Abstract  The use of IR spectroscopy for the evaluation of the Lewis and Bronsted acidity of microporous systems is illustrated having recourse to examples concerning zeolites, heteropolyacids and sulfonated membranes (NAFION). Methods based on the perturbation of the OH modes by interaction with basic probe molecules are illustrated as well as on the perturbation of the internal modes of the probe itself. The use of H-2 as probe is also debated by discussing new data specifically obtained for this review. The illustrated case examples are mainly obtained from the experience gained by the Turin group in 20 years.

Abstract  Every year a large amount of ammonia is mechanically compressed with a low efficiency (∼65%) as an environmentally friendly chemical for fuel storage, transportation, food preservation and air conditioning. Electrochemical compression with a high efficiency (93%) offers an opportunity for substantial energy savings. But ammonia is never considered electrochemically compressible because of the known decomposition at high applied potentials. The concept of using a carrier gas to co-compress ammonia was proposed but never experimentally validated. Here for the first time, we realized electrochemical compression of ammonia by using a proton exchange membrane as an NH4(+) conductor and hydrogen as a carrier to avoid decomposition. The ammonia transfer mechanism and kinetics in a Nafion membrane was investigated and verified using electro-analytical methods, and the continuous electrochemical ammonia compression at a constant voltage of 200 mV with a stable current density for 7 hours has been demonstrated. NH4(+) transports in the Nafion membrane by hopping and vehicular mechanisms with a high NH4(+) conductivity of 4 × 10(-2) S cm(-1) at 50% RH and 70 °C, and a constant transfer ratio of 2 between NH3 and H2 ensure a stable and high compression rate.

Abstract  (E)-Methyl-N'-nitrobenzylidene-benzenesulfonohydrazide (MNBBSH) compounds were synthesized using a condensation procedure from the derivatives of nitrobenzaldehyde and 4-Methyl-benzenesulfonylhydrazine, which crystallized in ethanol and methanol as well as characterized by FTIR, UV-Vis, (1)H-NMR, and (13)C-NMR. MNBBSH structure was confirmed using a single crystal X-ray diffraction technique and used for the detection of selective yttrium ion (Y(3+)) by I-V system. A thin layer of MNBBSH was deposited onto a glassy carbon electrode (GCE) with 5% nafion for the sensitive and selective Y(3+) sensor. The modified MNBBSH/GCE sensor is exhibited the better electrochemical performances such as sensitivity, limit of detection (LOD), linear dynamic range (LDR), limit of quantification (LOQ), short response time, and long term storage ability towards the selective metal ion (Y(3+)). The calibration curve of 2-MNBBSH/GCE sensor was plotted at +1.1 V over a broad range of Y(3+) concentration. Sensitivity, LOD, LDR and LOQ of the fabricated sensor towards Y(3+) were calculated from the calibration curve and found as 1.90 pAμM(-1) cm(-2), 10.0 pM, 1.0 nM~1.0 mM and 338.33 mM respectively. The 2-MNBBSH/Nafion/GCE sensor was applied to the selective determination of Y(3+) in spiked samples such as industrial effluent and real water samples from different sources, and found acceptable and reasonable results.

