1. Fluorescence Anisotropy
Dimensions of Perylene-Labeled Foldamers in Solution Determined by Time-Resolved Fluorescence Anisotropy
Hunter Little, Jean Duhamel | Department of Chemistry | University of Waterloo – Xuesong Li, Ivan Huc | Institut Européen de Chimie Biologique Université Bordeaux 2 | Pessac, France
Introduction
Procedure
Effect of Temperature
Foldamers are novel synthetic macromolecules that naturally fold. They adopt a well defined conformation in the crystalized form, but little is known about them in solution.
Samples were prepared by dissolving the foldamers in distilled in glass toluene purchased from Caledon and diluted to 2.3 x 10-6 M
Fluorescence decays analysed by fitting the polarized decays to the Equations 1 and 2:
The rotational time is obtained from the expression of the anisotropy given in Equation 3.
Foldamers
(1)
Macromolecules that naturally fold
Made of aromatic or peptide analogue backbones.
Behave similarly to naturally occurring macromolecules such as DNA
Offer new insight into helical handedness
(2)
Figure 4. Rotational time adjusted for temperature and solvent viscosity plotted as a function of foldamer length (Δ) T= 25 °C, (●) 35 °C (◊), and 75 °C
(3)
Fluorescence Anisotropy
Rotational Time
After adjusting for temperature and viscosity changes, the corrected rotational time (fT/h) is not affected by temperature. It demonstrates that the foldamers do not denature in toluene up to a temperature of 75 oC.
Uses plane polarized light to measure the rotational diffusion coefficient of the dye in solution
A larger anisotropy value corresponds to a more hindered dye
Conclusions
Foldamer Structure
Foldamers seem to retain their helical conformation while in solution
Annealing the foldamers at high temperature does not denature the foldamers over the temperature range examined
Acknowledgments
Figure 3. Rotational Time of Foldamers as determined by Fluorescence anisotropy.
Figure 1. Chemical structure of foldamers. Degree of polymerization is equal to 2, 8,16, or 32
Works Cited
Steady increase in rotational time as length increases before it seems to plateau around 20 – 25 units
Approximating the foldamers as cylindrical helices, the diameter was calculated to be 1.4 nm
While this is smaller than the diameter of 2 nm determined from X-ray crystallography, the difference might be attributed to the difference in experimental techniques, fluorescence anisotropy being based on the Brownian motion of the macromolecule in solution.
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Figure 2. X-Ray structure of 48-mer foldamer helix1