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 1,081 records · Page 60Linked to original sources
PubMed2001

Potential tuberculostatic agents: micelle-forming copolymer poly(ethylene glycol)-poly(aspartic acid) prodrug with isoniazid.

With the objective of obtaining slow-acting isoniazid derivatives, of potential use as chemoprophylactics or chemotherapeutics in tuberculosis, the micelle-forming copolymer of poly(ethylene glycol)-poly(aspartic acid) prodrug with isoniazid was synthesized. The derivative obtained was found to be active in Mycobacterium tuberculosis culture, with a minimal inhibitory concentration (MIC) 5.6 times lower than that of the tuberculostatic drug.

Antitubercular Agents↗
PubMed2004

Synthesis and characterization of poly(dimer acid-brassylic acid) copolymer and poly(dimer acid-pentadecandioic acid) copolymer.

Poly(dimer acid-brassylic acid) [P(DA-BA)] copolymers and poly(dimer acid-pentadecandioic acid) [P(DA-PA)] copolymers were prepared by melt polycondensation of the corresponding mixed anhydride prepolymers. The copolymers were characterized by Fourier transform infrared (FTIR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), wide angle x-ray powder-diffraction, and thermal gravimetric analysis (TGA). In vitro studies show that all the copolymers are degradable in phosphate buffer at 37 degrees C, and leaving an oily dimer acid residue after hydrolysis for the copolymer with high content of dimer acid. The release profiles of hydrophilic model drug, ciprofloxcin hydrochloride, from the copolymers, follow first-order release kinetics. All the preliminary results suggested that the copolymer might be potentially used as drug delivery devices.

Alkanes↗
PubMed2004

Titration of poly(dA-dT) . poly(dA-dT) in solution at variable NaCl concentration.

CD and uv absorption data showed that high molecular weight poly(dA-dT) . poly(dA-dT), at 298 K, undergoes an acid-induced transition from B-double helix to random coil in NaCl solutions of different concentrations, ranging from 0.005 to 0.600M. Similarly, titration of the polynucleotide with a strong base causes duplex-to-single strands transition. The base- and acid-induced transitions were both reversible by back-titration (with an acid or, respectively, with a base): the apparent pKa were the same in both directions. However, the number of protons per titratable site (adenine N1) required to reach half-denaturation was in great excess over the stoichiometric value; to a much larger extent, the same effect was observed also for the deprotonation of the N3H sites of thymine. Moreover, in the basic denaturation experiments, at low salt concentrations ([NaCl]< or =0.300M) less acid than calculated was needed to back-titrate the base excess to half-denaturation. Both effects could be qualitatively justified on the basis of the counterion condensation theory of polyelectrolytes and considering the energy barrier created by the negatively charged phosphodiester groups to the penetration of the OH- ions inside the double helix and the screening effect of the Na+ ions on such charges, in the deprotonation experiments.

Chemistry Techniques, Analytical↗
PubMed1989

Molecular mechanics studies on poly(purine).poly(pyrimidine) sequences in DNA: polymorphism and local variability.

Energy minimization has been carried out on three poly(purine).poly(pyrimidine) sequences--d(G)10.d(C)10, d(A)10.d(T)10, and d(AG)5.d(CT)5--using the molecular mechanics program AMBER (Assisted Model Building and Energy Refinement). In order to extensively scan the conformational space available, five different helical models were studied, three of them being right-handed helices while the other two were left helical. For all three sequences the right-handed A- and B-type helices are energetically slightly preferred over the left helices, but the energy difference between the various right-handed helices is only marginal. A detailed analysis has been carried out to characterize the local structural variability in the refined structures, both in terms of torsion angles as well as other parameters such as base-pair tilt, wedge roll, and wedge tilt, etc. All three sequences exhibit similar structural features for a particular form, but both the forms A and B show significant deviations from fiber models. In particular, the A-form structures have higher unit rise (2.7 A), and lower unit twist (31 degrees) and base-pair tilt (12 degrees), compared to the fiber model, which has corresponding values of 2.56 A, 32.7 degrees, and 20 degrees, respectively. All these changes indicate that the refined models are closer to the A-form structure observed in crystals of oligonucleotides. In the refined B-for models, the helical parameters are close to the fiber B-form, although the torsion angles show considerable variations. None of the three sequences examined, including the d(A)n.d(T)n sequence, show any pronounced curvature for the B-form structure.

