Atomic absorption determination of Cd, Co, Cu, Fe, Ni in viscous aqueous solutions of poly(ethyleneimine) using a high-pressure flow and nebulization system for sample introduction

Summary The influence of increasing concentration of water-soluble polymers on the analytical signals for Cd, Co, Cu, Fe, Ni in flame atomic absorption spectrometry with hydraulic high-pressure nebulization (HHPN) and pneumatic nebulization (self uptake mode) has been studied using aqueous solutions of poly(ethyleneimine) (PEI) as examples. For a solution of 50 g/l polymer, HHPN sample introduction leads to a 5.0 (Cd), 8.8 (Co), 17 (Cu), 7.1 (Fe) and 22 (Ni) fold higher sensitivity compared to pneumatic nebulization. Even at polymer concentrations of more than 100 g/l HHPN operation is still possible without any problems, whilst such viscous solutions cannot be transferred into an aerosol by a pneumatic nebulizer.     

Sensitivity of redox reactions of dyes to variations of conditions created in mass spectrometric experiments

Redox behaviour of four imidazophenazine dye derivatives under mass spectrometric conditions of matrix-assisted laser desorption/ionization (MALDI), laser desorption/ionization (LDI) from metal and graphite surface, electrospray, low temperature secondary ion mass spectrometry (LT SIMS) and fast atom bombardment (FAB) was studied and distinctions in the reduction-dependent spectral patterns were analyzed from the point of view of different quantities of protons and electrons available for reduction in different techniques. The reduction products [M + 2H](+*), [M + 3H](+) and M(-*), [M + H](-) were observed in the positive and negative ion modes, respectively, which permitted to suggest independent occurrence of reduction and protonation/deprotonation processes. LDI from graphite substrate was the only technique that allowed us to obtain abundant negative ions of all dye derivatives. The yield of field ionization (FI) or field desorption (FD) mechanism to ion formation under LDI from rough graphite surface has been addressed. The sensitivity of reduction of the dyes to variation of reduction-initiating agents confirms high redox activity of the dyes essential for their functioning in natural and artificial systems.     

On the Most Powerful Chemical Traps for Bis(methoxycarbonyl)carbene (=2‐Methoxy‐1‐(methoxycarbonyl)‐2‐oxoethylidene)

The efficiency and validity of different chemical substrates for trapping bis(methoxycarbonyl)carbene (=2‐methoxy‐1‐(methoxycarbonyl)‐2‐oxoethylidene; 1 ) is dependent on the conditions of carbene generation. On conventional photolysis of dimethyldiazomalonate (=2‐diazopropanedioic acid dimethyl ester; 2 ) by long‐wave UV light (through a Pyrex filter, λ>290 nm), the most powerful trap for carbene 1 in the series of substrates Me₂S, MeOH, cyclohexane, and pyridine is Me₂S (with an efficiency ratio of ca. 6 : 4 : 2 : 1, resp.). When short‐wave decomposition of diazomalonate 2 is employed (through a quartz filter, λ>210 nm), more reliable and useful chemical traps for bis(methoxycarbonyl)carbene ( 1 ) are pyridine and cyclohexane, whose adducts with 1 are rather stable under short‐wave‐irradiation conditions. Application of alcohols for the trapping of 1 proves to be preferential when simultaneous monitoring of carbene and oxoketene formation during photolysis is necessary.     

Synthesis and Structures of Two Isomeric 4‐Diazo‐2,3,4,5‐tetrahydrofuran‐3‐ones

The two regioisomeric 4‐diazo‐2,3,4,5‐tetrahydrofuran‐3‐ones 6 and 7 were prepared via the common intermediate 2,3,4,5‐tetrahydro‐2,2‐dimethyl‐5,5‐diphenylfuran‐3‐one ( 8 ). Diazo transfer with 2,4,6‐triisopropylbenzenesulfonyl azide yielded 6 , whereas 7 was obtained via oxidation of the monohydrazone 12 , which was prepared selectively from tetrahydrofuran‐3,4‐dione 11 . The crystal structures of 6 and 7 have been established by X‐ray crystallography.     

