Cyanide reaction with ninhydrin: elucidation of reaction and interference mechanisms.

A new sensitive spectrophotometric method has recently been developed for the trace determination of cyanide with ninhydrin. Cyanide ion was supposed to act as a specific base catalyst. Nevertheless, this paper demonstrates that the reported assay is based on a novel reaction of cyanide with 2,2-dihydroxy-1,3-indanedione, which affords purple or blue colored salts of 2-cyano-1,2,3-trihydroxy-2H indene. Hydrindantin is merely an intermediary of the reaction. The formation of a stable and isolable ninhydrin-cyanide compound has been confirmed by its preparation in crystalline form. Also, it is thoroughly characterized by elemental as well as MS, IR, UV/VIS and 1H NMR analyses. The Ruhemann's sequence of reactions of cyanide with ninhydrin has been reconsidered and an adequate mechanism of the reaction is proposed. As a consequence, the interference of oxidizers as well as copper, silver and mercury ions with the cyanide determination has been elucidated.     

Polysilane‐Cycloimmonium Salts: New Materials for Organic Semiconductors

Summary: This work presents the first synthesis of a new polymer obtained by catalytic addition of the Si H groups of a poly[methyl(H)silane‐co‐methylphenylsilane] backbone to an N‐(allyl)cycloimmonium salt. This hybrid polymer was characterized by spectroscopic analysis, thermogravimetric analysis and gel‐permeation chromatography (GPC). The pendant N‐(allyl)cycloimmonium segments lead to the formation of molecular dipoles, as evidenced by electrical polarization experiments.

Structure of the polysilane‐cycloimmonium salt.     

Heat affected zones in polymer laser marking

Laser marking is based on the laser heating of the subjected material, the heating being below the melting temperature or thermal degradation starting point. Within and nearby the mark, the material is chemically, physically and mechanically affected. This means that the main characteristics are changing in such a way that the material is ageing. Thermal and mechanical analysis can be used to determine the modification of the material, which is important and necessary to know for predicting its use lifetime. This paper investigates the physical and mechanical modification of the polymer HDPE100, when laser marking is applied. Burst stress, elongation and relaxation modulus were determined for the base material, within the heat affected zone and within the laser burned mark. Information on the crystallization rate and on the elongation viscosity is also reported. According to the results, the polyethylene has very fast crystallization and that affects the marking process if lower than appropriate maintaining during heating process is applied. It becomes stabile after 0.23 min, when it is tested at 103 °C. The elongation viscosity was analysed and values of 10⁵ Pa s were recorded for 10 s, which is a usual time of applying pressure. The performed analysis revealed about 10 % difference between the relaxation modulus of the irradiated and non-irradiated HDPE.     

Self-assembled architecture based on triiron-substituted polyoxomolybdate anion and positively charged polymer

A new self-assembled multilayer architecture was constructed by successive deposition of poly(4-vinylpyridine) partially quaternized with ethylamine (B) and Keggin trilacunary polyoxomolybdate [Aα-PFe₃^III(H₂O)₃Mo₉O₃₇]⁶⁻ (PFe₃Mo₉) on the Au electrode surface, covered with 3-mercapto-1-propanesulfonic acid (MPS). Surface plasmon resonance and cyclic voltammetry measurements were performed at Au/MPS/B/PFe₃Mo₉/B interface in order to investigate the structure and the electrochemical behavior of this electrode. Due to the presence of PFe₃Mo₉, the Au/MPS/B/PFe₃Mo₉/B-modified electrode showed electrocatalytic activity towards H₂O₂ amperometric detection. Additionally, when GOx was deposited as the outermost layer on the abovementioned multilayer structure, the Au/MPS/B/PFe₃Mo₉/B/GOx-modified electrode was able to detect glucose.     

Crystal and Molecular Structures of Two 1:1 Adducts of bis(O-ethyl dithiocarbonato-S,S′)manganese(II): Mn(S2COCH2CH3)2 (1,10-phenanthroline) and Mn(S2COCH2CH3)2 (2,2′-bipyridyl)

Abstract  

Distorted octahedral coordination geometries based on a N₂S₄ donor set are found in each of the molecular structures of the title complexes Mn(S₂COCH₂CH₃)₂ (1,10-phenanthroline) (1) and Mn(S₂COCH₂CH₃)₂ (2,2′-bipyridyl) (2). Analyses of the geometric parameters indicate that the five-membered ring in (1) has significantly more aromatic character than the analogous ring in (2). In terms of coordination of the xanthate ligands, one ligand in (1) is considerably more aromatic than the remaining ligands. This latter feature allows for the formation of C−H···π (S₂C) interactions leading to a supramolecular chain in (1). By contrast, in (2), the crystal packing is dominated by C−H···O contacts, which lead to a supramolecular chain with 4₁ symmetry, which combine with C−H···S contacts to consolidate the three-dimensional architecture. Unit cell data for (1): hexagonal, space group R ^ˉ3, a = 35.228(5) and c = 9.0086(13) ?; and for (2): tetragonal, space group I4₁/a, a = 31.120(7) and c = 8.306(2) ?.     

Concomitant polymorphism and conformational isomerism in 4‐acetylresorcinol

Two polymorphs of the title compound [systematic name: 1‐(2,4‐dihydroxyphenyl)ethanone], C₈H₈O₃, were investigated. The known structure [designated (I‐M); P2₁/c, Z = 4; previously investigated at room temperature by Robert, Moore, Eichhorn & Rillema (2007). Acta Cryst. E 63 , o4252] was redetermined at low temperature, and a new form [(I‐O); P2₁2₁2₁, Z = 12] was discovered in the same sample. In both forms, the molecules are planar (apart from the methyl H atoms) and they contain intramolecular O—H...O=C hydrogen bonds. In polymorph (I‐M), molecules are linked into chains by a single intermolecular O—H...O hydrogen bond, and the chains are linked into sheets by two C—H...O hydrogen bonds. Three O—H...O hydrogen bonds link the molecules of polymorph (I‐O) into chains and neighbouring chains are connected by one C—H...O interaction to form an offset layer structure. Two weak methyl C—H...O interactions link the layers.     

General tridiagonal random matrix models, limiting distributions and fluctuations

In this paper we discuss general tridiagonal matrix models which are natural extensions of the ones given in Dumitriu and Edelman (J. Math. Phys. 43(11): 5830–5847, 2002; J. Math. Phys. 47(11):5830–5847, 2006). We prove here the convergence of the distribution of the eigenvalues and compute the limiting distributions in some particular cases. We also discuss the limit of fluctuations, which, in a general context, turn out to be Gaussian. For the case of several random matrices, we prove the convergence of the joint moments and the convergence of the fluctuations to a Gaussian family. The methods involved are based on an elementary result on sequences of real numbers and a judicious counting of levels of paths.