Structure Of Solid Phase Research Articles

Purification and characterization of an endo-1,4--glucanase from Bacillus cereus

A cellulase produced by Bacillus cereus (B. cereus), isolated from the local soil, was purified to homogeneity from culture broth. The enzyme had a molecular mass of 51.3 kDa. The optimal cellulase activity was at pH 8 and at the temperature of 55°C. The enzyme was stable at 50°C in the pH range of 5 to 9. The enzyme was stable up to 55°C above which stability decreased rapidly after incubation for 1 h. The enzyme showed the highest activity with carboxymethyl cellulose. Slight activity was also observed towards cellulose in the filter paper and xylan. For carboxymethyl cellulose, the cellulase had a Km of 2.12 mg/ml and Vmax of 5.37 μg/ml·min. The activity of the enzyme was not influenced by Fe2+, Zn2+, urea, EDTA, Ca2+, Co2+, K+ and Na+, but it was increased by 13% in the presence of Mn2+. Ba2+, C2O42-, Mg2+ and Cu2+caused a loss in the enzyme activity. The FT-IR spectrum of this carboxymethyl cellulase (CMCase) showed the characteristic cellulase peaks. Infrared spectrum of the amide I and II bands of the CMCase showed that secondary structure of the CMCase mainly consists of α-helix structures in solid phase. This enzyme (the cellulase produced by B. cereus) is of high value in the industry applications (such as laundry) in the future. Key words: Cellulase, Bacillus cereus, purification, characterization.

Investigations of Formation of Molecular Sieve SAPO-34

Crystallization of a catalytically important molecular sieve SAPO-34 was examined under dry gel conversion conditions including steam-assisted conversion (SAC) and vapor-phase transport (VPT). The progressive changes in the structure of solid gel phases were monitored by powder XRD, SEM, and several solid-state NMR techniques involving 31P, 27Al, 29Si, and 13C. The results suggest that the formation pathways under VPT and SAC appear to be similar: SAPO-34 crystallizes from a semicrystalline precursor with a layered structure held mainly by weak nonbonding interactions. AFM data indicate that the crystal growth mechanism is “birth and spread” and that the fast nucleation on the (001) crystal face likely results from simultaneous transformation of many small domains of precursor to SAPO-34 via cooperative bond breaking and reforming. 29Si NMR results suggest that Si incorporation occurs slowly via amorphous aluminosilicate species. These findings provide new physical insights into the formation of SAPO-34.

State of uranyl phosphates and arsenates in aqueous solutions

The state of uranyl phosphates and arsenates (UO2)3(PO4)2·nH2O and (UO2)3(AsO4)2·nH2O in aqueous solutions in the interval of pH 1–14 was studied by X-ray diffraction, IR spectroscopy, thermography, and chemical analysis. The composition and structure of the initial solid phases vary depending on the solution acidity. The equilibrium constants of the reactions occurring in the heterogeneous systems (UO2)3(BVO4)2·nH2O (BV = P, As)-aqueous solution were calculated. The speciation diagrams of the solid phases and equilibrium solutions were plotted.

Geometrical structures in solution and solid phase of poly(propargyl ester)s prepared by using a [Rh(norbornadiene)Cl]2-cocatalyst

Propargyl esters, HCCCH2OCOCnH2n+1 (1: n = 3, 2: n = 5, 3: n = 9, and 4: n = 13), were polymerized using a [Rh(nbd)Cl]2 catalyst and cocatalyst in an appropriate solvent at 0 °C and 40 °C. Number average molecular weights, Mn of the resulting polymers, poly(1)–poly(4), were 8000–54,000, and its dispersities (Mw/Mn)s and the yields were estimated to be 1.6–3.6 and ca. ∼99%, respectively. These polymers were soluble in CHCl3, CH2Cl2, and THF, and insoluble in CH3OH and DMF. The amines, e.g., 2,6-dimethylpyridine and triethylamine worked well as the cocatalysts for the polymerization to give the yields, 93% and 88%, respectively. Further N,N-diethylaniline gave the maximum in cis%, 74%, although pyridine, aniline, pyrrole or imidazole did not work effectively. Remarkable line broadening phenomenon, LBP observed in the 1H NMR spectra of poly(1) and poly(2) prepared at 0 °C or 40 °C, and poly(3) prepared at 40 °C was correlated with the polymerization temperature and the radical concentration generated in the polymer. The LBP was interpreted by the dipole–dipole interaction between the protons in the polymer and unpaired electrons due to carbon radicals generated by the rotational scission of the cis CC bonds during the polymerization. Their UV–vis spectral shape of poly(1)–poly(4) depended on the polymerization temperature and/or the alkyl chain length in the polymer. The XRD powder patterns of poly(3) prepared at 0 °C, and poly(4)s prepared at 0 °C and 40 °C showed layer crystal structures with a slightly bent herringbone confirmed by molecular mechanics calculation. The λmax values of poly(4) prepared at 40 °C in methanol showed 317 nm and 340 nm in the solution and on the alumina, respectively.

