Low-temperature FTIR spectroscopy provides evidence for protein-bound water molecules in eubacterial light-driven ion pumps.

Light-driven H+, Na+ and Cl- pumps have been found in eubacteria, which convert light energy into a transmembrane electrochemical potential. A recent mutation study revealed asymmetric functional conversion between the two pumps, where successful functional conversions are achieved exclusively when mutagenesis reverses the evolutionary amino acid sequence changes. Although this fact suggests that the essential structural mechanism of an ancestral function is retained even after gaining a new function, questions regarding the essential structural mechanism remain unanswered. Light-induced difference FTIR spectroscopy was used to monitor the presence of strongly hydrogen-bonded water molecules for all eubacterial H+, Na+ and Cl- pumps, including a functionally converted mutant. This fact suggests that the strongly hydrogen-bonded water molecules are maintained for these new functions during evolution, which could be the reason for successful functional conversion from Na+ to H+, and from Cl- to H+ pumps. This also explains the successful conversion of the Cl- to the H+ pump only for eubacteria, but not for archaea. It is concluded that water-containing hydrogen-bonding networks constitute one of the essential structural mechanisms in eubacterial light-driven ion pumps.

Reaction Mechanism of the Multiple-Electron Oxygen Reduction Reaction on the Surfaces of Gold and Platinum Nanoparticles Loaded on Titanium(IV) Oxide.

Au and Pt nanoparticles with varying mean particle size and comparable loading amounts were loaded on the surface of TiO2 (Au/TiO2 and Pt/TiO2, respectively). The photocatalytic activities of Au/TiO2 and Pt/TiO2 for the oxygen reduction reaction (ORR) in an aerated aqueous solution containing 4% ethanol were compared under ultraviolet-light irradiation at 298 K. The initial rate of H2O2 generation (or H2O2 formation rate) in the Au/TiO2 system is much greater than that in the Pt/TiO2 system regardless of the metal particle size. To clarify the origin for the striking difference in the activity, the photocatalytic ORR on the model slabs (M28/(TiO2)32 and M50/(TiO2)96, M = Au and Pt) was simulated by density functional theory (DFT) calculations taking the solvation effect into consideration. The DFT calculations clearly show that regardless of the cluster size, H2O2 formation more easily occurs structurally and energetically for the Au/TiO2 system, whereas H2O is generated with the O-O bond cleavage in the Pt/TiO2 system.

Gold-Nanoparticle-Loaded Carbonate-Modified Titanium(IV) Oxide Surface: Visible-Light-Driven Formation of Hydrogen Peroxide from Oxygen.

Gold nanoparticle-loaded rutile TiO2 with a bimodal size distribution around 10.6 nm and 2.3 nm (BM-Au/TiO2 ) was prepared by the deposition precipitation and chemical reduction (DP-CR) technique. Visible-light irradiation (λ>430 nm) of the BM-Au/TiO2 plasmonic photocatalyst yields 35 µm H2 O2 in aerated pure water at irradiation time (tp )=1 h, and the H2 O2 concentration increases to 640±60 µm by the addition of 4 % HCOOH as a sacrificing electron donor. Further, a carbonate-modified surface BM-Au/TiO2 (BM-Au/TiO2 -CO3 (2-) ) generates a millimolar level of H2 O2 at tp =1 h with a quantum efficiency (Φ) of 5.4 % at λ=530 nm under the same conditions. The recycle experiments confirmed the stable performance of BM-Au/TiO2 .

Size-Dependence of the Activity of Gold Nanoparticle-Loaded Titanium(IV) Oxide Plasmonic Photocatalyst for Water Oxidation.

Mesoporous TiO2 nanocrystalline film was formed on fluorine-doped tin oxide electrode (TiO2 /FTO) and gold nanoparticles (NPs) of different sizes were loaded onto the surface with the loading amount kept constant (Au/TiO2 /FTO). Visible-light irradiation (λ>430 nm) of the Au/TiO2 /FTO photoanode in a photoelectrochemical cell with the structure of photoanode|0.1 m NaClO4 aqueous solution|Ag/AgCl (reference electrode)|glassy carbon (cathode) leads to the oxidation of water to oxygen (O2 ). We show that the visible-light activity of the Au/TiO2 /FTO anode increases with a decrease in Au particle size (d) at 2.9≤d≤11.9 nm due to the enhancement of the charge separation and increasing photoelectrocatalytic activity.

Room-temperature selective oxidation of 2-naphthol to BINOL using a Au/SrTiO3-H2O2 catalytic system.

Gold nanoparticle-loaded SrTiO3 (Au/SrTiO3) effectively catalyzes the selective C-C bond formation between 2-naphthol molecules to yield BINOL in the presence of H2O2, and the catalytic activity increases with decreasing Au particle size (d) in the range 2.6 ≤ d ≤ 8.9 nm.

Mechanism of the Multiple-Electron Oxygen Reduction Reaction in the Presence of the Binuclear Cu(acac)2 Complex.

The potential of the electron for the serial oxygen reduction reaction is calculated by DFT in an aqueous solution in the presence and absence of Cu(acac)2 complex. The study provides interesting information about the rational design of complex-semiconductor hybrid photocatalysts and cathodes for polymer electrolyte membrane fuel cells.

A strong support-effect on the catalytic activity of gold nanoparticles for hydrogen peroxide decomposition.

Catalytic activity of gold nanoparticle (NP)-loaded metal oxide semiconductors (Au/MOs) for H(2)O(2) decomposition and chemoselective oxidation of cinnamyl alcohol to cinnamaldehyde strongly depends on both the kind of the MO-supports and the Au particle size, and Au/SrTiO(3) exhibits an extraordinary high level of activity for the H(2)O(2) decomposition exceeding that of Pt/TiO(2).

In situ liquid phase synthesis of hydrogen peroxide from molecular oxygen using gold nanoparticle-loaded titanium(IV) dioxide photocatalyst.

Gold nanoparticle loading has led to a drastic enhancement of TiO(2)-photocatalized generation of H(2)O(2) from O(2) with a unique inversed volcano-type relation between the activity and Au particle size.

Light wavelength-switchable photocatalytic reaction by gold nanoparticle-loaded titanium(IV) dioxide.

Surface plasmon resonance excitation of gold nanoparticle-loaded on titanium(IV) dioxide (Au/TiO(2)) by visible light (lambda > 420 nm) has led to selective oxidation of thiol to disulfide, whereas the reaction is reversed by UV light irradiation (lambda > 300 nm).