Abstract  The solution chemistry of complex [Co{(Me)2(μ-ET)cyclen}(H2O)2](3+) containing a fully substituted tetraammine ligand designed for the avoidance of base-conjugated substitution mechanisms in the 6-8 pH range has been studied. The study should shed some light on the possible involvement of such Co(III) skeleton in inert interactions with biomolecules. The reactivity and speciation of the complex has been found similar to that of the parent cyclen derivative with the presence of mono- and bis-hydroxo-bridged species; at pH < 7.1, all reactivity has been found to be related to the aqua/hydroxo monomeric complexes. Under these pH conditions, the substitution reactions of the aqua/hydroxo ligands by chloride, inorganic phosphate, thymidine, cytidine 5'-monophosphate (5'-CMP), and thymidine-5'-monophosphate (5'-TMP) have been studied at varying conditions; ionic strength has been kept at 1.0 NaClO4 due to the high concentration of 2-(N-morpholino)ethanesulfonic acid (MES) or N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES) used to ensure buffering. Except for chloride, the process occurs neatly in a one or two step process, showing dissociatively activated substitution mechanisms, having in general large ΔH(⧧), positive ΔS(⧧), and values of ΔV(⧧) close to those corresponding to the liberation of an aqua ligand to the reaction medium. The actuation of noticeable encounter-complex formation equilibrium constants has been found to be the determinant for the reactions with nucleosides and nucleotides, a clear indication of the relevance of hydrogen-bonding interactions in the reactivity of these molecules, even in this highly ionic strength medium. For the substitution of the active aqua/hydroxo ligands with 5'-TMP, the first substitution reaction produces an Nthymine-bound 5'-TMP complex that evolves to a bis-5'-TMP with an Nthymine,Ophosphate-bonding structure. The formation of outer-sphere complexes between the dangling phosphate group of the Nthymine-bound 5'-TMP and the thymine moiety of another entering 5'-TMP has been found to be responsible for this fact, which leaves only the phosphate group for coordination available.

Abstract  A colourimetric sensor capable of simultaneously measuring oxidative status (OS) in terms of the hazard produced by reactive oxygen species (ROS) and antioxidant activity (AOA) in regard to ROS-scavenging ability of antioxidant compounds was developed. The coloured cationic semi-quinone derivatives, caused by ROS oxidative degradation of N,N-dimethyl-p-phenylene diamine hydrochloride (DMPD) in pH 5.7 acetate-buffered medium, were formed in solution and immobilized on a perfluorosulfonate-based Nafion membrane. ROS, namely hydroxyl (·OH) and superoxide (O2(·-)) radicals, were produced by Fenton/UV and xanthine/xanthine oxidase methods, respectively. The pink-coloured, (+)-charged chromophore (referred to as DMPD-quinone or DMPDQ), resulting from the reaction between DMPD and ROS, could be completely retained on the solid membrane sensor by electrostatic interaction with the anionic sulfonate groups of Nafion. After equilibration, the Nafion membrane surface was homogeneously coloured enabling an absorbance measurement at 514 nm, while the aqueous phase completely lacked colour. Antioxidants, when present, caused an absorbance decrease on the membrane due to their ROS scavenging action, giving rise to less DMPDQ production. The absorbance decrease on the sensor was linearly dependent on antioxidant concentration over a reasonable concentration range, enabling the simultaneous determination of OS and AOA-against ROS. The proposed antioxidant sensing method was tested in synthetic and real antioxidant mixtures, and validated against standard antioxidant capacity assays (i.e. ABTS and CUPRAC) for a variety of polyphenolic and antioxidant compounds. The dynamic linear ranges of antioxidants with the DMPD sensor in protection against hydroxyl and superoxide radicals generally varied within the micromolar to a few tens of micromolar concentration interval over one order-of-magnitude. Choosing three representative compounds in the high (epigallocatechin gallate), medium (quercetin) and low (p-coumaric acid) molar absorptivity range, the detection limits ranged within the concentration intervals of 0.2-0.9 μM, 0.3-0.8 μM, and 4-14 μM, respectively, depending on the radical scavenged.

Abstract  An effective electrochemiluminescence (ECL) sensor based on Nafion/poly(sodium 4-styrene sulfonate) (PSS) composite film-modified ITO electrode was developed. The Nafion/PSS/Ru composite film was characterized by atomic force microscopy, UV-vis absorbance spectroscopy and electrochemical experiments. The Nafion/PSS composite film could effectively immobilize tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)(3)(2+)) via ion-exchange and electrostatic interaction. The ECL behavior of Ru(bpy)(3)(2+) immobilized in Nafion/PSS composite film was investigated using tripropylamine (TPA) as an analyte. The detection limit (S/N=3) for TPA at the Nafion/PSS/Ru composite-modified electrode was estimated to be 3.0 nM, which is 3 orders of magnitude lower than that obtained at the Nafion/Ru modified electrode. The Nafion/PSS/Ru composite film-modified indium tin oxide (ITO) electrode also exhibited good ECL stability. In addition, this kind of immobilization approach was simple, effective, and timesaving.

