bluuebunny/crossref_metadata_2025 huggingface dataset:
The stability of dolomite in landfill leachate-collection systems
Authors: Bennett Peter J , Longstaffe Frederick J , Rowe R Kerry
Published: April 2011

This study uses several approaches to examine whether calcium-containing aggregate such as dolostone is a suitable drainage material for landfill leachate-collection systems. The thermodynamic stability of carbonate drainage materials has been assessed using published leachate data from landfills in the United Kingdom and leachate sampled from four large landfill sites of variable age in southern Ontario. Electron-microbeam techniques have been used to check for dissolution in dolomitic stone exhumed from the drainage layer of the Keele Valley Landfill leachate-collection system and from experiments that simulated landfill conditions. The mineralogy of cover soils applied daily to the landfill has been compared to the drainage stone and detrital material occluding pore space in the leachate-collection system to evaluate their relative contributions to clogging. The data suggest that dissolution of dolomitic drainage stone is not significant and contributes little to the clogging of landfill leachate-collection systems. However, crystallization of secondary calcite occurs about the dolomitic stones and sizeable quantities of inorganic fines, including dolomite, were present within some samples of "clog material" exhumed from the Keele Valley collection system. Most of the dolomitic fines probably were generated during construction of the collection system; such creation of fines ought to be minimized in future landfill developments.Key words: leachate-collection system, landfills, clogging, mineralogy, leachate chemistry.
Numerical modeling of vertical drains with smear and well resistance installed in soft clay
Authors: Indraratna B , Redana I W
Published: April 2011

This study describes the behavior of embankments stabilized with prefabricated vertical drains installed in soft clay foundations, based on several fully instrumented case histories selected from Thailand and Malaysia. A multidrain analysis is conducted based on an equivalent, plane strain model developed by the authors. The deformation of soft clay beneath an embankment (i.e., along and away from the centerline) is predicted and compared with the available field measurements. The effects of both smear and well resistance are incorporated in the analytical formulation, which is used in conjunction with the modified Cam-clay theory. It is demonstrated that the installation of vertical drains significantly increases the rate of settlement, improves the dissipation of pore-water pressure, and decreases the lateral deformation of the soft clay foundation. To obtain better predictions, especially of pore pressures and lateral displacements, the equivalent discharge capacity of the drains needs to be modeled appropriately. The inclusion of the effects of smear and well resistance in the analysis of vertical drains improves the accuracy of predictions significantly, in comparison with the field measurements.Key words: clay, consolidation, embankment, finite element method, settlement, smear zone, vertical drain.
An analysis of the stability of thawing slopes, Ellesmere Island, Nunavut, Canada
Authors: Harris Charles , Lewkowicz Antoni G
Published: April 2011

Active-layer detachment slides are locally common on Fosheim Peninsula, Ellesmere Island, where permafrost is continuous, the active layer is 0.5-0.75 m thick, and summer temperatures are unusually high in comparison with much of the Canadian High Arctic. In this paper we report pore-water pressures at the base of the active layer, recorded in situ on two slopes in late July and early August 1995. These data form the basis for slope stability analyses based on effective stress conditions. During fieldwork, the factor of safety within an old detachment slide on a slope at Hot Weather Creek was slightly greater than unity. At "Big Slide Creek," on a slope showing no evidence of earlier detachment failures, the factor of safety was less than unity on a steep basal slope section but greater than unity elsewhere. In the upper slope, pore-water pressures were only just subcritical. Sensitivity analyses demonstrate that the stability of the shallow active layer is strongly influenced by changes in soil shear strength. Possible mechanisms for reduction in shear strength through time include weathering of soils and gradual increases in basal active layer ice content. However, we suggest here that soil shearing during annual gelifluction movements is most likely to progressively reduce shear strengths at the base of the active layer from peak values to close to residual, facilitating the triggering of active-layer detachment failures.Key words: detachment slides, Ellesmere Island, pore-water pressures, gelifluction.
Hydraulic conductivity of bentonite-sand mixtures
Authors: Sivapullaiah P V , Sridharan A , Stalin V K
Published: April 2011

The use of bentonite alone or amended with natural soils for construction of liners for water-retention and waste-containment facilities is very common. The importance of bentonite content in reducing the hydraulic conductivity of liners is well recognised. The study illustrates the role of the size of the coarser fraction in controlling the hydraulic conductivity of the clay liner. It has been shown that at low bentonite contents the hydraulic conductivity of the liner varies depending on the size of the coarser fraction apart from clay content. At a given clay content, the hydraulic conductivity increases with an increase in the size of the coarser fraction. But when the clay content is more than that which can be accommodated within the voids of the coarser fractions, the hydraulic conductivity is controlled primarily by clay content alone. Four different methods of predicting hydraulic conductivity of the liners are presented. Using two constants, related to the liquid limit, the hydraulic conductivity can be predicted at any void ratio.Key words: clays, hydraulic conductivity, liquid limit, liners, void ratio.
A full-scale stability experiment on a diaphragm wall trench
Authors: Tsai Jiin-Song , Jou Lee-Der , Hsieh Hsii-Sheng
Published: April 2011

This paper presents the results of a full-scale field experiment on the stability of a slurry-filled diaphragm wall trench. The objective of this experiment was to observe the failure pattern of a slurry-supported trench excavated in sandy ground. Ground responses, including settlement and lateral deformation of the surrounding ground adjacent to the experimental trench, were carefully monitored during the experiment. The stability of the trench was examined by lowering the slurry level in stages. The trench was deliberately failed. Field observations indicated that the experimental trench failed in 2 h in a progressive sliding pattern that resulted in a near-hemispherical cave-in of the adjacent ground. In this paper, a failure mechanism of the trench is proposed and an analytical method is adopted to back-analyze the stability of the trench. The stability of the trench and the failure pattern can be accurately analyzed using the method of Tsai and Chang.Key words: full-scale experiment, field test, slurry trench, stability analysis.
Effect of foundation flexibility on the across-wind response of reinforced concrete chimneys with free-standing liners
Authors: Galsworthy Jon K , Naggar M Hesham El
Published: April 2011

