Lectures & Events

Magnetic Resonance Seminar

Intracellular metabolites that give rise to quantifiable MR resonances are excellent structural probes for the intracellular space, and are oftentimes specific, or preferential enough to a certain cell type to provide information that is also cell-type specific. In the brain, N-acetylaspartate (NAA) and glutamate (Glu) are predominantly neuronal/axonal in nature, whereas soluble choline compounds (tCho), myo-inositol (mI) and glutamine (Gln) are predominantly glial. The diffusion properties of these metabolites, examined by diffusion weighted MR spectroscopy (DWS) exclusively reflect properties of the intracellular milieu, thus reflecting properties such as cytosolic viscosity, macromolecular crowding, tortuosity of the intracellular space, the integrity of the cytoskeleton and other intracellular structures, and in some cases – intracellular sub-compartmentation and exchange. The presentation will introduce the basic methodological concepts of DWS and the particular challenges of acquiring robust DWS for accurate estimation of metabolite diffusion properties. Subsequently, the unique ability of DWS to characterize cell-type specific structural and physiological features will be demonstrated, followed by several applications of DWS to discern cell-type specific intracellular damage in disease, especially in multiple sclerosis (MS) and in neuropsychiatric systemic lupus erythematosus (NPSLE). Also discussed are the advantages and the challenges of performing DWS at ultrahigh field will follow, and the possibilities of combining DTI/DWI and DWS in a combined analysis framework aimed at better characterizing tissue microstructural properties in health and disease. The presentation will conclude with examples of the potential of DWS to monitor and quantify cellular energy metabolism, where enzymatic processes may affect the diffusion properties of metabolites involved in metabolism. Leiden University Medical Center

Chemical Biology of Cellular Carbohydrates

University of Konstanz

Chemical and Biological Physics Lunch Club Seminar

Chemical and Biological Physics, WIS

Joint Chemical and Biological Physics and Organic Chemistry Seminar

The replacement of fossil fuels by a clean and renewable energy source is one of the most urgent and challenging issues our society is facing today, which is why intense research is devoted to this topic recently. Nature has been using sunlight as the primary energy input to oxidize water and generate carbohydrates (a solar fuel) for over a billion years. Inspired, but not constrained, by nature, artificial systems [1] can be designed to capture light and oxidize water and reduce protons or other organic compounds to generate useful chemical fuels. In this context this contribution will present a variety of molecular water oxidation catalysts based on transition metal complexes, together with their activity in homogeneous phase and anchored on solid surfaces to generate electro- and photo-anodes. A detailed analysis of their performance will be discussed. Institute of Chemical Research of Catalonia (ICIQ), Institute of Science and Technology, Tarragona and Department de Química Universitat Autònoma de Barcelona

Chemical and Biological Physics Lunch Club Seminar

Cracks, the major vehicle for material failure, tend to accelerate to high velocities in brittle materials. In three-dimensions, cracks generically undergo a micro-branching instability at about 40% of their sonic limiting velocity. Recent experiments showed that in sufficiently thin systems cracks unprecedentedly accelerate to nearly their limiting velocity without micro-branching, until they undergo an oscillatory instability. Despite their fundamental importance and apparent similarities to other instabilities in condensed-mater physics and materials science, these dynamic fracture instabilities remain poorly understood. They are not described by the classical theory of cracks, which assumes that linear elasticity is valid inside a stressed material and invokes an extraneous local symmetry criterion to predict crack paths. Here we develop a theory of two-dimensional dynamic brittle fracture capable of predicting arbitrary paths of ultra-high-speed cracks in the presence of elastic nonlinearity without extraneous criteria. We show that cracks undergo a dynamic oscillatory instability controlled by small-scale elastic nonlinearity near the crack tp. This instability occurs above an ultra-high critical velocity and features an intrinsic wavelength that increases proportionally to the ratio of the fracture energy to an elastic modulus, in quantitative agreement with experiments. This ratio emerges as a fundamental scaling length assumed to play no role in the classical theory of cracks, but shown here to strongly influence crack dynamics. The degree of universality of the instability is also demonstrated. Those results pave the way for resolving other long-standing puzzles in the failure of materials. A tutorial-like talk

Annual Pearlman lecture

Department of Chemistry, UC Berkeley

Chemistry Colloquium

Duke University

Chemistry Colloquium

Ohio State University

Chemistry Colloquium

Johns Hopkins School of Medicine

Chemistry Colloquium

University of Chicago

Chemistry Colloquium

UT Southwestern Medical Center