bluuebunny/crossref_metadata_2025 huggingface dataset:
The influence of constitutive models on self-boring pressuremeter interpretation in clay
Authors: Pye Christropher Nigel
Published: April 2011

A comparison of the elastic-perfectly plastic (EPP) and hyperbolic (HB) theories for interpreting loading and unloading parts of self-boring pressuremeter (SBP) tests in clay is presented. Computer-aided modelling (CAM) is used to analyze 60 SBP tests in clay to obtain shear modulus (G), undrained shear strength (Su), and in situ total horizontal geostatic stress (σHo). It is shown that the technique of CAM is consistent, repeatable, and simple to use. For all tests analyzed by both models the inferred horizontal geostatic stresses are identical and comparable to "lift-off" measurements. A small systematic difference is found between the two models for the undrained shear strength of soft and stiff clays. The shear modulus valves derived from the EPP model are unrelated to the true modulus of the soil. There is, however, a semiempirical relationship between the HB model and pressuremeter unload–reload (UR) shear modulus. Key words : clay, self-boring pressuremeter, elastic-perfectly plastic, hyperbolic.
Triaxial relaxation testing of a frozen sand
Authors: Ladanyi Branko , Benyamina M.B.
Published: April 2011

The objective of this investigation was to evaluate the potential use of the laboratory stress relaxation test to determine the creep and strength properties of frozen soils. This paper presents the results of a series of laboratory step-loaded relaxation tests performed on frozen Ottawa sand under triaxial compression conditions and compares three different interpretation methods for deducing from the test results the creep and strength parameters of frozen soils. Key words : frozen sand, triaxial test, relaxation, creep parameters.
In situ creep of frozen soil, Fenghuo Shan, Tibet Plateau, China
Authors: Wang B. , French Hugh M.
Published: April 2011

Field measurements of frozen soil creep in the upper 3.0 m of permafrost indicate that creep occurs in both winter and summer. Between 1992 and 1993, the mean rate of creep ranged from 0.44 cm at 1.6 m depth to 0.16 cm at 2.8 m depth but there was extreme variability. Creep parameters n and A, as defined by the power flow law, were calculated from field data. Parameter n ranged between 1.96 and 2.29 and increased with depth, while A decreased with depth. Comparisons of creep rates for different permafrost environments suggest that ground temperature largely controls the magnitude of permafrost creep. Key words : permafrost, creep parameters, Tibet Plateau.
Yielding of sensitive clays: micromechanical considerations
Authors: Prasad K Nagendra , Murthy BR Srinivasa , Vatsala A , Sitharam T G
Published: April 2011

Test results reported on several natural sensitive soils show significant anisotropy of the yield curves, which are generally oriented along the coefficient of earth pressure at rest (K0) axis. An attempt is made in this paper to explain the anisotropy in yielding from microstructural considerations. An elliptic pore, with particle domains aligned along the periphery of the pore, and with the major axis of the pore being oriented along the direction of the in situ major principal stress, is chosen as the unit of microstructure. An analysis of forces at the interdomain contacts around the ellipse is carried out with reference to experimentally determined yield stress conditions of one soil, and a yield criteria is defined. The analysis, with the proposed yield criteria, enables one to define the complete yield curve for any other soil from the results of only two tests (one constant eta compression test with eta close to eta sub K0, where eta is the stress ratio (= q/p) and eta sub K0 is the stress ratio corresponding to anisotropic K0 compression, and another undrained shear test). Predicted yield curves are compared with experimental yield curves of several soils reported in the literature.Key words: sensitive clays, yield criteria, anisotropy, microstructure.
Strain-rate effects in pressuremeter testing using a cuboidal shear device: experiments and modeling
Authors: Penumadu Dayakar , Skandarajah Arumugam , Chameau Jean-Lou
Published: April 2011

The objective of the present research was to study the effect of rate of probe expansion in pressuremeter testing for cohesive soil. Emphasis in this paper was given to quantifying and modeling the effect of strain rate on the undrained shear strength. The strain path followed by an element of clay adjacent to the expanding probe was simulated using an automated flexible boundary cuboidal shear device (CSD) typically up to a magnitude of strain level of 10%. Two types of soil (kaolin, kaolin-silica mix) were used consistently for all the testing. Repeatable cubical cohesive specimens were obtained from a high water content slurry consolidation technique. K0consolidation was performed by using a constant vertical stress - zero lateral strain boundary condition using a closed-loop pneumatic system. A series of strain-controlled tests with increasing strain rates from 0.01 to 5%/min was performed under undrained conditions. The effects of increase of strain rate on shear stress - strain behavior and undrained shear strength were quantified. A numerical model based on cylindrical cavity expansion theory which accounts for higher strain rate and its variation with radial distance from an expanding probe membrane was calibrated using the single-element CSD test data.Key words: strain rate, pressuremeter, stress-strain, shear strength, strain path, cavity expansion.
Bearing capacity of model piles driven into dense overconsolidated sands
Authors: Foray P , Balachowski L , Colliat J -L
Published: April 2011

