A three phase hollow fiber liquid‐phase microextraction for quantification of lamotrigine in plasma of epileptic patients by capillary electrophoresis

A three phase hollow fiber liquid‐phase microextraction technique combined with capillary electrophoresis was developed to quantify lamotrigine (LTG) in plasma samples. The analyte was extracted from 4.0 mL of a basic donor phase (composed of 0.5 mL of plasma and 3.5 mL of sodium phosphate solution pH 9.0) through a supported liquid membrane composed of 1‐octanol immobilized in the pores of the hollow fiber, and to an acidic acceptor phase (hydrochloric acid solution pH 4.0) placed in the lumen of the fiber. The extraction was carried out for 30 min at 500 rpm. The eletrophoretic analysis was carried out in 130 mmol/L MES buffer, pH 5.0 with a constant voltage of +15 kV and 20°C. Sample injections were performed for 10 s, at a pressure of 0.5 psi. The detection was performed at 214 nm for both LTG and the internal standard lidocaine. Under the optimized conditions, the method showed a limit of quantification of 1.0 μg/mL and was linear over the plasmatic concentration range of 1.0–20.0 μg/mL. Finally, the validated method was applied for the quantification of LTG in plasma samples of epileptic patients.     

5‐Substituted Benzothiophenes: Synthesis,Mechanism, and Kinetic Studies

The kinetics of the reaction of 4‐methoxythiophenoxyacetaldehyde diethyl acetal, 4‐nitrothiophenoxyacetaldehyde diethyl acetal, and 3‐methoxythiophenoxyacetaldehyde diethyl acetal in polyphosphoric acid has been explained. The kinetic behavior has been explained on the basis of aided simulation and on the basis of density functional theory calculations showing a different pathway for 4‐nitrothiophenoxyacetaldehyde diethyl acetal and for 4‐methoxythiophenoxyacetaldehyde diethyl acetal. In this last case, a very fast competing reaction to the dimerization product was observed.     

Efficient heuristics for the workover rig routing problem with a heterogeneous fleet and a finite horizon

Onshore oil fields may contain hundreds of wells that use sophisticated and complex equipments. These equipments need regular maintenance to keep the wells at maximum productivity. When the productivity of a well decreases, a specially-equipped vehicle called a workover rig must visit this well to restore its full productivity. Given a heterogeneous fleet of workover rigs and a set of wells requiring maintenance, the workover rig routing problem (WRRP) consists of finding rig routes that minimize the total production loss of the wells over a finite horizon. The wells have different loss rates, need different services, and may not be serviced within the horizon. On the other hand, the number of available workover rigs is limited, they have different initial positions, and they do not have the same equipments. This paper presents and compares four heuristics for the WRRP: an existing variable neighborhood search heuristic, a branch-price-and-cut heuristic, an adaptive large neighborhood search heuristic, and a hybrid genetic algorithm. These heuristics are tested on practical-sized instances involving up to 300 wells, 10 rigs on a 350-period horizon. Our computational results indicate that the hybrid genetic algorithm outperforms the other heuristics on average and in most cases.     

Characterization and evaluation of free and nanostructured ursolic acid incorporated in cosmetic formulation using thermal analysis

The ursolic acid (UA) increases the skin’s barrier function and acts in epidermal differentiation of keratinocytes in the epidermis, promoting cell renewal. Besides the mentioned properties UA also has antioxidant, antimicrobial, and anti-irritant functions to cosmetic formulations. Thus, it is necessary formulation studies to insure the development of quality cosmetic products containing this active, increasing its antioxidant potential within nanoparticles. This study aims to characterize and evaluate the thermal behavior of UA in free and nanostructured forms, and both incorporated into a cosmetic base formulation, using thermogravimetry and differential scanning calorimetry. Through the study were observed that free UA, in the embedded nanoparticles and in base formulation exhibited different behavior in similar thermal profile and relative to the presence of UA. The UA remained stable to a temperature of 250 °C and the technique has been shown to be effective for characterizing UA, evaluate water content, and stability of the formulation base.     

Versatility of the Biginelli reaction: Synthesis of new biphenyl dihydropyrimidin-2-thiones using different ketones as building blocks

A multi-component synthesis of biphenyl dihydropyrimidin-2-thiones from 1-phenylthiourea, aldehydes and ketones or di-ketones has been demonstrated. The reaction proceeded well for aldehydes with electron donor or acceptor substituents under mild conditions.