Negative ion mass spectra of chlorine-containing molecules

The negative ion mass spectra of chlorine-containing molecules have been measured using a double focusing mass spectrometer with a photographic plate detector. The formulae of the negative ions not previously assigned using an electron multiplier detector have now been assigned.     

Amino acid end-group in commercial heparin. III. Determination of the number of amino groups of amino acid and hexosamine residues per heparin molecule

The reactions of heparin with 2,4,6-trinitrobenzenesulfonic acid (TNBS) were studied spectrometrically. Seven different commercial heparins were used in this study. The amino groups react with TNBS to form equimolar amounts of trinitrophenylated (TNP) amino groups and bisulfite ions. The TNP-amino groups further react with bisulfite ions to form the monosubstituted anionic sigma complex. The absorption spectrum with two maxima at approximately 350 nm and approximately 420 nm, characteristic of either the TNP-amino groups or the complex, was analyzed for the reaction of TNBS with heparin. It was shown that the reactivities of TNBS with amino groups from α-amino acid and hexosamine residues are greatly different. By combining the results of the reaction kinetics and the reaction of heparin with Sanger's reagent, the number of the α-amino groups and the free amino groups in hexosamine residues were determined. These data have been performed with a range of heparins from different commercial sources, of different activities and physical characteristics. No correlation was found between the free amino contents of these heparins and biological potency. © 1993 John Wiley & Sons, Inc.     

A modified Ortega method to evaluate the activation energies of solid state reactions

The application of the average linear integral isoconversional method developed by Ortega for evaluating the activation energies of solid state reactions may be hindered by experimental noise and the uncertainties associated with selecting appropriate reaction segments. This paper suggests a procedure, called the modified Ortega method, which can avoid or minimize these hindrances. By applying the modified Ortega method to the kinetic analyses of both simulated and experimental data, a more consistent dependence of the activation energy on the extent of reaction conversion was found with those calculated from the modified Vyazovkin method and the Friedman method.     

Synthesis of pyrido[1′,2′:1,2]imidazo[4,5-b]quinoxalines

Synthesis of pyrido[1′,2′:1,2]imidazo[4,5-b]quinoxalines by the facile cyclizations of 2,3-dichloroquinoxalines with 2-aminopyridines and of 2-amino-3-chloroquinoxalines with various substituted pyridines is described.     

A novel dinuclear cyclometalated iridium complex bridged with 1,4-bis[pyridine-2-yl]benzene: its structure and photophysical properties

The synthesis, structure, and photophysical properties of a new cyclometalated dinuclear iridium complex, (ppy)2Ir(mu-BPB)Ir(ppy)2 [ppy = 2-phenylpyridine, BPB = 1,4-bis(pyridin-2-yl)benzene], have been investigated.     

Application of a diphosphinidenecyclobutene ligand in the solvent-free copper-catalysed amination reactions of aryl halides

1,2-Diphenyl-3,4-bis[(2,4,6-tri-tert-butylphenyl)phosphinidene]cyclobutene was used as an additive ligand in copper-catalysed amination reactions of halobenzenes with amines in the presence of base to afford the corresponding secondary or tertiary amines in good to excellent yields.     

The first bowl-shaped stable neutral radical with a corannulene system: synthesis and characterization of the electronic structure

[structure: see text] A bowl-shaped neutral radical with a corannulene system has been designed and synthesized for the first time as a stable solid in air. An unequivocal characterization of the electronic properties of the radical shows that an appreciable amount of spin delocalization extends onto the corannulene unit's curved surface.     

Synthesis and nanostructure of strong polyelectrolyte brushes in amphiphilic diblock copolymer monolayers on a water surface

We synthesized an ionic amphiphilic diblock copolymer, poly(hydrogenated isoprene)-b-poly(styrenesulfonic acid) (PIp-h2-b-PSS), by living anionic polymerization, and the nanostructure of its monolayer spread on a water surface was directly investigated by the in situ X-ray reflectivity technique. The monolayer of the diblock copolymer on a water surface had a smooth hydrophobic PIp-h2 layer on water and a "carpet"/polymer brush double layer in a hydrophilic sodium polystyrene sulfonate (PSSNa) layer under the water. The surface pressure dependence and PSSNa chain length dependence of the PIp-h2 layer thickness and the brush nanostructure were quantitatively studied. The effect of salt concentration in the subphase was also investigated in aqueous solutions containing 0-2 M NaCl. The salt effect on monolayer structure occurred at around 0.2 M. The thickness of the PSS brush layer decreased at salt concentrations above 0.2 M, while no structural change was observed below 0.2 M. This critical salt concentration is thought to be related to the balance of ionic concentrations inside the brush and in bulk solution.     

Semiempirical Pm3 Quantum Mechanics Calculations of Carbohydrate Crystals

ABSTRACT

Miniature crystal models of six small carbohydrates were examined using the PM3 semiempirical quantum mechanics method. The minicrystal structures, consisting of 27 sugar residues, were optimized by the combined procedure of partial optimization and reconstruction of the model, while maintaining the original crystal symmetries. All of the minicrystals were successfully optimized without exhibiting a great increase in an energy at any reconstruction step. Some minicrystals showed a prolonged behavior of optimization cycles. A major source of structure change appeared to arise from hydroxyl group rotations wherein the largest movements mostly occurred in an early optimization stage. No significant deformations in geometry of either residues or hydrogen bonds were observed in the final minicrystal structures. The thermodynamic values calculated for the optimized minicrystals were in reasonably good agreement with the literature data. The present study indicated that the PM3 semiempirical method successfully predicted the basic features of intermolecular hydrogen bonding involved in a condensed system.