bluuebunny/crossref_metadata_2025 huggingface dataset:
Nascent HF† and HSO(2A′) formations in the elementary reactions of F + H2S and HS + O3 and the internal energy distributions
Authors: Yoshimura Yasunori , Kasai Toshio , Ohoyama Hiroshi , Kuwata Keiji
Published: May 2006

Chemiluminescence of the vibrationally excited HF† and of the electronically excited HSO* in the 2A′ state were observed in the elementary reactions of F + H2S and HS + O3. In the F + H2S reaction, the vibrational populations of HF† in ν = 3 and 4 were found to be nonstatistical but the rotational distribution in the ν = 4 state was found to be Boltzmann-like with a rotational temperature of 700 K, confirming similar data obtained by different methods. The HSO* emission was observed in the HS + O3 elementary reaction. The spectrum of HSO* characterized by broad vibrational bands indicates nonstatistical excitation for the rotational and vibrational states. Keywords: chemiluminescence, internal energy distribution, F + H2S, HS + O3, HF†, HSO*.
Densities, viscosities, and refractive indexes of tert-butyl methyl ether + butyl alcohols at 298.15 K
Authors: Riggio Roque , Martinez Hector E. , de Salas Norma Z. , Ramos Juan F.
Published: May 2006

Densities, viscosities, and refractive indexes of three binary systems, tert-butyl methyl ether +n-butanol, +sec-butanol, +isobutanol, have been determined at 298.15 K and atmospheric pressure over the complete composition range. We also report calculated excess properties including molar volume, viscosity, and Gibbs free energy for the activation of flow for these systems. Keywords: binary systems, excess properties.
Some physicochemical characteristics of molten salts derived from trimethylsulfonium bromide
Authors: Ma M. , Johnson K.E.
Published: May 2006

Ambient temperature melts were derived from trimethylsulfonium bromide (TMSuBr) and AlBr3, AlCl3, or HBr. The aluminum halide melts have low-wavelength UV cutoffs and single-band 1H NMR spectra. In the TMSuBr–HBr system, the formation of HBr2− and likely existence of H2Br3− are indicated by 1H NMR and IR spectra. Conductivity and viscosity data indicate stronger TMSu+–anion interactions than those between substituted imidazolium and halide anions. A Grotthus mechanism may operate for conduction in TMSuBr:HBr melts. Keywords: ambiant temperature melts, trimethylsulfonium–anion itneractions, Grotthus mechanism.
Synthesis and characterization of various unsubstituted and mono-N-substituted tetraazamacrocycles
Authors: Meunier I. , Mishra A.K. , Hanquet B. , Guilard R. , Cocolios P.
Published: May 2006

Syntheses of tetraazamacrocycles have been carried out by using p-toluenesulfonyl chloride as protective group. The [14(ane) N4] and [15(ane) N4] were also obtained by the template synthesis. Mono-N-functionalization of tetraazamacrocycles was accomplished by reaction of a fivefold excess of the free macrocycles with 1 equivalent of a suitable alkylating or arylating reagent. The key point of the synthesis lies in the use of an excess of the macrocycle over the substituting reactants to reduce the formation of polysubstituted derivatives, and in the easy separation of the excess of unreacted macrocycle. All the products were characterized on the basis of spectral studies (1H andl3C NMR, including 2D NMR and NOE difference studies) and mass spectrometry. Keywords: tetraazamacrocycles, improved synthesis, protective group, N-tosylation, template synthesis, NOE difference spectroscopy.
Model potential in spectral representation form. Its fidelity to the frozen-core operator and comparison with other model potentials
Authors: Katsuki Shinichi
Published: May 2006

The model potential, in which the Coulomb and exchange core operators are converted to the matrix elements by use of the spectral representation technique, should be equivalent to the frozen-core operator, if the basis set of the spectral representation is complete. Its fidelity to the frozen-core operator is examined in this paper through a thorough study of basis set convergence in both the spectral space and the atomic orbital space, along with comparison with the Sakai–Huzinaga and the Huzinaga–Seijo–Barandiaran–Klobukowski model potentials. The RHF molecular calculations on N2, P2, As2, Sb2, PN, and AsN show that the present model potential can approximate, with reliable accuracy, the results obtained from the frozen-core calculations. Keywords: model potential, spectral representation, molecular orbital calculation, electronic structure.
Calorimetric investigations of aqueous amino acid and dipeptide systems from 288. 15 to 328. 15 K
Authors: Hakin Andrew W. , Duke Michelle M. , Groft Lori L. , Marty Jocelyn L. , Rushfeldt Matthew L.
Published: May 2006

Densities and heat capacities have been measured for aqueous solutions of L-asparagine, L-glutamine, glycylglycine, glycyl-L-valine, glycyl-L-asparagine, and glycyl-DL-leucine at 288.15, 298.15, 313.15, and 328.15 K. These data have been used to calculate apparent molar volumes, V2,ø, and apparent molar heat capacities, Cp,2,ø, which in turn have been used to obtain standard state volumes, [Formula: see text] and heat capacities, [Formula: see text] The semi-empirical modelling procedures of Helgeson, Kirkham, and Flowers have been used to subdivide the calculated standard state volume and heat capacity data into solvation and nonsolvation contributions. The nonsolvation components of the standard state properties are used in group additivity analyses. These analyses yield structural contributions to standard state volumes and heat capacities for the CH(NH2)CO2H, CH2, OH, COOH, CH, CONH2, and CONH groups. The temperature dependences of these contributions are discussed. Some comments are reported concerning the practicality of using the thermodynamic properties of aqueous amino acid and peptide systems as the basis for modelling standard state thermodynamic properties of aqueous protein systems. Keywords: heat capacities, densities, volumes, amino acids, peptides, group additivity.
Electrocatalytic hydrogenation of conjugated enones on nickel boride, nickel, and Raney nickel electrodes
Authors: Mahdavi Behzad , Chambrion Philippe , Binette Julie , Martel Eric , Lessard Jean
Published: May 2006

