Faculty of Science
Faculty of Science
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Faculty of Science
Department of Chemistry
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Ultrafast Chiral Spectroscopy for Stereocontrolled Photochemistry
Research Project  | 1 Project Members

Chiral molecules exist in two forms, called enantiomers, which are mirror images of each other but non-superimposable. Even though enantiomers share most chemical and physical properties, they may differ greatly in their (bio-)chemical activities, which turns chirality into a key design feature for (bio-)chemical function. In this spirit, the incorporation of chiral structures into photoactive molecular systems has emerged as a powerful strategy to control their photochemical functions: uni-directional molecular motors, chiral photocatalysts, and chiral metal nano-structures permit new levels of stereocontrol over mechanical motion, energy transfer, and electric charge-carriers on the nanoscale, with applications ranging from the construction of nanoscale machines to the light-driven synthesis of enantiopure compounds. However, the direct characterization and optimization of the chiral photoexcited states that drive these processes has remained a formidable challenge, due to a lack of analytical techniques with chiral sensitivity and sufficient time resolution to capture the excited state dynamics – especially in the native solution phase of many photochemical processes. To address this gap, I will build on previous breakthrough studies to deliver a new laser-based chiral spectroscopy technique with femtosecond time resolution and ultra-broad spectral detection from the visible to the far ultraviolet (UV) regime. These capabilities will be unique world-wide and open the path to resolve the stereocontrol mechanisms of chiral photoactive systems that have thus far remained inaccessible. For the chiral photochemistry community, this can be transformative: the direct analysis of excited state chirality promises design strategies that have previously been difficult to pursue. This project will establish the conceptual foundations for these strategies by focusing on the three processes that are the fundamental building blocks of most photoactive systems: photoisomerization, excitation energy transfer, and electric charge carrier dynamics. In a joint effort with experts in chiral synthesis, the project will study their stereocontrol via tailor-made chiral compounds, as summarized in the project goals:


Goal 1: Ultrafast chiral spectroscopy. This project will deliver an ultrafast laser spectroscopy setup with unprecedented time resolution and chiral sensitivity. Via novel photonic technology it will cover the entire deep-UV window (190-300 nm) for the first time, which encodes the chiral structures of many (bio-)chemical systems.


Goal 2: Stereocontrol of mechanical motion in molecular motors. Tracking the motion of synthetic molecular machines has remained a challenge, as the dynamics may cover multiple time and length scales. This project will capture the kinetics of chiral molecular motors in real-time, thereby informing future design improvements.


Goal 3: Stereocontrol of energy transfer in luminescent complexes. Circularly polarized luminescence (CPL) from chiral organo(-metallic) materials promises applications in mobile phone screens and bio-sensing. This project will determine the mechanisms of record-breaking CPL complexes to develop rational design guidelines.


Goal 4: Sterecontrol of charge-carrier dynamics in gold nanoparticles. Chiral metal nanoparticles hold tremendous promise as photosensitizers for enantioselective photochemistry. This project will determine the coupling of their chiral structural morphology to the underlying electric charge-carrier dynamics on opposite ends of the size scale: in large plasmonic nanohelices (>30 nm) and in molecule-like gold nanoclusters (<3 nm).


Impact: This project will establish ultrafast chiral spectroscopy as a new analytical tool for photochemistry and advance current capabilities for stereocontrolling photochemical processes in a wide range of molecular systems. It will thus have a strong impact on multiple disciplines developing photoactive materials, from enantioselective photocatalysis to nano-material science. Additionally, this project addresses two high-impact challenges in ultrafast spectroscopy: (1) expanding it to the far-UV spectral regime, and (2) developing a new method that combines high time and structural resolution in liquids.

