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A symphony of light: frequency comb lasers and new frontiers in ultrafast spectroscopyMelanie. A.R. Reber, PhD Friday, March 18, 2022 Frequency comb lasers were initially developed as a tool for metrology and precision measurement, such as improving optical clocks. Metrology requires precise knowledge of a frequency and thus, by the Heisenberg uncertainty principle, one loses knowledge of time. However, frequency combs are also ultrafast lasers! Often described as “a million stable lasers at once”, it isn’t surprising that their utility in ultrafast spectroscopy has largely been overlooked. I will explain what a frequency comb is and how we can have both frequency precision and ultrafast (~10-15 s) time resolution. Ultrafast timescales are the timescales of molecular vibrations and bond-breaking, which as chemists a very relevant timescale. I will explain how we use the unique properties of frequency combs to bring ultrafast spectroscopies to new frontiers in chemistry. Specifically, we have improved the sensitivity, spectral resolution, and broadband detection of ultrafast spectroscopies. I will describe our new methods for ultrafast transient absorption spectroscopy and multidimensional spectroscopy that show four (or more!) orders-of-magnitude improvement in sensitivity compared to previous best methods. This means that we can now use these powerful ultrafast techniques on molecules in molecular beams, an entirely new direction for these spectroscopies. I will talk about some of our first experiments, which have application in combustion chemistry and solar cell chemistry. |
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Phase Behavior of Water-based Liquid Crystals and their Applications in BiologyKarthik Nayani, PhD Friday, April 1, 2022 Liquid crystals are anisotropic fluids within which constituent molecules orient preferentially along a chosen direction, resulting in orientational elasticity. In this talk, I will present on the discovery of water-based liquid crystals whose phase behavior can be tuned to have interesting applications in two biological contexts. First, we show that the osmotic pressure of these phases can be isotonic with the interior of red blood cells and generate mechanical stresses that drive changes in cell shape. The responses of biological cells to mechanical stress are central to the functioning of living systems, and cellular dysfunction is often characterized by change in biomechanical response. The mechanical properties of red blood cells, for instance, are altered by Sickle cell disease and Malaria, but facile methods for high throughput characterization of the mechanical properties of individual cells do not exist. The shape responses of an initially uniform population of red blood cells to liquid crystal elasticity, characterized through confocal and optical microscopy, revealed a wide variance in their final strained shapes thus unmasking the heterogeneity in the mechanical properties of individual cells. The variance in shape responses of red blood cells to liquid crystal elasticity is interpreted via use of numerical simulations to obtain the dispersion in the values of the shear-moduli of the cell membranes within a population of cells. On a fundamental level, the presentation will outline new structure-property relationships for strained soft biomaterials in a liquid crystalline host. The principles outlined in this presentation can be applied to a wide bevy of human cells permitting rapid and parallel characterization of mechanical properties of individual cells within a population. Secondly, we show for the first time the formation of complex coacervates of these liquid crystal phases with polyelectrolytes. Complex coacervates are formed by liquid-liquid phase separation of an aqueous solution of oppositely charged ions. We show the formation of liquid crystalline coacervates via the addition of very low concentrations of a liquid crystal former with polycations, and they appear as droplets in solution. Surprisingly, the local liquid crystal former concentration in these droplets is significantly higher than their surroundings, leading to characteristic bipolar configuration when observed via polarized optical microscopy. These characteristic textures were then employed for rapid sensing of proteins via the liquid crystal textural transformations. We also elucidate the charge-driven formation of LC-coacervates by characterizing trends in their compositions, optical textures, and rheology via systematic variations in total charge, ionic strength, and temperature of the solutions. Finally, we show the potential of Isothermal Titration Calorimetry in determining the binding energies and stoichiometry of the interactions of the polyelectrolytes with liquid crystal formers. |
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Getting cool stuff for free: lessons from our multicellularity LTEEWilliam Croft Ratcliff, PhD Friday, April 15, 2022 The origin of multicellularity was one of the most significant innovations in the history of life. Our understanding of the evolutionary processes underlying this transition remains limited, however, mainly because extant multicellular lineages are ancient and most transitional forms have been lost to extinction. We bridge this knowledge gap by evolving novel multicellularity in vivo, using the 'snowflake yeast' model system. In this talk, I'll focus on our most Multicellularity Long-Term Evolution Experiment (MuLTEE), in which we've put snowflake yeast through ~5,000 generations of selection. We'll examine how snowflake yeast evolve to be ~20,000x larger, and ~10,000x biophysically tougher than their ancestors through a clever change in the way that cells interact within the group. Through a combination of multicellular biophysics and synthetic biology, we'll examine how two key steps in this transition: a multicellular life cycle and heritability of multicellular traits, arise 'for free'. If time permits, we'll examine early steps in the evolution of cellular differentiation. Our approach, which allows for the study of macroevolutionary processes over microevolutionary timescales, demonstrates that multicellularity is less evolutionarily constrained than previously thought. |
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Microtubule deacetylation enables in vivo collective cell migration by tuning cell stiffness in relation to substrate stiffnessAbdul Malmi-Kakkada, PhD Friday, April 22, 2022 Cells in multicellular organisms migrate during tissue formation, regeneration and immune defense. Cells migrate in vivo by exerting forces on surrounding tissue structures with cell-substrate mechanical interaction shown to be important in cell migration. By combining computational modeling and in vivo experimental data from Xenopus laevis embryos we show that neural crest cell stiffness is dynamically reduced in response to the temporal stiffening of the mesoderm - the substrate upon which neural crest cells move. We discover that the reduction in neural crest cell stiffness and consequently its migration is triggered by microtubule deacetylation mediated by Piezo1. We show that the effect of microtubule deacetylation on cell movement is well characterized by the stiffness ratio between the substrate(sub) and the cell (E_sub/E_cell). As lowering microtubule acetylation and consequently cell stiffness rescues cell migration in soft substrates, we provide evidence that an optimal cell-to-substrate stiffness ratio is important in allowing for collective cell migration rather than a fixed value of substrate stiffness. |
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Seminar series sponsored by: Augusta University Research Institute, College of Science and Mathematics, Department of Chemistry and Physics