The selectivity of the electrocatalytic hydrogenation (ECH) of conjugated enones to the corresponding carbonyl compounds has been investigated in aqueous methanol under constant current at nickel boride, fractal nickel, and Raney nickel electrodes made of pressed powders. The influence of various parameters (water percentage, pH, concentration of substrate, and current density) on the selectivity of the carbon–carbon double bond hydrogenation was studied with cyclohex-2-en-1-one at nickel boride electrodes. Under given electrolysis conditions, fractal nickel electrodes were found to give the highest selectivity. The selectivity of the ECH of a variety of conjugated enones at fractal nickel electrodes was determined under electrolysis conditions that gave the best selectivity with cyclohexenone at nickel boride electrodes. Keywords: electrocatalytic hydrogenation, α,β-unsaturated ketones, selective hydrogenation, nickel based cathodes.
The crystal structure of 2-(4-bromophenyl)-4-(2-fluoroethyl)-5,6-dihydro-4H-1,3,4-oxadiazine hydrochloride, an octopaminergic insecticide/miticide
Authors: Dekeyser Mark A. , Harrison W. Ashley , Taylor Nicholas J. , Downer Roger G.H.
Published: May 2006

The crystal structure of 2-(4-bromophenyl)-4-(2-fluoroethyl)-5,6-dihydro-4H-1,3,4-oxadiazine hydrochloride, a new octopamine agonist, has been established by Patterson and Fourier methods and refined to a final R value of 0.0293 for 2123 absorption-corrected observed data. The crystals are monoclinic, a = 14.336(3), b = 12.649(3), c = 6.989(1) Å, β = 93.48(1)°, and the space group is P21/c. Its structural similarities with the crystal structure of the invertebrate neurotransmitter, octopamine, are described and support the hypothesis that the pesticidal properties of dihydrooxadiazines are, at least partially, due to perturbation of octopaminergic systems. Keywords: dihydrooxadiazine, octopamine agonist.
Effect of a hydrophobic amino acid at position (i −1) on the stability of β-turns in hydrophilic pentapeptides as studied by NMR and molecular mechanics
Authors: Liu Xiaohong , Fraga Serafin , Otter Albin , Kotovych George , Scott Paul G.
Published: May 2006

A detailed NMR study of the peptide NAc-FDEKA-NH2 in aqueous and in CD3OH/H2O solutions as well as the N-acetylpentapeptide amides YDEKA, VDEKA, GDEKA, and the protected tetrapeptide NAc-DEKA-NH2 in methanolic solutions indicates the importance of the first amino acid (at i −1) on stabilizing the type I β-turn. The data illustrate the hydrophobic stabilization of this turn, which is present in FDEKA, YDEKA, and VDEKA. For GDEKA and DEKA, the NMR data indicate that this turn is not present. Molecular mechanics calculations support this conclusion and indicate that for FDEKA and GDEKA the type I β-turn is distorted in both the vacuum and the solvated structures. For the solvated structures, the Cα(i) − Cα(i + 3) distance is 4.87 Å for FDEKA and 6.00 Å for GDEKA, which are to be compared with the value of 4.64 Å for an ideal type I β-turn, i.e., the distortion is far greater in GDEKA than in FDEKA. The calculations can be interpreted to indicate the presence of two major conformations in solution. Keywords: β-turns, FDEKA, pentapeptide.
Alkyne transformations at RhMn centres. Facile conversion between parallel and perpendicular alkyne binding modes and conversions to vinyl groups
Authors: Wang Li-Sheng , Cowie Martin
Published: May 2006

The heterobinuclear complex [RhMn(CO)4(dppm)2] (1) (dppm = Ph2PCH2PPh2) reacts with alkynes (RC≡CR; R = CO2Me (DMAD), CF3 (HFB)) to yield the alkyne-bridged products [RhMn(CO)4(μ-RC2R)(dppm)2] (3a, 3b), in which the alkyne binds parallel to the metals. These species lose one carbonyl to yield two isomers in which the bridging alkyne group is either parallel or perpendicular to the Rh–Mn vector (4 or 5). Unusually facile interconversion between these two alkyne binding modes occurs. Protonation of the different alkyne-bridged species appears to occur at the metals with subsequent transfer to the alkyne ligand, yielding a series of vinyl complexes. These vinyl complexes are also obtained from the reaction of the hydride-bridged complex [RhMn(CO)4(μ-H)(dppm)2][BF4] (2) with alkynes. A related vinyl species [RhMn((CH3)C=CH2)(CO)4(dppm)2][BF4] (9a) is obtained in the reaction of 2 with allene. Also obtained in the allene reaction is the isomeric η1-allyl complex [RhMn(η1-CH2C(H)=CH2)(CO)4(dppm)2][BF4] (9b), which converts to 9a upon refluxing. The methyl analogues [RhMnCH3(CO)4(dppm)2][X] (X = SO3CF3, I) have been characterized and their structural formulations offer support for those of the vinyl species. Keywords: heterobinuclear, alkyne complexes, vinyl complexes.
1994 McBryde Medal Award Lecture Investigations of organized monolayer films for biosensor development
Authors: Krull Ulrich J. , Heimlich Michael S. , Kallury Krishna M.R. , Piunno P.A.E. , Brennan John D. , Brown R. Stephen , Nikolelis Dimitrios P.
Published: May 2006

