Summary

Van der Waals and molecular cluster ions, the guiding thread of this concerted research action, are important objects for fundamental research in chemistry and astrophysics but also for analytical and materials science applications. The question at the heart of our proposal was: How can cluster ion beams be engineered, characterized and used to control the transfer and ionization of complex (bio)molecules, for the design of new surface architectures and for enhanced mass spectrometry? Around this central theme, more specific scientific questions were investigated in detail in each research work package. They concerned the spectroscopic study of ionic complexes (WP1), the transfer of large intact biomolecules from the solid to a surface through the gas phase (WP2) and the investigation of ionization under cluster ion impacts for improving sensitivity in secondary ion mass spectrometry – SIMS (WP3). This project aimed thus at a better understanding of the production of cluster ions, of their properties, and of their interactions with target molecules. The generated knowledge paves the way to important developments in cluster spectroscopy, (nano)fabrication of organic and biological layers, and 3D chemical characterization by mass spectrometry.

In the first work package (WP1), methods were developed to produce atomic and molecular cluster ion beams, which were then studied by high-resolution spectroscopy. The in-depth spectroscopic study of molecular and cluster ions delivered key information for their detection in astrophysical environments as well as for the understanding of model chemical reactions. First, experimental photodissociation spectra of N₂O⁺ have been measured in our homebuilt instrument and successfully compared to rovibronic simulations. Then, a full spectroscopic study of water-nitrogen complexes: N2-D2O/N2-DOH was conducted by R. Glorieux. The results of this analysis were used to move forward in the spectroscopic study of N2-H2O. New measurements in the OD stretching region of the water molecule inside the Ar-D2O complex were also interpreted. Finally, a beam of [(H₂O)_m-(CO₂)_n]⁺ clusters was also obtained and characterized, which also constitutes a very promising cluster ion source for improved ionization in SIMS (see WP3). Other achievements are well illustrated in the publication list (PUB # 1,3,9,10).

In a second work package (WP2), the potentialities of cluster ion beams to transfer non-volatile and fragile biomolecules from a target onto a collecting surface were evaluated and exploited. Target layers of proteins and enzymes of increasing complexity (bradykinin, insulin, lysozyme, trypsin, etc.) could be transferred intact in UHV using Ar_1500-5000⁺ ions by V. Delmez (PUB # 4,7,12). The effect of the size, conformation and distribution of the target molecules on their transfer and final conformation, distribution and bioactivity were investigated. In particular, enzymatic activity assays demonstrated the preservation or easy recovery in solution of the three-dimensional structure of the transferred lysozymes (PUB # 7). The importance of parameters related to the cluster ions (size, energy) were unraveled, in particular, the inverse dependence of the intact fraction of transferred biomolecules on the energy per atom (E/n) in the cluster ion projectile. The transfer of complex assemblies of polyelectrolytes and proteins have also been investigated. The acquired knowledge also allowed us to design biosurfaces presenting architectures that cannot be attained by deposition from solution (PUB # 12). Complementary molecular transfer approaches and the transfer of mass-selected ions will be explored in this last year of the project owing to our new homemade instrument (see WP4). In parallel, molecular dynamics simulations helped understand the mechanisms of intact emission for such macromolecules and predicted that even larger molecules (~60 kDa) should be desorbed without fragmentation provided that the right cluster projectile size and energy are selected (PUB # 11).

The third work package (WP3) focused on producing molecular ions with a significantly improved yield for imaging mass spectrometry. It implied further understanding of ionization processes under the action of cluster ions. Matrix molecules were first deposited on the samples to be analyzed using a homemade sublimation device and/or in situ molecular transfer by Ar cluster ions, like in WP2. The advantage of the latter approach, introduced in this project, is that it can be combined in an automated 3D imaging protocol because the whole sequence of: 1.matrix transfer on the sample surface/2.high resolution imaging/3.molecular depth-profiling is conducted in situ and can be repeated at will without returning to atmospheric pressure (PUB #8). The influence of the nature of the matrix molecules (MALDI matrices, etc.) on ionization was first evaluated and tested on various tissue samples in collaboration with our colleagues of the De Duve Institute and Pharmacy School of UCLouvain. Other types of matrices, such as metal-organic complexes were also investigated, and their ionization efficiency compared for a series of samples, with a view to enhance ionization, and to better understand its mechanisms. In parallel, an innovative approach for solid biosample molecular analysis was developed by B. Tomasetti, involving the full sputtering and transfer of a microvolume of bio/tissue sample on a specifically designed collector covered with an efficient ionizing matrix or an array of matrices in order to detect a wider range of molecular signals and take advantage of all the material sputtered upon ion etching. In this last year of the project, we eventually hope to be able to use our newly developed beams of [(H₂O)_m-(CO₂)_n]⁺ clusters (see WP1) for improving ionization in SIMS.

Finally, the fourth work package (WP4) was dedicated to the build-up of a specifically designed instrument, including a cluster ion source and associated mass selection, a tailored chamber with the target and collector, and a column for the mass selection of transferred ions. While the design and installation were being finalized, the scientific researches of WP1-3 were tackled using a first cluster source prototype and a state-of-the-art ToF-SIMS, available in our laboratories.

List of PhDs accomplished within the ARC

The following PhD thesis were or are being accomplished within the iBEAM project

· Raghed BEJJANI, Conception, construction and validation of scientific instruments to study the

spectrum of cold ionic species, 10/2021.

· Vincent DELMEZ, Transferring biomolecules with gas cluster ion beams, 11/2022.

