Qing-Yu Gao

Preparation and drug controlled-release of polyion complex micelles as drug delivery systems

Block copolymers, poly(N-vinylprrolidone)-block-poly(styrene-alter-maleic anhydride) (PVP-b-PSMA) and poly(N-vinylprrolidone)-block-poly(N,N-dimethylaminoethyl methacrylate) (PVP-b-PDMAEMA), were synthesized by reversible addition- fragmentation chain transfer (RAFT) polymerization. In aqueous media, this a pair of oppositely-charged diblock copolymers could self-assemble into stable and narrow distribution polyion complex micelles (PICMs). Transmission electron micrographs (TEM) and dynamic light scattering (DLS) analysis showed that the micelles to be spherically shaped with mean hydrodynamic diameter around 70nm. In addition, the PICMs display ability to response to external stimuli. All of theses features are quite feasible for utilizing it as a novel intelligent drug delivery system. In order to assess its application in biomedical area, release profiles of coenzyme A (Co A) from PICMs were studied under both simulated gastric and intestinal pH conditions. The release was much quicker in pH 7.4 buffer than in pH 2.0 solution. Based on these results, these PICMs could be a potential pH-sensitive carrier for colon-specific drug delivery system.

Preparation, characterization and drug release behavior of polyion complex micelles

Double-hydrophilic block copolymer composed of poly(N-vinylpyrrolidone) (PVP) and poly(styrene-alter-maleic anhydride) (PSMA) has been synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. Poly(N-vinylpyrrolidone)-block-poly(styrene-alter-maleic anhydride) (PVP-b-PSMA) thus formed was characterized by gel permeation chromatography (GPC), (1)H nuclear magnetic resonance ((1)H NMR) spectroscopy and FTIR spectroscopy. In acid solution, this block copolymer spontaneously formed polyion complex (PIC) micelles with a cationic polyelectrolyte, chitosan. The PSMA/chitosan polyelectrolyte complex formed an inner core while PVP chains surrounded it as a shell. Transmission electron micrographs (TEMs) and dynamic light scattering (DLS) showed the PIC micelles to be spherically shaped, with mean hydrodynamic diameter around 146 nm. The model drug coenzyme A (CoA) was loaded into the micelles and the in vitro drug release behavior was investigated. We found that by manipulating the pH value and salt concentration of the release solution, it was possible to control the releasing rate of CoA.

Self-assembled Polyion Complex Micelles based on PVP-b-PAMPS and PVP-b-PDMAEMA for Drug Delivery

The double hydrophilic block copolymer, poly(N-vinylpyrrolidone)-block-poly(2-acrylamido-2-methyl-1-propanesulfonic acid), was synthesized by reversible addition-fragmentation chain transfer RAFT polymerization. Gel permeation chromatography, 1H-NMR, and FTIR were used to determine the structure and composition. In aqueous media, this block copolymer spontaneously forms polyion complex (PIC) micelles with an oppositely charged block copolymer, poly(N-vinylpyrrolidone)-block-poly(N, N-dimethylaminoethyl methacrylate). Dynamic light scattering and transmission electron micrograph showed that the micelles were <200 nm in diameter and had a narrow single distribution. The release profiles of folic acid, incorporated into the micelles, showed remarkable pH responsive behavior. The PIC micelles exhibited good biocompatibility based on MTT assay with human embryonic kidney (HEK293) cells. These PIC micelles have the potential as pH-sensitive carriers for drug delivery.

ABC triblock copolymers with pH-responsive LCST for controlled drug delivery

The thermo- and amphiphilic ABC triblock copolymers, single-methoxypoly(ethylene glycol)-b-poly(N-isopropylacrylamide-co-acrylic acid)-b-poly(methyl methacrylate), were synthesized by reversible addition fragmentation chain transfer radical polymerization. The triblock copolymers were characterized by Fourier transform infrared spectroscopy, 1H-NMR, and gel permeation chromatography. The copolymers self-assemble into thermo-responsive nano-sized micelles in aqueous media. Transmission electron microscopy and dynamic light scattering showed that the micelles were regularly spherical in shape with an average diameter ~120 nm. Fluorescence analysis indicated that the triblock copolymer had a low critical micelle concentration of 2.5 mg/L in aqueous media at pH 7.4 and room temperature. The lower critical solution temperature (LCST) of the micelles could be altered by simply changing the pH. The LCST of the triblock copolymer at pH 5.5 was altered to 37.5 ° C (close to physiological temperature) by copolymerizing N-isopropylacrylamide with acrylic acid. When the pH was increased to 7.4, the LCST increased to 55°C and it decreased to 33°C when the pH was 2.0. The micelles exhibited good biocompatibility with human embryonic kidney cells, when the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay was performed. The controlled release of folic acid (FA) from FA-loaded micelles under different conditions was evaluated. The rate and amount of the drug released were greater above the LCST than below it.

