Influence of the preparation method on the morphology of templated NiCo<Subscript>2</Subscript>O<Subscript>4</Subscript> spinel

The synthesis of NiCo₂O₄ spinel by several nanocasting strategies (i.e., multi-step nanocasting, one-step nanocasting and soft-templating), in which nickel and cobalt nitrates are used as precursors and Pluronic P123 as surfactant, is explored. First, in the multi-step nanocasting, the effect of the impregnation method (evaporation, solid–liquid and two-solvent) of the SBA-15 silica template on the morphology of NiCo₂O₄ replica is investigated. The evaporation method seems to be the best choice to obtain mesoporous NiCo₂O₄ powder which, after calcination at 375 °C and subsequent template removal, displays the highest surface area (93.1 m²/g). We have also checked the feasibility of the one-step nanoscating approach for the synthesis of ordered NiCo₂O₄ arrays, though this methodology entails severe difficulties, mainly related to the different decomposition temperature of the nitrate precursors and the P123 surfactant. Finally, randomly oriented, aggregated NiCo₂O₄ nanoparticles are obtained by means of P123 surfactant-assisted soft-templating approach.     

Voltammetric Analysis of Phytochelatin Complexation in Ternary Metal Mixtures Supported by Multivariate Analysis and ESI‐MS

The competitive binding of Cu²⁺, Cd²⁺ and Pb²⁺ in ternary mixtures by the phytochelatins PC₂ and PC₅ (PC_n; (γGlu‐Cys)_n‐Gly, n=2 and 5) are examined by voltammetry, which allows one to follow the displacements of the voltammetric signals induced by the competitive binding among the metal ions towards PC₂ or PC₅ complexation, and direct injection positive‐mode Electrospray Ionization Mass Spectrometry (ESI‐MS), in order to obtain the stoichiometries of the complexes. Voltammetric data are analyzed by Gaussian Peak Adjustment (GPA), which is a recently developed multivariate analysis method for nonlinear electrochemical data. Different complexes have been detected or deduced their presence, depending on the experimental conditions. Ternary complexes CuCdPC_n and CdPbPC_n were detected for both PC₂ and PC₅, while the ternary CuPbPC_n complex was only detected for PC₂. Some of the complexes have been only detected by ESI‐MS because in some cases voltammetry data could not be totally resolved, even by using GPA. The quaternary CdPbCuPC_n complex has been detected for PC₅, but for PC₂ data are not so conclusive. In summary, the signal evolution for mixed CdCuPC_n complexes is quite different. These observations could be a reflection of an antagonistic effect for the case of PC₂ and a synergetic one for PC₅.     

Template Effects in SN2 Displacements for the Preparation of Pseudopeptidic Macrocycles

Macrocyclisation reactions of C₂‐symmetric pseudopeptides containing central pyridine‐derived spacers are affected by the presence of different anions. The selection of the proper anion gives excellent results for the preparation of the corresponding macrocyclic structures. Kinetic studies show that the presence of those anions enhances both the yield and the rate of the reaction. Computational studies at the B3LYP/6‐31G* level have allowed us to rationalise the experimental results. The obtained transition states (TSs) show that the interaction between the anion and the open‐chain pseudopeptidic chain has a stabilising effect. The anion stabilises the two TSs involved: the first one, which involves the formation of the initial bond between the two subunits and leads to an open‐chain intermediate, and the second one, which precedes the formation of the cyclic structure. The optimum anion (Br^? when the central spacer is derived from 2,6‐bis(aminomethyl)pyridine, is able to act as a template, in that it forces the two ends of the open‐chain intermediate to approach each other by forming hydrogen bonds with the two amino acid subunits present in the intermediate. This stabilises the second TS to a greater extent than the first one, and thus, favours macrocyclisation over the competing oligomerisation reactions. The computational calculations also allowed us to predict the outcome of new experiments. Accordingly, the synthesis of the pseudopeptidic macrocycle derived from 2,6‐diaminopyridine was not successful under the optimised conditions previously used. Nevertheless, calculations predicted that in this case Cl^? should be more efficient than Br^?, and this was subsequently experimentally confirmed. Interestingly, the presence of different substituents on the constituent amino acids seems to play a minor role in the overall process.     

Nerve agent simulant detection by using chromogenic triaryl methane cation probes

Two triaryl methane cations have been used as probes for colorimetric detection of nerve agent simulants. Buffered mixed aqueous solutions of 1 and 2 showed bathochromic shifts in the presence of DCNP (diethylcyanophosphonate) and DCP (diethylchlorophosphate). The colour modulation can be observed to the naked eye. Appropriate mechanisms for the recognition event are proposed.     

Photoelastic stress analysis of splinted and unitary implant-supported prostheses

The aim of this study was to evaluate the effects that splinting and different lengths of implants have on the stress distribution in implant-supported prostheses by photoelastic analysis. A total of five photoelastic resin models were made with different proposed situations, and 400 load applications were performed for the analysis. Compared with the unitary prosthesis, the splinted implant-supported prosthesis acted favorably in the distribution of stresses and strains to the implant (p < 0.001). The increase in length was a significant factor in the stress distribution (p < 0.05) and, ultimately, the overall reduction in stress. It was concluded that the splinted implant-supported prosthesis behaved better biomechanically compared with the unitary prosthesis.     

Arylation of aryl chlorides,a convenient method for the synthesis of new potential triazolic fungicides

We evaluated two alternative routes for the arylation of known chlorinated fungicides. The first pathway involved a S_RN1 substitution, followed by Stille reaction, while the second consisted in a one step reaction by the Suzuki coupling. Both methodologies were useful to obtain new products that could be potential fungicides.     

Improvement of residual bilinearization by particle swarm optimization for achieving the second‐order advantage with unfolded partial least‐squares

The combination of unfolded partial least‐squares (U‐PLS) with residual bilinearization (RBL) provides a second‐order multivariate calibration method capable of achieving the second‐order advantage. RBL is performed by varying the test sample scores in order to minimize the residues of a combined U‐PLS model for the calibrated components and a principal component model for the potential interferents. The sample scores are then employed to predict the analyte concentration, with regression coefficients taken from the calibration step. When the contribution of multiple potential interferents is severe, particle swarm optimization (PSO) helps in preventing RBL to be trapped by false minima, restoring its predictive ability and making it comparable to the standard parallel factor (PARAFAC) analysis. Both simulated and experimental systems are analyzed in order to show the potentiality of the new technique. Copyright © 2007 John Wiley & Sons, Ltd.