Ivan Trentin - Academia.edu (original) (raw)

Papers by Ivan Trentin

Advanced Functional Materials

Molecular metal oxides, or polyoxometalates (POMs) offer unrivalled properties in areas ranging f... more Molecular metal oxides, or polyoxometalates (POMs) offer unrivalled properties in areas ranging from catalysis and energy conversion through to molecular electronics, biomimetics and theranostics. While POMs are ubiquitous metal oxide model systems studied in most areas of chemistry and materials science, their technological deployment is often hampered by their molecular nature, as this leads to increased degradation, leaching and loss of reactivity, particularly when harsh applications, such as water electrolysis, thermal catalysis or highly basic/acidic reaction solutions are targeted. Therefore, immobilization of POMs on heterogeneous substrates has recently become a central theme in POM research. While early studies focused mainly on metal oxide and semiconductor supports, more recently, POM integration in soft matter matrices including polymers, conductive polymers, hydrogels and stimuliresponsive matrices have led to breakthroughs in multifunctional composite design. This Progress Report will summarize the recent pioneering studies in this emerging field, highlight current challenges which need to be overcome to allow a more widespread technological deployment and provide the authors' view of some of the most promising future directions of the research field. In addition, we provide an unprecedented summary of the correlations between structure (on the molecular, nano-and microscale) and resulting reactivity, so that materials design beyond empirical studies can be further developed. We believe that this timely Progress Report will serve as a focal point to further develop the field, as well as point of reference for newcomers in the area of knowledge-driven bottom up materials design. Given this broad range of interest groups, we believe that Advanced Functional Materials is the ideal journal for this Progress Report. The combination of hard and soft matter-often thought of as inorganic and organic components, can yield functional composites with unique and otherwise inaccessible properties. Prime examples are found in Nature, where biomineralization forms bones in vertebrates or shells in molluscs. These composites combine mechanical strength with flexibility and offer structural stabilization and protection. These materials are composed of hard inorganic components, e.g. calcium carbonate, CaCO3 or hydroxy apatite, Ca5[OH(PO4)3], and polymeric soft matter, e.g. collagens, which are combined to give new structures and unique function. [1] In this Perspective, we will explore the combination of polymeric soft matter matrices with molecular metal oxides-polyoxometalates (POMs)-as a unique class of composites where structure, reactivity and function can be controlled on the molecular level, while giving macroscopic materials suitable for technological device integration, e.g. as membranes, films or gels. 1.1. The relevance of embedding molecular metal oxide species in soft matter. [2,3] Soft matter: The 21 st century may rightfully be called the era of soft matter. The term "soft matter" was officially introduced in science by Pierre-Gilles de Gennes in his noble prize lecture in 1991. [4] In contrast to hard matter, which is characterized by structural rigidity and strong (e.g. covalent or ionic interactions), soft matter possesses properties in between solids and liquids and is dominated by weaker, intermolecular interactions (e.g. dipolar or hydrogen bonding interactions) between the constituents. These systems are flexible and are responsive to external forces or stimuli. Further, "soft matter" features structuring on different length scales from nano-to micrometers, and the macroscopic behavior of soft matter is dictated by non-covalent, intermolecular interactions. Based on these characteristics, polymers, colloids, surfactants, organic and metal-organic films, liquid crystals, vesicles, biological object etc, are all examples of soft matter. [5] Among those, polymers represent a thriving and promising field which was established about 100 years ago by Staudinger. [6] Later on, the discovery of living anionic polymerization in 1956 [7] and stereoregular polyolefins [8] provided facile access to materials on a large scale. The interest in polymers as industrial materials was also driven by the invention of 3D printing in the 1980s, which provided access to hierarchically complex architectures, which were not achievable by conventional manufacturing technologies. [2] In addition, the discovery of controlled polymerization techniques in the 1990s significantly increased the portfolio of accessible materials and functionalities. [9] Another breakthrough in soft matter was the development of block copolymers which chemically link two or more polymer-chains into one compound, resulting in unusual structure and new function. [10] In the last three decades the focus of polymer chemistry has shifted to stimuli-responsive or "smart" materials, which adapt to environmental changes by changes of structure or reactivity, enabling application in sensing, drug delivery, self-healing coatings, or tunable catalyst supports. [11][12] With the development of polymer chemistry, the interest to incorporate inorganic materials into polymers also emerged. Significant influence on development of such polymer-inorganic nanocomposites can be ascribed to the discovery of "chimie douce" in 1980s. [13] With that, sol-gelbased approaches were established as an alternative to traditional high-temperature "shake and bake" chemistry and the resulting (composite) materials were characterized by extended organic-inorganic interfaces. The combination complementary properties of organic (soft) and inorganic (hard) matter opened up the way for materials with unique, sometimes even synergistic, characteristics. [14] This led to extensive applications in fields like sensing, bio-imaging, photovoltaics, or in catalysis. [3] Figure 1: Historic overview of POM-polymer hybrid materials Hard and soft matter composites: In the classical approach of catalytically active hybrid materials often a catalyst is grafted or anchored on the surface of an inorganic support (e.g. silica, titania, or alumina). The obtained heterogeneous catalyst typically shows high thermal stability, good performance and can be easily recycled. [15] The reverse approach, where inorganic catalytic species are attached to a (structured) polymeric surface is less common, presumably due to a (perceived) lower stability of soft matter. However, polymer-supported catalysts open avenues which would not be possible with classical inorganic supports. Soft matter offers superior local control of the catalyst environment, e.g. by careful selection of building block for nanostructured polymer matrices. This can even enable approaches wher polymers model the well-defined reaction-spaces of biological systems, e.g. enzymes. [16] This allows control over morphology, chain folding, and the presence of functional groups at the molecular level and could even result in the formation of artificial enzymes. [17] In addition, selection of stimuli responsive block allows to obtain smart catalytic materials in which the catalytic function can be controlled by external stimuli like changes in pH, temperature, or irradiation with light of a specific wavelength. [18] The selectivity and activity of the material can also be tuned by variation of local polarity in the vicinity of the catalytic center. [19] Currently, plenty of different inorganic materials were used for formation of polymer-inorganic composites, however in this review we focus only on polyoxometalate-polymer hybrids. Polyoxometalates: POMs are ideal molecular components for integration into soft matter matrices, based on their structural versatility combined with an enormous range of applications: POMs are molecular metal-oxide anions, typically based on early transition metals (group 5, 6) in their highest oxidation states. [20-22] POMs self-assemble spontaneously in solution by oligo-condensation reactions of oxometalate precursors (e.g. MoO4 2-, WO4 2-), sometimes in the presence of templating anions (e.g. halides, oxo-anions, etc.). [23] POMs contain between 2 and 368 metal centres, are typically in the 1-5 nm size range and can feature several tens of negative charges. [20-22] POM structure formation is difficult to predict, but can be influenced by secondary reaction parameters including solvent, pHvalue, temperature, pressure and others. [20] To-date, POM chemistry is dominated by W-, Mo-and Vbased POMs, as these metal feature the ideal combination of high positive charge, suitable ionic radius and availability of empty d-orbitals to stabilize terminal oxo ligands by d-p π-bonding. [20-22] Over the last decades, advances in synthesis, characterization and mechanistic understanding have led to breakthroughs in POM applications ranging from (photo-)catalysis, [24,25] energy conversion/storage, [26] molecular magnetism and electronics [27,28] through to bio-medicine, [29-31] and artificial enzymes. [30] Of particular interest over the last decade was the development of POMs covalently functionalized with organic groups to merge the fields of metal oxide and organic chemistry. [32,33] In addition, the redox-activity of POMs renders them ideal components for chargetransfer and storage as well as (photo-)redox catalysis. In addition, surface protonation of POMs makes them intriguing acid catalysts. [34] Metal functionalization of the POM cluster shell can be used to

