Kinetic study in water-ethylene glycol cationic, zwitterionic, nonionic, and anionic micellar solutions

The spontaneous hydrolysis of phenyl chloroformate was studied in water-ethylene glycol, EG, cationic, zwitterionic, nonionic, and anionic micellar solutions, the surfactants being tetradecyltrimethylammonium bromide, tetradecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate, tricosaoxyethylene glycol ether, and sodium dodecyl sulfate. The dependence of the observed rate constant on surfactant concentration as well as on the percentage by weight of EG, varying from 0 to 50 wt %, was investigated. Information about changes in the critical micelle concentrations, in the micellar ionization degrees (for ionic surfactants), in the aggregation numbers, and in the polarity of the interfacial region of the micelles upon changing the weight percent of EG was obtained through conductivity, surface tension, spectroscopic, and fluorescence measurements. A simple pseudophase model was adequate to rationalize the kinetic data. Micellar medium effects were explained by considering charge-charge interactions and polarity, ionic strength, and water content in the micellar interfacial region. The acceleration of the reaction produced by an increase in the amount of EG present in the mixture was explained on the basis of the substantial decrease in the equilibrium binding constant of phenyl chloroformate molecules to the micelles, resulting in the contribution of the reaction taking place in the bulk water-EG phase being more important. The weight percent of EG did not substantially influence the rate constant in the micellar pseudophase.     

Kinetic wavelength-pair method as an alternative approach to simultaneous multi-component analysis

The kinetic wavelength-pair method involves adapting a well established principle to the simultaneous kinetic-based determination of two or more compounds with diode-array detection. It relies on measuring the difference in the rate of change of the absorbance with time at two preset wavelength pairs such that the values of these measuring parameters are the result of the contribution of one or two components. The theoretical basis adapted to first-order kinetic-based determinations was established and checked on four systems. The method thus developed was compared with other differential kinetic methods and applied to the resolution of formaldehyde-acrolein mixtures.     

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.     

Small molecule fluorescent probes for the detection of amyloid self-assembly in vitro and in vivo

The misfolding and aggregation of amyloidogenic polypeptides are characteristics of many neurodegenerative syndromes including Alzheimer's and Parkinson's disease. There is a major interest in the availability of amyloid-specific probes that exhibit fluorescence properties, for its use as reporters of protein aggregation in spectroscopy and microscopy methodologies. In this review, we intend to provide an overview of novel fluorescence-based probes and procedures applied for addressing fundamental aspects of amyloid self-assembly in vitro and in vivo. We highlight the utilization in vitro of several small-molecule fluorescent probes as extrinsic and site-specific reporters of amyloid formation, including single-molecule determinations. Detection of amyloid self-assembly employing compounds such as JC-1, DCVJ, ANS derivatives and luminescent conjugated polymers, as well as site-specific probes such as pyrene and ESIPT is discussed. We further review novel fluorescent probes developed for the non-invasive optical imaging of protein aggregates in vivo, including BTA-1, Methoxy-X04, NIAD-4 and CRANAD-2. Availability of increasingly versatile amyloid-specific fluorescent probes is having a very positive impact in the drug discovery and diagnostics fields.     

Effect of Extraction Methods and In Vitro Bio-Accessibility of Microencapsulated Lemon Extract

The extraction of bioactive compounds from fruits, such as lemon, has gained relevance because these compounds have beneficial properties for health, such as antioxidant and anticancer properties; however, the extraction method can significantly affect these properties. High hydrostatic pressure and ultrasound, as emerging extraction methods, constitute an alternative to conventional extraction, improving extractability and obtaining extracts rich in bioactive compounds. Therefore, lemon extracts (LEs) were obtained by conventional (orbital shaking), ultrasound-assisted, and high-hydrostatic-pressure extraction. Extracts were then microencapsulated with maltodextrin at 10% (M10), 20% (M20), and 30% (M30). The impact of microencapsulation on LEs physicochemical properties, phenolics (TPC), flavonoids (TFC) and relative bio-accessibility (RB) was evaluated. M30 promoted a higher microencapsulation efficiency for TPC and TFC, and a longer time required for microcapsules to dissolve in water, as moisture content, water activity and hygroscopicity decreased. The RBs of TPC and TFC were higher in microcapsules with M30, and lower when conventional extraction was used. The data suggest that microencapsulated LE is promising as it protects the bioactivity of phenolic compounds. In addition, this freeze-dried product can be utilized as a functional ingredient for food or supplement formulations.     