Symmetry-adapted-cluster configuration interaction study of the doublet states of HCl+: potential energy curves, dipole moments, and transition dipole moments

The electronic structure of the HCl(+) molecular ion has been calculated using the general-R symmetry-adapted-cluster configuration interaction (SAC-CI) method. The authors present the potential energy curves, dipole moments, and transition dipole moments for a series of doublet states. The data are compared with the previous CASSCF and MCSCF calculations. The SAC-CI results reproduce quite well the data available in literature and extend the knowledge on the HCl(+) electronic structure for several higher states. The calculated R-dependent behavior of both dipole moments and transition dipole moments for a series of bound and unbound states reveals an intricate dissociation process at intermediate distances (R>R(e)). The pronounced maxima in transition dipole moment (TDM) describing transitions into high electronic states (X (2)Pi-->3 (2)Pi, X (2)Pi-->3 (2)Sigma, 2 (2)Pi-->3 (2)Pi, 3 (2)Pi-->4 (2)Pi) occur at different interatomic separations. Such TDM features are promising for selection of excitation pathways and, consequently, for an optimal control of the dissociation products.     

Synthesis and electrophilic cyclization reactions of diphenyl 3‐methylhexa‐ 1,3,4‐trien‐3‐yl phosphine oxide

Diphenyl 3‐methylhexa‐1,3,4‐trien‐3‐yl phosphine oxide can be readily prepared via an atom‐economical 2,3‐sigmatropic rearrangement of the mediated alkenynyl phosphinite formed in situ by a reaction of 2‐methylhex‐5‐en‐3‐yn‐2‐ol with diphenylchlorophosphine. Electrophilic cyclization reactions of prepared 1‐vinylallenyl phosphine oxide were investigated as it was established that the reactions proceeded with formation of heterocyclic compounds with participation of the allenic and/or 1,3‐dienic part of the vinylallenic system with neighboring group participation of the phosphoryl and/or vinylic group. © 2012 Wiley Periodicals, Inc. Heteroatom Chem 23:345–351, 2012; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.21023     

Synthesis of 6‐Aminopropyl‐6H‐indolo[2,3‐b]quinoxaline Derivatives

A series of 6‐(3‐aminopropyl)‐6H‐indolo[2,3‐b]quinoxalines were synthesized with high yields by the reaction of 6‐(3‐chloropropyl)‐6H‐indolo[2,3‐b]quinoxaline and corresponding amines in presence of tetrabutylammonium iodide in boiling toluene or dimethylformamide at room temperature. It was found that boiling of 6‐(3‐chloropropyl)‐6H‐indolo[2,3‐b]quinoxaline in acetone with sodium iodide or in acetic acid lead to intramolecular cyclization product.     

Tribological Properties of Poly(Para-Phenylene Sulfide) and its Carbon Fiber Composites with Water Lubrication

Tribological properties of poly(para-phenylene sulfide) (PPS) with different molecular mass were studied. PPS properties were compared with the same properties of its carbon fiber-filled plastics. For the interpretation of tribological test results an especial role was assigned to the load capacity of materials. The concept of load capacity permits consideration of different tribological dependencies as phase diagrams. The structure of the samples was characterized by X-ray diffraction and differential scanning calorimetry techniques.     

Correlation of Electronic and Magnetic Properties of Thin Polymer Layers with Cobalt Nanoparticles

Nanoparticles (NPs) of cobalt are synthesized in shallow layers of polyimide using 40 keV implantation of Co⁺ ions with a few different fluences at various ion current densities. Nucleation of individual NPs at low fluencies and their percolation at high fluencies are crucial processes governing the electrical and magnetic properties of the metal/polymer nanocomposites that can be controlled by the implantation regimes. In particular, one can tune the magnetoresistance between negative and positive through appropriate choice of ion fluence and current density. The found non‐monotonous dependence of the magnetoresistance on the applied magnetic field allows suggestion of spin‐dependent domain wall scattering affecting the electron transport. The samples implanted with low fluencies demonstrate superparamagnetic behavior down to very low blocking temperatures. For high fluence (1.25 × 10¹⁷ cm⁻²) the transition to ferromagnetic ordering is observed that is related to the increased magnetic interaction of NPs.     

On Residual Properties of Pure Braid Groups of Closed Surfaces

We prove that pure braid groups of closed surfaces are almost-direct products of residually torsion free nilpotent groups and hence residually torsion free nilpotent. As a corollary, we prove also that braid groups on 2 strands of closed surfaces are residually nilpotent.