· Robin GLORIEUX, High-resolution photodissociation spectroscopy of small molecular clusters, planned 12/2023.

· Benjamin TOMASETTI, New approaches for biosurface tailoring, planned 9/2024.

Several postdoctoral fellows also contributed to the project: K. Moshkunov, A. Roucou, B. Hays, J. Fréreux, A. Bogomolov.

List of master theses

· Arnaud Bertrand – Fabrication of thin protein layers using ionized cluster beams (2019).

· Thomas Daphnis – Biomolecule transfer using large cluster ion beams (2020).

· Benjamin Tomasetti – Ionization enhancement in SIMS using organic matrices (2020).

· William Borsos – Soft desorption and transfer of non-covalent complexes using gas cluster ion beams (2021).

· Charline van Hinderdael – Improvement of protein transfer using gas cluster ion beams (2022).

· Victoire Stavaux – Development of mass spectrometry imaging for endometrium tissues (2022).

· Colin Nicolay – New approaches for improved ionization in SIMS imaging (2023).

List of publications

The following articles were published specifically on topics studied within the ARC project. Publications with two or more co-promoters (in bold) should be considered as “common publications”.

1.      C. Lauzin, A.C. Imbreckx, T. Foldes, T. Vanfleteren, N. Moazzen-Ahmadi, M. Herman, High-resolution spectroscopic study of the H₂O–CO₂ van der Waals complex in the 2OH overtone range, Molecular Physics, (2019) 1-9.

2.      A. Delcorte, C. Poleunis, Mechanistic Insight into Gas Cluster-Induced Sputtering of Kilodalton Molecules using Kinetic Energy Distribution Measurements, J. Phys. Chem. C 123 (2019) 19704−19714.

3.      C. Lauzin, A. C. Imbreckx, T. Foldes, T. Vanfleteren, N. Moazzen-Ahmadi, M. Herman, High-resolution spectroscopic study of the H₂O–CO₂ van der Waals complex in the 2OH overtone range, Molecular Physics 118(11), e1706776, (2020).

4.      A. Delcorte, V. Delmez, Ch. Dupont-Gillain, C. Lauzin, H. Jefford, M. Chundak, C. Poleunis, K. Moshkunov, Large cluster ions: Soft local probes and tools for organic and bio surfaces, Phys. Chem. Chem. Phys. 22, 17427-17447 (2020). (2020 PCCP HOT Articles)

5.      M. Chundak, C. Poleunis, V. Delmez, H. Jefford, L. Bonnaud, A. M. Jonas, A. Delcorte, Argon gas cluster fragmentation and scattering as a probe of the surface physics of thermoset polymers, Applied Surface Science 533, 147473 (2020).

6.      R. Bejjani, A. Roucou, X. Urbain, K. Moshkunov, G. Vanlancker, C. Lauzin. STARGATE: a new instrument for high-resolution photodissociation spectroscopy of cold ionic species, Review of Scientific Instruments, 2021, 92(3), 033307.

7.      V. Delmez, H. Degand, C. Poleunis, K. Moshkunov, M. Chundak, Ch. Dupont-Gillain, A. Delcorte, Deposition of Intact and Active Proteins In Vacuo Using Large Argon Cluster Ion Beams, J. Phys. Chem. Letters, 2021, 12, 952-957.

8.      K. Moshkunov, B. Tomasetti, V. Delmez, J. Quanico, G. Baggerman, F. Lemiere, Ch. Dupont-Gillain, I. Gilmore, A. Delcorte, Molecular ion signal enhancement using sputter-transferred matrix in Secondary Ion Mass Spectrometry, Analyst, 2021, 146, 6506-6519.

9.      O. Asvany, C. R. Markus, A. Roucou, S. Schlemmer, S. Thorwirth, C. Lauzin. The fundamental rotational transition of NO⁺. Journal of Molecular Spectroscopy, 2021, 378, 111447.

10.   A. S. Bogomolov, A. Roucou, R. Bejjani, M. Herman, N. Moazzen-Ahmadi, C. Lauzin, “The rotationally resolved symmetric 2OH excitation in H₂O-CO₂ observed using pulsed supersonic expansion and CW-CRDS” Chemical Physics Letters, 2021, 774, 138606.

11.   A. Delcorte, A microscopic view of macromolecule transfer in the vacuum using gas and bismuth clusters, J. Phys. Chem. C, 2022, 126 (16), 7307-7318.

12.   V. Delmez, B. Tomasetti, T. Daphnis, C. Poleunis, C. Lauzin, C. Dupont-Gillain, A. Delcorte, Gas cluster ion beam as a versatile soft-landing tool for the controlled construction of thin (bio)films, ACS Applied Bio Materials, 2022, 5 (7), 3180-3192.

13.   S. Bertolini, A. Delcorte, Reactive molecular dynamics simulations of lysozyme desorption under Ar cluster impact, Appl. Surf. Sci. 2023, 631, 157487.

14.   T. Daphnis, B. Tomasetti, V. Delmez, K. Vanvarenberg, V. Préat, C. Thieffry, P. Henriet, C. Dupont-Gillain, A. Delcorte, Improvement of Lipid Detection in Mouse Brain and Human Uterine Tissue Sections Using In Situ Matrix Enhanced Secondary Ion Mass Spectrometry, Journal of the American Society for Mass Spectrometry 2023, published online.

15.   B. Tomasetti, C. Lauzin, A. Delcorte, Enhancing Ion Signals and Improving Matrix Selection in Time-of-Flight Secondary Ion Mass Spectrometry with Microvolume Expansion Using Large Argon Clusters, Anal. Chem. 2023, published online.