Two-dimensional nonlinear optical activity spectroscopy of coupled multi-chromophore system

Abstract

Most biomolecules are chiral. A variety of optical activity measurement techniques have been extensively used to study chiral natures of complicated biological molecules such as proteins and nucleic acids. Recently, coherent two-dimensional (2D) spectroscopic techniques have been developed and widely used to study structures and dynamics of biomolecules via measuring couplings between chromophores. However, such 2D optical spectroscopic methods utilizing linearly polarized beams do not provide information on the molecular chirality. Thus, we have theoretically shown that novel 2D optical activity measurement techniques based on three- and four-wave-mixing schemes are of use to obtain the 2D spectrum of a chiral molecule. Particularly, we carried out numerical simulations of 2D optical activity spectra of polypeptides and a light-harvesting complex. These methods utilizing circularly polarized beams and related spectroscopic techniques will be of great use in understanding and elucidating the underlying mechanisms of ultrafast chemical and conformational changes of chiral biomolecules in the future.

Dynamic localization of electronic excitation in photosynthetic complexes revealed with chiral two-dimensional spectroscopy

“…The helical motion of excitations around the rings of LH2 induces a magnetic transition dipole moment that provides the dominant contribution to the optical activity. 2-4 The precise orientation of the constituent chromophores and their interaction energies dictates the optical response and reproduces the CD spectra of LH2 complexes. 32 Because the chiral signal arises from the corkscrew-like motions of the electrons induced by the strong interactions between chromophores and their environment, these measurements probe the delocalized nature of the electronic structure around the ring.…”

“…By controlling the relative polarization of the incoming pulses, we selectively measure a chiral tensor element while eliminating the stronger achiral contributions. 2,29 Formally, our scheme depicted in Figure 1 yields a spectrum proportional to measuring the difference in nonlinear response after excitation with left- versus right-circularly polarized light. 30 Similar strategies have been experimentally realized in the infrared region of the spectrum for both linear 7 and second-order experiments.…”

“…1 Microscopically, optical chirality arises from corkscrew-like motion of electrons after excitation belying asymmetric interactions of the electron with its environment. 2-4 Femtosecond and time-resolved measurements of optical activity represent a frontier for understanding functional materials and chemical dynamics. 5-8 In photosynthetic complexes, transient fluctuations in the protein scaffold cause chiral optical response to change following photoexcitation as the delocalization length of the exciton dynamically contracts.…”

Opportunities for chiral discrimination using high harmonic generation in tailored laser fields

“…In the condensed phase, several breakthroughs have been achieved [17,18] using non-linear chiroptical spectroscopy [17,18,19,20]. In the gas phase, where isolated compounds can be studied, such measurements are a lot more challenging due to low density of samples, so that no ultrafast measurement at ∼ 10 1 fsec time scale has yet been reported.…”

Coherent Control Protocol for Separating Energy-Transfer Pathways in Photosynthetic Complexes by Chiral Multidimensional Signals

“…5,6 It has been applied to resolve weak spectral features in peptides and in light-harvesting complexes. 13-17 In our earlier work, we demonstrated how various laser pulse configurations may be designed to separate coherent dynamics from dissipative energy relaxation. 18 CI signals show a richer 2D peak pattern and enhance the differences between the spectra from two species of the photosynthetic bacteria.…”