Nanostructures DOI: 10.1002/ange.200604039 Hierarchical Self-Assembly in Solutions Containing Metal Ions, Ligand, and Diblock Copolymer** YunYan,*NicolaasA.M.Besseling,AriedeKeizer,AntoniusT.M.Marcelis,MarkusDrechsler, andMartienA.CohenStuart* Complex coacervate core micelles (C3Ms) are self-assembled nanoparticles formed by mixing aqueous solutions of a polyion- neutral diblock copolymer and an oppositely charged polyelectrolyte. [1] Before mixing, none of the con- stituent molecules are capable of forming self-assembled structures. It is only upon mixing that a driving force for micellization arises, namely, electrostatic interaction between the charged polymers. The micellar core, composed of an electrostatic complex, is stabilized against unbound growth by electroneutral segments of the diblock copolymer. These kinds of micelles have been denoted as “polyion complex micelles” (PIC micelles) by Harada and Kataoka, [2] or “block ionomer complexes” (BICs) by Kabanov et al. [3] Since the driving force for micellization is the tendency of the oppositely charged polyelectrolytes to form a complex coacervate phase, the term “complex coacervate core micelles” (C3Ms) was introduced by us. [1] Charged biomole- cules can also be used as homopolyelectrolytes to for C3Ms with diblock copolymer. In this way, C3Ms have great potential as nanoscale carriers for the delivery of charged compounds such as DNA and proteins. [4–6] Herein we address the question as to whether it is possible to fabricate self-assembled objects such as C3Ms with reversible supramolecular polymers, which are self-assembled chains themselves. Such chains are typically responsive: their chain length is not fixed but can adjust to variables such as temperature, concentration, etc. Water-soluble, charged supramolecular polymers indeed exist—namely, in the form of coordination polymers. The purpose of this study is to show that it is the responsiveness of these polymers which enables the formation of a new kind of hierarchical self-assembled nanostructures. In general, a coordination complex is formed by metal– ligand interaction; [7–9] chain formation becomes possible when an organic molecule having two such ligands is mixed with metal ions. Supramolecular polyelectrolytes based on coordination bonds have been reported, but most of them are either not water soluble [10–13] or they carry only a few charges per unit length of chain. [13–15] Also, many metal/ligand combinations form rather long-lived, nearly permanent bonds. [16] However, the metal–bisligand system developed by Vermonden et al. [8,9] is water soluble, has high charge density, and responds quickly to changes in concentration and composition, as expected for a truly reversible system. The diblock copolymer used in the current study is poly(2- vinyl-N-methylpyridinium iodide)-b-poly(ethylene oxide) (PMVP 41 -b-PEO 205 ) (Scheme 1a), which is obtained by quaternization of poly(2-vinylpyridine)-b-poly(ethylene oxide) (PVP 41 -b-PEO 205 ). The supramolecular coordination polymer which Vermonden etal. used was prepared by mixing equimolar amounts of zinc nitrate and a bisligand compound based on pyridine-2,6-dicarboxylic acid groups connected at the 4-position of the pyridine ring by four ethylene oxide spacers (L 2 EO 4 , Scheme 1b) [8] (where the Scheme 1. Structure of a) PMVP 41 -b-PEO 205 diblock copolymer, b)L 2 EO 4 , and c) illustration of the formation of a Zn-L 2 EO 4 (1:1) coordination polymer. [*] Dr. Y. Yan, Dr. N. A. M. Besseling, Dr. A. de Keizer, Prof. Dr. M. A. Cohen Stuart Laboratory of Physical Chemistry and Colloid Science Wageningen University Dreijenplein 6, 6703 HB Wageningen (The Netherlands) Fax: (+ 31)317-483-777 E-mail: yun.yan@wur.nl martien.cohenstuart@wur.nl Dr. A. T. M. Marcelis Laboratory of Organic Chemistry, Wageningen University Dreijenplein 8, 6703 HB Wageningen (The Netherlands) Dr. M. Drechsler Makromolekulare Chemie II, Universität Bayreuth 95440 Bayreuth (Germany) [**] We thank Prof. Y. Talmon of the Technion-Israel Institute of Technology (Israel) and Prof. H. Hoffmann of the University Bayreuth (Germany) for discussions on the cryo-TEM image. Financial support from the EU POLYAMPHI/Marie Curie program (RT6-2002, proposal 505027) and SONS Eurocores program (Project JA016-SONS-AMPHI) is acknowledged. M.D. gratefully acknowledges financial support from the Deutsche Forschungsge- meinschaft (SFB 481). Supporting information for this article is available on the WWW under http://www.angewandte.org or from the author. Angewandte Chemie 1839 Angew. Chem. 2007, 119, 1839–1841 # 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim