Interface mixing in Co/Cu: in situ electrical conductivity measurements on pulsed-laser-deposited multilayers

By providing the experimental possibility to monitor the electrical conductivity of metallic multilayers prepared by laser ablation during their growth in situ, information can be obtained on interface mixing effects. This is demonstrated for (5 nmCo/5 nmCu)_n multilayers ablated by a UHV–193 nm ArF–Pulsed Laser Deposition (PLD) system. Varying the laser fluence from 4.2 Jcm^-2 to 12.3 Jcm^-2 allows a corresponding variation of the fraction f of energetic particles within the ablated plume as well as of their average energy. As a result of such a bombardment-assisted deposition, mixing effects occur for both growth sequences, Co on top of Cu as well as Cu on top of Co. As expected, these mixing effects are most pronounced for high laser fluences and significantly decrease for fluences close to the ablation threshold. Comparison to TRIDYN Monte Carlo simulations allow one to extract estimates for the fraction f of energetic particles as well as for their average energy. PACS 73.40.Jn; 73.61.At; 75.47.Np; 81.15.Fg     

Total Synthesis and Biological Investigation of (−)‐Artemisinin: The Antimalarial Activity of Artemisinin Is not Stereospecific

Here, we describe an efficient and diversity‐oriented entry to both (?)‐artemisinin ( 1 ) and its natural antipode (+)‐artemisinin, starting from commercially and readily available S‐(+)‐ and R‐(?)‐citronellene, respectively. Subsequently, we answered the still open question regarding the specificity of artemisinins action. By using a drug‐sensitive Plasmodium falciparum NF54 strain, we showed that the antimalarial activity of artemisinin is not stereospecific. Our straightforward and biomimetic approach to this natural endoperoxide enables the synthesis of artemisinin derivatives that are not accessible through applying current methods and may help to address the problem of emerging resistance of Plasmodium falciparum towards artemisinin.     

Diasterio- und enantioselektive Reduktion von β-Ketoestern mit Cyclopentanon-, Cyclohexanon-, Piperidon- und Tetralon-Struktur durch nicht fermentierende Bäcker-Hefe

Diastereo- and Enantioselective Reduction of beta;-Keto Esters Derived from Cyclopentanone, Cyclohexanone, Piperidone and Tetralone by ‘Non-fermenting’ Baker's Yeast Under ‘non-fermenting’ conditions, i.e. in tap water, in the absence of nutrients baker's yeast (25–380 g/g of substrate, aerobic) reduces β-keto esters such as those mentioned in the title with better selectivity than under the normally employed ‘fermenting’ conditions (sugar and nutrients, CO₂ development). With the β- keto esters containing the tetralone substructure, large amount of yeast are required (250–380 g/g); the substrate disappears in the biomass, and the desired reduction product can be extracted after reaction times of up to a week at 30°. The configuration of most products( 16–24 ) is established. Generally, the (R)-β-keto ester is reduced faster than the (S)-enantiomer (the two esters are in equilibrium under the reactio conditions), and the hydride transfer takes place preferentially from the diastereotopic Re-face. The β-hydroxy esters thus available are useful starting materials for syntheses of enantiomerically pure compounds (EPC).     

Emulsifier-free emulsion polymerization with ionic comonomer

Emulsion polymerization of styrene in the absence of emulsifier with K₂S₂O₈ as initiator produced uniform latices. Incorporation of ca. 0.5% ionic comonomer (sodium styrenesulfonate) reduced the particle size from the range 0.5–1.0 μm achieved in prior emulsifier free formulations to a range of 0.15–0.40 μm. Some advantages achieved by incorporation of ionic comonomer were higher polymer content and independently controllable surface charge density. Particle diameter varied as the 0.64 power of the ratio of ionic strength to comonomer, as the ?0.20 power of initiator concentration, and as the 0.46 power of monomer content. Kinetic data suggest that copolymerization takes place in the aqueous phase, and that nuclei for particle growth are formed by precipitation of the initially water-soluble copolymer. The latex is stabilized by sulfonic acid groups of the comonomer, as well as by sulfate end groups from the initiator.     

Kinetic characterization ofpenicillium citrinum lipase in AOT/lsooctane-reversed micelles

A lipase from a wild strain ofPenicillium citrinum was encapsulated in AOT/isooctane-reversed micelles, and the kinetic parameters were studied relative to triolein hydrolysis. Lipolytic activity was strongly dependent on the water amount in the system (W_o) and presented a bell-shaped curve for this parameter, with a maximum in the range of W_o 10–15. Optimum conditions for enzyme activity were pH 8.0 and 45?C. The influence of substrate concentration was also studied. The enzyme showed a Michaelis-Menten behavior and the apparent kinetics constants were calculated as beingV _max.app. - 120 U/mg and K_mapp = 49.2 mM.