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Exploring and Controlling Chemistry Using Quantum Logic
Research Project  | 1 Project Members
Over the past years, the development of experimental techniques for the coherent manipulation and control of single isolated quantum systems has made impressive progress. Such "quantum-logic" methods are also highly attractive in a chemical context in view of unravelling and controlling the quantum dynamics of molecular collisions and chemical reactions. However, for complex quantum systems like molecules, these techniques are still in their infancy and their considerable potential remains to be unlocked. The aim of the present project is to merge the fields of quantum science and chemical dynamics by advancing quantum technologies to polyatomic molecular ions and applying them to the study of ion-molecule collisions and chemical reactions. For this purpose, we have recently developed a quantum-non-demolition technique which enables the readout and spectroscopy of the quantum state of a single molecular ion without destroying the molecule or even perturbing its quantum state [Science 367 (2020), 1213]. In the present project, we will apply this method to achieve a complete projective state preparation of single molecular ions in specific Zeeman- hyperfine-spin-rovibronic levels as a starting point for collision studies and use the same methods to sen- sitively detect the quantum state of the collision product. In this way, state-to-state experiments on the single-molecule level will be realised using a quantum-logic state readout. In combination with Stark- decelerated beams of neutral molecules, we will be able to study for the first time completely state- and energy-controlled ion-molecule elastic, inelastic and reactive collisions. In particular, we will be able to explore the role of the hyperfine and Zeeman states in collisions involving molecular ions, which is largely uncharted territory. The quantum-non-demolition nature of our detection scheme will allow us to reach measurement sensitivities several orders of magnitude higher compared to previously used destruc- tive methods and thus enable an unprecedented precision in the study of ionic collisional processes. By introducing quantum-logic approaches to the study of molecular collisions, the present project will establish a new paradigm for probing molecular processes and a new frontier in studies of chemical dy- namics. The extension of our methods to polyatomics will also make a broad range of molecular systems available for applications in the quantum sciences including quantum bits, quantum memories, quantum simulations and quantum sensing.
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Light-Driven Charge Accumulation based on Earth-Abundant High-Potential Photosensitizers
Research Project  | 1 Project Members
Lichtinduzierte Elektronentransfer-Reaktionen sind chemische Elementarschritte, die in der biologischen Photosynthese eine zentrale Rolle spielen. Ein grundlegendes Verständnis dieser Elementarschritte ist daher für die Umwandlung von Sonnenergie in chemisch gespeicherte Energie in künstlichen Photosynthese-Systemen von Interesse. Chemische Modellverbindungen, in denen ein Elektronen-Donor, eine lichtabsorbierende Einheit (der sogenannte Photosensibilisator) und ein Elektronen-Akzeptor kovalent miteinander verbunden sind, eignen sich besonders gut für grundlegende Untersuchungen, weil in solchen Triaden-Verbindungen die Elektronentransfer-Prozesse direkt beobachtbar sind. Bisherige Untersuchungen an Triaden-Verbindungen fokussierten vor allem auf die lichtinduzierte Übertragung von einzelnen Elektronen. In der biologischen Photosynthese werden jedoch pro Reaktionsumsatz meist mehrere Elektronen benötigt und daher hat die Natur Wege gefunden, mehrere Elektronen zu akkumulieren. In Triaden-Verbindungen ist dies bislang erst selten gelungen. In diesem Forschungsvorhaben sollen daher die Grundlagen der lichtgetriebenen Elektronen-Akkumulation in Triaden-Verbindungen erforscht werden. Frühere Studien an Triaden-Verbindungen verwendeten ausserdem sehr oft Photosensibilisatoren, die aus Edelmetallen bestehen. In diesem Projekt geht es auch darum, auf kostengünstigeren Metallen aufgebaute Triaden-Verbindungen zu untersuchen. Dies scheint aus Gründen der Nachhaltigkeit wünschenswert, und andererseits können von neuartigen Photosensibilisatoren besonders günstige Elektronentransfer-Eigenschaften erwartet werden.
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Synthetische Nanoskalige Objekte: Bausteine für funktionale Materialien und Funktionseinheiten
Research Project  | 10 Project Members
The proposal follows the SNF advice of a single project per applicant in division II. It is divided in five subprojects, each being the subject of a PhD thesis. In spite of the different research targets, they have enough overlap enabling the fruitful exchange of knowledge and mutual developments required to build up a joint group identity. All five projects focus on current challenges in nanotechnology, molecular devices, and supramolecular materials, which are addressed by novel strategies and innovative molecular designs of functional structures. The five subprojects are briefly described in the following: (I) «Geländer»-molecules and helical architectures: «Geländer»-molecules consist of two periodically interlinked oligomers which compensate their length mismatch by wrapping the longer one helically around the shorter one, resembling the shape of the banister (Geländer in German) of a spiral staircase. The here promoted new designs profit from right-angled connections resulting in a simplified symmetry of the building blocks which should make longer oligomers synthetically accessible. A second strategy based on o-tetraphenylene building blocks is geared towards helical «plait»-type oligomers. (II) mechanosensitive model compounds for molecular junctions are based on cyclophane-type architectures enabling to tune the extent of the coupling between their subunits mechanically. With small [2.2]paracyclonaphthane derivatives the effect of torque motion shall be explored, while a