Evaluation of a novel composite based on functionalized multi-walled carbon nanotube and iron phthalocyanine for electroanalytical determination of isoniazid

A novel platform for electroanalysis of isoniazid based on graphene-functionalized multi-walled carbon nanotube as support for iron phthalocyanine (FePc/f-MWCNT) has been developed. The FePc/f-MWCNT composite has been dropped on glassy carbon forming FePc/f-MWCNT/GC electrode, which is sensible for isoniazid, decreasing substantially its oxidation potential to +200 mV vs Ag/AgCl. Electrochemical and electroanalytical properties of the FePc/f-MWCNT/GC-modified electrode were investigated by cyclic voltammetry, electrochemical impedance spectroscopy, scanning electrochemical microscopy, and amperometry. The sensor presents better performance in 0.1 mol L^?1 phosphate buffer at pH 7.4. Under optimized conditions, a linear response range from 5 to 476 μmol L^?1 was obtained with a limit of detection and sensitivity of 0.56 μmol L^?1 and 0.023 μA L μmol^?1, respectively. The relative standard deviation for 10 determinations of 100 μmol L^?1 isoniazid was 2.5%. The sensor was successfully applied for isoniazid selective determination in simulated body fluids.     

A regular perturbation analytical‐numerical method for the evolution of precancerous lesions caused by the human papillomavirus

A numerical method is developed to analyze the behavior of the evolution of the lesions at the cervical cells caused by the human papillomavirus. The model to be solved consists in a one‐dimensional nonlinear advection–diffusion‐reaction equation. Such equation is approximated by a consistent explicit difference scheme which is based on regular perturbation theory. A constructive procedure for the numerical scheme is given and finally an illustrative example of the evolution of a mild dysplasia is included. © 2014 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 31: 847–855, 2015     

Automated microsystem for electrochemical detection of cancer markers

The development of a fully automated microsystem housing an amperometric immunosensor is presented. The microfluidic cell integrates reagent storage and electrochemical immunodetection and was applied for the detection of breast cancer markers. The main advantage of this system is that no external fluidic storage is required and the instrumental setup is thus greatly simplified. The fluidics of the microsystem is computer controlled and requires minimal end-user intervention. The analytical performance of the device was compared with a manually driven system and applied for the amperometric detection of the carcinoembryonic antigen (CEA) and cancer antigen 15-3 (CA15-3). This automation methodology greatly improves the analytical performance of the immunosensor in terms of accuracy and reproducibility as evidenced by a reduction of LOD observed for CEA and CA15-3 with respect to a manually driven system. Finally, the automated microsystem was applied for the analysis of real patient serum samples, demonstrating excellent correlation with a commercial ELISA.     

In situ physical or covalent trapping of phthalocyanine macrocycles within porous silica networks

An effective way of trapping phthalocyanines inside porous silica has been achieved when an aqueous solution of these macrocyclic species is reacted in situ with silicon alkoxide. The resultant porous gel network can encapsulate a myriad of metal phthalocyanine molecules at relatively high concentrations and, most importantly, in a disaggregated way. By employing this method metal sulfophthalocyanines of Fe, Co, Ni, Cu, Al, Eu or Sm can be encapsulated within SiO₂ xerogels. Here, the chemical entrapment of phthalocyanines inside silica gel pore networks is accomplished by the attachment of bifunctional groups to the walls of these substrates; while one of these moieties is directly linked to the macrocycle end groups, the other one is covalently bonded to the silanol groups resting on the SiO₂ walls. Furthermore, when the proper concentrations of phthalocyanine species, H₂O, silicon alkoxide, and HCl are reacted together, it is possible to obtain monolithic translucent silica xerogels. This latter property provides straightforward evidence of the innate fluorescence of the trapped macrocycles. The average size of the cavities encapsulating the macrocyclic molecules range from 2.0 to 3.6 nm; the precise size depends on the cation present in the complex and on the identity and position of the substituent groups at the periphery of the macrocycle. When the silica network is prepared from standard and/or organo-substituted alkoxides, the aggregation, degradation or stability of the macrocyclic species trapped in silica cavities depends on the nature of the alkyl group attached to the pore walls.     