Our interests have focused on the investigation and development of biosensors that use chemically selective membranes to measure the concentration of specific species in complex media. One fundamental idea is that protein, which can bind selectively to a specific organic or biochemical species, can be incorporated into an ordered lipid or surfactant membrane assembly such that selective binding events lead to changes in the structure of the membrane (transduction) that can be measured quantitatively. The primary advantage of this method of detection is that it is applicable to interactions of enzymes, antibodies, receptors, and lectins, and it may be extended to investigations of DNA/RNA hybridization. This detection method therefore provides a sensitive generic strategy for sensor applications. The central problem to be solved is how the alteration of the structure of a membrane that is caused by binding events of protein or genetic material can give rise to an analytical signal. We have been focusing our efforts in the areas of fluorescence spectroscopy and electrochemical methods. The electrochemical methods rely on detection in changes of the permeability of membranes to ions and provide systems with very low background signal, leading to the possibility of detection of single molecular-binding events. Fluorescent systems operate on the basis that a chemically selective membrane containing a fluorescent indicator can provide an analytical signal caused by the change of the structure of the membrane due to the binding events. Keywords: fluorescence, lipid membrane, electrochemistry, receptor, biosensor.
Abinitio interpretation of conformer stabilization through bonding in the acetyl derivatives of two representative heterocyclic methine bases
Authors: Gough Kathleen M. , Millington Janice
Published: May 2006

Abinitio calculations (STO-3G and 3-21G* basis sets) have been performed on 2 and 3 to determine the most favorable structure and to provide an estimate of the barrier to internal rotation of the acyl group. The Z configuration is preferred in 2, the E configuration in 3, with calculated barriers to internal rotation of 79.9 and 68.7 kJ/mol, respectively, at the 3-21G* level. The wave functions from the 3-21G* calculations are analyzed with the theory of atoms in molecules. The identification of bond critical points characteristic of a closed shell interaction establishes the existence of a weak bond between [Formula: see text] in 2 and between [Formula: see text] in 3, for the preferred configurations. The energy required to break this bond as well as the loss of extended conjugation throughout the hetero ring and its side chain are responsible for the asymmetry in the barrier. These findings provide a theoretical explanation for experimental observations on this class of molecules in which one conformer is preferred to any other and only one crystal structure is identified. Keywords: nonbonded sulfur–oxygen interaction, closed shell interaction, hydrogen bonding, 3-21G* basis set, theory of atoms in molecules.
Regiocontrolled functionalization of seven-membered ring via nucleophilic cycloheptenyl-η3-allyltitanium complexes
Authors: Szymoniak Jan , Felix Didier , Besançon Jack , Moïse Claude
Published: May 2006

A new "electron-reversed" method for the functionalization of a seven-membered ring is developed. Cycloheptenyl-η3-allyltitanocene complexes derived from cycloheptatriene react with aldehydes or carbon dioxide to afford, respectively, the mixture of isomeric 1,4- and 1,3-cycloheptadienyl carbinols 3a–e and 2a–e or methyl esters 7 and 6. The 3/2 and 7/6 ratios increase with increasing steric hindrance in the electrophile. Moreover, these may be significantly increased by introducing tert-butyl substituents on the Cp rings of the starting titanocene dichloride. The regiochemistry of the reaction was rationalized in terms of the equilibrium between the two envisageable allylic complexes. The reaction constitutes the first direct entry to functionalized 1,4-cycloheptadienes, some of which are related to biologically active compounds. Keywords: η3-allyltitanium complexes, cycloheptadiene derivatives, regiocontrol, electron reversal.
Molecular and electronic structures of the purple chromophore RC(NH2)(NSePh) (R = H, 4-CH3C6H4)
Authors: Chivers Tristram , McGregor Katherine , Parvez Masood , Vargas-Baca Ignacio , Ziegier Tom
Published: May 2006

The reaction of Li[4-CH3C6H4C(NSiMe3)2] with PhECl (E = S, Se) in a 1:1 molar ratio produces the monosubstituted derivatives 4-CH3C6H4C(NEPh)[N(SiMe3)2] (3b, E = Se; 3d, E = S). The thermolysis of 3b at 130 °C produces PhSeN(SiMe3)2 and 4-CH3C6H4CN. Crystals of 3b slowly acquire a purple stain upon prolonged standing at 23 °C owing to the formation of 4-CH3C6H4C(NH2)(NSePh) (4c, λmax = 551 nm). The formamidine derivative HC(NH2)(NSePh) (4a, λmax = 472 nm) was isolated from the reaction of HCN2(SiMe3)3 with PhSeCl (1:3 molar ratio) in dichloromethane. The structure of 4a was shown by X-ray crystallography to involve a syn configuration at the [Formula: see text] bond and hydrogen bonding between amino nitrogen atoms. The crystals of 4a are monoclinic, space group P21 (No. 4), with a = 7.514(1), b = 5.575(1), c = 8.925(1) Å, β = 100.71(1)°, V = 367.40(6) Å3, and Z = 2. The final R and Rw values were 0.055 and 0.060, respectively. The 1H and 77Se NMR spectra indicate that both 4a and 4c exist as a mixture of tautomers in THF solution. DFT calculations for the model tautomers HC(NH2)(NER) and HC(NH)(NHER) (E = S, Se; R = H, Ph) show that the former is more stable in all cases, but the difference in total bonding energy is smaller for selenium than for sulfur (17.5 vs. 29 kJ mol−1). The visible absorption band for 4a is assigned to the HOMO–LUMO transition (ΔE = 2.90 eV, λmax = 427 nm) of the minor tautomer. Keywords: formamidine, tautomer, selenium, purple chromophore.
Dosage comparatif des produits issus de la dégradation alcaline des hexoses
Authors: Dubois Marie-France , Rigal Luc , Gaset Antoine
Published: May 2006

The mixture of hexoses and carboxylic acids produced by alkaline degradation of fructose was analyzed quantitatively by high-performance liquid chromatography. A pulsed amperometric detector with two Carbopac Dionex columns in series was employed in the assay of sugars (glucose, fructose, mannose, sorbose, and psicose), while a conductimeter with an HPICE AS1 Dionex column was employed for carboxylic acids (lactic, glyceric, glycolic, formic, and acetic). This sensitive and reproducible method obviated sample pretreatment. The results were compared with those of enzymatic assays and HPLC determinations using Biorad HPX87C and HPX87P columns in series for the sugars, and an Interaction ORH 801 column for the carboxylic acids. The behaviour of fructose, glucose, and mannose in alkaline medium was compared. Keywords: hexoses, polyhydroxylic acids, isomerization, alkaline degradation, high-performance ionic liquid chromatography.
Conformational dependence of electronic spectra and zero-field splitting parameters in 2-naphthylphenylcarbene
Authors: Parisel Olivier , Berthier Gaston , Migirdicyan Eva
Published: May 2006