Heterogeneous light-driven catalysis is a cornerstone of sustainable energy conversion schemes su... more Heterogeneous light-driven catalysis is a cornerstone of sustainable energy conversion schemes such as solar water splitting. However, to date most catalytic studies in the field focus on bulk analyses quantifying the amount of produced hydrogen and oxygen. Here, we report on ex situ and operando studies with micrometer to nanometer resolution of a heterogenized catalyst/photosensitizer system. As a model, the molecular photosensitizer [Ru(bpy)3]2+and the molecular metal oxide water oxidation catalyst [Co4(H2O)2(PW9O34)2]10- were co-immobilized within a nanoporous block copolymer membrane via electrostatic interactions. In a yet unprecedented approach, operandoscanning electrochemical microscopy (...

Journal of Molecular Structure, 2021

Abstract Multistep synthetic procedures were established for the preparation of a set of four com... more Abstract Multistep synthetic procedures were established for the preparation of a set of four compounds serving as models for aspects of molybdopterin (mpt), a unique ligand system in the active sites of molybdenum and tungsten dependent oxidoreductases. The synthesized compounds were investigated with various analytical techniques including single crystal X-ray structural determination and the measurement of the specific pKa values of all four compounds in the non-aqueous solvent acetonitrile, which range from 11.09 to 11.82. The obtained physico-chemical data supported by theoretical analysis indicate that even functional groups quite far away from the cofactor sites which are reactive can have an impact on characteristics which are important for the reactivity. The data were used to identify the likely protonation sites on the model compounds and thereby allow for a better understanding of molybdopterin's potential active role in transformations in the active sites of oxidoreductases in relation to specific functional groups of mpt with respect to protonation events and tautomerization.

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Chemical Communications, 2020

3D-printed polymer mesh substrates are converted to composite microstructured electrodes for the ... more 3D-printed polymer mesh substrates are converted to composite microstructured electrodes for the electrocatalytic oxygen evolution reaction by stepwise functionalization with a conductive nickel layer and a nickel-iron hydroxide catalyst.

The synthesis of pterin-dithiolene ligands was achieved by employing the radical nucleophilic sub... more The synthesis of pterin-dithiolene ligands was achieved by employing the radical nucleophilic substitution, i.e. the so-called “Minisci- Reaction”1. This protocol was used for the first time by Professor W. Pfleiderer on pterin substrates2 and proved a powerful method for the preparation of 6 acyl-pterins in course of this work. Subsequent construction of the dithiolene ring facilitates the synthesis of pterin-dithiolene ligands with completely unprotected pterin moieti. The molybdenum cofactor is probably one of the most relevant discoveries in the recent history of pterin chemistry and biochemistry. Many efforts have been made for the preparation of compounds able to mimic the features of the Moco ligand system called "Molybdopterin". In fact, the study of MPT models enables a deeper understanding of the “mechanism of function” of this cofactor and most importantly, lays the foundation for a potential treatment for the Moco related diseases MoCOD and iSOD.

Advanced Functional Materials

Journal of Molecular Structure, 2021

Chemical Communications, 2020