Characterisation of poly(neutral red) modified carbon film electrodes; application as a redox mediator for biosensors

The polymer redox mediator, poly(neutral red) (PNR), has been synthesised and characterised electrochemically to investigate the best electropolymerisation and mediation conditions for application in enzyme biosensors and to clarify the mechanism of action. Neutral red was electropolymerised by potential cycling on carbon film electrode substrates by allowing the monomer to be oxidised during the full 20 cycles of polymerisation or reducing the positive limit of the potential window after the first 2 cycles to impede monomer oxidation with a view to obtaining longer polymer chains and a lesser degree of branching. Comparison was made with glassy carbon substrates. The PNR films on carbon film electrodes were characterised using cyclic voltammetry and electrochemical impedance spectroscopy, as well as in glucose biosensors prepared with PNR. Glucose oxidase enzyme was immobilised by encapsulation in silica sol-gel and compared with that obtained by cross-linking with glutaraldehyde. The biosensors were evaluated by chronoamperometry in 0.1 M phosphate buffer saline solution, pH 7.0, and showed evidence of electron transfer between the enzyme cofactor flavin adenine dinucleotide and PNR dissolved in the enzyme layer competing with PNR-mediated electrochemical degradation of H₂O₂ formed during the enzymatic process. This paper is dedicated to Professor Dr. Algirdas Vaskelis on the occasion of his 70th birthday.     

Families of curves with ordinary singular points on regular surfaces

Sunto Fissata una superficie algebrica liscia X sopra un campo algebricamente chiuso e di caratteristica 0, e una curva ridotta C su X, si introduce, per ogni -upla di numeri naturali m₁,..., m, uno schema W=W(C, m₁,..., m), parametrizzante le curve del sistema lineare ¦C¦ con punti multipli ordinari di molteplicità almeno m₁,..., m. Si studia W in relazione con la configurazione delie singolarità e delle componenti irriducibili di C. Si prova in particolare un teorema di «virtuale connessione», che permette di stabilire l'esistenza di curve irriducibili in alcuni di tali schemi W.

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Membro del G.N.S.A.G.A. del C.N.R.     

First evaluation of the thermodynamic properties for spheres to elongated micelles transition of some propanediyl-alpha,omega-bis(dimethylalkylammonium bromide) surfactants in aqueous solution

The apparent and partial molar enthalpies, apparent molar volumes, and adiabatic compressibilities at 298 K of the aqueous solutions of the cationic gemini surfactants propanediyl-alpha,omega-bis(octyldimethylammonium bromide) (8-3-8) and propanediyl-alpha,omega-bis(dodecyldimethylammonium bromide) (12-3-12) have been measured as a function of concentration. The trends of the partial molar enthalpies versus concentration are the first well documented thermodynamic evidence of sphere to rod transition in the micellar phase, involving a detectable quantity of heat, and allow the determination of the change in enthalpy associated with this transition. The changes in enthalpies upon micellization and for the sphere to elongated micelles transition, DeltaH(s)(-->)(r), have been obtained from the experimental data by using a pseudo-phase transition approach: -1.5 kJ mol(-1) for 8-3-8 and -3.9 kJ mol(-1) for 12-3-12. No evidence of the above transition is found in the trends of volumetric properties versus m. The apparent adiabatic molar compressibilities for the compounds under investigation are also reported here for the first time: a negative group contribution for the methylene group is evaluated, when the surfactants are present in solution as a single molecule, reflecting its solvation structure. In the micellar phase, the -CH(2)- group contribution becomes positive. A value of 1.17 x 10(-3) cm(3) bar(-1) mol(-1) for the change in adiabatic molar compressibility upon micellization is obtained. The lower values of the methylene group contributions to the volumetric properties for the monomers support the hypothesis of partial association of the chains before the cmc.     

[(4,4‐Dimethyl‐2‐oxo‐1,3‐oxazolidin‐3‐yl)methyl]phosphonic acid

The title compound, C₆H₁₂NO₅P, was synthesized as an inter­mediate phase in a search for new N‐(phosphono­methyl)glycine derivatives. The mol­ecules are held together by O—H⋯O hydrogen bonds, forming chains along the b axis in the crystal structure. The observed mol­ecular structure is compared with that calculated by the density functional theory method.     

Domain and hull-enclosed area distributions in two-dimensional coarsening

We obtain the exact distribution of the areas enclosed by domain boundaries (“hulls”) during the coarsening dynamics of a two-dimensional nonconserved scalar field. We prove that the number of hulls per unit area that enclose an area greater than A has the form N_h(A,t)=2c/(A+λt), where . This result is also a demonstration of the validity of the dynamical scaling hypothesis in this system. We also show that domain areas (regions of aligned spins) have a similar distribution.     

Assessment of the surfactant-dye binding degree method as an alternative to the methylene blue method for the determination of anionic surfactants in aqueous environmental samples

The surfactant to dye binding degree (SDBD) method is proposed for the routine monitoring of anionic surfactants in aqueous environmental samples and their analytical features compared with those provided by the standard methylene blue (MB) method. This new analytical approach is based on the effect that anionic surfactants exert on the binding degree of the cationic surfactant didodecyldimethylammonium bromide (DDABr) to the anionic dye Coomassie Brilliant Blue G (CBBG). The formation of DDABr-CBBG aggregates is monitored photometrically. The analytical applicability of the proposed method was demonstrated by determining anionic surfactants in tap, river and swamp water, and raw and treated sewage. The mean recoveries obtained ranged between 99 and 101%. The SDBD method offers important advantages over the classical MB method: it is more sensitive, selective, precise, simple and rapid; the analytical response is independent of the molecular structure of the anionic surfactants, and the volume of sample required for analysis and the consumption of organic solvents are significantly reduced.     

