Thermo- and pH-sensitive comb-type grafted poly(N,N-diethylacrylamide-co-acrylic acid) hydrogels with rapid response behaviors

Poly(N,N-diethylacrylamide) with a terminal hydroxyl end group (PDEA-OH) was synthesized by radical telomerization of N,N-diethylacrylamide (DEA) monomer using 2-hydroxyethanethiol as a chain transfer agent. Macromonomer of thermo-sensitive PDEA was synthesized by condensation reaction of PDEA-OH with acryloyl chloride. The macromonomer was characterized by FTIR and ¹H NMR, and the molecular weight was determined by GPC. Thermo- and pH-sensitive comb-type grafted poly(N,N-diethylacrylamide-co-acrylic acid) (PDEA-co-AA) hydrogels (GHs) were successfully prepared by grafting PDEA chains with freely mobile ends onto the backbone of a cross-linked (PDEA-co-AA) network. The results showed that the deswelling behavior of the hydrogels was dependent on the test temperature. At 45 °C (beneath the VPTT of the hydrogels), both the normal-type hydrogels (NHs) and comb-type grafted P(DEA-co-AA) hydrogels had lower deswelling rates. While at 60 °C (far beyond the VPTT of the hydrogels), the deswelling rates of the GHs were faster than that of the NHs. Furthermore, pulsatile stimuli-responsive studies indicated that the GHs had excellent thermo-reversibility and were superior to the NHs in the magnitude of their swelling ratios to temperature changes. However, the reversibility to pH changes was poor for both the NHs and the GHs.     

Synthesis and phase separation of amine-functional temperature responsive copolymers based on poly(N-isopropylacrylamide)

Free radical copolymerizations of N-isopropyl acrylamide (NIPAM) and cationic N-(3-aminopropyl) methacrylamide hydrochloride (APMH) were investigated to prepare amine-functional temperature responsive copolymers. The reactivity ratios for NIPAM and APMH were evaluated in media of different ionic strength (r_NIPAM = 0.7 and r_APMH = 0.7-1.2). Phase separation behavior of the random copolymers with only 5 mol% of the APMH was found to be suppressed in pure water at temperatures up to 45 °C due to electrostatic repulsion among the cationic amine groups randomly distributed along the copolymer chain. Alternate sequential addition of PNIPAM/APMH mixtures and pure NIPAM was used to provide increased control of the location of APMH units along the chain. Consequently (close to) homo-PNIPAM block(s) were formed as evidenced by its characteristic phase transition at 33 °C. The influences of the monomer feeding time and feeding interval time to the APMH distribution were investigated to prepare copolymers with thermo-induced phase separation under physiologically relevant temperature and to determine the extent of conjugation to poly(ethylene oxide).     

Poly(2-N-carbazolylethyl acrylate)-modified silica as a new polymeric stationary phase for reversed-phase high-performance liquid chromatography

Poly(2-N-carbazolylethyl acrylate) having terminal trimethoxysilyl groups was newly synthesized by radical polymerization and immobilized onto the silica surface (Sil-CEA). The chromatographic property of Sil-CEA was examined by applying polycyclic aromatic hydrocarbons as solutes. Poly(4-vinylpyridine)-modified silica (Sil-VP) and monomeric octadecylated silica (ODS) columns were used as the reference columns. Less sensitivity to molecular hydrophobicity and enhanced molecular planarity selectivity were obtained with Sil-CEA compared to ODS. On the other hand, high retention factors for the analyzed solutes and an opposite elution order for linear and disc-shaped solutes were obtained with Sil-CEA compared with Sil-VP. In this paper, the application for separation of tocopherols was also described.     

Synthesis of 9-arylamino- and (Z)-9-arylimino-9H-pyrrolo[1,2-a]indoles by reactions of 2-(pyrrol-1-yl)benzaldehydes with aryl amines

Heating mixtures of 2-(pyrrol-1-yl)benzaldehydes and aryl amines under argon afforded 9-arylamino-9H-pyrrolo[1,2-a]indoles, via cyclization of the resulting 2-(pyrrol-1-yl)benzaldimine intermediates. Heating in the presence of oxygen afforded (Z)-9-arylimino-9H-pyrrolo[1,2-a]indoles, which were successfully hydrolyzed with hydrochloric acid to give pyrrolo[1,2-a]indol-9-ones.     

