Selective detection of cyanogen halides by BN nanocluster: a DFT study.

The electronic sensitivity and adsorption behavior toward cyanogen halides (X-CN; X = F, Cl, and Br) of a B12N12 nanocluster were investigated by means of density functional theory calculations. The X-head of these molecules was predicted to interact weakly with the BN cluster because of the positive σ-hole on the electronic potential surface of halogens. The X-CN molecules interact somewhat strongly with the boron atoms of the cluster via the N-head, which is accompanied by a large charge transfer from the X-CN to the cluster. The change in enthalpy upon the adsorption process (at room temperature and 1 atm) is about -19.2, -23.4, and -30.5 kJ mol-1 for X = F, Cl, and Br, respectively. The LUMO level of the BN cluster is largely stabilized after the adsorption process, and the HOMO-LUMO gap is significantly decreased. Thus, the electrical conductivity of the cluster is increased, and an electrical signal is generated that can help to detect these molecules. By increasing the atomic number of X, the signal will increase, which makes the sensor selective for cyanogen halides. Also, it was indicated that the B12N12 nanocluster benefits from a short recovery time as a sensor.

Dark-field oxidative addition-based chemosensing: new bis-cyclometalated PtII complexes and phosphorescent detection of cyanogen halides.

Heavy metal complexes that are phosphorescent at room temperature are becoming increasingly important in materials chemistry, principally due to their use in phosphorescent organic light-emitting devices (OLEDs). Their use in optical sensory schemes, however, has not been heavily explored. Homoleptic bis-cyclometalated Pt(II) complexes are known to undergo oxidative addition with appropriate electrophiles (principally alkyl halides) by either thermal or photochemical activation. We have applied this general reaction scheme to the development of a phosphorescence-based sensing system for cyanogen halides. To carry out structure-property relationship studies, a series of previously unreported Pt(II) complexes was prepared. Most of the complexes (excluding those that incorporated substituents on the ligands that forced steric crowding in the square plane) were strongly orange-red phosphorescent (Phi = 0.2-0.3) in a room-temperature oxygen-free solution. These sterically demanding ligands also accelerated the addition of cyanogen bromide to these complexes but slowed the addition of methyl iodide, indicating that the oxidative addition mechanisms for these two electrophiles is different. The lack of solvent-polarity effect on the addition of BrCN suggests a radical mechanism. Oxidative addition of BrCN to the metal complexes in solution or dispersed in poly(methyl methacrylate) gave blue-shifted emissive Pt(IV) complexes. The blue-shifted products give a dark-field sensing scheme that is in sharp contrast to energy transfer-based sensing schemes, which have limited signal-to-noise because of the presence of lower-energy vibronic bands of the energy donor that can overlap with the emission of the acceptor.

Quantification of aqueous cyanogen chloride and cyanogen bromide in environmental samples by MIMS.

Membrane introduction mass spectrometry (MIMS) was developed and verified for the direct quantification of cyanogen chloride (CNCl) and cyanogen bromide (CNBr) in environmental samples without any sample workup. Factors including the membrane temperature and the liquid flow rates were examined for system optimization. The MIMS method provided linear responses for three orders of magnitude of concentrations. The instrument detection limits of CNCl and CNBr were 1.2 and 3.8 microg/L, respectively, and the method detection limits of CNCl and CNBr were both 1.7 microg/L. Effects of pH and the water matrix including synthetic water, saline water, natural surface water, and wastewater, on the responses were also examined. A pH ranging from 3 to 10 did not affect the quantification. The average recoveries of CNCl and CNBr in the water matrixes tested were 98.5% and 92.7%, respectively. The use of the MIMS method in on-line monitoring of the formation of cyanogen halide was demonstrated in chlorination of aqueous solutions containing glycine and bromide ions. The results indicated the important role of bromide ions in cyanogen halide speciation.

Simultaneous determination of cyanogen chloride and cyanogen bromide in treated water at sub-microg/L levels by a new solid-phase microextraction-gas chromatographic-electron-capture detection method.

A headspace solid-phase microextraction (HS-SPME) procedure has been developed and applied for the determination of cyanogen halides in treated water samples at microg/L concentrations. Several SPME coatings were tested, the divinylbenzene-Carboxen-polydimethylsiloxane fiber being the most appropriate coating. GC-electron-capture detection was used for separation and quantitation. Experimental parameters such as sample volume, addition of a salt, extraction time and desorption conditions were studied. The optimized method has an acceptable linearity, good precision, with RSD values <10% for both compounds, and it is sufficiently sensitive to detect ng/L levels. HS-SPME was compared with liquid-liquid microextraction (US Environmental Protection Agency Method 551.1) for the analysis of spiked ultrapure and granular activated carbon filtered water samples. There was good agreement between the results from both methods. Finally, the optimized procedure was applied to determine both compounds at the Barcelona water treatment plant (N.E. Spain). Cyanogen chloride in treated water was <1.0 microg/L and cyanogen bromide ranged from 3.2 to 6.4 microg/L.

Dilated cardiomyopathy is associated with an increase in the type I/type III collagen ratio: a quantitative assessment.

