bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and redox chemistry of octaethylporphyrin complexes of ruthenium(II) and ruthenium(III)
Authors: Barley Mark , Becker James Y. , Domazetis George , Dolphin David , James Brian R.
Published: May 2006

The syntheses and characterization of some new octaethylporphyrin complexes of ruthenium(II) and ruthenium(III) are described; the complexes are Ru(OEP)(P″Bu3)2, Ru(OEP)(CO)L (L = PPh3, P″Bu3), [Ru(OEP)(P″Bu3)2]Br, and Ru(OEP)(P″Bu3)Br, where OEP is the dianion of octaethylporphyrin. The Ru(OEP)(CO)EtOH complex, 1, which reversibly loses the ethanol ligand in CH2Cl2 solution, undergoes a one-equivalent oxidation at the porphyrin ligand to generate the cation-radical [Ru(OEP)•+(CO)]+; a purple species of 2A2u ground state, produced electrochemically in perchlorate media, can coordinate bromide to generate a green 2A1u ground state species that also results from oxidation of 1 using bromine. Coordination of pyridine to [Ru(OEP)•+(CO)]+ yields the Ru(OEP)•+(CO)py species that can also be formed by electrochemical oxidation of Ru(OEP)(CO)py. Addition of tertiary phosphines (PR3) to the cation-radical carbonyl species can lead to formation of [Ru(OEP)(PR3)2]+, via an internal electron transfer process from Ru(II) to the OEP•+ that appears to be triggered by loss of the CO ligand. A reversible one-electron electrochemical oxidation of Ru(OEP)(P″Bu3)2 at 0.03 V (vs. Ag/AgCl) in CH2Cl2 also gives the ruthenium(III) biphosphine cation, while a further one-electron oxidation at 1.2 V generates [Ru(OEP)•+(P″Bu3)2]2+, a ruthenium(III) π-cation radical characterized by esr. The [Ru(OEP)(P″Bu3)2]Br complex decomposes in the solid state to a mixture of Ru(OEP)(P″Bu3)Br, formed together with free phosphine via an intramolecular ligand exchange, and Ru(OEP)(P″Bu3)2, formed by reduction of the initial ionic ruthenium(III) cation with the phosphine that appears as [P″Bu3Br]Br.
Skeletal isomerization of cyclohexene on AlPO4 catalysts
Authors: Campelo J. M. , Garcia A. , Gutierrez J. M. , Luna D. , Marinas J. M.
Published: May 2006

The skeletal isomerization of cyclohexene, in a microcatalytic pulse reactor, was investigated by using aluminium orthophosphates (Al/P = 1) as catalysts. An attempt has been made to correlate the isomerization activity with the acid properties of the solids, measured by means of the irreversible adsorption of different organic bases in cyclohexane, at 298 K, using a spectrophotometric method.Apparent rate constants were calculated in terms of the kinetic model of Bassett and Habgood. Selectivity studies led to the conclusion that 1-MCP and 3-MCP were competitive products. Correlation between the kinetic selectivity factor, σ, and the number of strong acid sites has been sought.A possible parallel reaction pathway is proposed, which agrees with both the observed rates and selectivities.
Studies of the dihedral angle of a crowded diselenide by X-ray crystallography and ultraviolet spectroscopy
Authors: Back Thomas G. , Codding Penelope W.
Published: May 2006

Bis(di-tert-butylmethyl) diselenide (4) is the first example of a diselenide with an abnormal obtuse dihedral angle resulting from steric crowding. Its value was determined to be 112.1(3)° by X-ray crystallography, as compared with typical dihedral angles of 74–87° for other diselenides. The uv spectrum of 4 supports a similar conformation in solution.
Cyclotétra(λ3-phosphazanes) dérivant de diamines-1,2. Précurseurs de composés du phosphore dicoordonné
Authors: Malavaud Christian , M'Pondo Théophile N'Gando , Lopez Lucien , Barrans Jean , Legros Jean-Pierre
Published: May 2006

Cyclotetraphosphazanes 2 and 5 obtained from 1,2-diamines are 1,3,2-diazaphosphole oligomers leading to the monomeric form by either thermal equilibrium or by complexing with boron trifluoride. The dicoordinated form stabilized by an orthophenylene ring could explain the reactivity of 4,5-benzo 1,3,2-diazaphosphole 3 with compounds having a mobile hydrogen; these reactions were a 1.2 type addition while butanol led to a 1.1 type addition with complexed 1,3,2-diazaphospholes 4 and 8.
Influence of temperature and concentration on the densities and viscosities of solutions of CsNO3 in a low-melting nitrate melt
Authors: Abraham Maurice , Abraham Marie-Christine
Published: May 2006

The densities and viscosities of solutions of CsNO3 in a low melting nitrate melt (AgNO3 + TlNO3) have been measured in the temperature range 371–403 K. The mole fraction XCs of CsNO3 in the solution was varied between 0 and 0.1. The viscosities follow an Arrhenius relation:[Formula: see text]in which both ln A and E* were found to be linear functions of XCs:[Formula: see text]These results are explained considering the preservation of ionic species in the mixtures when the mole fraction XCs is varied, and the assumption of the predominance of short range interactions.
The structure of a minor alkaloid from Argemonegrandiflora Sweet subsp•grandiflora
Authors: Mitchell R. E. , Kerr K. Ann , Benn M. H.
Published: May 2006

Grandiflorine, a minor alkaloid of Argemonegrandiflora Sweet subsp•grandiflora, is shown to be identical with ribasine (and most likely limogine) and have the carbinolamine ether-bridged indanobenzazepine structure 1.
The crystal and molecular structure of bis(2,3-butanedione dioximato)chloro-(hydroxodiphenylarsine)cobalt(III): assignment of the nature of the arsenic-based ligand
Authors: Pizzey Monica , Mihichuk Lynn , Barton Richard J. , Robertson Beverly E.
Published: May 2006