Towards dimension expanders over finite fields

In this paper we study the problem of explicitly constructing a dimension expander raised by [3]: Let \mathbbFⁿ \mathbb{F}^n be the n dimensional linear space over the field \mathbbF\mathbb{F}. Find a small (ideally constant) set of linear transformations from \mathbbFⁿ \mathbb{F}^n to itself {A _i } _i∈I such that for every linear subspace V ⊂ \mathbbFⁿ \mathbb{F}^n of dimension dim(V)<n/2 we have

Characterization of galactooligosaccharides derived from lactulose

Galactooligosaccharides are non-digestible carbohydrates with potential ability to modulate selectively the intestinal microbiota. In this work, a detailed characterization of oligosaccharides obtained by transgalactosylation reactions of the prebiotic lactulose, by using β-galactosidases of different fungal origin (Aspergillus oryzae, Aspergillus aculeatus and Kluveromyces lactis), is reported. Oligosaccharides of degree of polymerization (DP) up to 6 were detected and quantified by HPLC-ESI MS from a complex mixture produced by transgalactosylation reaction with A. oryzae (GOSLuAo), whereas only carbohydrates up to DP4 and DP5 were found for those obtained from the reaction with β-galactosidases from K. lactis (GOSLuKl) and A. aculeatus (GOSLuAa), respectively. Disaccharides (galactosyl-galactoses and galactosyl-fructoses) and trisaccharides were characterised in the three mixtures by GC-MS as their trimethylsilyl oximes. Galactosyl- and digalactosyl-glycerols were produced during the transgalactosylation reaction of lactulose with β-galactosidases from A. aculeatus and K. lactis, due to the presence of glycerol as enzyme stabiliser.     

OFFGEL isoelectric focusing and polyacrylamide gel electrophoresis separation of platinum-binding proteins

In this work a 2D electrophoretic separation procedure able to maintain the integrity of platinum-protein bonds has been developed. The method is based on the use of sequential OFFGEL isoelectric focussing (IEF) and PAGE. A systematic study of the reagents used for PAGE, for OFFGEL-IEF separation, and post-separation treatment of gels (such as enzymatic digestion and sample preparation for MS analysis) was tackled regarding their suitability for the identification of platinum binding proteins using standard proteins incubated with cisplatin. The distribution of platinum in high and low molecular weight fractions (separated by cut-off filters) was determined by ICP-MS, which allows evaluating platinum-protein bond stability under the conditions studied. SDS-PAGE in the absence of β-mercaptoethanol or dithiotreitol preserved the platinum-protein bonds. In addition, neither the influence of the electric field during the electrophoretic separation, nor the processes of fixing, staining and destaining of proteins in the gel did result in the loss of platinum from platinum binding proteins. SDS-PAGE under non-reducing conditions provides separation of platinum-binding proteins in very narrow bands with quantitative recoveries. Different amounts of platinum-bound proteins covering the range 0.3-2.0 μg were separated and mineralised for platinum determination, showing good platinum linearity. Limits of detection for a mixture of five standard proteins incubated with cisplatin were between the range of 2.4 and 13.9 pg of platinum, which were satisfactory for their application to biological samples. Regarding OFFGEL-IEF, a denaturing solution without thiourea and without dithiotreitol is recommended. The suitability of the OFFGEL-IEF for the separation of platinum binding proteins of a kidney cytosol was demonstrated.     

