bluuebunny/crossref_metadata_2025 huggingface dataset:
Some thermodynamic and transport properties of lithium salts in mixed aprotic solvents and the effect of water on such properties
Authors: Couture Lorraine , Desnoyers Jacques E. , Perron Gérald
Published: May 2006

In a continuing study on the optimization of the electrolyte medium for high-energy lithium batteries, volumes, heat capacities, and specific conductivities of LiClO4 and LiBr were measured in mixtures of γ-butyrolactone (BUTY) and 1,2-dimethoxyethane (DME) and of propylene carbonate (PC) and BUTY. These results are compared with those of the electrolytes in the pure solvents. Phase diagrams are also reported when appropriate. The effect of addition of water to these binary and ternary systems was investigated with the same techniques. The mixtures DME–BUTY, PC–DME, DME–H2O, and BUTY–H2O are typical of mixtures of aprotic solvents and mixtures of aprotic solvents and water. The electrolytes at high concentrations in aprotic solvents of low dielectric constants are largely associated. The medium still conducts electrolytically since the ion pairs are in a state that resembles to a large extent that of a molten salt. With some systems at high concentration, stable solvates persist in the solution medium, as evidenced mostly by heat capacities, and are in equilibrium with either the excess solvent or unsolvated molten salts. In mixed solvents, the properties of electrolytes can largely be predicted from the binary systems and by the coexistence of these solvates. The properties of water in DME, BUTY, or mixtures of the two solvents are modified significantly in the presence of LiBr but only slightly with LiClO4. These specific interactions, which affect the heat capacities much more than the volumes and which are especially large with the system LiBr–DME, could be responsible for the decrease in reactivity of water with lithium metal in an aprotic medium in the presence of certain electrolytes. Key words: LiClO4, LiBr, γ-butyrolactone, dimethoxyethane, propylene carbonate, lithium battery, aprotic solvent, water, association, solvates, solid–liquid phase diagrams, volumes, heat capacities, specific conductivities.
Chromatographie à contre courant et micelles inverses pour la séparation et l'extraction de cations métalliques
Authors: Berthod Alain , Xiang Jun , Alex Serge , Gonnet-Collet Colette
Published: May 2006

Countercurrent chromatography (CCC) is a separation technique in which the stationary phase is a liquid. Diethylhexyl phosphoric acid (DEHPA) forms reverse micelles in heptane. Metallic ions, located in an aqueous phase, can be extracted into the aqueous core of the reverse micelles in the heptane phase. A CCC apparatus can be considered as a powerful mixing and extracting machine with efficiency above several hundreds of theoretical plates. La3+, Ce3+, Pr3+, and Nd3+ lanthanide cations were separated using CCC with a DEHPA-containing heptane stationary phase. Studying the retention variations with aqueous mobile phase pH, it was possible to determine the lanthanide extraction constants and separation coefficients. Overloading conditions are described. Frontal chromatography was performed using a Co2+ and Ni2+ solution. The Co2+ ions were concentrated in the heptane + DEHPA stationary phase, a part of the solution was deionized, and another part was enriched in only Ni2+ ions. This method also produced the extraction constants and separation coefficients. The use of CCC with a complexing stationary phase can be applied to any cation for ion filtering and concentration, or for deionization of aqueous phases. Key words: countercurrent chromatography, CCC; ion extraction, ion filtering, deionization, lanthanides, transition metals.
Chemical mapping of the active site of the glucoamylase ofAspergillus niger
Authors: Lemieux Raymond U. , Spohr Ulrike , Bach Mimi , Cameron Dale R. , Palcic Monica M. , Frandsen Torben P. , Stoffer Bjarne B. , Svensson Birte
Published: May 2006

A recently developed technique for the probing of the combining sites of lectins and antibodies, to establish the structure of the epitope that is involved in the binding of an oligosaccharide, is used to study the binding of methyl α-isomaltoside by the enzyme glucoamylase. The procedure involved the determination of the effects on the kinetics of hydrolysis of both monodeoxygenation and mono-O-methylation at each of the seven hydroxyl groups in order to gain an estimate of the differential changes in the free energies of activation, ΔΔG≠. As expected, from previous publications, both deoxygenation and O-methylation of OH-4 (reducing unit), OH-4′, or OH-6′ strongly hindered hydrolysis, whereas the kinetics were virtually unaffected by either the substitutions at OH-2 or structural changes at C-1. The substitutions at OH-3 caused increases of 2.1 and 1.9 kcal/mol in the ΔΔG≠. In contrast, whereas deoxygenation of either OH-2′ or OH-3′ caused much smaller (0.96 and 0.52 kcal/mol) increases in ΔΔG≠, the mono-O-methylations resulted in severe steric hindrance to the formation of the activated complex. The relatively weak effects of deoxygenation suggest that the hydroxyl groups are replaced by water molecules and thereby participate in the binding by contributing effective complementarity. Methyl α-isomaltoside was docked into the combining site of the X-ray crystal structure at 2.4 Å resolution of the complex with the inhibitor acarbose. A fit free of steric interactions with the protein was found that has the methyl α-glucopyranoside unit in the normal4C1conformation and the other glucose unit approaching a half-chair conformation with the interunit fragment defined by the torsion angles [Formula: see text] The model provides a network of hydrogen bonds that appears to well represent the activated complex formed by the glucoamylase with both maltose and isomaltose since the structures appear to provide a sound rationale for both the specificity and catalysis provided by the enzyme. Key words: monodeoxy and mono-O-methyl derivatives of methyl α-isomaltoside, enzyme binding domain, functioning of glucoamylase, differential changes in free energy of activation, characteristics of hydrogen bonding networks.
1995 Merck Frosst Award Lecture Quinone methides: relevant intermediates in organic chemistry
Authors: Wan Peter , Barker Beverly , Diao Li , Fischer Maike , Shi Yijian , Yang Cheng
Published: May 2006

