Cyclic tetra{5,15-di-[p(-methoxypolyethyleneoxy)phenyl]-10,20-[p-oxyphenyl] methylen porphyrin}, cy-[O-(H2-PTPEG2)-O-CH2-]4, a water soluble macromolecule consisting of four porphyrin units [each with two long -methoxypolyethyleneoxy (PEG) branches bound on its peripheral positions] linked by means of four methylenoxy bridges, was prepared by an interfacial etherification reaction. Structural and spectroscopic characterization of cy-[O-(H2-PTPEG2)-O-CH2-]4 and of its cobalt-derivative {cy-[O-(Co-PTPEG2)-O-CH2-]4} was performed by means of MALDI-TOF mass spectrometry, NMR, UVvis, and circular dichroism spectroscopy. The data obtained from the cy-[O-(Co-PTPEG2)-O-CH2-]4/Gramicidin-S mixture showed that some evident spectral changes were compatible with the formation of a supramolecular structure between the porphyrinic nanobox and the Gramicidin S (a polypeptide having a relevant pharmacological importance). These preliminary data highlight how cy-[O-(H2-PTPEG2)-O-CH2-]4 and/or its metalled derivatives, for their both chemical composition and structural arrangement, have promising properties for applications as a drug carrier in aqueous media. (c) 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013