Libin Bai

Helical columnar liquid crystals based on dendritic peptides substituted perylene bisimides

New columnar liquid crystals based on perylene bisimides (PBIs) were synthesized by introducing dendritic peptides onto the two ends of the imide. The self-assembly behaviour of PBIs in solution and in film was investigated through temperature-dependent and solvent-dependent ultraviolet-visible absorption spectroscopy. The mesomorphic behaviour was studied by polarizing optical microscopy, differential scanning calorimetry, small-angle X-ray diffraction and temperature-dependent Fourier transform infrared spectroscopy. Ordered columnar mesophases were observed for PBIs at room temperature. Circular dichroism studies demonstrate that these materials exhibit supramolecular optical activity in the liquid crystalline state, which is attributed to helical columnar organization. The hydrogen bonds at the periphery of PBIs result in the ordered columnar mesophases structure with small inter-disk distances of 3.4 A

Water-Soluble Fluorescent Probes Based on Dendronized Polyfluorenes for Cell Imaging

Novel water-soluble dendronized fluorescent polyfluorenes (DFPFs) are prepared from hydrophilic monomers and hydrophobic comonomers. Incomplete energy transfer is found to result in a two-color emission of the DFPFs at around 410 and 650 nm. The incomplete energy transfer can be attributed to the poor compatibility between the fluorene and benzothiadiazole units. Polyethylene oxide (PEO) encapsulation of the DFPFs shows over 90% cell viability, indicating good biocompatibility. These DFPFs show differential cellular uptake. P1 with fewer PEO chains exhibits limited cellular membrane uptake and low brightness in cells. By contrast, P3 with more PEO chains is efficiently internalized by cells and accumulated in the cytoplasm. A strong fluorescence from whole cells is also observed.

A novel water-soluble fluorescent polymer based on perylene bisimides dyes: one-pot preparation and its bio-imaging

Abstract Perylene bisimides dye-based water-soluble fluorescent polymer P3, N,N’-bis(3-amyl)-1-bromo-7-{4’-[3’’-(S-poly(N-acryloyl ethylene diamine hydrochloride)-2’’’-methyl propionic acid)propionyloxy hexyloxy]phenyl} perylene-3,4:9,10-tetracarboxylic bisimides, was synthesized with polyelectrolyte modification via one-pot reaction (the reduction reaction of trithioester and click reaction between the thiol group and carbon–carbon double bond were simultaneously conducted in one pot with high conversion). One-pot method can overcome the limitation that usual click reaction between thiol and other groups has low conversion because thiol group is subject to rapid oxidation during purification and storage. Chemical, structural, and optical properties of P3 and intermediate products were fully characterized by nuclear magnetic resonance spectroscopy, Fourier transform infrared, gel permeation chromatograph, UV–vis spectra, and fluorescence spectra, respectively. The results revealed that P3 displayed excellent water solubility and not only exhibited red strong fluorescence emission band in water but also had the similar photoluminescent spectra to those of intermediate products (M4 and P2) in chloroform. Allowing for the potential application in biological detection field, cell viability and live cell imaging with the presence of P3 were further investigated with Hela cells. The results showed that P3 had low cytotoxicity with strong intracellular fluorescence entry. Meanwhile, with the augment of concentration of P3 (0–0.500 mg mL−1), the cell uptake and accumulation of P3 increased and thereby result in enhancement of the intracellular fluorescence. These experiment results suggested that P3 had enormous potential as a fluorescence probe to be an important component in biological detection field.

