Supramolecular Interactions in Chemomechanical Polymers

Abstract

ConspectusMolecular recognition is the basis for the operation of most biological functions; outside of nature, it has also been developed to a high degree of sophistication within the framework of supramolecular chemistry. More recently, selective noncovalent interactions-which constitute molecular recognition-are being used in intelligent new materials that transform chemical signals into actions, such as the release of drugs. The presence of supramolecular binding sites allows chemomechanical polymers to operate as sensors and actuators within a single unit without the need for any additional devices such as transducers or power supplies.A polymer can be designed so that a particular chemical substance, most often in aqueous surroundings, will trigger either a large expansion or a large contraction, depending on the mechanism. The translation of binding energy into mechanical motion can, with a suitable arrangement of the materials in tubes or on flexible films, be harnessed for unidirectional drives, flow control, the liberation of drugs, or the uptake of toxic compounds, among other applications. Miniaturization of the polymer particles allows one to enhance both the sensitivity and speed of the response, which is of particular importance in sensing.The basis for the selective response to external effector compounds, such as metal ions, amino acids, peptides, or nucleotides, is their noncovalent interaction with complementary functions covalently bound to the polymer network. With suitable polymers, selectivity between structural isomers-and even between enantiomers-as triggers can be achieved. As with supramolecular complexes in solution, the underlying interactions in polymers comprise a variety of noncovalent binding mechanisms, which are not easy to distinguish and quantify-and more so with polymers, which are not monodisperse. In this Account, we present systematic comparisons of different polymers and effector classes that allow, for the first time, the characterization of these contributions in chemomechanical polymers: they comprise ion pairing, metal coordination, stacking, cation-π, dispersive, and hydrophobic forces. In contrast, hydrogen bonding has a major role primarily in the hydrogel network structure.The fully reversible polymer volume changes are essentially determined by water uptake or release. In gels derived from boronic acid, glucose can serve as a cross-linking effector in promoting contractions via strong, reversible covalent bond formation in a highly distinctive manner. Cooperativity between two different effector compounds is more frequently seen with such polymers than in solution: it leads to logical AND gates by different motions of the particles, with a direct communication link to the outside world. For example, with a polymer that bears several recognition sites, triggering peptides induce motion only if Zn 2+ or Cu 2+ ions are simultaneously present.The molecular recognition mechanisms that cause volume changes in polymers share similarities with extensively studied supram...

Information Processing with Molecules—Quo Vadis?

“…[87] The Schneider group delivered proof-of-principle for the utility of chemomechanical polymers as actuators (machines) or in drug delivery. [84] This application potential together with the demonstrated logic switching opens interesting perspectives for the further career of these "intelligent" materials.…”

“…Well defined three-dimensional size changes in the millimeter range were discussed in a series of reports about chemomechanical polymers developed by the Schneider group. [84] These polymers contain various functional recognition sites for effector molecules, which are attracted via ion-pairing, hydrogen bonding, cation- interactions, metal complexation, hydrophobic effects, etc. (see two example polymers in Scheme 18).…”

Development of DNA Based Active Macro–Materials for Biology and Medicine: A Review

“…The focus of this review is the macroscopic materials designed, synthesized, and applied based on or inspired by DNA and the application of these materials specifically for biology and medicine. Changes in the nanoscale structures can trigger macroscopic changes in the materials (Schneider & Strongin 2009). For these macro-materials, incorporation of DNA into the structural design confers a number of possibilities that would otherwise not be feasible.…”

Bausteine mit Hohlräumen in supramolekularen Gelen

“…[4,5] Herkömmliche Polymergele werden durch vernetzte kovalent gebundene Polymere gebildet, die aufquellen und ein Vielfaches ihres Eigengewichts an Lösungsmittel aufnehmen können. [6] Dagegen werden supramolekulare Gele im Allgemeinen aus niedermolekularen organischen Verbindungen aufgebaut, die sich über nichtkovalente Wechselwirkungen zu supramolekularen Netzwerken zusammenlagern, welche dann in der Lage sind, Lösungsmittelmoleküle aufzunehmen. Da solche Gele durch viele schwache, reversible Wechselwirkungen zusammengehalten werden, stellen die supramolekularen Gele eine besonders reaktionsfähige und regulierbare Form von weichem Material dar.…”