The phase behavior of two-dimensional symmetrical mixtures in a weak external field of square symmetry

Using Monte Carlo simulation methods in the grand canonical and semigrand canonical ensembles, we study the phase behavior of two-dimensional symmetrical binary mixtures of Lennard-Jones particles subjected to a weakly corrugated external field of a square symmetry. It is shown that the both vapor-liquid condensation and demixing transition in the liquid phase are not appreciably affected by a weakly corrugated external field. On the other hand, even a weakly corrugated external field considerably influences the structure of solid phases and the liquid-solid transition. In particular, the solid phases are found to exhibit uniaxially ordered distorted hexagonal structure. The triple point temperature increases with the corrugation of the external field, while the triple point density becomes lower when the surface corrugation increases. The changes in the location of the triple point are shown to lead to the changes of the phase diagram topology. It is also demonstrated that the solid phase undergoes a demixing transition, which is also very slightly affected by the weakly corrugated external potential. The demixing transition in the solid phase is shown to belong to the universality class of the Ising model.

Solution structure of copper-seamed C-alkylpyrogallol[4]arene nanocapsules with varying chain lengths

The stability of copper-seamed C-alkylpyrogallol[4]arene hexamers with varying chain lengths in solution has been studied using small-angle neutron scattering (SANS). The progression in diameter of spherical capsules with increasing alkyl chain lengths of copper-seamed hexamers in solution suggests both robustness as well as a close correlation between the solid phase and solution phase structures.

Positronium as a probe of structure and stability of solid phases in binary n-alkane mixtures

Annihilation of triplet ortho-positronium (o-Ps) in binary mixture of odd numbered n-alkanes was investigated. Sensitivity of o-Ps lifetime to the size of free volumes in the sample structure allows to distinguish not only the phases of solid but also some details of their structure. It was found that in the rigid phase o-Ps locates in the interlamellar gap. In mixed systems the o-Ps lifetime in that phase is longer than in neat compounds due to the change of molecular arrangements around the gap. In the case of n-tricosane + n-nonadecane mixture a transient structure appears when the n-tricosane content is between 3% and 10%. Directly after the increase of temperature to the range of 285–292 K the sample transforms to the rotator phase, but returns (at least partially) to the previous rigid structure with recovery time constant of many hours. Above 292 K the structure is stable.

Generalized eigenproblem of hybrid matrix for Floquet wave propagation in one-dimensional phononic crystals with solids and fluids

A method based on the solution to a generalized eigenproblem of hybrid matrix is presented for stable analysis of Floquet wave propagation in one-dimensional phononic crystals with solids and fluids. The method overcomes the numerical instability in the standard eigenproblem of transfer matrix, thus enabling Floquet waves to be determined reliably. The recursion relations of hybrid matrix for periodic multilayered structure of various solid and/or fluid phases are formulated. Dispersion relation and omnidirectional reflection for one-dimensional phononic crystals with solids and fluids are discussed. The frequency–thickness range of phononic bandgap is determined conveniently based on the Floquet wavenumbers.

Bis(dicyanomethylene)squarate squaraines in their 1,2- and 1,3-forms: Synthesis, crystal structure and spectroscopic study of compounds containing alkali metals and tetrabutylammonium ions

In this paper, we describe a new synthetic methodology and the spectroscopic characterization of two squaraines 1,2- and 1,3-substituted, named sodium 1,2-bis(dicyanomethylene)squarate and sodium 1,3-bis(dicyanomethylene)squarate. The squaraine species are derived from 1,2-dihydroxycyclobuten-3,4-dione, also known as squaric acid. A modification in the synthetic route has been developed in order to improve the yield in the synthesis of the 1,3-derivative: the in situ use of the 1,3-dianilinesquarate intermediate. In both cases, an excess basic medium was added to the solution containing all the reactants. These squaraines consist of a cyanine-type chromophore with high thermal stability and several different spectroscopic properties. In addition, it was made a comparative analysis based on the spectroscopic study of the 1,3- and 1,2-compounds, as well as their derivatives with several metal alkalis (K +, Rb +, Mg 2+, Ca 2+, Sr 2+ and Ba 2+), besides tetrabutylammonium ion (TBA). The vibrational spectroscopic data demonstrate the centrosymmetric structure in solid state phase of the 1,3-compound due to non-coincidence between the infrared and Raman bands in the vibrational spectra. The crystal structures were also obtained for Ca 2+ and Ba 2+ ions with the 1,3-isomer. These salts crystallize in different space groups, also showing very distinct coordination properties and intermolecular interactions. This study provides a sound basis for the future expansion of structural and spectroscopic investigations of this interesting group of metal–ligand compounds as building blocks systems in supramolecular chemistry.