Model piles were driven into dense siliceous sand samples and tested in a large calibration chamber. Axial tension and compression tests were performed on open-ended pipe piles. The objective of this research was to study the effect of overconsolidation on the bearing capacity of piles driven into dense sands representative of North Sea soil conditions. Emphasis was put on points of interest for the offshore petroleum industry in particular: dense to very dense normally consolidated (NC) and overconsolidated (OC) sands, unit end bearing and unit skin friction capacities, and comparison with tip resistances from cone penetration tests. Design parameters are proposed for computing the axial bearing capacity of piles driven into dense to very dense siliceous sands. They are compared with those given in the current American Petroleum Industry's Recommended Practice 2A document. A relationship between CPT cone resistance and ultimate unit end bearing and skin friction capacities of piles is also proposed.Key words: model test, dense sand, offshore pile driving, axial capacity, end bearing, skin friction, design parameters, cone penetrometer.
Modélisation du comportement du milieu granulaire en fonction de l'écrasement des grains
Authors: Rahma Afif
Published: April 2011

The influence of grain crushing under high stress levels is introduced in the elasto-plastic constitutive law (Hujeux's model) using additional variables that change with the physical and mechanical properties of the grains. These variables are defined as functions of the amount of dissipated plastic work, which is proposed as a parameter for describing the material yield. The results of computer simulations along oedometric and triaxial paths indicate a very good agreement between the experimental curves and the numerical solutions. The proposed modifications are therefore validated.Key words: correlation, grain crushing, constitutive law, modelization, plastic work.[Journal translation]
A strain rate dependent constitutive model for clays at residual strength
Authors: Wedage AMP , Morgenstern N R , Chan D H
Published: April 2011

Plasticity theory is extended to incorporate strain rate effects on the residual shear strength of clays. The clay is assumed to behave elastically before yielding and then in a perfectly plastic manner with no volume change during yielding. The Mohr-Coulomb failure criterion is used in the rate-dependent model in which the strain rate affects the mobilized effective friction angle of the material. During initial yielding and subsequent plastic deformation, the stress and strain states at a point will satisfy the rate-dependent yield function (loading function). When the effective plastic strain rate decreases to a threshold strain value, the loading surface moves, or collapses, to the static yield surface. A constant volume flow rule is used to calculate plastic deformation. The computed stress-strain relationship is formulated in two parts, namely a rate-independent part and a rate-dependent part. The rate-independent part is the same as that used in classical elastoplastic formulations, whereas the rate-dependent part is dependent on the current strain rate of the material. The use of the model is illustrated using a numerical example simulating a two-dimensional plane strain test.Key words: constitutive relationship, finite element, plasticity theory, pre-sheared clay, rate effects, residual strength.
A hyperbolic model for volume change behavior of collapsible soils
Authors: Habibagahi G , Mokhberi M
Published: April 2011

Finite element computer programs are frequently used to analyze and design embankments and similar earth structures. In most of the available computer programs, lack of a proper constitutive relationship to deal with volume change when an increase in the degree of saturation occurs, namely collapse phenomena, is a major handicap. In this paper, volume change results obtained from isotropic compression tests conducted on unsaturated compacted soil specimens are presented. Dependence of the bulk modulus of the soil on water content is investigated. Next, a hyperbolic formulation for volume change behavior of unsaturated soils taking into account variation of soil water content is presented. This hyperbolic model relates mean applied stress, volume change, and water content and represents a three-dimensional surface, the so-called "state surface". Suitability of the proposed model to predict collapse phenomena is verified by examining the model prediction against available experimental data.Key words: hyperbolic, unsaturated soil, collapse, volume change, suction pressure, bulk modulus.
Une méthodologie de cartographie des zones potentiellement instables Application à la région d'Al Hoceima (Maroc)
Authors: Margaa Khalid , Abdelgader Ahmed
Published: April 2011

The Al Hoceima region presents several instability features. Some zones remain relatively stable, but others are subject to signs of instability factors or to active slides. The aim of this study is to establish the different instabilities mapping and to define, in hierarchic order, their potential risk. This work was conducted by selecting all factors influencing stability : geological, hydrogeological, and geotechnical parameters, thus we develop a zoning procedure that permits us to quantify the potential hazards.This study shows that major potential hazards zones are essentially caused by the presence of weak cohesive layers (clay) interbedded within other, mostly stronger, formations in addition to the steep slopes, the intense fracturing, and the presence of a high piezometric surface.Finally, our results are proved by comparison to others obtained from the ZERMOS and P.E.R. cartography modes.Key words: Rif-Maroc, lithologie, évaluation, instabilité, cartographie.
Probabilistic analysis of consolidation with prefabricated vertical drains for soil improvement
Authors: Hong H P , Shang J Q
Published: April 2011

Prefabricated vertical drains are often used to accelerate the consolidation and to gain strength in soft clayey soils. The consolidation process depends on several uncertain parameters including the coefficients of consolidation and coefficients of permeability in vertical and horizontal directions and the discharge capacity of the vertical drains. A sensitivity analysis of the degree of consolidation to these uncertain parameters is presented for clayey deposits. Results of the analysis suggest that the most important uncertain parameter that affects the consolidation process is the horizontal coefficient of consolidation. The implication of this uncertain parameter in the design of prefabricated vertical drains for soil improvement is discussed. Two approaches are proposed for selecting drain spacing employing a design value of the horizontal coefficient of consolidation. One of the approaches is probability based and the other is minimum expected cost based.Key words: consolidation, prefabricated vertical drains, drain spacing, probability, expected cost, optimal design.
The influence of degree of saturation on the coefficient of aqueous diffusion
Authors: Lim P C , Barbour S L , Fredlund D G
Published: April 2011