Random copolymers of N-isopropylacrylamide and methacrylic acid monomers with hydrophobic spacers: pH-tunable temperature sensitive materials

Two series of random copolymers of N-isopropylacrylamide (NIPAAm) and comonomers derived from methacrylic acid with a different number of methylene units as hydrophobic spacers (n=4, 7 and 10) were synthesized via free radicals. The first series was prepared having the acid groups methoxy-protected while the second series have the acid groups free. The NIPAAm-copolymers of both series were prepared varying the comonomer content from 5 to 20 mol%. All the copolymers were characterized by FTIR, DSC, ¹H NMR and SLS. The aqueous solution behaviour of the copolymers having methoxy-protected acid groups shows that the comonomer increases the hydrophobicity of the copolymer chain and decreases its lower critical solution temperature (LCST). For the copolymers having free acid groups, hydrogen-bonding is responsible for a further decrease in the LCST of these copolymers in pure water. In buffer solutions, every acid comonomer have a critical ionization degree (α_crit) above which the LCST increases with increasing comonomer content while at an ionization degree lower than α_crit the LCST decreases with increasing comonomer content. In dependence of comonomer content, number of methylene units in the spacer and the pH of the buffer solution, the LCST of the copolymers can be varied widely, showing that these random copolymers have pH-tunable temperature sensitivity.     

Synthetic studies of erythromycin derivatives: 6-O-methylation of (9S)-12,21-anhydro-9-dihydroerythromycin A derivatives

Synthetic studies on methylation of erythromycin derivatives were conducted. Methylation of 6 resulted in the formation of the C-3′ quaternary ammonium salts with a rate faster than 6-O-methylation. In dipolar aprotic solvent and under strong base conditions, 6-O-methylation, C-3′ quaternary ammonium salts formation and 2-C-methylation proceeded simultaneously to yield a mixture of three different products 7, 8 and 9. The quaternary ammonium salts were converted back to the corresponding tertiary amines 2, 10 and starting material 6 by employing sodium 4-pyridinethiolate as a N-demethylation reagent. The 6-O-methylation was eventually achieved in a good yield when a carbobenzyloxy (Cbz) group was utilized to protect the C-3′-dimethylamino group of 4. In this report, we will discuss the details of different reaction courses in the methylation of (9S)-12, 21-anhydro-9-dihydroerythromycin A derivatives.     

Complexation between poly(N,N-diethylacrylamide) and poly(acrylic acid) in aqueous solution

The complexation between poly(N,N-diethylacrylamide) (PDEA) and poly(acrylic acid) (PAA) in aqueous solution was studied by viscometric, potentiometric, and fluorescence techniques. It was found that an interpolymer complex formed between the two polymers through hydrogen bonding interactions with the stoichiometry of r=0.6 (r is unit molar ratio of PAA/PDEA), and the complex formation show the dependence on pH values. The phase behaviour studies showed that the lower critical solution temperature of the PDEA-PAA aqueous solution gradually increased with the increasing of r from 0.01 to 0.15, until a soluble system in the whole temperature region was obtained, which remained in the range of r=0.15-0.3. At higher PAA concentrations, when r is above 0.3, the system appeared phase separation, and almost no temperature dependence was observed. Based on these conclusion and structure characteristics of PDEA and PAA, a model containing only short sequences of monomer residues was proposed for the structure of PDEA-PAA complex.     

Novel water-soluble fluorescent polymer containing recognition units: Synthesis and interactions with PC12 cell

New water-soluble fluorescent poly(N-vinylpyrrolidone) (PVP) containing carbonylhydrazide recognition units was synthesized by free radical polymerization of N-vinylpyrrolidone in the presence of mercaptoacetic acid as chain transfer agent and then being modified by 1-pyrenebutyric acid hydrazide. FT-IR, ¹H NMR, gel permeation chromatography-multi-angle laser light scattering and fluorescence spectroscopy were used to characterize these polymers. Results of fluorescence measurements show that these polymers have a good affinity for deoxyribonucleic acid (DNA). The interactions with PC12 cell results indicated that the polymer with suitable molecular weight could penetrate into PC12 cell and emit fluorescence. This water-soluble polymer with recognition units and high luminescence can be used as a promising fluorescent probe for measurements of biomacromolecules and cells.     