Molecular Dynamics Study of Stability of Solid Solutions and Amorphous Phase in the Cu–Al System

The relative stability of fcc and bcc solid solutions and amorphous phase with different compositions in the Cu–Al system is studied by molecular dynamics simulations with n-body potentials. For Cu1−xAlx alloys, the calculations show that the fcc solid solution has the lowest energies in the composition region with x < 0.32 or x > 0.72, while the bee solid solution has the lowest energies in the central composition range, in agreement with the ball-milling experiments that a single bcc solid solution with 0.30 < x < 0.70 is obtained. The evolution of structures in solid solutions and amorphous phase is studied by the coordination number (CN) and bond-length analysis so as to unveil the underlying physics. It is found that the energy sequence among three phases is determined by the competition in energy change originating from the bond length and CNs (or the number of bonds).

Synthesis of Crystallized Mesoporous Tantalum Oxide and Its Photocatalytic Activity for Overall Water Splitting under Ultraviolet Light Irradiation

The well-ordered two-dimensional hexagonal (2D-hex) structure of mesoporous Ta2O5 was maintained after crystallization with the aid of SiO2 reinforcement, which was removed after crystallization. The photocatalytic activity of the mesoporous Ta2O5 for overall water splitting under ultraviolet (UV) irradiation was improved by changing the solid phase structure from amorphous to crystalline by nearly 1 order of magnitude. The resulting photocatalytic activity of NiOx(3.0 wt %)-loaded crystalline mesoporous Ta2O5 for water decomposition (3360 μmol·h−1 of H2 and 1630 μmol·h−1 of O2 evolution at the initial 1 h) was found to show one of the highest activities among so far reported photocatalysts under similar conditions. The high activity is attributable to the efficient transfer of the excited electrons and holes from inside to the surface of the catalyst through thin-walled crystalline phase.

Structure and electrochemical characteristics of melted composite Ti 0 .10 Zr 0 .15 V 0 .35 Cr 0.10Ni 0.30–LaNi 5 hydrogen storage alloys

The structure and electrochemical characteristics of melted composite Ti 0.10Zr 0.15V 0.35Cr 0.10Ni 0.30 + x% LaNi 5 ( x = 0, 1, 5 and 10) hydrogen storage alloys have been investigated systematically. XRD shows that the matrix phase structure of V-based solid solution phase with a BCC structure and C14 Laves phase with hexagonal structure is not changed after adding LaNi 5 alloy. However, the amount of the secondary phase increases with increasing LaNi 5 content. Field emission scanning electron microscopy–energy dispersive spectroscopy (FESEM–EDS) shows that the C14 Laves phase contains more Zr and the white lard phase has a composition close to (Zr, Ti)(V, Cr, Ni, La) 2. The electrochemical measurements show that the hysteresis effect decreases dramatically with increasing x. The activation performance, the low temperature dischargeability, high rate dischargeability and cyclic stability of composite alloy electrodes increase greatly with increasing x. The maximum discharge capacity first increases as x increases from 0 to 5 and then decreases when x increases further from 5 to 10. The improvement of the electrochemical characteristics caused by adding LaNi 5 seems to be related to formation of the secondary phase.

Electronic Structures of Single Component Molecular Metals Based on Ab initio Calculation

We perform a systematic study of electronic structures based on the ab initio calculations for single component molecular metals, Ni(tmdt) 2 , Au(tmdt) 2 , Au(tmstfdt) 2 , Cu(dmdt) 2 , and Zn(tmdt) 2 . First, we discuss the central metal dependence of the character of states around highest occupied molecular orbital (HOMO) [or singly occupied molecular orbital (SOMO)] and lowest unoccupied molecular orbital (LUMO) for isolated molecules and show that the stable structure of each isolated molecule is properly predicted. For solid state of Ni(tmdt) 2 , Au(tmdt) 2 , and Au(tmstfdt) 2 , the molecular shape is planar and the HOMO–LUMO separation in the Ni complex or the (HOMO - 1)–SOMO separation in the Au complexes is smaller than the inter-molecular interaction, which leads to the metallic state of Ni(tmdt) 2 and a unique antiferromagnetic state of Au(tmdt) 2 . For Cu(dmdt) 2 and Zn(tmdt) 2 , their two intra-molecular lingands are strongly twisted. Theoretically we obtain a stable antiferromagnetic solution for the solid state of the Cu complex. The theoretical electronic structures of solid phases of the Cu complex and Zn complex are compared with available experimental information.

