Colloquia

Most efficient chemical processes used in industry rely on heterogeneous catalysis. While the search for more sustainable processes and the changes in environmental policies impose the continuous development of more efficient catalysts, we have currently little understanding of the structure of the actives in these processes. Hence, due to their inherent complexity, heterogeneous catalysts have been mostly developed empirically.

Here, we will show how constructing active sites, one atom at a time on surfaces, enables molecular-level understanding and implementation of rational approaches for the improvement of catalytic processes. We will first illustrate how this approach enables to generate selective single-site catalysts. We will next show how from these isolated (single) sites, one can generate and understand far more complex systems such as supported nanoparticles, where interfaces, alloying… play a critical role. This lecture will be developed around these themes and will show how the development of advanced characterization tools augmented by computational approaches can provide useful information to bridge the gap between fundamental and applied (industrial) catalysis.

Enzymes are usually described through local active-site chemistry. Yet many catalytic cycles recruit global motion that spans the protein fold. This talk traces a physical chain from sequence to function: internal dynamics generate deformation; deformation sharpens specificity; strain carries force across the fold; viscoelasticity sets the operative timescale; and proteins tune one another’s activity. The result is a physical picture in which enzymes act as sequence-encoded viscoelastic machines, with catalysis coupled to mechanics.

Halide perovskites have become one of the most influential semiconductor materials platformssince 2012, combining outstanding optoelectronic performance with an unusually versatile structural and chemical design space. I will focus on how the field moved rapidly from the margins to the mainstream, and on the key early milestones that defined its trajectory. Three- and two-dimensional (3D and 2D) halide perovskites are an exceptional class of organic-inorganic semiconductors, distinguished by their remarkable carrier lifetimes and structural adaptability. Over the past15 years, these materials have achieved record efficiencies in solar cells, light-emitting devices, and radiation detection, driving rapid advancements in optoelectronic technologies. A critical next step is to deepen our understanding of how organic spacers influence their structure, properties, and performance. This presentation will explore the origins of the field, examine the current state of structure-property relationships, and provide guidelines for the selection and integration of organic spacers into crystalline materials and optoelectronic devices. Recent insights are shedding light on which organic spacer cations can effectively stabilize different perovskite structures.

Two-dimensional materials are atomically thin crystals with a huge variety of physico-chemical properties. By stacking such materials into heterostructures we can combine the electrical, optical, and vibrational excitations of different materials with atomic control over their interfaces. Despite the great selection of 2D materials existing today, we desire novel routes for their preparation in addition to cleaving them from layered bulk parent compounds.

In this talk I discuss a concept for novel 2D materials from organic molecules: Growing molecules into well-defined 2D and 1D lattices. We prepared 2D lattices of flat aromatic molecules using hexagonal boron nitride and graphene as atomically smooth substrates. The molecules are well separated in space and oriented side-by-side so that electrons and vibrations are confined to the individual building blocks. However, the interaction between their optical and vibrational transition dipole moments gives rise to collective states that can propagate inside the lattices. One-dimensional molecular lattices are grown by filling carbon- and boron-nitride nanotubes leading to giant J aggregates inside the tubes. We discuss how to use molecular lattices for advance molecular-2D-material heterostructures and how to manipulate their emergent optical excitations.

At modest temperatures, and especially above 1000 K, most of the entropy of solids comes from atomic vibrations. In 1907, Einstein proposed a quantized harmonic oscillator as a starting point. Today, normal modes of crystal vibrations are quantized, and the quanta are called "phonons." Phonons in crystals were first measured by inelastic neutron scattering in the 1950s.

Using inelastic neutron scattering and electronic structure calculations, we have compared the entropy from phonons to the entropy obtained by calorimetry. In short, excellent agreement is found when all known sources of entropy are included, such as from electrons, spins, and interactions between phonons, electrons, and spins. Interactions that cause only small departures from harmonic behavior are treated with many-body perturbation theory.

Neutron scattering revealed new anharmonic features in the phonon spectra of NaBr and Cu2O. These anharmonic features, such as phonon frequency doubling and intermodulation sidebands, can be understood with molecular dynamics or methods based on the Heisenberg-Langevin equation or the Schrödinger-Langevin equation. For Cu2O and ZnO, we found diffuse inelastic intensity (DII) at high energies, well above the phonon bands. This DII originates from brief anharmonic interactions between atoms as they vibrate, and is a new probe of anharmonic interatomic potentials.