Chimneys with free-standing liners are often analyzed as fixed base cantilever beams, ignoring the effect of soil-structure interaction on their response. However, soil-structure interaction influences the dynamic response of chimneys in two ways: it alters the natural frequencies, damping ratios, and mode shapes, and it results in coupling of the response of the liner and the shell. In this analysis, the stack was modelled as a continuous cantilever beam with distributed stiffness and mass supported by a flexible foundation. It was found that the relative shell-liner deflection for the flexible foundation case was approximately 35% higher than that for the fixed base case. This increase in deflection may exceed design tolerances for a chimney cap and may lead to liner and (or) shell damage if combined with other adverse conditions such as aerodynamic interference effects with other chimneys. The base forces in the shell decrease significantly due to the foundation flexibility, with values as low as 50% of those of the fixed case. The base forces in the liner were approximately 35% of shell base forces for the fixed base case. These forces are not accounted for in the design of liners using the fixed base assumption. It was concluded that the effects of the foundation flexibility are significant and must be included in the analysis of chimneys with free-standing liners. This is especially true for chimneys in regions with low seismic activity, since the design of the liner would be based on minimal lateral forces.Key words: soil-structure interaction, chimneys, dynamic response, wind.
Compressibility behaviour of remoulded, fine-grained soils and correlation with index properties
Authors: Sridharan A , Nagaraj H B
Published: April 2011

Correlating engineering properties with index properties has assumed greater significance in the recent past in the field of geotechnical engineering. Although attempts have been made in the past to correlate compressibility with various index properties individually, all the properties affecting compressibility behaviour have not been considered together in any single study to examine which index property of the soil correlates best with compressibility behaviour, especially within a set of test results. In the present study, 10 soils covering a sufficiently wide range of liquid limit, plastic limit, and shrinkage limit were selected and conventional consolidation tests were carried out starting with their initial water contents almost equal to their respective liquid limits. The compressibility behaviour is vastly different for pairs of soils having nearly the same liquid limit, but different plasticity characteristics. The relationship between void ratio and consolidation pressure is more closely related to the shrinkage index (shrinkage index = liquid limit - shrinkage limit) than to the plasticity index. Wide variations are seen with the liquid limit. For the soils investigated, the compression index relates better with the shrinkage index than with the plasticity index or liquid limit.Key words: Atterberg limits, classification, clays, compressibility, laboratory tests.
The effect of aspirin-HSA complexation on the protein secondary structure
Authors: Neault J F , Novetta-Delen A , Arakawa H , Malonga H , Tajmir-Riahi H A
Published: April 2011

This study was designed to determine the secondary structure of human serum albumin (HSA) in the presence of aspirin in H2O and D2O solutions at physiological pH, using aspirin concentrations of 0.0001-5 mM with final protein concentration of 2% w/v. UV-vis spectra and Fourier transform infrared (FTIR) difference spectroscopy with its self-deconvolution, second derivative resolution enhancement, and curve-fitting procedures were applied to characterize the drug binding mode, the binding constant, and the protein secondary structure in the aspirin-HSA complexes. Spectroscopic evidence showed that no aspirin-protein interaction occurs at very low drug concentration (0.0001 mM), whereas at higher drug contents (0.001-0.1 mM) the aspirin anion binding (H-bonding) is mainly through the ε-amino NH3+group with overall binding constant of K = 1.4 × 104M-1. At high drug concentrations (1-5 mM), acetylation of Lys-199 was observed. Aspirin binding results in protein secondary structural changes from that of the α-helix 55% (free HSA) to 49%, β-sheet 22% (free HSA) to 31%, β-anti 12% (free HSA) to 4% and turn 11% (free HSA) to 16% in the aspirin-HSA complexes..Key words: aspirin, protein, drug, binding mode, binding constant secondary structure, FTIR spectroscopy.
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, H+) being transferred. II. Analysis of electron-pair interactions from intracule and extracule densities
Authors: Fradera Xavier , Duran Miquel , Mestres Jordi
Published: April 2011

The nature of the hydrogen transferred in the CH3/CH4+, CH3/CH4·, and CH3/CH4- systems is investigated by analyzing the topology of the contracted intracule and extracule electron-pair densities and their respective Laplacians. The CH3/CH4+, CH3/CH4·, and CH3/CH4- systems are taken as simple models for the study of hydride (H-), hydrogen (H·), and proton (H+) transfer reactions, respectively, under a constrained C-C distance. The study is focused on the comparison of the intracule and extracule densities at the intermediate structures for the three H-transfer reactions, complementing a previous investigation of the same model reactions based on the analysis of one-electron densities. The results obtained by analyzing the contracted electron-pair densities are consistent with those obtained from the analysis of one-electron densities. The electronic nature of the H atom being transferred in the three systems can be differentiated by the topologies of the corresponding intracule and extracule densities. However, the analysis underlies also the difficulties to interpretation of the topologies of contracted electron-pair densities, as different electron-electron interactions may contribute to the same point in the intracule or extracule spaces. In particular, for the systems studied, the contribution of the electron-electron interaction associated to the probability of having two electrons on the H being transferred is not reflected separately neither in the intracule nor in the extracule distributions. Nevertheless, the nature of the H being transferred can still be studied by comparing the importance of the electron-electron interactions associated to the probability of having one electron in C and one in the transferring H. The effects of inclusion of electron correlation are also discussed by means of (HF-CISD//HF) intracule and extracule density difference maps.Key words: hydrogen transfer, electron-pair density, intracule density, extracule density, topological density analyisis.
Crystal structure and ferromagnetic behavior of a cis-Co(II) complex with nitronyl nitroxide
Authors: Sun Bai-Wang , Zhao Qi-Hua , Liao Dai-Zheng , Jiang Zong-Hui , Yan Shi-Ping , Wang Geng-Lin , Yao Xin-Kai , Wang Hong-Gen
Published: April 2011