Synthesis and characterization of polyion complex micelles and their controlled release of folic acid.

Stable and narrow distribution polyion complex micelles (PICMs) were prepared in an aqueous milieu through electrostatic interaction between a pair of oppositely charged block copolymers poly(N-vinylpyrrolidone)-block-poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PVP-b-PAMPS) and monomethoxy poly(ethylene glycol)-block-poly(4-vinyl pyridine) (PEG-b-P4VP). The critical aggregate concentration (CAC), hydrodynamic size, and surface morphology of the prepared PICMs were characterized by fluorescence spectroscopy, dynamic light scattering (DLS), and transmission electron microscopy (TEM), respectively. The resulting CAC and the average diameter of the PICMs were about 43 mg/L and 121 nm, indicating high structural stability of micelles and a size favorable for delivery of drug. In addition, the PICMs exhibited good biocompatibility using the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay with human embryonic kidney (HEK293) cells. All of these features are quite feasible for utilizing the PICMs as a novel intelligent drug delivery system. In order to assess its application in the biomedical area, the model drug folic acid (FA) was loaded into the micelles and the in vitro drug release behavior was investigated. We found that by manipulating the pH value and salt concentration of the release solution, it was possible to control the release rate of FA.

Self-assembled polyion complex micelles for sustained release of hydrophilic drug

Graft copolymer polyethylenimine–graft–poly(N-vinylpyrrolidone) (PEI-g-PVP) was prepared by coupling mono carboxyl-terminated PVP (PVP–COOH) with PEI using N,N′-dicyclohexylcarbodiimide (DCC) and N-hydroxysuccinimide (NHS) as coupling agents. In aqueous medium, PVP–g–PEI can self-assemble into stable polyion complex micelles with an oppositely charged block copolymer, poly(N-vinylpyrrolidone)–block–poly(2-acrylamido-2-methyl-1-propanesulphonic acid) (PVP-b-PAMPS). Transmission electron microscopy images showed that these micelles were regularly spherical in shape. The micelle size determined by size analysis was around 142 nm. To estimate their feasibility as vehicles for drugs, the model drug folic acid (FA) was incorporated into the cores of the micelles via electrostatic interactions. In vitro release test of FA showed that the drug-release rates are dependent on the pH value of the release media. Based on these results, we can conclude that the polyion complex micelles prepared from the PEI-g-PVP/PVP-b-PAMPS copolymers have great potential as drug delivery nanocarriers.

Vinyl monomers bearing chromophore moieties and their polymers. IV. Fluorescence and photosensitizing behavior of 8-acryloyloxyquinoline and its polymer

Acrylic monomers bearing electron-donating quinolyl moiety, i.e., 8-acryloyl-oxyquinoline (AQ) was prepared and polymerized. It was found that the fluorescence intensity of AQ was much lower than that of P(AQ) at the same chromophore concentration. The fluorescence of P(AQ) could be quenched by electron-deficient vinyl monomers, such as acrylonitrile (AN) and methyl methacrylate (MMA). This is another example of the fluorescence structural self-quenching effect termed by us previously, and demonstrates again that this phenomenon is not an accidental but a general one for acrylic monomers bearing electron-donating chromophores. The photopolymerization of acrylonitrile (AN) sensitized by AQ and P(AQ) as well as combining with carbon tetrabromide (CBr 4 ) was studied kinetically. From the rates of the polymerization (Rp) and overall activation energies obtained for these four systems, it was found that Rp sensitized by the binary systems was much higher than by AQ or P(AQ) alone, while the molecular weights of the resulting P(AN) were lower. The fluorescent analysis of the resulting P(AN)in solution showed that the sensitizers also entered into the P(AN) chains. A mechanism of charge transfer complex (CTC) formation was tentatively suggested for the photopolymerization of AN initiated by these four systems.

Vinyl monomers bearing chromophore moieties and their polymers. VI. Synthesis and photochemical behavior of acrylic monomer bearing phenoxazine moiety and its polymer

