Manuel Tsotsalas

Porous coordination polymer hybrid device with quartz oscillator: effect of crystal size on sorption kinetics.

A new strategy to synthesize monodispersed porous coordination polymer (PCP) nanocrystals at room temperature was developed and utilized for the formation of PCP thin films on gold substrates with fine control over the crystal sizes using the coordination modulation method. Hybridization of these PCP thin films with an environment-controlled quartz crystal microbalance system allowed determining the adsorption properties for organic vapors (methanol and hexane). In the case of high sensitivity (at the low-concentration dosing of analytes), the sensor response depended on the crystal size but not on the type of analyte. In contrast, at the high-concentration dosing, a clear dependence of the sorption kinetics on the analyte was observed due to significant sorbate-sorbate interaction.

Encapsulating 111In in Nanocontainers for Scintigraphic Imaging: Synthesis, Characterization, and In Vivo Biodistribution

A new strategy for the radiolabeling of porous nanocontainers has been developed, and the first experiments in vivo are reported. Our approach consists of the use of nanometer-sized zeolites whose channels have been filled with the positively charged gamma-emitter (111)In(3+) via simple ion exchange. To avoid leaching of the isotope under physiological conditions, the entrances of the channels have been closed using a specifically designed molecular stopcock. This stopcock has a positively charged group that enters the channels and entraps the loaded radionuclides via electrostatic and steric repulsion. The other side of the stopcock is a bulky triethoxysilane group that can covalently bind to the walls of the zeolite entrances, thereby irreversibly closing the channels. The surface of the zeolites has been functionalized with different chemical groups in order to investigate the different biodistributions depending of the nature of the functionalizations. Preliminary in vivo experiments with Wistar rats have been performed and showed the potential of the approach. This strategy leads to a nanoimaging probe with a very high density of radioisotopes in a confined space, which is highly stable in physiological solution and could allow a large variety of functionalities on its external surface.

Fabrication of highly uniform gel coatings by the conversion of surface-anchored metal-organic frameworks

We report the fabrication of 3D, highly porous, covalently bound polymer films of homogeneous thickness. These surface-bound gels combine the advantages of metal-organic framework (MOF) materials, namely, the enormous flexibility and the large size of the maximum pore structures and, in particular, the possibility to grow them epitaxially on modified substrates, with those of covalently connected gel materials, namely, the absence of metal ions in the deposited material, a robust framework consisting of covalent bonds, and, most importantly, pronounced stability under biological conditions. The conversion of a SURMOF (surface-mounted MOF) yields a surface-grafted gel. These SURGELs can be loaded with bioactive compounds and applied as bioactive coatings and provide a drug-release platform in in vitro cell culture studies.

Dynamic microcrystal assembly by nitroxide exchange reactions.

The synthesis, modification, and controlled self-assembly of hybrid nanomaterials are areas of great interest and a promising growing research field. Nanoor microscopic inorganic building blocks can be assembled through covalent reactions with suitable functionalities to generate large functional materials with tuneable size and morphology. The beauty of this approach is that single inorganic building blocks can be connected in such a way that they can keep their individual properties but in addition, through controlled assembly, generate new functions not present in the separate components. This approach also allows the generation of novel materials with individual nanoor macroscopic properties, such as anisotropy or polarizability, that can be translated into macroscopic properties. The controlled organization of length, properties, and geometry of nanoor micro-objects through “soft” linkers could lead to new classes of hybrid systems, which are potential materials for electronic and optical devices, as biomaterials for sensors, or as scaffolds for tissue or bone regeneration. The choice of suitable systems for ordering crystals by controlled assembly still remains a difficult task. This is due to the fact that the objects often do not have ideal surfaces, their functionalization can not be easily controlled, and the insertion of chemical groups in spatially resolved areas in order to allow the specific geometric growth is extremely hard. Moreover, for larger building blocks, weak intermolecular forces are not sufficient for the desired assembly process. However, weak interactions and hence reversibility of the assembly is essential for creating more sophisticated materials. Herein we report a new approach for the assembly of organic–inorganic hybrid microcrystals by using nitroxide exchange reactions. Thermal radical nitroxide exchange reactions have been successfully used for synthesis and functionalization of polymers and polymer brushes. In these processes, thermal C O bond homolysis in alkoxyamines leads to transient carbon-centered radicals and persistent nitroxide radicals. Diffusion of these radicals out of the solvent cage is followed by trapping with the nitroxide radicals to reform alkoxyamines. If homolysis of an alkoxyamine is performed in presence of an additional nitroxide radical, scrambling is observed and the thermodynamic product will be obtained (Scheme 1).