polycyclic porphyrin hexamer will be assembled with two stacked states with large difference in their expansion. Based on a «upended» porphyrin type structure, even the coupling of the single electrons of two parallel radical planes might be investigated. (III) B-field sensitive macrocyclic model compounds are loop-shaped macrocycles consisting of a conjugated periphery decorated with terminal anchor groups enabling their integration in single molecule junction experiments. The intention is to detect the contribution of the Lorentz force to the molecules transport current. With a compact and twisted OPE type macrocycle, the axial chirality of the immobilized structure might become specifiable in the transport experiment. (IV) synthesis of an armchair carbon nanotube (CNT) is an interesting synthetic strategy for the controlled wet chemical assembly of an armchair CNT. A belt fragment of a CNT shall be obtained from a macrocycle by a reaction sequence, which can subsequently be repeatedly applied to control the length of the CNT. (V) approaches towards molecular textiles are based on the development of a cross-type junction acting a covalent template arranging the precursors at the water/air interface. Upon interlinking within the LB-film and cleavage of the template, textile-type interwoven molecular films should be obtained. The potential of the cross-type junction for superstructures will be investigated as well.
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Quantum technologies for molecular precision spectroscopy
Research Project  | 1 Project Members
In recent years, impressive advances in the cooling, manipulation and quantum control of ultracold trapped atoms and atomic ions have been achieved which enabled spectroscopic measurements with an unprecedented precision. Similarly precise spectroscopic experiments on molecules open up a range of new scientific perspectives including tests of new physical concepts, the implementation of new fre- quency standards, accurate evaluations of physical theories such as quantum electrodynamics, precise determinations of fundamental constants and exact studies of the properties of molecules and their con- stituent particles. They also lay the foundations for applications of molecules in the realm of modern quantum science such as quantum information and quantum sensing. However, the complex energy-level structure of molecules and the absence of optical cycling transitions in most molecular systems constitute a major challenge for their state preparation, laser cooling, state detection, coherent manipulation and, therefore, precise spectroscopic characterisation. Molecular ions confined in radiofrequency traps and sympathetically cooled by simultaneously trap- ped atomic ions have proven a promising route for overcoming these obstacles. We have recently devel- oped a new experimental scheme enabling the readout of the quantum state of a single trapped molecular ion without destroying the molecule and indeed the quantum state itself. This quantum-non-demolition technique enables spectroscopic experiments with four to five orders of magnitude faster duty cycles than previous destructive state-readout techniques and concomitant improvements in spectroscopic sensitivity and precision. Such "quantum-logic" methods represent a paradigm change in the way spectroscopic experiments are performed on molecules. In the present project, we will harness the potential of this new approach to perform highly sensitive spectroscopic measurements on the hyperfine, rotational and vibrational energy- level structure of the homonuclear diatomic ion N+2 with unprecedented precision. N+2 has previously been identified as an ideal system for molecular precision measurements. In a recent comprehensive the- oretical screening, we have explored suitable clock transitions within the energy-level manifolds of N+2 which will be characterised experimentally in the present project. We will make use of a newly estab- lished infrastructure for the distribution of the Swiss primary frequency standard at the Swiss metrology institute METAS in Berne to our laboratory in Basel via an optical fibre link. Referencing all our laser sources to the METAS standard will allow us to reach an absolute measurement precision on the level of 10−15 thus establishing a new frontier in the precision of spectroscopic measurements on molecular ions across different frequency domains. The clock transitions to be probed here are predicted to also exhibit excellent coherence properties and are therefore attractive candidates for molecular quantum bits with prospective applications in quantum science. In summary, using quantum-logic techniques for state readout in combination with remote calibration to the Swiss primary frequency standard via a fibre link, the present project will introduce new methods for molecular frequency metrology and establish new limits in the measurement precision of the hyper- fine, rotational and vibrational spectroscopy of molecular ions. In this framework, we will also perform the first direct rotational spectroscopy on a homonuclear diatomic ion. Besides their immediate relevance for molecular spectroscopy, the targeted results are expected to be of importance for the wider field of frequency metrology and the development of new frequency standards, for atomic, molecular, optical and chemical physics by introducing new concepts to probe and interrogate molecules, for quantum science by establishing quantum bits with very high coherence properties and also for fundamental physics by setting new constraints on a possible time variation of the electron-proton mass ratio.
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Exploring Sequence-Function Landscapes of Therapeutic Enzymes using Single-Cell Hydrogel Encapsulation and Deep Sequencing
Research Project  | 3 Project Members