The role of degree of saturation on the coefficient of diffusion of contaminants in the aqueous phase is presented and theoretical models for predicting the coefficient of diffusion at any degree of saturation are described. Three predictive models were developed based on three different diffusion modes: diffusion in parallel and series arrangements and combination of both. Diffusion tests were conducted on a sand at various water contents ranging from saturation to the residual degree of saturation using potassium and chloride ions as tracers to verify the applicability of the models. Results from the diffusion tests showed a decrease in effective diffusion coefficient of potassium with a decrease in degree of saturation. The functional relationship between the normalized diffusion coefficient for potassium and the degree of saturation is slightly nonlinear. The results for chloride also showed a decreasing trend, although the data were quite scattered and further verification is needed. Model verification based on the results for potassium showed that among the three models proposed, the model which combines the diffusion pathways in parallel and series arrangements provides the best fit to the experimental data.Key words: unsaturated, contaminant transport, aqueous diffusion, degree of saturation.
Using geographic information system and knowledge base system technology for real-time planning of site characterization activities
Authors: Tsai Yi-Chang , Frost J David
Published: April 2011

Site characterization activities involving a variety of different tools and techniques are a key component of any environmental rehabilitation program. Depending on the specific characteristics and requirements of the project, a range of tools can be used to characterize the surface and subsurface conditions. The results will be subject to specific limitations which will apply to a particular tool in terms of the depth investigated and the resolution of the measurements obtained as a result of the sensor capacity and background noise conditions. This paper presents a methodology that can be used to evaluate the relative merits of alternative sampling plans for a site and assist in identifying the optimal sampling plan taking into account the amount and type of prior information. This methodology allows new test results to be incorporated in real time as "prior information" as the site investigation proceeds. The methodology is implemented using a geographic information system (GIS) and a knowledge base system (KBS). Factors considered in the methodology include the effective measured area, the likely target characteristics, surface and subsurface noise conditions, and the level of confidence that exists about the possible source location as a result of prior studies at the site. The results of a sensitivity study are presented. An example is used to demonstrate the capability of the prototype system to assess different test configurations.Key Words: characterization, GIS, KBS, planning, quality.
The behavior of loose gassy sand
Authors: Grozic J L , Robertson P K , Morgenstern N R
Published: April 2011

Methane gas, found in loose deltaic deposits, can contribute to the triggering of flow liquefaction of submarine slopes. The behavior of loose gassy sand is studied in the laboratory using monotonic consolidated undrained triaxial compression tests. Samples consisted of reconstituted Ottawa sand prepared to degrees of saturation ranging from 80 to 100%. Gas contents were determined using a time domain reflectometry miniprobe with a series of calibrations relating apparent dielectric constant to degree of saturation. The results indicate that loose gassy sands can strain soften and experience flow liquefaction. If the degree of saturation is lower than the "cut-off" value, for a specific void ratio, flow liquefaction will not occur.Key words: triaxial testing, liquefaction, Ottawa sand, gassy, unsaturated.
Landslide risk assessment: prediction of travel distance
Authors: Finlay P J , Mostyn G R , Fell R
Published: April 2011

The Geotechnical Engineering Office of Hong Kong database of landslides for the period 1984-1993, containing over 3000 landslide records, and data for major landslides before this period were made available for a landslide risk assessment study. Data from over 1100 of these landslides in man-modified slopes were collated, processed, and analyzed statistically. Multiple regression models, based on slope geometry, were developed for the prediction of landslide travel on a horizontal surface below the slope. Although developed for slopes in Hong Kong, the models can be applied in similar geological situations (weathered granite and other weathered volcanics) and are suited for landslide risk zoning in areas below man-modified slopes and for the assessment of risks from individual cuts and fills.Key words: landslide, travel distance, risk, risk assessment.
The bearing capacity of saline ice sheets: centrifugal modelling
Authors: Langhorne P J , Stone KJL , Smith C C
Published: April 2011

Artificial sea ice sheets have been frozen in a centrifuge using novel techniques which yield reproducible ice growth rates and result in ice sheets of uniform thickness. The upper surface of these ice sheets has been subjected to an increasing load applied over a limited area, the maximum sustained load giving the bearing capacity at high inertial acceleration. Such centrifugal modelling techniques produce ice sheets with bearing capacities in agreement with existing field and laboratory data. In particular, the influence of indentor diameter and loading rate is examined and the centrifuge data are found to behave in the same manner as existing data with respect to both of these variables. All data are compared with a number of theoretical descriptions of bearing capacity, and these comparisons are discussed with regard to their impact on the applicability of the centrifuge modelling technique on ice penetration problems.Key words: centrifugal modelling, sea ice, bearing capacity.
Some insights into the performance of an experimental soil cover near London, Ontario
Authors: Simms Paul H , Yanful Ernest K
Published: April 2011

