Preparation and characterization of nano-sized Pt-Ru/C catalysts and their superior catalytic activities for methanol and ethanol oxidation

Carbon-supported PtRu nanoparticles (Ru/Pt: 0.25) were prepared by three different methods; simultaneous reduction of PtCl(4) and RuCl(3) (catalyst I) and changing the reduction order of PtCl(4) and RuCl(3) (catalysts II and III) to enhance the performance of the anodic catalysts for methanol and ethanol oxidation. Structure, microstructure and surface characterizations of all the catalysts were carried out by X-ray diffraction (XRD), transmission electron microscopy (TEM) coupled with energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The results of the XRD analysis showed that all catalysts had a face-centered cubic (fcc) structure with different and smaller lattice parameters than that of pure platinum, showing that the Ru incorporates into the Pt fcc structure by different ratios in all the catalysts. The typical particle sizes of all catalysts were in the range of 2-3 nm. The most active and stable catalyst for methanol and ethanol oxidation is catalyst III, in which a large amount (more than 90%) of PtRu alloy formation was observed. It has been found that this catalyst is about 8.0 and 33.4 times more active at ～0.60 V towards the methanol and ethanol oxidation reactions, respectively, compared to the commercial Pt catalyst.     

Efficient plasmid DNA cleavage by copper(II) complexes of 1,4,7-triazacyclononane ligands featuring xylyl-linked guanidinium groups

Three new metal-coordinating ligands, L(1), L(2), and L(3), have been prepared by appending o-, m-, and p-xylylguanidine pendants, respectively, to one of the nitrogen atoms of 1,4,7-triazacyclononane (tacn). The copper(II) complexes of these ligands are able to accelerate cleavage of the P-O bonds within the model phosphodiesters bis(p-nitrophenyl)phosphate (BNPP) and [2-(hydroxypropyl)-p-nitrophenyl]phosphate (HPNPP), as well as supercoiled pBR 322 plasmid DNA. Their reactivity toward BNPP and HPNPP is not significantly different from that of the nonguanidinylated analogues, [Cu(tacn)(OH(2))(2)](2+) and [Cu(1-benzyl-tacn)(OH(2))(2)](2+), but they cleave plasmid DNA at considerably faster rates than either of these two complexes. The complex of L(1), [Cu(L(1)H(+))(OH(2))(2)](3+), is the most active of the series, cleaving the supercoiled plasmid DNA (form I) to the relaxed circular form (form II) with a k(obs) value of (2.7 ± 0.3) × 10(-4) s(-1), which corresponds to a rate enhancement of 22- and 12-fold compared to those of [Cu(tacn)(OH(2))(2)](2+) and [Cu(1-benzyl-tacn)(OH(2))(2)](2+), respectively. Because of the relatively fast rate of plasmid DNA cleavage, an observed rate constant of (1.2 ± 0.5) × 10(-5) s(-1) for cleavage of form II DNA to form III was also able to be determined. The X-ray crystal structures of the copper(II) complexes of L(1) and L(3) show that the distorted square-pyramidal copper(II) coordination sphere is occupied by three nitrogen atoms from the tacn ring and two chloride ions. In both complexes, the protonated guanidinium pendants extend away from the metal and form hydrogen bonds with solvent molecules and counterions present in the crystal lattice. In the complex of L(1), the distance between the guanidinium group and the copper(II) center is similar to that separating the adjacent phosphodiester groups in DNA (ca. 6 ?). The overall geometry of the complex is also such that if the guanidinium group were to form charge-assisted hydrogen-bonding interactions with a phosphodiester group, a metal-bound hydroxide would be well-positioned to affect the nucleophilic attack on the neighboring phosphodiester linkage. The enhanced reactivity of the complex of L(1) at neutral pH appears to also be, in part, due to the relatively low pK(a) of 6.4 for one of the coordinated water molecules.     