Base Sequence↗
PubMed1991

Effect of basic oligopeptides on the B-Z transition of poly(dG-dC). poly(dG-dC) in water-methanol solutions.

The effect of basic oligopeptides (Lys-Ala-Ala)n (n = 1-5, 10) and (Lys-Leu-Ala)n (n = 1-4) on the B-Z transition of poly(dG-dC).poly(dG-dC) in water-methanol solutions was investigated using CD and uv spectroscopy. In the absence of peptides, the concentration of methanol at the midpoint of the B-Z transition is 64% at 25 degrees C. The transition is temperature dependent and the B conformation is preferred at higher temperatures. All peptides tested shift the midpoint of the B-Z transition to lower concentrations of methanol. For shorter peptides this effect increases with an increasing number of monomeric units, showing the importance of the number of positive charges in the peptide molecule. Al conditions of low methanol content, the trimer and tetramer of the (Lys-Leu-Ala)n series have a greater effect on the B-Z transition than the corresponding oligomers of the (Lys-Ala-Ala)n series. This indicates an important influence of the presence of hydrophobic groups in the peptide side chains on the binding. In the presence of peptides, the B-Z transition is also temperature dependent and the B conformation is preferred at higher temperatures. The addition of peptides results in an increase of the transition midpoint and of the transition width. These parameters were used for the calculation of the transition enthalpy delta HB-Z in 65% methanol, which is -1.15 +/- 0.25 kcal/base pair. Since the van't Hoff enthalpy delta HVH calculated from the temperature dependence of the B-Z transition in the absence of peptides is -130 kcal/mol, the length of the cooperative unit is about 110 base pairs. The results suggest that the mechanism of Z-DNA induction is similar but not identical with that involved in the action of metal cations in aqueous solution.

Amino Acid Sequence↗
PubMed2005

Locally Addressable Electrochemical Patterning Technique (LAEPT) applied to poly(L-lysine)-graft-poly(ethylene glycol) adlayers on titanium and silicon oxide surfaces.

The protein-resistant polycationic graft polymer, poly(L-lysine)-g-poly(ethylene glycol) (PLL-g-PEG), was uniformly adsorbed onto a homogenous titanium surface and subsequently subjected to a direct current (dc) voltage. Under the influence of an ascending cathodic and anodic potential, there was a steady and gradual loss of PLL-g-PEG from the conductive titanium surface while no desorption was observed on the insulating silicon oxide substrates. We have implemented this difference in the electrochemical response of PLL-g-PEG on conductive titanium and insulating silicon oxide regions as a biosensing platform for the controlled surface functionalization of the titanium areas while maintaining a protein-resistant background on the silicon oxide regions. A silicon-based substrate was micropatterned into alternating stripes of conductive titanium and insulating silicon oxide with subsequent PLL-g-PEG adsorption onto its surfaces. The surface modified substrate was then subjected to +1800 mV (referenced to the silver electrode). It was observed that the potentiostatic action removed the PLL-g-PEG from the titanium stripes without inducing any polyelectrolyte loss from the silicon oxide regions. Time-of-flight secondary ions mass spectroscopy and fluorescence microscopy qualitatively confirmed the PLL-g-PEG retention on the silicon oxide stripes and its absence on the titanium region. This method, known as "Locally Addressable Electrochemical Patterning Technique" (LAEPT), offers great prospects for biomedical and biosensing applications. In an attempt to elucidate the desorption mechanism of PLL-g-PEG in the presence of an electric field on titanium surface, we have conducted electrochemical impedance spectroscopy experiments on bare titanium substrates. The results showed that electrochemical transformations occurred within the titanium oxide layer; its impedance and polarization resistance were found to decrease steadily upon both cathodic and anodic polarization resulting in the polyelectrolyte desorption from the titanium surface.