ortho and para-Quinone methides (2-methylene-3,5-cyclohexadien-1-one and 4-methylene-2,5-cyclohexadien-1-one, respectively) are intermediates in a variety of important chemical systems. In particular, o-quinone methides are useful in synthesis for the construction of chroman ring systems. A brief account of the relevance of quinone methide chemistry will be provided. This is followed by a review of recent studies from our laboratory on efficient methods for the photogeneration of quinone methides, concentrating on the use of hydroxy-substituted benzyl alcohols in aqueous media. It is shown that this method is general since it provides access to o-, m-, and p-quinone methide isomers. When appropriately substituted, all of these quinone methide isomers have been spectroscopically characterized by laser flash photolysis, making this technique the one of choice for studying the dynamics of these reactive intermediates. The mechanism of photochemical generation from hydroxybenzyl alcohols and extensions of the reaction to photogeneration of fluorenyl and biphenyl quinone methides will also be presented. Key words: quinone methide, biphenyl quinone methide, carbocation, photosolvolysis, photodehydroxylation, hetero-Diels–Alder reaction.
Structure and wavelength modification in retinylidene iminium salts
Authors: Elia George R. , Childs Ronald F. , Britten James F. , Yang Daniel S.C. , Santarsiero Bernard D.
Published: May 2006

The spectroscopic and structural properties of the perchlorate and triflate salts of N-n-butyl-retinylidene imine, 2 and 3, have been examined in solution and solid phases. In solution these salts were found to exhibit very similar UV and NMR spectroscopic properties. However, in the solid state marked differences in their absorption spectra (2, λmax = 504 nm; 3, λmax = 445 nm) and13C NMR spectra were found. The structures of the two salts were determined by X-ray crystallography. The cations in each of the salts were shown to have very similar conformations, detailed structures, and packing in their crystal lattices. The differences in the spectroscopic properties of the salts in the solid state could not be accounted for on the basis of any structural differences in the cations themselves. In terms of cation–anion interactions, a strong hydrogen bonding interaction was found in each case between the N-H proton and an oxygen atom of the counterion. However, there were significant differences between the two salts in terms of the [Formula: see text] internuclear distances (2, [Formula: see text] and in 3, 2.85(1) Å). The results are strongly suggestive that the wavelength and positive charge delocalization in retinylidène iminium salts are controlled by variation of the distance between the anion and the proton bonded to the Schiff base nitrogen atom. The work reported here represents the first examples of secondary retinylidene iminium salts containing an N-alkyl substituent to be successfully analyzed by X-ray crystallography. The relationship of these observations in the solid state to the spectroscopic properties of the natural visual pigments is explored. Key words: retinylidène iminium salts, iminium salts, cation–anion interactions.
The role of hydrogens in stabilizing organic ions
Authors: Wiberg Kenneth B. , Schleyer Paul von Rague , Streitwieser Andrew
Published: May 2006

The changes in electron density that result from processes in which ions are formed were examined using both electron density difference maps and calculations of electron populations using Bader's theory of atoms in molecules. The processes include the loss of an electron from a neutral precursor forming a radical cation, the loss of an electron from a free radical forming a carbocation, the addition of a proton to ammonia, the addition of an electron to a free radical forming a carbanion, and the loss of a proton from a neutral precursor forming an anion. In the reactions forming cations, the new positive charge resides mainly at the hydrogens, and the heavy atoms generally gain electron density. The anion-forming reactions lead to negative charge being shared among atoms but, again, much of the charge appears at the hydrogens. σ–π polarization is an important feature of the charge distribution in all of the ions. There is an advantage to placing the charge at the periphery of an ion since this will minimize its electrostatic energy. Key words: electron density, anions, cations, radical cations, σ–π polarization.
Delocalized bonding in tetrahedral organo-transition metal clusters: an EHMO study of metal vertex rotations in Co2Fe(CO)9S, CpMoCo2(CO)8CR, and in Cp2Mo2(CO)4(RC≡CR)
Authors: Malisza Krisztina L. , Li Lijuan , McGlinchey Michael J.
Published: May 2006

Molecular orbital calculations at the extended Hückel level are used to rationalize the barriers to vertex rotation in the tetrahedral metal cluster complexes FeCo2(CO)9S, 2, and (C5H5)MoCo2(CO)8CH, 3. It is shown that, in accord with experimental observations on 2, rotation of an Fe(CO)3 fragment through 60° brings about a weakening of the metal–metal bonding interactions within the FeCo2 triangle. In the MoCo2 cluster, 3, rotation of the CpMo(CO)2 fragment about an axis joining the molybdenum to a central point within the tetrahedron gives rise to three minima in which the cyclopentadienyl ring is oriented proximal or distal relative to the capping carbynyl moiety, or in the plane of the three metals. The rotation trajectory of the CpMo(CO)2 vertices in Cp2Mo2(CO)4(HC≡CH), 4, has been elucidated by means of a Bürgi–Dunitz analysis of the X-ray crystal structures of a series of related clusters in which the CpMo(CO)2 units exhibit a range of orientations. The calculations suggest that the barriers to vertex rotations in 4 are primarily of steric rather than electronic origin. Key words: metal clusters, vertex rotations, EHMO calculations.
Zero-temperature equation-of-motion of electron pair in the BCS theory of superconductivity
Authors: Tachibana Akitomo
Published: May 2006

