bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of nonporous polyurethane (PU) membranes and porous PU thin films as sample supports for MALDI-MS of wheat proteins
Authors: McComb Mark E , Oleschuk Richard D , Chow Art , Perreault Hélène , Dworschak Ragnar G , Znamirowski Marek , Ens Werner , Standing Kenneth G , Preston Ken R
Published: April 2011

Non-porous polyurethane (PU) membranes and porous PU thin films are used as sample supports for MALDI-TOFMS. Mass spectra obtained are compared with those acquired using metal targets and the crushed matrix method. The compounds characterized are wheat proteins which consist of moderately water-soluble gliadins, and of water-insoluble low molecular weight (LMW) and high molecular weight (HMW) glutenins. Mass spectra obtained using the PU supports are in general of good quality, and this method of sample preparation is the most convenient for sample handling. In the case of gliadins and LMW glutenins, the spectra obtained on PU are comparable with those obtained using metal supports. Isolation of the LMW and HMW wheat proteins characterized in this study requires the use of buffers incompatible with MALDI. Spectra of samples containing buffer components on PU supports are of better quality than those obtained using the crushed matrix method. This effect is attributed to stronger protein binding onto the PU supports, which allows for extensive washing and removal of water soluble buffer components. The PU film, when cast onto a MALDI probe, is porous and flat in topology. The differences in surface characteristics between the PU film and the PU membrane result in slight variations in the mass spectra. The extent of surface charging, observed significantly using 50 µm thick PU membranes, decreases with 25 µm membranes and becomes insignificant with PU thin films. An important advantage of using the PU supports is the possibility of preparing samples on the film or membrane in the field and of analysing them at a later time. This is especially important when samples are susceptible to chemical degradation in solution. These proteins are known to degrade while stored in solution. We have thus incorporated the use of PU membranefilm supports into our routine analysis of these proteins.Key words: gliadins, glutenins, MALDI, membrane supports, polymeric supports, time-of-flight analysis.
Incorporation of13C glucose into nicotinamide inE. coliand inS. cerevisiae
Authors: Gupta Ram Nath , Hemscheidt Thomas , Sayer Brian G , Spenser Ian D
Published: April 2011

The mode of incorporation into nicotinamide of label from13C-labeled samples of D-glucose, in Escherichia coli and Saccharomyces cerevisiae, was determined by means of13C NMR spectroscopy. The results, which confirm and extend early studies with radioactive tracers, permit a definitive choice to be made between alternative biogenetic proposals.Key words: nicotinic acid, nicotinamide, biosynthesis, glucose incorporation,13C NMR.
Glutathione radical: Intramolecular H abstraction by the thiyl radical
Authors: Rauk A , Armstrong D A , Berges J
Published: April 2011

Ab initio computations (B3LYP/6-31G(D)) were used to predict transition structures and energies of activation for intramolecular H atom transfer to a thiyl radical (RS.) from the α-CH bonds of glutathione (1) and from the model compounds, N-formylcysteinylglycine (2) and N-(2-thioethanyl)-γ-glutamine (3). For each compound, transition structures were located by in vacuo calculations on the neutral non-zwitterionic system. Thermodynamic functions derived at the same level and single point calculations at the B3LYP/6-311+G(3df,2p) level, were used to derive free energies of activation (ΔG[Formula: see text]) and reaction (ΔG°). For abstraction of the α-CH (Gly) by the thiyl radical in the gas phase, ΔG[Formula: see text] = 134 kJ mol1 if the amide link to Gly is in the more stable (Z)-configuration, and ΔG[Formula: see text] = 52 kJ mol1 if it is in the less stable (E)-configuration. The isomerization of the amide group requires about 95 kJ mol1. Previous studies had indicated that for intramolecular reaction of the thiyl radical at α-CH (Cys), ΔG[Formula: see text] = 110 kJ mol1. The lowest energy pathway for intramolecular H-transfer to the thiyl radical is from α-CH (Gln), ΔG[Formula: see text] = 3742 kJ mol1, and corresponds rather well with experimental results in solution (ΔG[Formula: see text] = 43 kJ mol1). The calculated free energy change for the equilibrium between thiyl and α-C forms of the glutathione radical is ΔG° = 54 kJ mol1. The value estimated from experimental data is ΔG° = 37 kJ mol1. The agreement between the energies from theory in the gas phase and experiment in solution suggests that the free energies of solvation of reactant thiyl radical, transition structures for H abstraction, and the product α-C-centred radical, are very similar. The effects of solution were estimated by two continuum models (SCIPCM and COSMO). The SCIPCM model yields results very similar to the gas phase, predicting a modest lowering of the activation free energy. The results from the COSMO method were inconclusive as to whether a rate enhancement or decrease could be expected.Key words: glutathione, thiyl radical, α-C-radical, hydrogen transfer.
Alternating copolymerization of ω-perfluoroalkyl-1-alkenes with carbon monoxide catalyzed by homogeneous and polymer-supported Pd-complexes
Authors: Nozaki Kyoko , Shibahara Fumitoshi , Elzner Stephan , Hiyama Tamejiro
Published: April 2011

Alternating copolymerization of fluorinated olefins (CnF2n+ 1)(CH2)mCH=CH2 (1) and carbon monoxide was carried out using cationic Pd(II)-(R,S)-BINAPHOS complexes (2) as catalysts. To obtain polymeric products sufficiently, existence of at least two methylenes in 1 were essential (m [Formula: see text] 2). The products thus obtained formed polyspiroketal (4) rather than polyketone (3), the structures being determined by solid- and solution-state NMR and IR analyses. The water contact angle was 108° for a sample of 4f when it was casted on a glass surface from C6F6 solution.Key words: copolymer, fluoroalkene, carbon monoxide, palladium, contact angle.
Asymmetric hydroformylation of styrene catalyzed by platinum complexes of chiral diphosphites with atropisomeric terminal moieties
Authors: Bakos J , Cserépi-Szucs S , Gömöry Á , Hegedüs C , Markó L , Szöllosy Á
Published: April 2011

