The nature of the silicaphilic fluorescence of PDMPO
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Buehler_The nature.pdf
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Author(s)
Parambath, Mithun
Hanley, Quentin S.
Martin-Martinez, Francisco J.
Giesa, Tristan
Buehler, Markus J.
Perry, Carole C.
Date Issued
December 2015
Journal
Physical Chemistry Chemical Physics
Publisher
Royal Society of Chemistry
Citation
Parambath, Mithun, Quentin S. Hanley, Francisco J. Martin-Martinez, Tristan Giesa, Markus J. Buehler, and Carole C. Perry. “The Nature of the Silicaphilic Fluorescence of PDMPO.” Phys. Chem. Chem. Phys. 18, no. 8 (2016): 5938–5948. © 2015 Royal Society of Chemistry
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Final published version
Abstract
PDMPO (2-(4-pyridyl)-5-((4-(2-dimethylaminoethylaminocarbamoyl)methoxy)phenyl)oxazole), has unique silica specific fluorescence and is used in biology to understand biosilicification. This ‘silicaphilic’ fluorescence is not well understood nor is the response to local environmental variables like solvent and pH. We investigated PDMPO in a range of environments: using UV-vis and fluorescence spectroscopy supported by computational data, (SPARC, molecular dynamics simulations, density functional theory calculations), dynamic light scattering and zeta potential measurements to understand the PDMPO–silica interaction. From absorption data, PDMPO exhibited a pK[subscript a] of 4.20 for PDMPOH[2+ over 2] to PDMPOH[superscript +]. Fluorescence emission measurements revealed large shifts in excited state pK[* over a] values with different behaviour when bound to silica (pK[* over a] of 10.4). PDMPO bound to silica particles is located in the Stern layer with the dye exhibiting pH dependent depolarising motion. In aqueous solution, PDMPO showed strong chromaticity with correlation between the maximum emission wavelength for PDMPOH[superscript +*] and dielectric constant (4.8–80). Additional chromatic effects were attributed to changes in solvent accessible surface area. Chromatic effects were also observed for silica bound dye which allow its use as a direct probe of bulk pH over a range far in excess of what is possible for the dye alone (3–5.2). The unique combination of chromaticity and excited state dynamics allows PDMPO to monitor pH from 3 to 13 while also reporting on surface environment opening a new frontier in the quantitative understanding of (bio)silicification.
MIT Department
Massachusetts Institute of Technology. Department of Civil and Environmental Engineering
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DOI of Published Version
https://doi.org/10.1039/c5cp05105c
