Mössbauer spectroscopy of supported bimetallic catalysts: 1∶5 FeM/SiO2 (M=Ru,Rh, Pd,Ir, Pt)

Mössbauer spectra of SiO₂-supported bimetallic FeM (M=Ru, Rh, Pd, Ir, and Pt) with FeM=15 arter treatments such as reduction, exposure to CO and passivation in air are described and compared with previous results obtained on 11 FeM/SiO₂ catalysts.     

Thermal conductivity and specific heat of amorphous Zr0.67Ni0.33 after structural relaxation

Low-temperature measurements of the thermal conductivity (0.3KT5K) and of the specific heatC (0.07KT3.5K) of splat-cooled amorphous superconducting Zr_0.67Ni_0.33(T _c 2.7K) after different annealing stages are reported. increases progressively (up to 55%) after annealing. An analysis of with the help of normal-state measurements belowT _c in an overcritical field shows that the phonon-electron scattering remains unaltered after annealing. Hence the increase in must be entirely attributed to structure-induced (intrinsic) scattering, i.e. by two-level tunneling states (TLS) at low temperatures (T1K). The specific heat shows a small decrease aboveT _c (by 8%) which is attributed to a small diminution of the electronic density of states at the Fermi level and to a small increase in the Debye temperature. ForTT _c where TLS dominate, the specific heatC decreases less upon annealing than expected from the increase of in the standard tunneling model. This points to a change in the TLS relaxation time spectrum upon annealing, as observed previously for Zr _x Cu_1–x glasses.     

FeRu/TiO2 and Fe/TiO2 catalysts after reduction and Fischer-Tropsch synthesis studied by Mössbauer spectroscopy

A series of TiO₂-supported bimetallic FeRu catalysts with different Fe:Ru ratios (; 101; 31; 11; 13) has been studied by means of in situ Mössbauer spectroscopy. The influence of reduction and Fischer-Tropsch synthesis on the state of iron in the FeRu/TiO₂ catalysts will be derived.     

THE FLUORESCENCE DECAY OF REDUCED NICOTINAMIDES IN AQUEOUS SOLUTION AFTER EXCITATION WITH A UV-MODE LOCKED Ar ION LASER

Abstract— The fluorescence decay kinetics of the reduced nicotinamides NMNH, NADH and NADPH in aqueous solution were investigated using an Ar ion laser, mode locked in the UV, as source of excitation and single photon counting electronics in the detection system allowing for a time resolution in the picosecond range. Analysis of the experimental fluorescence decay showed that the dinucleotides did not follow a single exponential decay law. Good fitting was accomplished with a sum of two exponentials. The mononucleotide fluorescence decay was a single exponential for at least 95% of its amplitude.
The heterogeneity in lifetimes of the fluorescence of the dinucleotides was interpreted in terms of an exciplex mechanism.     

Pincer-porphyrin hybrids

[reaction: see text] Starting from tetrakis(3,5-bis(bromomethyl)phenyl)porphyrin, pincer-porphyrin hybrid molecules (tetrakis(ECE-pincer)porphyrin; E = N, P, S) based on a tetraphenylporphyrin skeleton have been prepared in high yields. These multi-ligand site compounds could be selectively metalated at their peripheries, which was shown by X-ray crystallography.     

Quantitative thermogravimetric analysis of binary mixtures

Thermogravimetric analysis is used to determine the amounts of Mg(OH)₂ and Mg(CH₃COO)₂in a mixture thereof. The application and suitability of different analysis methods are discussed. In the first method the mass losses in the temperature ranges as indicated by the decomposition of the pure compounds were used. Results obtained using these temperature ranges were unusable. The percentage mass losses due to the decomposition of Mg(OH)₂ and Mg(CH₃COO)₂ were then determined in a second method using the minimum in the derivative mass vs. temperature curves. The results obtained by this method compared well with the actual values for mixtures containing more than 15% magnesium acetate. The third method employed the total experimental mass loss of both decomposition reactions. The results obtained using this method compared well to the actual values, giving a R ² value of more than 0.99. This method of using the total mass losses can however only be used for binary mixtures that consist only of magnesium hydroxide and magnesium acetate. This revised version was published online in August 2006 with corrections to the Cover Date.     

Bidentate ligands formed by self-assembly

A novel supramolecular strategy to prepare bidentate ligands via the assembly of functionalised monomeric ligands on a dimeric zinc(II) porphyrin template is presented; the assembled bidentate ligands show chelating behaviour and their rhodium complexes display enhanced selectivity in the hydroformylation compared to the non-template analogue.     

