Skip to main content Accessibility help
×
Home

Information:

  • Access

Actions:

      • Send article to Kindle

        To send this article to your Kindle, first ensure no-reply@cambridge.org is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about sending to your Kindle. Find out more about sending to your Kindle.

        Note you can select to send to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.

        Find out more about the Kindle Personal Document Service.

        Amphiphilic fluorescent copolymers via one-pot synthesis of RAFT polymerization and multicomponent Biginelli reaction and their cells imaging applications
        Available formats
        ×

        Send article to Dropbox

        To send this article to your Dropbox account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your <service> account. Find out more about sending content to Dropbox.

        Amphiphilic fluorescent copolymers via one-pot synthesis of RAFT polymerization and multicomponent Biginelli reaction and their cells imaging applications
        Available formats
        ×

        Send article to Google Drive

        To send this article to your Google Drive account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your <service> account. Find out more about sending content to Google Drive.

        Amphiphilic fluorescent copolymers via one-pot synthesis of RAFT polymerization and multicomponent Biginelli reaction and their cells imaging applications
        Available formats
        ×
Export citation

Abstract

In this contribution, we devoted ourselves to fabricating aggregation-induced emission (AIE) activity copolymers via one-pot combination of RAFT polymerization and Biginelli reaction for the first time. When the feeding ratio of TPB was 33.5%, the molar fraction of TPB was, respectively, about 14.2 and 22.5% in PEG-PTE1 copolymers by two-step strategy and PEG-PTE2 copolymers by one-pot strategy with the similar structure. The Mn of PEG-PTE1 increased to 59,300 from 52,800 of PEG-AE presoma with narrow PDI, which was more than Mn of PEG-PTE2 with 52,300. As compared with PEG-PTE2, when the feeding ratio of TPB was 48.6%, the molar fraction of TPB increased to 32.6% in PEG-PTE3. In aqueous solution, the as-obtained PEG-PTE2 copolymers can self-assemble into fluorescent organic nanoparticles (FONs) with 100–180 nm spherical morphology, the maximal emission peak of which presented at 460 nm with the obvious AIE phenomenon. Moreover, due to the low toxicity and excellent cell dyeing behavior, the as-prepared PEG-PTE2 copolymers displayed great potential for biomedical applications.

Introduction

Multicomponent reactions (MCRs) include a combination of three or more constituents in a single vessel to fabricate an anticipant product with properties of all the reactant components, which avoided the intricacy separation and purification of complex to attain the purpose of high effect and low cost [1, 2, 3, 4]. Moreover, MCRs have been a fascination as versatile tools for chemists to construct heterocyclic compounds, which would pave a straightforward way to fabricate novel libraries of polymers and might broad study of MCRs in interdisciplinary fields [5]. Currently, owing to the atoms economy, excellent modular, efficient, and environmentally friendly properties [6, 7, 8], a variety of MCRs have been reported such as Mannich reaction, Passerini reaction, Hantzsch reaction, MALI reaction, Biginelli reaction, and Ugi reaction [9]. As end-products of Biginelli reaction, the 3,4-dihydropyrimidin-2(1H)-one (DHPM) derivatives were considered as a well-known class of cardiovascular drugs serving as calcium channel modulators and confirmed to be the central structure of many medicines such as the barrier reagent of Ca2+ ion avenue [10, 11]. Hence, they are very important in the pharmacological applications such as calcium channel modulators, mitotic kinesin inhibitors, antimalarial, antitubercular, and A2B adenosine receptor antagonists [12, 13, 14]. Therefore, the number of publications and patents about the synthesis of DHPMs derivatives reaction is increasing every year [15]. Many researches indicated that some heterocycles from Biginelli reaction could restrain the combination of HIV viruses and CD4 cells, which would possibly be a novel drug for curing AIDS [16]. Recently, due to the high efficiency and yield, tolerance to the extensive reactions conditions, and varied functional groups, Biginelli reaction has been a very powerful tool in polymer chemistry. A thiourea-contained polycondensate with highly reactive activity was easily synthesized via the Biginelli polycondensation, which might be a versatile platform to fabricate novel functional polymers [17]. Inspiration from nature’s two-stage strategy for the efficient synthesis of numerous proteins using limited amino acids, a two-stage fabrication method was successfully developed via the combination of ultra-fast RAFT polymerization and Biginelli reaction, which opened a new way for the effective preparation and characterization of new series of polymers with abundant diversity and functions [18].