One-dimensional exciton diffusion in perylene bisimide aggregates

The dynamics and mobility of excitons in J-aggregates of perylene bisimides are investigated by transient absorption spectroscopy with a time resolution of 50 fs. The transient spectra are compatible with an exciton delocalization length of two monomers and indicate that vibrational and configurational relaxation processes are not relevant for the spectroscopic properties of the aggregates. Increasing the pump pulse energy and in that way the initial exciton density results in an accelerated signal decay and pronounced exciton-exciton annihilation dynamics. Modeling the data by assuming a diffusive exciton motion reveals that the excitons cannot migrate freely in all three directions of space but their mobility is restricted to one dimension. The observed anisotropy supports this picture and points against direct Fo?rster-transfer-mediated annihilation between the excitons. A diffusion constant of 1.29 nm(2)/ps is deduced from the fitting procedure that corresponds to a maximal exciton diffusion length of 96 nm for the measured exciton lifetime of 3.6 ns. The findings indicate that J-aggregates of perylene bisimides are promising building blocks to facilitate directed energy transport in optoelectronic organic devices or artificial light-harvesting systems.     

One-dimensional magnetic inorganic-organic hybrid nanomaterials

One-dimensional (1D) magnetic inorganic-organic hybrid nanomaterials bear both the intrinsic magnetic properties of the inorganic components and the functionality and responsiveness of their organic part. In this tutorial review, we first emphasize various synthetic strategies for this type of materials: (i) template-directed synthesis employs different preformed templates such as channels in solids, mesostructures self-assembled from block copolymers, cylindrical polymer brushes, 1D biological templates and other existing 1D templates; (ii) electrospinning, which provides a simple and efficient technique that can lead to a potential large-scale production; (iii) 1D conjugation of building blocks which combines the physical attraction of magnetic nanoparticles in a magnetic field with chemical crosslinking and stabilization. The properties, functions and the future trends of these materials are also briefly introduced. It is foreseeable that these hybrid materials will play more and more important roles in the ever-advancing miniaturization of functional devices.     

Elucidating the origin of diastereoselectivity in a self-replicating system: selfishness versus altruism

We have investigated a diastereoselective self‐replicating system based on a cycloaddition of a fulvene derivative and a maleimide using a two‐pronged approach of combining NMR spectroscopy with computational modelling. Two diastereomers are formed with identical rates in the absence of replication. When replication is enabled, one diastereomer takes over the resources as a “selfish” autocatalyst, while exploiting the competitor as a weak “altruist”, resulting in a diastereoselectivity of 16:1. We applied 1D and 2D NMR spectroscopic techniques supported by ab initio chemical shifts as well as ab initio molecular dynamics simulations to study the structure and dynamics of the underlying network. This powerful combination allowed us to decipher the energetic and structural rationale behind the observed behaviour, while static computational methods currently used in the field did not.     

First examples of oxaphosphirane pentacarbonylchromium(0) and -molybdenum(0) complexes: synthesis, structures and reactions

Synthesis of the first oxaphosphirane chromium(0) and molybdenum(0) complexes of the type [{(R(1)PCH(R(2))-O}M(CO)(5)] (R(1) = C(5)Me(5)) (8a-e, 15a-e) and (R(1) = CH(SiMe(3))(2)) (9a-e, 16a-e) via reaction of dichloro(organo)- (1, 2, 10, 11) and chloro(organo)phosphane complexes (3,4,12) with lithium bases and aldehydes 7a-e is reported. Furthermore, bicyclic 1,3-oxaphospholane complexes 17 and 18 have been obtained via O-protonation of oxaphosphirane complexes 8a and 15a with HCl. All complexes were characterized by NMR, IR spectroscopic, mass spectrometric investigations and, in addition, single-crystal X-ray structures of complexes 8a-e, 9a,c, 15a,b,e, 16a-c, 17, 18 are presented and discussed.     

Electronic coupling through intramolecular π-π interactions in biscobaltocenes: a structural, spectroscopic, and magnetic study

The paramagnetic dinuclear complexes 1,8-bis(cobaltocenyl)naphthalene (2) and 1,8-bis[(pentamethyl-η(5)-cyclopentadienyl)(η(5)-cyclopentadiendiyl)cobalt(II)]naphthalene (4) were synthesized. The molecular structures were characterized by X-ray structure analysis and consisted of two cobaltocenes linked through a distorted naphthalene clamp. Electronic interactions between the two cobalt atoms were observed by cyclic voltammetric studies. Superconducting quantum interference device (SQUID) measurements of the pure compounds and diluted in their diamagnetic iron derivatives, as well as variable-temperature NMR spectroscopy experiments in solution are presented. Magnetic measurements revealed an antiferromagnetic coupling of the electrons in complexes 2 and 4. From NMR spectroscopy experiments, Curie behavior in the temperature range from -60 to +60 °C can be deduced. The electronic structure and magnetic behavior is supported by results of broken-symmetry DFT and multireference calculations along with UV/Vis spectroscopic data, which revealed an intramolecular through space π-π interaction between the cobaltocene units.     