Bis(hexafluoroacetylacetonate)cobalt(II), Co(hfac)2, reacted with the nitronyl nitroxide radical 2-(4-methylphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, NITPhMe, to yield an octahedral adduct of formula Co(hfac)2(NITPhMe)2. The X-ray crystal structure shows that it crystallizes in the space group P1, with a = 9.837(3), b = 11.618(3), c = 20.502(4) Å, α = 81.22(2), β = 87.93(2), γ = 72.24(3)º, V = 2205(1) Å3, Z = 2. The mechanism of ferromagnetic exchange between cobalt(II) and the radical can be qualitatively understood in terms of a charge-transfer interaction (J being 25.7 cm-1, the Hamiltonian is written in the form H = -2J(SRad1·SCo + SCo·SRad2)).Key words: crystal structure, cobalt(II) complex, nitronyl nitroxide, magnetic property.
Radicals from fragmentation of benzyloxymethoxycarbenes in solution
Authors: Merkley Nadine , El-Saidi Manal , Warkentin John
Published: April 2011

2-Benzyloxy-2-methoxy-5,5-dimethyl-Δ3-1,3,4-oxadiazolines, including the parent as well as p-substituted analogues, undergo thermolysis at 100°C in benzene to afford a mixture of products. Two primary fragmentations of the oxadiazolines were identified. The major pathway involves 1,3-dipolar cycloreversion to N2 and the corresponding carbonyl ylides. The latter dissociate to acetone and the corresponding benzyloxy(methoxy)carbenes, which undergo fragmentation to ArCH2 and MeOCO radical pairs that recombine to afford methyl arylacetates. Carbene dimers were not observed, showing that the fragmentation process is faster than carbene dimerization. A second fragmentation pathway observed for the oxadiazolines is an alternative cycloreversion to the corresponding benzyl methyl carbonate and 2-diazopropane. Products from diazopropane included acetone azine and, in some instances, traces of propene.Key words: benzyloxy(methoxy)carbene, carbene, radical pair, rearrangement.
A novel route to chlorodimethylsilane
Authors: Chrusciel Jerzy J
Published: April 2011

A new efficient laboratory method of preparation of chlorodimethylsilane (Cl(CH3)2SiH) has been elaborated, which is a modification of the Eaborn et al. method (34) and is based on a transsilylation reaction of substituted (amino)dimethylhydrosilanes, R2NSiMe2H (R2 = Me2, Et2, (CH2)n, etc.) with dimethyldichlorosilane (Me2SiCl2). The reaction proceeds at reflux, at 70°C, preferably with an excess of Me2SiCl2. The most important feature of this novel method is a recovery of intermediate (amino)chlorodimethylsilanes (R2NSiMe2Cl), which can be again reduced to R2NSiMe2H. The transsilylation mechanism has been proven by reaction of (diethylamino)methylphenylsilane with Me2SiCl2. The products of this latter reaction are HMePhSiCl and R2NSiMe2Cl, thus a disproportionation mechanism has been excluded. New substituted bis(amino)dimethylsilanes ((R2N)2SiMe2), (amino)dimethylchlorosilanes (R2NSiMe2Cl), and (amino)dimethylhydrosilanes (R2NSiMe2H) have been synthesized and characterized by NMR and IR.Key words: chlorodimethylsilane, (CH3)2SiHCl, synthesis, new laboratory method, transsilylation mechanism.
Excess molar volumes and viscosities of binary mixtures of some n-alkoxyethanols with propylamine at 298.15 K
Authors: Pal Amalendu , Sharma Sanjay , Kumar Harsh
Published: April 2011

Excess molar volumes (VEm) and dynamic viscosities (η) for five (alkoxyethanol + propylamine) mixtures have been measured as a function of composition at 298.15 K and atmospheric pressure. The alkoxyethanols were 2-methoxyethanol, 2-(2-methoxyethoxy)ethanol, 2-(2-ethoxyethoxy)ethanol, 2-(2-butoxyethoxy)ethanol, and 2-{2-(2-methoxyethoxy)ethoxy}ethanol. The excess molar volumes VEm are all negative over the whole composition range. The viscosity data have been correlated by the methods of Kendall and Monroe, Grunberg and Nissan, Tamura and Kurata, Hind, Katti and Chaudry, and with McAllister correlations. From the experimental data, deviations in the viscosity (Δη) have been calculated. The results are discussed in terms of the interaction between components.Key words: excess volume, viscosity, binary mixtures.
Excess molar volumes and viscosities of binary mixtures of triethylene glycol dimethyl ether (triglyme) with chloroalkanes at 298.15 K
Authors: Pal Amalendu , Dass Gurcharan
Published: April 2011

Excess molar volumes (VEm) and viscosities (η) for mixtures of triethylene glycol dimethyl ether + dichloromethane, + trichloromethane, and + tetrachloromethane have been determined at 298.15 K and atmospheric pressure over the whole concentration range. From the experimental results, deviations in viscosities (Δ ln η) have been calculated. These properties were fitted to the polynomial relations to obtain the coefficients and the standard deviations. The results have been analysed in terms of molecular interactions between components.Key words: experiments, data, excess volume, viscosity deviation, binary mixtures.
Peptide models XXVII. An exploratory ab initio study on the 21st amino acid side-chain conformations of N-formyl-L-selenocysteinamide (For-L-Sec-NH2) and N-acetyl-L-selenocysteine-N-methylamide (Ac-L-Sec-NHMe) in their γL backbone conformation
Authors: Vank Judith C , Sosa Carlos P , Perczel Andras , Csizmadia Imre G
Published: April 2011

