Title
Exploring the boundaries of direct detection and characterization of labile isomers – a case study of copper(II)-dipeptide systems
Author
Eszter N Toth, Nora V Nagy, Antal Rockenbauer, Gábor Peintler, Bela Gyurcsik
Year
2017
Journal
Dalton Transactions
Abstract
The investigation of the linkage isomers of biologically essential and kinetically labile metal complexes in aqueous solutions poses a challenge, as these microspecies cannot be separately studied. Therefore, derivatives are commonly used to initially determine the stability or spectral characteristics of at least one of the isomers. Here we directly detect the isomers, describe the metal ion coordination sphere, speciation and thermodynamic parameters by synergistic application of temperature dependent EPR and CD spectroscopic measurements in copper(II)–dipeptide systems including His-Gly and His-Ala ligands. The ∆H = (–23 +-4) kJ/mol value of the standard enthalpy change corresponding to the peptide-type to histamine-type isomerisation equilibrium of the [CuL]+ complex was corroborated by several techniques. The preferential coordination of the side-chains was observed at lower temperatures, whereas, metal-binding of the backbone atoms became favourable upon increasing temperature. This study exemplifies the necessity of using temperature dependent multiple methodology for reliable description of similar systems for upstream applications.
Instrument
J-815
Keywords
Circular dichroism, Coordination chemistry, Thermal stability, Thermodynamics