Spiroimidazolidinone library derivatives on SynPhase lanterns

Optimization and solid-phase synthesis of new spiroimidazolidinone derivatives as highly functionalized templates is reported. The synthesis of 1,4,8-triazaspiro[4.5]decan-2-one derivatives was performed on SynPhase lanterns from dipeptides anchored on the solid support and N-protected piperidone. A library of 180 discrete compounds was prepared.     

Bulk CO oxidation on platinum electrodes vicinal to the Pt(111) surface

Bulk CO oxidation has been studied on platinum stepped surfaces belonging to the series Pt(S)[n(111) × (111)], using a hanging meniscus rotating disk electrode (HMRDE) configuration. The general shape of the voltammograms is not significantly affected by the presence of the steps. However, the curves shift towards negative values as the step density increases. Thus, in the positive-going scan, a linear relationship is observed for the dependence of the potential for the ignition peak vs the step density for surfaces with terraces wider than five atoms, shorter terraces deviate from this behavior. In the negative-going scan, a similar situation is observed for the potential where the current drops to zero. In this case, Pt(111) electrode also deviates from the expected behavior because of the formation of the ordered bisulfate adlayer on the electrode. The anion readsorption process is also observed by recording the HRMDE voltammograms at a high scan rate. All these results have been analyzed in light of a common mechanism, discussing the possible role of the steps in the stability and reactivity of the CO adlayer. In memoriam of Francisco C. Nart, an excellent scientist, colleague, and friend.     

Wave-based control of non-linear flexible mechanical systems

The need to achieve rapid and accurate position control of a system end-point by an actuator working through a flexible system arises frequently, in cases from space structures to disk drive heads, from medical mechanisms to long-arm manipulators, from cranes to special robots. The system’s actuator must then attempt to reconcile two, potentially conflicting, demands: position control and active vibration damping. Somehow each must be achieved while respecting the other’s requirements. Wave-based control is a powerful solution with many advantages over previous techniques. The central idea is to consider the actuator motion as launching mechanical waves into the flexible system while simultaneously absorbing returning waves. This simple, intuitive idea leads to robust, generic, highly efficient, adaptable controllers, allowing rapid and almost vibrationless re-positioning of the remote load (tip mass). This gives a generic, high-performance solution to this important problem that does not depend on an accurate system model or near-ideal actuator behaviour. At first sight wave-based control assumes superposition and therefore linearity. This paper shows that wave-based control is also robust (or can easily be made robust) to non-linear behaviour associated with non-linear elasticity and with large-deflection effects.     

Selective catalytic reduction at quasi-perfect Pt(100) domains: a universal low-temperature pathway from nitrite to N2

The highly selective conversion of nitrite to N(2) at a quasi-perfect Pt(100) electrode in alkaline media was investigated with a particular emphasis on its structure sensitivity and its mechanism. High-quality (100) terraces are required to optimize the catalytic activity and steer the selectivity to N(2): defects of any symmetry dramatically reduce the N(2) evolution at [(100) × (110)] and [(100) × (111)] surfaces. On the other hand, nitrite reduction proves to be an additional example of the unique intrinsic ability of (100) surfaces to catalyze reactions involving bond breaking and successive bond formation. In the present case, (100) is able to reduce nitrite to NH(2,ads), which in a certain potential window combines with NO(ads) to give N(2) in a Langmuir-Hinshelwood reaction. Our findings are similar to those for other processes generating N(2), from bacterial anoxic ammonia oxidation ("anammox") to the high-temperature NO + NH(3) reaction at Pt(100) crystals under ultra-high-vacuum conditions, thus suggesting that the combination of these two nitrogen-containing species is a universal (low-temperature) pathway to N(2). The advantages of this pathway over other N(2)-generating pathways are pointed out.     

Fundamental aspects of HCOOH oxidation at platinum single crystal surfaces with basal orientations and modified by irreversibly adsorbed adatoms

Oxidation of formic acid at Pt(hkl) electrodes with basal orientations and modified by irreversibly adsorbed adatoms is revisited. It was shown that the adatoms of the nitrogen group enhance the electrocatalytic activity through long-range electronic effects in the case of Pt(111) substrates or through shorter third-body effects when adsorbed at Pt(100) electrodes. In both cases, it appears that free platinum sites were required. Special attention is given here to the reactivity at Pt(110) substrates. It is found that maximum electrocatalysis is observed at fully blocked surfaces. This result points out again structure sensitivity effects for this characteristic reaction. Unlike the more compact planes, in which the enhancement of the oxidation rate was explained through essentially rigid models for the adlayer, it is suggested that the resulting enhancement observed at Pt(110) substrates could be explained if some adatom mobility is considered.     

Electrochemical oxidation of ethylene glycol on Pt single crystal electrodes with basal orientations in acidic medium

Ethylene glycol electrooxidation on platinum using voltammetry is shown to be a structure sensitive reaction. Among the three basal planes, Pt(111) shows the lowest activity for the oxidation of the organic, although the reaction takes place at lower potential values. The poisoning intermediate can be isolated on each orientation and identified as a CO-like species, its formation taking place in a wide potential range. The stability of the voltammetric profiles during continuous cycling suggests that these CO-like species are the main stable adsorbed residues on Pt(100) and Pt(111). The loss of activity observed with repeated cycling on Pt(110) in a potential range excluding oxygen adsorption is explained by a structural modification of the surface.     

Evidence of water reorientation on model electrocatalytic surfaces from nanosecond-laser-pulsed experiments

The behavior of water at the interface formed between a quasi-perfect Pt(111) single-crystal electrode and an aqueous electrolyte solution is studied by means of the laser-induced temperature jump method. This method is based on the use of nanosecond laser pulses to suddenly increase the temperature at the interface. The measurement of the response of the interface toward the laser heating under coulostatic conditions provides evidence on the net orientation of water at the interface. Especially interesting is the study of the effect on the interfacial water caused by the selective deposition of foreign metal adatoms, because these bimetallic systems usually exhibit appealing electrocatalytic properties. The T-jump methodology shows that the surface composition strongly affects the interaction of water with the surface. The most representative parameter to characterize this interaction is the potential where water reorientation occurs; this potential shifts in different directions, depending on the relative values of the electronegativity of the adatom and the substrate. These results are discussed in the light of available information about the effect of adatom deposition on the work function and the surface potential of the modified surface. Finally, some implications on the enhancement of the electrocatalytic activity are briefly discussed.