Investigations on electrochemical α-methoxylation of selected dipeptides

Voltamperometric studies on the indirect electrochemical α-methoxylation of Boc-Pro-Gly-OMe and Boc-Val-Gly-OMe in MeOH in the presence of NaCl or NaBr as the mediator suggested that the first reaction step was a direct N-halogenation of the dipeptide by active chlorine or bromine adsorbed on the electrode surface. The kind of mediator (NaCl or NaBr), its concentration, the current density, and the applied electric charge had a significant influence on the reaction course. In the case of Boc-Pro-Gly-OMe, the use of sodium bromide was necessary to obtain a relatively high ratio of α-monomethoxylation to α,α-dimethoxylation. For Boc-Val-Gly-OMe, the selectivity for α-monomethoxylation was close to 100%, independently of the mediator. Optimisation of the selected electrolysis parameters allowed us to significantly improve the yield and selectivity of the α-methoxylation of Boc-Pro-Gly-OMe (Kardassis et al. Tetrahedron 54:3471, 1998) and to obtain good results in the α-methoxylation of Boc-Val-Gly-OMe.     

Surface chemistry of SnO2 nanowires on Ag-catalyst-covered Si substrate studied using XPS and TDS methods

In this paper we investigate the surface chemistry, including surface contaminations, of SnO₂ nanowires deposited on Ag-covered Si substrate by vapor phase deposition (VPD), thanks to x-ray photoelectron spectroscopy (XPS) in combination with thermal desorption spectroscopy (TDS). Air-exposed SnO₂ nanowires are slightly non-stoichiometric, and a huge amount of C contaminations is observed at their surface. After the thermal physical desorption (TPD) process, SnO₂ nanowires become almost stoichiometric without any surface C contaminations. This is probably related to the fact that C contaminations, as well as residual gases from air, are weakly bounded to the crystalline SnO₂ nanowires and can be easily removed from their surface. The obtained results gave us insight on the interpretation of the aging effect of SnO₂ nanowires that is of great importance for their potential application in the development of novel chemical nanosensor devices.     

Composites prepared from polyurethanes modified with silicone-acrylic nanopowders

Linear polyurethanes were obtained the reaction of 1,6-hexamethylene diisocyanate with poly(ɛ-caprolactone)diol and butane-1,4-diol. Synthesis was carried out in the presence of 1, 3 and 5 wt.% of polydimethylsiloxane-poly(methyl methacrylate) core–shell nanopowder. Solutions of resulting polyurethanes were cast on PTFE plates and dried at 140 °C to form films. The presence of structures originating from modifier was confirmed by IR and XPS spectroscopy. DSC analysis revealed the presence of crystalline phase in all samples. Contact angles were determined using standard fluids and surface free energy parameters were calculated. The results of these investigations proved that modification with silicone-acrylic nanopowder resulted in significant increase in hydrophobicity of polyurethane surfaces Changes in surface characteristics were also reflected in surface images obtained in AFM studies. It is suggested that the polyurethane composites obtained in this study can be tested as coatings for biomedical applications.     

Effect of Basic Factors of Preparation on Characteristics,Hydrolytic Degradation,and Drug Release From Poly(ester-anhydride) Microspheres

Functional poly(ester-anhydride) microspheres were prepared using emulsion solvent evaporation (ESE) and phase inversion methods (PIM). The poly(ester-anhydride)s were obtained by polycondensation of sebacic acid (SBA) and oligo(3-allyloxy-1,2-propylene succinate) terminated with carboxyl groups (OSAGE). The effects of various parameters, including: polymer and emulsifier concentrations, stirring speed and molecular weight of polyvinyl alcohol (PVA) used as emulsifier on size, size distribution and morphology of microspheres obtained by ESE technique were examined. The size of microspheres obtained was in the range 2–30 µm and depended mainly on the stirring rate in emulsion formulation process, as well as concentration of polymer solution used. Molecular weight of PVA, and its concentration in aqueous phase, significantly influenced tendency to agglomeration of microparticles formed, but only slightly changed the size of microspheres. The present study demonstrated that the ESE method can be useful to formulate, from functional poly(ester-anhydride)s, small (2–3 µm) or large (20–30 µm) microspheres with relatively narrow size distribution. Such microspheres were loaded with three model compounds (rhodamine B, p-nitroaniline, and piroxicam) with different water solubility and their release characteristics were examined. In the present study microparticles were also obtained by alternative phase inversion method to compare mainly stability of polymers during formulation of microspheres by both techniques.     