By projecting the BCS ground state of superconducting electron condensate on the N-electron Hilbert space, a real-space equation-of-motion is obtained for the electron pair function [Formula: see text] at absolute zero temperature (T = 0):[Formula: see text]where ρN−2 denotes electron density of the (N – 2)-electron condensate given as[Formula: see text]Since the exchange-correlation potential is given as an explicit functional of electron density, this equation represents the fundamental working equation for the new density functional theory of superconductivity. The 2nd-order density matrix ΓN(1, 2|1′, 2′) projected on the N-electron Hilbert space satisfies[Formula: see text]so that asymptotically[Formula: see text]where [Formula: see text] denotes the center-of-mass coordinate of electrons e1and e2; this is considered the ODLRO (off-diagonal long-range order) at T = 0 projected on the N-electron Hilbert space. A new attractive potential analysis for the two-electron scattering problem (A. Tachibana, Bull. Chem. Soc. Jpn. 66, 3319 (1993); Int. J. Quantum Chem. 49, 625 (1994)) is straightforwardly applicable to the present equation-of-motion, and we can also plug in the vibronic interaction for the enhancement of the attractive force. Our approach is purely mathematical and basic, restricted merely at T = 0, but proves to serve as a real-space analysis of the pair function itself. Key words: equation-of-motion of electron pair, BCS theory, superconductivity, electron pair function, density functional theory.
From topology to geometry
Authors: Eberhart Mark
Published: May 2006

A systematic study of the charge density topologies corresponding to a number of transition metal aluminides with the B2 structure indicates that unstable crystal structures are sometimes associated with uncharacteristic topologies. This observation invites the speculation that the "distance" to a topological instability might relate to a metals phase behavior. Following this speculation, a metric is imposed on the topological theory of Bader, producing a geometrical theory, where it is now possible to assign a distance from a calculated charge density topology to a topological instability. For the cubic transition metals, these distances are shown to correlate with single crystal elastic constants, where the metals that are furthest from an instability are observed to be the stiffest. Key words: crystal structure, charge density topology, mechanical properties, brittle/ductile failure.
Comparative electronic analysis between hydrogen transfers in the CH4/CH3+, CH4/CH3•, and CH4/CH3− systems: on the electronic nature of the hydrogen (H−, H•, and H+) being transferred
Authors: Mestres Jordi , Duran Miquel , Bertrán Juan
Published: May 2006

A comparative electronic analysis of the generally termed hydrogen transfers between CH4 and the CH3+, CH3•, and CH3− fragments is presented. These systems are taken as simple models of hydride (H−), hydrogen (H•), and proton (H+) transfers between two carbon fragments (in these simple cases being modelized by two CH3+, CH3•, and CH3− fragments, respectively). The study is mainly focused on analysis of the electronic nature of the type of hydrogen being transferred in each system, and for this reason a topological analysis of charge density distributions was performed. Computation of Bader atomic charges and construction of the charge density, gradient vector field, and Appalachian of the charge density maps reveal the specific features of the electronic nature of the transferring H−, H•, and H+. Moreover, characterization of the bond critical points on the charge density surface permits clarification of the differences in atomic interactions between H−, H•, and H+ and the carbon belonging to each CH3+, CH3•, and CH3− fragment, respectively. A charge density redistribution analysis is also performed to quantify the reorganization of the electron density when going from the reactant complex to the transition state. Finally, effects of inclusion of the correlation energy at the MP2 and CISD levels are also discussed. Key words: electron density, hydrogen transfer, topological density analysis, molecular similarity, Bader density analysis.
Probe of cadmium(II) binding on soil fulvic acid investigated by113Cd NMR spectroscopy
Authors: Chung Kun H. , Rhee Seog W. , Shin Hyun S. , Moon Christopher H.
Published: May 2006

Binding of cadmium(II) on soil fulvic acid (FA) was investigated over a range of fulvate-to-cadmium concentration ratios (8 – 59 equiv. mol−1) using113Cd NMR spectroscopy. The113Cd chemical shift of cadmium bound on fulvate was observed in a more downfield region (δ −20.4 to −15.6) than that bound on synthetic polymers, poly(acrylic acid) (PAA: δ −36.6 to −38.2), poly(methacrylic acid) (PMAA: δ −34.0 to −25.4), and poly(vinyl benzoic acid) (PVBA: δ −34.7 to −31.2). The calculated values of individual chemical shifts for the species CdL+and CdL2(L: carboxylate) formed in Cd(II)–carboxylate systems (e.g., acetate, benzoate) are δ −22 to −24 and δ −39 to −40, respectively. The relative downfield shift of cadmium(II)–fulvate suggests that functional groups (e.g., hydroxyl and neutral N donor) other than carboxylates may be involved in cadmium coordination. The chemical shifts of cadmium complexes of hydroxycarboxylates (e.g., glycolate) or carboxylates containing neutral N donor (e.g., picolinate) were generally observed in more downfield regions than their carboxylate counterparts. Key words: fulvic acid, polyfunctionality, binding sites, chemical shift,113Cd NMR.
Interaction between tetracyanoethylene and naphthalene in reverse micelles of AOT in n-hexane. The electron-donor properties of AOT
Authors: Biasutti M. A. , Silber Juana J.
Published: May 2006

The electron donor–acceptor (EDA) interaction between TCNE and naphthalene (Naph) in n-hexane and reverse micelles of AOT in n-hexane was studied by UV–visible spectroscopy with the aim of determining the influence of the micellar media on the EDA interaction. The spectra of the mixtures of TCNE–Naph in n-hexane show two typical maxima at 418 and 534 nm, assigned to the formation of a π–π EDA complex. In the micellar media a new band is observed at 398 nm. When the spectra of TCNE in n-hexane are studied in the presence of AOT two new bands at 398 and 418 nm are detected. These bands are consistent with an EDA interaction between TCNE and AOT as n-donor. The stability constants of this interaction were calculated for AOT concentrations below the CMC and in the micellar media at different W(W = [H2O]/[AOT]). The results give evidence of the tendency of AOT to interact very strongly with electron acceptors. Moreover, in the system TCNE–Naph in the micellar media it is shown that Naph and AOT compete to form a complex with TCNE. The formation constants of the complexes of AOT–Naph in the micelle system were determined at W = 0 and 5. Despite the competition of AOT for TCNE the stability constant for the complex TCNE–Naph is higher than in homogeneous media, probably due to the high local concentration of the acceptor in the micelle. Key words: reverse micelles, aerosol-OT, tetracyanoethylene, naphthalene, electron donor–acceptor complexes.
The generator coordinate Dirac–Fock method applied to beryllium-like atomic species
Authors: Jorge F.E. , Silva A.B.F. Da
Published: May 2006

