Looking inside solid supports. Confocal Raman Microscopy of polymer beads

Transcription

1 Looking inside solid supports Confocal Raman Microscopy of polymer beads

2 Talk Outline Solid Phase Supports Fluorescence studies Confocal Raman Microscopic Maps Diffusion vs. Reaction Kinetics Dry beads: Is what you see real? Edge effects Summary

3 Resin Beads and Active Site Location Are sites on resin beads are uniformly distributed on PS, TentaGel and Glass beads? Which sites react first? Probe with Fluorescence & Raman

4 Issues with Fluorescence Dyes have large absorption cross- sections as well as high fluorescence quantum yields. No. of sites approx 2-4 pmols so the concentration in 1 µm m diameter bead is ca...3 mol dm -3 At even moderate loadings there will be significant absorption traversing the bead. S. R. McAlpine, S. L. Schreiber, Chem. Eur. J. 1999, 5, 3528

5 Fluorescent Bleaching and Broadening PEGA resin, swollen in water, loading 2%, laser power 1% TG resin, swollen in water, loading 1%, laser power 1% Loading =2% PS Resin Unswollen

6 Loading =.1% PS Resin Unswollen Loading =1% PS Resin Unswollen Fluorescence and Line Shape on Resin Beads Loading =2% PS Resin Unswollen Interactions between dye molecules can be significant

7 Raman Spectrum of PS Resin Exact peak position does depend on structure and environment but shifts small CN COOH Intensity CN NC N COOH Add CN Tags O COOH COOH CN CN ν / cm -1 HOOC N

8 Bead-Site + R-CN TAG reagent sites Loading kinetics Expt 2nd order kinetics Loading Fraction Time / s 1 2 3

9 PS Dioxane - 4-cyanobenzoic acid - TentaGel Dioxane Reaction Diffusion

10 PS in Dioxane Uniform Distribution - Reaction Slower Than Diffusion 8 Relative Intensity distance / µ m

11 PS in Dioxane No trend in the CN peak position

12 PS Bead in DMF Hole in the centre fills in with reaction time 25 Relative Intensity Time / min Distance / µm

13 But is what you see what you get? The spherical surface of the beads act as a lens when the refractive index of the bead differs from the surroundings The focal plane moves away from the equatorial plane as the image is scanned across the bead. So, are you seeing where you think you are looking?

14 Depth resolution ca 5 µm flat polymer on Si 35 AIR 3 25 Silicon Polymer Depth in Microns

15 Lens effects Same refractive index Air / Air Air / PS Air / Polystyrene Ray Traces for Different Bead Offsets: 1,2,3,4, 49 µm

16 Looking from underneath shows how little of the bead is probed by the scan

17 Are Swollen Beads OK? Many polymer beads swell in solvents and typically double in diameter 7/8 of the bead by volume is solvent Relative Peak Intensity Depth and Width measurements of the same swollen bead, confocal Depth Width n swollen ~ n solvent Distance / µm

18 Relative Intensity PS Bead in DMF distance / µ m Same pattern seen in the CN peak position. & intensity Relative Intensity This suggests the bead environment at the very edge may be different from inside. Time / min distance / mm Shift / cm-1

19 PS Bead in dioxane Polymer (blue) and CN Tag Raman (red) peaks Relative Intensity Polymer Tag Distance / µ m The CN tag seems to have a broader distribution than the polymer is there a diffuse outer polymer layer?

20 Accessibility of solid supports Beaded materials were loaded with the peptide 4-cyanobenzoic acid- Gly-Pro-Leu-Gly-Leu-Phe-Ala-Arg- OH,, incubated with the enzyme and the CN Raman peak monitored MMP 12 Thermolysin MMP 13 Clostridium NEP Collagenase kda TG no cleavage no cleavage no cleavage no cleavage no cleavage PEGA cleavage cleavage no cleavage no cleavage no cleavage CPG 155 cleavage cleavage cleavage cleavage cleavage

21 Summary Raman Spectroscopy of Beads Raman spectroscopy provides a very useful probe of the spatial distribution of reactive sites within a polymer bead. The kinetics of reactions at these sites can be observed. The spectra are sensitive to the nature of the environment around these sites.

22 Summary Beads Uniform distribution of reactive sites throughout the beads. The spatial distribution of reacted sites depends on the polymer type and solvent (and reaction time). Balance between reaction rate and FACSS Oct diffusion 24 rate.

23 Acknowledgements CCE Southampton Jurgen Kress, Riccardo Zanaletti, Abigail Rose, Mark Bradley, William Brocklesby, Helen Stanford, Lu Shin GlaxoSmithKline Mark Ladlow, Geoff Mellor, Malcolm Skingle Funding & Support J.G. Frey Univ. EPSRC, Univ. Southampton, CCE, Renishaw