This theme focuses on understanding the physico-chemical mechanisms operating in natural systems of astrochemical, geochemical, atmospheric or biological interest. It relies on state-of-the-art equipment using vibrational spectroscopy coupled with original sample environments developed in the group allowing advanced in situ and/or operando investigations.

Chemical and structural characterization of biomolecules

Tip-Enhanced Raman Spectroscopy (TERS) is used to perform the chemical and structural characterisation of biomolecules/biomaterials involved in neurodegenerative diseases (Alzheimer's disease especially), in collaboration with CBMN (UMR5248) and IMN (UMR5293). Significant spectral differences between low-toxicity Aβ(1-42) amyloid fibrils and highly toxic oligomers were identified at the single fibril scale, thus suggesting the possibility to distinguish different species in amyloid plaques of injured neuronal tissue. In addition, fibrils formed by aggregation of Tau protein fragments in the presence of a phospholipid cofactor in the inner cytoplasmic membrane were found to be a mixture of protein and phospholipid, rather than a pure protein assembly. No spectroscopic technique had previously been able to demonstrate this point. The supramolecular chirality of amyloid fibrils was also studied by infrared (IR) absorption and vibrational circular dichroism (VCD) during the fibrillation process of the peptide fragment 71-82 of α-synuclein protein, in the presence or absence of phospholipids, in the framework of a collaboration with the Université Laval at Québec (Canada). We showed that the helicity of the twisted ribbons depends on the concentration of the peptide as well as the peptide/phospholipid molar ratio and vary over time by forming supra-structures with right handed helicity.

Reactivity of atmospheric aerosols

The study of the formation and ageing of atmospheric aerosols is an important societal challenge. Understanding the physico-chemical processes operating at the scale of the individual particle is essential for a better assessment of their impact on climate change, air quality and health. The research we are developing concerns, on the one hand, the ageing of secondary organic aerosols (SOA) and, on the other hand, the atmospheric fate of iodine in the context of a serious nuclear power plant accident. These studies are conducted in close collaboration with EPOC (UMR5805) and the L2EC of the “Institut de Radioprotection et de Sûreté Nucléaire” (IRSN), but also through international collaborations (South Korea, Argentina, Japan). We have developed a methodology for the automated analysis by Raman spectroscopy of atmospheric particles sampled on supports. The characterization of submicronic SOA particles by Tip-Enhanced Raman Spectroscopy (TERS), allows a better understanding of their ageing, in particular their hygroscopicity and viscosity properties. The development of an original device composed of an acoustic levitation cell coupled to Raman micro-spectrometry and mass spectrometry is essential for studying reactivity of model organic particles with in situ conditions.

Gas hydrates: geoscience and astrophysics

Gas hydrates ('nanoporous ice' encapsulating gases such as methane, carbon dioxide or monoxide, nitrogen) exist naturally in terrestrial (e.g. ocean sea floor) and potentially extraterrestrial (Titan, Mars, comet 67P, etc.) environments. They would be involved in the chemical composition (atmospheres, oceans, etc.) of planets and comets. The understanding of their physico-chemical properties (formation mechanism, molecular selectivity, structural stability, substrate-hydrate interfaces) is crucial and several studies have been carried out thanks to the group's platform (Raman under controlled pressure/temperature), the ISM modelling unit (DFT calculations), the expertise on large scale facilities (neutron/synchrotron facilities) and the collaborations at local (ICMCB, IECB, etc.), national (in the frame of the national research consortium GDR2026 CNRS “HYDRATES”, IFREMER, Univ. Pau, Univ. Besançon, etc.) and international (Spain – Euskampus, US, Brazil, Japan, etc.) levels. We have highlighted a set of new properties concerning their formation mechanisms (impact of substrate-hydrate interfaces and coexistence of various phases), their structural meta-stability and their capability to selectively capture chemical species.

Characterization of molecules from vines and wine

Non-invasive and non-destructive analysis of wines by optical spectroscopy is a major concern for the wine industry. Raman spectroscopy is a relevant tool with the major challenge that wine is essentially composed of water and ethanol, the other compounds (sugars, polyphenols etc.) being in too low concentrations to be observed. For the first time, we performed a detailed interpretation of Raman resonance and fluorescence spectra based on TD-DFT calculations and demonstrated that the analysis of white wines with 325 nm excitation allowed the identification of the different hydroxycinnamic acids in their composition. We also studied, in collaboration with “Institut des Sciences de la Vigne et du Vin” (ISVV), how stereochemistry of lyoniresinol molecule from oak barrels influences the taste of wine. In addition, we have established the absolute configuration of the two diasteromers of the viniferin molecule (E-ε-viniferin and E-ω-viniferin) from stalks of grapevine and shown that the two diastereomers are present as a mixture of enantiomers depending on the grape variety.

Photo-reactivity of carbon molecules trapped on icy grains in the interstellar medium

The approach combining spectroscopy experiments of isolated species in cryogenic matrices and a multi-scale and multi-method theoretical approach (DFT, classical and quantum dynamics), allowed us to study the role of water in the photo-oxidation reactions of PAHs (polycyclic aromatic hydrocarbons). Thanks to the environmental effects (argon matrix, water ice) on the geometry of water aggregates and their complexes with PAHs, we have demonstrated the photo-oxidation of PAHs by small water aggregates under UV-visible irradiation at >230 nm, whereas it was thought that only water ice allowed these photo-reactions at λ < 200 nm. We measured the evolution of the infrared spectra and ionization potentials of PAHs adsorbed on water ice and showed the influence of the ice structure on the photo-oxidation of PAHs. We also characterized the very low temperature photo-reactivity of iron atoms with water and the possible production of hydrogen. These studies have implications for astrochemistry, for the assignment of the AIB and DIB bands, for feeding astrochemical models of gas grains and for the interpretation of future JWST data. This project was conducted in collaboration with LCPQ (UMR 5626), PhLAM (UMR 8523), and CELIA (UMR 8202).

Ongoing projects

Our research projects mainly concern (1) the study of the chemical and photochemical ageing of secondary organic aerosols in the atmosphere at the scale of the individual particle, (2) the study of the physico-chemical factors impacting the macroscopic properties of naturally occuring gas hydrates in order to evaluate the quantities of entrapped gas and finally (3) the spectroscopic study of amyloid fibrils formed from Aβ(1-42) peptides and α-synuclein proteins involved in Alzheimer’s and Parkinson's diseases respectively. Our main objectives are the determination of the processes and mechanisms at the nanometric and molecular levels as well as the study of surfaces, interfaces and structural properties. This work on real samples will require (1) the adaptation and optimization of existing spectroscopic tools in the group (TERS, SERS, VCD, Hyper-Rayleigh and Hyper-Raman instruments) and (2) the development of new couplings of advanced spectroscopic techniques (TERS nano-indentation, Raman/FTIR/diffraction coupling) together with sample environments (TERS in liquid media, TERS in controlled temperature and gas environment, levitation/FTIR/MS) in order to reproduce environmental conditions as faithfully as possible. This multidisciplinary research with a strong societal impacts (for example: climate change, health…) will be carried out in the framework of local, national and international collaborations.