Visible-light photocatalysis of ZnO deposited on nanoporous Au

ZnO deposited on nanoporous Au showed photocatalytic decomposition toward methyl orange under visible light, unlike ZnO sputtered on flat Au without a nanoporous structure. First-principles calculations suggested that the surface lattice disorder in nanoporous Au induced a band gap narrowing and a large built-in electric field in the adjacent ZnO, resulting in the visible-light photocatalytic response.     

Protein-protein interaction of a Pharaonis halorhodopsin mutant forming a complex with Pharaonis halobacterial transducer protein II detected by Fourier-transform infrared spectroscopy

Pharaonis halorhodopsin (pHR) functions as a light-driven inward chloride ion pump in Natoronomonas pharaonis, while pharaonis phoborhodopsin (ppR; also called pharaonis sensory rhodopsin II, pSRII), is a light sensor for negative phototaxis. ppR forms a 2:2 complex with its cognate transducer protein (pHtrII) through intramembranous hydrogen bonds: Tyr199(ppR)-Asn74(pHtrII) and Thr189(ppR)-Glu43 (pHtrII), Ser62(pHtrII). It was reported that a pHR mutant (P240T/F250Y), which possesses the hydrogen-bonding sites, impairs its pumping activity upon complexation with pHtrII. In this study, effect of the complexation with pHtrII on the structural changes upon formation of the K, L(1) and L(2) intermediates of pHR was investigated by use of Fourier-transform infrared spectroscopy. The vibrational changes of Tyr250(pHR) and Asn74(pHtrII) were detected for the L(1) and L(2) intermediates, supporting that Tyr250(pHR) forms a hydrogen bond with Asn74(pHtrII) as similarly to Tyr199(ppR). The conformational changes of the retinal chromophore were never affected by complexation with pHtrII, but amide-I vibrations were clearly different in the absence and presence of pHtrII. The molecular environment around Asp156(pHR) in helix D is also slightly affected. These additional structural changes are probably related to blocking of translocation of a chloride ion from the extracellular to the cytoplasmic side during the photocycle.     

Ultrafast dynamics of the carbonyl stretching vibration in acetic acid in aqueous solution studied by sub-picosecond infrared spectroscopy

Vibrational energy relaxation of the carbonyl CO stretching modes of CH3COOD and CD3COOD in D2O is studied by frequency-resolved infrared pump-probe spectroscopy. The spectral change caused by the vibrational excitation includes two dynamical components with the time constants of 450 and 980 fs for CH3COOD and 390 and 930 fs for CD3COOD. The two dynamical components exhibit different spectral properties. There are two species of acetic acid forming different complexes with solvent water molecules. The time constants are almost the same for CH3COOD and CD3COOD, suggesting that the vibrational energy deposited to the carbonyl group is first distributed among vibrational modes not related to the methyl group.     

Heterometallic integer-spin analogues of S = 9/2 Mn4 cubane single-molecule magnets

A family of distorted heterometallic cubanes, [Mn (III) 3Ni (II)(hmp) 3O(N 3) 3(O 2CR) 3], where O 2CR (-) is benzoate ( 1), 3-phenylpropionate ( 2), 1-adamantanecarboxylate ( 3), or acetate ( 4) and hmp (-) is the anion of 2-pyridinemethanol, was synthesized and structurally as well as magnetically characterized. These complexes have a distorted-cubane core structure similar to that found in the S = 9/2 Mn 4 cubane family of complexes. Complexes 1, 3, and 4 crystallize in rhombohedral, hexagonal, and cubic space groups, respectively, and have C 3 molecular symmetry, while complex 2 crystallizes in the monoclinic space group Cc with local C 1 symmetry. Magnetic susceptibility and magnetization hysteresis measurements and high-frequency electron paramagnetic resonance (HFEPR) spectroscopy established that complexes 1-4 have S = 5 spin ground states with axial zero-field splitting (ZFS) parameters ( D) ranging from -0.20 to -0.33 cm (-1). Magnetization versus direct-current field sweeps below 1.1 K revealed hysteresis loops with magnetization relaxation, definitely indicating that complexes 1-4 are single-molecule magnets that exhibit quantum tunneling of magnetization (QTM) through an anisotropy barrier. Complex 2 exhibits the smallest coercive field and fastest magnetization tunneling rate, suggesting a significant rhombic ZFS parameter ( E), as expected from the low C 1 symmetry. This was confirmed by HFEPR spectroscopy studies on single crystals that gave the following parameter values for complex 2: gz = 1.98, gx = gy = 1.95, D = -0.17 cm (-1), B 4 (0) = -6.68 x 10 (-5) cm (-1), E = 6.68 x 10 (-3) cm (-1), and B 4 (2) = -1.00 x 10 (-4) cm (-1). Single-crystal HFEPR data for complex 1 gave g z = 2.02, gx = gy = 1.95, D = -0.23 cm (-1), and B 4 (0) = -5.68 x 10 (-5) cm (-1), in keeping with the C 3 site symmetry of this Mn 3Ni complex. The combined results highlight the importance of spin-parity effects and molecular symmetry, which determine the QTM rates.     