Quantum mechanical calculations using ab initio and semi-empirical methods have been carried out for elucidating the electronic structure and geometry of 2-naphthylphenylcarbene conformers. The Z/cis conformer has the lowest ground state triplet energy, the lowest triplet–triplet (T0–T1) transition energy, as well as the largest zero-field splitting parameter D. A clear-cut relationship between the D value and the geometry is pointed out. Keywords: carbenes, conformational isomerism, triplet–triplet transitions, CS-INDO/CI calculations, ZFS D parameters.
Role of the reaction parameters in the direct synthesis of aromatic polyamides
Authors: Mariani Alberto , Mazzanti Sabina L.E. , Russo Saverio
Published: May 2006

A thorough study, devoted to analyzing the role of various reaction parameters in the direct synthesis of poly(p-phenylene terephthalamide) and poly(p-benzamide), activated by triphenyl phosphite, is described. The effects of temperature, salt type and concentration, amount of triphenyl phosphite and its stepwise introduction, as well as monomer and reagent concentrations, are considered. The inherent viscosity values of the above aromatic polyamides are higher than those reported in the literature for analogous syntheses and are comparable to the values of typical samples obtained by the acyl chloride routes. Keywords: poly(p-benzamide), poly(p-phenylene terephthalamide), triphenylphosphite, direct synthesis, aromatic polyamides.
Proton dissociation of aqueous organic acids studied by multivariate chemometrics
Authors: Aruga Roberto
Published: May 2006

Thermodynamic data of proton dissociation of 75 organic acids belonging to four classes (protonated amines, aliphatic carboxylic acids, benzoic acids, phenols) have been processed by multivariate chemometric techniques. The variables consist of conventional thermodynamic quantities (Gibbs function, enthalpy, entropy) and of partial components of these quantities (internal and external, electrostatic and nonelectrostatic components). The above data refer to the aqueous medium, at 25 °C and I = 0 mol dm−3. The Gibbs function of deprotonation in the gas phase and the Hammett σ constant have also been considered. Multivariate techniques include Principal Component Analysis, Factor Analysis, and feature selection. Factor Analysis and related concepts have proved to be useful in defining the causes of differences in acid strengths and their respective importance. Keywords: acid dissociation data, chemometrics of; chemometrics of acid dissociation data; factor analysis of acid dissociation data; principal component analysis of acid dissociation data; thermodynamics of acid dissociation.
Mechanistic variations in the formation of benzocyclooctatetraene from benzobicyclo[4.2.0]octa-2,4,7-triene
Authors: Bender Christopher Owen
Published: May 2006

Benzocyclooctatetraene (i.e., COT, 2) is the major product from the thermolysis and direct photolysis of 2,3-benzobicyclo[4.2.0]octa-2,4,7-triene (i.e., triene 1). It is also a minor product from the sensitized irradiation of 1. The mechanism of the reaction 1 → 2 was investigated using deuterium-labelled triene (i.e., 1a/b), which was prepared in a two-step procedure from a known triene mixture (1a) containing deuterium at both C-4 (43%) and C-5 (97%): the thermolysis of 1a led to labelled COT 2a, which upon direct irradiation (λ ≥ 310 nm) gave the deuterated triene mixture 1a/b in good chemical yield (61%) but in low quantum efficiency (Φ ≈ 0.0001). The COT produced from the direct irradiation (Corex filter) of 1a/b possessed different deuterium distributions than when generated thermally or from triplet sensitization (p-dimethylaminobenzophenone), as determined by 1H NMR integration. The observed deuterium-labelling patterns are in accord with a Zimmerman di-π-methane rearrangement being involved in formation of the COT from S1, of triene 1, while a mechanism proceeding by initial cleavage of the cyclobutene C1—C6 bond appears to operate during the thermal or sensitized (T1) generations of 2. Key words: mechanisms, rearrangements, photochemistry, di-π-methane.
Transannular Diels–Alder cyclization of substituted 13-membered trienes. An approach to the B.C.D.[6.6.5] rings of the 14β-hydroxysteroids
Authors: Langlois Pascal , Soucy Pierre , Dory Yves L. , Deslongchamps Pierre.
Published: May 2006

The transannular Diels–Alder strategy has been applied to three 13-membered macrocyclic trienes whose characteristics are: a cis-trans diene and a cis methoxymethyl enol ether as the diénophile. The successful trials led to three 6.6.5 tricyles having a trans-syn-cis geometry exactly as in the B.C.D. rings of the 14β-hydroxysteroids. Key words: transannular, Diels–Alder, 14β-hydroxysteroids, 13-membered rings.
Crystal chemistry of tetraradial species. Part 8. Mix and match: cation geometry, ion packing, hydrogen bonding, and π–π interactions incis-2,2′-bipyridinium(1+) and 1,10-phenanthrolinium(1+) tetraphenylborates — and what about proton sponges?
Authors: Bakshi Pradip K. , Cameron T. Stanley , Knop Osvald
Published: May 2006

