1. Bidirectional Photocontrol of Peptide Conformation
Photoisomerization
Angew. Chem. 2012, 124, 6558 – 　　　　　　Ｃ
Bidirectional Photocontrol of Peptide Conformation
with a Bridged　Azobenzene Derivative
Subhas Samanta, [a] Chuanguang Qin, [ｂ] Alan J. Lough, [a] G. Andrew Woolley [a]
[a] Dr. S. Samanta, Dr. A. J. Lough, Prof. G. A.Woolley
　　Dept. of Chemistry, University of Toronto、Canada
[ｂ] Prof. C. Qin
　　School of Life Science, Northwestern Polytechnical University,　Ｃｈｉｎａ

2. Introduction
Challenge in Photocontrol - Combination of conformational change with complete bidirectional switching.
Incomplete Photoswitching-Normal azobenzenes-Overlap of absorbance spectra

3. J. AM. CHEM. SOC , Highly Efficient Reversible Z-E Photoisomerization of a Bridged Azobenzene with Visible Light through Resolved S1(nπ*) Absorption Bands Ron Siewertsen, Hendrikje Neumann, Bengt Buchheim-Stehn, Rainer Herges,, Christian Nather, Falk Renth,, and Friedrich Temps,

4. Biomolecular photoswitching - By red shift of switching wavelength
Stability against reduction by glutathione.
Introduction into biomolecules - Thiol-reactive cross-linker photoswitch (3).

6. UV/VIS Spectral results
n-∏* transitions red shift of 2
Cis- 10 nm
Trans-15 nm
- 90 nm red shift compared to cis
PSS, 70:30 trans/cis.
No absorption of cis at long wavelength.
Green light irradiation repopulates
　　> 99.7 % cis.
Colour – Cis (pale yellow)
Trans (Reddish purple)

7. Intramolecular cross-linking of 3 with pairs of Cys
residues of peptide
Greater photocontrol- Selectivity with one isomer
Molecular dynamics simulation on the isolated
cross linker
Cys residues spaced at i, i+11 – Matches with trans
– Does not with cis
Trans-helical conformation
　Cis-Nonhelical conformation

8. CD spectral and thermal relaxation results
Trans isomer n-∏* transition
senses the chiral environment of peptide

9. Reduction by glutathione
Cis isomer -Resistant to reduction
Trans isomer-Prone to reduction

10. Conclusions
Bridged azobenzene derivative 3-An effective photoswitch for the photocontrol of peptide conformation with visible light.
Complete bidirectional photoswitching
Bioactive peptides could be held in an “off” (nonhelical) conformational state for long periods of time,　then pulsed “on” (helical) with violet light and “off” again　with green light.
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