Molecular and hybrid systems for solar-to-chemical energy conversion

My Ph.D. thesis was dedicated to the exploration of different paths to convert sunlight into the shape of chemical bonds, by the formation of solar fuels. During the past three years, I have focused my research on two of these, namely molecular hydrogen H2 and the reduced nicotinamide adenine dinucleotide enzyme cofactor NAD(P)H. The first could become the ideal energy carrier for a truly clean energy system; it currently represents the best chance to liberate humanity from its dependence on fossil fuels. To address this, I studied different systems which can achieve proton reduction upon light absorption. More specifically, part of my work was aimed to the development of a cost-effective and stable catalyst in combination with a well-known photochemical cycle. To this extent, I worked on transition metal oxides which, as demonstrated in this work, have been identified as promising H2 evolution catalysts, showing excellent activity, stability, and previously unreported versatility. Another branch of my work on hydrogen production dealt with the use of a new class of polymeric semiconductor materials to absorb light and convert it into H2. The second solar fuel mentioned above is a key component of the most powerful methods for chemical synthesis: enzyme catalysis. The high cost of the reduced forms prohibits large-scale utilization, so artificial photosynthetic approaches for regenerating it are being intensively studied. The first system I developed exploits the tremendous reducing properties of a scarcely known ruthenium complex which is able to reduce NAD+. Lastly, I sought to revert the classical role of the sacrificial electron donor to an active component of the system and, to boost the process, I build up an autonomous microfluidic system able to generate highly reproducible NAD(P)H amount, demonstrating the superior performance of microfluidic reactors over batch and representing another successful photochemical NAD(P)H regeneration system.

Synthesis, multiscale-multiphase characterization and applications of thiophene-based biohybrids

Biohybrid derivatives of π-conjugated materials are emerging as powerful tools to study biological events through the (opto)electronic variations of the π-conjugated moieties, as well as to direct and govern the self-assembly properties of the organic materials through the organization principles of the bio component. So far, very few examples of thiophene-based biohybrids have been reported. The aim of this Ph. D thesis has been the development of oligothiophene-oligonucleotide hybrid derivatives as tools, on one side, to detect DNA hybridisation events and, on the other, as model compounds to investigate thiophene-nucleobase interactions in the solid state. To obtain oligothiophene bioconjugates with the required high level of purity, we first developed new synthetic ecofriendly protocols for the synthesis of thiophene oligomers. Our innovative heterogeneous Suzuki coupling methodology, carried out in EtOH/water or isopropanol under microwave irradiation, allowed us to obtain alkyl substituted oligothiophenes and thiophene based co-oligomers in high yields and very short reaction times, free from residual metals and with improved film forming properties. These methodologies were subsequently applied in the synthesis of oligothiophene-oligonucleotide conjugates. Oligothiophene-5-labeled deoxyuridines were synthesized and incorporated into 19-meric oligonucletide sequences. We showed that the oligothiophene-labeled oligonucletide sequences obtained can be used as probes to detect a single nucleotide polymorphism (SNP) in complementary DNA target sequences. In fact, all the probes showed marked variations in emission intensity upon hybridization with a complementary target sequence. The observed variations in emitted light were comparable or even superior to those reported in similar studies, showing that the biohybrids can potentially be useful to develop biosensors for the detection of DNA mismatches. Finally, water-soluble, photoluminescent and electroactive dinucleotide-hybrid derivatives of quaterthiophene and quinquethiophene were synthesized. By means of a combination of spectroscopy and microscopy techniques, electrical characterizations, microfluidic measurements and theoretical calculations, we were able to demonstrate that the self-assembly modalities of the biohybrids in thin films are driven by the interplay of intra and intermolecular interactions in which the π-stacking between the oligothiophene and nucleotide bases plays a major role.

Novel bio-based amine curing agents for epoxy resins: the way towards fully bio-based composite materials

Epoxy resins are widely used in many applications, such as paints, adhesives and matrices for composites materials, since they present the possibility to be easily and conveniently tailored in order to display a unique combination of characteristics. In literature, various examples of bio-based epoxy resins produced from a wide range of renewable sources can be found. Nevertheless, the toxicity and safety of curing agents have not been deeply investigated and it was observed that all of them still present some environmental drawback. Therefore, the development of new environmentally friendly fully bio-based epoxy systems is of great importance for designing green and sustainable materials. In this context, the present project aims at further exploring the possibility of using bio-based compounds as curing agents for epoxy resin precursors. A preliminary evaluation of several amine-based compounds demonstrated the feasibility of using Adenine as epoxy resin hardener. In order to better understand the crosslinking mechanism, the reaction of Adenine with the mono-epoxy compound Glycidyl 2-methylphenyl ether (G2MPE), was study by 1H-NMR analysis. Then Adenine was investigated as hardener of Diglycidil ether of bisphenol A (DGEBA), which is the simplest epoxy resin based on bisphenol A, in order to determine the best hardener/resin stoichiometric ratio, and evaluate the crosslinking kinetics and conversion and the final mechanical properties of the cured resin. Then, Adenine was tested as hardener of commercial epoxy resins, in particular the infusion resin Elan-tron® EC 157 (Elantas), the impregnation resin EPON™ Resin 828 (Hexion) and the bio-based resin SUPER SAP® CLR (Entropyresins). Such systems were used for the production of composites materials reinforced with chopped recycled carbon fibers and natural fibers (flax and jute). The thermo-mechanical properties of these materials have been studied in comparison with those ones of composites obtained with the same thermosetting resin reinforced with chopped virgin carbon fibers.