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 78,556 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We report the synthesis and characterization of DNA-grafted poly(N-isopropylacrylamide) (PNIPAM) micelles, their assembly into multilayered thin films, and the subsequent generation and poly(ethylene glycol) (PEG) functionalization of DNA-PNIPAM microcapsules. Multilayer films were assembled by sequentially depositing DNA-grafted PNIPAM micelles containing the cDNA sequences polyA(30) or polyT(30) (i.e., PNIPAM-A(30) or PNIPAM-T(30)). DNA-polymer microcapsules were obtained by the alternate deposition of PNIPAM-A(30) and PNIPAM-T(30) onto silica particles, followed by removal of the template core. Upon removal of the silica core particle, shrinkage of between 30 and 50% was observed for the microcapsules. The presence of PNIPAM within the DNA-polymer hybrid film reduces the permeability of the microcapsules to macrosolutes (e.g., dextran) compared with microcapsules made solely of DNA. The hydrophobic core of the DNA-grafted PNIPAM micelles was designed to contain alkyne "click" groups, which were exploited to covalently couple azide-bearing low-fouling PEG to the DNA-PNIPAM microcapsules. The combination of hydrophobic and reactive "click" nanodomains, along with the degradability of DNA, offers a multifunctional and versatile DNA-polymer capsule system that is envisioned to find applications in the controlled delivery of therapeutics.
ACS Nano 2009 Jan 27
PMID:Assembly and functionalization of DNA-polymer microcapsules. 1920 71

An amphiphilic tris(dibenzoylmethanato)europium(III) (Eu(DBM)(3)) coordinated P(MMA-co-EIPPMMA)-co-P(NIPAAm-co-NDAPM) copolymer was synthesized, which exhibited good biocompatibility and emitted strong red luminescence (MMA, methyl methacrylate; EIPPMMA, 4-(1-ethyl-1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)phenyl methacrylate; NIPAAm, N-isopropylacrylamide; NDAPM, (N-(3-dimethylamino)propyl)methacrylamide). The copolymer could self-assemble into micelles of size around 260 nm, and the micelles were thermosensitive at around body temperature. The drug-loaded micelles showed thermosensitive controlled drug release, and the paclitaxel loaded micelles were capable of being internalized into the tumor cells (A549) and exhibited obvious inhibition to the growth of A549 cells. Importantly, in vivo study showed the self-assembled micelles of Eu(DBM)(3) coordinated P(MMA-co-EIPPMMA)-co-P(NIPAAm-co-NDAPM) copolymer uptaken by the larvae of zebrafish could be easily tracked and be eliminated from the body within several days.
ACS Nano 2008 Jan
PMID:Cellular internalization and in vivo tracking of thermosensitive luminescent micelles based on luminescent lanthanide chelate. 1920 56

Novel colloidal composites have been designed to incorporate multiple functionalities that allow optical detection, magnetic manipulation, molecular trapping, and thermal response. Such particles are made of gold nanoparticle cores covered by a thin layer of metallic nickel and a poly(N-isopropylacrylamide) (pNIPAM) shell. While the gold cores provide efficient optical response through localized surface plasmon resonances, nickel allows external magnetic manipulation and the pNIPAM shell can be swollen or collapsed as a function of temperature, thus allowing capture and release of various types of molecules.
ACS Nano 2009 Oct 27
PMID:Synthesis of multifunctional composite microgels via in situ Ni growth on pNIPAM-coated Au nanoparticles. 1976 39