An experimental soil cover constructed near London, Ontario, 23.2 m × 15.2 m in plan area, has been monitored for 2 years for percolation and water-content data. The cover was a multilayer system consisting of a compacted till barrier soil placed between evaporation and drainage barriers of sandy gravel. Half of the cover was capped with coarse stone to prevent erosion and the other half was covered with topsoil to facilitate revegetation. High percolation rates and substantial desiccation of the barrier soil were reported under the topsoil protection layer. Unsaturated-saturated liquid and vapour flow modelling shows that the topsoil may act as a capillary barrier to infiltration, thereby promoting desiccation of the underlying compacted till. Percolation through the cover was measured using lysimeters filled with 5-16 cm (2-6 in.) diameter stone placed directly underneath the compacted till. Though the field lysimeters report water and laboratory tests show no evidence of flow partitioning between coarse stone and gravel, two-dimensional unsaturated-saturated liquid flow modelling of the lysimeter-cover interaction predicts that the lysimeters should not report significant water. Phenomena not simulated by the modelling, which include macrostructure flow in the barrier soil, trickle flow in the coarse stone, and vapour diffusion, are investigated and discussed. Consideration of vapour flow yields results that are inconsistent with the predictions of the liquid flow modelling. Key words: capillary barrier, lysimeters, soil covers, unsaturated flow, vapour flow.
Undrained shear strength of clean sands to trigger flow liquefaction
Authors: Yoshimine M , Robertson P K , (Fear) Wride C E
Published: April 2011

This paper attempts to evaluate the undrained shear strength of sand during flow failures, based on both laboratory testing and field observations. In the laboratory, the minimum shear resistance during monotonic loading was taken as the undrained strength, based on the criterion of stability. Triaxial compression, triaxial extension, and simple shear test data on clean sand were examined and it was revealed that the undrained shear strength ratio could be related to the relative density of the material provided that the initial stress, piprime, was less than 500 kPa. Three previous flow failures involving sand layers with relatively low fines contents and reliable cone penetration test (CPT) data were studied. Using existing calibration chamber test results, the Toyoura sand specimen densities in the laboratory tests were converted to equivalent values of CPT penetration resistance. The undrained shear strengths measured in the laboratory for Toyoura sand were compared with those from the case studies. It was found that the behaviour of sand in simple shear in the laboratory was consistent with the field performance observations. Triaxial compression tests overestimated the undrained strengths, and triaxial extension tests underestimated the undrained strengths. From both the simple shear test result and the CPT field data, the threshold value of clean sand equivalent cone resistance for flow failure was detected. Based on these observations, a CPT-based guideline for evaluating the potential for flow failure of a clean sand deposit is proposed. Key words: liquefaction, flow, laboratory testing, in situ test, case histories.
Numerical simulation of debris flows
Authors: Chen H , Lee C F
Published: April 2011

A key requirement in the assessment of landslide risk in such densely populated urban areas as Hong Kong consists of the prediction of potential runout distance or the extent of the subsequent debris flow. This paper presents a three-dimensional dynamic model of unsteady gravity-driven debris flow. The Lagrangian Galerkin finite element method is used to determine the nodal velocity and depth of soil column elements within the sliding mass, with the momentum and mass conservation mathematically closed within the soil column elements. The numerical solution also features a lumped mass matrix and a volume-weighted procedure. The method of least squares approximation plays a smoothing role which enhances stability and efficiency of the numerical solution scheme. The nodal elevation during sliding is obtained via a dynamic bilinear interpolation of the elevation function for the base of the sliding mass. Furthermore, the accuracy, robustness, and generality of this method are validated by experimental results. Its application to the Shum Wan Road landslide and the Fei Tsui Road landslide, both of which occurred during a heavy rainstorm in Hong Kong on 13 August 1995 and involved fatalities, gives reasonable results in comparison to the field observations. A variety of rheological constitutive relationships have already been coded in the present program to provide flexibility and adaptability in practical applications.Key words: debris flows, three-dimensional dynamic model, runout distance.
Undrained anisotropy ofK0-consolidated silt
Authors: Zdravkovic Lidija , Jardine Richard J
Published: April 2011

Direct measurements of the initial shear strength and yielding anisotropy of a dense, K0-consolidated silt are described and interpreted within a bounding-surface framework. The experiments were performed using the Imperial College large hollow cylinder apparatus, in which samples were sheared undrained with a range of orientations, α, of the major principal stress, σ1, following initial K0consolidation. The interpretation is aided by data from oedometer and triaxial stress path tests. Strongly anisotropic stiffness, yielding, undrained strength, and mobilized angle of shearing resistance, ϕ', characteristics are revealed. The effects of drained and undrained stress changes applied to the samples after K0consolidation are also described.Key words: anisotropy, hollow cylinder, K0consolidation, silt, bounding surface.
Mass loading and the rate of clogging due to municipal solid waste leachate
Authors: Rowe R Kerry , Armstrong Mark D , Cullimore D Roy
Published: April 2011

The results of laboratory column tests conducted to assess the effect of the mass loading on the clogging of porous media are presented. The tests were conducted using actual leachate from the Keele Valley Landfill under saturated, anaerobic conditions. It is shown that clogging is greatest where there is the greatest mass loading (near the inlet in this case, but likely near the collection pipes in a field situation). An empirical relationship between the hydraulic conductivity and drainable porosity is presented. Even though it is shown that higher flow rates give rise to less efficient bioreactors, the columns with high flow still experience greater rates of clogging than those with low flow. The columns were found to be severely clogged when the drainable porosity had decreased to about 10% of the initial value. The bulk (wet) density of the clog material is found to range between 1.6 and 2 Mg/m3 and, on a dry mass basis, 27% of the clog is calcium and 47% is carbonate. The columns were colonized by a diverse consortium of bacteria including methanogens, sulfate-reducing, and denitrifying bacteria, with methanogens being dominant in the portion of the column where clogging was most severe.Key words: leachate collection, clogging, porous media, mass loading, flow rate, anaerobic, microbial.
Determination of passive earth pressure coefficients by the method of triangular slices
Authors: Zhu Da-Yong , Qian Qihu
Published: April 2011

