Use of novel cardanol-porphyrin hybrids and their TiO₂-based composites for the photodegradation of 4-nitrophenol in water

Cardanol, a well known hazardous byproduct of the cashew industry, has been used as starting material for the synthesis of useful differently substituted "cardanol-based" porphyrins and their zinc(II), copper(II), cobalt(II) and Fe(III) complexes. Novel composites prepared by impregnation of polycrystalline TiO? powder with an opportune amount of "cardanol-based" porphyrins, which act as sensitizers for the improvement of the photo-catalytic activity of the bare TiO?, have been used in the photodegradation in water of 4-nitrophenol (4-NP), which is a toxic and bio-refractory pollutant, dangerous for ecosystems and human health.     

Comparison of univariate and multivariate calibration for the determination of micronutrients in pellets of plant materials by laser induced breakdown spectrometry

The application of laser induced breakdown spectrometry (LIBS) aiming the direct analysis of plant materials is a great challenge that still needs efforts for its development and validation. In this way, a series of experimental approaches has been carried out in order to show that LIBS can be used as an alternative method to wet acid digestions based methods for analysis of agricultural and environmental samples. The large amount of information provided by LIBS spectra for these complex samples increases the difficulties for selecting the most appropriated wavelengths for each analyte. Some applications have suggested that improvements in both accuracy and precision can be achieved by the application of multivariate calibration in LIBS data when compared to the univariate regression developed with line emission intensities. In the present work, the performance of univariate and multivariate calibration, based on partial least squares regression (PLSR), was compared for analysis of pellets of plant materials made from an appropriate mixture of cryogenically ground samples with cellulose as the binding agent. The development of a specific PLSR model for each analyte and the selection of spectral regions containing only lines of the analyte of interest were the best conditions for the analysis. In this particular application, these models showed a similar performance, but PLSR seemed to be more robust due to a lower occurrence of outliers in comparison to the univariate method. Data suggests that efforts dealing with sample presentation and fitness of standards for LIBS analysis must be done in order to fulfill the boundary conditions for matrix independent development and validation.     

Gold nanoparticles in an ionic liquid phase supported in a biopolymeric matrix applied in the development of a rosmarinic acid biosensor

Gold nanoparticles dispersed in 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid (Au-BMI·PF(6)) were supported in chitin (CTN) chemically crosslinked with glyoxal and epichlorohydrin to obtain a new supported ionic liquid phase (SILP) catalyst with high catalytic activity, and providing an excellent environment for enzyme immobilization. This modified biopolymer matrix (Au-BMI·PF(6)-CTN) was used as a support for the immobilization of the enzyme peroxidase (PER) from pea (Pisum sativum), and employed to develop a new biosensor for rosmarinic acid (RA) determination in pharmaceutical samples by square-wave voltammetry. In the presence of hydrogen peroxide, the PER catalyzes the oxidation of RA to the corresponding o-quinone, which is electrochemically reduced at a potential of +0.14 V vs. Ag/AgCl. Under optimized conditions, the resulting peak current increased linearly for the RA concentration range of 0.50 to 23.70 μM with a detection limit of 70.09 nM. The biosensor demonstrated high sensitivity, good repeatability and reproducibility, and long-term stability (15% decrease in response over 120 days). The method was successfully applied to the determination of RA content in pharmaceutical samples, with recovery values being in the range of 98.3 to 106.2%. The efficient analytical performance of the proposed biosensor can be attributed to the effective immobilization of the PER enzyme in the modified CTN matrix, the significant contribution of the high conductivity of the ionic liquid, the facilitation of electron transfer promoted by gold nanoparticles, and the inherent catalytic ability of these materials.     

