GC-MS Analysis of Biological Nitrate and Nitrite Using Pentafluorobenzyl Bromide in Aqueous Acetone: A Dual Role of Carbonate/Bicarbonate as an Enhancer and Inhibitor of Derivatization

Carbon dioxide (CO₂) and carbonates, which are widely distributed in nature, are constituents of inorganic and organic matter and are essential in vegetable and animal organisms. CO₂ is the principal greenhouse gas in the atmosphere. In human blood, CO₂/HCO₃⁻ is an important buffering system. Inorganic nitrate (ONO₂⁻) and nitrite (ONO⁻) are major metabolites and abundant reservoirs of nitric oxide (NO), an endogenous multifunctional signaling molecule. Carbonic anhydrase (CA) is involved in the reabsorption of nitrite and nitrate from the primary urine. The measurement of nitrate and nitrite in biological samples is of particular importance. The derivatization of nitrate and nitrite in biological samples alongside their ¹⁵N-labeled analogs, which serve as internal standards, is a prerequisite for their analysis by gas chromatography–mass spectrometry (GC-MS). A suitable derivatization reagent is pentafluorobenzyl bromide (PFB-Br). Nitrate and nitrite are converted in aqueous acetone to PFB-ONO₂ and PFB-NO₂, respectively. PFB-Br is also useful for the GC-MS analysis of carbonate/bicarbonate. This is of particular importance in conditions of pharmacological CA inhibition, for instance by acetazolamide, which is accompanied by elevated concomitant excretion of nitrate, nitrite and bicarbonate, as well as by urine alkalization. We performed a series of experiments with exogenous bicarbonate (NaHCO₃) added to human urine samples (range, 0 to 100 mM), as well as with endogenous bicarbonate resulting from the inhibition of CA activity in healthy subjects before and after ingestion of pharmacological acetazolamide. Our results indicate that bicarbonate enhances the derivatization of nitrate with PFB-Br. In contrast, bicarbonate decreases the derivatization of nitrite with PFB-Br. Bicarbonate is not a catalyst, but it enhances PFB-ONO₂ formation and inhibits PFB-NO₂ formation in a concentration-dependent manner. The effects of bicarbonate are likely to result from its reaction with PFB-Br to generate PFB-OCOOH. Nitrate reacts with concomitantly produced PFB-OCOOH to form PFB-ONO₂ in addition to the direct reaction of nitrate with PFB-Br. By contrast, nitrite does not react with PFB-OCOOH to form PFB-NO₂. Sample acidification by small volumes of 20 wt.% aqueous acetic acid abolishes the effects of exogenous and endogenous bicarbonate on nitrite measurement.     

Determination of N-Acetyl-l-cysteine Ethyl Ester (NACET) by Flow Injection Analysis and Spectrophotometric Detection Using Different Thiol-Sensitive Ligands

A new flow injection spectrophotometric method for the determination of N-acetyl-l-cysteine ethyl ester (NACET) was developed and validated. The method is based on the reduction of Cu(II)-ligand complexes to chromophoric Cu(I)-ligand complexes with the analyte. The studied ligands were neocuproine (NCN), bicinchoninic acid (BCA) and bathocuproine disulfonic acid (BCS). The absorbance of the Cu(I)-ligand complex was measured at 458, 562 and 483 nm for the reactions of NACET with NCN, BCA and BCS, respectively. The method was validated in terms of linear dynamic range, limit of detection and quantitation, accuracy, selectivity, and precision. Experimental conditions were optimized by a univariate method, yielding linear calibration curves in a concentration range from 2.0 × 10⁻⁶ mol L⁻¹ to 2.0 × 10⁻⁴ mol L⁻¹ using NCN; 2.0 × 10⁻⁶ mol L⁻¹ to 1.0 × 10⁻⁴ mol L⁻¹ using BCA and 6.0 × 10⁻⁷ mol L⁻¹ to 1.2 × 10⁻⁴ mol L⁻¹ using BCS. The achieved analytical frequency was 90 h⁻¹ for all three ligands. The method was successfully employed for NACET determination in pharmaceutical preparations, indicating that this FIA method fulfilled all the essential demands for the determination of NACET in quality control laboratories, as it combined low instrument and reagent costs with a high sampling rate.     

