bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic Characteristics of a Direct Methanol Fuel Cell
Authors: Wang Maohai , Guo Hang , Ma Chongfang
Published: May 2006

The detailed dynamic characteristics of direct methanol fuel cells need to be known if they are used for transportable power sources. The dynamic response of a direct methanol fuel cell to variable loading conditions, the effect of cell temperature and oxygen flow rate on the cell response, and the cell response to continuously varying cell temperatures were examined experimentally. The results revealed that the cell responds rapidly to variable current cycles and to continuously varying cell temperatures. The increasing rate of gradual loading significantly influences the dynamic behavior. The effects of cell temperature and oxygen flow rate on the cell dynamic responses are considerable, but the cell voltage differences over the range of cell temperatures and oxygen flow rates are small for gradual loading. The cell response value to cell temperature during decreasing temperature is lower than that during increasing temperature.
Turbulence Structures Downstream of a Localized Injection in a Fully Developed Channel Flow
Authors: Haddad M. , Labraga L. , Keirsbulck L.
Published: May 2006

The effects of localized blowing through a porous strip on a turbulent channel were studied experimentally. The measurements were conducted downstream of the porous strip for three blowing rates: 3%, 5%, and 8% (of the velocity at the centerline of the channel). It was found that the injection affects several turbulence parameters. Indeed, blowing decreases the skin friction while it increases the turbulence intensities and the Reynolds stresses. A study of cross-correlations in the streamwise and spanwise direction’s showed that both inclination angles in the (x,y) and (x,z) planes were increased with blowing.
Intercomparison of methods for image quality characterization. II. Noise power spectruma)
Authors: Dobbins James T. , Samei Ehsan , Ranger Nicole T. , Chen Ying
Published: May 2006

Second in a two‐part series comparing measurement techniques for the assessment of basic image quality metrics in digital radiography, in this paper we focus on the measurement of the image noise power spectrum (NPS). Three methods were considered: (1) a method published by Dobbins et al. [Med. Phys. 22, 1581–1593 (1995)], (2) a method published by Samei et al. [Med. Phys. 30, 608–622 (2003)], and (3) a new method sanctioned by the International Electrotechnical Commission (IEC 62220‐1, 2003), developed as part of an international standard for the measurement of detective quantum efficiency. In addition to an overall comparison of the estimated NPS between the three techniques, the following factors were also evaluated for their effect on the measured NPS: horizontal versus vertical directional dependence, the use of beam‐limiting apertures, beam spectrum, and computational methods of NPS analysis, including the region‐of‐interest (ROI) size and the method of ROI normalization. Of these factors, none was found to demonstrate a substantial impact on the amplitude of the NPS estimates ( relative difference in NPS averaged over frequency, for each factor considered separately). Overall, the three methods agreed to within when averaged over frequencies .
Under Suspicion
Authors: Scholes Derek T.
Published: May 2006

Intuition
. A Novel.
By Allegra Goodman
. Dial (Random House), New York, 2006. 351 pp. $25, C$35. ISBN 0-385-33612-8.

This novel centers on a postdoctoral researcher who obtains results that seem too good to be true, results his sometimes girlfriend and fellow postdoc believes are fraudulent
Modeling the Dynamic Regulation of Nitrogen Fixation in the Cyanobacterium
Trichodesmium
sp
Authors: Rabouille Sophie , Staal Marc , Stal Lucas J. , Soetaert Karline
Published: May 2006

A physiological, unbalanced model is presented that explicitly describes growth of the marine cyanobacterium
Trichodesmium
sp. at the expense of N
2
(diazotrophy). The model involves the dynamics of intracellular reserves of carbon and nitrogen and allows the uncoupling of the metabolism of these elements. The results show the transient dynamics of N
2
fixation when combined nitrogen (NO
3
−
, NH
4
+
) is available and the increased rate of N
2
fixation when combined nitrogen is insufficient to cover the demand. The daily N
2
fixation pattern that emerges from the model agrees with measurements of rates of nitrogenase activity in laboratory cultures of
Trichodesmium
sp. Model simulations explored the influence of irradiance levels and the length of the light period on fixation activity and cellular carbon and nitrogen stoichiometry. Changes in the cellular C/N ratio resulted from allocations of carbon to different cell compartments as demanded by the growth of the organism. The model shows that carbon availability is a simple and efficient mechanism to regulate the balance of carbon and nitrogen fixed (C/N ratio) in filaments of cells. The lowest C/N ratios were obtained when the light regime closely matched nitrogenase dynamics.
Identifying Functionally Important Mutations from Phenotypically Diverse Sequence Data
Authors: Jensen Kyle , Alper Hal , Fischer Curt , Stephanopoulos Gregory
Published: May 2006

Here we present a simple statistical method to determine the phenotypic
contribution of a single mutation from libraries of mutants with
diverse phenotypes in which each mutant contains a multitude of
mutations. The central premise of this method is that,
given
M
phenotypic classes, mutations that do not affect the
phenotype should partition among the
M
classes according to a
multinomial distribution. Deviations from this distribution are
indicative of a link between specific mutations and phenotypes. We
suggest that this method will aid the engineering of functional nucleic
acids, proteins, and other biomolecules by uncovering target sites for
rational mutagenesis. As a proof of the principle, we show how the
method can be used to deduce the individual effects of mutations in a
set of 69 P
L
-λ promoter variants. Each of these
promoters was generated by error-prone PCR and incorporated numerous
mutations. The activity of the promoters was assayed using flow
cytometry to measure the fluorescence of a green fluorescent protein
reporter gene. Our analysis of the sequences of these mutants revealed
seven positions having a statistically significant correlation with
promoter activity. Using site-directed mutagenesis, we constructed
point mutations for several sites, both statistically significant and
insignificant, and combinations of these sites. Our results show that
the statistical method correctly elucidated the phenotypic
manifestations of these mutations. We suggest that this method may be
useful for expediting directed evolution experiments by allowing both
desired and undesired mutations to be identified and incorporated
between rounds of
mutagenesis.
arsRBOCT
Arsenic Resistance System Encoded by Linear Plasmid pHZ227 in
Streptomyces
sp. Strain FR-008
Authors: Wang Lianrong , Chen Shi , Xiao Xiang , Huang Xi , You Delin , Zhou Xiufen , Deng Zixin
Published: May 2006