Synthesis of β-amino-α-trifluoromethyl alcohols and their applications in organic synthesis

A comprehensive overview on methods applied for syntheses of β-amino-α-trifluoromethyl alcohols, including stereocontrolled variants, is presented. In addition, reported cases of the exploration of β-amino-α-trifluoromethyl alcohols for the preparation of trifluoromethylated peptidomimetics and other biologically active, fluorinated compounds are discussed. Attractive opportunities for their applications as organocatalysts are also presented.     

Determination of methylmercury in marine sediment samples: Method validation and occurrence data

The determination of methylmercury (MeHg) in sediment samples is a difficult task due to the extremely low MeHg/THg (total mercury) ratio and species interconversion. Here, we present the method validation of a cost-effective fit-for-purpose analytical procedure for the measurement of MeHg in sediments, which is based on aqueous phase ethylation, followed by purge and trap and hyphenated gas chromatography–pyrolysis–atomic fluorescence spectrometry (GC–Py–AFS) separation and detection. Four different extraction techniques, namely acid and alkaline leaching followed by solvent extraction and evaporation, microwave-assisted extraction with 2-mercaptoethanol, and acid leaching, solvent extraction and back extraction into sodium thiosulfate, were examined regarding their potential to selectively extract MeHg from estuarine sediment IAEA-405 certified reference material (CRM). The procedure based on acid leaching with HNO₃/CuSO₄, solvent extraction and back extraction into Na₂S₂O₃ yielded the highest extraction recovery, i.e., 94 ± 3% and offered the possibility to perform the extraction of a large number of samples in a short time, by eliminating the evaporation step. The artifact formation of MeHg was evaluated by high performance liquid chromatography coupled to inductively coupled plasma mass spectrometry (HPLC–ICP–MS), using isotopically enriched Me²⁰¹Hg and ²⁰²Hg and it was found to be nonexistent. A full validation approach in line with ISO 17025 and Eurachem guidelines was followed. With this in mind, blanks, selectivity, working range (1–800 pg), linearity (0.9995), recovery (94–96%), repeatability (3%), intermediate precision (4%), limit of detection (0.45 pg) and limit of quantification (0.85 pg) were systematically assessed with CRM IAEA-405. The uncertainty budget was calculated and the major contribution to the combined uncertainty (16.24%, k = 2) was found to arise from the uncertainty associated with recovery (74.1%). Demonstration of traceability of measurement results is also presented. The validated measurement procedure was applied to the determination of MeHg incurred in sediments from a highly polluted and scarcely studied area in the Caribbean region.     

Mechanism of Thyroxine Deiodination by Naphthyl‐Based Iodothyronine Deiodinase Mimics and the Halogen Bonding Role: A DFT Investigation

This paper deals with a systematic density functional theory (DFT) study aiming to unravel the mechanism of the thyroxine (T4) conversion into 3,3′,5‐triiodothyronine (rT3) by using different bio‐inspired naphthyl‐based models, which are able to reproduce the catalytic functions of the type‐3 deiodinase ID‐3. Such naphthalenes, having two selenols, two thiols, and a selenol–thiol pair in peri positions, which were previously synthesized and tested in their deiodinase activity, are able to remove iodine selectively from the inner ring of T4 to produce rT3. Calculations were performed including also an imidazole ring that, mimicking the role of the His residue, plays an essential role deprotonating the selenol/thiol moiety. For all the used complexes, the calculated potential energy surfaces show that the reaction proceeds via an intermediate, characterized by the presence of a X?I?C (X=Se, S) halogen bond, whose transformation into a subsequent intermediate in which the C?I bond is definitively cleaved and the incipient X?I bond is formed represents the rate‐determining step of the whole process. The calculated trend in the barrier heights of the corresponding transition states allows us to rationalize the experimentally observed superior deiodinase activity of the naphthyl‐based compound with two selenol groups. The role of the peri interactions between chalcogen atoms appears to be less prominent in determining the deiodination activity.     

Optimization of Microwave-Assisted Michael Addition Reaction Catalyzed by L-Proline in Ionic Liquid Medium Using Response Surface Methodology

Michael addition reactions of aldehyde to β-nitrostyrene catalyzed by L-proline were investigated by using controlled, monomode microwave-assisted technique in a closed vessel system. Ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim]NTf₂) was used as the reaction medium to replace the commonly used volatile organic solvents and as a good absorbing solvent during Michael reaction under the influence of microwave irradiation. The Michael product is clean and generates good yields in short reaction times with moderate results on enantioselectivity (ee). In this work, optimization of proline-catalyzed Michael reaction was carried out using response surface methodology (RSM) based on a three-factor-three-level central composite design (CCD). Various reaction parameters including catalyst loading (5–30 mol%), reaction time (5–40 min), and substrate (2–5 equivalent ratio) were investigated. A high Michael yield (96.5%) with 36.9 ee% was obtained at the optimum conditions of 10.0 mol% catalyst loading, 5.0 min reaction time, and 2.0 substrate equivalent ratio.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.]