bluuebunny/crossref_metadata_2025 huggingface dataset:
State-dependant dilatancy in critical-state constitutive modelling of sand
Authors: Li Xiang-Song , Dafalias Yannis F , Wang Zhi-Liang
Published: April 2011

A bounding-surface hypoplasticity model is modified to incorporate the basic premises of critical-state soil mechanics and cover both dense and loose sand behavior. The modification consists of rendering the phase-transformation line a function of the state parameter, which measures the difference between the current and critical void ratios at the same value of p, such that when the state parameter is zero, the phase-transformation line becomes identical to the critical-state line in q-p space. As a result the dilatancy depends on the state in a way that yields a zero value at critical state. This dependence allows a realistic modelling of the response of a sand in either loose or dense state, or in the transition from one state to another state. A comparison between model simulations and a sequence of experimental results for drained, undrained, monotonic, and cyclic loading conditions shows that the proposed concept and modelling technique work effectively over a wide range of densities and confining pressures using a unique set of parameters (or parameter dependence) for a given sand.Key words: bounding surface, critical state, dilatancy, phase transformation, soil plasticity, state parameter.
A numerical study of steady state evaporative conditions applied to mine tailings
Authors: Rassam Daud W , Williams David J
Published: April 2011

The suction profile of a desiccating soil is dependent on the water table depth, the soil-water retention characteristics, and the climatic conditions. In this paper, an unsaturated flow model, which simulates both liquid and vapour flow, was used to investigate the effects of varying the water table depth and the evaporation rate on the evaporative fluxes from a desiccating tailings deposit under steady-state conditions. Results obtained showed that at a critical evaporation rate, beyond which evaporation is no longer dictated by climatic conditions, the matric suction profiles remain basically unchanged. The critical evaporation rate varies inversely with the water table depth. It is associated with the maximum evaporative flux that might be extracted from a soil at steady-state conditions. The time required to establish steady-state conditions is directly proportional to the water table depth, and it acquires a maximum value at the critical evaporation rate. A detailed investigation of the movement of the drying front demonstrated the significance of attaining a matric suction of about 3000 kPa on the contribution to flow in the vapour phase.Key words: matric suction, mine tailings, potential evaporation, steady state evaporative conditions, surface evaporative flux.
A rate-dependent model for the ductile behavior of salt rocks
Authors: Aubertin Michel , Julien Michel R , Servant Stéphane , Gill Denis E
Published: April 2011

Salt rocks, such as potash and rock salt, show a complex mechanical behavior that is rate and history dependent. Various approaches exist to represent the main features of the response of these rocks through constitutive models. The approach proposed in this paper is to formulate the constitutive equations using internal state variables (ISV) in the context of the unified theory of inelastic flow. To illustrate the application of this approach, the authors use an updated version of a viscoplastic model with reduced expressions for laboratory triaxial tests at relatively high confining pressure. It is shown that, under these conditions, mixed hardening of salt rocks can be described through a combination of scalar and directional ISV. The authors also describe in some detail a procedure to obtain the material parameters for the model equations. The paper shows some characteristics of the model response for various loading paths, illustrating the good agreement with experimental observations and highlighting some of the differences with a classical isotropic hardening model.
Field observations of clogging in a landfill leachate collection system
Authors: Fleming I R , Rowe R K , Cullimore D R
Published: April 2011

The findings from a rare opportunity to exhume, examine, and sample a granular underdrain leachate collection system at a large municipal landfill site are reported. The "clear stone" drainage blanket was constructed from uniform, coarse gravel (with a nominal 50 mm particle size) obtained by crushing dolomitic limestone. After exposure to municipal landfill leachate for 1-4 years, the drainage stone was found to contain a considerable mass and volume of clog and slime materials. These were composed of mineral precipitates, fine granular particulate, and biofilm, growing under the ambient anaerobic conditions prevalent below the landfilled waste. The spatial distribution, physical and hydraulic properties, and chemical and microbiological composition of this material were examined and compared with similar material recovered from a laboratory mesocosm. The findings suggest a theoretical framework for a model of clogging behaviour of leachate collection drains at municipal solid waste landfill sites.Key words: municipal waste, leachate, clogging, drainage, biofilm, cementation.
Characterization of geotechnical variability
Authors: Phoon Kok-Kwang , Kulhawy Fred H
Published: April 2011

Geotechnical variability is a complex attribute that results from many disparate sources of uncertainties. The three primary sources of geotechnical uncertainties are inherent variability, measurement error, and transformation uncertainty. Inherent soil variability is modeled as a random field, which can be described concisely by the coefficient of variation (COV) and scale of fluctuation. Measurement error is extracted from field measurements using a simple additive probabilistic model or is determined directly from comparative laboratory testing programs. Based on an extensive literature review, the COV of inherent variability, scale of fluctuation, and COV of measurement error are evaluated in detail, along with the general soil type and the approximate range of mean value for which the COVs are applicable. Transformation uncertainty and overall property uncertainty are quantified in a companion paper.Key words: inherent soil variability, measurement error, coefficient of variation, scale of fluctuation, geotechnical variability.
Elastic viscoplastic consolidation modelling and interpretation of pore-water pressure responses in clay underneath Tarsiut Island
Authors: Yin Jian-Hua , Zhu Jun-Gao
Published: April 2011

