Revealing the Structure and Dynamics of Small-molecule Solutions and Proteins Using Theoretical Vibrational Spectroscopy

Download or read book Revealing the Structure and Dynamics of Small-molecule Solutions and Proteins Using Theoretical Vibrational Spectroscopy written by and published by . This book was released on 2014 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Due to the sensitivity of vibrational chromophores to their local environments, linear and ultrafast vibrational spectroscopy have proven to be very useful techniques for studying the structure and dynamics of condensed phases. Because spectroscopic techniques encode information related to the time-dependent configuration of an entire system into spectra resolved over at most a few dimensions, however, it is very difficult to interpret vibrational line shapes in a detailed and unambiguous manner. One approach to surmounting this difficulty is to calculate vibrational line shapes from molecular dynamics (MD) simulations by employing vibrational response theory and spectroscopic maps. (The maps relate observables in classical MD simulations to quantum spectroscopic quantities.) Once validated by comparison of experimental and theoretical line shapes, MD simulations can be used as an unequivocal basis for the interpretation of vibrational spectra. Here, we employ this approach in order to gain insight into small-molecule solutions and proteins. After sketching the theoretical formalism underlying the calculations of vibrational spectra (Chapter 2), vibrational spectroscopic analysis of the urea/water (Chapter 3) and cyanide/water (Chapter 4) solutions is presented. Analysis of linear infrared (IR) line shapes provides information concerning the local solvation structure of these molecules, while analysis of two-dimensional IR and anisotropy decay yields insight into frequency and rotational dynamics. The remainder of this work concerns the vibrational spectroscopy of the amide I (mostly CO-stretch) band of proteins. After presenting additional theoretical formalism and maps for protein spectroscopy (Chapter 5), the maps are evaluated by examining IR spectra for a single conformation of an alpha-helical model peptide in the gas phase (Chapter 6). These methods are then applied to evaluate the 2D IR spectra of two important biological systems: polyglutamine (Chapter 7) and the potassium ion channel KcsA (Chapter 8). Notably, these studies employ isotope-labeling techniques to isolate the vibrational response of a subset of amide I modes in a non-perturbative fashion. Finally, extensions to the theory are presented to enable the computation of amide I vibrational sum-frequency generation spectra (Chapter 9), which are expected to be sensitive to the structures of interfacial proteins.