Spectroscopic studies on the photostability and photoactivity of metallo-tetraphenylporphyrin in micelles

Inspired by natural photosynthesis, we employed polymeric micelles to enhance the water solubility and photostability of hydrophobic metallo-tetraphenylporphyrin (metallo-TPP) by complexation with poly(ethylene glycol)-block-poly(4-vinylpyridine) (PEG-b-P4VP) via axial coordination. The structure and photochemical properties of the complex micelles were characterized by UV-visible spectroscopy, fluorescence spectroscopy, and laser light scatting. The photostability and electron transfer ability of metalloporphyrins in the micelles were investigated under continuous irradiation. The results show that metallo-TPPs entrapped in the micellar cores possess higher photostability and better electron transfer ability. The hydrophobic metalloporphyrins remains active inside the micelles which is reminiscent of chlorophyll protein complex in photosynthesis. The use of micelle thus may provide a promising system on designing photocatalysts for targeting applications in solar energy conversion and photodynamic tumor therapy (PDT).     

Enhanced stability of ZnTPPS by polymeric gold nanoparticles in acidic aqueous solutions

Novel kind of core-shell corona complex micelles were prepared, which enhanced both the hydrolytic stability and the photostability of water-soluble zinc tetrakis(4-sulfonatophenyl) porphyrin (ZnTPPS) in acidic aqueous solutions. The core-shell gold nanoparticles (AuNPS) were synthesized by reducing HAuCl₄ and di-thioester terminated block copolymer, poly(Nisopropylacrylamide)-block-poly(4-vinylpyridine) (PNIPAM-b-P4VP). The complex micelles with gold core, P4VP/ZnTPPS shell and PNIPAM corona were formed by simple mixing of gold nanoparticles and ZnTPPS. The photochemical properties of the complex micelles were studied by UV–Visiblespectroscopy and fluorescence spectroscopy. The results showed trapping of ZnTPPS in the positively charged micellar shell that effectively prevented demetallation of the ZnTPPS that would occur in acidic aqueous solutions. Furthermore, with appropriate concentration of gold nanoparticles, ZnTPPS in the complex micelle had excellent photostability by suppression of generation of reactive oxygen species (ROS). The enhanced stability of ZnTPPS in acidic aqueous media could be extensively used for photocatalysis and in solar cells.     

Hydrogen bond mediated supramolecular micellization of diblock copolymer mixture in common solvents

We report a new approach toward preparing self-assembled hydrogen-bonded complexes having vesicle and patched spherical structures from two species of block copolymers in nonselective solvents. Two diblock copolymers, poly(styrene-b-vinyl phenol) (PS-b-PVPh) and poly(methyl methacrylate-b-4-vinylpyridine) (PMMA-b-P4VP), were synthesized through anionic polymerization. The assembly of vesicles from the intermolecular complex formed after mixing PS-b-PVPH with PMMA-b-P4VP in THF was driven by strong hydrogen bonding between the complementary binding sites on the PVPH and P4VP blocks. In contrast, well-defined patched spherical micelles formed after blending PS-b-PVPh with PMMA-b-P4VP in DMF: the weaker hydrogen bonds formed between the PVPh and P4VP blocks in DMF, relative to those in THF, resulted in the formation of spherical micelles having compartmentalized coronas consisting of PS and PMMA blocks.     

Solubilization of C60 using ultrasound and amphiphilic block copolymers in acidic aqueous solutions

Fullerene (C₆₀), the third carbon allotrope, has shown great potential in photoelectric materials and drug delivery. However, the low solubility of C₆₀ in polar solvents, especially in water, is the major limiting factor for further applications. The use of ultrasound and amphiphilic block copolymers, poly(ethylene glycol)-block-poly(4-vinylpyridine) (PEG-b-P4VP), helped to disperse C₆₀ in acidic aqueous solutions. As characterized by dynamic light scattering, transmission electron microscopy, and UV-visible spectroscopy, the C₆₀ colloids had a core-shell structure with C₆₀ aggregated in the micellar cores. The photosensitized generation of singlet oxygen using C₆₀-bound polymer micelle was confirmed by the iodide method. More importantly, C₆₀ and metalloporphyrin complexes could be synthesized by the self-assembly between PEG-b-P4VP/C₆₀ micelle and metalloporphyrin. The stability of metalloporphyrin increased in the presence of the PEG-b-P4VP/C₆₀ micelle. This study provides a method for the solubilization of C₆₀ with many potential applications in biomedicals and photovoltaics.     