It has been reported that the excess pore-water pressure in clay underneath Tarsiut caisson retained island increased for many months following completion of construction (with vertical load unchanged). It was thought that this increase might be caused by the creep behaviour of the soft clay. However, the phenomenon of excess pore-water pressure increase under constant loading has not been simulated successfully at the Tarsiut Island site. In this paper, a newly developed elastic viscoplastic (EVP) model is implemented in a finite element (FE) program for consolidation analysis. This FE program is used to model the consolidation behaviour of the clay under Tarsiut Island loading. The phenomenon of pore-water pressure increase with time following completion of construction of the island has been successfully simulated using the FE program with the new EVP model. The mechanism of the pore-water pressure increase is explained. It is found that the creep compression nature of the clay is the main internal factor causing the increase. However, the volumetric strain (change) produced due to the dissipation of excess pore-water pressure is the external factor which combines with the internal factor to cause decreasing effective stress and increasing pore-water pressure.Key words: elastic, viscoplastic, finite element, pore-water pressure, consolidation, creep, clay.
A case study of hydraulic fracturing using finite element methods
Authors: Ng Axel KL , Small John C
Published: April 2011

Hydraulic fracturing can occur in the clay core of an earth and rock-fill dam if the vertical effective stress in the core is reduced to levels that are small enough to allow a tensile fracture to occur. This situation may arise if the total stress in the core is reduced by the "arching effect" where the core settles relative to the rock-fill shoulders of the dam. Water pressure increases in the core which occur on first impounding of water will reduce effective stresses further, and if they reach low enough values, a fracture will occur. The design of earth dams to resist hydraulic fracture is therefore of great importance (especially those dams with thin vertical or near-vertical central cores), as there have been several dam failures in the past that have been attributed to hydraulic fracture. This paper presents a method of predicting hydraulic fracture in the core of earth and rock-fill dams by using a numerical procedure based on the finite element method. The finite element procedure makes use of special joint elements that allow fluid flow and fracture to be modeled and is an advance over previous methods in that it allows the complete history of pore-pressure development in the core of a dam to be simulated. A study of the behaviour of the Hyttejuvet Dam, which was thought to have failed due to hydraulic fracturing, is also carried out, and the results of the analysis suggest that the failure of the dam was probably due to hydraulic fracturing that occurred during first filling of the reservoir. The fractures predicted occur at about the location that the actual fracture was thought to have been located. Key words: hydraulic fracture, earth and rock-fill dams, finite element method.
Critical state strength parameters of saturated clays from the modified Cam clay model
Authors: Chang Ming-Fang , Teh Cee Ing , Cao LaiFa
Published: April 2011

The evaluation of critical state strength parameters is important, especially with the introduction of limit state design. The modified Cam clay (MCC) model is often used, but it is suitable mainly for evaluating the critical state strength parameters from triaxial compression tests on isotropically consolidated soils. The initial stress condition of a natural soil is usually anisotropic, and the stress paths imposed by external loading could deviate from that of a simple triaxial compression. The use of MCC in practice deserves careful consideration. This paper describes a proposed extension of the MCC model for the evaluation of critical state strength parameters from undrained triaxial and plane strain tests on anisotropically consolidated clays. Using Lade's failure criterion and the plastic potential of MCC, a generalized yield surface is determined and the relationships between the critical state internal friction angles from various triaxial and plane strain tests are obtained. By relating the isotropic overconsolidation ratio to the conventional overconsolidation ratio (OCR), a procedure is suggested for the prediction of critical state undrained shear strength (su) for clays. The undrained strength normalized by the preconsolidation pressure is not a constant but a function of the angle of internal friction and the OCR. For overconsolidated clay, the predicted undrained strength ratio (su/σVO) for the triaxial compression condition is larger than that for the plane strain compression condition. Comparisons of predicted results with published data indicate that the procedure is applicable to various compression tests on normally and lightly to moderately overconsolidated clays. Key words: stress anisotropy, clay, constitutive model, critical state, laboratory test, shear strength parameters.
Settlement rate of foundations on unsaturated soils
Authors: Ausilio Ernesto , Conte Enrico
Published: April 2011

This paper deals with the one-dimensional consolidation of unsaturated soils due to the application of external loads. A simple equation is derived that enables one to predict the rate of settlement of shallow foundations with time. This equation uses the constitutive relationships proposed by Fredlund and Morgenstern to define the volume change of unsaturated soils, and relates the settlement rate to the average degree of consolidation for both the water and air phases. A series of examples is shown to demonstrate the feasibility and usefulness of the derived equation. Key words: one-dimensional consolidation, unsaturated soil, degree of consolidation, rate of settlement.
On compression characteristics of Ariake clays
Authors: Hong Zhenshun , Tsuchida Takashi
Published: April 2011

J.B. Burland proposed that the void index aids in assessing the compressibility of various sedimentary clays. The extensive data on sensitive Ariake clays are used in this study to investigate the compression behavior using the void index. The analysis results indicate that the compression curves of remolded Ariake clays can be normalized by the void index proposed by Burland. It is found, however, that most natural Ariake clays lie above the sedimentation compression line. Salt removal and cementation are considered to be the most probable causes for such a phenomenon for Ariake clays. Furthermore, a relatively good relationship is found between the in situ void ratio of Ariake clays and the effective overburden pressure. The relationship can be expressed by a straight line in a bilogarithmic plot, herein designated field state line (FSL) for Ariake clays. Key words: Ariake clays, compression curve, intrinsic compression line, field state line, oedometer test, sedimentation compression line, void index.
Analysis of calibration chamber plate load tests
Authors: Lee Junhwan , Salgado Rodrigo
Published: April 2011