The recently formulated generator coordinate Dirac–Fock method for relativistic closed-shell atoms is applied to the Be atom and Be-like ions Ne6+, Ar14+, and Sn46+ in order to assess its efficacy for light atomic systems. The Dirac–Fock equations are integrated numerically in the generator coordinate Dirac–Fock method so as to generate Gaussian basis sets for the atomic species under study. The results obtained with the application of the generator coordinate Dirac–Fock method in this work for Dirac–Fock–Coulomb and Dirac–Fock–Breit energies for Be-like ions are in excellent agreement with Declaux's benchmark numerical calculations, and are better than the Dirac–Fock–Coulomb and Dirac–Fock–Breit energies obtained with even-tempered Gaussian-type function calculations. For the Be atom, the Dirac–Fock–Coulomb energy result obtained with the generator coordinate Dirac–Fock method is lower than the corresponding value obtained with the Declaux's numerical finite-difference program. Key words: Dirac–Fock–Coulomb energy, Dirac–Fock–Breit energy, Gaussian basis sets, generator coordinate Dirac–Fock method.
1995 Fisher Scientific Award Lecture Reflections of an atmospheric chemist wondering why he won an analytical chemistry award
Authors: Schiff H.I.
Published: May 2006

The author recalls his scientific career starting with electrochemistry and gas phase kinetics and leading, largely by serendipity, to atmospheric chemistry and measurements in the atmosphere using rockets and stratospheric balloons. The scientific problems met along the way required measurements with instruments that were not commercially available and required development of new methods and techniques. These included mass spectrometry, chemiluminescence, and tunable Diode Laser Absorption Spectrometry (TDLAS) to measure trace concentrations of gases in the lower and upper atmosphere. TDLAS is considered to be the method of choice where freedom from interferences, high sensitivity, and fast time response are required. Lead salt laser diodes operate in the near infrared where most molecules of atmospheric interest have strong fundamental absorptions. The research groups at York University and at Unisearch Associates have been pioneers in applying this powerful technique to atmospheric measurements in a variety of environments including the pristine air over the Pacific, at the top of Mauna Loa, at the Grand Canyon, and the polluted air of Los Angeles and other major cities. The results of recent measurements of the emissions of two strong greenhouse gases, CF4 and C2F6, from Quebec aluminium refineries are described. More recently a family of instruments based on near-infrared laser diodes have been developed that can make remote-sensing measurements of a number of pollutants in ambient air and industrial stacks. Examples of passive, on-road, remote-sensing measurements of automobile exhaust emissions of CO and CO2, and of in-stack emissions of HF are presented. Another remote-sensing instrument that has been developed is an improved visible and UV Differential Optical Absorption Spectrometer (DOAS) capable of measuring, remotely and simultaneously, a number of important pollutants. Examples of measurements of NO, NO2, O3, benzene, and toluene are presented. Key words: air measurements, instruments, remote sensing.
A deuterium NMR study of guest molecular dynamics in tris(5-acetyl-3-thienyl) methane inclusion compounds
Authors: Sidhu Paul S. , Bell Jason , Penner Glenn H. , Jeffrey Kenneth R.
Published: May 2006

Deuterium nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation times (T1) are used to investigate the guest molecular dynamics of tris(5-acetyl-3-thienyl) methane (TATM) inclusion compounds. The seven guests: acetonitrile, nitromethane, dimethyl sulfoxide, benzene, mesitylene, ortho-xylene, and para-xylene show a wide variety of motional behaviour. The reorientation of acetonitrile in TATM and nitromethane in TATM were both modelled as precession on a cone, the base of which is more elliptical in shape for nitromethane, as would be expected considering their molecular symmetries. DMSO in TATM does not undergo any reorientation other than methyl rotation at the temperatures investigated. At low temperatures, the 2H lineshape and the deuterium spin-lattice relaxation time both depend on the rate of methyl rotation. Activation barriers of 11.7 (±0.4) kJ/mol and 11.2 (±0.5) kJ/mol were found from the two techniques, respectively. Benzene undergoes sixfold reorientation about the principal molecular axis; however, the rate is still greater than 108 Hz down to 113 K. The spin-lattice relaxation time profile does not reach a minimum on decreasing temperature to 112 K, while the slope of this plot provides an activation energy of 4.1 (±0.4) kJ/mol for the sixfold reorientation. The deuterium NMR spectra of mesitylene-d9 in TATM can be simulated using a model where the guest occupies two different sites in the TATM lattice, with the guest molecules performing in-plane C3 rotation either very rapidly (k > 108 Hz) or very slowly (k < 103 Hz), with the relative populations of each changing with temperature. Another model proposed suggests the possibility that there is a continuous distribution of motional rates, the median of which is increasing with temperature. This second model is more realistic; however, too many parameters are present to consider a detailed fit. Finally, both o-xylene and p-xylene are rigidly held in the TATM clathrate, while rotation of the methyl groups is rapid. Key words: inclusion compounds, solid state deuterium NMR spectroscopy, molecular dynamics.
Monomeric and dimeric V(III) complexes supported by organic amides
Authors: Berno Pietro , Moore Mark , Minhas Ravinder , Gambarotta Sandro
Published: May 2006