A new procedure is proposed for determination of passive earth pressure coefficients using triangular slices within the framework of the limit equilibrium method. The potential sliding mass is subdivided into a series of triangular slices, rather than vertical slices as usual, with inclinations of the slice bases to be determined. The forces between two adjacent slices (interslice forces) are expressed in terms of interslice force coefficients, and recursive equations for solving interslice coefficients are derived. By using the principle of optimality, the critical inclinations of slice bases, minimum interslice force coefficients, and passive earth pressure coefficients are determined. A form of function for describing the distribution of interslice force inclination (interslice force function) is suggested and the scaling parameter contained in the function is determined by satisfying the moment equilibrium condition for the final sliding mass. Comparisons are made with other accepted methods and tables for passive earth pressure coefficients are presented for practical use.Key words: passive earth pressure coefficient, retaining walls, limit equilibrium method, the principle of optimality.
Modèle de comportement dynamique cyclique de sols en grandes déformations
Authors: Jouanna Paul , Mabssout Mokhtar
Published: April 2011

A two-parameter cyclic empirical law, as used traditionnally by the engineer, is not able to fit the dynamic behaviour of soils under large strains. When simulating the classical laboratory results, a Hardin-Drnevich law associated with Masing's rule, although able to fit satisfactorily the average strain modulus with only two parameters (Go, α), is not adapted for fitting the damping factor at moderate and high strains. To overcome this limitation, a modified empirical law with three parameters (Go, α, β) is proposed. According to the initial law, parameter Gocharacterizes low strains and parameter α allows simulating the average modulus. The extra parameter β is used for adjusting the damping factor, as obtained by Masing's rule, to the experimental results at high strain.Key words: soil behaviour, dynamic, cyclic, large deformation, hysteresis, damping.
Medium-sized cyclophanes. part 51. Acylation of [2.2]metaparacyclophanes: through-space electronic interactions between two benzene rings
Authors: Yamato Takehiko , Tokuhisa Kiwamu , Tsuzuki Hirohisa
Published: April 2011

The acylation of 8-methyl- (1b) and 8-methoxy[2.2]metaparacyclophane 1c with 1.1 equiv. of acetyl chloride in CS2 solution in the presence of aluminum chloride afforded 15-acetyl-8-methyl- (2b) and 12-acetyl-8-methoxy[2.2]metaparacyclophanes (3c) with 65 and 41% yields, respectively. The different orientations for the electrophilic substitution were observed to be dependant on the substituent at the 8 position. On the other hand, when the same reaction was carried out under the same reaction conditions with the corresponding 5-tert-butyl derivatives (11), ipso-acetylation at the tert-butyl group was observed along with acetylation on the para-benzene ring. The substituent effect on the 8-position was also observed in the present ipso-acetylation. The ipso-acylation at the tert-butyl group of 5-tert-butyl-8-methoxy[2.2]metaparacyclophane (11c) is attributed to the highly activated character of the aryl ring and the increased stabilization of a sigma-complex intermediate arising from the dienone-type sigma-complex intermediate possible in the case of a internal methoxy substituent. However, the present ipso-acetylation has not been observed in mild reaction conditions such as acetyl chloride in the presence of TiCl4 catalyst due to deactivation of the second aromatic ring by the introduced acetyl group on the para-benzene ring. The mechanism of these novel reactions is also discussed.Key words: cyclophanes, electrophilic aromatic substitution, regioselectivity, through-space electronic interaction, ipso-acylation.
Solid state stereochemistry of crown ethers: X-ray crystal structure and 13C NMR studies of the LiNCS complex of 1,4,7,11-tetraoxacyclotetradecane
Authors: Buchanan G W , Driega A B , Yap G PA
Published: April 2011

The title complex is asymmetric in the crystal due to the spatial orientation of the NCS function. The space group has been determined to be P21 with a = 9.496(3), b = 8.736(3), c = 9.676(3) Å, β = 117.859(5)°, and Z = 2. The solid state 13C NMR spectrum is consistent with the lack of symmetry in the crystal and there is little evidence for large amplitude motion in the macrocycle as determined from the dipolar dephased spectrum.Key words: macrocyclic crown ether, lithium complex.
Preparation of homoallylic alcohols by reaction of aldehydes with η3-allyl- and η3-crotylmolybdenum complexes
Authors: Gable Kevin P , Shanmugham M Sundaram , White James D
Published: April 2011

η3-Allyl and η3-methallyl complexes of molybdenum react with aldehydes to give homoallylic alcohols in preparative yields when water is used as a proton source, but the scope of the reaction is narrowed in the case of the η3-crotylmolybdenum complex by the formation of both transposed and nontransposed products.Key words: molybdenum, allylation, chelate model, transposition.
Silver-catalyzed asymmetric amination of silyl enol ethers
Authors: Yamashita Yasuhiro , Ishitani Haruro , Kobayashi Shu
Published: April 2011

