1. Protein Inhibition and Photoactivation of a Ruthenium(II)-Cobalt(III) Bimetallic Complex Through Electron Transfer
Leah Oliemuller

2. Cardiovascular Disease
Blood clots related to many fatal diseases: strokes, heart disease, heart attacks
Current clotbusters in use need to be administered in narrow 4 hour window from symptom onset
Common clotbusters:
-tissue plasminogen activator (TPA)
-tenecteplase
-alteplase
-urokinase
-reteplase
-streptokinase

3. Coagulation Cascade
Author: Graham Beards (own work)

4. Inherent problems associated with clot busters
Develop new approach to inhibit the cascade
inert reactive
coordination complexes!
[Ru(bpy)2dppz]2+
Garner, R. N.; Gallucci, J. C.; Dunbar, K. R.; Turro, C. Inorg. Chem. 2011, 57, 8936.
Heidary, D. K.; Howerton, B. S.; Glazer, E. C. J. Am. Chem. 2014, 57, 8936.
Hurtado, R. R.; Harney, A. S.; Heffern, M. C.; Holbrook, R. J.; Holmgren, R. A.; Meade, T. J. J. Mol. Pharmaceutics 2012, 9, 325.
[Ru(bpy)2(5CNU)2]2+
Co(III)-sb
NAMI-A

5. Co(III)-Schiff base
Fine tuning of the axial ligand to exchange with histidine residues on targeted protein
Inhibition dependent upon axial ligand exchange
Equatorial acacen (bis(acetylacetone)ethylenediimine) ligand remains inert
Needs to be improved:
-axial ligands must remain inert until photoactivation
-biocompatibility
Hurtado, R. R.; Harney, A. S.; Heffern, M. C.; Holbrook, R. J.; Holmgren, R. A.; Meade, T. J. J. Mol. Pharmaceutics 2012, 9, 325.
Peterson, M. D.; Holbrook, R. J.; Meade, T. J., Weiss, E. A. J. Am. Chem. Soc. 2013, 135,
Matosziuk, L. M.; Holbrook, R. J.; Manus, L. M.; Heffern, M. C.; Ratner, M. A.; Meade, T. J. Dalton Trans. 2013, 42, 4002.

6. New Modifications
Covalently attached Ru(II) fragment provides water solubility
Lowest energy absorption band on Ru(II) fragment at 455 nm
Holbrook, R. J.; Weinberg, D. J.; Peterson, M. D.; Weiss, E. A.; Meade, T. J. J. Am. Chem. Soc. 2015, 137 (9), 3379.

7. Holbrook, R. J. ; Weinberg, D. J. ; Peterson, M. D. ; Weiss, E. A
Holbrook, R. J.; Weinberg, D. J.; Peterson, M. D.; Weiss, E. A.; Meade, T. J. J. Am. Chem. Soc. 2015, 137 (9), 3379.

8. Quantum yields: 0.031 (3.1%) 0.022 (2.2%)
Holbrook, R. J.; Weinberg, D. J.; Peterson, M. D.; Weiss, E. A.; Meade, T. J. J. Am. Chem. Soc. 2015, 137 (9), 3379.
(ko = kr + knr, where kr is radioactive decay and knr is nonradiative decay)
Quantum yields:
0.031 (3.1%) (2.2%)
Smaller quantum yields suggest shorter lifetimes, this is consistent with the presence of an additional decay pathway

9. Transient Absorption Spectroscopy
Used to determine the time scale of the electron transfer between the Ru(II)-bpy and Co(III)-sb
Photoexcitation at ground-state bleach λabs = 460 nm
ΔOD = (IRF)A1e-t/τr
Abrahamsson, M. L. A.; Baudin, H. B.; Tran, A.; Philouze, C.; Berg, K. E.; Raymond-Johansson, M. K.; Sun, L.; Akermark, B.; Styring, S.; Hammarstrom, L. Inorg. Chem. 2002, 41, 1534.
ΔOD = (IRF)A1e-t/τr
ΔOD = (IRF)(A1e-t/τ1+A2e-t/τ2)