Selenocysteine is expected to have 9 × 9 = 81 conformations [3 × 3 = 9 backbone: ψ (g+,a,g-) × ϕ (g+,a,g-) and 3 × 3 = 9 side-chain: χ1 (g+,a,g-) × χ2 (g+,a,g-)]. In the present study, all the torsional modes of the side-chain (χ1: rotation about the Cα-Cβ and χ2: rotation about the Cβ-Se bonds) were investigated in the relaxed γL backbone [(ϕ,ψ); (g-,g+)] conformation. Seven out of the nine expected minima were found at the RHF/3-21G level of theory for N-formyl-L-selenocysteinamide (For-L-Sec-NH2) and N-acetyl-L-selenocysteine-N-methylamide (Ac-L-Sec-NHMe). The stabilization energy exerted by the -CH2-SeH side-chain has been compared with that of -CH2-SH and -CH2-OH. Relative energies of the various conformers were also obtained via single point calculations at the B3LYP/6-31G(d,p) level of theory. Topological analysis of the electron density has been performed by Bader's Atoms in Molecule (AIM) approach using the results. The structures were also optimized at the B3LYP/6-31+G(d,p) level of theory.Key words: selenocysteine side-chain conformations, ab initio MO study, Multidimensional Conformational Analysis (MDCA), Atoms in Molecules (AIM), Bader's electron density analysis.
Synthesis, solid state structure, and solution behaviour of the lighter lanthanide bis(trimethylsilyl)amido chlorides, [Ln{N(SiMe3)2}2(THF)(µ-Cl)]2 (Ln = Ce, Nd)
Authors: Berg David J , Gendron Roland AL
Published: April 2011

The synthesis of [Ln{N(SiMe3)2}2(THF)(µ-Cl)]2 (Ln = Ce, 1; Nd, 2) by reaction of sodium bis(trimethylsilyl)amide (2 equiv.) with LnCl3 is reported. The same complexes were also isolated from the ligand redistribution reactions of Ln[N(SiMe3)2]3 and LnCl3 (2:1 ratio) in THF at 80°C. The crystal structure of 2, determined by X-ray diffraction, revealed a centrosymmetric dimer with bridging chlorides and pentacoordinate metal centres. 1H NMR studies show that the solid state structure is not maintained in solution. NMR evidence for the presence of Ln[N(SiMe3)2]3 and two other bis(trimethylsilyl)amide containing species, presumably Ln[N(SiMe3)2]Cl2(THF)x and Ln[N(SiMe3)2]2Cl(THF)y, is presented.Key words: lanthanide, amide, neodymium, cerium, crystal structure, X-ray, nuclear magnetic resonance, redistribution.
Titrage infrarouge de l'acide phosphorique
Authors: Baril Jocelyn , Max Jean-Joseph , Chapados Camille
Published: April 2011

The titration of phosphoric acid by sodium hydroxide was performed by infrared (IR) spectroscopy with the objective of obtaining the infrared spectra of the pure ionic species and determining their abundance as a function of pH. In the series of spectra, taken in the pH range of 0.18-13.4, the subtraction of neutral water, acidic water, and basic water was made. Factor analysis (FA) was then applied to the series of spectra to obtain the objective. First, we found the four most abundant species : H3PO4 (pH 0-4), H2PO-4 (pH 0-9), HPO4-2 (pH 4-14), and PO4-3 (pH 9-14). Secondly, we found three complexes in small quantities : H3PO4H2PO4(pH 0-4),H2PO4HPO24 (pH 4-9), and HPO24PO34 (pH 9-14). The equilibrium constants of these species with the parent molecules are 0.65, 0.63, and 0.4 L/mol, respectively. Thirdly, we found residual water that was closely bound to the ionic species which formed hydrates. The pKa values obtained from the IR titration were used to obtain the theoretical concentration of the four principal species as a function of pH. The resulting distribution curve was found to be coincident with the distribution curve obtained by IR.Key words : infrared spectroscopy, FT-IR, aqueous solutions, factor analysis, titration, phosphoric acid, pH.
Improved simple synthesis of cyclic sulfates from trimethylsilyl chlorosulfonate
Authors: Bassindale Alan R , Katampe Ibrahim , Taylor Peter G
Published: April 2011

Reaction of iodosobenzene and trimethylsilyl chlorosulfonate followed by removal of the solvent and trimethylchlorosilane gives phenyliodosulfate. This can be used without further purification to prepare cyclic sulfates from alkenes, including vinylsilanes. Previous results have shown that if the trimethylchlorosilane is not removed, sultones are formed and a possible explanation of this behaviour is given.Key words: silicon, vinylsilanes, cyclic sulfate, phenyliodosulfate.
The synthesis of hydroxysmirnovine
Authors: Yadav Veejendra K , Williams Philip , Benn Michael
Published: April 2011

The synthesis of N-(4-acetamidobutyl)-N-((Z)-4-hydroxy-3-methyl-2-butenyl) guanidine confirmed this as the structure of the natural product hydroxysmirnovine.Key words: hydroxysmirnovine, synthesis, naturally occurring guanidines.
A facile new procedure for the deprotection of allyl ethers under mild conditions
Authors: Hu Yun-Jin , Dominique Romyr , Das Sanjoy Kumar , Roy René
Published: April 2011

