The title reaction has been studied and it has been found that in the presence of oxygen a catalytic path for the oxidation of cysteine to cystine is established. The rate law is presented, and the mechanism is discussed on the basis of observed effects of the reagent concentrations on the extrapolated initial absorbance of the solution at 522 nm, and on the experimental pseudo-first-order rate of disappearance of colour. Cyanide ion has a remarkable influence on the course of the reaction.'rHE: ion pentacyanonitrosylferrate(2 -) (nitroprusside) is known to react with a wide variety of b a ~e s . l -~ Several types of interaction have been described, involving either direct reaction of the NO group with the incomiEg base or previous reaction with hydroxide ion to generate a reactive intermediate. In a number of cases, penta-c3.."x~onitritoferrate(Ris first generated by reaction wit 1-1 hydroxide and subsequently aquated .4Tlic reaction of cysteine with pentacyanonitrosylferrate(2-1 was first described over 40 years ago,5 and lias b t ~: ~ proposed as a test for this amino-acid. Reactions with other sulphur-containing bases have also beeu described, namely HS-,6 thioglycolic acid,7 other
Fe-doped synthetic geomimetic chrysotile nanocrystals represent a reference standard to investigate the health hazard associated with asbestos fibers and constitute interesting inorganic nanotubes for specific technological applications in light harvesting systems, optoelectronics and photonics. As the fiber toxicity is catalyzed by iron ions in specific crystallographic sites and the mechanical behaviour of synthetic chrysotile nanotubes is strongly affected by the iron doping extent, the characterization of Fe substitution to Mg and/or Si sites in the chrysotile structure appears highly important. By EPR, DRS spectroscopic analyses and magnetic investigations, Mg and/or Si ion replacement by Fe(3+) in a synthetic geomimetic chrysotile structure has been investigated. The results highlight that, as a function of the Fe doping extent and of the Fe doping process, iron can replace both Mg and Si sites. The contemporary iron substitution into the octahedral and tetrahedral sheets is associated with the presence of both of isolated Fe(3+) centres in high-spin 3d(5) configuration (S = 5/2, (6)A(1)((6)S)) in O(h) and T(d) symmetry and of intra-lattice clustered species. Increasing the Fe doping extent increases the concentration of aggregated species, while magnetic susceptibility confirms a paramagnetic anisotropy. The results allow to define the opportunity of using or not metallic Fe during the synthesis to obtain doped chrysotile nanocrystals with tailored morphological and structural properties suitable as a reference to study asbestos toxicity and apt to prepare new inorganic nanotubes and quantum wires for innovative technological applications.
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