Formation of third generation poly(pyrazolyl)borate ligands from alkyne coupling reactions of Fe[(p-IC6H4)B(3-Rpz)3]2 (R = H, Me; pz = pyrazolyl): pathways toward controlling an iron(II) electronic spin-state crossover

Sonogashira coupling reactions of terminal alkynes with Fe[(p-IC6H4)B(3-Mepz)3]2 (pz = pyrazolyl ring) yield Fe[(p-PhC2C6H4)B(3-Mepz)3]2 (2), Fe[(p-Me3SiC2C6H4)B(3-Rpz)3]2 (R = H, 3a, R = Me, 3b), and Fe[(p-HC2C6H4)B(3-Mepz)3]2 (R = H, 4a, R = Me, 4b), a series of new complexes containing "third generation" poly(pyrazolyl)borate ligands. Complex 2 undergoes a fairly gradual iron(II) electronic spin-state crossover with a 30 K hysteresis, whereas complex 3b is an unusual example of a complex with equivalent iron(II) sites in the high-spin form that shows an abrupt 50% spin crossover. For complex 4b, 50% of the iron(II) sites undergo a gradual spin-state transition between 185 and 350 K with an activation energy of 1590 +/- 30 cm(-1) and a T(1/2) = 280 K and, for the remaining iron(II) sites, an abrupt cooperative spin-state crossover between 106 and 114 K. The crystal structures of 4b obtained for each of the three distinct electronic spin states reveal two crystallographically different iron(II) sites, and analysis of the molecular/supramolecular structures indicates that the difference in the degree of pyrazolyl ring tilting in the ligands between the two sites, rather than the strength of the intermolecular forces, play a prominent role in determining the temperature of the spin-state crossover.     

Redox-Neutral Syntheses and Electrochemical Studies of 10-Bromo-Substituted Light-Stable Antivitamin B12 Candidates

This publication describes the straightforward and redox-neutral synthesis of 10-bromophenylethynylcobalamin and its facile conversion to 10-bromoaquacobalamin. In this approach, the phenylethynyl ligand acts as convenient light-stable protecting group that is removed in quantitative yield under acidic conditions. The proteolytic cleavage at pH 2.0 was studied under pseudo-first-order conditions and is 1.5 times slower than that of phenylethynylcobalamin with a hydrogen instead of a bromine at C(10). Preliminary electrochemical studies of organometallic ethynyl-Cbls (Cbl=cobalamin) are reported for the first time. A reduction potential of −0.94 V vs. Ag/AgCl was determined for the Co^III/Co^I reduction of 10-bromophenylethynylcobalamin. The positive potential shift of 180 mV compared to phenylethynylcobalamin is in agreement with earlier electrochemical studies of related cyanocobalamins.     

Octadecyl silica membrane disks modified with a new Schiff's base for the preconcentration of lead and copper before their determination in water samples

A simple and fast method for the extraction and determination of ppt level of Pb2+ and Cu2+ ions using octadecyl-bonded silica membrane disks modified by a new tetradentates Schiffs base [Bis(2,4-dimethoxy benzaldehyde) ethylen diimine](TDSB) and inductively coupled plasma atomic emission spectrometry is described. Extraction efficiency, and influence of flow rate, pH, type and the least amount of acid for stripping of Cu2+ and Pb2+ from the modified disks and break through volume were evaluated. The maximum capacity of the membrane disks modified by 5 mg of TDSB used was found to be 347 +/- 7 and 470 +/- 6 microg of copper and lead, respectively. The concentration factor is 500 (for 2500 mL water sample and flow rate of 20 mL min(-1)) and detection limit of the proposed method is 12.5 and 150.5 pg/ml for Cu2+ and Pb2+, respectively. The method was applied to the determination of Cu2+ and Pb2+ ions from various water, wastewater, black tea, and hot pepper samples.     

Epoxidation of alkenes with molecular oxygen and isobutyraldehyde catalyzed by immobilized vitamin B12 within Al-MCM-41

Vit-B₁₂/ Al-MCM-41 catalyzed successfully the epoxidation either of cis or trans — stilbene with O₂ as oxidant and isobutyraldehyde as co-reductant with 86–98% reactivity and 97–100% selectivity. Other olefins such as norbornene and styrene undergo epoxidation reaction under similar conditions with good to fair selectivity. Details of the reactions will be presented in this article.     