A novel isomerization of O-allyl glycosides into prop-1-enyl glycosides was observed instead of cross-metathesis during an olefin metathesis reaction using Grubbs' ruthenium benzylidene catalyst (Cy3P)2RuCl2=CHPh (1), N-allyltritylamine, and N,N-diisopropylethylamine as necessary auxiliary reagents. In the search for a better catalytic system, it has been found that dichlorotris(triphenylphosphine)ruthenium(II), [(C6H5)3P]3RuCl2, (2) was much more efficient for the isomerization of allylic ethers. The labile prop-1-enyl group was easily hydrolyzed using HgCl2-HgO and the hemiacetals (25-32) were isolated in excellent yields (ca. 90%).Key words: allyl ether, carbohydrate, Grubbs' catalyst, isomerization, metathesis, deprotection.
The use of the RambergBäcklund rearrangement for the formation of aza-macrocycles: a total synthesis of manzamine C
Authors: MaGee David I , Beck Ellen J
Published: April 2011

A total synthesis of the marine alkaloid manzamine C has been accomplished. A Ramberg-Bäcklund reaction was used as a key step to construct the required azacycloundecene ring.Key words: alkaloid, macrocycle, RambergBäcklund, manzamine C.
On the possible formation of Si=O, Si=S, and Si=Se double bonds via the reaction of silylenes with oxirane, thiirane, and selenirane, respectively. An ab initio theoretical study
Authors: Apeloig Yitzhak , Sklenak Stepan
Published: April 2011

The reactions between silylene, H2Si, and the three-membered ring compounds, oxirane (9), thiirane (10), and selenirane (11), which provide possible routes to Si=X (X = O, S, Se) double bonds were studied by ab initio calculations at the MP2 and QCISD correlated levels of theory employing the polarized 6-31G** basis set. The calculations show that the three reactions are all highly exothermic, (61.8, 45.2, 52.9 kcal/mol at MP2/6-31G**//MP2/6-31G** for X = O, S, Se, respectively). In the gas phase, at 0 K, these reactions are predicted to be also spontaneous (i.e., the calculated transition states are lower in energy than the reactants). At 298 K, entropy contributions result in small barriers on the ΔG surface for X = O, S (7.4 kcal/mol for both reactions at QCISD (full)/6-31G**), but for X = Se the reaction remains spontaneous. Thus, the calculations suggest that these reactions are viable routes for the preparation of compounds with Si=X (X = O, S, Se) double bonds. The first step in all the reactions is the barrier-less formation of an encounter-complex between the silylene and the X atom of the precursor. For X = O, S, these complexes are predicted to be sufficiently stable to be observed in a matrix. The reaction steps which follow depend on X; for X = O fragmentation of the silylene-XC2H4 complex proceeds in two steps via a biradical intermediate, while for X = S and X = Se the fragmentation occurs in a single step. The first ab initio calculations for H2Si=Se are reported.Key words: silylene, silanone, silanethione, silaneselone.
Medium-sized cyclophanes. Part 53.1 Synthesis and conformational studies, and photoinduced cyclization of syn-[n.2]metacyclophanenes
Authors: Yamato Takehiko , Fujita Koji , Futatsuki Keigo , Tsuzuki Hirohisa
Published: April 2011

A series of [n.2]metacyclophanenes (3) and (6) were prepared in good yields by a McMurry cyclization of 1,n-bis(3-acetyl-4-methoxyphenyl)alkanes (2) and 1,3-bis(3-formyl-4-methoxyphenyl)propane (5), respectively. Compounds 3b, 3c exist in the syn-conformation due to the steric repulsion between the methyl groups at the ethano bridge and the methoxy groups at the aromatic rings while compound 6 prefers the anti-conformation typical of [3.2]metacyclophanes. The assignment of syn-conformations has been confirmed by 1H NMR analyses and X-ray diffraction studies. Photoinduced transannular cyclization of [n.2]metacyclophanenes (3) and (6) in the presence of iodine as an oxidant afforded phenanthrene-anellated polycyclic aromatic hydrocarbons. Apparently, the rate of the photocyclization of anti-6 was found to be much faster than that of syn-3b and almost completed within 1 h. Thus, the different reactivities for the irradiation of syn- and anti-conformer were observed. The reason for the present preference for the formation of trans-dihydrophenanthrene rather than cis-dihydrophenanthrene as the intermediate might be attributable to the more stable chair form transition state than boat one and the conformational fixation to the chair form in the ground and transition state is possible in the anti-conformer.Key words: cyclophanes, strained molecule, McMurry reaction, CC coupling, conformation analysis, cyclizations, photolysis, transannular reactions, transition states.
An experimental and theoretical approach to the study of the properties of parabanic acid and related compounds: synthesis and crystal structure of diethylimidazolidine-2-selone-4,5-dione
Authors: Arca Massimiliano , Demartin Francesco , Devillanova Francesco A , Isaia Francesco , Lelj Francesco , Lippolis Vito , Verani Gaetano
Published: April 2011

The syntheses of the first examples of selenoparabanic acid derivatives (dialkylimidazolidine-2-selone-4,5-dione, 3eR R = Me, Et, Bu) are presented along with the X-ray crystal structure determination of 3eEt. To gain an insight in the properties of parabanic acid derivatives on the basis of their electronic structures, we report the results of comparative hybrid-DFT calculations performed on parabanic, thioparabanic, and selenoparabanic acids (3aH, 3bH, and 3eH) and on their N,N' -dimethyl derivatives (3aMe, 3bMe, and 3eMe). Calculations show that the different nature of the frontier orbitals of 3aR compared to those of 3bR and 3eR, might account for the different reactivities of these compounds. Moreover, the weak donor character of 3bR and 3eR towards molecular di-iodine, estimated by FT-Raman measurements is in agreement with the calculated NBO-charge distribution.Key words: selenation, selenoparabanic derivatives, crystal structure, DFT calculations.
A study of micellization and the thermodynamic properties of a series of aqueous sodium cyclohexyl alkanoate surfactants
Authors: MacInnis Judith A , Marangoni D Gerrard , Palepu R
Published: April 2011

