Premium
Bimetallic Complexes of Spiro‐Azacrown Ligands as Catalysts of Phosphoester and Phosphoric Anhydride Cleavage
Author(s) -
Wang Qi,
Mikkola Satu,
Lönnberg Harri
Publication year - 2004
Publication title -
chemistry and biodiversity
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.427
H-Index - 70
eISSN - 1612-1880
pISSN - 1612-1872
DOI - 10.1002/cbdv.200490094
Subject(s) - phosphodiester bond , chemistry , bimetallic strip , catalysis , cleavage (geology) , polymer chemistry , organic chemistry , medicinal chemistry , stereochemistry , biochemistry , rna , geotechnical engineering , fracture (geology) , engineering , gene
The ability of bimetallic homo‐ and heteronuclear complexes of two spiro‐linked ligands, viz. a biazacrown ( i.e. , 2,6,10,14,18,22‐hexaazaspiro[11.11]tricosane ( 1 )) and an azacrowncrown ether ( i.e. , 14,17,20,23,26‐pentaoxa‐2,6,10‐triaza‐spiro[11.15]heptacosane ( 2 )), to promote the cleavage of the phosphoester linkage of dinucleoside 3′,5′‐phosphates and the phosphoric anhydride bridge of dinucleoside 5′,5′‐triphosphates was studied. In both reactions, the bimetallic homonuclear Cu 2+ and Zn 2+ complexes were better catalysts than their monometallic counterparts. The acceleration was two‐ to five‐fold with the phosphoester cleavage and 3‐ to 20‐fold with the phosphoric anhydride cleavage. Interestingly, the most‐efficient catalyst of the phosphoester cleavage was the heterodinuclear Ni 2+ ,Zn 2+ complex of 1 , the catalytic activity of which was up to 5‐ and 100‐fold that of the homodinuclear Zn 2+ and Ni 2+ complexes, respectively. Moreover, this cooperative acceleration was observed to depend on the identity of the 5′‐linked nucleoside: 3′,5′‐UpU and 3′,5′‐ApU were cleaved much faster than 3′,5′‐UpA, and no cooperative acceleration was observed with 3′,5′‐ApA. The reaction was second‐order in hydroxide ion concentration, suggesting that a double deprotonation took place on going from the initial to the transition state. Evidently, in addition to deprotonation of the attacking 2′‐OH group, N(3)H of the 5′‐linked uridine was displaced by one of the metal ions of the cleaving agent. With the phosphoric anhydride cleavage, no similar cooperativity of two different metal ions was observed, but the greatest rate‐acceleration was achieved with the homodinuclear Cu 2+ complexes.