To study the nature of steric and electronic effects of diphosphites, a novel diphosphite was synthesized and tested with regard of its catalytic performance in the hydroformylation of styrene catalyzed by platinum complexes. The novel ligand 3 was prepared by the reaction of enantiomerically pure pentane-2,4-diol with (S)-2-chloro-5,5',6,6',7,7',8,8'-octahydro-dinaphtho[2,1-d:1',2'-f][1,3,2]dioxaphosphepine based on H8-BINOL (H8-BINOL = 5,5',6,6',7,7',8,8'-octahydro-1,1'-bi-2-naphthol). For a comparative study, the BINOL (1,1'-bi-2-naphthol) based analogue 4 of 3 has also been synthesized. The highest chemoselectivity to aldehyde (71%) and regioselectivity to branched aldehyde (85%) with an enantiomer excess (ee) of 86% was obtained with the platinum(II)-SnCl2 catalytic system associated with (2S,4S)-bis(S)-3.Key words: asymmetric hydroformylation, chirality, homogeneous catalysis, P ligands, platinum.
Using secondary alpha deuterium kinetic isotope effects to determine the stereochemistry of an E2 reaction; the stereochemistry of the E2 reaction of 1-chloro-2-phenylethane with potassium tert-butoxide in tert-butyl alcohol
Authors: Smith Peter James , Crowe David AJ , Westaway Kenneth Charles
Published: April 2011

Isotopic labelling studies have shown that the E2 reaction of 1-chloro-2-phenylethane with potassium tert-butoxide in tert-butyl alcohol occurs via an anti-periplanar stereochemistry. This demonstrates that the different secondary alpha deuterium kinetic isotope effects found for the high and low base concentrations and in the presence of 18-crown-6 ether are because of changes in transition state structure that occur when the form of the reacting base changes rather than to a change in the stereochemistry of the reaction.Key words: E2 reaction, stereochemistry, secondary alpha deuterium kinetic isotope effects, transition state.
Synthetic dyes: simple and original ways to 4-substituted flavylium salts and their corresponding vitisin derivatives
Authors: Roehri-Stoeckel Christine , Gonzalez Emmanuel , Fougerousse André , Brouillard Raymond
Published: April 2011

Flavylium salts substituted at the 4-position have been prepared according to a Grignard reaction of some flavones with appropriate alkyl- and aryl-magnesium bromides. Among these compounds, 4-methyl flavylium salts were gently reacted with aromatic aldehydes, affording new anthocyanidin pigments, some of which are of the vitisin family. These are the first examples of chemically synthesized vitisidins (aglycones of vitisins). Compared to the more common flavylium salts, they demonstrate a large bathochromic shift (from about 100200 nm), thus providing blue-violet and green colours, so difficult to obtain with anthocyanidins in general.Key words: 4-substituted flavylium chlorides, vitisin aglycones, blue-violet and green anthocyanidin pigments.
A fluorescent host-guest complex of cucurbituril in solution: a molecular Jack O'Lantern
Authors: Wagner Brian D , Fitzpatrick Shannon J , Gill Monica A , MacRae Andrew I , Stojanovic Natasa
Published: April 2011

Fluorescence enhancement of a probe molecule in solution by the container molecule cucurbituril (CB) is reported for the first time. The fluorescence of the probe 2-anilinonaphthalene-6-sulfonate (2,6-ANS) in aqueous Na2SO4 solution is found to increase by a maximum factor of 5.0 upon addition of cucurbituril. This fluorescence enhancement is the result of the formation of a hostguest inclusion complex, in which the guest 2,6-ANS is incorporated inside the cavity of the host, cucurbituril. Measurement of the enhancement as a function of cucurbituril concentration yielded a value of the equilibrium constant (K) of 52 ± 10 M1. It is proposed that the mode of inclusion involves the phenyl group of the 2,6-ANS, because of the relatively small size of the cucurbituril cavity. It is further proposed that the observed enhancement is a result of loss of rotational mobility of the phenyl ring relative to the naphthyl fluorophore of 2,6-ANS upon inclusion of the phenyl ring. Since the name cucurbituril is derived from the Latin word for "pumpkin," this fluorescent host-guest complex is referred to as a "molecular Jack O'Lantern," with the 2,6-ANS serving as the candle.Key words: hostguest chemistry, fluorescence, cucurbituril, inclusion compounds.
Elimination, ring-contraction, and fragmentation reactions of 1-thioflavanone 1-oxides
Authors: Somogyi László
Published: April 2011

Epimeric thioflavanone sulfoxides (2b) were selectively transformed into thioflavone (1a), thioaurone (3a), and di(2-cinnamoylphenyl) disulfide (4). Disulfide 4 can be recyclized into thioaurones (3ac) and thioflavanones (2a,5) with heterolysis of the SS bond. The 3-p-anisylidene sulfoxide analog of 2b (6) transforms, with fragmentation, into 4'-methoxythioaurone 3b.Key words: chalcone, ring contraction, sulfoxides, thioaurones, thioflavonoids.
Synthesis and decarboxylation of Δ2-cephem-4,4-dicarboxylic acids
Authors: Wolfe Saul , Ro Stephen , Kim Chan-Kyung , Shi Zheng
Published: April 2011

Penicillin V was converted in 14 steps into Δ2-cephems having hydrogen at C-3, hydrogen or ethyl at C-2, and two methoxycarbonyl, two benzyloxycarbonyl, or one methoxycarbonyl and one benzyloxycarbonyl substituent at C-4. Deprotection of these Δ2-cephem-4,4-dicarboxylic acid esters by alkaline hydrolysis (in the case of methyl esters) or hydrogenolysis (in the case of benzyl esters) led in all cases to rapid decarboxylation of the Δ2-cephem-4,4-dicarboxylic acid or Δ2-cephem-4,4-dicarboxylic acid monoester. With hydrogen at C-2, hydrolysis of the dimethyl ester with 1 equiv of base produced a Δ2-cephem. With 2 equiv of base, and with all compounds having methyl at C-2, hydrolysis or hydrogenolysis afforded 4α-substituted-Δ2-cephems.

