Complete oxidation of acetaldehyde and toluene over a Pd/WO(3) photocatalyst under fluorescent- or visible-light irradiation

Acetaldehyde was completely oxidized to CO(2) over a Pd/WO(3) photocatalyst under fluorescent-light irradiation in a flow-type reactor, and Pd/WO(3) was also used to completely oxidize toluene to CO(2) in a batch reactor under visible-light irradiation.     

Total synthesis of (-)-amathaspiramide F

The stereoselective total synthesis of the marine alkaloid (-)-amathaspiramide F (1) was achieved from the alpha-hydoxy-alpha-ethynylsilane 2. The crucial steps in this synthesis involved not only the enolate Claisen rearrangement of the alpha-acyloxy-alpha-alkenylsilane 6 for the construction of the nitrogen-containing quaternary carbon center, but also the chemoselective formation of the azaspirohemiaminal 12 using heptamethyldisilazane as the methylamine equivalent and the regioselective dibromination of the phenol moiety of 12 using n-Bu(4)NBrCl(2).     

Viscosity dependence of the kinetic parameters of the radical ion pair in homogeneous solution determined by optically detected X- and ku-band electron spin resonance

We investigated the dynamics of the radical ion pairs formed by photoinduced electron-transfer reaction from zinc tetraphenyl porphyrin to 2-methyl-1,4-naphthoquinone in mixtures of 2-propanol and cyclohexanol. By the irradiation of a resonant X- (9.16 GHz) or Ku-band (17.41 GHz) microwave pulse, the time profiles of the transient absorptions was modified and the yields of escaping radical ions decreased. From these experiments, we determined the kinetic parameters of the radical ion pairs at various solvent viscosities. The recombination rates of the singlet pairs were (4 +/- 4), (8 +/- 3), and (16 +/- 3) x 10(6) s(-1) at 5, 10, and 15 cP, respectively. The escape rates were (1.7 +/- 0.2), (1.4 +/- 0.1), and (0.9 +/- 0.2) x 10(6) s(-1) at 5, 10, and 15 cP, respectively. The viscosity dependence of the kinetic parameters was followed by the simple continuum diffusion model.     

Kaempferol tri- and tetraglycosides from the flowers of Clematis cultivar

A new kaempferol glycoside, kaempferol 3-O-alpha-rhamnopyranosyl-(1 --> 2)-[alpha-rhamnopyranosyl-(1 --> 6)-beta-glucopyranoside]-7-O-beta-glucopyranoside (2) was isolated from the flowers of Clematis cultivar "Jackmanii Superba", together with a known kaempferol 3-O-alpha-rhamnopyranosyl-(1 --> 6)-beta-glucopyranoside-7-O-beta-glucopyranoside (1). The chemical structures of the isolated glycosides were established by UV, LC-MS, characterization of acid hydrolysates, and 1H and 13C NMR spectroscopy.     

Arrays of double-decker porphyrins on highly oriented pyrolytic graphite

Three double-decker complexes of cerium(IV) were synthesized, which commonly have a 5,10,15,20-tetrakis(4-docosyloxyphenyl)porphyrin (C22OPP) moiety as one of the two tetrapyrrole rings. The three complexes-Ce(Pc)(C22OPP), Ce(C22OPP)2, and Ce(BPEPP)(C22OPP)-are distinguished by the other rings, which are Pc (=phthalocyanine), C22OPP, and BPEPP (=5,15-bis[4-(phenylethynyl)phenyl]porphyrin), respectively. The rate of inter-ring rotation of Ce(BPEPP)(C22OPP) was estimated to be approximately 3 s(-1) in solution at room temperature. These complexes assemble into ordered arrays at the interface of 1-phenyloctane and the highly oriented pyrolytic graphite surface, owing to the affinity of the long alkyl chains toward the surface, as revealed by means of scanning tunneling microscopy (STM) with molecular resolution. The shape of the upper ring is reflected in the STM image. Thus, Ce(Pc)(C22OPP), Ce(C22OPP)2, and Ce(BPEPP)(C22OPP) were observed as circular, square, and elliptic features, respectively. Possible molecular arrangements in the array of Ce(BPEPP)(C22OPP) are proposed by comparing STM images and molecular models. In the mixed arrays of Ce(BPEPP)(C22OPP) and H2(C22OPP), the double-decker complexes were distinguished by brighter features. Competitive adsorption experiments showed that the adsorption of Ce(BPEPP)(C22OPP) is less favorable than that of H2(C22OPP) by DeltaG(app) = 2.7 kJ mol(-1). Ce(BPEPP)(C22OPP) molecules appeared elliptic when placed within their own row, while they appeared isotropic when flanked by H2(C22OPP) molecules. Implications of the differences in the observed shapes to the inter-ring rotation are discussed.     

