Reversible Self-Assembly of Gold Nanoparticles Based on Co-Functionalization with Zwitterionic and Cationic Binding Motifs*.

We report a pH- and temperature-controlled reversible self-assembly of Au-nanoparticles (AuNPs) in water, based on their surface modification with cationic guanidiniocarbonyl pyrrole (GCP) and zwitterionic guanidiniocarbonyl pyrrole carboxylate (GCPZ) binding motifs. When both binding motifs are installed in a carefully balanced ratio, the resulting functionalized AuNPs self-assemble at pH 1, pH 7 and pH 13, whereas they disassemble at pH 3 and pH 11. Further disassembly can be achieved at elevated temperatures at pH 1 and pH 13. Thus, we were able to prepare functionalized nanoparticles that can be assembled/disassembled in seven alternating regimes, simply controlled by pH and temperature.

Supramolecular polymers with reversed viscosity/temperature profile for application in motor oils.

We report novel supramolecular polymers, which possess a reversed viscosity/temperature profile. To this end, we developed a series of ditopic monomers featuring two self-complementary binding sites, either the guanidiniocarbonyl pyrrole carboxylic acid (GCP) or the aminopyridine carbonyl pyrrole carboxylic acid (ACP). At low temperatures, small cyclic structures are formed. However, at elevated temperatures, a ring-chain transformation leads to the formation of a supramolecular polymer. We demonstrate that this effect is dependent on the concentration of the solution and on the polarity of the solvent. This effect can counteract the loss of viscosity of the solvent at elevated temperatures, thus opening an application of our systems as viscosity index improvers (VIIs) in working fluids. This was tested for different motor oils and led to the identification of one compound as a promising VII.

Dual pH-Induced Reversible Self-Assembly of Gold Nanoparticles by Surface Functionalization with Zwitterionic Ligands.

The dual pH-induced reversible self-assembly (PIRSA) of Au-nanoparticles (Au NPs) is reported, based on their decoration with the self-complementary guanidiniocarbonyl pyrrole carboxylate zwitterion (GCPZ). The assembly of such functionalized Au NPs is found at neutral pH, based on supramolecular pairing of the GCPZ groups. The resulting self-assembled system can be switched back to the disassembled state by addition of base or acid. Two predominant effects that contribute to the dual-PIRSA of Au NPs are identified, namely the ionic hydrogen bonding between the GCPZ groups, but also a strong hydrophobic effect. The contribution of each interaction is depending on the concentration of GCPZ on NPs, which allows to control the self-assembly state over a wide range of different water/solvent ratios.

A stimuli responsive two component supramolecular hydrogelator with aggregation-induced emission properties.

In this contribution we describe a novel hydrogelator based on four guadiniumcarbonylpyrrole units in combination with aggregation-induced emission active aromatic thioethers which undergo self-assembly into fibrills in aqueous media as visible in AFM and TEM measurements. These fibrills are weakly luminescent and unable to induce gelation. Upon addition of malonic acid a cross-linking of the single fibres was detected leading to the formation of a highly emissive stable hydrogel. This gel responds to several external stimuli such as heat, shaking as well as pH changes.

Formation of Twisted ß-Sheet Tapes from a Self-Complementary Peptide Based on Novel Pillararene-GCP Host-Guest Interaction with Gene Transfection Properties.

Small peptides capable of assembling into well-defined nanostructures have attracted extensive attention due to their interesting applications as biomaterials. This work reports the first example of a pillararene functionalized with a guanidiniocarbonyl pyrrole (GCP)-conjugated short peptide segment. The obtained amphiphilic peptide 1 spontaneously self-assembles into a supramolecular ß-sheet in aqueous solution based on host-guest interaction between pillararene and GCP unit as well as hydrogen-bonding between the peptide strands. Interestingly, peptide 1 at low concentration shows transitions from small particles to "pearl necklace" assemblies, and finally to branched fibers in a time-dependent process. At higher concentration, it directly assembles into twisted ß-sheet tapes. Notably, without pillararene moiety, the control peptide A forms α-helix structure with morphology changing from particles to bamboo-like assemblies depending on concentration, indicating a significant role of the pillararene-GCP host-guest interaction for the secondary structure formation. Moreover, peptide 1 can serve as an efficient gene transfection vector.