Femtosecond conical intersection dynamics of tryptophan in proteins and validation of slowdown of hydration layer dynamics Jin Yang, Luyang Zhang, Lijuan Wang, and Dongping Zhong 06/21/2013 Department of Physics The Ohio State University

2Outline nIntroduction: motivation of the study nStructure of the indole moiety: side chain of Trp nFemtosecond time-resolved anisotropy measurement nData analysis nResults nInsight into protein hydration studies

3Introduction nTryptophan (Trp or W) has been developed as a powerful optical probe to study protein hydration dynamics nObservation: at the blue side of the fluorescence emission, protein show slower dynamics nTrp has two nearly degenerated excited state 1 L a and 1 L b nIt is suspected that the internal conversion between 1 L a and 1 L b might smear the initial ultrafast decay at the blue side of protein hydration dynamics

4 Structure of the indole moiety: side chain of Trp a)The permanent dipole moments of indole in the ground state (S 0 ) and the two excited states 1 L a and 1 L b. b)Transition dipole moments between ground state and excited states. 1.L. Sobolewski and W. Domcke, Chem. Phys. Lett. 315, 293 (1999). 2.D. Zhong, Adv. Chem. Phys. 143, 83 (2009).

5 Femtosecond time-resolved anisotropy measurement

6 Data Analysis Upon 290nm excitation Dephasing time constant T 2 For more details, please refer to the Supporting Information of the following article: J. Yang, L. Zhang, L. Wang, and D. Zhong, J. Am. Chem. Soc. 134, (2012). Conical intersection time constant  IC Excited state dynamics assuming no 1 L b state: With nearly degenerated states 1 L a and 1 L b :

7 Data Analysis

8Results  The native state of protein GB1 as well as 9 designed mutants have been studied.  The parallel, perpendicular fluorescence transients and the anisotropy are fitted simultaneously with the same parameters (e.g.  IC ).  The internal conversion of Trp in protein happens in tens of fs as show by the anisotropy dynamics.  The plateau is determined by the value of

9Results The time scale for conical intersection (internal conversion) between 1 L a and 1 L b states is 40-80fs. There is no clear correlation between the fluorescence emission maximum and  IC. The plateau value of the anisotropy after IC dynamics is related with the relative absorption of 1 L a and 1 L b states. When, c(t)=b(t)=0, a(t)≈a b (t) and the anisotropy is

10 Insight into protein hydration studies

11Acknowledgement Advisor: Dr. Dongping Zhong Colleague: Dr. Luyuan Zhang Lijuan Wang This work was supported by the National Science Foundation and the National Institute of Health.