The characterization and polymorphism of α-Glycine in the presence of butyric acid

The present study aims to investigate the effect of butyric acid used as an additive and its concentration ranging between 50?ppm and 250?ppm during the polymorphic phase transformation of β-glycine to α-glycine. Analysis includes a continuous measurement of the ultrasonic velocity and periodically the X-ray diffraction (XRD) pattern. Morphological characterization shows that the α-glycine crystals obtained in pure media are smooth, prismatic shapes, and that butyric acid plays a major role in crystal shape change. SEM imaging and morphology analysis indicates that the presence of butyric acid to media results in shorter, rounded and aggregated crystals. Further analyses of Fourier Transform Infrared Spectroscopy (FTIR), zeta potential measurements, and elemental analysis reveals that butyric acid adsorbs on the crystals’ surface and changes both the surface charge and the elemental composition of the crystals obtained. In addition, thermal decomposition behaviors of the crystals are investigated and the obtained data is modeled using the thermal decomposition kinetic models of FWO, KAS, and Tang. Based on the data of the FWO kinetic model, the average activation energy of the crystals obtained in butyric acid media is calculated as 118.8?±?17.0?kJ/mol, which is higher than that of crystals obtained in pure media.     

Synthesis of Tyr-Pro-Phe-Val-Glu-L-[3,4-3H]Pro-Ile,Tyr-D-Ala-Phe-Gly-Tyr-L-[3,4-3H]Pro-Ser-NH2, and Tyr-D-Ala-Phe-Gly-Tyr-D-[3,4-3H]Pro-Ser-NH2, Labeled Analogs of Human β-Casomorphin and Dermorphin

Analogs of human -casomorphin and dermorphin, unsaturated in the proline unit, were prepared. Procedures were developed for tritium labeling of these peptides. It was advantageous to introduce the label before deprotection, since in this case the reaction can be performed in an aprotic solvent. Tritiation before deprotection ensured 5-6 times higher molar radioactivity of the products.     

Behaviour of the complex dielectric function and energy loss spectrum of copper in the [110] direction in the energy range 2 < ħω ⩽ 4 Rydberg

The complex wave vector- and frequency-dependent dielectric function, (q,) = ₁ (q,) + ₂ (q,), for copper is calculated using realistic band energies and wave functions. The Bloch states _bk (r) are obtained from the modified augmented plane wave method (MAPW) with the Chodorow potential. Results are presented for the principal direction ofq, [110]. About 70 bands and 60 plane waves at 10k-points in the 1/48th of the Brillouin zone are considered. An additional peak was found at the energy loss spectrum of copper whose centre is situated near 2.1 Rydberg, its centre moves gradually to the high energy side with increasing |q|. According to our knowledge, it is the first time this result has been calculated theoretically or even measured experimentally in the [110] direction for copper.     

Hydrothermal Crystallization in the Systems LiOH–MO2–GeO2–H2O (M = Ti, Sn) at 500°C and 0.1 GPa: Li2Ti[5]Ge[4]O5 and Li2Ge[6]Ge2 [4]O6 Phase Relations

