Is the Filinov integral conditioning technique useful in semiclassical initial value representation methods?

The utility of the Filinov integral conditioning technique, as implemented in semiclassical initial value representation (SC-IVR) methods, is analyzed for a number of regular and chaotic systems. For nonchaotic systems of low dimensionality, the Filinov technique is found to be quite ineffective at accelerating convergence of semiclassical calculations since, contrary to the conventional wisdom, the semiclassical integrands usually do not exhibit significant phase oscillations in regions of large integrand amplitude. In the case of chaotic dynamics, it is found that the regular component is accurately represented by the SC-IVR, even when using the Filinov integral conditioning technique, but that quantum manifestations of chaotic behavior was easily overdamped by the filtering technique. Finally, it is shown that the level of approximation introduced by the Filinov filter is, in general, comparable to the simpler ad hoc truncation procedure introduced by Kay.     

UVA-ketoprofen-induced hemoglobin radicals detected by immuno-spin trapping

Ketoprofen (3-benzoyl-alpha-methylbenzeneacetic acid, KP) is a widely used nonsteroidal anti-inflammatory drug (NSAID) that causes both phototoxicity and photoallergy. Here, we investigated the formation of hemoglobin radicals, in both purified hemoglobin and red blood cells (RBC), induced by ultraviolet A (UVA)-KP by using "immuno-spin trapping," a novel approach that combines the specificity of spin trapping with the sensitivity of antigen-antibody interactions. The methemoglobin (metHb) radicals react covalently with 5,5-dimethyl-1-pyrroline N-oxide (DMPO) to form nitroxyl radical adducts that are oxidized to the corresponding nitrone adducts, which in turn are specifically recognized by antiserum against DMPO nitrone. We found that the formation of nitrone adducts in metHb depended on the UVA dose, the KP concentration and the presence of DMPO, as determined by enzyme-linked immunosorbent assay and Western blotting. Adduct formation decreased when irradiation was carried out in the presence of catalase or nitrogen, suggesting that H2O2 plays a key role in KP-UVA-induced metHb radical formation. KP in the dark did not generate metHb radical-derived nitrone adducts, whereas UVA alone resulted in the formation of metHb radical-derived nitrone adducts that increased with UVA dose from 4 to 10 J/cm2. However, KP (25 and 200 microM) plus UVA (4 and 10 J/cm2) resulted in a significant increase in the formation of metHb radical-derived nitrone adducts as compared with UVA or KP alone, indicating that KP photosensitized the production of the metHb radicals in the presence of UVA. In contrast, no metHb radical-derived nitrone adduct was detected in the absence of DMPO, even though KP and UVA were present. We also detected the hemoglobin radical formation in RBC as well as in hemolysates. The endogenous antioxidants and exogenous reduced glutathione inhibited the protein radical formation. These studies have shown that the immuno-spin-trapping technique can be used to detect radical damage in proteins as a result of photosensitizing reactions. The successful detection of protein radical formation caused by KP photosensitization could help further understand the photoallergic effect of this NSAID.     

Synthesis of N,N-Dialkyl-N'-arylhydrazines via palladium-catalyzed N-arylation by using N,N-dialkylhydrazines/2LiCl adducts

[reaction: see text] The reaction of N,N-dialkylhydrazine/2LiCl adducts with aryl bromides in the presence of Pd(2)(dba)(3) as the palladium source, Xantphos or X-phos as the ligands, toluene as the solvent, and NaOBu-t as the base provides an efficient route to N,N-dialkyl-N'-arylhydrazines. Best results were obtained by using N,N-dialkylhydrazine/2LiCl adducts prepared in situ, omitting their isolation.     

A conductive metal–organic framework photoanode

We report the development of photosensitizing arrays based on conductive metal–organic frameworks (MOFs) that enable light harvesting and efficient charge separation. Zn₂TTFTB (TTFTB = tetrathiafulvalene tetrabenzoate) MOFs are deposited directly onto TiO₂ photoanodes and structurally characterized by pXRD and EXAFS measurements. Photoinduced interfacial charge transfer dynamics are investigated by combining time-resolved THz spectroscopy and quantum dynamics simulations. Sub-600 fs electron injection into TiO₂ is observed for Zn₂TTFTB–TiO₂ and is compared to the corresponding dynamics for TTFTB–TiO₂ analogues that lack the extended MOF architecture. Rapid electron injection from the MOF into TiO₂ is enhanced by facile migration of the hole away from the interfacial region. Holes migrate through strongly coupled HOMO orbitals localized on the tetrathiafulvalene cores of the columnar stacks of the MOF, whereas electrons are less easily transferred through the spiral staircase arrangement of phenyl substituents of the MOF. The reported findings suggest that conductive MOFs could be exploited as novel photosensitizing arrays in applications to slow, and thereby make difficult, photocatalytic reactions such as those required for water-splitting in artificial photosynthesis.

We report the development of photosensitizing arrays based on conductive metal–organic frameworks (MOFs) that enable light harvesting and efficient charge separation.     