In the arsenic resistance gene cluster from the large linear plasmid pHZ227, two novel genes,
arsO
(for a putative flavin-binding monooxygenase) and
arsT
(for a putative thioredoxin reductase), were coactivated and cotranscribed with
arsR1-arsB
and
arsC
, respectively. Deletion of the
ars
gene cluster on pHZ227 in
Streptomyces
sp. strain FR-008 resulted in sensitivity to arsenic, and heterologous expression of the
ars
gene cluster in the arsenic-sensitive
Streptomyces
strains conferred resistance on the new hosts. The pHZ227 ArsB protein showed homology to the yeast arsenite transporter Acr3p. The pHZ227 ArsC appears to be a bacterial thioredoxin-dependent ArsC-type arsenate reductase with four conserved cysteine thioredoxin-requiring motifs.
Campylobacter curvus
-Associated Hepatic Abscesses: a Case Report
Authors: Wetsch Nicole M. , Somani Karim , Tyrrell Gregory J. , Gebhart Carol , Bailey R. J. , Taylor Diane E.
Published: May 2006

Campylobacter curvus
was isolated from blood cultures of a patient with liver abscesses. Bacterial identification involved Gram staining, biochemical analysis, gas-liquid chromatography, and 16S rRNA sequencing. The difficulty in isolation, identification, and growth of the species confirms previous work that these organisms may be overlooked by conventional detection methods.
Syntheses related to the carbohydrate moiety in lincomycin
Authors: Howarth G. B. , Lance D. G. , Szarek W. A. , Jones J. K. N.
Published: May 2006

Addition of nitroethane to 1,2:3,4-di-O-isopropylidene-α-D-galacto-hexodialdo-1,5-pyranose (3) gave a mixture of β-nitro alcohols (4), which was acetylated to afford a mixture of β-nitro acetates (5). Dehydroacetylation of the latter gave cis- and trans-6,7,8-trideoxy-1,2:3,4-di-O-isopropylidene-7-C-nitro-α-D-galacto-oct-6-enose (6 and 7) in a ratio of about 6:1, respectively. Addition of ammonia to the cis-nitroolefin (6) gave rapidly a mixture of two stereoisomeric vic-nitroamines (8), which was acetylated to furnish a mixture of two 6-acetamido-6,7-dideoxy-7-C-nitro derivatives (9). The same products (9) were obtained by the action of ammonia in aqueous tetrahydrofuran upon the preponderant β-nitro acetate, followed by acetylation. Vinylation of the aldehyde 3 gave a mixture of allylic alcohols (10); the preponderant epimer was obtained pure in crystalline form. The various 8-carbon sugar derivatives are of interest as potential intermediates in the synthesis of the carbohydrate moiety in lincomycin.
Action of some bases on the tropylium cation
Authors: McGeachin S. G.
Published: May 2006

The tropylium cation has been treated with the hindered bases triphenylmethyl sodium, 2,6-dimethoxy-phenyl lithium, and 2,4,6-tri-t-butylphenyl lithium to give substituted cycloheptatrienes. Where possible its reaction with tertiary amines follows Reaction Scheme 1 to give immonium salts which can be hydrolyzed to tropylated aldehydes and ketones. Its reaction with trimethylamine gives the quaternary ammonium salt which on exposure to the atmosphere is decomposed to trimethylammonium fluoborate and a mixture of tropone and ditropyl ether.
Steroid derivatives of cysteamine and cysteine
Authors: Wheeler Owen H. , Reyes-Zamora Cesar
Published: May 2006

A number of androstenone, estrone, and pregnenone derivatives of cysteamine have been prepared by reacting the steroid amines with ethylene monothiolcarbonate. The amides of androstenone carboxylic acid with mercaptoethylamine and cysteine have also been prepared.
Conformational analysis of 1,4-disubstituted cyclohexanes. III. trans-1,4-Di(trifluoroacetoxy)cyclohexane
Authors: Wood Gordon , Woo E. P. , Miskow M. H.
Published: May 2006

By the low temperature nuclear magnetic resonance integration method the standard free energy difference between the diequatorial and the diaxial forms of 1-H,4-H-trans-1,4-di(trifluoroacetoxy)-cyclohexane-d8 was found to be 77 ± 5 cal/mole. The conformational free energy (−ΔG0) of the trifluoroacetoxy group in the monosubstituted cyclohexane was 485 ± 4 cal/mole at the same temperature. The non-additivity of the −ΔG0 values is discussed in terms of transannular electrostatic interaction.
Evidence for the formation of exo and endo aziridines in the reaction of cis–endo and cis–exo-bicyclo[2•2•1]-5-heptene-2,3-dicarboxylic anhydride and benzenesulfonyl azide
Authors: Oehlschlager A. C. , Zalkow L. H.
Published: May 2006

Benzenesulfonyl azide has been found to react with cis–endo and cis–exo bicyclo[2•2•1]-5-heptene-2,3-dicarboxylic anhydride to give in both cases, predominantly the more hindered endo aziridine in addition to the exo aziridine in apparent violation of the "exo-addition rule" (3). The stereochemistry of the aziridine rings were determined by nuclear magnetic resonance analysis and by conversion of the endo-aziridine-exo-anhydride to 2-endo-benzenesulfonamidobicyclo[2•2•1]heptane. The endo-aziridine-endo-anhydride has been previously (4) converted into a lactone-N-benzenesulfonyl-lactam.
A nuclear magnetic resonance study of the conformations of triribonucleoside diphosphates, diribonucleoside phosphates, 5′-ribonucleoside phosphates, and ribonucleosides of uracil and cytosine; temperature dependence of the base proton chemical shifts
Authors: Smith Ian C. P. , Blackburn B. J. , Yamane Tetsuo
Published: May 2006