OBJECTIVES: The aim of this study was to quantify total collagen and the type I/type III collagen ratio and their localization in hearts with dilated cardiomyopathy. BACKGROUND: Patients with dilated cardiomyopathy have an increase in intramyocardial fibrillar collagen. Types I and III are the main constituents and have different physical properties that may affect cardiac compliance. METHODS: Nineteen hearts with dilated cardiomyopathy were studied (17 cardiac explants, 2 hearts obtained at autopsy) and compared with reference hearts. Total collagen was determined by hydroxyproline analysis. Collagen types I and III were analyzed using the cyanogen bromide method and immunohistochemical analysis followed by microdensitophotometric quantification. Localization of collagen types I and III was established at the light and electron microscopic levels. Immunoelectron microscopy provided information regarding their localization. RESULTS: Total collagen and the collagen type I/type III ratio were increased in hearts with dilated cardiomyopathy (p < 0.05). Electron microscopy showed a diffuse increase in collagen fibrils in the endomysium; the perimysium showed an inhomogeneous increase. Collagen fibrils were thicker, and fibrous long-spacing collagen occurred in the endomysium. Immunoelectron microscopic findings confirmed an increase in type I collagen. CONCLUSIONS: Hearts with dilated cardiomyopathy have a statistically significant increase in the collagen type I/type III ratio. The changes occur in the endomysium and perimysium, although with differences in distribution. These changes in intramyocardial collagen may be clinically relevant because they may affect cardiac rigidity and, therefore, eventually may render the heart less compliant. Further studies are needed to evaluate at what point in the course of the disease these changes appear.

ADP-induced platelet aggregation depends on the conformation or availability of the terminal gamma chain sequence of fibrinogen. Study of the reactivity of fibrinogen Paris 1.

Fibrinogen Paris I contains a mutant gamma chain that is longer than the normal chain, resulting in altered fibrin polymerization and cross-linking. Because these functions involve the carboxy-terminal region of the gamma chain, we decided to determine whether fibrinogen Paris I or the isolated Paris I gamma chain supports normal ADP-induced platelet aggregation, a function that requires the ultimate 12 residues of the normal gamma chain (400 through 411). Aggregation of ADP-stimulated normal platelets was defective with fibrinogen Paris I and markedly depressed with the gamma Paris I chain. These findings prompted us to characterize the carboxy-terminal structure of the region of the gamma Paris I chain responsible for this activity. The carboxy-terminal cyanogen bromide (CNBr) peptide of the normal gamma chain (385 through 411) or that from gamma Paris I was isolated by differential adsorption to triethylene-tetramine resin or by reverse-phase high-performance liquid chromatography (HPLC). The CNBr peptide from the Paris I gamma chain was identical to that of the normal gamma chain in its retention time on HPLC, its amino acid composition, and its sequence. Thus, the primary structure of the gamma Paris I chain from residue 384 through 411 is normal, indicating that a peptide insertion has occurred upstream from residue 384, resulting in an impairment of those physiologic functions attributable to the carboxy-terminal end of the gamma chain from position 384 (ie, cross-linking, ADP-induced platelet aggregation, and at least a portion of the gamma chain polymerization site). These observations demonstrate that the gamma chain platelet recognition site in the fibrinogen molecule is necessary but not alone sufficient to support normal ADP-induced platelet aggregation. There appears to be an additional requirement for normal conformation of the gamma chain or availability of its terminal sequence during the interaction of fibrinogen with platelets.

Destruction of cyanogen bromide and inorganic cyanides.

Cyanogen bromide in water and seven organic solvents and sodium cyanide in water may safely and efficiently (greater than 99.7%) be destroyed using sodium hydroxide (1 M) solution and commercially available sodium or calcium hypochlorite. Details are given of an analytical procedure which can be used to check the final reaction mixture for the presence of residual cyanogen bromide or cyanide.

Structural studies on yeast 3-phosphoglycerate kinase. Linear arrangement of the CNBr fragments, partial amino acid sequence of the inner part of the polypeptide chain, and analyses of the N-terminal domain of the protein.

The purpose of this work was to contribute to the study of the covalent structure of yeast 3-phosphoglycerate kinase. First, we undertook the complete alignment of the four fragments produced by cyanogen-bromide cleavage and which constitute the intact protein; we then established the total amino acid sequence of a 30-residue peptide and the N-terminal sequence of a 65-residue peptide. Second, we analyzed the acetylated state of the protein. The analyses of the acid fraction "P" obtained after digestion of 3-phosphoglycerate kinase by pronase enabled us to determine the N-terminal sequence of this enzyme as N-acetylserylglycine. Third, we isolated, purified and analyzed seven tryptic peptides from a fragment containing 102 amino acids coming from the N-terminal end of the protein. The peptides occupying the N- and C-terminal ends of this fragment were also identified.

Basement membranes: structural and biosynthetic considerations.

Basement membranes are extracellular matrices synthesized by a variety of cells including the basal cells of the epidermis; the respiratory, gastrointestinal, and glandular epithelium; the capillary endothelium; the epithelial cells of the glomerulus, the renal tubule, and the lens capsule; and the endothelium of Descemet's membrane. Basement membranes in the mature animal are free of lipids, DNA, and proteoglycans and are composed of dissimilar protein subunits. One of these is a procollagen-like molecule associated with a noncollagenous matrix glycoprotein. The proportion of the latter component varies among basement membranes. These various subunits are stabilized by hydrogen bonds, disulfide bonds, and aldehyde-derived cross-links which are so extensive that they render the basement membranes highly insoluble. Immunochemical studies indicate three distinct antigenic components which correspond to the collagenous moiety, its nonhelical extension, and the matrix glycoprotein. The collagen component of basement membranes, free of the nonhelical extension, is composed of three identical alpha-chains. It is highly rich in hydroxylysine, 3- and 4-hydroxyproline and contains 4 to 8 residues of half-cystine. It contains 38 residues of glucosyl-galactosyl-hydroxylysine per chain and minimal amounts of mannose, glucosamine, and fucose. Newly synthesized basement membrane collagen is secreted in the extracellular space as the precursor molecule "procollagen." This molecule does not undergo conversion to collagen but interacts with the matrix glycoprotein to give rise to the appropriate structure.