Directed-site percolation clusters: The scaling function in dimensions two to six

Exact series for lattices of dimension between 2 and 6 are used to report on the asymptotic features of the scaling function for the average number of clusters in directed percolation, close to, and away from, the most recent estimated intervals forp _c . Scanning of the noncritical regions yields exponent ranges compatible with the undirected percolation equivalents. Close top _c the scaling function varies fairly linearly in terms of the variablez=(p–p _c )s and this result is rather stable particularly bearing in mind the modestly available precision forp _c in higher dimensionalities.     

Collapse transition and cyclomatic number distribution of directed lattice animals

We computed the specific heat of directed lattice animals using a Monte Carlo method for various animals sizesN, withN up to 100 on the square andN up to 125 on the simple cubic lattices. The specific heat as a function of the temperature for various animal sizes exhibits peaks which seem to approach a collapse transition temperature monotonically from below with increasingN. A least square fit together with finite-size scaling then gives both the transition temperature T_c and the specific heat exponent for these two lattices. The cyclomatic number distributions for the number of animals with fixed animal sizeN are also calculated and these seem to obey a scaling law for largeN. On leave from Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing, China.     

Cluster numbers by series in directed percolation

Cluster numbersn _s from exact expansions for directed percolation in dimensions 2 to 4 are studied at various probability values. The main considerations as regards the asymptotic behaviour are that: $$(i) n_s \propto \exp ( - const s^Z ) for p< p_c (Z = 1) and p > p_c \left( {Z = 1 - \frac{1}{d}} \right).$$ (ii) at the critical thresholdn _s ～s ^?τ+1, although the data can only be reconciled with existing estimates for the exponent if the scaling ansatz is refined to include a first correction.     

Ticlopidine quantification in human plasma by high-performance liquid chromatography coupled to electrospray tandem mass spectrometry. Application to bioequivalence study

A rapid, sensitive and specific method to quantify ticlopidine in human plasma using clopidogrel as the internal standard (IS) is described. The analyte and the IS were extracted from acidified plasma by liquid-liquid extraction using diethyl ether-hexane (80 : 20, v/v). The extracts were analyzed by high-performance liquid chromatography coupled to electrospray tandem mass spectrometry (HPLC/MS/MS). Chromatography was performed isocratically on a Jones Genesis C(8) 4 microm analytical column (150 x 4.1 mm i.d.). The method had a chromatographic run time of 3.0 min and a linear calibration curve over the range 1.0-1000 ng ml(-1) (r(2) > 0.999427). The limit of quantification was 1.0 ng ml(-1). This HPLC/MS/MS procedure was used to assess the bioequivalence of two ticlopidine 250 mg tablet formulations (ticlopidine test formulation from Apotex do Brasil, Brazil, and Ticlid from Sanofi-Synthelabo, standard reference formulation). A single 250 mg dose of each formulation was administered to healthy volunteers. The study was conducted using an open, randomized, two-period crossover design with a 2 week washout interval. Since the 90% confidence interval for C(max) and area under the curve ratios were all inside the 80-125% interval proposed by the US Food and Drug Administration, it was concluded that ticlopidine formulation from Apotex do Brasil is bioequivalent to Ticlid formulation with respect to both the rate and the extent of absorption.     

A theoretical study of nonlinearity in heterocyclic hydrogen-bonded complexes

Ab initio calculations are performed at the MP2/6-311++G(d,p) and DFT/B3LYP/6-311++G(d,p) theoretical levels to obtain geometries, H-bond energies and harmonic infrared vibrational properties for the Cs symmetry structures of heterocyclic hydrogen-bonded complexes, CnHmY-HX. The H-bond lengths in DFT/B3LYP calculation level are in better agreement with the experimental values than the MP2 results. The geometry optimization are interpreted in terms of hydrogen bond nonlinearity represented by theta; and phi angles, once the hydrogen bond is formed among n-electrons pairs of the heteroatom in heterocyclic and the hydrogen atom in HX. The hydrogen bond energy after of the zero-point vibrational energy (ZPE) and basis set superposition error (BSSE) corrections are overestimated at DFT/B3LYP, whereas the MP2 BSSE corrections are very large than corresponding DFT/B3LYP. For example, the BSSE corrections for the C2H4S-HNC complex are 7.60 and 0.09 kJ mol(-1) in MP2 and DFT/B3LYP calculations levels, respectively. The new vibrational modes in infrared harmonic spectrum arising from complexation show several interesting features, especially the intermolecular stretching mode.     