Multidynamic Crystalline Molecular Rotors Comprising an N-Heterocyclic Carbene Binuclear Au(I) Complex Bearing Multiple Rotators

We report multidynamic molecular rotations in crystals using a concave-shape N-heterocyclic carbene (NHC) binuclear Au(I) complex rotor bearing pyrazine and tetrahydrofuran (THF) molecules as multicomponent rotators. Single-crystal X-ray diffraction (XRD) measurements revealed that two THF molecules are located near the central pyrazine encapsulated by two bulky NHC ligands. From ²H solid-state NMR analysis, it was observed that the pyrazine rotated in a 2-fold site exchange with a 180° rotational angle and a 31 kJ mol⁻¹ energy barrier, while the THF molecules showed a 23°-38° libration with a lower energy barrier (14 kJ mol⁻¹). Interestingly, the pyrazine rotation was accelerated when the THF molecules rotated in fast site exchange with a large angle of libration, suggesting that the rotators exhibit multidynamics in a correlated manner.     

Unraveling Inter‐ and Intrachain Electronics in Polythiophene Assemblies Mediated by Coordination Nanospaces

Strong interchain interactions render unsubstituted polythiophene un‐fusible, non‐melting, and insoluble. Therefore, control of the packing structure, which has a profound effect on the optical and electronic properties of the polymer, has never been achieved. Unsubstituted polythiophene was prepared in the one‐dimensional channels of [La(1,3,5‐benzenetrisbenzoate)]_n, where polymer chains form unprecedented assembly structures mediated by the host framework. It is noteworthy that the emission and carrier transport properties were drastically changed by varying the number of chains within a particular assembly. The response of the composite to additional guests is also examined as a method to use the composites as low‐concentration sensors. Our findings show that the encapsulation of polymer chains in host materials is a facile method for understanding the intrinsic properties of conjugated polymers, along with controlling and enhancing their functions.     

Charge‐Transfer Phase Transition of a Cyanide‐Bridged FeII/FeIII Coordination Polymer

Heterometallic Prussian blue analogues are known to exhibit thermally induced charge transfer, resulting in switching of optical and magnetic properties. However, charge‐transfer phase transitions have not been reported for the simplest FeFe cyanide‐bridged systems. A mixed‐valence Fe^II/Fe^III cyanide‐bridged coordination polymer, {[Fe(Tp)(CN)₃]₂Fe(bpe)?5 H₂O}_n, which demonstrates a thermally induced charge‐transfer phase transition, is described. As a result of the charge transfer during this phase transition, the high‐spin state of the whole system does not change to a low‐spin state. This result is in contrast to FeCo cyanide‐bridged systems that exhibit charge‐transfer‐induced spin transitions.     

Hydrogen embrittlement in a magnesium grain boundary: a first-principles study

First-principles fully relaxed tensile and shear test simulations were performed on Σ10(1124)/[1100] tilt Mg grain boundary (GB) models, with and without H segregation, to investigate mechanisms of H embrittlement of Mg. Strengthening as a result of covalent-like characteristics of Mg-H bonds prevailed over weakening of Mg-Mg bonds resulting from charge transfer; as a result, an H atom strengthened the GB. In addition, because the strong Mg-H bonds suppressed macroscopic GB fracture, elongation to failure was not reduced by H segregation. However, the resistance to GB shearing was increased by H segregation. It is therefore suggested that H segregation enhances crack growth at the GB, because dislocation emission from the crack tip is suppressed, resulting in H embrittlement of Mg.     

Measurement of a pauli and orbital paramagnetic state in bulk gold using x-ray magnetic circular dichroism spectroscopy

We show that bulk gold (Au) exhibits temperature-independent paramagnetism in an external magnetic field by x-ray magnetic circular dichroism spectroscopy at the Au L(2) and L(3) edges. Using the sum-rule analysis, we obtained a magnetic moment of 1.3 × 10(-4) μB/atom in an external magnetic field of 10 T and a paramagnetic susceptibility of 8.9 × 10(-6) for the 5d orbit. The induced paramagnetism in bulk Au is characterized by a large (≈ 30%) orbital contribution. This orbital component was retained even when Au atoms formed nanoparticles, playing an important role in stabilizing the spontaneous spin polarization in the Au nanoparticles.     

Local structure around phosphorus and silicon in the CaO–SiO2–PO2.5 system

The local structure of phosphorus and silicon in the molten CaO–SiO₂–PO_2.5 slag system was investigated by magic angle spinning nuclear magnetic resonance (MAS-NMR). The ³¹P MAS-NMR spectra revealed that phosphorus was present primarily as the monophosphate complex ion PO₄^3?, with a small amount of diphosphate ion also present. Their relative ratio to total phosphorus was independent of the phosphate concentration of the sample. In the case of the ²⁹Si MAS-NMR, the mean number of the non-bridging oxygen atoms associated with tetrahedrally coordinated silicon decreased as the phosphate concentration increased at a fixed CaO/SiO₂ ratio. This indicates that the nonbridging oxygen atoms around the silicon were replaced by bridging oxygen atoms around the phosphorus as the phosphate concentration in the samples increased.To elucidate the basicity dependence of the structure of slag, the relationship between the structure and optical basicity was also investigated. The relative ratio of Qⁿ (Qⁿ means the silicon atoms tetrahedrally bonded with “n” number of bridging oxygen atoms) strongly depends on the optical basicity. These optical basicity dependencies of the structures of phosphorus and silicon can be explained clearly by the basicity equalization concept (Duffy and Ingram, 1976) [12].