The Co(II) cobaloximes, (B)Co(dmgH)2 (where B = phosphine or phosphite; dmgH = dimethylglyoximato monoanion) react with (C6H5)2AsCl to form ClCo(dmgH)2B and a compound of formula C20H25AsClCoN4O5. A crystal structure analysis of the arsenic compound indicated it to be bis(2,3-butanedione dioximato)chloro(diphenylhydroxoarsine)cobalt(III), [(C6H5)2As(OH)Co(dmgH)2Cl]. The crystals are orthorhombic, space group Pna21, a = 15.334(2), b = 11.173(2), c = 13.745(4) Å at 19(2) °C with Z = 4. The structure has been refined by the least-squares method to a weighted residual of 0.071 using 2345 independent reflections. The Co atom is bonded equatorially to two dmgH ligands (average [Co—N] = 1.89(1) Å) with a Cl atom above this plane ([Co—Cl] = 2.252(2) Å) and the As atom of the (C6H5)2As(OH) group below it ([Co—As] = 2.322(1) Å). The [As—O] bond length is 1.781(7) Å, corresponding to a single bond and is consistent with the observed H atom on the oxygen atom.
Complexes with macrocyclic ligands. II. The crystal structures of HgCl2•18-crown-6 and CdCl2•18-crown-6, and the FAB mass spectrum of HgCl2•18-crown-6
Authors: Paige Christopher Robin , Richardson Mary Frances
Published: May 2006

HgCl2 and CdCl2 form 1:1 complexes with 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6). The complexes are isostructural. The metal coordination is hexagonal bipyramidal, with chlorine atoms strongly coordinated in the axial positions and the 18-crown-6 in the equatorial place. The symmetry of the complex is crystallographically required to be [Formula: see text], but is very nearly [Formula: see text]. The Hg—Cl, Hg—O, Cd—Cl, and Cd—O distances are 2.314(1), 2.825(4), 2.3645(5), and 2.752(1) Å, respectively. Crystals of HgCl2•18-crown-6 are rhombohedral, space group [Formula: see text], a = 7.746(2) Å, α = 95.26(3)°, Z = 1 unit of HgCl2C12H24O6, R = 0.026 for 543 independent reflections with θ < 25°, I > 3σ(I). Crystals of CdCl2•18-crown-6 are also rhombohedral, space group [Formula: see text], a = 7.712(3) Å, α = 95.57(2)°, Z = 1 unit of CdCl2C12H24O6, R = 0.022 for 534 independent reflections with θ < 25°, I > 3σ(I).
Reagents and synthetic methods. 31. Silylations with N-trimethylsilyl-2-oxazolidinone (TMSO)
Authors: Aizpurua Jesús M. , Palomo Claudio , Palomo Antonio L.
Published: May 2006

Silylation of ketones, alcohols, mercaptans, and carboxylic acids with N-trimethylsilyl-2-oxazolidinone (TMSO) and triflic acid as catalyst has been described from synthetic and mechanistic points of view.
Chemiluminescence from the reactions of ozone with sulphur compounds
Authors: Arora P. K. , Chatha J. P. S.
Published: May 2006

Emissions from excited SO2 in its singlet state (1B1, and/or 1A2) and triplet state (3B1) have been observed in gas-phase chemiluminescent reactions of ozone with a number of sulphur compounds. The compounds studied are carbon disulphide, thiophene, diallyl sulphide, diallyl disulphide, dimethyl sulphide, dimethyl disulphide, and thiophenol. The reaction pathways responsible for the formation of excited molecules are discussed. The remarkable similarity between the emission spectra of the reactions and the chemiluminescence from the SO + O3 reaction confirms that SO is a precursor for the observed chemiluminescence. Disulphides are found to be more chemiluminescent than monosulphides. The absence of chemiluminescence from HCHO* in the reactions of ozone with allyl sulphide and disulphide indicates that the attack of ozone molecule is on the C—S bond in organic sulphides.
Optical and magnetic resonance studies of the interaction of metallo tetraphenylporphyrins with nitrobenzofuroxan
Authors: Chandrashekar T. K. , Krishnan V.
Published: May 2006

Metallo tetraphenylporphyrins form 1:1 molecular complexes with 4,6-dinitrobenzofuroxan. The molecular association is described in terms of π–π interaction with porphyrins functioning as donors. The association constants and thermodynamic parameters have been evaluated using optical absorption and 1H nmr spectral methods. Based on the binding constants, the donor ability of various metalloporphyrins can be arranged in the following order: Pd(II) > Co(II) > Cu(II) > Ni(II) ~ VO(IV) ~ 2H > Zn(II). Electron paramagnetic resonance studies of the complexes reveal that the π-complexation results in changes in the electronic structure of the central metal ions which are reflected in the changes in the M–N σ bonding. The dipolar contribution to the acceptor proton chemical shifts in the CoTPP complex has been partitioned from ring current contributions using the shifts observed in the ZnTPP complex. The shifts, along with the line broadening ratios observed for the CoTPP complex, are used to arrive at the possible solution structures of the complexes.
Quantum chemical and statistical thermodynamic investigations of anesthetic activity. 3. The interaction between CH4, CH3Cl, CH2Cl2, CHCl3, CCl4, and an O—H … O hydrogen bond
Authors: Hobza Pavel , Sandorfy Camille
Published: May 2006

The equilibrium for a water dimer (modelling an O—H … O hydrogen bond in a biomolecule) interacting with CH4, CH3Cl, CH2Cl2, CHCl3, or CCl4 is examined by quantum chemical and statistical thermodynamic means. It is shown that the presence of an acidic hydrogen in the molecule as well as its relatively high polarizability are the necessary conditions for anesthetic activity.
The crystal and molecular structure of syn-9-phenyl-2,11-dithia[3,3]metacyclophane
Authors: Anker Willem , Beveridge Kathy A. , Bushnell Gordon W. , Mitchell Reginald H.
Published: May 2006

