Optical fiber biosensor coupled to chromatographic separation for screening of dopamine, norepinephrine and epinephrine in human urine and plasma

An optical fiber biosensor has been developed for the determination of catecholamines (dopamine, norepinephrine and epinephrine) based on the recognition capacity of the enzyme laccase. In this study, a glass tube constituted by a fused silica fiber coated with a film of polystyrene/divinylbenzene resin (PS/DVB) was used for catecholamines separation. Firstly, the analyzer was tested for calibration and its analytical performance for catecholamines detection was compared with a classical analytical method, namely high performance liquid chromatography-electrochemical detector (HPLC-ED). The developed analytical device shows a high potential for catecholamines quantification with a detection limit of 2.1, 2.6 and 3.4 pg mL⁻¹ for dopamine, norepinephrine and epinephrine, respectively. The analytical sensitivity, inferred from the slope of the calibration curves established for a range of concentrations between 5 and 125 pg mL⁻¹, was found to be 0.344, 0.252 and 0.140 dB/pg mL⁻¹ for dopamine, norepinephrine and epinephrine, respectively. Furthermore, catecholamines speciation with the PS/DVB fiber was completely achieved in 3 min. The analytical performance of the reported sensor was also evaluated and found adequate for catecholamines determination in human urine and plasma samples.     

Leptogorgolide, a biogenetically interesting 1,4-diketo-cembranoid that reinforces the oxidation profile of C-18 as taxonomical marker for octocorals

The cembranoid 1 and the furanocembranolides 2-4 along with the known pukalide were isolated from Leptogorgia sp. and their structures determined spectroscopically. The 1,4-diketo-cembranoid 1 follows an oxidation pattern of C-18 that reinforces the concept of oxidation profile of C-18 as taxonomical marker for octocorals. The co-occurrence within a species of furanocembranolide/1,4-diketo-cembranoid congeners 1/2-4 raises the question about which one is the biogenetic precursor. A biogenetic pathway is proposed.     

Pt supported on carbon nanofibers as electrocatalyst for low temperature polymer electrolyte membrane fuel cells

Carbon nanofibers synthesized via the thermo catalytic decomposition of methane were investigated for the first time as an electrocatalyst support in PEMFC cathodes. Their textural and physical properties make them a highly efficient catalyst support for cathodic oxygen reduction in low temperature PEMFC. Tests performed in MEAs showed that Pt supported on carbon nanofibers exhibited an enhancement of ca. 94% in power density at 0.600 V, in comparison with a commercial catalyst supported on conventional carbon black, Pt/Vulcan XC-72R.     

Energetics of some sulphur heterocycles

The present work is part of a broader research program on the energetics of formation of heterocycles, aiming the study of the enthalpic effects of the introduction of different substituents into heterocycles. In this work we present the results of the thermochemical research on sulphur heterocycles of the type substituted thiophenes with different kind of substituents, mainly alkyl, ester, acetyl, carboxamide, acetamide, carbonitrile and carboxaldehyde. The standard (p ^o=0.1 MPa) molar enthalpies of formation, in the condensed phase, at T=298.15 K, of a large number of substituted thiophenes, were derived from their standard massic energies of combustion, measured by rotating-bomb combustion calorimetry, while the standard molar enthalpies of vaporization or sublimation of those compounds were obtained either by high temperature Calvet Microcalorimetry, or by the temperature dependence of their vapour pressures determined by the Knudsen effusion technique. The standard molar enthalpies of formation, of the studied sulphur heterocycles in the gaseous phase, were then derived. The results are interpreted in terms of structural contributions to the energetics of the substituted thiophenes, the internal consistency of the results is discussed and, whenever appropriate and possible, empirical correlations are suggested for the estimation of standard molar enthalpies of formation, at T=298.15 K, of substituted thiophenes. A Table of enthalpic increments for different group substituents in positions 2 or 3 of the thiophene ring has been established.     

Probing the Bioactive Conformation of an Archetypal Natural Product HDAC Inhibitor with Conformationally Homogeneous Triazole‐Modified Cyclic Tetrapeptides

Fooling enzymes with mock amides : Analogues of apicidin, a cyclic‐tetrapeptide inhibitor of histone deacetylase (HDAC), were designed with a 1,4‐ or 1,5‐disubstituted 1,2,3‐triazole in place of a backbone amide bond to fix the bond in question in either a trans‐like or a cis‐like configuration. Thus, the binding affinity of distinct peptide conformations (see picture) could be probed. One analogue proved in some cases to be superior to apicidin as an HDAC inhibitor.