The Behavior of Phosphorus Reagents Towards Substituted Diazine and Hydrazine Derivatives

Summary. The reaction of dibenzoyldiazine with phosphorus ylides afforded the new 2-[(benzoylhydrazono)phenylalkyl]but-2-enedioic acid dialkylesters. Moreover, ethyl-2(triphenylphosphoranylidene)propionate reacts with dibenzoyldiazine to give the olefinic compound and triphenylphosphine oxide. On the other hand, oxovinylidene-triphenylphosphorane reacts with dibenzoyldiazine to give a new phosphorane adduct. Trialkyl phosphites react with dibenzoyldiazine to yield the dialkyl phosphonate products. The reaction of dibenzoylhydrazide with Wittig reagents gave rise to the new 3,7-diphenylpyrazolo[1,2-α]pyrazole-1,5-diones. Possible reaction mechanisms are considered, and the structural assignments are based on analytical and spectroscopic results.     

Magnetite Nanoparticles Immobilized Pectinase: Preparation,Characterization and Application for the Fruit Juices Clarification

In this work, pectinase was immobilized on the surface of silica‐coated magnetite nanoparticles via covalent attachment. The magnetite‐immobilized enzyme was characterized by Fourier transform infrared spectroscopy, X‐ray powder diffraction, scanning electron microscopy and vibrating sample magnetometery techniques. Response Surface Methodology using Minitab Software was applied for statistical designing of operating conditions in order to immobilize pectinase on magnetic nanoparticles. The optimal conditions were obtained at 30 °C and pH 5.5 with 42.97 μl pectinase for 2 h. The immobilization yield was 50.6% at optimized conditions. Compared to the free pectinase, the immobilized pectinase was found to exhibit enhanced enzyme activity, better tolerance to the variation of pH and temperature, and improved storage stability. Both free and immobilized samples reduced the viscosity of apple juice from 1.12 to 0.88 and 0.92 mm²s^?1, respectively, after 30 min at their optimum temperature. Furthermore, the immobilized enzyme could be reused six consecutive cycles and the efficiency loss in viscosity reduction was found to be only 8.16%.     

Synthesis,characterization and optical properties of ZnO nanoparticles with controlled size and morphology

Zinc oxide monodispersed nanoparticles were synthesized using a modified polyol process without any requirement to use a catalyst or calcination step at high temperature. The morphology and the size of the resulting oxide particles were adjusted by using several synthesis parameters (temperature, alkaline ratio, hydrolysis ratio, etc.). The increasing of the alkaline ratio results in a great change of the elaborated particles morphology that evolved from irregular and anisotropic forms (conical, nanorod-like and elliptical) to spherical one. A growth mechanism of these particles was proposed on the basis of zincite crystal structure and the morphology evolution as a function of the synthesis parameters. The photoluminescence spectra show UV-excitonic and visible emission bands. The strongest intensity of the visible emission was observed in nanorod-like particles, which implies an increased fraction of oxygen vacancies in this sample. The rod-like particles with 1 μm length show the dominant UV-emission, which evidences their improved stoichiometry.     

The zeta potential of PMMA in contact with electrolytes of various conditions: Theoretical and experimental investigation

Many unit operations required in microfluidics can be realised by electrokinetic phenomena. Electrokinetic phenomena are related to the presence of electrical surface charges of microfluidic substrates in contact with a liquid. As surface charges cannot be directly measured, the zeta potential is considered as the relevant parameter instead. PMMA is an attractive microfluidic substrate since micron‐sized features can be manufactured at low costs. However, the existence of PMMA surface charges is not well understood and the zeta potential data found in the literature show significant disagreement. In this article, we present a thorough investigation on the zeta potential of PMMA. We use computations of the potential distribution in the electrical double layer to predict the influence of various electrolyte parameters. The generated knowledge is compared to extensive experiments where we investigate the influence of ionic strength, pH, temperature and the nature of the electrolyte. Our findings imply that two different mechanisms influence the zeta potential depending on the pH value. We propose pure shielding in the acidic and neutral milieus while adsorption of co‐ions occurs along with shielding in the alkaline milieu.     

Selective and Efficient Oxidation of Sulfides to Sulfoxides Using Ceric Ammonium Nitrate (CAN)/Brönsted Acidic Ionic Liquid

A selective and efficient procedure for the oxidation of sulfides to the corresponding sulfoxides is reported using ceric ammonium nitrate in the presence of methylimidazolium hydrogensulfate as Brönsted acidic ionic liquid ([Hmim]HSO ₄ ) as the solvent under mild conditions. The use of nontoxic and inexpensive materials, straightforward procedure, short reaction times, and good yields of the products are the major advantages of this method.