The crystal structure of syn-9-phenyl-2,11-dithia[3,3]metacyclophane, 6, has been determined by single crystal X-ray diffraction and refined to an R value of 0.0723. The crystal structure is triclinic with a = 9.573(2), b = 12.010(4), c = 8.433(2) Å, α = 108.02(2)°, β = 95.95(2)°, γ = 102.25(3)°, and the space group is [Formula: see text] with two molecules per cell, D(meas) = 1.313 g cm−3, D(calc) = 1.306 g cm−3. The bridging S atoms differ in their conformations so that the S … S distance is 6.391 Å. The metacyclophane rings have a distance of 3.57 Å between their centres and form a dihedral angle of 20.5°. The phenyl substituent forms an angle of 78.6° with the adjacent ring and has an ortho H-atom very close to the internal H-atom of the opposite ring. The phenyl substituted aromatic ring is non-planar and in a shallow boat form, the ring atoms C(11) (internal) and C(14) being 0.038(4) and 0.037(5) Å out-of-plane on the outside, the methylene C substituents are 0.212(5) and 0.199(5) Å out-of-plane on the inside. The first atom of the phenyl group is in the bowsprit position and is 0.274(4) Å above the mean plane on the outer side of the molecule. The opposite metacyclophane ring is less strained but in a similar boat form with the methylene C-atoms 0.092(4) and 0.067(6) Å to the inside. The mean bond angle at S is 103.5(2)°, the angles at C (methylene) range from 113.3(3)° to 118.0(3)°.The variable temperature 1Hmr spectra results are consistent with the syn conformer 6 being dominant in solution and frozen at temperatures <60 °C as conformer A, with only relatively restricted further twisting of the biphenyl being found at ambient temperature.
Reduction of benzylideneacetone derivatives with Pd/SiO2–AlPO4 as catalyst and cyclohexene as hydrogen donor
Authors: Alba A. , Aramendia A. , Borau V. , Garcia-Raso A. , Jimenez C. , Marinas J. M.
Published: May 2006

The hydrogen transfer reduction of benzylideneacetone derivatives p-X-C6H4—CH=CH—CO—R (X = —OCH3, H; R = C6H5, alkyl, OR, OH) using cyclohexene as hydrogen donor has been studied. The selective reduction of the C=C bond is observed and the effects of the nature of X and R, solvent, catalyst, and reaction temperature on the initial reaction rate are analyzed. In all cases, and for any substrate or catalyst, the reaction is first-order with respect to the hydrogen donor and acceptor.
Transposition des cations radicaux aminés en spectrométrie de masse
Authors: Audier Henri Edouard , Denhez Jean Pierre , Milliet Arielle , Sozzi Georges
Published: May 2006

It is demonstrated in mass spectrometry that alkylamines substituted at C2 and containing weak internal energy isomerize in the gas phase into intermediary ions composed of ionized cyclopropanes complexed with an ammonia molecule. This process is induced by a C3 hydrogen shift on the nitrogen atom. After opening of the cyclopropane, the dissociation of these complexes leads to m/z 44, 58, and 72 ions having [CH3(CH2)nCH NH2] structures. The mechanism of their formation is demonstrated by the MIKE spectra of 13C and deuterium labelled compounds. The experimental results are in good agreement with those described by Gross etal., who studied the fragmentation of the complexes formed during the reaction between substituted ionized cyclopropanes and ammonia in the gas phase.
Addition d'ylures d'azométhine aux méthoxycarbonyl cyclopentènes et cyclohexènes benzocondensés. Diastéréosélectivité de la cycloaddition
Authors: Vebrel Joël , Grée Danielle , Carrié Robert
Published: May 2006

Azomethine ylids add stereospecifically to 3-methoxycarbonyl-1-2-dihydronaphthalenes substituted in the 1 or 2 position. The diastereospecificity of the reaction is discussed. The behaviour of 2- or 3-methoxycarbonyl indenes and of 4-methoxycarbonyl-1,2-dihydronaphthalene is also studied.
Pyrolysis products of 1-(1-phenylcyclohexyl)piperidine (PCP)
Authors: Beaver Rodney W. , Jones Louis A.
Published: May 2006

PCP was pyrolyzed in air at 400°, 600°, and 800 °C and the yield of HCN produced was barely detectable at 400 °C, 2.3% at 600 °C, and 5.1% at 800 °C. Gas chromatography (gc) and gc/mass spectrometry (gc/ms) showed the only pyrolysis products produced at 400 °C to be phenylcyclohexane and 1-phenylcyclohexene with 60–70% of the PCP recovered. Only trace amounts of PCP survived the 600 °C pyrolysis, the majority of the pyroproducts being polynuclear aromatics (PNAs) with three or fewer rings. The 800 °C pyrolysis yielded minor amounts of four-ring PNAs, the remainder being similar to the 600 °C products but differing in the relative amounts. Minor amounts of aza-arenes were produced in the 600 °C and 800 °C pyrolyses and separation techniques are described.
Biphasic hydrogenation of olefins, dienes, and α,β-unsaturated carbonyl compounds catalyzed by the dimer of chloro(1,5-hexadiene)rhodium
Authors: Januszkiewicz Krzysztof R. , Alper Howard
Published: May 2006

Olefins, dienes, and trienes can be hydrogenated in an aqueous–organic two-phase medium using the dimer of chloro(1,5-hexadiene)rhodium as the catalyst. Selective reduction of the double bond of α,β-unsaturated carbonyls occurs in high yields. These reactions occur at room temperatures and atmospheric pressure, and are simple to work-up.
Total synthesis of steroids. Part 2. Preparation of C-10 methylated steroids. Regio- and stereocontrol in a diene addition to methyl Z-2-methyl-4-oxo-2-pentenoate
Authors: Das Jagabandhu , Dickinson Robert A. , Kakushima Masatoshi , Kingston Gregory M. , Reid Gary R. , Sato Yasuhiko , Valenta Zdenek
Published: May 2006