Living polymerization has been a favorite tool to fabricate functional copolymers with well-defined and predesigned structures [19]. Among the normal living polymerization methods of anionic polymerization, cation polymerization, reversible addition-fragmentation chain transfer (RAFT) polymerization, and atom transfer radical polymerization (ATRP), RAFT is versatile technique to fabricate functional polymers due to its excellent tolerance to many functional monomers and solvents [20]. Amphiphilic PPEGMA-b-PMMA block copolymer nanoparticles were successfully prepared by RAFT polymerization-induced self-assembly (PISA), the particle diameter of which gradually increased with the target DP of the PMMA increasing [21]. Otherwise, linking multiblock copolymers to solid substrate’s surfaces was very important for both fundamental studies and applications. One combination of RAFT polymerization and click chemistry was employed to synthesize highly pure multiblock copolymers tethered to silica particles, and the one-pot strategy seems more attracting than the incremental route [20]. By combination of tandem RAFT polymerization, azide–alkyne cycloaddition reaction, and a subsequent de-grafting reaction, a series of silica-polymer hybrids with highly pure block copolymers was described in detail, which played an important role in material properties [22]. Moreover, RAFT was also actively applied for the construction of fluorescence-active functional polymers [23]. A self-healable hydrogel with fluorescence activity was prepared by ring opening polymerization (ROP) and RAFT via incorporation of ionic block copolymers (BCPs) with fluorescence response, which may be a potential for smart materials in the applications of tissue engineering and sensing fields in the near future [24]. By photoinitiating RAFT polymerization, TPE-poly(St-PEGMA) copolymers with aggregation-induced emission (AIE)-activity were successfully fabricated, which showed great potential for biomedical applications due to their optical and biocompatibility [25]. As an attracting candidate for monitoring dynamic processes and bioimaging therapies, dual-functional copolymeric nanoparticles (NPs) with near-infrared (NIR) fluorescence imaging and prodrug were prepared in situ RAFT-mediated aqueous dispersion polymerization [26].

The one-pot MCRs synthesis depended on the most economical step to obtain the products. The idea of constructing one-pot polymerization system was attracting wide attention in the area of polymer chemistry. The substrates of Biginelli reaction have cheap price, low toxicity, and smell with high safety, the DHPMs products of which have extensive biology and pharmacology activity. In this contribution, novel AIE-based copolymers were successfully prepared via one-pot smart combination of RAFT polymerization and in situ Biginelli reaction for the first time. First, the AEMA functional monomers participated in RAFT polymerization with a hydrophilic PEGMA monomer and resulted in functional copolymers, which would in situ occurred Biginelli reaction with other two components of TPB dye and urea, and produced a new fluorescent copolymer with DHPM ring. The as-prepared PEG-PTE would tend to self-assemble into fluorescent organic nanoparticles (FONs) in aqueous solution and exhibited promising biology imaging applications due to high water dispersibility, good fluorescence, and excellent biocompatibility. Furthermore, in order to fully evaluate the combination of RAFT polymerization and Biginelli reaction, the other effects of the reactants feeding ratio and two-step method on the copolymers structure were also investigated in detail.

Results and discussion

In this paper, the fabrication of amphiphilic fluorescent PEG-PTE copolymers via “one-pot” combination of RAFT polymerization and multicomponent Biginelli reaction is demonstrated in Scheme 1. Here, taking TPB dye and urea as the other two model components of Biginelli reaction, AEMA was used as the vinyl monomer for the 1,3-dione functional group source. The multicomponent Biginelli reaction would bring a pyrimidin ring, which was linked to AEMA monomer, producing another new monomer PTE-MA. The as-prepared hydrophobic PTE-MA monomer would participate in RAFT polymerization with hydrophilic PEGMA monomer to obtain amphiphilic fluorescent copolymers PEG-PTE with transformed DHPM rings. In aqueous solution, the amphiphilic PEG-PTE copolymers would tend to self-assemble into NPs and internalized by cells.

Scheme 1: One-pot synthesis process of PEG-PTE copolymers based on RAFT polymerization and Biginelli reaction and their cell imaging application.

Figure 1 described the gel-permeation chromatograph (GPC) with PDIs and 1H NMR curves of the PEG-AE and PEG-PTE copolymers with the various molar fractions of AEMA and PEGMA. The GPC analysis showed that the RAFT procedure was well controlled, and PDIs of the copolymers were about 1.30, which indicated that the process had the characteristic of living polymerization. As compared with PEG-AE copolymers, the weight average molecular (Mn) of PEG-PTE1 copolymers increased to 59,300 from 52,800 of PEG-AE copolymers; moreover, the 1H NMR spectrum of PEG-PTE1 obviously presented the characteristic CH proton peak of the pyrimidin-2-one ring at 5.30 ppm with the aromatic hydrogen peaks at the range of 7.00–7.06 ppm [27], implying that the TPB dye was successfully incorporated into the PEG-AE intermediate chains via Biginelli reaction. The peaks at 4.05 ppm and 4.26 ppm were, respectively, assigned to the ester groups of poly-(PEG) and AEMA. Referring to the integral ratio of the peaks at 5.30, 4.05, and 4.26 ppm, the molar fraction of TPB and AEMA in PEG-PTE1 copolymers was about 14.2 and 19.0%. Instead of the two-step method by one-pot method, the Mn of PEG-PTE2 decreased to 52,300 from 59,300 of PEG-PTE1, implying that the Biginelli reaction possibly affected the chain propagation rate to a certain degree; however, the peak at 5.30 ppm in PEG-PTE2 copolymers was more obvious and the peak at 4.26 ppm in PEG-PTE2 copolymers obviously decreased, indicating that the Biginelli reaction of one-pot method was more complete than that of two-step method. On the basis of the above computational method of PEG-PTE1, the molar fraction of TPB dye and AEMA in the PEG-PTE2 was, respectively, about 22.5 and 10.5%. In order to further investigate the influence of various reaction conditions on the copolymers structure, when the feed ratio of TPB increased to 48.6% of PEG-PTE3 copolymers from 33.5% of PEG-PTE2 copolymers, the corresponding Mn of PEG-PTE3 decreased to 32,800 from 52,300 of PEG-PTE2 and the molar fraction of TPB dye increased to about 32.6% in PEG-PTE3 copolymers.

