Accurate and absolute diffusion measurements of Rhodamine 6G in 
low-concentration aqueous solutions by the PGSE-WATERGATE sequence

Majer, Günter; Zick, K.

doi:10.1063/1.4919054

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Accurate and absolute diffusion measurements of Rhodamine 6G in low-concentration aqueous solutions by the PGSE-WATERGATE sequence

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Majer, Günter
Cellular Biophysics, Max Planck Institute for Medical Research, Max Planck Society;

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Citation

Majer, G., & Zick, K. (2015). Accurate and absolute diffusion measurements of Rhodamine 6G in low-concentration aqueous solutions by the PGSE-WATERGATE sequence. The Journal of Chemical Physics, 142(16): 164202, pp. 1-5. doi:10.1063/1.4919054.

Cite as: https://hdl.handle.net/11858/00-001M-0000-0028-EA4C-C

Abstract

A pulsed field gradient spin-echo nuclear magnetic resonance (NMR) sequence with solvent suppression (PGSE-WATERGATE) was applied to accurately measure the diffusion coefficients of Rhodamine 6G (Rh6G) in low-concentration aqueous solutions. Three samples with Rh6G concentrations of CRh6G = 1, 4.5, and 25 μM were investigated. The precise determination of the diffusion coefficients in this low-concentration range was made possible by using a cryogenically cooled NMR probe and by the effective solvent suppression of the PGSE-WATERGATE sequence. The present results bridge the gap between diffusion data measured by fluorescence correlation spectroscopy in the single molecule limit and diffusivities obtained by pulsed field gradient NMR (PFG-NMR) without solvent suppression at higher concentrations. To further extend the concentration range, the diffusion coefficient of Rh6G was also measured on a sample with CRh6G = 410 μM by PFG-NMR. The overall concentration dependence of the Rh6G diffusion at 25 °C is discussed in terms of dimerization of the Rh6G molecules. The concentration-dependent monomer/dimer proportion is deduced from the diffusion data.