Biosensing Techniques↗
PubMed2004

Cylindrical micelles from the aqueous self-assembly of an amphiphilic poly(ethylene oxide)-b-poly(ferrocenylsilane) (PEO-b-PFS) block copolymer with a metallo-supramolecular linker at the block junction.

A supramolecular AB diblock copolymer has been prepared by the sequential self-assembly of terpyridine end-functionalized polymer blocks by using Ru(III)/Ru(II) chemistry. By this synthetic strategy a hydrophobic poly(ferrocenylsilane) (PFS) was attached to a hydrophilic poly(ethylene oxide) (PEO) block to give an amphiphilic metallo-supramolecular diblock copolymer (PEO/PFS block ratio 6:1). This compound was used to form micelles in water that were characterized by a combination of dynamic and static light scattering, transmission electron microscopy, and atomic force microscopy. These complementary techniques showed that the copolymers investigated form rod-like micelles in water; the micelles have a constant diameter but are rather polydisperse in length, and light scattering measurements indicate that they are flexible. Crystallization of the PFS in these micelles was observed by differential scanning calorimetry, and is thought to be the key behind the formation of rod-like structures. The cylindrical micelles can be cleaved into smaller rods whenever the temperature of the solution is increased or they are exposed to ultrasound.

Journal Article↗
PubMed2006

Assembly of nanotubes of poly(4-vinylpyridine) and poly(acrylic acid) through hydrogen bonding.

Nanotubes of poly(4-vinylpyridine) (PVP) and poly(acrylic acid) (PAA) were fabricated by hydrogen bonding based on layer-by-layer (LbL) assembly. The uniform and flexible tubular structures were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). FTIR and X-ray photoelectron spectroscopy (XPS) measurements confirm the formation of hydrogen bonds in the assembled nanotubes. PAA can be released from the assembled PAA/PVP nanotubes in a basic aqueous solution to give the walls of the tubes a porous structure. Such assembled nanotubes can be considered as carriers for catalysts or drugs, especially in aqueous solution against capillary force.

Acrylic Resins↗
PubMed2005

Multilayer poly(vinyl alcohol)-adsorbed coating on poly(dimethylsiloxane) microfluidic chips for biopolymer separation.

A poly(dimethylsiloxane) (PDMS) microfluidic chip surface was modified by multilayer-adsorbed and heat-immobilized poly(vinyl alcohol) (PVA) after oxygen plasma treatment. The reflection absorption infrared spectrum (RAIRS) showed that 88% hydrolyzed PVA adsorbed more strongly than 100% hydrolyzed one on the oxygen plasma-pretreated PDMS surface, and they all had little adsorption on original PDMS surface. Repeating the coating procedure three times was found to produce the most robust and effective coating. PVA coating converted the original PDMS surface from a hydrophobic one into a hydrophilic surface, and suppressed electroosmotic flow (EOF) in the range of pH 3-11. More than 1,000,000 plates/m and baseline resolution were obtained for separation of fluorescently labeled basic proteins (lysozyme, ribonuclease B). Fluorescently labeled acidic proteins (bovine serum albumin, beta-lactoglobulin) and fragments of dsDNA phiX174 RF/HaeIII were also separated satisfactorily in the three-layer 88% PVA-coated PDMS microchip. Good separation of basic proteins was obtained for about 70 consecutive runs.

DNA↗
PubMed2006

Poly(methyl methacrylate) CE microchips replicated from poly(dimethylsiloxane) templates for the determination of cations.