The micellization and the thermodynamic properties of a series of sodium cyclohexyl alkanoates of the general formula C6H11(CH2)nCOONa (where n = 1, 2, 3, 4) were investigated employing conductivity, density, surface tension, viscosity, speed of sound, luminescence probing experiments, and Fourier transform infrared (FT-IR) spectroscopy. The critical micelle concentrations (cmcs) and the aggregation numbers indicate that these surfactants have high cmc values and low aggregation numbers when compared to other single-headed surfactants (most notably the sodium alkanoates). Thermodynamic properties, obtained from the mass action model, indicate that micellization is spontaneous and entropically driven. The saturation area per molecule, the free energies of adsorption, and the efficiency and effectiveness of adsorption were determined through surface tension measurements. The presence of the cylcohexyl ring appears to influence the surface properties of micellization. Both the effectiveness and the efficiency of these surfactants, in lowering the surface tension of water, are lower than that of the straight chain alkanoates.Key words: thermodynamics, micellization, aggregation numbers, speed of sound, and spectroscopy.
Synthesis of 5-alkyl- and 5-aryl-1,5-dihydro-2H-pyrrol-2-ones via coupling of 5-chloro-1,5-dihydro-2H-pyrrol-2-ones with organometallic compounds
Authors: Nikitin Kirill V , Andryukhova Nonna P
Published: April 2011

5-Chloro-1,5-dihydro-2H-pyrrol-2-ones are easily alkylated at the 5-position by organomagnesium or organozinc compounds and diethyl sodiomalonate leading to corresponding 5-alkyl-1,5-dihydro-2H-pyrrol-2-ones in high yields.Key words: organometallic compounds, alkylation, 1,5-dihydro-2H-pyrrol-2-one.
Catalysis of the methanolysis of acetylimidazole by lanthanum triflate
Authors: Neverov Alexei A , Brown R S
Published: April 2011

Methanolysis of acetylimidazole (1) and N-acetylimidazolepentamine-Co(III) (2) was found to be markedly accelerated in the presence of La(OTf)3. Potentiometric titration of a solution of La3+(OTf-)3 gave a pKa for the metal bound CH3OH of 7.22. The kinetics of methanolysis of 1 and 2 were measured at 25°C at various pH under buffered conditions as a function of increasing La3+. Analysis of both the kinetic and potentiometric data indicates that the catalytically active species is a La3+-dimer, bridged by two methoxides, (CH3OH)nLa3+(CH3O-)2La3+(CH3OH)n. The maximum second-order rate constants for attack of the dimer on 1 and 2 are 1.50 × 103 M-1 s-1 and 1.42 × 102 M-1 s-1 respectively and both processes adhere to titration of a La3+(CH3OH) to generate the active form. The results are explained in terms of a mechanism where the methoxy-bridged La3+ dimer transiently breaks a La3+-OCH3 bond to expose both a CH3O- nucleophile and a La3+ which can act as a Lewis acid. Unlike the situation in water, the methanol results indicate that the medium greatly stabilizes and solubilizes the active dimer without the necessity of creating specially designed ligands to stabilize the dinuclear core.Key words: lanthanum ion, catalysis, methanolysis, activated amide.
Molecular characterization of petroporphyrins in crude oil by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry
Authors: Rodgers Ryan P , Hendrickson Christopher L , Emmett Mark R , Marshall Alan G , Greaney Mark , Qian Kuangnan
Published: April 2011

Petroporphyrin compositional analysis of a heavy crude oil has been realized by isolation and subsequent ESI-FT-ICR mass spectrometric analysis of the porphyrin-containing fractions. Vanadium octaethyl (V=O(II)OEP) and nickel octaethyl (Ni(II)OEP) porphyrin standards were analyzed to determine favorable electrospray ionization conditions and provide insight as to the molecular species present (e.g., adducts, multimers). Standard V=O(II)OEP and Ni(II)OEP solutions revealed the presence of both monomer and dimer species with a greater relative abundance of monomers. In contrast, mass spectral analysis of a porphyrin fraction from Cerro Negro crude oil was dominated by dimeric species. MS3 analysis identified a dioctylphthalate (DOP) contaminant, likely introduced during fractionation of the crude oil. DOP-porphyrin complexes and porphyrin-porphyrin dimers were then identified. Infrared multiphoton dissociation (IRMPD) of dimeric species produced the corresponding monomers with minimal fragmentation. The monomeric petroporphyrins were analyzed to reveal the metal (Ni(II) or V=O(II)), porphyrin type (e.g., etio vs. DPEP), and distribution of alkylation.Key words: petroporphyrin, porphyrin, petroleum, electrospray ionization, mass spectrometry, Fourier transform, ion cyclotron resonance, ICR, FT-ICR, FTMS.
Formation and reactivity of the zirconium ethylene complexes [η5-C5H3-1,3-(SiMe2CH2PR2)2]Zr(η2-CH2=CH2)(X) (R = Me, Pr i; X = Br, C5H5)
Authors: Fryzuk Michael D , Duval Paul B , Rettig Steven J
Published: April 2011