Synthesis backbone-dual-responsive of hyperbranched poly(bis(N,N-ethyl acrylamide))s by RAFT

Hyperbranched poly(bis(N,N-ethyl acrylamide))s (HPNAMs) with many vinyls as terminal groups were synthesized successfully using reversible addition fragmentation chain transfer polymerization (RAFT). Detailed analyses, based on the molecular weight, α value, degree of branching (DB), and lower critical solution temperature (LCST) obtained from nuclear magnetic resonance (NMR), multi detector-size exclusion chromatography (MDSEC), ultravioletvisible (UV-vis) spectroscopy, and dynamic light scattering (DLS), indicate that we acquired backbone-temperature and pH responsive HPNAM. Factors, such as DB, molecular weight, and pH value, that affect the LCST were investigated. It was found that the molecular weights of the hyperbranched polymers show significant influence on the LCSTs. For the HPNAMs with low molecular weight, the LCSTs decreased as the DB increased, and the LCSTs can also be adjusted by changing the pH value of solutions. Furthermore, the result of cell cytotoxicity indicates that this new dual responsive hyperbranched polymer has low cytotoxicity and exhibits potential for biomedical applications.

A new method for synthesizing hyperbranched polymers with reductive groups using redox/RAFT/SCVP

The novel hyperbranced polymers containing reductive groups were successfully prepared and characterized using redox/reversible addition fragmentation chain transfer (RAFT)/self-condensing vinyl polymerization (SCVP) method. Several redox initiating chemicals such as Cu(III)/-CONH2, Ce(IV)/-CONH2 and Ce(IV)/-OH were chosen to increase the free radical generating rate, and the chain transfer agent (CTA) was used to reduce the molecular chain propagating rate, in order to obtain polymers with high degree of branching. Detailed analyses based on the molecular weight, α value and the degree of branching of polymers (DB) obtained from 1H-NMR spectra and multi detector size exclusion chromatography (MDSEC) suggested the acquiring of hyperbranced polyacrylamides with Cu(III)/-CONH2 and Ce(IV)/-CONH2 as initiator in the presence of the CTA. Meanwhile, the as-prepared poly(N-hydroxymethyl acrylamide) (PNHAM) with higher DB value (0.48) proved that using Ce(IV)/-OH as the initiator could increase the free radical generating rate and diminish the gap between the propagating rate and the initiation rate during the reaction procedure. In addition, the effect of oxidant concentration on the Mark-Houwink index (α) value and the DB was also studied.

A Novel Water-Soluble Fluorescence Probe with Wash-Free Cellular Imaging Capacity Based on AIE Characteristics

A potential real-time imaging water-soluble fluorescent polymer (P3) is facilely prepared via one-pot method. For P3, tetraphenylethene unit serves as the fluorescent unit, poly(acryloyl ethylene diamine) (a kind of polyelectrolyte) with specific degree of polymerization acts as water-soluble part. 1 H-NMR, gel permeation chromatography (GPC), UV-vis spectroscopy, photoluminescence (PL), and confocal laser scanning microscopy are undertaken to characterize the structure and property of P3. The results of wash-free cellular imaging show that the signal-to-noise ratio is high as the concentration of P3 is 50 μg mL-1 . In addition, the pH-responsive and Cd2+ -responsive are also investigated in this paper. The results coming from pH-responsive show that P3 solution displays significant fluorescence under near neutral. And the result from the cellular imaging shows that intracellular fluorescence intensity enhances with the augment of concentration of Cd2+ , which reveals that P3 can give a hint to resolve the dilemma of traditional fluorescent dyes used as living cellular fluorescent probe.

The Synthesis of Backbone Thermo and pH Responsive Hyperbranched Poly(Bis(N,N-Propyl Acryl Amide))s by RAFT

Hyperbranched poly(methylene-bis-acrylamide), poly(bis(N,N-propyl acryl amide)) (HPNPAM) and poly(bis(N,N-butyl acryl amide)) were synthesized by reversible addition-fragmentation chain transfer polymerization. HPNPAMs showed lower critical solution temperature (LCST) due to an appropriate ratio between hydrophilic and hydrophobic groups. The effects of reaction conditions on polymerization were investigated in detail. The structure of HPNPAM was characterized by 1H NMR, FT-IR, Muti detector-size exclusion chromatography (MDSEC) and Ultravioletvisble (UV-Vis). The α value reached 0.20 and DB was 90%, indicating HPNPAMs with compact topology structure were successfully prepared. LCSTs were tuned by Mw and the pH value of the solution. The change of molecular size was assayed by dynamic light scattering and scanning electron microscope. These results indicated that the stable uniform nanomicelles were destroyed and macromolecules aggregated together, forming large particles as temperature exceeded LCST. In addition, after the cells were incubated for 24 h, the cell viability reached 80%, which confirmed this new dual responsive HPNPAM had low cytotoxicity.

