Year: 2016
Type: editorial
Abstract: Living organisms exploit solar light to gain metabolic energy, view the world around them, and synthesize complex molecules like vitamin D. Solar radiation, mostly its UV part, also has detrimental effects such as DNA photolesion formation. The study of these natural processes is a traditional focus of photobiology, but exciting new research directions are gaining importance and impact. Increasingly, light-dependent processes are developed into tools to study and manipulate biological systems—optogenetics being a prime example. Natural systems also serve as inspiration for biomimetic technologies, such as artificial photosynthesis and the development of photovoltaic devices. Light-induced processes are triggered when photon absorption creates electronically excited states. These states have a fleeting existence. Radiative decay generally limits the lifetime of singlet excitations to be no greater than 1–10 ns, but actual lifetimes may be orders of magnitude shorter when nonradiative decay is important. For life to profit from or be harmed by these excitations, it dictates that the primary processes occur on this or shorter timescales. This requires diagnostic—above all, spectroscopic—tools with time resolution down to femtoseconds. Photobiology was one of the key motivations for developing pulsed lasers, nonlinear frequency conversion schemes, and pump–probe setups. Although many of these instruments are commercialized nowadays, rendering them accessible to an ever-broader community, method development is still a focus for many research groups. The same applies to theoretical and computational studies in the field. Such studies are indispensable for assigning electronic states, correlating spectroscopic signatures with molecular structures, and understanding dynamics. This special issue on “Fast Spectroscopy of Biosystems” compiles some recent studies in the field, but cannot provide a comprehensive overview. We hope, however, that the broad range of topics gives the reader an idea of the vital importance of fast spectroscopy in the study of biosystems. The special issue also includes studies on traditional photobiology subjects. In a theoretical study, Malý et al. cover energy-transfer processes in light-harvesting complexes of the photosynthetic apparatus. The detrimental effects of light caused by the intrinsic photolability of DNA lesions are covered by Keane et al. as well as Teimoory and Loppnow. An example of a quantum chemical study on photo-excited DNA building blocks can be found in the paper by Wu et al., whereas studies by Changenet-Barret et al. and Fröbel et al. cover the effects of exogenous agents on the photochemistry of DNA. Furthermore, the repair of the DNA lesions by photolyase is the topic of a study by Müller et al. Several contributions give examples of light-dependent processes as tools to trigger or study biological processes. Kitzig et al. review work on the photoswitch hemithioindigo. As a photoresponsive moiety in a peptide, it may trigger conformational dynamics, which then may be traced by time-resolved infrared spectroscopy. With a similar approach—but a different switch, namely azobenzene—Lorenz et al. investigate the photomodulation of the triple-helical structure of a collagen model. Pulsed lasers may also induce conformational changes in a peptide in the absence of a photoswitch through temperature jumps caused by intense infrared laser pulses. Popp et al. rely on these jumps to study the dynamics of β-sheet peptides. In addition, equilibrium dynamics, that is, thermal fluctuations, can be studied by light-induced processes. Dave et al. employ Förster resonance energy transfer (FRET) to address protein folding. In the contribution by Rodenberg et al., part of an artificial water-splitting system inspired by photosynthesis is investigated in great kinetic detail. Through all of the contributions in this special issue, the readers can familiarize themselves with the typical tools of fast spectroscopy. Fluorescence markers such as pyrene are sensitive labels for time-resolved studies, and a photodynamic comparison of three different RNA nucleotide analogs is presented by Reuss et al. Femtosecond fluorescence spectroscopy relying on optical gates traces the fate of primary excitations. With transient UV/Vis absorption spectroscopy, “all” states populated in the course of a photo-process may be addressed. When it comes to molecular structures of these states, time-resolved vibrational (infrared and Raman) spectroscopy is very powerful. A method for ultrafast Raman spectroscopy (FSRS) is also reviewed by Dietze and Mathies. Wolfgang Zinth's 65th birthday last year motivated us to guest-edit this special issue. We are very grateful to ChemPhysChem for providing the means to produce this topical issue. Wolfgang Zinth studied physics at the Technical University of Munich (TU Munich). In 1976, he joined the group of Wolfgang