The formation and reactivity of the zirconium ethylene complexes R[P2Cp]Zr(η2-CH2=CH2)(X) (2a: R = Pri, X = Br; 2b: R = Me, X = Br; 4a: R = Pri, X = C5H5; R[P2Cp] = (η5-C5H3-1,3-(SiMe2CH2PR2)2)) are described. Ethylene complexes 2a and 2b are prepared from a reaction of R[P2Cp]ZrCl3 (1a: R = Pri; 1b: R = Me) with 2 equiv of EtMgBr, presumably via β-H elimination from the diethyl intermediate R[P2Cp]ZrCl(CH2CH3)2. The structure of 2b was determined by X-ray crystallography. Addition of carbon monoxide to 16-electron 2 displaces the ethylene ligand to generate the carbonyl complex R[P2Cp]Zr(CO)2Br (5a: R = Pri; 5b: R = Me), which is stable only under an atmosphere of CO. The corresponding CO reaction with 18-electron 4a to give the metallocene monocarbonyl analogue Pr[P2Cp]Zr(η5-C5H5)(CO) (6a) is considerably slower. 2a exhibits fluxional exchange of one carbonyl ligand with bulk 13CO in solution; the kinetic parameters for this exchange process are ΔH  = 9.2(5) kcal mol1 and ΔS  = 17(2) cal mol1 K1. The addition of diphenylacetylene to 2a yields the alkyne complex Pr[P2Cp]Zr(η2-PhCCPh)Br (7a), which exists in solution as two isomers in equilibrium. A solid-state X-ray structure determination for the minor isomer syn-7a was performed.Key words: zirconium, cyclopentadienyl phosphine, alkyne, metallocyclopropane.
Palladium-catalyzed alternating copolymerization of carbon monoxide with olefins bearing carbamate and amide functionalities
Authors: Moineau Christophe , Mele Giuseppe , Alper Howard
Published: April 2011

The copolymerization of carbon monoxide with different olefins bearing carbamate and amide functionalities was effected using [Pd(CH3CN)4](BF4)2 as the catalyst and (R,R)-Me-DUPHOS (2:1 (v/v) MeNO2MeOH or CH2Cl2 as the solvent). The products constitute a new class of functionalized copolymers, and were found to be optically active with a mixture of 1,4-ketone and spiroketal repeating units in the backbone. The influence of different parameters on the copolymerization of methyl N-(3-butenyl)carbamate with carbon monoxide was examined.Key words: copolymerization, carbon monoxide, olefins bearing carbamate and amide functionalities.
New chaotic behavior and its effective control in BelousovZhabotinsky reaction
Authors: Li Yan-Ni , Song Hao , Cai Zun-Sheng , Chen Lan , Hou Zhe , Wei Qing-Li , Wu Ben-Xiang , Zhao Xue-Zhuang
Published: April 2011

A new "spiral-in-to-spiral-out" mixed-mode type chaos of the BelousovZhabotinsky (BZ) reaction in a continuous flow stirred tank reactor (CSTR) is observed. We discussed its evolution and characterization in detail. We controlled the new chaos into steady periodic behavior by two control methods: (i) a self-adaptive delayed feedback controlling scheme; and (ii) a linear self-interacting feedback controlling scheme.Key words: BZ-CSTR reaction, chaos, control.
Thermodynamic of metal complexation of the macrocyclic antibiotic rifampicin
Authors: Shehatta I , Kenawy I , Askalany A H , Hassan Ayman A
Published: April 2011

The acid-base and complexation equilibria of rifampicin with H+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+, and Pb2+were studied by means of potentiometry. The stoichiometric equilibrium constants were determined in 50% (v/v) methanol-water medium at different temperatures and constant ionic strength (0.05 M KCl). It was established that rifampicin has two proton-binding sites. The distribution diagram of the corresponding ionic species as a function of pH is given and indicated that rifampicin exists predominantly in the zwitterionic form at pH [Formula: see text] 5. The thermodynamic parameters of protonation and complexation were derived and discussed. The formation of the complexes is spontaneous, more favourable at lower temperatures, entropically unfavourable, and an enthalpy-driven process. The order of the changes in Gibbs energy and enthalpy accompanying the complexation was found to be Mn2+< Co2+< Ni2+< Cu2+> Pb2+> Zn2+> Cd2+> Hg2+in accordance with the well-known sequence of Irving and Williams. The transition series contraction energy (Er(Mn-Zn)), and the ligand field stabilization energy (δH) were calculated from the enthalpy changes.Key words: rifampicin, thermodynamics, potentiometry, and complexation.
Excess properties for acetophenone + butanols at 298.15 K
Authors: Riggio Roque , Ramos Juan F , Martinez Hector E
Published: April 2011

Densities, viscosities, and refractive indexes of binary systems acetophenone + n-butanol, + sec-butanol, and + 2-methyl-1-propanol have been measured at 298.15 K and atmospheric pressure, over the whole composition range. The excess values of molar volume, viscosity, Gibbs free energy of activation of viscous flow, and internal pressure were calculated from experimental measurements. Based on the variations of the excess functions with composition, conclusions about the molecular interactions in these kinds of mixtures were obtained.Key words: excess properties, binary mixtures, butanols, acetophenone.
Synthesis, characterization and chemistry of bis-(pentafluorophenyl)boryl ferrocene
Authors: Carpenter Bryon E , Piers Warren E , Parvez Masood , Yap Glenn PA , Rettig Steven J
Published: April 2011

Bis-(pentafluorophenyl)boryl ferrocene, 1, was prepared via borylation of ferrocene with HB(C6F5)2 or via a transmetallation reaction involving FcHgCl and ClB(C6F5)2 in 8791% yield. The compound is characterized by a deep maroon colour. A significant intramolecular ironboron interaction is manifested in the solution spectroscopic (Fe [Formula: see text] B charge transfer band at ~230 nm, ε = 1.33 × 104) and solid-state crystallographic data (Fe-B = 2.924 Å) This interaction has an impact on the Lewis acidity of the boron center which, unlike the related compound B(C6F5)3, does not strongly bind Lewis bases such as acetone, THF, or acetonitrile. However, an adduct between the stronger base PMe3 and 1 forms readily and this complex (2) was fully characterized. The electron withdrawing -B(C6F5)2 group causes 1 to be oxidized at +450 mV relative to ferrocene. Oxidation of 1 with [NO][BF4], AgOSO2CF3, or AgC6F5 leads to the zwitterionic ferrocenium borates 3-F, 3-OTf, and 3-C6F5, respectively. Each of these compounds was characterized spectroscopically and via X-ray crystallography. The properties of these compounds relative to 1 suggest that oxidation of the iron center significantly enhances the Lewis acidity of the boron center. Due to the σ-donating ability of the borate substituents, zwitterions 3 are weaker oxidizing agents than unsubstituted ferrocenium salts.Key words: organoboranes, ferrocene derivatives, Lewis acids.
Nature of the active silane alcoholysis catalyst in the RuwClx(CO)y(PMe3)z (w, x, y, z = 1 or 2) system; Ru2(µ-Cl)2Cl2(CO)4(PMe3)2 as a new catalyst for silane alcoholysis in a polar solvent
Authors: Chung Mee-Kyung , Ferguson George , Robertson Valerie , Schlaf Marcel
Published: April 2011

