Understanding CO oxidation on the Pt(111) surface based on a reaction route network

Analysis of a reaction on a solid surface is an important task for understanding the catalytic reaction mechanism. In this study, we studied CO oxidation on the Pt(111) surface by using the artificial force induced reaction (AFIR) method. A systematic reaction path search was done, and the reaction route network was created. This network included not only bond rearrangement paths but also migration paths of adsorbed species. Then, the obtained network was analyzed using a kinetics method called rate constant matrix contraction (RCMC). It is found that the bottleneck of the overall reaction is the CO2 generation step from an adsorbed CO molecule and an O atom. This result is consistent with the Langmuir-Hinshelwood (LH) mechanism with O-2 dissociation discussed in previous studies. The present procedure, i.e., construction of the reaction route network by the AFIR method followed by application of the RCMC kinetics method to the resultant reaction route network, was fully systematic and uncovered two aspects: the impact of the existence of multiple paths in each bond rearrangement step and an entropic contribution arising from short-range migration of adsorbed species

Theoretical study on mechanism of the photochemical ligand substitution of fac-[Re-I(bpy)(CO)(3)(PR3)](+) complex

The mechanism of the CO ligand dissociation of fac-[Re-I(bpy)(CO)(3)P(OMe)(3)](+) has theoretically been investigated, as the dominant process of the photochemical ligand substitution (PLS) reactions of fac-[Re-I(bpy)(CO)(3)PR3](+), by using the (TD-)DFT method. The PLS reactivity can be determined by the topology of the T-1 potential energy surface because the photoexcited complex is able to decay into the T-1 state by internal conversions (through conical intersections) and intersystem crossings (via crossing seams) with sufficiently low energy barriers. The T-1 state has a character of the metal-to-ligand charge-transfer ((MLCT)-M-3) around the Franck-Condon region, and it changes to the metal-centered ((MC)-M-3) state as the Re-CO bond is elongated and bent. The equatorial CO ligand has a much higher energy barrier to leave than that of the axial CO, so that the axial CO ligand selectively dissociates in the PLS reaction. The single-component artificial force induced reaction (SC-AFIR) search reveals the CO dissociation pathway in photostable fac-[ReI(bpy)(CO)(3)Cl]; however, the dissociation barrier on the T-1 state is substantially higher than that in fac-[ReI(bpy)(CO)(3)PR3](+) and the minimum-energy seams of crossings (MESXs) are located before and below the barrier. The MESXs have also been searched in fac-[Re-I(bpy)(CO)(3)PR3](+) and no MESXs were found before and below the barrier

An energy decomposition and extrapolation scheme for evaluating electron transfer rate constants: A case study on electron self-exchange reactions of transition metal complexes

A simple approach for analyzing electron transfer (ET) reactions is proposed based on energy decomposition and extrapolation schemes. The present energy decomposition and extrapolation-based electron localization (EDEEL) method represents the diabatic energies for the initial and final states using the adiabatic energies of the donor and acceptor species and their complex. A scheme to estimate ET rate constants efficiently is also proposed by combining it with the Marcus theory. EDEEL is semi-quantitative by directly evaluating the seam-of-crossing region of two diabatic potentials. In a numerical test, EDEEL successfully provided ET rate constants for electron self-exchange reactions of thirteen transition metal complexes with reasonable accuracy. Furthermore, its energy decomposition and extrapolation schemes give all the energy values required in the activation strain model (ASM) analysis. The ASM analysis using EDEEL provided rational interpretations of the variation of the ET rate constants depending on the transition metal complexes. Its extension combining two computational levels was discussed to further reduce its computational costs. These results suggest that EDEEL is useful in efficiently evaluating ET rate constants and obtaining a rational understanding of their magnitudes

Hansen Solubility Parameter Analysis on Dispersion of Oleylamine-Capped Silver Nanoinks and their Sintered Film Morphology

