Preparation,evaluation and characterization of quercetin-molecularly imprinted polymer for preconcentration and clean-up of catechins

Molecularly imprinted polymer (MIP) for solid extraction and preconcentration of catechins have been successfully prepared by a thermal polymerization method using quercetin as template, 4-vinylpyridine as functional monomer and ethylene glycol dimethacrylate as crosslinker. A solution mixture of acetone and acetonitrile was used as porogen. Systematic investigations of the influence of monomer, cross-linker, porogen, as well as polymerization conditions on the properties of the MIPs were carried out. The quercetin MIPs were evaluated according to their selective recognition properties for quercetin, structurally related compounds (catechin, epigallocatechin gallate and epicatechin) and a unrelated compound of similar molecular size (α-tocopherol). Good binding was observed for quercetin, catechin and epigallocatechin gallate with an optimized MIP in a solid phase extraction system. Adsorption and kinetic characteristics were evaluated for catechins which indicated that the synthesized polymer had high adsorption capacity and contained homogeneous binding sites. Chemical and morphological characterization of the MIP was investigated by FTIR, SEM and BET, which confirmed a high degree of polymerization. Finally, the MIP was successfully applied to the clean-up and preconcentration of catechins from several natural samples.     

Regioselective synthesis of fused pyrazolo[1,5-a]pyrimidines by reaction of 5-amino-1H-pyrazoles and β-dicarbonyl compounds containing five-membered rings

Reactions of 3-substituted-5-amino-1H-pyrazoles with 2-acetylcyclopentanone or 2-ethoxycarbo-nylcyclopentanone lead to the regioselective formation of a new series of cyclopentapyrazolo[1,5-a]pyrimidines in good yields. When 2-acetylbutyrolactone was used, the reaction provided 6-(2-hydroxyethyl)pyrazolo[1,5-a]pyrimidinone and/or the intermediate (3Z)-3-{1-[(5-R-1H-pyrazol-3-yl)amino]ethylidene}-4,5-dihydrofuranone. This indicates that the cyclization proceeds with butyrolactone ring opening as the last step. Several aspects of this regioselective reaction, including mechanistic and structural studies, are considered.     

Interaction studies between photochromic spiropyrans and transition metal cations: the curious case of copper

A series of four spiropyrans bearing different substituents on the indolic nitrogen were synthesized and their capability of binding mono and bivalent transition metal cations in solution was assessed via UV-visible absorption spectroscopy. All the compounds responded selectively to the presence of Cu(ii) ions producing intense absorption bands in the visible region of their spectra. Bidimensional (1)H-NMR and MALDI-TOF MS spectroscopies revealed the formation of SP dimers mediated by Cu(ii). This is the first example of cross-coupling mediated by copper(ii) in mild conditions causing the symmetric dimerization of spiropyran dyes.     

Solutions of the Allen-Cahn equation which are invariant under screw-motion

Let ${\phi(x)}$ be a rational function of degree >?1 defined over a number field K and let ${\Phi_{n}(x,t) = \phi^{(n)}(x)-t \in K(x,t)}$ where ${\phi^{(n)}(x)}$ is the nth iterate of ${\phi(x)}$ . We give a formula for the discriminant of the numerator of Φ _n (x, t) and show that, if ${\phi(x)}$ is postcritically finite, for each specialization t ₀ of t to K, there exists a finite set ${S_{t_0}}$ of primes of K such that for all n, the primes dividing the discriminant are contained in ${S_{t_0}}$ .     

Fluorene: An extended experimental thermodynamic study

This work reports new experimental thermodynamic results on fluorene. Vapor pressures of both crystalline and liquid phases were measured using a pressure gauge (capacitance diaphragm manometer) and Knudsen effusion methods over a wide temperature range (292.20 to 412.16) K yielding accurate determination of enthalpy and entropy of sublimation and of vaporization. The enthalpy of sublimation was also determined using Calvet microcalorimetry. The enthalpy of fusion was derived from vapor pressure results and from d.s.c. experiments. Static bomb calorimetry was used to determine the enthalpy of combustion of fluorene from which the standard enthalpy of formation in the crystalline phase was calculated. The enthalpy of formation in the gaseous phase was calculated combining the result derived for the crystalline phase with the enthalpy of sublimation.     

Computer simulations of thermo-sensitive microgels: quantitative comparison with experimental swelling data

In this work, a quantitative comparison between experimental swelling data of thermo-sensitive microgels and computer simulation results obtained from a coarse-grained model of polyelectrolyte network and the primitive model of electrolyte is carried out. Polymer-polymer hydrophobic forces are considered in the model through a solvent-mediated interaction potential whose depth increases with temperature. The qualitative agreement between simulation and experiment is very good. In particular, our simulations predict a gradual shrinkage with temperature, which is actually observed for the microgels studied in this survey. In addition, the model can explain the swelling behavior for different contents of ionizable groups without requiring changes in the hydrophobic parameters. Our work also reveals that the abruptness of the shrinkage of charged gels is considerably conditioned by the number of monomeric units per chain. The swelling data are also analyzed with the Flory-Rhener theory, confirming some limitations of this classical formalism.     

Analysis of Bile Acids Profile in Human Serum by Ultrafiltration Clean-up and LC-MS/MS

Bile acids (BAs) are useful biomarkers for the diagnosis of many diseases. The pathologies related to bile acid synthesis are often expressed in the first years of life and may lead to serious liver injury. Here we present a sensitive and rapid method for the analysis of the main 14 bile acids in human serum by liquid chromatography-tandem mass spectrometry. The chromatographic separation is performed using a core–shell column which provides improved separation, highly desirable considering the small structural differences among the analytes. All isomeric BAs of interest were resolved in less than 9 min. Sample pretreatment consisted in ultrafiltration of serum after addition of methanol by means of centrifugal filter devices. The calculated LOQs ranged between 2 and 5 ng mL⁻¹ with linearity of the calibration curves in the 5–5,000 ng mL⁻¹ range for all the BAs. The extraction recoveries for all the analytes were higher than 80 %. Intra-day and inter-day coefficients of variation were all below 15 %. The method proposed has been validated and has been applied for the analysis of serum of pediatric patients. This simple procedure allowed minimal consumption of serum sample (about 100 μL) and a rapid assay, easily implementable in routine analysis.

     

Fabrication and characterization of polymer-based magnetic composite nanotubes and nanorods

Herein we present the simple fabrication of magneto-polymer nanostructured composites. Specifically, large aspect ratio polymer-based magnetic nanotubes and nanorods have been prepared by means of wetting nanoporous hard templates with loaded polymer melts and solutions, respectively. Morphological characteristics of both one-dimensional composite nanostructures were evaluated by scanning electron microscopy. Moreover, important parameters of the materials such as elemental composition and distribution of the metallic elements were determined by means of X-ray diffraction, and Rutherford backscattering. The different confinement topology of the nanoparticles within the nanorods and the nanotubes leads to a stronger (i.e. ferro-) magnetic response of nanotube arrays, as determined by magnetometry. The magnetic measurements also allowed estimating the concentration of nanoparticles by means of properly fitting experimental data to a sum of different magnetic contributions to the total magnetic moment. The morphological, structural, compositional and magnetic characteristics of nanotubes and nanorods are related to the different wetting approaches used. It has to be noted that, to our knowledge, we present here the first example of nanoparticulated polymer-based composite nanotubes synthesized from the melt, which, indeed seems to be at the origin of their high morphological and compositional quality. The potential of Rutherford backscattering spectroscopy for characterizing soft composite nanostructures has to be also remarked.