R

Christy F. Landes Carmen G. Reznik, Nicel Estillore, Rigoberto Advincula,

Switchable Transport in Supported

Polyelectrolyte Membranes

LANDES

RESEARCH GROUP

Rice University Department of Chemistry

Motivation: Tunable Molecular/Charge Transport in Charged and Crowded Environments

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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 ControlledSingle Pathways

Degenerate and Competitive Pathways

Tightly ControlledSingle Pathways

Processes may proceed via:

The Polymer Brush1,2

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:

-

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-

---

-

---

-

---

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2Advincula, et al., Polymer Brushes: Synthesis, Characterization and Applications, Wiley-VCH, 2004

1Prucker, Rühe,, Macromolecules, 1998, 31, 602-613

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

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1Whiting, et al. Nanoletters, 2006, 6, 573-578

A strong connection has been demonstrated between nanostructure & transport1

Charged Molecule Transport :

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Poly(styrene sulfonate) polymer brush

Rhodamine 6G

Evaluation of: 1) Translational Transport4 , 2) Rotational Transport5

via Surface Initiated Polymerization1

Properties: high density

water soluble

simple synthesis

The Environment

1Prucker, Rühe, Macromolecules, 1998, 31, 602-613

Bodipy – R6G(base structureof dye shown)

Alexa 555(Alexa 546 shown here)

Probe Molecules:

4Reznik, Landes et al., JPC B, 112, 10890–108975Reznik,Estillore, Advincula ,Landes, JPC B, 113,14611–14618

Methods and Materials: Experimental Configuration

Signal Trajectory

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APD

APD

Polarized Light Splitter

)()(

)()()(

//

//

tItI

tItItA

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Elson, Madge , Biopolymers, 1974, 13, 1-27Aragon, Pecora , JCP, 1976, 64, 1791

Methods and Materials: FCS and SM Polarization Resolved Spectroscopy

Axelrod, Biophys. J, 1979, 78, 557-574Forkey, et al., Prog. Biophys. Mol. Biol., 2000, 74, 1-35

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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?

Signal acquired at 10 us and binned to 1 ms

DATA: Single Molecule Events

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R6G over PSS brush (pH 7):300 ms trace, AC decay time 440 ms

R6G dye diffusing in water

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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

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Electrostatic coupling affects diffusion of the counterion:

--

--H+H+H+

H+

H+

H+

+

+

-

-

-

-

-

-

--

H+

H+

+

counter ion

Acidified co-solvent increases diffusionrates in the PSS brush

DATA: Switchable Diffusion

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 Slow Diffusion 

RatesDiffusion Rates in 

Water

R6G 440 ms 22 us 

Bodipy 89 ms 16  us

Alexa 6 ms 32 us

DATA: Transport Response to Charged Molecular Species

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Charged Molecular Transport

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Data: MultipleTransport Modes Indicated in FCS

Tcherniak, Reznik, Link, Landes, Analytical Chemistry, 2009, 746-754

  Slow DiffusionIntermediate Diffusion

Bulk-Like Diffusion

R6G 436 ms 8.9 ms X

Bodipy 89 ms 3.7 ms 22 us 

Alexa X  6 ms 32 us 

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

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RESEARCH GROUP

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RESEARCH GROUP

Additional Investigations:

• Extended SM evaluation of orientation as a function of time:- 3 detectors1

- 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

1Fourkas, Opt. Lett., 2001, 26, 211-213

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:

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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

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:

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