bluuebunny/crossref_metadata_2025 huggingface dataset:
Nuclear charge distribution in fission: fractional cumulative yields of isotopes of krypton and xenon in 249Cf(nth,f) and 250Cf(sp.f)
Authors: Meixler H.-H. , Wolfsberg K. , Denschlag H. O.
Published: May 2006

The fractional cumulative yields (%) of the following rare gas isotopes were determined radiochemically in the thermal neutron induced fission of 249Cf and in the spontaneous fission of 250Cf and the following results were obtained for the two processes, respectively: 89Kr: 77.6 ± 1.5, —; [Formula: see text], [Formula: see text]; [Formula: see text];139Xe: 32.0 ± 3.5, 23.6 ± 6.0; 140Xe: 12.5 ± 2.0, 14.7 ± 7.0; 141Xe: 4.0 ± 0.3, [Formula: see text]; 142Xe: 0.9 ± 0.1, ≤ 3.61, and 143Xe: 0.22 ± 0.08, —. The results are discussed with respect to the systematies of nuclear charge distribution in fission.
The reaction of tetrasulphur dinitride with norbornadiene; the crystal and molecular structure of S4N2•C7H8, an eight-membered C2S4N2 heterocycle
Authors: Koenig Hans , Oakley Richard T. , Cordes A. Wallace , Noble Mark C.
Published: May 2006

The reaction of tetrasulphur dinitride with norbornadiene produces the 1:1 adduct S4N2•C7H8; X-ray crystallographic analysis of this compound reveals that olefin addition cleaves one of the sulphur–sulphur bonds of S4N2, yielding a novel eight-membered C2S4N2 ring. Crystals of S4N2•C7H8 are monoclinic, space group P21/c, a = 6.127(1), b = 17.369(1), c = 9.580(1) Å, β = 106.74(1)°, V = 1003.8(5) Å3Z = 4. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.039. The S—S—N—S—N—S fragment of the C2S4N2 ring is planar to within 0.15 Å. The S—C—C—S unit is folded out of this plane to produce a dihedral angle of 74.5°.
Solutions of the generalized rate law for vibrational relaxation of a pure diatomic gas
Authors: Teitelbaum Heshel
Published: May 2006

The generalized rate law for the relaxation of the vibrational energy of a pure diatomic gas, AB, derived earlier, is solved analytically for a variety of initial conditions corresponding to shock tube, laser-excited fluorescence, and chemical activation experiments. The resulting expressions can be used to easily predict whether a given system will relax according to a V–V or a T–V mechanism or both. The initial conditions and the molecular anharmonicity are shown to be as important, if not more important, for this purpose than the ratio of T–V and V–V rate constants. Behind shock waves the energy relaxes exponentially with a T–V time constant. The initial distribution remains Boltzmann. In laser or chemical activation experiments the energy does not relax exponentially, leading to phenomenological time "constants" [Formula: see text] or [Formula: see text] which are not constant in time and prevent direct comparisons with shock tube data. It is only after an incubation period during which the vibrational energy is redistributed via V–V processes that the energy then exchanges with translational energy and decays. Prescriptions are given to extract T–V and V–V rate constants from such data. The initial degree of laser excitation, a, and the time regime probed, t/τ, must be known for this purpose. However, when direct overtone excitation is used, a careful choice of α can lead to extraction of the T–V constant directly. Even though the vibrational energy itself does not relax exponentially, it is shown that the mean energy, [Formula: see text], and the mean squared energy, [Formula: see text], relax in such a way that the quantity [Formula: see text] does decrease exponentially with a time constant very closely related to the V–V rate constant for 2AB(ν = 1) → AB(ν = 2). A short survey of various laser and chemical excitations in the literature is presented and analyzed in terms of initial conditions. In general, the larger the degree of excitation and the higher the quantum numbers of the excited levels, the more V–V character does the energy relaxation have.
Hétérobicycles sulfurés dérivés de l'α-thioglycérol. Synthèse d'alkyl-2,8-dioxa-6-thiabicyclo[3.2. 1]octanes
Authors: Gelas Jacques , Teppaz-Misson Marc
Published: May 2006

The synthesis of 2,8-dioxa-6-thiobicyclo[3.2.1]octanes, substituted by alkyl or phenyl groups in positions 1, 4, or 7, is described. Four synthetic routes are compared: (i) action of sodium sulfide on 2,4-dichloro-1,3-dialkyldioxolanes; (ii) action of sodium sulfide on the ditosylates of 2,4-dihydroxyalkyl-1,3-dioxolanes; (iii) action of α-haloketones on α-thioglycerol; and (iv) action of α-hydroxyketones on α-thioglycerol. The structures of the dioxathiabicyclooctanes have been established by proton nmr (mass spectra have already been described) and chemically confirmed by desulfurization by Raney Nickel. [Journal translation]
Nonadditive effects of polysubstitution in CH4 and CH3: a test of abinitio and semiempirical MO methods
Authors: Baird N. Colin
Published: May 2006

The effects to the bond lengths and molecular energy of making multiple substitutions at the same carbon atom in methane and the methyl free radical are studied using various molecular orbital methods. All abinitio calculations were based upon the Hartree–Fock formalism (unrestricted in the case of free radicals) and employed the STO-3G (with d orbitals on chlorine), 3-21G, and 4-31G bases, the last both with and without a set of Gaussian d orbitals on the carbon. The semiempirical methods used were the MINDO/3 and MNDO methods of Dewar and co-workers; computations for polysubstituted ethanes by these two methods also arc reported. The abinito methods which use a split valence shell basis set account very well for the trends in bond lengths and heats of formation, at least when the polysubstituent is fluorine or hydroxyl. In contrast, the semiempirical calculations and the abinitio STO-3G results gave very poor results. Finally, the role of interactions between the AH bonds in a variety of hydrides AHn is illustrated using experimental energetics.
Donor numbers: 27Al quadrupole relaxation as a measure of solvent donicity towards the sodium ion
Authors: Day Marion C. , Medley James H. , Ahmad Naseer
Published: May 2006

