Dynamic IR Peak Coalescence and Ultrafast Chemical Exchange Reactions Studied by Two Dimensional Infrared Spectroscopy

Dynamic IR Peak Coalescence and Ultrafast Chemical Exchange Reactions Studied by Two Dimensional Infrared Spectroscopy
Author: Matthew Cody Zoerb
Publisher:
Total Pages: 150
Release: 2012
Genre:
ISBN:

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Vibrational spectroscopy is one of the most powerful techniques in chemistry due to its ability to report direct information on the geometries and nuclear motions of complex molecules. At thermal equilibrium, rearrangements between different, or equivalent, molecular structures help to define the reactivity of the system. On the ultrafast timescale, these chemical exchange reactions may cause features in the vibrational spectrum to become averaged. The Bloch equations have been used previously to quantitatively predict the rates of such reactions. This approach has been quite successful in NMR spectroscopy where exchange on the microsecond timescale is often sufficient to cause peak coalescence. The application of the Bloch equations to IR spectroscopy has been debated due to the presence of other contributions to the vibrational lineshape that may prevent an accurate description of the relevant dynamics. Two dimensional infrared spectroscopy (2D-IR) is a time resolved ultrafast technique that is capable of directly measuring the kinetics of chemical exchange at thermal equilibrium where there is no net change in the populations of reactants and products. This work examines two model systems that display dynamic IR peak coalescence. A group of mixed valence dimers of trinuclear ruthenium clusters have exhibited a wide range of IR coalescence that is sensitive to solvent, temperature, and ligand substitution. No electron exchange was observed by 2D-IR during the timescale required for peak coalescence. The two isomers of a square pyramidal ruthenium dithiolene compound also result in highly coalesced spectra. The equilibrium populations, as well as the extent of peak coalescence, are strongly dependent on temperature and solvent. The experimental results of this second project were largely inconconclusive; however, future work with density functional theory calculations looks promising for revealing more information on these dynamics. Ultimately, the application of the Bloch equations to IR spectra is not generally reliable. While this type of analysis may still yield accurate results in some special cases, it is very difficult to distinguish legitimate exchange induced coalescence from similar broadened lineshape features, and this approach should be avoided.

Watching Ultrafast Molecular Motions with 2D IR Chemical Exchange Spectroscopy

Watching Ultrafast Molecular Motions with 2D IR Chemical Exchange Spectroscopy
Author: Michael D. Fayer
Publisher: World Scientific
Total Pages: 383
Release: 2011
Genre: Science
ISBN: 9814355623

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This unique volume presents a comprehensive but accessible introduction to the field of ultrafast two-dimension infrared (2D IR) vibrational echo spectroscopy based on the pioneering work of Professor Michael D Fayer, Department of Chemistry, Stanford University, USA. It contains in one place a qualitative introduction to the field of 2D IR spectroscopy and a comprehensive set of scientific papers that underlie the qualitative discussion. The introductory material contains several detailed illustrations, and is based on the Centenary Lecture at the Indian Institute of Science given by Professor Fayer July 16, 2008 as part of the celebration of the 100th anniversary of the founding of IIS in Bangalore, India. The second part of the volume contains reprints of Fayer's relevant papers. The compilation will be very useful because it presents the historical background, motivation, methodology, and experimental results at a level that is accessible to the non-expert. The reprints of the scientific papers, from review articles to detailed theoretical papers, provide rigorous supporting material so that the reader can delve as deeply as desired into the subject.

Ultrafast Infrared Vibrational Spectroscopy

Ultrafast Infrared Vibrational Spectroscopy
Author: Michael D. Fayer
Publisher: CRC Press
Total Pages: 475
Release: 2013-03-04
Genre: Science
ISBN: 1466510145

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The advent of laser-based sources of ultrafast infrared pulses has extended the study of very fast molecular dynamics to the observation of processes manifested through their effects on the vibrations of molecules. In addition, non-linear infrared spectroscopic techniques make it possible to examine intra- and intermolecular interactions and how su

Temperature-jump 2D IR Spectroscopy to Study Protein Conformational Dynamics

Temperature-jump 2D IR Spectroscopy to Study Protein Conformational Dynamics
Author: Kevin Chapman Jones
Publisher:
Total Pages: 324
Release: 2012
Genre:
ISBN:

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Temperature-jump (T-jump) two-dimensional infrared spectroscopy (2D IR) is developed, characterized, and applied to the study of protein folding and association. In solution, protein conformational changes span a wide range of timescale from nanoseconds to minutes. Ultrafast 2D IR spectroscopy measures time-dependent structural changes within the protein ensemble by probing the frequency changes associated with amide I backbone vibrations. Combining 2D IR with a perturbing laser-induced T-jump enables the study of conformational dynamics from 5 ns to 50 ms. To access a finer time-sampling of the conformational evolution, a one-dimensional variant of 2D IR, heterodyne-detected dispersed vibrational echo spectroscopy (HDVE), is implemented. The framework for interpreting transient HDVE and 2D IR spectra is developed, and we propose a method to remove the linear absorption distortions along both frequency axes. We first present the T-jump 2D IR spectra of a dipeptide to reveal the general amide I baseline response expected in the absence of conformational change. To facilitate the analysis of T-jump data, singular value decomposition (SVD) is employed for reducing noise, identifying the number of distinguishable states, and separating spectral changes based on shared timescales. Finally, T-jump 2D IR spectroscopy is applied to study the unfolding of ubiquitin, disordering of the 12-residue p-hairpin peptide trpzip2 (TZ2), and the dissociation of insulin dimers to monomers. Experimental results for ubiquitin highlight the importance of linear absorption corrections for interpretation of the data. In response to the T-jump, 2D IR results indicate p-sheet structure melts in ubiquitin with a small amplitude (~10 gs) and large amplitude (17 ms) response. Isotope-labeling T-jump experiments on TZ2 allow for the proposal of a free energy surface in which transitions from a native and misfolded state proceed through a disordered hub-like state with a 1-2 gs timescale. Multiple timescales are observed in the T-jump induced dissociation of insulin. Based on their spectral features and concentration dependence, the insulin timescales can be assigned to dissociation, disordering, and oligomerization processes. With these applications, we demonstrate the capability of T-jump 2D IR spectroscopy to reveal detailed molecular dynamics.

