Structural and NMR investigations of the ternary adducts of twenty alpha-amino acids and selected dipeptides with a chiral, diaqua-ytterbium complex.
A detailed investigation of the nature of the binding of each of the 20 common alpha-amino acids and various selected dipeptides to a chiral, diaqua-ytterbium complex in aqueous solution has been carried out. Analysis of the dipolar 1H NMR paramagnetic shifts suggests that the alpha-amino acids form a common chelated structure within a nine-coordinate mono-capped square antiprismatic coordination environment, with the amine N axially disposed. Crystal structures of nine chelated YbL1-amino acid adducts (Gly, Ala, Ser, Thr, Met) confirm this. The ternary complexes with dipeptides (e.g. Gly-Ala, Gly-Ser, Gly-Met, Gly-Asp, Gly-Asn, Gly-His, Ser-Met, Asp-Phe, His-Gly) also favour the terminal amine as the axial donor with the proximate amide group binding to generate a five-ring chelate. Evidence for chelation through side-chain functionality was found only in the case of N-terminal Asp. The chiral environment about the ytterbium ion upon amino acid binding has also been probed using near-IR circular dichroism spectroscopy.
Dickins
Rachel S
RS
Department of Chemistry, University of Durham, South Road, Durham, UKDH1 3LE. r.s.dickins@durham.ac.uk
Batsanov
Andrei S
AS
Howard
Judith A K
JA
Parker
David
D
Puschmann
Horst
H
Salamano
Stefania
S
D000596:Amino Acids / Q000737:chemistry*; D002942:Circular Dichroism; D004151:Dipeptides / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D015394:Molecular Structure; D013237:Stereoisomerism; D015018:Ytterbium / Q000737:chemistry*
D000596:Amino Acids; D004151:Dipeptides; D015018:Ytterbium