Reaction of VCl3(THF)3 with two equivalents of R2NLi (R = Cy, Me3Si) yielded the two corresponding complexes (Cy2N)2V(μ-Cl)2Li(THF)2 (1) and [(Me3Si)2N]2VCl(THF) (2). Both complexes decomposed in hot toluene. In the case of complex 1 the reaction led to dimerization and formation of the dimeric [(Cy2N)2V(μ-Cl)]2 (3). Reaction of 2 with NaBH4 yielded the unprecedented borohydride derivative [(Me3Si)2N]2V(BH4)(THF) (4). The structures of all the complexes were elucidated by X-ray analysis. Key words: vanadium, trivalent, amide, borohydride, dinuclear
Observation of buttressing effect and hindered rotation about C(sp2)—C(sp2) single bond in styrenes coordinated to a ruthenium cation, Cp(diphosphine)Ru+
Authors: Ohkita Kenzo , Asano Hideo , Kurosawa Hideo , Hirao Toshikazu , Miyaji Yohko , Ikeda Isao
Published: May 2006

Complexes of (η5-cyclopentadienyl)(bis(di-p-tolylphosphino)ethane)ruthenium(II) cation with some styrenes containing meta or para substituants were prepared and their NMR spectra examined in detail. Variable-temperature NMR studies on the unsubstituted and para-substituted styrene analogues demonstrated occurrence of a restricted rotation about the C(sp2)—C(sp2) single bond of the styrenes where one of the ortho hydrogens of the styrene phenyl group receives a very large diamagnetic shielding effect by one of the phosphine tolyl groups. Similar studies on the meta-substituted styrene complexes showed existence of two unequally populated conformational isomers arising from the similar restricted rotation where the meta substituent in the dominant isomer was placed further away from the C=C group. The origin of such conformational isomerism was deduced to be the buttressing effect of the meta substituent transmitted via the ortho-hydrogen atom. Key words: buttressing effect, hindered rotation, Ru–styrene complex.
Pd(0)-catalyzed addition of Me3SnSnMe3 to α,β-alkynic aldehydes and ketones. Synthesis of (Z)-β-trimethylstannyl α,β-alkenic aldehydes and ketones. Preparation and synthetic uses of substituted (Z)-4-trimethylstannyl-1,3-butadienes
Authors: Piers Edward , Tillyer Richard D.
Published: May 2006

Treatment (dry tetrahydrofuran, reflux) of the α,β-alkynic aldehydes 26–28 and ketones 29–36 with Me3SnSnMe3 in the presence of a catalytic amount of (Ph3P)4Pd provides fair to excellent yields of the corresponding (Z)-β-trimethylstannyl α,β-alkenic aldehydes 41–43 and ketones 44–51. The carbonyl compounds 41–51, upon reaction with methylenetriphenylphosphorane under suitable conditions, are smoothly converted into the (Z)-4-trimethylstannyl-1,3-butadienes 61–71, respectively. Treatment of the aldehyde 41 with the anion of trimethyl phosphonoacetate and the aldehyde 42 with the anion of the phosphonoacetate 73 produces excellent yields of the 5-trimethylstannyl-2,4-heptadienoates 72 and 74, respectively. The synthetic potential of (Z)-4-trimethylstannyl-1,3-butadienes is illustrated by the conversion of 62 into the functionalized, stereodefined conjugated dienes 76 and 78 and by transformation of 87 into the structurally novel diene 84. Diels–Alder reactions of 84 with tetracyanoethylene and dimethyl acetylenedicarboxylate provide the spiro[3.5]nonane derivatives 88 and 89, respectively. Key words: Diels–Alder cycloaddition, organocopper(I), transmetallation, alkylidenecyclobutane, (E)-4-lithio-1,3-butadienes, spiro[3.5]nonane.
Novel (fulvalene)dichromium alkyl and acyl complexes of the types FvCr2(CO)6−nLnRR′ and Et4N[FvCr2(CO)6−nLnR] (R, R′ = Me, CH2CN, COMe; L = CO, PMe2Ph; n = 0, 1, 2)
Authors: Kovács István , Baird Michael C.
Published: May 2006

The compound FvCr2(CO)6Me2 (1) is obtained, via the intermediate formation of Et4N[FvCr2(CO)6Me] (2), by stepwise addition of 2 equivalents of methyl iodide to (Et4N)2[FvCr2(CO)6]; the analogous cyanomethyl compounds FvCr2(CO)6(CH2CN)2 (3) and Et4N[FvCr2(CO)6(CH2CN)] (4) are formed similarly. Compound 1 readily undergoes CO insertion upon treatment with 2 equivalents of PMe2Ph, giving rise to trans,trans-FvCr2(CO)4(PMe2Ph)2(COMe)2 (6), also in two steps via trans-FvCr2(CO)5(PMe2Ph)(Me)(COMe) (8). The neutral methyl "half" of 2 reacts similarly with PMe2Ph to form Et4N[trans-FvCr2(CO)5(PMe2Ph)(COMe)] (7), while the anionic "half" of 2 is alkylated with ClCH2CN to give FvCr2(CO)6(CH2CN)Me (5). Treatment of 5 with PMe2Ph also results in CO insertion into the Cr—Me bond to give trans-FvCr2(CO)5(PMe2Ph)(CH2CN)(COMe) (10). Although 3 is inert to both substitution and insertion reactions with PMe2Ph, the phosphine-substituted dialkyl (fulvalene)dichromium complex trans,trans-FvCr2(CO)4(PMe2Ph)2(CH2CN)2 (9) is prepared by reaction of ClCH2CN with (Et4N)2[FvCr2(CO)4(PMe2Ph)2]. Key words: chromium, metal–metal bonds, fulvalene.
Thiophenophane metal complexes IV. Effects from ligand changes outside the coordination sphere
Authors: Lucas C. Robert , Liu Shuang
Published: May 2006

