Multi-mode two-dimensional infrared spectroscopy of peptides and proteins

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2008.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Vita.Includes bibliographical references.In this thesis, a methodology for understanding structural stability of proteins through multi-mode two-dimensional infrared (2D IR) spectroscopy is developed. The experimental framework for generation of broadband infrared lasers and robust new approaches to 2D IR spectroscopy are demonstrated. Long-term phase stability is achieved through the development of a passively stabilized diffractive optic and wedge interferometer. A new approach for acquisition of 2D IR spectra in the pump-probe geometry reduces overall experimental complexity. These technological advances extend the capabilities of 2D IR to further resolve inter- and intramolecular couplings, relaxation pathways and structural kinetics in complex systems. Characterization of multi-mode spectra is first performed on model protein systems to reveal detailed information on the effects of solvation and structure on the amide vibrations. Differences in vibrational coupling, transition dipole angles and the anharmonic potential of the amide vibrations of isotopologues of N-methylacetamide arise from significant change in the local mode composition of the amide II band due to isotopic substitution of the peptide group. Extension of multi-mode 2D IR to study the amide I'-II' spectra of an ideal protein system, poly-L-lysine, provides direct evidence for the structural sensitivity of the amide II' vibration, particularly to the !-helix moiety. This structural sensitivity arises from through bond coupling and structure induced symmetry and orientation of adjacent residues. Integration of these tools with hydrogen exchange techniques allows for the protein structural kinetics and stability to be observed through protein-solvent interactions with enhanced structural sensitivity relative to amide I spectroscopy alone.The amide II' diagonal provides a measure of the degree of exchange and the cross peaks between the structurally sensitive amide I/I' vibration and the solvent exposure sensitive amide II and II' modes reveal the location of exchange. Partial exchange of the secondary structure of ubiquitin is revealed by correlation of the different amide signatures through analysis of cross peak line shapes, positions and amplitudes. Results provide direct evidence for a highly stable helix and labile "-sheet structure.by Lauren P. DeFlores.Ph.D

The SuperCam Remote Sensing Instrument Suite for Mars 2020

International audienceThe Mars 2020 rover, essentially a structural twin of MSL, is being built to a) characterize the geology and history of a new landing site on Mars, b) find and characterize ancient habitable environments, c) cache samples for eventual return to Earth, and d) demonstrate in-situ production of oxygen needed for human exploration. Remote-sensing instrumentation is needed to support the first three of these goals [1]. The SuperCam instrument meets these needs with a range of instrumentation including the highest-resolution remote imaging on the rover, two different techniques for determining mineralogy , and one technique to provide elemental compositions. All of these techniques are co-boresighted, providing rapid comprehensive characterization. In addition, for targets within 7 meters of the rover the laser shock waves brush away the dust, providing cleaner surfaces for analysis. SuperCam will use an advanced version of the AEGIS robotic target selection software

The SuperCam Instrument Suite on the Mars 2020 Rover: Science Objectives and Mast-Unit Description

On the NASA 2020 rover mission to Jezero crater, the remote determination of the texture, mineralogy and chemistry of rocks is essential to quickly and thoroughly characterize an area and to optimize the selection of samples for return to Earth. As part of the Perseverance payload, SuperCam is a suite of five techniques that provide critical and complementary observations via Laser-Induced Breakdown Spectroscopy (LIBS), Time-Resolved Raman and Luminescence (TRR/L), visible and near-infrared spectroscopy (VISIR), high-resolution color imaging (RMI), and acoustic recording (MIC). SuperCam operates at remote distances, primarily 2-7 m, while providing data at sub-mm to mm scales. We report on SuperCam's science objectives in the context of the Mars 2020 mission goals and ways the different techniques can address these questions. The instrument is made up of three separate subsystems: the Mast Unit is designed and built in France; the Body Unit is provided by the United States; the calibration target holder is contributed by Spain, and the targets themselves by the entire science team. This publication focuses on the design, development, and tests of the Mast Unit; companion papers describe the other units. The goal of this work is to provide an understanding of the technical choices made, the constraints that were imposed, and ultimately the validated performance of the flight model as it leaves Earth, and it will serve as the foundation for Mars operations and future processing of the data.In France was provided by the Centre National d'Etudes Spatiales (CNES). Human resources were provided in part by the Centre National de la Recherche Scientifique (CNRS) and universities. Funding was provided in the US by NASA's Mars Exploration Program. Some funding of data analyses at Los Alamos National Laboratory (LANL) was provided by laboratory-directed research and development funds

Aqueous alteration processes in Jezero crater, Mars—implications for organic geochemistry

The Perseverance rover landed in Jezero crater, Mars, in February 2021. We used the Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) instrument to perform deep-ultraviolet Raman and fluorescence spectroscopy of three rocks within the crater. We identify evidence for two distinct ancient aqueous environments at different times. Reactions with liquid water formed carbonates in an olivine-rich igneous rock. A sulfate-perchlorate mixture is present in the rocks, which probably formed by later modifications of the rocks by brine. Fluorescence signatures consistent with aromatic organic compounds occur throughout these rocks and are preserved in minerals related to both aqueous environments