Weak exchange interaction supported by a biologically relevant long chemical bridge in a Cu-peptide model compound

Author(s)

Vieira‚ E.D. ; Casado‚ N.M.C. ; Facchin‚ G. ; Torre‚ M.H. ; Costa-Filho‚ A.J. ; Calvo‚ R.

• Document type: Journal article
• Source: Inorganic Chemistry; v. 45, n. 7, p. 2942-2947, 2006.

Abstract

The copper complex of the dipeptide L-alanyl-L-phenylalanine, catena-(L-alaninate-L-phenylalaninate-copper(II) monohydrate), identified as Cu(II)Ala-Phe, provides a convenient system to study a weak exchange interaction between unpaired spins transmitted through a biologically relevant long chemical bridge (18.34 angstrom). In this complex, the copper ions are arranged in two symmetry-related anisotropic layers parallel to the ab plane at 13.17 angstrom, separated by a double layer of water molecules. The equatorial-equatorial bridge considered as the most relevant path for exchange interactions between copper ions in neighbor layers contains I I diamagnetic atoms (including three hydrogens), with two covalent amidate bridges plus three weak and moderate H bonds that go across the water layer. This interaction was studied using electron paramagnetic resonance in single-crystal samples, at 9.5 and 34.5 GHz. The measured magnitude of the interlayer interaction, vertical bar J(3)vertical bar/k(B) = 1.7(2) x 10(-3) K, is discussed in terms of values obtained for similar paths in other model compounds and in proteins. These results in model systems provide information that may be important in understanding biological functions at the molecular level. (AU)

• FAPESP's process: 03/09859-2 - Electron paramagnetic resonance in structural studies of proteins, peptides, biomembranes, polymers, model molecules and their complexes with transition metals
• Grantee: Otaciro Rangel Nascimento
• Support Opportunities: PRONEX Research - Thematic Grants