Modified gas-permeable silicone rubber membranes for covalent immobilisation of enzymes and their use in biosensor development

Novel enzyme membranes are introduced. Modified polymeric gas-permeable layers were developed enabling biological components which have available reactive groups (-NH2, -OH, -SH, -COOH) to couple covalently on to their surfaces. Therefore, gas-permeable two component room temperature vulcanizing (2K-RTV) silicone rubber was modified using additional cross-linking agents. Triethoxysilanes with functional groups on their side chains such as epoxy or amino groups were used. A special attribute of the resulting gas-permeable membranes is that their formation and modification occur simultaneously during one reaction step. IR spectroscopy was used to observe the changes in the polymeric structure due to the reaction with the additional cross-linking agents. Sensors equipped with these layers are suitable to measure dissolved gases such as O2, CO2 and NH3 consumed or produced by enzymes converting their substrates. Determination of glucose, a well investigated enzymatic detection process, was chosen to demonstrate the applicability of the enzyme immobilisation. Glucose oxidase was immobilised on the membranes and glucose was detected by amperometric measurement of oxygen consumption. It is expected that this immobilisation method will also be useful for miniaturised planar biosensors.     

Fluorotrimethyl[(Z)-pentafluoropropen-1-yl]phosphorane: Structure,Bonding, and Reactivity

In this contribution we report on fluorotrimethyl[(Z)-pentafluoropropen-1-yl]phosphorane as a phosphorus based fluorinating reagent. Its solid state structure can be described as a trigonal bipyramid featuring elongated axial bonds due to the formation of a 3-center 4-electron bond. Abstraction of the fluoride ion leads to a shortening of the axial P–C bond. Thus the title compound can be utilized for substitution of bromine with fluorine and for the transfer of fluoride ions onto electrophilic compounds. Reaction with Sn(C₂F₅)₂Br₂ afforded salt [P(CH₃)₃(C₃F₅)]₂[Sn(C₂F₅)₂F₄]. When fluorotrimethyl[(Z)-pentafluoropropen-1-yl]phosphorane was treated with P(C₂F₅)₂F the primarily produced anion is sufficiently nucleophilic to attack the propenyl group of the cation in β-position to the phosphorus atom to yield zwitterionic [Me₃PCF=C(CF₃)–PF₃(C₂F₅)₂].     

TRANSFORMATIONS OF 1,2,3-BENZOTHIADIAZOLE

Abstract

The experimental evidence concerning the nitration of 1,2,3-benzothiadiazole is conflicting. We have found that 4-nitro- and 7-nitro-1,2,3-benzothiadiazole are the major products, while from 6-chloro-1,2,3-benzothiazole 6-chloro-7-nitro-benzothiadiazole (I) was formed as the only product.     

Hopf-algebraic renormalization of QED in the linear covariant gauge

In the context of massless quantum electrodynamics (QED) with a linear covariant gauge fixing, the connection between the counterterm and the Hopf-algebraic approach to renormalization is examined. The coproduct formula of Green’s functions contains two invariant charges, which give rise to different renormalization group functions. All formulas are tested by explicit computations to third loop order. The possibility of a finite electron self-energy by fixing a generalized linear covariant gauge is discussed. An analysis of subdivergences leads to the conclusion that such a gauge only exists in quenched QED.     

New Fluorinated Poly(imide siloxane) Random and Block Copolymers with Variation of Siloxane Loading

Several new random and block copoly(imide siloxane)s have been prepared by the solution polycondensation of commercially available 4,4′-oxydianiline (ODA) and amino-propyl terminated polydimethylsiloxane (APPS) with 4,4′-(hexafluoro-isopropylidene)diphthalic anhydride (6FDA). The siloxane loading was kept to 10, 20, 30, 40 and 50 wt% in the copolymers. The random copolymers were prepared by a one pot solution imidization technique, and two pot solution imidization technique was adopted for the synthesis of the block copolymers. The diamine ODA and the dianhydride 6FDA composed the hard block segment, while APPS and 6FDA composed the soft block segment. The hard block length was kept constant while the soft block lengths were varied by varying the siloxane loading. Accordingly, block copoly(imide siloxane)s were prepared on increasing the soft block lengths (DP) from 3 to 6, 10, 18 and 36 for fixed hard block length of 22. The resulting polymers have been well characterized by IR, NMR and GPC techniques. Thermal and mechanical properties of the random and block copolymers were compared with the already reported homopolyimide without siloxane moiety.     

Metallo Phthalocyanines bearing 2‐Isopropyl‐6‐methylpyrimidin‐4‐yloxy Substituents: Synthesis,Characterization, Aggregation Behavior,Antioxidant and Antibacterial Activity,and Electronic Properties

A novel phthalonitrile derivative bearing 2‐isopropyl‐6‐methylpyrimidin‐4‐yloxy substituents at peripheral positions was synthesized by a nucleophilic substitution reaction. Metallophthalocyanines were obtained from the reaction of the novel phthalonitrile with metal Zn, Cu, Co, and Ni salts. The characterization of the compounds was performed using elemental analysis as well as UV/Vis, FT‐IR, and ¹H‐NMR spectroscopy. The aggregation behaviors of phthalocyanine complexes were also investigated. These metallophthalocyanines do not show any aggregation behavior between 10^–4–10^–6 M concentration range in THF. The antioxidant activities of the synthesized compounds were evaluated using three different tests: 2, 2‐diphenyl‐1‐picrylhydrazyl (DPPH) radical scavenging, metal chelating activity, and reducing power assays. All the compounds exhibited various antioxidant activities. In addition, antimicrobial activity of the compounds was tested over four gram positive and two gram negative bacteria. Moreover, the ground‐state geometries of the complexes were optimized using density functional theory (DFT) methods at B3LYP/6‐31G(d, p) level in order to obtain information about the 3D arrangements and electronic structure.     

Investigation of chemical activity,SCHIFF base reactions and staining effects of some amino acids by spectrophotometric and theorical methods

In this study, the staining properties of selected amino acids with Brassica oleraceae extract in alum and alum-free media were investigated. Basic, acidic and neutral amino acids (arginine, glutamic acid and glycine) were used to investigate the effect of staining. It was determined that all amino acids were stained in alum media. In the second step, the R group of amino acids found in the proteins of the cell nucleus was reacted with salicyl aldehyde. This reaction was successful only with Arginine. The staining properties of the newly formed compound were also investigated in alum and alum-free environments. Evaluation of the results was done using FT-IR and ¹H NMR methods. All compounds were optimized with the Gaussian G09 program (DFT/B3LYP/6.311 ?G(d.p) basic set. HOMO, LUMO and HOMO-LUMO gap values were determined. Chemical reaction capabilities of amino acids were discussed with the help of HOMO-LUMO gap values.     

In Situ Grignard Metalation Method for the Synthesis of Hauser Bases

The in situ Grignard Metalation Method (iGMM) is a straightforward one-pot procedure to quickly produce multigram amounts of Hauser bases R₂N-MgBr which are valuable and vastly used metalation reagents and novel electrolytes for magnesium batteries. During addition of bromoethane to a suspension of Mg metal and secondary amine at room temperature in an ethereal solvent, a smooth reaction yields R₂N-MgBr under evolution of ethane within a few hours. A Schlenk equilibrium is operative, interconverting the Hauser bases into their solvated homoleptic congeners Mg(NR₂)₂ and MgBr₂ depending on the solvent. Scope and preconditions are studied, and side reactions limiting the yield have been investigated. DOSY NMR experiments and X-ray crystal structures of characteristic examples clarify aggregation in solution and the solid state.