The crystal structures at −20 °C of cis-2,2′-bipyridinium(1+) (BPTB, P21/n, a = 9.249(3), b = 14.093(7), c = 20.285(3) Å, β = 92.86(2)°, Z = 4) and 1,10-phenanthrolinium(1+) (PTB, P21/c, a = 11.194(2), b = 13.837(3), c = 18.303(3) Å, β = 107.82(1)°, Z = 4) tetraphenylborates have been determined. Inasmuch as 1,10-phenanthroline is an aromatically bridged cis-2,2′-bipyridine, monoprotonation results, in both systems, in the formation of an intra-cation N—H … N′ hydrogen bond, the geometric and spectroscopic properties of which we have investigated. The cation skeleton in PTB is planar to 0.03(2) Å; in BPTB the dihedral angle between the two cation ring planes is 5.2°. In the pale yellow PTB there are significant π–π stacking interactions that persist into solution. The effect of protonation on the geometry of the 2,2′-bipyridine and 1,10-phenanthroline systems is examined in considerable detail and compared with the corresponding effects in the paraquat(2+) and similar cations. On both geometric and spectroscopic (infrared spectra between 10 and 295 K) evidence, the N—H … N′ hydrogen-bonding interaction is stronger in BPTB; in PTB this interaction is among the weakest reported in crystals, the ν(NH) stretching frequency at 10 K being as high as 3279 cm−1. A detailed comparison of the geometries of the intra-cation N—H … N′ bonds in BPTB and PTB with those in classical and modified proton-sponge cations has led to the formulation of criteria useful in predicting the occurrence of proton-sponge-like properties. Key words: bipyridinium ions, hydrogen bonding, phenanthrolinium ions, proton sponges, tetraphenylborates.
Solvent effects on the reactivity of solvated electrons with organic solutes in 1-butylamine–water mixtures
Authors: Zhao Yixing , Freeman Gordon R.
Published: May 2006

The values of the rate constants of the reactions of es− with the efficient scavengers nitrobenzene and acetone are ≥ 2 × 106 m3 mol−1 s−1 in the whole range of 1-butylamine–water mixtures at 298 K; the reaction rates in the mixed solvents vary approximately as the solvent fluidity. In pure butylamine at 298 K, k2(es− + nitrobenzene) = 84 × 106 m3 mol−1 s−1 and k2(es− + acetone) = 7.3 × 106 m3 mol−1 s−1. The values of the rate constants of the reactions of es− with the inefficient scavengers phenol and toluene are < 2 × 105 m3 mol−1 s−1 in the whole range of 1-butylamine–water mixtures at 298 K and have a maximum at 50 mol% water and a minimum at 99 mol% water. In pure 1-butylamine at 298 K, k2(es− + phenol) = 1.0 × 104 m3 mol−1 s−1 and k2(es− + toluene) = 0.28 × 104 m3 mol−1 s−1. The reaction rates with inefficient scavengers show strong dependence on the solvent composition and selective solvation of electron and scavenger. In the amine-rich region (0–30 mol% water), the rate constants increase with the increase of viscosity, indicating the chemical participation of solvent molecules in the reaction. In the water-rich region from 50 to 99 mol% water, the decrease of the rate constants indicates the nonhomogeneous solvation of the electrons by water and of the organic solutes by 1-butylamine. From 99 mol% to pure water the rate constant increases rapidly, which we attribute to insufficient 1-butylamine to coat the phenol or toluene molecules. The variation of the activation energies E2 for the efficient scavengers, 14–27 kJ mol−1, are similar to the variation of Eη in the mixed solvents. The values of E2 for the inefficient scavengers are from 15 to 38 kJ mol−1 for phenol and from 6 to 21 kJ mol−1 for toluene. Both k2 and E2 for the inefficient scavenger reactions show a correlation with the temperature coefficient −dEAmax/dT of the optical absorption of es− in the mixed solvents, but the reason is obscure. Key words: 1-butylamine–water solvent, solvated electron, organic solutes, reactivity, solvent effects.
Self-assembly of short and long-chain n-alkyl thiols onto gold surfaces: A real-time study using surface plasmon resonance techniques
Authors: Debono Reno F. , Loucks Glenn D. , Manna Deborah Della , Krull Ulrich J.
Published: May 2006

Gold surfaces coated with monolayers of alkyl thiols are significant in the field of biosensors and chromatography. There is a general concern about the quality of coatings in terms of surface density and voids. The self-assembly of the short-chain hexane (C6) thiol and long-chain dodecane (C12) and hexadecane (C16) thiols to polycrystalline gold surfaces has been investigated in situ and in real time using surface plasmon resonance (SPR) spectroscopy and surface plasmon microscopy (SPM). The self-assembly was followed based on observed changes in reflectivity at a fixed angle of incidence as a function of time. Our results indicate that the data for hexane, dodecane, and hexadecane thiol adsorption to gold surfaces were best fit by a two-step process rather than a one-step process. The mechanism may involve fast adsorption to the surface to give 80% (C12, C16) or 50% (C6) coverage followed by a slow (100-fold slower) "rearrangement" of the adsorbed thiol. SPM shows these surfaces to be smooth and homogenous at a 4 μm scale. An understanding of the process of rearrangement could lead to control of the quality of coatings for analytical applications. Key words: surface plasmon, alkyl thiols, gold, monolayer, kinetics, ellipsometry, microscopy.
Kinetic energy analysis of atomic multiplets. II. smdn configurations
Authors: Koga Toshikatsu , Aoki Hidenori , Thakkar Ajit J.
Published: May 2006

A kinetic energy analysis of total energy differences in 822 atomic multiplets arising from smdn (m = 0,1,2; n = 2–8) electronic configurations is performed within the nonrelativistic, restricted Hartree–Fock framework. For the 444 multiplets arising from the dn and s2dn configurations of 27 atoms in groups 2–10, a very good linear correlation between the total energy difference and the kinetic energy difference of the outermost d-electrons is demonstrated. For the 378 multiplets arising from the sdn configuration, on the other hand, a good linear correlation is obtained provided that the multiplets are classified into groups based on spin multiplicity. Key words: kinetic energy, atomic multiplets, smdn configurations, Hartree–Fock approximation.
Non-additivity of intermolecular forces in helium and beryllium clusters
Authors: Novaro O.
Published: May 2006