A twelve-step total synthesis of 14-epi-androsta-4,9(11),15-triene-3,17-dione from methyl vinyl ketone, 2-methylcyclo-hexane-1,3-dione, acetylene, and methyl Z-2-methyl-4-oxo-2-pentenoate is described. Crucial steps include a stereo- and regio-selective diene addition, an efficient formation of ring D by C-acylation of an acetyl group, and a selective bromine substitution at C-15 in a 15,17-dione intermediate. The stereo- and regioselectivity of the diene addition is generalized for certain other bifunctional aliphatic dienophiles.
Structural and spectroscopic studies of dipotassium 3,3,3′,3′-tetramethylcystinate trihydrate, K2[C10H18N2O4S2]3H2O
Authors: Faggiani Romolo , Howard-Lock Helen Elaine , Lyne Lock Colin James , Martins Maria Lurdes , Smalley Philip Stuart
Published: May 2006

The compound dipotassium 3,3,3′,3′-tetramethylcystinate trihydrate, K2[C10H18O4N2S2]3H2O, has been prepared and characterized by single crystal X-ray diffraction. Crystals were monoclinic, P21a = 6.160(1), b = 26.473(8), c = 6.193(1) Å, β = 113.94(1)°, with two formula units in the unit cell. Intensities were measured on a Syntex P21, diffractometer with use of MoKα radiation. The structure was solved by standard methods and refined to R1 = 0.0469, R2 = 0.0472 based on 2303 independent observed reflections. The C—S bonds (1.877(6), 1.891(6) Å) are longer than in many similar compounds although the S—S bond (2.040(2) Å) is not. The C—S—S—C torsional angle (108.7(3)°) is larger than normal in dithiol compounds. Other distances and angles are normal. Two types of potassium coordination are present, one a distorted octahedron, the other a distorted trigonal prism. In addition to the ionic interactions, hydrogen bonds involving the water molecules are important in stabilizing the structure.
Comparison of methods for determination of boron in heavy water moderator
Authors: Green L. W. , Davey E. C. , Gulens J. , Longhurst T. H. , Mislan J. P.
Published: May 2006

Five analysis methods were compared for the determination of boron in heavy water moderator: isotope dilution mass spectrometry, spectrophotometry, neutron activation, inductively coupled plasma – atomic emission spectrometry, and ion selective electrode potentiometry. Ten samples were analysed by each method; the results showed close agreement between all of the methods. Only mass spectrometry achieved the required precision (<1% rsd) for samples taken during initial reactor operation, but all of the methods achieved sufficient precision (<10% rsd) for samples taken during normal operation. For samples for which the 10B concentration must be determined, only mass spectrometry and neutron activation are applicable.
Photoréactivité des complexes nitriles – cuivre (I) et (II). II. Système cyanure d'allyle – cuivre (I) et (II)
Authors: Bolte Michèle , Femaire Jacques
Published: May 2006

Through complexation with copper I, the allyl cyanide ligand has been shown to be converted in the dark into cis + trans crotonitrile. The photoreactivity of allyl cyanide – copper II complexes provides evidence that the ligand behaves like an α,β unsaturated nitrile. In both cases, the copper atom is bonded with the nitrogen atom of the allyl cyanide by charge transfer from the ligand to the metal (LMCT).
Examination of the molecular properties of D-fructose and L-sorbose by abinitio LCAO-MO calculations
Authors: Szarek Walter A. , Korppi-Tommola Sirkka-Liisa , Martin Olivier R. , Smith Jr. Vedene H.
Published: May 2006

Abinitio SCF LCAO-MO calculations at the STO-3G level have been performed on β-D-fructopyranose (1) and α-L-sorbopyranose (2) using crystallographic data as the geometrical input. Molecular properties of 1 and 2 are discussed in terms of orbital energies, total energy, ionization potentials, Mulliken population analysis, and electrostatic potentials, with a particular emphasis on the possible consequences of these features as regards the sweet taste of these two ketoses. No correlation was found, for example, with the electrostatic, point-charge distribution since the calculated hydrogen-bonding abilities would lead to the prediction of 2 being sweeter than 1. On the other hand, non-bonded overlap populations between oxygen and hydroxyl-hydrogen atoms reveal the presence of intramolecular interactions, which may have a determinant influence on the taste of these molecules and which could explain why D-fructose is much sweeter than its epimer at C-5, namely, L-sorbose.
On the spin trapping of cyanatyl (•NCO) radicals by nitrosodurene
Authors: Rehorek Detlef , Janzen Edward G.
Published: May 2006

Spin trapping experiments with cyanatyl radicals and nitrosodurene show that the triazene-1,3-dioxyl radical described earlier has the structure as indicated for I.
The marticins: confirmation of structure, elucidation of biosynthetic origin by 13Cmr studies, and revision of stereochemical assignments
Authors: Holenstein Jürg E. , Stoessl Albert , Kern Heinz , Stothers J. B.
Published: May 2006

The structure of the phytotoxin marticin 7a has been confirmed on the basis of 1H and 13Cmr data for the methyl ester 7c, but these and other considerations have led to a revision of the stereochemistry assignable to the isomeric isomarticin from 7b to 13. Incorporation of [1,2-13C2]- and [2-13C1]-acetates into 7a, isolated as 7c, has established a heptaketide origin for its fusarubin (1) moiety, and the tricarboxylic acid cycle as the biogenetic source of the remaining C3 fragment, only the first three turns of the cycle making significant contributions.
Surface photochemistry: 13C enrichment by photolysis on silica gel
Authors: Johnston Linda J. , Wong S. King
Published: May 2006

The enrichment of the 13C isotope by partial photolysis of dibenzyl ketone on silica gel has been demonstrated. The 13C enrichment is substantial and is parallel to the increase in the probability of geminate radical recombination on a silica surface as compared with that in solution. A substantial 13C enrichment was also observed for the rearranged starting material, 1-phenyl-4′-methylacetophenone. The single-stage isotope separation factors are different for the two ketones although both are isomers derived from the same benzyl–phenylacetyl radical pairs.
On Worrall's dilactams. Structural corrections
Authors: Butler Douglas N. , Datta Sushil
Published: May 2006

The structures of a number of polycyclic diamides available via the action of ammonia on exo,exo-5,6-dibromonorbomane-endo,endo-2,3-dicarboxylic anhydride have been shown to be incorrectly reported. These substances all possess a nortricyclyl skeleton, e.g. 8, 9, and 10.
Preparation and transformations of allenic ketones and 3(2H)-furanones
Authors: Wolff Steven , Agosta William C.
Published: May 2006