Preparation of two thiophenophane polythioether macrocycles and 11 of their complexes of Cu(I), Cu(II), Ag(I), and Pd(II) is described. The single crystal X-ray structure of [(CuBr)2(L1)x is reported: space group Pcma, a = 8.7120(6), b = 10.7791(5), c = 12.0929(5) Å, Z = 2, Rf = 0.052, Rw = 0.036 for 521 reflections. Variable-temperature magnetic susceptibility measurements for [(CuCl2)2(L1)] and [(CuCl2)2(L2)] reveal weak antiferromagnetic and weak ferromagnetic coupling, respectively. Cyclic voltammograms of these compounds display two unequal waves in acetonitrile solvent but only one in nitromethane or dimethyl sulfoxide. 1H NMR spectra of {[(η-C3H5)Pd]2(L1)}{PF6}2 and {[(η-C3H5)Pd]2(L2)}{PF6}2 in various solvents show different temperature responses. These magnetic, electrochemical, and NMR effects are discussed in the light of structural differences at sites in the two ligands that are outside the coordination spheres. Key words: magnetic susceptibility, copper, thioether, electrochemistry.
Study of the coordinated system Pb(II) – neutral valine – valinate ion
Authors: Miquel Teresa María Borges , Sánchez Mercedes Lemus , Macías Josefa Castro , Placeres Jesús César Rodríguez
Published: May 2006

The polarographic method has been applied to the study of the mixed-coordinated system (Pb(II) – neutral valine – valinate ion, in aqueous medium, I = 1.0 mol L−1 (NaClO4) and 25 ± 0.1 °C. The stabilization of the following complexes: [Pb(HV)]2+ (β10 = 9.7), [Pb(HV)2]2+ (β20 = 28), [Pb(HV)(V)]+ (β11 = 3.3 × 104), [Pb(V)]+ (β01 = 3.7 × 104), and [Pb(V)2] (β02 = 2.8 × 107) was observed. Key words: polarography, Pb(II), valine, speciation.
A study of the vacuum pyrolysis of 4-diazoisothiochroman-3-one with Hel ultraviolet photoelectron spectroscopy
Authors: Werstiuk N.H. , Ma J. , Roy C.D. , Kresge A.J. , Jefferson E.A.
Published: May 2006

A newly developed ultraviolet photoelectron spectrometer apparatus that utilizes a tunable 50 W CW CO2 laser as a directed heat source is used to study the vacuum pyrolysis of 4-diazoisothiochroman-3-one (1a). Analysis of the pyrolysate with ultraviolet photoelectron spectroscopy shows that 1a undergoes a facile pyrolysis at a laser power level of less than 26 W, yielding two new compounds: thiaketene 3a, the product of a Wolff rearrangement, and benzocyclobutenthione (6a), which can be derived from thiacarbene 4a, the decarbonylation product of 3a. Activation enthalpies/energies calculated at the AM1 and ab initio levels of theory indicate that, unlike the case of 4-diazoisochroman-3-one (1b), the Wolff rearrangement of the incipient carbene may be concerted with loss of nitrogen from 1a. The activation enthalpy/energy calculated for the decarbonylation of 3a is significantly higher (AM1, 20.5 kcal/mol; RHF/6-31G(d), 11.7 kcal/mol; MP2(full)//RHF/6-31G(d), 14.3 kcal/mol) than the activation enthalpy/energy for the decarbonylation of 3b. This result is in keeping with the fact that we detect 3a, but 3b is not found in detectable amounts in the pyrolysate of 1b. Key words: vacuum pyrolysis, 4-diazoisothiochroman-3-one, HeI ultraviolet photoelectron spectroscopy, AM1 and ab initio calculations.
Reactions of hydroxamidovanadate with peptides: Aqueous equilibria and crystal structure of oxobis(hydroxamido)-glycylglycinatovanadium(V)
Authors: Paul Pradip C. , Angus-Dunne Sarah J. , Batchelor Raymond J. , Einstein Frederick W.B. , Tracey Alan S.
Published: May 2006

Bis(hydroxamido)hydroxooxovanadate has been found to undergo favourable condensation reactions with simple peptides such as glycylglycine, glycylglycylglycine, or glycyltyrosine to afford, in each case, three products in the approximate ratio 1:3.5:0.2. The three products had the same ligand stoichiometry and, in the case of glycylglycine, an overall formation constant of 3.3 × 103 M−1 for the addition of GlyGly to bis(hydroxamido)vanadate. The 51V chemical shift range of the products (close to −850 ppm) overlaps that of the starting complexes and the products may well have a coordination geometry similar to the parent complexes. The chemical shifts observed for these materials are in the range of chemical shifts observed for peroxovanadium complexes. A crystalline monomeric complex with a single glycylglycinato ligand was obtained and its crystal structure determined. The complex is zwitterionic and has a pentagonal bipyramidal coordination at vanadium with the glycine-NH2 functionality coordinated in the plane of the two hydroxyalamine ligands and the amido carbonyl oxygen in the apical position. Some comparisons with peroxovanadium complexes are drawn. Crystal structure of V(O)(ONH2)2(GlyGly)•H2O: monoclinic, space group Cc; Z = 4; a = 9.1340(9) Å; b = 16.3355(15) Å; c = 7.1149(6) Å; β(°) = 103.020(7); V = 1034.31 Å3; T = 295 K; RF = 0.21 for 2513 data (I0 ≥ 2.5σ(I0)) and 197 variables. Keywords: vanadate, hydroxylamine, N-methylhydroxylamine, oxobis(hydroxamido)glycylglycinatovanadium(V), peptide complex, glycylglycine, 51V NMR, crystal structure.
Spectroscopic and crystallographic studies of phosphino adducts of gallium(III) iodide
Authors: Brown Martyn A. , Castro Jesus A. , Tuck Dennis G.
Published: May 2006