A novel method for the rapid fabrication of poly(methyl methacrylate) (PMMA) microfluidic chips using poly(dimethylsiloxane) (PDMS) templates has been demonstrated. The PDMS molds were fabricated by soft lithography. The dense prepolymerized solution of methyl methacrylate containing thermal and UV initiators was allowed to polymerized between a PDMS template and a piece of a 1 mm thick commercial PMMA plate under a UV lamp. The images of microchannels on the PDMS template were precisely replicated into the synthesized PMMA substrates during the UV-initiated polymerization of the prepolymerized solution on the surface of the PMMA plate at room temperature. The polymerization could be completed within 10 min under ambient temperature. The chips were subsequently assembled by thermal bonding of the channel plate and the cover sheet. The new fabrication method obviates the need for specialized replication equipment and reduces the complexity of prototyping and manufacturing. Nearly 20 PMMA chips were replicated using a single PDMS mold. The attractive performance of the new microfluidic chips has been demonstrated by separating and detecting cations in connection with contactless conductivity detection. The fabricated PMMA microchip has also been successfully employed for the determination of potassium and sodium in environmental and biological samples.

Cations, Monovalent↗
PubMed2002

Improvement of the functions of osteoblasts seeded on modified poly(D,L-lactic acid) with poly(aspartic acid).

One of the challenges in the field of tissue engineering is the development of biomaterial/cell interactions. For the purposes of the present study, two molecular weights of poly(aspartic acid) (PASP) were used to modify poly(D,L-lactic acid) (PDLLA) films in order to enhance their cell affinity. The properties of the PDLLA-modified surfaces and the controls were investigated by water contact angle measurement and electron spectroscopy for chemical analysis (ESCA). These data reflect the change in the biocompatibility of modified PDLLA surfaces. Then rat osteoblasts were seeded onto these modified surfaces and on controls to examine their effects on cell adhesion and proliferation. Cell morphologies on these surfaces were studied by scanning electron microscopy (SEM), and cell viability was evaluated with a MTT assay. In addition, differentiated cell function was assessed by measuring alkaline phosphatase (ALP) activity. The results suggest that PASP-modified surfaces may enhance the interactions between osteoblasts and PDLLA films.

Alkaline Phosphatase↗
PubMed2002

Adsorbed poly(ethyleneoxide)-poly(propyleneoxide) copolymers on synthetic surfaces: spectroscopy and microscopy of polymer structures and effects on adhesion of skin-borne bacteria.

Poly(ethyleneoxide)-copoly(propyleneoxide) (PEO-PPO) polymer coatings were evaluated for their resistance to the attachment of the marker organism Serratia marcescens and the skin-borne bacteria Staphylococcus epidermidis. The copolymers were adsorbed onto poly(styrene) films-chosen as simplified physicochemical models of skin surfaces-and their surface characteristics probed by contact angle goniometry, attenuated total reflectance-Fourier transform infrared (ATR-FTIR), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). These functional surfaces were then presented to microbial cultures, bacterial attachment was assessed by fluorescence microscopy and AFM, and the structures of the polymer films examined again spectroscopically. Surface characterization data suggest that the adsorbed copolymer was partially retained at the surface and resisted bacterial attachment for 24 h. Quantitative evaluation of cell attachment was carried out by scintillation counting of (14)C-labeled microorganisms in conjunction with plate counts. The results show that a densely packed layer of PEO-PPO copolymer can reduce attachment of skin commensals by an order of magnitude, even when the coating is applied by a simple adsorptive process. The work supports the hypothesis that adhesion of microorganisms to biological substrates can be reduced if a pretreatment with an appropriate copolymer can be effected in vivo.

Adsorption↗
PubMed2002

Modulation of marrow stromal osteoblast adhesion on biomimetic oligo[poly(ethylene glycol) fumarate] hydrogels modified with Arg-Gly-Asp peptides and a poly(ethyleneglycol) spacer.