The temperature dependence of the nuclear magnetic resonance spectra of U, C, 5′-UMP, 5′-CMP, UpU, and CpU indicates a specific deshielding of the base proton at position-6 by an hydroxyl, phosphodiester, or phosphate group at position-5′, and demonstrates that in these compounds the bases exist in the anti conformation. Similar experiments on the wobble pair UpUpU and UpUpC suggest that the spatial arrangements of both trinucleoside diphosphates are identical, and that in these arrangements the bases are predominantly in the anti conformation.
Excess thermodynamic properties of isopropanol–n-decanol mixtures
Authors: Singh Jaswant , Pflug H. D. , Benson G. C.
Published: May 2006

Molar excess Gibbs free energies, obtained from static vapor pressure measurements on isopropanol–n-decanol mixtures over the temperature range 20–50 °C, are reported. Results of direct determinations of heats and volumes of mixing at 25 °C are also presented.
Mass spectra of organometallic compounds. VI. Some indenylmetal derivatives and related compounds
Authors: King R. B.
Published: May 2006

The mass spectra of the following complexes have been investigated: (a) the indenylmolybdenum carbonyl derivatives CH3Mo(CO)3C9H7, π-C3H5Mo(CO)2C9H7, π-CH3SCH2Mo(CO)2C5H5, and C9H7Mo(CO)2I; (b) the bisindenyl derivative (C9H7)2Fe; (c) the series of compounds C5H5FeC9H7, C5H5FeC9H9, and C5H5FeC9H11 with different degrees of hydrogenation of the π-indenyl ligand. The following features of particular interest were noted: (a) evidence for the existence of small amounts of the new compound π-C3H5Mo(CO)2C9H6C3H5 in the sample of π-C3H5Mo(CO)2C9H7; (b) evidence for the pyrolysis of C9H7Mo(CO)2I to give [C9H7MoI2]2 and (C9H7)2MoCOI; (c) evidence for the fragmentation of C9H7Fe+ to give the ion C9H7+ and a neutral iron atom; (d) evidence for parallel pathways for fragmentation of the parent ion from C5H5FeC9H11 involving elimination of CH3, C2H4, C3H5, C5H6, and H2. Diagnostic features from the mass spectrum for the presence of a π-indenyl ligand in a complex appear to be the ions C9H8+, C9H7+, C7H5+, C5H3+, and C9H72+.
Phenoxo complexes of copper(II)
Authors: Harrod J. F.
Published: May 2006

A series of phenoxo complexes of copper(II) containing a variety of halophenoxo ligands and a variety of amine ligands has been prepared. The thermal stability of the complexes with regard to the decomposition reaction:[Formula: see text]was found to be lower with those ligands, L, which increase the oxidizing power of the copper(II) and vice versa.The intense absorption bands in the visible region exhibited by these complexes have been assigned to a metal-to-ligand charge transfer process.
Evidence for reversible intermediate formation in cyclopentenone cycloaddition
Authors: Mayo P. de , Nicholson A. A. , Tchir M. F.
Published: May 2006

The usual kinetics for product formation lead to variable values of kd, the rate constant for decay of the responsible triplet. On the assumption that at least one intermediate is formed which gives either products, or reverts to starting materials, a value near 108 s−1 is obtained for kd both from cyclopentene and hex-3-ene cycloadditions.
Syntheses of 8-acetoxy-4-twistanone, twistane, 1-twistanol, 1-twistylamine, and 1-twistane carboxylic acid
Authors: Bélanger A. , Lambert Y. , Deslongchamps P.
Published: May 2006

8-Acetoxy-4-twistanone (8) has been obtained in one-step from decalin dione 4 and a rigorous chemical proof has been obtained by chemical conversion of 8 into 4-twistanone (6). Twistane (1), 1-twistanol (15), 1-twistane carboxylic acid (17), and 1-twistylamine (20) have also been synthesized from compound 8 and chemical proofs are included.
Monomolecular films of compounds with potential dermophilic and prophylactic properties. Esters of dihydroxyacetone
Authors: Quintana Ronald P. , Garson Lorrin R. , Lasslo Andrew
Published: May 2006

The synthesis of 1,3-diundecanoyloxyacetone (1) and 1-undecanoyloxy-3-hydroxyacetone (2) is reported. The properties of 1, spread as a pure monomolecular film and in mixed films with stearic acid, were determined and evaluated. Compound 2 did not form films. The compounds were designed to exert, potentially, long-lasting insect-repellent activity subsequent to anchoring to the skin.
The Wallach rearrangement. Part V. Acid catalyzed hydrolysis of azobenzene-4-hydrogen sulfate
Authors: Buncel E. , Strachan W. M. J.
Published: May 2006

In relation to the intermediacy of azobenzene-4-hydrogen sulfate in the Wallach rearrangement of azoxybenzene, the potassium salt has been characterized and subjected to examination under acidic conditions. A pKa value of −2.14 has been obtained, for N-protonation. The sulfate salt hydrolyzes to p-hydroxyazobenzene in acid media and the rate of the reaction has been measured over the region 22–42% H2SO4 at 25° spectrophotometrically. A correlation between rate and acidity function indicates that a two-proton process is involved; a reactive species is proposed having a nitrogen and the phenolic oxygen protonated. The relevance of these findings to Wallach rearrangement studies is discussed.
A distorted tetrahedral copper(II) complex: 1,2-bis(diphenylphosphineoxido)ethane copper(II) chloride
Authors: Mathew M. , Palenik Gus J.
Published: May 2006

