Vibrationally resolved two-photon electronic spectra including vibrational pre-excitation:Theory and application to VIPER spectroscopy with two-photon excitation

Following up on our previous work on vibrationally resolved electronic absorption spectra including the effect of vibrational pre-excitation [J. von Cosel et al., J. Chem. Phys. 147, 164116 (2017)], we present a combined theoretical and experimental study of two-photon induced vibronic transitions in polyatomic molecules that are probed in the Vibrationally Promoted Electronic Resonance experiment using two-photon excitation (2P-VIPER). In order to compute vibronic spectra, we employ time-independent and time-dependent methods based on the evaluation of Franck-Condon overlap integrals and Fourier transformation of time-domain correlation functions, respectively. The time-independent approach uses a generalized version of the FCclasses method, while the time-dependent approach relies on the analytical evaluation of Gaussian moments within the harmonic approximation including Duschinsky rotation effects. For the Coumarin 6 dye, two-dimensional 2P-VIPER experiments involving excitation to the lowest-lying singlet excited state S1 are presented and compared with corresponding one-photon (1P)-VIPER spectra. In both cases, coumarin ring modes and a CO stretch mode show VIPER activity, albeit with different relative intensities. Selective pre-excitation of these modes leads to a pronounced redshift of the low-frequency edge of the electronic absorption spectrum, which is a prerequisite for the VIPER experiment. Theoretical analysis underscores the role of interference between Franck-Condon and Herzberg-Teller effects in the two-photon experiment, which is at the root of the observed intensity distribution

Time-Resolved Visible and Infrared Study of the Cyano Complexes of Myoglobin and of Hemoglobin I from Lucina pectinata

AbstractThe dynamics of the ferric CN complexes of the heme proteins Myoglobin and Hemoglobin I from the clam Lucina pectinata upon Soret band excitation is monitored using infrared and broad band visible pump-probe spectroscopy. The transient response in the UV-vis spectral region does not depend on the heme pocket environment and is very similar to that known for ferrous proteins. The main feature is an instantaneous, broad, short-lived absorption signal that develops into a narrower red-shifted Soret band. Significant transient absorption is also observed in the 360–390nm range. At all probe wavelengths the signal decays to zero with a longest time constant of 3.6ps. The infrared data on MbCN reveal a bleaching of the C≡N stretch vibration of the heme-bound ligand, and the formation of a five-times weaker transient absorption band, 28cm−1 lower in energy, within the time resolution of the experiment. The MbC≡N stretch vibration provides a direct measure for the return of population to the ligated electronic (and vibrational) ground state with a 3–4ps time constant. In addition, the CN-stretch frequency is sensitive to the excitation of low frequency heme modes, and yields independent information about vibrational cooling, which occurs on the same timescale

Vibrational Spectroscopic Map, Vibrational Spectroscopy, and Intermolecular Interaction

© 2020 American Chemical Society. Vibrational spectroscopy is an essential tool in chemical analyses, biological assays, and studies of functional materials. Over the past decade, various coherent nonlinear vibrational spectroscopic techniques have been developed and enabled researchers to study time-correlations of the fluctuating frequencies that are directly related to solute-solvent dynamics, dynamical changes in molecular conformations and local electrostatic environments, chemical and biochemical reactions, protein structural dynamics and functions, characteristic processes of functional materials, and so on. In order to gain incisive and quantitative information on the local electrostatic environment, molecular conformation, protein structure and interprotein contacts, ligand binding kinetics, and electric and optical properties of functional materials, a variety of vibrational probes have been developed and site-specifically incorporated into molecular, biological, and material systems for time-resolved vibrational spectroscopic investigation. However, still, an all-encompassing theory that describes the vibrational solvatochromism, electrochromism, and dynamic fluctuation of vibrational frequencies has not been completely established mainly due to the intrinsic complexity of intermolecular interactions in condensed phases. In particular, the amount of data obtained from the linear and nonlinear vibrational spectroscopic experiments has been rapidly increasing, but the lack of a quantitative method to interpret these measurements has been one major obstacle in broadening the applications of these methods. Among various theoretical models, one of the most successful approaches is a semiempirical model generally referred to as the vibrational spectroscopic map that is based on a rigorous theory of intermolecular interactions. Recently, genetic algorithm, neural network, and machine learning approaches have been applied to the development of vibrational solvatochromism theory. In this review, we provide comprehensive descriptions of the theoretical foundation and various examples showing its extraordinary successes in the interpretations of experimental observations. In addition, a brief introduction to a newly created repository Web site (http://frequencymap.org) for vibrational spectroscopic maps is presented. We anticipate that a combination of the vibrational frequency map approach and state-of-the-art multidimensional vibrational spectroscopy will be one of the most fruitful ways to study the structure and dynamics of chemical, biological, and functional molecular systems in the future

Transient 2D-IR spectroscopy : towards ultrafast structural dynamics of peptides and proteins