Catalytic amination of silyl enol ethers with azo diester compounds was investigated. It was shown that Cu(OTf)2 or AgOTf had high catalytic activity and that AgOTf was the most efficient among the catalysts tested in the reactions. In asymmetric reactions, the AgClO4-BINAP system showed high enantioselectivity. In a mixture of toluene or mesitylene and THF, silyl enol ethers reacted with dibenzyl azodicarboxylate (DBnAD) smoothly to afford the corresponding amination adducts in excellent yields with up to 86% ee.Key words: amination, amino acid, asymmetric synthesis, chiral catalyst, silver.
Organometallic oxides: preparation of the cluster [(η-C5Me5)Mo]4O7by reduction of [(η-C5Me5)MoCl(O)]2(μ-O) or (η-C5Me5)MoCl2(O)
Authors: Bottomley Frank , Sanchez Victor , Thompson Robert C , Womiloju Olusola O , Xu Zhiqiang
Published: April 2011

Reduction of [(η-C5Me5)MoCl(O)]2(μ-O) or (η-C5Me5)MoCl2(O) with sodium or magnesium amalgam, magnesium turnings, or tributyltin hydride produced [(η-C5Me5)Mo]4O7, with [(η-C5Me5)Mo(O)(μ-O)]2as a co-product. [(η-C5Me5)Mo]4O7was characterized by X-ray diffraction, mass spectrometry,1H NMR and IR spectroscopies, and magnetism. Crystals of [(η-C5Me5)Mo]4O7contained a tetrahedral [(η-C5Me5)Mo]4unit (Mo-Mo = 2.909 (3) Å) with the Mo4O7core having the structure Mo4(μ2-O(b))3(µ2-O(c))3(µ3-O(a)) (3). Microcrystalline samples of [(η-C5Me5)Mo]4O7were paramagnetic over the temperature range 2-300 K, with an effective moment of 1.26 μBat 300 K. [(η-C5Me5)Mo]4O7was also paramagnetic in chloroform solution, over the temperature range 223-298 K, with an effective moment of 1.43 µBat 298 K. The1H NMR spectrum showed a broad resonance at 16.3 ppm (Δν1/2= 113 Hz) and two narrow resonances at 1.89 ppm and 1.69 ppm (Δν1/2= 5 Hz). The magnetism and NMR spectra showed that [(η-C5Me5)Mo]4O7existed in two forms which were in equilibrium in solution. One form was paramagnetic (S = 1), with the Mo4O7core having the geometry 3, and the other was diamagnetic (S = 0), with the Mo4O7core having the geometry 4.Key words: cluster, cyclopentadienyl, molybdenum, oxide, paramagnetism.
Kinetics of acetal and orthobenzoate hydrolysis as probes of cyclodextrin-guest binding
Authors: Tee Oswald S , Hussein Samer MI , Turner Isabelle E , Yazbeck Ogaritte J
Published: April 2011

Acid-catalyzed hydrolysis of acetophenone dimethyl acetal (ADMA) and trimethyl orthobenzoate (TMOB) is retarded by cyclodextrins (CDs): α-CD, β-CD, hb-β-CD = "hydroxypropyl-β-cyclodextrin", and γ-CD. The observed first order rate constants (kobs) vary with [CD] in the manner expected for 1:1 binding between the substrates and the CDs. Similar behaviour was found recently for the hydrolysis of benzaldehyde dimethyl acetal (BDMA). With β-CD and hp-β-CD, the binding of all three substrates (BDMA, ADMA, TMOB) is strong and the CD-bound forms have very little reactivity. By contrast, substrate binding by α-CD is much weaker, and the CD-bound forms have appreciable, though reduced, reactivity. Substrate binding by γ-CD is also relatively weak, but the bound substrates have very low reactivities. The hydrolysis reactions of ADMA, TMOB, and BDMA have been evaluated as kinetic probes of the binding of guests to CD hosts. For α-CD, β-CD, and hp-β-CD, the addition of guests reduces the amount of free CD and thereby alleviates retardation of the hydrolysis by the CD. The resultant increases in hydrolysis rates can be analyzed to provide estimates of CD-guest dissociation constants, KG. For aliphatic alcohols and ketones binding to β-CD and hp-β-CD, all three probe reactions provide values of KG that agree well with each other and with literature values determined by other methods. The approach does not work well with α-CD because of its much weaker binding of the kinetic probes and their less pronounced dependence of kobs on [α-CD]. In the case of γ;-CD, the approach cannot be used because added guests cause a further lowering in the rate of hydrolysis, suggesting the formation of an unreactive ternary (substrate·CD·guest) complex.Key words: acetal, hydrolysis, cyclodextrin, host-guest, binding.
Photoinduced birefringence in copolymers containing Disperse Red 1 and styrene
Authors: Iftime Gabriel , Fisher Lana , Natansohn Almeria , Rochon Paul
Published: April 2011

A series of copolymers of 4'-[[[2-(methacryloyloxy)ethyl]ethyl]amino]-4-nitroazobenzene (DR1M) and an optically "inert" styrene comonomer were tested for photoinduced birefringence. The level of saturated birefringence increased linearly with the content of DR1M in the copolymer. The birefringence per mole of azo chromophore was constant along the copolymer series.Key words: azobenzene, photoinduced birefringence, copolymers, trans-cis isomerization.
Reductive deposition of Au3+(aq) on oxidized silicon surfaces
Authors: Süzer Sefik , Dag Ömer
Published: April 2011