The solid state structures of the compounds GaI3•PPh3 and Ga2I6•dppe ( dppe = 1,2-bis(diphenylphosphino)ethane ) have been determined. For the former, in which the GaI3P core has C3v symmetry, the structure is trigonal, with a = 14.961(2) Å, c = 16.509(3) Å, V = 3199.5(4) Å3, Z = 6, space group [Formula: see text]. In Ga2I6•dppe, the ligand bridges two GaI3P centres; the structure is monoclinic, a = 10.196(7) Å, b = 15.363(1) Å, c = 23.027(9) Å, β = 98.735(4)°, V = 3565.1(3.2) Å3Z = 4, space group P21/n The use of 31P NMR spectroscopy shows that GaI3•PPh3 is slightly dissociated in nonaqueous solution, and the effect of adding Ph3P or I− has been investigated. Similar studies with Ga2I6•dppe are also reported. In each system, four-coordination at gallium is dominant; an equally important factor is the dimerization of uncomplexed GaI3 to Ga2I6 in these solutions. Keywords: gallium(III) iodide, complexes, phosphorus, NMR, crystallography.
Electrolytic conductivity of crystal violet based quaternary ammonium polyelectrolytes in N,N′-dimethylformamide and dimethyl sulfoxide
Authors: Singh Meenakshi , Kumar Anil , Easo Shirley , Prasad B.B.
Published: May 2006

Electrolytic conductivities of crystal violet based quaternary ammonium polyelectrolytes in very dilute solutions of dimethylformamide and dimethyl sulfoxide at 25 °C have been investigated. The electrolytic conductivity (κ) as a function of concentration for systems having a reduced charge density (ξ) greater than unity revealed a very narrow range of linearity in the dilute region. A modest correlation has been made with the counterion condensation and the polycation conformations in order to explain the relative magnitude of limiting equivalent conductivities. Keywords: conductance, polyelectrolyte, aprotic solvent, solvation, counterion condensation.
The direct electrochemical synthesis of some metal derivatives of lapachol
Authors: Oliveira E.H. De , Medeiros G.E.A. , Peppe C. , Brown Martyn A. , Tuck Dennis G.
Published: May 2006

The electrochemical oxidation of a sacrificial metal anode (M = Zn, Cd, Cu) in an acetonitrile solution of 2-hydroxy-3-(3-methyl-2-butenyl)-1,4-naphthoquinone, lapachol, C15H14O3 (=HL) gives ML2. The results are in keeping with earlier work on direct electrochemical synthesis in related systems. Adducts with 2,2′-bipyridine (bpy) and N,N,N′,N′-tetramethylethanediamine (tmen) have also been prepared. The structure of the 2,2′-bipyridine adduct of Cu(lapacholate)2 has been established by X-ray crystallography. The parameters are triclinic, space group [Formula: see text], a = 12.748(59) Å, b = 13.859(49) Å, c = 11.770(59) Å, α = 108.30(4)°, β = 108.08(3)°, γ = 68.94(3)°, Z = 2, R = 0.059 for 2256 unique reflections. The copper atom is in a distorted CuN2O2O2′ environment. The mechanism of the formation of this Cu(lapacholate)2 is discussed. Keywords: electrochemical synthesis, lapachol, X-ray crystallography, copper(II) complex.
Synthesis and characterization of organometallic hydro-tris-pyrazolylborate derivatives of scandium via alkane elimination
Authors: Blackwell James , Lehr Corinne , Sun Yimin , Piers Warren E. , Pearce-Batchilder Susan D. , Zaworotko Michael J. , Young Jr. Victor G.
Published: May 2006

Reaction between the potassium salts of the hydro-tris-pyrazolylborate ligands TpMe'Me and TptBu'Me and the tris THF adduct of scandium trichloride lead to isolation of the scandium complexes (TpMe,Me)ScCl2(THF), 1a, and (TptBu,Me)ScCl2, 1b, in 65 and 49% yield, respectively. Subsequent reactions between 1a and 1b and alkyl lithium reagents RLi (R = Me, CH2SiMe3, and CH(SiMe3)2) gave the lithium salts of the Tp ligands as the major isolated products in all cases but one. The complex (TpMe,Me)Sc(CH2SiMe3)2(THF), 2a, could be obtained contaminated with at least 10% TpMe,MeLi via this methodology. A salt-free alkane elimination route to bis-trimethylsilylmethyl complexes 2a and the THF-free (TptBu,Me)Sc(CH2SiMe3)2, 2b, involving reaction between in situ generated Sc(CH2SiMe3)3(THF)2 and the protonated ligands, TpR,MeH, gave samples of the desired bis-alkyl derivatives in 67 and 87% yield, respectively. In solution, complexes 2a and 2b are both fluxional at room temperature. These dynamic processes were frozen out on the NMR time scale at lower temperatures and interpreted on the basis of the 1H NMR spectra obtained as well as information obtained from the solid state structures of both compounds, 2a: monoclinic, space group P21/c, a = 11.765(4) Ǻ, b = 14.8311(20) Ǻ, c = 20.891(5) Ǻ, β = 105.69(3)°, V = 3509.4(15) Ǻ3, Z = 4, R = 0.088, Rw = 0.082. 2b: triclinic, space group [Formula: see text], a = 11.9427(2) Ǻ, b = 20.3641(3) Ǻ, c = 26.5602(2) Ǻ, α = 112.192(1)°, β = 100.569(1)°, γ = 92.928(1)°, V = 5830.38(14) Ǻ3, Z = 6, R = 0.0500, Rw = 0.1137. Keywords: organoscandium complexes, hydro-tris-pyrazolylborate ligands, alkane elimination.
Identification of iridals as piscicidal components of Iridaceous plants and their conformations associated with CD spectra
Authors: Miyake Yoko , Ito Hideyuki , Yoshida Takashi
Published: May 2006

Upon toxicity-guided fractionation of the extractives of the Irisgermanica rhizomes and I. japonica roots using killie-fish (Oryziaslatipes), 12 iridal-type triterpenoids including three new iridals were isolated as piscicidal constituents. Of these, iriflorental, iripallidal, and γ-irigermanal exhibited a potent activity at a concentration of less than 1 μg/mL. The structures of new iridals, irisgermanicals A (7), B (10), and C (11), from I. germanica were elucidated based on the spectral analysis. The absolute configuration at C-13 of the known spiroiridal (15) from I. japonica, which remained to be solved, was defined as R on the basis of NOE measurement. The hitherto unreported correlation between the Cotton effects in the CD spectra of some iridals and their conformations was also discussed on the basis of molecular modeling. Keywords: Irisgermanica, Irisjaponica, iridal-type triterpenoid, piscicidal activity, CD spectra.
Photochemical nucleophile–olefin combination, aromatic substitution (photo-NOCAS) reaction, Part 13. The scope and limitations of the reaction with cyanide anion as the nucleophile
Authors: Arnold Donald R. , McManus Kimberly A. , Chan Mary S.W.
Published: May 2006