A new method is presented for the determination of solvent donicity towards the sodium ion that avoids solvent–solvent interactions. Using the systemNaAlEt4–benzene–donorthe response of the 27Al quadrupole relaxation to anion symmetry as a function of donor: Na+ ratio is monitored by both 27Al line widths and methylene 1H absorptions. The assumption is made that anion symmetry is dependent on the cation–anion interaction which is dependent on the stability of the donor–Na+ solvates. The ordering of donors is found to differ from the generally accepted listing. A ranking of seventeen donors is given.
Biosynthesis of antifungal stress metabolites from potato: observation of hydride shifts via the "β-hop" from incorporation of [2-2H3,2-13C]acetate and 13Cmr
Authors: Stoessl Albert , Stothers J. B.
Published: May 2006

The proposed migration of hydrogen from C-5 to C-4 in the biosynthesis of the potato phytoalexins lubimin (2). rishitin (5), and 3-hydroxylubimin (6) has been studied by incorporation of [2-2H3,2-13C]acetate. Direct observation of the predicted β-shift of the C-5 signal produced by 2H at C-4 provided conclusive confirmation of the hydride (deuteride) shift. Results of some [4,4-2H2]mevalonate incorporation experiments followed by 2Hmr are also described.
Spectrométrie de masse du chloro-1 diméthoxy-2,6 naphtalène; comparaison de données théoriques et expérimentales
Authors: Richer Jean-Claude , Odiot Simone
Published: May 2006

In an unambiguous manner we have synthesized 1-chloro-2,6-dimethoxy-d3-naphthalene (5) and examined its electron impact mass spectrum. We report here calculations on the relative stabilities of 1-chloro and 5-chloro-6-methoxy-2-naphthols (4a and 4b) and on the relative stabilities of the O—CH3 bond in the 2 and 6 positions of compound 5. [Journal translation]
Mass spectrometric analysis of the products from the isotopomeric cationic intermediates in the solvolysis of 1,2-dianisyl-2-p-(2H3)methoxyphenyl[2-13C]vinyl bromide in 70% HOAc – 30% H2O
Authors: Lee Choi Chuck , Yu Xian-Da , Fiakpui Charles Y.
Published: May 2006

Solvolyses were carried out with 6.0 mM doubly labeled 1,2-dianisyl-2-p-(2H3)methoxyphenyl[2-13C]vinyl bromide in 70% HOAc – 30% H2O in the presence of 0, 1, 5, 10, or 400 molar equivalents of added NaOAc. The distributions of products derived from the 4 possible isotopomeric trianisylvinyl cationic intermediates were determined from the mass spectra of the isotopomeric dianisyl ketones obtained from degradation of the reaction products, the spectra being obtained by the chemical ionization technique in order to minimize possible complications by multiple fragmentations. The mass spectrometrie results obtained showed agreement with previously obtained 14C scrambling data and with the 13C scramblings obtained in the present study using 13C nmr. Increasing amounts of added NaOAc had the effect of decreasing the extents of scrambling from 1,2-anisyl shifts as previously observed. However, the formation of products from all 4 possible doubly labeled isotopomeric trianisylvinyl cations definitely demonstrated the occurrence of successive 1,2-anisyl shifts in the trianisylvinyl cation, and the detection of such successive shifts was not possible in previous work using a singly labeled substrate. The observed distribution of products derived from the 4 isotopomeric cations could be calculated assuming various contributions from equilibrations among these isotopomeric cations, and the mechanistic implications of the results are discussed.
Hydrolysis of phosphoranes containing a perfluoropinacolyl ring
Authors: Janzen Alexander F. , Lemire Alberta E. , Marat Ronald Kirk , Queen Alan
Published: May 2006

The hydrolysis of phosphoranes Ph2P(pfp)Cl, Ph2P(pfp)OR, PhP(pfp)(OR)2, and (RO)3P(pfp), containing a perfluoropinacolyl (pfp) ring, occurs under neutral, basic, or acidic conditions and leads to the formation of acyclic perfluoropinacolyl products, i.e. R2P(O)OC(CF3)2C(CF3)2OH, as determined by 1H, 19F, 31P, 13C nmr and ir studies. In the presence of a base, all trifluoromethyl groups in Ph2P(O)OC(CF3)2C(CF3)2OH are equilibrated, as verified by 19F and 13C nmr; and from the variable temperature 19F nmr line-shape analysis the activation parameters for this exchange process were found to be: Ea = 36.0 ± 3 kJ mol−1, ΔH≠ = 33.5 ± 3 kJ mol−1, ΔS≠ = −86 ± 8 J K−1 mol−1, [Formula: see text]. The reactions of phosphoranes with HF were briefly investigated.
Réactions radicalaires du percarbonate de O,O-tert-butyle et O-isopropényle: acétonylations assistées par un co-amorceur
Authors: Jaouhari Rabih , Filliatre Claude , Villenave Jean-Jacques
Published: May 2006

By decomposition in alkanes, ethers, ketones, acids, esters and nitriles of equimolecular mixtures of O,O-tert-butyl and O-isopropenyl peroxycarbonate and tert-butyl peroxyacetate, the "assisted" acetonylation of the solvents has been accomplished. The presence of the co-initiator allows the yield of the free radical acetonylation to be markedly improved: the formation of the by-product acetonylacetone is avoided and the yield of acetonylated derivatives is strongly enhanced while the regioselcetivity of the processes is preserved and even increased in some cases.
Uranium recovery from phosphate ores through sintering
Authors: Guirguis L. A.
Published: May 2006

The use of an alkaline reactant for phosphate processing is an alternative to the current methods of using acid reagents.In this work the possibilities of attacking low-grade phosphate ores by sintering with sodium carbonate at moderate temperature are considered. The carbonate liquor obtained by a water leach contains uranium in the form of uranyl tricarbonate complex, as well as the equivalent dissolved phosphate. Uranium from such liquor was recovered as sodium uranate on addition of sodium hydroxide, while pure sodium phosphate, useful as a chemical, was recovered by fractional crystallization.Finally, a flowsheet was designed for the proposed process.
Synthesis of (±)-trixagol by an electrophilic cyclization of an allylsilane
Authors: Armstrong Rosemary J. , Weiler Larry
Published: May 2006