Crystallization in the LiH–Ti₂–Ge₂–H₂O and LiOH–SnO₂–GeO₂–H₂O hydrothermal systems was studied at 500°C and 0.1 GPa. The phases crystallizing in the Ti system are Li₂Ti^[5]Ge^[4]O₅, Li₂Ge^[6]Ge₂ ^[4]O₆(OH)₂, Li₃HGe₄ ^[6]Ge₃ ^[4]O₁₆ · 4H₂O, and Li₂Ge^[4]O₃ (Ge in four- or sixfold oxygen coordination, and Ti in fivefold oxygen coordination). Over a wide range of TiO₂ : GeO₂ molar ratios (6 : 1 to 1 : 1), the dominant phase is Li₂Ge^[6]Ge₂ ^[4]O₆(OH)₂. At higher GeO₂ contents (TiO₂ : GeO₂ = 1 : 2 to 1 : 6), both Li₂Ti^[5]Ge^[4]O₅ and Li₂Ge^[6]Ge₂ ^[4]O₆(OH)₂ crystallize. The crystallization fields of Ge-containing phases at TiO₂ : GeO₂ = 1 : 2 to 1 : 6 are (in order of increasing LiOH concentration) GeO₂ (rutile structure), Li₂Ti^[5]Ge^[4]O₅ + Li₂Ge^[6]Ge₂ ^[4]O₆(OH)₂, and Li₂Ti^[5]Ge^[4]O₅ + Li₂Ge^[6]Ge₂ ^[4]O₆(OH)₂ + Li₂Ge^[4]₃ + Li₃HGe₄ ^[6]Ge₃ ^[4]O₁₆ · 4H₂O. The phases crystallizing in the Sn system are Li₂Ge^[6]Ge₂ ^[4]O₆(OH)₂, Li₃HGe₄ ^[6]Ge₃ ^[4]O₁₆ · 4H₂O, and Li₂Ge^[4]O₃. Tin is present in the form of SnO₂ only. The structures of Li₂Ti^[5]Ge^[4]O₅ and Li₂Ge^[6]Ge₂ ^[4]O₆(OH)₂ are characterized by the simplest type of matrix assembly: direct packing of substructural precursor units and their two-dimensional growth in various crystallographic directions.     

Characterization and corrosion behavior of electroless Ni–P/nano-SiC coating inside the CO2 containing media in the presence of acetic acid

In this research, Ni–P and Ni–P/nano-SiC coatings were applied on the X70 steel substrate successfully without any surfactant. Then, CO₂ corrosion in the presence of acetic acid (HAc) was investigated using electrochemical techniques. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) techniques were used for surface analyses of the coatings. The electrochemical behavior of corrosion was investigated using polarization test and electrochemical impedance spectroscopy (EIS). XRD pattern of Ni–P/nano-SiC coating was very similar to that of Ni–P coating. EDS results demonstrated the presence of SiC particles in the coating. SEM images confirmed the presence of SiC nano-particles with almost uniform distribution in the coating. The corrosion current density was less in the Ni–P and Ni–P/nano-SiC coated samples than uncoated X70 steel. Ni–P/nano-SiC coated sample had the most corrosion resistance because of less effective metallic area available for corrosive media. The overall protection mechanism of Ni–P and Ni–P/nano-SiC coatings was achieved by formation of a layer of adsorbed hypophosphite anions (H₂PO₂⁻).     

Thermal conductivity and electrical resistivity of the T′ phase and the T phase in 2-1-4 oxide superconductors

The temperature dependences of the thermal conductivity,(T), and the electrical resistivity,(T), of sintered samples of Nd_1.85Ce_0.15CuO_4–y (NCCO) and Pr_1.85Ce_0.15CuO_4–y (PCCO) with the T phase, and La_1.85Sr_0.15CuO_4–y (LSCO) and La_1.935Ca_0.065CuO_4–y (LCCO) with the T phase, have been measured. The superconducting transition temperatureT _con , of NCCO, PCCO, LSCO, and LCCO were 26.4, 23.0, 37.1, and 8.8 K, respectively. The enhancement of(T) below justT _con such as seen in 1-2-3 oxide superconductors was not clearly observed.(T) for the samples of NCCO and PCCO showed a pronounced maximum such as that of sapphire crystal around 30 and 40 K, respectively. For these samples of NCCO and PCCO, it has been shown that the analysis based on the various phonon scattering mechanisms is in good agreement with our experiment.     

