Face-centered Cube Research Articles

Optimization of the separation of anticonvulsant agents in mixed micellar liquid chromatography by experimental design and regression models

The chemometrics approach was applied for the optimization of separation of anticonvulsant agents in mixed micellar liquid chromatography (MLC). To optimize the separation of eight anticonvulsant agents, the effect of six experimental parameters on retention was investigated by means of multivariate analysis. The factors considered were the organic modifier concentration in the mobile phase, the length of the alkyl chain of the organic modifier, the concentration of sodium dodecyl sulfate (SDS) and Brij-35, pH of the mobile phase, and temperature. The experiments were performed according to a face centered cube response surface experimental design. Then, in order to optimize the separation, Pareto-optimality method was employed. The obtained regression models were characterized by both descriptive and predictive ability ( R 2≥97.8% and R cv 2≥93.7%) and allowed the chromatographic separation of the anticonvulsant drugs with a good resolution and a total analysis time within 50 min.

The first coordination number for liquid metals

A simple and absolute method for the calculation of the first coordination number for any pure, isotropic liquid element is presented. The liquid density and the position for the first peak of the radial distribution function, assumed to be the atomic diameter, are the only parameters required. The coordination number for liquid metals that exhibit a BCC (body-centred cube) solid structure averages 7.4 while the first coordination number for liquid metals with a FCC (face-centred cube) or CPH (close-packed hexagonal) solid structure averages 7.1. Those liquid elements that have less closed-packed solid structures have a first coordination number less than 7.0. The calculation also correctly predicts the first coordination number for liquid Se to be 2.4, consistent with its chain-like structure. The calculated values for the liquid element coordination numbers are consistent with the decrease in density of a few percent that occurs upon melting and appear to be related to the Engel–Brewer valence of the solid, which suggests that the electron structure of the solid may be retained upon melting. The first coordination numbers for liquid Ge and Si were calculated to be 5.0 and 4.7, respectively, larger than the value of 4.0 for solid structures. The increase in coordination number upon melting accounts for the increase in density of Ge and Si that occurs upon melting.PACS No.: 61.20.Gy

Constraint Logic Programming approach to protein structure prediction

BackgroundThe protein structure prediction problem is one of the most challenging problems in biological sciences. Many approaches have been proposed using database information and/or simplified protein models. The protein structure prediction problem can be cast in the form of an optimization problem. Notwithstanding its importance, the problem has very seldom been tackled by Constraint Logic Programming, a declarative programming paradigm suitable for solving combinatorial optimization problems.ResultsConstraint Logic Programming techniques have been applied to the protein structure prediction problem on the face-centered cube lattice model. Molecular dynamics techniques, endowed with the notion of constraint, have been also exploited. Even using a very simplified model, Constraint Logic Programming on the face-centered cube lattice model allowed us to obtain acceptable results for a few small proteins. As a test implementation their (known) secondary structure and the presence of disulfide bridges are used as constraints. Simplified structures obtained in this way have been converted to all atom models with plausible structure. Results have been compared with a similar approach using a well-established technique as molecular dynamics.ConclusionsThe results obtained on small proteins show that Constraint Logic Programming techniques can be employed for studying protein simplified models, which can be converted into realistic all atom models. The advantage of Constraint Logic Programming over other, much more explored, methodologies, resides in the rapid software prototyping, in the easy way of encoding heuristics, and in exploiting all the advances made in this research area, e.g. in constraint propagation and its use for pruning the huge search space.

Biological waste-treatment of hydrocarbon residues: effects of humic acids on the degradation of toluene

The biological degradation potential on toluene of the bacteria Pseudomonas fluorescens isolated from soil, as influenced by humic acids, was investigated. The major environmental factors considered of interest for this experiment were temperature, pH of the media, and agitation (rpm), which were optimized using Response Surface Methodology. A face-centered cube design was adopted for this study, and the optimal values for these factors were predicted by the resulting experimental equations. The degradation of toluene by P. fluorescens was tested by incorporating different concentrations (0.02, 0.04, 0.06, 0.08 and 0.10%) of humic acids, extracted from peat moss, in a hydrocarbon degradation medium. The results showed that the microbial degradation of toluene was inhibited by the presence of humic acids.