Fabrication of biofunctional complex micelles with tunable structure for application in controlled drug release

In acidic solution, complex micelles were formed by diblock copolymers of poly (ethylene glycol)-b-poly (ε-caprolactone) (PEG-b-PCL) and folate-poly (2-(dimethylamino) ethyl methylacrylate)-b-poly (ε-caprolactone) (Fol-PDMAEMA-b-PCL) with a PCL core, a mixed PEG/Fol-PDMAEMA shell. The surface charge of the complex micelles was positive at acidic surroundings for the protonated PDMAEMA. With increasing pH value to 7.4 (above pK _a of PDMAEMA), these micelles could convert into a core-shell-corona (CSC) structure composing a hydrophobic PCL core, a collapsed PDMAEMA shell, and a soluble PEG corona. Compared to core-shell micelles formed by PEG-b-PCL, micelles with CSC structure can prolong degradation by enzyme. Doxorubicin was physically loaded into the PCL core. The drug release rate was pH-dependent. At pH 5.5, complex micelles with core-shell structure showed faster drug release rate, while at pH 7.4, complex micelles gained CSC structure which control the drug release at a lower rate. The multifunctional complex micelles were prepared for enhanced tumor therapy.     

Multiple morphological micelles formed from the self-assembly of poly(styrene)-b-poly(4-vinylpyridine) containing cobalt dodecyl benzene sulfonate

A series of supramolecular block copolymers were prepared using poly(styrene)-b-poly(4-vinylpyridine)(PS-b-P4VP) which coordinated with cobalt dodecyl benzene sulfonate (Co(DBS)₂) in tetrahydrofuran (THF). Fourier transformation infrared spectroscopy (FTIR), UV-vis absorption spectroscopy (UV) and differential scanning calorimetry (DSC) showed that Co(DBS)₂ coordinated to the lone electron pairs of the pyridine nitrogens in the P4VP block and leaded to complexes. The supramolecular block copolymers could self-assemble into nanosized micelles with different shapes and dimensions in THF, depending on the number of Co(DBS)₂ groups per 4-vinylpyridine (repeat unit was denoted by n) and the ratio between PS block length and P4VP block length. Transmission electron microscopy (TEM) results showed that when the number of repeat units of P4VP was more than that of PS, micelles with different interesting shapes such as spheres, rods, vesicles, large compound vesicles (LCVs) and the large compound micelles (LCMs) were observed if increasing the content of the Co(DBS)₂ in PS-b-P4VP copolymer/THF solution; When the number of repeat units of P4VP was less than that of PS, the micelle morphologies changed from spheres to rods, bi-layer, and LCMs if the Co(DBS)₂ content was increased progressively.     

Responsive polymer-based multicolor fluorescent probes for temperature and Zn2+ ions in aqueous media