Abstract  Stability of four dissimilar basic proteins (chymotrypsinogen A, ribonuclease A, cytochrome c, lysozyme) in the complex with four polyanions (heparin, poly(vinylsulfate), poly(4-styrene-sulfonate), Nafion) has been studied by differential scanning calorimetry. The polyanions were chosen because of their different charge density and hydrophobicity. Relative hydrophobicity of polyanions have been compared by three different parameters: (i) partition coefficient determined in octanol/water system, (ii) electrocapillary curves obtained by the method of controlled convection, and (iii) change in absorbance of small cationic amphiphilic molecule, aminoacridine, due to interaction with polyanion. Our results suggest that stability of proteins in the complex with polyanions negatively correlate with charge-related properties of the proteins such as isoelectric point and surface charge density and hydrophobicity of the polyanions.

Abstract  Robust water oxidation catalysts using earth abundant metals are required as part of an overall scheme to convert sunlight into fuels. Here, we report the immobilization of [[Formula: see text]O(5)(terpy)(4)(H(2)O)(2)](ClO(4))(6) (terpy = 2,2';6',2″-terpyridine), [Mn(4)O(6)(tacn)(4)](ClO(4))(4) (tacn = 1,4,7-triazacyclononane), and manganese dioxide nanoparticles in Nafion on fluorine-doped tin oxide conducting glass electrodes. The electrodes are illuminated with white light in the presence of an applied potential and the resulting photocurrent is assigned to the oxidation of solvent water. Photodecomposition of the tetrameric complexes results in a material that is more active for light-driven electrooxidation of water. The reactivity, wavelength dependence, and stability of the compounds in Nafion under illumination are discussed.

Abstract  A thin film of Nafion, of approximately 5 μm thickness, asymmetrically deposited onto a 6 μm thick film of poly(ethylene terephthalate) (PET) fabricated with a 5, 10, 20, or 40 μm microhole, is shown to exhibit prominent ionic diode behavior involving cation charge carrier ("cationic diode"). The phenomenon is characterized via voltammetric, chronoamperometric, and impedance methods. Phenomenologically, current rectification effects are comparable to those observed in nanocone devices where space-charge layer effects dominate. However, for microhole diodes a resistive, a limiting, and an overlimiting potential domain can be identified and concentration polarization in solution is shown to dominate in the closed state.

Abstract  An adsorptive stripping voltammetric (AdSV) method is presented for the simultaneous determination of Pb(II) and Cd(II) at trace levels in natural waters, based on metal complexation with pyrogallol red (PR) and subsequent adsorptive deposition on a Nafion-mercury coated glassy carbon electrode (NHgFE). Pyrogallol red forms complexes with a metal:ligand stoichiometry of 1:1 with Pb(II) and of 1:2 with Cd(II). Optimal analytical conditions were pH 4.0 (acetate buffer); C(PR)=2.8 μmol L(-1); E(ads)=-0.40 V vs. Ag/AgCl; t(ads)=100 s. The linear calibration curves ranged from 1.0 μg L(-1) to 16.0 μg L(-1) for Pb(II) and from 1.0 μg L(-1) to 13.0 μg L(-1) for Cd(II). The detection limits (S/N=3) were 0.05 μg L(-1) for Pb(II) and 0.01 μg L(-1) for Cd(II). The relative standard deviation was 1.0% and 2.0% (n=7), respectively, for a solution containing 5.0 μg L(-1) Pb(II) and Cd(II). The method was validated by determining Pb(II) and Cd(II) in certified reference waste water (SPS-WW1). Finally, the method was applied to the determination of Pb(II) and Cd(II) in commercial mineral water samples after UV digestion.