Optimizing stabilizers and solvents is crucial for obtaining highly dispersed nanoparticle inks. Generally, nonpolar (hydrophobic) ligand-stabilized nanoparticles show superior dispersibility in nonpolar solvents, whereas polar ligand (hydrophilic)-stabilized nanoparticles exhibit high dispersibility in polar solvents. However, these properties are too qualitative to select optimum stabilizers and solvents for stable nanoparticle inks, and researchers often rely on their experiences. This study presents a Hansen solubility parameter (HSP)-based analysis of the dispersibility of oleylamine-capped silver nanoparticle (OAm-Ag NP) inks for optimizing ink preparation. We determined the HSP sphere of the OAm-Ag NPs, defined as the center coordinate, and the interaction radius in 3D HSP space. The solvent’s HSP inside the HSP sphere causes high dispersibility of the OAm-Ag NPs in the solvent. In contrast, the HSPs outside the sphere resulted in low dispersibility in the solvent. Thus, we can quantitatively predict the dispersibility of the OAm-Ag NPs in a given solvent using the HSP approach. Moreover, the HSP sphere method can establish a correlation between the dispersibility of the particles in inks and the sintered film morphology, facilitating electronic application of the nanoparticle inks. The HSP method is also helpful for optimizing stabilizers and solvents for stable nanoparticle inks in printed electronics

Antibacterial and Antibiofilm Photodynamic Activities of Lysozyme-Au Nanoclusters/Rose Bengal Conjugates

Antibacterial photodynamic therapy (aPDT) utilizes reactive oxygen species such as singlet oxygen (1O2) and free radicals via photosensitizers, which are light and light-sensitive agents, to reduce bacterial infections. It has been utilized as a treatment for dental diseases in place of antibiotic therapies. However, aPDT does not always cause the desired therapeutic effect due to the instability of organic photosensitizers and the formation of bacterial biofilms. To promote the antibacterial and antibiofilm effects of aPDT, we have proposed a lysozyme (Lys)-gold nanoclusters (Au NCs)/rose bengal (Lys-Au NCs/RB) conjugate as a novel photosensitizer. This conjugate was found to effectively impede the growth of both gram-positive and gram-negative bacteria when exposed to white light-emitting diode (LED) irradiation. The photoexcited Lys-Au NCs/RB showed significantly higher antibacterial activity than photoexcited Lys-Au NCs or RB alone. The synergistic effect is a result of the combination of Lys (an antibacterial protein) and enhanced 1O2 generation related to resonance energy transfer (RET) in the Au NCs/RB conjugate. Photoexcited Lys-Au NCs/RB increased the effects of aPDT in a dose- and time-dependent manner. Furthermore, the photoexcited Lys-Au NCs/RB successfully decreased Streptococcus mutans biofilm formation. However, in contrast, it did not have a negative effect on the proliferation, adhesion, or spread of mammalian cells, indicating low cytotoxicity. Lys-Au NCs/RB is a novel photosensitizer with low cytotoxicity that is capable of bacterial inactivation and the suppression of biofilm formation, and could help to improve dental treatments in the future

Computational searches for crystal structures of dioxides of group 14 elements (CO2, SiO2, GeO2) under ultrahigh pressure

In this study, we focused on the effect of pressure on the crystal structures of dioxides of group 14 elements,i.e.SiO2, GeO2, and CO2. Systematic searches for their crystal structures using the artificial force induced reaction method generated 219 and 147, 102 and 63, and 148 and 76 structures for SiO2, GeO2, and CO2, respectively, at 1 and 10(6)atm. At 1 atm, cristobalite-like, quartz, anatase-like, and stishovite were stable structures for SiO(2)and GeO2. At 10(6)atm, structures of stishovite and CaCl(2)type were relatively stable for SiO(2)and GeO2. At 1 atm of CO2, molecular crystals were the most stable, whereas, quartz-like and cristobalite-like structures were obtained as stable structures at 10(6)atm. We discuss these pressure dependent structural variations systematically using the obtained structural dataset