Effect of water during the quantitation of formate in photocatalytic studies on CO2 reduction in dimethylformamide

The effect of the water concentration on the quantitation of formate from dimethylformamide in the presence of electron-donating bases using ion chromatography is reported. This observation has important implications in the area of the photocatalytic reduction of CO(2), where formate levels are often used to calculate catalyst turnover numbers.     

Recognition of sialylated poly-N-acetyllactosamine chains on N- and O-linked glycans by human and avian influenza A virus hemagglutinins

Human influenza viruses are proposed to recognize sialic acids (pink diamonds) on glycans extended with poly-LacNAc chains (LacNAc=(yellow circle+blue square)). N- and O-linked glycans were extended with different poly-LacNAc chains with α2-3- and α2-6-linked sialic acids recognized by human and avian influenza viruses, respectively. The specificity of recombinant hemagglutinins (receptors in green) was investigated by using glycan microarray technology.     

High quality dispersions of hexabenzocoronene in organic solvents

We have studied the exfoliation and dispersion of hexabenzocoronene (HBC) in 28 different solvents. We see a wide range of dispersed concentrations and aggregation states, all of which can be related to the solvent properties. To a first approximation, the dispersed concentration is maximized for solvents with Hildebrand solubility parameter close to 21 MPa(1/2), similar to graphitic materials such as nanotubes and graphene. We have also studied the concentration dependence of the absorbance and photoluminescence of HBC for both a good solvent, cyclohexyl pyrrolidone (CHP), and a poor solvent, tetrahydrofuran (THF). In both cases, we observe features that can be associated with either individual molecules or aggregates, allowing us to establish metrics both for aggregate and individual molecule content. While the aggregate content always increases with concentration, good solvents disperse individual molecules at relatively high concentrations while poor solvents display aggregation even at low concentrations. Using these metrics, we determine that large populations of individual molecules are present at low concentrations in certain solvents with Hildebrand solubility parameters close to 21 MPa(1/2). However, the aggregation state of HBC is considerably more sensitive to solvent Hildebrand parameter for halogenated solvents than for amide solvents. We find a combination of high overall concentrations and large populations of individual molecules in four solvents: cyclohexyl pyrrolidone, 1-chloronaphthalene, 1-bromonaphthalene, and 1,2,4-trichlorobenzene. Scanning tunnelling microscopy (STM) measurements show the formation of self-assembled monolayers at the interface between a HBC-solvent dispersion and a highly oriented pyrolytic graphite (HOPG) substrate. Similar structures were observed on ultrathin supports by aberration-corrected transmission electron microscopy (TEM). Also observed were graphitic objects of size ~1 nm consistent with monomers or aggregated stacks of very few monomers. We believe this is strong evidence of the presence of individual molecules in dispersions prepared with appropriate solvents.     

Observation of the d3Pi(g)<--c3Sigma(u)+ band system of C2

A new band system of C(2), d (3)Pi(g)<--c (3)Sigma(u) (+) is observed by laser induced fluorescence spectroscopy, constituting the first direct detection of the c (3)Sigma(u) (+) state of C(2). Observations were made by laser excitation of c (3)Sigma(u) (+)(v(")=0) C(2), produced in an acetylene discharge, to the d (3)Pi(g)(v(')=3) level, followed by detection of Swan band fluorescence. Rotational analysis of this band yielded rotational constants for the c (3)Sigma(u) (+)(v(")=0) state: B(0)=1.9218(2) cm(-1), lambda(0)=-0.335(4) cm(-1) and gamma(0)=0.011(2) cm(-1). The vibrational band origin was determined to be nu(3-0)=15861.28 cm(-1).     

Rearrangements in Model Peptide‐Type Radicals via Intramolecular Hydrogen‐Atom Transfer

Intramolecular H‐atom transfer in model peptide‐type radicals was investigated with high‐level quantum‐chemistry calculations. Examination of 1,2‐, 1,3‐, 1,5‐, and 1,6[C ? N]‐H shifts, 1,4‐ and 1,7[C ? C]‐H shifts, and 1,4[N ? N]‐H shifts (Scheme 1), was carried out with a number of theoretical methods. In the first place, the performance of UB3‐LYP (with the 6‐31G(d), 6‐31G(2df,p), and 6‐311+G(d,p) basis sets) and UMP2 (with the 6‐31G(d) basis set) was assessed for the determination of radical geometries. We found that there is only a small basis‐set dependence for the UB3‐LYP structures, and geometries optimized with UB3‐LYP/6‐31G(d) are generally sufficient for use in conjunction with high‐level composite methods in the determination of improved H‐transfer thermochemistry. Methods assessed in this regard include the high‐level composite methods, G3(MP2)‐RAD, CBS‐QB3, and G3//B3‐LYP, as well as the density‐functional methods B3‐LYP, MPWB1K, and BMK in association with the 6‐31+G(d,p) and 6‐311++G(3df,3pd) basis sets. The high‐level methods give results that are close to one another, while the recently developed functionals MPWB1K and BMK provide cost‐effective alternatives. For the systems considered, the transformation of an N‐centered radical to a C‐centered radical is always exothermic (by 25 kJ ? mol^?1 or more), and this can lead to quite modest barrier heights of less than 60 kJ ? mol^?1 (specifically for 1,5[C ? N]‐H and 1,6[C ? N]‐H shifts). H‐Migration barriers appear to decrease as the ring size in the transition structure (TS) increases, with a lowering of the barrier being found, for example when moving from a rearrangement proceeding via a four‐membered‐ring TS (e.g., the 1,3[C ? N]‐H shift, CH₃? C(O)? NH^. → ^.CH₂? C(O)? NH₂) to a rearrangement proceeding via a six‐membered‐ring TS (e.g., the 1,5[C ? N]‐H shift, ^.NH? CH₂? C(O)? NH? CH₃ → NH₂? CH₂? C(O)? NH? CH₂^.).     