Abstract  Porous carbon nanofibers codoped with nitrogen and sulfur (NFs) were prepared by pyrolysis of trithiocyanuric acid, silica nanospheres and polyacrylonitrile (PAN) followed by electrospinning. The NFs were used to modify a glassy carbon electrode (GCE) which then displayed highly sensitive response to traces of Cd(II). Compared to a bare GCE and a Nafion modified GCE, the GCE modified with codoped NFs shows improved sensitivity for Cd(II) in differential pulse anodic sweep voltammetry. The stripping peak current (typically measured at 0.81 V vs. Ag/AgCl) increases linearly in the 2.0-500 μg·L-1 Cd(II) concentration range. This is attributed to the large surface area (109 m2·g-1), porous structure, and high fraction of heteroatoms (19 at.% of N and 0.75 at.% of S). The method was applied to the determination of Cd(II) in (spiked) tap water where it gave recoveries that ranged between 96% and 103%. Graphical abstract Schematic of a glassy carbon electrode (GCE) modified with N- and S-codoped porous carbon nanofibers (N,S-PCNFs). This GCE has good selectivity for cadmium ion (Cd2+) which can be determined by differential pulse anodic sweeping voltammetry (DPASV) with a detection limit as low as 0.7 ng·mL-1.

Abstract  Modification of carbon materials, especially graphene-based materials, has wide applications in electrochemical detection such as electrochemical lab-on-chip devices. A glassy carbon electrode (GCE) modified with chemically alternated graphene oxide was used as a working electrode (glassy carbon modified by graphene oxide with sulphur containing compounds and Nafion) for detection of nucleobases in hydrolysed samples (HCl pH = 2.9, 100 °C, 1 h, neutralization by NaOH). It was found out that modification, especially with trithiocyanuric acid, increased the sensitivity of detection in comparison with pure GCE. All processes were finally implemented in a microfluidic chip formed with a 3D printer by fused deposition modelling technology. As a material for chip fabrication, acrylonitrile butadiene styrene was chosen because of its mechanical and chemical stability. The chip contained the one chamber for the hydrolysis of the nucleic acid and another for the electrochemical detection by the modified GCE. This chamber was fabricated to allow for replacement of the GCE.

Abstract  Interactions of nerve G-agents (sarin and soman) and their simulants DMMP (dimethyl methylphosphonate) and DIFP (diisopropyl fluorophosphate) with water and components of polyelectrolyte membranes are studied using ab initio calculations in conjunction with thermodynamic modeling using the conductor-like screening model for real solvents (COSMO-RS). To test reliability of COSMO-RS calculations, we measured the vapor-liquid equilibrium in DMMP-water mixtures and found quantitative agreement between computed and experimental results. Using COSMO-RS, we studied the interactions of phosphororganic agents with the characteristic fragments of perfluorinated and sulfonated polystyrene (sPS) polyelectrolytes, which are explored for protective clothing membranes. We found that both simulants, DIFP and DMMP, mimic the thermodynamic properties of G-agents reasonably well; however, there are certain specific differences that are discussed. We also suggested that sPS-based polyelectrolytes have less affinity for phosphorganic agents compared to prefluorinated polyelectrolytes similar to Nafion.

