Spectroscopic characterization of the interactions between poly(2-(trimethylamino)ethyl methacrylate) chloride and the xanthene dyes, 2', 7'-difluorofluorescein and 2, 4, 5, 7-tetraiodofluorescein

Lauren J Duvall; Elijah T G Sowers; Cody J Graham; Frederick Jutton; Edward E Remsen

doi:10.1016/j.saa.2023.122710

Spectroscopic characterization of the interactions between poly(2-(trimethylamino)ethyl methacrylate) chloride and the xanthene dyes, 2', 7'-difluorofluorescein and 2, 4, 5, 7-tetraiodofluorescein

Spectrochim Acta A Mol Biomol Spectrosc. 2023 Sep 5:297:122710. doi: 10.1016/j.saa.2023.122710. Epub 2023 Apr 6.

Authors

Lauren J Duvall¹, Elijah T G Sowers¹, Cody J Graham¹, Frederick Jutton², Edward E Remsen³

Affiliations

¹ Mund-Lagowski Department of Chemistry and Biochemistry, Bradley University, 1501 West Bradley Avenue, Peoria, IL 61625, USA.
² CMC Materials, Incorporated, 870 North Commons Drive, Aurora, IL 60504, USA.
³ Mund-Lagowski Department of Chemistry and Biochemistry, Bradley University, 1501 West Bradley Avenue, Peoria, IL 61625, USA. Electronic address: eremsen@bradley.edu.

PMID: 37068441
DOI: 10.1016/j.saa.2023.122710

Abstract

Intermolecular interactions in buffered aqueous solution between the polycation, poly(2-(trimethylamino)ethyl methacrylate) chloride (pTMAEMC) and two anionic xanthene dyes, 2', 7'-difluorofluorescein (Oregon Green 488) and 2, 4, 5, 7-tetraiodofluorescein (Erythrosin B), are characterized using multiple optical spectroscopic methods. Visible absorption spectroscopy indicates the formation of ground-state pTMAEMC-dye complexes. Benesi-Hildebrand binding isotherm analysis of visible absorption spectra for pTMAEMC-dye mixtures quantifies the strength of binding interactions producing the complexes. For both Oregon Green 488 (OG) and Erythrosin B (EB) in mixtures with pTMAEMC, the concentration of the solution's sodium acetate buffer at a fixed pH alters the binding constants, K_b, suggesting that ionic strength plays a key role in determining the binding affinity of pTMAEMC for the dyes. Comparison of K_b, for the dyes indicates stronger binding of EB under all solution conditions. Steady-state fluorescence emission spectroscopy, fluorescence quenching, excited-state fluorescence lifetime measurements and fluorescence correlation spectroscopy provide complementary data for the interactions between pTMAEMC and the dyes. Mixtures of pTMAEMC with the dyes produce fluorescence enhancements and fluorescence quenching which exhibit a dependence on the buffer concentration used in the mixture. Excited-state lifetime analysis indicates that OG interacts with pTMAEMC through ground-state interactions while EB exhibits both ground-state and excited-state interactions with pTMAEMC. The spectroscopic measurements suggest that a polyelectrolyte effect for pTMAEMC due to ionic strength variation produced by the buffer concentration affects the dye binding profile of the polycation. This conclusion is supported by fluorescence correlation spectroscopy (FCS) analyses of the hydrodynamic diameter changes in pTMAEMC-OG binding in low buffer concentration (low ionic strength) solution. FCS analyses of pTMAEMC-OG mixtures also reveal diversity in the complexes formed in low ionic strength solution suggesting that other xanthene dyes will exhibit similar binding behaviors in mixtures with pTMAEMC as a function of solution ionic strength.

Keywords: Fluorescence correlation; Fluorescence emission; Fluorescence lifetime; Polyelectrolyte molecular weight; Polyelectrolyte-dye binding; Visible absorption.