New results on nonadditive effects on small beryllium clusters are presented using the LCAO-MO-SCF method including variational and perturbational (MP-4) configuration effects. Three- and four-body contributions to the interaction energy of these clusters are dominant, and are used to explain the very different behaviour of bulk beryllium as compared to liquid helium. This is relevant because the atomic ground states of Be and He are strikingly similar (1s22s2: 1S0 and 1s2: 1S0) and also He2 and Be2 share the honour of being the two hardest-to-detect dimers in the whole periodic system. The similitude is lost for larger Hen and Ben systems because the former, as was shown by R.F.W. Bader 25 years ago, have very small three-body energies (≤ 1%). Ben clusters will be shown here to have three-body energies that actually outweigh the pairwise additive ones. The consequences of this are discussed. Key words: intermolecular forces, non-additivity, He and Be clusters.
Some results on the electrostatic energy of ionic crystals
Authors: Essén Hanno , Nordmark Arne
Published: May 2006

We define a class of ionic cyrstals, the alternating Bravais lattice ionic crystals, which has the NaCl and CsCl structures as members. We calculate the electrostatic energy of finite pieces and study the convergence to the macroscopic Madelung limit. For the one-parameter family of trigonal lattices we calculate the dependence of the electrostatic energy on the parameter. The NaCl and CsCl structures correspond to minima, the CsCl minimum being deeper. This is due to long-range effects; for small clusters the NaCl structure is favored. We also study the Madelung constant of simple cubic lattices as a function of spatial dimension, and discuss the results. We finally calculate the electrostatic repulsion of two constant unit charge distributions in the unit cube. This quantity, a six-dimensional integral, can be integrated analytically five times, leaving a simple one-dimensional integral to be done numerically. Key words: ionic crystal, Madelung constant, ionic cluster, electrostatic energy.
Orthogonal effective atomic orbitais in the topological theory of atoms
Authors: Mayer I.
Published: May 2006

A simple formalism has been developed permitting us to extract, from the molecular wave functions, the effective orthogonal atomic orbitais characterizing the actual state of the atom in the molecule within the framework of Bader's topological theory of atoms. This may give important conceptual connections between the SCF wave functions obtained in the large-scale ab initio calculations, or even at the Hartree–Fock limit, and the traditional atomic orbital picture. The method is based on some partial orthogonality properties of the non-orthogonal localized molecular orbitais constructed by requiring a maximal weight in the given atomic domain, or in another selected molecular fragment. (The use of such localized orbitais may also be of independent interest.) Key words: effective atomic orbitais, atomic orbitais from molecular wave functions, non-orthogonal localized orbitais, topological theory of atoms, Bader's theory of atoms in molecules.
Charge density study with the Maximum Entropy Method on model data of silicon. A search for non-nuclear attractors
Authors: Vries R.Y. de , Briels W.J. , Fell D. , Velde G. te , Baerends E.J.
Published: May 2006

In 1990 Sakata and Sato applied the maximum entropy method (MEM) to a set of structure factors measured earlier by Saka and Kato with the Pendellösung method. They found the presence of non-nuclear attractors, i.e., maxima in the density between two bonded atoms. We applied the MEM to a limited set of Fourier data calculated from a known electron density distribution (EDD) of silicon. The EDD of silicon was calculated with the program ADF-BAND. This program performs electronic structure calculations, including periodicity, based on the density functional theory of Hohenberg and Kohn. No non-nuclear attractor between two bonded silicon atoms was observed in this density. Structure factors were calculated from this density and the same set of structure factors that was measured by Saka and Kato was used in the MEM analysis. The EDD obtained with the MEM shows the same non-nuclear attractors that were later obtained by Sakata and Sato. This means that the non-nuclear attractors in silicon are really an artefact of the MEM. Key words: Maximum Entropy Method, non-nuclear attractors, charge density. X-ray diffraction.
Topological analysis of electron momentum densities and the bond directional principle: the first-row hydrides, AH, and homonuclear diatomic molecules, A2
Authors: Wang Jiahu , Clark B. James , Schmider Hartmut , Smith Vedene H.
Published: May 2006

Topological analysis of electron momentum densities of the first-row hydrides and homonuclear diatomic molecules has been carried out. The densities and their curvatures were calculated from wave functions of near Hartree–Fock quality using a Slater basis. The bond directional principle has been discussed through the topological properties of electron momentum densities. Basis set effects on the topological features have also been addressed. Key words: electron momentum density, the bond directional principle, topological analysis, first-row hydrides, homonuclear diatomic molecules.
A gas-to-solid phase methanolysis method for the analysis of small amounts of oligosaccharides
Authors: Asres Daniel Derbie , Perreault Hélène
Published: May 2006

A gas-to-solid phase methanolysis method for the analysis of oligosaccharides is presented. The advantages of using this new gas-to-solid phase method, as opposed to conventional bulk phase techniques, are described, along with comparisons of results obtained from both techniques. The reliable bulk phase methanolysis methods are used as benchmarks for assessing the extent of completion of the gas-to-solid reactions. Gas chromatographic – mass spectrometric (GC–MS) data show that, in general, higher temperatures and longer reaction times are required for completion of the gas-to-solid methanolysis process than for completion of the bulk phase reaction. On the other hand, the gas-to-solid procedure requires only minimal amounts of substrate that would be difficult to characterize using bulk phase methanolysis due to losses during clean-up procedures. Gas-to-solid methanolysis reactions of permethylated di- and trisaccharides were investigated (GC–FID and GC–MS), following initial experiments performed in order to characterize the GC retention times and mass spectra of permethylated standard monosaccharides. Conversion of neutral disaccharides, as well as neutral and acidic trisaccharides, to their respective monosaccharides was successful using the gas-to-solid method. The GC–FID and GC–MS traces show that the gas-to-solid method gives a cleaner reaction than the bulk phase method. Key words: oligosaccharides, methanolysis, permethylation, gas chromatography – mass spectrometry, mass spectrometry.
Spectroscopic and crystallographic studies of phosphino adducts of indium(III) iodide
Authors: Brown Martyn A. , Tuck Dennis G. , Wells Edward J.
Published: May 2006