Kaiser, one of the laser pioneers. After his PhD and habilitation, he became Professor at the TU Munich in 1987. Since 1991, he has held a chair at the Ludwig Maximilian University of Munich (LMU Munich). He has published more than 250 scientific papers, is member of various prestigious institutions including the Bayerische Akademie der Wissenschaften, and, in 2013, received the lifetime award of the Time-Resolved Vibrational Spectroscopy (TRVS) Conference. This special issue very well mirrors Wolfgang Zinth's research interests. From the late 1970s onwards, he developed lasers and spectroscopic setups to trace fast molecular processes. He used these instruments to address photobiology in the strict definition. He published groundbreaking papers on the primary processes of bacterial photosynthesis as well as on those occurring in bacteriorhodopsin. For approximately ten years, he has also worked on the detrimental effects of light. His group was the first to trace the formation of a DNA photolesion in real time. When it comes to light as a tool, he pioneered the application of photoswitches, such as azobenzene, in the investigation of fast protein dynamics. Needless to say, Wolfgang Zinth has also contributed to biomimetic aspects of photoinduced processes, and he maintains a keen interest in the implications of photosynthesis for man-made devices. The three of us guest editors have had the great pleasure and privilege of collaborating with Wolfgang Zinth on a number of these fascinating topics. We look forward to continuing to do so in the future. Peter Gilch studied Chemistry at the University of Konstanz (Germany), where he received his diploma working with Ulrich E. Steiner in 1995. For his PhD project, he joined Marie-Elisabeth Michel-Beyerle's group at the TU Munich (Germany), where he worked on magnetic field effects on ultrafast electron-transfer reactions. For his thesis (1999), he received the Albert Weller award of the German Chemical Society (GdCh). He then became a member of Wolfgang Zinth's group at the LMU Munich (Germany), where he studied vibrational relaxation and developed setups for femtosecond fluorescence and Raman spectroscopy. After his Habilitation in 2005, he continued his research at the LMU Munich as a Privatdozent. During that time, he started studies on photoreactive nitroarenes and DNA photolesions. In 2009, he accepted a Professorship at the HHU Düsseldorf (Germany). This Professorship was first financed by the German Science Foundation (DFG, Heisenberg program). His group in Düsseldorf employs time-resolved spectroscopy to investigate UV-induced DNA lesions, fast singlet–triplet transitions, and complex photoreactions. They also work on a novel type of Raman microscopy, femtosecond stimulated Raman microscopy (FSRM). Bern Kohler earned a PhD in Physical Chemistry from MIT (USA) in 1990. He performed postdoctoral research, first with Prof. Urs P. Wild at the ETH Zürich (Switzerland) and subsequently with Prof. Kent R. Wilson at the University of California, San Diego (USA). He was Assistant through Full Professor in the Department of Chemistry at The Ohio State University (USA) between 1995 and 2009, after which he moved his research group to Montana State University (USA). In the summer of 2016, he will return to The Ohio State University as Professor and Ohio Eminent Scholar in the Department of Chemistry and Biochemistry. The Kohler research group uses femtosecond spectroscopy to study excited electronic states of DNA. A second research focus concerns the study of primary events in nanomaterials of interest for solar energy conversion and photocatalysis. Josef Wachtveitl studied Physics at the University of Regensburg (Germany) and at the University of Colorado Boulder (USA). He received his PhD in the group of Dieter Oesterhelt at the Max-Planck-Institute for Biochemistry in Martinsried (Germany), where he started to work on the primary light reactions of bacterial photosynthesis. After research visits to Argonne National Laboratory (USA) und CEA Saclay (France), he joined Wolfgang Zinth's group at the LMU Munich (Germany). Two years after his habilitation, in 1998, he was appointed Professor for Physical Chemistry at the Goethe-University Frankfurt/Main (Germany). Since 2004 he has been Full Professor for Physical Chemistry, and from 2004 to 2010 he was also Professor in the Institute for Biophysics. He initiated biophysics as a Bachelor/Master degree program, which has been offered since 2008 in Frankfurt. Real-time observation of fastest chemical and biological reactions is the main research focus of his group. Special interest lies in the reaction dynamics of molecular systems like optical switches and cages, natural and artificial photosynthetic complexes, as well as bioactive model systems for peptide and RNA folding.
Source: ChemPhysChem
Authors: Peter Gilch, Bern Kohler, Josef Wachveitl
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W2336064281