Dianion-controlled supramolecular assembly of copper(II)-arginine complex ion

In order to clarify the self-organization and structure-determining factors in the [Cu(L- or D-Arg)(2)](2+) -containing systems (Arg = arginine), we s tudied the solution and crystal structures of [Cu(L-Arg)(2)](2+)-X2- system s, where X refers to dinegative tetrahedral anions, sulfate or 1,3-benzened isulfonate (m-bs(2-)), by electronic absorption, circular dichroism (CD), a nd ESR spectroscopic methods and X-ray structural analysis. The molecular s tructure of [Cu(L-Arg)(2)](SO4) exhibited a planar Cu(II) geometry with the two coordinated amino groups in the cis configuration due to the hydrogen bonds with SO42-, and the complex with X2- = m-bs(2-) assumed the trans con figuration without hydrogen bonds with m-bs(2-). The crystal structure of [ Cu(L-Arg)(2)](SO4) showed that the complex cations were bound with the anio ns to form a right-handed double-strand single-helical structure, whereas t hat of [Cu(L-Arg)(2)](m-bs(2-)) revealed that the complex ions were bound w ith each other through the guanidinium-coordinated carboxylate hydrogen bon ds to form a 3-dimensional layer structure with the m-bs(2-) ions connectin g the layers by hydrogen bonds. The D-Arg analog of the complex with isopht halate (m-pa(2-)) used in place of m-bs(2-), [Cu(D-Arg)(2)](m-pa(2-)), was shown to assume the cis configuration and form a left-handed double-helical structure. The configuration of the Cu(II) plane was predictable on the ba sis of the structural requirements for the hydrogen bonding with X2- Compar ison of the absorption spectra of [Cu(L-Arg)(2)](X) in the solid state and in aqueous solution indicated that the complexes in solution are more in th e cis configuration than in the trans. The CD spectra of the sulfate system exhibited a unique spectral behavior, which suggested formation of stronge r hydrogen bonds between coordinated amino groups and the sulfate ion. Fact ors determining the observed self-organized structures were comparatively d iscussed in connection with unique infinite right- or left-handed double-he lical structures of the [Cu(L- or D-Arg)(2)](2+) -X2- systems reported prev iously (N. Ohata, H. Masuda, and O. Yamauchi, Angew. Chem., Int. Ed. Engl. 35 (1996) 531). (C) 2000 Elsevier Science S.A. All rights reserved.