Coherent Control for Spectroscopy and Manipulation of Biological Dynamics

Abstract

Motivated originally by the goal of steering a photoreaction into desired product channels, the concept of coherent control is to adapt the spectral and temporal characteristics of the excitation light to the inherent molecular resonances and dynamics, such that these can be selectively addressed and manipulated. In the last decade, the ultrafast dynamics of many atomic and molecular quantum systems in the gas and condensed phase have been controlled successfully. Motivations in chemistry are now 1) to perform spectroscopy by coherent control, which requires a deeper understanding of control mechanisms, 2) to treat more complex, biological photoreactions, and 3) the pragmatic use of coherent control techniques, for example, for pulse compression or enhanced contrast in multiphoton microscopy. As examples for 1) and 2) we review here the combined effort and interplay of conventional spectroscopy and coherent control experiments, applied to the energy flow in the light-harvesting complex LH2 from bacterial photosynthesis. Closed-loop control experiments allowed the characteristic coupling frequency of internal conversion in the carotenoid in LH2 to be extracted. Open-loop three-pulse control experiments, on the other hand, could directly observe an anticipated Raman-excited carotenoid ground state. As a variant of difference spectroscopy, coherent control has thus served to gain complementary spectroscopic knowledge about the energy flow in carotenoids by comparing natural to manipulated dynamics. Finally, we propose future coherent control experiments on the electronic state structure of carotenoids and discuss prospects of coherent control for other biological chromophores.

A General control mechanism of energy flow in the excited state of polyenic biochromophores

“…Such out-of-plane backbone motion in the carotenoid as part of a Light harvesting complex (LHC) has been discussed as the source of conformational change affecting the biological function. 9,35 …”

“…[6][7][8][9][10][11][12] In this field, specially shaped laser fields can select or suppress a transient spectral signature, leading potentially to the identification of all internal degrees of freedom directly involved in an energy transfer reaction.…”

Trichromatic π-Pulse for Ultrafast Total Inversion of a Four-Level Ladder System

“…Control of population transfer in multiphoton transitions in atoms and molecules with laser pulses is a fundamental tool that has been extensively investigated in quantum optics since the advent of ultrashort pulses due to its value in several areas, including nonlinear spectroscopy [1], femtochemistry and biology [2], or in quantum information and in the quantum engineering of light states [3], where quantum systems need to be fully controlled. Several techniques have been reported for control of population transfer between a pair of quantum states involving multiphoton transitions, such as spectral shaping of the fields illuminating the medium [4,5], adiabatic methods [6][7][8][9] and π-pulse polychromatic control [10][11][12][13].…”

Measuring enzyme binding using shaped ultrafast laser pulses

“…The general technique is known as quantum-control spectroscopy [2], where a molecular response is measured as a function of pulse shape instead of the frequency of a single excitation source. In this paper we use quantum-control spectroscopy to discriminate between unbound and enzyme-bound forms of the metabolically important, intrinsically fluorescent biomolecule NADH (reduced nicotinamide adenine dinucleotide) [3].…”