Hydride generation atomic fluorescence spectrometric determination of As, Bi, Sb, Se(IV) and Te(IV) in aqua regia extracts from atmospheric particulate matter using multivariate optimization

A highly sensitive and simple method, based on hydride generation and atomic fluorescence detection, has been developed for the determination of As, Bi, Sb, Se(IV) and Te(IV) in aqua regia extracts from atmospheric particulate matter samples. Atmospheric particulates matter was collected on glass fiber filters using a medium volume sampler (PM1 particulate matter). Two-level factorial designs have been used to optimise the hydride generation atomic fluorescence spectrometry (HG-AFS) procedure. The effects of several parameters affecting the hydride generation efficiency (hydrochloric acid, sodium tetrahydroborate and potassium iodide concentrations and flow rates) have been evaluated using a Plackett-Burman experimental design. In addition, parameters affecting the hydride measurement (delay, analysis and memory times) have been also investigated. The significant parameters obtained (sodium tetrahydroborate concentration, sodium tetrahydroborate flow rate and analysis time for As; hydrochloric acid concentration and sodium tetrahydroborate flow rate for Se(IV); and sodium tetrahydroborate concentration and sodium tetrahydroborate flow rate for Te(IV)) have been optimized by using 2ⁿ + star central composite design. Hydrochloric acid concentration and sodium tetrahydroborate flow rate were the significant parameters obtained for Sb and Bi determination, respectively. Using a univariate approach these parameters were optimized. The accuracy of methods have been verified by using several certified reference materials: SRM 1648 (urban particulate matter) and SRM 1649a (urban dust). Detection limits in the range of 6 × 10⁻³ to 0.2 ng m⁻³ have been achieved. The developed methods were applied to several atmospheric particulate matter samples corresponding to A Coruña city (NW Spain).     

Preparation of porous methacrylate monoliths with oxidized single-walled carbon nanohorns for the extraction of nonsteroidal anti-inflammatory drugs from urine samples

Microchimica Acta - A copolymer was prepared from glycidyl methacrylate, ethylene glycol dimethacrylate and oxidized single-walled carbon nanohorns via photo-polymerization and used in spin columns...     

Evaluation of the performance of single‐walled carbon nanohorns in capillary electrophoresis

This paper describes for the first time the use of single‐walled carbon nanohorns (SWNHs) as pseudostationary and stationary phases for EKC and CEC, respectively, taking advantage of their characteristic features, such as conical‐end termination, formation of spherical assemblies dahlia‐flower like superstructure and easy functionalization. The use of SWNHs as pseudostationary phase for EKC required the study of their dispersion in different surfactants as well as their compatibility with the electrophoretic system. The carboxylation and subsequent immobilization of carboxylated SWNHs in fused‐silica capillary to obtain useful, reproducible and stable stationary phases for CEC has also been investigated, with promising results. The electrophoretic separations obtained for water‐soluble vitamins in both modalities (EKC and CEC) have been systematically compared with those obtained with single‐walled carbon nanotubes.     

Supramolecular systems-based extraction-separation techniques coupled to mass spectrometry

The combination of supramolecular chemistry and MS has not only been fruitful in the field of gas-phase fundamental studies of host-guest complexes and supramolecular assemblies. Mass spectrometric analysis has also benefited from the ability of supramolecular systems to behave as pseudophases in which solutes partition from the bulk solvent phase. Supramolecular systems-based extraction and concentration schemes and separation techniques have been widely used in different fields of analytical chemistry and are ideally suited for coupling with MS. This review describes the present status of the application of supramolecular chemistry in mass spectrometric analysis and includes topics such as the use of coacervative liquid-liquid extraction and hemimicelle/admicelle-based SPE of organic compounds prior to chromatography and electrophoresis. It also discusses the recent advances in enantioselective analysis using CD in electrophoresis- and chromatography-MS. The potential and analytical challenges of these approaches in environmental and bioanalytical chemistry, where one can expect significant developments in the future, are outlined.     

A Shooting Algorithm for Optimal Control Problems with Singular Arcs

In this article, we propose a shooting algorithm for a class of optimal control problems for which all control variables appear linearly. The shooting system has, in the general case, more equations than unknowns and the Gauss–Newton method is used to compute a zero of the shooting function. This shooting algorithm is locally quadratically convergent, if the derivative of the shooting function is one-to-one at the solution. The main result of this paper is to show that the latter holds whenever a sufficient condition for weak optimality is satisfied. We note that this condition is very close to a second order necessary condition. For the case when the shooting system can be reduced to one having the same number of unknowns and equations (square system), we prove that the mentioned sufficient condition guarantees the stability of the optimal solution under small perturbations and the invertibility of the Jacobian matrix of the shooting function associated with the perturbed problem. We present numerical tests that validate our method.