatin functions, such as transcription and DNA damage response. Thus, the chemical catalyst will be a useful tool to manipulate epigenome for unraveling epigenetic mechanisms in living cells.

Theoretical calculations with DFT, MP2 to MP4(SDQ), and CCSD(T) methods clearly display that the Cp 2 Zr-mediated coupling reaction of two acetylene molecules easily takes place through a nonsymmetrical transition state with nearly no barrier and significantly large exothermicity but the M(PH 3 )-mediated reaction (M ) Ni, Pt) takes place through a symmetrical transition state with either a considerably large activation barrier for M ) Pt or a moderately large activation barrier for M ) Ni. The charge-transfer (CT) interaction between the d orbital of the transition-metal center and the π*-π* bonding couple of two acetylene molecules plays an important role for the C-C bond formation in the M(PH 3 )mediated coupling reaction, which needs a symmetrical transition state structure. On the other hand, a CT interaction between the d π -π* back-donation orbital of Cp 2 Zr(C 2 H 2 ) and the π* orbital of the second acetylene molecule is strongly formed in the Cp 2 Zr-mediated coupling reaction, which leads to a nonsymmetrical transition state structure. These differences are reasonably interpreted by the d π -π* back-donation of Cp 2 Zr(C 2 H 2 ) being much stronger than that of M(PH 3 )(C 2 H 2 ). This is because the early-transition-metal element has d orbitals at higher energy than does the late-transition-metal element. The Ni(PH 3 )mediated coupling reaction takes place with a smaller activation barrier than does the Pt-(PH 3 )-mediated reaction. This result is interpreted by noting that the 3d transition-metal element has d orbitals at higher energy than does the 5d transition-metal element. Also, (MeO) 2 Zr-mediated coupling reaction proceeds with nearly no barrier, in spite of the fact that the d orbital is at lower energy in (MeO) 2 Zr(C 2 H 2 ) than that in Cp 2 Zr(C 2 H 2 ). This is because the MeO group is flexible and gives rise to little steric repulsion between ligands and substrates.

Rh(I) and Pt(0) complexes of Si 2 H 2 species were theoretically investigated. RhCl(PMe 3 ) 2 -(Si 2 H 2 ) (2-Rha) containing vinylidene-type Si 2 H 2 species is the most stable among various Rh(I) complexes of Si 2 H 2 , while the vinylidene-type Si 2 H 2 species (2) is much less stable than the most stable 2H-bridged Si 2 H 2 species (3) by 11.5 kcal/mol, where the energy calculated by the DFT method is given hereafter. RhCl(PMe 3 ) 2 (Si 2 H 2 ) (1-Rh) containing acetylene-type Si 2 H 2 species easily isomerizes to the Rh complex (4-Rh) of the 1H-bridged Si 2 H 2 species with a small activation barrier (2.6 kcal/mol). Complex 4-Rh further isomerizes to 2-Rha with a very small activation barrier (1.9 kcal/mol), while RhCl(PMe 3 ) 2 (Si 2 H 2 ) (3-Rh) containing the 2H-bridged Si 2 H 2 species isomerizes to 2-Rha with a considerable activation barrier (11.8 kcal/mol). Pt(PR 3 ) 2 (Si 2 H 2 ) (3-Pt or 3-Pt′ for R ) H or Me, respectively) containing the 2H-bridged Si 2 H 2 species has almost the same energy as the Pt complex (2-Pta or 2-Pta′) of the vinylidene-type Si 2 H 2 species; the energy difference is only 0.2-0.3 kcal/mol. Pt(PR 3 ) 2 (Si 2 H 2 ) (1-Pt and 1-Pt′) containing the acetylene-type Si 2 H 2 species is moderately less stable than 3-Pt and 3-Pt′ by 6.6 (4.9) kcal/mol, while the acetylene-type Si 2 H 2 species (1) is much less stable than 3 by 20.0 kcal/mol, where the energy values for R ) H and Me are given without parentheses and in parentheses, respectively. Complex 1-Pt isomerizes to 4-Pt with a moderate activation barrier (5.4 kcal/mol), which further isomerizes either to 2-Pt with a very small activation barrier (1.9 kcal/mol) or to 3-Pt with a moderately small activation barrier (4.1 kcal/mol). From these results, several theoretical predictions are proposed, as follows: (1) The vinylidene-type Si 2 H 2 species is stabilized by Rh(I) and Pt(0) complexes. (2) The acetylene-type Si 2 H 2 species is stabilized by the Pt(0) complex. And, (3) the vinylidene-type Si 2 H 2 species can be isolated as the Rh(I) complex.

Cell biology is tightly regulated by post-translational modifications of proteins. Methods to modulate post-translational modifications in living cells without relying on enzymes or genetic manipulation are, however, largely underexplored. We previously reported that a chemical catalyst (DSH) conjugated with a nucleosome-binding ligand can activate an acyl-CoA and promote site-selective lysine acylation of histones in test tubes. In-cell acylation by this catalyst system is challenging, however, mainly due to the low cell permeability of acyl-CoA and the propensity of DSH to form inactive disulfide. Here, we report a new catalyst system effective for in-cell acylation, comprising a cell-permeable acyl donor and pro-drugged DSH. Using E. coli dihydrofolate reductase and trimethoprim as a model protein and ligand pair, the catalyst system enabled site-selective acylation of the target protein in living cells. The findings will lead to the development of useful chemical biology tools and new therapeutic strategies capable of synthetically modulating post-translational modifications.

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