Rhodamine B methacrylate monomer

Both TEA (1.44 g, 14.3 mmol) and methacryloyl chloride (0.97 g, 10.7 mmol) were sequentially added at 0 °C to a solution of rhodamine B alcohol (19) (5.93 g, 9.80 mmol) in DCM (100 mL),. After 1 h, the temperature was raised to ambient temperature and the mixture stirred for a further 12 h. The volatiles were then removed under reduced pressure and the residue purified by a preeluted flash chromatography (Si02) using methaiiol/triethylamine (95/5), to give rhodamine B methacrylate monomer as purple glassy solid in 72% yield. 

Synthesis of the rhodamine B methacrylate monomer as a fluorescent probe... 

The resulting rhodamine B methacrylate monomer was obtained with high purity and gave a Kx. = 566 nm with A-em. = 587 nm in 10 mM PBS buffer (pH... 

Figure 1. Absorption (dashed line) and emission (solid line) spectra of the rhodamine B methacrylate monomer in 10 mM PBS buffer (pH 7.1).

Figure 5. Tog, SEC-FL-HPLC ofBSA poly(PEGMA 75-co-rhodamine B methacrylate) bioconjugate and of the rhodamine B methacrylate monomer.

Fluorescent bioconjugates were prepared by in situ incorporation of the fluorescent probe during the synthesis of the polymer by copolymerization of fluorescent monomers with polyfethylene glycol) methyl ether methacrylate (PEGMA475) or with dimethyl aminoethyl methacrylate (DMAEMA). Both the hostasol methacrylate monomer (/<5) and novel fluorescent methacrylate monomer derived from rhodamine B (Scheme 1) were employed. 

The method proposed by Francis et al. (19) allowed the preparation of a rhodamine B-based alcohol which was subsequently transformed into the corresponding methacrylate monomer by reaction with methacryloyl chloride. This synthetic route was chosen for three main beneficial reasons (i) contrary to secondary amides of rhodamine, tertiary amides to not undergo intramolecular cyclization which results in a loss of fluorescence (ii) this fluorescent compound is highly soluble in aqueous solutions and retains its fluorescence emission under a broad range of pH and (iii) it enlarges our range of fluorescent probes. 

As expected, solutions of the bioconjugates in phosphate buffer (10 mM, pH = 7.1) exhibited a strong fluorescence in agreement with the respective excitation/emission spectra of the rhodamine B and hostasol methacrylate fluorescent monomers (Figure 4). 

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