Premium
Dinuclear Titanium( IV ) Complexes from Amino Acid Bridged Dicatechol Ligands: Formation, Structure, and Conformational Analysis
Author(s) -
Albrecht Markus,
Napp Matthias,
Schneider Matthias,
Weis Patrick,
Fröhlich Roland
Publication year - 2001
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20010917)7:18<3966::aid-chem3966>3.0.co;2-z
Subject(s) - stereochemistry , chemistry , ligand (biochemistry) , amino acid , crystallography , helix (gastropod) , chirality (physics) , residue (chemistry) , peptide , chiral symmetry , receptor , biochemistry , physics , biology , ecology , quantum mechanics , snail , nambu–jona lasinio model , quark
Amino acid bridged dicatechol ligands 3 a–e ‐H 4 form dinuclear double‐stranded coordination compounds [( 3 a–e ) 2 Ti 2 (OCH 3 ) 2 ] 2− with titanium( IV ) ions. Due to the directionality of the ligands, the chirality of the strand, and the chiral complex units, up to seven isomers, I–VII , can be obtained for the double‐stranded complexes of ligands 3 a–e ‐H 4 . The composition of the mixture of isomeric compounds in solution is strongly dependent on the conditions of complex formation. Under thermodynamic control, only a few isomers are obtained, one of which is the major component of the mixture. X‐ray structure analyses were performed for K 2 [( 3 b ) 2 Ti 2 (OH) 2 ] and K 2 [( 3 d ) 2 Ti 2 (OH) 2 ] (type I ), and for the meso complex Na 2 [( 3 e )( 3 e′ )Ti 2 (OCH 3 ) 2 ]. A conformational analysis that uses Ramachandrans method revealed that the conformation of the amino acids in the ligand strands can be compared with those found for amino acids in helical peptide structures. The most favored isomer of [( 3 ) 2 Ti 2 (OCH 3 ) 2 ] 2− appears to be of type I , with the catecholamide unit located at the N terminus of the ligand strand that binds to a Λ ‐configurated titanium( IV ) complex unit and the dihydroxybenzyl group at the C terminus that coordinates to a Δ ‐configurated titanium( IV ) complex unit. The Λ configuration at the N terminus induces the conformation of a right‐handed helix in the amino acid residue, while the Δ configuration induces the less favored left‐handed helix.