Enantiotopic discrimination in the deuterium NMR spectrum of solutes with S4 symmetry in chiral liquid crystals

Enantiotopic discrimination in the NMR spectra of prochiral rigid solutes in chiral liquid crystals (CLC), by the ordering mechanism, is limited to molecules possessing one of the four, so called, "allowed" symmetries, D(2d), C(2v), C(s), and S(4). So far, such spectral discrimination was demonstrated only for solutes possessing one of the first three symmetries. In this work, we present deuterium NMR measurements on a rigid S(4) compound dissolved in a chiral nematic solvent and demonstrate, for the first time, enantiotopic discrimination in such symmetry. The measurements were performed on the isotopically normal icosane derivative (1) and on its isotopomer (1-d(8)), specifically deuterated in its four core methylene groups. As a CLC solvent, a lyotropic mesophase, consisting of a solution of poly-γ-benzyl-L-glutamate (PBLG) in pyridine, was employed. For comparison with a corresponding achiral liquid crystal (ALC) solvent, a solution of a racemic mixture of poly-γ-benzylglutamate (PBG) of similar composition in the same co-solvent was used. The spectra were recorded at 92.1 MHz using the 2D Q-COSY Fz sequence with proton decoupling. In the CLC solvents they exhibited clear discrimination due to different enantiotopic sites, with components displaced symmetrically, at frequencies below and above those in the corresponding ALC, as expected for discrimination by ordering. Two procedures were employed for correlating the enantiotopic sites in the CLC spectra. For 1-d(8) the dipolar cross-peaks in a 2D (2)H-(2)H COSY-90 experiment provided identification of signals belonging to the same methylene (and hence the same enantiotopic) groups. For 1 the correlation was achieved using a least-square-deviation fitting of the experimental quadrupole splittings with respect to those expected from the molecular geometry. These results, with appropriate symmetry considerations were used to determine the symmetric (S(zz)) and antisymmetric (S(xy) and S(xx)-S(yy)) components of the Saupe ordering matrix. Interpretation of the NMR spectra of prochiral solutes in CLC suffers from the ambiguity in identifying the signals with specific enantiotopic groups. For this reason only the relative (but not the absolute) signs of the antisymmetric elements of the ordering matrix can be determined. For the S(4) group this leads to sign ambiguity in the rhombic term in the diagonalized ordering matrix. Similar (but not identical) ambiguities occur for solutes belonging to the other allowed groups. In a concluding section of the paper, the ambiguities in the antisymmetric order parameters for the various allowed groups are compared and their physical meaning are discussed.     

Electronic structures of Group 9 metallocorroles with axial ammines

The electronic structures of metallocorroles (tpfc)M(NH(3))(2) and (tfc)M(NH(3))(2) (tpfc is the trianion of 5,10,15-(tris)pentafluorophenylcorrole, tfc is the trianion of 5,10,15-trifluorocorrole, and M = Co, Rh, Ir) have been computed using first principles quantum mechanics [B3LYP flavor of Density Functional Theory (DFT) with Poisson-Boltzmann continuum solvation]. The geometry was optimized for both the neutral systems (formal M(III) oxidation state) and the one-electron oxidized systems (formally M(IV)). As expected, the M(III) systems have a closed shell d(6) configuration; for all three metals, the one-electron oxidation was calculated to occur from a ligand-based orbital (highest occupied molecular orbital (HOMO) of B(1) symmetry). The ground state of the formal M(IV) system has M(III)-Cπ character, indicating that the metal remains d(6), with the hole in the corrole π system. As a result the calculated M(IV/III) reduction potentials are quite similar (0.64, 0.67, and 0.56 V vs SCE for M = Ir, Rh and Co, respectively), whereas the differences would have been large for purely metal-based oxidations. Vertically excited states with substantial metal character are well separated from the ground state in one-electron-oxidized cobalt (0.27 eV) and rhodium (0.24 eV) corroles, but become closer in energy in the iridium (0.15 eV) analogues. The exact splittings depend on the chosen functional and basis set combination and vary by ~0.1 eV.     

Molecular recognition of ADP over ATP in aqueous solution by a polyammonium receptor containing a pyrimidine residue

The synergistic action of the different binding groups of the polyfunctional HL receptor leads to the recognition of ADP over ATP in water, with a selectivity coefficient of up to 116, a phenomenon which is unprecedented in the context of synthetic receptors in water. The recognition is mostly due to the good matching between H(3)L(2+) and the protonated forms of ADP.