Kinetic study of the reaction between iodide and N-chloramines

We carried out a kinetic study of the reaction between iodide ion and various primary N-chloramines and found it to be first-order in the latter. Experiments also showed the rate constant for the reaction to be directly proportional to the iodide and hydrogen ion concentrations. The influence of the buffer concentration reveals the presence of general acid catalysis processes. © 1996 John Wiley & Sons, Inc.     

A Spectroscopy-based Methodology for Rapid Screening and Characterization of Phytochrome Photochemistry in Search of Pfr-favored Variants

Phytochromes are photosensitive proteins with a covalently bound open-chain chromophore that can switch between two principal states: red light absorbing Pr and far-red light absorbing Pfr. Our group has previously shown that the bacteriophytochrome from Xanthomonas campestris pv. campestris (XccBphP) is a bathy-like phytochrome that uses biliverdin IXα as a co-factor and is involved in bacterial virulence. To date, the XccBphP crystal structure could only be solved in the Pr state, while the structure of its Pfr state remains elusive. The aims of this work were to develop an efficient screening methodology for the rapid characterization and to identify XccBphP variants that favor the Pfr form. The screening approach developed here consists in analyzing the UV-Vis absorption behavior of clarified crude extracts containing recombinant phytochromes. This strategy has allowed us to quickly explore over a hundred XccBphP variants, characterize multiple variants and identify Pfr-favored candidates. The high-quality data obtained enabled not only a qualitative, but also a quantitative characterization of their photochemistry. This method could be easily adapted to other phytochromes or other photoreceptor families.     

碳和硼的笼状原子簇及其关系

碳笼烯C_(60)的发现及碳笼烷C-(60)H_(60)的制备,激励人们去探索合成新的碳元素类似物和其它元素的类似物。本文利用碳和硼的笼型烷烃的化学键和几何特征,讨论碳和硼的笼状原子簇骨架的共轭关系,推导其中一些高对称化合物的原子数和几何结构,并讨论其稳定性。 1 碳和硼的笼状原子簇骨架的共轭关系     

Kinetics of the formation,decomposition, and disproportionation reactions of N-chlorobutylamines

The formation of N-chlorobutylamines is a reaction of order one with respect to hypochlorite and amine, and order ?1 with respect to OH^?. Kinetic studies show that N-chlorobutylamines undergo decomposition in basic aqueous media, and disproportination (with formation of N,N-dichloramines) in acidic media, mechanisms are put forward for both these processes. © 1995 John Wiley & Sons, Inc.     

Use of Experimental Design to Develop a Method for Analysis of 1,3-Dichloropropene Isomers in Water by HS-SPME and GC–ECD

A simple and reliable method has been established for determination of cis and trans-1,3-dichloropropene (1,3-DCP) in water by headspace solid-phase microextraction (HS-SPME) then GC–ECD. An experimental design with two steps was performed to determine the best experimental conditions for extraction of the 1,3-DCP isomers. First, a 2⁶⁻² fractional factorial design was conducted to screen for significant conditions. Second, a central composite design (CCD) was performed to optimise the variables. The best experimental extraction conditions were: polydimethylsiloxane–divinylbenzene (PDMS–DVB)-coated fibre, 20-min extraction time, 12 °C extraction temperature, 300 g L⁻¹ NaCl, and 20 mL headspace volume in 40-mL vial. Under these conditions the method detection limit (MDL) was 0.5 ng L⁻¹ for cis-1,3-DCP and 1.0 ng L⁻¹ for trans-1,3-DCP. The method quantification limit (MQL) was 1.2 ng L⁻¹ for cis-1,3-DCP and 3.0 ng L⁻¹ for trans-1,3-DCP. For both isomers the relative standard deviation (RSD) for analysis of 50 ng L⁻¹ or 0.5 μg L⁻¹ of the isomer mixture was less than 8%. When the proposed method was applied to surface (river) water and tapwater samples from Gipuzkoa province (Spain) the target analytes were not detected. The method was also used to investigate the presence of the isomers in leachates from agricultural soil. A mixed solution was added to samples of two different soils and 1,3-DCP isomers were quantified in leachate obtained from the samples.     

Study of the acid–base properties of fulvic acid-like substances extracted from senescent leaves of eucalyptus and oak

The acid-base properties of two fulvic acids (FA) extracted from senescent leaves of eucalyptus and oak were characterized by carrying out potentiometric titrations at two FA concentrations and four ionic strengths (0.005 M <[KNO(3)] <1.0 M). Experimental data were analyzed by means of the master curve approach, which includes an electrostatic spherical double layer model, and the Langmuir-Freundlich isotherm was used to fit the data. The contribution of the electrostatic effect to the proton binding reaction was lower than that observed for soil fulvic acids. The chemical heterogeneity of both samples was described by two acid sites with p Ks of about 4 and 7.5, the most abundant being the carboxylic site of p K = 4.     

3He(e,e′pp) and 3He(e,e′pn) reactions at AmPS and MAMI

This paper reports on measurements of the ³He(e,e′pp) reaction measured at AmPS and the ³He(e,e′pn) reaction measured at MAMI. The measurements were performed in similar kinematics to allow a comparison to be made between the cross sections of the two reactions. Results are shown for both reactions together with a comparison for the ³He(e,e′pp) data with continuum Faddeev calculations.     

The kinetics and mechanism of the decomposition of N-chloroleucine

At 298 K the rate constant for the decomposition of N-chloroleucine has the constant value 3.20 × 10⁻⁴ s⁻¹ over the range pH 5–12, increases with increasing acidity at pH < 5, and increases with pH at pH > 12. A mechanism is put forward which explains these results.