10. Transient Absorption Spectroscopy
Overlaying TA spectra of 1a at varying times of light exposure
Ground state bleach is the depopulation of 1a ground state
Recovers from 3MLCT state via phosphorescence
ground state bleach
TA spectra of 1.64 × 10-4 M 1a in 100mM phosphate buffer at pH 7.4 in water following photoexcitation at 460 nm
Recovery of ground state for the covalently bound Ru-Co complex 1 from 3MLCT state through phosphorescence as well as charge transfer and charge recombination

11. Transient Absorption Spectroscopy
Compound 1a
ΔOD = (IRF)A1e-t/τ1
τ1 = 470 ns =
Compound 1
ΔOD = (IRF)(A1e-t/τ1+A2e-t/τ2)
Kinetic traces extracted from TA spectra of 1 and 1a at 465 nm
τ1 = 470 ns =
τ2 = 38 ns =
Faster ground state recovery for compound 1

12. Separating Charge Transfer and Charge Recombination?
Previous models used to describe the entire second decay pathway, need to distinguish ket from kbet
Measures the intensity of photons emitted over time
Emission dynamics reflected by emission from the populated 3MLCT state
Depopulation of the 3MLCT state achieved through ko or ket, not influenced by kbet
Time Correlated Single Photon Counting (TCSPC)

13. Time Correlated Single Photon Counting (TCSPC)
Using the same ΔOD models:
τ1 = = 490 ns
τ2 = = 50 ns
Opperman, K. A.; Mecklenburg, S. L.; Meyer, T. J., Inorg. Chem. 1994, 33, 5295.
TCSPC kinetic traces of Ru(II)-bpy 3MLCT emission of 7.0 × 10-6 M 1 and 1a in pH mM phosphate buffer following photoexcitation at 445 nm
TA spectroscopy TCSPC
τ1 = 470 ns τ1 = 490 ns
τ2 = 38 ns τ2 = 50 ns
Similar time constants!

14. Determining Conformational Gating
Is the pathway limited by sterics or electronics?
Estimate of PET driving force
Rehm-Weller approximation:
ΔGPET = E1/2(RuIII) – E1/2(CoII) – ΔE0,0

15. Determining Conformational Gating
Estimate of PET rate constants
Marcus Theory:
Leads to relative ratios of rate constants:
kPET of compound 2 = 15 times greater than kPET of compound 1
kPET of compound 3 = 50 times greater than kPET of compound 1
Hoffman, B. M.; Ratner, M. A. J. Am. Chem. Soc. 1987, 109, 6237.
Farid, S.; Dinnocenzo, J. P.; Markel, P. B.; Young, R. H.; Shulka, D.; Guirado, G. J. Am. Chem. Soc. 2011, 133,
Yoshimura, A.; Nozaki, K.; Ikeda, N.; Ohno, T. J. Am. Chem. Soc. 2009, 131, 7521.
1; R,R’ = -H,-H
2; R,R’ = -Me,-H
3; R,R’ = -Me,-Me

16. Determining Conformational Gating
Experimental Results
Complex τ1 (ns) τ2 (ns) 1a 2a 3a
Tkachenko, N. V.; Tauber, A. Y.; Grandell, D.; Hynninen, P. H.; Lemmetyinen, H. J. Phys. Chem. A. 1999, 103, 3646.
Batteas, J. D.; Harriman, A.; Kanda, Y.; Mataga, N.; Nowak, A. K. J. Am. Chem. Soc. 1990, 112, 126.
Conclusion: The τ2 time constants are too similar to be described by the predicted rate constants

17. Light-Activated Axial Ligand Substitution
The electron transfer to cobalt populates Co-L antibonding orbitals leading to dissociation of the axial ligands
Histidine mimic 4MeIm chosen as competitive ligand
Im = imidazole
4MeIm
Histidine

18. Light-Activated Axial Ligand Substitution
Complex 1 in presence of equal equivalents of Im and 4MeIm produces 1:2:1 ratio of products
50% total bonds Co-Im
50% total bonds Co-4MeIm
Matosziuk, L. M.; Holbrook, R. J.; Manus, L. M.; Heffern, M. C.; Ratner, M. A.; Meade, T. J. Dalton Trans. 2013, 42, 4002.