Determination of Bismuth in Bottled and Mineral Water Samples at Trace Levels by T-Shaped Slotted Quartz tube-Atom Trap-Flame Atomic Absorption Spectrometry

An accurate and reliable analytical method for the determination of bismuth at trace levels in bottled and mineral water samples has been developed based on hydrogen assisted T-shape slotted quartz tube-atom trap-flame atomic absorption spectrometry (T-SQT-AT-FAAS). Conventional FAAS is not sufficiently sensitive to measure trace and ultra-trace levels of metals due to the low nebulization efficiency and short residence time of atoms in the light path. To overcome this problem, atom trapping with a T-shaped slotted quartz tube was coupled to the FAAS system. Bismuth atoms were trapped on the surface of T-SQT and released by hydrogen gas, which provided a reducing environment. All of the system parameters such as flame type, hydrogen flow rate, the height of T-SQT from the burner head, and trapping period were optimized to enhance the analytical signal to attain low detection limits. After obtaining the optimum conditions, the limit of detection and limit of quantitation of the developed method were found to be 0.95 and 3.2?µg L^?1, respectively. Recovery values were obtained between 90% and 104% that showed good accuracy and applicability of the proposed method to the analysis of bottled and mineral water samples.     

Design of liquid crystals with ‘de Vries-like’ properties: the effect of an ethynyl spacer in the core structure

We investigate the origins of ‘de Vries-like’ liquid crystalline behaviour by introducing an ethynyl spacer in the core of the tricarbosilane-terminated 5-phenylpyrimidine mesogens QL16-6 and QL17-6. The rationale for this structural change is based on the assumption that an ethynyl spacer would create more free volume in the core sub-layer and therefore decrease the orientational order parameter S₂ in the SmA phase. The tricarbosilane-terminated mesogens WL41-5 and WL42-6 with a 5-(phenylethynyl)pyrimidine core in either a normal or inverted orientation were synthesised, and their mesomorphic and ‘de Vries-like’ properties characterised using polarised optical microscopy, differential scanning calorimetry, birefringence measurements, small–angle (SAXS) and 2D X-ray scattering. Reduction factors R derived from SAXS and optical tilt angle measurements suggest that neither WL41-5 (R = 0.49) nor WL42-6 (R = 0.80) exhibit ‘de Vries-like’ properties. The S₂(T) profiles show an increase in orientational order with decreasing temperature and a sharp discontinuity at the SmA-SmC transition, which is consistent with ‘de Vries-like’ behaviour. However, the L_eff(T) profiles suggest an increase in interdigitation that reduces the positive effect of increasing S₂ in compensating for the molecular tilt.     

Polycyclic aromatic hydrocarbon and ionic compositions of atmospheric bulk deposition samples at a national park under the influence of intense barbecue smoke

The main aim of this study was to present the effects of barbecue smoke on a small-scale environment, a national park under the influence of intense barbecue smoke, and to scientifically support the sustainable usage of the park. Twelve-weekly bulk deposition samples were collected directly at the barbecuing area, and the samples were analysed for 16 US EPA’s priority PAH compounds and major ions. The mean concentrations of the individual PAHs in the bulk deposition samples ranged from 11.8 ng L^?1 (Ane) to 1085 ± 581 ng L^?1 (IcdP). The most frequently observed PAH compounds in the bulk deposition samples were Np, Anp, Flr, Phe, An, Flu, BkF, BaP and IcdP. The mean total PAH deposition fluxes were determined as 3.6 ± 5.6 µg m^?2 day^?1. The chloride, potassium and the sulphate fluxes were determined as 145.2 ± 267.8 µg m^?2 day^?1, 182.9 ± 291.9 µg m^?2 day^?1, and 111.9 ± 65.9 µg m^?2 day^?1, respectively. Dominant ions in the bulk deposition samples were potassium ion, chloride and sulphate which addressed as the fingerprint of barbecue grilling.