Dr. Marina Kuimova, Imperial College (London)

Molecular Rotors Measure Intracellular Viscosity

Organic Chemistry Seminar Series

Viscosity is one of the main factors which influence diffusion in condensed media. In a cell viscosity can play a role in several diffusion mediated processes, such as drug delivery, signalling and mass transport. Previously, alterations in viscosity in cells and organs have been linked to malfunction; however, mapping viscosity on a single-cell scale remains a challenge.

We have imaged viscosity inside individual cells using fluorescent probes, called molecular rotors, in which the speed of rotation about a sterically hindered bond is viscosity-dependent [1, 2, 3]. This approach enabled us to demonstrate that viscosity distribution in a cell is highly heterogeneous and that the local microviscosity in hydrophobic cell domains can be up to 100x higher than that of water. These conclusions have been confirmed by monitoring the decay and reaction rates of short-lived excited state of molecular oxygen, singlet oxygen, O2(a1Î"g), on a single cell level [4].

We have also shown that the intracellular viscosity increases dramatically during light activated cancer treatment, called Photodynamic therapy (PDT) [2]. We have demonstrated the effect of such viscosity increase on intracellular reactions by directly monitoring dynamic changes in the rates of formation and decay of a short lived toxic intermediate, crucial in PDT, singlet molecular oxygen, O2(a1Î"g), in light perturbed cells [2] and under conditions of controlled singlet oxygen production in viscous medium [5]..

References
[1]. M. K. Kuimova, G. Yahioglu, J. A. Levitt, K. Suhling, J. Amer. Chem. Soc., 2008, 130, 6672
[2]. M. K. Kuimova, S. W. Botchway, A. W. Parker, M. Balaz, H. A. Collins, H. L. Anderson, K. Suhling, P. R. Ogilby, Nature Chem., 2009, 1, 69
[3]. J. A. Levitt, M. K. Kuimova, G. Yahioglu, P.-H. Chung, K. Suhling, D. Phillips, J. Phys. Chem. C, 2009, 113, 11634
[4]. M. K. Kuimova, G. Yahioglu, P. R. Ogilby, J. Amer. Chem. Soc., 2009, 131, 332
[5]. M. K. Kuimova, M. Balaz, H. L. Anderson, P. R. Ogilby, J. Amer. Chem. Soc., 2009, 131, 7948

For more information contact Dr. Kyril Solntsev (404-385-3117).