Voltammetric and surface-enhanced resonance Raman spectroscopic characterization of cytochrome C adsorbed on a 4-mercaptopyridine monolayer on silver electrodes

To combine voltammetric techniques with surface-enhanced resonance Raman scattering (SERRS), cytochrome c (cyt c) was immobilized on a roughened silver electrode chemically modified with a self-assembled monolayer (SAM) of 4-mercaptopyridine (PySH). All measurements were performed on the same electrode in a homemade spectroelectrochemical cell suitable for such applications. Cyt c on a PySH-SAM shows a quasi-reversible, monoelectronic, adsorption-controlled CV response with a formal reduction potential of -0.061 V (vs SCE), which is comparable to the values found for native cyt c adsorbed on different SAMs. SERRS spectra proved that cyt c adsorbed on a PySH monolayer is present in the native conformer (the B1 state). Voltammetric and SERRS experiments at high ionic strength revealed that the interaction between the SAM and the protein is electrostatic in nature. In conclusion, PySH was found to be suitable for adsorption of cyt c at SERRS-active silver surfaces. In comparison with other SAMs, PySH requires less time (10 min vs 12-18 h) to form a long-time durable and reproducible coating on the roughened electrode surface.     

Synthesis of 5-cyanopyrazolo[3,4-b]pyridines in the reaction of 5-amino-3-methyl-1-phenylpyrazole with arylidene derivatives of malonodinitrile and ethyl cyanoacetate

This paper describes the synthesis of a new series of 6-amino-4-aryl-5-cyanopyrazolo[3,4-b]pyridines 4 and 4-aryl-5-cyano-6H-pyrazolo[3,4-b]pyridin-6-ones 5 from the reaction of 5-amino-3-methyl-1-phenylpyrazole 1 with arylidene derivatives of malonodinitrile 2 and ethyl cyanoacetate 3 . The structure of the final compounds was determined on the basis of nmr measurements, especially by ¹H, ¹H-, ¹H, ¹³C-COSY, DEPT and X-ray diffraction.     

A consistent approach to variable bubble-point systems

Here, it is shown that the “traditional approach” to variable bubble-point problems, using black-oil models, is not consistent, because it violates the “bubble-point conservation law.” In order to have a consistent approach, it is necessary to incorporate shocks—discussed in previous papers—in which the bubble-point is discontinuous. A “consistent approach” is applied to specific examples, and results compared with those of the “traditional” one. The conclusion that the “traditional approach” generally yields large errors for the production rates and other parameters of interest in the oil industry, is reached. © 1997 John Wiley & Sons, Inc.     

Production of PHAs from agricultural waste material

Polyhydroxyalkanoates (PHAs) are biodegradable substitutes to fossil fuel plastics that can be produced from renewable raw materials such as saccharides, alcohols and low-molecular-weight fatty acids. They are completely degradable to carbon dioxide and water through natural microbiological mineralization. Consequently, neither their production nor their use or degradation have a negative ecological impact. By keeping closed the cycle of production and re-use, PHAs can enable at least part of the polymer-producing industry to switch from ecologically harmful end-of-the-pipe production methods towards sounder technologies. Up to now such polyesters have been produced biotechnologically from refined raw materials (e.g. glucose and sodium propionate), but they can as well be produced much cheaper from agricultural waste materials (e.g. molasses, maltose, glycerol phase from biodiesel production, whey), as long as these materials have a known composition and are available in appropriate quantities. Yield factors and specific rates for growth and PHA accumulation are shown for 3 strains of Alcaligenes latus for different agricultural waste carbon sources.     

Stationary solutions for the parity-even sector of the CPT-even and Lorentz-covariance-violating term of the standard model extension

In this work, we focus on some properties of the parity-even sector of the CPT-even electrodynamics of the standard model extension. We analyze how the six non-birefringent terms belonging to this sector modify the static and stationary classical solutions of the usual Maxwell theory. We observe that the parity-even terms do not couple the electric and magnetic sectors (at least in the stationary regime). The Green’s method is used to obtain solutions for the field strengths E and B at first order in the Lorentz-covariance-violating parameters. Explicit solutions are attained for point-like and spatially extended sources, for which a dipolar expansion is achieved. Finally, an Earth-based experiment is presented that can lead (in principle) to an upper bound on the anisotropic coefficients as stringent as      

Ultra-low background measurements of decayed aerosol filters

Aerosol samples collected on filter media were analyzed using HPGe detectors employing varying background-reduction techniques in order to experimentally evaluate the opportunity to apply ultra-low background measurement methods to samples collected, for instance, by the Comprehensive Test Ban Treaty International Monitoring System (IMS). In this way, realistic estimates of the impact of low-background methodology on the sensitivity obtained in systems such as the IMS were assessed. The current detectability requirement of stations in the IMS is 30 μBq/m³ of air for ¹⁴⁰Ba, which would imply ~10⁶ fissions per daily sample. Importantly, this is for a fresh aerosol filter. One week of decay reduces the intrinsic background from radon daughters in the sample allowing much higher sensitivity measurement of relevant isotopes, including ¹³¹I. An experiment was conducted in which decayed filter samples were measured at a variety of underground locations using Ultra-Low Background (ULB) gamma spectroscopy technology. The impacts of the decay and ULB are discussed.     