Microstructural and magnetic properties of magnetic fluid based on magnetite coated with tartaric acid

An aqueous magnetic fluid based on iron oxide particles as solid nano-magnetic phase was prepared by applying the chemical precipitation method. Tartaric acid (C4H6O6) was used to functionalize magnetic cores. Physical tests have been performed in order to reveal the microstructural and magnetic features, their optimization being needed for biomedical utilization. The particles’ size was investigated using transmission electron microscopy (TEM), atomic force microscopy (AFM) and magnetization measurements. Fourier transform infrared absorption spectra (FT-IR) have been recorded aiming to get some information on the solid phase structure. 1. Introduction. Recently, the synthesis of magnetic materials on the nano-scale has become a field of increased interest due to the mesoscopic properties shown by nanoparticles of quantum dimensions located in the transition region between atoms and bulk solids. Magnetic fluids (ferrofluids) are two-phase systems, consisting of small ferri- and ferromagnetic nanoparticles dispersed in a liquid [1]. Because the size of the magnetic particles lies in the nanometer range (often around 10 nm in diameter), those suspensions are referred to as magnetic nano-colloids. The colloidal nanoparticles are subject to random displacement due to their bombardment by impulsive forces from the solvent molecules, in which they are dispersed. Colloidal stability is assured by coating the nanoparticles with shells of a nonmagnetic molecular surfactant, which prevents close approach of the magnetic cores, thereby, reduces the possibility of aggregation via Van der Waals or dipolar attractions. When the dipolar interactions are much stronger than the thermal energies, particle chains start growing and forming more complex structures, depending on the particle volume fraction, size distribution, temperature or a magnetic field applied [2]. The colloidal stability of magnetic fluids is a complex issue related to the synthesis procedure followed, including the nature of surfactant(s) and carrier liquids used [3]. The magnetic fluid stability is the main characteristic that determines the possibility to exploit magnetic fluids in different industrial and biomedical applications. Magnetic fluids are said to be superparamagnetic, meaning that they are attracted by a magnetic field but retain no residual magnetism after the field is removed [1]. When the magnetic nanoparticles are dispersed in an ionic solution, the dissociation of ionogenic groups is followed by the differential adsorption on the particle surface generating a particle surface potential. Biophysicists pay more and more attention to the magnetic nanoparticles functionalized with a biocompatible nonmagnetic molecular surfac

High pressure phase equilibria in methane + waxy systems : 1. Methane + heptadecane

Fluid–fluid and fluid–solid phase equilibrium were experimentally determined under pressure on the system methane + heptadecane using a full visibility cell. Measurements were performed using the synthetic method on mixtures ranging from pure heptadecane to 99% of methane. The liquid–solid phase transitions were investigated up to 90 MPa and fluid phase boundary was studied in the temperature domain from 293 to 373 K. The appearance of a minimum in the three phase (V–L–S) equilibrium curve is discussed and it is shown that the difference in the solid phase structure and the presence of a solid–solid phase transition do not affect significantly the phase diagram determined.

Effect of Isothermal Holding Temperature on Globularization of Primary Solid Phase in Multiplex-Type Slurry Cup

In order to produce a high quality and cost effective part in the rheocasting process for an automobile industry it has been important to develop a slurry-on-demand process, which can manufacture the semi-solid slurry having a fine and globular structure of primary solid phase. The morphology of primary solid phase of semi-solid slurry is coarsened and globularized during an isothermal holding process in a solid-liquid region. Accordingly, in this paper, the microstructural evolution of semi-solid slurry during the isothermal holding at a various temperature in solid-liquid region was investigated to examine a coarsening and globularization behavior of primary solid phase. The semi-solid slurry of Al alloy was produced in a slurry maker using a multiplex-type slurry cup that we developed recently. A size of primary solid phase was the finer at the higher holding temperature, but under a constant holding time a roundness degree of primary solid phase was the lower at the lower holding temperature. Also, a coarsening rate of primary solid phase was not considered to be affected significantly by a holding temperature even though a little lower coarsening rate was obtained at the higher holding temperature.