The estimation of base resistance is a key step in the design of piles embedded in moderately dense to dense sand. Calibration chamber plate load tests are sometimes used to investigate the base load - settlement relationship of nondisplacement piles in sand. In such tests, the sand specimens are carefully prepared to simulate the installation of nondisplacement piles. In this paper, calibration chamber tests are analyzed using the finite element method; experimental and numerical results are compared. The finite element models are axisymmetric and use a nonlinear, elastic-plastic constitutive model. Plate resistance values predicted using the finite element analysis are shown to be in good agreement with measured values, which validates the proposed numerical model. Questions regarding the existence of calibration chamber size effects have not, to this date, been adequately addressed. Finite element analyses of both pile base resistance and plate resistance for sands with various relative densities and stress states show that size effects are usually small for settlement levels of interest in practice. This suggests that the use of calibration chambers in pile base capacity studies is justified.Key words: calibration chambers, plate load tests, constitutive modeling, size effects, piles, sands.
Hydrological response of hillslope soils above a debris-slide headscarp
Authors: Fannin R J , Jaakkola J
Published: April 2011

The Jamieson Creek debris slide initiated in thin soils over a competent bedrock surface, on a planar section of hillslope, during a heavy rainstorm in November 1990. An array of automated piezometers and tensiometers was placed along a 22 m wide section of the headscarp in 1997 to monitor the temporal variation of pore-water pressures. Interpretation of the data addresses the hydrologic response to the storms in October and November 1997. The piezometers, which were designed for installation by driving, reveal very localized responses in what otherwise appears to be a uniform soil matrix. Peak positive pressures occur at the time of maximum rainfall intensity. The tensiometers indicate the hydrological response at the ground surface appears uncoupled from that at the bedrock interface. Implications of the extreme spatial variability in pore-water pressure are evaluated for conceptual models of hillslope hydrology. The assumption of parallel seepage flow is widely adopted in translational slope stability analyses, imposing a linear distribution of pore-water pressure with depth. None of the reported field data are consistent with such a linear distribution with depth or a uniform response across the slope.
Performance of shallow foundations on clay deposits in Montréal Island
Authors: Silvestri Vincent
Published: April 2011

This paper reports the results of a geotechnical investigation and a 3 year monitoring program of clay deposits in Montréal Island, on which are founded five typical residential buildings. The sites were provided with foundation wall elevation pins, ground movement plates, deep settlement points, piezometers and shallow water level gauges, aluminium tubes for the measurement of volumetric weights and water contents, and irrigation systems. Data recorded show that for the relatively dry summer of 1991 ground and foundation settlements were more pronounced on the nonirrigated sites.Key words: shallow foundations, clay deposits, performance, urban environment, monitoring.
Tire-reinforced earthfill. Part 1: Construction of a test fill, performance, and retaining wall design
Authors: Garga Vinod K , O'Shaughnessy Vince
Published: April 2011

The satisfactory disposal of scrap tires is a major environmental problem worldwide. This waste occupies valuable space in landfill sites, and tire stockpiles pose serious health and fire hazards. The use of scrap tires as reinforcement for construction of retaining walls and slopes is a viable method towards reduction of this waste. This paper describes the construction of a 57 m high × 17 m wide instrumented test fill, comprising both retaining wall and reinforced slope sections. Approximately 10 000 whole tires and tires with one sidewall removed, tied together with polypropylene rope, were used in both cohesionless and cohesive backfills. The testing program also included plate loading tests, field pull-out tests on tire mats, water-quality assessment in the field and laboratory, and other complementary laboratory testing. This first paper, in a series of three, demonstrates the practical feasibility of constructing reinforced earth fills using scrap tires. Results of large plate load tests and the field behaviour with particular reference to the design of the retaining wall sections are presented. The paper emphasizes the role of negative wall friction in increasing the active thrust when the retaining wall becomes more compressible than the backfill. Recommendations for the design of retaining walls using scrap tires are presented.Key words: scrap tires, earth reinforcement, retaining walls, reinforced slopes, plate load test, construction, performance.
The role of clay minerals and the effect of H+ ions on removal of heavy metal (Pb2+) from contaminated soils
Authors: Li Loretta Y , Li Raymond S
Published: April 2011

The importance of the surface charge of clay minerals (fixed or variable) and the effect of H+ ions on the adsorption and removal of Pb2+ ions from contaminated soil are investigated using kaolinite (variable charge) and two illitic (fixed charge) soils with pH 3.9 and 9.2. The adsorption-desorption characteristics of Pb2+ ions were determined using batch equilibrium tests and acid leach tests with various acids used to leach the soils. Under the same adsorption conditions, illitic soil adsorbed much more Pb2+ ions than kaolinite. The difference is largely due to the surface charges on the clay minerals. Removal of Pb2+ ions from variable-charge minerals (e.g., kaolinite) requires much less effort than removal of Pb2+ ions from constant-charge minerals (e.g., illite). The surface charge of a clay mineral has an important effect. By increasing the number of H+ ions available in the soil system with a buffer solution such as NaOAc-HOAc, heavy metals adsorbed on the clay surface are expelled to pore water. The increase in H+ ions in the soil system also assists in dissolving any metal carbonates, thereby increasing the solubility of heavy metals in illitic soil. The more H+ ions available in the pore fluid, the more Pb2+ ions can be released from the system.Key words: clay minerals, sorption, desorption, heavy metal, hydrogen ion, electrokinetic, acid leach.
Track and support rehabilitation for a mine company railroad
Authors: Raymond Gerald P
Published: April 2011