In contrast, simpler benzyl or methyl acetamidomalonates could be deprotected without difficulty to afford stable malonic acids. Reasons for the differences in ease of decarboxylation were examined using semiempirical (AM1) and ab initio (3-21G) molecular orbital calculations. The decarboxylation barriers of unionized cephem or acetamido malonic acids were found to be high (3540 kcal mol1). Although the monoanion of acetamidomalonic acid retained a high barrier, the epimeric monoanions of a Δ2-cephem malonic acid decarboxylated with barriers of only 2 kcal mol1.Key words: mercaptoazetidinone, bromomalonate esters, MO calculations, sulfoxides, hydrogenolysis.
Generation, electrocyclic ring opening, and unprecedented conversion of a 3-acylaminoazetinone into cis-3,4-disubstituted azetidinones
Authors: Wolfe Saul , Ro Stephen , Shi Zheng
Published: April 2011

An attempt to synthesize the nucleus of cefaclor by insertion of an appropriately functionalized rhodium carbene into a β-lactam NH bond leads instead to attack at sulfur, followed by fragmentation into a four-membered thietanone and a four-membered 3-acylaminoazetinone. The azetinone undergoes electrocyclic ring opening, with a calculated half-life of 11 s at 40°C, to a trans-disubstituted vinyl isocyanate, but can be trapped by saturated, unsaturated allylic and benzylic alcohols to form 3,4-disubstituted azetidinones in which the cis- isomer predominates.Key words: rhodium carbene, torquochemical, azetinone, mercaptoazetidinone.
Stereoelectronic and conformational effects on the stereochemical course of reduction of bicyclo[3.3.1]nonane 1,3-diketones
Authors: Butkus Eugenius , Stoncius Arvydas , Malinauskiene Jule , Tomoda Shuji , Kaneno Daisuke
Published: April 2011

The stereoselectivity of the reduction of bicyclo[3.3.1]nonane 1,3-diketones was studied. The experimental data of π-facial stereoselection of the reduction of the carbonyl group were successfully rationalized by the application of the exterior frontier orbital extension (EFOE) model. The observed facial diastereoselectivity of the carbonyl reduction of bicyclo[3.3.1]nonane diketones could be reasonably explained by the ground-state facial anisotropy of the frontier orbital extension, steric effects, and the intrinsic reactivity of carbonyl groups. Although the EFOE density and PDAS values predicted the enhanced reactivity at the C-2 carbonyl compared to C-9 carbonyl, transition-state calculations at the B3LYP/6-31+G(d,p) level showed that the reactivity of C-9 and C-2 in a hydride addition to both carbonyl groups should be nearly the same. The EFOE analysis also strongly indicated that in the second hydride reduction step the corresponding oxobicyclononanolates are most likely to be involved in the reduction as the major species rather than the free hydroxyketones. The antiperiplanar effects in the transition states of the LiAlH4 reduction as measured by both the elongation and the natural bond population of the antiperiplanar bonds clearly indicated they should not be an essential factor of the facial diastereoselection of studied diketones.Key words: bicyclo[3.3.1]nonanedione, EFOE model, reduction, stereoselectivity, transition state.
Chiral aluminum complexes as catalysts in asymmetric Baeyer-Villiger reactions of cyclobutanones
Authors: Bolm Carsten , Beckmann Oliver , Palazzi Chiara
Published: April 2011

BINOL-aluminum complexes were successfully employed as mediators and catalysts in asymmetric Baeyer-Villiger rearrangements of cyclobutanones. Good enantioselectivies were achieved with only 15 mol% of the chosen chiral Lewis acid. The enantiomeric excesses obtained have never been reached before in such metal-catalyzed Baeyer-Villiger reactions.Key words: aluminum, asymmetric catalysis, lactones, oxidations, rearrangement.
Diastereotopic group recognition in the solid state  A unique intramolecular β-cyclodextrin inclusion complex
Authors: Reetz Manfred T , Rudolph Joachim , Goddard Richard
Published: April 2011

The phenomenon of diastereotopic group recognition has been structurally documented for the first time. A diphenylphosphine-modified β-cyclodextrin having two diastereotopic phenyl groups in close vicinity to the inner cavity of this host was prepared. The crystal structure analysis reveals selective intramolecular complexation of one of the two diastereotopic phenyl groups.Key words: supramolecular chemistry, stereotopic group recognition, cyclodextrins, intramolecular complexation.
The use of palladium chloride as a precatalyst for the amination of aryl bromides
Authors: Zhang Xiao-Xiang , Harris Michele C , Sadighi Joseph P , Buchwald Stephen L
Published: April 2011

The use of palladium chloride as a precatalyst for the amination of aryl bromides is reported. To overcome the poor solubility of palladium chloride in commonly used solvents, a procedure was developed in which PdCl2 was preheated with neat amine in the presence of a phosphine ligand before the addition of the other reaction components. This protocol is effective for a broad range of substrate combinations using several types of phosphine ligands.Key words: palladium chloride, amination, aryl bromide, phosphine ligand.
2000 Maxxam Award Lecture Unified theory of extraction
Authors: Pawliszyn Janusz
Published: April 2011

