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By using modifiers in platinum catalysts it is possible to modulate the hydrogenation selectivity in α , β -unsaturated aldehydes carbonyl bond with regard to olefinic bond hydrogenation. The challenge is to find an emergent catalytic material able to produce 100% unsaturated alcohol. In this field, 1% Pt/ZnO catalysts were tested in hydrogenation of crotonaldehyde, in gas phase, at atmospheric pressure. The catalysts were prepared by impregnation of ZnO from two different precursors, H 2 PtCl 6 and Pt(NH 3 ) 4 (NO 3 ) 2 , followed by calcination at 673 K and tested after reduction at different temperatures, 473–773 K. The ex-nitrate and ex-chloride catalysts showed quite different catalytic behaviors. The ex-chloride was much more active and selective; in certain conditions 90% crotyl alcohol selectivity was reached. Different techniques (TPR, XRD, TEM, XPS, FTIR) were used to characterize both types of catalysts and to correlate the structure and the reactivity. The Lewis acidity of ZnO after the reduction treatment and the formation of PtZn alloy were found to be the key factors leading to high crotyl alcohol yield. It was proposed that modification of the electronic properties of platinum both by alloying to zinc and by Lewis acidity of the support reinforced by chlorine changes the adsorption mode of crotonaldehyde by favoring the binding of the terminal oxygen of the molecule to the electronically modified platinum atom.

Two zeolites were coked using cyclohexene at 620 K; one had a low Si/Alf ratio (HY), the other was ultrastabilized (HYS). It was found that oxygen regeneration occurred at 770 K or above, whereas ozone was effective at 450 K or less,e.g. under conditions such that the HY sample was still thermally stable.

Serine beta-lactamases contribute widely to the beta-lactam resistance phenomena. Unfortunately, the intimate details of their catalytic mechanism remain elusive and subject to some controversy even though many "natural" and "artificial" mutants of these different enzymes have been isolated. This paper is essentially focused on class C beta-lactamases, which contain a Tyr (Tyr150) as the first residue of the second conserved element, in contrast to their class A counterparts, in which a Ser is found in the corresponding position. We have modified this Tyr residue by site-directed mutagenesis. On the basis of the three-dimensional structure of the Enterobacter cloacae P99 enzyme, it seemed that residues Glu272 and His314 might also be important. They were similarly substituted. The modified enzymes were isolated and their catalytic properties determined. Our results indicated that His314 was not required for catalysis and that Glu272 did not play an important role in acylation but was involved to a small extent in the deacylation process. Conversely, Tyr150 was confirmed to be central for catalysis, at least with the best substrates. On the basis of a comparison of data obtained for several class C enzyme mutants and in agreement with recent structural data, we propose that the phenolate anion of Tyr150, in conjunction with the alkyl ammonium of Lys315, acts as the general base responsible for the activation of the active-site Ser64 during the acylation step and for the subsequent activation of a water molecule in the deacylation process. The evolution of the important superfamily of penicillin-recognizing enzymes is further discussed in the light of this proposed mechanism.

Adsorption of CH3SH and CH3OH on activated NaX and NaY zeolites has been studied by IR spectroscopy. Only NaX is able to provoke the dissociative adsorption of CH3SH at room temperature and that of CH3OH at 623 K. Results are discussed taking into account sodium cations in the SIII position.

The Poisson-Boltzmann method was used to compute the pK(a) values of titratable residues in a set of class C beta-lactamases. In these calculations, the pK(a) of the phenolic group of residue Tyr150 is the only one to stand out with an abnormally low value of 8.3, more than one pK(a) unit lower than the measured reference value for tyrosine in solution. Other important residues of the catalytic pocket, such as the conserved Lys67, Lys315, His314, and Glu272 (hydrogen-bonded to the ammonium group of Lys315), display normal protonation states at neutral pH. pK(a) values were also computed in catalytically impaired beta-lactamase mutants. Comparisons between the relative k(cat) values and the Tyr150 pK(a) value in these mutants revealed a striking correlation. In active enzymes, this pK(a) value is always lower than the solution reference value while it is close to normal in inactive enzymes. These results thus support the hypothesis that the phenolate form of Tyr150 is responsible for the activation of the nucleophilic serine. The possible roles of Lys67 and Lys315 during catalysis are also discussed.

The screening of the open reading frames identified in the whole yeast genome has allowed us to discover 34 proteins belonging to the mitochondrial carrier family. By phylogenetic study, they can be divided into 27 subfamilies including ADP/ATP, phosphate and citrate carriers, putative oxoglutarate and GDC carriers and 22 new subfamilies. Topology predictions using the 'positive inside rule' approach have shown that the yeast carriers are similarly oriented with both extremities exposed to the cytosol. In each subfamily, a strict conservation of the charged residues in the six transmembrane alpha-helices is observed, suggesting a functional role for these residues and the existence of 27 functionally distinct carriers.

Dissociative adsorption of H2 on ZnO, apart from the bands due to OH and ZnH stretching vibrations, gives rise to bands at ca. 840 and 810 cm–1 which can be attributed to the bending modes of these surface structures. Analysis of the integrated intensities of the bands arising after H2 and HD adsorption at 100 and 300 K shows that both the 840 and 810 cm–1 bands are due to ZnOH group vibrations. Their shift after 18O isotope substitution of surface oxygen, only 1 and 2 cm–1, respectively, implies that they cannot be associated with the Zn—O vibration or its overtone enhanced by Fermi resonance. They should be attributed to two bending modes of surface hydroxyls. After HD and D2 adsorption a band for the OD bending vibration was detected at 637 cm–1. In accordance with these data, νOH(D)+δOH(D) combinations were observed at 4297 and 3195 cm–1, which give the values of 807 and 611 cm–1 for δOH and δOD, corresponding, apparently, to the more intense low-frequency component.