Swern oxidation of allenic alcohols 7 and 10 gives the corresponding ketones 3 and 12. Reaction of 3 with ruthenium tetroxide yields the stable acyl ketene 17 and the acyloxy α-diketone 20 as well as pivalil (4). Formation of 20 by way of the 3(2H)-furanone 22 is suggested, since oxidation of 3 and 12 with osmium tetroxide followed by dehydration provides the corresponding furanones 22 and 26 in good yield. Epoxidation of 3 furnishes some 20 as well as 27 and 29, the first stable keto allene oxide and bisepoxide, respectively. On thermolysis 27 rearranges to furanone 22. The double bond of 22 is cleaved by peracid to form 20; similar treatment of 31a, b leads to cleavage of the double bond accompanied by Baeyer–Villiger oxidation, with formation of the carboxylic acids corresponding to methyl esters 33a, b as the major products.
Controlled coupling of aminoglycoside antibiotics to proteins for use in homogeneous enzyme immunoassays
Authors: Singh Prithipal , Pirio Marcel , Leung Danton K. , Tsay Yuh-Geng
Published: May 2006

Selective N-acylation of aminoglycoside antibiotics with the N-hydroxysuccinimide ester of methyldithioacetic acid, followed by reaction with methanethiol or dithioerythritol, gives sulfhydryl labeled antibiotics. Alternatively, the nucleophilic sulfhydryl group is incorporated into an antibiotic by treatment with N-acetyl-d,l-homocysteine thiolactone. These derivatives couple readily with proteins that have previously been modified with bromoacetylglycyl groups to provide conjugates for use in the development of homogeneous enzyme immunoassays.
Restricted rotation about arene–oxygen bonds in some 1,3-di-tert-butyl-2-methoxyarenedicarbonylphosphorus(III)chromium compounds
Authors: Campi Eva M. , Gatehouse Bryan M. K. , Jackson W. Roy , Rae Ian D. , Wong Margaret G.
Published: May 2006

The 1H nmr spectra of 1,3-di-tert-butyl-2-methoxybenzenedicarbonyltriphenylphosphinechromium (5) and some related compounds at low temperatures show the presence of two species which interconvert with free energy of activation near 50 kJ mol−1. The species differ in the orientation of the methoxy with respect to the chromium, since the same type of process is observed in a chelate complex in which a phosphinite ligand on chromium is also attached to the arene. Hindered rotation about the arene–chromium axis is not involved. The crystal structure of 5 shows the Ph3P anti to the methoxy and the O-methyl group proximal to chromium.
A definitive synthesis of 2-[(5-methyl-s-triazolo[4,3-c]quinazolin-3-yl)thio]-N-benzylacetanilide and other reactions of its precursors
Authors: Hand Elli Smakula , Baker David C.
Published: May 2006

Treatment of 2-methyl-4-chloroquinazoline 2 with hydrazine gave 2-methyl-4-hydrazinoquinazoline 3 which was converted to 5-methyl-3-mercapto-s-triazolo[4,3-c]quinazoline 4, followed by S-alkylation with chloro-N-benzylacetanilide to give 6. The hydrazine 3 was converted to the hydrazone 9 with acetone, to 3,5-dimethyltriazolo[4,3-c]-quinazoline 10 with acetic anhydride, and to 5-methyl-s-tetrazolo[1,5-c]-quinazoline 12 via a nitroso intermediate 11 with nitrous acid. Compound 3 and its derivatives 4, 6, 10, and 12 differed from those alleged to have these structures. The previously reported compounds cannot have these structures since X-ray diffraction studies established that the structure of the common precursor is 3. The mercaptotriazole 4 was air oxidized to the disulfide 20 and hydrolyzed to 2-methyl-3-hydrazinothiocarbony]-4(3H)-quinazolinone 19. The reaction of 4 with carbon disulfide gave a side-product for which the 5-methylquinazolino[3,4-c]-1,2,4-thiadiazol-2-thione 21 is suggested. The 1H nmr chemical shifts of the quinazoline methyl substituent are near δ 3 ppm in the fully aromatic compounds and at higher field when the heterocycle is non-aromatic.
Phosphorescence of naphthalene-labelled colloidal polymer particles. The α-methyl relaxation of one microphase in a multicomponent material
Authors: Winnik Mitchell A. , Pekcan Onder , Croucher M. D.
Published: May 2006

Nonaqueous dispersions of poly(methyl methacrylate) (PMMA) particles, sterically stabilized with polyisobutylene (PIB), were prepared with naphthalene (N) groups covalently incorporated into the PMMA chains. These materials have a complex morphology of phase-separated PMMA and PIB microdomains, with the N groups in the PMMA microphases. The phosphorescence intensity and decay times of the N groups were measured as a function of temperature over the range 77–295 K for dispersions in methylcyclohexane and for freeze-dried powder samples. An Arrhenius treatment of the radiationlcss decay rate showed a change in slope at −35 °C. The activation energy for the radiationless decay process is 3.8 kcal/mol in the −35 – +22 °C temperature region, identical to that found for pure PMMA by nmr for chain motion associated with the a-methyl relaxation process. We believe that the phosphorescence experiment is sensitive to the diffusion of oxygen and other impurities in the sample. These rates increase as the temperature is raised, enhancing the rate of phosphorescence quenching. These experiments indicate that phosphorescence measurements on labelled samples are suitable for studying relaxation processes within individual microphases of a polyphasic composite material.
Chemistry of spectinomycin: its total synthesis, stereocontrolled rearrangement, and analogs
Authors: Hanessian Stephen , Roy René
Published: May 2006

The total stereocontrolled synthesis of the antibiotic spectinomycin is described, based on the regiospecific functionalization and manipulation of appropriate starting materials. The tertiary ketol rearrangement of the antibiotic and its derivatives was studied and the stereochemical identity of spectinoic acid was established by chemical correlation. Dihydrospectinomycin derivatives undergo unusual solvolysis reactions.
Nucleophilic substitution of meso-nitrooctaethylporphyrins
Authors: Gong Liang-Chu , Dolphin David
Published: May 2006