1,5-Dienes containing an allylsilane are cyclized by Lewis acids to methylenecyclohexanes. The trimethylsilyl group exerts a strong activating and directing influence on the regioselectivity of this cyclization. The monocyclic compound 10 was converted into the diterpene, (±)-trixagol (3).[Formula: see text]
Acidity measurements in THF. III. Aldimines and ketimines
Authors: Fraser Robert R. , Bresse Monique , Chuaqui-Offermanns Noemi , Houk K. N. , Rondan N. G.
Published: May 2006

The relative acidities of fiteen aldimines and ketimines have been measured in THF using either 13C nmr spectroscopy or trapping experiments with methyl iodide. The pKA's are found to vary over a range of more than four pK units. The effects of structure on acidity indicate the acid-weakening effect of alkyl substitution in ketimines to be due to steric effects. This interpretation is supported by the results of abinitio calculations. The data also permit a quantitative estimation of the preference for the syn configuration of lithiated imines to be at least four kcal/mol. The anti selectivity previously reported for the lithiation of endocyclic imines can be accounted for by angular constraints, as indicated by both abinitio calculations and pKa data on this class of imine.
Structure and conformation of the anticodon nucleoside 5-methoxyuridine in the solid state and in solution
Authors: Birnbaum George I. , Blonski Wayne J. P. , Hruska Frank E.
Published: May 2006

not available
An esr and CIDEP study of the photoreduction of chromone and chromanone and their organometallic radical adducts
Authors: Adeleke Babatunde B. , Weir Douglas , Depew M. Catherine , Wan Jeffrey K. S.
Published: May 2006

The esr and CIDEP results show that the photoreduction of chromones and chromanones by phenol and by triethylamine proceeds via a spin polarized T(n,π*) triplet state which abstracts a hydrogen atom from the donor. Both chromone and chromanone are found to be reactive to the addition of organometallic radicals to form some radical adducts, including organotin, organosilicon, and organogermane.
Destruction des oxydes d'azote à pression atmosphérique
Authors: Dessaux Odile , Goudmand Pierre , Moreau Gérard , Mutel Brigitte
Published: May 2006

Active nitrogen produced at atmospheric pressure by a microwave discharge is found to require less energy consumption for the decomposition of nitrogen oxides. Important parameters improving the energy cost are described: NOx must be introduced in a visually well-limited zone where the nitrogen atom concentration is maximum, the energy cost is then nearly equal to the theoretical cost.
Synthetic and kinetic studies of the reversible addition of a bridging NSN fragment to the electron-rich heterocycles (R2PN)(SN)2 (R = Me, Ph, F)
Authors: Burford Neil , Chivers Tristram , Oakley Richard T. , Oswald Tom
Published: May 2006

The oxidative addition of Cl2 (using SO2Cl2) to the six-membered ring (R2PN)(SN)2 (R = Me, Ph) produces the mixed phosphazene–thiazyl heterocycles, (R2PN)(NSCl)2, which react with Me3SiNSNSiMe3 to give the bicyclic compounds R2PS3N5. The latter undergo thermal decomposition, at ca. 100 °C in toluene, via reductive elimination of an NSN unit to regenerate (R2PN)(SN)2 in high yield. Kinetic measurements of this process, using 31P nmr spectroscopy, yield an activation energy of 102.4 ± 6.0 kJ mol−1 for the release of the NSN fragment from Me2PS3N5. The thermolysis route has been used to prepare the thermally unstable (F2PN)(SN)2, characterized as a 1:1 adduct with norbornadiene.
Open-chain nitrogen compounds. Part V. Hydroxymethyltriazenes: synthesis of some new alkyl homologues of the anti-tumour 3-methyl-3-hydroxymethyltriazenes and preparation of the derived acetoxymethyl-, benzoyloxymethyl-, and methoxymethyltriazenes
Authors: Hemens Chantal M. , Manning Hartford W. , Vaughan Keith , LaFrance Ronald J. , Tang York
Published: May 2006

The synthesis of some new 1-aryl-3-alkyl-3-hydroxymethyltriazenes is described. The method of coupling a diazonium salt with an alkylamine/formaldehyde mixture has been extended to (a) some diazonium ions with para substituents other than—M groups, (b) those with substituents in the ortho position, and (c) to homologous alkylamines (e.g. ethylamine, propylamine, etc.). Hydroxymethyltriazenes can also be prepared by the reaction of a 1-aryl-3-methyltriazene with formaldehyde. Several new derivatives of the hydroxymethyl function have been prepared. Reaction with acetic anhydride or benzoyl chloride in pyridine affords respectively the acetoxymethyl- and benzoyloxymethyl-triazenes; the acetates and benzoates react readily with methanol to give the novel methoxymethyltriazenes. This is the first report of a series of dialkyltriazenes with an ether linkage in the α position. An ether of this type has also been obtained directly from the diazonium fluoroborate salt by coupling with a mixture of benzylamine and formaldehyde in ethanolic solution.
Rhodium(I) complexes containing bidentate pyrazolylgallate ligands. X-ray crystal structures of [Me2Gapz2]Rh(COD), [Rh(μ-3,5-Me2pz)(CO)2]2, and [Rh(μ-3,5-Me2pz)(COD)]2
Authors: Louie Brenda M. , Rettig Steven J. , Storr Alan , Trotter James
Published: May 2006