X-ray photoelectron spectroscopy (XPS) is used to determine the oxidation state of gold deposited from an aqueous solution of AuCl4- on to various oxidized surfaces of silicon. Although the observed Au4f signal decreased with the thickness of the oxide layer, the oxidation state of Au was determined as 0 for all the samples analyzed. From the angular dependence of the Si2p and Au4f signals it was determined that Au is deposited on top of the oxidized surfaces of metallic silicon. It is postulated that from an aqueous solution of AuCl4-, gold would deposit in its zerovalent form on to any surface due to its large and positive electrochemical reduction potential (ε°red(Au3+ /Au) = +1.50 V) and the substrate plays a role only in providing active deposition sites. To further support the proposal, it is shown that the same process takes place even in inert and hydrophobic polypropylene substrates. Similarly, it is also shown that more gold deposits if the surface of the polypropylene is made less hydrophobic (but probably more active) via the industrially used corona discharge treatment.Key words: XPS, gold, electroless deposition, oxidized silicon surface.
Synthesis of 8-epi-castanospermine and 6,7,8-tri-epi-castanospermine
Authors: St-Denis Yves , Chan Tak Hang
Published: April 2011

8-epi-Castanospermine (11) and 6,7,8-tri-epi-castanospermine (12) were synthesized from the hydroxyproline precursor 13 which was obtained enantioselectively via an enzymatic process.Key words: castanospermine, synthesis of, enzymatic reduction, enzymatic resolution, asymmetric synthesis.
Nuclear magnetic shielding tensors for the carbon, nitrogen, and selenium nuclei of selenocyanates - a combined experimental and theoretical approach
Authors: Bernard Guy M , Eichele Klaus , Wu Gang , Kirby Christopher W , Wasylishen Roderick E
Published: April 2011

The principal components of the carbon, nitrogen, and selenium chemical shift (CS) tensors for several solid selenocyanate salts have been determined by NMR measurements on stationary or slow magic-angle-spinning powder samples. Within experimental error, all three CS tensors are axially symmetric, consistent with the expected linear geometry of these anions. The spans (Ω) of the carbon and selenium CS tensors for the selenocyanate anion (SeCN-) are approximately 300 and 800 ppm, respectively, much less than the corresponding values for carbon diselenide (CSe2). This difference is a consequence of the difference in the CS tensor components perpendicular to the C infiniti symmetry axes in these systems. Ab initio calculations show that the orbital symmetries of these compounds are a significant factor in the shielding. For CSe2, efficient mixing of the σ and π orbitals results in a large paramagnetic contribution to the total shielding of the chemical shielding tensor components perpendicular to the molecular axis. Such mixing is less efficient for the SeCN-, resulting in a smaller paramagnetic contribution and hence in greater shielding in directions perpendicular to the molecular axis.Key words: selenocyanates, solid-state NMR, carbon shielding tensors, nitrogen shielding tensors, selenium shielding tensors, ab initio calculations.
Analysis of the electrode kinetics of Ni(II) reduction at the DME in the presence of nicotine
Authors: Crespo-Pinilla M S , Infante A B , Mata-Pérez F
Published: April 2011

A study of the prewave of the Ni2+- nicotine system was carried out under the experimental conditions when the influence of electroreduction of nicotine is negligible. The kinetics of Ni(II) reduction in nicotine media on the dropping mercury electrode were studied by direct current Tast polarography (DCTP) via the determination of the Koutecky's parameter, χ and the influence of different variables was analyzed. An electrochemical study of the prewave was also made by using various polarographic techniques. Values of χ depend on the nicotine concentration, pH, ionic strength (ψ-effect), and on the nature of the supporting electrolyte. The αn product (χ = transfer coefficient, n = number of electrons) and the stoichometric number,v, were determined. The prewave is interpreted as a surface reaction, the main features of the mechanism being its catalytic nature. The discharge is a two electron step and reaction between species of opposite charge is rate-determining.Key words: catalytic, prewave, polarography, nickel(II), nicotine.
Crystallographic and spectroscopic studies of adducts of indium (III) iodide with two cyclic ketones
Authors: Brown M A , Tuck D G
Published: April 2011

Indium(III) iodide forms a 1:1 adduct with 9-xanthenone, of quasi-tetrahedral structure; triclinic, a = 10.805(4), b = 11.494(4), c = 7.493 (2) Å, α = 104.12(3), β = 106.35(3), γ = 91.165(3)°, V = 860.8(5) Å3, Z = 2, space group P1-. With 9-fluorenone, the adduct has 1:2 stoichiometry, and approximately D3h symmetry in the InI3O2 kernel; the structure is triclinic, a =11.212(2), b = 16.504(3), c = 7.537(2) Å, α = 94.57(2), β = 109.05(1), γ = 91.165(15)°, V = 1312.6(4) Å3, Z = 2, space group P1-. The solid structures, and the solution chemistry, are compared with those of related neutral derivatives of indium(III) halides.Key words: Indium(III) iodide, solution chemistry, crystal structures, adducts.
Synthesis of novel pentacyclic β-lactam antibacterial agents
Authors: Andreotti Daniele , Biondi Stefano , Donati Daniele , Lociuro Sergio , Pain Gilles
Published: April 2011