Nitrooctaethylporphyrins readily undergo nucleophilic aromatic substitution in the presence of HCl or HBr. In the presence of methoxide, nucleophilic addition to give a porphodimethane occurs, followed by autoxidation to the methoxyporphyrin. Unlike the nitrated complexes, the chlorosubstituted porphyrins exhibit redox potentials similar to those of unsubstituted analogs. Meso-halogenated porphyrins do, however, show steric distortion due to the bulk of the halogen atoms.
Thermolysis of unsymmetrically substituted vinylcyclopropanes. Regarding the effect of oxygen substituents on the site-selectivity of homo-[1,5]-sigmatropic hydrogen migrations
Authors: Piers Edward , Maxwell Anderson Richard , Moss Neil
Published: May 2006

Thermal rearrangement of compounds 1, 8–11, and 20 results, in each case, in the exclusive migration of the hydrogen (HΛ) not associated with the oxygen substituent. On the other hand, thermolysis of 19, 22, and 23 provides, in each case, a mixture of the two possible sigmatropic rearrangement products. Similar bond reorganization of the hydrocarbon 21 affords the dienes 27 and 28 (98:2, respectively). On the basis of these results, along with those reported earlier, it is proposed that in the transition states for these rearrangements (a) there is an accumulation of electron density at the carbon from which the hydrogen migrates, and (b) this carbon center has a planar or nearly planar geometry.
Five-coordinate dicarbonyl complexes of rhodium(I): [RhX(CO)2(PPh3)2] (X = Cl, Br, I)
Authors: Sanger Alan R.
Published: May 2006

The complexes trans-[RhX(CO)PPh3)2] (1, X = Cl, Br, I) react with CO to form [RhX(CO)2(PPh3)2] (2), and not to form cis-[RhX(CO)(PPh3)2]. Complexes 2 contain equivalent axial carbonyl ligands. It is proposed that a series of dicarbonyl complexes, including 2, is formed during decarbonylation reactions catalyzed by 1.
Crystal and molecular structure of 3-ethyl-4-hydroxy-1,2,3(4H)-benzotriazine and 6-chloro-4-hydroxy-3-methyl-4-phenyl-1,2,3-benzotriazine
Authors: Lai Kwong Khee , Schwalbe Carl H. , Vaughan Keith , Lafrance Ronald J. , Whiston Clive D.
Published: May 2006

The crystal structures of the title compounds have been determined from X-ray data collected on a four-circle diffractometer and refined by the full-matrix least-squares method. The former compound crystallizes in the orthorhombic system, space group Pbcn, with a = 14.346(8), b = 7.239(1), c = 17.276(2) Å, and has been refined to a conventional R factor of 0.043 for 890 observed reflections. Corresponding results for the latter compound are monoclinic, P21/n, a = 12.222(4), b = 7.482(2), c = 14.170(8) Å, β = 94.06(4)°, R = 0.060 for 2128 observed data. The triazine rings of both compounds exhibit short N(1)—N(2) bonds and tetrahedral geometry at C(4); however, the ring is puckered in the first compound but flat in the second. Molecules in both crystals are linked by [Formula: see text] hydrogen bonds.
Preparation and properties of a linked porphyrin–cyclodextrin
Authors: Gonzalez Monica C. , Weedon Alan C.
Published: May 2006

The synthesis of the linked porphyrin–cyclodextrin 3 and its zinc complex 4 is described and their characterization by 1H nmr, l3C nmr, circular dichroism, ultraviolet, and infrared spectroscopy is reported. The linked porphyrin–cyclodextrin compounds exhibited perturbed electronic absorption and emission spectra which are consistent with their adopting two conformations, one extended with little interaction between the porphyrin and cyclodextrin, and the other folded with the cyclodextrin weakly complexed to the porphyrin. Quenching of the porphyrin excited state of 3 by benzoquinone was examined by measurement of the fluorescence lifetime as a function of quinone concentration; the results suggest that the porphyrin excited state can be quenched intermolecularly by benzoquinone and also intramolecularly by quinone complexed within the cyclodextrin cavity.
Étude physico-chimique des solutions concentrées en acide phosphorique par voie électrochimique. Propriétés acido-basiques et oxydo-réductrices
Authors: Louis C. , Bessière J.
Published: May 2006

Acid–base properties in 1 to 14 M H3PO4 solutions are characterized with a R0(H) acidity function and [Formula: see text], [Formula: see text], [Formula: see text] functions which respectively represent the H+ activity in these media and their ability to give [Formula: see text], [Formula: see text], [Formula: see text] species. The thermodynamic limits of potential and the nature of the ionization equilibrium are studied. H and R acidity levels in phosphoric media are compared to those of sulfuric, hydrochloric, and hydrofluoric acid media. The identity of their R0(H) acidity level for the same value of water activity is shown.
Stereoselective total syntheses of (±)-sinularene and (±)-5-epi-sinularene: a general intramolecular Diels–Alder approach to tricyclic sesquiterpenes
Authors: Antczak Kazimierz , Kingston John F. , Fallis Alex G.
Published: May 2006

Stereoselective total synthesis of (±)-sinularene and (±)-5-epi-sinularene are described. The sequence employs a "blocked" cyclopentadiene in which the cyclopropane unit also serves as a latent methyl group. Thus intramolecular [4 + 2] cycloaddition of the substituted methyl spiro[2.4]hepta-4,6-dien-1-yl)-2-pentenoate 11 affords 5-benzyloxy-6-isopropyl-8-carbomethoxytetracyclo[5.4.01,7.02,4.02,9]undec-10-ene (12) which after selective hydrogenolysis generates the tricyclo[4.4.01,6.02,8]decane (sinularene) ring system. Removal of the secondary hydroxyl function (Ph3P/CCl4/CH3CN; H2/Pd/C), reduction of the methyl ester (LiAlH4), and introduction of the exocyclic double bond (acetate pyrolysis, 550 °C) completes the synthesis of (±)-sinularene in 14 steps from cyclopentadiene. A parallel series of reactions employing the isopropyl epimer of 12 affords (±)-5-epi-sinularene.
Total assignment of the 13C spectrum of taraxasteryl acetate by 13C–13C connectivity experiments and determination of the stereochemistry of taraxasterol by X-ray diffraction
Authors: Reynolds William F. , Sawyer Jeffery F. , Enriquez Raúl G. , Escobar Laura I. , Chavez Marco A. , Shoolery James N.
Published: May 2006

