1,721,010 research outputs found
Reactivity of vinyl sulphonic esters: the solvolytic behaviour of B-aryloxyvinyl sulphonates
No full text
Kinetic Amplification of the Enantioselective Cleavage of Ą-Amino Acid Esters by Metallomicelles
No full textSelf-Assembling in Surfactant Aggregates: an Alternative Way to the Realization of Fluorescent Chemosensors for Cu(II) Ions
No full textMimicking enzymes: Cooperation between organic functional groups and metal ions in the cleavage of phosphate diesters
No full textA series of ligands derived from the bis-2-pyridinylmethylamine structure, which bear either additional hydroxyl or aromatic amino groups, were prepared and their Zn-II complexes were studied as catalysts for the cleavage of bis-p-nitrophenyl phosphate (BNP) and 2-hydroxypropyl-p-nitrophenyl phosphate (HPNP) diesters. A comparative kinetic study indicated that the insertion of organic groups, capable of acting as nucleophiles or as hydrogen-bond donors, substantially increases the hydrolytic activity of the metal complex. Dissection of the effects of the individual groups revealed that the increase in reactivity can reach up to three orders of magnitude. The improved efficiency of the systems studied, combined with the benefits resulting from the low pK(a) value of the active nucleophile, result in an acceleration of the BNP cleavage at pH 7 of six orders of magnitude. The pH-dependent reactivity profiles follow a bell-shaped curve and the maximum reactivity is observed at pH 9. The mechanism of the reactions and the structure of the complexes were investigated in detail by means of kinetic analysis, NMR spectroscopy experiments, and theoretical calculations. The reactivity of the complexes that cleave HPNP closely resembles the reactivity observed for BNP, but the accelerations achieved are lower as a result of different reaction mechanisms
A Mechanistic Study on Alcohol Oxidations with Oxygen Catalysed by TPAP-Doped Ormosils in Supercritical Carbon Dioxide
No full text
Dinuclear Metal Complexes Based on all cis 2,4,6-triamino-1,3,5-trihydroxycyclohexane as Catalysts of Phosphate Esters Cleavage
No full textTwo dimetallic ligands 2 and 3 for transition metal ions were obtained by connecting two all-cis- 2,4,6-triamino-cyclohexane-1,3,5-triol (TACI, 1) subunits via 1,3- or 1,4-xylyl linkers. Their dimetallic Cu-II and Zn-II complexes were investigated as catalysts for the cleavage of the phosphate diesters 2,4-dinitrophenyl ethyl phosphate (DNPEP) and 2-hydroxypropyl p-nitrophenyl phosphate (HPNP) and the triester 2,4-dinitrophenyl diethyl phosphate (DNPDEP). The results of a comparative kinetic study using the monometallic complexes of TACI as a reference indicate that the Cu-II complexes of 2 and 3 are virtually inert; this finding is ascribed to the formation of intra-complex p-hydroxo bridges that prevent the required interactions with the substrate. On the other hand, the dimetallic Zn-II complexes produce remarkable accelerations, particularly in the case of the HPNP transesterification. The dimetallic systems are more efficient than the TACI.Zn-II complex in promoting the hydrolysis of HPNP at pH values close to neutrality (7.0-7.8). In this case, the effects of cooperativity between the two metal centers were highlighted in a detailed kinetic study; the catalytic efficiency seems to be related to the stronger binding of the substrate to the dimetallic Zn-II complexes. Additionally, in this case, although to a much lesser extent than in the case of the Cu-II counterparts, the formation of p-hydroxo bridges apparently hampers the catalytic efficiency, as indicated also by the observation that the activity of the dimetallic complexes increases as the distance between the two metal centers increases, which, thus, thwarts the formation of intermetallic bridges
- …
