Mechanochemically synthesized pyrite and its electrochemical behavior as cathode for lithium batteries

Journal of Solid State Electrochemistry - This study presents a simple and scalable synthesis of pyrite (FeS2) starting from S and Fe powders, which involves high-energy ball milling of precursor...     

Rotation-tunneling analysis of the origin band in the tropolone pi(*)<--pi absorption system

The tunneling-split origin band of the tropolone A (1)B(2)-X (1)A(1) (pi(*)<--pi) absorption system was interrogated under ambient, bulk-gas conditions by exploiting high-resolution degenerate four-wave mixing techniques. The inherent complexity of this spectral region was alleviated by performing polarization-resolved measurements, with judicious selection of transverse characteristics for the incident and detected electromagnetic fields enabling rovibronic transitions to be discriminated according to their attendant changes in rotational angular momentum, DeltaJ. Quantitative simulation of recorded data sets showed the vibrationless level of the electronically excited state to be bifurcated by Delta(0) (A)=19.846(25) cm(-1), representing a factor of 20 increase in proton-transfer efficiency over the corresponding level of the ground electronic state. Spectroscopic parameters extracted for the 0(+) and 0(-) manifolds of A (1)B(2) tropolone yield unexpectedly large values of the inertial defect, DeltaI(0(+) ) (A)=-0.802(86) amu A(2) and DeltaI(0(-) ) (A)=-0.882(89) amu A(2), strongly suggesting that a loss of molecular planarity accompanies the pi(*)<--pi electron promotion. These results, as well as complementary information deduced for interloping hot-band resonances, are discussed in terms of the unique structural and dynamical properties exhibited by tropolone and related proton-transfer species.     

Hydroxypropyl-β-cyclodextrin effect on the fluorescence of auxin and skatole and on the simultaneous determination of binary mixtures of indole compounds in urine by first derivative spectrofluorimetry

The effect of hydroxypropyl-β-cyclodextrin (HPβCD, β-cyclodextrin (βCD) derivative) was determined on the fluorescence emission spectra of skatole (3-methylindole, MI) and auxin (indole 3-acetic acid, IA). The experiments were conducted at excitation wavelength (λ_ex) = 280 nm, in aqueous solutions at different pH values, with and without HPβCD as receptor. The enhanced fluorescence in the presence of the receptor showed a 1:1 host–guest interaction and the values of the association constants K_A were between 100 and 200 mol⁻¹ L. The effects of methanol and propanol with and without receptor were also studied. The limit of detection (L_D) for the HPβCD enhanced fluorimetric method at pH = 7.00 were 0.279 and 0.765 ng mL⁻¹ for MI and IA, respectively. For the determination of indole compounds with closely overlapping spectral bands a zero-crossing first derivative spectrofluorimetric method with or without HPβCD is described. Binary mixtures of MI or IA with melatonin (N-acetyl-5-methoxytryptamine, M) or 5-methoxytryptamine (5-methoxy-3-(2-aminoethyl)indole, 5M) were analysed in the presence of HPβCD. In the absence of receptor, binary mixtures of MI with IA and M with 5M were determined. The matrix effect was evaluated in urine samples by the method of standard addition. Good apparent recoveries were found for each indolic compound by the direct method (98–105% with R.S.D. 0.5–5%) and for mixtures of them by the first derivative method (90–105% with R.S.D. 1–5%) indicating the applicability of them with the advantage of their simplicity, low cost in materials, no time consuming and no requirement of the use of a sophisticate calibration program.     

Comparative study of the electrochemical behavior and analytical applications of (bio)sensing platforms based on the use of multi-walled carbon nanotubes dispersed in different polymers

This review present a critical comparison of the electrochemical behavior and analytical performance of glassy carbon electrodes (GCE) modified with carbon nanotubes (CNTs) dispersed in different polymers: polyethylenimine (PEI), PEI functionalized with dopamine (PEI-Do), polyhistidine (Polyhis), polylysine (Polylys), glucose oxidase (GOx) and double stranded calf-thymus DNA (dsDNA). The comparison is focused on the analysis of the influence of the sonication time, solvent, polymer/CNT ratio, and nature of the polymer on the efficiency of the dispersions and on the electrochemical behavior of the resulting modified electrodes. The results allow to conclude that an adequate selection of the polymers makes possible not only an efficient dispersion of CNTs but also, and even more important, the building of successful analytical platforms for the detection of different bioanalytes like NADH, glucose, DNA and dopamine.     

Carboxylated,Fe‐Filled Multiwalled Carbon Nanotubes as Versatile Catalysts for O2 Reduction and H2 Evolution Reactions at Physiological pH

The development of new electrocatalysts for the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) at physiological pH is critical for several fields, including fuel cells and biological applications. Herein, the assembly of an electrode based on carboxyl‐functionalised hydrophilic multiwalled carbon nanotubes (MWCNTs) filled with Fe phases and their excellent performance as electrocatalysts for ORR and HER at physiological pH are reported. The encapsulated Fe dramatically enhances the catalytic activity, and the graphitic shells play a double role of efficiently mediating the electron transfer to O₂ and H₂O reactants and providing a cocoon that prevents uncontrolled Fe oxidation or leaching.     