Thermosensitive poly(N-isopropylacrylamide-co-acrylamide) hydrogels: Synthesis, swelling and interaction with ionic surfactants

Thermosensitive hydrogels were prepared by free-radical polymerization in aqueous solution from N-isopropylacrylamide (NIPA) and acrylamide (AAm) monomers. N,N-Methylenebis(acrylamide) (MBAAm) was used as a crosslinker. A kinetic study of the absorption determined the transport mechanism. The diffusion coefficients of these hydrogels were calculated for the Fickian mechanism. It was shown that the swelling behavior of the P(NIPA-co-AAm) hydrogels can be controlled by changing the amount of MBAAm. The swelling equilibrium of the P(NIPA-co-AAm) hydrogels was also investigated as a function of temperature in aqueous solutions of the anionic surfactant sodium dodecyl sulfate (SDS) and the cationic surfactant dodecyltrimethylammonium bromide (DTAB). In SDS and DTAB solutions, the equilibrium swelling ratio of the hydrogels increased, this is ascribed to the conversion of non-ionic P(NIPA-co-AAm) hydrogel into polyelectrolyte hydrogels due to binding of surfactant molecules through the hydrophobic interaction. Additionally, the amount of free SDS and DTAB ions was measured at different temperatures by a conductometric method, it was found that the electric conductivity of the P(NIPA-co-AAm)—surfactant systems depended strongly on both the type and concentration of surfactant solutions.     

Study on interaction between Tb(III) and poly(N-isopropylacrylamide)

A new kind of the thermo-sensitive and fluorescent complex of poly(N-isopropylacrylamide) (PNIPAM) and Tb(III) was synthesized by free radical polymerization, in which PNIPAM was used as a polymer ligand. The complex was characterized by using X-ray photoelectron spectroscopy (XPS), ultraviolet-visual (UV), Fourier transform infrared (FT-IR) and fluorescence spectroscopy. The results from the experiments indicated that there is a strong interaction between PNIPAM and Tb(III), leading to a decrease in the electron density of nitrogen and oxygen atoms and an increase in the electron density of Tb(III) in the PNIPAM containing Tb(III) by contrast with PNIPAM and Tb(III), respectively, meanwhile, exhibiting that the Tb(III) is mainly bonded to oxygen atoms in the polymer chain of PNIPAM and formed the complex of PNIPAM-Tb(III). After forming the PNIPAM-Tb(III) complex, the emission fluorescence intensity of Tb(III) in the PNIPAM-Tb(III) complex is significantly enhanced because the effective intramolecular energy transfer from PNIPAM to Tb(III). Especially, the emission intensity of the fluorescence peak at 547 nm can be increased as high as 145 times comparing with that of the pure Tb(III). The intramolecular energy transfer efficiency for fluorescence peak at 547 nm can reach as high as 68%. The fluorescence intensity is related the weight ratio of Tb(III) and PNIPAM in the PNIPAM-Tb(III) complex. When the weight ratio is 1.4%, the maximum fluorescence enhancement can be obtained. Nevertheless, the lower critical solution temperature of PNIPAM containing a low content of Tb(III) has not obviously changed after the formation of the complex of PNIPAM-Tb(III) by the interaction between PNIPAM and Tb(III). This novel thermosensitive and fluorescence characterization of the PNIPAM-Tb(III) complex may be useful in the fluorescence systems and the biomedical field.     

Synthesis and characterization of thermoresponsive isopropylacrylamide-acrylamide hydrogels

In this study, hydrogels of poly(N-isopropylacrylamide-co-acrylamide) having a thermoresponsive character were prepared by a redox polymerization method. NIPAM-co-AAm hydrogels with different thermoresponsive properties were obtained by changing the initial NIPAM/AAm mole ratio and crosslinker concentration.Equilibrium-swelling ratio, dynamic swelling ratio and dynamic deswelling ratio were evaluated for all hydrogel systems. The fast shrinking was observed with all gels. The time required for equilibrium shrinking increased with the increase of acrylamide content in the gel.     

