Reading of Protein Surfaces in the Native State at Micromolar Concentrations by a Chirogenetic Porphyrin Probe

The recognition of some globular proteins was carried out in aqueous solution, at micromolar concentrations, by using an uncharged symmetrical cobalt–porphyrin (Co–P). By means of UV/Vis, induced circular dichroism, and fluorescence spectroscopy techniques, it was ascertained that the interactions between specific amino acid residues and Co–P occurred on the protein surface. In particular, spectroscopic evidence showed the formation of supramolecular complexes without disruption of the native structure of the proteins and, furthermore, that signal changes were characteristic of each Co–P/protein system, so that they could be used as a highly sensitive analytical tool for protein recognition. The relative association constants were proportional to the protein molecular masses (and then to the number of amino acid residues).     

Polymeric membranes conditioning for sensors applications: mechanism and influence on analytes detection

In this work, we studied an ion-exchange membrane based on an inert polymer skeleton in which it is dispersed and anchored a molecule with charged groups able to discriminate and bind positive or negatively charged ions present in a sample. In order to be ready to work, electromembranes need a complex procedure called activation or conditioning. Although most of the known literature looks at the subject from an electrochemical point of view, we put forward a structural approach. Membrane conditioning, in fact, is considered a required step to improve sensor performances and to allow the collection of reproducible data. Even if this operation is carefully followed by all the operators working with sensors equipped with a membrane, it looks like that a thoroughly explanation of the working mechanism and a detailed balance of cost and gains has still not been carried out. As a consequence, we suggest a bulk or membrane approach, where the landscape is mainly characterized by the long-range structure of the membrane itself. Our findings suggest that membrane conditioning has to be carried out carefully and the advantages of this pre-treatment can be appreciated especially for very low concentration measurements. The need for the conditioning mainly results from the necessity of a complete permeation of all the different tortuous channels constituting the membrane itself.     

Determination of cylindrospermopsin in freshwaters and fish tissue by liquid chromatography coupled to electrospray ion trap mass spectrometry

Cylindrospermopsin (CYN) is a toxic alkaloid‐like compound produced by some strains of cyanobacteria, procariotic organisms occurring in water blooms, observed worldwide in eutrophic lakes and drinking water reservoirs. Methods for determination of CYN in freshwater and fish muscle by liquid chromatography coupled to electrospray ion trap mass spectrometry are herein described. The performances of both methods are reported; ion trap LC/ESI‐MS/MS resulted highly selective and reliable in unambiguous identification of CYN, based on monitoring the precursor ion and three product ions. The methods developed showed satisfactory mean recoveries (higher than 63.6%) and relative standard deviations, ranging from 5.8 to 9.8%. The limits of quantification at 0.10 ng/mL in freshwaters and 1.0 ng/g in fish muscle, respectively, allow for determination of CYN also in early contamination stages. Ion trap LC/ESI‐MS/MS was successfully applied to the identification and quantification of CYN in water and cyanobacteria extracts from Lake Averno, near Naples, representing the first case of contamination described in southern Italy. Copyright © 2009 John Wiley & Sons, Ltd.     

Nanofibers composite vanadium oxide/polyaniline: synthesis and characterization of an electroactive anisotropic structure

This contribution describes the synthesis of a hybrid nanocomposite constituted by vanadium oxide/polyaniline (PAni) with an interesting fibrilar morphology. Nanofibers can be obtained as main reaction products of nanocomposite V₂O₅/PAni and hexadecylamine after hydrothermal treatment. In general, nanocomposite nanofibers present a typical length varying from 1 to 10 μm and a width varying from 15 to 400 nm. Electrochemical experiments have shown a specific capacity of about 150 A h kg⁻¹ during the 10 initials cycles, revealing a promissory material for utilization as cathode for ion-Li batteries.     

The directed profitable location Rural Postman Problem

In this paper we introduce an extension of the well known Rural Postman Problem, which combines arc routing with profits and facility location. Profitable arcs must be selected, facilities located at both end-points of the selected arcs, and a tour identified so as to maximize the difference between the profit collected along the arcs and the cost of traversing the arcs and installing the facilities. We analyze properties of the problem, present a mathematical programming formulation and a branch-and-cut algorithm. In an extensive computational experience the algorithm could solve instances with up to 140 vertices and 190 arcs and up to 50 vertices and 203 arcs.     

Acid-base properties of the N3 ruthenium(ii) solar cell sensitizer: a combined experimental and computational analysis

We report a combined spectro-photometric and computational investigation of the acid-base equilibria of the N3 solar cell sensitizer [Ru(dcbpyH(2))(2)(NCS)(2)] (dcbpyH(2) = 4,4'-dicarboxyl-2,2' bipyridine) in aqueous/ethanol solutions. The absorption spectra of N3 recorded at various pH values were analyzed by Single Value Decomposition techniques, followed by Global Fitting procedures, allowing us to identify four separate acid-base equilibria and their corresponding ground state pK(a) values. DFT/TDDFT calculations were performed for the N3 dye in solution, investigating the possible relevant species obtained by sequential deprotonation of the four dye carboxylic groups. TDDFT excited state calculations provided UV-vis absorption spectra which nicely agree with the experimental spectral shapes at various pH values. The calculated pK(a) values are also in good agreement with experimental data, within <1 pK(a) unit. Based on the calculated energy differences a tentative assignment of the N3 deprotonation pathway is reported.     

Evidence of the participation of electronic excited states in the mechanism of positronium formation in substitutional Tb(1-x)Eu(x)(dpm)3 solid solutions studied by optical and positron annihilation spectroscopies

Positronium formation in the bimary molecular solid solutions Tb(1-x)Eu(x) (dpm)(3) (dpm = dipivaloylmethanate) has been investigated. A strong linear correlation between the (5)D(4) Tb(iii) energy level excited state lifetime and the positronium formation probability has been observed. This correlation indicates that the ligand-to-metal charge transfer LMCT states act in both luminescence quenching and positronium formation inhibition, as previously proposed. A kinetic mechanism is proposed to explain this correlation and shows that excited electronic states have a very important role in the positronium formation mechanism.     

Phanquinone as a suitable derivatization reagent in micellar electrokinetic chromatography and HPLC analysis of amino acids

Phanquinone (chemically: 4,7-phenanthroline-5,6-dione) was applied as an original precolumn derivatization reagent for amino acids followed by separation using MEKC with UV detection (240 nm). The derivatization reaction was carried out at 68 degrees C in the presence of aqueous phosphate buffer (pH 8.0) and it was found to be complete after 30 min. Twelve derivatized standard amino acids were separated in about 22 min under MEKC conditions using sodium cholate (250 mM) as the surfactant in phosphate buffer (20 mM, pH 9.0). The developed method was validated for the analysis of D,L-phosphoserine (D,L-p-Ser) and L-glutamine (L-Gln); good linearity (r > 0.999) was achieved in the calibration range of 0.25-2.5 micromol/mL. The sensitivity of the MEKC method (LOD 0.1 micromol/mL; LOQ 0.25 micromol/mL, RSD% <5.0%, n = 3) was found to be adequate for quantitation of amino acids in pharmaceuticals. Quantitative applications of the validated MEKC method were carried out by the analysis of commercially available oral polyaminoacid formulations (tablets and extemporaneous solutions) containing L-Gln and D,L-p-Ser; the obtained results were found to be in agreement with those from a validated reference RP-HPLC method.