The synthesis and characterization of the complexes [Me2Gapz2]Rh(LL) (where LL = COD, (CO)2, (PPh3)2, or (PPh3)(CO)), incorporating the bidentate, chelating, dimethylbis(1-pyrazolyl)gallate ligand are described. Non-rigidity in solution has been demonstrated by 1H nmr studies for some of the complexes. A crystal structure determination of the COD complex has confirmed the boat conformation for the Ga—(N—N)2—Rh six-membered ring in this complex in the solid state. In addition, the solid state structures of the 3,5-dimethylpyrazolyl bridged dirhodium complexes [Rh(μ-3,5-Me2pz)(CO)2]2 and [Rh(μ-3,5-Me2pz)(COD)]2 have been determined. Crystals of [Me2Gapz2]Rh(COD) are orthorhombic, a = 22.7447(8), b = 11.9776(5), c = 6.4635(3) Å, Z = 4, space group Pnma; those of [Rh(μ-3,5-Me2pz)(CO)2]2 are monoclinic, a = 8.7403(6), b = 16.3594(6), c = 25.434(2) Å, β = 95.286(3)°, Z = 8, space group P21/c; and those of [Rh(μ-3,5-Me2pz)(COD)]2 are triclinic, a = 10.350(2), b = 11.401(2), c = 12.355(2) Å, α = 112.485(7), β = 99.394(9), γ = 105.387(8)°, Z = 2, space group [Formula: see text]. All three structures were solved by conventional heavy atom techniques and were refined by full-matrix least-squares procedures to final conventional R values of 0.026, 0.024, and 0.037 for 1824, 5135, and 6109 reflections with I ≥ 3σ(I), respectively. In each case the Rh atoms have distorted square planar coordination geometry. Important mean structural parameters are Rh—N = 2.087(2), Rh—C = 2.129(2), [Formula: see text] for [Me2Gapz2]Rh(COD); Rh—N = 2.063(6), Rh—CO = 1.852(9), [Formula: see text] for [Rh(μ-3,5-Me2pz)(CO)2]2; and Rh—N = 2.084(1), Rh—C = 2.131(7), [Formula: see text] for [Rh(μ-3,5-Me2pz)(COD)]2.
Attempts to develop new synthetic entries into the tricyclo[3.3.0.03,7]octane skeleton
Authors: Camps Pelayo , Figueredo Marta
Published: May 2006

The attempts to synthesize dimethyl tricyclo[3.3.0.03,7]octane-1,5-dicarboxylate, 1, and some related compounds by formation of a C3—C7 bond from appropriate bicyclo[3.3.0]octane derivatives, either through intramolecular C—H carbene insertion or by ketone-to-cyclopentanol photocyclization, are described. Two alternative syntheses for the key precursor, dimethyl cis-3-oxobicyclo[3.3.0]octane-1,5-dicarboxylate, 2, are included. Also, the formation of dimethyl 3-hydroxytricyclo[3.3.0.03,7]octane-1,5-dicarboxylate, 24, by reduction of dimethyl cis-3,7,dioxobicyclo[3.3.0]octane-1,5-dicarboxylate, 9, under Clemensen-like reaction conditions is reported.
Alkylammonium hexachlorostannates(IV), (RnNH4−n)2SnCl6: crystal structure, infrared spectrum, and hydrogen bonding
Authors: Knop Osvald , Cameron T. Stanley , James Margaret Ann , Falk Michael
Published: May 2006

not available
Ortho-diquaternary aromatic compounds. V. Chirality and structure in hindered benzenes and napthalenes
Authors: Barclay L. Ross C. , Brownstein Sydney , Gabe Eric J. , Lee F. L.
Published: May 2006

Ortho-disubstituted aromatics with bulky substituents are distorted so that the substituents are above and below the approximate plane of the aromatic system. This introduces chirality which was observed by proton resonance spectroscopy with and without the use of a chiral shift reagent. The more nearly planar naphthalene systems invert their chiral configurations more rapidly. Crystals of 1,2-benzenediacetic acid, α,α,α′,α′-tetramethyldimethyl ester are monoclinic, space group A2/a with a = 10.665(3), b = 8.467(2), c = 17.198(4) Å and β = 105.94(2)°. The torsion angle between the 1,2 substituents is 12.1°. Crystals of 2,3-naphthalene diacetic acid, α,α,α′,α′-tetramethyldimethyl ester are also monoclinic, space group P21/c with a = 9.0992(14), b = 18.849(3), c = 11.319(2) Å and β = 113.88(1)°. The analogous torsion angle in this case is 8.9°.
Some investigations of the chemistry of tellurium chloride pentafluoride, its reaction with caesium fluoride, and the preparation of cis and trans methoxytellurium(VI) chloride tetrafluoride, (CH3O)TeClF4
Authors: Lawlor Lawrence J. , Passmore Jack
Published: May 2006

The reaction of TeClF5 with CH3OH, and CH3OSiMe3, leads to a mixture of cis- and trans-(CH3O)TeClF4 in a ratio of 1:6, as well as some unidentified Te(IV) product. The vibrational spectrum of the 1:6 mixture of cis- and trans-(CH3O)TeClF4 was accounted for on the basis of the predominant pseudo-C4vtrans isomer. TeClF5 is unreactive towards anhydrous HF, SbF5, AlCl3, SO2, F2, and ClF at room temperature. Over the temperature range 70–250 °C it thermally decomposes to TeF6, TeF4, and Cl2. It slowly reacts with CsF to form CsTeF5, TeF6, Cl2, and small amounts of ClF, and with HNMe2 it is also reduced to form TeF4•HNMe2.
Abinitio SCF + CI calculation of rotational energy barriers in CH2—X—CH2 species
Authors: Volatron F.
Published: May 2006

The rotational energy barriers in CH2—X—CH2 species (X = NH, O, CH2) are calculated by means of abinitio SCF + CI calculations. With the most sophisticated CI calculations, they are found to be equal to 36.1, 20.6, and 1.1 kcal/mol for X = NH, O, and CH2, respectively. These values are briefly discussed with respect to the valence bond analysis of the wave function.
Structural elucidation of the capsular polysaccharide of Neisseriameningitidis group H
Authors: Michon Francis , Roy René , Jennings Harold J. , Ashton Fraser E.
Published: May 2006

The capsular polysaccharide from newly isolated Neisseriameningitidis group H elaborates a structurally unique polysaccharide which is the group specific antigen. The polysaccharide contains D-galactose, glycerol, and phosphate in the molar ratio of 1:1:1 and is composed of the following basic repeating unit:[Formula: see text]The polysaccharide contains O-acetyl groups, in the molar ratio of 0.8:1.0 with D-galactose, which are essential to the formation of the major group specific determinant based on serological experiments described. Although all the O-acetyl groups are located on D-galactopyranosyl residues, the substitution pattern is complex, 60% of the residues being substituted at O-3 and 20% at O-2.
Nouvelle synthèse électrochimique de γ-bisdioxolannes symétriques et dissymétriques
Authors: Daubié Christophe , Bacquet-Einhorn Cathy , Lelandais Daniel
Published: May 2006

