No abstract

Solvent molecules influence the reactions of molecular hydrogen and oxygen on palladium nanoparticles. Organic solvents activate to form reactive surface intermediates that mediate oxygen reduction through pathways distinct from reactions in pure water. Kinetic measurements and ab initio quantum chemical calculations indicate that methanol and water cocatalyze oxygen reduction by facilitating proton-electron transfer reactions. Methanol generates hydroxymethyl intermediates on palladium surfaces that efficiently transfer protons and electrons to oxygen to form hydrogen peroxide and formaldehyde. Formaldehyde subsequently oxidizes hydrogen to regenerate hydroxymethyl. Water, on the other hand, heterolytically oxidizes hydrogen to produce hydronium ions and electrons that reduce oxygen. These findings suggest that reactions of solvent molecules at solid-liquid interfaces can generate redox mediators in situ and provide opportunities to substantially increase rates and selectivities for catalytic reactions.

Prevacuolar compartments (PVCs) are membrane-bound organelles that mediate protein traffic between Golgi and vacuoles in the plant secretory pathway. Here we identify and define organelles as the lytic prevacuolar compartments in pea and tobacco cells using confocal immunofluorescence. We use five different antibodies specific for a vacuolar sorting receptor (VSR) BP-80 and its homologs to detect the location of VSR proteins. In addition, we use well-established Golgi-markers to identify Golgi organelles. We further compare VSR-labeled organelles to Golgi organelles so that the relative proportion of VSR proteins in Golgi vs. PVCs can be quantitated. More than 90% of the BP-80-marked organelles are separate from Golgi organelles; thus, BP-80 and its homologs are predominantly concentrated on the lytic PVCs. Additionally, organelles marked by anti-AtPep12p (AtSYP21p) and anti-AtELP antibodies are also largely separate from Golgi apparatus, whereas VSR and AtPep12p (AtSYP21p) were largely colocalized. We have thus demonstrated in plant cells that VSR proteins are predominantly present in the lytic PVCs and have provided additional markers for defining plant PVCs using confocal immunofluorescence. Additionally, our approach will provide a rapid comparison between markers to quantitate protein distribution among various organelles.

Oxide-supported Pt-group single atoms and clusters in the subnanometer size regime maximize the metal utilization and have shown extraordinary catalytic properties for many reactions including selective hydrogenation. Establishing relations between the metal nuclearity and electronic and catalytic properties is crucial for catalyst design. Here, we varied the nuclearity of Pt supported on TiO2 from single atoms to subnanometer clusters to larger nanoparticles to develop such relations for acetylene hydrogenation. We show that, in contrast to the low selectivity on large Pt nanoparticles, in the subnanometer size regime, Pt exhibits remarkably high selectivity to ethylene. Through a combination of X-ray photoelectron spectroscopy and calorimetry, we demonstrate that the origin of high selectivity is the decreased electron density on Pt and destabilization of C2H4 as the Pt nuclearity decreases. However, as the Pt nuclearity decreased, the activity for H2 activation and acetylene hydrogenation decreased, indicating a trade-off between activity and selectivity. The results show that, while different properties emerge in the subnanometer regime, Pt supported on TiO2 appears to be bound by similar scaling and Brønsted–Evans–Polanyi relationships as on metal surfaces.

As ingle-atom Pt 1 /CeO 2 catalyst formed by atom trapping (AT, 800 8 8Ci na ir) shows excellent thermal stability but is inactive for CO oxidation at lowt emperatures owing to over-stabilization of Pt 2+ in ah ighly symmetric square-planar Pt 1 O 4 coordination environment. Reductive activation to form Pt nanoparticles (NPs) results in enhanced activity;h owever, the NPs are easily oxidized, leading to drastic activity loss. Herein we showthat tailoring the local environment of isolated Pt 2+ by thermal-shock( TS) synthesis leads to ah ighly active and thermally stable Pt 1 /CeO 2 catalyst. Ultrafast shockwaves (> 1200 8 8C) in an inert atmosphere induced surface reconstruction of CeO 2 to generate Pt single atoms in an asymmetric Pt 1 O 4 configuration. Owing to this unique coordination, Pt 1 d+ in ap artially reduced state dynamically evolves during CO oxidation, resulting in exceptional low-temperature performance.C Oo xidation reactivity on the Pt 1 /CeO 2 _TS catalyst was retained under oxidizing conditions.

We examined the cell cycle dynamics of the retinoblastoma (RB) protein complex in the unicellular alga Chlamydomonas reinhardtii that has single homologs for each subunit-RB, E2F, and DP. We found that Chlamydomonas RB (encoded by MAT3) is a cell cycle-regulated phosphoprotein, that E2F1-DP1 can bind to a consensus E2F site, and that all three proteins interact in vivo to form a complex that can be quantitatively immunopurified. Yeast two-hybrid assays revealed the formation of a ternary complex between MAT3, DP1, and E2F1 that requires a C-terminal motif in E2F1 analogous to the RB binding domain of plant and animal E2Fs. We examined the abundance of MAT3/RB and E2F1-DP1 in highly synchronous cultures and found that they are synthesized and remain stably associated throughout the cell cycle with no detectable fraction of free E2F1-DP1. Consistent with their stable association, MAT3/RB and DP1 are constitutively nuclear, and MAT3/ RB does not require DP1-E2F1 for nuclear localization. In the nucleus, MAT3/RB remains bound to chromatin throughout the cell cycle, and its chromatin binding is mediated through E2F1-DP1. Together, our data show that E2F-DP complexes can regulate the cell cycle without dissociation of their RB-related subunit and that other changes may be sufficient to convert RB-E2F-DP from a cell cycle repressor to an activator.

The intrinsic correlation of gold nanoclusters with graphene quantum dots in terms of photo-induced charge transport for photoelectrochemical water splitting was revealed.

Plants accumulate and store proteins in protein storage vacuoles (PSVs) during seed development and maturation. Upon seed germination, these storage proteins are mobilized to provide nutrients for seedling growth. However, little is known about the molecular mechanisms of protein degradation during seed germination. Here we test the hypothesis that vacuolar sorting receptor (VSR) proteins play a role in mediating protein degradation in germinating seeds. We demonstrate that both VSR proteins and hydrolytic enzymes are synthesized de novo during mung bean (Vigna radiata) seed germination. Immunogold electron microscopy with VSR antibodies demonstrate that VSRs mainly locate to the peripheral membrane of multivesicular bodies (MVBs), presumably as recycling receptors in day 1 germinating seeds, but become internalized to the MVB lumen, presumably for degradation at day 3 germination. Chemical cross-linking and immunoprecipitation with VSR antibodies have identified the cysteine protease aleurain as a specific VSR-interacting protein in germinating seeds. Further confocal immunofluorescence and immunogold electron microscopy studies demonstrate that VSR and aleurain colocalize to MVBs as well as PSVs in germinating seeds. Thus, MVBs in germinating seeds exercise dual functions: as a storage compartment for proteases that are physically separated from PSVs in the mature seed and as an intermediate compartment for VSR-mediated delivery of proteases from the Golgi apparatus to the PSV for protein degradation during seed germination.