Highly phosphorescent iridium complexes containing both tridentate bis(benzimidazolyl)-benzene or -pyridine and bidentate phenylpyridine: synthesis, photophysical properties, and theoretical study of Ir-bis(benzimidazolyl)benzene complex

Novel mixed-ligand Ir(III) complexes, [Ir(L)(NwedgeC)X]n+ (L = N/\C/\N or N/\N/\N; X = Cl, Br, I, CN, CH3CN, or -CCPh; n = 0 or 1), were synthesized, where N/\CwedgeN = bis(N-methylbenzimidazolyl)benzene (Mebib) and bis(N-phenylbenzimidazolyl)benzene (Phbib), N/\N/\N = bis(N-methylbenzimidazolyl)pyridine (Mebip), and N/\C = phenylpyridine (ppy) derivatives. The X-ray crystal structures of [Ir(Phbib)(ppy)Cl] and [Ir(Mebib)(mppy)Cl] [mppy = 5-methyl-2-(2'-pyridyl)phenyl] indicate that the nitrogen atom of the ppy ligand is located trans to the coordinating carbon atom in Me- or Phbib, while the coordinating carbon atom in ppy occupies the trans position of Cl. [Ir(Mebip)(ppy)Cl]+ showed a quasireversible Ir(III/IV) oxidation wave at +1.05 V, while the Ir complexes, [Ir(Mebib)(ppy)Cl], were oxidized at +0.42 V versus Fc/Fc+. The introduction of an Ir-C bond in [Ir(Mebib)(ppy)Cl] induces a large potential shift of 0.63 V in a negative direction. Further, the oxidation potential of [Ir(Mebib)(Rppy)X] was altered by the substitution of R, R', and X groups. Compared to the oxidation potential, the first reduction potential revealed an almost constant value at -2.36 to -2.46 V for [Ir(L)(ppy)Cl] (L = Mebib and Phbib) and -1.52 V for [Ir(Mebip)(ppy)Cl. The UV-vis spectra of [Ir(Mebib)(R-ppy)X] show a clear singlet metal-to-ligand charge-transfer transition around 407 approximately 425 nm and a triplet metal-to-ligand charge-transfer transition at 498 approximately 523 nm. [Ir(Mebip)(ppy)Cl]+ emits at 610 nm with a luminescent quantum yield of Phi = 0.16 at room temperature. The phosphorescence of [Ir(Mebib)(ppy)X] was observed at 526 nm for X = CN and 555 nm for X = Cl with the high luminescent quantum yields, Phi = 0.77 approximately 0.86, at room temperature. [Ir(Phbib)(ppy)Cl] shows the emission at 559 nm with a luminescent quantum yield of Phi = 0.95, which is an unprecedentedly high value compared to those of other emissive metal complexes. Compared to the luminescent quantum yields of the Ir(ppy)2(L) derivatives and [Ir(Mebip)(ppy)Cl]+, the neutral Ir complexes, [Ir(L)(R-ppy)X] (L = Me- or Phbib), reveal very high quantum yields and large radiative rate constants (kr) ranging from 3.4 x 10(5) to 5.5 x 10(5) s(-1). The density functional theory calculation suggests that these Ir complexes possess dominantly metal-to-ligand charge-transfer and halide-to-ligand charge-transfer excited states. The mechanism for a high phosphorescence yield in [Ir(bib)(ppy)X] is discussed herein from the perspective of the theoretical consideration of radiative rate constants using perturbation theory and a one-center spin-orbit coupling approximation.     

Synthesis of Orthorhombic Mo‐V‐Sb Oxide Species by Assembly of Pentagonal Mo6O21 Polyoxometalate Building Blocks

Mix and match : The pentagonal [Mo₆O₂₁]^n? polyoxomolybdate building block assembles with other sources of Mo, V, and Sb ions to form an orthorhombic Mo‐V‐Sb oxide. The first single‐crystal X‐ray analysis of an orthorhombic Mo–V‐based oxide, a promising catalyst for light alkane selective oxidation known as the “M1 phase”, revealed the structure of the compound.

     

Weighted relaxation for multigrid reduction in time

Current trends in computer architectures now mean that faster computation speed must come primarily from increased concurrency, not faster clock speeds, which are stagnating. Thus, this situation creates bottlenecks for serial algorithms, including the well-known bottleneck for sequential time-integration, where each individual time-value (i.e., time-step) is computed sequentially. One approach to alleviate this and achieve parallelism in time is with multigrid. In this work, we consider multigrid-reduction-in-time (MGRIT), a multilevel method applied to the time dimension that computes multiple time-steps in parallel. Like all multigrid methods, MGRIT relies on the complementary relationship between relaxation on a fine-grid and a correction from the coarse grid to solve the problem. All current MGRIT implementations are based on unweighted-Jacobi relaxation; here we introduce the concept of weighted relaxation to MGRIT. We derive new convergence bounds for weighted relaxation, and use this analysis to guide the selection of relaxation weights. Numerical results then demonstrate that by choosing appropriate non-unitary relaxation weights, one can achieve faster convergence rates and lower iteration counts for MGRIT when compared with unweighted relaxation. In most cases, weighted relaxation yields a 10%–20% saving in iterations, which is significant when using large high-performance computers. For A-stable integration schemes, results also illustrate that under-relaxation can restore convergence in some cases where unweighted relaxation is not convergent.     

Polarized light-induced anisotropy depending on polymer matrices studied by polarized ftir spectroscopy

Polarized-light induced anisotropy of Disperse Orange 3 (DO3) depending on the polymer matrices was investigated by polarized FTIR spectroscopy. The dynamic behavior of the azo dyes doped in a series of methacrylate polymers was analyzed in terms of the orientation factors. Two factors, the free volume and the local polarity of matrices, are found to govern the dynamic behavior of DO3. It was found that induced anisotropy for trans and cis isomers varies depending on Tg of polymer matrix. Further, the thermal isomerization rate depend on the isomerization mode which is governed by the matrix polarity. The branched-alkyl chains are considered to block the interaction between ester groups and DO3 and introduce the DO3 molecules into the less polar environment.