Self-Assembly of Discrete Metal Complexes in Aqueous Solution via Block Copolypeptide Amphiphiles

Abstract

The integration of discrete metal complexes has been attracting significant interest due to the potential of these materials for soft metal-metal interactions and supramolecular assembly. Additionally, block copolypeptide amphiphiles have been investigated concerning their capacity for self-assembly into structures such as nanoparticles, nanosheets and nanofibers. In this study, we combined these two concepts by investigating the self-assembly of discrete metal complexes in aqueous solution using block copolypeptides. Normally, discrete metal complexes such as [Au(CN)2]−, when molecularly dispersed in water, cannot interact with one another. Our results demonstrated, however, that the addition of block copolypeptide amphiphiles such as K183L19 to [Au(CN)2]− solutions induced one-dimensional integration of the discrete metal complex, resulting in photoluminescence originating from multinuclear complexes with metal-metal interactions. Transmission electron microscopy (TEM) showed a fibrous nanostructure with lengths and widths of approximately 100 and 20 nm, respectively, which grew to form advanced nanoarchitectures, including those resembling the weave patterns of Waraji (traditional Japanese straw sandals). This concept of combining block copolypeptide amphiphiles with discrete coordination compounds allows the design of flexible and functional supramolecular coordination systems in water.

Self‐assembly of Soluble Nanoarchitecture using Hybrids of Diblock Copolypeptide Amphiphiles with Copper Rubeanate Hydrates in Water and Their Electrooxidation Reaction

“…In our previous work, diblock copolypeptide amphiphiles were found to form hybrid structures with metal complexes via a flexible self‐assembling process in water. These supramolecular hybrids exhibited specific and hierarchical nanostructures such as nanowires, nanoeclipses, nanosquares, nanorectangles [22–24] . In addition, it was found that these nanostructures exhibited reverse spin transitions, photoluminescence, and lower‐critical‐solution‐temperature (LCST)‐type transitions with spin crossover phenomena, which had not been previously observed in the solid state or in crystals [23,34] .…”

“…Diblock polypeptide amphiphiles 1–6 (Figure 1) were synthesized using previously published living polymerization methods [22–24] (see the Supporting Information for details, and Table S1). The polypeptide segment chain lengths were chosen to enhance the solubility of these compounds in water, and also to enhance the packing of the polypeptides into supramolecular assemblies, which would result in the formation of nanostructures.…”

“…In contrast, assemblies of diblock copolypeptide amphiphiles are suitable for integration with organic molecules, tissues, cells and proteins, depending on balance between hydrophilic and hydrophobic polypeptide segments and without an artificial moiety such as alkyl chain. These copolypeptide structures can be used to tune not only inorganic materials but also coordination compounds [22–24] . The inherent functional self‐assembling abilities of these copolypeptide amphiphiles could potentially lead to their application as structural templates for inorganic compounds as well as for the intelligent transformation of such coordination compounds involving dynamic tuning of the electronic states of these materials.…”

Helical-Ribbon and Tape Formation of Lipid Packaged [Ru(bpy)3]2+ Complexes in Organic Media

“…Moreover, the assembly of metal complexes has been suggested as a basis for forming molecular device system such as biodiagnostics, photovoltaics, and organic light-emitting diodes [18,19]. Ideally, the characteristics of such systems would be tunable by controlling the spatial arrangement of the metal complexes, resulting in optical interaction among metal complexes with linkage of weakly non-covalent interaction such as hypochromic effect [20], aromatic interaction [21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37], metallophilic interaction [38,39,40,41,42,43,44,45,46,47,48], and so on.…”

Supramolecular control of reverse spin transitions in cobalt(ii) terpyridine complexes with diblock copolypeptide amphiphiles

“…In our previous research, we developed an alternative approach to the design of metal complexes by compounding diblock copolypeptide amphiphiles, resulting in metal-metal interactions that generated photoluminescence in water. 21 Various diblock copolypeptide amphiphiles with metal cyanide complexes were found to exhibit unique morphologies, such as the formation of an elliptical shape with a woven pattern based on the alignment of the metal complexes. This technique of combining amphiphilic molecules with discrete coordination compounds makes it possible to design flexible, reversible and signal-responsive supramolecular coordination systems.…”