The scope of the photochemical nucleophile–olefin combination, aromatic substitution (photo-NOCAS) reaction has been extended to include cyanide anion as the nucleophile. Highest yields of adducts were obtained when the alkene or diene has an oxidation potential less than ca. 1.5 V (SCE). No adducts were obtained from 2-methylpropene (9), oxidation potential 2.6 V. Oxidation of cyanide anion, by the radical cation of the alkene or diene, can compete with the combination. With the alkenes, 2,3-dimethyl-2-butene (2) and 2-methyl-2-butene (10), both nitriles and isonitriles were obtained; isonitriles were not detected from the reactions involving the dienes, 2-methyl-1,3-butadiene (11), 2,3-dimethyl-1,3-butadiene (12), 4-methyl-1,3-pentadiene (13), 2,4-dimethyl-1,3-pentadiene (14), and 2,5-dimethyl-2,4-hexadiene (6). The specificity, nitrile versus isonitrile, is explained in terms of the Hard-Soft-Acid-Base (HSAB) principle. The photo-NOCAS reaction also occurs with the allene, 2,4-dimethyl-2,3-pentadiene (15), cyanide combining at the central carbon. Factors influencing the regiochemistry of the combination step, Markovnikov versus anti-Markovnikov, have been defined. Cyanide anion adds preferentially to the less alkyl-substituted, less sterically hindered, end of an unsymmetric alkene or conjugated diene radical cation, forming the more heavily alkyl-substituted radical intermediate. High-level abinitio molecular orbital calculations (MP2/6-31G*//HF/6-31G*) have been used to determine the effect of alkyl substitution on the stability of the intermediates, β-cyano and β-isocyano alkyl radicals, and products, alkyl cyanides and isocyanides. The more heavily alkyl-substituted radical is not necessarily the more stable. The product ratio (Markovnikov versus anti-Markovnikov) must be kinetically controlled. Keywords: photochemistry, radical ions, electron transfer, nitriles, isonitriles.
Monosaccharide permethylation products for gas chromatography - mass spectrometry: how reaction conditions can influence isomeric ratios
Authors: Asres Daniel Derbie , Perreault Hélène
Published: May 2006

Methylation analysis has been widely used for determination of carbohydrate structures by mass spectrometry. Permethylation of monosaccharides yields mixtures of anomeric pyranosides and furanosides. This paper discusses the influence of some of the permethylation reaction parameters on the proportions of isomeric products obtained. The ratios of three five- and six-membered ring products obtained from two permethylated monosaccharides, D-galactose and L-fucose, have been determined as a function of reaction parameters. The method of Ciucanu and Kerek (1) (methyl iodide in dimethyl sulfoxide (DMSO) in the presence of sodium hydroxide (NaOH)) was used as a starting point. The "conventional" method consists of mixing all of the reagents with the substrate and allowing the reaction to proceed with stirring. Both D-galactose and L-fucose under these conditions produced two main permethylated isomers, a furanoside and a pyranoside, along with two other minor isomeric components. We have investigated the effect on the proportion of products obtained of mixing DMSO, substrate, and NaOH for various times prior to the addition of methyl iodide. Results for D-galactose showed that shorter times enhanced the formation of permethylated furanoside isomers, while reducing the proportion of pyranosides. In other sets of experiments, the time and temperature of reaction, following the addition of methyl iodide, were studied. The indication is that 15 min are sufficient to produce complete methylation, with longer reaction times yielding the same results. Again for D-galactose, low reaction temperatures (ca. 10 °C) favored formation of furanoside products. Higher temperatures yielded higher pyranoside/furanoside ratios. Higher quantities of NaOH also favored formation of the main galactopyranoside product. As for L-fucose, the ratio of the main furanoside vs. pyranoside products obtained by permethylation varied in a way similar to permethylated galactoside. Thus, higher temperatures and longer reaction times favored the main fucopyranoside product. Gentler conditions (i.e., shorter reaction times and lower temperatures) significantly favored the formation of the main fucofuranoside product. These results are interesting as they show the possibility of controlling the relative abundance of permethylated isomers of fucose and galactose. They also constitute a warning to chemists who use methylation procedures in their analyses, to the effect that permethylation products may vary considerably if the reaction conditions are not carefully controlled. Keywords: glucose, galactose, fucose, TLC, GC–MS, permethylation, monosaccharides.
A study of the electrochemical synthesis of ZnO thin films
Authors: Gu Z.H. , Fahidy T.Z. , Hornsey R. , Nathan A.
Published: May 2006

The principal characteristics of the cathode deposition of zinc oxide from slightly acidified aqueous zinc nitrate solution at 65 °C were studied via potentiodynamic electrolysis, potentiostatic electrolysis, and X-ray diffraction patterns. The results indicate the reliability of a low-temperature electrolytic path of synthesis, and avenues of further exploration. Keywords: zinc oxide, cathode deposition, XRD patterns, FBM theory.
A note on the thermodynamics of intercalation
Authors: Parsons Roger
Published: May 2006

The thermodynamics of an electrochemical cell with an intercalation electrode is discussed in the light of two recent analyses (Gerischer et al. J. Electrochem. Soc. 141, 2297 (1994) and Li et al. J. Electrochem. Soc. 141, 2310 (1994)). The assumptions necessary to obtain a simple result are emphasized. Keywords: thermodynamics, intercalation electrode.