Unsymmetrical Metallosupramolecular Polycondensation of Expanded L-Amino Acid Containing Platinum(II) Complex in Nonpolar Solvents

The construction of a well-designed three-dimensional structure is promising for the development of artificial enzymes with outstanding functions. A combination of chiral polypeptides and metallosupramolecular polymers is a promising candidate for this purpose. An expanded L-amino acid containing platinum(II) complex was designed and unsymmetrically polymerized via metallosupramolecular polycondensation in nonpolar solvents. The resulting expanded polypeptide was analyzed through 1H NMR spectroscopy, circular dichroism (CD), and theoretical calculations accompanied by X-ray analysis of a model compound and elementary reactions. The molar mass of the polymer was estimated through end-group analysis and 1H diffusion-ordered NMR spectroscopy (DOSY). The DOSY spectra demonstrate that at least 17-mer is present in chloroform. The CD spectra reflect the local structure of the monomer unit and suggest the presence of two conformers in a dynamic equilibrium. The entire structure of the polymer is considered to be a fluctuating mixture of chiral helices. The synthetic procedure in this study will be applied to construct chiral molecular architectures leading functional polymer materials.