Bioluminescent flow sensor for the determination of L-(+)-lactate

The amount of L-lactate in biological fluids (serum, plasma and cerebrospinal fluid) was determined by monitoring the reduced form of nicotinamide adenine dinucleotide (NADH) produced by immobilised lactate dehydrogenase (LDH), with bacterial bioluminescent enzymes immobilised on a separate nylon coil. The LDH catalysed the reaction of L-lactate with NAD; this reaction took place in a nylon coil that preceded the coil for the bioluminescent detection. The co-immobilisation of alanine aminotransferase (ALT) with LDH improved the lactate transformation by 117-183%. The response was linear from 0.1 to 50 micron mol l(-1) at 25 degrees C for the LDH - ALT reactor. The intra- and inter-assay coefficients of variation were less than 5% and the recoveries ranged from 93 to 106%. The results agreed well with those obtained with a spectrophotometric method and with the normal reference values.     

Development of porous metal oxide thin films by co-evaporation

This paper focuses on the development of mixed metal oxide thin films and physical characterization of the films. The films were produced by co-evaporation of titanium oxide and tungsten oxide powders. This allowed the development of titanium oxide-tungsten oxide films as analyzed using XPS. Examination in the SEM and AFM showed that the films were nanoporous with the pore size and pore orientation varying as a function of the deposition angle. UV-vis spectra of the films show an increase of transmittance with increasing deposition angle which is attributed to the structure and porosity of the films. Raman analysis indicated that the as-deposited films have broad and weak Raman characteristics, attributed to the nanocrystal nature of the films and the presence of defects, and the peak broadening deceases after annealing the film, as expected.     

Synthesis of benzofurazan derivatization reagents for carboxylic acids in liquid chromatography/electrospray ionization-tandem mass spectrometry

The applicability of benzofurazan derivatization regents to carboxylic acids analysis in LC/ESI-MS/MS (high-performance liquid chromatography/electrospray ionization tandem mass spectrometry) was examined. The product ion spectra of DAABD-AE {4-[2-(N,N-dimethylamino)ethylaminosulfonyl]-7-(2-aminoethylamino)-2,1,3-benzoxadiazole}, DAABD-PZ {4-[2-(N,N-dimethylamino)ethylaminosulfonyl]-7-N-piperazino-2,1,3-benzoxadiazole}, DAABD-PiCZ {4-[4-carbazoylpiperidin-1-yl]-7-[2-(N,N-dimethylamino)ethylaminosulfonyl]-2,1,3-benzoxadiazole}, DAABD-ProCZ {4-[2-carbazoylpyrrolidin-1-yl]-7-[2-(N,N-dimethylamino) ethylaminosulfonyl]-2,1,3-benzoxadiazole} and DAABD-Apy {4-[2-(N,N-dimethylamino)ethylaminosulfonyl]-7-(3-aminopyrrolidin-1-yl)-2,1,3-benzoxadiazole}, and their acetylated compounds were obtained. An intense fragment ion at m/z 151 corresponding to (dimethylamino)ethylaminosulfonyl moiety was observed in each spectra, suggesting that these reagents were suitable for ESI-MS/MS analysis. DAABD-AE, DAABD-APy and DAABD-PZ were applied to the analysis of octanoic acid and it was found that DAABD-AE and DAABD-APy gave high signal intensity suitable for LC/ESI-MS/MS.     

The disordered molecular structure of (3aRS,7aRS)‐1,3‐dinitrosooctahydro‐1H‐benzimidazole

The title compound, C₇H₁₂N₄O₂, was obtained by nitrosation of the aminal cage (2R,7R,11S,16S)‐1,8,10,17‐tetraazapentacyclo[8.8.1.1^8,17.0^2,7.0^11,16]icosane. The crystal structure is a racemic mixture of RR and SS enantiomers. The asymmetric unit contains two crystallographically independent half‐molecules, one having two partially occupied conformers with refined occupancy factors of 0.747 (3) and 0.253 (3). The molecules sit across twofold axes. The unique molecules each form chains parallel to [001], with molecules connected by intermolecular C—H...O hydrogen bonds. The bonding between adjacent chains is weak. The analysis of eight different crystals confirmed the presence of disordered and nondisordered molecules in the same structure as a regular feature.     

Pulsed amperometric detection (PAD) of diuretic drugs in herbal formulations using a gold electrode following ion-pair chromatographic separation

Herein, we present a new method based on separation by ion-pair chromatography with pulsed amperometric detection for evaluating various diuretics, including hydrochlorothiazide, chlorthalidone, furosemide, and amiloride, which are adulterants in herbal-based pharmaceutical formulations. The amperometric detection cycle (time?=?2 s) was performed at a gold electrode by applying a detection potential (E1) of +800 mV for 0.4 s and an oxidation potential (E2) of +1,000 mV for 0.40 s, followed by a reduction potential (E3) of ?200 mV for 1.20 s. The mobile phase for separating the diuretics was composed of 5 mmol L^?1 phosphate buffer and 0.3 mmol L^?1 sodium dodecyl sulfate in 50 % (v/v) methanol (pH 4.5). This method enabled the quantification of the drugs at low concentrations (i.e., 0.08 mg/capsule for hydrochlorothiazide, 0.01 mg/capsule for chlorthalidone, and 0.007 mg/capsule for furosemide). Twenty-six herbal formulations were analyzed, and eight samples (30.8 %) were found to contain diuretics that were added to the final composition (declared or not).     