Figure 1: (a) The GPC traces (DMF) (PEG-AE, Mn = 52,800, PDI = 1.23; PEG-PTE1, Mn = 59,300, PDI = 1.24; PEG-PTE2, Mn = 52,300, PDI = 1.35; PEG-PTE3, Mn = 32,800, PDI = 1.24) and (b) 1H NMR spectrum (CDCl3) of the obtained PEG-AE and fluorescent copolymers PEG-PTE.

To investigate the amphiphilic property and effect of self-assembly of PEG-PTE copolymers in aqueous solution, Fig. 2(a) gave typical TEM images of microphase separated morphologies of PEG-PTE2 FONs. From the TEM images, the dark regions represented PEG-PTE2 subphase [28] and the size was 100–180 nm with the spherical morphology, indicating that the effective self-assembly owing to the successful incorporation of PEGMA monomers and TPB dye into the PEG-PTE2 copolymers via RAFT and Biginelli reaction. Moreover, successful fabrication of PEG-PTE2 copolymers is further confirmed by FT-IR spectra as shown in Fig. 2(b). For the spectrum of PEG-PTE2 copolymers, the characteristic peak at 1100 cm−1 was assigned to C–O stretching vibration in PEGMA, and the stretching vibration peaks C=O in PEGMA and AEMA obviously presented at 1710 cm−1 with C=C peaks of TPB at 1640 cm−1. Another peak at 2880 cm−1 should attribute to the stretching vibration of characteristic –CH2- and –CH3 in PEGMA and AEMA. From the above analysis, the anticipant copolymer structure was successfully prepared by the one-pot combination of RAFT polymerization and Biginelli reaction.

Figure 2: (a) TEM image of PEG-PTE2 FONs in water solution, scale bar = 1000 nm; (b) FT-IR spectra of TPB dye, PEG-AE, and PEG- PTE2 copolymers.

In order to continually evaluate dispersibility and optical characteristics of PEG-PTE2 in water solution, their UV and fluorescence curves were described in Figs. 3(a) and 3(b). The UV curve presented obvious absorption in the ultraviolet region with two major absorption peaks at 240 and 290 nm, which should assign to the π → π* and n → π* transition of the TPB polycyclic aromatic and pyrimidin rings [29, 30, 31]. Moreover, PEG-PTE2 copolymers had very little absorption when the incident wavelength was more than 400 nm, implying that absorbance of PEG-PTE2 copolymers was not nearly affected by the Mie effect or light scattering of the NP suspensions due to their excellent dispersibility in the aqueous solution [32]. The PEG-PTE2 copolymers are expected to present excellent fluorescence owing to the incorporation of TPB dye. As shown in Fig. 3(b), the fluorescence spectrum of PEG-PTE2 FONs in aqueous solution had the evident fluorescence with the maximum emission peak at 480 nm; however, in the THF solution, the fluorescence was not almost be observed, indicating the clear AIE feature. When PEG-PTE2 molecules in the ground state S0 were excited by external ultraviolet light λ1, they would absorb the corresponding radiation energy λ1 and were excited to higher excitation states S1 and S2. The PEG-PTE2 molecules in the excitation states S1 and S2 were astable, and soon afterward, they would return to S0. When PEG-PTE2 were in THF solution, the relaxation energy from S1 and S2 to S0 would be consumed by molecules rotation or thermal energy owing to the active intramolecular rotation. While in water solution with the FONs aggregation forms, this rotation was restricted due to the intramolecular interactions such as C–H⋯π and C–H⋯H–C and the nonradiative path was blocked; thus, the radiation decay is activated with emitting radiation λ2 [33, 34].

