Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Poly T”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 163 records · Page 9Linked to original sources
PubMed1990

Netropsin binding to poly[d(IC)].poly[IC)] and poly[d(GC].poly[d(GC)]: a computer simulation.

The thermodynamic cycle perturbation approach has been used to calculate the difference in the free energy of binding of netropsin to two different DNA molecules. In the computer simulations, all the inosine residues have been gradually 'mutated' into guanosine in a DNA dodecamer and in a complex of the same dodecamer with netropsin. The difference in binding free energy of about 4.3 kcal mol-1 agrees well with the experimentally determined value of 4.0 kcal mol-1. One structural determinant of the specificity seems to be the width of the minor groove in the two complexes.

Guanidines↗
PubMed2002

Preparation, characterization, and drug release behaviors of drug nimodipine-loaded poly(epsilon-caprolactone)-poly(ethylene oxide)-poly(epsilon-caprolactone) amphiphilic triblock copolymer micelles.

Amphiphilic triblock copolymers, poly(epsilon-caprolactone)-poly(ethylene oxide)-poly(epsilon-caprolactone) (PCL-PEO-PCL), were synthesized by ring opening polymerization of epsilon-caprolactone initiated with the hydroxyl functional groups of poly(ethylene glycol) at both ends of the chain. The micelles composed of this type of copolymer had such a structure that both ends of the PEO chain were anchored to the micelle. The critical micelle concentration of the block copolymer in distilled water was determined by a fluorescence probe technique using pyrene. As the hydrophobic components of the block copolymer increased, the critical micelle concentration value decreased. To estimate the feasibility as novel drug carriers, the block copolymer micelles were prepared by precipitation of polymer from acetone solution into water. From the observation of transmission electron microscopy, the micelles exhibited a spherical shape. Nimodipine was incorporated into the hydrophobic inner core of micelles as a lipophilic model drug to investigate the drug release behavior. The PEO/PCL ratio of copolymer was a main factor in controlling micelle size, drug-loading content, and drug release behavior. As PCL weight ratio increased, the micelle size and drug-loading content increased, and the drug release rate decreased.

Calcium Channel Blockers↗
PubMed2005

Synthesis and drug release behavior of poly (trimethylene carbonate)-poly (ethylene glycol)-poly (trimethylene carbonate) nanoparticles.

ABA-type triblock copolymers poly (trimethylene carbonate)-poly (ethylene glycol)-poly (trimethylene carbonate) were synthesized by ring-opening polymerization of trimethylene carbonate initiated by dihydroxyl poly (ethylene glycol). The critical micelle concentration of amphiphilic triblock copolymers in aqueous solution was determined by fluorescence spectroscopy using 9-chloromethyl anthracene as fluorescence probe. Core-shell-type nanoparticles were prepared by the dialysis technique. Transmission electron microscopy images showed that these nanoparticles were regularly spherical in shape. Micelle size determined by dynamic light scattering is 50-160 nm. Anticancer drug methotrexate (MTX) as model drug was loaded in the polymeric nanoparticles. X-ray powder diffraction spectra showed that model drugs were molecularly dispersed in the core. In vitro release behavior of MTX was investigated.

Antineoplastic Agents↗
PubMed2006

Poly(trimethylene carbonate) and monomethoxy poly(ethylene glycol)-block-poly(trimethylene carbonate) nanoparticles for the controlled release of dexamethasone.

In this study, single emulsion and salting out methods were employed to prepare poly(trimethylene carbonate) (PTMC) and monomethoxy poly(ethylene glycol)-block-poly(trimethylene carbonate) (mPEG-PTMC) nanoparticles. Well-defined nanoparticles of a PTMC homopolymer were prepared using poly(vinyl alcohol) (PVA) as a stabilizer. The average size of the nanoparticles can be adjusted by varying the stirring speed and polymer concentration. These particles can be readily freeze-dried and redispersed, with little influence on the average particle size and size distribution. Nanoparticles based on amphiphilic mPEG-PTMC can be prepared without an additional stabilizer. In this case, the size of the obtained nanoparticles did not vary much and ranged between 95 and 120 nm. These nanoparticles could be freeze-dried and redispersed as well. Using the salting out method, dexamethasone was loaded into PTMC and mPEG-PTMC nanoparticles at a highest efficiency of respectively 54% and 88%. With the single emulsion method, the loading efficiencies were, respectively, 91% and 72%. These drug-loaded particles were stable in time for at least 20 weeks. It was found that the release of dexamethasone from these nanoparticles was diffusion-controlled and could be sustained for 14 to 60 days. Depending on the nature of the polymer employed and the preparation method, dexamethasone diffusion coefficients varied between 4.8 x 10(-18) and 22.6 x 10(-18) cm(2)/s.

Anti-Inflammatory Agents↗
PubMed2001

Poly(ethylene glycol)-poly(L-lactide) diblock copolymer prevents aggregation of poly(L-lactide) microspheres during ethylene oxide gas sterilization.