Formation and decomposition of N‐alkylnaphthalimides: experimental evidences and ab initio description of the reaction pathways

The kinetics of hydrolysis of 1,8‐N‐butyl‐naphthalimide (1,8‐NBN) to 1,8‐N‐butyl‐naphthalamide (1,8‐NBAmide) and of 2,3‐N‐butyl‐naphthalimide (2,3‐NBN) to 2,3‐N‐butyl‐naphthalamide (2,3‐NBAmide), as well as the formation of the respective anhydrides from the amides were investigated in a wide acidity range. 1,8‐NBN equilibrates with 1,8‐NBAmide in mild alkali. Under the same conditions 2,3‐NBN quantitatively yields 2,3‐NBAmide. Over a wide range of acidities the reactions of the 1,8‐ and 2,3‐N‐butyl‐naphthalamides (or imides) yield similar products but with widely different rates and at distinct pH's. Anhydride formation in acid was demonstrated for 1,8‐NBAmide. The reactions mechanisms were rationalized in the manifold pathways of ab initio calculations. The differences in rates and pH ranges in the reactions of the 1,8‐ and 2,3‐N‐butyl‐naphthalamides were attributed to differences in the stability of the tetrahedral intermediates in alkali as well as the relative stabilities of the five and six‐membered ring intermediates. The rate of carboxylic acid assisted 1,8‐N‐Butyl‐naphthalamide hydrolysis is one of the largest described for amide hydrolysis models. Copyright © 2010 John Wiley & Sons, Ltd.     

Comparative study on the thermal behavior of two similar triterpenes from birch

A comparative study on the thermal behavior of betuline and betulinic acid was performed using a TG–FTIR hyphenated technique. The comparison was focused on the kinetic of the relevant thermal-induced phenomenon. Using three different data processing strategy, that is, Friedman, Flynn–Wall–Ozawa, and nonparametric kinetic, homogeneous values for the activation energy were obtained, especially by betulinic acid. The advantages of the nonparametric kinetic method were revealed, especially by obtaining the explicit kinetic parameters of the conversion function, without any “a priori” hypothesis.     

Partially sulfonated ethylene–vinyl alcohol copolymer as new substrate for 3,4‐ethylenedioxythiophene vapor phase polymerization

A new conducting composite polymer film is obtained by vapor phase polymerization of 3,4‐ethylenedioxythiophene (EDOT) on a biocompatible polyanion derived from the partial sulfonation (32%) of statistical ethylene vinyl alcohol copolymer (EVAL32). EVALS32 and the oxidant (iron(III) p‐toluenesulfonate, [PTS]) are contemporaneously spin coated from a methanol/water solution on glass slide. EVALS32–PTS‐coated glass slides are exposed to EDOT vapors, and the polymerization is followed by Vis–NIR spectroscopy. We observed that PEDOT slowly grows into the bulk of EVALS32 matrix. Thanks to the sulfonic groups of the polyanion acting as doping agents, a highly conjugate p‐doped EVALS32‐PEDOT composite film with a good conductivity (1.6 × 10² S cm^?1), transparency, and stability in water is obtained. The EVALS32–PEDOT film seems an ideal candidate for the preparation of organic devices to be applied in electronics, biosensor, or actuation technology. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1203–1210     

Effect of dialkyldimethylammonium vesicles on the thiolysis of p-nitrophenyl acetate

Cationic surfactant vesicles, prepared by an alcohol injection technique and characterized by gel filtration, are extremely effective at increasing the rate of ester thiolysis at near neutral pH.     

Decarboxylation of 6-nitrobenzisoxazole-3-carboxylate in mixed micelles of zwitterionic and positively charged surfactants