The pharmaceutical industry is rapidly transitioning from small molecule therapeutics towards biologics. Among the various classes of biologics under development, therapeutic enzymes are gaining attention as molecular entities that can catalyze specific chemical reactions in the body to achieve a therapeutic effect. Therapeutic enzymes can be delivered systemically as full proteins or incorporated into gene therapies to transduce target cells with specific functionality in vivo. In these envisioned applications, understanding sequence-function relationships of therapeutic enzymes will play a crucial role. There is therefore an urgent need for improved methods for molecular analysis and enhancement of therapeutic enzymes. Naturally occurring enzyme sequences are typically not suitable as biopharmaceuticals due to general lack of stability, developability, and/or activity. In this context, molecular enhancement by improvement of colloidal stability, catalytic turnover rate, substrate binding affinity, and/or sensitivity to environmental conditions are essential steps in enabling therapeutic enzymes to reach their full potential. The establishment of rapid design, build, test, and learn (DBTL) cycles and the analysis of large-scale sequence-function relationships for therapeutic enzymes will be crucial for the advancement of leading therapeutic strategies.The Nash Lab at the University of Basel/ETH Zurich focuses on engineering and biophysics of artificial biomolecular systems. We recently developed an ultrahigh throughput enzyme screening strategy that outperforms multi-well robotic assays and automation by several orders of magnitude. We are now able to screen genetic libraries of catalytic enzymes using a one-pot reaction followed by fluorescence activated cell sorting (FACS). Our system is based on localized enzyme-triggered polymerization of a hydrogel capsule around individual yeast cells. Our goal is to utilize the ultrahigh throughput nature of this system to analyze sequence-function landscapes of enzymes on an unprecedented scale.
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Novel Catalysis by Transition Metal Phosphides and Chalcogenides Using Molecular Perspectives on their Interfacial Chemistry
Research Project  | 3 Project Members
The global demand for functionalized chemical products requires active and selective catalysts. Many current technologies are based on rare and expensive noble metal catalysts. Transition metal phosphides and the biomimetic transition metal chalcogenides are promising earth-abundant replacements for noble metal catalysts in many processes. These binary materials (M n X m ) show promise for catalytic water splitting and hydrotreating, but have barely been explored in catalysis for fine-chemical synthesis. The stability, conductivity, and promising catalytic properties of M n X m suggest that there is a plethora of catalysis and electrocatalysis yet to be discovered. Due to their binary composition, M n X m surfaces will likely exhibit complementary selectivity compared to conventional metal catalysts. The goal of the proposed research program is to develop M n X m materials as catalysts for complex chemistry and added-value chemical products. The aim is to broadly survey catalysis of reductive and oxidative transformations with M n X m . The catalytic properties of M n X m will be tuned by chemical surface modifications. The rational development of M n X m as catalysts will rest on fundamental studies of structure, thermochemistry, and interfacial reactivity of the operative surfaces on a molecular-level. This will be achieved by spectroscopic surface characterization, especially in-situ surface-enhanced infrared absorption spectroscopy, stoichiometric equilibration reactions with selected reagents, and parallel study of anchored molecular analogues. The combination of catalytic survey and catalyst tuning with the underlying fundamentals will be a powerful approach to reveal novel catalysis by transition metal phosphides and chalcogenides with properties and selectivity that are currently unattainable for metal catalysts. This research could open up great opportunities for the technological application of inexpensive, earth-abundant binary materials for chemical synthesis.
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ExploDProteins
Research Project  | 1 Project Members
Here I propose to use small molecules to degrade proteins specifically around sites of DNA damage by using the damage itself as a homing signal. The approach will create new ways to study DNA damage, but will also offer translational possibilities in cancer. Cancer cells are often acutely sensitive to DNA damage because they have one or more faulty DNA damage response pathways - a feature that makes them highly dependent on their remaining DNA repair systems. We will pioneer two novel and related chemical approaches for selectively degrading proteins by modulating DNA damage response pathways with bifunctional DNA damaging molecules. We will do this by reprogramming E3 ligases. E3 ligases are multi-protein complexes that catalyse the formation of polyubiquitin chains on its substrates, leading to their degradation in the protein recycling station known as the proteasome. A recent revolutionary advance in chemical biology is to use small molecules to change the specificity of E3 ligases, leading to the degradation of user-defined proteins. By degrading proteins instead of inhibiting them, these small molecules achieve levels of functional modulation typically only possible with genetic techniques. We are inspired by this new protein degradation technology, but will take it in a new direction. Chemical damage of DNA recruits E3 ligases as well as critical DNA damage response proteins in preparation for DNA repair. We will invent a new generation of small molecule protein degradation catalysts and reagents by repurposing these natural responses to DNA damage. We will accomplish our goal with three aims: Aim 1: Use DNA damage as a homing signal for induced protein degradation Aim 2: Use direct repair of DNA damage by the repair protein methylguanine methyltransferase (MGMT) to promote the degradation of other proteins Aim 3: Promote pleiotropic protein degradation by recruiting broadly acting E3 ligases to sites of DNA damage I propose an ambitious project that will create conceptually novel ways to study the DNA damage response and potentially build new medicines.