The electrochemical reduction of α-iodinated dioxolanes leads to the preparation of a series of symmetrical and non-symmetrical γ-bisdioxolanes. [Journal translation]
Studies on γ-irradiated aqueous solutions of amino acids with functional groups by the spin-trap high-performance liquid chromatography – electron spin resonance method
Authors: Iguchi Naohisa , Moriya Fumio , Makino Keisuke , Rokushika Souji , Hatano Hiroyuki
Published: May 2006

Aqueous solutions of L-glutamine, L-asparagine, sodium L-glutamate, sodium L-aspartate, L-serine, and L-threonine were γ-irradiated in the presence of a spin trap, 2-methyl-2-nitrosopropane. Stable spin adducts produced in the irradiated solutions were analyzed by the spin-trap hplc–esr method. The spin adducts of the following short-lived radicals were found and identified: H2NCOCH2CH2ĊHCOO− (1), [Formula: see text] and [Formula: see text] for L-glutamine; [Formula: see text] (2) for L-asparagine; −OOCCH2CH2ĊHCOO− (3) and [Formula: see text] for sodium L-glutamate; −OOCCH2ĊHCOO− (4) and [Formula: see text] (5) for sodium L-aspartate; [Formula: see text] and HOCH2ĊHCOO− (6) for L-serine; CH3CH(OH)ĊHCOO− (7) and [Formula: see text] for L-threonine. The free radicals, 1, 3, 4, 6, and 7, were due to the reaction of the hydrated electron [Formula: see text] with these amino acids and the other adducts were due to the attack of hydroxyl radical (•OH). The two diastereomeric pairs of spin adducts of the short-lived radicals, 2 and 5, could be individually separated by the technique utilized.
A synthesis of (+)-aphidicol-15-ene
Authors: Kelly Ronald B. , Lal G. Sankar , Gowda Gopala , Rej Rabindra N.
Published: May 2006

A stereospecific synthesis of (+)-aphidicol-15-ene is described. Pursuing a concept successfully applied to our total synthesis of stemarin and the stemodane diterpenoids, the C/D ring system was elaborated by functional group manipulation and rearrangement of a 6-hydroxybicyclo[2.2.2]octan-2-one system.
Pyrones. X. Lateropyrone, a new antibiotic from the fungus Fusariumlateritium Nees
Authors: Bushnell Gordon William , Li Yun-Long , Poulton Gerald Arthur
Published: May 2006

Lateropyrone, 5-hydroxy-9-methoxy-2-methyl-4H,6H-pyrano[3,4-g]-1-benzopyran-4,6-dione-8-carboxylic acid, 1, has been isolated from cultures of the fungus Fusariumlateritium Nees, and shown to have inhibitory activity against the growth of a gram-positive bacterium and a yeast. A crystal structure of the dimethyl derivative of lateropyrone, 2, was determined. The crystals are monoclinic, space group P21/c, with a = 9.663(4), b = 22.317(9), c = 7.747(5) Å, β = 113.03(4)°, Dc = 1.496 g cm−3, V = 1538(1) Å3, T = 25 °C, C17H14O8. The structure was refined to R = 0.0543 by least squares using 2100 observed, independent reflections measured on a 4-circle diffractometer, to obtain 241 parameters. The linearly fused tricyclic ring system is only approximately planar. In- and out-of-plane distortions are rationalized in terms of molecular overcrowding.
S-Adenosylcoenzyme M and (±) S-methyl adenosylcoenzyme M. Preparation and role in methane biosynthesis
Authors: Cullen William R. , Dolphin David , Hoffman Dale , Trip Everard
Published: May 2006

5′-S-(2-Sulphoethyl)-5′-deoxy-5′-thioadenosine (S-adenosylcoenzyme M), 5, was prepared from adenosine by reacting its 2′,3′-isopropylidine tosylate with the disodium salt of coenzyme M (NaSCH2CH2SO3Na) followed by removal of the protecting group. Methylation of 5 to give methylsulphonium (±) S-adenosylcoenzyme M, 6, was achieved with methyl iodide in acetic acid. Neither 5 nor 6 stimulated methane production from cell free preparations of M. thermoautotrophicum, negating the possibility of a biochemical analogy between 6 and S-adenosylmethionine (SAM).
Facile synthesis of the enantiomers of frontalin
Authors: Johnston B. D. , Oehlschlager A. C.
Published: May 2006

S-(−)- and R-(+)-frontalin (1,5-dimethyl-6,8-dioxabicyclo[3.2.1]octane) were prepared from (E)-2-methyl-2,6-heptadiene-1-ol utilizing the Sharpless asymmetric epoxidation reaction to induce chirality. The six-step synthetic sequence proceeded in approximately 50% overall yield and was found to be suitable for the preparation of multi-gram quantities of either enantiomer with ≥ 90% ee.
Reactions of α-aryl carbonyl compounds with lithium ester enolates
Authors: Veen Reinhout H. Van Der , Geenevasen Jan A. J. , Cerfontain Hans
Published: May 2006

This report describes the synthesis of β-hydroxy esters in good yields by reaction of α-aryl substituted ketones and phenylethanal with lithium methyl acetate and derivatives as anionoid reagents. The incomplete substrate conversion is ascribed to the enolate formation of the α-aryl carbonyl compounds, which concurrent reaction is negligibly small with aliphatic carbonyl compounds. The conversion of β-tetralone with lithium methyl acetate has been examined in some detail.
Flash photolysis of phenylacetatopentaminecobalt(III) in aqueous solution. Generation of benzyl radicals and their reversible trapping by cupric ions in homogeneous and micellar solutions
Authors: Scaiano J. C. , Leigh W. J. , Ferraudi G.
Published: May 2006

The photodecomposition of [Co(NH3)5OC(O)CH2C6H5](ClO4)2 is a convenient source of benzyl radicals in aqueous systems. The radicals react with cupric ions with a rate constant of (2.1 ± 0.2) × 107 M−1 s−1 to yield a complex that is formed reversibly. This complex can decay to Cu(I), but at high radical concentrations the recombination of benzyl radicals in equilibrium with it can become the predominant decay path. The reaction of benzyl radicals (from 1,3-diphenylacetone) in anionic micelles in the presence of Cu2+ leads to strong signals from the same intermediate, CuCH2C6H52+.
syn–anti Stereoselection in the Diels–Alder reactions of spiro[bicyclo[2.2.2]octane-2,1′-[2,4]cyclopentadiene]
Authors: Burnell D. Jean , Goodbrand H. Bruce , Kaiser Stephanie M. , Valenta Zdenek
Published: May 2006