Abstract  The authors report on a microneedle-based amperometric nonenzymatic glucose sensor for painless and continuous monitoring of glucose. It consists of 3 × 5 sharp stainless steel microneedles micromachined from a stainless steel substrate. The microneedles are 600 and 100 μm in height and width, respectively. Nafion and platinum black were sequentially coated onto the tip of gold-coated microneedles and used for nonenzymatic (direct) sensing of glucose. Attractive features of the modified microneedle electrode include (a) a low working potential (+0.12 V vs. Ag/AgCl), (b) a linear response in the physiologically relevant range (1-40 mM), (c) a sensitivity as high as 175 μA mM-1 cm-2, (d) a 23 μM detection limit, and (e) a response time of 2 s. The sensor also exhibits good reproducibility and stability. The sensor is selective for glucose even in the presence of 10-fold higher concentrations of ascorbic acid, lactic acid, dopamine, uric acid, and acetaminophen. Graphical abstract Schematic representation of the fabrication sequence for a nonenzymatic electrochemical glucose sensor using Nafion and platinum black coated microneedle electrode array. The sensor is based on measuring the faradaic current at +0.12 V vs. Ag/AgCl by the direct electrochemical oxidation of glucose to gluconic acid on the surface of a Pt black sensing layer.

Abstract  Composite membranes composed of highly conductive and selective layer-by-layer (LbL) films and electrospun fiber mats were fabricated and characterized for mechanical strength and electrochemical selectivity. The LbL component consists of a proton-conducting, methanol-blocking poly(diallyl dimethyl ammonium chloride)/sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (PDAC/sPPO) thin film. The electrospun fiber component consists of poly(trimethyl hexamethylene terephthalamide) (PA 6(3)T) fibers in a nonwoven mat of 60-90% porosity. The bare mats were annealed to improve their mechanical properties, which improvements are shown to be retained in the composite membranes. Spray LbL assembly was used as a means for the rapid formation of proton-conducting films that fill the void space throughout the porous electrospun matrix and create a fuel-blocking layer. Coated mats as thin as 15 μm were fabricated, and viable composite membranes with methanol permeabilities 20 times lower than Nafion and through-plane proton selectivity five and a half times greater than Nafion are demonstrated. The mechanical properties of the spray coated electrospun mats are shown to be superior to the LbL-only system and possess intrinsically greater dimensional stability and lower mechanical hysteresis than Nafion under hydrated conditions. The composite proton exchange membranes fabricated here were tested in an operational direct methanol fuel cell. The results show the potential for higher open circuit voltages (OCV) and comparable cell resistances when compared to fuel cells based on Nafion.

Abstract  The design and fabrication of noble-metal-free hydrogenevolution electrocatalysts with high activity is significant to future renewable energy systems. In this work, self-supported NiMo carbide nanowires on carbon cloth (Ni3 Mo3 C@NPC NWs/CC; NPC=N,P-doped carbon) were developed through an electropolymerization-assisted procedure. During the synthesis process, NiMoO4 nanowires were first grown on CC through a hydrothermal reaction that was free of any polymer binder such as Nafion. By use of electropolymerization, the as-prepared NiMoO4 NWs/CC sample was then coated by a layer of polypyrole (PPy) that served as the carbon source for subsequent conversion into Ni3 Mo3 C@NPC NWs/CC by carbothermal reduction. The experimental results indicated that judicious choices of the amount of coated PPy and the pyrolysis temperature were essential for obtaining the pure-phase, nanowire array structure of Ni3 Mo3 C@NPC NWs/CC. Benefitting from the pure phase of the bimetallic carbide, the unique architecture of the nanowire array, and its self-supported nature, the optimized Ni3 Mo3 C@NPC NWs/CC electrode exhibited excellent performance in the hydrogen evolution reaction (HER) in both acidic and alkaline media. Low overpotentials of 161 and 215 mV were required to afford a high current density of 100 mA cm-2 toward the HER in acidic and alkaline media, respectively, and the catalytic activity was maintained for at least 48 h, which puts Ni3 Mo3 C@NPC NWs/CC among the best HER electrocatalysts based on metallic carbides yet reported.

Abstract  The use of a mediator to detect a nonabsorbing analyte during spectroelectrochemical modulation is demonstrated. The charge-selective composite film of Nafion-SiO2 was used to entrap the mediator, Ru(bipy)3(2+). The change in deltaA as detected by attenuated total reflection was then observed upon addition of the analyte, ascorbate. The effects of scan rate, concentration of mediator, film thickness, and analyte charge were studied to achieve optimal sensor conditions. The model sensor exhibited a linear range from 0.26 to 2.0 mM (R2 = 0.998).