Figure 3: (a) UV-Vis curve of PEG-PTE2 copolymers in water solution; (b) fluorescence emission spectra of PEG-PTE2 FONs, inset is the fluorescent image of PEG-PTE2 FONs at 365 nm UV light [left bottle (in water), right bottle (in THF)].

It was basic and necessary for FONs to have great biocompatibility for their promising biomedical application [35, 36, 37, 38]. As shown in Figs. 4(a)–4(c), optical microscopy images indicated that HepG2 cells could keep their normal morphology after they were incubated with PEG-PTE2 FONs. Even when the concentration of PEG-PTE2 FONs increased to 80 mg/mL, the morphology did not obviously change. In order to evaluate the biocompatibility of obtained PEG-PTE2 FONs, their cytocompatibility for HepG2 cells was investigated by the CCK-8 assay as shown in Fig. 5 through the 450 nm absorbance value of formazan dye taking 620 nm as the reference value [39, 40]. After incubating with 10–120 μg/mL PEG-PTE2 FONs for 8 and 24 h, no obvious decrease of cells viability could be observed; moreover, it was still more than 95% even when the concentration of PEG-PTE2 FONs increased to 120 μg/mL. From the above analysis, the as-prepared PEG-PTE2 FONs exhibit great cytocompatibility with HepG2 cells.

Figure 4: Biocompatibility evaluations of PEG-PTE2 FONs. (a–c) Optical microscopy images of HepG2 cells incubated with different concentrations of PEG-PTE2 FONs for 24 h, (a) control cells, (b) 20 μg/mL, and (c) 80 μg/mL.

Figure 5: Cell viability of PEG-PTE2 FONs with HepG2 cells.

In consideration of the uniform spherical morphology, good fluorescence, great biocompatibility, and high dispersibility of PEG-PTE2 FONs, their effect on biological imaging and cell uptake behavior was further investigated by CLSM referred to the reported literature [41, 42]. As shown in Figs. 6(a)–6(c), the black regions should be the location of cell nucleus, which were surrounded by the areas with strong fluorescence. These results indicated that PEG-PTE2 FONs could enter into cells by the endocytosis of the HepG2 cells and mainly distributed in the cytoplasma owing to the size difference of PEG-PTE2 FONs and cell nucleus [43]. DHPMs derivatives from Biginelli reaction have the excellent pharmacology activity and biological reaction activity, which was the important intermediates of hypotensor, anticarcinogen, antibacterial drug, antagonist of calcium ion, and natural base [44, 45]. Moreover, due to the high efficiency, atom economy, and reliability under broad conditions [18], it was very convenient and effective for Biginelli reaction to incorporate some multicomponents such as imaging agents, drugs, prodrug monomers, and targeting agents into functional polymers with a combination of RAFT polymerization. Hence, one-pot combination of RAFT polymerization and Biginelli reaction provided an attractive avenue for multifunctional imaging and theranostic platforms.

Figure 6: CLSM images of HepG2 cells incubated with 40 μg/mL of PEG-PTE2 FONs: (a) bright field, (b) excited with a 405 nm laser, and (c) merged image of (a) and (b). Scale bar = 20 μm.

Conclusions

In summary, we have developed a novel strategy for fabrication of AIE-active PEG-PTE FONs via one-pot smart combination of RAFT polymerization and MCRs Biginelli reaction for the first time. The product structure from one-pot method was similar with that from two-step method but has obviously higher incorporation of TPB dye in PEG-PTE copolymers. Owing to high water dispersibility, good fluorescence, excellent cell dyeing behavior, remarkable photostability, and excellent biocompatibility, the as-prepared PEG-PTE copolymers were promising for biological imaging application. As compared with the strategy of AIE-active FONs on the basis of polymerizable or functional AIE monomer, this novel contribution has many advantages. First, it avoided the complex purification process of intermediates for the fabrication of AIE-active copolymers. Second, the chemical structure together with the physicochemical properties of the fluorescence copolymers can be easily adjusted via the RAFT polymerization and Biginelli reaction. More importantly, this work provides novel ideas to fabricate some clean and multifunctional FONs for cell imaging application through incorporating some various functional components such as drugs, imaging agents, and targeting agents by Biginelli reaction.

Experimental procedure

Materials and characterization

2-(Acetoacetoxy)ethyl methacrylate (AEMA, Aladdin, 95%), urea (Aladdin, AR), anhydrous magnesium chloride (Aladdin, 99%), and poly(ethylene glycol) monomethacrylate (PEGMA, Mn = 475, J & K Chemical, AR) were all used as purchased in China. Azodiisobutyronitrile (AIBN, Aladdin, 99%) was recrystallized twice from acetone before use. 4-(1,2,2-triphenylvinyl)benzaldehyde (TPB) dye and the chain transfer agent (CTA) of 4-cyano-4-(ethylthiocarbonothioylthio)pentanoic acid were fabricated according to the previous literature methods [46, 47, 48, 49].