Indium(III) iodide forms both 1:1 and 1:2 adducts with triphenylphosphine, depending on the reaction conditions, and especially on the solvent used. The complex InI3•PPh3 involves four-coordination at indium; the structure is trigonal, with a = 15.105(4) Å, c = 16.769(7) Å, V = 3313(2) Å3, Z = 6, and space group [Formula: see text]. Crystals were also obtained in which InI3•PPh3 and InI3(PPh3)2 are present in a 1:1 ratio; these are also trigonal, a = 15.473(4) Å, c = 41.701(7) Å, V = 8646.1(1.8) Å3,Z = 3 + 3 and space group [Formula: see text]. The 1:2 adduct has approximately D3h symmetry in the InI3P2 kernel. The bond distances and angles are discussed; in particular, the In—P bonds are extremely weak in the 1:2 adduct. This compound has been shown by 31P NMR to undergo complete dissociation in solution to InI3•PPh3 and PPh3. The addition of R4NI (R = n-C3H7, n-C4H9) causes quantitative conversion to InI4− and free Ph3P. Similar experiments are reported for the compound InI3(dppe) (dppe = 1,2-bis(diphenylphosphino)ethane), whose structure is an infinite chain of InI3 units linked through In-P-C2H4-P-In coordination. The crystal structure showed that InI3(dppe) cocrystallizes with an equimolar quantity of dppe; these crystals are cubic, a = 41.445(14) Å, b = 15.944(8) Å, c = 16.533(11) Å, p = 102.02(4)°, V = 10 685(9) Å3, Z = 4 + 4, space group C2/c, Solid state and solution phase results are discussed in terms of the coordination chemistry of indium(III). Key words: indium, phosphorus, coordination chemistry, multinuclear NMR, X-ray crystallography.
Thermodynamic properties of micellization of sodium dodecyl sulfate in binary mixtures of ethylene glycol with water
Authors: Gracie Kim , Turner Dale , Palepu R.
Published: May 2006

Micellar properties of sodium dodecyl sulfate (SDS) in aqueous mixtures of ethylene glycol (EG) were determined using techniques such as conductivity, density, EMF, surface tension, viscosity, ultrasonic velocity, and spectroscopy (fluorescence). The effective degree of disssociation of micelles (α) was determined using three different methods. Thermodynamics of micellization were obtained from the temperature dependence of critical micelle concentrations (cmc) values. The difference in Gibbs energies of micellization [Formula: see text] of SDS, between water and mixed solvent systems, was calculated to evaluate the influence of cosolvent on the micellization process. Surfactant aggregation numbers (Ns) obtained from static fluorescence quenching methods indicated a decrease in the aggregation numbers with increasing concentration of ethylene glycol in the binary solvent mixtures. In addition, the micropolarity of the micellar interior was determined from the pyreneI1/I3 ratios. These values were consistent with a decrease in the micropolarity surrounding the probe molecule as the EG content in the solvent mixture was increased. Key words: thermodynamics, micellization, aggregation numbers, ultrasonic velocity, degree of dissociation.
Theoretical and experimental approaches to the effects of solvation on the small internal rotational potential of benzal fluoride
Authors: Schaefer Ted , Bernard Guy M. , Bekkali Younes , McKinnon David M.
Published: May 2006

The internal rotational potential for benzal fluoride is computed at various levels of molecular orbital theory, including correlation-gradient, MP2 (frozen core) methods. The perturbations of the potential caused by solvents are calculated with the Onsager model (ellipsoidal cavity with l = 6 in the multipole expansion) as well as with the self-consistent isodensity – polarizable continuum model (SCI–PCM). Analysis of the 1H and 19F nuclear magnetic resonance spectra in cyclohexane-d12 and acetone-d6 solutions yields long-range spin–spin coupling constants from which the expectation values of [Formula: see text] can be derived. These expectation values can be compared with those calculated from the theoretical internal rotational potential. Reasonable agreement is found for potentials obtained from MP2/6-31G* approaches in both solvent models. Long-range coupling constants between 19F and 13C nuclei are also reported and provide very rough checks of the [Formula: see text] values. For the isolated molecule an additivity scheme based on the potential for benzyl fluoride reproduces much of the potential for benzal fluoride except for a deviation caused by the rather larger relative magnitude of the fourfold component in the latter. The minimum in the potential for benzal fluoride occurs for a torsional angle, [Formula: see text] of 90° corresponding to a conformation in which the C—H bond of the side chain lies in a plane perpendicular to the phenyl plane and is rationalized on the basis of electrostatic forces. The conformations of minimum energy for the benzyl and benzal fluorides and chlorides are compared and contrasted. The magnitudes of the internal potentials of the fluorides are only a little larger than thermal energies at 300 K and can become smaller than the latter in soludon. Key words: NMR spectroscopy, of benzal fluoride; spin–spin coupling constants, long range in benzal fluoride; solvent effects, on internal rotational potential in benzal fluoride; molecular orbital computations, structure, internal rotational potential, and its solvent perturbations in benzal fluoride; benzal fluoride, 1H, 19F, and 13C NMR on, internal rotational potential, MO computations.
The preparation and characterization of SeCl3SbF6, improved syntheses of MCl3(As/Sb)F6(M = S, Se), and the X-ray crystal structure determination of SeCl3AsF6and a new phase of SBr3SbF6
Authors: Passmore Jack , Boyle Paul D. , Schatte Gabriele , Way Todd , Cameron T. Stanley
Published: May 2006

Alternative and, in some cases, improved syntheses of the salts MX3(As/Sb)F6(M = S, Se) and SCl3(SbCl6/AlCl4) are described. In addition, the synthesis of SeCl3SbF6is reported. The compounds were characterized by FT–Raman spectroscopy and the X-ray crystal structures of SeCl3AsF6(also77Se NMR) and a new phase of SBr3SbF6were determined. Crystals of SeCl3AsF6and SBr3SbF6are monoclinic, space group P21/c with [values for SBr3SbF6in brackets] a = 7.678(1) [8.137(1)] Å, b = 9.380(3) [9.583(2)] Å, c = 11.920(3) [12.447(2)] Å, β = 98.19(2)° [97.36(1)]°, V = 849.72(3) [962.6(3)] Å3,z = 4, Dx = 2.925 [3.502] Mg m−3, R = 0.0525 [0.055], and Rw = 0.0554 [0.060] for 1151 [1472] observed reflections. Key words: MX3+salts, FT–Raman spectroscopy, X-ray crystal structures of SeCl3AsF6, SBr3SbF6, and preparation of SeCl3SbF6.
Synthesis and biological evaluation of carbon-substituted C-4 derivatives of podophyllotoxin
Authors: Lear Yvonne , Durst Tony
Published: May 2006