     

Air‐Stable {(C5H5)Co} Catalysts for [2+2+2] Cycloadditions

Cobalt cyclopentadienyl complexes incorporating a fumarate and a CO ligand (see picture) efficiently catalyze inter‐ and intramolecular [2+2+2] cycloadditions of alkynes, nitriles, and/or alkenes to give benzenes, pyridines, or 1,3‐cyclohexadienes. Unlike catalysts such as [CpCo(CO)₂] or [CpCo(C₂H₄)₂] (Cp=C₅H₅), they are air‐stable, easy to handle, compatible with microwave conditions, and do not necessarily require irradiation to be active.

     

Applications of capillary electrophoresis to the determination of antibiotics in food and environmental samples

In this paper we review applications of capillary electrophoresis (CE) to the determination of antibiotic residues in food derived from animals and in environmental samples. Although many CE methods have been used to determine antibiotics in the pharmaceutical field (drug quality control or therapeutic monitoring in biological samples), food and environmental applications have been increasing in recent years. Due to the maximum residue limits established by the EU, in Directive 2377/90/EEC, for foodstuffs of animal origin and considering the low levels that can be found in environmental or waste waters or soils, different strategies to increase sensitivity have been developed, including off-line preconcentration, on-line stacking modes to use higher sample volumes, or in-line solid-phase extraction. Also, several detection techniques, such as fluorescence, laser-induced fluorescence, electrochemical detection, or mass spectrometry have been used; the last of these also enables unequivocal identification of the residues, required by Commission Decision 2002/657/EC. All these aspects will be discussed in this paper, in relation to the main groups of antibiotics used in veterinary and human medicine, for which applications in food and environmental samples have been developed by using CE as an efficient alternative to liquid chromatography.     

Crystallographic Characterization of Dipyridylamine Derivatives

Abstract  

Dipyridylamine has been coupled with phenyl groups to yield new organic ligands. During the course of one reaction a lithium salt of dipyridylamine was isolated as the product. These new compounds were characterized by single crystal X-ray diffraction, which reveals that π–π stacking interactions as well as hydrogen bonding permeate the isolated compounds in the solid state. BrPhDPA, compound 1, crystallizes in the monoclinic P2₁ space group with cell parameters a = 5.8291(1), b = 8.8504(2), c = 13.2341(3) ? and β = 91.928(1)°. 3-ThPh(DPA)₂, compound 4, crystallizes in the orthorhombic C2/c space group with cell parameters a = 14.8033(7), b = 11.4124(4), c = 16.11780(7) ? and β = 115.911(3)°. Finally the lithium salt, [Li(HDPA)(H₂O)₂](H₂DPA)(Cl)₂(H₂O), compound 5, crystallizes in the monoclinic Cmcm space group with cell parameters a = 14.043(3), b = 12.370(3) and c = 13.389(3) ?.     

Histamine Molecule and Dianion Oxalate are Efficient Blocks for Building 2D Supramolecular Networks

Abstract  

One salt and two Cu(II) complexes (H₂hsm)(ox), 1, [Cu(hsm)(ox)], 2, and [Cu(hsm)(ox)H₂O], 3, have been synthesized and X-ray characterized (hsm is histamine and ox²⁻ is the oxalate dianion). Starting from the prochiral tetracoordinated complex 2, pentacoordinated complex 3 crystallizes as a racemic mixture of the enantiomeric Δ and Λ isomers, in space group P2₁/c. In all cases, the side chain of the hsm group is gauche, allowing the formation of strong hydrogen bonds in the salt 1, and to chelate the metal center in complexes 2 and 3. The combination hsm/ox seems to favor the formation of 2D supramolecular structures (planes or wavy planes), through efficient networks of N–H···O hydrogen bonds. Cell parameters: 1, P2₁/c, a = 6.260 (2) ?, b = 11.500 (4) ?, c = 12.525 (4) ?, β = 104.047 (17)o; 2, C2/c, a = 10.7966 (13) ?, b = 15.5622 (16) ?, c = 11.3996 (15) ?, β = 106.261 (11)o; 3, P2₁/c, a = 7.0627 (6) ?, b = 7.1323 (6) ?, c = 20.0296 (19) ?, β = 91.529 (7)o.