The initial support and tie foundation problems of a railroad track built in 1974 to carry axle loads 21% greater than presently (1998) permitted under interchange laws at a speed of 88 km/h are presented. Some of the concerns related to and affecting the final rehabilitation that resulted in a final satisfactory performance are documented. The foundation engineer's interest is directed to the ballast, the tie, and to a lesser extent the rail's behaviour. Cobble-sized (75-150 mm) river gravel was used as the source for the ballast in the rehabilitation. The ballast's satisfactory performance has permitted the establishment of guidelines for future use of this type source of material where suitable quarried rock is not available. The railroad's satisfactory performance after rehabilitation has proven that the design concepts involving 36 t (40 tons) axle loads operating on 60 kg/m (119 lb/yd) continuously welded rail, concrete ties, and ballast manufactured by crushing from a river aggregate were achievable.Key words: railway track, concrete ties, ballast aggregate, aggregate, crushed face, rail, 36 t (40 tons) axle loads.
Identification of preferential flow effects on hydraulic conductivity measurements using a fluorescent tracer
Authors: Al Tom A , Blowes David W
Published: April 2011

Core samples were collected from fractured and unfractured zones within fine-grained, unconsolidated mine tailings. The hydraulic conductivity of the core samples was measured in a constant-head permeameter. A fluorescent dye tracer was added to the constant-head reservoir in the permeameter. The tests were run for approximately 48 h, then the cores were sectioned to observe the distribution of dye. Flow through the fractures results in hydraulic conductivity measurements up to one order of magnitude greater than that of unfractured tailings. Observations of the dye distribution in samples following permeameter measurements are used to identify cases where preferential flow in fractures has influenced the hydraulic conductivity measurements. The dye tracer distribution also indicates where measurement errors may be suspected due to flow leakage around the core sample.Key words: tracers, hydraulic conductivity, fractures, tailings.
Static and seismic passive earth pressure coefficients on rigid retaining structures
Authors: Soubra A -H
Published: April 2011

The passive earth pressure problem is investigated by means of the kinematical method of the limit analysis theory. A translational kinematically admissible failure mechanism composed of a sequence of rigid triangles is proposed. This mechanism allows the calculation of the passive earth pressure coefficients in both the static and seismic cases. Quasi-static representation of earthquake effects using the seismic coefficient concept is adopted. Rigorous upper-bound solutions are obtained in the framework of the limit analysis theory. The numerical results of the static and seismic passive earth pressure coefficients are presented and compared with the results of other authors.Key words: limit analysis, passive pressure, earthquake.
Soil-geotextile interface friction by direct shear tests
Authors: Lee K M , Manjunath V R
Published: April 2011

This paper describes large-size direct shear tests on soil-geotextile interfaces. Medium-grained, uniform sand and three varieties of woven and nonwoven geotextiles manufactured with different techniques are utilized to investigate the soil-geotextile interface friction coefficient (f*). Tests were carried out using an apparatus specifically designed for interface testing, and results were compared with those obtained from the conventional direct shear equipment. The results obtained from this study indicated that the determination of peak interface behaviour was not a trivial matter, as the results were significantly affected by the boundary and testing conditions of the testing apparatus. The residual interface behaviour was investigated by multiple reversal direct shear tests. Since the use of multiple reversal direct shear tests on the proposed apparatus can impose a high degree of shear displacement and stress uniformity on the soil-geotextile interface, a more reliable definition of the residual interface friction can be obtained. The results indicate that woven-nonwoven geotextile interfaces exhibit a significant postpeak strength loss after a number of shear cycles. In the case of woven geotextiles, this is attributed to the opening up of the filaments associated with the physical damage caused during shear, whereas for nonwoven geotextiles it is due to the pulling out or tearing of filaments.Key words: geotextile, direct shear test, interface friction coefficient, peak shear strength, residual shear strength.
On the reduction of tertiary radicals by samarium diiodide (SmI2)
Authors: Nagashima Tadamichi , Rivkin Alexey , Curran Dennis P
Published: April 2011

Reduction of o-iodophenyl 3-methylbut-2-enyl ether with samarium diiodide generates mixtures of 3-isopropyl-2,3-dihydrobenzofuran and 3-(2-propenyl)-2,3-dihydrobenzofuran along with a small amount of dimer. If a source of deuterium is present during the reduction, then the 3-isopropyl product predominates and this product is labeled with one deuterium. However, attempts to quench the putative tertiary organosamarium reagent by adding a deuterium source after the reduction were not very successful at room temperature. But at 0°C, the organosamarium reagent was generated (at least to the extent of about 50%, as measured by deuterium quenching), and its decomposition was followed over time by a series of quenching experiments. The results suggest that tertiary radicals are reduced to a significant extent by SmI2 to form an anionic (presumably alkylsamarium) species. This species is thermally unstable and decomposes to the corresponding reduced and eliminated products. The reduced product is consistently formed in slight excess over the eliminated one, and the mechanism of formation of these products is not yet clear.Key words: samarium diiodide, SmI2, reduction, alkyl samarium.
Neutral hyperconjugation and one-bond couplings between heavy atoms
Authors: Lambert Joseph B , Shawl Catherine E , Basso Ernani
Published: April 2011

