The origin of sticking between a hydroperoxy radical and a water surface

An understanding of how gas-phase radicals in the earth's atmosphere become incorporated with liquid-phase cloud droplets is a vital part of understanding the chemical budgeting of these highly reactive species. Recent studies have suggested that hydroperoxy radicals (HO2) have an affinity for binding to a water surface. The calculations presented here are used to extricate the components of the attractive contribution of the intermolecular interactions that are responsible for the unusually strong binding between the hydroperoxy radical and a water surface. The analyses reveal that, for the binding of an HO2 radical to a water surface, the two water molecules nearest the radical are the most relevant to the bonding and the addition of other water molecules has little affect on the bonding between the radical and the two nearest waters. These results suggest that, once the HO2 is bound to the surface, the binding is a relatively local phenomenon. Identifying the properties responsible for the strong attraction is an important result that can be used to identify other radical systems whose chemistry might be impacted by the presence of water.     

Isodifferential derivative approach to the spectrophotometric determination of nickel and cobalt mixtures

A graphical method for measuring derivative amplitudes in binary mixtures with overlapping spectra is described. The method is based on the interference-free character of the isodifferential points in the derivative calibration graphs. Cobalt and nickel mixtures are analyzed in the range 0.01–2.5 μg ml^?1 by the formation of coloured chelates with benzyl-2-pyridylketone 2-pyridylhydrazone, with relative standard deviations ?1.5%.     

Evaluation and validation of commercially available enzyme-linked immunosorbent assays (ELISAs) specific for atrazine, chlorpyrifos, and diazinon in aqueous phase

The performance of commercially available microtiter plate enzyme-linked immunosorbent assays (ELISA) kits specific for the determination of triazines (atrazine), chlorpyrifos, and diazinon was evaluated for sensitivity, intra-assay repeatability, and accuracy using samples of known concentration in aqueous solution. Mean percent recovery values were not significantly different among concentrations for diazinon (One-way parametric ANOVA, P=0.46, n=72). However, mean percent recovery values were significantly different among concentrations for both atrazine and chlorpyrifos analyses (One-way parametric ANOVA, P<0.0001, n=36 for both analyses), and were highly dependent on concentrations for chlorpyrifos (% recovery=−0.155 (concentration)+238.448, r²=0.91, P<0.0001, n=36). All methods demonstrated a high degree of statistical separation between readings at various concentrations (One-way parametric ANOVA followed by Student-Neuman-Keuls (SNK) multiple range test, P<0.0001 for all analyses) and a close correlation between known concentrations and concentrations derived from ELISA for all three analytes (diazinon, r=0.985, P<0.0001, n=72; atrazine r=0.967, P<0.0001, n=36; chlorpyrifos r=0.947, P<0.0001, n=36). Statistical comparisons between known concentrations and concentrations derived from ELISAs showed that diazinon values were significantly (P<0.01, n=12 per concentration level) overestimated for all concentration levels. Chlorpyrifos concentrations were significantly (P<0.01, n=6 per concentration level) overestimated at lower concentrations and significantly (P<0.01, n=6 per concentration level) underestimated at higher concentrations. ELISA-derived atrazine concentrations were statistically similar to known concentrations for most concentration levels (P>0.05, n=6 per concentration level). Results indicate that ELISA kits are excellent for screening purposes, although consistent overestimation of ELISA for diazinon at all concentration levels and chlorpyrifos at lower concentrations levels must be resolved before the kits can be used routinely for regulatory compliance monitoring.     

1,3-bis(diarylmethylidene)-2-methylidenecyclohexanes in cycloaddition and cyclodimerization reactions. The role of stereoelectronic factors

Cycloaddition and cyclodimerization reactions of 1,3-dibenzylidene- and 1,3-bis(p-methoxybenzylidene)-2-methylidenecyclohexanes, i.e., the diaryltrienes with fixed S-cis-configurations of exocyclic double bonds are studied. These compounds undergo in situ cyclodimerization of the [4 + 2]-type upon dehydration of the precursor tertiary alcohols and form endo-adducts in the Diels-Alder reaction with N-phenylmaleimide. In the presence of CF3COOH, acid-catalyzed cyclodimerization takes place leading to methylidene-substituted spirocyclodimers, which undergo intramolecular cyclization upon prolonged contact with CF3COOH to form a fused carbocyclic system containing a central, 'three-petal' fragment of six-membered rings.     

Convergence and stability of implicit runge-kutta methods for systems with multiplicative noise

A class ofimplicit Runge-Kutta schemes for stochastic differential equations affected bymultiplicative Gaussian white noise is shown to be optimal with respect to global order of convergence in quadratic mean. A test equation is proposed in order to investigate the stability of discretization methods for systems of this kind. Herestability is intended in a truly probabilistic sense, as opposed to the recently introduced extension of A-stability to the stochastic context, given for systems with additive noise. Stability regions for the optimal class are also given.Partially supported by the Italian Consiglio Nazionale delle Ricerche.     

Assessment of murine neuroblastoma (N1E-115) resting membrane potential by confocal microscopy

Digital imaging (confocal microscopy) and a slow potentiometric dye (tetramethylrhodamine methyl ester) were used to assess the resting membrane potential (V _m) of murine neuroblastoma cells (N1E-115). The averageV _m was found to be –64.0±2.0 mV. The difference between this and the previously reported higher values was attributed to the use of glass microelectrode techniques that probably caused mechanical injury to the cell membranes: Digital imaging of N1E-115V _m was found to be sensitive, reproducible, fast, and simple.     

Polarographic study of a triazolobenzodiazepine: Estazolam

Summary The polarographic behaviour of 8-chloro-6-phenyl-4H-s-triazolo(4,3-a)-(1,4)-benzodiazepine (estazolam) was studied in the pH range 3–10. The reduction process is irreversible and the current is diffusion-controlled. The linear relationship between current and estazolam concentration permits its polarographic determination in the range 3.4·10^–7–1.0·10^–4 M. The detection limit was 1.7·10^–7 M. The reproducibility of the method in terms of its relative standard deviation was 1.00% and 1.14% using ten determinations at the 2.4·10^–5 M and 3.4·10^–6 M levels respectively.

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Polarographische Untersuchung des Triazolbenzodiazepins Estazolam

     

Porosity estimation of concrete by ultrasonic NDE

The increasing number of concrete structures with symptoms of premature deterioration due to environmental action demands procedures to estimate the durability of this type of component. Concrete durability is related to porosity, which determines the intensity of interactions of the material with aggressive agents. The pores and capillaries inside the structure facilitate the destructive processes that generally begin in the surface. In this work, an ultrasonic NDE technique to estimate the porosity of concrete is developed. The method is based on the analysis of the mechanical behaviour of mortar probes built with calibrated sand, in which the concentration of water-cement mixture has been varied. In this sense, data of sound velocity are correlated with data of porosity, which have been previously measured by destructive measurements.