Self-assembly of nanoparticles on the surface of ionic crystals: Structural properties

With a suitable combination of ligand-stabilised nanoparticle suspension and ionic salt solutions, it is possible to produce microcrystals that are coated with nanoparticles. The self-assembly process of coating microcrystals by gold nanoparticles (NP) is mediated by the crystal lattice. This is the so-called CLAMS process - a generic process for self-organisation of nanoparticles on the surface of crystals [M. Murugeshan, D. Cunningham, J.-L. Martnez-Albertos, R. Vrcelj, B.D. Moore, Chem. Commun. (2005) 2677]. We are exploring here the structural properties of these self-assembled structures by using different imaging techniques.     

An Efficient Route to Phenylselenoethers in the Presence of Ag2O

An efficient protocol for the preparation of phenylselenoethers from unsaturated alcohols using phenylselenenyl halides at room temperature was developed. The procedure employs phenylselenenyl chloride and bromide, some Δ ⁴- and Δ ⁵-alkenols and Ag₂O, as an additive, to generate the tetrahydropyrans or tetrahydrofurans. This method permits the preparation of cyclic phenylselenoethers in high yields and under extremely mild conditions.     

Mechanism of inactivation of inducible nitric oxide synthase by amidines. Irreversible enzyme inactivation without inactivator modification

Nitric oxide synthases (NOS) are hemoproteins that catalyze the reaction of L-arginine to L-citrulline and nitric oxide. N-(3-(Aminomethyl)benzyl)acetamidine (1400W) was reported to be a slow, tight-binding, and highly selective inhibitor of iNOS in vitro and in vivo. Previous mechanistic studies reported that 1400W was recovered quantitatively after iNOS fully lost its activity and modification to iNOS was not detected. Here, it is shown that 1400W is a time-, concentration-, and NADPH-dependent irreversible inactivator of iNOS. HPLC-electrospray mass spectrometric analysis of the incubation mixture of iNOS with 1400W shows both loss of heme cofactor and formation of biliverdin, as was previously observed for iNOS inactivation by another amidine-containing compound, N5-(1-iminoethyl)-L-ornithine (L-NIO). The amount of biliverdin produced corresponds to the amount of heme lost by 1400W inactivation of iNOS. A convenient MS/MS-HPLC methodology was developed to identify the trace amount of biliverdin produced by inactivation of iNOS with either 1400W or L-NIO to be biliverdin IXalpha out of the four possible regioisomers. Two mechanisms were previously proposed for iNOS inactivation by L-NIO: (1) uncoupling of the heme peroxide intermediate, leading to destruction of the heme to biliverdin; (2) abstraction of a hydrogen atom from the amidine methyl group followed by attachment to the heme cofactor, which causes the enzyme to catalyze the heme oxygenase reaction. The second mechanistic proposal was ruled out by inactivation of iNOS with d3-1400W, which produced no d2-1400W. Detection of carbon monoxide as one of the heme-degradation products further excludes the covalent heme adduct mechanism. On the basis of these results, a third mechanism is proposed in which the amidine inactivators of iNOS bind as does substrate L-arginine, but because of the amidine methyl group, the heme peroxy intermediate cannot be protonated, thereby preventing its conversion to the heme oxo intermediate. This leads to a change in the enzyme mechanism to one that resembles that of heme oxygenase, an enzyme known to convert heme to biliverdin IXalpha. This appears to be the first example of a compound that causes irreversible inactivation of an enzyme without itself becoming modified in any way.     

Precipitation and recrystallization of uniform CuCl particles formed by aggregation of nanosize precursors

Uniform, spherical CuCl particles were obtained by mixing aqueous solutions of CuCl ₂ and ascorbic acid in the presence of polyvinylpyrrolidone (PVP) as dispersing agent. The size and the uniformity of the resulting particles depended on the volume ratio of the reactant solutions, their concentrations, the distribution of the stabilizers, and the mixing method. The single jet precipitation yielded large spheres of broad size distributions, while the particles obtained by the double jet technique were rather uniform in size. The final colloidal CuCl particles were formed by the aggregation of nanocrystals, initially generated in the system. Depending on the pH of the reaction mixture, these particles slowly change to large CuCl crystals on aging in the mother liquor.     

Spectrophotometric method for the determination of demeclocycline using sodium molybdate as analytical reagent

By means of spectroscopic methods it has been found that demeclocycline reacts with molybdate ions forming a complex compound [MoO₃HDMTC]^2–. The relative stability constant of this compound has been determined by applying spectrophotometric methods. Under optimum conditions for complex formation a very sensitive spectrophotometric method for the estimation of demeclocycline in the concentration range 5.0–35.1 g/ml is proposed. The detection limit of the method is 2.5 g/ml of demeclocycline. The relative standard deviation (n=10) varies between 0.76% and 1.46%. The method proved to be accurate and sensitive for the analysis of the demeclocycline content in tablets.