1. R Christy F. Landes Carmen G. Reznik, Nicel Estillore, Rigoberto Advincula, Switchable Transport in Supported Polyelectrolyte Membranes LANDESRESEARCH GROUPLANDESRESEARCH GROUP Rice University Department of Chemistry

2. Motivation: Tunable Molecular/Charge Transport in Charged and Crowded Environments LANDESRESEARCH GROUPLANDESRESEARCH GROUP Frauenfelder, H.; Sligar, S.G.; Wolynes, P.G. Science 1991, 1598. Wang, Y.; Baskin, J.S.; Xia, T.; Zewail, A. Proc. Natl. Acad. Sci. USA, 2004,18000. Papoian, G. Proc. Natl. Acad. Sci. USA 2008, 14237. Loosely Controlled Single Pathways Degenerate and Competitive Pathways Tightly Controlled Single Pathways Processes may proceed via:

3. The Polymer Brush 1,2 Polymer chains end-grafted to a surface Our Model Synthetic System High Density Ordered Environment Polyelectrolyte Brushes Charge distributed along the polymer chain Polymer Thin Layer: - - - - - - - - - - - - - - - - LANDESRESEARCH GROUPLANDESRESEARCH GROUP 2 Advincula, et al., Polymer Brushes: Synthesis, Characterization and Applications, Wiley-VCH, 2004 1 Prucker, Rühe,, Macromolecules, 1998, 31, 602-613

4. Tunable response: Polymer Brush Thin Films: Tunable and responsive structural properties Modify physical/responsive properties via polymer chemistry: Internal microstructures Heterogeneous surface coverage Electroactive polymers LANDESRESEARCH GROUPLANDESRESEARCH GROUP 1 Whiting, et al. Nanoletters, 2006, 6, 573-578 A strong connection has been demonstrated between nanostructure & transport 1

5. Charged Molecule Transport : LANDESRESEARCH GROUPLANDESRESEARCH GROUP Poly(styrene sulfonate) polymer brush Rhodamine 6G Evaluation of: 1) Translational Transport 4, 2) Rotational Transport 5 via Surface Initiated Polymerization 1 Properties: high density water soluble simple synthesis The Environment 1 Prucker, Rühe, Macromolecules, 1998, 31, 602-613 Bodipy – R6G (base structureof dye shown) Alexa 555 (Alexa 546 shown here) Probe Molecules: 4 Reznik, Landes et al., JPC B, 112, 10890–10897 5 Reznik,Estillore, Advincula,Landes, JPC B, 113,14611–14618

6. Methods and Materials: Experimental Configuration Signal Trajectory LANDESRESEARCH GROUPLANDESRESEARCH GROUP

7. APD Polarized Light Splitter LANDESRESEARCH GROUPLANDESRESEARCH GROUP Elson, Madge, Biopolymers, 1974, 13, 1-27 Aragon, Pecora, JCP, 1976, 64, 1791 Methods and Materials: FCS and SM Polarization Resolved Spectroscopy Axelrod, Biophys. J, 1979, 78, 557-574 Forkey, et al., Prog. Biophys. Mol. Biol., 2000, 74, 1-35

8. LANDESRESEARCH GROUPLANDESRESEARCH GROUP Multiple Regions Heterogeneous Transport - Multiple kinds of transport possible Multiple Interactions - -Coulomb -Steric By what mechanisms does transport occur? Can modes of transport be selected for?

9. Signal acquired at 10 us and binned to 1 ms DATA: Single Molecule Events LANDESRESEARCH GROUPLANDESRESEARCH GROUP R6G over PSS brush (pH 7): 300 ms trace, AC decay time 440 ms R6G dye diffusing in water

10. LANDESRESEARCH GROUPLANDESRESEARCH GROUP DATA: Heterogeneous Modes of Transport Translation Adsorption Highly Oriented States Strong associations State Switching Non-Oriented States Weak association Reznik, Landes et al., JPC B, 112, 10890–10897 Reznik,Estillore, Advincula,Landes, JPC B, 113,14611–14618

11. LANDESRESEARCH GROUPLANDESRESEARCH GROUP Electrostatic coupling affects diffusion of the counterion: - - - - H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ + + - - - - - - - - H+H+ H+H+ + counter ion Acidified co-solvent increases diffusion rates in the PSS brush DATA: Switchable Diffusion

12. LANDESRESEARCH GROUPLANDESRESEARCH GROUP Slow Diffusion Rates Diffusion Rates in Water R6G440 ms22 us Bodipy89 ms16 us Alexa6 ms32 us DATA: Transport Response to Charged Molecular Species

13. LANDESRESEARCH GROUPLANDESRESEARCH GROUP Charged Molecular Transport

14. LANDESRESEARCH GROUPLANDESRESEARCH GROUP Data: MultipleTransport Modes Indicated in FCS Tcherniak, Reznik, Link, Landes, Analytical Chemistry, 2009, 746-754 Slow Diffusion Intermediate Diffusion Bulk-Like Diffusion R6G436 ms8.9 msX Bodipy89 ms3.7 ms22 us AlexaX 6 ms32 us

15. Brownian Dynamics Simulation Increased electrostatic coupling leads to a shifted AC function, reflecting slower diffusion Potential Field in b) is an order of magnitude stronger than in a) Modeling the Effect of the Electrostatic Field on the AC function: Reznik, et al. JPCB, 2008 LANDESRESEARCH GROUPLANDESRESEARCH GROUP

16. LANDESRESEARCH GROUPLANDESRESEARCH GROUP Additional Investigations: Extended SM evaluation of orientation as a function of time: - 3 detectors 1 - advancement of techniques to allow lower time resolution (correlation techniques) Control of charge transport via electrical switching 1)Construct a microelectrode device on a glass coverslip using physical vapor deposition techniques. 2)Grow polymer brush on the electrode device 3)Measure diffusion and orientation effects as a function of electric field strength 1 Fourkas, Opt. Lett., 2001, 26, 211-213

17. Conclusions Using SM spectroscopy, combined with FCS, we have observed Complex Transport Mechanisms for single molecule probes with a variety of charge structures diffusing in association with a strong polyelectrolyte brush: LANDESRESEARCH GROUPLANDESRESEARCH GROUP Modes of transport in Include: - non associated/bulk water diffusion - both strong and weak brush association states: from diffusion near/within the brush system, to restricted diffusion and adsorption - polarization state switching Predominate modes of transport are dependent upon: - Coulomb and steric considerations - dye and solvent charge structure And we have provided – experimental evidence of stimuli responsive switchable transport functionality in the polymer brush

18. And for Funding: The Texas Center for Superconductivity NIH Molecular Biophysics Training Grant (T32 GM008280), Keck Center for Interdisciplinary Bioscience Training Rice University PRF The Whole Landes Research Group And Saumya Khatua, Wei-Shun Chang, Alexei Tcherniak, and Dr. Stephan Link Thanks to: LANDESRESEARCH GROUPLANDESRESEARCH GROUP