The molecular weights and molecular weight distributions of PEG-AE and PEG-PTE copolymers were acquired from a Shimadzu LC-20AD (Japan) GPC system equipped with a Shimadzu RID-10A a refractive index (RI) detector, which was carried out at 35 °C taking N,N-dimethyl formamide (DMF) as the eluent with 1.0 mL/min flow rate and was calibrated by standard polystyrene. 1H NMR spectra of PEG-AE and PEG-PTE copolymers were recorded on a JEOL JNM-ECA 400 (400 MHz) spectrometer by using CDCl3 as the solvent and tetramethylsilane as an internal standard. Transmission electron microscopy (TEM) was acquired from a high-resolution electron microscope JEOL JEM-2100F (Japan), and the samples for TEM observation were fabricated by placing and then drying a drop of PEG-PTE2 suspension on a carbon-coated copper grid. UV-Vis spectrum of PEG-PTE2 in aqueous solution was recorded on a Shimadzu UV-2450 UV-Vis spectrophotometer. Fluorescence spectra of PEG-PTE2 in water and THF solution were recorded on a PE LS-55 spectrophotometer. Fourier transform infrared (FT-IR) measurements of TPB dye, PEG-AE, and EG-PTE2 copolymers were carried out on a PerkinElmer (Waltham, MA) Spectrum 100-IR spectrophotometer by a KBr method and a reflection mode.

Preparation of poly(poly(ethylene glycol) monomethacrylate-2-(acetoacetoxy)ethyl methacrylate) (PEG-AE)

AIBN (4.6 mg, 0.028 mmol) and CTA (7.75 mg, 0.029 mmol) were first added into a Schlenk tube with a magnetic stir bar. After the Schlenk tube was deoxidized through the vacuum-nitrogen cycle method for five times, AEMA (0.288 g, 1.35 mmol) and PEGMA (1.272 g, 2.68 mmol) in 5 mL toluene solvent were injected into under a N2 atmosphere. The above mixture was kept at 70 °C of oil bath for 36 h, and subsequently, the mixture was purified three times by precipitation from THF to petroleum ether after the solvent was removed by rotary evaporator under low pressure. Finally, the product was dried under vacuum at 45 °C, which was named as PEG-AE, yield: 1.15 g.

Preparation of poly(poly(ethylene glycol) monomethacrylate-(3,4-dihydropyrimidin-2(1H)-one-tetraphenylethylene)) (PEG-PTE1)

TPB (93.3 mg, 0.259 mmol), urea (21.6 mg, 0.36 mmol), magnesium chloride (2.3 mg, 0.024 mmol), and PEG-AE (300 mg) were first added into a Schlenk tube with a magnetic stir bar, which was then deoxidized five times through the vacuum-nitrogen cycle method. Subsequently, 2.0 mL of acetic acid was injected into the Schlenk tube under a N2 atmosphere, which was kept in an oil bath at 70 °C for 36 h. The reaction mixture was successively dialyzed in water, methanol, and acetone for 2 days. The copolymers was purified four times by precipitation from THF to petroleum ether after the solvent was removed by rotary evaporator under low pressure. Finally, the product was dried under vacuum at 50 °C, which was named as PEG-PTE1, yield: 0.32 g.

One-pot preparation of poly(poly(ethylene glycol) monomethacrylate-(3,4-dihydropyrimidin-2(1H)-tetraphenylethylene)) (PEG-PTE2 and PEG-PTE3)

TPB (93.2 mg, 0.259 mmol), urea (22.3 mg, 0.37 mmol), magnesium chloride (2.4 mg, 0.022 mmol), AIBN (1.0 mg, 0.0060 mmol), and CTA (1.54 mg, 5.8 × 10−3 mmol) were first added into a Schlenk tube with a magnetic stir bar, which was then deoxidized for five times through the vacuum-nitrogen cycle method. Then, a 2.0 mL mixed solvent of toluene and acetic acid (v/v = 3:1) with AEMA (55.4 mg, 0.259 mmol) and PEGMA (244 mg, 0.513 mmol) were injected into the Schlenk tube under a N2 atmosphere, which was kept in an oil bath at 70 °C for 36 h. Subsequently, the reaction mixture was successively dialyzed in water, methanol, and acetone for 2 days. The copolymers were purified four times by precipitation from THF to petroleum ether after the solvent was removed by rotary evaporator under low pressure. Finally, the product was dried under vacuum at 50 °C, which was named as PEG-PTE2, yield: 0.32 g. Reading the above procedure for reference, when the feed molar ratio of TPB increased to 48.6%, the corresponding copolymers were named as PEG-PTE3, yield: 0.29 g. Finally, the samples of 10 mg PEG-PTE1, PEG-PTE2, and PEG-PTE3 were, respectively, added to 10 mL H2O, then shaken until it had been dissolved completely, which was used to investigate its self-assembly in H2O solvent.

