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.     

Application of monosaccharides derivatives in colloidal processing of aluminum oxide

Obtaining highly loaded, time-stable and relatively low viscosity suspensions approaches colloidal processing to be very convenient and effective route of shaping of nanopowders. In order to obtain well dispersed, homogenous ceramic slurries, certain additives are given. Saccharides, particularly monosaccharides, as well as their derivatives, were found to be a group of effectively working processing agents in case of alumina, which has been used as a solid phase of highly loaded nanosuspensions. This class of chemical compounds can be described by a series of advantages – they are non-toxic, water-soluble, inexpensive, etc. In this paper suspensions of nano- and submicro-alumina powders with addition of d-fructose, 1-O-methyl-d-fructose, d-glucose and 3-O-acrylic-d-glucose have been studied in terms of their rheological properties, moreover the properties of as-received green bodies have been presented.     

The properties of soldering mask hardened by means of UV using acrylate and methacrylate oligomers

The properties of soldering masks based on epoxyacrylic, epoxymethacrylic esters, and monomers: 2-ethylhexyl acrylate, triethylene glycol dimethacrylate, and triethylene glycol phthalate dimethacrylate have been described. The thixotropic properties, printability, adhesion to the surface, and resistance to soldering have been determined. © 1995 John Wiley & Sons, Inc.     

Removal of antimony from copper by injection of soda ash

The removal of Sb from molten copper is of importance in the development of processes which can smelt copper concentrates directly into copper in a single furnace. A promising method is injection of oxygen and sodium carbonate in a modified anode furnace. This study encompassed a thermodynamic analysis of the impurity removal reactions and an experimental investigation of antimony removal from molten copper in a 15 kW induction furnace. The results showed that the reaction was controlled by diffusion of Sb in the metal phase. The reaction between metal and injected flux can be divided into two subprocesses-. (1) “transitory contact” reaction to the injected flux particles as they rise through the melt and (2) “permanent contact” reaction across the interface between the metal bath and the supernatant slag layer. On the basis of the experimental work, the overall volumetric mass transfer coefficient (cm³/s) at 1473 K was expressed in terms of the two subprocesses as follows:(k _d A) _ov = (k _d A) _pc +(k _d A) _tc = 1.25Q _g ^0.29 + 0.28(H Q _f ) whereQ _g is the injection gas flow rate in normal liters per minute,H is the depth of injection in centimeters, andQ _f the rate of flux injection in grams per second.     

Twist,tilt, and symmetric grain boundaries in hexagonal materials

Grain boundaries of characteristic geometry, e.g., twist, tilt, and symmetric boundaries are often used as reference boundaries in analyses of boundary networks in polycrystalline materials. This article deals with the issue of proper identification of characteristic boundaries in the case of materials with hexagonal D _6h symmetry. To identify all boundaries of characteristic types, both analytical calculations and numerical searches are used. The first approach provides exact parameters of the characteristic boundaries, whereas the second one gives boundaries which can be classified as characteristic if some tolerance is allowed. In both methods, all symmetrically equivalent boundary representations are taken into consideration. The obtained sets of twist, tilt, symmetric, and 180°-tilt boundaries are presented in the form of two-dimensional maps containing stereographic projections of the corresponding boundary plane normals for selected grain misorientations. These diagrams facilitate interpretation of experimental distributions of grain boundaries; with the representation used, they can be directly linked to experimental distributions. Examples of such diagrams for lattice parameter ratios c/a of $\sqrt{5/2}$ and $\sqrt{20/21}$ are presented. They are compared to example boundary distributions in Ti alloy and distributions of WC/WC boundaries in WC–Co composites available in the literature.     

Application of composites to impact energy absorption

The sleeve, conical simple composite elements and polymer foam filled composite conical element behaviour during failure are presented and discussed. The impact energy in these elements is absorbed in progressive fracture process. Possibilities of energy absorption panels – the great structures made from simple elements in a certain military and civilian field are demonstrated.     

Changes in structure of psoas major and minor and semitendinosus muscles of calves, heifers and cows during post-mortem ageing

Changes occurring during post-mortem ageing in structure of psoas major and minor (PM) and semitendinosus (ST) muscles of calves, heifers and cows were observed. Samples from muscles taken 3 h after slaughter and after 6 and 12 days of storage at the temperature of 4?°C were analysed using light and transmission electron microscopy. Three hours after slaughter muscle fibres were close to each other and sarcomeres showed normal structure of A- and I-bands, M-lines and Z-disks. The space between myofibrils and sarcolemma and also between single myofibrils in muscle fibres increased during storage. Structure of sarcomeres underwent continuous degradation, length of sarcomeres increased due to enlargement of I-bands accompanied by Z-disk degradation. During ageing structural changes in myofibrils took place faster, were more intensive in muscles of younger animals and were more extensive and faster in PM than in ST muscles.     

X-ray scattering investigations of acrylonitrileethylene oxide block copolymers

Wide angle (WAXS) and small angle (SAXS) X-ray scattering studies are reported on block copolymers of acrylonitrile with ethylene oxide. A distinct structural similarity between the copolymers and acrylonitrile homopolymer has been found. Considerable porosity of the copolymers has been shown. The porosity very largely governs the scattering power. It was found that the pores are three dimensional “particles” (scattering exponent α = 4), probably with smooth surfaces (surface fractal dimension d_s = 2).