The crystal structure of 1,2-bis(diphenylphosphineoxido)ethane copper(II) chloride has been determined by X-ray diffraction techniques. The compound is the first structural determination of a CuCl2–phosphineoxide adduct and exhibits some very large distortions from the ideal tetrahedral symmetry. The Cl—Cu—O angle is 140.2° and the Cu—Cl distance of 2.195 Å is shorter than in other CuCl2 complexes.
Conformations and configurations of some chlorosulfated α- and β-D-pentopyranosyl chlorides
Authors: Jennings H. J.
Published: May 2006

The conformations of the fully chlorosulfated α- and β-D-xylopyranosyl and lyxopyranosyl chlorides in deuteriochloroform solution have been studied by proton magnetic resonance spectroscopy. The analysis of the spectra indicated that the anomeric effect is a factor in determining the conformational preference of the pentopyranosyl chlorides, as each existed predominantly in the conformation in which the chlorine was axial. A number of factors involving the synthesis of these chlorides have also been elucidated.
Reaction of metallic nitrilotriacetates with histamine
Authors: Beauchamp A. L. , Israeli J. , Saulnier H.
Published: May 2006

Cu(II), Ni(II), Co(II), and Zn(II) nitrilotriacetates (MeX−) react with histamine nitrate (LH+) to form a protonated mixed complex MeXLH where the metal appears to be bound only to the tertiary imidazolic nitrogen of histaminium ion. At higher pH values the proton dissociates to yield a mixed complex ion MeXL− in which both the imidazolic nitrogen and the terminal amino group are coordinated. The formation constants of these species were calculated from the potentiometric titration curves.
Kinetic studies of the substitution reactions of the cis-dihalotetracarbonylmanganate(I) ions
Authors: Smith Frank E. , Butler Ian S.
Published: May 2006

The substitution reactions of (C2H5)4[cis-Mn(CO)4X2], where X = Br or I, with a variety of ligands, L, were observed to take place with the loss of halide ion, X−, to form cis-Mn(CO)4LX and (C2H5)4NX. The reaction rates in s-tetrachloroethane were first order in substrate, independent of both the nature and the concentration of L, and decreased with increasing atomic weight of the halogen. A dissociative mechanism involving the breaking of a manganese–halogen bond as the rate-determining step is proposed. It is postulated that the order of reactivity of the substrates is most probably the result of an entropy rather than an enthalpy effect. The substitution reactions of (C2H5)4N[cis-Mn(CO)4BrI] in s-tetrachloroethane were also studied kinetically and found to be first order in substrate and independent of the nature and concentration of L. The products of these reactions, however, were mixtures of cis-Mn(CO)4LBr and cis-Mn(CO)4LI, and (C2H5)4NBr and (C2H5)4NI. A solvent study of the reaction between (C2H5)4N[cis-Mn(CO)4Br2] and P(C6H5)3 indicated that the rate of reaction tended to increase with increasing polarity of the solvent.
Nuclear recoil reactions in organomanganese compounds. III. Mn(CO)5
Authors: Jong I. G. de , Srinivasan S. C. , Wiles D. R.
Published: May 2006

Experimental evidence is presented which shows that upon neutron irradiation of the compounds Mn2(CO)10, CpMn(CO)3, and CH3CpMn(CO)3 the recoiling 56Mn atom gathers carbonyl radicals to stabilize itself in the group Mn(CO)5, with about 10% radiochemical yield. Basically, the experiments involved addition of iodine to the irradiated compound and identification of the radioactive IMn(CO)5 by carrier techniques. It is suggested that in Mn2(CO)10 targets, the species produced is the •Mn(CO)5 radical itself. Some experimental data are given to show that this radical is stable for over 1 h in the solid at room temperature, but decomposes rapidly above about 60°. The radical decomposes in 20–30 s in solution. In both other target compounds, the species produced is chemically more stable, although it reacts rapidly with iodine. This species is found to be HMn(CO)5, which occurs to the extent of 10–12% in CpMn(CO)3. CH3Mn(CO)5 was also detected in CH3CpMn(CO)3 targets, and its yield was found to be a function of the concentration of isooctane used as diluent in the targets.Results from other studies are discussed in the light of the present data, and it is concluded that in general, in neutron-irradiated metal carbonyl compounds, the recoil atom is able to accumulate carbonyl radicals to a greater extent than is consistent with the composition of the target compound.
Methyl and trifluoromethyl radical attack on ethers
Authors: Arthur N. L. , Gray Peter , Herod A. A.
Published: May 2006

The reactions of CF3 radicals with dimethylether and diethylether and of CH3 radicals with dimethylether and diisopropylether have been studied. The photolyses of acetone and hexafluoroacetone were used as radical sources; all rate constants are based on the rate constants for radical dimerization. The Arrhenius parameters measured are as follows[Formula: see text]
Electrochemiluminescence of carbazole
Authors: Santhanam K. S. V. , O'Brien R. N. , Kirk A. D.
Published: May 2006

Effect of supporting electrolytes in the electrochemiluminescence of carbazole has been studied with a view to understanding more about the mechanism of the chemiluminescence process. Comparison of the emission spectrum with its fluorescence and phosphorescence spectra suggests that the excited state is not carbazole. The intense chemiluminescence observed with tetra-n-butyl ammonium iodide as supporting electrolyte has been examined.
Organoantimony compounds. I. Infrared spectra of some trimethyl- and triphenyl-antimony derivatives
Authors: Goel R. G. , Joshi P. N. , Ridley D. R. , Beaumont R. E.
Published: May 2006

Organoantimony compounds of the type R3SbX and (R3Sb)2OX, where R is methyl or phenyl, and X is a bivalent anionic group such as SeO4, CrO4, or C2O4, have been prepared. Structural characteristics of these compounds have been determined by studying their infrared spectra in the solid state between 4000 and 250 cm−1. The spectral results indicate that in both types of compounds the anion X is coordinated to the R3Sb or (R3Sb—O—SbR3) group resulting in non-ionic, five coordinate, polymeric structures.
Polarographic reduction of D-mannurono-γ-lactone
Authors: Johnston J. R. , Thibert R. J.
Published: May 2006

