Analysis of Free and Total Glycerol in Biodiesel Using an Electrochemical Assay Based on a Two‐Enzyme Oxygen‐Electrode System

In this work, an electroenzymatic methodology based on two coupled enzymatic activities (glycerokinase and glycerol‐3‐phosphate oxidase) was developed using an oxygen Clark‐type electrode for the determination of free and total glycerol in biodiesel samples. The enzymatic conversion of glycerol consumes oxygen, which is measured amperometrically in a Clark‐type electrode and correlated with the concentration of glycerol in the sample. The electroenzymatic method proposed showed a good linear correlation coefficient (R=0.9990) with a linear response in the concentration range of 6.25×10^?5 to 6.25×10^?4% (w/v) and limits of detection and quantification at 1.0×10^?5% and 3.0×10^?5% (w/v), respectively. Good correlations were found between the results obtained in this work and those by the gas chromatography technique (R=0.9994). The proposed method was shown to be promising for the analysis of glycerol in biodiesel samples, with a simple and inexpensive methodology compared with the gas chromatography technique.     

Potential of a metal-organic framework as a new material for solid-phase extraction of pesticides from lettuce (Lactuca sativa), with analysis by gas chromatography-mass spectrometry

The metal-organic framework (∞)[(La(0.9)Eu(0.1))(2)(DPA)(3)(H(2)O)(3)] was tested for extraction of pyrimicarb, procymidone, malathion, methyl parathion and α- and β-endosulfan from lettuce, with analysis using GC/MS in SIM mode. Experiments were carried out in triplicate at two fortification levels (0.1 and 0.5?mg/kg), and resulted in recoveries in the range of 78-107%, with RSD values between 1.6 and 8.0% for (∞)[(La(0.9)Eu(0.1))(2)(DPA)(3)(H(2)O)(3)] sorbent. Detection and quantification limits ranged from 0.02 to 0.05?mg/kg and from 0.05 to 0.10?mg/kg, respectively, for the different pesticides studied. The method developed was linear over the range tested (0.05-10.0?μg/mL), with correlation coefficients ranging from 0.9990 to 0.9997. Comparison between (∞)[(La(0.9)Eu(0.1))(2)(DPA)(3)(H(2)O)(3)] and conventional sorbent (silica gel) showed better performance of the (∞)[(La(0.9)Eu(0.1))(2)(DPA)(3)(H(2)O)(3)] polymeric sorbent for all pesticides tested.     

First dynamic kinetic resolution of selenium-containing chiral amines catalyzed by palladium (Pd/BaSO4) and Candida antartica lipase (CAL-B)

An efficient method for chemoenzymatic dynamic kinetic resolution of selenium-containing chiral amines (organoselenium-1-phenylethanamines) has been developed, leading to the corresponding amides in excellent enantioselectivities and high isolated yields. This one-pot procedure employs two different types of catalysts: Pd on barium sulphate (Pd/BaSO₄) as racemization catalyst and lipase (CAL-B) as the resolution catalyst.     

Multivariate optimization by exploratory analysis applied to the determination of microelements in fruit juice by inductively coupled plasma optical emission spectrometry

A method for the direct determination (without sample pre-digestion) of microelements in fruit juice by inductively coupled plasma optical emission spectrometry has been developed. The method has been optimized by a 2³ factorial design, which evaluated the plasma conditions (nebulization gas flow rate, applied power, and sample flow rate). A 1:1 diluted juice sample with 2% HNO₃ (Tetra Packed, peach flavor) and spiked with 0.5 mg L^− 1 of Al, Ba, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sb, Sn, and Zn was employed in the optimization. The results of the factorial design were evaluated by exploratory analysis (Hierarchical Cluster Analysis, HCA, and Principal Component Analysis, PCA) to determine the optimum analytical conditions for all elements. Central point condition differentiation (0.75 L min^− 1, 1.3 kW, and 1.25 mL min^− 1) was observed for both methods, Principal Component Analysis and Hierarchical Cluster Analysis, with higher analytical signal values, suggesting that these are the optimal analytical conditions. F and t-student tests were used to compare the slopes of the calibration curves for aqueous and matrix-matched standards. No significant differences were observed at 95% confidence level. The correlation coefficient was higher than 0.99 for all the elements evaluated. The limits of quantification were: Al 253, Cu 3.6, Fe 84, Mn 0.4, Zn 71, Ni 67, Cd 69, Pb 129, Sn 206, Cr 79, Co 24, and Ba 2.1 µg L^− 1. The spiking experiments with fruit juice samples resulted in recoveries between 80 and 120%, except for Co and Sn. Al, Cd, Pb, Sn and Cr could not be quantified in any of the samples investigated. The method was applied to the determination of several elements in fruit juice samples commercialized in Brazil.     