The relationship has been examined between bond order and one-bond couplings involving heavy atoms, as modulated by neutral hyperconjugation. Two systems have been studied in which either an aromatic ring or a double bond can influence, through hyperconjugation, the α and β bonds (respectively, CiC and CiM in =C-C-M). Hyperconjugation may be modulated by substituents on the aromatic ring or double bond or by placement of different atoms (M = C, Si, Ge, or Sn) at the β position. The α bond exhibits no relationship between coupling constant and neutral hyperconjugation, but the β bond shows a strong relationship.Key words: hyperconjugation, germanium, σ-π conjugation, silicon, tin.
Heck reaction using palladium complexed to dendrimers on silica
Authors: Alper Howard , Arya Prabhat , Bourque S Christine , Jefferson Gary R , Manzer Leo E
Published: April 2011

Polyamidoamine dendrimers, constructed on the surface of silica, were phosphonated using diphenylphosphinomethanol (prepared in situ) and complexed to form a palladium-dimethyl TMEDA complex. This catalyst was found to be effective in the Heck reaction of aryl bromides with both butyl acrylate and styrene, affording coupling products in moderate to good yields. The heterogeneous palladium catalyst can also be recycled and reused with only moderate reduction in activity.Key words: dendrimer, Heck, palladium, silica.
A new strategy for synthesis of attached rings
Authors: Overman Larry E , Pennington Lewis D
Published: April 2011

The first investigation of the use of pinacol-terminated Prins cyclizations to form attached rings is reported. Treatment of triisopropylsilyl ethers of (Z)- or (E)-[2-(6,6-dimethoxyhexylidene)cyclohexanol with SnCl4 provides bicyclic products having attached rings. The approach is synthetically useful in the Z alkylidenecyclohexane series, proceeding selectively by a pathway involving carbon migration in the pinacol rearrangement step, to provide methoxy epimers of 1-(2-methoxycyclohexyl)cyclopentylcarboxaldehyde. Reaction of the corresponding E stereoisomer is more complex and yields a mixture of products resulting from both hydride and carbon migration in the pinacol rearrangement step.Key words: Prins cyclization, pinacol rearrangement, attached rings.
Calodendroside A: a taxifolin diglucoside from the stem bark of Ochna calodendron
Authors: Messanga Bernard Blaise , Sondengam Beibam Luc , Bodo Bernard
Published: April 2011

A new flavanone diglucoside, calodendroside A (1), was isolated from the methanolic extract of the stem bark of Ochna calodendron (Ochnaceae) and its structure elucidated as (2R,3R) taxifolin-3-O-glucosyl-(1> 2)-glucoside by means of chemical and spectroscopic evidence including 1H-1H and 1H-13C COSY NMR. The connection of the two sugar moities was determined by the use of the heteronuclear multiple bond connectivities experiment (HMBC). To our knowledge, the present report is the first describing the isolation of a flavonoid diglucoside from a member of the Ochnaceae family.Key words: Ochna calodendron, Ochnaceae, stem bark, flavanone diglucoside, calodendroside A.
Distribution of microamounts of some M2+ions during ZnSO4·7H2O crystallization
Authors: Smolik Marek
Published: April 2011

Distribution coefficients (D) of trace amounts of Ni2+, Co2+, Mg2+, Cd2+, Cu2+, Mn2+, Ca2+, and Fe2+have been determined during crystallization of ZnSO4·7H2O. Their dependencies on the ionic radii of M2+ions, solubilities and structures of the corresponding sulfates as well as their abilities to form solid solutions with ZnSO4·7H2O have been analyzed. The D values are in the range <0.006 (DCa) - 1.61 (DNi) and depend mainly on similarity of the structures of the corresponding sulfates and the ability of MSO4·nH2O to form solid solutions with ZnSO4·7H2O. The order of lowering some of the determined distribution coefficients (DNi> DMg> DCo> DFe> Dcu) exactly agrees with increase of the deformation trend of octahedral coordination of corresponding ions resulting from their electronic configuration. The D coefficients do not depend on similarity of size of ionic radii of microcomponent (rM2+) to macrocomponent (rZn2+), however for ions forming monoclinic sulfate hydrates at 20°C (Co2+, Fe2+, Cd2+, Ca2+) this dependence of distribution coefficients on rM2+is linear in a plot of log D against ionic radius. The effect of solubilities of corresponding sulfates in water on the D coefficients is complex and clouded by crystal-chemical factors.Key words: crystallization, zinc(II) sulfate heptahydrate, cocrystallization, distribution coefficients D (Henderson-Kracek, Khlopin), distribution of trace impurities.
Antiviral activity of arylnaphthalene and aryldihydronaphthalene lignans
Authors: Cow Christopher , Leung Carmen , Charlton James L
Published: April 2011

A practical method for large scale synthesis of 1-arylnaphthalene and 1-aryl-1,2-dihydronaphthalene lignans is described. The method makes use of the classic Stobbe condensation followed by regioselective reactions that provide access to both the common and retrolactone lignans, e.g., 2 and 3. A total of 25 compounds, many of which are known natural products, were prepared and their antiviral activity against human cytomegalovirus measured.Key words: lignan, Stobbe, arylnaphthalene, antiviral.
Di[(hydroxyalkyl)dimethylammonium] tris[benzene-1,2-diolato(2)]silicates and their germanium analogs: syntheses, crystal structure analyses, and NMR studies
Authors: Tacke Reinhold , Stewart Alistair , Becht Joachim , Burschka Christian , Richter Ingo
Published: April 2011

