Activated C,H-Acids: N-Alkyl-9-fluorenimines. Preliminary communication

N-Substituted 9-fluorenimines 1 are easily prepared from primary amines or aminoesters and 9-fluorenimine: their conjugate carbanions 2 are formed by the action of alkoxides and are reprotonated to 1 or to the tautomeric 9-alkylidenamino-fluorenes 3 depending upon substituents.     

Reactions of novel mono- and difluoroacetyltrialkylsilanes with sulfur and phosphorus ylides

The reactions of difluoroacetyltrialkylsilanes with methylidene triphenylphosphorane and benzylidene triphenylphosphorane are affected by the nature of the silyl substituents giving either the enol silyl ether or normal Wittig product exclusively, or mixture of both. Reactions with Horner-Emmons type ylide gave only the alkene products. Reactions of mono- and difluoroacetyltrialkylsilanes with dimethylsulfoxonium methylide gave the enol silyl ether products exclusively. Conversion of an enol silyl ether to an epoxide was effected with m-CPBA.     

Immobilization of acetylcholinesterase on screen-printed electrodes: comparative study between three immobilization methods and applications to the detection of organophosphorus insecticides

The analytical performance of three acetylcholinesterase (AChE) screen-printed biosensors designed for the detection of pesticides are evaluated. Bioencapsulation of the enzyme in a sol-gel composite and immobilization by metal-chelate affinity were compared with the entrapment of the enzyme in a photopolymerisable polymer. A very low amount of enzyme ranging between 0.8 and 1.2 mIU was immobilized on the electrode surface in each approach. The sensors exhibited a storage stability of over 6 months when the enzyme was encapsulated in a polymer film. Pesticide concentrations in the range of 10⁻⁸ to 10⁻⁹ M paraoxon, dichlorvos and chlorpyrifos ethyl oxon could be detected according to each configuration by following an incubation time of 20 min.     

Palladium-catalyzed C–H alkenylation of quinoxaline N-oxide enabled by a mono-N-protected amino acid

The efficient alkenylation of quinoxaline N-oxide was achieved via Pd-catalyzed C–H activation, using the assistance of a mono-N-protected amino acid. Further deoxygenation of the 2-styrylquinoxaline-N-oxides yielded the corresponding styrylquinoxaline derivatives.     

Affinity electrochromatography of acidic drugs using a liposome-modified capillary

Liposomes can be effectively deposited on the inner surface of a capillary wall by flushing the electrophoretic system with a liposome suspension followed by air-drying of the capillary and removal of the excess of loosely bound liposomes by a 0.1 M NaOH wash. It was demonstrated that capillaries prepared in this way could be used for studies of analyte (drug)–liposome binding. The results were expressed as free binding energy changes [Δ(ΔG⁰)] relatively to an arbitrarily selected standard (acetylsalicylic acid). The results were compared to [Δ(ΔG⁰)] changes obtained from binding studies effected by capillary electrophoresis using a stable liposome plug in a capillary with minimized endoosmotic flow. Good agreement of data reported in the literature (without correction for the residual endoosmotic flow), our previous data obtained in a similar way (however, after the correction for the residual endoosmotic flow) and data obtained by the immobilized liposome affinity electrochromatography reported in this communication was achieved.     

Bridged bimetallic complexes of molybdenum tris(dimethylpyrazolyl)borates

Summary The syntheses of [MoL^*(NO)(OR)NHC₆H₄NH₂)], [MoL^*(NO)I(NHC₆H₄NHMoL^*(NO)(OR)] (L^*=tris(3,5-dimethylpyrazolyl)borate; R=Me, Et,n-Pr,i-Pr,n-Bu and C₅H₁₁), and [{MoL^*(NO)(OR)}₂NHC₆H₄NH] (R=Me, Et andn-Pr) are described, the compounds being characterised by elemental analyses, i.r. and¹H n.m.r. spectroscopy.     

Ultrahigh vacuum deposition of L-cysteine on Au(110) studied by high-resolution X-ray photoemission: from early stages of adsorption to molecular organization

We report on a high-resolution X-ray photoemission spectroscopy study on molecular-thick layers of L-cysteine deposited under ultrahigh vacuum conditions on Au(110). The analysis of core level shifts allowed us to distinguish unambiguously the states of the first-layer molecules from those of molecules belonging to the second layer. The first-layer molecules strongly interact with the metal through their sulfur headgroup. The multipeaked structure of the N 1s, O 1s, and C 1s core levels is interpreted in terms of different molecular moieties. The neutral acidic fraction (HSCH2CH(NH2)COOH) is abundant at low coverage likely associated with isolated molecules or dimers. The zwitterionic phase (HSCH2CH(NH3+)COO-) is largely dominant as the coverage approaches the monolayer limit and is related to the formation of ordered self-assembled molecular structures indicated by electron diffraction patterns. The occurrence of a small amount of cationic molecules (HSCH2CH(NH3+)COOH) is also discussed. The second-layer molecules mainly display zwitterionic character and are weakly adsorbed. Mild annealing up to 100 degrees C leads to the desorption of the second-layer molecules leaving electronic states of the first layer unaltered.     

Optimization of glucoamylase production by Aspergillus niger in solid-state fermentation

Glucoamylase production by Aspergillus niger in solid-state fermentation was optimized using factorial design and response surface techniques. The variables evaluated were pH and bed thickness in tray, having as response enzyme production and productivity. The bed thickness in tray was the most significant variable for both responses. The highest values for glucoamylase production occurred using pH 4.5 and bed thickness in the inferior limits at 2.0–4.2 cm. For productivity, the optimal conditions were at pH 4.5 as well and bed thickness from 4.4 to 7.5 cm. The optimal conditions for glucoamylase production while obtaining high activity without loss of productivity were pH 4.5 and bed thickness in tray from 4.0 to 4.5 cm, which resulted in an enzyme production of 695 U/g and productivity of 5791 U/h.     

Detection of organophosphorus insecticides with immobilized acetylcholinesterase – comparative study of two enzyme sensors

Two-enzyme systems based on acetylcholinesterase (AChE) - a mono-enzyme system based on AChE, with p-aminophenyl acetate as substrate, and a bi-enzyme system based on AChE and tyrosinase, with phenyl acetate as substrate - have been studied for detection of organophosphate insecticides. The analytical performance and detection limits for determination of the pesticides were compared for the two AChE configurations. The enzyme loading, pH, and applied potential of the bi-enzyme system were optimised. When phenyl acetate was used as substrate for AChE activity the phenol generated by enzymatic hydrolysis was determined with a second enzyme, tyrosinase. Amperometric measurements were performed at 100 mV and -150 mV relative to the Ag/AgCl reference electrode for the mono-enzyme and bi-enzyme systems. Screen-printed sensors were used to detect the organophosphorus pesticides paraoxon and chlorpyrifos ethyl oxon; the detection limits achieved with phenyl acetate as substrate were 5.2x10(-3) mg L(-1) and 0.56x10(-3) mg L(-1), respectively.