We report on the fabrication of fluorescent and multicolor probes for Zn²⁺ ions and temperature from a mixture of three types of fluorophore-labeled responsive block copolymers in aqueous media. Quinoline-based Zn²⁺-recognizing fluorescent monomer ZQMA, red-emitting rhodamine B-based monomer RhBEA, and blue-emitting coumarin derivative Coum-OH, were synthesized first. A ZQMA-labeled well-defined double hydrophilic block copolymer (DHBC), PEG-b-P(MEO₂MA-co-ZQMA), was synthesized via reversible addition-fragmentation chain-transfer (RAFT) polymerization of 2-(2-methoxyethoxy)ethyl methacrylate (MEO₂MA) and ZQMA by utilizing a PEG-based macroRAFT agent. Following similar procedures, PEG-b-P(St-co-RhBEA) amphiphilic diblock copolymer and PEG-b-P(MEO₂MA-co-Coum) DHBC were also synthesized, where P(St-co-RhBEA) was a RhBEA-labeled polystyrene (PS) block. At room temperature in aqueous solution, almost nonfluorescent PEG-b-P(MEO₂MA-co-ZQMA) can effectively bind Zn²⁺ ions, leading to prominent green fluorescence enhancement due to the coordination of ZQMA with Zn²⁺ ions. However, by mixing red-emitting PEG-b-P(St-co-RhBEA) and blue-emitting PEG-b-P(MEO₂MA-co-Coum) with PEG-b-P(MEO₂MA-co-ZQMA) at an appropriate ratio, three color transitions could be observed. In the absence of Zn²⁺ ions, a mixed pink fluorescent originating from Coum and RhBEA was observed; upon the addition of a certain amount of Zn²⁺ ions, the green fluorescence enhanced dramatically, leading to a white fluorescence readout. By further increasing the amount of Zn²⁺ ions, the green fluorescence further enhanced and overwhelmed the blue and red emissions, leading to a green-dominant mixed-fluorescence emission. In addition, upon increasing the temperature, the fluorescence of Coum decreased considerably due to the fluorescence-resonance energy transfer (FRET) between Coum and ZQMA moieties. In this way, a ratiometric fluorescent thermometer can be constructed.     

Stimuli-responsive behavior of complex micelles based on double hydrophilic block copolymer and fluorescent indicator

The double hydrophilic block copolymer poly(ethylene glycol mono-methyl ether)-block-poly(4-vinylpyridine) (mPEG₄₃-b-P4VP₁₁₅) was synthesized by atom transfer radical polymerization. The structure, molecular weight and molecular weight distribution of mPEG₄₃-b-P4VP₁₁₅ were characterized by ¹H-NMR and gel permeation chromatography combined with laser light scattering technique. The complex micelles based on mPEG₄₃-b-P4VP₁₁₅ and the disodium 2-naphthol-3,6-disulfonate were obtained in acid aqueous solution. The morphologies of the complex micelles were observed by transmission electron microscopy. The revertible temperature and pH-responsive behaviors of complex micelles were studied by dynamic light scattering and fluorescence techniques.     

A strategy to stabilize the confined chiral TPPS J-aggregate by ionic block copolymer

Poly(ethylene glycol)-block-poly(4-vinylpyridine) (PEG-b-P4VP), with a poly-cation building block, forms electrostatic complexes with the J-type chiral pre-aggregates of 5,10,15,20-tetrakis (4-sulfonatophenyl) porphyrin (TPPS) in the water inner-phase of the TX-100 reverse microemulsion at pH 1.0 using l-tryptophan as the chiral source. The complexation with PEG₄₅-b-P4VP₆ prevents these chiral pre-aggregates from contacting with each other during the percolation of the droplets, so as to stabilize the circular dichroism intensity and the size of the complexes. After breaking the microemulsion, the PEG₄₅-b-P4VP₆/TPPS aggregates are also prevented from further clustering at optimized ratio of [polymer]/[TPPS], so these complex aggregates disperses in acetone with spherical morphology and well maintain their size and chiral signal for further storing. This method can be considered as one of extracting the confined chiral aggregates as an isolated form apart from the reverse microemulsion.     