Key aspects of crystalline Mo-V-O-based catalysts active in the selective oxidation of propane

Mo-V-O-based complex metal oxide catalysts were synthesized hydrothermally for the first time, characterized structurally and tested in the selective oxidation of propane to acrylic acid, and the results obtained were compared on the basis of catalyst crystal structures in order to clarify key aspects of alkane selective oxidation over multifunctional metal oxide catalysts. The catalysts tested were black solids of rod-shaped crystals, which had a layer structure in the direction of fiber axis and various high dimensional arrangements of metal octahedra in the cross-section plane. A strong dependency on the octahedra arrangements and a facet dependency were observed, and the roles of metal elements in the course of selective oxidation of propane were clarified by comparing the catalytic performance of various Mo-V-O-based catalysts. We discuss the multi-functional character derived from high dimensional structures of the catalysts and mechanism of the selective oxidation of propane.     

Synthesis and structural characterization of a cocrystal salt containing acriflavine and 3,5-dinitrobenzoic acid

An acriflavine cocrystal salt with 3,5-dinitrobenzoic acid (stoichiometry 1:3) was synthesized and structurally characterized. This is the first crystal structure containing the acriflavine moiety to be documented and also the first in which a trimer of an aromatic monocarboxylic acid has been identified. In the crystal packing the trimers of 3,5-dinitrobenzoic acid form a porous organic framework, in the voids of which are located π-stacked columns of acriflavine cations.     

A Twist‐Bend Nematic (NTB) Phase of Chiral Materials

New chiral dimers consisting of a rod‐like and cholesterol mesogenic units are reported to form a chiral twist‐bend nematic phase (N_TB*) with heliconical structure. The compressibility of the N_TB phase made of bent dimers was found to be as large as in smectic phases, which is consistent with the nanoperiodic structure of the N_TB phase. The atomic force microscopy observations in chiral bent dimers revealed a periodicity of about 50 nm, which is significantly larger than the one reported previously for non‐chiral compounds (ca. 10 nm).     

Sierpiński-triangle fractal crystals with the C_(3v) point group

Self-similar fractals are of importance in both science and engineering. Metal-organic Sierpin′ ski triangles are particularly attractive for applications in gas separation, catalysis and sensing. Such fractals are constructed in this study by using 1208 V-shaped 4,400-dicyano-1,10:30,100-terphenyl molecules and Fe atoms on Au(1 1 1), and studied in detail by low-temperature scanning tunneling microscopy. Density functional theory calculations are employed to rationalize the invisible Fe atoms in STM images. Monte Carlo simulations are performed to understand the formation mechanism of the surface-supported fractal crystals.     

Fabrication and characterisation of gold nano-particle modified polymer monoliths for flow-through catalytic reactions and their application in the reduction of hexacyanoferrate

Polymer monoliths in capillary (100 μm i.d.) and polypropylene pipette tip formats (vol: 20 μL) were modified with gold nano-particles (AuNP) and subsequently used for flow-through catalytic reactions. Specifically, methacrylate monoliths were modified with amine-reactive monomers using a two-step photografting method and then reacted with ethylenediamine to provide amine attachment sites for the subsequent immobilisation of 4 nm, 7 nm or 16 nm AuNP. This was achieved by flushing colloidal suspensions of gold nano-particles through each aminated polymer monolith which resulted in a multi-point covalent attachment of gold via the lone pair of electrons on the nitrogen of the free amine groups. Field emission scanning electron microscopy and scanning capacitively coupled conductivity detection was used to characterise the surface coverage of AuNP on the monoliths. The catalytic activity of AuNP immobilised on the polymer monoliths in both formats was then demonstrated using the reduction of Fe(III) to Fe(II) by sodium borohydride as a model reaction by monitoring the reduction in absorbance of the hexacyanoferrate (???) complex at 420 nm. Catalytic activity was significantly enhanced on monoliths modified with smaller AuNP with almost complete reduction (95 %) observed when using monoliths agglomerated with 7 nm AuNPs.