Amphiphilic Perylene Bisimide–Polymer Conjugates by Cysteine-Based Orthogonal Strategy: Vesicular Aggregation, DNA Binding, and Cell Imaging

Abstract

Perylene bisimides (PBIs) with high quantum yields and high chemical and photophysical stabilities are usually suffering from poor solubility in various solvents, including water, which restricts their use in biomedical and other applications. Thus, in this study, as-synthesized hydrophilic poly(1-vinylimidazole) (PVim) is introduced at both the imide positions of the hydrophobic PBI unit by using L-cysteine (Cys) bearing two orthogonally reactive groups to produce a water-and organicsoluble PBI-based polymer conjugate. To do so, first, L-cysteine is used for thiol-mediated radical polymerization of 1-vinylimidazole (Vim). In the next step, the cysteine-end-capped poly(1-vinylimidazole) (Cys−PVim) with free −NH 2 is coupled with perylene-3,4,9,10-tetracarboxylic dianhydride (PDA) by employing a onestep microwave-assisted reaction to produce PBI−(Cys−PVim) 2 conjugate. The solution optical properties of this conjugate are thoroughly investigated to ascertain the extent of aggregation among PBIs units in both aqueous and organic media. The aqueous PBI−(Cys−PVim) 2 solution emits characteristic green fluorescence of PBI under UV irradiation of 365 nm wavelength. Owing to the presence of a protonable imidazole moiety, the PBI−(Cys−PVim) 2 conjugate shows pH-dependent optical properties. The amphiphilic PBI−(Cys−PVim) 2 molecules undergo self-assembly into vesicular nanostructures in water as confirmed from cryo-and high-resolution-transmission electron microscopy. The conjugate binds with ctDNA and plasmid DNA in water to form polyplexes. The fluorescent PBI−(Cys−PVim) 2 conjugate with low cytotoxicity and high quantum yield is efficiently used for the imaging of HeLa cells. The cellular uptake of the conjugate is studied at different time intervals and at different pHs using fluorescence microscopy.

End‐/side‐chain fluorescent polymer conjugates: Stimuli‐responsiveness and biological applications

“…133 Very recently, we reported the synthesis of PBIbased poly(vinylimidazole) (PBI-Poly14, Scheme 4A) and poly(ionic liquid)s (PILs) (PBI-Poly15, Scheme 4A) conjugates. 19,134 In the first work, we have performed a cysteine (Cys)-mediated radical polymerization of vinylimidazole (Vim) to prepare cysteine-end-capped PVim, which was then coupled through its terminal NH 2 group with both the cyclic anhydride groups of PDA in a microwave reactor to produce water-/ organic-soluble fluorescent PBI-(Cys-PVim) 2 conjugate (Figure 3). 19 Whereas, in the other work, a one-pot microwaveassisted polymerization/condensation reaction technique was used to prepare PBI-PIL conjugates, as depicted in Figure 4.…”

“…19,134 In the first work, we have performed a cysteine (Cys)-mediated radical polymerization of vinylimidazole (Vim) to prepare cysteine-end-capped PVim, which was then coupled through its terminal NH 2 group with both the cyclic anhydride groups of PDA in a microwave reactor to produce water-/ organic-soluble fluorescent PBI-(Cys-PVim) 2 conjugate (Figure 3). 19 Whereas, in the other work, a one-pot microwaveassisted polymerization/condensation reaction technique was used to prepare PBI-PIL conjugates, as depicted in Figure 4. Three different as-synthesized alkylvinylimidazolium ionic liquid monomers were utilized separately for performing the thiol-mediated radical polymerization in the presence of cysteine in conjugation with AIBN as an initiator.…”

“…In this direction, we recently reported a pHsensitive PBI-(Cys-PVim) 2 (PBI-Poly14, Figure 3) conjugate, which showed two absorption peaks at 470 and 445 nm, and emission peaks at 487 and 517 nm. 19 It was observed that each of the two absorption peaks and emission peaks merged into a single broad peak in solution and their intensities were decreased, when the pH was decreased from 11 to 2. This phenomenon resulted from the aggregation among the attached PVim chains under acidic conditions.…”

“…In addition, tagging of a hydrophobic dye with a hydrophilic polymer led to the formation of an amphiphilic conjugate with high self-assembling capability, generating fluorescent nanoassemblies with a wide range of applicability in different areas, including biology. 19,24,25 A detailed survey of the literature reveals that the incorporation of fluorescent organic dyes into a polymer can be achieved by adopting various strategies. One such strategy is the utilization of the traditional "grafting from" approach, which is commonly employed in surface modification with polymers via surface-confined polymerizations.…”

“…Another well-known approach, "grafting to," has also been extensively utilized to covalently attach dye molecules with pre-formed polymers that are functionalized with reactive groups (Scheme 1). 19,30 It is important to note that the pre-formed polymers are mostly prepared by employing different controlled polymerization techniques, allowing easier functionalization and control over their molecular weights. Note that this review primarily covers the research work of the last 15 years regarding the development of fluorescent-labeled polymers using these strategies and studies of their self-assembly and stimuli-responsive properties, as well as biological applications.…”