We report on reversible temperature-triggered swelling transitions in hydrogen-bonded multilayer films of a polycarboxylic acid and stimuli-responsive block copolymer micelles (BCMs). A neutral hydrogen-bonding temperature-responsive diblock copolymer, poly(N-vinylpyrrolidone)-b-poly(N-isopropylacrylamide) (PVPON-b-PNIPAM), was synthesized by macromolecular design via the interchange of xanthates (MADIX). The block copolymer exhibited reversible micellization, forming PNIPAM-core micelles with PVPON coronae in 0.01 M buffer solutions at temperatures higher than 34 degrees C, or in solutions with high salt concentrations (C(NaCl) > 0.4 M) at 20 degrees C. The PVPON-b-PNIPAM BCMs were then assembled with poly(methacrylic acid) (PMAA) at acidic pH and higher temperature using the layer-by-layer (LbL) technique. Within the hydrogen-bonded multilayer, BCMs were stabilized through hydrogen bonding between PVPON and PMAA units and, unlike in solution, did not dissociate into unimers in low-salt solution at T < 34 degrees C. Instead, PVPON-b-PNIPAM BCMs reversibly swelled within film in response to temperature- or salt-concentration variations, reflecting collapse and dissolution of the BCM PNIPAM cores. The capacity of BCM/PMAA films to retain hydrophobic molecules was also dramatically dependent on temperature and/or ionic strength. The characteristic release time of pyrene from a [BCM/PMAA](10) film decreased from 80 to 10 min upon a decrease in temperature from 37 to 20 degrees C. In addition, at 20 degrees C, ionic strength was also capable of controlling the collapse of PNIPAM micellar cores and the subsequent film swelling and pyrene release rate. Incorporation of stimuli-responsive BCM micelles within LbL films opens new opportunities in designing nanoscale films capable of controlling molecular swelling, transport, and diffusion in response to environmental stimuli.
ACS Nano 2009 Nov 24
PMID:Temperature-induced swelling and small molecule release with hydrogen-bonded multilayers of block copolymer micelles. 1979 44

We demonstrate that the optical properties of gold nanoparticles can be used to detect and follow stimuli-induced changes in adsorbed macromolecules. Specifically, we investigate thermal response of anionic diblock and uncharged triblock copolymers based on poly(N-isopropylacrylamide) (PNIPAAM) blocks adsorbed onto gold nanoparticles and planar gold surfaces in a temperature range between 25 and 60 degrees C. By employing a palette of analytical probes, including UV-visible spectroscopy, dynamic light scattering, fluorescence, and quartz crystal microbalance with dissipation monitoring, we establish that while the anionic copolymer forms monolayers at both low and high temperature, the neutral copolymer adsorbs as a monolayer at low temperatures and forms multilayers above the cloud point (T(C)). Raising the temperature above T(C) severely affects the optical properties of the gold particle/polymer composites, expelling associated water and altering the immediate surroundings of the gold nanoparticles. This effect, stronger for the uncharged polymer, is related to the amount of polymer adsorbed on the surface, where a denser shell influences the surface plasmon band to a greater degree. This is corroborated with light scattering experiments, which reveal that flocculation of the neutral polymer-coated particles occurs at high temperatures. The flocculation behavior of the neutral copolymer on planar gold surfaces results in multilayer formation. The observed effects are discussed within the framework of the Mie-Drude theory.
ACS Nano 2010 Feb 23
PMID:Temperature-dependent optical properties of gold nanoparticles coated with a charged diblock copolymer and an uncharged triblock copolymer. 2007 33

A simple method for preparing solvent-resistant nanofibers with a thermal-sensitive surface has been developed by the combined technology of reversible addition-fragmentation chain-transfer (RAFT) polymerization, atom transfer radical polymerization (ATRP), electrospinning, and "click chemistry". Initially, well-defined block copolymers of 4-vinylbenzyl chloride (VBC) and glycidyl methacrylate (GMA) (PVBC-b-PGMA) were prepared via RAFT polymerization. Electrospinning of PVBC-b-PGMA from a solution in tetrahydrofuran gave rise to fibers with diameters in the range of 0.4-1.5 microm. Exposure to a solution of sodium azide (NaN(3)) not only affords nanofibers with azido groups on the surface but also leads to a cross-linking structure in the nanofibers. One more step of "click chemistry" between the PVBC-b-PGMA nanofibers with azido groups on the surface (PVBC-b-PGMA(-N3)) and alkyne-terminated polymers of N-isopropylacrylamide (NIPAM) (PNIPAM(AT)), which were prepared by ATRP, allows the preparation of a PVBC-b-PGMA nanofiber with thermal-sensitive PNIPAM brushes on the surface (PVBC-b-PGMA-g-PNIPAM). PVBC-b-PGMA-g-PNIPAM nanofibers exhibit a good resistance to solvents and thermal-responsive character to the environment, having a hydrophobic surface at 45 degrees C (water contact angle approximately 140 degrees) and having a hydrophilic surface at 20 degrees C (water contact angle approximately 30 degrees).
ACS Appl Mater Interfaces 2009 Feb
PMID:Smart nanofibers from combined living radical polymerization, "click chemistry", and electrospinning. 2035 8