The synthesis, characterisation, phase behaviour and swelling of temperature sensitive physically crosslinked poly(1-vinyl-2-pyrrolidinone)/poly(N-isopropylacrylamide) hydrogels

Physically crosslinked complexes of polyvinyl pyrrolidinone-poly (N-isopropylacrylamide) (PVP-PNIPAAm) were prepared by photopolymerisation from a mixture of the monomers 1-vinyl-2-pyrrolidinone and N-isopropylacrylamide. IR spectroscopy and calorimetry were used to characterise the resulting xerogels. By alternating the monomer feed ratio, copolymers were synthesised to have their own distinctive lower critical solution temperature (LCST). The transition temperature of the gels was established using cloud point measurement and modulated differential scanning calorimeter (MDSC). This ability to shift the phase transition temperature of the copolymers provides excellent flexibility in tailoring transitions for specific uses. Swelling experiments were performed on the copolymer disks in distilled water at varying temperatures to establish the behaviour of the gels above and below phase transition temperature. The results obtained show that below transition temperature, the gels are water soluble but above this temperature they are slightly less water soluble; significantly less water soluble; or water insoluble; depending on the composition and LCST of the gel.     

Synthesis and in vitro antitumor activity of phthalimide polymers containing podophyllotoxin

Polymer-linked PT (podophyllotoxin) conjugates have been designed to improve the therapeutic efficacy of PT. A new PT-conjugate, 3,6-endo-methylene-1,2,3,6-tetrahydrophthalimido-acetamidoglycinylglycine podophyllotoxin ester (ETPA-gly-gly-PT), was synthesized by covalently coupling its hydroxyl group onto the phthalimido monomer through a glycine-glycine-glycine spacer. Its homo- and copolymer with acrylic acid (AA) were prepared by photopolymerization using 2,2-dimethoxy-2-phenylacetophenone (DMP) as a photoinitiator. ETPA-gly-gly-PT and its polymers were characterized by IR and proton NMR spectra. The ETPA-gly-gly-PT content in the copolymer obtained by elemental analysis was 44 wt%. The number-average molecular weights of the polymers determined by gel permeation chromatography were as follows: M_n = 13,500 for poly(ETPA-gly-gly-PT), M_n = 17,000 for poly(ETPA-gly-gly-PT-co-AA). The in vitro antitumor activity of these conjugates and polymers were determined and used to evaluate the potential applications in antitumor drugs. The IC₅₀ values indicated that the synthesized ETPA-gly-gly-PT and its polymers against cancer cells were much better inhibitors than PT.     

Study on interaction between Tb(III) and poly(N-isopropylacrylamide)-g-poly(N-isopropylacrylamide-co-styrene) core-shell nanoparticles

Based on the synthesis of poly(N-isopropylacrylamide-co-styrene) P(NIPAM-co-St) and poly(N-isopropylacrylamide) (PNIPAM) grafted P(NIPAM-co-St) core-shell nanoparticle, a new kind of thermoresponsive and fluorescent complex of Tb(III) and PNIPAM-g-P(NIPAM-co-St) (PNNS) was successfully prepared. The PNNS-Tb(III) complex was characterized with the different techniques. It was found that when PNNS with the core-shell structure interact with Tb(III), Tb(III) mainly bonded to O of the carbonyl groups of PNNS, forming the novel PNNS-Tb(III) complex. After forming the complex, the emission fluorescence intensity of Tb(III) in the complex is significantly enhanced. Especially, the maximum emission intensity of the PNNS-Tb(III) complex at 545 nm is enhanced about 223 times comparing to that of the pure Tb(III) because the effective intramolecular energy transfer from PNNS to Tb(III). The intramolecular energy transfer efficiency from PNNS to Tb(III) reaches 50%. The fluorescence intensity is related the weight ratio of Tb(III) and PNNS in the PNNS-Tb(III) complex. When the weight ratio of Tb(III) and the PNNS is 12 wt%, the enhancement of the emission fluorescence intensity at 545 nm is highest. This novel fluorescence characterization of the PNNS-Tb(III) complex may be useful in the fluorescence systems and the biomedical field.     