Gold complexes with dithiothiophene ligands: a metal based on a neutral molecule

The gold complexes n-Bu4N[Au(alpha-tpdt)2] (5), n-Bu4N[Au(dtpdt)2] (4) and n-Bu4N[Au(tpdt)2] (6) based on new dithiothiophene ligands (alpha-tpdt= 2,3-thiophenedithiolate, dtpdt=2,3-dihydro-5,6-thiophenedithiolate and tpdt = 3,4-thiophenedithiolate) have been prepared and characterised. These gold(III) complexes are diamagnetic, but they can be oxidised with iodine to the paramagnetic compounds [Au(alpha-tpdt)2] (8), [Au(dtpdt)2] (7) and n-Bu4N[[Au(tpdt)2]n-2] (9), which were isolated as fine powders and which exhibit paramagnetic susceptibilities that are almost temperature independent with room temperature values of 2.5 x 10(-4), 2.0 x 10(-4) and 5 x 10(-4) emu x mol(-1), respectively. Interestingly, the neutral complex [Au(alpha-tpdt)2] (8) as a polycrystalline sample displays the properties of a metallic system with a room temperature electrical conductivity of 6 S x cm(-1) and a thermoelectric power of 5.5 microVK(-1); this is the first time that this metallic property has been observed in a molecular system based on a neutral species.     

Structural and vibrational characterisation of 3-amino-1-propanol a concerted SCF-MO ab initio, Raman and infrared (matrix isolation and liquid phase) spectroscopy study

Results obtained for the isolated and liquid 3-amino-1-propanol by a concerted molecular orbital and vibrational spectroscopic approach are reported. The relative energies and both structural and vibrational data of the different conformers of the studied compound were calculated using the extended 6-31G* basis set both at the HF-SCF and MP2 ab initio levels of theory and the theoretical results used to interpret Raman and infrared experimental data. In the gaseous phase and for the molecule isolated in an Argon matrix, monomeric 3-amino-1-propanol exists as a mixture of conformers, the first and second lowest energy forms corresponding to conformers which exhibit an intramolecular OH-N hydrogen bond (forms I and II). On the other hand, in the pure liquid, where intermolecular H-bonding occurs, the monomeric unit within the aggregates assumes a conformation similar to that of the third most stable form found for the isolated molecule situation (form III), which is characterised by having a weak intramolecular NH-O bond. The experimental data obtained for the pure liquid also reveals the presence of monomeric form I in this phase, a result that is in consonance with the strongly stabilizing OH-N intramolecular hydrogen bond that is present in this conformer.     

Distribution of the sizes of two dimensional lattice animals as a function of perimeter or energy

Cluster configurations grouped by perimeter and surface energy (measured in terms of boundary bonds) are investigated on the triangular lattice. It is shown that considerable departures from normality occur, at least for reasonably large perimeter values. The possible shape of the limiting distributions is clarified and their sensitivity to the suppression of internal holes discussed.On leave from: Centro de Fisica, Faculdade de Ciencias, Universidade de Porto, Portugal     

Syntheses and structures of molybdenum and tungsten pentabenzylcyclopentadienyl complexes: new chlorination reactions

[M(CpBz)(CO)₃CH₃] (M=Mo, 2a, W, 2b; CpBz=C₅(CH₂Ph)₅) have been prepared and reacted with PCl₅ and PhI · Cl₂. Depending on the metal and on the chlorinating reagent used [Mo(CpBz)(η²-COCH₃)Cl₃], 3, [W(CpBz)Cl₄], 4, [Mo(CpBz)(CO)₃Cl], 5 and [Mo(CpBz)Cl₄], 6 have been obtained. The molecular structures of all compounds are reported and two conformations have been characterised for the benzyl substituents. In complexes 2a, 2b and 5 one phenyl ring bends towards the metals while in 3 and 4 the five phenyls point opposite to the metals.     

Spectroscopic study of the water-soluble organic matter isolated from atmospheric aerosols collected under different atmospheric conditions

The composition of the water-soluble organic matter from fine aerosols collected in a rural location during two different meteorological conditions (summer and autumn) was investigated by UV-vis, synchronous fluorescence (with Δλ = 20 nm), FT-IR and CPMAS-¹³C NMR spectroscopies. A seasonal variation in the concentration of total carbon, organic carbon and water-soluble organic carbon was confirmed, with higher values during the autumn and lower values during the summer season. The chemical characterisation of the water-soluble organic matter showed that both samples are dominated by a high content of aliphatic structures, carboxyl groups and aliphatic carbons single bonded to one oxygen or nitrogen atom. However, the autumn sample exhibits a higher aromatic content than the summer sample, plus signals due to carbons of phenol, ketones and methoxyl groups. These signals were attributed to lignin breakdown products which are likely to be released during wood combustion processes. The obtained results put into evidence the major contribution of biomass burning processes in domestic fireplaces during low temperature conditions into both the concentration and the bulk chemical properties of the WSOC from fine aerosols.