No significant differences were found between the syn to anti adduct ratios established for the Diels–Alder cycloadditions, both thermal and catalysed, of spiro[bicyclo[2.2.2]octane-2,1′-[2,4]cyclopentadiene] (1) to a variety of dienophiles. This suggests that, in the exo region, the distance between the addends at the transition state is approximately the same in all the cases studied.
Heat conduction in thermal transfer printing
Authors: Sanders D. J.
Published: May 2006

The physical properties of thermal transfer materials arc reviewed. Thermal conductivities and thermal contact resistances were measured for commercial Ink Donor Films (IDF's) with base films of condenser paper or polyethylene terephthalate, and for experimental base materials such as regenerated cellulose, polypropylene, and polyimide. Theoretical models of heat transport in IDF's are presented to demonstrate how the intrinsic thermal properties affect the IDF's performance in thermal transfer printing. To a first order approximation, the sensitivity of an IDF can be characterized by the time taken for heat to diffuse across it. Thermal transfer test patterns for commercial and experimental IDF's were evaluated for sensitivity, and the experimental results were compared to the theoretical predictions.
High-resolution 13C CP/MAS solid-state nmr investigation of the thermal degradation of poly(methylvinylketone)
Authors: Fyfe C. A. , McKinnon M. S.
Published: May 2006

The structural changes occurring in poly(methylvinylketone) when exposed to high temperatures have been investigated by high-resolution 13C solid-state nmr. The degradation proceeds via the aldol condensation of pendant ketone groups to form a cyclic β-hydroxy ketone which is dehydrated to the cyclic α,β-unsaturated ketone. As the degradation continues there is the formation of polycyclic structures and aromatization of the sample.
13C CP/MAS nuclear magnetic resonance of crystalline methylxylopyranosides
Authors: Taylor Michael G. , Marchessault Robert H. , Perez Serge , Stephenson Peter J. , Fyfe Colin A.
Published: May 2006

The 13C nmr spectra of solids, acquired using the Cross Polarization/Magic Angle Spinning (CP/MAS) technique, are very sensitive to the detailed nature of crystalline packing. These effects are illustrated in the CP/MAS spectra of the α and β anomers of methyl-D-xylopyranoside. In the spectrum of the α anomer, which crystallizes with two molecules per unit cell, individual spectra can be resolved for the two molecules in the asymmetric unit of this crystal.
Analogs of cannabinoids: synthesis of some 7H-indolo-, 5H-imidazolo, 7H-benzimidazolo[1,2-c] [1,3]benzoxazines – novel ring systems
Authors: Mahesh V. K. , Maheswari Mamta , Sharma Rakesh , Sharma Rashmi
Published: May 2006

Tetrahydrocannabinol 1, the active constituent of CannabissativaLinn, is a well-known CNS-active compound and introduction of a nitrogen atom at the ring junction of the pyran and alicyclic ring is of considerable interest. This prompted the synthesis of 7H-indolo[1,2-c] [1,3]-, 5H-imidazolo[1,2-C] [1,3],- and 7H-benzimidazolo[1,2-c] [1,3]-benzoxazine, a novel heterocyclic system. 2-(2′-Hydroxyphenyl) indoles, 2-(2′-hydroxyphenyl) imidazoles, and 2-(2′-hydroxyphenyl) benzimidazoles are suitable intermediates for the preparation of this type of benzoxazines, as the second heterocycle (ring B) can then be constructed by introduction of a methylene bridge between the hydroxyl of the 2′-hydroxy phenyl substituent and the imino group of the heterocyclic system.
Crystal and molecular structure of fac-[dimethylbis(1-pyrazolyl)gallato-N,N′]-(triphenylphosphine)tricarbonylrhenium(I)
Authors: Louie Brenda M. , Rettig Steven J. , Storr Alan , Trotter James
Published: May 2006

Crystals of fac-[dimethylbis(1-pyrazolyl)gallato-N,N′](triphenylphosphine)tricarbonylrhenium(I) are triclinic, a = 9.479(2), b = 16.258(4), c = 20.412(6) Å, α = 110.06(1), β = 95.46(1), γ = 92.65(2)°, Z = 4, space group [Formula: see text] The structure was solved by conventional heavy-atom methods and was refined by full-matrix least-squares procedures to R = 0.027 and Rw = 0.031 for 5965 reflections with I ≥ 3σ(I). The two crystallographically independent molecules have nearly identical structures. The coordination about Re is distorted fac-octahedral with mean bond lengths: Re—P = 2.538(4), Re—N = 2.201(5), Re—CO(trans to P) = 1.931(1), and Re—CO(trans to N) = 1.913(9) Å. The ReGaN4 chelate rings have twisted boat conformations with cross-ring [Formula: see text] separations of 3.9396(7) and 3.8981(8) Å.
Synthèse et hydrolyse d'orthoesters trioxa-2,7,8 bicyclo[3.2.1] octanes et trioxa-2,8,9 bicyclo[3.3.1] nonanes
Authors: Bouab Otmane , Lamaty Gérard , Moreau Claude
Published: May 2006

The rates of hydrolysis of 1-substituted 2,7,8-trioxabicyclo[3.2.1]octanes and 2,8,9-trioxabicyclo[3.3.1]nonanes (R = H, CH3, C6H5) have been determined at two temperatures in dioxan/water (60:40 by volume). These new results confirm the behaviour generally observed in the hydrolysis of orthoesters which have a favourable conformation to hydrolyze under stereoelectronic control.
Synthesis of 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone, a potent mutagen
Authors: Padmapriya Abeysinghe A. , Just George , Lewis Norman G.
Published: May 2006

