Miriam Simon

Toward Bioderived Intelligent Nanocarriers for Controlled Pollutant Recovery and pH-Sensitive Binding

The pH-triggered formation of supramolecular complexes between the cationic biopolysaccharide chitosan and an environmentally friendly anionic surfactant is exploited for the formulation of selective and controlled-recovery systems. A strong advantage of this system is the very small pH range in which the binding/release process takes place. Because of this high pH responsiveness, chitosan-surfactant complexes are employed for the sequestration of various compounds by binding or releasing them from the complexes. In particular, the selective recovery of a model hydrophobic pollutant in the presence of a hydrophilic one is presented. The process is highly selective and effective, with more than 90% of the hydrophobic dye and ca. 10% of the hydrophilic dye recovered. Furthermore, the method can be extended to the selective recovery of metal ions, and in both cases, the original surfactant and chitosan mixture can be recovered, thereby rendering this an efficient and sustainable process. These showcase experiments depict quite different scenarios in which pH-responsive fully biodegradable polysaccharide-surfactant complexes can be employed and may substitute synthetic products in various fields, e.g., wastewater treatment, cosmetics, and agriculture, thereby yielding environmentally improved approaches.

Structure and dynamics of polyelectrolyte surfactant mixtures under conditions of surfactant excess

Oppositely charged polyelectrolyte (PE) surfactant mixtures can self-assemble into a large variety of mesoscopic structures, so-called polyelectrolyte surfactant complexes (PESCs). These structures directly affect the macroscopic behavior of such solutions. In this study, we investigated mixtures of the cationically charged PE JR 400 and the anionic surfactant SDS with the help of different neutron scattering and fluorescence methods. While an excess of PE charges in semi-dilute solutions causes an increase of viscosity, it has been observed that an excess of surfactant charges reduces the viscosity while precipitation is observed at charge equilibrium. The increase in viscosity had been investigated before and was attributed to the formation of cross links between PE chains. In this publication we focus our attention on the reduction of viscosity which is observed with an excess of surfactant charges. It is found that the PE chains form relatively large and densely packed clusters near the phase boundary on the surfactant rich side, thereby occupying less space and reducing the viscosity. For even higher surfactant concentrations, individual surfactant decorated PE chains are observed and their viscosity is found to be similar to that of the pure PE.

Structural control of polyelectrolyte/microemulsion droplet complexes (PEMECs) with different polyacrylates

Polyelectrolyte/microemulsion complexes (PEMECs) are very versatile hybrid systems, combining high loading capacities of microemulsions with larger-scale structuring induced by polyelectrolytes.

Catenation and Aggregation of Multi-Cavity Coordination Cages

A series of metal-mediated cages, having multiple cavities, was synthesized from PdII cations and tris- or tetrakis-monodentate bridging ligands and characterized by NMR spectroscopy, mass spectrometry, and X-ray methods. The peanut-shaped [Pd3 L1 4 ] cage deriving from the tris-monodentate ligand L1 could be quantitatively converted into its interpenetrated [5Cl@Pd6 L1 8 ] dimer featuring a linear {[Pd-Cl-]5 Pd} stack as an unprecedented structural motif upon addition of chloride anions. Small-angle neutron scattering (SANS) experiments showed that the cigar-shaped assembly with a length of 3.7u2005nm aggregates into mono-layered discs of 14u2005nm diameter via solvophobic interactions between the hexyl sidechains. The hepta-cationic [5Cl@Pd6 L1 8 ] cage was found to interact with polyanionic oligonucleotide double-strands under dissolution of the aggregates in water, rendering the compound class interesting for applications based on non-covalent DNA binding.