Acknowledgments

This research was supported by the Natural Science Foundation of Guangdong Province (2018A030313784), the National Science Foundation of China (Nos. 51673107 and 21574073), and the Science and Technology Project of Zhongshan City of China (2018B1112).

References

1.Nagarajaiah, H., Mukhopadhyay, A., and Moorthy, J.N.: Biginelli reaction: An overview. Tetrahedron Lett. 57, 5135 (2016).
2.Rotstein, B.H., Zaretsky, S., Rai, V., and Yudin, A.K.: Small heterocycles in multicomponent reactions. Chem. Rev. 114, 8323 (2014).
3.Tao, L., Zhao, Y., Yang, B., Wei, Y., and Wu, H.B.: Multicomponent click chemistry in polymer synthesis-new opportunity for polymer chemistry. Acta Polym. Sin., 1482 (2016).
4.Wu, H.B., Yang, L., and Tao, L.: Polymer synthesis by mimicking nature’s strategy: The combination of ultra-fast RAFT and the Biginelli reaction. Polym. Chem. 8, 5679 (2017).
5.Xue, H.D., Zhao, Y., Wu, H.B., Wang, Z.L., Yang, B., Wei, Y., Wang, Z.M., and Tao, L.: Multicomponent combinatorial polymerization via the Biginelli reaction. J. Am. Chem. Soc. 138, 8690 (2016).
6.Dong, J.D., Liu, M.Y., Jiang, R.M., Huang, H.Y., Wan, Q., Wen, Y.Q., Tian, J.W., Dai, Y.F., Zhang, X.Y., and Wei, Y.: Synthesis and biological imaging of cross-linked fluorescent polymeric nanoparticles with aggregation-induced emission characteristics based on the combination of RAFT polymerization and the Biginelli reaction. J. Colloid Interface Sci. 528, 192 (2018).
7.Jiang, R., Liu, H., Liu, M., Tian, J., Huang, Q., Huang, H., Wen, Y., Cao, Q.Y., Zhang, X., and Wei, Y.: A facile one-pot Mannich reaction for the construction of fluorescent polymeric nanoparticles with aggregation-induced emission feature and their biological imaging. Mater. Sci. Eng., C 81, 416 (2017).
8.Zhu, C., Yang, B., Zhao, Y., Fu, C., Tao, L., and Wei, Y.: A new insight into the Biginelli reaction: The dawn of multicomponent click chemistry? Polym. Chem. 4, 5395 (2013).
9.Mao, T.F., Liu, G.Q., Wu, H.B., Wei, Y., Gou, Y.Z., Wang, J., and Tao, L.: High throughput preparation of UV-protective polymers from essential oil extracts via the Biginelli reaction. J. Am. Chem. Soc. 140, 6865 (2018).
10.Wang, S.Q., Fu, C.K., Wei, Y., and Tao, L.: Exploration of multicomponent polymerization system. Prog. Chem. 26, 1099 (2014).
11.Kappe, C.O.: Biologically active dihydropyrimidones of the Biginelli-type-a literature survey. Eur. J. Med. Chem. 35, 1043 (2000).
12.Crespo, A., Maatougui, A.E., Biagini, P., Azuaje, J., Coelho, A., Brea, J., Loza, M.I., Cadavid, M.I., Garcia-Mera, X., Gutierrez-de-Teran, H., and Sotelo, E.: Discovery of 3,4-dihydropyrimidin-2(1H)-ones as a novel class of potent and selective A2B adenosine receptor antagonists. ACS Med. Chem. Lett. 4, 1031 (2013).
13.Kaur, H., Machado, M., Kock, C., Smith, P., Chibale, K., Prudencio, M., and Singh, K.: Primaquine-pyrimidine hybrids: Synthesis and dual-stage antiplasmodial activity. Eur. J. Med. Chem. 101, 266 (2015).
14.Joshi, R.R., Barchha, A., Khedkar, V.M., Pissurlenkar, R.R.S., Sarkar, S., Sarkar, D., Joshi, R.R., Joshi, R.A., Shah, A.K., and Coutinho, E.C.: Targeting dormant tuberculosis bacilli: Results for molecules with a novel pyrimidone scaffold. Chem. Biol. Drug Des. 85, 201 (2015).
15.Simurova, N. and Maiboroda, O.: Biginelli reaction-an effective method for the synthesis of dihydropyrimidine derivatives. Chem. Heterocycl. Compd. 53, 413 (2017).
16.Akhaja, T.N. and Raval, J.P.: 1,3-Dihydro-2H-indol-2-ones derivatives: Design, synthesis, in vitro antibacterial, antifungal and antitubercular study. Eur. J. Med. Chem. 46, 5573 (2011).