Host–guest system of 4-nerolidylcatechol in 2-hydroxypropyl-β-cyclodextrin: preparation, characterization and molecular modeling

The interaction of 4-nerolidylcatechol (4-NRC), a potent antioxidant agent, and 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) was investigated by the solubility method using Fourier transform infrared (FTIR) methods in addition to UV–Vis, ¹H-nuclear magnetic resonance (NMR) spectroscopy and molecular modeling. The inclusion complexes were prepared using grinding, kneading and freeze-drying methods. According to phase solubility studies in water a B_S-type diagram was found, displaying a stoichiometry complexation of 2:1 (drug:host) and stability constant of 6494 ± 837 M^?1. Stoichiometry was established by the UV spectrophotometer using Job’s plot method and, also confirmed by molecular modeling. Data from ¹H-NMR, and FTIR, experiments also provided formation evidence of an inclusion complex between 4-NRC and HP-β-CD. 4-NRC complexation indeed led to higher drug solubility and stability which could probably be useful to improve its biological properties and make it available to oral administration and topical formulations.     

Aromatic nitro substitution reaction between 4‐nitro‐N‐n‐butyl‐1,8‐naphthalimide and n‐heptanethiol in water–methanol binary mixtures

The second‐order rate constants of thiolysis by n‐heptanethiol on 4‐nitro‐N‐n‐butyl‐1,8‐naphthalimide (4NBN) are strongly affected by the water–methanol binary mixture composition reaching its maximum at around 50% mole fraction. In parallel solvent effects on 4NBN absorption molar extinction coefficient also shows a maximum at this composition region. From the spectroscopic study of reactant and product and the known H‐bond capacity of the mixture a rationalization that involves specific solvent H‐donor interaction with the nitro group is proposed to explain the kinetic data. Present findings also show a convenient methodology to obtain strongly fluorescent imides, valuable for peptide and analogs labeling as well as for thio‐naphthalimide derivatives preparations. Copyright © 2008 John Wiley & Sons, Ltd.     

The effect of micellization on the EPR spectra and reactivity of 2,2,4,4‐tetramethylpiperidinoxyl (TEMPO) radicals

A series of 4‐alkanoyloxy‐2,2,6,6‐tetramethylpiperidinoxyl radicals was prepared, and their reactivity in water vis‐à‐vis antioxidant Trolox was compared. Spectral (electron paramagnetic resonance) and dynamic‐light‐scattering measurements suggested the formation of micelles for the more hydrophobic members of the series. The observed increase in reactivity for the micelle‐forming radicals reflected the increased local concentration of the radical fragment on the micellar interface. Copyright © 2016 John Wiley & Sons, Ltd.     

Designing Artificial 3D Helicates: Unprecedented Self‐Assembly of Homo‐octanuclear Tetrapods with Europium

Herein, we report on the rational design, preparation and characterization of a novel homo‐octanuclear helicate, which results from a spatial extension of the central tetranuclear platform. The 3D supramolecular assembly is obtained by complexing europium(III) with a new hexatopic tripodal ligand. The isolated octanuclear helicate is fully characterized by different methods clearly evidencing the structure predicted with molecular modelling. The ligand preorganization plays a crucial role in a successful self‐assembly process and induces the formation of a well‐defined triple‐stranded helical structure. This prototypal octanuclear edifice accommodating functional lanthanides within a 3D scaffold offers attractive perspectives for further applications.     

The potential of TEMPO-oxidized nanofibrillar cellulose beads for cell delivery applications

The advanced development of cell carriers for regenerative medicine and cell therapy demands materials able to sustain cell viability prior to their delivery to the target tissue, an ability that can be controlled by the shape, size and degradability of the matrix. TEMPO-oxidized nanofibrillar cellulose (ToNFC) macromolecules are negatively charged and therefore can be easily formulated by ionotropic gelation into beads of varying sizes that can release their payload through an erosion-controlled process. We report here for the first time on the preparation of ToNFC beads via ionic gelation using CaCl₂ and on their loading with OSTEO-1 rat bone cells, with a view to examine their capacity of sustaining the cell viability and of releasing the bone cells in a controlled manner. The initial results obtained demonstrate that ToNFC is able to protect the OSTEO-1 cells and to maintain their viability for at least 2 weeks. Following gradual disintegration of the beads, a significant cell release and subsequent proliferation was observed after 7 days. These results indicate the considerable potential of nanofibrillar cellulose (ToNFC) for applications in cell therapy and regenerative medicine.