The dimeric complex Ru2(µ-Cl)2Cl2(CO)4(PMe3)2 (1) forms an active silane alcoholysis complex in the polar solvent N,N-dimethylamino-acetamide (DMA). The dynamic behaviour of 1 in DMF-d7 solution has been investigated by variable temperature (VT) 1H NMR. The solid state structures of 1 and cis,cis,trans-RuCl2(CO)2(PMe3)2 (3) have been determined by single crystal X-ray diffractometry. Using ethylene glycol - triethylsilane as a model system, the catalytic activity of 1 in DMA is compared to that of a series of known silane alcoholysis catalysts, including RhCl(PPh3)3, PdX2 (X = Cl-, OAc-), and cis,cis,trans-[IrH2S2L2]SbF6 (L = PPh3, S = THF). Complex 3 is not an active silane alcoholysis catalyst in this solvent, but is active in nonpolar solvents. Its structure and spectroscopic signature is, however, different from that of a previously reported catalyst of the same composition.Key words: silane alcoholysis, polar solvent, ruthenium catalyst.
A computational approach to seeking methylmercury(II) thiolate calix[4]arene hosts for both octasulfur and organosulfur compounds as guests
Authors: Knoblauch Stephan , Koch H Fred , Polydore Catherine , Roundhill D Max
Published: April 2011

Calculations have been carried out on the conformational preferences of calix[4]arene thiols and their methylmercury(II) derivatives. Calculations have also been carried out on hostguest combinations of methylmercury(II) ethanethiolate calix[4]arenes and 1,4-dithiacyclohexane, octasulfur, thiacyclopropane, and thiophene. For the 1,4-dithiacyclohexane, thiacyclopropane, and thiophene guests, calculations have been carried out for both 1:1 and 1:4 ratios of the methylmercury(II) ethanethiolate calix[4]arene to the sulfur containing guests. For octasulfur only the 1:1 hostguest ratio has been considered because it has four sulfurs that are conformationally arranged to bind to the four mercury(II) centers. The computational results generally show that hostguest formation is enthalpically favored over the separated molecules in cases where adducts with mercury-sulfur donor atom interactions are allowed to reach energy minima.Key words: calixarene, methylmercury, octasulfur, organosulfur compounds.
Iron complexes of the N(CH2CH2S)33(NS3) ligand with isocyanide co-ligands.
Authors: Cooper Lyndsey , Davies Sian C , Dilworth Jonathan R , Hughes David L , Konkol Marcin , Richards Raymond L , Sanders J Roger , Sobota Piotr
Published: April 2011

The complexes NEt4[Fe(NS3)(CNR)] (1), [Fe{Fe(NS3)(CNR)}2-S,S' ] (2), [Co{Fe(NS3)(CNMe)}2-S,S' ] (3), and [Ni{Fe(NS3)(CNMe)}2-S,S' ] (4) (R = Me, t-Bu, or C6H11(Cy)) have been prepared and the X-ray crystal structures of NEt4[Fe(NS3)(CNMe)] (1a) and [Fe{Fe(NS3)(CNCy)}2-S,S' ] (2c) have been determined. Mössbauer and IR spectroscopic data and room temperature magnetic moments for these complexes are reported.Key words: iron, cobalt, nickel, thiolate, isocyanide.
Epoxide of a ketene acetal. The first 2,2-dialkoxyoxirane to be isolated
Authors: Dawid Malgorzata , Venneri Paul C , Warkentin John
Published: April 2011

Dimethoxycarbene, generated at 110°C in benzene by thermolysis of 2,2-dimethoxy-5,5-dimethyl-Δ3-1,3,4-oxadiazoline, reacted with cyclohexanone to afford 2,2-dimethoxyspiro[2.5]-1-oxaoctane. It is the first oxirane of a ketene acetal that could be isolated and characterized by 1H NMR-, 13C NMR-, and IR spectroscopy. The identical oxirane might be expected from conrotatory cyclization of the appropriate carbonyl ylide. That ylide was generated under identical conditions by thermolysis of an oxadiazoline precursor (3,4-diaza-2,2-dimethoxy-1-oxaspiro[4.5]dec-3-ene) (14). The ylide could either cyclize or fragment to dimethoxycarbene and cyclohexanone. Addition of 4-tert-butylcyclohexanone, to trap dimethoxycarbene in competition with the cyclohexanone generated from 14 and, to leave the ylide closure pathway as the only route to the oxirane, showed that the carbonyl ylide does cyclize. However, fragmentation of the carbonyl ylide is relatively fast compared to its cyclization and most of it fragments to dimethoxycarbene and cyclohexanone. Oxirane formation from the carbene and ketone is probably either a concerted cycloaddition or it occurs in two steps, by nucleophilic attack at the carbonyl carbon to form the CC bond first, prior to ring closure. If the carbene is bonded first to O of the carbonyl group, as it is in the carbonyl ylide, subsequent formation of the CC bond is too slow, relative to fragmentation of the ylide, to afford the oxirane ring efficiently.Key words: carbonyl ylide, dialkoxyoxirane, dimethoxycarbene, oxadiazoline, oxirane.