Physico-chemical and thermochemical studies of the hydrolytic conversion of amorphous tricalcium phosphate into apatite

The conversion of amorphous tricalcium phosphate with different hydration ratio into apatite in water at 25 °C has been studied by microcalorimetry and several physical-chemical methods. The hydrolytic transformation was dominated by two strong exothermic events. A fast, relatively weak, wetting process and a very slow but strong heat release assigned to a slow internal rehydration and the crystallization of the amorphous phase into an apatite. The exothermic phenomenon related to the rehydration exceeded the crystalline transformation enthalpy. Rehydration occurred before the conversion of the amorphous phase into apatite and determined the advancement of the hydrolytic reaction. The apatitic phases formed evolved slightly with time after their formation. The crystallinity increased whereas the amount of HPO₄²⁻ ion decreased. These data allow a better understanding of the behavior of biomaterials involving amorphous phases such as hydroxyapatite plasma-sprayed coatings.     

Utility of N‐[4‐(N‐Substituted Sulfamoyl)Phenyl] Cyanothioformamides in the Synthesis of Heterocyclic Compounds

The novel cyanothioformamides 2a‐d were prepared by treatment of isothiocyanatosulfonamides 1a‐d with potassium cyanide at room temperature. Cyclocondensation of compounds 2b,c with phenyl isocyanate as electrophile furnished the corresponding imidazolidines 3a,b . The reactivity of compound 3a towards some nitrogen nucleophiles was investigated. Thus, the thiosemicarbazone 4 and imidazo[4,5‐b]quinoxaline 6 were synthesized by condensation of compound 3a with thiosemicarbazide and o‐phenylenediamine, respectively. Treatment of 3a with hydrochloric acid afforded compound 7 . Our investigation was extended to include the reactivity of cyanothioformamide 2 towards o‐aminophenol, anthranilic acid, and o‐phenylenediamine and yielded the corresponding heterocycles 9 , 11 and 13 derivatives, respectively. Structures of the synthesized compounds were established by their elemental analysis and spectral data.     

In situ assembled ZIF superstructures via an emulsion-free soft-templating approach

Assembling well-defined MOF superstructures remains challenging as it requires easily removable hard templates or readily available immiscible solutions for an emulsion-based soft-template approach. In this work, a single-step emulsion-free soft templating approach is reported to spontaneously prepare hollow ZIF-8 and ZIF-67 colloidosomes with no further purification. These superstructures can load different enzymes regardless of the size and charge with a high encapsulation efficiency of 99%. We envisage that this work will expand the repertoires of MOF superstructures by the judicious selection of precursors and the reaction medium.

An emulsion-free approach for the preparation of hollow ZIF-8 superstructures in a single step is established based on metal sulfate hydrates in methanol.     

A β-glucosidase from Sclerotinia sclerotiorum

The filamentous fungus Sclerotinia sclerotiorum, grown on a xylose medium, was found to excrete one β-glucosidase (β-glu x). The enzyme was purified to apparent homogeneity by ammonium sulfate precipitation, gel filtration, anion-exchange chromatography, and high-performance liquid chromatography (HPLC) gel filtration chromatography. Its molecular mass was estimated to be 130 kDa by HPLC gel filtration and 60 kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis, suggesting that β-glu x may be a homodimer. For p-nitrophenyl β-d-glucopyranoside hydrolysis, apparent K _m and V _max values were found to be 0.09 mM and 193 U/mg, respectively, while optimum temperature and pH were 55–60°C and pH 5.0, respectively. β-Glu x was strongly inhibited by Fe²⁺ and activated about 35% by Ca²⁺. β-Glu x possesses strong transglucosylation activity in comparison with commercially available β-glucosidases. The production rate of total glucooligosaccharides (GOSs) from 30% cellobiose at 50°C and pH 5.0 for 6 h with 0.6 U/mL of enzyme preparation was 80 g/L. It reached 105 g/L under the same conditions when using cellobiose at 350 g/L (1.023 M). Finally, GOS structure was determined by mass spectrometry and ¹³C nuclear magnetic resonance spectroscopy.     