13C–13C connectivity (INADEQUATE) experiments have been used to reassign the 13C spectrum of taraxasteryl acetate. This shows that there were ten errors in an earlier 13C spectral assignment for this compound. An X-ray diffraction investigation of taraxasterol shows that ring E adopts a slightly distorted boat conformation. It is suggested that severe steric interactions in the chair form force it to adopt this unusual conformation. On the basis of the 1H–1H coupling constants, it is concluded that taraxasteryl acetate adopts a very similar conformation in solution. Crystals of taraxasterol–ethanol solvate are orthorhombic, space group P21,21,21, wih a = 7.447(1) Å, b = 17.637(2) Å, c = 22.269(4) Å, U = 2925 Å3, and Dcalc = 1.07 g cm−3 for Z = 4.
Inter-ring dihedral angles in polychlorinated biphenyls from photoelectron spectroscopy
Authors: Dynes J. J. , Baudais F. L. , Boyd R. K.
Published: May 2006

A proposal that the physiological activity of a chlorinated biphenyl is related to its degree of molecular planarity is explored through experimental measurements of inter-ring dihedral angles in the gas phase. A known correlation between the difference between fourth and first ionization energies of substituted biphenyls (via photoelectron spectroscopy), and the thermally averaged inter-ring dihedral angle as established by electron diffraction techniques, is confirmed and exploited for the present purpose. The expectation, based on both qualitative and quantitative theoretical considerations, that increased ortho substitution causes an increase in inter-ring angle, is confirmed. However, the observation that, for 2,2′-substituted halobiphenyls the only observed conformation is the near-syn form, is not easy to explain, and is discussed in terms of a non-bonding attractive force between halogen atoms.
An exciplex probe for end-to-end cyclization of polystyrene. Cyclization dynamics of polymers. 15
Authors: Winnik Mitchell A. , Sinclair Andrew M. , Beinert Gérard
Published: May 2006

An asymmetrically end-labelled polystyrene of low polydispersity has been synthesized. The labels are pyrene and dimethylaniline, which can form an emissive exciplex from excited pyrene. End-to-end cyclization rate constants [Formula: see text] have been calculated from fluorescence decay data in a variety of solvents. Steady-state measurements are also presented. Correction of the [Formula: see text]'s for differences in solvent viscosity yields cyclization rate constants of 0.7 × 106 s−1 in good solvents and about twice this in poor (sub-θ) solvents. Cyclization rate constants [Formula: see text] in toluene and cyclohexane at 22 °C obtained using this pyrene/dimethylaniline exciplex probe are compared with those obtained previously using a pyrene/pyrene excimer probe.
Prospects for solar synthesis. II. Study of the photocyclization of α-(o-tolyl)acetophenone in solution and in crosslinked ethylene – vinyl acetate beads
Authors: Guillet J. E. , MacInnis W. K. , Redpath A. E.
Published: May 2006

Studies of the photocyclization of α-(o-tolyl)acetophenone dissolved in crosslinked ethylene–vinyl acetate beads show that quantum yields close to unity can be achieved, even in the solid polymer matrix. In preliminary experiments using solar radiation it was demonstrated that the rates of photochemical transformations are close to those calculated from the photon energy distribution of the solar spectrum.
A blind chemist's approach to automated scientific information
Authors: Cartier Jean-Pierre , Paquin Francine
Published: May 2006

Computer access to chemical information by a blind chemist is made possible with a VersaBraille system (Braille Information Processor). The CAS database of the DIALOG system is used in this updating assay. Preliminary trials showed the need to establish a rigorous procedure to avoid loss of data. In this study, a functional method is suggested as a substratum to circumvent costly problems.
Ligand field and Rydberg assignments of the PtCl42− spectrum: a relativistic MS-Xα study
Authors: Goursot A. , Chermette H.
Published: May 2006

Relativistic MS-Xα calculations are reported for a PtCl42− cluster. Good agreement with experiment is obtained for the optical spectrum. A ligand field approach has been used to evaluate the d–d transitions through the use of a strong field matrix, where the crystal field parameters have been replaced by values derived from the Xα calculation. The high intensity spectrum is clearly interpreted in terms of Rydberg Pt 5d → 6p transitions.
Discriminative interactions between chiral molecules: internal discrimination in 1,2-difluorohydrazine
Authors: Zahradník Rudolf , Schneider Bohdan , Hobza Pavel , Havlas Zdenêk , Huber Hanspeter
Published: May 2006

1,2-Difluorohydrazine represents a model for studying short-range discriminative interactions between two chiral radicals. Possible diastereomeric structures of the system were theoretically investigated by means of nonempirical SCF quantum chemical calculations. Four minima and six saddle points separating them were found on the potential energy surface. All the stable structures and one transition complex were completely optimized. Thermodynamic properties for the equilibrium between the two most stable conformers (meso and chiral) of difluorohydrazine are as follows (in kJ/mol): [Formula: see text], [Formula: see text] (standard state: ideal gas at 101.325 kPa, 298 K).
Triethylammonium halides, Et3NHX (X = Cl, Br, I): simple structure, complex spectrum
Authors: James Margaret Ann , Cameron T. Stanley , Knop Osvald , Neuman Murray , Falk Michael
Published: May 2006

