ACS Physical Chemistry Au最新文献

The combination of materials to improve properties of interest has become one of the strategies widely used for numerous applications, including new catalysts, over the last few decades. In this study, silver molybdate (β-Ag₂MoO₄) microcrystals were efficiently obtained by the hydrothermal method, obtaining composites with different amounts of graphene oxide (GO) (1, 2.5, 5, 7.5, and 10%, w/w) using the conventional hydrothermal method. The incorporation of GO on silver molybdate was confirmed by X-ray diffraction (XRD) and Raman spectroscopy, where the vibrational modes and crystallographic planes characteristic of the materials of interest were highlighted. The images collected by scanning electron microscopy (SEM) revealed the occurrence of plate-shaped structures (shells) anchored to the surface of the silver molybdate microcrystals (core). The optical properties showed that the materials presented E_gap between 3.34 and 3.39 eV, where the sample with 7.5% of GO (GO@β-AgMo_7.5) was the one that presented energy for the conduction band, largely favorable to the formation of superoxide radicals through the photoexcitation process of electrons. The catalytic tests demonstrated that, among the samples obtained in this study, the sample with 7.5% of GO (GO@β-AgMo_7.5) exhibits superior photocatalytic performance against the dye rhodamine B (RhB) in an aqueous medium. Thus, the kinetics constant for photolysis (absence of catalysts) and for the sample β-AgMo and the sample with 7.5% of GO (GO@β-AgMo_7.5) are 0.38 × 10^–3, 12 × 10^–3, and 23.72 × 10^–3 min^–1, respectively. Therefore, it is 62.5 times more efficient in the degradation of the RhB dye, which confirms the promising photocatalytic properties of the obtained composite.

Of the attributes that determine the performance of electroactive film-based devices, the least well quantified and understood is the spatial distribution of the component species. This is critical since it dictates the transport rates of all the mobile species (electrons, counterions, solvent, analyte, and reactant) and the film mechanical properties (as exploited in actuator devices). One of the few techniques able to provide individual species population profiles in situ is specular neutron reflectivity (NR). Historically, this information is obtained at the cost of poor time resolution (hours). Here we show how NR measurements with event mode data acquisition enable both spatial and temporal resolution; the latter can be selected postexperiment and varied during the transient. We profile individual species at “buried” interfaces under dynamic electrochemical conditions during polypyrrole electrodeposition and Cu deposition/dissolution. In the case of polypyrrole, the film is homogeneous throughout growth; there is no evidence of dendrite formation followed by solvent (water) displacement. Correlation of NR-derived film thickness and coulometric assay allows calculation of the solvent volume fraction, ϕ_S = 0.48. In the case of Cu in a deep eutectic solvent, the complexing nature of the medium results in time-dependent metal speciation: mechanistically, dissolution does not simply follow the deposition pathway in reverse.

Many important processes in cells depend on the transfer of protons through water wires embedded in transmembrane proteins. Herein, we have performed more than 55 μs all-atom simulations of the light-harvesting complex of a diatom, i.e., the fucoxanthin and chlorophyll a/c binding protein (FCP) from the marine diatom Phaeodactylum tricornutum. Diatoms are unique models to study natural photosynthesis as they exert an efficient light-harvesting machinery with a robust pH-dependent photoprotective mechanism. The present study reports on the dynamics of an FCP monomer, a dimer, and a tetramer at varying pH values. Surprisingly, we have identified at low pH a water channel across FCP that selectively hydrates and protonates the acrylate of a Chl-c2 pigment located in the middle of the membrane. These results are further supported by QM/MM calculations and steered MD simulations on the proton dynamics. It is shown that proton hopping events between the lumenal and stromal sides of the membrane through the observed water channel are highly disfavored. This hindrance is due to the presence of residues Arg31 and Lys82 close to the acrylate, along with an hydronium desolvation penalty that shows close similarities to the water conductance in aquaporins. Furthermore, we provide strong evidence that this identified water channel is governing the transition between light-harvesting and photoprotective states of the major FCP complex in the diatom P. tricornutum.

Time-resolved extreme ultraviolet spectroscopy was used to investigate photodissociation within the iodobenzene C-band. The carbon–iodine bond of iodobenzene was photolyzed at 200 nm, and the ensuing dynamics were probed at 10.3 nm (120 eV) over a 4 ps range. Two product channels were observed and subsequently isolated by using a global fitting method. Their onset times and energetics were assigned to distinct electron transfer dynamics initiated following site-selective ionization of the iodine photoproducts, enabling the electronic states of the phenyl fragments to be identified using a classical over-the-barrier model for electron transfer. In combination with previous theoretical work, this allowed the corresponding neutral photochemistry to be assigned to (1) dissociation via the 7B₂, 8A₂, and 8B₁ states to give ground-state phenyl, Ph(X), and spin–orbit excited iodine and (2) dissociation through the 7A₁ and 8B₂ states to give excited-state phenyl, Ph(A), and ground-state iodine. The branching ratio was determined to be 87 ± 4% Ph(X) and 13 ± 4% Ph(A). Similarly, the corresponding amount of energy deposited into the internal phenyl modes in these channels was determined to be 44 ± 10 and 65 ± 21%, respectively, and upper bounds to the channel rise times were found to be 114 ± 6 and 310 ± 60 fs.

Purple bacteria possess two ring-shaped protein complexes, light-harvesting 1 (LH1) and 2 (LH2), both of which function as antennas for solar energy utilization for photosynthesis but exhibit distinct absorption properties. The two antennas have differing amounts of bacteriochlorophyll (BChl) a; however, their significance in spectral tuning remains elusive. Here, we report a high-precision evaluation of the physicochemical factors contributing to the variation in absorption maxima between LH1 and LH2, namely, BChl a structural distortion, protein electrostatic interaction, excitonic coupling, and charge transfer (CT) effects, as derived from detailed spectral calculations using an extended version of the exciton model, in the model purple bacterium Rhodospirillum rubrum. Spectral analysis confirmed that the electronic structure of the excited state in LH1 extended to the BChl a 16-mer. Further analysis revealed that the LH1-specific redshift (∼61% in energy) is predominantly accounted for by the CT effect resulting from the closer inter-BChl distance in LH1 than in LH2. Our analysis explains how LH1 and LH2, both with chemically identical BChl a chromophores, use distinct physicochemical effects to achieve a progressive redshift from LH2 to LH1, ensuring efficient energy transfer to the reaction center special pair.

Herein, we report on the ultrafast photodissociation of nickel tetracarbonyl─a prototypical metal–ligand model system─at 197 nm. Using mid-infrared transient absorption spectroscopy to probe the bound C≡O stretching modes, we find evidence for the picosecond time scale production of highly vibronically excited nickel dicarbonyl and nickel monocarbonyl, in marked contrast with a prior investigation at 193 nm. Further spectral evolution with a 50 ps time constant suggests an additional dissociation step; the absence of any corresponding growth in signal strongly indicates the production of bare Ni, a heretofore unreported product from single-photon excitation of nickel tetracarbonyl. Thus, by probing the deep UV-induced photodynamics of a prototypical metal carbonyl, this Letter adds time-resolved spectroscopic signatures of these dynamics to the sparse literature at high excitation energies.