Crystal Structure of Diaqua(1,2-bis(2-(o-hydroxyphenoxy)ethyloxy)ethane)(perchlorato-O)strontium Perchlorate Hydrate

The aqua complex of podand 1,2-bis(2-(o-hydroxyphenoxy)ethyloxy)ethane (L) with strontium perchlorate of the composition [Sr(ClO4)L(H2O)2]+ · ClO4– · H2O (I) was synthesized and studied using X-ray diffraction analysis: space group P21/c, a = 16.195 A, b = 11.382 A, c = 16.646 A, β = 117.01°, Z = 4. The structure was solved by direct method and anisotropically refined by the full-matrix least-squares method to R = 0.069 for 4278 independent reflections (CAD4 autodiffractometer, λMoKα). Structure I contains complex cation [Sr(ClO4)L(H2O)2]+ of the host–guest type. The Sr2+ cation (coordination number 9) is coordinated to all six O atoms of the L podand, O atom of a disordered ClO4– ligand, and two O atoms of two water molecules. The coordination polyhedron of Sr2+ is irregular; in a rough approximation, it can be described as a face-centered cube. The crystal structure of I contains an infinite three-dimensional network of the O–H···O hydrogen bonds joining the complex cations, ClO4– anions, and molecules of crystallization water.

The isotropic shear modulus of multicomponent Fe-base solid solutions

A critical analysis of the available experimental data for the effect of alloying elements on the isotropic shear modulus of bcc (body-centered cube) Fe– X ( X=Al, Be, C, Co, Cr, Ge, Ir, Mn, Ni, Pt, Re, Rh, Ru, Si and V) solid solutions is carried out. The total effect of a solute on the shear modulus is decomposed into two contributions: the electronic (or chemical) and the volumetric. A systematic trend of the electronic contribution is demonstrated as a function of electron-to-atom ( e/a) ratio and the ground-state electronic configuration of the solute atom. Based on the demonstrated trend, we predict the chemical contribution of the shear modulus of Cu, Mo, N, Nb, Ti and W in ferromagnetic α-Fe (bcc), and that of Ti and V in paramagnetic γ-Fe [face-centered cube (fcc)]. These along with the corresponding volumetric contributions enable us to predict the total effect of a solute on the shear modulus in α-Fe and γ-Fe. In the case of γ-Fe, we derive the chemical and volumetric contributions of Ni and Pt from the experimental shear modulus data of paramagnetic Fe–Ni and Fe–Pt alloys while those of C, Co, Cr, Mn, Mo, N and Si are derived from the shear modulus of paramagnetic Fe–Ni– X alloys. In the case of Al, Be, Cu, Ge, Ir, Nb, Re, Rh , Ru and W, the total effect on the shear modulus is calculated by assuming that the electronic contribution to the shear modulus in γ-Fe is the same as in α-Fe. To calculate the isotropic shear modulus of multicomponent bcc and fcc solid solutions, we propose linear superposition laws. The proposed relationships are validated using the experimental data of a large number of multicomponent alloys having austenitic, ferritic, and lath martensitic microstructures. It is demonstrated that for all three microstructures, in most cases the shear modulus can be predicted with an accuracy of ±3% in multicomponent solid solutions. It is also found that the high dislocation density in lath martensite accounts for a decrease in shear modulus by about 5% compared to the ferritic counterpart. We also demonstrate that the temperature dependence of shear modulus in multicomponent bcc and fcc solid solutions is similar to that of pure α- and γ-Fe, respectively, for up to about 800 K.

Method development and validation for the chiral separation of peptides in the presence of cyclodextrins using capillary electrophoresis and experimental design

The present study describes the application of statistical experimental design to the optimization of enantioselective separations of peptides in capillary electrophoresis in order to obtain optimal operating conditions for routine work. Hydroxypropyl-β-cyclodextrin was used as chiral selector and Ala–PheOMe as model peptide. The experiments were performed according to a face centered cube response surface experimental design for obtaining information how the factors such as concentration of the chiral selector, pH, buffer concentration and voltage affected the two response goals, resolution and analysis time. In order to achieve the simultaneous optimization of these two major electrophoretic performance goals for efficient and fast separation, the Derringer desirability functions were tested. While in the predefined experiments the analysis time for baseline separation was 25 min the desirability functions proposed a CE method, which diminished the analysis time and permitted the complete separation of the peptide enantiomers within 9 min.

Microstructure and texture formation in extruded lead sulfide (galena)

Lead sulfide (galena) of different purity and grain size was extruded through a round and rectangular die at temperatures between 773 and 923 K. Global and local lattice preferred orientations (here referred to as textures) were measured by neutron and electron back-scattering diffraction. Tension leads to a <100> <111> double fibre texture. Pure shear deformation yields texture components near the ideal face-centered cubic metal brass, copper, Goss and cube positions. The intensity of the components depends on the purity and/or grain size. The microstructure is partially recrystallized. Electron back-scattering diffraction indicates that in tension the <100> and in pure shear the Goss and cube components are associated with dynamic recrystallization. The deformation texture can be qualitatively explained by the full and relaxed constraints Taylor model using slip on {100}<110>, {110}<110> and {111}<110> systems. The texture formation in lead sulfide compares well with that observed for other ionic crystals with the NaCl-structure as well as for face-centered cubic metals with a high stacking fault energy.

