Zn(II) binding by the dipyridine-containing macrocycles L1-L3 has been analyzed by means of potentiometric measurements in aqueous solutions. These ligands contain one (L1, L2) or two (L3) 2,2'-dipyridine units as an integral part of a polyamine macrocyclic framework having different dimensions and numbers of nitrogen donors. Depending on the number of donors, L1-L3 can form stable mono- and/or dinuclear Zn(II) complexes in a wide pH range. Facile deprotonation of Zn(II)-coordinated water molecules gives mono- and dihydroxo-complexes from neutral to alkaline pH values. The ability of these complexes as nucleophilic agents in hydrolytic processes has been tested by using bis(p-nitrophenyl) phosphate (BNPP) as a substrate. In the dinuclear complexes the two metals play a cooperative role in BNPP cleavage. In the case of the L2 dinuclear complex [Zn2L2(OH)2]2+, the two metals act cooperatively through a hydrolytic process involving a bridging interaction of the substrate with the two Zn(II) ions and a simultaneous nucleophilic attack of a Zn-OH function at phosphorus; in the case of the dizinc complex with the largest macrocycle L3, only the monohydroxo complex [Zn2L3(OH)]3+ promotes BNPP hydrolysis. BNPP interacts with a single metal, while the hydroxide anion may operate a nucleophilic attack. Both complexes display high rate enhancements in BNPP cleavage with respect to previously reported dizinc complexes, due to hydrophobic and pi-stacking interactions between the nitrophenyl groups of BNPP and the dipyridine units of the complexes.

Zn(II) Coordination to Polyamine Macrocycles Containing Dipyridine Units. New Insights into the Activity of Dinuclear Zn(II) Complexes in Phosphate Ester Hydrolysis / C. BAZZICALUPI; A.BENCINI; E.BERNI; A.BIANCHI; P.FORNASARI; C.GIORGI; B.VALTANCOLI. - In: INORGANIC CHEMISTRY. - ISSN 0020-1669. - STAMPA. - 43:(2004), pp. 6255-6265. [10.1021/ic049754v]

Zn(II) Coordination to Polyamine Macrocycles Containing Dipyridine Units. New Insights into the Activity of Dinuclear Zn(II) Complexes in Phosphate Ester Hydrolysis

BAZZICALUPI, CARLA;BENCINI, ANDREA;BIANCHI, ANTONIO;GIORGI, CLAUDIA;VALTANCOLI, BARBARA
2004

Abstract

Zn(II) binding by the dipyridine-containing macrocycles L1-L3 has been analyzed by means of potentiometric measurements in aqueous solutions. These ligands contain one (L1, L2) or two (L3) 2,2'-dipyridine units as an integral part of a polyamine macrocyclic framework having different dimensions and numbers of nitrogen donors. Depending on the number of donors, L1-L3 can form stable mono- and/or dinuclear Zn(II) complexes in a wide pH range. Facile deprotonation of Zn(II)-coordinated water molecules gives mono- and dihydroxo-complexes from neutral to alkaline pH values. The ability of these complexes as nucleophilic agents in hydrolytic processes has been tested by using bis(p-nitrophenyl) phosphate (BNPP) as a substrate. In the dinuclear complexes the two metals play a cooperative role in BNPP cleavage. In the case of the L2 dinuclear complex [Zn2L2(OH)2]2+, the two metals act cooperatively through a hydrolytic process involving a bridging interaction of the substrate with the two Zn(II) ions and a simultaneous nucleophilic attack of a Zn-OH function at phosphorus; in the case of the dizinc complex with the largest macrocycle L3, only the monohydroxo complex [Zn2L3(OH)]3+ promotes BNPP hydrolysis. BNPP interacts with a single metal, while the hydroxide anion may operate a nucleophilic attack. Both complexes display high rate enhancements in BNPP cleavage with respect to previously reported dizinc complexes, due to hydrophobic and pi-stacking interactions between the nitrophenyl groups of BNPP and the dipyridine units of the complexes.
2004
43
6255
6265
C. BAZZICALUPI; A.BENCINI; E.BERNI; A.BIANCHI; P.FORNASARI; C.GIORGI; B.VALTANCOLI
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Utilizza questo identificatore per citare o creare un link a questa risorsa: https://hdl.handle.net/2158/250852
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