Water electrolysis produces hydrogen and oxygen using electricity. The hydrogen and oxygen evolution reactions are typically coupled in time and space, occurring simultaneously in electrolytic cells divided by membranes into cathodic and anodic compartments. This division increases the electrolyzers cost and limits their lifetime, efficiency and ability to use intermittent electricity from solar and wind power plants. To address these limitations, we develop novel electrochemical and chemical cycles that decouple the hydrogen and oxygen evolution reactions in time and/or place. First, we used nickel (oxy)hydroxide electrodes to mediate the hydroxide ion exchange between the cathode and anode that generate hydrogen and oxygen in separate cells, enabling safe operation without membranes. Next, we developed an electrochemical – chemical cycle that use nickel (oxy)hydroxide electrodes to generate hydrogen and oxygen in different stages with separate electrolyte flows. Nowadays, we use bromide/bromate ions to store oxygen in one cell and release it in another cell, enabling continuous operation without membranes. These processes provide disruptive opportunities (as well as new challenges) to reshape century-old water electrolysis to fit for green hydrogen production using renewable electricity.

Stretched out from end-to-end, the human genome is a two meter long polymer chain. But this one-dimensional polymer is arranged inside a three-dimensional nucleus, so that genomic elements far apart along DNA can come into close spatial proximity. This interplay between linear genomic space, in which the heteropolymer’s complex monomer sequence is arrayed, and three-dimensional nuclear space, where the polymer actively interacts with its environment, gives rise to the genome’s 3D architecture. It has long been known that this architecture has the potential to regulate gene activity and drive cellular identity and function. Yet for decades, the principles governing the genome's shape were largely unknown.

My research has focused on deciphering these principles—developing technologies to map the genome’s 3D structure and using the resulting maps to discover fundamental folding mechanisms in living cells. We and our collaborators have shown that the polymer chain adopts conformations at multiple scales: simple physical constraints at large scales, domain formation and compartmentalization at intermediate scales, and highly regulated, non-equilibrium loop extrusion events at fine scales.

I will also show how we've applied these methods to accelerate genome sequencing, enabling us to study the evolution of chromosome architecture across the tree of life. This has led to the discovery of chromosome (sub)fossils in the remains of extinct creatures, and revealed how the DNA in these fossils gradually loses its shape over deep time.

2D materials offer vast variability, with nearly unlimited combinations of composition, properties, and structures. This versatility can be further extended through layer stacking and twisting, enabling unique electronic and mechanical behaviours. The diversity in chemical composition necessitates various approaches for their crystal growth and chemical modifications.

This discussion will cover the synthesis and crystal growth methods for different classes of 2D materials, including chalcogenides, halides, chalcogen-halides, and beyond. The impact of experimental conditions on their structural and functional properties will also be explored.

Exfoliation techniques, particularly those involving intercalation, provide a pathway for obtaining large-area monolayer flakes and bulk intercalated compounds with tailored properties. The effects of these methods on material characteristics will be examined. Additionally, chemical exfoliation methods for materials with layered structures held together by covalent bonds will be presented.

Finally, the applications of 2D materials across multiple fields will be discussed, including electronics, energy storage, catalysis, and beyond. This overview aims to highlight the transformative potential of 2D materials from fundamental synthesis to practical technological implementations.

To reach real sustainability for today’s preferred ‘sustainable’ types of energy, viz. electrical ones as solar (photovoltaic, PV, & wind; thermal solar & hydroelectric, which also store) and chemical ones as reduced CO2 [food], H2 & batteries, also the enabling materials need to be sustainable. Alas, mostly they are not, and that is a problem.  As sustainability implies long life spans, it is thought to be incompatible with modern society’s pillars of continuing growth & consumerism. This is a serious issue that, while outside the scope of this lecture, adds to the science & technology challenge to return to repairable devices, and repair-friendly designs, with as best option self-healing,** the most relevant option for micro- and macro-electronic device materials. The sustainable materials challenge is reminiscent of the sustainable energy one, i.e., we need to go from science fiction to reality. Starting with bio-solar conversion, via ionics and organic material self-healing, we get to inorganic light ßà electricity conversion compounds. Emphasis will be on PV materials, as in hindsight those already provide (confirm) some material self-healing criteria. Once (many) more experimental properties data will become available (& accessible), deep learning may guide further discovery.