Relaxor state and electric relaxations induced by the addition of Bi and Mn ions to Pb(Zr0.70Ti0.30)O3 ceramics

The (1 − x)Pb(Zr_0.70Ti_0.30)O₃–xBiMn₂O₅ ceramics (PZT-BM), where x = 0, 0.02, 0.055, 0.11, 0.15, 0.22 and 1, were studied. We determined how addition of nonpolar BM influenced electrical properties of the ferroelectric PZT ceramics. Impedance spectroscopy measurements in broad frequency and temperature ranges were performed and several contributions to impedance response were identified. A crossover to the relaxor state was observed in the PZT-BM ceramics by doping with Bi and Mn ions. The relaxation times for the electric conductivity relaxation and dipole relaxation were estimated from electric modulus representation of the data. Activation energy values of the conductivity process, estimated for T > 510 K, decreased from 0.82 to 0.37 eV when BM content increased. The occurrence of the high-frequency dipole relaxation was assigned to the charge transfer of Ti³⁺/Ti⁴⁺, Zr³⁺/Zr⁴⁺ and Mn³⁺/Mn⁴⁺ ions. Occurrence of the ferroelectric relaxor features were deduced from the non-Arrhenius dependence of the relaxation times. Superposition of the relaxor features and electric relaxations provides high value permittivity (ε′ > 1000) in wide temperature range (~ 250–573 K). This effect corresponds to the disorder and precipitation of ions that were shown using x-ray photoelectron spectroscopy and the time of flight–secondary ion mass spectrometry.     

Solution Combustion Synthesis of nanoscale Cu-Cr-O spinels: Mechanism,properties and catalytic activity in CO oxidation

Nano-structured Cu-Cr-O-based catalysts were successfully prepared by Solution Combustion Synthesis (SCS), and it has been found that their physical properties and atomic structure depend (in a complex way) on the initial composition of SCS processing, that the temperature of combustion and composition of initial mixture influences metal concentration in the nanocomposite, and that metal formation is going through metal oxide reduction by NO, H₂, CO. Presence of CO, NH₃ and H₂ in the gas phase, during SCS, was determined chromatographically. Connection between structural changes during reaction and properties of final nanocomposite material was determined. The catalysts were characterized by XRD, SEM/EDX, and their catalytic activity has been determined in CO oxidation. The pore structure of the samples was calculated with the Barrett-Joyner-Halenda (BJH) academic model, and the specific surface area was calculated with the Brunauer-Emmett-Teller (BET) adsorption equation. The specific surface area of the catalysts is varied between 10 m²/g and 37 m²/g. Understanding the interrelationships between activity of catalyst and the ensuing atomic structure has allowed a degree of optimization of the catalytic properties of the new catalysts.     

Further evidence of responsibility of impurities in MgO for variability in its basicity and catalytic performance in oxidative coupling of methane

Further evidence was delivered that certain impurities, which could be contained in MgO samples, might be responsible for observed variability in MgO basicity and catalytic performance in oxidative coupling of methane. The surface basicity/base strength distribution of a series of MgO samples containing or not containing Ca and Na impurities was determined by a temperature-programmed desorption of CO₂. It was revealed that samples containing Ca and Na impurities have much more medium, strong and very strong basic sites. The surface basicity of MgO samples containing added alkali or alkaline earth compounds or water was characterized by a test reaction of transformation of 2-butanol. It was confirmed that the introduction of these compounds to a pure MgO enhanced both its basicity and activity in oxidative coupling of methane.     

Studies on the synthesis of sodium ates (NaH2PO4, Na2HPO4, Na3PO4) using membrane electrolysis

Comparative studies have been carried out on the electrosynthesis of sodium phosphates in the cathode compartment of an industrial membrane cell supplied with phosphoric acid of concentrations ranging from 1 to 2 mol dm^–3. The anode compartment of the cell was supplied with brine containing 25% NaCl. Du Pont Nafion^® membranes of types N-423, N-901 and N-961 were used. It was found that current efficiencies for the production of sodium phosphates exceeded 96%, this being higher than that for sodium hydroxide and, in spite of the different properties of the membranes, these efficiencies were similar. With N-423 membrane, the current efficiency was 2 3% lower than that for other membranes, but at the same time, the voltage of the cell was lower by 8 12%. Thus, N-423 membrane gives better performance during sodium phosphate synthesis as compared to membranes N-901 and N-961.     

Polymerization of 2-hydroxyethyl acrylate and methacrylate <Emphasis Type="Italic">via</Emphasis> Michael-type addition

Summary 2-Hydroxyethyl acrylate was polymerized by use of few basic andlor nucleophilic initiators. The reactions proceeded via Michael-type addition of hydroxyl groups to carbon-carbon double bonds. The resulted polymers have an ether-ester chain structure and M_n values in order of up to 9000. The results were compared with those obtained previously for 2-hydroxyethyl methacrylate, where just oligomers having M_n of ca 1000 had been achieved.