17.Zhao, Y., Wu, H.B., Zhang, Y.Y., Wang, X., Yang, B., Zhang, Q.D., Ren, X., Fu, C.K., Wei, Y., Wang, Z.M., Wang, Y.R., and Tao, L.: Postpolymerization modification of poly(dihydropyrimidin-2(1H)-thione)s via the thiourea–haloalkane reaction to prepare functional polymers. ACS Macro Lett. 4, 843 (2015).
18.Ren, X., Yang, B., Zhao, Y., Zhang, X.Y., Wang, X., Wei, Y., and Tao, L.: One-pot polymer conjugation on carbon nanotubes through simultaneous π–π stacking and the Biginelli reaction. Polymer 64, 210 (2015).
19.He, W.W., Jiang, H.J., Zhang, L.F., Cheng, Z.P., and Zhu, X.L.: Atom transfer radical polymerization of hydrophilic monomers and its applications. Polym. Chem. 4, 2919 (2013).
20.Huang, Y.K., Hou, T.T., and Cao, X.Q.: Synthesis of silica-polymer hybrids by combination of RAFT polymerization and azide-alkyne cycloaddition ‘click’ reactions. Polym. Chem. 1, 1615 (2010).
21.Peng, J.Y., Tian, C., Zhang, L.F., Cheng, Z.P., and Zhu, X.L.: The in situ formation of nanoparticles via RAFT polymerization-induced self-assembly in a continuous tubular reactor. Polym. Chem. 8, 1495 (2017).
22.Zhao, G.D., Zhang, P.P., Zhang, C.B., and Zhao, Y.L.: Facile synthesis of highly pure block copolymers by combination of RAFT polymerization, click reaction and de-grafting process. Polym. Chem. 3, 1803 (2012).
23.Jiang, R.M., Liu, M.Y., Huang, Q., Huang, H.Y., Wan, Q., Wen, Y.Q., Tian, J.W., Cao, Q.Y., Zhang, X.Y., and Wei, Y.: Fabrication of multifunctional fluorescent organic nanoparticles with AIE feature through photo-initiated RAFT polymerization. Polym. Chem. 8, 7390 (2017).
24.Banerjee, S.L., Hoskins, R., Swift, T., Rimmer, S., and Singha, N.K.: A self-healable fluorescence active hydrogel based on ionic block copolymers prepared via ring opening polymerization and xanthate mediated RAFT polymerization. Polym. Chem. 9, 1190 (2018).
25.Zeng, G.J., Liu, M.Y., Jiang, R.M., Huang, Q., Huang, L., Wan, Q., Dai, Y.F., Wen, Y.Q., Zhang, X.Y., and Wei, Y.: Self-catalyzed photo-initiated RAFT polymerization for fabrication of fluorescent polymeric nanoparticles with aggregation-induced emission feature. Mater. Sci. Eng., C 83, 154 (2018).
26.Tian, C., Niu, J.Y., Wei, X.R., Xu, Y.J., Zhang, L.F., Cheng, Z.P., and Zhu, X.L.: Construction of dual-functional polymer nanomaterials with near-infrared fluorescence imaging and polymer prodrug by RAFT-mediated aqueous dispersion polymerization. Nanoscale 10, 10277 (2018).
27.Wang, Z.L., Yu, Y., Li, Y.S., Yang, L., Zhao, Y., Liu, G.Q., Wei, Y., Wang, X., and Tao, L.: Post-polymerization modification via the Biginelli reaction to prepare water-soluble polymer adhesives. Polym. Chem. 8, 5490 (2017).
28.Wei, R.B., He, Y.N., and Wang, X.G.: Diblock copolymers composed of a liquid crystalline azo block and a poly(dimethylsiloxane) block: Synthesis, morphology and photoresponsive properties. RSC Adv. 4, 58386 (2014).
29.He, Y.N., He, W., Liu, D., Gu, T.H., Wei, R.B., and Wang, X.G.: Synthesis of block copolymers via the combination of RAFT and a macromolecular azo coupling reaction. Polym. Chem. 4, 402 (2013).
30.Wei, R.B., Wang, X.G., and He, Y.N.: Synthesis of side-on liquid crystalline diblock copolymers through macromolecular azo coupling reaction. Eur. Polym. J. 69, 584 (2015).
31.Wei, R.B., Wang, X.G., and He, Y.N.: Synthesis, self-assembly and photo-responsive behavior of AB2 shaped amphiphilic azo block copolymer. Chin. Chem. Lett. 26, 857 (2015).
32.Zhang, X., Chi, Z., Zhang, J., Li, H., Xu, B., Li, X., Liu, S., Zhang, Y., and Xu, J.: Piezofluorochromic properties and mechanism of an aggregation-induced emission enhancement compound containing N-hexyl-phenothiazine and anthracene moieties. J. Phys. Chem. B 115, 7606 (2011).