A series of hydrogels containing a biodegradable dextran (Dex) chain grafted with a hydrophobic poly(-caprolactone)-2-hydroxylethyl methacrylate (PCL-HEMA) chain and a thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) chain were synthesized. The molecular weight of PCL-HEMA was determined by gel permeation chromatography, and the inner morphology of the hydrogel was observed by scanning electron microscopy. The release profiles from the hydrogels were investigated using bovine serum albumen as a model drug. It was found that the release behavior could be adjusted by varying the composition of the hydrogel. In vitro cytotoxicity studies of the hydrogels showed that the copolymer Dex-PCL-HEMA/PNIPAAm exhibited low cytotoxicity. The in vivo degradation and histological studies demonstrated that the hydrogels had good biocompatibility and were promising for use as an injectable polymeric scaffold for tissue engineering applications.
ACS Appl Mater Interfaces 2009 Feb
PMID:Toward the development of partially biodegradable and injectable thermoresponsive hydrogels for potential biomedical applications. 2035 19

Freestanding quasi-two-dimensional ultrathin films (e.g., 41 nm thick polymer nanosheets) were produced, on which stimuli-responsive 47 nm thick polymer brushes were constructed by atom transfer radical polymerization (ATRP) of poly(N-isopropylacrylamide). The resulting surfaces of the multilayered polysaccharide ultrathin films were evaluated by ellipsometry, IR imaging, in situ variable-temperature atomic force microscopy (AFM), and contact angle measurements. The morphological transformation of the freestanding polymer nanosheet bearing thermoresponsive polymer brushes was observed macroscopically through reversible structural color changes at the air-water interface. The dynamic shape change of the nanosheet was also monitored with the addition of a surfactant such as sodium n-dodecylsulfate to reduce the hydrophobicity of the surface. It was then demonstrated that the highly flexible freestanding polymer nanosheet is capable of acting as a unique platform for inducing stimuli-responsive behavior in nanomaterials.
ACS Appl Mater Interfaces 2009 Jul
PMID:Hydrodynamic transformation of a freestanding polymer nanosheet induced by a thermoresponsive surface. 2035 42

Four series of poly(N-isopropylacrylamide) (PNIPAM) (core)/poly(N-isopropylacrylamide-co-3-acrylamidophenylboronic acid) (P(NIPAM-AAPBA)) (shell) microgels were synthesized by the modification of PNIPAM (core)/poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPAM-AA)) (shell) microgels with 3-aminophenylboronic acid (APBA). Their thermosensitive behaviors were studied by dynamic light scattering. Two or three phase transitions were detected depending on the shell thickness. These transitions were confirmed by the first derivative plot of the turbidity data. The first transition occurring at about 17 degrees C was assigned to that of the P(NIPAM-AAPBA) shell, whereas the second and third ones, which occur at about 22 and 28 degrees C, respectively, were assigned to that of the PNIPAM core. These results indicate that the influences of a shrunk P(NIPAM-AAPBA) shell on the different parts of the PNIPAM core are different. As the outer part, or the "shell" part of the PNIPAM core, directly connects with the P(NIPAM-AAPBA) shell, its phase transition temperature is reduced to a larger degree as compared with that of the inner part, or the "core" part. Glucose-induced swelling was observed for all the microgels, indicating their glucose-sensitivity. However, the degree of glucose-induced swelling is much smaller than that of the pure P(NIPAM-AAPBA) microgels.
ACS Appl Mater Interfaces 2010 Mar
PMID:Thermally induced phase transition of glucose-sensitive core-shell microgels. 2035 78

For developing thermoresponsive chromatographic matrices with a strong hydrophobicity, poly(N-isopropylacrylamide-co-n-butyl methacrylate) (poly(IPAAm-co-BMA)) brush grafted silica beads were prepared through a surface-initiated atom transfer radical polymerization (ATRP) with a CuCl/CuCl(2)/Me(6)TREN catalytic system in 2-propanol at 25 degrees C for 16 h. The prepared beads were characterized by chromatographic analysis. Chromatograms of the benzoic-acid family and phenol as model analytes were obtained with high-resolution peaks because of their strong hydrophobic interactions to the densely grafted hydrophobized copolymers on the beads. Retention times of the analytes increased with the increase in BMA composition ratio. Dehydration of grafted copolymer with large BMA composition was performed at low temperature. These results indicated that the copolymer-brush-grafted surface prepared by ATRP was an effective tool for separating hydrophilic analytes at low temperature through modulating the strong hydrophobic interaction.
ACS Appl Mater Interfaces 2010 Apr
PMID:Thermoresponsive polymer brush surfaces with hydrophobic groups for all-aqueous chromatography. 2038 Mar 88


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