The search for new antibacterial agents still represents an active area of research. In this paper the synthesis of a new class of β-lactam agents characterized by an interesting antibacterial profile is reported; together with a description of the most significant synthetic aspects encountered during this work.Key words: β-lactams, pentacyclic, O-alkylation, trinem.
Hydrogen bonded supramolecular structures: a further insight into the diamine-diol recognition and self-assembly
Authors: Roelens Stefano , Dapporto Paolo , Paoli Paola
Published: April 2011

A new H-bonded supramolecular assembly of the diamine-diol family has been obtained from (1R,2R)-1,2-diaminocyclohexane (DAC) and (S)-1-phenyl-1,2-ethanediol (PED). The structure was characterized by single-crystal X-ray analysis and showed the typical architecture of DAC based assemblies, consisting of a three-stranded helicate coiling around a H-bonded core, with a predictable helicity sense determined by the configuration of DAC. The new assembly, while reconfirming the unique role of DAC as a powerful assembler of supramolecular structures, demonstrated that the C2 symmetry of diol partners employed so far is not essential for assembling helicates, although chirality is. In the case of the adduct between (1R,2R)-1,2-diaminocyclohexane and (2R,3R)-2,3-butanediol, molecular recognition and self-assembly have been shown to take place even in the absence of solvent, in the gas phase, where long crystals were formed by spontaneous organized aggregation of diamine-diol units. A thorough analysis of the results from the present and previous investigations has lead to a deeper understanding of the key features of the diamine-diol molecular code and of the requirements for recognition and assembly.Key words: supramolecular, hydrogen bonding, molecular recognition, self-assembly, diamines, diols.
An exploratory ab initio study on the conformations of ethylguanidine in its neutral [CH3-CH2-NH-C(=NH)NH2] and protonated [CH3-CH2-NH-C(NH2)2] forms
Authors: Mak Melody L , Salpietro Salvatore J , Enriz R Daniel , Csizmadia Imre G
Published: April 2011

To explore the conformation intricacies of the guanidine group in the arginine side chain, ab initio computations have been carried out with ethylguanidine and the ethyl guanidinium ion. HF computations have been performed using 3-21G and 6-31G basis sets and DFT calculations were carried out at the B3LYP/6-31G(d) level of theory. The ethyl guanidinium ion has a single isomer due to its internal symmetry, although this structure has at least three conformations. However, several structures were found and optimized for ethylguanidine, involving the endo- and exo- orientation of the lone NH and torsional angle χ6, as well as the torsional modes associated with χ4and χ5. Torsional angle χ5gives rise to s-cis and s-trans structures.Key words: ethylguanidine, ethylguanidinium ion, ab initio MO, arginine side-chain, conformational analysis.
Trifluoroacetic acid-mediated intramolecular formal N-H insertion reactions with amino-α-diazoketones: a facile and efficient synthesis of optically pure pyrrolidinones and piperidinones
Authors: Yang Hua , Jurkauskas Valdas , Mackintosh Nicole , Mogren Tobias , Stephenson Corey RJ , Foster Katherine , Brown William , Roberts Edward
Published: April 2011

Trifluoroacetic acid (TFA) was found to promote intramolecular formal N-H insertion reactions. Upon treatment with TFA, optically pure N-Boc-β'-amino-α-diazoketones (5a-c) and N-Boc-γ'-amino-α-diazoketones (10a-d) can be converted, with retention of chirality, into pyrrolidinones (11a-c) and piperidinones (12a-d), respectively, with concomitant removal of the Boc group, in good to excellent yields.Key words: α-diazoketone, amino acid, pyrrolidinone, piperidinone, N-H insertion.
Synthetic applications of the ruthenium-catalyzed hydrogenation via dynamic kinetic resolution
Authors: Ratovelomanana-Vidal Virginie , Genêt Jean-Pierre
Published: April 2011

This review summarizes some recent work in the field of homogeneous ruthenium-catalyzed hydrogenation via dynamic kinetic resolution. The hydrogenation reaction of various α-substituted β-oxo esters using chiral ruthenium(II) catalysts is presented as well as the synthesis of some key intermediates of pharmaceutical interest.Key words: dynamic kinetic resolution, ruthenium, hydrogenation, α-substituted β-keto ester.
Metal supported catalysts obtained by sol-gel in the hydrosilylation of phenylacetylene with R3SiH organosilanes (R3 = Ph3, Ph2Me, and PhMe2)
Authors: Jiménez Rafael , López Juan Manuel , Cervantes Jorge
Published: April 2011

The hydrosilylation reaction of phenylacetylene, generated on the surface of solid catalysts (such as Pt and Ru) supported on inorganic matrices such as MgO obtained by the sol-gel process, yields vinylsilanes as the main products. The products' distribution, specific activity, and turnover reactions were determined for the case of the hydrosilylation reaction of PhC = CH with R3SiH (R = Ph3, Ph2Me, and PhMe2). For Ph3SiH and Ph2MeSiH, the presence of β-trans and α isomers is observed. Addition of PhMe2SiH to phenylacetylene leads to the formation of β (cis and trans) and α isomers. These catalytic systems provide a new synthetic route to SiC bond formation.Key words: Vinylsilanes, sol-gel catalysts, hydrosilylation and phenylacetylene.