Controlled RAFT Polymerization and Zinc Binding Performance of Catechol-Inspired Homopolymers

Incorporation of catechols into polymers has long been of interest due to their ability to chelate heavy metals and their use in the design of adhesives, metal–polymer nanocomposites, antifouling coatings, and so on. This paper reports, for the first time, the reversible addition–fragmentation chain transfer (RAFT) polymerization of a protected catechol-inspired monomer, 3,4-dimethoxystyrene (DMS), using commercially available trithiocarbonate, 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT), as a chain transfer agent. Our identified RAFT system produces well-defined polymers across a range of molecular weights (5–50 kg/mol) with low molar mass dispersities (<i><i><i>Đ</i></i></i>, <i>M</i>_w/<i>M</i>_n < 1.3). Subsequent facile demethylation of poly­(3,4-dimethoxystyrene) (PDMS) yields poly­(3,4-dihydroxystyrene) (PDHS), a catechol-bearing polymer, in quantitative yields. Semiquantitative zinc binding capacity analysis of both polymers using SEM/EDXA has demonstrated that both PDMS and PDHS have considerable surface binding (65% and 87%, respectively), although the films deposited from PDMS are of a better quality and processability due to solubility and lower processing temperatures

Ceullular uptake of dual core/shell-labeled microspheres, assessed by FACS.

<p>Cellular uptake of shell-conjugated, DY-630 core-labelled microspheres by HeLa cells, as measured by flow cytometry: a) shell conjugated to fluoresceinamine 9a; b) shell conjugated to GFP 10a.</p

Confocal microscopy of microspheres.

<p>Confocal microscope images of DY-630 labelled microspheres conjugated to GFP <b>10a</b>: a) excited at 633 nm; b) excited at 488 nm; c) composite image showing co-localization of DY630 and GFP fluorescence. Scale bar = 4 µm.</p

Cellular uptake of core-labeled microspheres, assessed by FACS.

<p>Percentage cellular uptake of DY-630 labelled microspheres <b>8</b> by HeLa cells, as measured by flow cytometry: a) <b>8a</b> (1 µm diameter); b) <b>8b</b> (500 nm diameter).</p

Flow cytometry analysis of microspheres.

<p>Flow cytometry analysis of a) unlabelled microspheres <b>7a</b> (negative control); b) DY-630 labelled microspheres <b>8a</b>; c) DY-630 labelled microspheres <b>8b</b></p

Fluorescent microscopy of beadfected HeLa cells.

<p>Fluorescence microscope images obtained from a Z stack set of images (approximately 0.5 µm z-steps, taken from the top to the bottom focal plane of the cells, 10–12 slices in total) of HeLa cells beadfected with a sample of DY-630-labelled microspheres conjugated via their shells to GFP 10a: a) under irradiation at 633 nm to show DY-630 fluorescence; b) under irradiation at 433 nm to show GFP fluorescence. In each case the cells have been fixed and their nuclei stained with 4',6-diamidino-2-phenylindole (DAPI). Scale bar = 10 µm.</p

Composition and sizing data of microspheres <b>4</b> and <b>6a</b>–<b>h.</b>

a<p>ratio determined on the basis of mass</p><p>Mean diameter and standard deviation of thiouronium-functionalized microspheres <b>4</b> and <b>4a</b> and core-shell microspheres <b>6a</b>–<b>h</b>, as measured dispersed in water using a laser diffractometer.</p

Confocal microscopy of a single microsphere.

<p>An overlay confocal microscope image of a DY-630 labelled microsphere conjugated to GFP <b>10a</b>: excited at 633 nm (core, red) and at 488 nm (shell, green). Scale bar = 2 µm.</p

Fluorescent labeling of core-shell microspheres.

<p>Reaction conditions: i) DMF, MeOH, RT, 16 h; ii) DMF, RT, 2 h; iii) EDAC, MES pH 5.5, DMF, RT, 18 h; iv)EDAC, MES pH 6.5, NaOH, RT, 2.5 h.</p

Synthesis of core-shell microspheres.

<p>Reaction conditions: i) PVP 58k, azobis<i>iso</i>butyronitrile (AIBN), hexadecane, 70°C, 16 h ii) AIBN, hexadecane, SDS(aq), RT 70°C, 5 h.</p