Highly selective and sensitive voltammetric sensor based on modified multiwall carbon nanotube paste electrode for simultaneous determination of ascorbic acid,acetaminophen and tryptophan

A carbon-paste electrode modified with multiwall carbon nanotubes (MWCNTs) was used for the sensitive and selective voltammetric determination of ascorbic acid (AA) in the presence of 3,4-dihydroxycinnamic acid (3,4-DHCA) as mediator. The mediated oxidation of AA at the modified electrode was investigated by cyclic voltammetry (CV), chronoamperommetry and electrochemical impedance spectroscopy (EIS). Also, the values of catalytic rate constant (k), and diffusion coefficient (D) for AA were calculated. Using square wave voltammetry (SWV), a highly selective and simultaneous determination of AA, acetaminophen (AC) and tryptophan (Trp) has been explored at the modified electrode. The modified electrode displayed strong function for resolving the overlapping voltammetric responses of AA, AC and Trp into three well-defined voltammetric peaks. In the mixture containing AA, AC and Trp, the three compounds can well separate from each other with potential differences of 200, 330 and 530 mV between AA and AC, AC and Trp and AA and Trp, respectively, which was large enough to determine AA, AC and Trp individually and simultaneously.     

Recent advantages in the metal (bulk and nano)-catalyzed S-arylation reactions of thiols with aryl halides in water: a perfect synergy for eco-compatible preparation of aromatic thioethers

Transition-metal-catalyzed C–S cross-coupling reactions comprise one of the most efficient methods for the synthesis of biologically and synthetically important aryl sulfide derivatives. Among the various solvents used in this cross-coupling reaction (ionic liquids, water, organic, and aqueous biphasic solvents), neat water have attracted notable interest in recent years due to its properties such as non-toxicity, non-flammability, renewability, and widely availability compared with other solvents. Since several catalytic systems for this green synthesis of aryl sulfides have been reported from 2007 to present, a comprehensive review on this interesting field seems to be timely. In this study, we discuss the most representative and interesting reports on the synthesis of aryl sulfides via metal-catalyzed cross-coupling of thiols with aryl halides in water. Mechanistic aspects of the reactions are considered and discussed in detail.     

Microwave Absorption Properties of Polyaniline/Carbonyl Iron Composites

In this work, carbonyl iron (CI) containing polya- niline composites (PANI+CI) were prepared via in-situ polymerization of aniline in an aqueous solution containing different amounts of CI as the magnetic filler for the micro- wave absorbers. The incorporation of the magnetic powder to the PANI matrix was confirmed by X-ray diffraction (XRD), IR and SEM. Synthesized PANI+CI composite particles were subsequently added to an epoxy resin matrix to produce related R-PANI+CI composites. Study of thermal properties by thermogravimetric analysis revealed enhanced thermal stability of the composites. The electromagnetic-absorbing properties were studied by measuring the reflection loss in the frequency range of 8.0 to 12.0 GHz. The experimental results indicated that the electromagnetic wave absorbing properties of PANI+CI composites are dependent on the PANI/CI weight ratio. The good reflection loss of the composite at the optimum PANI/CI weight ratio of 1:6 suggests its potential applicability as a good radar absorber.     

Thermodynamic analysis of carbon dioxide reforming of methane in view of solid carbon formation

A thermodynamic equilibrium analysis on the multi-reaction system for carbon dioxide reforming of methane in view of carbon formation was performed with Aspen plus based on direct minimization of Gibbs free energy method. The effects of CO₂/CH₄ ratio (0.5-3), reaction temperature (573-1473 K) and pressure (1-25 atm) on equilibrium conversions, product compositions and solid carbon were studied. Numerical analysis revealed that the optimal working conditions for syngas production in Fischer-Tropsch synthesis were at temperatures higher than 1173 K for CO₂/CH₄ ratio being 1 at which about 4 mol of syngas (H₂/CO = 1) could be produced from 2 mol of reactants with negligible amount of carbon formation. Although temperatures above 973 K had suppressed the carbon formation, the moles of water formed increased especially at higher CO₂/CH₄ ratios (being 2 and 3). The increment could be attributed to RWGS reaction attested by the enhanced number of CO moles, declined H₂ moles and gradual increment of CO₂ conversion. The simulated reactant conversions and product distribution were compared with experimental results in the literatures to study the differences between the real behavior and thermodynamic equilibrium profile of CO₂ reforming of methane. The potential of producing decent yields of ethylene, ethane, methanol and dimethyl ether seemed to depend on active and selective catalysts. Higher pressures suppressed the effect of temperature on reactant conversion, augmented carbon deposition and decreased CO and H₂ production due to methane decomposition and CO disproportionation reactions. Analysis of oxidative CO₂ reforming of methane with equal amount of CH₄ and CO₂ revealed reactant conversions and syngas yields above 90% corresponded to the optimal operating temperature and feed ratio of 1073 K and CO₂:CH₄:O₂ = 1:1:0.1, respectively. The H₂/CO ratio was maintained at unity while water formation was minimized and solid carbon eliminated.     