Starting from tetrachloroacetone 1 and (carbomethoxymethylene)triphenylphosphorane 4, the title compound 16 was prepared in five steps in 44% yield. Spectroscopic and chromatographic data indicated that this material was identical to a potent mutagen isolated from kraft pulp chlorination effluent. Various mutant Salmonellatyphimurium strains (TA 98, 100, and 1537) behaved similarly when incubated with either 16 or the isolated mutagen.
Equilibrium structures, proton affinities, and ionization potentials of the fluoroacetones
Authors: Choi Sai Cheng , Boyd Russell J.
Published: May 2006

Theoretical calculations on the fluoroacetones and their conjugate acids exhibit an inverse dependence of the proton affinity on the number of fluorine substituents. The good correlation between increasing proton affinity and decreasing ionization potential is attributed to the observation that the ionization of a nonbonding electron is essentially localized at a single atom whieh is also the site of protonation. The best quantitative agreement between the theoretical and experimental proton affinities is obtained at the 6-31G* level, while the STO-3G basis set leads to a satisfactory account of the additivity of fluorine substituents. The calculations corroborate the experimental interpretation of the preferred conformations of p-fluoroacetone molecules in terms of the presence of an intramolecular hydrogen bond between the carbonyl proton and the F on the adjacent carbon. Only one type of equilibrium conformation is predicted for the fluorinated acetones, whereas two types of equilibrium conformations are predicted for the conjugate bases.
The biosynthesis of cyclopropane fatty acids. III. pH Dependence of methyl hydrogen exchange: gas chromatographic – mass spectral studies
Authors: Buist Peter H. , Findlay Judy M.
Published: May 2006

L-Methionine-methyl-d3 was administered to Lactobacillusplantarum and the deuterium content of the biosynthetic lactobacillic acid examined by gc–ms. By conducting the biosynthetic experiments in media of varying pH, it was shown that the production of d1-cyclopropane fatty acid increases with decreasing pH. Factors such as culture age and total activity of cyclopropane synthetase do not directly influence the extent of exchange.
Kinetics and mechanism of the oxidation of benzenediols and ascorbic acid by bis(1,4,7-triazacyciononane)nickel(III) in aqueous perchlorate media
Authors: McAuley A. , Spencer Lee , West P. R.
Published: May 2006

The reactions of the outer-sphere electron transfer reagent, Ni(9-aneN3)23+, (bis(1,4,7-triazacyclononane)nickel(III) ion) with ascorbic acid, hydroquinone, catechol, and resorcinol have been investigated. The absence of any proton related equilibria with the oxidant provides a means of ascribing the observed inverse hydrogen ion dependences to reactions of the dissociated ascorbate or quinolate ions, (HA−). The data are consistent with the rate-determining one-electron transfer reactions:[Formula: see text]followed by rapid oxidation of the radical ions formed. In the reaction with ascorbic acid, k1 ~ 0 and k2 (T = 25° C) = 5.2 × 106 M−1 s−1 (ΔH≠ = 10.1 ± 2.5 kcal mol−1, ΔS≠ = 5.7 ± 5.1 cal mol−1 K−1). For hydroquinone, catechol, and resorcinol, k1 = 2.9 × 103, 2.8 × 102, and ~0 M−1 s−1and k2 = 6.9 × 109, 4.1 × 109, and 2.8 × 108 M−1 s−1, respectively. These data have been combined with those from other similar reactions leading, by use of a Marcus correlation, to self-exchange rate constants for the HAsc−/HAsc• couple of 3.5 × 105 M−1 s−1 and for the H2Quin0/+ and H2cat0/+ systems of 5 × 107 and 2 × 107 M−1 s−1, respectively. The importance of the effect of bond-reorganisation on electron transfer is discussed.
A nuclear magnetic resonance study of the self-association of adriamycin and daunomycin in aqueous solution
Authors: McLennan I. J. , Lenkinski R. E. , Yanuka Y.
Published: May 2006

A study of the self-association of the anthracycline antibiotics adriamycin and daunomycin was undertaken in D2O and methanol using nmr at 400 MHz. From the concentration dependence of the 2H linewidths obtained on selectively deuterated daunomycin it was determined that daunomycin forms a dimer in aqueous solution. The concentration dependence of the chemical shift of the 4 methoxy group of adriamycin was fit to a dimer model in which only the non-protonated neutral species of adriamycin participated in the self-association process. The data were in agreement with the dimer model if a pK of 7.4 was used. The pH dependence of the self-association was fit to two ionizations, one with a pK of 8.2 and the other with a pK of 8.8. The latter pK was attributed to the ionization of the phenol based on the work of Eksborg. It was concluded that only the deprotonated amine of adriamycin took part in the dimerization process. The dimerization of adriamycin is characterized by a ΔS of approximately 3 cal deg−1 M−1 and a ΔH of −3.45 kcal M−1. At room temperature the association constant for the dimerization process was found to be 4.0 × 105 M−1. These results were discussed in terms of earlier studies by Barthelemy-Clavey etal., Martin, and Chaires etal.
Charge transfer electron–exciton complexes in single crystals
Authors: Mavroyannis Constantine
Published: May 2006

We have considered the excitation spectrum arising from the coherent electron–exciton pairing in crystals at low temperatures. For the pairing processes, three different types of excitons have been considered: Frenkel excitons (tightly bound), Wannier–Mott excitons (loosely bound), and excitons of the intermediate binding. Expressions for the gap functions and transition temperatures at which metal-to-nonmetal phase transitions occur have been derived and discussed for each type of pairing. In the electron pairing with the intermediate exciton, the dispersion relations which determine the exciton and the electron–exciton modes are solved numerically and the derived results are graphically presented. The physical picture for the electron–exciton coupled modes is analogous to that for polaritons and magnon–phonon modes in crystals.
Raman intensity calculations with the CNDO method. Part III: N,N-dimethylamide – water complexes
Authors: Schmid Eduard D. , Brodbek Eleonore
Published: May 2006