A crystal structure determination has shown that the ethyl groups in the three isostructural (P63mc, Z = 2) triethylammonium halides, Et3NHX (X = Cl, Br, I), at room temperature are orientationally disordered and the [Formula: see text] groups are linear by symmetry. The unusual extent and complexity of the NH and ND stretching absorptions in the ir spectra of all three compounds between 10 and 293 K are discussed in terms of Fermi resonance interactions. The centroid ν(NH) and ν(ND) frequencies extracted from the spectra correlate with the [Formula: see text] distances. It is shown that if Fermi resonance is the sole cause of the complexity of the stretching absorptions, then these centroids represent the ν(NH) and ν(ND) frequencies unperturbed by Fermi resonance. The centroid frequencies in the three halides are unusually low, pointing to strong [Formula: see text] hydrogen bonding.
Metal oxide coated p–n junction silicon electrodes for photoelectrochemical solar energy conversion
Authors: Tsubomura Hiroshi , Nakato Yoshihiro , Hiramoto Masahiro , Yano Hiroyuki
Published: May 2006

Photoelectrochemical properties of p+–n junction silicon electrodes, abbreviated as p+n–Si, coated with thin oxide films of titanium, tungsten, or iron have been investigated in aqueous solutions of hydrogen iodide and iodine. The films were deposited by electron-beam evaporation of the metal oxide sinters. The photocurrent in a p+n–Si electrode coated with TiO2 increased dramatically when it was heated at temperatures higher than 500 °C, though the O/Ti atomic ratio as determined by ESCA analysis was unchanged. The fill factor of the photovoltaic cell composed of this electrode, a platinum counter electrode and an aqueous solution of 7.6 M HI and 0.03 M I2 was improved by coating with ruthenium or its oxide. The photovoltaic cell attained a high solar to electrical energy conversion efficiency of 9.3% (AM1), with an open circuit photovoltage of 0.58 V, a short circuit photocurrent of 26.6 mA cm−2 and a fill factor of 0.61. The photocurrent was stable for 350 h. For the cases of electrodes coated with a Fc2O3 or WO3 film, high fill factors were obtained even without ruthenium coating. The effect of the nature of Si – metal oxide junctions, the donor density in the oxide, the relations between the flat band potential of the oxide and the redox potential of the solution, etc., on the conversion efficiency was discussed.
Characterization of DNA structures by infrared spectroscopy: double helical forms of poly(dG-dC)•poly(dG-dC), poly(dD8G-dC)•poly(dD8G-dC), and poly(dG-dm5C)•poly(dG-dm5C)
Authors: Taboury J. A. , Liquier J. , Taillandier E.
Published: May 2006

Infrared spectroscopy in the 1750–700 cm−1 region is used to characterize the right- and left-handed helices of poly(dG-dC)•poly(dG-dC) with sodium counterions. The use of polymers selectively deuterated on the C8 of guanines and methylated on the C5 of cytosines allows us to propose explanations for several spectroscopic modifications which occur under the B → Z transition. Similar substitutions on nucleosides and nucleotides are used so as to assign base absorptions in poly(dG-dC)•poly(dG-dC). A set of ir bands characteristic of DNA conformations, which can be used in studies of interactions with this polynucleotide and to identify the left handed Z conformation in more complex systems, is proposed.
Fractionation of organic extracts of environmental water samples by low pressure column chromatography and high performance liquid chromatography techniques
Authors: Moore R. A. , Karasek F. W.
Published: May 2006

Prefractionation procedures based on high performance liquid chromatography (hplc) and low pressure column chromatography (lpcc) were developed and applied to the separation of components in extracts of environmental samples. Effective fractionation was obtained using solvent systems based on hexane, carbon tetrachloride, dichloromethane, and ether for elution on lpcc Florisil and hplc silica columns. This facilitated the identification of over thirty compounds consisting mainly of aliphatic and polyaromatic hydrocarbons, phthalate esters, phenols, and pesticides in environmental samples extracted from water. Chromatographic background levels were minimized, and compounds whose chromatographic peaks were unresolved before fractionation were isolated into separate fractions. This afforded more highly reliable gc/ms identifications. Prefractionation also served to retard the rapid degradation of capillary columns which was caused by the injection of unfractionated samples.
Novel hydrogen bonding in crystalline tetra-n-butylammonium salts of catechol halides
Authors: Khan Masood A. , McCulloch Archibald W. , McInnes A. Gavin
Published: May 2006

The crystal structures of [N(n-C4H9)4] [catechol … Cl] (1) and [N(n-C4H9)4] [catechol … Br] (2) have been determined by X-ray analysis which showed that the two structures are isomorphous, with the orthorhombic space group Pbca, Z = 8. The cell dimensions and final R-values are: (1) a = 15.323(2), b = 16.166(2), c = 19.713(2) Å, R = 0.048 for 1361 observed reflections; (2) a = 15.432(1), b = 16.244(2), c = 19.824(1) Å, R = 0.041 for 1958 observed reflections. The crystal structures consist of discrete tetra-n-butylammonium cations and catechol halide anions. Catechol forms two strong hydrogen bonds to a single halide ion giving a pattern of hydrogen bonding unique for such systems.
Synthesis and biological activity of nucleoside analogs involving modifications in the carbohydrate ring
Authors: Szarek Walter A. , Pinto B. Mario , Iwakawa Masaharu
Published: May 2006

The synthesis of a variety of nucleoside analogs involving modifications in the carbohydrate ring is described. In particular, 6-substituted purin-9-yl derivatives of 1-oxa-4-thiacyclohexane and 1,4-dioxacyclohexane have been synthesized. A number of 6-chloropurin-9-yl derivatives of substituted 1-oxa-4-thiacyclohexane have also been derived from the parent compounds by way of a Pummerer rearrangement. A route to nucleoside analogs of 1-oxa-4-thiacyclohexane from naturally occurring nucleosides is illustrated for the case of inosine. A route to nucleoside analogs in which the carbohydrate moiety is replaced by an acyclic moiety bearing α,β-unsaturated esters is also illustrated for the case of uridine. The results of biological screening of these analogs and others previously synthesized in our program against leukemia L-1210 cells in vitro are presented; some of these compounds showed marginal antitumor activity. The screening results of selected compounds against the human HeLa cell line in vitro are also presented; none of the compounds that were tested showed significant inhibitory activity of cell growth.