The aromatic enhancement in the axial‐flow spherical packed‐bed membrane naphtha reformers in the presence of catalyst deactivation

Because of some disadvantages of conventional tubular reactors (CTRs), the concept of spherical membrane reactors is proposed as an alternative. In this study, it is suggested to apply hydrogen perm‐selective membrane in the axial‐flow spherical packed‐bed naphtha reformers. The axial flow spherical packed‐bed membrane reactor (AF‐SPBMR) consists of two concentric spheres. The inner sphere is supposed to be a composite wall coated by a thin Pd‐Ag membrane layer. Set of coupled partial differential equations are developed for the AF‐SPBMR model considering the catalyst deactivation, which are solved by using orthogonal collocation method. Differential evolution optimization technique identifies some decision variables which can manipulate the input parameters to obtain the desired results. In addition to lower pressure drop, the enhancement of aromatics yield by the membrane layer in AF‐SPBMR adds additional superiority to the spherical reactor performance in comparison with CTR. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

Variants in the PPARGC1A Gene may Influence the Effect of Fat Intake on Resting Metabolic Rate in Obese Women

Recent studies have shown that dietary intake and genetic variants play a decisive role in the risk of obesity. Therefore, this study was designed to examine the interaction between dietary fat and PPARGC1A polymorphisms on the level of resting metabolic rate (RMR). We enrolled 288 Iranian overweight and obese women in this cross‐sectional study. We sequenced the 648 b.p. DNA in Exon 8 of PPARGC1A gene. We analyzed the two single‐nucleotide polymorphisms, namely rs11290186 and rs2970847, in this region. All participants were assessed for RMR, dietary intake, and body composition. This study demonstrated that total cholesterol and insulin levels were positively associated with T allele carriers of rs2970847. Moreover, the A‐deletion allele carrier of the rs11290186 genotype had higher triacylglycerol and insulin concentrations. The current study revealed that, after adjustment for energy intake, the AA genotype of PPARGC1A (rs11290186) had a direct association with polyunsaturated fatty acids and linoleic acid intakes. Another important finding in our study was that there was an interaction seen between fat and saturated fatty acids intake with the PPARGC1A genotypes. Women with fat intakes of more than 30% of calorie intake per day and the A‐deletion genotype had a lower RMR and RMR/fat free mass (FFM). It seems that the PPARGC1A polymorphisms lead to the downregulation of insulin signaling and subsequently insulin resistance. In addition, the interactions between the PPARGC1A polymorphisms (rs11290186) and the level of dietary fat intake probably can have an effect on RMR and RMR/FFM in obese women.     

FORCE TRANSDUCER MODELING OF RECTANGULAR,V–SHAPED,AND DAGGER CANTILEVER PROBES BASED ON ATOMIC FORCE MICROSCOPY

Real-time monitoring of the nano-particle manipulation process by atomic force microscope (AFM) is almost impossible since the manipulator of the AFM is used as either the imaging or manipulation tool at a given instant. As one approach to this problem, researchers scan the area where the target particle exists, before and after the nano-manipulation. Thus, by using some fixed reference features, the new relative position of the particle is obtained from the images. However, this imaging is offline, and unexpected problems during nano-manipulation process cannot be detected. In this article, force transducer of the AFM rectangular, V-shaped, and dagger cantilevers, which convert the three-dimensional deflections measured by the detection system to corresponding three-dimensional force, are modeled and compared. So there would be a feedback from the real-time force system during nano-manipulation process, which can be utilized for better understanding and reliable handling of nano-particles. Furthermore, the manipulation forces are affected directly by spring constants of cantilever. Hence, the cantilever is the most significant and sensitive component of the AFM. Therefore, variations of the lateral, longitudinal, and normal spring constants of the mentioned cantilever for different geometrical parameters are analyzed and discussed.     

Going downstream in a project-based firm: Integration of distributors in the delivery of complex systems

Research on the integration of different actors in project business has centered on the upstream value chain and a project-based firm's relationship with suppliers. The downstream delivery chain also includes an integration challenge as some project-based firms use distributors to sell and deliver systems. The purpose of this paper is to highlight the importance of integrating with distributors in the delivery of complex systems. A qualitative case study was conducted in one project-based firm. Different distributor capabilities were identified and grouped into business, relational, marketing, and delivery capabilities. Different integration mechanisms were mapped at business and project levels, and divided into control-, cooperation-, and development-oriented mechanisms. The findings show that distributor capabilities related to complex system delivery develop through repetitive collaboration across projects. The stable position of distributors in the downstream value chain facilitate the use of integration mechanisms at the business level and development-oriented integration approach at the project level.