The sample preparation step in an analytical process typically consists of extraction of components of interest from a sample matrix. This procedure can vary in degree of selectivity, speed, and convenience depending on the approach and conditions used as well as on geometric configurations of the extraction phase and conditions. Optimization of this process aids enhancement in performance of the overall analysis. Proper design of the extraction devices and procedures facilitates rapid and convenient on-site implementation, coupling to separationquantification, and (or) automation. The key to rational choice, optimization, and design is an understanding of fundamental principles governing mass transfer of analytes in multiphase systems. There is a tendency to divide extraction techniques according to random criteria. In this article, common principles among different extraction techniques are emphasized and a unified approach based on convolution of mathematical functions describing individual steps is presented. This approach considers gas, solvent, liquid polymer, and solid surfaces as extraction phases and air, water, and solids as sample matrices. The parameters that affect the kinetics of extraction techniques are emphasized resulting in new calibration strategies and novel geometric designs.Key words: separations, extractions, microextractions, mass transfer, multiphase equilibria.
Volumes of activation for electrode processes of various charge-types in nonaqueous solvents
Authors: Matsumoto Mitsuru , Lamprecht Delanie , North Michael R , Swaddle Thomas W
Published: April 2011

Volumes of activation (ΔVel) are reported for electron transfer at a Pt electrode of Mn(CN-cyclo-C6H11)62+/+in acetonitrile, acetone, methanol, and propylene carbonate, and of Fe(phen)33+/2+in acetonitrile. In all cases, ΔVelis markedly positive, whereas for the homogeneous self-exchange reactions of these couples in the same solvents the corresponding parameter is known to be strongly negative. The rate constants for the electrode reactions correlate loosely with the mean reactant diffusion coefficients (i.e., with solvent fluidity) and the ΔVelvalues with the volumes of activation for diffusion (i.e., for viscous flow), consistent with solvent dynamical control of the electrode reaction rate in organic solvents. A detailed analysis of ΔVelvalues of the kind presented for a couple with an uncharged member (Zhou and Swaddle, Can. J. Chem. 79, 841 (2001)) fails, however, either because of ion-pairing effects with these more highly charged couples or because of breakdown of transition-state theory in predicting the contribution of the activational barrier. Attempts to measure ΔVelfor the oxidation of the uncharged molecule ferrocene at various electrodes in acetonitrile were unsuccessful, although ΔVelwas again seen to be clearly positive.Key words: electrode kinetics, volumes of activation, nonaqueous electron transfer, solvent dynamics.
Molar excess volumes of ternary mixtures containing ether
Authors: Sharma V K , Romi
Published: April 2011

Molar excess volumes (VEijk) of 1,3-dioxolane (i) + benzene (j) + cyclohexane (k); 1,3-dioxolane (i) + benzene (j) + n-hexane (k); and 1,3-dioxolane (i) + benzene (j) + n-heptane (k) ternary mixtures have been measured dilatometrically as a function of composition at 298.15 K. The observed data have been analysed in terms of (i) Graph theoretical approach; (ii) Flory's theory; and (iii) Lacombe and Sanche's theory of liquid mixtures. It has been observed that VEijk values predicted by graph theoretical approach compare better with the corresponding experimental values than with the VEijk data predicted by other approaches.Key words: molar excess volumes, molar volume interaction parameters, connectivity parameter of third degree 3ξ.
Electrocatalytic hydrogenation of octyl aldehyde over Pd catalysts
Authors: Cirtiu Ciprian M , Ménard Hugues
Published: April 2011

The electrocatalytic hydrogenation (ECH) of octyl aldehyde (octanal) to octyl alcohol (octan-1-ol) was investigated using commercial Pd/alumina catalysts in aqueous ethanol. The influence of different parameters, such as catalyst support, current intensity, polarity of solvent, supporting electrolyte, and octanal concentration, on the electrocatalytic hydrogenation of octanal was studied.Key words: octanal, octan-1-ol, Pd/alumina catalyst, electrocatalytic hydrogenation.
Synthesis and characterization of intramolecularly coordinated alanes with new sterically demanding trisyl-based ligands
Authors: Lund Clinton L , Stanga Olimpiu , Quail J Wilson , Müller Jens
Published: April 2011

Five new intramolecularly coordinated aluminum species, whose molecular structures have been elucidated in solution by NMR spectroscopy and in the solid state by single crystal X-ray analysis, are described. All species are equipped with a trisyl-based ligand with a pyridyl donor group [Pytsi stands for -C(SiMe3)2SiMe2(2-C5H4N)]. While the compound (Pytsi)AlMeCl was accessible either from Li(THF)(Pytsi) and MeAlCl2 or from (Pytsi)AlCl2 and LiMe, the tert-butyl derivative (Pytsi)AltBuCl could only be obtained from Li(THF)(Pytsi) and tBuAlCl2. Attempted synthesis of (Pytsi)AltBuCl from (Pytsi)AlCl2 and LitBu or from (Pytsi)AlCl2 and tBuMgCl failed. Three other compounds (3-5) were synthesized and can be described as derivatives of (Pytsi)AlMe2 with additional groups in the ortho position of the pyridyl group. Compound 3 carried a Me group in the ortho position, while compounds 4 and 5 were equipped with Ph and 2,6-diisopropylphenyl moieties, respectively.Key words: aluminum, trisyl ligands, methyl alanes.
A new microwave-assisted synthetic approach to novel pyrimido[4,5-d]pyrimidines
Authors: Kidwai Mazaahir , Priya  , Rastogi Shweta , Singhal Kavita
Published: April 2011

An environmentally benign approach for the synthesis of novel 7-substituted 5-aryl-1H-pyrimido[4,5-d]pyrimidine-2,4-diones, using mineral supports for their catalytic role and as energy transfer media, is described. The methodology eliminates the usage of solvent during the reaction. The rate enhancement and high yield is attributed to the coupling of solvent-free conditions with microwaves. Further, the role of various supports is studied during the reaction and it is concluded that a MW-assisted basic alumina catalysed reaction is the best in terms of catalysis as well as reaction time and yield.Key words: microwave (MW) irradiation, SBT, pyrimido[4,5-d]pyrimidines, alumina, environmentally benign.
EFGShield — A program for parsing and summarizing the results of electric field gradient and nuclear magnetic shielding tensor calculations
Authors: Adiga Samyuktha , Aebi Dominic , Bryce David L
Published: April 2011

