Electrochemical properties of a ruthenium complex immobilized as thin films and in carbon paste electrodes

The electrochemical properties of mer-[RuCl₃(dppb)(4-pic)] (dppb = Ph₂P(CH₂)₄PPh₂, 4-pic = CH₃C₅H₄N), Rupic, in CHCl₃ are governed by the formation of species such as [Ru₂Cl₅(dppb)₂], [Ru₂(dppb)₂Cl₄(4-pic)] and trans-[RuCl₂(dppb)(4-pic)₂] upon the reduction of “[RuCl₂(dppb)]”. The overall behavior depends on whether Rupic is immobilized in cast or Langmuir–Blodgett (LB) films, or incorporated into a carbon paste electrode (CPE). In cyclic voltammograms, one redox process appears for LB/Rupic films and CPE/Rupic, at E_pa = 0.35 V, E_pc = 0.25 V vs SCE, and E_pa = 0.32 V, E_pc = 0.24 V vs Ag/AgCl, respectively. This redox process was ascribed to the Ru^III/Ru^II charge transfer. For cast films the redox pair was poorly defined, with E_pa = 0.27 V and E_pc = 0.20 V. The reason for the difference lies in the phase separation and formation of aggregates onto ITO for the cast film, in contrast to the LB film. With aggregation, the formation of species occurring in solution is impaired for Rupic in cast films. The electrochemical properties for Rupic in LB films and incorporated into CPE allowed the electrocatalytic activity of Rupic to be exploited in sensors for dopamine and ascorbic acid.     

Micro-focused ultrasonic solid-liquid extraction (muFUSLE) combined with HPLC and fluorescence detection for PAHs determination in sediments: optimization and linking with the analytical minimalism concept

Analytical minimalism is a concept that deals with the optimization of all stages of an analytical procedure so that it becomes less time, cost, sample, reagent and energy consuming. The guide-lines provided in the USEPA extraction method 3550B recommend the use of focused ultrasound (FU), i.e., probe sonication, for the solid–liquid extraction of Polycyclic Aromatic Hydrocarbons, PAHs, but ignore the principle of analytical minimalism. The problems related with the dead sonication zones, often present when high volumes are sonicated with probe, are also not addressed. In this work, we demonstrate that successful extraction and quantification of PAHs from sediments can be done with low sample mass (0.125 g), low reagent volume (4 ml), short sonication time (3 min) and low sonication amplitude (40%). Two variables are here particularly taken into account for total extraction: (i) the design of the extraction vessel and (ii) the solvent used to carry out the extraction. Results showed PAHs recoveries (EPA priority list) ranged between 77 and 101%, accounting for more than 95% for most of the PAHs here studied, as compared with the values obtained after soxhlet extraction. Taking into account the results reported in this work we recommend a revision of the EPA guidelines for PAHs extraction from solid matrices with focused ultrasound, so that these match the analytical minimalism concept.     

Simplerealizations of generalized measurements in quantum mechanics

This paper discusses the approach to the analysis of measurements in quantum mechanics which is based on a set of "detection operators" forming a resolution of identity. The expectation value of each of these operators furnishes the counting rate at a detector for any object state that is prepared. "Predictable measurements" are those for which there is a representation in which only one element of each diagonal matrix representing each operator is not zero. A set of commuting detection operators defines the class of "spectral measurements", which may be either predictable or not. An even more general definition of measurement may be given by abandoning the requirement of commutativity of the detection operators. In this case one cannot define an observable which corresponds to a single self-adjoint operator, which violates the standard theory of quantum mechanical measurement. Simple experimental realizations of each of these classes of measurement are suggested.     

Quinones from plants of northeastern Brazil: structural diversity, chemical transformations, NMR data and biological activities

The present review focus in quinones found in species of Brazilian northeastern Capraria biflora, Lippia sidoides, Lippia microphylla and Tabebuia serratifolia. The review cover ethnopharmacological aspects including photography of species, chemical structure feature, NMR datea and biological properties. Chemical transformations of lapachol to form enamine derivatives and biological activities are discussed.     

Approximating the chance-constrained capacitated vehicle routing problem with robust optimization

4OR - The Capacitated Vehicle Routing Problem (CVRP) is a classical combinatorial optimization problem that aims to serve a set of customers, using a set of identical vehicles, satisfying the...     

Extraction of Ascorbate Oxidase from <Emphasis Type="Italic">Cucurbita maxima</Emphasis> by Continuous Process in Perforated Rotating Disc Contactor Using Aqueous Two-Phase Systems

The ascorbate oxidase is the enzyme used to determine the content of ascorbic acid in the pharmaceutical and food industries and clinics analyses. The techniques currently used for the purification of this enzyme raise its production cost. Thus, the development of alternative processes and with the potential to reduce costs is interesting. The application of aqueous two-phase system is proposed as an alternative to purification because it enables good separation of biomolecules. The objective of this study was to determine the conditions to continuously pre-purify the enzyme ascorbate oxidase by an aqueous two-phase system (PEG/citrate) using rotating column provided with perforated discs. Under the best conditions (20,000 g/mol PEG molar mass, 10% PEG concentration, and 25% citrate concentration), the system showed satisfactory results (partition coefficient, 3.35; separation efficiency, 54.98%; and purification factor, 1.46) and proved suitable for the pre-purification of ascorbate oxidase in continuous process.     