The rate of decarboxylation of 6-nitrobenzisoxazole-3-carboxylate, NBOC, was determined in micelles of N-hexadecyl-N,N,N-trimethylammonium bromide or chloride (CTAB or CTAC), N-hexadecyl-N,N-dimethyl-3-ammonium-1-propanesulfonate (HPS), N-dodecyl-N,N-dimethyl-3-ammonium-1-propanesulfonate (DPS), N-dodecyl-N,N,N-trimethylammonium bromide (DTAB), hexadecylphosphocholine (HPC), and their mixtures. Quantitative analysis of the effect on micelles on the velocity of NBOC decarboxylation allowed the estimation of the rate constants in the micellar pseudophase, k(m), for the pure surfactants and their mixtures. The extent of micellar catalysis for NBOC decarboxylation, expressed as the ratio k(m)/k(w), where k(w) is the rate constant in water, varied from 240 for HPS to 62 for HPC. With HPS or DPS, k(m) decreased linearly with CTAB(C) mole fraction, suggesting ideal mixing. With HPC, k(m) increased to a maximum at a CTAB(C) mole fraction of ca. 0.5 and then decreased at higher CTAB(C). Addition of CTAB(C) to HPC, where the negative charge of the surfactant is close to the hydrophobic core, produces tight ion pairs at the interface and, consequently, decreases interfacial water contents. Interfacial dehydration at the surface in equimolar HPC/CTAB(C) mixtures, and interfacial solubilization site of the substrate, can explain the observed catalytic synergy, since the rate of NBOC decarboxylation increases markedly with the decrease in hydrogen bonding to the carboxylate group.     

Self-assembled monolayer of nickel(II) complex and thiol on gold electrode for the determination of catechin

Self-assembled monolayers of a nickel(II) complex and 3-mercaptopropionic acid on a gold electrode were obtained for determination of catechin by square wave voltammetry. The complex [Ni^IIL] with L = [N-(methyl)-N′-(2-pyridylmethyl)-N,N′-bis(3,5-di-tert-butyl-2-hydroxybenzyl)-1,3-propanediamine[nickel(II)] was synthesized and characterized by ¹H NMR, IR, and electronic spectroscopies and electrochemical methods. The optimized conditions obtained for the electrodes were 0.1 mol L⁻¹ phosphate buffer solution (pH 7.0), frequency of 80.0 Hz, pulse amplitude of 60.0 mV and scan increment of 10.0 mV. Under these optimum conditions, the resultant peak current on square wave voltammograms increases linearly with the concentration of catechin in the range of 3.31 × 10⁻⁶ to 2.53 × 10⁻⁵ mol L⁻¹ with detection limits of 8.26 × 10⁻⁷ mol L⁻¹. The relative standard deviation for a solution containing 1.61 × 10⁻⁵ mol L⁻¹ catechin solution was 2.45% for eight successive assays. The lifetime of the Ni(II) complex-SAM-Au electrode was investigated through testing every day over 4 weeks. The results showed apparent loss of activity after 20 days. The results obtained for catechin in green tea samples using the proposed sensor and those obtained by electrophoresis are in agreement at the 95% confidence level.     

Exfoliated graphite nanoplatelets and gold nanoparticles based electrochemical sensor for determination of levodopa

This paper describes a rapid, accurate, and sensitive method for the determination of levodopa in a pharmaceutical sample using a glassy carbon electrode modified with a hybrid nanocomposite constituted of exfoliated graphite nanoplatelets dispersed in a suspension of gold nanoparticles in carboxymethylcelullose (AuNP-CMC-xGnP/GCE). The nanocomposite was characterized by scanning electron microscopy, transmission electron microscopy, UV-Vis spectroscopy, and zeta potential. Electrochemical characterization of the proposed sensor by cyclic voltammetry and electrochemical impedance spectroscopy indicated that the nanocomposite used for the electrode modification facilitated electron transfer. Using square-wave voltammetry (SWV) under optimized conditions (0.50% (m/v) of AuNP-CMC-xGnP, 0.1 mol L^?1 sulfuric acid, frequency 30 Hz, pulse amplitude 50 mV, and scan increment 6.0 mV), the calibration curve showed a linear range for levodopa from 5 to 50 μmol L^?1, with a limit of detection of 0.5 μmol L^?1. The sensor demonstrated good repeatability and electrode-to-electrode repeatability, with relative standard deviations of 2 and 4%, respectively. The proposed method was successfully applied to quantify levodopa in a pharmaceutical sample by SWV, showing good accuracy. Recoveries of 98 to 107% demonstrated that the method is suitable for practical applications. Therefore, the proposed sensor represents a useful tool for rapid and accurate determination of levodopa.