Evaluation of the odd-even effect in limits of detection for electron microprobe analysis of natural minerals

Limit of detection (LOD), being a fundamental quality parameter for analytical techniques, has been recently investigated and a systematic behavior has been observed for most odd-even element pairs for many techniques. However, to the best of our knowledge very few LOD data are available in published literature for electron microprobe analysis; these consist of three papers, two being on rare-earth elements and the third covering a large number of elements of atomic number between 21 and 92. These data confirm the systematic behavior of LODs for many odd-even pairs. To initiate to full this gap, we determined LODs for several major rock-forming chemical elements from Na to Fe with atomic numbers between 11 and 26, during the microprobe analysis of common minerals (olivine, plagioclase, pyroxene, amphibole, quartz, and opaques) in volcanic rocks. The odd-even effect of nuclear stability seems to be present in LOD data for most odd-even pairs investigated. Nevertheless, the experimental strategy concerning the reference materials, calibration procedure, and blank measurements, should be substantially modified to better evaluate the systematic behavior of LOD values in microprobe analysis.     

Determination of polybrominated diphenyl ethers in water and soil samples by cloud point extraction-ultrasound-assisted back-extraction-gas chromatography–mass spectrometry

A novel and efficient analytical methodology is proposed for extracting and preconcentrating polybrominated diphenyl ethers (PBDEs) from samples of environmental interest prior gas chromatography–mass spectrometry (GC–MS) analysis. It is based on the induction of micellar organized medium by using a non-ionic surfactant (Triton X-114) to extract the target PBDEs. To enable coupling the efficient extracting technique with GC analysis, ultrasound-assisted back-extraction (UABE) into an organic solvent was required. Several factors, including surfactant type and concentration, equilibration temperature and time, ionic strength, pH and buffers nature and concentration were studied and optimized over the extraction efficiency of the proposed technique. Under optimal experimental conditions, the target analytes were quantitatively extracted achieving an enrichment factor of 250 when 10 mL aliquot of ultrapure water spiked with PBDE-standard mixture (10 pg mL⁻¹ each PBDE) was extracted. Method detection limits (MDLs) calculated with aqueous PBDEs solutions as three times the signal-to-noise ratio (S/N), ranged from 1 to 2 pg mL⁻¹ with RSDs values ≤8.5% (n = 5). The coefficients of estimation of the calibration curves obtained following the proposed methodology were ≥0.9987 and linear range of all PBDEs was 4–150 pg mL⁻¹. The proposed methodology was validated by carrying out a recovery study by spiking the samples at two different concentration levels of PBDEs (10 and 50 pg mL⁻¹ for waters samples). Recoveries values in the range of 96–106% for water samples were obtained showing satisfactory robustness of the method for analyzing PBDEs in water samples. The proposed methodology was applied for the analysis of PBDEs: 2,2′,4,4′-tetraBDE (BDE-47), 2,2′,4,4,5-pentaBDE (BDE-99), 2,2′,4,4,6-pentaBDE (BDE-100) and 2,2,4,4′,5,5′-hexaBDE (BDE-153) in water samples, including drinking, lake, river water and soil samples. Significant quantities of PBDEs were not found in the analyzed samples.     

Carbon dioxide solubility in 1-ethyl-3-methylimidazolium trifluoromethanesulfonate

In this work, we present new solubility results for carbon dioxide in the ionic liquid 1-ethyl-3-methylimidazolium trifluoromethanesulfonate for temperatures ranging from (303.2 to 343.2) K and pressures up to 5.9 MPa using a thermogravimetric microbalance. Carbon dioxide solubilities were determined from absorption saturation (equilibrium) results at each fixed temperature and pressure. The buoyancy effect was accounted for in the evaluation of the carbon dioxide solubility. A highly accurate equation of state and a group contribution predictive method for carbon dioxide and for ionic liquids, respectively, were employed to determine the effect of buoyancy on carbon dioxide solubility. The solubility measurements are presented as a function of temperature and pressure. An extended Henry’s law equation was used to correlate the present experimental solubility values and the result was satisfactory.