Evaluation of the controlled release ability from the poly(2-hydroxyethyl methacrylate-co-3,9-divinyl-2,4,8,10-tetraoxaspiro[5.5]-undecane) polymer network synthesized in the presence of β-cyclodextrin

The study presents the possibility to use the 2-hydroxyethyl methacrylate--HEMA copolymer with a comonomer with spiroacetal moiety, 3,9-divinyl-2,4,8,10-tetraoxaspiro[5.5]-undecane)-U, as polymer network for loading the indomethacin--INN as drug model, and also, the controlled release evaluation of the prepared bioactive system. The macromolecular compounds were prepared by radical dispersion polymerization in the presence of a pair of surfactants. The use of cyclodextrin as surfactant allowed the building of the host-guest complexes by inclusion of hydrophobic molecules. Also, the cyclodextrin supplemented the hydrogen bonds and the hydrophobic interactions responsible for the stability of the achieved complexes. The copolymers composition and the INN inclusion onto the polymeric matrix were confirmed by FTIR analysis. The porous structure of the lyophilized P(HEMA-U) samples was illustrated by SEM images. The swelling studies evidenced the interdependence between P(HEMA-U) network properties and the spiroacetal moiety amount. Thus, the copolymers presented the increase of the equilibrium swelling degree with pH and temperature. Also, the polymeric matrices manifested dual sensitivity with pH and temperature. The in vitro release of the INN drug from the polymeric network as well as the in vivo experimental studies evidenced the benefit consequence of the spiroacetal compound presence. The clinical observation of the experimental groups does not show any behavioral modifications to suggest a possible toxic effect of these polymeric formulations with and without INN.     

Competition between superconductivity and insulating magnetic state in κ-(BEDT-TTF)2Cu[N(CN)2]Cl: Effects of pressure, magnetic field, and partial anion substitution

Systematic experimental study of the electrical transport and static magnetization reveals a direct and delicate interplay between magnetism and superconductivity in the organic material-(BEDT-TTF)₂Cu[N(CN)₂]Cl, displayed through the specific temperature-pressure phase diagram, and such new effects for organic solids as the reentrant superconductivity in zero applied magnetic field and high-field-induced interchange between superconductivity and the nonmetallic resistive phase in the high-pressure region.     

New quaternary alkali metal,rare earth (3+) thiophosphate,K2SmP2S7 with both [P2S6]4− and [PS4]3− anions

A new quaternary alkali metal, rare earth thiophosphate was synthesized by the ceramic method and characterized by single crystal X-ray diffraction: K₂SmP₂S₇ crystallizes in the monoclinic space group C2 (no. 5) with the unit cell parameters a = 22.746(5) Å, b = 6.7362(13) Å, c = 8.9004(18) Å, β = 99.68(3)°, V = 1344.3(5) Å³ and Z = 2. The phase K₂SmP₂S₇ can be better described as K₄Sm₂[PS₄]₂[P₂S₆] because it contains in the crystal structure both discrete anions [PS₄]^3? and [P₂S₆]^4?. The crystal structure consists of infinite chains of ¹_∞[SmPS₄] that are linked together through the ethane-like [P₂S₆]^4? anions to form two-dimensional layers. The packing of K₂SmP₂S₇ is formed by layers of ²_∞[Sm₂[PS₄]₂[P₂S₆]]^4? separated by K⁺ cations. K₂SmP₂S₇ was characterized by Raman and Fourier transform infrared (FTIR) spectroscopy and SEM-EDX microprobe analyses. The optical band gap of K₂SmP₂S₇ was determined by UV–vis diffuse reflectance measurements to be 2.59 eV.     

Synthesis,characterization and crystal structure of a novel Strandberg-type polyoxoselenomolybdate Rb4[Se2Mo5O21]·2H2O

An inorganic compound formulated as Rb₄[Se₂Mo₅O₂₁]·2H₂O (1) has been isolated by conventional solution method and structurally characterized by single-crystal X-ray diffraction methods, scanning electron microscopy (SEM), powder XRD, IR, UV–vis spectra, and cyclic voltammetry measurements. This compound crystallizes in the monoclinic system, space group C2 with unit a = 19.701 (3) Å, b = 10.296 (2) Å, c = 12.134 (4) Å, β = 106.96 (2)° and Z = 4. The crystal structure of (1) is built up from a Strandberg clusters connected through hydrogen-bonding interactions into a three-dimensional supramolecular network.     

