Physical Chemistry seminars

Living systems select one molecular handedness, making the origin of homochirality a central problem in understanding how life began. David Lacoste examines how this asymmetry can emerge in autocatalytic chemical networks when they contain sufficiently many chiral species and operate far from equilibrium. Polymerization greatly expands molecular diversity, raising the question of whether it can also generate and preserve a preference for one handedness. The talk develops this connection through an RNA reactor model, studying the conditions under which template-directed ligation and polymerization produce and maintain homochirality.

Donna Blackmond examines two linked problems in the origin of life: how an initially balanced mixture of molecular mirror images could acquire a handedness bias, and how that small bias could be amplified. She compares four experimental approaches using chemical kinetics and solid–solution equilibria. The first is asymmetric autocatalysis, including the Soai reaction and kinetic models connecting self-replication with suppression of the opposite enantiomer. Blackmond distinguishes this powerful model from a demonstrated prebiotic pathway. She then discusses amplification through eutectic partitioning and through attrition-enhanced deracemization, where dissolution, crystal growth and interconversion can produce a single-handed solid. The final approach incorporates stereochemical selection into plausible prebiotic chemistry. Examples explore reciprocal enrichment involving sugars and amino-acid precursors. The lecture argues that accounts of how biological building blocks arose must explain their chirality alongside their synthesis.

Cement is the main binding agent in concrete, literally gluing together rocks and sand into the most-used synthetic material on Earth. However, cement production is responsible for significant amounts of man- made greenhouse gases—in fact if the cement industry were a country, it would be the third largest emitter in the world. Alternatives to the current, environmentally harmful cement production process are not available essentially because the gaps in fundamental understanding hamper the development of smarter and more sustainable solutions. The ultimate challenge is to link the chemical composition of cement grains to the nanoscale physics of the cohesive forces that emerge when mixing cement with water. Cement nanoscale cohesion originates from the electrostatics of ions accumulated in a water-based solution between like-charged surfaces but it is not captured by existing theories because of the nature of the ions involved and the high surface charges. Surprisingly enough, this is also the case for unexplained cohesion in a range of colloidal and biological matter. About one century after the early studies of cement hydration, we have quantitatively solved this notoriously hard problem and discovered how cement cohesion develops during hydration. I will discuss how 3D numerical simulations that feature a simple but molecular description of ions and water, together with an analytical theory that goes beyond the traditional continuum approximations, helped us demonstrate that the optimized interlocking of ion-water structures determine the net cohesive forces and their evolution. These findings open the path to scientifically grounded strategies of material design for cements and have implications for a much wider range of materials and systems where ionic water-based solutions feature both strong Coulombic and confinement effects, ranging from biological membranes to soils. Construction materials are central to our society and to our life as humans on this planet, but usually far removed from fundamental science. We can now start to understand how cement physical-chemistry determines performance, durability and sustainability.

This talk aims to show how new physical methods can advance biological and biomedical research. A major advance in physical chemistry in the last two decades has been the development of quantitative methods to directly observe individual molecules in solution, attached to surfaces, in the membrane of live cells or more recently inside live cells. These single-molecule fluorescence studies have now reached a stage where they can provide new insights into important biological problems. After presenting the principles of these methods, I will give some examples from our current research to probe the molecular basis of neurodegeneration. Here we have used single-molecule fluorescence to detect and analyse the low concentrations of soluble protein aggregates thought to be responsible for Alzheimer’s disease and determine the mechanisms by which they damage neurons. Lastly, I will describe how fundamental science aimed at watching single molecules incorporating nucleotides into DNA gave rise to a new rapid method to sequence DNA that is now widely used.