Spectral and magnetic properties of phenylazo-6-aminouracil complexes

Complexes of Co(II), Ni(II) and Cu(II) with substituted phenylazo-6-aminouracils containing (-H, p-OH, p-CH(3), p-OCH(3) p-COOH) have been synthesized and characterized by elemental analysis, magnetic measurements and spectral measurements (IR, UV-Vis, ESR). Infrared spectra assigned the fundamental bands of the major groups, O-H, N-H, C-H, C=O, C=N, N=N, C-N and C-O (nu, delta and gamma modes of vibrations). The absence of nu(OH) and the appearance of nu(C=O) in the infrared spectra of the free ligands of 5-(p-tolyl and p-anisylazo)-6-aminouracil, assigned the keto structure, whereas in cases of 5-(phenyl, p-hydroxyphenyl and p-carboxyphenylazo)-6-aminouracil ligands, the data showed strong nu(OH) and nu(C=O) bands to assign keto-enol tautomerisms. The modes of interactions between the ligands and the metals were discussed, where oxygen and nitrogen atoms (of amino-amide groups) are involved in chelation. The azo group was not involved in chelation for all the prepared complexes except those of copper complexes derived from 5-(phenyl, p-tolyl, p-hydroxyphenyl and p-carboxyphenylazo)-6-aminouracils. The room temperature effective magnetic moment values, the Nujol mull spectra and ESR proved that all the prepared complexes were of octahedral geometry, except the nickel complex derived from 5-(phenylazo)-6-aminouracil and cobalt complex derived from 5-(p-carboxy-phenylazo)-6-aminouracil were square planar.     

KMo5O13 and KNb1.76Sb3.24O13

The title compounds, potassium pentamolybdenum oxide, KMo₅O₁₃, and potassium niobate antimonate or potassium niobium antimony oxide (1/1.76/3.24), KNb_1.76Sb_3.24O₁₃, were synthesized by solid‐state reactions and are isomorphous in space group Cmcm. The structure of the Mo complex has three unique Mo atoms and consists of MoO₆ octahedra sharing edges to form Mo₂O₆ pairs and Mo₃O₉ triplets, which, in turn, form layers by sharing corners. These layers are linked together in the [100] direction, yielding a three‐dimensional network similar to that of KSb₅O₁₃. This framework delimits interconnected tunnels, running approximately along the [110] and [10] directions, in which K⁺ ions are located. In the isomorphous KNb_1.76Sb_3.24O₁₃ structure, one of the Mo sites in KMo₅O₁₃ is replaced by Sb and the other two Mo sites have been replaced by Nb/Sb.     

Vacancies in the solids of low molecular weight organic compounds observed by positron annihilation

PAL were measured for several low molecular organic compounds, normal and cyclic-hydrocarbons and their perfluorinated ones, from room temperature down to about 40 K, and information about the vacancies in them has been extracted from ₃ andI ₃. Normally the size of vacancies were larger in the solids comprising larger molecules, showing thato-Ps can represent the vacancy size. In a special case of perfluorocyclohexane whose solid had to be prepared by sublimation the vacancy size was larger than expected. In all the solid molecules studied twoo-Ps states could be observed and their relative importance could easily change showing a hysteresis-like behavior. At further lower temperatures of around 40 K theo-Ps state with longer lifetime and larger intensity became overwhelming for all molecules. Also ₃ andI ₃ were not very sensitive to most of the phase transitions, including the melting points.     

Chromium(III) complexes of naturally occurring amino acids

Summary Amino acid complexes of CrCl₃Py₃ have been prepared and studied by elemental analysis, magnetic susceptibility, vibrational (i.r.), electronic and circular dichroism spectroscopy. Two peaks in the visible spectra are assigned to a d-d transition in pseudo octahedral symmetry. The spectrochemical parameters (Dq, B and ₃₅) for the complexes were calculated which confirm that pyridine nitrogen and/or chlorine are not removed. Prolonged heating or bubbling of air through the solution of CrCl₃-Py₃ containing l-(-)-histidine or l-(-)-threonine for several hours enhanced formation of chromium (VI).     

Synthetic strategies and functional reactivity of versatile thiophene synthons

Abstract

Thiophenes are a highly important group of heterocycles and have been of great interest to researchers due to their various reactivities. Many synthetic strategies are used to generate functionalized thiophene derivatives. Several reactions are described, depending on the reactivity of the substituents attached to the thiophene nucleus toward different nucleophiles to yield the versatile thiophene products. Many diverse applications have been utilized for thiophenes from medicinal chemistry to material science.