A computer program (EFGShield) is described that simplifies and summarizes the output from electric field gradient (EFG) and nuclear magnetic shielding tensor calculations performed independently using existing quantum chemical software. In addition to summarizing tensor magnitudes according to conventions commonly used by solid-state NMR spectroscopists, the program provides Euler angles relating the orientations of the EFG and shielding tensor principal axis systems (PAS). An atomic coordinate file is generated that also contains dummy atoms representing the orientations of the EFG and shielding tensor PASs in the molecular framework. We demonstrate the functionality of the program using calculations of the chlorine EFG and shielding tensors for strontium chloride dihydrate and calcium chloride dihydrate. Several models of the chloride environment in these compounds are tested, including those where point charges are used to represent the extended three-dimensional lattices within the self-consistent charge field perturbation approach. The results highlight both the shortcomings and successes of traditional localized orbital-based basis sets in the description of the NMR properties of extended systems. We anticipate that EFGShield will be a useful tool for spectroscopists using quantum chemical software to aid in the interpretation of experimental data.Key words: quantum chemical calculations, computer program, electric field gradient tensor, quadrupolar coupling constant, nuclear magnetic shielding tensor, Euler angles, alkaline earth chloride hydrates.
Self-assembled coating for modification of the electro-osmotic flow in nonaqueous capillary electrophoresis using formamide
Authors: Diress Abebaw G , Lucy Charles A
Published: April 2011

The use of pure nonaqueous solvents in capillary electrophoresis (CE) can alter the separation selectivity and enhance the solubility of hydrophobic compounds and enables the use of higher voltages. However, control of the electro-osmotic flow (EOF) is essential. In this work, we report the use of self-assembled coatings for EOF modification and elimination of analyte adsorptions onto silica capillaries in pure formamide. Bilayer capillary coatings derived from the double chain cationic surfactant dimethyldioctadecylammonium bromide (2C18DAB) reverses the EOF in buffers such as acetate, formate, and phosphate. Reversed EOF of >1.1 × 10–4 cm2/Vs enables the separation of the pharmaceutical drugs propranolol, metoprolol, chloroquine, and chloropheniramine in less than 5 min with efficiencies of 0.2–0.5 million plates/m (66 000 to 165 000 plates). Chemical and physical factors affecting the coating stability and their influence on separation speed and efficiency of the cationic drugs in formamide are also investigated.Key words: capillary electrophoresis, cationic surfactants, electro-osmotic flow, formamide, nonaqueous solvents.
PROTON MAGNETIC RESONANCE AND INFRARED SPECTRA OF SOME COMPLEXES OF N,N-DIMETHYLACETAMIDE
Authors: Carty A. J.
Published: April 2011

Proton magnetic resonance spectra of some complexes of In, Zn, Cd, and Sn halides and perchlorates with N,N-dimethylacetamide (DMA) have been measured in acetone-d6. Low field shifts of the methyl resonances of DMA on complex formation are dependent on metal and anion. The similarity of the spectra of all the complexes suggests only oxygen-coordinated DMA in solution. Infrared spectra in the range 2 000–625 cm−1 are recorded. Changes in the C—O and C—N stretching frequencies of the ligand on coordination are consistent with oxygen-bonded DMA both in the solid complexes and in solution.The new compounds Zn(ClO4)2•6DMA, Cd(ClO4)2•6DMA, CdI2•2DMA, and SnCl4•2DMA are reported.
TOTAL CROSS SECTIONS FOR IONIZATION BY ELECTRON IMPACT
Authors: Harrison A. G. , Jones E. G. , Gupta S. K. , Nagy G. P.
Published: April 2011

Total cross sections for ionization by 75 V electrons have been measured for a wide range of molecules. On the whole the results are in agreement with the cross sections reported by Lampe etal. rather than those reported by Otvos and Stevenson. The results fit neither a single linear correlation with molecular polarizability nor a simple postulate of additivity of atomic ionization cross sections.
Nuclear magnetic resonance studies. X. Determination of the thermodynamic parameters of the self-association of tricyclic aromatic aldehydes in solution
Authors: Gurudata  , Klinck R. E. , Stothers J. B.
Published: April 2011

The temperature dependence of the formyl proton shieldings of 9-anthraldehyde and 9-phenanthraldehyde in chloroform solutions has been measured. Four concentrations in the range 0.5–5.0 mole % were examined over the temperature interval − 60 to + 90 °C. From these results, the enthalpies and entropies of formation have been estimated for the complex formed by the self-association of two aldehyde molecules. The calculations indicate the ΔH and ΔS values to be − 1.9 ± 0.3 kcal/mole and − 6 ± 1 e.u., respectively. These results are compared with other available data.
Synthesis of mono-O-(2-diethylaminoethyl)-d-glucoses and distribution of substituent groups in O-(2-diethylaminoethyl)cellulose
Authors: Roberts E. J. , Rowland S. P.
Published: April 2011

O-(2-Diethylaminoethyl)cellulose (degree of substitution 0.048) was prepared by reacting cotton cellulose, in the form of fabric, with 2-diethylaminoethyl chloride in the presence of excess sodium hydroxide at room temperature. The modified cellulose was hydrolyzed and the substituted glucoses were identified by chromatographic comparison with authentic 2-O-, 3-O-, and 6-O-(2-diethylaminoethyl)-d-glucoses in the form of their trimethylsilyl ethers. Syntheses of authentic 2-O-, 3-O-, and 6-O-(2-diethylaminoethyl)-d-glucoses are described. The relative distribution of 2-diethylaminoethyl groups among the 2-O-, 3-O-, and 6-O-positions of the d-glucopyranosyl residue of cotton cellulose was found to be 1.27:0.35:1.00.
Nucleophilicity of low-valent metal complexes. I. The reactions of platinum(0) complexes with alkyl and acyl halides
Authors: Cook C. D. , Jauhal G. S.
Published: April 2011

