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Article Dans Une Revue Chemical Reviews Année : 2020

Introduction: Bond Specific Spectroscopy of Peptides and Proteins

Résumé

From the early days of peptide and protein investigations, vibrational spectroscopy has occupied a special place among the physical chemistry methods used, thanks to its intrinsic capability to resolve vibrational features due to covalent bonds and its sensitivity upon the environment of these bonds, in particular H-bonding. Due to the size of these systems, however, traditional spectroscopy often faces crowded features, from which relevant information, in particular spectroscopic assignment, is difficult to extract. Spectroscopists, however, have taken up the challenge, relying on various, often multidimensional strategies to overcome the effects of complexity, depending upon the environment of the molecules studied, i.e., solution, thin films, or even gas phase. Reviews in this special issue, together with a few others recently published, illustrate the various instrumental strategies developed, the recent trends in the corresponding fields, and their applications to model or real systems. In the condensed phase, one of the keys to specificity is to rely on spatial selectivity, e.g., by selecting the environment of the proteins observed, through a surface-sensitive diagnostic, like surface-enhanced Vibrational Sum-Frequency Generation (Weidner) or by focusing on specific probes of the system, e.g. chiral centers, interrogated through Vibrational Optical Activity measurements (Keiderling) or by an external perturbation, related to the function of the molecule, and monitoring the change through Infrared Difference Spectroscopy (Lorenz-Fonfria). Alternatively, multidimensional spectroscopy can also be implemented, e.g. 2D-IR (1) and also Resonance Raman Spectroscopy (Hildebrandt), whose diagnostic selectivity stems from electronic states of the system. Most importantly, many of these techniques, amenable to pump–probe experiments, have the benefit of time resolution, at various time scales, depending upon the physics of the interaction, allowing us to successfully document both the corresponding structural changes and the dynamics of the systems studied: reaction centers in proteins, protein folding, structural dynamics of interfacial proteins, etc. In the gas phase, the lack of sensitivity has led experimentalists to turn to so-called action spectroscopies, where the IR absorption is monitored through changes in the system, e.g., fragmentation (IR-induced multiphoton dissociation) of ionic species (2) or ground state depopulation of cold neutrals (IR/UV double resonance experiments) (submitted for consideration is a paper by Gerhards et al.). During the past decades, these efforts benefited from the development of laser vaporization, electrospray ionization techniques, and exquisite spectral resolutions can be achieved thanks to efficient cooling in supersonic expansion for neutrals or in cryogenic traps for ions. (3,4) Availability of new IR sources, including table-top parametric oscillators and free electron lasers, whose range now attains the THz region (Rijs), also greatly contributed to the success of this field. The selectivity achieved in the gas phase experiments paved the way to conformation-specific IR spectroscopy, which was even further improved for charged species, through a coupling with ion mobility spectroscopy. (5) Applications encompass the assessment of H-bond strengths in peptides, competition issues within the conformational landscape of small peptides, their aggregation (submitted for consideration is a paper by Gerhards et al.), or their slow backbone motions (Rijs), etc. IR multiphoton dissociation, coupled to mass spectrometry, is also used to characterize ions through action spectroscopy. (2,6,7) Despite its lack of conformational selectivity, it turns out to be of uttermost interest to characterize structural details of biological significance, e.g. to monitor the post-translational modifications borne by the peptides under scrutiny (Fornarini). Finally, gas phase studies also enable pump–probe experiments, where the reactive processes following a UV photon absorption can be characterized, in particular their dependence upon the structure (Grégoire). Specific excited state dynamical processes find applications in mass spectrometry, for an advanced characterization and analysis of charged peptides and more generally of biomolecules (Brodbelt). Needless to say that these impressive experimental developments all benefited from an active synergy with theoretical advances in ground state structural and vibrational modeling (8) and in the quantum chemistry description of electronic excited states (9) and of their dynamics. (10) Particularly obvious is the cross fertilization of quantum chemistry modeling and “spectroscopic grade” gas phase experiments. This thematic issue provides an overview of recent developments and results, covering a broad range of vibrational spectroscopic methods. It is organized according to the size of the systems treated and to their environment, going from neutral gas phase model systems, peptide ions, peptides in solution, to proteins. I would like to thank the Editor, Professor Joachim Heberle, for his encouragements, his team for their efficient support, as well as all the authors for their contributions, and wish the reader pleasure and enjoyment along this promenade in the vibrational landscape of peptides and proteins.

Dates et versions

cea-04444565 , version 1 (07-02-2024)

Identifiants

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Michel Mons. Introduction: Bond Specific Spectroscopy of Peptides and Proteins. Chemical Reviews, 2020, 120 (7), pp.3231-3232. ⟨10.1021/acs.chemrev.0c00196⟩. ⟨cea-04444565⟩
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