Treatment of Si(OMe)4 with three molar equivalents of 1,2-C6H4(OH)2 (= 1,2-dihydroxybenzene) and two molar equivalents of HO(CH2)nNMe2 (n = 2, 3) in acetonitrile at room temperature yields the λ6Si-silicates (HO(CH2)nNMe2H)2(SiL3) (5: n = 2; 6: n = 3; L2 = 1,2-C6H4(O)22 (= benzene-1,2-diolato(2))). The analogous λ6Ge-germanates (HO(CH2)nNMe2H)2(GeL3) (7: n = 2; 8: n = 3) were synthesized analogously starting from Ge(OMe)4. Compounds 5·2CH3CN and 6-8 were structurally characterized by single-crystal X-ray diffraction. In addition, aqueous solutions of the Si/Ge analogs 5/7 and 6/8 were studied by NMR spectroscopy. The title compounds may be regarded as model systems for the transport and storage of silicon in biological systems and as tools to investigate biosilification.Key words: hexacoordinate silicon, hexacoordinate germanium, silicon biochemistry
Addition reactions of a dialkyl- and a diarylsilylene to cyanides RCN: Different pathways? (1)
Authors: Weidenbruch Manfred , Meiners Frank , Saak Wolfgang
Published: April 2011

Di-tert-butylsilylene, generated by photolysis of hexa-tert-butylcyclotrisilane, reacts with the triple bond of adamantane-1-carbonitrile to furnish the 1,3-diaza-2,5-disilacyclohexa-3,6-diene 5. However, treatment of 2,2-dimethylpropanenitrile with dimesitylsilylene affords the azadisilacyclobutene ring system 6. The structures of 5 and 6 were determined by X-ray crystallography.Key words: silicon, silylene, silaheterocycles, X-ray crystallography.
Adducts of sila-, germa-, and stannaethenes Me2E=C(SiMe3)2 (E = Si, Ge, Sn) with anthracene: syntheses, structures, thermolyses
Authors: Wiberg Nils , Wagner Susanne , Vasisht Sham-Kumar , Polborn Kurt
Published: April 2011

The [4 + 2] cycloadducts of Me2E=C(SiMe3)2 (E = Si, Ge, Sn) and anthracene are prepared by reaction of an excess of anthracene in benzene with the [2 + 2] cycloadduct of Me2Si=C(SiMe3)2 and Ph2C=NSiMe3 at 130°C, with Me2Ge(OPh)-CLi(SiMe3)2 at 100°C, and with Me2SnBr-CNa(SiMe3)2 at 80°C, respectively. The mentioned adducts act as sources for the ethenes Me2E=C(SiMe3)2 above 100°C, the intermediate formation of which has been demonstrated by trapping experiments with 2,3-dimethylbutadiene (formation of a [4 + 2] and an ene reaction product). The half life time of the anthracene adducts with E = Si, Ge, and Sn in the presence of DMB (= 2,3-dimethylbutadiene) in benzene on thermolysis at 130°C (first order reactions) is found to be 141, 12, and 0.3 h, respectively. In the absence of DMB, thermolysis of the cycloadducts leads in benzene as reaction medium exclusively to the dimers of the Me2E=C(SiMe3)2 intermediates. In toluene as reaction medium ene products of Me2E=C(SiMe3)2 are observed in addition to the dimers. The ene products are not isolable as such, but only after migration of the Me2E-CH(SiMe3)2 substituents. The formed derivatives C6H5CH2EMe2CH(SiMe3)2 of toluene in part give a second ene reaction with another Me2E=C(SiMe3)2 molecule. X-ray structure analyses of the mentioned sources in fact prove the latter to be normal [4 + 2] cycloadducts of Me2E=C(SiMe3)2 and anthracene.Key words: silaethene, germaethene, stannaethene, [4 + 2] anthracene adducts, [4 + 2] cycloadditions and reversions, ene reactions, X-ray structure analyses.
A solid-state 133Cs nuclear magnetic resonance and X-ray crystallographic study of cesium complexes with macrocyclic ligands
Authors: Wong Alan , Sham Simon , Wang Suning , Wu Gang
Published: April 2011

We report solid-state NMR determination of the 133Cs chemical shift anisotropy (CSA) for a series of cesium complexes with macrocyclic ligands. It was found that the isotropic 133Cs chemical shifts are related to the number of oxygen atoms to which the Cs+ ion is coordinated. The 133Cs chemical shifts were found to correlate with average Cs-O distances. We also attempt to use the established correlation to deduce Cs+ coordination environment for compounds with unknown structures. We also report the X-ray determination of the crystal structure for Cs(DB18C6)2SCN1/2CH3OH1/2H2O. The compound crystallizes in monoclinic, a = 14.503(2), b = 15.152(3), c = 39.989(6) Å, β = 90.796(8)°, space group P21/c, Z = 8. There are two independent molecules in the asymmetric unit cell where each of the two Cs+ ions is coordinated to two DB18C6 ligand molecules forming a sandwich-type structure.Key words: solid state NMR, alkali metal, 133Cs chemical shift, macrocyclic ligand, crystal structure.
An unusually large secondary α-deuterium kinetic isotope effect in hydride ion SN2 reactions
Authors: Koerner Terry , Westaway Kenneth Charles , Poirier Raymond A , Wang Y.
Published: April 2011