The nucleophilic behavior of zero-valent platinum complexes toward a variety of covalent molecules has been studied. Although too rapid for convenient kinetic studies to be made, oxidative addition reactions of this type enable a number of novel organo-platinum(II) derivatives to be prepared without the use of conventional organometallic reagents. Cleavage of carbon–halogen bonds in unsaturated molecules of the type —C≡≡CX and CH==CHX is very fast, and the rate of reaction appears to depend little on the electronegativity of the carbon atom to which the halogen is bonded. Similar reactions occur between the zero-valent platinum species and acyl and sulfonyl halides. The S-sulfinate and acyl platinum derivatives, when heated, lose SO2 and CO, respectively, with the formation of alkyl or aryl platinum complexes.
Photochemistry of nitroso compounds in solution. VI. Photolysis of N-nitrosamides in acidic media
Authors: Chow Y. L. , Lee A. C. H.
Published: April 2011

The photolyses of several N-nitrosamides in acidic media were studied and compared with the photolysis of N-nitrosamines on the one hand, and with the thermolysis of N-nitrosamides on the other. The course of the photolysis was found to be similar to that of the N-nitrosamine photolysis, namely, (i) photo-elimination of [NOH], and (ii) a light-catalyzed denitrosation. In contrast to the exclusive cleavage of the nitrogen–carbonyl bond in the thermal decomposition of the N-nitrosamides, photolysis results in fission of the nitrogen–nitrogen bond.
Polarographic studies of α-substituted cystines
Authors: Thibert R. J. , Walton R. J.
Published: April 2011

The polarographic determination of some α-substituted cystines in 0.1 N hydrochloric acid, with thymol as a maximum suppressor, was investigated. A linear relationship of the diffusion current to the concentration of the compound was observed. The influence of substituent, thymol concentration, and pH on the apparent half-wave potential and shape of the polarograms was determined. The systems were not reversible.Potentiometric titration curves were obtained for the α-substituted cystines.
The photolysis of benzil in cyclohexane solution
Authors: Bunbury David L. , Wang Chiou Tong
Published: April 2011

Benzil has been irradiated in cyclohexane solution. The principal products are: benzoic acid; benzal-dehyde; phenyl cyclohexyl ketone; benzoin; benzoin benzoate; a compound tentatively identified as desyl benzoyloxydesyl ether; another compound not yet identified; and approximately one-third of the reacted benzil that was not accounted for. A small amount of unsaturation is also found. As long as there is enough benzil present (presumably to absorb all of the light) the benzil disappearance is linear with time. All products appear at the shortest times checked and so cannot be secondary products. If one neglects the benzoic acid approximately 19% of the benzoyl groups that react do so in the form of benzoyl radicals. No evidence for phenyl radical formation was found. The upper limit for the quantum yield of benzil disappearance at 366 mμ is 0.25. The benzoic acid does not arise directly during the photolysis but only when the solution is exposed to oxygen during the work-up. Preliminary experiments in cumene solution have shown that the amount of benzil lost for the same length of irradiation increases by a factor of about 1.5. In 2-propanol solution the increase is by a factor of 2.5. When 2-propanol is the solvent, a new product appears which is most probably the dimer of the ketyl radical which is formed when an excited benzil abstracts a hydrogen atom. This product is very unstable.
Mass spectra of tetrahydroquinolines
Authors: Draper P. M. , MacLean D. B.
Published: April 2011

The mass spectra of 1,2,3,4-tetrahydroquinoline and 5,6,7,8-tetrahydroquinoline have been recorded. The spectra of the 1-d1, 2,2-d2, 3,3-d2, and 4,4-d2 analogues of 1,2,3,4-tetrahydroquinoline, and the spectra of the 5-d1, 6,6-d2, and 8,8-d2 analogues of 5,6,7,8-tetrahydroquinoline have aided in the interpretation of the fragmentation mechanisms. The spectra of both isomers are characterized by fragment ions at M–1, M–15, and M–16 while the 5,6,7,8-isomer has an additional peak at M–28. The spectra of 2-, 3-, 4-, and 6-methyl-1,2,3,4-tetrahydroquinolines have also been examined. Substitution of a hydrogen by a methyl group in the 2- and 4-positions results in an intense M–15 peak, and substitution in the 3-position results in a peak at M–29. The main features of these spectra can be predicted from the proposed fragmentation pathways of the parent tetrahydroquinoline.
The deamination of 16-acetyl-17-aminoandrosta-5,16-dien-3β-ol
Authors: Rodríguez-Hahn L. , Romo J.
Published: April 2011

The deamination of 16-acetyl-17-aminoandrosta-5,16-dien-3β-ol (2a) with nitrous acid afforded two products. Their structures have been established as 3a and 3b.
Conversion of β-chloro-L-alanine to α-carbobenzoxy-DL-diaminopropionic acid
Authors: Benoiton Leo
Published: April 2011

Several N-acyl-β-chloroalanine esters have been prepared from the ester which was obtained by chlorination of L-cystine diester. Reaction of benzoyl-β-chloro-L-alanine ethyl ester with potassium phthalimide followed by acid hydrolysis yielded DL-diaminopropionic acid. Reaction of carbobenzoxy-β-chloro-L-alanine ethyl ester with potassium phthalimide followed by saponification and mild acid hydrolysis yielded α-carbobenzoxy-DL-diaminopropionic acid. The racemization took place during the amination step.
The AlCl3–LiAlH4 reduction of Δ9(11)-12-oxo and Δ9(11)-12-hydroxy steroids
Authors: Ziegler P. , Grivas J. C.
Published: April 2011

Desoxycholic acid and 3α,12α-dihydroxypregnane were transformed to the corresponding Δ9(11)-12-oxo compounds. These steroids and their NaBH4 reduction products were then hydrogenolyzed with AlCl3–LiAlH4 to provide Δ9(11)-compounds in good yield.
Kinetic studies of metalloporphyrin formation. Part I. Mn(II) with hematoporphyrin
Authors: Brisbin Doreen A. , Balahura Robert J.
Published: April 2011