Enzyme-assisted acidolysis of borage (Borago officinalis L.) and evening primrose (Oenothera biennis L.) oils: incorporation of omega-3 polyunsaturated fatty acids.

Lipase-catalyzed acidolysis of borage (Borago officinalis L.) and evening primrose (Oenothera biennisL.) oils with long-chain omega3 polyunsaturated fatty acids (PUFA), namely, eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids, was carried out in hexane, and the products were analyzed using gas chromatography. The most effective lipase for incorporation of omega3 PUFA into these oils was Pseudomonas sp. as compared to lipases from Mucor miehei and Candida antarctica. Response surface methodology was used to obtain a maximum yield of EPA+DHA incorporation while using the minimum amount of enzyme possible. The process variables studied were the amount of enzyme (150-350 units), reaction temperature (30-60 degrees C), and reaction time (6-30 h). All experiments were carried out according to a face-centered cube design. Under optimum conditions, incorporation of EPA+DHA was 35.5% in borage oil and 33. 6% in evening primrose oil. The modified borage and evening primrose oils containing gamma-linolenic acid, EPA, and DHA were successfully produced and may have potential health benefits.

A new multivariate approach for the optimisation of the simultaneous distillation–extraction technique for free fatty acids using a face centred cube experimental design: application to Parmigiano–Reggiano cheese

A face centred cube (FCC) experimental design was used to investigate effects of extraction time, solvent temperature and sample temperature on the simultaneous distillation–extraction (SDE) extraction yields of 13 fatty acids from Parmigiano–Reggiano cheese, and to find the best extraction conditions for these compounds. Each factor was tested at three levels; 20 experiments were carried out, each producing 13 responses. In order to create a mathematical model representing the relationships between factors and responses and to determine the best conditions for the SDE procedure, GC peak areas were processed by using the multiple regression analysis. The backward stepwise selection of the regression coefficients led to the identification of seven groups of compounds having similar behaviour with respect to the three variables investigated. The same set of models was found by performing principal component analysis (PCA) on the t-values of the regression coefficients of the unrefined polynomials and cluster analysis on the scores of the 13 acids obtained by PCA. The best experimental conditions were evaluated for each compound. The use of the FCC experimental design allowed to evaluate not only the main effects of the variables analysed, but also curvature effects and interaction effects among them.

A new architecture in lithium amide chemistry: synthesis of [{(c-C5H9)N(H)}12(O)Li14], a cage molecule containing a salt-like, distorted, face-centered cube of lithium cations

Synthesised in the presence of trace quantities of water, which can account for its central oxo anion, the tetradecalithium title compound represents a rare three-dimensional, high-oligomeric cage arrangement in an area generally populated by psudo-two-dimensional ring and ladder structures.

CRITICAL OSMOTIC PRESSURE OF COLLOIDS

The osmotic pressure for electrocratic colloids is considered. Assuming monodispersed colloidal particles arranged in face-centered cube (fcc) or body-centered cube (bcc) structures, we calculate the critical osmotic pressures of colloids in the framework of DLVO theory. The quantitative dependences of critical osmotic pressures upon physical parameters (such as particle radius and concentration of ions in medium, etc.) are obtained. These theoretical results may provide better knowledge about van der Waals forces and double layer structures of these suspensions when they are compared with experimental results.

Whey protein gels: fracture stress and strain and related microstructural properties

The fracture properties of the true shear stress and true shear strain of whey protein isolate (WPI) gels were adjusted to targeted values by varying protein, sodium chloride and calcium chloride concentrations. Changes in stress and strain were varied independently and related to the microstructural properties of area fraction, surface volume, chord length distribution, mean volume weighted diameter and fractal dimension using a face-centered cube statistical design. Light and scanning electron micrographs revealed no overall relationship among fracture properties and microstructure. However surface volume and fractal dimension differed due to type of mineral present. These properties differentiated fine-stranded and particulate gels. It was concluded that identical fracture properties can be produced in fine-stranded and particulate gels.

Finding the face-centered cube in the cubic closest packed structure

Demonstrating that the cubic closest packed structure is identical to the face-centered cubic using a physical model; includes instructions for constructing the model.

Determination of the crystal structure and composition of Li6Be4OH12 by the stochastic method.

Because of the failure to find a structure for LiBeH3 with a face-centered unit cube with edge 5.09 A, the x-ray powder pattern has been reindexed for a body-centered unit cube with edge 7.24 A. Application of the principles of structural chemistry leads to the formula Li6Be4OH12 and to a structure involving Be4OH12 clusters formed by 4 BeOH3 tetrahedra with their O corner shared, Be--(H,O) bond length 1.59 A, and with the clusters joined to one another by Li with octahedral or rectangular-planar coordination of 6 H or 4 H, Li-H bond lengths about 1.92 A.