Theoretical calculations at the HF/6-31+G* level suggest the secondary α-deuterium kinetic isotope effects for hydride ion SN2 reactions are much larger than expected for the structure of the transition state. The secondary α-deuterium kinetic isotope effects for the SN2 reactions between sodium borohydride (hydride ion) and para-methyl- and para-chlorobenzyl chlorides are much larger than expected as the theoretical calculations suggest. It appears the secondary α-deuterium isotope effects are larger than expected for the structure of the SN2 transition state because the hydride ion is too small to affect the CαH(D) out-of-plane bending vibrations in the transition state.Key words: secondary α-deuterium kinetic isotope effects, SN2, nucleophilic substitution, transition state, substituent effects.
CP/MAS NMR and X-ray crystallographic characterization of trans-PdX2(PPh2vinyl)2 (X = Cl, I); UV and Et2O·BF3 reaction studies, including the formation of [Pd(µ-Cl)(PPh2vinyl)2]2[BF4]2
Authors: Hursthouse Michael B , Kelly David G , Light Mark E , Toner Andrew J
Published: April 2011

The complexes PdCl2(PPh2vinyl)2 and PdI2(PPh2vinyl)2 have been prepared and crystallographically characterized as their trans square planar isomers. Trans-PdCl2(PPh2vinyl)2 exists in a centrosymmetric structure with a planar PdCl2P2 core whereas trans-PdI2(PPh2vinyl)2 shows no local Pd-centred symmetry and significant distortion of the PdI2P2 core from planarity. Crystallographic data is in accord with the 31P{1H} CP/MAS NMR spectra of the two complexes, which display a single resonance for the chloro-complex and two resonances for the iodo-complex. UV irradiation of CH2Cl2 solutions of PdCl2(PPh2vinyl)2 followed by re-dissolution in CDCl3 indicates no permanent chemical change. However, post-irradiation CP/MAS 31P{1H} NMR spectroscopy demonstrates the presence of trans-PdCl2(PPh2vinyl)2 in two solid state structures, plus cis-PdCl2(PPh2vinyl)2. PdI2(PPh2vinyl)2 exists only in its trans form in both solid state and solution. Irradiation results in phosphine displacement and the formation of sym-[PdI2(PPh2vinyl)]2 and free phosphine, the latter being characterized as Ph2P(O)vinyl following aerobic oxidation. PdCl2(PPh2vinyl)2 reacts in the presence of Et2O·BF3 to afford [Pd(µ-Cl)(PPh2vinyl)2]2[BF4]2 whereas PdI2(PPh2vinyl)2 is recovered in 95% yield, with the remaining material undergoing phosphine abstraction to form sym-[PdI2(PPh2vinyl)]2.Key words: palladium, phosphine, alkene, isomerization, CP/MAS.
Electrochemical studies of Schiff base compounds derived from antipyrine nucleus in ethanolic buffer solutions
Authors: El-Hallag Ibrahim S , El-Hefnawy Gad B , Moharram Youssef I , Ghoneim Enass M
Published: April 2011

The electrochemical behaviour of Schiff base compounds derived from an antipyrine nucleus was investigated in 30% (v/v) ethanolic buffer solutions (pH 3-11) using various electrochemical techniques at mercury electrode. The results showed that, the total limiting current of each of the studied compounds corresponds to 2-electron transfer process. The mechanistic pathway of the electrode reaction of the investigated compounds at mercury electrode, the effect of the medium, and the evaluation of the electrode reaction parameters were illustrated and discussed.Key words: Schiff base, antipyrine nucleus, electrode reaction, electrochemical parameters, cyclic voltammetry.
A low temperature reversible phase transition for 1,1'-bis-(ferrocenyldimethylsilyl)ferrocenylene, (η5-FcSiMe2C5H4)2Fe, an oligomeric model for silyleneferrocenylene polymers
Authors: Antipin Mikhail Yu , Vorontsov Ivan I , Dubovik Irene I , Papkov Vladimir , Cervantes-Lee Francisco , Pannell Keith H
Published: April 2011

We have reinvestigated the solid state structure of 1,1'-bis-(ferrocenyldimethylsilyl)ferrocenylene, (η5-FcSiMe2C5H4)2Fe, Fc = (η5-C5H5)Fe(η5-C5H4). Using a DSC technique we observed a reversible phase transition for this compound at 169(3)K with ΔH = 1.1 kJ/mol, and ΔS = 6.54 J/mol K. A single crystal X-ray diffraction study has demonstrated that this phase change involves a transformation from a high temperature phase, space group P21/c, Z = 2, to a triclinic low temperature phase, space group P[Formula: see text], Z = 4. The phase transition involves the loss of the molecular crystallographic center of symmetry and rotations about the terminal and central cyclopentadienyl ring pairs. The results are compared to those reported for ferrocene.Key words: solid state, phase transition, silyleneferrocenylene.
Reaction of dimethoxycarbene with strained cyclic carbonyl compounds
Authors: Venneri Paul C , Warkentin John
Published: April 2011

A cyclopropanone, a cyclopropenone, cyclobutanones, a cyclobutane-1,3-dione, and a cyclobutene-1,2-dione reacted with dimethoxycarbene to afford acetals of the next larger ring by formal insertion of the carbene into a CC bond α to the carbonyl group. When either of two saturated α-ring carbons could be involved in the process, the ring expansion was selective, affording primarily the product of apparent insertion into the more substituted ring bond. With 2,3-dimethoxycyclobutene-1,2-dione, insertion occurred between the carbonyl groups and with β-propiolactone it occurred at the lactone bond. β-Propiolactam, however, reacted by insertion of the carbene into the NH bond.Key words: β-propiolactone, cyclobutanone, cyclobutananedione, cyclopropanone, dialkoxycarbene.
The synthesis of pyrido(2,3,4-kl)acridine unit of some marine alkaloids
Authors: Ozturk Turan , McKillop Alexander
Published: April 2011

