Changes in the hydrogenative ring-opening mechanism of cyclohexene oxide over Cu/SiO2 resulting from the addition of cyclohexene, a major product

The ring-opening mechanism influencing effect of a major product in the cyclohexene oxide–D₂ system was investigated over a Cu/SiO₂ catalyst. This product is cyclohexene, thus, the hydrogenative ring opening of a 1:1 cyclohexene oxide–cyclohexene mixture was studied in the presence of D₂ at 403 K in a closed circulation reactor. It was found that the mechanism of single C–O scission was not affected, but that of the double C–O scission was changed. Simultaneous bond cleavage was the major route of ring opening in the additive-free system and it became consecutive on cyclohexene addition. Added cyclohexene was hydrogenated with a very low rate, but it transformed the surface of the catalyst and, thus, facilitated the change in the mechanism. An explanation concerning the seemingly anomalous lack of deuterium in a product (cyclohexane) not seen in the additive-free system is also suggested. This revised version was published online in November 2006 with corrections to the Cover Date.     

Monotectic Al/Cd alloys with homogeneously dispersed Cd-droplets stabilized by strontium aluminide precipitates

Al-rich Al–Sr alloys contain dispersed Al₄Sr precipitates in the Al-matrix. When melted and emulsified together with a smaller volume of Cd, Cd-rich droplets are formed (being immiscible with the Al-rich liquid). The Al₄Sr precipitates prefer the Al/Cd interface, stabilizing the Cd droplets in the Al-matrix. The contact angle of the Cd-rich liquid on Al₄Sr intermetallic phase under the Al-rich liquid alloy is about 90°, being ideal for emulsion stabilization. In this way, Al/Cd monotectic alloys can be produced with homogeneously dispersed Cd particles. The key to the success of this process is the in-situ formation of strontium aluminide precipitates stabilizing the Cd droplets in the liquid Al/Cd emulsion.     

Every free algebra in the variety generated by the representable dynamic algebras is separable and representable

Kozen [4] and Pratt [7] defined the class SDA of separable dynamic algebras. V denotes the variety generated by SDA. After Lemma 5.6 [7,p. 18], Pratt raised the question whether every free V-algebra is separable or not. Here we prove that every free V-algebra is separable and is isomorphic to a Kripke structure, i.e. is representable. These statements improve Lemma 5.6 and Theorem 6.1 in [7, pp. 18-19] respectively. We also provethat the class KDA of representable dynamic algebras is closed under direct products, and hence KDA is an infinitary quasi-variety.     

A novel way for ethoxylation with basic catalysts

Ethoxylation of dodecyl alcohol catalyzed by alkali hydroxides are accelerated by adding complexing agents for the alkali ions. The rate of ethoxylation could be increased by crown ether and dodecyl alcohols of a higher degree of ethoxylation. The effect is more pronounced with the crown ether; thus, reactions not taking place under other circumstances could also be carried out. The complexing additives have no significant effect on the molar mass distribution, The reaction could also be accelerated by using more bulky organic cations (e.g., triethylbenzylammonium ion) instead of the alkali cation.     

Controlled Synthesis of Pt3Sn/C Electrocatalysts with Exclusive Sn–Pt Interaction Designed for Use in Direct Methanol Fuel Cells

Alloy-type Sn–Pt/C electrocatalysts with Pt/Sn = 1.8–3.0 ratios and exclusive Sn–Pt interaction have been prepared by means of controlled surface reactions (CSRs). As demonstrated by XRD, the incorporation of Sn onto Pt/C was achieved satisfactorily yielding a near-stoichiometric fcc Pt₃Sn alloy phase along with a certain amount of the Pt_(1 ? x)Sn_x solid solution. The content and dispersion of the fcc Pt₃Sn phase within the electrocatalysts can be controlled by tuning the reaction conditions of CSRs. No evidence of the presence of SnO₂ phases in the Sn-modified Pt/C samples was found by means of the XRD and EDS analysis. According to in situ XPS studies, the pre-treatment in hydrogen at 350 °C resulted in complete reduction of tin to Sn⁰. These results demonstrate that the method of CSRs is a powerful tool to create of Pt–Sn bimetallic nanoparticles exclusively, without tin introduction onto the carbon support. The performance of the intermetallic SnPt/C catalysts in the CO and methanol electrooxidation reactions depends on the actual composition of the exposed surface and the size of bimetallic particles. In the consecutive tin introduction the decrease of the amount of SnEt₄ precursor added per period, accompanied with an increase of the number of anchoring periods, resulted in an increase of the activity in both electrooxidation reactions as a consequence of an optimal balance of Pt/C ratio, the content of fcc Pt₃Sn phase and metal particle size. It was demonstrated that the increasing tin content above a certain (optimal) amount gives rise to a negative effect on the catalyst performance in the CO and methanol electrooxidation.     

Attachment and proliferation of human osteoblast-like cells (MG-63) on laser-ablated titanium implant material

Demand is increasing for shortening the long (3–6 months) osseointegration period to rehabilitate patients' damaged chewing apparatus in as short a time as possible. For dental implants, as for biomaterials in general, the bio- and osseointegration processes can be controlled at molecular and cellular levels by modification of the implant surface. One of the most promising of such surface modifications is laser ablation, as demonstrated by our previous results [46]. Commercially pure (CP4) sand-blasted, acid-etched titanium disks (Denti® System Ltd., Hungary) were irradiated with a KrF excimer laser (248 nm, fluence 0.4 J/cm², FWHM 18 ns, 2000 pulses), or with a Nd:YAG laser (532 nm, 1.3 J/cm², 10 ns, 200 pulses) then examined by SEM, AFM, and XPS. In vitro attachment (24 h) and proliferation (72 h) of MG-63 osteoblast cells were investigated via dimethylthiazol-diphenyl tetrazolium bromide (MTT), alamarBlue (AB) assays alkaline phosphatase quantification (ALP) and SEM. SEM and AFM revealed significant changes in morphology and roughness. XPS confirmed the presence of TiO₂ on each sample; after Nd:YAG treatment a reduced state of Ti (Ti^3 +) was also observed. MTT, AB and ALP measurements detected an increase in the number of cells between the 24- and 72 hour observations; however, laser treatment did not affect cell attachment and proliferation significantly.     

A novel cyclic RGD-containing peptide polymer improves serum-free adhesion of adipose tissue-derived mesenchymal stem cells to bone implant surfaces

Seeding of bone implants with mesenchymal stem cells (MSCs) may promote osseointegration and bone regeneration. However, implant material surfaces, such as titanium or bovine bone mineral, fail to support rapid and efficient attachment of MSCs, especially under serum-free conditions that may be desirable when human applications or tightly controlled experiments are envisioned. Here we demonstrate that a branched poly[Lys(Ser_i-DL-Ala_m)] polymer functionalized with cyclic arginyl-glycyl-aspartate, when immobilized by simple adsorption to tissue culture plastic, surgical titanium alloy (Ti6Al4V), or Bio-Oss^® bovine bone substitute, significantly accelerates serum-free adhesion and enhances seeding efficiency of human adipose tissue-derived MSCs. Moreover, when exposed to serum-containing osteogenic medium, MSCs survived and differentiated on the peptide-coated scaffolds. In summary, the presented novel polypeptide conjugate can be conveniently used for coating various surfaces, and may find applications whenever quick and efficient seeding of MSCs is required to various scaffolds in the absence of serum.