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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.
Gated hybrid delivery systems: En route to sensory materials with inherent signal amplification
(2013)
Hybrid nanoparticles with a large specific surface area are a particularly exciting vehicle for delivery applications. Such highly porous or container-like structures, usually prepared from silica and frequently from gold, can incorporate a large number of chemical substances such as drug and/or indicator molecules. When equipped with a chemically or physically addressable gating function at the openings of the voids, the release of the cargo can be controlled at will. Because many more molecules can be stored as cargo in the pores of the support than there are functional groups as anchoring sites for the gating entities attached to the outer surface (for efficient pore capping), the systems possess inherent features of (signal) amplification. The present article will introduce various design strategies for different types of physical (light, temperature, magnetism) and chemical (pH, metal ions, anion, small organic molecules, enzymes) stimuli in connection with drug and indicator release. We will highlight exciting aspects of combining both features in theranostic applications and will stress which requirements still have to be met by many of the systems to be readily applicable in a sensory context.
The combination of suitable nanoscopic inorganic supports with supramolecular concepts and bioconjugation strategies opens up exciting perspectives for the development of bioinorganic and organicinorganic hybrid materials with improved functionalities. Many of the examples from the period 2004 to mid-2007 reviewed here bridge the gap between molecules, materials sciences, biochemistry, and nanotechnology. The synergistic use of these approaches has led to the advancement of various functions such as enhanced recognition, amplified signaling, the controlled assembly and disassembly of aggregates and 3-D architectures. Many of the implemented active functions can be carried out in a reversible and directed fashion on purpose by triggering with an external stimulus. These ideas bring tunability to properties of inorganic solids and new perspectives of application to biochemical and supramolecular concepts. Classic inorganic chemistries such as metal or semiconductor nanoparticles, silica or carbon materials, and coordination chemistry are thus elevated to another level of sophistication and contribute significantly to frontier research areas in directed transport and delivery, nanoelectronics and mechanics, chip technology, smart materials, memory devices, and bioanalytics.
The article discusses representative examples published in the field of functional biomimetic chemistry of hybrid materials between 2004 and mid-2007. First, we focus on the modification of morphological aspects of (bio)organicinorganic hybrid materials to create sophisticated gating and switching mechanisms. The architecture of the systems is presented and the elements of control by external stimuli that have been established in recent years, such as optical, electrochemical, chemical, thermal, or magnetic means, are described. Various functions ranging from (site-specific) delivery to indication at the nanometric level are reported. Next we develop the idea of utilizing hybrid frameworks for biomimetic signaling inspired by the way nature has created binding pockets and the concept of induced-fit. Such a merging of inorganic scaffolds with supramolecular concepts results in enhanced molecular recognition and signaling. Finally selected recent advances in the field of hybrid biomimetic motors both of linear and rotary types are presented. The contribution shows how novel biomimetic functions can arise from synergisms between specifically designed hybrid materials and the implementation of supramolecular and/or bioorganic concepts.
Supramolecular interactions are vital processes in many chemical sensors, biochemical assays, and other analytical detection schemes. On the background of the current, rapidly developing, and constantly changing requirements for (bio)analytical techniques, the classical molecular host is increasingly overburdened to accomplish a specific analytical task with the desired selectivity and sensitivity. Instead, other signaling strategies have to be conceived that overcome the limits in signal output, dynamic range, or compound targeting, which are imminent to various traditional methods. A very promising approach is the combination of concepts of supramolecular chemistry with nanostructured or nanoscopic inorganic materials, that is, the development of hybrid sensor materials. Such hybrids often lead to improved functionality and enhanced performance, and the present chapter discusses the contributory features in relation to the major aspects, which are related to the enhanced coordination by the preorganization of binding sites, signal amplification by the preorganization on surfaces, aggregation‐mediated signaling, surface‐modification‐based signaling, the tuning of selectivity through polarity and size, and gated signaling.
Test strips that in combination with a portable fluorescence reader or digital camera can rapidly and selectively detect chemical warfare agents (CWAs) such as Tabun (GA), Sarin (GB), and Soman (GD) and their simulants in the gas phase have been developed. The strips contain spots of a hybrid indicator material consisting of a fluorescent BODIPY indicator covalently anchored into the channels of mesoporous SBA silica microparticles. The fluorescence quenching response allows the sensitive detection of CWAs in the μg m−3 range in a few seconds.
