EQCM study of the p- and n-doping processes of a poly[4,4-bis(butylsulphanyl)-2,2-bithiophene]

Electrogenerated deposits of poly[4,4^′-bis(butylsulphanyl)-2,2^′-bithiophene] have been characterised in the presence of different supporting electrolytes, by coupling current (charge) to microgravimetric measurements from the electrochemical quartz crystal microbalance (EQCM). The simultaneous collection of voltammetric measurements and of data relative to mass changes shows the influence exerted by the nature of the supporting electrolyte on the charge-discharge steps of both p- and n-doping processes. Interestingly, the microgravimetric data collected corresponding to the pre-peaks of both doping processes suggest the occurrence of two opposite motions of ions (ingress into and exit out from the polymer) in the relevant potential region, giving a contribution to the study of the `residual charge' phenomenon.     

Deposition of SiOx Films from Hexamethyldisiloxane/Oxygen Radiofrequency Glow Discharges: Process Optimization by Plasma Diagnostics

Optical emission and Fourier transform infrared absorption diagnostics have been carried out in hexamethyldisiloxane/oxygen RF discharges for studying the effects of the feed composition and the power on the deposition of SiO₂—like thin films. Ex situ FTIR absorption has been utilized to monitor organic moieties and silanol groups in the film. It is shown that carbon-free films can be obtained by highly diluting the monomer in oxygen, while medium-to-high power is necessary to abate silanol groups. These two conditions represent the optimization criterion to obtain excellent barrier films for food packaging applications.     

High-performance liquid chromatography and capillary electrophoresis: methodological challenges for the determination of biologically relevant low-aliphatic aldehydes in human saliva

Tobacco smoke is involved in the pathogenesis of cardiovascular and respiratory diseases and also has a local toxic effect in the oral cavity. Low-aliphatic aldehydes, such as formaldehyde, acetaldehyde and acrolein, are among the main components of mainstream cigarette smoke and their local noxious and carcinogenic effects in the oral cavity and upper gastrointestinal tract are well-known. Although various studies have been performed so far to determine their content in cigarette smoke, none has included the direct measurement of these compounds in the saliva of smoking and nonsmoking subjects. Thus, in an attempt to verify whether typical chromatographic (high-performance liquid chromatography, HPLC) and/or electrophoretic (capillary electrophoresis, CE) techniques could be reliable methods for determining the levels of these analytes in human saliva, we submitted specimens obtained from a selected population of heavy, moderate, and nonsmoking subjects to HPLC and CE analyses. Both methods showed good reproducibility in terms of migration times and peak height and/or areas and had comparable linearity. Quantitative analyses performed on the specimens investigated evidenced a 3.5-fold increase of low-aliphatic aldehydes in saliva of nonsmoking subjects after they have smoked a single cigarette and a further 2-fold increase of these compounds in saliva of smokers with a daily consumption of 10 or more cigarettes.     

Straightforward entry into 5-hydroxy-1-aminopyrrolines and the corresponding pyrroles from 1,2-diaza-1,3-butadienes

The synthesis of 5-hydroxy-1-aminopyrroline-3-carboxylic acid derivatives and 5-unsubstituted-1-aminopyrrole-3-carboxylic acid derivatives from 1,2-diaza-1,3-butadienes and aldehydes is presented. These domino reactions offer the advantage of executing multistep transformation without intermediate workup procedures. The stereoselectivity of ring closure to 5-hydroxy-1-aminopyrroline-3-carboxylic acid derivatives and phenyl transposition to 2,3-diphenyl-1-aminopyrrole-3-carboxylic acid derivatives are also studied.     

Isotope dilution method for the assay of rotenone in olive oil and river waters by liquid chromatography/multiple reaction monitoring tandem mass spectrometry

A new approach for the assay of rotenone (1) by isotope dilution mass spectrometry is presented. The extreme toxicity of rotenone, a natural phytodrug with insecticidal and piscicidal activity, recently banned by national and international environmental protection agencies, calls for the development of sensitive and accurate methods of analyses. Accordingly, the proposed protocol is based on the availability of the labeled internal standard rotenone‐d₃ (3) which can be conveniently prepared by consecutive and specific mono‐O‐demethylation, and remethylation with methyl iodide‐d₃. The sensitivity of the method is confirmed by the very low limit of detection (LOD) and quantitation (LOQ) values achieved in the assay of 1 in two distinct fortified matrices, and is further supported by the observed accuracy values. Copyright © 2009 John Wiley & Sons, Ltd.     