Abstract  Electrochemical measurements using voltammetry or amperometry at carbon-fiber microelectrodes have been used in vitro and in vivo to examine regulatory mechanisms for the central dopamine system. In many of these experiments, dopamine efflux concentrations under control conditions are determined followed by their alterations in response to a drug treatment. The present study demonstrates that some drugs can affect dopamine measurements, not only by their expected pharmacological action but also by directly altering the microelectrode responsivity. The commonly used reuptake inhibitors GBR 12909 (10 microM) and nomifensine (5 microM) drastically reduce electrode sensitivity and, in the case of nomifensine, increase the time to reach a plateau in response to dopamine boluses (i.e. reduced 'frequency response'). Cocaine (10 microM) and WIN 35428 (2 microM) have negligible effect on these indices. This decrease in sensitivity was found in both nafion and non-nafion coated electrodes. Further, the reduction in sensitivity seen in non-nafion coated electrodes was not prevented by increasing the reversal potential (from +1.0 to +1.3 V) and voltage scan rate (from 350 to 450 V/s). These data suggest that care must be taken when interpreting data from voltammetric or amporometric experiments using carbon electrodes where GBR 12909 or nomifensine are used, especially at high concentrations. Furthermore, wherever possible, direct effects of a drug on electrode sensitivity and frequency response should be determined.

Abstract  This study sought to investigate effects of short-chain fatty acids and CO2 on intracellular pH (pHi) and mechanisms that mediate pHi recovery from intracellular acidification in cultured ruminal epithelial cells of sheep. pHi was studied by spectrofluorometry using the pH-sensitive fluorescent indicator 2',7'-bis (carboxyethyl)-5(6')-carboxyfluorescein acetoxymethyl ester (BCECF/AM). The resting pHi in N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES)-buffered solution was 7.37 +/- 0.03. In HEPES-buffered solution, a NH4+/NH3-prepulse (20 mM) or addition of butyrate (20 mM) led to a rapid intracellular acidification (P < 0.05). Addition of 5-(N-ethyl-N-isopropyl)-amiloride (EIPA: 10 microM) or HOE-694 (200 microM) inhibited pHi recovery from an NH4+/NH3-induced acid load by 58% and 70%, respectively. pHi recovery from acidification by butyrate was reduced by 62% and 69% in the presence of EIPA (10 microM) and HOE-694 (200 microM), respectively. Changing from HEPES-(20 mM) to CO2/HCO3(-)-buffered (5%/20 mM) solution caused a rapid decrease of pHi (P < 0.01), followed by an effective counter-regulation. 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS; 100 microM) blocked the pHi recovery by 88%. The results indicate that intracellular acidification by butyrate and CO2 is effectively counter-regulated by an Na+/H+ exchanger and by DIDS-sensitive, HCO3(-)-dependent mechanism(s). Considering the large amount of intraruminal weak acids in vivo, both mechanisms are of major importance for maintaining the pHi homeostasis of ruminal epithelial cells.