Novel oligo[poly(ethylene glycol) fumarate] (OPF) hydrogels functionalized with cell adhesion peptides were prepared, and the effects of incorporated peptide density and macromolecular structure of hydrogels on attachment and morphology of marrow stromal cells (MSCs) were evaluated. Poly(ethylene glycol) (PEG; number average molecular weight of 930, 2860, and 6090) was used to synthesize OPF. A model peptide, Gly-Arg-Gly-Asp (GRGD), was incorporated into OPF hydrogels after being coupled to acrylated PEG of molecular weight 3400. The increase of incorporated peptide concentration enhanced MSC attachment to OPF hydrogels of PEG of molecular weight of 930 and 2860. However, the number of attached MSCs to OPF hydrogels of PEG (molecular weight 6090) remained constant regardless of the peptide density. The length of PEG in OPF also influenced cell attachment. When 1 micromole peptide/g hydrogel was incorporated into the OPF hydrogels, the degree of cell attachment at 12 h relative to the initial seeding density was 93.9 +/- 5.9%, 64.7 +/- 8.2%, and 9.3 +/- 6.6% for OPF hydrogels prepared with PEG of molecular weights of 930, 2860, and 6090, respectively. However, the crosslinking density of hydrogels did not significantly affect cell attachment. The interaction was sequence specific, in that MSC attachment to GRGD-modified hydrogels was competitively inhibited when cells were incubated in the presence of 0.5 mM soluble GRGD before cell seeding. These results suggest that we can modulate MSC attachment to OPF hydrogels by altering the peptide density and the molecular structure of OPF hydrogels.

Animals↗
PubMed2002

Fabrication and surface modification of macroporous poly(L-lactic acid) and poly(L-lactic-co-glycolic acid) (70/30) cell scaffolds for human skin fibroblast cell culture.

The fabrication and surface modification of a porous cell scaffold are very important in tissue engineering. Of most concern are high-density cell seeding, nutrient and oxygen supply, and cell affinity. In the present study, poly(L-lactic acid) and poly(L-lactic-co-glycolic acid) (70/30) cell scaffolds with different pore structures were fabricated. An improved method based on Archimedes' Principle for measuring the porosity of scaffolds, using a density bottle, was developed. Anhydrous ammonia plasma treatment was used to modify surface properties to improve the cell affinity of the scaffolds. The results show that hydrophilicity and surface energy were improved. The polar N-containing groups and positive charged groups also were incorporated into the sample surface. A low-temperature treatment was used to maintain the plasma-modified surface properties effectively. It would do help to the further application of plasma treatment technique. Cell culture results showed that pores smaller than 160 microm are suitable for human skin fibroblast cell growth. Cell seeding efficiency was maintained at above 99%, which is better than the efficiency achieved with the common method of prewetting by ethanol. The plasma-treatment method also helped to resolve the problem of cell loss during cell seeding, and the negative effects of the ethanol trace on cell culture were avoided. The results suggest that anhydrous ammonia plasma treatment enhances the cell affinity of porous scaffolds. Mass transport issues also have been considered.

Cells, Cultured↗
PubMed2002

Effect of poly(ethylene glycol) molecular weight on tensile and swelling properties of oligo(poly(ethylene glycol) fumarate) hydrogels for cartilage tissue engineering.