The kinetics of the formation of Mn(III) hematoporphyrin in glacial acetic acid has been studied spectrophotometrically.On addition of Mn(II) to porphyrin in glacial acetic acid a species which appears to be the monocation immediately is formed and is then converted to Mn(III) hematoporphyrin at a rate suitable for kinetic studies.The rates of reaction were measured at 45, 50, and 55 °C and the activation energies were calculated.
Oxidations involving silver. I. Kinetics of the anodic oxidation of silver in alkaline electrolytes
Authors: Clarke T. G. , Hampson N. A. , Lee J. B. , Morley J. R. , Scanlon B.
Published: April 2011

The kinetics of the electrochemical oxidation of silver to Ag2O in NaOH have been studied at different temperatures and hydroxyl ion concentrations. The enthalpy of activation was found to be ~ 5 kcal/mole. The kinetics of oxidation of Ag2O to AgO are discussed.
Cinétique de l'oxydation de l'alcool benzylique par l'ion cérique
Authors: Paquette D. , Zador M.
Published: April 2011

not available
γ-Radiolysis of cyclohexane with electron scavengers. VI. N2O and SF6 as electron scavengers in the vapor phase
Authors: Sagert N. H. , Robinson R. W. , Blair A. S.
Published: April 2011

The γ-radiolysis of cyclohexane has been examined in the vapor phase using N2O and SF6 as electron scavengers. Both N2O and SF6 reduce the hydrogen yield from 4.6 to 3.0 G units, indicating that 3.0 G units of hydrogen have neutral species as precursors, while 1.6 G units have electrons as precursors.Radiolysis of cyclohexane vapor with more than 2% N2O produces 10.4 G units of cyclohexene and 11.5 of nitrogen. Carbon dioxide reduces both these yields; the extrapolated value of G(N2) is equal to G(electrons) at infinite CO2 concentration. Thus O− is likely a precursor of that part of the nitrogen yield in excess of G(electrons), and of the cyclohexene yield associated with this nitrogen yield.The first order molecular detachment of hydrogen is unaffected by electron scavengers, showing that most of this first order yield has neutral precursors. The implications for Dyne's general mechanism of hydrocarbon radiolysis are discussed.
Infrared study of the adsorption, desorption, and degassing processes of trimethyl-borate on a porous high-silica glass system
Authors: Shimizu Michie , Gesser H. D.
Published: April 2011

Infrared absorption has been applied to the process of adsorption, desorption, and degassing of trimethyl-borate on porous high-silica glass. The adsorbate was shown to react with the silanol and siloxane surface groups at room temperature to form ≡Si—OCH3 and =B—OCH3 as well as CH3OH which after high temperature degassing left ≡SiOH and =BOH on the surface.
Ion–solvent interaction of tetraalkylammonium ions in solvents of high dielectric constant. Part I. Conductance and Walden product of tetraalkylammonium ions in N-methylacetamide at different temperatures
Authors: Singh Raj Deo , Rastogi Pushti Prakash , Gopal Ram
Published: April 2011

Ion–solvent interaction of the tetraalkylammonium ions (R4N+) in N-methylacetamide has been studied from the point of view of electrical conductance and the derived Walden product. The results indicate R4N+ ions to be structure breakers in this solvent, quite opposite to their general behavior in aqueous solutions. The effect is conspicuous in the smaller Me4N+ and Et4N+ ions, but is less marked in the larger ions.
Effect of proton acceptors on the condensed phase radiolysis of cyclohexane-d12 in cyclopentane
Authors: Stone J. A.
Published: April 2011

C2H5OH decreases the HD and D2 yields from small concentrations of c-C6D12 in c-C5H10. The results are consistent with a previous suggestion that the enhanced yields in this system are due to exothermic charge transfer. Charge transfer to c-C6D12 is only ~ 10% as efficient as proton transfer to C2H5OH at 4.1 mole % c-C6D12 or C2H5OH. Experiments at 196 and 77 °K suggest that resonance charge transfer in the cyclopentane matrix may occur to some extent.
Apparent activation energies for electrical conduction of solid and liquid germanium(II) sulfide
Authors: D'Amboise M. , Handfield G. , Bourgon M.
Published: April 2011

The specific conductivity of germanium(II) sulfide has been measured, under an inert atmosphere, from room temperature to the boiling point (750 °C). Interpretation of the results indicates that the intrinsic conductivity is observed in the solid in the upper temperature range: the calculated energy gap is 1.58 eV which coincides with the value of the optical gap for indirect transition. The calculated energy gap of liquid GeS is 2.3 eV and it is shown that the increase in the gap occurs on melting and is not due to a transformation in the solid.
The chemical interpretation and the temperature dependence of the 14N nuclear quadrupole resonance of aniline and several derivatives
Authors: Yim C. T. , Whitehead M. A. , Lo Donald H.
Published: April 2011

The 14N nuclear quadrupole resonance frequencies of aniline, o- and p-phenylene diamine, and p-chloro-, p-bromo-, and p-iodo-aniline were measured with a super-regenerative oscillator over a temperature range from 77 to 292 °K. The temperature dependence is analyzed. The chemical interpretation of the quadrupole coupling constants and asymmetry parameters is described.
Ion–molecule reactions in methyl mercaptan and methyl-d3 mercaptan
Authors: Nagy G. P. , Thynne J. C. J. , Harrison A. G.
Published: April 2011

The ion–molecule reactions occurring in CH3SH and CD3SH have been identified and rate constants measured for ions of 3.4 eV ion exit energy. The reaction CD3SH+ + CD3SH involves predominantly transfer of the mercaptyl hydrogen.
Effect of substituents on the chemical shift of benzylic protons
Authors: Fraser Robert R. , Gurudata  , Renaud Roger N. , Reyes-Zamora Cesar , Swingle Robert B.
Published: April 2011