Thiol-ene Reaction: An Efficient Tool to Design Lipophilic Polyphosphoesters for Drug Delivery Systems

Poly(ethylene glycol)-b-polyphosphoester (PEG-b-PPE) block copolymer nanoparticles are promising carriers for poorly water soluble drugs. To enhance the drug loading capacity and efficiency of such micelles, a strategy was investigated for increasing the lipophilicity of the PPE block of these PEG-b-PPE amphiphilic copolymers. A PEG-b-PPE copolymer bearing pendant vinyl groups along the PPE block was synthesized and then modified by thiol-ene click reaction with thiols bearing either a long linear alkyl chain (dodecyl) or a tocopherol moiety. Ketoconazole was used as model for hydrophobic drugs. Comparison of the drug loading with PEG-b-PPE bearing shorter pendant groups is reported evidencing the key role of the structure of the pendant group on the PPE backbone. Finally, a first evidence of the biocompatibility of these novel PEG-b-PPE copolymers was achieved by performing cytotoxicity tests. The PEG-b-PPE derived by tocopherol was evidenced as particularly promising as delivery system of poorly water-soluble drugs.     

pH-responsive pseudorotaxane between comblike PEO-grafted triblock polymer and α-cyclodextrin

The pH-responsive inclusion complexation of comblike triblock polymer, P2VP-b-PPEOMA-b-P2VP, with α-cyclodextrin (α-CD) was studied. The triblock polymer was prepared by reversible addition–fragmentation chain transfer polymerization (RAFT) and formed inclusion complexes (ICs) after selective threading of the PEO segment of the triblock polymer through the cavities of α-CD units. For comparison, PPEOMA homopolymer was prepared, and the inclusion complexation with α-CD was also studied. The formed ICs were characterized by XRD and ¹H NMR. The results revealed that P2VP-b-PPEOMA-b-P2VP can form ICs with α-CD even when forming micelles, and the introduction of P2VP had a great influence on the solution property and the stoichiometry of EO to CD of the inclusion complexes depending on the concentration and the pH of the solution.     

A simple method to prepare highly ordered PS-b-P4VP block copolymer template

A control strategy for tuning the film morphology of asymmetric polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) block copolymers (BCPs) is reported. After preparation of the film by spin-coating method, the as-cast films were annealed in different solvent vapor. It is found that chloroform is a wonderful solvent for forming PS-b-P4VP regular pattern. Otherwise, with changing the concentration of PS-b-P4VP, cylindrical or parallel nanostructures could be attained. The PS-b-P4VP films with cylindrical structure are used as template to deposit FePt nanoparticles into the pores. Nanoparticles reaching the bottom of the holes form a disordered magnetic array.     

Fabrication of polymeric micelles with core–shell–corona structure for applications in controlled drug release

Thermo-responsive polymeric micelles of poly (ethylene glycol)-b-poly(2-hydroxyethyl methacrylate-g-lactide)-b-poly(N-isopropylacrylamide) (PEG-P(HEMA-PLA)-PNIPAM) with core–shell–corona structure were fabricated for applications in controlled drug release. The graft copolymer of PEG-P(HEMA-PLA)-PNIPAM was self-assembled into core–shell micelles with a densely PLA core and mixed PEG/PNIPAM shells at 25 °C in aqueous media. By increasing the temperature above the lower critical solution temperature of PNIPAM, these core–shell micelles could be converted into core–shell–corona micelles because of the collapse of PNIPAM block on the PLA core as the inner shell and the soluble PEG block stretching outside as the outer corona. Anticancer drug doxorubicin (DOX) was loaded in the polymeric micelles as a model drug. Compared with polymeric micelles formed by liner PEG-b-PLA-b-PNIPAM triblock copolymer, these polymeric micelles exhibited higher loading capacity, and release of DOX from the polymeric micelles with core–shell–corona structure was well-controlled.     