Concepts and Methods of 2D Infrared Spectroscopy

Concepts and Methods of 2D Infrared Spectroscopy
Author: Peter Hamm
Publisher: Cambridge University Press
Total Pages: 297
Release: 2011-02-24
Genre: Science
ISBN: 1139497073

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2D infrared (IR) spectroscopy is a cutting-edge technique, with applications in subjects as diverse as the energy sciences, biophysics and physical chemistry. This book introduces the essential concepts of 2D IR spectroscopy step-by-step to build an intuitive and in-depth understanding of the method. This unique book introduces the mathematical formalism in a simple manner, examines the design considerations for implementing the methods in the laboratory, and contains working computer code to simulate 2D IR spectra and exercises to illustrate involved concepts. Readers will learn how to accurately interpret 2D IR spectra, design their own spectrometer and invent their own pulse sequences. It is an excellent starting point for graduate students and researchers new to this exciting field. Computer codes and answers to the exercises can be downloaded from the authors' website, available at www.cambridge.org/9781107000056.

Coherent Two-dimensional Infrared Spectroscopy

Coherent Two-dimensional Infrared Spectroscopy
Author: Nurettin Demirdöven
Publisher:
Total Pages: 257
Release: 2003
Genre:
ISBN:

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This thesis provides an introduction to experimental techniques used in two-dimensional (2D) infrared (IR) spectroscopy, outlines how third-order nonlinear response of a multi-level vibrational system is calculated, and provides a detailed methodology of line shape analysis in 2D spectroscopy. Specific emphasis is given to inherent sensitivity of 2D spectroscopy to correlated spectral broadening. The signatures of highly correlated transition energy fluctuations in a model system of two strongly coupled carbonyl stretching vibrations are reflected by the elongation of the cross peaks along the diagonal of the 2D spectrum. The dynamics of this correlation is monitored by the changes in the 2D line shapes and successfully modeled using a correlated spectral diffusion model. The sensitivity of 2D IR spectroscopy to interactions between multiple vibrational coordinates is also explored in conformationally complex polypeptides and proteins with well-defined secondary structures. 2D IR spectroscopy of [beta]-hairpins and globular proteins with antiparallel (AP) [beta]-sheet domains is studied to identify 2D markers of AP [beta]-sheet conformation. The experiments on [beta]-hairpins and proteins with varying percentage of [beta]-sheet character showed that the formation of cross peaks between the two characteristic vibrational modes of AP [beta]-sheets is a marker of AP [beta]-sheet secondary structure. The intensity, location and line shapes of the cross peaks are qualitatively related to the size, geometry and the conformational variations in the AP [beta]-sheet structure.

One- and Two-dimensional Infrared Spectroscopic Studies of Solution-phase Homogeneous Catalysis and Spin-forbidden Reactions

One- and Two-dimensional Infrared Spectroscopic Studies of Solution-phase Homogeneous Catalysis and Spin-forbidden Reactions
Author:
Publisher:
Total Pages:
Release: 2008
Genre:
ISBN:

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Understanding chemical reactions requires the knowledge of the elementary steps of breaking and making bonds, and often a variety of experimental techniques are needed to achieve this goal. The initial steps occur on the femto- through picosecond time-scales, requiring the use of ultrafast spectroscopic methods, while the rate-limiting steps often occur more slowly, requiring alternative techniques. Ultrafast one and two-dimensional infrared and step-scan FTIR spectroscopies are used to investigate the photochemical reactions of four organometallic complexes. The analysis leads to a detailed understanding of mechanisms that are general in nature and may be applicable to a variety of reactions.

Dynamic NMR Spectroscopy

Dynamic NMR Spectroscopy
Author: J. Sandström
Publisher:
Total Pages: 246
Release: 1982
Genre: Science
ISBN:

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Hyperpolarization Methods in NMR Spectroscopy

Hyperpolarization Methods in NMR Spectroscopy
Author: Lars T. Kuhn
Publisher: Springer
Total Pages: 311
Release: 2013-09-13
Genre: Science
ISBN: 364239728X

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Elucidating Organic Reaction Mechanisms using photo-CIDNP Spectroscopy, by Martin Goez. Parahydrogen Induced Polarization by Homogeneous Catalysis: Theory and Applications, by Kerstin Münnemann et al. Improving NMR and MRI Sensitivity with Parahydrogen, by R. Mewis & Simon Duckett. The Solid-state Photo-CIDNP Effect, by Jörg Matysik et al. Parahydrogen-induced Polarization in Heterogeneous Catalytic Processes, by Igor Koptyug et al. Dynamic Nuclear Polarization Enhanced NMR Spectroscopy, by U. Akbey & H. Oschkinat. Photo-CIDNP NMR Spectroscopy of Amino Acids and Proteins, by Lars T. Kuhn.