Mass spectra of synthesized mixed bromochloroacetic acids

Mass spectra of methyl esters of three common drinking water chlorination by-products, bromodichloroacetic acid, dibromochloroacetic acid and tribromoacetic acid, are presented. The spectra are obtained in electron impact and chemical ionization modes, using a quadrupole mass spectrometer. Proposed fragment ion assignments are presented in detail. Fragment clusters were identified from their m/z values and confirmed with their relative isotope ratios. The detailed mass spectra presented are especially useful because standards for these drinking water contaminants are not yet commercially available.     

Solution structure of papain as studied by molecular mechanics and molecular dynamics techniques

In this paper, we report the molecular mechanics and molecular dynamics studies of the hydration of papain using the AMBER and CHARMm programs. We studied papain in an environment with minimal hydration involving only the X-ray waters and also in the hydrated environment by adding an extra 9 Å layer of water around the residues. The effect of nonbond cutoff was studied by performing minimizations with 8 Å and 15 Å nonbond cutoffs using the program AMBER. Two different solvent models—a constant dielectric and a distance-dependent dielectric—were considered. The AMBER-minimized structure and the average structure obtained from the CHARMm simulations for papain solvated with X-ray waters are presented and compared with the X-ray crystal structure results. Results of a similar comparison of the hydrated structures were also presented. The calculated root mean square deviation between the minimized structure and the X-ray structure is smaller for the hydrated system than for the system hydrated with only the X-ray waters. Results of the molecular mechanics and molecular dynamics simulations were presented for the various regions of papain. The hydration of the active site of papain and the effect of hydration on the torsional motion of the active site residues are presented. © 1996 by John Wiley & Sons, Inc.     

Main‐chain syndioregic nonlinear optical polymers. II. Extended pi conjugation and improved thermal properties

Recent results concerning the synthesis of new main‐chain syndioregic nonlinear optical polymers are presented. In particular, the synthesis of polymers with extended pi conjugation in the chromophore and chromophores with improved thermal stability are presented. The nonlinear optical coefficient of several of the polymers and the optical loss at 1.3 and 1.55 μm were measured and are discussed. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2824–2839, 2000     

Large area mapping of non-metallic inclusions in stainless steel by an automated system based on laser ablation

Large area compositional mapping (>6 mm²) using a fast and automated system based on laser-induced plasma spectrometry is presented. The second harmonic of a flat top Nd:YAG laser beam was used to generate a microline plasma on the sample surface. The emitted light from the microline plasma was imaged onto the entrance slit of an imaging spectrograph and was detected by an intensified charge-coupled device to generate a spatially and spectrally resolved data set. Individual LIPS images, each measuring roughly 2500×2500 μm with spatial resolution of 50 μm between adjacent craters and 4.8 μm along the microline are presented. These large area maps were acquired in less than 1 min. Steel samples containing MnS and TiN inclusions were chosen as the most adequate for this study. The results are presented for the characterization of inclusionary material in stainless steel products in terms of morphology, distribution and abundance.     

Electronic states of ketene radical cation

The doublet electronic states of ketene, and ketene-d₂, radical cations produced by photoionisation with Helα (58.4 nm) and Hellα (30.4 nm) radiation, were studied by photoelectron spectroscopy. Seven such states were found below 28 eV ionisation energy and were assigned by comparison with the ionisation energies calculated by the correlated PNO-CEPA approach. The agreement is within ≈ 0.3 eV of the experimental data. An analysis of the contributions of reorganisation and correlation effects to the calculated ionisation energies is presented. The vibrational frequencies exciteα in four of the states of ketene-d₂ and ketene are presented and discussed in view of the assignments.     

The Chemistry of 4-Substituted Oxazaphosphorinanes (OAP) (Tools for Cancer Research and Therapy)

Abstract

Novel chemical approaches resulted in 4-substituted OAP derivatives, linked by a sulfur, orygen or nitrogen atom to C-4. The cis- and trans-epimers were stereoselectively synthesized from the key intermediate 4-hydroxycyclophosphamide. An alternative route will be presented. The stereochemistry of 4-substituted OAP are confirmed by single crystal X-ray analysis and by NMR-spectra for more than 50 compounds. The connectivities of the nuclei observed in the homonuclear and heteronuclear COSY plots are summarized with data. In aqueous solution 4-substituted OAP are hydrolyzed with a half-life at physiological conditions of a few minutes for S-derivatives and of about 20 hours for the more stable N-derivatives. The pH-dependance of the hydrolysis rates including epimerisation and transthioacetalisation are submitted. Pharmacokinetical and biological activity data are presented.     