19. Reaction progress measured in NMR tube in dark conditions and photoactivation with three LED lights (λirr = 455 nm, 4-W, 300 lumens output per light)
Faster ligand exchange achieved with light activation
Reactive in dark conditions

20. Reported time constants: Dark – 22 min Light – 4 min
Time dependent NMR spectra showing the change in Co-Im and Co-4MeIm peaks in dark conditions and upon photoactivation of 1 with three 455 nm LED lights
Reported time constants:
Dark – 22 min
Light – 4 min

21. Inhibition of α-Thrombin
Faster inhibition of human α-thrombin using photoactivation with LED lights (same illumination method using histidine mimic)
kdark = 6.8 × 10-5 s-1
klight = 3.8 × 10-4 s-1

22. Conclusions
Selective photoexcitation of Ru(II)-bpy increases the axial ligand reactivity of Co(III)-sb through PET
Faster ligand exchange using histidine mimic 4MeIm occurs faster in light conditions than in dark conditions
Photoexcitation of compound 1 increases the rate of inhibition of α-thrombin relative to dark conditions
Proposed mechanism of intramolecular electron transfer from Ru(II)-bpy to Co(III)-sb

23. Conclusions Electron Transfer:
Previous studies report axial ligand exchange due to reduction of Co(III) to Co(II) Schiff base analogues through a PET process
Covalently linked Ru(II) and Co(III) required for electron transfer to occur, PET pathway unavailable to bimolecular system
Conformational gating due to alkyl linker
Photoactivation using PbS quantum dots and LED lights show similar enhancement of axial exchange reactivity
Applicable in biologically relevant conditions

24. References Acknowledgements Notes Dr. Claudia Turro
Garner, R. N.; Gallucci, J. C.; Dunbar, K. R.; Turro, C. Inorg. Chem. 2011, 57, 8936.
Heidary, D. K.; Howerton, B. S.; Glazer, E. C. J. Am. Chem. 2014, 57, 8936.
Hurtado, R. R.; Harney, A. S.; Heffern, M. C.; Holbrook, R. J.; Holmgren, R. A.; Meade, T. J. J. Mol. Pharmaceutics 2012, 9, 325.
Peterson, M. D.; Holbrook, R. J.; Meade, T. J., Weiss, E. A. J. Am. Chem. Soc. 2013, 135,
Matosziuk, L. M.; Holbrook, R. J.; Manus, L. M.; Heffern, M. C.; Ratner, M. A.; Meade, T. J. Dalton Trans. 2013, 42, 4002.
Holbrook, R. J.; Weinberg, D. J.; Peterson, M. D.; Weiss, E. A.; Meade, T. J. J. Am. Chem. Soc. 2015, 137 (9), 3379.
Abrahamsson, M. L. A.; Baudin, H. B.; Tran, A.; Philouze, C.; Berg, K. E.; Raymond-Johansson, M. K.; Sun, L.; Akermark, B.; Styring, S.; Hammarstrom, L. Inorg. Chem. 2002, 41, 1534.
Opperman, K. A.; Mecklenburg, S. L.; Meyer, T. J., Inorg. Chem. 1994, 33, 5295.
Hoffman, B. M.; Ratner, M. A. J. Am. Chem. Soc. 1987, 109, 6237.
Farid, S.; Dinnocenzo, J. P.; Markel, P. B.; Young, R. H.; Shulka, D.; Guirado, G. J. Am. Chem. Soc. 2011, 133,
Yoshimura, A.; Nozaki, K.; Ikeda, N.; Ohno, T. J. Am. Chem. Soc. 2009, 131, 7521.
Tkachenko, N. V.; Tauber, A. Y.; Grandell, D.; Hynninen, P. H.; Lemmetyinen, H. J. Phys. Chem. A. 1999, 103, 3646.
Batteas, J. D.; Harriman, A.; Kanda, Y.; Mataga, N.; Nowak, A. K. J. Am. Chem. Soc. 1990, 112, 126.
Dr. Claudia Turro
Dr. Thomas J. Meade
Notes
The presenter declares no competing grade interest