5G/NGPON Evolution and Convergence: Developing on Spatial Multiplexing of Optical Fiber Links for 5G Infrastructures

ABSTRACT

The offering of demanding telecommunication services as promised by the 5G specifications raise the necessity for high capacity, flexible, adaptive, and power conserving fronthaul. Toward this goal, the role of the passive optical network which is responsible for interconnecting the central office (CO) with the cell-sites is crucial. Among the latest related technologies that need to be integrated in the context of the next generation passive optical networks (NGPONs), the most promising for increasing the provided bandwidth, is the optical spatial multiplexing. In this paper, we present the key 5G technologies, focusing on spatial division multiplexing, which constitutes the main innovation of the blueSPACE 5G Infrastructure Public Private Partnership (5G PPP) project. Exploiting the recent developments on multicore fibers (MCFs), optical beamforming networks (OBFNs), analog radio over fiber (ARoF), and spatial-spectral resources granularity in the context of Spectrally Spatially Flexible Optical Networks (SS-FONs), we describe a complete approach for the 5G fronthaul, emphasizing on the efficient allocation of optical resources while aiming at minimizing energy consumption. The modeled optimization problem is thoroughly presented, and the introduced scheme is evaluated through a real-world based simulation scenario, exhibiting quite promising results.     

Large Plastic Deformation of Isotactic Poly(propylene) (iPP) Evaluated by WAXD Techniques

Summary: Commercial isotactic poly(propylene) (iPP), obtained in bars, was annealed and submitted to different levels of plastic deformation by uniaxial plane compression using a special device which permits well controlled temperature and strain rate. The evolution of the microstructure was followed at different degrees of deformation by wide angle x-ray diffraction (WAXD) techniques. The spherulite fragmentation process, lamellar orientation and destruction of the crystallites is argued, according to collected analytical data in the flow direction (FD), the loading direction (LD) and the lateral or constrain direction (CD). The evaluation of the WAXD patterns in terms of diffraction line position, intensity and width, permits to affirm that, while the large plastic deformation occurs, the crystalline net suffers anisotropic deformation, the crystallites become preferentially oriented along the flow direction and the crystalline phase diminish in amount indicating lesser and smaller crystallites. The gradual lamellae fragmentation occurs, starting with apparent crystalline size of approximately 30 nm for the non-deformed material and gradually decreasing to approximately 15 nm for the 70% deformed one.     

Sur la reéduction modulo p des polynoômes absolument irreéductibles

 On the reduction modulo p of absolutely irreducible polynomials. Let K be a number field and F(X,Y) be an absolutely irreducible polynomial of K[X,Y]. In this note, using an effective version of Riemann-Roch theorem and a version of the implicit functions theorem, we calculate a positive number A such that if ℘ is prime ideal of the ring of integers of K with norm , then the reduction of F(X,Y) modulo ℘ is an absolutely irreducible polynomial. (Réu le 1 Février 1999; en forme finale 21 Septembre 1999)     

Calabi–Yau Black Holes and (0,4) Sigma Models

When an M-theory fivebrane wraps a holomorphic surface › in a Calabi-Yau 3-fold X the low energy dynamics is that of a black string in 5 dimensional — =1 supergravity. The infrared dynamics on the string worldsheet is an — = (0,4) 2D conformal field theory. Assuming the 2D CFT can be described as a nonlinear sigma model, we describe the target space geometry of this model in terms of the data of X and ›. Variations of weight two Hodge structures enter the construction of the model in an interesting way.     

A simple method for solving the diophantine equation Y2 = X4 + aX3 + bX2 + cX + d

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A simple method for solving the diophantine equation Y2 = X4 + aX3 + bX2 + cX + d

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Water‐Soluble Carbon Nanotubes by Redox Radical Polymerization

Water‐soluble single‐ and multi‐walled carbon nanotubes (CNTs) were prepared by grafting polyacrylamide chains from the graphitic surface via ceric ion‐induced redox radical polymerization. The reducing functionalities were covalently attached to the tubes by peroxide‐assisted radical reaction. The results showed that polymer chains were grafted onto CNTs by the redox process. The redox radical polymerization initiated by carbon nanotube‐bearing functionalities not only provides a powerful strategy for modifying the carbon nanostructures but also gives us the knowledge of their sidewall chemistry.