From Inulin to Fructose Syrups Using Sol–Gel Immobilized Inulinase

The present work aims to provide the basic characterization of sol–gel immobilized inulinase, a biocatalyst configuration yet unexploited, using as model system the hydrolysis of inulin to fructose. Porous xerogel particles with dimensions in slight excess of 10 μm were obtained, yielding an immobilization efficiency of roughly 80%. The temperature– and pH–activity profiles displayed a broader bell-shaped pattern as a result of immobilization. In the latter case, a shift of the optimal pH of 0.5 pH units was observed towards a less acidic environment. The kinetic parameters estimated from the typical Michaelis–Menten kinetics suggest that immobilization in sol–gel did not tamper with the native enzyme conformation, but on the other hand, entrapment brought along mass transfer limitations. The sol–gel biocatalyst displayed a promising operational stability, since it was used in more than 20 consecutive 24-hour batch runs without noticeable decay in product yield. The performance of sol–gel biocatalyst particles doped with magnetite roughly matched the performance of simple sol–gel particles in a single batch run. However, the operational stability of the former proved poorer, since activity decay was evident after four consecutive 24-hour batch runs.     

The investigation of sensing mechanism of ethanol vapour in polymer-nanostructured carbon composite

Polymer-nanostructured carbon composites (PNCC) using three different polymers as composite matrix materials (polyvinylacetate (PVAc), polyethylene glycol (PEG) and ethylene-vinylacetate copolymer (EVA)) have been developed. High structure carbon black Printex XE2 (Degussa AG) was used as a composites filler. Ethanol vapour sensor-effect of composites was determined as a change of electrical resistance as the composite was held in ethanol vapour for 30 seconds. Reversibility of electrical resistance of PNCC, response stability and repeatability have been measured and compared. The electrical resistance response of EVA-nanostructured carbon composite (EVA-NCC) to ethanol vapour as a function of vinylacetate content in the copolymer has been evaluated. Promising ethanol vapour sensor-effect has been observed for PEG-NCC followed by PVAc-NCC and EVA-NCC.     

Room temperature photoluminescence of BCT prepared by Complex Polymerization Method

It was used the Complex Polymerization Method to synthesize barium calcium titanate powders (BCT). Crystalline Ba_0.8Ca_0.2TiO₃ perovskite-type phase could be identified by X-ray diffraction and confirmed by Raman spectroscopy in the powders heat treated at 600 °C. Inherent defects, linked to structural disorder, facilitate the photoluminescence emission. The photoluminescent emission peak maximum was around of 533 nm (2.33 eV) for the Ba_0.8Ca_0.2TiO₃. The photoluminescence process and the band emission energy photon showed dependence of both the structural order–disorder and the thermal treatment history. The results revealed that Ba_0.8Ca_0.2TiO₃ (BCT20) is a highly promising candidate material for optical applications.     

Phytochrome structure: A new methodological approach

Higher plants use the protein phytochrome as a photosensor. In physiological temperatures phytochrome exists in two forms: Pr and Pfr. The chromophore of phytochrome is an open-chain tetrapyrrole. On the pathway from Pr to Pfr four intermediates (Lumi-R, Meta-Ra, Meta-Rb, and Meta-Rc) can be distinguished, while only two (Lumi-F and Meta-F) can be seen on the way back from Pfr to Pr. We have used the x-ray structure of the C-Phycocyanin protein Fremyella diplosiphon bacteria as a template to build a model (∼200 atoms) that includes only the chromophore and five amino acids of the phytochrome (Arg316–Cys321–His322–Leu323–Gln324) around it. Using the existing experimental evidences, we have proposed a three-dimensional (3D) structure for Pr, Pfr, and intermediates and a mechanism for the photoisomerization as well. Structures were fully optimized using AM1 (Unichem package on a Cray J90-NACAD). Using the INDO/S method of Zerner and co-workers, we calculated the absorption spectra of the model compounds and compared them with the experimental data. The oscillator strength ratio is an indicator of the chomophore conformation in biliproteins. The calculated spectra reproduces well the spectra of the phytochrome (Pr, Pfr, and intermediates) except for the lower energy band. This result is attributed to the small number of amino acids in the models. The calculated ratios (f_VIS/f_UV−f_osc of visible band over f_osc of UV band and f₂/f₁−f_osc of second absorption band over f_osc of first absorption band) for the models match very well the experimental ratios obtained for the phytochrome (Pr, Pfr, and intermediates). This supports the proposed mechanism for the photoisomerization process. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 1145–1157, 1998     

Molecular modeling on platelet-activating factor (PAF) and new proposed PAF antagonists

Platelet-activating factor (PAF) is an autacoid derived from cellular membrane phospholipids in response to chemical or physical stimuli. It has been identified as 1-O-alkyl-2-acetyl-sn-glyceryl-3-phosphocholine; the alkyl group is composed of 16 or 18 carbon atoms in human cells. PAF can cause a series of pathophysiological effects, related to inflammatory and allergic diseases such as asthma, gastric ulcerations, transplant rejections, psoriasis, cerebral, renal, and myocardial ischemia. As PAF biological action is a result of interactions with specific receptors on target cells, several specific PAF receptor antagonists have been proposed for therapeutic control of the pathological states in which PAF is implicated. In this work we have calculated at AM1 level 16 conformations of a model (alkyl = octyl) of (R)-PAF. We have used these conformations and calculated structures of two hetrazepines (WEB 2086 and E 6123), FR 128998 and RP 59227, known antagonists of PAF activity currently under development, to test a recently proposed pharmacophore map. Our results suggest that the model is too rigid. Having this in mind, we used the pharmacophore model to evaluate the potential activity of a new series of proposed PAF receptor antagonists based on bicyclo[3.3.0]-2-oxaoctane. The results were used to decide which compounds should receive priority in synthesis. The synthetic results and pharmacological profiles of the new derivatives will be published elsewhere. © 1996 John Wiley & Sons, Inc.