Preparation of highly dispersed Pt + Ru alloy clusters and the activity for the electrooxidation of methanol

A new method for the preparation of Pt + Ru binary catalyst has been developed which provides a simple way of obtaining a specific surface area (ca. 80 m 2 g −1) more than 3 times larger than that obtained by conventional methods. This method is based on the co-deposition of fine oxides of platinum and ruthenium in atomic scale in a mixed salt solution of these metals followed by reduction with hydrogen bubbling. It was revealed that the binary catalyst prepared by this method forms alloy clusters of their solid solution, in which platinum atoms are replaced by ruthenium atoms on the lattice points of a face-centred cube in the region of Ru/Pt ratios less than 0.75. The supported alloy on carbon black exhibited an extremely high catalytic activity during the electrooxidation of methanol; i.e. ca. 200 mA cm −2 at 0.4 V and a limiting current of more than 1 A cm −2 when Ru/Pt = 1/1. From a comparison of the relationship between the composition of the alloy and the activity with that of an ad-electrode having ruthenium ad-atoms with a well-defined coverage, it was concluded that the composition of the alloy cluster surface is probably the same as that of the cluster bulk.

The Aldine crime & justice annual : edited by Seymour Halleck, Paul Lerman, Sheldon L. Messinger, Norval Morris, Patrick V. Murphy, and Marvin E. Wolfgang. Aldine-Atherton, Inc. (529 South Wabash Avenue, Chicago, Illinois 60605), 1975, 541 pp., hardcover - $18.50.

Submicron-cerium oxide particles were synthesized by applying hypergravity using ammonium bicarbonate (precipitant) and cerium nitrate hexahydrate (precursor). The influence of the concentration, pH, dispersant loading, flow rate, rotation speed of the hypergravity rotating bed, calcination temperature, and time on the cerium oxide particle size were examined by zeta potential, solid–liquid contact angle, thermo-gravimetry–differential scanning calorimetry, scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. The cerium oxide particles were highly dispersed, with an average particle size of 200 nm. Calcining at 650 °C for 1.5 h afforded the smallest particles. The crystallite size and fraction crystallinity increased with prolonged calcination. Crystalline cerium dioxide grew along three crystal planes, forming a complete face-centered cube, affording high hardness and activity of the polishing powder. The optimal conditions were: cerium nitrate concentration: 0.7 mol/L, cerium nitrate/ammonium bicarbonate molar ratio: 1:3, dispersant mass fraction: 3%, cerium nitrate initial pH: 4–5; the precursor solution was adjusted to pH 9 with ammonia water. Hypergravity coprecipitation with 1.5 h calcination afforded submicron-sized cerium oxide with a uniform size distribution using ammonium bicarbonate in an industrially viable process. The simple and low-cost manufacturing process may enable the development of hypergravity-assisted chemical synthesis technology.

The liver of the slender salamander Batrachoseps attenuatus. I. The structure of its crystalline inclusions.

The structure of the crystalline inclusions found in Batrachoseps liver cells is described and it is shown that the most symmetric unit cell upon which the crystal lattice is built is a face-centered cube. Taking into consideration the physical properties of a face-centered cubic structure, an attempt is made to determine the nature of the macromolecules that comprise the crystal. It is concluded on the basis of available evidence that the macromolecules probably represent serum lipoproteins. The intracellular synthesis of the crystals and the possible functions they may subserve in the animal are discussed. A comparison is made between the crystals and granules in rat hepatocytes discussed by Bruni and Porter (1965).

Face-centered cube and cubical close-packing

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTFace-centered cube and cubical close-packingE. De Barry Barnett Cite this: J. Chem. Educ. 1958, 35, 4, 186Publication Date (Print):April 1, 1958Publication History Received3 August 2009Published online1 April 1958Published inissue 1 April 1958https://doi.org/10.1021/ed035p186RIGHTS & PERMISSIONSArticle Views55Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (421 KB) Get e-Alerts Get e-Alerts

The structure of crystals of purified Mahoney poliovirus

Crystals of Mahoney strain poliovirus have been examined to determine their crystal structure. It was concluded from these studies that the crystals were isometric or nearly so with habit being octahedral with minor development of the cube faces; and with unit packing, within the crystals, being that of a face-centered cube. Electron micrographs of fractured crystals showed virus particles in cube (100) and octahedron (111) faces and also a few surfaces fractured along the (110) plane. The size of the particles within the crystal, as measured in a (111) plane, was found to be 27.3 ± 1.4 g μ. A value of 1.535 ± 0.003 was determined for the index of refraction, but this is of doubtful worth because the degree of hydration of the crystal was unknown.