Formation of gold nanoparticles in diblock copolymer micelles with various reducing agents

Gold nanoparticles (Au NPs) were prepared by the reduction of HAuCl₄ acid incorporated into the polar core of poly(styrene)-block-poly(2-vinylpyridine) (PS-b-P2VP) copolymer micelles dissolved in toluene. The formation of Au NPs was controlled using three reducing agents with different strengths: hydrazine (HA), triethylsilane (TES), and potassium triethylborohydride (PTB). The formation of Au NPs was followed by transmission electron microscopy, UV–Vis spectroscopy, isothermal titration calorimetry (ITC), and dynamic light scattering (DLS). It was found that the strength of the reducing agent determined both the size and the rate of formation of the Au NPs. The average diameters of the Au NPs prepared by reduction with HA, TES, and PTB were 1.7, 2.6, and 8 nm, respectively. The reduction of Au(III) was rapid with HA and PTB. TES proved to be a mild reducing agent for the synthesis of Au NPs. DLS measurements demonstrated swelling of the PS-b-P2VP micelles due to the incorporation of HAuCl₄ and the reducing agents. The original micellar structure rearranged during the reduction with PTB. ITC measurements revealed that some chemical reactions besides Au NPs formation also occurred in the course of the reduction process. The enthalpy of formation of Au NPs in PS-b-P2VP micelles reduced by HA was determined.     

Double‐hydrophilic block copolymer for encapsulation and two‐way pH change‐induced release of metalloporphyrins

A double hydrophilic block copolymer composed of poly(acrylic acid) (PAA) and poly(4‐vinyl pyridine) (P4VP) was obtained through hydrolysis of diblock copolymer of poly(tert‐butyl acrylate) (PtBA) and P4VP synthesized using atom transfer radical polymerization. Water‐soluble micelles with PAA core and P4VP corona were observed at low (acidic) pH, while micelles with P4VP core and PAA corona were formed at high (basic) pH. Two metalloporphyrins, zinc tetraphenylporphyrin (ZnTPP) and cobalt tetraphenylporphyrin (CoTPP), were used as model compounds to investigate the encapsulation of hydrophobic molecules by both types of micelles. UV–vis spectroscopic measurements indicate that micelles with P4VP core are able to entrap more ZnTPP and CoTPP as a result of the axial coordination between the transition metals and the pyridine groups. The study found that metalloporphyrins encapsulated by the micelles with PAA core could be released on pH increase, while those entrapped by the micelles with P4VP core could be released on pH decrease. This behavior originates from the two‐way pH change‐induced disruption of PAA‐b‐P4VP micelles. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1734–1744, 2006     

Aggregation Behavior of Poly(ethylene glycol)-block-poly (γ-benzyl L-glutamate)-graft-poly(ethylene glycol) Copolymer and its Blends with Poly(γ-benzyl L-glutamate) Homopolymer in Mixed Solvents

Poly(ethylene glycol)-block-poly(γ-benzyl L-glutamate)-graft-poly(ethylene glycol) (PEG-b-PBLG-g-PEG) copolymer was synthesized by the ester exchange reaction of PBLG-block-PEG copolymer with mPEG. The self-association behaviors of PEG-b-PBLG-g-PEG and its blends with PBLG homopolymer in the mixtures of ethanol and dimethylformamide (DMF) were investigated by transmission electron microscopy (TEM), dynamic light scattering (DLS), and viscometry. Effects of the introduction of PBLG homopolymer, the grafting ratio, and the DMF content on the self-association behaviors of PEG-b-PBLG-g-PEG copolymer in the mixtures of ethanol and DMF were mainly researched. It was revealed that PEG-b-PBLG-g-PEG copolymer could self-assemble to form polymeric micelles with a core-shell structure in various shapes from different preparation conditions. The critical micelle concentration (CMC) and the average particle diameter of the micelles formed by PEG-b-PBLG-g-PEG copolymer in the mixed solvents also changed with different preparation conditions.     