Terpenoids from Croton regelianus

Two new terpenoids, the bisnorditerpene rel‐(5β,8α,10α)‐8‐hydroxy‐13‐methylpodocarpa‐9(11),13‐diene‐3,12‐dione ( 1 ) and the guaiane sesquiterpene rel‐(1R,4S,6R,7S,8aR)‐decahydro‐1‐(hydroxymethyl)‐4,9,9‐trimethyl‐4,7‐(epoxymethano)azulen‐6‐ol ( 2 ), together with seven known compounds, were isolated from Croton regelianus var. matosii. The structures of the isolated compounds were determined by HR‐ESI‐TOF and a combination of 1D‐ and 2D‐NMR experiments.     

Further Withaphysalin Derivatives from Acnistus arborescens

Two new epimeric chlorinated withaphysalins, rel‐(4β,5β,6α,18S,22R)‐ and rel‐(4β,5β,6α,18R,22R)‐6‐chloro‐18,20‐epoxy‐18‐ethoxy‐4,5‐dihydroxy‐1‐oxowitha‐2,24‐diene‐26,22‐lactone ( 1 and 2 resp.), together with the new rel‐(4β,5β,6α,18R,22R)‐6‐chloro‐18,20‐epoxy‐4,5‐dihydroxy‐18‐methoxy‐1‐oxowitha‐2,24‐diene‐26,22‐lactone ( 3 ) and rel‐(3β,4β,5β,6β,18R,22R)‐5,6:18,20‐diepoxy‐3,18‐diethoxy‐4‐hydroxy‐1‐oxowith‐24‐ene‐26,22‐lactone ( 4 ) were isolated from the leaves of Acnistus arborescens and named withaphysalins T–W, respectively. The final structures and the complete ¹H‐ and ¹³C‐NMR assignments of the three chlorowithaphysalins 1 – 3 were performed by means of HR‐ESI‐MS and 1D‐ and 2D‐NMR experiments, including COSY, HSQC, and HMBC, beside comparison with spectral data of analogous compounds from the literature. The structure of 4 was also confirmed by means of a single‐crystal X‐ray diffraction analysis.     

Partition behavior and partial purification of hexokinase in aqueous two-phase polyethylene glycol/citrate systems

This study dealt with the partition behavior and partial purification of hexokinase (HK) from baker’s yeast by liquid-liquid extraction using aqueous two-phase polyethylene glycol (PEG)/citrate systems. First, we investigated the effect of agitation type (vortex and 8 rpm rotation) on the stability of the system, and then the effects of sodium citrate concentration, PEG concentration, and molar mass of PEG on the partition coefficient of this enzyme by using a 2⁵ factorial experimental design. The results of this factorial experiment showed the possibility of a partial purification of HK by using two extraction steps, since the enzyme preferentially migrated to the top phase and the total proteins (mainly contaminants) remained in the bottom phase. The purification factor (Pur _TOP) of the enzyme in the top phase was 1.87, and the partition coefficient of the total proteins (K _Prot ) was 0.47.     

Electrochemical Studies of an Iron Porphyrin Immobilized on Nb2O5/SiO2 and Its Application for Simultaneous Determination of Dopamine and Ascorbic Acid Using Multivariate Calibration Methodology

This paper shows an application of a first generation porphyrin, FeTPPCl 5,10,25,20‐tetraphenylporphyrin iron(III) chloride (FeTPPCl or FeTPP⁺) immobilized on a inorganic matrix, SiO₂/Nb₂O₅ (niobium oxide grafted on silica gel surface, designated as SiNb) to the preparation of a carbon paste electrode (CPE). The carbon paste modified with a FeTPP⁺ immobilized on SiO₂/Nb₂O₅ (SiNb), designated as CPE/SiNb/FeTPP, was applied for simultaneous electrochemical determination of dopamine (DA) and ascorbic acid (AA). Because of the overlapping of the voltammetric peaks of DA and AA, the multivariate calibration methodology based on partial least square regression (PLSR) was proposed. The data pre‐treatment used in this process was mean centering and to choose the principal components number a cross validation procedure was used (leave‐one‐out). Five principal components were necessary to obtain the lowest PRESS (prediction residual error sum of squares). The statistics showed that this model explains approximately 95.2% of the variance from the data set. Using this model, high correlation between actual and predicted concentrations was observed, mainly for higher dopamine (maximum relative error of 8%) and ascorbic acid (maximum relative error of 10%) concentrations. For low analytes concentrations the relative error increases to 35% for AA. Considering the similarity of the voltammetric response of the analytes, the results obtained were satisfactory and showed the promissory capability of the CPE/SiNb/FeTPP coupled multivariate calibration methods for simultaneous voltammetric analysis of DA and AA.