The polarographic reduction of D-mannuronolactone is a diffusion controlled process, and is analytically applicable over the concentration range 20–100 μg lactone per ml. The addition of KH2PO4 gives similar results to those obtained with D-glucuronolactone, but the results suggest that the D-mannuronolactone ring is less reactive.
Anilinium chloride as a model for the transition state for benzyl chloride solvolysis
Authors: Lee Ikchoon , Hyne J. B.
Published: May 2006

The solvent composition dependence of the partial molal volume of the transition state of benzyl chloride solvolysing in water–ethanol mixtures is compared with that of anilinium chloride and a number of quaternary alkyl ammonium chlorides. It is concluded that anilinium chloride is not a good electrostatic model for the benzyl chloride transition state even though it may be a fair structural model. The partial molal volume of tetraethylammonium chloride is very similar to that of the transition state suggesting that charge development in the activation process is far from being fully ionic.
A 19F nuclear magnetic resonance investigation of the formation of Sb2F11− and SbnF5n+1− in the CsF–SbF5, t-butyl halide–SbF5, and tetraalkylammonium hexafluoroantimonate–SbF5 systems
Authors: Bacon J. , Dean P. A. W. , Gillespie R. J.
Published: May 2006

Fluorine nuclear magnetic resonance spectra have been obtained for the t-butyl fluoride–SbF5, t-butyl chloride–SbF5, tetraethylammonium hexafluoroantimonate–SbF5, and cesium fluoride–SbF5 systems, both with and without SO2 solvent. In SO2 solution the anion is Sb2F11− for all the systems, any remaining SbF5 being converted to SbF5•SO2. It is concluded that in the systems that do not contain SO2, higher polymeric anions SbnF5n+1−, where n > 2, are present. t-Butyl chloride and t-butyl fluoride give the t-butyl carbonium ion, as has been previously reported. Tetrabutylammonium and benzyltri-methylammonium cations appear to decompose to a carbonium ion and an adduct SbF5•NR3 in the presence of SbF5.
Positive ion reactions
Authors: Fite Wade L.
Published: May 2006

Progress over the past five years in the measurement of rate coefficients and cross sections for interactions between positive ions and neutral molecules of particular interest to aeronomy is reviewed. Emphasis is placed on the methods of experimentation developed for studies in the range of thermal energies and slightly above. Along with discussion of the range of applicability of each of the techniques, illustrated by examples of measurements on processes of aeronomic interest, some evaluation of limitations of applicability and reliability of the measurements is made. A table summarizing results obtained to date on processes pertaining to the atmospheres of the earth and neighboring planets is presented.
Some benzophenanthridine alkaloids from Bocconiaarborea
Authors: MacLean D. B. , Gracey D. E. F. , Saunders J. K. , Rodrigo R. , Manske R. H. F.
Published: May 2006

The minor alkaloids of B. arborea have been identified. Three of them have been shown to be dihydro-sanguinarine, oxysanguinarine, and 11-O-methyldihydrochelerythrine respectively. The structure of the fourth has been established by physical methods and by synthesis as the hitherto unknown 1,3-bis(11-hydrochelerythrinyl)acetone. It does not appear to be an artefact. The high resolution mass spectra of some dihydrochelerythrine derivatives are discussed.
Azaindoles. Part I. The syntheses of 5-aza- and 5,7-diazaindoles by the non-catalytic thermal indolization of 4-pyridyl- and 4-pyrimidylhydrazones respectively
Authors: Crooks P. A. , Robinson B.
Published: May 2006

The thermal indolization of a series of 4-pyridyl- and 4-pyrimidylhydrazones has been investigated. Under these conditions, isobutyraldehyde and 2-methylbutyraldehyde 4-pyridylhydrazones afford only 5-aza-2,3-dimethylindole and 5-aza-2-ethyl-3-methylindole respectively, and both ethyl methyl ketone and isobutyraldehyde 4-pyrimidylhydrazones afford only 5,7-diaza-2,3-dimethylindole. Several attempts to effect a Chichibabin amination on 5-aza-2,3-dimethyl- and 5-aza-1,2,3-trimethylindole led only to the recovery of starting material.
Lignans and related phenols. Part IX. Observations on the spectroscopic characterization and conformational analysis of apo-compounds of the arylnaphthalene class
Authors: Ayres D. C.
Published: May 2006

The need for further spectroscopic characterization of apo-compounds of type 1 is discussed and details of proton magnetic resonance (p.m.r.) and optical rotatory dispersion (o.r.d.) spectra are given. Analysis of these spectra is relevant to the assignment of structure to the recently isolated thomasic acid and also reveals unusual conformational features in compounds of this group.
Selective reduction of esters with sodium trimethoxyborohydride
Authors: Bell R. A. , Gravestock M. B.
Published: May 2006

The rate of reduction of representative methyl esters with sodium trimethoxyborohydride decreases in the order primary > secondary > tertiary. Sodium trimethoxyborohydride reduces with 100% selectivity the secondary ester group in the alicyclic diester–acid 2c.
On the mechanism of the Doebner–Miller reaction
Authors: Forrest T. P. , Dauphinee G. A. , Miles W. F.
Published: May 2006

The reaction of acetaldehyde and aniline in deuterated media has led to substituted tetrahydroquinaldines. Analysis of the deuteration pattern indicates that the previously accepted mechanism of the reaction is incorrect. An alternative mechanism is proposed.
Electron spin resonance studies of radicals condensed from irradiated water vapor: reactions of the radicals
Authors: Wardman P. , Seddon W. A.
Published: May 2006

