Comparative study of thermal and photo-induced reactions of NO on particulate and flat silver surfaces

Adsorption states, thermal reactions, and photoreactions at photon energies 2.3–4.7 eV of NO dimers and monomers have been compared between 8-nm silver nanoparticles (Ag NPs) formed on an Al₂O₃/NiAl(110) substrate and flat Ag(111) surfaces, by thermal desorption (TPD) and by photodesorption using mass selected time-of flight measurements. On the Ag NPs, the (NO)₂ and NO species are bound more weakly and with broader variation of adsorption states, compared to Ag(111). For (NO)₂ excitation of the Mie plasmon of the Ag NPs with p-polarized 3.5-eV photons enhances the photodesorption cross section (PCS) of NO from (NO)₂ by a factor 15 compared to Ag(111); even off the plasmon resonance up to 3-fold PCS enhancement is obtained which we ascribe to hot electron confinement. However, since translational energy distributions of photodesorbed NO are roughly the same on Ag NPs and on Ag(111), common mechanisms of photoexcitation and photoreactions apply on both types of surfaces, and neither enhancement modifies the photoinduced dynamics. Stronger particle-induced influences are observed for the photoinduced NO monomer by changes in its properties, chemical environments, and formation/decay kinetics.Our results show that NPs can lead to considerable changes of efficiency and, under favorable cases, also of branching of photoinduced surface reactions.     

Synthesis of All Stereoisomers of RK460 and Evaluation of Their Activity and Selectivity as Abscisic Acid Receptor Antagonists

The PYR/PYL/RCAR protein families have recently emerged as receptors of the phytohormone abscisic acid (ABA, 1 ), which regulates plant responses to environmental stress. These families have multiple members with different physiological actions, and so selective agonists or antagonists are needed both as tools to elucidate functional differences and as lead compounds for agrochemicals. We previously identified RK460 (rac- 3 a ) as a PYR1-selective antagonist, and showed that it possesses five stereocenters on a 6,5-cis-bicyclo skeleton. Here, we synthesized all the stereoisomers of RK460 and evaluated their activity towards a panel of receptors. Relative stereochemistry as well as absolute stereochemistry was important for selective action.     

Temperature–pressure shuffling outlier flooding method enhances the conformational sampling of proteins

Outlier flooding method (OFLOOD) is an efficient conformational sampling method developed by the authors. In the present study, to further enhance the conformational sampling efficiency, a set of parameters (temperatures and pressures) specified as inputs in the original OFLOOD were shuffled before restarting the short-time molecular dynamics (MD) simulations. Because of the diversity of these parameters, it was confirmed that the extended OFLOOD becomes superior to the original one in finding the folding pathways of Trp-cage. © 2019 Wiley Periodicals, Inc.     

Reversible and stable redox behavior of a Pt(II) bis(dithiobenzoate)-type complex attributed to rotaxane-based stabilization

A three-dimensionally insulated Pt(II) bis(dithiobenzoate) complex with a [1]rotaxane structure was synthesized using permethylated cyclodextrins. We have confirmed macrocyclic insulation is necessary to yield the Pt(II) bis(dithiobenzoate) complex with high selectivity. Furthermore, the formed Pt(II) complex showed highly stable and reversible two-step redox behavior in cyclic voltammetry due to the three-dimensional insulation.     

Energy quantization of chaos with the semiclassical phases alone

The mechanism of energy quantization is studied for classical dynamics on a highly anharmonic potential, ranging from integrable, mixed, and chaotic motions. The quantum eigenstates (standing waves) are created by the phase factors (the action integrals and the Maslov index) irrespective of the integrability, when the amplitude factors are relatively slowly varying. Indeed we show numerically that the time Fourier transform of an approximate semiclassical correlation function in which the amplitude factors are totally removed reproduces the spectral positions (energy eigenvalues) accurately in chaotic regime. Quantization with the phase information alone brings about dramatic simplification to molecular science, since the amplitude factors in the lowest order semiclassical approximation diverge exponentially in a chaotic domain.     

Multilayer characterization by energy dispersive X-ray reflectivity technique

An experimental setup was developed to verify the feasibility of silicon drift detector to be used for the multilayer characterization by means of multilayer energy dispersive X-ray reflectivity. Such a detector allows high count rates up to 3 × 10⁵ cps and can be used in principle for the direct beam intensity measurement, which is to be done for the X-ray multilayer reflectivity patterns obtaining. A series of measurements were performed for Mo/B₄C multilayer sample. A quality of the experimentally obtained data turns out to be enough to perform a sample structure exploration using a numerical procedure of experimental data fitting. Due to low cost and short time, required for the measurements, an experimental technique proposed has a good perspective to be used for some practical applications in industry.     

Total Synthesis of (−)‐ and (+)‐Decarbamoyloxysaxitoxin and (+)‐Saxitoxin

Playing the sax : The enantioselective total syntheses of (?)‐ and (+)‐decarbamoyloxysaxitoxin (doSTX) and (+)‐saxitoxin (STX) are reported. A new methodology was developed for the synthesis of STXs, featuring discriminative reduction of the nitro group and N? O bond in nitroisoxazolidine.

     

Radiation-induced oxidation of polymers. Effect of antioxidant and antirad agent on oxygen consumption and gas evolution

The effects of antioxidants and of an antirad agent mixed in polyethylene and ethylene-propylene copolymer were investigated by means of oxygen consumption and gas evolution. The antioxidants were NBC, Irganox 1010, and DPPD, and the antirad agent was propyl fluoranthene (PFR). A small amount of the antioxidant (0.5 phr) in polymer decreased oxygen consumption by one-half or one-third compared with pure polymer, but the activity was lost with increasing irradiation. The antirad agent also decreased oxygen consumption and it was assumed to act as the energy transfer agent in the polymer matrix.     

Matrix-isolation infrared and ultraviolet spectroscopic studies of less stable conformers of 1,3,5-hexatriene

The infrared spectra of the 3-trans and 3-cis isomers of 1,3,5-hexatriene in low-temperature Ar matrices deposited from a high-temperature nozzle or deposited under irradiation of the Hg 253.7 nm light show a number of new bands. Correspondingly, the ultraviolet spectra of the 3-trans isomer observed under similar experimental conditions show a new absorption at 276 nm. Most of these new infrared bands and the new ultraviolet absorption are attributable to less stable isomers which have the planar s-cis conformation [or gauche conformation(s) close to the planar s-cis] about either one or both of the two CC bonds.