title: Isomerism of [64Cu-NOTA-Bn]-labeled radiotracers: separation of two complex isomers and determination of their interconversion energy barrier using ion pair chromatography.
abstract: The model complex [(64)Cu((S)-p-NH(2)-Bn-NOTA)](-) ([(64)Cu]1) was used to study the isomerism of [(64)Cu-NOTA-Bn]-labeled radiotracers. Two complex isomers [(64)Cu]1a and [(64)Cu]1b, which were formed at a ratio of 1:9 during the complexation of [(64)Cu]Cu(2+) with (S)-p-NH(2)-Bn-NOTA, were separated using ion pair chromatography. To study the interconversion, the nonradioactive complex isomers Cu1a and Cu1b were separated and thermally treated at 90 °C in both ammonium acetate solution and deionized water. A faster interconversion rate was observed for both isomers with lower concentrations of ammonium ions. At the end of reaction, the thermodynamic Cu1a to Cu1b equilibrium ratio was 6:94. The particular energy barriers of the interconversion for Cu1a and Cu1b were 130 kJ mol(-1) and 140 kJ mol(-1). Spectrophotometric measurements with Cu1a and Cu1b revealed two isomers adopting different geometrical configurations.
authors.affiliation: Turku PET Centre, University of Turku, Kiinamyllynkatu 4-8, 20520 Turku, Finland. schlesin@gmx.de
authors.forename: Joern
authors.initials: J
authors.lastname: Schlesinger
authors.forename: Johan
authors.initials: J
authors.lastname: Rajander
authors.forename: Janne A
authors.initials: JA
authors.lastname: Ihalainen
authors.forename: Dinesh
authors.initials: D
authors.lastname: Ramesh
authors.forename: Patrik
authors.initials: P
authors.lastname: Eklund
authors.forename: Veronica
authors.initials: V
authors.lastname: Fagerholm
authors.forename: Pirjo
authors.initials: P
authors.lastname: Nuutila
authors.forename: Olof
authors.initials: O
authors.lastname: Solin
mesh_terms: D000085:Acetates / Q000737:chemistry; D005591:Chemical Fractionation; D002845:Chromatography; D056831:Coordination Complexes / Q000737:chemistry* / Q000378:metabolism; D003300:Copper / Q000378:metabolism*; D004355:Drug Stability; D006571:Heterocyclic Compounds / Q000737:chemistry* / Q000378:metabolism; D006573:Heterocyclic Compounds, 1-Ring; D006863:Hydrogen-Ion Concentration; D007536:Isomerism; D008968:Molecular Conformation; D049268:Positron-Emission Tomography; D011849:Radioactive Tracers; D012996:Solutions / Q000737:chemistry; D013696:Temperature; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
chemical_list: D000085:Acetates; D056831:Coordination Complexes; D006571:Heterocyclic Compounds; D006573:Heterocyclic Compounds, 1-Ring; D011849:Radioactive Tracers; D012996:Solutions; D014867:Water; C048993:1,4,7-triazacyclononane-N,N',N''-triacetic acid; D003300:Copper; C018824:ammonium acetate