Multicenter validation of PCR-based method for detection of Salmonella in chicken and pig samples

As part of a standardization project, an interlaboratory trial including 15 laboratories from 13 European countries was conducted to evaluate the performance of a noproprietary polymerase chain reaction (PCR)-based method for the detection of Salmonella on artificially contaminated chicken rinse and pig swab samples. The 3 levels were 1-10, 10-100, and 100-1000 colony-forming units (CFU)/100 mL. Sample preparations, including inoculation and pre-enrichment in buffered peptone water (BPW), were performed centrally in a German laboratory; the pre-PCR sample preparation (by a resin-based method) and PCR assay (gel electrophoresis detection) were performed by the receiving laboratories. Aliquots of BPW enrichment cultures were sent to the participants, who analyzed them using a thermal lysis procedure followed by a validated Salmonella-specific PCR assay. The results were reported as negative or positive. Outlier results caused, for example, by gross departures from the experimental protocol, were omitted from the analysis. For both the chicken rinse and the pig swab samples, the diagnostic sensitivity was 100%, with 100% accordance (repeatability) and concordance (reproducibility). The diagnostic specificity was 80.1% (with 85.7% accordance and 67.5% concordance) for chicken rinse, and 91.7% (with 100% accordance and 83.3% concordance) for pig swab. Thus, the interlaboratory variation due to personnel, reagents, thermal cyclers, etc., did not affect the performance of the method, which will be proposed as part of a developing international PCR standard.     

The Cα?C internal rotation in α-alkyl substituted carbonyls and thiocarbonyls: CH(CH3)2C(X)YH (X,Y O or S)

The C_α? C internal rotation in 2-methylpropionic, 2-methylthiopropionic (thiol and thion forms) and 2-methyldithiopropionic acids was studied by the ab initio SCF-MO method using 3-21G and 3-21G + d(0.65S) basis sets. Energies and structures of several conformations of these molecules, determined by gradient geometry refinement, are reported and used to assess the effects of oxygen-by-sulphur substitution on molecular properties. The nature and relative importance of intramolecular interactions involving both the α-methyl substituents and the C(?X)Y (X, Y? O or S) fragment are also discussed.     

Determination of cadmium in indium phosphide by electrothermal atomic absorption spectrometry and ion-selective electrode potentiometry

 Two independent methods for the determination of cadmium in cadmium-doped indium phosphide have been developed. Electrothermal atomic absorption spectrometry (ETAAS) utilized both platform atomization and a chemical modifier composed of magnesium nitrate and orthophosphoric acid. As the matrix mass was found to influence the cadmium sensitivity, matrix matched calibration standards were necessary. The detection limit (3s_B) is 0.20 μg/g for a 100 mg sample. The electrochemical method employed a solid-state cadmium sulfide-silver sulfide electrode as potentiometric sensor. An excess of indium (III) influenced the electrode response. A preliminary chelation-extraction of indium with acetylacetone at pH 5.0 in acetate buffer overcame the interference. The detection limit of the ISE-potentiometric method is 10 μg/g for a 200 mg sample. Two indium phosphide single crystals grown from melts doped with cadmium sulfide or cadmium telluride were analyzed for their cadmium content. Received: 27 August 1996/Revised: 27 January 1997/Accepted: 30 January 1997     

Silicon polypodands: a new class of efficient solid-liquid phase-transfer catalysts

Silicon polypodands 1-7 were found to be powerful complexing agents of alkali metal salts, even in low polarity media (chlorobenzene) and hence very efficient phase-transfer catalysts. Their catalytic activity was measured in typical anion-promoted reactions under solid-liquid phase-transfer catalysis (SL-PTC) conditions. It is mainly determined by the complexing ability of the ligand, increasing with the number of silicon atoms and binding sites. Comparison with traditional phase-transfer catalysts showed that these polypodands are better catalysts not only than open-chain PEG400Me₂ and TRIDENT, but even than more sophisticated macrocyclic polyethers such as DCH18C6.     

Nitric oxide interaction with cytochrome c' and its relevance to guanylate cyclase. Why does the iron histidine bond break?

Soluble guanylate cyclase (sGC), the mammalian receptor for nitric oxide (NO), is a heme protein with a histidine as the proximal ligand. Formation of a five-coordinate heme-NO complex with the associated Fe-His bond cleavage is believed to trigger a conformational change that activates the enzyme and transduces the NO signal. Cytochrome c' (cyt c') is a protobacteria heme protein that has several similarities with sGC, including the ability to form a five-coordinate NO adduct and the fact that it does not bind oxygen. Recent crystallographic characterization of cyt c' from Alcaligenes xylosoxidans (AXCP) has yielded the discovery that exogenous ligands are able to bind to the Fe center from either side of the porphyrin plane. In this paper, we explore the molecular basis of the NO interaction with AXCP using hybrid quantum-classical simulation techniques. Our results suggest that Fe-His bond breaking depends not only on the iron-histidine bond strength but also on the existence of a local minimum conformation of the protein with the histidine away from the iron. We also show that AXCP is a useful paradigm for NO interaction with heme proteins, particularly regarding the activation/deactivation mechanism of sGC. The results presented here fully support a recently proposed model of sGC activation in which NO is not only the iron ligand but also catalyzes the activation step.     

Threefolds in ℙ5 with a 3-dimensional family of plane curveswith a 3-dimensional family of plane curves

A classification theorem is given of smooth threefolds of ?⁵ covered by a family of dimension at least three of plane integral curves of degreed≧2. It is shown that for such a threefoldX there are two possibilities:

1. X is any threefold contained in a hyperquadric;
2. d≦3 andX is either the Bordiga or the Palatini scroll.