Surface PEGylation of nanoparticles designed for biomedical applications is a common and straightforward way to stabilize the materials for in vivo administration and to increase their circulation time. This strategy becomes less trivial when MRI active porous nanomaterials are concerned as their function relies on water/proton-exchange between the pores and bulk water. Here we present a comprehensive study on the effects of PEGylation on the relaxometric properties of nanozeolite LTL (dimensions of 20 × 40 nm) ion-exchanged with paramagnetic GdIII ions. We evidence that as long as the surface grafting density of the PEG chains does not exceed the “mushroom” regime (conjugation of up to 6.2 wt % of PEG), Gd-LTL retains a remarkable longitudinal relaxivity (38 s–1 mM–1 at 7 T and 25 °C) as well as the pH-dependence of the longitudinal and transverse relaxation times. At higher PEG content, the more compact PEG layer (brush regime) limits proton/water diffusion and exchange between the interior of LTL and the bulk, with detrimental consequences on relaxivity. Furthermore, PEGylation of Gd-LTL dramatically decreases the leakage of toxic GdIII ions in biological media and in the presence of competing anions, which together with minimal cytotoxicity renders these materials promising probes for MRI applications.@en

The aerobic organocatalytic oxidation of alcohols was achieved by using water-soluble sodium anthraquinone sulfonate. Under visible-light activation, this catalyst mediated the aerobic oxidation of alcohols to aldehydes and ketones. The photo-oxyfunctionalization of alkanes was also possible under these conditions.

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Selective oxyfunctionalizations of inert C−H bonds can be achieved under mild conditions by using peroxygenases. This approach, however, suffers from the poor robustness of these enzymes in the presence of hydrogen peroxide as the stoichiometric oxidant. Herein, we demonstrate that inorganic photocatalysts such as gold–titanium dioxide efficiently provide H₂O₂ through the methanol-driven reductive activation of ambient oxygen in amounts that ensure that the enzyme remains highly active and stable. Using this approach, the stereoselective hydroxylation of ethylbenzene to (R)-1-phenylethanol was achieved with high enantioselectivity (>98 % ee) and excellent turnover numbers for the biocatalyst (>71 000).

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Neutron activation is widely applied for thepreparation of radioactive isotopes to be used in imaging and/or therapy. The type of diagnostic/therapeutic agents varies fromsmall chelates coordinating radioactive metal ions to complexnanoparticulate systems. Design of these agents often relies onconjugation of certain organic functionalities that determine theirpharmacokinetics, biodistribution, targeting, and cell-penetratingabilities, or simply on tagging them with an optical label. Theconjugation chemistry at the surface of nanoparticles and theirfinal purification often require laborious procedures that becomeeven more troublesome when radioactive materials are involved.This study represents a thorough investigation on the effects ofneutron activation on the organic moieties of functionalizednanoparticles, with special focus on166Ho2O3particles conjugated with PEG-fluorescein and PEG-polyarginine motives.Spectroscopic and thermogravimetric analyses demonstrate only a limited degradation of PEG-fluorescein upon irradiation of theparticles up to 10 h using a thermal neutronflux of 5×1016m−2s−1. Cell experiments show that the polyarginine-basedmechanisms of membrane penetration remain unaltered after exposure of the functionalized particles to the mixedfield ofneutrons and gammas present during activation. This confirms that radiation damage on the PEG-polyarginines is minimal.Intrinsic radiations from166Ho do not seem to affect the integrity of conjugated organic material. Thesefindings open up a newperspective to simplify the procedures for the preparation of functionalized metal-based nanosystems that need to be activated byneutron irradiation in order to be applied for diagnostic and/or therapeutic purposes.@en

Multimodal imaging techniques are emerging in medical diagnosis. The synergistic combination of imaging techniques, such as MRI and PET/SPECT, is highly useful to strengthen each of the individual imaging modalities while reducing any of their disadvantages. In recent years, the progress of technical integration of imaging scanners has led to a clear motivation to design multimodal agents by chemists that can be used simultaneously and hence profit optimally of the new hybrid imaging scanners. Nanoscaffolds combining discrete functions (e.g. magnetic, radioactive, optical or therapeutic) are particularly interesting in this regard. There has been an increasing endeavour to design and synthesize multifunctional nanocomposites for practical applications in dual imaging modalities such as MRI-optical, MRI-PET, PET-optical, PET-CT, MRI-SPECT. Chapter 1 of this thesis summarizes the state-of-the-art in the development of multimodal probes for medical imaging and therapy, in which the roles of metal ions are highlighted. Chapters 2-5 focus on the exploration of porous nanomaterials, e.g. zeolite LTL in particular, which is suitable for the above-mentioned purposes due to their ability to accommodate large amounts of lanthanide ions through ion-exchange of alkali cations that counterbalance the AlO4- of the crystalline framework. The surface chemistry and biocompatibility study are also included. Chapter 6 describes a facile methodology to synthesize the lanthanide-nanoparticles with controllable size and application of the synthesized materials as MRI contrast agents. Chapter 7 shows that these versatile materials are also applicable in a very different field: they are very efficient in the storage and release of oxygen. In conclusion, the findings of the thesis mainly provide insights into the merits and understanding of zeolite-based MR imaging probes. @en

Lanthanide oxysulfates have the ability to store and release large volumes of oxygen under oxidizing/reducing conditions, rendering them interesting as automotive catalysts. Herein we demonstrate a remarkable improvement of both processes by utilization of nanoparticles compared to the bulk materials. A further improvement of the catalytic activity was achieved by cost-effective doping with 1.9 wt% of Ni.@en