Synthesis of poly(vinyl acetate)-b-poly(4-vinylpyridine) block copolymers by a combination of cobalt-mediated radical polymerization and RAFT polymerization and their use in dispersion polymerization under UV radiation

Well-defined poly(vinyl acetate)-block-poly(4-vinylpyridine) (PVAc-b-P4VP) block copolymers were synthesized for the first time by a combination of cobalt-mediated radical polymerization (CMRP) and reversible addition–fragmentation chain transfer (RAFT) polymerization, and were used to prepare PVAc-b-P4VP hairy polystyrene (PSt) particles. PVAc end-capped by a cobalt(II) acetylacetonate complex was first synthesized by the CMRP of vinyl acetate, after which the cobalt complex was modified into a dithiobenzoate group for the RAFT polymerization of 4-vinylpyridine. The hairy PSt particles were synthesized by the dispersion polymerization of St using the PVAc-b-P4VP as both a macro-initiator and a colloidal stabilizer under UV radiation. The average size of PSt particles synthesized with 20 wt.% of PVAc-b-P4VP (M _n = 39,500 g/mol) was 136 nm (CV = 19.2%). Very small Au nanoparticles were successfully immobilized on the surface of the PSt particles.     

Synthesis,Characterization and Aqueous Solution Behavior of a pH-responsive Double Hydrophilic Block Copolymer

The pH-responsive double hydrophilic block copolymer poly(ethylene glycol)-b-poly(methacylic acid-co-4-vinyl benzylamine hydrochloride salt) (PEG-b-PMAA/PVBAHS) was synthesized. A series of PEG-b-PMAA/PVBAHS with different molecule weights and compositions were characterized by IR, ¹H-NMR, elemental analysis and TGA. With different MAA/VBAHS ratio, the PEG-b-PMAA/PVBAHS copolymers had the different isoelectric point (IEP). Supermolecular structures of the block copolymers could be formed by the interionic interactions at different solution pH. Experiment results showed that the structures of the pH-responsive copolymers in aqueous solution could be changed at different pH environments. The aggregation of this double hydrophilic block copolymer in aqueous solution was determined by both of solution pH and copolymer composition.     

Micellization and luminescence of PEG-b-P4VP/Europium(III)/1,10-phenanthroline complex

Luminescent micelles were prepared through the self-assembly of poly(ethylene glycol)-block-poly(4-vinylpyridine) (PEG₁₁₄-b-P4VP₆₁) and Europium(III) (Eu(III)), with P4VP/Eu(III) as the core, and PEG as the corona. 1,10-phenanthroline (Phen) was assembled into the core of the micelles to sensitize the luminescence. The presence of Phen results into the increasing of apparent average hydrodynamic diameters (D_h^app {\hbox{D}}_{\rm{h}}^{\rm{app}} ) of the micelles. All Eu(III)-containing micelles emitted the characteristic fluorescence of Eu(III). The intensity of luminescence increased with the presence and the increasing quantity of Phen in the complex micelles due to the effective energy transferring of Phen in the “antenna effect”.     

Self‐assembled complexes of poly(acrylic acid) and poly(styrene)‐block‐poly(4‐vinyl pyridine)

Polymer complexes were prepared from high molecular weight poly(acrylic acid) (PAA) and poly(styrene)‐block‐poly(4‐vinyl pyridine) (PS‐b‐P4VP) in dimethyl formamide (DMF). The hydrogen bonding interactions, phase behavior, and morphology of the complexes were investigated using Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), dynamic light scattering (DLS), atomic force microscopy (AFM), and transmission electron microscopy (TEM). In this A‐b‐B/C type block copolymer/homopolymer system, P4VP block of the block copolymer has strong intermolecular interaction with PAA which led to the formation of nanostructured micelles at various PAA concentrations. The pure PS‐b‐P4VP block copolymer showed a cylindrical rodlike morphology. Spherical micelles were observed in the complexes and the size of the micelles increased with increasing PAA concentration. The micelles are composed of hydrogen‐bonded PAA/P4VP core and non‐bonded PS corona. Finally, a model was proposed to explain the microphase morphology of complex based on the experimental results obtained. The selective swelling of the PS‐b‐P4VP block copolymer by PAA resulted in the formation of different micelles. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1192–1202, 2009