Post-translational modifications of histones play a central role in regulating all cellular processes requiring access to DNA. Monoubiquitinated histone H2B-K120 is a hallmark of actively transcribed genes that plays multiple roles in activating transcription, while monoubiquitinated histone H2A-K119 is abundant in heterochromatin, which is transcriptionally silent. Our structural studies have revealed how histone H2B is specifically ubiquitinated and deubiquitinated, and ubiquitinated H2B stimulates histone methylation. We have also shown how ubiquitin can regulate access to the nucleosome acidic patch, a hotspot for interactions with other chromatin-modifying enzymes. I will also discuss recent studies of a histone kinase that has an unusual mode of binding nucleosomes.

Single-molecule force spectroscopy (SMFS) enables high-resolution insights into the kinetics and mechanisms of biomolecular interactions. In this talk, I will present how SMFS, helps uncover key principles in nucleic acid and protein folding. Examples discussed will include the microsecond invasion kinetics of toehold-mediated strand displacement (TMSD) of DNA and RNA as well as mRNA-Roquin interactions, which regulate mRNA degradation via specific 3’UTR hairpin structures. Finally, we study chaperone-mediated unfolding of the glucocorticoid receptor (GR), demonstrating how Hsp70/Hsp40 unfolds GR in discrete ATP-driven steps, stabilizing novel intermediates and acting as an unfoldase. These studies showcase SMFS as a powerful tool to resolve biomolecular dynamics providing new insights into RNA structure-function relationships and chaperone-mediated protein regulation.

Quantum effects play a central role in low temperature collisions. Particularly important is the formation of metastable scattering resonances that lead to temporary trapping of the colliding particles. Observation of such states has long been limited to laser cooled species, leaving chemically relevant molecules such as hydrogen out of reach. I will present our method that uses high magnetic field gradients to merge two molecular beams circumventing the laser cooling step. It allows us to perform collisions with molecular hydrogen at energies reaching 0.001 K. I will show the fingerprints of quantum resonances on observable properties and also highlight the astounding effect of the internal molecular structure and symmetry. Finally, I will discuss how a moving magnetic trap decelerator can serve as stepping stone towards the direct laser cooling of diatomic radicals.

In this contribution, NMR and other integrated structural biology studies will be presented that investigate the role of coding and non-coding mRNAs in guiding protein translation.

First, we will discuss how the choice of mRNA-codons can impact protein folding. In all genomes, most amino acids are encoded by more than one codon. Synonymous codons can modulate protein production and folding, but the mechanism connecting codon usage to protein homeostasis is not known. 2D NMR spectroscopic data suggest that structural differences are associated with different cysteine oxidation states of the purified proteins, providing a link between translation, folding, and the structures of isolated proteins.

Second, we investigate the coupling of cysteine oxidation, disulfide bond formation and structure formation in nascent chains. Thiol groups of cysteine residues undergo S-glutathionylation and S-nitrosylation and form non-native disulfide bonds. Thus, covalent modification chemistry occurs already prior to nascent chain release as the ribosome exit tunnel provides sufficient space even for disulfide bond formation which can guide protein folding.

Third, we present our work on non-coding translational riboswitches are cis-acting RNA regulators that modulate the of genes during translation initiation. Our investigation thus unravels the intricate dynamic network involving RNA regulator, ligand inducer and ribosome protein modulator during translation initiation.

In my lecture, I will showcase how designing new materials and exploring their fundamental properties can lead to innovative concepts and practical applications in organic chemistry. We will begin by discussing the synthesis of novel halo-organic compounds that enable the stereoselective catalytic synthesis of biologically relevant chiral organofluorides.

     The talk will primarily focus on the versatile chemistry of N-Heterocyclic Nitrenium ions (NHNs) – the nitrogen-based analogs of ubiquitous N-Heterocyclic Carbenes. We will demonstrate their unique coordination abilities, analyze their properties, and highlight their role in stabilizing elusive species.1,2 Nitrenium ions represent a novel family of nitrogen-based Lewis acids3 and serve as efficient metal-free catalysis, frustrated Lewis pairs partners4 and platform for isolating valuable radicals.5 Finally, we will demonstrate how the fundamental understanding nitrenium properties led to the development of triazenolysis reaction - an aza-version of the canonical alkene ozonolysis.6

References:

[1] Nat. Chem. 2011, 5, 525.

[2] Chem.Sci. 2014, 5, 1305.

[3] J. Am. Chem. Soc. 2017, 139, 4062.

[4] Angew. Chem. Int. Ed. 2020, 59, 23476.

[5] J. Am. Chem. Soc. 2022, 144, 23642; J. Am. Chem. Soc. 2024, 146, 19474.

[6] Nat. Chem. 2025, 17, 101.