Hydrostatic extrusion of polyoxymethylene

The hydrostatic extrusion behavior of polyoxymethylene (POM) is described. Extrusions were performed at 164°C for a range of different molecular weight grades. Excellent unflawed lengths of extrudate were obtained with axial Young's moduli, measured at room temperature, reaching values as high as 24 GPa. The extrusion characteristics are discussed in terms of the very strong dependence of the flow stress of POM on strain and strain rate and pressure. In addition to measurements of Young's modulus over a wide temperature range, data for shear modulus and transvers modulus are also presented. A limited amount of other structural measurements is presented.     

Influence of the anion on the surface tension of 1-ethyl-3-methylimidazolium-based ionic liquids

The air–liquid interfacial tensions of eight ionic liquids, from (298 to 343) K, are presented in this work. The studied ionic liquids are formed by the fixed 1-ethyl-3-methylimidazolium cation combined with the anions acetate, dicyanamide, dimethylphosphate, methylphosphonate, methanesulfonate, thiocyanate, tosylate, and trifluoromethanesulfonate. The selected ionic liquids allowed a comprehensive study through the influence of the anion nature on the surface tension and on their surface ordering. A slight dependence of the surface tension with the ionic liquid molar volume was identified. The surface thermodynamic functions are mainly controlled by the anion which constitutes a given ionic liquid. The hypothetical critical temperatures of all ionic liquids were estimated by means of the Eötvos and Guggenheim correlations and are presented.     

Picosecond spectroscopic investigations of diphenylcarbene protonation

The details of the picosecond kinetic investigation of diphenylcarbene (Ph₂C:) protonation with H₂O, MeOH, EtOH and 2-propanol by optical absorption technique are presented. The protonation reactions were monitored by detection of the diphenylcarbenium ion (Ph₂C⁺H). Evidence of solvent induced alteration of the singlet-triplet energy level of Ph₂C:, and involvement of an excited carbene singlet state in the protonation of Ph₂C: diphenylcarbene with H₂O are presented.     

The problem of the low-frequency dispersion in the case of polymer film electrodes — an experimental impedance study on Au|poly(o-phenylenediamine) electrodes

Electrochemical impedance spectra are presented for Au|poly(o-phenylenediamine) electrodes in contact with 1 mol dm⁻³ perchloric acid solution. The roughness of the gold substrate and the film thickness, respectively, were systematically varied. The results obtained affirm that the dispersion of the low-frequency capacitance is connected with the inhomogeneity of the surface film, and the role of the surface roughness of the gold substrate is minor, if any, in the development of the CPE behaviour, which is in contrast to some hypotheses presented recently.     

15N NMR spectroscopy of some azines

¹⁵N NMR shielding data are presented for 56 cyclic azines in 0.5 M dimethyl sulfoxide solutions with 0.01 M increments of Cr(acac)₃ added for each nitrogen atom in the molecules. For the polyazines, the ¹⁵N signal assignments were based on ²J(NH) interactions and some INDO/S-SOS shielding calculations. The effects of α-, β- and γ-methyl and conjugated ring substitution on nitrogen shielding are presented and discussed, as are the influences arising from fusion with alicyclic and aromatic rings at various positions. The effects of a second nitrogen atom on the shielding of the first one are shown to be critically dependent on both their relative positions and on the position of fusion of conjugated ring systems.     

Laser Induced Breakdown Spectroscopy application for ash characterisation for a coal fired power plant

The aim of this work was to apply the LIBS technique for the analysis of fly ash and bottom ash resulting from the coal combustion in a coal fired power plant. The steps of presented LIBS analysis were pelletizing of powdered samples, firing with laser and spectroscopic detection. The analysis “on tape” was presented as an alternative fast sampling approach. This procedure was compared with the usual steps of normalized chemical analysis methods for coal which are coal calcination, fluxing in high temperature plasma, dilution in strong acids and analyzing by means of ICP-OES and/or AAS.     

