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The combination of nanomaterials as solid supports and supramolecular concepts has led to the development of hybrid materials with improved functionalities. These hetero-supramolecular ideas provide a means of bridging the gap between molecular chemistry, materials sciences, and nanotechnology. In recent years, relevant examples have been reported on functional aspects, such as enhanced recognition and sensing by using molecules on preorganized surfaces, the reversible building of nanometer-sized networks and 3D architectures, as well as biomimetic and gated chemistry in hybrid nanomaterials for the development of advanced functional protocols in three-dimensional frameworks. This approach allows the fine-tuning of the properties of nanomaterials and offers new perspectives for the application of supramolecular concepts.
We conceptualize a novel approach towards enzyme assays based on the reversible and competitive binding of a fluorescent dye and the substrate as well as product of an enzymatic reaction to a macrocyclic host. This method was termed 'supramolecular tandem assay', and has been applied to inhibitor and activator screening, sensor array development, and enantiomeric excess determination of amino acids. The simple and rapid read-out by fluorescence allows their straightforward implementation into high-throughput screening.
A set of strained aromatic macrocycles based on [n]cyclo2,7-(4,5,9,10-tetrahydro)pyrenylenes is presented with size dependent photophysical properties. The K-region of pyrene was functionalized with ethylene glycol groups to decorate the outer rim and thereby confine the space inside the macrocycle. This confined space is especially pronounced for n = 5, which leads to an internal binding of up to 8.0×104 M–1 between the ether-decorated [5]cyclo-2,7-pyrenylene and shape complementary crown ether–cation complexes.
Both, the ether-decorated [n]cyclo-pyrenylenes as well as one of their host–guest complexes have been structurally characterized by single crystal X-ray analysis. In combination with computational methods the structural and thermodynamic reasons for the exceptionally strong binding have been elucidated. The presented rim confinement strategy makes cycloparaphenylenes an attractive supramolecular host family with a favorable, size-independent read-out signature and binding capabilities extending beyond fullerene guests.
Here we characterize new metal-functionalized amphiphilic diblock copolymers, developed for both surface and solution molecular recognition applications. Polybutadiene-block-poly(ethylene oxide) copolymers functionalized with nitrilotriacetic acid and tris(nitrilotriacetic acid) were complexed with nickel(II) to obtain coordination sites for oligohistidine residues of model proteins. Mixtures of functionalized polymers with the respective non-functionalized block copolymers self-assemble in aqueous solution into vesicular structures with a controlled density of the metal end-groups on their surface. In solution, binding of His6-tagged green fluorescent protein (EGFP) and red fluorescent protein (RFP) to the vesicle surface was quantified by fluorescence correlation spectroscopy. Small-angle X-ray scattering indicates an increase of the membrane thickness by 2-3 nm upon protein binding. Block copolymer monolayers at the air-water interface and on solid support served as a model system to characterize the protein-decorated membranes by Brewster angle microscopy and AFM. High resolution AFM of solid-supported, hydrated monolayers indicates that the proteins form densely packed and partially ordered arrays with the cylindrically shaped EGFP molecules lying flat on the surface of the films.
Real-time and real-space analysis of heavy and transition metal ions employing fluorescent sensor molecules has received much attention over the past few years. Since many of these cations possess intrinsic properties that usually quench the fluorescence of organic dye molecules, a lot of research has lately been devoted to designing fluorescent probes that show complexation-induced fluorescence enhancement. Such an analytical reaction would be highly desirable in terms of increased sensitivity and selectivity. However, in this particular field of sensor research, the photophysical and photochemical mechanisms involved as well as the chemical constitutions of the sensor molecules employed are rather diverse and up to now, very few attempts have been made to establish some general concepts for rational probe design. By analyzing various systems published by other researchers as well as own work, this contribution aims at an elucidation of some of the underlying principles of heavy and transition metal ion-enhanced emission.