Electrons and hydroperoxyl radicals are trapped in polycrystalline ice after irradiation of water vapor and rapid condensation to 77 °K. Using higher sample flow rates than in the earlier work of Seddon, Smith, and Bindner, the electron spin resonance spectra of the trapped electrons (et−) were obtained in both H2O and D2O ice with negligible interference from the underlying HO2• (DO2•) radicals. Addition of C(NO2)4, H2O2, (CH3)2SO, and O2 as radical scavengers confirmed the earlier prediction that reactions with the radicals do not occur in the vapor phase in this system. The results with C(NO2)4 and H2O2 also provided chemical evidence consistent with the spectroscopic assignment for HO2• (DO2•) radicals. Experiments with added isobutylene suggested that hydrogen atoms are formed (possibly in a post-irradiation reaction during condensation) and are also produced on photobleaching et− at 77 °K.
Studies on metal hydroxy compounds. VI. Kinetics of thermal decomposition of zinc and cadmium halide (Cl, F) derivatives
Authors: Ramamurthy P. , Secco E. A.
Published: May 2006

Kinetics of thermal decomposition of zinc and cadmium hydroxides along with their halide (Cl, F) derivatives are reported. The kinetic results are discussed in terms of the appropriate reaction mechanism. The rates are also discussed using activated complex theory in a manner outlined by Cordes (9) where the effect of molecular rotation in both the reactants and the activated complex is considered. Furthermore, the abnormally high preexponential factors are speculated to have their origin in an active translational mode on the surface.
Nuclear magnetic resonance investigation of intermediates formed by the action of nucleophiles on substituted stilbenes
Authors: Fyfe C. A.
Published: May 2006

A nuclear magnetic resonance investigation of the colored species formed by the action of bases on a series of α-cyano-4-nitro-4′-X-stilbenes characterizes these as the intermediate carbanions formed by the addition of base to the β-carbon atom of the double bond. The nuclear magnetic resonance spectra reveal that, whereas there is free rotation about the β-phenyl—Cβ and Cβ—Cα bonds in these adducts, there is restricted rotation around the α-phenyl—Cα bond due to very substantial delocalization of the negative charge into this ring. It has been verified that the same intermediates are formed by the action of bases on either the cis or trans isomers of α-cyano-4-nitrostilbene. The relation of these observations to the theory of alkene nucleophilic substitution reactions is discussed.
Synthesis of buf-20(21)-enolides and bufa-20,22-dienolides
Authors: Pettit George R. , Fessler Dyral C. , Paull Kenneth D. , Hofer Peter , Knight John C.
Published: May 2006

A practical three-step procedure for converting an aldehyde to a 5-substituted dihydro-2-pyrone or by an additional step to the corresponding 2-pyrone has been summarized. Synthesis of 2-pyrone 5, buf-20(21)-enolide 9 (and Δ5-derivative) and bufadienolide 10 were used for illustration.
Raman and far infrared spectra of s-trinitrobenzene and s-trinitrobenzene-d3
Authors: Shurvell H. F. , Norris A. R. , Irish D. E.
Published: May 2006

Raman spectra have been recorded of s-trinitrobenzene and s-trinitrobenzene-d3 both in solution and in the solid phase. Eighteen of the 22 Raman active fundamentals in D3h have been observed for both molecules.Two fundamentals have been observed in the far infrared spectrum of each molecule.
Complexes du germanium(IV) et du bore(III) avec des o-diphénols substitués
Authors: Meilleur R. , Benoit R. L.
Published: May 2006

Complex formation between germanium(IV) and boron(III) and some substituted o-diphenols H2L has been studied by potentiometric and spectrophotometric methods. Correlations are established between the stability constants of GeL32− and BL(OH)2− complexes and the acidity constants of the diphenols.
Chemistry of metal hydrides. VI. Cationic platinum(II) carbonyls stabilized with tertiary arsines and stibines
Authors: Cherwinski W. J. , Clark H. C.
Published: May 2006

The synthesis of [Pt2Cl2(R3M)4][BF4]2, and its cleavage with carbon monoxide to form the cationic carbonyl species [PtCl(CO)(R3M)2]+ is described for R = ethyl or phenyl, and M = As or Sb. A comparison of the physical properties and spectroscopic data of these compounds, and the analogues for M = P is made with related complexes of other transition metals.Only trans-[PtCl(CO)(Et3As)2][BF4] reacts with water to give trans-[PtHCl(Et3As)2] and carbon dioxide. trans-[PtCl(CO)(Ph3As)2][BF4] reacts readily with methanol or ethanol to give an alkoxy carbonyl [PtCl(COOR)(Ph3As)2], where R = CH3 or C2H5. Unlike their phosphine analogues, these species and the stibine-stabilized cationic carbonyls do not produce the corresponding hydrides on reaction with water in the presence of a salt catalyst. These differences in chemical reactivity are related to the basicity of the ligands.
The mechanism of passivation of nickel as determined by an automatic recording ellipsometer
Authors: Reddy A. K. N. , Rao B.
Published: May 2006

The process of anodic passivation of nickel in acid solutions has been investigated by means of an automatic recording ellipsometer in which the light emerging from a rotating analyzer has been electronically processed to yield a continuous read-out of the changes of polarization state of light reflected from a nickel anode during a galvanostatic transient. Digital computer analysis of the ellipsometric data has revealed: (a) the existence of an induction time for film formation; (b) a linear growth law for the film during a time interval commencing with the induction time and ending before the passivation time; (c) the occurrence of passivation when the absorption coefficient of the film jumps from a near-zero value to a fractional value; and (d) continuous changes of the refractive index of the film during the period of film growth. These phenomena are consistent with a model in which (a) a pre-passive film forms and thickens by a dissolution–precipitation mechanism, (b) the growth of the film is accompanied by its electrochemical oxidation, (c) the film growth–oxidation process continues until the pre-passive film is transformed into an electronically-conducting material, and (d) the conversion of the pre-passive film into an electronic conductor constitutes the essence of the so-called active–passive transition.
On the absence of triplet ketene in ketene excited in the region 2800–3660 Å
Authors: Grossman M. , Semeluk G. P. , Unger I.
Published: May 2006

