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Impact of ring size on the copper(II) coordination abilities of cyclic tetrapeptides |
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| Authors: | Justyna Brasuń Agnieszka Matera-Witkiewicz Alessandro Pratesi Luigi Messori |
| Institution: | a Department of Inorganic Chemistry, Wroc?aw Medical University, Szewska 38, 50-139 Wroc?aw, Poland b Laboratory of Biopolymer Structure, Intercollegiate Faculty of Biotechnology, Medical University of Gdańsk, K?adki 24, 80-822 Gdańsk, Poland c Laboratory of Peptides and Proteins Chemistry and Biology, Department of Organic Chemistry “Ugo Schiff”, University of Florence, Via della Lastruccia 3, 50019 Sesto Fiorentino, Firenze, Italy d Laboratory of Metals in Medicine (METMED), Department of Chemistry, University of Florence, Via della Lastruccia 3, 50019 Sesto Fiorentino, Firenze, Italy |
| Abstract: | A new, 14-membered, tetraza cyclic tetrapeptide containing histidine and lysine side-chains, c(β3homoLysdHisβ-AlaHis), was designed, synthesized and characterized; its copper(II) binding properties were investigated in dependence of pH by potentiometric and spectroscopic methods. In line with previous studies of similar systems, the progressive involvement of amide nitrogens in copper(II) coordination was evidenced for pH values greater than 6. At physiological pH the dominant species consists of a copper(II) center coordinated by two amide nitrogens, an imidazole nitrogen and a water molecule. In contrast, at pH values higher than 8.7, a copper(II) coordination environment consisting of four amide nitrogens in the equatorial plane and the axial imidazole ligands is formed as clearly indicated by spectroscopic data and theoretical calculations. The behavior of this 14-membered cyclic tetrapeptide is compared to that of its 12-membered cyclic analog, particular attention being paid to the effects of ring size on the respective copper(II) binding abilities. |
| Keywords: | Cu complexes Cyclopeptide Stability constants |
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