Absolute differential Raman scattering coefficients of hydrogen bondedN,N-dimethylformamide (DMF) – water complexes and a N,N-dimethylacetamide (DMA) – water complex are calculated with a variational method within the CNDO approximation using an extended basis set. Changes of Raman intensities caused by intermolecular interactions are modeled in our Raman intensity calculations and the calculated intensities of the amide I (C=O stretching), OCN bending, and N—(Me)2 stretching vibration of the DMF (and DMA) – water complexes are compared with the experimental absolute Raman intensities of DMF and DMA dissolved in water. The calculated Raman intensities of characteristic normal modes of DMF and DMA and their 1:2 amide – water model are in good agreement with the experimental data. The results show that it is possible to obtain qualitative information on solute – solvent interactions from Raman intensity calculations of complex molecular systems like hydrated DMF and DMA.
A study of the molecular–cellular interface in visual photoreceptors by light scattering photometry
Authors: Borys T. , Deshpande S. , Jones R. , Abrahamson E. W.
Published: May 2006

The correlation of molecular events with structural changes within the cell requires a non-destructive relaxation technique that can be adapted to measure such cellular changes in a time range of milliseconds to minutes. Light scattering relaxation techniques have proved useful for such studies as they can often be measured simultaneously or in parallel with absorption or fluorescence spectral changes characterizing molecular or macromolecular processes. Such techniques are proving useful in the study of photobiological processes such as visual photoreception where specific cytological changes produced photochemically can be effected by alternate controlled perturbations such as osmotic shrinking or swelling of cell organelles and (or) whole cells. This paper illustrates how light scattering relaxation spectrophotometry can be applied to the correlation of molecular and cellular events in visual photoreceptors.
A comparison of the electron impact and fast atom bombardment mass spectra of some group IV organometallic halides
Authors: Miller Jack M. , Fulcher Adrian
Published: May 2006

The positive ion fast atom bombardment (FAB) mass spectra of a series of group IV organometallic halides, (phenyl)3MCl (M = Ge, Sn, Pb), (phenyl)3PbX (X = Cl, Br, I) and Sn(phenyl)nCl4−n are reported in a sulfolane matrix, and compared to their corresponding EI spectra. The use of other matrix liquids such as glycerol thioglycerol, diamylphenol, 18-crown-6/tetraglyme, and p-nitrophenyloctylether are discussed. Disappointingly FAB, like EI, does not produce significant parent ions for group IV organometallics. The FAB and EI spectra are remarkably similar with one major exception. In EI, the loss of a phenyl is preferred over the loss of a halide, while in FAB the reverse is the case, strongly suggesting that the primary ionization occurs in the condensed phase.
Reactions of amines with β-(phenylseleninyl)vinyl sulfones derived from the selenosulfonation of acetylenes. Formation of enamine sulfones
Authors: Back Thomas G. , Collins Scott , Law Kwok-Wai
Published: May 2006

β-(Phenylseleno)vinyl sulfones 2 were prepared from the selenosulfonation of acetylenes and were oxidized to the corresponding selenoxides 3. These were treated insitu with morpholine (4) or pyrrolidine (5) to afford the corresponding enamine sulfones 6 and, in those cases where 3 were derived from terminal acetylenes, their selenenylated analogues 7. The formation of the latter was enhanced by adding benzeneselenenyl chloride to the reaction mixture, and suppressed by the presence of selenenic acid scavengers such as enamine 10 or ethyl vinyl ether. In several instances the enamine sulfones were hydrolyzed to β-keto sulfones prior to work-up. A mechanistic rationale for the formation of 6 and 7 is presented. Selenoxide 3f behaved anomalously when treated with pyrrolidine and underwent isomerization to an allyl selenoxide, followed by [2,3] sigmatropic rearrangement to produce allyl alcohol 18. Selenoxide 3f was reduced by N,N-dimethylhydrazine to the selenide 2f.
Regiospecific synthesis of cyclopentane analogs of (2′- and 3′-deoxy-threo-pentofuranosyl)-uracil and -2-thiouracil nucleosides
Authors: Hronowski Lucjan J.J. , Szarek Walter A.
Published: May 2006

Aminohydroxycyclopentanemethanols are important precursors for the synthesis of cyclopentane analogs of purine and pyrimidine nucleosides. The regiospecific synthesis of two new aminohydroxycyclopentanemethanols, 17 and 22, is described. In these syntheses the desired configuration in the cyclopentane ring is obtained by opening the cis-acetoxy-1,3-cyclopentanedicarboxylic acid anhydride 3 with either ammonia or methanol. The attack by each nucleophile occurs at the carbonyl carbon farthest away from the acetoxy group to give a carbamoyl or an ester function at this position. Since the ester function is destined to become the hydroxymethyl substituent and the carbamoyl function the amino substituent, the type of nucleophile used to open the anhydride determines whether the 2-deoxy or the 3-deoxy isomer is obtained. Coupling of the aminohydroxycyclopentanemethanols with 3-ethoxypropenoyl isocyanate followed by cyclization of the acyl ureas in 2 N H2SO4 gave two new cyclopentane analogs of uracil nucleosides. Coupling of the aminohydroxycyclopentanemethanols with 3-ethoxypropenoyl isothiocyanate followed by cyclization of the acyl thioureas in 15 N aqueous ammonia gave two new cyclopentane analogs of 2-thiouracil nucleosides.
Disproportionation of HDS in the liquid phase
Authors: Halliday James D. , Bindner Patrick E.
Published: May 2006

The deuteron–proton liquid phase isotopic disproportionation constant in hydrogen sulphide, K1, defined for the equilibrium[Formula: see text]has been measured at 25.7 °C. The value of K1 was 3.99 ± 0.11, based upon direct measurements of the concentrations of the three molecular species H2S, HDS, and D2S by 1H and 2H nuclear magnetic resonance spectroscopy (nmr) of carefully purified samples. This compares with the theoretical vapour phase isotopic distribution constant Kv = 3.92, calculated from ideal gas vapour phase isotopic partition function ratios (1, 2).
A study of reaction mechanisms of methane in a radio-frequency glow discharge plasma using radical and ion scavengers
Authors: Hiraoka K. , Aoyama K. , Morise K.
Published: May 2006

When 1 Torr of methane was decomposed in a radio-frequency glow discharge plasma, ethane, ethylene, and acetylene were produced as major products. In order to determine the relative importance of radical and ionic processes for the formation of these major products, iodine and ammonia were used as radical and ion scavengers, respectively. It was found that the major products were formed mainly by radical processes and the contribution of ionic processes is within the experimental error. The mechanisms for the formation of ethane, ethylene, acetylene, and C3 ~ C4 compounds were discussed.