An acrylic monomer having phenoxazine moiety, i.e., N-acryloylphenoxazine ( APO ), has been synthesized by dehydrochlorination of N-(3-chloropropionyl) phenoxazine with 1,5-diazabicyclo [5.4.0]undec-5-ene in dimethyl sulfoxide. The monomer can be polymerized with AIBN as an initiator. The photochemical behavior, including the fluorescence and photosensitizing properties of this monomer and its polymer, has been studied. It has been recorded that the absorption spectrum of polymer P(APO) displays a few blue shifts compared with its monomer APO. It has also been observed that the fluorescence emission intensity of the monomer is dramatically lower than that of its polymer at the same chromophore concentration. This may be ascribed to the charge transfer interacting between the coexisting electron-accepting acrylic carbon-carbon double bond and the electron-donation phenoxazine moiety in APO, intramolecularly or intermolecularly on excitation. The fluorescence of the APO polymer, which does not have carbon-carbon double bond, can be quenched by electron-deficient unsaturated nitriles and esters, clarifying that the electron-deficient carbon-carbon double bond does play an important role for the fluorescence quenching of the monomer. Thus, we term such phenomena as structural self-quenching effect, differing from the concentrational self-quenching effect, which is caused mainly by concentrational factors. The fluorescence quenching of P(APO) by C 60 has also been demonstrated. The formation of the charge transfer complex of P(APO) with C 60 in the ground state is revealed by the upward deviation from the linearity of the Stern-Volmer plot. APO can act as a photoinitiator to sensitize the photopolymerization of vinyl monomers such as acrylonitrile in dimethyl formamide and pursued kinetically. From the ultraviolet analysis of the PAN sensitized by APO, it is proved that APO not only sensitizes the photopolymerization of AN, but also incorporates in the PAN chain.

Vinyl monomers bearing chromophore moieties and their polymers. VII. Synthesis, photochemical, and initiation behavior of acrylic monomers bearing phenothiazine oxide moieties and their polymers

Four acrylic monomers bearing phenothiazine oxide moieties, that is, N-acryloyl-phenothiazine-5-oxide (APTO), N-acryloyl-2-chlorophenothiazine-5-oxide (ACPTO), N-acryloyl-phenothiazine-5,5-dioxide (APTDO), and N-acryloyl-2-chlorophenothiazine-5,5-dioxide (ACPTDO) were synthesized by oxidation of corresponding N-acryloyl-phenothiazine (APT) and N-acryloyl-2-chlorophenothiazine (ACPT) using sodium perborate as an oxidant. These monomers could easily be polymerized by initiation of AIBN. The emission fluorescence spectra of the monomers and their polymers were recorded, and the results indicated that these 4 new monomers possess a fluorescence structural self-quenching effect (SSQE), as we have reported previously. Moreover, with the change of the electronic structure of sulfur atom in the phenothiazine chromophore, that is, from sulfide to sulfoxide and sulfone groups, the tendency of SSQE of these monomers is in the order of APT > APTO > APTDO. This would be ascribed mainly to the decrease of electron-donating abilities of monomers in a sequence of sulfide, sulfoxide, and sulfone groups; that is, at the sulfur atom of these monomers, APT has 2 lone-pair electrons, APTO has 1 lone-pair electrons, and APTDO completely loses its lone-pair electrons. Based on the exciplex formation, the monomers APTO, APTDO, ACPO, and ACPTDO could act as sensitizers for the photopolymerization of acrylonitrile (AN). The combination of APTO or ACPTO with organic peroxides such as BPO could also initiate the polymerization of vinyl monomers, such as AN, by redox nature.

Vinyl monomers bearing chromophore moieties and their polymers. IX. Initiation and photochemical behavior of water and liposoluble acrylic monomers having pyrimidinyl moiety and their polymers

Two acrylic monomers bearing a pyrimidinyl moiety, N-acryloyl-N′-2-pyrimidinylpiperazine (APMP) and N-methacryloyl-N′-2-pyrimidinylpiperazine (MPMP), are prepared by reactions of N-2-pyrimidinylpiperazine with corresponding acryloyl chlorides in the presence of triethylamine. APMP and MPMP can be polymerized either by using radical initiators such as azobisisobutylonitrile or potassium persulfate (KPS) or by UV light irradiation without any sensitizer. APMP, MPMP, and their polymers are water soluble and liposoluble. They can act as sensitizers to initiate the photopolymerizations of acrylonitrile (AN) in DMF and acrylamide (AAm) or N-acryloylmorpholine (AMPL) in an aqueous medium. They can also act as one component of a redox initiation system by combining with KPS to initiate the polymerization of AAm in an aqueous medium, and a superhigh molecular weight up to 106–107 for P(AAm) or 105–106 for P(AMPL) is obtained. The above polymerizations are pursued kinetically. The mechanism of the photopolymerizations initiated by MPMP or P(MPMP) are confirmed by an electron spin resonance study. By the fluorescent analysis of PAN and P(AAm) initiated by MPMP, APMP, or their polymers we confirm that they not only initiate the polymerization but also enter the polymer chains. The fluorescence spectra of MPMP, APMP, and their polymers are recorded. A fluorescence structural self-quenching effect is also observed. The fluorescence of P(MPMP) can be quenched by adding electron-deficient unsaturated compounds such as methacrylonitrile, AN, fumaronitrile, tetracyanoethylene, methyl acrylate, and methyl methacrylate and the correlation between the Stern–Volmer constants and the electron deficiency of the quenchers is described. The fluorescence quenching of P(MPMP) by a water-soluble C60 derivative is also demonstrated.