The sensitized biacetyl emission technique was used in an attempt to detect triplet ketene molecules, which might be formed when ketene is excited by light ranging in wavelength from 2800 to 3600 Å. No sensitized emission was observed in this exciting wavelength region thus confirming the recent results of Voisey (1) which also show that triplet ketene is not produced when ketene is excited by light between 2800 and 3200 Å, and that the triplet CH2 found in such systems must arise from some source other than triplet ketene.
Free radical hydrobromination of propargyl bromide and bromoallene
Authors: Kopecky Karl R. , Grover Shima
Published: May 2006

Rearrangement is observed in the free-radical hydrobromination of propargyl bromide. Between −20 and +30 °C in n-pentane or ether solution, 1,2-dibromopropene is the major product. A detailed stereochemical and kinetic study of the reaction indicates that the 1,2-dibromopropene is formed via bromoallene which results from the loss of a bromine atom from the first formed 1,3-dibromo-2-propenyl radical. Only 1/3 to 1/2 of the bromoallene diffuses away from its bromine atom partner. The remainder of the bromoallene recombines within the solvent cage with its bromine atom partner at a rate which is competitive with its rate of rotation with respect to the bromine atom. When the free radical hydrobromination of propargyl bromide is carried out at −78° in liquid hydrogen bromide, the 1,3-dibromo-2-propenyl radical can be trapped to a large extent by the hydrogen bromide to form cis-1,3-dibromopropene. The stereochemistry of this addition reaction >99% trans. A small amount of 1,2-dibromopropene which is 77% trans is also formed. Under the same conditions a 3:1 mixture of 1,2- and 1,3-dibromopropenes is produced from bromoallene. The 1,3-dibromopropene produced from bromoallene is >95% cis, while the 1,2-dibromopropene consists of a 49:51 cis:trans mixture of isomers.
Liquid-phase oxidation of 2-butene in the presence of benzaldehyde
Authors: Tsuchiya Fujio , Ikawa Tsuneo
Published: May 2006

The co-oxidation of cis- and trans-2-butene and benzaldehyde at 110 °C has been carried out in benzene and the mechanism of epoxide formation has been investigated by examining the ratio of cis- to trans-epoxides. The results indicate that epoxides were formed by two mechanisms, one involving the benzoylperoxy radical to give about half cis and half trans epoxides and the other by stereospecific epoxidation with perbenzoic acid. Experimental results show that the stereospecific character of epoxidation increases with the reaction time and the concentration of benzaldehyde, but does not depend on the concentration of 2-butene.
1,2,3,4,5-Pentaphenylimidazolium benzoate
Authors: Smith James G. , Ghonima Hazem M. H.
Published: May 2006

The compound reported to be N,N′-dibenzoyl-N,N′-diphenylstilbene-α,α′-diamine is shown to be 1,2,3,4,5-pentaphenylimidazolium benzoate.
Nuclear magnetic resonance spectrum and deuteration of porphobilinogen lactam and its derivatives
Authors: Kim Y. C.
Published: May 2006

Derivatives of porphobilinogen are distinguished from those of its lactam in that the C4- and C7- protons of the latter show homoallylic coupling, J4,7 = 2.5–3.0 Hz (150°) and the C4-protons are exchangeable in alkaline solution.
Partition coefficients of some N-alkyl- and N,N-dialkyl-derivatives of some cinnamamides and benzalcyanoacetamides in the system cyclohexane–water
Authors: Delaney A. D. , Currie D. J. , Holmes H. L.
Published: May 2006

Substituent constants, π, and substituent interaction constants, π interaction, for the groups —CONHR and —CONRR have been derived which allow the calculation of the partition coefficients of the title compounds.
Functional group and substituent effects, both steric and electronic, upon the ultraviolet absorption spectra of some N-alkyl- and N,N-dialkyl-derivatives of some cinnamamides and benzalcyanoacetamides
Authors: Delaney A. D. , Currie D. J. , Holmes H. L.
Published: May 2006

Conjugative and steric constants for N-substituted carboxyamide groups have been derived which allow the calculation of the long wavelength absorption maxima of N-alkyl- and N,N-dialkyl-derivatives of cinnamamide and benzalcyanoacetamide. Deviations between calculated and observed values indicate that there may be steric interference between bulky N,N-dialkylcarboxyamide groups and the benzylic hydrogen atom.
Identification of di-O-, tri-O-, and tetra-O-methylmannoses by gas–liquid chromatography
Authors: Bhattacharjee S. S. , Gorin P. A. J.
Published: May 2006

not available
Secondary reactions in the photolysis and pyrolysis of azoethane
Authors: Strausz O. P. , Berkley R. E. , Gunning H. E.
Published: May 2006

A brief study has been made of the secondary reactions occurring in the thermolysis and photolysis of azoethane. In thermolysis the important secondary products found are ethyl 2-butyl diimide and ethanal diethylhydrazone. In photolysis tetraethyl hydrazine has also been detected in substantial yields.The possible role of secondary reactions in the thermolysis and photolysis of azo compounds is discussed.
Quantum yield of Hg 6(3P1) sensitization of hydrogen
Authors: Pollock T. L. , Jakubowski E. , Gunning H. E. , Strausz O. P.
Published: May 2006

The quantum yield for the mercury photosensitized decomposition of hydrogen has been measured using the ethylene scavenging technique and has been found to be equal to unity.
Reactions of dimethyl acetylenedicarboxylate. III. Reactions with diamines and anthranilic acid
Authors: Khetan Sushil K. , George M. V.
Published: May 2006

Dimethyl acetylenedicarboxylate reacts with m-phenylenediamine, p-phenylenediamine and 2,2′-diaminobiphenyl, giving rise to the corresponding bisenamines, having the furmarate geometry. These bisenamines are thermally cyclized to 4(1H)-quinolone derivatives and a selective mode of cyclization is observed. Anthranilic acid reacts with dimethyl acetylenedicarboxylate to give an enamine adduct which when heated in diphenyl ether undergoes cyclization to methyl 7-carboxy-3-oxo-2-indolinylidene-carboxylate. Further heating of this product results in the formation of methyl 3-oxo-2-indolinylidene-carboxylate.
Characterization of plant coumarins by combined gas chromatography, ultraviolet absorption spectroscopy, and nuclear magnetic resonance analysis
Authors: Steck Warren , Bailey B. K.
Published: May 2006