Thermal expansion properties of organic crystals: a CSD study

The thermal expansion properties of crystalline organic compounds are investigated by data mining of the Cambridge Structural Database (CSD). The mean volumetric thermal expansion coefficient is 168.8 × 10⁻⁶ K⁻¹ and the mean uniaxial thermal expansion coefficient is 71.4 × 10⁻⁶ K⁻¹, based on 745 and 1129 different observations, respectively. Normal and anomalous coefficients can be identified using these values and the associated standard deviations. The anisotropy of the thermal expansion is also evaluated and found to have a very broad distribution. 4719 different structures, comprising 4093 different molecular compounds and 626 additional polymorphs have been analyzed on their thermal expansion properties. Approximately 34% of these structures may have at least one orthogonal axis with negative thermal expansion, much more than generally believed. Moreover 127 structures have been identified which could have negative volumetric thermal expansion. Experimental validation using a robust protocol with data collected at more than 2 different temperatures is required to validate these cases.

The thermal expansion properties of crystalline organic compounds are investigated by data mining of the Cambridge Structural Database (CSD). Negative uniaxial thermal expansion is much more common than generally believed.     

Preclinical evaluation of a novel water-soluble chlorin E6 derivative (BLC 1010) as photosensitizer for the closure of the neovessels

In the present study, photodynamic activity of a novel photosensitizer (PS), Chlorin e(6)-2.5 N-methyl-d-glucamine (BLC 1010), was evaluated using the chorioallantoic membrane (CAM) as an in vivo model. After intravenous (i.v.) injection of BLC 1010 into the CAM vasculature, the applicability of this drug for photodynamic therapy (PDT) was assessed in terms of fluorescence pharmacokinetics, i.e. leakage from the CAM vessels, and photothrombic activity. The influence of different PDT parameters including drug and light doses on the photodynamic activity of BLC 1010 has been investigated. It was found that, irrespective of drug dose, an identical continuous decrease in fluorescence contrast between the drug inside and outside the blood vessels was observed. The optimal treatment conditions leading to desired vascular damage were obtained by varying drug and light doses. Indeed, observable damage was achieved when irradiation was performed at light doses up to 5 J/cm(2) 1 min after i.v. injection of drug doses up to 0.5 mg/kg body weight(b.w.). However, when irradiation with light doses of more than 10 J/cm(2) was performed 1 min after injection of drug doses up to 2 mg/kg body weight, this led to occlusion of large blood vessels. It has been demonstrated that it is possible to obtain the desired vascular occlusion and stasis with BLC 1010 for different combinations of drug and/or light doses.     

Ab initio calculation of the NH(3sigma-)-NH(3sigma-) interaction potentials in the quintet, triplet, and singlet states

We present the ab initio potential-energy surfaces of the NH-NH complex that correlate with two NH molecules in their 3sigma- electronic ground state. Three distinct potential-energy surfaces, split by exchange interactions, correspond to the coupling of the S(A) = 1 and S(B) = 1 electronic spins of the monomers to dimer states with S = 0, 1, and 2. Exploratory calculations on the quintet (S = 2), triplet (S = 1), and singlet (S = 0) states and their exchange splittings were performed with the valence bond self-consistent-field method that explicitly accounts for the nonorthogonality of the orbitals on different monomers. The potential surface of the quintet state, which can be described by a single Slater determinant reference function, was calculated at the coupled cluster level with single and double excitations and noniterative treatment of the triples. The triplet and singlet states require multiconfiguration reference wave functions and the exchange splittings between the three potential surfaces were calculated with the complete active space self-consistent-field method supplemented with perturbative configuration interaction calculations of second and third orders. Full potential-energy surfaces were computed as a function of the four intermolecular Jacobi coordinates, with an aug-cc-pVTZ basis on the N and H atoms and bond functions at the midpoint of the intermolecular vector R. An analytical representation of these potentials was given by expanding their dependence on the molecular orientations in coupled spherical harmonics, and representing the dependence of the expansion coefficients on the intermolecular distance R by the reproducing kernel Hilbert space method. The quintet surface has a van der Waals minimum of depth D(e) = 675 cm(-1) at R(e) = 6.6a0 for a linear geometry with the two NH electric dipoles aligned. The singlet and triplet surfaces show similar, slightly deeper, van der Waals wells, but when R is decreased the weakly bound NH dimer with S = 0 and S = 1 converts into the chemically bound N2H2 diimide (also called diazene) molecule with only a small energy barrier to overcome.