Peptide and protein dynamics extend over a continuum of timescales from seconds to the sub-picosecond range. For dynamics on a millisecond and slower timescale NMR spectroscopy represents a powerful structure resolving method. For faster processes in the liquid phase there is clearly a need for a method offering high time resolution and, at the same time, sufficient structure sensitivity. Nonlinear two-dimensional femtosecond infrared spectroscopy (2D-IR) combines structure sensitivity with high time resolution. So far, however, 2D-IR has been applied only to systems in equilibrium. The extension of 2D-IR to transient structures in the non-equilibrium regime seems very promising, not only for polypeptide dynamics but for the investigation of molecular dynamics in general. To this end the technique of transient 2D-IR spectroscopy (T2D-IR) is developed in this dissertation. The dissertation consists of two parts: In Part I 'Phototriggered Peptide Dynamics and Secondary Structure Formation' new tools for time resolved IR spectroscopy are introduced, that allow to investigate nonequilibrium dynamics of polypeptides in unprecedented detail. Built-in molecular photoswitches are employed to trigger and control peptide dynamics. Two peptide systems are discussed - a cyclic octapeptide based on the thioredoxin reductase active site as well as a photoswitchable alpha-helix. Part II 'Principles and Applications of Two-Dimensional and Transient Two-Dimensional IR Spectroscopy' starts with a comparison of different 2D-IR techniques. The idea of 2D-IR structure determination is introduced. The groundwork of T2D-IR is developed and different T2D- IR pulse sequences are investigated with respect to their information content. Finally, the first application of T2D-IR to the conformational transition of a photoswitchable peptide is demonstrated. Dynamik von Peptiden und Proteinen erstreckt sich über Kontinuum von Zeitskalen von Sekunden bis in den Subpicosekundenbereich. Dynamik im Bereich von Millisekunden oder langsamer kann mit Hilfe der NMR Spektroskopie untersucht werden. Zur Untersuchung schnellerer Prozesse mangelt es jedoch an eine Methode, die sowohl die nötige Zeitauflösung als auch eine ausreichende Strukturempfindlichkeit bietet. Nichtlineare zwei-dimensionale Femtosekunden-Infrarotspektroskopie (2D-IR) vereint Strukturempfindlichkeit mit hoher Zeitauflösung. Bisher wurde 2D-IR jedoch nur auf Systeme im Gleichgewicht angewandt. Eine Erweiterung der Methode auf transiente Strukturen im Nichtgleichgewicht wäre von grossem Interesse - nicht nur zur Untersuchung der Dynamik von Polypeptiden sondern zur Untersuchung von Moleküldynamik im Allgemeinen. Diese Erweiterung wird in der vorliegenden Arbeit mit Entwicklung der Transienten 2D-IR Spektroskopie (T2D-IR) vollzogen. Im Teil I der Arbeit 'Phototriggered Peptide Dynamics and Secondary Structure Formation' werden neue Methoden der zeitaufgelösten Infrarotspektroskopie eingeführt, die eine detailierte Untersuchung der Nichtgleichgewichtsdynamik von Polypeptiden ermöglichen. Zum Auslösen und Steuern von Konformationsänderungen werden molekulare Photoschalter eingesetzt. Es werden zwei Modelpeptide vorgestellt: ein cyclisches Oktapeptid, dessen Sequenz dem Aktiven Zentrum einer Thioredoxin Reduktase entspricht, sowie eine photoschaltbare alpha-helix. Teil II 'Principles and Applications of Two-Dimensional and Transient Two-Dimensional IR Spectroscopy' beginnt mit einem Vergleich verschiedener 2D-IR Implementationen. Die Idee der 2D- IR Strukturbestimmung wird vorgstellt. Experimentelle und theoretische Grundlagen der T2D-IR Spektroskopie werden eingeführt. Verschiedene T2D-IR Pulssequenzen werden im Hinblick auf ihren Informationsgehalt untersucht. Die Entwicklungen in Teil I und II bilden die Grundlage der Untersuchung eines photoschaltbaren Peptides mit T2D-IR Spektroskopie

Celebrating 25 years of 2D IR spectroscopy

[No abstract available]11Nsciescopu

Two-dimensional infrared spectroscopy of photoswitchable peptides

We present a detailed discussion of the complimentary fields of the application of two-dimensional infrared (2D-IR) spectroscopy in comparison with two-dimensional nuclear magnetic resonance (2D-NMR) spectroscopy. Transient 2D-IR (T2D-IR) spectroscopy of nonequilibrium ensembles is probably one of the most promising strengths of 2D-IR spectroscopy, as the possibilities of 2D-NMR spectroscopy are limited in this regime. T2D-IR spectroscopy uniquely combines ultrafast time resolution with microscopic structural resolution. In this article we summarize our recent efforts to investigate the ultrafast structural dynamics of small peptides, such as the unfolding of peptide secondary structure motifs. The work requires two ingredients: 2D-IR spectroscopy and the possibility of triggering a structural transition of a peptide on an ultrafast timescale using embedded or intrinsic photoswitches. Several photoswitches have been tested, and we discuss our progress in merging these two pathways of research

Transient 2D-IR Spectroscopy: Towards a Molecular Movie

In NMR spectroscopy, multidimensional methods allow for fascinating insights into molecular structure and dynamics. With the introduction of ultra fast two-dimensional in frared spectroscopy, these concepts now enter the optical domain, measuring couplings and correlations between molecular vibrations with picosecond time resolution. The time resolution is sufficient to investigate transient species far away from equilibrium during fast photo chemical reactions in real-time. Numerous applications of the method are found in chemistry and in biophysics