Lipase-catalyzed esterification of citronellol with lauric acid in supercritical carbon dioxide/co-solvent media

Direct esterification of citronellol and lauric acid catalyzed by immobilized lipase B from Candida antarctica was performed in supercritical carbon dioxide with different organic solvents and ionic liquids serving as co-solvents. The highest concentration of citronellol laurate after 1 h of reaction performance (3.95 mmol/g substrates) was obtained in SC CO₂ with ethyl methylketone serving as a co-solvent. The optimal temperature and pressure for citronellol laurate synthesis in SC CO₂/EMK medium was determined to be 60 °C and 10 MPa.     

Enzymatic fatty ester synthesis

Fatty ester synthesis with immobilized 1,3-specific lipase fromMucor miehei is described. 1,2-Isopropylidene glycerol produced by condensation of glycerol with acetone was esterified with oleic acid in the presence of aMucor miehei lipase (Lipozyme™) to obtain 1,2-isopropylidene-3-oleoyl glycerol. The effects of various process parameters (temperature and pressure) and various ratios (enzyme/substrate) have been investigated to determine optimal conditions for the esterification process. The highest conversion of oleic acid (80% w/w) was obtained at 55°C and 0.057 bar, while the optimal addition of lipase to substrate was determined to be 0.096 g per gram of reaction mixture. The esterification can be modeled successfully as a reverse second-order reaction. Thermodynamic properties of the reaction system at 55°C and 0.057 bar also were determined. Activation energy was 20.82 kJ/mole, entropy of activation −0,26 kJ/(K mole) and free energy of activation was 103.32 kJ/mole.     

Repurposing of 8-Hydroxyquinoline-Based Butyrylcholinesterase and Cathepsin B Ligands as Potent Nonpeptidic Deoxyribonuclease I Inhibitors

A library of 31 butyrylcholinesterase (BChE) and cathepsin B (CatB) inhibitors was screened in vitro for inhibition of deoxyribonuclease I (DNase I). Compounds 22 , 8 and 7 are among the most potent synthetic non-peptide DNase I inhibitors reported to date. Three 8-hydroxyquinoline analogues inhibited both DNase I and BChE with IC₅₀ values below 35 μM and 50 nM, respectively, while two nitroxoline derivatives inhibited DNase I and Cat B endopeptidase activity with IC₅₀ values below 60 and 20 μM. Selected derivatives were screened for various co-target binding affinities at dopamine D₂ and D₃, histamine H₃ and H₄ receptors and inhibition of 5-lipoxygenase. Compound 8 bound to the H₃ receptor and is highlighted as the most promising multifunctional ligand with a favorable pharmacokinetic profile and one of the most potent non-peptide DNase I inhibitors. The present study demonstrates that 8-hydroxyquinoline is a structural fragment critical for DNase I inhibition in the presented series of compounds.     

Spatially Selective Nucleation of Metal Clusters on the Tobacco Mosaic Virus

Tobacco mosaic virus (TMV) is a very stable nanotube complex of a helical RNA and 2130 coat proteins. The special shape makes it an interesting nano‐object, especially as a template for chemical reactions. Here we use TMV as a chemically functionalized template for binding metal ions. Different chemical groups of the coat protein can be used as ligands or to electrostatically bind metal ions. Following this activation step, chemical reduction and electroless plating produces metal clusters of several nanometers in diameter. The clusters are attached to the virion without destroying its structure. Gold clusters generated from an ascorbic acid bath bind to the exterior surface as well as to the central channel of the hollow tube. Very high selectivity is reached by tuning Pd^II and Pt^II activations with phosphate: When TMV is first activated with Pd^II, and thereafter metallized with a nickel–phosphinate bath, 3 nm nickel clusters grow in the central channel; when TMV from phosphate‐buffered suspensions is employed, larger nickel clusters grow on the exterior surface. Phosphate buffers have to be avoided when 3 nm nickel and cobalt wires of several 100 nm in length are synthesized from borane‐based baths inside the TMV channel. The results are discussed with respect to the inorganic complex chemistry of precursor molecules and the distribution of binding sites in TMV.     

Characteristics of Al/sub 2/O/sub 3//AllnN /GaN MOSHEMT

InAlN/GaN is a new heterostructure system for HEMTs with thin barrier layers and high channel current densities well above 1 A/mm. To improve the leakage characteristics of such thin-barrier devices, AlInN/GaN MOSHEMT devices with a 11 nm InAlN barrier and an additional 5 nm Al₂O₃ barrier (deposited by ALD) were fabricated and evaluated. Gate leakage in reverse direction could be reduced by one order of magnitude and the forward gate voltage swing increased to 4 V without gate breakdown. Compared to HEMT devices of similar geometry, no degradation of the current gain cutoff frequency was observed. The results showed that InAlN/GaN FETs with high channel current densities can be realised with low gate leakage characteristics and high structural aspect ratio by insertion of a thin Al₂O ₃ gate dielectric layer