A simple and convenient synthesis of pyrido(2,3,4-kl)acridine (1), the main skeleton of some marine alkaloids, via cyclization and intramolecular nitrene insertion, is described. The importance of the planarity of the molecule during the nitrene insertion is explained.Key words: pyridoacridine, marine alkaloids, nitrene insertion, quinoline, quinolinone.
A tosyliminium ion-based total synthesis of (±)-schefferine
Authors: Bianchi Darío A , Kaufman Teodoro S
Published: April 2011

The synthesis of the phenolic tetrahydroprotoberberine alkaloid (±)-schefferine is reported, featuring as key steps a tosyliminium ion-mediated Friedel-Crafts alkylation of eugenol dimethyl ether and an intramolecular Mitsunobu-type amination.Key words: total synthesis, (±)-schefferine, natural product, tosyliminium ion, Mitsunobu amination.
Aqueous nonelectrolyte solutions. Part XVII. Formula of hydrogen sulfide hydrate and its dissociation thermodynamic functions
Authors: Glew David N
Published: April 2011

Literature data for the saturation vapor pressure P(hl1g) of hydrogen sulfide hydrate with water, at 43 temperatures between quadruple points Q(hs1l1g) at 0.4°C and Q(hl1l2g) at 29.484°C, are properly represented by a six-parameter equation to give a standard error (SE) of 0.13% on a hydrate pressure measurement of unit weight. Equilibrium hydrogen sulfide and water fugacities and the gas and aqueous phase compositions are derived using the RedlichKwong equation of state. Literature data for the saturation vapor pressure P(hs1g) of hydrogen sulfide hydrate with ice, at 15 temperatures between 1.249 and 21.083°C, are properly represented by a two-parameter equation to give a SE of 0.26% on a single hydrate pressure measurement. Quadruple point Q(hs1l1g) is evaluated at temperature 0.413° with SE 0.042°C and at pressure 94.7 with SE 0.26 kPa. Using the thermodynamic method, described for deuterium sulfide D-hydrate, the equilibrium fugacities of hydrogen sulfide are used to define 43 equilibrium constants Kp(h[Formula: see text]l1g) for hydrate dissociation into water and hydrogen sulfide gas. The temperature dependence of ln Kp(h[Formula: see text]l1g) is represented by a three-parameter thermodynamic equation which gives both values and standard errors (i) for Kp(h[Formula: see text]l1g), and for δHot(h[Formula: see text]l1g) and δCpot(h[Formula: see text]l1g), the standard enthalpy and heat capacity changes for hydrate dissociation and (ii) for n = r the approximate formula number of the hydrate H2S·nH2O at each experimental temperature. The formula H2S·6.119H2O with standard error 0.029H2O is found for hydrogen sulfide hydrate with water at lower quadruple point Q(hs1l1g) 0.413°C: an approximate formula H2S·5.869H2O with SE 0.026H2O is found at upper quadruple point Q(hl1l2g) 29.484°C. These estimates for the formula of hydrogen sulfide hydrate at its quadruple points are not significantly different from those found for the deuterium sulfide D-hydrate.Key words: clathrate hydrate of hydrogen sulfide, hydrogen sulfide hydrate, formula of hydrogen sulfide hydrate, thermodynamics of clathrate hydrate dissociation, dissociation equilibrium constant of hydrogen sulfide hydrate, standard enthalpy and heat capacity changes for dissociation of hydrogen sulfide hydrate.
The tamoxifen cation reacts to give indene products
Authors: Sanchez Cristina , McClelland Robert A
Published: April 2011

The tamoxifen carbocation (Ph(Ar)C=CPh-CH+-CH3, Ar = 4-Me2NCH2CH2OC6H4) is generated from acetate and sulfate precursors by SN1 ionization in water. The cation exists in (E) and (Z) forms which equilibrate before reaction. The major products are the α-hydroxytamoxifens Ph(Ar)C=CPh-CHOH-CH3, both (E) 64% and (Z) 29%, with the ratio independent of the configuration of the starting ester. Two minor products with a total yield of 7% account for the rest of the products. These have been characterized as indenes derived from intramolecular cyclization, a 4.5% yield of the indene derived from cyclization into the Ar ring with 2.5% due to cyclization into the phenyl ring. Experiments in acid solutions (0.01-0.1 M HCl) starting with pure (E)- or (Z)-α-hydroxytamoxifen reveal that the two alcohols equilibrate. This occurs by H+-catalyzed formation of the carbocation followed by water capture. Occurring about 10-fold slower than this isomerization is an irreversible process resulting in the two indenes. This cyclization will result in the destruction of the α-hydroxytamoxifens upon exposure to acidic conditions and also makes the direct observation of the tamoxifen carbocation under super-acid conditions difficult, if not impossible. The indenes do form in low yield whenever the tamoxifen carbocation is generated from an SN1 precursor. Thus these products could serve as markers for the formation of the tamoxifen carbocation in cellular systems or in in vivo experiments.Key words: carbocation, indene, allylic cation, isomerization.