Abstract  To better understand the biology of snow leopard spermatozoa and to facilitate developing assisted reproduction, a series of studies was conducted to: 1) identify the component(s) of complex culture media responsible for the detrimental effect on sperm survival in vitro, 2) optimize medium for supporting sperm viability, and 3) evaluate sperm capacitation in vitro. Constituents of complex media were added systematically to phosphate-buffered saline (PBS) to isolate the factor(s) influencing snow leopard sperm motility in vitro. Sperm capacitation was also assessed following incubation in PBS with bovine serum albumin (BSA), fetal calf serum (FCS), or heparin. For maintaining sperm motility, there was no benefit (P > or = 0.05) to supplementing PBS with low (5%) or high (20%) concentrations of snow leopard serum (SLS) versus FCS or BSA. Likewise, adding supplemental energy substrates (pyruvate, glucose, lactate, or glutamine) did not enhance or hinder (P > or = 0.05) sperm motility. However, motility rapidly decreased (P < 0.05) with the addition of NaHCO3 to PBS or Ham's F10 nutrient mixture. Surprisingly, Ham's F10 with no buffering component or with both NaHCO3 and N-Z-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES) maintained sperm motility at levels similar (P > or = 0.05) to PBS. Although sperm motility in all treatments decreased with time, there was a strong inverse relationship (P < 0.01; r = 0.90) between motility and sample pH at 6 hours. Spermatozoa incubated in PBS containing FCS, BSA, or heparin did not undergo the acrosome reaction when exposed to calcium ionophore. In summary, alkaline pH has a profound detrimental effect on snow leopard sperm motility, and capacitation does not occur under conditions that normally promote this event in other felid species. These results clearly demonstrate a high degree of interspecific variation among felids in fundamental sperm function, and they provide evidence for the necessity of basic research when developing assisted reproduction in little-studied nondomestic species.

Abstract  A very sensitive immunosensor based on polyaniline/ Nafion/protein A (PA/NF/PrA) composite electrodes has been developed for the amperometric immunoanalysis with urease-labeled immunoreagents. The use of urease conjugated goat anti-RIgG (GaRIgG-Ur) as the labeled antibody and urea as the substrate with an amperometric detection at -200 mV (vs Ag/AgCl) resulted in a dynamic range of 50-2000 ng mL-1 and a low detection limit of 10 ng/mL (64 pM) for the immunoanalysis of rabbit immunoglobulin G (RIgG). Because of the special affinity between protein A and RIgG, the PA/NF/PrA electrode can be regenerated repetitively by changing the pH of the buffer solutions. Characteristics of the PA/NF/PrA/RIgG immunosensor and optimal conditions for the competitive immunoanalysis of RIgG with FIA were studied.

Abstract  The specially deposited Prussian Blue denoted as "artificial peroxidase" was used as a transducer for hydrogen peroxide. The electrocatalyst was stable, highly active, and selective to hydrogen peroxide reduction in the presence of oxygen, which allowed sensing of H2O2 around 0.0 V (Ag/AgCl). Glutamate oxidase was immobilized on the surface of the Prussian Blue-modified electrode in a Nafion layer using a nonaqueous enzymology approach. The calibration range for glutamate in flow injection system was 1 x 10(-7)-1 x 10(-4) M. The lowest concentration of glutamate detected (1 x 10(-7) M) and the highest sensitivity in the linear range of 0.21 A M-1 cm-2 were achieved. The influence of reductants was practically avoided using the low potential of an indicator electrode (0.0 V Ag/AgCl). The attractive performance characteristics of the glutamate biosensor illustrate the advantages of Prussian Blue-based "artificial peroxidase" as transducer for hydrogen peroxide detection.

Abstract  Six non-amino acid nitrogen compounds were examined as nitrogen source for growth of Streptomyces hygroscopicus and biosynthesis of rapamycin. Of the nitrogen sources studied, ammonium sulfate was the best with respect to formation of rapamycin, and supported cell growth comparable to the organic nitrogen sources used in the control chemically defined medium, i.e., aspartate, arginine plus histidine. In the new chemically defined medium, which is buffered with 200 mM 2-(N-morpholino)ethanesulfonic acid to prevent decline of pH during fermentation, an ammonium sulfate concentration of 40 mM was optimal for biosynthesis of rapamycin. Rapamycin production increased by more than 30% on both volumetric and specific bases as compared to the previous medium containing the three amino acids as nitrogen source.