33.Hong, Y., Lam, J., and Tang, B.: Aggregation-induced emission: Phenomenon, mechanism and applications. Chem. Commun., 4332 (2009).
34.Tong, H., Dong, Y., Hong, Y., Häussler, M., Lam, J., Sung, H., Yu, X., Sun, J., Williams, I., Kwok, H., and Tang, B.: Aggregation-induced emission: Effects of molecular structure, solid-state conformation, and morphological packing arrangement on light-emitting behaviors of diphenyldibenzofulvene derivatives. J. Phys. Chem. C 111, 2287 (2007).
35.Zhang, X., Yin, J., Peng, C., Hu, W., Zhu, Z., Li, W., Fan, C., and Huang, Q.: Distribution and biocompatibility studies of graphene oxide in mice after intravenous administration. Carbon 49, 986 (2011).
36.Zhang, X., Wang, S., Zhu, C., Liu, M., Ji, Y., Feng, L., Tao, L., and Wei, Y.: Carbon-dots derived from nanodiamond: Photoluminescence tunable nanoparticles for cell imaging. J. Colloid Interface Sci. 397, 39 (2013).
37.Zhang, X., Zhang, X., Wang, S., Liu, M., Tao, L., and Wei, Y.: Surfactant modification of aggregation-induced emission material as biocompatible nanoparticles: Facile preparation and cell imaging. Nanoscale 5, 147 (2013).
38.Zhang, X., Hu, W., Li, J., Tao, L., and Wei, Y.: A comparative study of cellular uptake and cytotoxicity of multi-walled carbon nanotubes, graphene oxide, and nanodiamond. Toxicol. Res. 1, 62 (2012).
39.Zhang, X., Qi, H., Wang, S., Feng, L., Ji, Y., Tao, L., Li, S., and Wei, Y.: Cellular responses of aniline oligomers: A preliminary study. Toxicol. Res. 1, 201 (2012).
40.Zhang, X., Hui, J., Yang, B., Yang, Y., Fan, D., Liu, M., Tao, L., and Wei, Y.: PEGylation of fluoridated hydroxyapatite (FAp):Ln3+ nanorods for cell imaging. Polym. Chem. 4, 4120 (2013).
41.Wan, Q., Liu, M.Y., Xu, D.Z., Huang, H.Y., Mao, L.C., Zeng, G.J., Deng, F.J., Zhang, X.Y., and Wei, Y.: Facile fabrication of amphiphilic AIE active glucan via formation of dynamic bonds: Self assembly, stimuli responsiveness and biological imaging. J. Mater. Chem. B 4, 4033 (2016).
42.Wan, Q., Wang, K., He, C.B., Liu, M.Y., Zeng, G.J., Huang, H.Y., Deng, F.J., Zhang, X.Y., and Wei, Y.: Stimulus responsive cross-linked AIE-active polymeric nanoprobes: Fabrication and biological imaging application. Polym. Chem. 6, 8214 (2015).
43.Li, H., Zhang, X., Zhang, X., Yang, B., Yang, Y., and Wei, Y.: Ultra-stable biocompatible cross-linked fluorescent polymeric nanoparticles using AIE chain transfer agent. Polym. Chem. 5, 3758 (2014).
44.Deshmukh, M., Salunkhe, S., Patil, D., and Anbhule, P.: A novel and efficient one step synthesis of 2-amino-5-cyano-6-hydroxy-4-aryl pyrimidines and their anti-bacterial activity. Eur. J. Med. Chem. 4, 2651 (2009).
45.Chitra, S., Devanathan, D., and Pandiarajan, K.: Synthesis and in vitro microbiological evaluation of novel 4-aryl-5-isopropoxycarbonyl-6-methyl-3,4-dihydropyrimidinones. Eur. J. Med. Chem. 45, 367 (2010).
46.Zhang, X., Chi, Z., Xu, B., Chen, C., Zhou, X., Zhang, Y., Liu, S., and Xu, J.: End-group effects of piezofluorochromic aggregation-induced enhanced emission compounds containing distyrylanthracene. J. Mater. Chem. 22, 18505 (2012).
47.Zhang, X., Liu, M., Yang, B., Zhang, X., and Wei, Y.: Tetraphenylethene-based aggregation-induced emission fluorescentorganic nanoparticles: Facile preparation and cell imaging application. Colloids Surf., B 112, 81 (2013).
48.Tao, L., Liu, J., and Davis, T.: Branched polymer-protein conjugates made from mid-chain-functional P(HPMA). Biomacromolecules 10, 2847 (2009).
49.Huang, Z., Zhang, X., Zhang, X., Yang, B., Zhang, Y., Wang, K., Yuan, J., Tao, L., and Wei, Y.: One-pot synthesis and biological imaging application of amphiphilic fluorescent copolymer via combination of RAFT polymerization and schiff base reaction. Polym. Chem. 6, 2133 (2015).