Optimization of Manufacturing Conditions of Semi-Solid Slurry in Multiplex-Type Slurry Cup

Recently, we have developed a slurry maker using a multiplex-type slurry cup for rheoforming process. In the present study, the optimum manufacturing condition of semi-solid slurry having a fine and globular structure of primary solid phase was investigated in the multiplextype slurry cup. A various manufacturing condition, such as a pouring temperature of melt, a preheating temperature of slurry cup, and a holding temperature and time of melt in slurry cup was varied to make a processing map of the semi-solid slurry for rheoforming process. Through the microstructural examination of primary solid phase of the interrupt-quenched semi-solid slurry of Al-7wt%Si-0.35wt%Mg alloy produced in the multiplex-type slurry cup under a various manufacturing condition, the optimum manufacturing condition of the semi-solid slurry for rheoforming process were a pouring temperature of melt of 650, a preheating temperature of slurry cup of 300, and an isothermal holding time of melt in slurry cup of 10min at 580.

Remarkable solvent effect on the structure and electrochemical properties of [M(bipyridyl) 3](ClO 4) 3 (M = Co, Fe and Ru) films

In low dielectric constant media the electrooxidation of bipyridyl complexes of transition divalent metal cations, such us Fe(II), Co(II), and Ru(II) results in the precipitation of microcrystalline film on the electrode surface. In most solvents, the film is reversibly reduced. However, films formed in the presence of acetonitrile are electrochemically inactive over a large potential range. The morphology and crystallographic structure of solid phase formed on the electrode surface during the electrochemical oxidation of bipyridyl complexes of Co(II), Fe(II), and Ru(II) have been investigated by the scanning electron microscopy (SEM), X-ray powder diffraction (XRD), Fourier transformation-IR/horizontal attenuated total reflectance (FT-IR/HATR) spectroscopy and elemental analysis. A correlation between the electrochemical properties and the structure of the film has been found. The electrochemically inactive films of Co(II) and Fe(II) complexes formed in the presence of acetonitrile in solution consist of densely packed column-like crystallites. They exhibit monoclinic symmetry P/2 m (no. 10). The other films formed in acetonitrile free solutions, form flower-like aggregates of orthorhombic symmetry Pmmm crystals (no. 47). These films are very porous.

Enthalpy and interfacial free energy changes of water capillary condensed in mesoporous silica, MCM-41 and SBA-15

The effect of confinement on the solid-liquid phase transitions of water was studied by using DSC and FT-IR measurements. Enthalpy changes upon melting of frozen water in MCM-41 and SBA-15 were determined as a function of pore size and found to decrease with decreasing pore size. The melting point also decreased almost monotonically with a decrease in pore size. Analysis of the Gibbs-Thomson relation on the basis of the thermodynamic data showed that there were two stages of interfacial free energy change after the constant region, i.e., below a pore size of 6.0 nm: a gradual decrease down to 3.4 nm and another decrease after a small jump upward. This fact demonstrates that the simple Gibbs-Thomson relation, i.e., a linear relation between the melting point change and the inverse pore size, is limited to the range not far from the melting point of bulk water. FT-IR measurements suggest that the decrease in enthalpy change and interfacial free energy change with decreasing pore size reflect the similarity of the structures of both liquid and solid phases of water in smaller pores at lower temperatures.

Solution, solid phase and computational structures of apicidin and its backbone‐reduced analogs

The recently isolated broad-spectrum antiparasitic apicidin (1) is one of the few naturally occurring cyclic tetrapeptides (CTP). Depending on the solvent, the backbone of 1 exhibits two gamma-turns (in CH(2)Cl(2)) or a beta-turn (in DMSO), differing solely in the rotation of the plane of one of the amide bonds. In the X-ray crystal structure, the peptidic C==Os and NHs are on opposite sides of the backbone plane, giving rise to infinite stacks of cyclotetrapeptides connected by three intermolecular hydrogen bonds between the backbones. Conformational searches (Amber force field) on a truncated model system of 1 confirm all three backbone conformations to be low-energy states. The previously synthesized analogs of 1 containing a reduced amide bond exhibit the same backbone conformation as 1 in DMSO, which is confirmed further by the X-ray crystal structure of a model system of the desoxy analogs of 1. This similarity helps in explaining why the desoxy analogs retain some of the antiprotozoal activities of apicidin. The backbone-reduction approach designed to facilitate the cyclization step of the acyclic precursors of the CTPs seems to retain the conformational preferences of the parent peptide backbone.