Characterization of N-vinyl carbazole/vinyl 4-tert-butyl-benzoate copolymers of several molar compositions: SEC, DSC and intramolecular excimers in dilute solutions

Several N-vinylcarbazole/vinyl p-tert-butyl-benzoate copolymers of different molar monomer compositions and their respective homopolymers have been synthesized by free-radical polymerization. Their solution properties were characterized by size-exclusion chromatography (SEC) coupled with a differential refractive index (RI) and multiangle light scattering (MALS). Differential scanning calorimetry (DSC) was also used to investigate the glass transition temperatures, T_g. In addition, steady-state fluorescence emission spectra in a dilute solution of several fluid and non-fluid solvents were obtained to study the influence of monomer composition on the intramolecular carbazole excimer formation. The amount of excimers strongly depends on the solvent nature and copolymer composition. Molecular Dynamics (MD) simulations on iso- and syndiotactic homopolymer and copolymer fragments were used to obtain the probability of the conformations that satisfy excimer requirements. The analysis of the MD trajectories allows us to evaluate the amount and types of intramolecular excimers for the different systems.     

Self-assembly of homopolymer and copolymers of N-4-hydroxyphenyl-acrylamide with diazoresin via H-bonding attraction

A kind of photoactive multilayer utrathin films has been fabricated via H-bonding attraction from hydroxyphenyl containing polymers as H-donor and diazoresin (DR) as H-acceptor by means of a self-assembly technique. The layer-by-layer deposition of two components is monitored spectrometrically and shows that the UV-VIS absorbance of the film increases linearly both at 250 nm (absorption of benzene nucleus) and at 383 nm (absorption of diazonium group), which indicates that the fabrication proceeds regularly. The nature of H-bonding between layers was verified by the determination of IR spectra of the film fabricated directly on a CaF₂ wafer. The stability of the films toward polar solvents increases dramatically after UV irradiation of the films. It was confirmed provisionally that the bond nature between the layers of the film changes from H-bonding to covalent bonding under UV irradiation. The photodecomposition of the -N₂⁺ groups of the film under UV light follows first order reaction kinetics and a mechanism of the photoreaction has been tentatively proposed.     

Effect of initial monomer concentration on the equilibrium swelling and elasticity of hydrogels

The linear swelling ratio α and the effective network chain length N of a series of poly(N,N-dimethylacrylamide) (PDMAAm) hydrogels were investigated as a function of the gel preparation concentration . PDMAAm hydrogels were prepared at a fixed cross-linker ratio but at various initial monomer concentrations. It was found that α is not a monotonic function of . As is increased, α first decreases up to about and remains constant in a narrow range of , but then it increases continuously. The -dependence of α is due to the variation of the network chain length N depending on the gel preparation concentration. In the range of below 0.1, N follows the scaling relationship , while at higher concentrations, N varies only slightly with . The increase of α with N obeys the relation , as predicted by the Flory-Rehner theory.     

Syntheses of (±)-9-epi-hederacine A and (±)-9-epi-hederacine B

Racemic syntheses of 9-epi-hederacine A and 9-epi-hederacine B have been achieved. Key transformations include a transannular hemiaminal formation for construction of the azabicyclo[3.2.1]octane core fused to a cyclopentane ring.     

Synthesis of 2-N-alkyl(aryl)amino-7-nitrobenzothiazoles

A highly efficient synthesis of 2-N-alkyl(aryl)amino-7-nitrobenzothiazoles has been developed. The key step involves intramolecular cyclization of a thiourea facilitated by the nitro group.     

Photophysical properties of PPP and PPV derivatives bearing polystyrene or polycaprolactone as side groups

This contribution reports on detailed photophysical investigations of poly(p-phenylene) PPP and poly(p-phenylene-vinylene) (PPV) derivatives laterally decorated with polystyrene (PPV-PSt) or poly(ε-caprolactone) (PPP-PCL, PPP-altPCL, PPV-PCL and PPV-PCL-Br). The polymers emit blue and exhibit very high relative and absolute photoluminescence quantum yield, Φ_f, in dilute solution, thin film (spin-coated and inkjet-printed) and bulk state. This is ascribed to the presence of the lateral macromolecules, which suppress the strong π-π interactions and consequently excimers formation. Lower Φ_f value was obtained for the bromine containing polymer and its corresponding model compound dibromodistyrylbenzene Br₂-DSB, which was ascribed to heavy atom effect enabling intersystem crossing from S₁ to T₁. However, studies at 77 K did not reveal phosphorescence, in contrast an enhancement of the fluorescence intensity with respect to room temperature measurement was observed.