r christy f. landes carmen g. reznik, nicel estillore, rigoberto advincula, switchable transport in...
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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
LANDES
RESEARCH 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 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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LANDES
RESEARCH GROUP
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
LANDES
RESEARCH GROUP
1Whiting, et al. Nanoletters, 2006, 6, 573-578
A strong connection has been demonstrated between nanostructure & transport1
Charged Molecule Transport :
LANDES
RESEARCH GROUP
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
LANDES
RESEARCH GROUP
APD
APD
Polarized Light Splitter
)()(
)()()(
//
//
tItI
tItItA
LANDES
RESEARCH GROUP
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
LANDES
RESEARCH 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?
Signal acquired at 10 us and binned to 1 ms
DATA: Single Molecule Events
LANDES
RESEARCH GROUP
R6G over PSS brush (pH 7):300 ms trace, AC decay time 440 ms
R6G dye diffusing in water
LANDES
RESEARCH 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
LANDES
RESEARCH GROUP
Electrostatic coupling affects diffusion of the counterion:
--
--H+H+H+
H+
H+
H+
+
+
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-
-
--
H+
H+
+
counter ion
Acidified co-solvent increases diffusionrates in the PSS brush
DATA: Switchable Diffusion
LANDES
RESEARCH GROUP
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
LANDES
RESEARCH GROUP
Charged Molecular Transport
LANDES
RESEARCH GROUP
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
LANDES
RESEARCH GROUP
LANDES
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:
LANDES
RESEARCH 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
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:
LANDES
RESEARCH GROUP
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