(N‐Heterocyclic carbene)Pd(triethylamine)Cl2 as precatalyst for the synthesis of Poly(triarylamine)s

The use of a highly active, air‐, and moisture‐stable N‐heterocyclic carbene‐palladium(II) complex for the polymerization of anilines and aryl dibromides or dichlorides by Buchwald‐Hartwig coupling is presented. In comparison to previous catalytic systems, higher molecular weight polymers with improved yields were obtained in shorter reaction times. The first examples of fabrication of OFETs with polytriarylamines synthesized with aryl dichlorides and anilines are also presented. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4904–4911     

Thermodynamic properties of uranium plutonium mixed carbides

High plutonium containing hyperstoichiometric mixed carbide fuels are used as driver fuel in the Fast Breeder Test Reactor at Kalpakkam, India. The enthalpy increment of the mixed carbide fuels were measured in the temperature range 1000–1800 K using a high temperature drop calorimeter. The results are presented and compared with the data available in the literature.     

The low temperature Fourier Transform Raman spectrum of polystyrenes

In a previous paper (Jones and Wesley, Spectrochimica Acta 47A (9/10), 1293 (1991)) the Fourier Transform (FT) Raman spectra of various polystyrenes were presented and differences in the spectra in terms of the configuration, conformation and crystallinity of the samples were discussed. In this paper the low temperature FT Raman spectra of polystyrenes are presented. The differences between the spectra as a function of temperature and crystallinity are discussed. It is clear that, although lowering the temperature is advantageous in improving the quality of the spectra, crystallinity is the key to quality in the spectra. Isomeric purity alone seems to be far less advantageous. It is proposed that the band near 1000 cm⁻¹ in this system can be used to estimate the crystallinity. The paper concludes with some comments on the very slow crystallization rate of typical isotactic polystyrene.     

Preparation, Characterization, and Evaluation of Immuno Carbon Nanotubes

Single-walled and multiple-walled carbon nanotubes were functionalized with bovine serum albumin protein to attain aqueous solubility and biocompatibility. These aqueous soluble carbon nanotube-protein conjugates were further conjugated with pathogen-specific antibody to form immuno carbon nanotubes. The experimental details on the conjugation and results from the characterization of the conjugates are presented. The potential of these immuno carbon nanotubes in the detection of pathogenic Escherichia coli O157:H7 was evaluated, and the evaluation results are discussed.     

Diastereoselective synthesis of substituted prolines via 5-endo-trig cyclisations of aza-[2,3]-Wittig sigmatropic rearrangement products

The major diastereoisomers of aza-[2,3]-Wittig sigmatropic rearrangement products from α-amino acid derivatives are susceptible to a rare nucleophilic 5-endo-trig cyclisations of an amine onto a non-conjugated vinylsilane in high yield and complete diastereocontrol. Five examples are presented, with cyclisation yields between 35 and 87%. A rationale for the stereoselectivity of the cyclisation is forwarded based upon the steric control factors that have been documented for the aza-[2,3]-Wittig sigmatropic rearrangement. A discussion of the mechanism in the context of the reaction conditions is also presented. Oxidation of the silyl group to a hydroxyl group and complete removal were demonstrated for synthetic utility.     

Synthesis of Aryl Ethers by Nonactivated Aromatic Nucleophilic Substitution Reactions

The results of a kinetic study of model reactions between substituted phenols and bromobenzene in the presence of potassium carbonate and the copper(I) chloride–8-hydroxyquinoline catalytic complex in N,N-dimethylformamide are presented. The reactions were found to obey a first-order rate law. Both orbital and charge interactions should be taken into account in a consideration of the effect of the structural characteristics of reactants on the rate of reaction. The kinetics of substitution of the phenoxide anion for an aromatically bound halogen atom in activated and nonactivated systems with the formation of practically valuable aryl ethers were comparatively studied. The results presented provide an opportunity to distinguish the common features and regularities of activated and nonactivated aromatic substitution in the test systems.     

Polymeric nature of selenium crystallization. II. Crystallization kinetics and secondary crystallization

The crystallization of elemental selenium has been studied in light of present concepts of crystallization in organic polymers. Bulk-crystallization kinetic data as measured by a dynamic density technique and spherulite growth-rate data as measured by optical microscopy are presented for the temperature range 70°C to 160°C. Plots of extent of isothermal crystallization versus time were sigmoidal in shape. Spherulite growth rates were constant for a given temperature and reached a maximum at approximately 130°C. Evidence is presented for secondary crystallization in selenium, and a model is proposed for destruction of chain folds with interlamellar crystallization during the spherulitic-to-“metallic” transformation above 100°C.