Several C-4 carbon-substituted analogues of podophyllotoxin, 1, were prepared by treatment of 1 with allyltrimethylsilane or trimethylsilylcyanide in the presence of boron trifluoride etherate. Alternatively, carbon substituents were introduced via additions to the carbobenzyloxy-protected C-4′-dimethylated podophyllotoxone. These 4′-dimethylated derivatives showed promising in vitro antitumour activity and were equally active against human colon cell line HT116 and two multidrug resistant cell lines. The alcohol 6 was evaluated in vivo but was found to be inactive. Key words: podophyllotoxin analogues, podophyllotox-4-one, C4 carbon substituted podophyllotoxins.
Synthesis of clustered D-GalNAc (Tn) and D-Galβ(1→3)GalNAc (T) antigenic motifs using a pentaerythritol scaffold
Authors: Hanessian Stephen , Qiu Dongxu , Prabhanjan Hubli , Reddy Gurijala V. , Lou Boliang
Published: May 2006

The tris(aminoethyl) and triamino derivatives of pentaerythritol have been used as scaffolds or templates for the attachment of immunologically relevant carbohydrates such as D-Galβ(1→3)GalNAc (T) and GalNAc (Tn), through amide linkages with the respective α-glycolyl and α-N-acetyl-L-serinyl glycosides. These clustered glycosidic motifs are intended as haptens for use in the preparation of tumor specific carbohydrate antigens and vaccines. Key words: glycoside synthesis, 2-thiopyridyl carbonate, glycosyl donors and glycopeptide motifs
Homoleptic carbonyl cations of palladium(I), palladium(II), platinum(II), and gold(I)—simplified synthetic routes to their fluoroantimonate(V) salts
Authors: Wang Changqing , Siu Sun Chau , Hwang Germaine , Aubke Friedhelm , Bach Christian , Bley Bianca , Bodenbinder Matthias , Willner Helge
Published: May 2006

The original synthetic routes to the new noble metal carbonyl cations [Au(CO)2]+and [M(CO)4]2+, M = Pd or Pt, as [Sb2F11]−salts are multi-step procedures that involve corrosive reagents and require commercially unavailable starting materials. We report here two general simplifications: (i) the sole use of liquid antimony(V) fluoride as reaction medium in a single-step carbonylation process, and (ii) the use of the commercially available chlorides AuCl3and MCl2, M = Pd or Pt, as starting materials, in addition to the binary fluorosulfates Au(SO3F)3, Pd[Pd(SO3F)6], and Pt(SO3F)4. The simplified routes developed here for [Au(CO)2][Sb2F11] and [M(CO)4][Sb2F11]2, M = Pd or Pt, should make these new reagents more easily available for wider use in synthesis. In addition, these routes are found suitable for the generation of new carbonyl cations of electron-rich metals. Key words: metal carbonyl cations of Au(I), Pd(I), Pd(II), and Pt(II); solvolysis reactions in liquid SbF5, reductive carbonylation in liquid SbF5; carbonylations in strong acidic media.
Synthesis of meso-phenyl-4,6-dipyrrins, preparation of their Cu(II), Ni(II), and Zn(II) chelates, and structural characterization of bis[meso-phenyl-4,6-dipyrrinato]Ni(II)
Authors: Brückner Christian , Karunaratne Veranja , Rettig Steven J. , Dolphin David
Published: May 2006

meso-Phenyldipyrromethanes can be oxidized by 2,6-dicyano-3,5-dichloro-para-benzoquinone (DDQ) to the corresponding meso-phenyldipyrrins. As expected, these novel, stable bipyrrolic pigments readily form metal chelates with copper(II), nickel(II), and zinc(II). Their UV–VIS spectra are compared with a series of known alkyl-substituted dipyrrin chelates and, based on the UV–VIS spectral analysis, the dihedral angle between the two ligands in the bis[meso-phenyldipyrrinato]Ni(II) complex was calculated to be 42°. The molecular structure of this complex was determined by X-ray crystallography, essentially confirming the calculation. Crystals of C30H22N4Ni are orthorhombic, a = 17.156(3), b = 35.217(1), c = 7.886(1) Å, Z = 8, space group Fddd. The structure was solved by direct methods and refined by full-matrix least-squares procedures to R = 0.040 and Rw = 0.031 for 1058 reflections with I ≥ 3σ(F2). The central nickel is coordinated in a distorted square-planar fashion by four nitrogens. The pair of the planar dipyrrinato ligands enclose a dihedral angle of 38.5°. This is the lowest angle reported for nickel(II) complexes of this kind. As a result of this, and in sharp contrast to previously described nickel(II) dipyrrin chelates, the central metal is diamagnetic. Key words: meso-phenyldipyrromethanes, meso-phenyldipyrrins, meso-phenyldipyrrinato transition metal chelates, X-ray crystallography.
Labdane diterpenes from the marine pulmonate gastropod Trimusculus peruvianus
Authors: San-Martín Aurelio , Quezada Elías , Soto Pilar , Rovirosa Juana , Palacios Yolanda
Published: May 2006

The marine gastropod mollusk Trimusculus peruvianus collected on the coast of Central Chile yielded four new labdane metabolites. The structural elucidation of all compounds was accomplished by spectral analysis. One diterpenoid showed modest antimicrobial activity. Key words: Trimusculus peruvianus, labdanes, marine mollusk.