Abstract  Bacterial cellulose is a versatile renewable biomaterial that can be used as a hydrophilic matrix for the incorporation of metals into thin, flexible, thermally stable membranes. In contrast to plant cellulose, we found it catalyzed the deposition of metals within its structure to generate a finely divided homogeneous catalyst layer. Experimental data suggested that bacterial cellulose possessed reducing groups capable of initiating the precipitation of palladium, gold, and silver from aqueous solution. Since the bacterial cellulose contained water equivalent to at least 200 times the dry weight of the cellulose, it was dried to a thin membranous structure suitable for the construction of membrane electrode assemblies (MEAs). Results of our study with palladium-cellulose showed that it was capable of catalyzing the generation of hydrogen when incubated with sodium dithionite and generated an electrical current from hydrogen in an MEA containing native cellulose as the polyelectrolyte membrane (PEM). Advantages of using native and metallized bacterial cellulose membranes in an MEA over other PEMs such as Nafion 117 include its higher thermal stability to 130 degrees C and lower gas crossover.

Abstract  Different models have been proposed that link the tubulin heterodimer nucleotide content and the role of GTP hydrolysis with microtubule assembly and dynamics. Here we compare the thermodynamics of microtubule assembly as a function of nucleotide content by van't Hoff analysis. The thermodynamic parameters of tubulin assembly in 30-100 mM piperazine-N,N'-bis(2-ethanesulfonic acid), 1 mM MgSO4, 2 mM EGTA, pH 6.9, in the presence of a weakly hydrolyzable analog, GMPCPP, the dinucleotide analog GMPCP plus 2 M glycerol, and GTP plus 2 M glycerol were obtained together with data for taxol-GTP/GDP tubulin assembly (GMPCPP and GMPCP are the GTP and GDP nucleotide analogs where the alpha beta oxygen has been replaced by a methylene, -CH2-). All of the processes studied are characterized by a positive enthalpy, a positive entropy, and a large, negative heat capacity change. GMPCP-induced assembly has the largest negative heat capacity change and GMPCPP has the second largest, whereas GTP/2 M glycerol- and taxol-induced assembly have more positive values, respectively. A large, negative heat capacity is most consistent with the burial of water-accessible hydrophobic surface area, which gives rise to the release of bound water. The heat capacity changes observed with GTP/2 M glycerol-induced and with taxol-induced assembly are very similar, -790 +/- 190 cal/mol/k, and correspond to the burial of 3330 +/- 820 A2 of nonpolar surface area. This value is shown to be very similar to an estimate of the buried nonpolar surface in a reconstructed microtubule lattice. Polymerization data from GMPCP- and GMPCPP-induced assembly are consistent with buried nonpolar surface areas that are 3 and 6 times larger. A linear enthalpy-entropy and enthalpy-free energy plot for tubulin polymerization reactions verifies that enthalpy-entropy compensation for this system is based upon true biochemical correlation, most likely corresponding to a dominant hydrophobic effect. Entropy analysis suggests that assembly with GTP/2 M glycerol and with taxol is consistent with conformational rearrangements in 3-6% of the total amino acids in the heterodimer. In addition, taxol binding contributes to the thermodynamics of the overall process by reducing the delta H degree and delta S degree for microtubule assembly. In the presence of GMPCPP or GMPCP, tubulin subunits associate with extensive conformational rearrangement, corresponding to 10% and 26% of the total amino acids in the heterodimer, respectively, which gives rise to a large loss of configurational entropy. An alternative, and probably preferable, interpretation of these data is that, especially with GMPCP-tubulin, additional isomerization or protonation events are induced by the presence of the methylene moiety and linked to microtubule assembly. Structural analysis shows that GTP hydrolysis is not required for sheet closure into a microtubule cylinder, but only increases the probability of this event occurring. Sheet extensions and sheet polymers appear to have a similar average length under various conditions, suggesting that the minimum cooperative unit for closure of sheets into a microtubule cylinder is approximately 400 nm long. Because of their low level of occurrence, sheets are not expected to significantly affect the thermodynamics of assembly.