Ph.D. Candidate: Charles Titus
Research Advisor: Kent Irwin
Date: Monday, November 16, 2020
Time: 11:30 AM PST
Zoom Meeting Link: https://stanford.zoom.us/j/93868353657
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Title: X-ray Spectroscopy of Dilute Metalloproteins with a Transition-Edge Sensor
Abstract: Proteins are some of the most complex and finely tuned molecules found in chemistry, responsible for critical tasks such as oxygen delivery, photosynthesis, or nitrogen fixation in cells. Although proteins are mostly composed of hydrogen, carbon, nitrogen, and oxygen, the active site is often a metal. Hemoglobin, responsible for carrying oxygen to the cells, utilizes iron to bond to O2. In order to understand these proteins, it is critical to understand the behavior of the bonding electrons of the metal center.
Core-level X-ray spectroscopy is a set of techniques that can yield deep insight into electronic structure. By exciting electrons to the unoccupied orbitals, we can probe the oxidation state, symmetry, and spin of a target element. However, for the most important proteins, the signal of interest is faint, and the samples prone to damage upon exposure to X-rays. New instruments are required that can collect data more quickly and with less noise, so that proteins and other challenging samples can be measured.
In this thesis, I present the development of a new instrument for X-ray spectroscopy at the Stanford Synchrotron Radiation Lightsource (SSRL), based on superconducting transition-edge sensors (TES). First, I will describe the capabilities of this detector, and show that it fills a substantial gap in the experimental capabilities of present X-ray instruments. Then I will detail a series of X-ray spectroscopy experiments that I performed with the TES. Using this instrument, I measured both extremely dilute and extremely damage-sensitive samples. This experience allowed us to finally obtain the first undamaged soft X-ray spectrum of oxyhemoglobin. This spectrum has allowed us to significantly constrain the electronic structure of hemoglobin.