Complexation of hexavalent U,Np, and Pu with cyclopropanecarboxylate anions. Crystal structure of the uranyl complexes {[UO2(bipy)(cpc)]2O2} and [UO2(cpc)2(H2O)2] (bipy = 2,2′-Bipyridine,cpc− = cyclopropanecarboxylate anion)

The complexation of hexavalent U, Np, and Pu with cyclopropanecarboxylate anions, cpc^?, in aqueous solutions was studied. The stepwise concentration stability constants of the complexes PuO₂(cpc) _i ^2?i (i = 1, 2, 3) are as follows: logK _1,2,3 = 2.63 ± 0.20, 1.61 ± 0.20, 1.43 ± 0.20, respectively; the overall concentration stability constant of the complex PuO₂(cpc) ₃ ^? is logβ₃ = 5.67 ± 0.60. The complexing properties of the cpc^? anion are very close to those of butyrate and isobutyrate anions. Two crystalline uranyl compounds were synthesized: {[UO₂(bipy)(cpc)]₂O₂} (bipy = 2,2′-bipyridine) and [UO₂(cpc)₂(H₂O)₂]. The specific feature of the first complex is that it contains peroxide ion. Its appearance may be due to the formation of the cationic moiety via hydrolytic uranyl dimer. The second compound forms a 3D structure, with the complexes linked via hydrogen bonds.     

Synthesis, Structure, and Properties of New Hybrid Nanocomposites Containing the [Mo6(μ3-Cl)8]4+ Cluster

A new type of hybrid nanocomposite material is produced via consecutive outer-sphere transformations of a Mo-containing cluster. Cluster monomers with the general formula (Bu₄N)₂[(Mo₆Cl₈)(CF₃COO)_{6 – n} CH₂=CHCOO _n ] (n= 1–3) are synthesized and characterized for the first time. The bulk radical copolymerization of such monomers with acrylic acid is an interfacial process and leads to the formation of hybrid (metal-containing polymeric) nanocomposites. The synthesized copolymers (1–5 wt % Mo, M 270000, 5–24 cluster units per polymer chain) are examined by nuclear magnetic resonance and IR spectroscopy. The results indicate that the copolymers contain stereoregular (syndiotactic) polyacrylic acid. The structure of the cluster-containing composites, the distribution of cluster units over the polymer chain, and the origin of stereoregularity in such systems are discussed. According to differential thermal analysis results, the introduction of clusters into the polymer chain has an insignificant effect on the thermal stability of the nanocomposites. The same is evidenced by the results on the molecular–topological properties of the nanocomposites.     

Molecular Complex of [60]Fullerene with 2-(4-thione-l,3-dithiolan-5-yliden)-4,5-dimethyl-1,3-diselenol [C60·2(DTDS)]: Synthesis,Crystal Structure and Properties

Abstract

New molecular complexes of [60]fullerene with 2-(4-thione-l,3-dithiolan-5-yliden)-4,5-dimethyl-l,3-diselenol [C₆₀·2(DTDS)] have been synthesized, crystal structure, IR spectral and electrochemical properties have been studied. Partial charge transfer has been found. An unusual shortening of the endocyclic S-C(sp²) bond in the DTDS molecule has been found to be stipulated by conformational vibrations of the >CH₂ group. A comparative analysis of the X-ray data for the [C₆₀·2(DTDS)] crystals and the quantum chemical calculations (SCF MO, 6-31G? basis) for the DTDS molecules and its radical ions showed charge transfer not to be the cause for the shortening of the exocyclic C=S bonds.     

