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The ultrafast photochemistry of vitamin D – Towards understanding the quantum biology of a self-regulating system
  Molecular Physics seminar

Monday 04 July 2016
from 11:00 to 12:00
at FA 31
Speaker : Enrico Tapavicza (California State University)
Abstract : The main source of vitamin D for humans is its generation by the sun’s ultraviolet (UV) light. Oral administration of large vitamin D quantities can lead to vitamin D overdose, which affects negatively many regulation cycles in our body. In contrast, overproduction of vitamin D due to extended sun exposure has never been observed [1]. It has been found that a complex network of vitamin D photo isomers that are connected by reversible chemical and photochemical reactions in our skin prevents vitamin D overproduction. The mechanism of the self-regulation is not well understood [2]. An important feature of the self-regulating cycle is its characteristic wavelength dependent photochemistry: UV light with longer wavelengths induces different photochemical reactions than UV light with short wavelengths. Thus, the distribution of photochemical isomers is a function of the spectral composition of the sun and varies with day time and time of the year. Furthermore, large absorption coefficients of some vitamin D isomers lead to an intrinsic sun protection upon extended UV light exposure, which reduces vitamin D production. In this talk, I will present new theoretical and experimental results that can explain several aspects of this self-regulating cycle. We combine ab initio molecular dynamics simulations based on quantum chemistry [3, 4, 6] with time-resolved femtosecond resolved experiments [5, 6, 7, 8, 9], to understand the photo dynamics of several vitamin D related photochemical reactions. In particular we are interested in how the specific geometry of vitamin D affects its photochemical reactivity. Furthermore, we want to understand the role of each individual vitamin D photo isomer in the self-regulating cycle. We acknowledge support by the California State University (CSU), Long Beach start-up fund and the CSU Program for Education and Research in Biotechnology (CSUPERB) fund. References: [1] J. MacLaughlin, R. Anderson, and M. Holick. Spectral character of sunlight modulates photosynthesis of previtamin D3 and its photoisomers in human skin. Science, 216(4549):1001–1003, 1982. [2] M. Norval, L. O. Bjorn, and F. R. de Gruijl. Is the action spectrum for the UV-induced production of previtamin D3 in human skin correct? Photochem. Photobiol. Sci., 9(1):11, 2010. [3] E. Tapavicza, A. M. Meyer, and F. Furche. Unravelling the details of vitamin D photosynthesis by non- adiabatic molecular dynamics simulations. Phys. Chem. Chem. Phys., 13:20986, 2011. [4] Tapavicza, G. D. Bellchambers, J. C. Vincent, and F. Furche. Ab initio non-adiabatic molecular dynamics. Phys. Chem. Chem. Phys., 15:18336–18348, 2013. [5] N. A. Anderson, J. J. Shiang, and R. J. Sension. Subpicosecond Ring Opening of 7-Dehydrocholesterol Studied by Ultrafast Spectroscopy. J. Phys. Chem. A, 103(50):10730, 1999. [6] Cyclohexadiene Revisited – a Time Resolved Photoelectron Spectroscopy and Ab Initio Study; Oliver Schalk,Ting Geng, Travis Thompson, Noel Baluyot, Richard D. Thomas, Enrico Tapavicza, Tony Hansson [7] C. Tang, A. Rury, M. B. Orozco, J. Egendorf, K. G. Spears, and R. J. Sension. Ultrafast electrocyclic ring opening of 7-dehydrocholesterol in solution: The influence of solvent on excited state dynamics. J. Chem. Phys., 134(10):104503, 2011. [8] B. C. Arruda, J. Peng, B. Smith, K. G. Spears, and R. J. Sension. Photochemical ring-opening and ground state relaxation in alpha-terpinene with comparison to provitamin D3. J. Phys. Chem. B, 117(16):4696–4704, 2013. [9] J. Meyer-Ilse, D. Akimov, B. Dietzek, Ultrafast Circular Dichroism Study of the Ring Opening of 7- Dehydrocholesterol, Chem. Phys. Lett., 3, 182-185, 2012.

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