Applications of Fluorescence Photobleaching Recovery ACS Polymer Group Raleigh, North Carolina Thursday, November 8

Gelation of “sticky” rods Helical  -polypeptide backbone, persistence length > 1000 Å PBLG: poly(benzyl-L-glutamate) PBLG is “sticky” but not very.

PSLG: a stickier wicket. PSLG: poly(stearyl-L-glutamate)

Very rigid  -helical polypeptide backbone Intramolecular Hydrogen Bonds Waxy Sidechains C 18 = Stearyl Self-solvating (well, sorta): Molten Rods—easier processing. Oriented Films/waveguides/chiral separation Polymer Physics of Rods in Solution, Gel & Melt More rigid and more soluble than those high-$$$ Air Force & NASA polymers Hey…they don’t have to be rigid—helix-to-coil transition Why everyone cares about these molecules again.

Idealized Rod Phase Diagram ISO  aa bb T LC

Very rigid rods! MwMw M w /M n by GPC/LS x = L/d  a (%)  b (%)  avg (%) Onsager 4/x Flory 239,    ,    ,   

Hypothetical Rod Phase Diagram With Gelation Transitions Overlaid  T Iso LC S1S1 P1P1 LL 1 S2S2 LL 2 P2P2

DSC can detect ISO-LC transition. Heat per molecule gives no trend.

Annealing perfects but does not alter gel structure. Suggests motion!

Labeling Does Not Bug the Helix §Computer Simulation §Intrinsic Viscosity §Static Light Scattering §Dynamic Light Scattering §Phase boundary determinations §Temperature- dependent studies

Modulation FPR Device * * * * AOM M M D RR DM OBJ S PMT PAOS TA/PVD L

Temperature-ramped modulation FPR

Everything can move, yet the structure remains

Sticky rods—remaining challenges Crosslink ‘em to lock in liquid crystal structure Solution behavior above the gel transition Rheological response EM’s of these gels Supercritical fluid drying of gels and LC’s

Problems related to entanglement Bulk polymers: welding, processing, phase separation, failure Solutions: rate of dissolving, intracellular transport, separations for genomics, joining PVC pipe!

Reptation—a theory to describe random snaking in polymer tangles T here once was a theorist from France Who wondered how molecules dance. "They're like snakes," he observed, "as they follow a curve, the large ones can hardly advance."* D ~ M -2 deGennes Need: better diffusion methods Problem: lots of things appear to obey this scaling law Suggests: look at the ignored systems, especially RODS *With apologies to Walter Stockmayer

See, e.g., Lodge & Muthukumar, J. Phys. Chem. 1996, 100,

Our Hypothesis Solutions containing rodlike diffusers may provide evidence for entanglement-like phenomena in solution…or at least prove interesting, fun and challenging. Evidence would be: sudden drop-offs in mobility with concentration, failure to follow continuum mechanics.

Rods should make effective probes. But very challenging: Early de Gennes paper on rod/coil diffusion: 19 citations Same era de Gennes paper on coil/coil reptation: 479 citations We may expect some problems! Why it’s worth it: composite precursor fluids, dissolution rate, phase sep’n rate, relation to GPC, CGE of rods, intracellular transport.

Studying “entangled” rods by Optical Methods Fluorescently labeled probe rod Unlabeled rods Solvent

L d LC formation  = 4/A 2  5/dL 2 Reduced # Density   dL 2 /5 Doi-Edwards-Onsager Reference Volumes for Rods = number density = # of rods per unit volume

Desirable rod properties Stiff—no bending Monodisperse (all the same size) Non-aggregating Water-soluble We don’t have to make ‘em! Let mother nature do the work: plants make viruses (unwillingly) with most of these qualities.

Seedlings  Sick Plants  And close-up of mosaic pattern. Doing our Part to Keep the “A” in LSU A&M

Two TMV’s in Transmission Electron Microscopy

An ear of corn has about as many kernels as TMV has protein subunits (ca. 2130). The protein subunits enfold a spiral-wound strand of RNA which will encode the next generation. TMV is more extended than an ear of corn.

Better Views

TMV Characterization Sedimentation, Electron Microscopy & DLS  Most TMV is intact.  Some TMV is fragmented.  weaker, faster mode in CONTIN decay analysis  Intact TMV is easy to identify  stronger, slower mode in CONTIN  It is easy to measure at low concentrations that avoid TMV-TMV interactions in DLS and we can use small amounts in FPR after dye attached. Huh?

Tobacco from the Carolinas to Connecticut

If tobacco goes away… “Traditionally in Kentucky great mounds of brush are piled and burned in February to prepare a bed for tobacco seedlings. I remember spending most of the day hauling and piling brush. My dad would start the fire in late afternoon and we would sit up most of a cold February or March night stoking the fire, watching the stars, and roasting hot dogs or marshmallows over the bonfire. Many times neighbors would stop by and sit with us for a spell around the fire, talking into the night.” From:

Modulation FPR Device a’la Lanni & Ware * * * * AOM M M D RR DM OBJ S PMT PAOS TA/PVD L SCOPE Measuring Translational Diffusion

FPR Data for TMV Solution: very low dye content.

D tracer self of TMV vs. c TMV

Rotation & Diffusion of TMV in Polymer Solutions – – – Hard to see rotation in FPR; try scattering Fabulous new autocorrelators for scattering  10 decades of time in one measurement! – – – Contrast for scattering stinks: everything scatters, esp. in aqueous systems where refractive index matching cannot hide matrix. Matrix Polymer Solvent TMV Probe