Cobalt-mediated synthesis of 2-(4-pyridyl)benzimidazole. x-ray structures of Co[2-(4-pyridyl)benzimidazole]2(H2O)2(NO3)2 and [Co(isonicotinate)(4-pyridiniumcarboxylate)(H2O)(NO3)]∞

We have observed an unusual example of cobalt-mediated cyclization of 4-pyridinecarboxaldehyde and 2-nitroaniline to afford 2-(4-pyridyl)benzimidazole under hydro(solvo)thermal conditions. Reaction of Co(NO₃)₂·6H₂O with 4-pyridinecarboxaldehyde and 2-nitroaniline in ethanol at 120°C gave a cobalt(II) coordination compound, Co[2-(4-pyridyl)benzimidazole]₂(H₂O)₂(NO₃)₂, 1. In contrast, when the hydro(solvo)thermal reaction was carried out between Co(NO₃)₂·6H₂O and isonicotinic acid in the presence of 2-nitroaniline at 110°C, a one-dimensional Co(II) coordination polymer with the formula of [Co(isonicotinate)(4-pyridiniumcarboxylate)(H₂O)(NO₃)]_∞, 2, resulted. The X-ray single crystal structures of both 1 and 2 are described. Interestingly, the isonicotinic acid in 2 exists as a 4-pyridiniumcarboxylate tautomer, and the pyridinium hydrogen atom forms a very strong hydrogen bond to the carboxylate oxygen of the 4-pyridiniumcarboxylate on an adjacent metal center. 1 forms a three-dimensional polymeric network through hydrogen bonding interactions, while 2 exists as a 2-D bilayer polymeric network through hydrogen bonding interactions.     

Effects of ZrO2 and Y2O3 dissolved in zyttrite on the densification and theα/β phase transformation of Si3N4 in Si3N4-ZrO2 composite

In Si₃N₄-ZrO₂ composite, the effects of zirconia and Y₂O₃ dissolved in zyttrite on the densification and the/ phase transformation of Si₃N₄ were studied using hot-pressing of Si₃N₄ with the addition of pure, 3, 6, and 8 mol% Y₂O₃-doped zirconia. Reaction couples between Si₃N₄ and ZrO₂ of zyttrite were made to observe the reaction phenomena. The addition of pure zirconia was not effective to obtain full density of the Si₃N₄-ZrO₂ composite. However, Y₂O₃ diffused from the added zyttrite promoted densification; the density of Si₃N₄ with 5 vol% pure ZrO₂ composite was 71% theoretical, and nearly full density (>97%) could be obtained in Si₃N₄ with 5 vol% 6, 8 mol% Y₂O₃-doped ZrO₂ composite. On the basis of observations of the Si₃N₄-pure ZrO₂ reaction couple, the reaction between Si₃N₄ and ZrO₂ resulted in the formation of Si₂N₂O phase, and the/ phase transformation of Si₃N₄ occurred via this Si₂N₂O phase. From the XRD analysis of the reaction layer between Si₃N₄ and zyttrite, it is suggested that the reaction products, Y₂Si₂O₇ and Y₂Si₃N₄O₃ phases, play an important role in the densification of Si₃N₄-zyttrite composite.     

Temperature dependence of the electrical conductivity in 4, 4′ bis(2-thenylideneamino)biphenyl and 4, 4′ bis(thenyldiphenyl-phosphinylmethyleneamino)biphenyl compounds

Correlation of the molecular structure and utilizing measurements of the electrical conductivity, activation energy of conduction of 4,4 bis(2-thenylideneamino)biphenyl (SB) and 4,4 bis(thenyl-diphenylphosphinylmethyleneamino)biphenyl (OPSB) compounds have been carried out. The results of the activation energies, obtained from the electrical conductivity measurements, as well as the energy gaps calculated from ultraviolet (u.v.) and visible spectra in the solid state indicate that the investigated compounds behave like semiconducting materials. The delocalized -electrons in addition to the lone pairs of electrons on the nitrogen atoms of the two compounds as well as the donor effect of diphenylphosphinyl groups of OPSB compound were considered as the main sources participating in the conduction processes.