The “Chemistry NAWAROS group” at BOKU University was amongst the first groups that started re-search on cellulosic aerogels as the “young, third generation” of aerogels. Basic studies aiming at the preparation of highly porous aerogels from different pulps revealed that the fragile, open-porous struc-ture of alcogels can be largely retained if supercritical carbon dioxide (scCO2) is used in the final dry-ing step. This technique was later adapted for converting shaped bacterial cellulose (BC) aquogels into ultra-lightweight aerogels that quantitatively retained shape and porosity. Cellulose phosphate (CP) aerogels were prepared for the first time via the Lyocell approach and have been tested with regard to hemocompatibility, growth and differentiation of skeletal stem cells. Based on previous work, the proposed project is intended to a) study the intriguing surface effects that distinguish bacterial cellulose aerogels from those obtained by regenerating plant cellulose from solu-tion, b) understand the distinct differences in retaining the fragile network structure during scCO2 dry-ing for the two types of aerogels, c) advance basic concepts (use of porogens, surfactants, templating, scCO2 antisolvent precipitation, chemical modification, cross-linking etc.) for tailoring the properties (porosity, aggregate microstructure, hemocompatibility, mechanical and chemical properties) of cellu-losic aerogels, d) to further develop analytical techniques for characterizing porous soft matter of such low densities (down to 5 mg cm-3), and e) to investigate the tailored cellulosic aerogels regarding their use in selected biomedical applications. The application of mechanically sufficiently stable, cellulose phosphate-based hemocompatible aero-gels with spread porosity including a sufficient percentage of macropores with diameters in the range of 50 = x = 400 µm as a novel cell scaffolding material for bone grafting is one main target of the proposed project. The envisaged work has been motivated by several recent findings: 1) cellulose phosphates can be safely processed to aerogels via the Lyocell route 2) cellulose phosphates are hemocompatible and non-toxic in cultured human osteoblasts and fibroblasts, 3) cellulose phosphorylation (moderate DS only) is a pre-requisite to biomineralization, i.e. the formation of calcium deficient hydroxyapatite (cdHap), 4) moderate calcification activates blood platelets without inducing an inflammatory response, 5) calcified cellulose phosphates support robust growth and spontaneous osteogenic differentiation of skeletal stem cells. Tailoring the properties of cellulosic aerogels for controlled release of bioactive compounds is a second main objective of the proposed work. Preliminary studies have shown that bioactive compounds can be homogenously loaded into cellulose aerogels by scCO2 antisolvent precipitation. Full retention of porosity and quantitative rewettability of BC aerogels render them promising matrices for controlled release application in wound treatment, skin care or drug dehabituation. Through a better understanding of the above-mentioned microstructural differences and hitherto puzzling surface effects it is expected that aerogels from commercial pulps can also be used in a multitude of applications (catalysis, filters, separation techniques, etc.) beyond the controlled release of bioactive compounds.

The presence of covalency in complexes of the 4f and 5f elements has been a source of intense research and controversy. This covalency have been probed by many spectroscopies, but there has been little use of NMR. The NMR shifts of paramagnetic substances have two contributions; the dipolar term arises from the dipolar magnetic interaction between the electronic magnetic moment of the paramagnetic center and the nuclear magnetic moment of the nucleus of interest, while the contact term is caused by a non zero spin density at the nucleus and is a signature of a spin density delocalization between the metal center and the ligand ; it probes the degree of covalency between the paramagnetic center and the ligand. For lanthanide complexes, these two contributions are unraveled thanks to a model proposed by Bleaney in the 70's, based on temperature and position dependence of the shifts. But this model is not suitable for actinides due to the larger interaction of the actinide orbitals with the ligands. The aim of the actipNMR project is to derive a model valid for actinides. To achieve that, the consortium gathers a team of experimentalists expert of pNMR in actinide complexes, a team of developers of relativistic quantum chemistry tools and a team of quantum chemists specialist in molecular magnetism. pNMR and X-ray data will be collected in a complete series of actinide complexes with the DOTAM ligand, new codes devoted to the calculation of pNMR shifts in actinide chemistry will be developed, the pNMR shifts will be computed in the whole series and the temperature dependence analyzed. This temperature dependence will be modeled either as a refinement of Bleaney's model or using a new paradigm, describing the properties of the complex thanks to statistical descriptors. This model should permit the discrimination between contact and dipolar contributions from experimental data, and consequently, to probe the degree of covalency in the late 5f actinides with N-donors ligand. This should impact the choice of the ligand for extraction processes.

The discovery of the mass-independent isotopic fractionations of sulfur and oxygen (S-MIF and O-MIF) has revolutionized the way fundamental geochemical questions are addressed and have produced one of the most iconic figures in geosciences, i.e. the presence of S-MIF in rocks older than 2.3 billion years and its sudden quasi disappearance thereafter. Regarding O-MIF, the majority of the anomalies observed on Earth originate from the ozone anomaly transferred to oxygen-bearing molecules. Although there are still uncertainties pertaining to the mechanisms of O-MIF transfers, they tend to pale into insignificance when compared to those on the exact processes creating S-MIF. There is now no general consensus on the origin of S-MIF in the atmosphere and all the proposed mechanisms are still highly debated in geosciences. Recently NASA has identified the resolution of the origin of S-MIF as one of the top priorities for its astrobiology program, recognizing the importance of MIF in solving the epic question of the origin of life and its interaction with the planetary environment. The identification and quantitative understanding of processes involved in creating and transferring MIF anomalies, a prerequisite for extracting the information embedded in isotopic data, would certainly lead to major advances in our comprehension of the geochemical and environmental evolution of our Earth, from its most primitive existence to the present day. In this project, we propose a multidisciplinary approach to re-examine the sources of MIF in sulfates using an integrated program of novel laboratory experiments, dedicated field studies and innovative multi-scale atmospheric photochemical modeling (including both O- and S-MIF as prognostic variables). First, using the successful isotopic methodology applied to sulfate from polar snow and ice core, we will assess the potential of sulfate leached from volcanic ash as tracers of atmospheric oxidation processes. Second, we plan to carry out a new set of chamber experiments on SO2-related production of S-MIF considering environmental conditions that are as close as possible to those of the stratosphere and of the presupposed Archean atmosphere. Third, for the first time, S-MIF and O-MIF isotope chemistry schemes will be coupled and implemented in models (i.e. a photochemical box/plume model and a global chemistry-transport model). As O-MIF has already largely demonstrated its capacity to probe sulfur oxidation mechanisms in the atmosphere, combining O-MIF and S-MIF analysis should represent a powerful approach to constrain better inferences on the origin of S-MIF. One of the aims is to improve our quantitative understanding of oxidation processes of volcanic and anthropogenic sulfur, and of the resulting production of aerosols. We will also assess the potential of this innovative approach for probing atmospheric chemistry in the distant past. Overall, by providing a much more robust basis for quantitative inferences from S-MIF and O-MIF data, the project will yield new constraints on fundamental questions regarding the late oxygenation of the atmosphere, the shift from an anaerobic to aerobic environment for life, and the reconstruction of the impact of volcanic eruptions and human activities on atmospheric oxidizing capacity and climate.