The design of comparatively simple and modularly configurable artificial systems able to communicate through the exchange of chemical messengers is, to the best of our knowledge, an unexplored field. As a proof-of-concept, we present here a family of nanoparticles that have been designed to communicate with one another in a hierarchical manner. The concept involves the use of capped mesoporous silica supports in which the messenger delivered by a first type of gated nanoparticle is used to open a second type of nanoparticle, which delivers another messenger that opens a third group of gated nanoobjects. We believe that the conceptual idea that nanodevices can be designed to communicate with one another may result in novel applications and will boost further advances towards cooperative systems with complex behavior as a result of the communication between simple abiotic individual components.
The article discusses representative examples published in the field of functional biomimetic chemistry of hybrid materials between 2004 and mid-2007. First, we focus on the modification of morphological aspects of (bio)organicinorganic hybrid materials to create sophisticated gating and switching mechanisms. The architecture of the systems is presented and the elements of control by external stimuli that have been established in recent years, such as optical, electrochemical, chemical, thermal, or magnetic means, are described. Various functions ranging from (site-specific) delivery to indication at the nanometric level are reported. Next we develop the idea of utilizing hybrid frameworks for biomimetic signaling inspired by the way nature has created binding pockets and the concept of induced-fit. Such a merging of inorganic scaffolds with supramolecular concepts results in enhanced molecular recognition and signaling. Finally selected recent advances in the field of hybrid biomimetic motors both of linear and rotary types are presented. The contribution shows how novel biomimetic functions can arise from synergisms between specifically designed hybrid materials and the implementation of supramolecular and/or bioorganic concepts.
The combination of suitable nanoscopic inorganic supports with supramolecular concepts and bioconjugation strategies opens up exciting perspectives for the development of bioinorganic and organicinorganic hybrid materials with improved functionalities. Many of the examples from the period 2004 to mid-2007 reviewed here bridge the gap between molecules, materials sciences, biochemistry, and nanotechnology. The synergistic use of these approaches has led to the advancement of various functions such as enhanced recognition, amplified signaling, the controlled assembly and disassembly of aggregates and 3-D architectures. Many of the implemented active functions can be carried out in a reversible and directed fashion on purpose by triggering with an external stimulus. These ideas bring tunability to properties of inorganic solids and new perspectives of application to biochemical and supramolecular concepts. Classic inorganic chemistries such as metal or semiconductor nanoparticles, silica or carbon materials, and coordination chemistry are thus elevated to another level of sophistication and contribute significantly to frontier research areas in directed transport and delivery, nanoelectronics and mechanics, chip technology, smart materials, memory devices, and bioanalytics.
This review highlights how the combination of supramolecular principles and nanoscopic solid structures enables the design of new hybrid sensing ensembles with improved sensitivity and/or selectivity and for the targeting of analytes for which selectivity is hard to achieve by conventional methods. Such ideas are bridging the gap between molecules, materials sciences and nanotechnology. Relevant examples will be detailed, taking into account functional aspects such as (1) enhanced coordination of functionalized solids, (2) enhanced signalling through preorganization, (3) signalling by assemblydisassembly of nanoscopic objects, (4) biomimetic probes utilizing discrimination by polarity and size and (5) distinct switching and gating protocols. These strategies are opening new prospects for sensor research and signalling paradigms at the frontier between nanotechnology, smart materials and supramolecular chemistry.
The inclusion of squaraine (SQ) dye I into the supercages of zeolite Y (structure code FAU) with a SiO2/Al2O3 ratio of 30 (Z30) through a two-step ship-in-the-bottle approach is reported, resulting in the squaraine-containing hybrid material Z30-SQ. Attempts to use the same synthetic procedure on sodium and ammonium Y zeolites were unsuccessful, stressing the importance of the presence of Brønsted acid centres in the Z30 zeolite. The reflectance spectra of Z30-SQ show a maximum in the typical squaraine monomer region at 618 nm and a shoulder at 570 nm. Spectral analyses revealed that the major species are SQ dimers and (tightly adsorbed) SQ monomers and SQ aggregates are only formed to a minor degree. The emission spectrum of Z30-SQ shows a single band at 669 nm. The sensory performance of this material was tested in the presence of volatile propylamine and propylthiol and other volatile organic compounds (acetone, ethanol, dichloromethane, hexane, acetonitrile, ethyl acetate, ethyl ether and acetic acid). The blue Z30-SQ material reacts with the thiol and amine derivatives, resulting in the bleaching of the solid and disappearance of the absorption band in the visible region, but does not undergo spectroscopic changes in the presence of other volatile organic compounds (VOCs). Whereas the reaction with propylamine is irreversible, a partial reversibility was found in the presence of the thiol. Theoretical investigations of the reactivity of I with several VOC molecules at the semi-empirical level reproduced well the experimentally observed reactivity.