The chemical shift of the benzylic protons in fifteen series of para-substituted toluenes bearing different groups in the alpha position are reported. In each series a plot of the chemical shift in tau units of the benzylic protons against the Hammett σ value of the para substituent is linear. The slopes of these plots vary from −0.20 to +0.01 p.p.m./σ. The variation of slopes appears to be conformationally dependent, an observation at odds with current theory. In two rigid systems having the same geometry the slope has been found to vary from −0.12 to −0.18 indicating a dependence on other factors as well. The effect of solvent on the slopes has been determined, and shows no correlation with solvent dielectric properties.
Transannular reactions in the dibenzo[a,d]cycloheptene series. IV. 10,5 Ketone–amide interactions
Authors: Davis M. A. , Dobson T. A. , Jordan J. M.
Published: April 2011

10-Ketodibenzocycloheptene-5-carboxamides undergo transannular interactions to form carbinolamides. This approach has been used to prepare a number of 11-substituted and -unsubstituted-10,11-dihydro-10,5-(iminomethano)-5H-dibenzo[a,d]cycloheptenes. The ketolactone 3 was a convenient starting material for the substituted compounds. It reacted readily with primary amines to give the carbinolamides 7 or 8, and underwent equally rapid transformations with secondary amines or alkali to furnish products derived from aerial oxidation, decarboxylation, ring contraction, and/or dimerization. The epoxynitrile 20 was converted by a 5-step sequence to the ketocarboxamide 27 which cyclized at once to the 11-unsubstituted carbinolamide 28. A modification of this sequence gave the carbinolamine 31.
Synthesis of D-chalcose
Authors: Lawton B. T. , Ward D. J. , Szarek W. A. , Jones J. K. N.
Published: April 2011

A facile synthesis of 4,6-dideoxy-3-O-methyl-D-xylo-hexose (D-chalcose) is described, which involves the preparation of methyl 4,6-dichloro-4,6-dideoxy-3-O-methyl-D-galactopyranoside (2) by a reaction with sulfuryl chloride, and its reduction to the dideoxy sugar by hydrogenation over Raney nickel.
Spin trapping by use of nitrosodurene and its derivatives
Authors: Konaka Ryusei , Terabe Shigeru , Mizuta Taiichi , Sakata Shigeru
Published: April 2011

In spin trapping the N-methyl-N-phenylaminomethyl radical with nitrosodurene, an esr spectmm exhibiting line width alternation was observed despite the normal spectral pattern found with the use of nitroso-tert-butane. Nitrosodurene derivatives, N-duryl nitrone and methyl N-duryl nitrone, have been revealed to be other excellent spin traps for the N-, 0-, and S-centered radicals. Spin adducts of these radicals, which can be independently prepared by spin trapping with nitrosodurene, are stable and can be easily discriminated by large differences in β-hydrogen splittings or characteristic patterns. Methyl N-duryl nitrone reacted with tert-butyl hydroperoxide to give a spin adduct which could be clearly distinguished in the esr spectra from the tert-butoxy adducts prepared independently from other sources. Accordingly, it seems to be the tert-butylperoxy adduct. Similarly, hydrogen peroxide gave a different spectrum from the hydroxy adducts. Alkyl hydroperoxides caused molecule-induced homolysis with the nitroso compounds to produce alkoxy adducts of the respective nitroso compounds. Some phenyl and duryl alkoxy nitroxides undergo decomposition to give alkyl radicals which were trapped by the nitroso compounds.
Simulation of isotropic electron spin resonance spectra: a transportable basic program
Authors: Oehler Uwe M , Janzen Edward G
Published: April 2011

A computer program written in BASIC is presented for the simulation of isotropic esr spectra using a microprocessor. Since BASIC is the most common microprocessor language, this program can easily be adapted to most microprocessors. Through the use of more efficient methods the capabilities of much larger FORTRAN programs, run on mainframe computers, are retained in the more restricted environment of the microprocessor. As a result, most spin trapping results can be dealt with easily. A number of sample simulations illustrate the program’s features.
Substituent effects in the kinetic analysis of free radical reactions with nitrone spin traps
Authors: Greenstock C L , Wiebe R H
Published: April 2011

The kinetics of reactions of the water radiolysis species with substituted phenyl-N-tert-butyl nitrones (PBN), have been studied directly, in situ, using a pulsed Van de Graaff accelerator and kinetic spectrophotometry. The spin trapping of other secondary radiation-induced electrophilic and nucleophilic free radical species was also studied. The mechanistic aspects of these reactions are discussed in terms of the kinetic data. The effect of structure and substituents on the rate of spin trapping was tested for five para-substituted PBN’s. It was found that electron-withdrawing groups increase the rate of nucleophilic reactions involving hydrated electrons, formyl anions, and α-hydroxyalkyl radicals with substitued PBN. Electron-donating substituents produce the opposite effect. These studies confirm that nitrones are effective spin traps because of their high reactivity towards radiation-induced free radicals. Caution must be observed, however, in view of their lack of specificity, in interpreting spin-trapping data in complex steady-state systems involving more than one primary or secondary radical species, or where unstable spin-adducts are formed.
Electron spin resonance and electron nuclear double resonance study of diastereomeric nitroxyl radicals produced by spin trapping
Authors: Kotake Yashige , Kuwata Keigi
Published: April 2011

Electron spin resonance and electron nuclear double resonance spectra of nitroxyl radicals having two asymmetric carbons on one side of the nitroxyl function were observed. The radicals were produced by the abstraction of hydrogen by photoexcited benzophenone from amines, ethers, and alcohols followed by spin trapping with phenyl-N-t-butyInitrone. The difference in esr parameters of diastereomers depends on the functional group attached to the asymmetric carbon. The nature of the intramolecular interaction which brings about this difference is discussed in detail.