Moment based approaches to value the risk of contingent claim portfolios

In this paper we describe and apply the estimating function methodology to value the risk of asset derivative portfolios. We first implement the Li’s model based on the first four moments and then we show the limits of this model in forecasting the maximum loss of contingent claims. In addition, we show that four moments are not enough to describe the behavior of the lower percentiles of derivatives. Finally, we propose a model that considers the first six moments and we compare the performances of these models proposing a backtest analysis on several historical and truncated asset derivative portfolios.     

Mass spectrometry study of PRL‐3 phosphatase inactivation by disulfide bond formation and cysteine into glycine conversion

The Phosphatase of Regenerating Liver‐3 (PRL‐3) is a cysteine‐based phosphatase (CBP) that is highly over‐expressed in liver metastasis in colorectal cancer and suspected to be involved in the progression from tumor to metastasis. During substrate‐specificity studies based on the screening of PRL‐3 phosphatase activity on several phosphorylated synthetic peptides, we observed a decrease in activity depending on sample aging and storage conditions. By liquid chromatography combined with selective alkylation and mass spectrometry, we found two main PRL‐3 inactivation pathways: a disulfide bond formation between the catalytic C104 and C49, blocking the enzyme in an inactive oxidized form, or the conversion of the catalytic C104 into glycine. We also found that the disulfide formation and the cysteine into glycine conversion are catalyzed by cations present in the sample after protein purification through a nickel column. By adding a cation chelator such as EDTA and de‐oxygenating the sample with argon, PRL‐3 phosphatase activity was preserved. These findings suggest that PRL‐3, like other CBPs, is sensitive to inactivation by catalytic cysteine oxidation and this has implications for future studies of its activity and specificity. Copyright © 2009 John Wiley & Sons, Ltd.     

Convenient preparation of (η-alkadiene)dichloroplatinum(II) complexes from [PtCl6] anions and their reduction to platinum(0) alkene complexes under phase-transfer catalysis conditions

Convenient one-pot reduction-complexation reactions of hexachloroplatinato(IV) anions to (η⁴-alkadiene)dichloroplatinum(II) complexes (η⁴-alkadiene = COD, DAE, DCPD, NBD) under suitable phase-transfer catalysis conditions are reported. Reduction to zerovalent platinum alkene complexes has been obtained in the presence of an excess of alkene, potassium formate and 18-crown-6 as phase-transfer catalyst (alkene = COD, NB, dba). The crystal and molecular structure of [Pt_1.03(dba)₃]·CH₂Cl₂ has been studied by X-ray diffraction methods: it can be described as a solid solution of Pt(dba)₃ and Pt₂(dba)₃, the mononuclear complex being largely prevailing.     

Host–guest interactions and their role in enantioselective hydrogenation of α-keto esters: An analysis of model systems

The interaction between cinchonidine and methyl pyruvate has been proposed as the key step leading to enantiodifferentiation in the enantioselective hydrogenation of α-ketoesters. In the present work, we employ ab initio MP2/6-31G(d) and MP2/6-31G(d,p) methods to carry out an analysis of the most relevant kind of interactions operating in representative model systems. These interactions are discussed in terms of orbital superposition and dipolar interaction. When approaching H₂CO to NH₃ at distances lower than 3.4 Å, orbital superposition is the predominant interaction, while at distances above 3.4 Å, both orbital superposition and dipolar interactions may contribute to stabilization, with a small prevalence of dipolar interactions. The stabilization energy at large distances (above 4.5 Å) is very small (about 0.5 kcal mol⁻¹), probably not enough to be responsible for the enantiodifferentiation process. Semiempirical calculations on the parent systems were also unable to reveal any special interaction which could be attributed to the enantiodifferentiation process.