1 3 DOI 10.1007/s00340-016-6526-5 Appl. Phys. B (2016) 122:253 Irradiation of myoglobin by intense, ultrashort laser pulses Juliah J. Chelliah 1 · S. V. K. Kumar 1 · Aditya K. Dharmadhikari 1 · Jayashree A. Dharmadhikari 2 · Deepak Mathur 1 Received: 4 July 2016 / Accepted: 6 September 2016 © Springer-Verlag Berlin Heidelberg 2016 decades, it has been established that the precursor of radi- ation-induced damage can be either terrestrial or extrater- restrial in origin. Cosmic rays constitute the main extrater- restrial culprit; collisions of these energetic particles with constituents of the earth’s upper atmosphere give rise to a gamut of energetic daughter products that induce deleteri- ous effects on living tissue. Beams of particles from accel- erators and reactors are terrestrial examples, giving rise to the formation of energetic secondary particles or high- energy electromagnetic radiation, X-rays, and gamma rays; these also induce deleterious effects on living tissue. There is, of course, naturally occurring radioactivity—both terres- trial and extraterrestrial—that also constitutes a biohazard for living matter. Within this scenario, proteins are gener- ally damaged through the generation of free radicals that are produced due to low-energy transfer radiation (LET) [3]. LET has, consequently, become a most useful parame- ter for representing radiation quality along with parameters like particle energy and atomic number [4]. Considerable work has been accomplished on how, at different values of LET, the formation of free radicals leads to radiation- induced damage and the consequent modification of living matter. In the case of proteins, the basic radiolytic effects may be classified as polymer backbone degradation, cross- link formation, modification of amino acid residue radi- cals, change in the protein’s conformation and its degree of crystallinity, oxidative degradation (when in the presence of O 2 ), and damage caused to one of the active sites in the enzymes [3, 5]. Recently, radiation-induced damage to living matter has also begun to be investigated using high-intensity laser pulses of ultrashort (femtosecond) duration. Ready avail- ability of sources of ultrashort pulses of near-infrared laser light has, in the course of the last few years, enabled inves- tigations to be made of how such pulses propagate through Abstract We probe the interaction of myoglobin with intense, femtosecond laser pulses. Significant spectral dif- ferences are found between native and the irradiated myo- globin. These arise from the disruption of the heme pros- thetic group: geometrical restructuring results in alteration of the oxidation state of Fe (from its initial +3 state) which is found to be reversible on timescales of ~4–6 h. Measure- ments taken upon addition of OH scavengers establish the key role played by these radicals in the overall dynamics. Myoglobin remains intact upon intense field irradiation, demonstrating the structural robustness of the polypeptide backbone. Experiments utilizing intense, ultrashort laser pulses are expected to open new horizons for following, with high sensitivity, changes in the oxidation state, chemi- cal environment, and electronic state of biomolecules in the aqueous phase. 1 Introduction It is known that the total protein concentration in a living cell is of the order of 15 % [1]. Hence, upon exposure of a cell to ionizing radiation, the protein component is also expected to be affected along with other cell constituents. The biological effect of such radiation is, of course, pre- dominantly determined by dosage, but the type of radiation seems to also play an essential role [2]. Over the last six * S. V. K. Kumar svkk@tifr.res.in 1 Tata Institute of Fundamental Research, 1 Homi Bhabha Road, Mumbai 400 005, India 2 Department of Atomic and Molecular Physics, Manipal University, Manipal 576 104, India