Spectrofluorimetric determination of serotonin and 5-hydroxyindoleacetic acid in urine with different cyclodextrin media

Alternative and sensitive spectrofluorimetric methods for the determination of hydroxyindoles, such as serotonin (5HT) and 5-hydroxyindoleacetic acid (5HIA), were developed on the basis of supramolecular interaction with cyclodextrin (CD) nanocavities (βCD and hydroxypropyl-βCD, HPCD) at different pH values. Both substrates and receptors have acidic protons, therefore the interactions produced in different systems were considered. The effects of neutral CD at pH 2.00 and 6.994, and of anionic CD at pH 13.00 on the specific acid-base species of the compounds at each pH were determined. In all the conditions studied, the fluorescence of the substrates in the presence of CD increased. The association constants (K_A, mol⁻¹ L) between the substrates and CD were determined (30-300) and interpreted. A zero-crossing first-derivative spectrofluorimetric method with and without HPCD was developed for the simultaneous determination of 5HT and 5HIA. The limits of detection (L_D, ng mL⁻¹) for the best conditions were 0.37 for 5HT and 0.50 for 5HIA at pH 2.00 with HPCD. These L_D proved to be better than others reported. The applicability of the direct and derivative spectrofluorimetric methods to urine samples was demonstrated with good recoveries 92-110% and R.S.D. 1-10%.     

Versatile method for the detection of covalently bound substrates on solid supports by DART mass spectrometry

Analysis of substrates directly on solid phase resins without the need for separate cleavage conditions remains an outstanding challenge in the field of solid phase synthesis. We now present the first example of simultaneous cleavage and mass spectrometric analysis of peptides from solid supports using direct analysis in real time (DART) mass spectrometry. We have shown that this method is compatible with a diverse array of solid phase resins and is suitable for analysis of both peptides and organic substrates.     

Triazine‐Carbon Nanotubes: New Platforms for the Design of Flavin Receptors

The synthesis of functionalised carbon nanotubes as receptors for riboflavin (RBF) is reported. Carbon nanotubes, both single‐walled and multi‐walled, have been functionalised with 1,3,5‐triazines and p‐tolyl chains by aryl radical addition under microwave irradiation and the derivatives have been fully characterised by using a range of techniques. The interactions between riboflavin and the hybrids were analysed by using fluorescence and UV/Vis spectroscopic techniques. The results show that the attached functional groups minimise the π‐π stacking interactions between riboflavin and the nanotube walls. Comparison of p‐tolyl groups with the triazine groups shows that the latter have stronger interactions with riboflavin because of the presence of hydrogen bonds. Moreover, the triazine derivatives follow the Stern–Volmer relationship and show a high association constant with riboflavin. In this way, artificial receptors in catalytic processes could be designed through specific control of the interaction between functionalised carbon nanotubes and riboflavin.     

Comparative effect of cyclodextrin nanocavities versus organic solvents on the fluorescence of carbamate and indole compounds

The effect of the addition of different amounts of organic solvents (S) on the fluorescence of aromatic compounds (C) and their inclusion complexes with β-cyclodextrin (βCD) and hydroxypropyl-β-cyclodextrin (HPCD) has been examined using steady-state measurements. Carbamate pesticides with different aromatic moiety, such as carbofuran (CF), promecarb (PC), carbaryl (CY) and bendiocarb (BC) were used, as well as indole derivatives with different polarity in their lateral chains, such as melatonin (M, neutral), 5-methoxytryptamine (MT, cation) and auxin (IA, anion). Their complexes in water show a fluorescence signal higher than that obtained for the free substrates in solvent:water mixtures (30%, v/v n-propanol or acetonitrile, and 50%, v/v methanol). The isofluorescent point (IF), the %IF and the F_85% are defined in order to evaluate the use of CD nanocavities as a non-polluting alternative for the analysis of the compounds analyzed.Apparent formation constants (K_AP, M⁻¹) for the complexes of C:HPCD at different solvent percentages were determined for CF and PC with methanol (MeOH), n-propanol (ProOH) and acetonitrile (ACN), and for indole compounds with ACN. A decrease in the K_AP values for the CF:HPCD (120–30) and PC:HPCD (2000–400) complexes occurs in accordance with the solvent affinities for CDs (MeOH < ACN < ProOH). Nevertheless, in the indolic series, the polar characteristics of MT, IA and M determine their behaviour in the presence of ACN. For the neutral substrate M, K_AP decreases with the increasing percentage of ACN (100–10). In contrast, for IA and MT (ionic substrates) K_AP increases (10–100).These results may be accounted for by two different mechanisms: the competition between C and S for the cavity of the receptor or the formation of ternary complexes C:S:CD with additional stabilization.     

Modeling,analysis and simulation of the human femur: prosthesis of femur head

We report the results obtained when carrying out the analysis of the strengths and strains that take place when prosthesis of femur head are implanted in the human femur. The modeling is made with tools provided by Computer Aided Geometry Design, using Non Uniform Rational B-Splines representations (NURBS). In the analysis of the strengths and strains, produced in the bone-cement-prosthesis interaction, partial differential equations of the coupled system are obtained for the displacements and deformations, that allow to analyze cases of physical and biological loads, under which will be work the implants during their useful life, which also is estimated; because of the frequent phenomenon of bony absorption and the consequent relaxation and loss of the replacement surgery. The obtained equations are solved by finite element method, with the corresponding estimation of the obtained errors. The simulations will be performed using high level software able to show realistic visualizations of the observed phenomena in real time. The fracture of the femur neck is a frequently observed trauma and has taken to the authors to make the present work. The obtained results will allow to make the modeling, analysis and simulation of other bony structures and the implants of the corresponding prosthesis. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)