Hyperbranched Glycopolymers of 2-(α-d-Mannopyranose) Ethyl Methacrylate and N,N’-Methylenebisacrylamide: Synthesis, Characterization and Multivalent Recognitions with Concanavalin A

A series of novel hyperbranched poly[2-(α-d-mannopyranosyloxy) ethyl methacrylate-co-N,N’-methylenebisacrylamide] (HPManEMA-co-MBA) are synthesized via a reversible addition fragmentation polymerization (RAFT). The dosage ratios of linear and branch units are tuned to obtain different degree of branching (DB) in hyperbranched glycopolymers. The DB values are calculated according to the content of nitrogen, which are facilely determined by elemental analysis. The lectin-binding properties of HPManEMA-co-MBA to concanavalin A (ConA) are examined using a turbidimetric assay. The influence of defined DB value and molecular weight of HPManEMA-co-MBA on the clustering rate is studied. Notably, HPManEMA-co-MBAs display a low cytotoxicity in the MTT assay, thus are potential candidates for biomedical applications.

Facile construction of a hyperbranched poly(acrylamide) bearing tetraphenylethene units: a novel fluorescence probe with a highly selective and sensitive response to Zn2+

Thermo-responsive hyperbranched copoly(bis(N,N-ethyl acrylamide)/(N,N-methylene bisacrylamide)) (HPEAM-MBA) was synthesized by using reversible addition–fragmentation chain-transfer polymerization (RAFT). Interestingly, the zinc ion (Zn2+) was found to have a crucial influence on the lowest critical solution temperature (LCST) of the thermo-responsive polymer. The tetraphenylethylene (TPE) unit was then introduced onto the backbone of the as-prepared thermo-responsive polymer, which endows a Zn2+-responsive “turn-off” effect on the fluorescence properties. The TPE-bearing polymer shows a highly specific response over other metal ions and the “turn-off” response can even be tracked as the concentration of Zn2+ reduces to 2 × 10−5 M. The decrement of fluorescence intensity was linearly dependent on the concentration of Zn2+ in the range of 4–18 μmol L−1. The flexible, versatile and feasible approach, as well as the excellent detection performance, may generate a new type of Zn2+ probe without the tedious synthesis of the moiety bearing Zn2+ recognition units.

Facile preparation of thermosensitive and water-soluble fluorescent polymer containing curcumin and its cell imaging

ABSTRACT A novel thermosensitive and water-soluble fluorescent polymer PNIPAM-curcumin (P2) containing curcumin unit was synthesized through one-pot method. The chemical structure and optical properties of compounds and polymer were characterized and tested. As the results turned out that P2 displayed excellent water solubility, thermosensitivity and exhibited strong fluorescence emission band in water. Moreover, P2 was further investigated by MTT assay and live cell imaging with HeLa cells. P2 did not have cytotoxicity in concentration of 200 µg · mL−1 within 48 h and the intracellular fluorescence intensity enhanced with the concentration of P2 varying from 0 to 500 µg · mL−1. According to the experimental results, as a fluorescence probe, P2 synthesized does not only possess nice water solubility but also has the advantage of no cytotoxicity, and it can easily enter the cells, which indicates that it is a characteristic of high sensitivity and responsiveness. Therefore, P2 will have immense potential to be applied in biomedical fields. GRAPHICAL ABSTRACT