A method for the characterization of sub-milligram quantities of plant coumarins has been devised. Each compound was purified by gas–liquid chromatography, and the collected material analyzed by a combination of ultraviolet absorption and nuclear magnetic resonance spectroscopy. The procedures developed were tested successfully on several plant extracts. Limettin and bergapten were identified in lime peel; angelicin, psoralen, and xanthotoxin in parsnips; and angelicin, xanthotoxin, and bergapten in Angelica leaves. Isopimpinellin was found in all three plant materials.
Conformational studies of some 5,9-dimethyl-6,7-benzomorphan diastereoisomers and related compounds
Authors: Casy A. F. , Parulkar A. P.
Published: May 2006

The proton magnetic resonance characteristics of some α/β diastereoisomeric 5,9-dimethyl-6,7-benzomorphans are reported for free base, hydrohalide, and methiodide forms, and differences between α- and β-signals are interpreted in terms of the piperidine ring fragment of the β-salts adopting skew-boat conformations. The steric course of quaternization of benzomorphan isomers is discussed from results of alkylations using trideuteriomethyl iodide and other experiments. A possible correlation between conformational and potency differences in analgesically active benzomorphan diastereoisomers and related compounds is discussed.
An estimation of the magnitudes of the contributions from spin polarization and from hyperconjugation to the hyperfine splitting constant of an hydroxylic proton
Authors: Gough T. E. , Taylor G. A.
Published: May 2006

Proton hyperfine splitting constants of monoprotonated p-benzosemiquinone are presented for a range of solvents and sample-temperatures. The dependences of these splittings upon temperature, together with the assumption that the hydroxyl group can be described as a torsional harmonic oscillator, are used to evaluate an equation linking aOH, the hyperfine splitting constant of the hydroxylic proton, in gauss, with ρO and ρC, the spin densities on the hydroxyl oxygen and on the adjacent carbon atoms, and θ, the dihedral angle between the O—H bond and the plane of the aromatic ring.[Formula: see text]Experimental evidence of a positive contribution to aOH is obtained from the spectra of monoprotonated durosemiquinone in tri-n-butylphosphate at elevated temperatures.
Ion exchange and solvent extraction equilibria in mixed electrolytes
Authors: Patil S. K. , Sharma H. D.
Published: May 2006

The distribution coefficients of 2-thenoyl trifluoroacetone (TTA) between the organic and aqueous phase containing mixtures of ClO4−, NO3−, Cl−, SCN−, and SO42− ions indicate that the activity coefficients of TTA in the aqueous phase are given by ln γ = ΣksiCsi where ksi and Csi are the salting-out parameter and molar concentration of the ith component, respectively. The salting-out effect on TTA follows the usual pattern for a non-electrolyte, i.e. SO42− > Cl− > Br− > ClO4− > SCN− for anions and Li+ > Na+ > H+. In the solvent extraction equilibria, the extraction behavior of the neutral species M(TTA)n may not be similar to that of TTA and thus stability constants determined by this method, wherein there are large changes of anion composition in the aqueous phase to maintain the ionic strength constant, may be in error. The ion exchange equilibria have also been investigated by determining distribution coefficients, D, of metal ions in trace concentrations in mixed electrolyte solutions. The large, poorly hydrated ions are salted into the resin phase in the presence of anions like ClO4− having the property of breaking the water structure. In mixed electrolytes containing perchlorate, nitrate, and chloride ion mixtures, the D values are difficult to rationalize on the basis of the activity coefficients of ions alone. The stability constants for the formation of CaCl+, CaNO3+, BaCl+, and BaNO3+ determined by the ion exchange method at μ = 1 are not in agreement with those obtained by the spectroscopic method.
Pyrazolines IX. Chemistry of some 3-cyano-3-carbomethoxy-1-pyrazolines
Authors: McGreer Donald E. , Wigfield Y. Y.
Published: May 2006

Product and kinetic studies have been made on the pyrolysis of a series of 3-cyano-3-carbomethoxy-1-pyrazolines substituted at C-4 with a methyl and an aryl group (phenyl, p-methoxyphenyl, and p-nitrophenyl). Evidence is presented supporting a transition state structure in which little progress to bond breaking of the C-5 to N bond has taken place at the transition state. The product distribution is largely dependent on the stereochemistry of the initial pyrazoline and to a lesser degree on the nature of the aryl group at C-4. The cis pyrazolines gave products resulting primarily from aryl migration while the trans pyrazolines gave products predominantly from methyl migration.
Thermal [2 + 3] cycloaddition of imino compounds to 3-aroylaziridines. Synthesis of imidazolidines
Authors: Lown J. W. , Moser J. P. , Westwood R.
Published: May 2006

3-Aroylaziridines react with a variety of imines and aryl-N-sulfonylimines in refluxing benzene to give imidazolidines in excellent yield. The orientation of the [2 + 3] cycloaddition of the intermediate azomethine ylids to the C=N double bond was proven by synthesis of specifically 5-deuterated imidazolidines. The reactions provide a convenient new general synthesis of imidazolidines.
The synthesis of silyl- and germyldiazoalkanes via tosylhydrazones
Authors: Brook A. G. , Jones Peter F.
Published: May 2006

Tosylhydrazones have been prepared from acylsilanes and -germanes. These may be converted in excellent yield by n-butyllithium to the metalloidal diazoalkanes under milder conditions than are required for the analogous carbon compounds. The diazoalkanes are far more stable than their carbon counterparts. These results, together with spectral shifts noted for the silyl and germyl compounds, are interpreted in terms of dπ–pπ bonding between the diazo group and the metalloid atom.