Ultrafast Electron Dynamics in a Biomolecule Initiated by Attosecond Pulses

Several european researchers have been able to induce and measure an ultrafast charge migration in a complex molecule. This phenomenon precede any structural rearrangement of molecules and is the basis of many biological processes. The work has been published[1] in the journal Science.

Figure: Snapshots of charge distribution on the most abundant conformer of the aminoacid phenylalanine. The charge density can take negative and positive values (yellow) or (purple). The charge migration from one end of the molecule to the other takes no more than three or four femtoseconds.

 

The work arises from a cooperation among several European researchers (among them the PI’s of two ERC AdG projects, ELYCHE project, with GA nº 227355 and XCHEM project, with GA nº 290853). A clear experimental evidence of ultrafast charge dynamics in the phenylalanine amino acid, after prompt ionization induced by attosecond pulses, has been found. Charge migration shows up as oscillations in the yield of a doubly-charged molecular fragment produced from ionization of a second electron by a probe pulse as a function of its delay time. Two main frequencies were measured: 0.24 PHz (corresponding to a period of 4.2 fs) and 0.36 PHz (period of 2.8 fs), thus confirming the electronic origin of the measured dynamics. Numerical simulations of the temporal evolution of the electronic wave packet created by the attosecond pulse strongly support the interpretation of the experimental data in terms of charge migration.

The ability to initiate and observe purely electronic dynamics in the building blocks of life represents a crucial step forward in attosecond science, which is progressively moving towards the investigation of more and more complex systems and can be considered as a first contribution towards attobiology.

Direct measurement of the ultrafast charge dynamics in an amino acid, initiated by attosecond pulses, represents a crucial benchmark for the extension of attosecond methodology to biology. In the same way in which femtosecond pulses have contributed (and still contribute) to the investigation and understanding of important biological processes, attosecond science offers the possibility to elucidate, on a temporal scale preceding nuclear motion, subtle processes ultimately triggering and determining the response of biomolecules. For instance, how the ultrafast motion of a hole in DNA created by a high-energy particle might initiate cell necrosis or mutation. The results obtained in the case of phenylalanine can be seen as the first experimental confirmation that attosecond pulses and techniques will be essential tools for understanding of dynamical processes on a temporal scale that is relevant for the evolution of crucial microscopic events at the heart of the macroscopic biological response of molecular complexes.

The picture shows XChem researchers directly involved in this work

[1] Ultrafast electron dynamics in phenylalanine initiated by attosecond pulses
F. Calegari, D. Ayuso, A. Trabattoni, L. Belshaw, S. De Camillis, S. Anumula, F. Frassetto, A. Palacios, P. Decleva, J. B. Greenwood, F. Martín, M. Nisoli
Science 346, 336-339 (2014). DOI:10.1126/science.1254061

Supplementary material: Watching phenylalanine change one quintillionth of a second at a time

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