The Wuttke group is committed to the discovery, design and development of new functional porous materials and their application in different fields. Our focus for several years has been on the design, synthesis, functionalization and characterization of novel metal-organic frameworks (MOFs). MOFs are a new class of materials synthesized in a building-block fashion from metal-ion vertices, interconnected by organic linker molecules in a self-assembly process, to create highly tailorable crystalline materials with pores of nanometer dimensions. Recent interest in MOFs is a consequence of the simultaneous occurrence of four important characteristics: i) crystallinity, ii) tuneable porosity and iii) the existence of strong metal-ligand interactions and iv) structural diversity. Owing to these key features MOFs are promising candidates for many applications such as gas storage, gas separation, catalysis, sensing, or drug delivery. The success of MOFs in these and other domains will depend on the availability of efficient ways for pore surface functionalization.
Novel functionalization concepts for MOFs
One major focus of our group is the development of novel functionalization concepts for MOFs and at the same time evaluating these concepts. A very important issue for us is to understand the advantageous but also the disadvantageous of different functionalization methods.
In this respect we recently developed an approach for postsynthetic modification of with carboxylic acids, acid anhydrides, and acid chlorides without additional solvent at elevated temperature was developed (reference). These results demonstrate the speediness, simplicity, and eﬀectiveness of the PSM approach for modiﬁcation of aminotagged MOFs with carboxylic acid derivatives in pure substance. Reaction times of 10 min and a huge variety of possible reactants from unpolar to polar allow a quick synthesis of a broad range of postfunctionalized porous materials for research purposes. Furthermore, this PSM strategy can be easily upscaled to an industrial level, producing large amounts functionalized MOFs for applications such as gas storage, gas puriﬁcation, gas separation, or catalysis.
Figure 1. PSM conditions of UiO-66(Zr)-NH2 with acetic anhydride(Ac2O) referred to 1 equiv of MOF compared to PSM yields and Langmuir surface areas.
Synthesis of functional MOFs for their application in the field of sensing
The goal of this project is to synthesize functional MOFs with an appropriate decoding unit (receptor and transducer) into the scaffold (Figure 2). Following the definition given by IUPAC, a chemical sensor is a device that transforms chemical information into an analytically useful signal. Therefore, to be deemed a sensor the system must incorporate a mechanism that can report the binding event to the macroscopic world. Here we try to incorporate and evaluate luminescence properties inside the MOF structure.
Figure 2. The complementary interaction between a guest analyte and a host binding pocket capable of reporting this binding event converts the receptor into a sensor. This Figure summarizes also the final goal of this project, where the reporter is a dye connected with a receptor. Both are integrated in the MOF structure resulting in a selective chemical sensor.
Design of “smart” multifunctional MOF nanocarriers for controlled and targeted drug delivery
The development and study of novel functionalized nanoparticles as drug delivery systems is the goal of this procject. The central idea is to design hybrid nanomaterials based on metal-organic frameworks (MOFs), which could offer a new platform for biomedical applications. These materials are expected to display novel and enhanced properties compared to more established nanomaterials such as polymers, gold nanoparticles, iron oxide nanoparticles, liposomes and mesoporous silica. MOF nanoparticles with well-defined and tuneable structures can be realized. Research is focus on the design of MOF nanoparticles with inner pore functionalization for controlled interaction with biologically active molecules, as well as outer functionality for target cell uptake, triggered drug release, and with surface shielding against unwanted interactions inside the physiological environment.The key challenge in this project is to advance the methodologies for the enhanced design of nanoparticles with the following goals:
- The nanocarrier should be biocompatible
- High loading and protection of the drug molecules
- Zero premature release before reaching the target
- Efficient cellular uptake
- Efficient endosomal escape
- Controllable rate of release to achieve an effective local concentration
- Cell targeting
The project is divided into two work packages A: ‘design of the nanocarriers’ and B: ‘in vitro and in vivo testing of the nanocarriers’ (Figure 3).Figure 3. Schematic illustration of the design and testing of multifunctional MOF nanocarriers for controlled and targeted drug delivery. The upper part shows the design of site-specific stimuli-responsive controlled MOF drug delivery systems (work package A). The lower part depicts the identification of the biodegradation stability, cell uptake and location of the nanocarriers as well as the controlled drug release (work package B).
In the first work package A, the design of site-specific stimuli-responsive controlled MOF drug delivery systems is the key task. It is the most important and challenging task in this project. The central goal of the second work package B is to identify and enhance the biodegradation stability, cell uptake and location of the nanocarriers as well as the controlled drug release by using established in vitro and in vivo pharmaceutical approaches. For this strongly interdisciplinary sub-project our group collaborates with different biophysics, pharmaceutical and medicine groups at the LMU and other universities.