Crystal morphology-directed framework orientation in porous coordination polymer films and freestanding membranes via Langmuir–Blodgettry

Porous coordination polymers (PCPs), with their ordered nanoporous systems and large surface areas, are very attractive for numerous applications that involve controlled molecular transport properties. To fully exploit their potential, a straightforward processing method to deposit the PCP crystals on various substrates and to create freestanding membranes with a controlled pore orientation is highly desirable. Here, we report a strategy to self-assemble PCP crystals into two-dimensional monolayers using Langmuir–Blodgettry. This approach allows the deposition on various substrates over several square centimeters, uniformly and with controllable density of the crystals. In addition we show that by controlling the morphology of the crystalline building blocks we can program their orientation on the substrates. Using a copper grid as the substrate, these assemblies can also be fabricated as freestanding sheets. This approach represents a very simple and scalable processing method to translate the orientation of the channel network from the individual crystal to the macroscopic scale, and can help to incorporate this interesting class of materials within advanced hierarchical systems.

Internalization Pathways of Anisotropic Disc‐Shaped Zeolite L Nanocrystals with Different Surface Properties in HeLa Cancer Cells

Information about the mechanisms underlying the interactions of nanoparticles with living cells is crucial for their medical application and also provides indications of the putative toxicity of such materials. Here the uptake and intracellular delivery of disc-shaped zeolite L nanocrystals as porous aminosilicates with well-defined crystal structure, uncoated as well as with COOH-, NH2 -, polyethyleneglycol (PEG)- and polyallylamine hydrochloride (PAH) surface coatings are reported. HeLa cells are used as a model system to demonstrate the relation between these particles and cancer cells. Interactions are studied in terms of their fates under diverse in vitro cell culture conditions. Differently charged coatings demonstrated dissimilar behavior in terms of agglomeration in media, serum protein adsorption, nanoparticle cytotoxicity and cell internalization. It is also found that functionalized disc-shaped zeolite L particles enter the cancer cells via different, partly not yet characterized, pathways. These in vitro results provide additional insight about low-aspect ratio anisotropic nanoparticle interactions with cancer cells and demonstrate the possibility to manipulate the interactions of nanoparticles and cells by surface coating for the use of nanoparticles in medical applications.

Impact of Molecular Clustering inside Nanopores on Desorption Processes

Understanding the sorption kinetics of nanoporous systems is crucial for the development and design of novel porous materials for practical applications. Here, using a porous coordination polymer/quartz crystal microbalance (PCP/QCM) hybrid device, we investigate the desorption of various vapor molecules featuring different degrees of intermolecular (hydrogen bonding) or molecule-framework interactions. Our findings reveal that strong intermolecular interactions lead to the desorption process proceeding via an unprecedented metastable state, wherein the guest molecules are clustered within the pores, causing the desorption rate to be temporarily slowed. The results demonstrate the considerable impact of the chemical nature of an adsorbate on the kinetics of desorption, which is also expected to influence the efficiency of certain processes, such as desorption by gas purge.

Hierarchically Functionalized Magnetic Core/Multishell Particles and Their Postsynthetic Conversion to Polymer Capsules

The controlled synthesis of hierarchically functionalized core/multishell particles is highly desirable for applications in medicine, catalysis, and separation. Here, we describe the synthesis of hierarchically structured metal-organic framework multishells around magnetic core particles (magMOFs) via layer-by-layer (LbL) synthesis. The LbL deposition enables the design of multishell systems, where each MOF shell can be modified to install different functions. Here, we used this approach to create controlled release capsules, in which the inner shell serves as a reservoir and the outer shell serves as a membrane after postsynthetic conversion of the MOF structure to a polymer network. These capsules enable the controlled release of loaded dye molecules, depending on the surrounding media.

Surface functionalization of conjugated microporous polymer thin films and nanomembranes using orthogonal chemistries

Conjugated microporous polymers (CMP) have attracted large interest due to their intrinsic porosity, outstanding stability and high variability. Here we present the surface modification of CMP thin films and nanomembranes via orthogonal chemistry. Using the light induced thiol–yne reaction for the functionalization provides the additional opportunity to photo-pattern the CMP materials.

Excitonically coupled states in crystalline coordination networks

When chromophores are brought into close proximity, noncovalent interactions (π-π/CH-π) can lead to the formation of excitonically coupled states, which bestow new photophysical properties upon the aggregates. Because the properties of the new states not only depend on the strength of intermolecular interactions, but also on the relative orientation, supramolecular assemblies, where these parameters can be varied in a deliberate fashion, provide novel possibilities for the control of photophysical properties. This work reports that core-substituted naphthalene diimides (cNDIs) can be incorporated into surface-mounted metal- organic structures/frameworks (SURMOFs) to yield optical properties strikingly different from conventional aggregates of such molecules, for example, formed in solution or by crystallization. Organic linkers are used, based on cNDIs, well-known organic chromophores with numerous applications in different optoelectronic devices, to fabricate MOF thin films on transparent substrates. A thorough characterization of the properties of these highly ordered chromophoric assemblies reveals the presence of non-emissive excited states in the crystalline material. Structural modulations provide further insights into the nature of the coupling that gives rise to an excited-state energy level in the periodic structure.