Sterilization procedure is one of the most important obstacles in the clinical applications of biodegradable microspheres. The microspheres prepared with poly(alpha-hydroxy acid) were severely aggregated during ethylene oxide (EO) gas sterilization, and could not be used in clinical applications. In this study, the effects of EO gas sterilization on the poly(L-lactide) (PLLA) microspheres were analyzed by nuclear magnetic resonance spectroscopy (1H-NMR), differential scanning calorimetry (DSC), gel permeation chromatography (GPC), scanning electron microscope (SEM) and size fractionation. The aggregation between the microspheres might be stimulated by high mobility of amorphous regions of PLLA on the microsphere surfaces since both water vapor and gas mixture can reduce glass transition temperature (Tg) of PLLA below the sterilization temperature. During EO gas sterilization, there were no changes in the molecular structure and the molecular weight of PLLA in microspheres, but there were changes in the crystallinity of PLLA in microspheres. In this study, poly(L-lactide)-poly(ethylene glycol) diblock copolymers (PLE) were blended with PLLA homopolymers in various ratios to design the microsphere suitable for EO gas sterilization. Aggregation of PLLA microspheres was markedly prevented when more than 4wt% of PLE was blended in the microspheres. This inhibition effect on aggregation may be due to the increased initial crystallinity of the microspheres, which help to maintain the microsphere morphology during EO gas sterilization.

Calorimetry, Differential Scanning↗
PubMedDate not supplied

Small-angle X-ray scattering study of the interaction of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) triblock copolymers with lipid bilayers.

The relationship between molecular architecture and the nature of interactions with lipid bilayers has been studied for a series of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers using small-angle X-ray scattering (SAXS) and thermal analysis (differential scanning calorimetry, DSC). The number of molecular repeat units in the hydrophobic poly(propylene oxide), PPO, block has been found to be a critical determinant of the nature of triblock copolymer-lipid bilayer association. For dimyristoyl-sn-glycero-3-phosphocholine (DMPC)-based biomembrane structures, polymers possessing a PPO chain length commensurate with the acyl chain dimensions of the lipid bilayer yield highly ordered, swollen lamellar structures consistent with well-integrated (into the lipid bilayer) PPO blocks. Triblock copolymers of lesser PPO chain length yield materials with structural characteristics similar to a simple dispersion of DMPC in water. Increasing the concentration (from 4 to 12 mol %) of well-integrated triblock copolymers enhances the structural ordering of the lamellar phase, while concentrations exceeding 16 mol % result in the formation of a hexagonal phase. Examination of temperature-induced changes in the structure of these mesophases (complex fluids) reveals that if the temperature is reduced sufficiently, all compositions exclude polymer and thus exhibit the characteristic SAXS pattern for hydrated DMPC bilayers. Increasing the temperature promotes better insertion of the polymers possessing PPO chain lengths sufficient for membrane insertion. No temperature-induced structural changes are observed in compositions prepared with PEO-PPO-PEO polymers that feature PPO length insufficient to permit full incorporation into the lipid bilayer.

Biocompatible Materials↗
PubMedDate not supplied

Degradation behavior of poly(epsilon-caprolactone)-b-poly(ethylene glycol)-b-poly(epsilon-caprolactone) micelles in aqueous solution.

Poly(epsilon-caprolactone)-b-poly(ethylene glycol)-b-poly(epsilon-caprolactone) triblock copolymers were synthesized by the ring-opening polymerization of epsilon-caprolactone in the presence of hydroxyl-terminated poly(ethylene glycol) with different molecular weights, using stannous octoate catalyst. Micelles prepared by the precipitation method with these triblock copolymers exhibit a core-shell structure. The degradation behaviors of these core-shell micelles in aqueous solution were investigated by FT-IR, 1H NMR, GPC, DLS, TEM, and AFM. It was found that the degradation behavior of micelles in aqueous solution was quite different from that of bulk materials. The size of the micelles increased in the initial degradation stages and decreased gradually when the degradation period was extended. The caprolactone/ethylene oxide (CL/EO) ratio in micelles measured by NMR also shows an increase at the initial degradation stage and a decrease at later stages. The morphology of these micelles became more and more irregular during the degradation period. We explain the observed behavior by a two-stage degradation mechanism with interfacial erosion between the cores and the shells followed by core erosion.

Caproates↗
PubMedDate not supplied

L-Phe end-capped poly(L-lactide) as macroinitiator for the synthesis of poly(L-lactide)-B-poly(L-lysine) block copolymer.

A poly(L-lactide)-b-poly(Nepsilon-(Z)-L-lysine) (PLLA-b-PZLys) block copolymer was synthesized through the ring-opening polymerization of Nepsilon-(Z)-lysine-N-carboxyanhydride using L-Phe-terminated PLLA as a macroinitiator. The L-Phe-terminated PLLA was prepared through a novel three-step process. First, the hydroxyl-terminated PLLA was synthesized through the ring-opening polymerization of L-lactide initiated by n-butanol under the existence of tin(II) ethylhexanoate. Subsequently, the complete capping of the hydroxyl end group of PLLA with BOC-L-Phe was achieved by using a mixed anhydride of BOC-L-Phe under the catalysis of 4-(1-pyrrolidinyl) pyridine. Finally, the free amino end group was obtained by removal of the t-butoxycarbonyl group through trifluoroacetic acid treatment under anhydrous condition. All these treatments were conducted under mild conditions, thus avoiding the breakdown of the PLLA backbone. Poly(L-lactide)-b-poly(L-lysine) block copolymer was produced after deprotection treatment of PLLA-b-PZLys. The structure of the block copolymer was confirmed by 1H NMR, IR, and GPC. Adjustment of the ratio of the NCA monomer to the macroinitiator could control the chain length of the PLys block.

Biocompatible Materials↗