This study was designed to determine the effect of changes in poly(ethylene glycol) (PEG) molecular weight on swelling and mechanical properties of hydrogels made from a novel polymer, oligo(poly(ethylene glycol) fumarate) (OPF), recently developed in our laboratory. Properties of hydrogels made from OPF with initial PEG molecular weights of 860, 3900, and 9300 were examined. The PEG 3900 formulation had a tensile modulus of 23.1 +/- 12.4 kPa and percent elongation at fracture of 53.2 +/- 13.7%; the PEG 9300 formulation had similar tensile properties (modulus: 16.5 +/- 4.6 kPa, elongation: 76.0 +/- 26.4%). However, the PEG 860 gels had a significantly higher modulus (89.5 +/- 50.7 kPa) and a significantly smaller percent elongation at fracture (30.1 +/- 6.4%), when compared with other formulations. Additionally, there were significant differences in percent swelling between each of the formulations. Molecular weight between crosslinks (M(c)) and mesh size were calculated for each OPF formulation. M(c) increased from 2010 +/- 116 g/mol with PEG 860 to 6250 +/- 280 g/mol with PEG 9300. Mesh size calculations showed a similar trend (76 +/- 2 A for PEG 860 to 160 +/- 6 A for PEG 9300). It was also found that these hydrogels could be laminated if a second layer was added before the first had completely crosslinked. Mechanical testing of these laminated gels revealed that the presence of an interfacial area did not significantly alter their tensile properties. These results suggest that the material properties of OPF-based hydrogels can be altered by changing the molecular weight of PEG used in synthesis and that multilayered OPF hydrogel constructs can be produced, with each layer having distinct mechanical properties.

Absorption↗
PubMed1988

Poly(dimethylsiloxane)-poly(ethylene oxide)-heparin block copolymers. I. Synthesis and characterization.

Amphiphilic block copolymers containing poly(dimethylsiloxane), poly(ethylene oxide), and heparin (PDMS-PEO-Hep) have been prepared via a series of coupling reactions using functionalized prepolymers, diisocyanates, and derivatized heparins. All intermediate steps of the synthesis yield quantifiable products with reactive end-groups, while the final products demonstrate bioactive, covalently bound heparin moieties. Due to the solvent systems required, commercial sodium heparin was converted to its benzyltrimethyl ammonium salt to enhance its solubility. The same procedure was applied to heparin degraded by nitrous acid in order to covalently couple it in solutions with the semitelechelic copolymers. As might be expected, this derivatization reduces the apparent bioactivity of the heparin. However, preliminary findings suggest that the bioactivity can be restored by reforming the heparin sodium salt.

Biocompatible Materials↗
PubMed1990

Poly(dimethylsiloxane)-poly(ethylene oxide)-heparin block copolymers. II: Surface characterization and in vitro assessments.

Amphiphilic block copolymers containing poly(dimethylsiloxane), poly(ethylene oxide), as well as heparin-coated glass beads and tubes were evaluated for the amounts and activities of surface-immobilized heparin. Because the amphiphilic copolymer system is thermodynamically predicted to demonstrate low-energy phase enrichment on the surfaces of air-cast films, studies were also undertaken to understand the in vitro results. Solvent-cast copolymer films have a heterogeneous microphase-separated structure according to transmission electron micrographs. Wilhelmy plate contact angle analysis indicates significant surface restructuring occurs upon hydration. Attenuated total reflectance infrared spectroscopy studies of the desiccated and hydrated films at two different sampling depths show compositional heterogeneity as a function of depth, as well as near surface restructuring allowing surface enrichment of the high-energy segments following contact with water. Significant concentrations of heparin are detected on the surface of these coatings by toluidine blue assays. In addition, a portion of the surface-bound heparin maintains its original bioactivity as determined by recalcification times, thrombin times, and Factor Xa assays. These substrates were also tested for platelet adhesion and activation reactions in vitro using polymer-coated beads in rabbit platelet-rich plasma. Heparinized polymers promoted low levels of platelet adhesion and serotonin release. Surface concentrations of heparin from bioactivity assays were then correlated with platelet adhesion and the extent of platelet release to assess the efficacy of this heparin-immobilized copolymer as a blood-compatible material or coating.

Animals↗
PubMed1990

Poly(dimethylsiloxane)-poly(ethylene oxide)-heparin block copolymers. III: Surface and bulk compositional differences.

Previously observed bioactivity of poly(dimethylsiloxane)-poly(ethylene oxide)-heparin (PDMS-PEO-Hep) triblock copolymers has prompted studies of the surface and bulk character of this copolymer using angular-dependent electron spectroscopy for chemical analysis (ADESCA), static secondary mass spectroscopy (SIMS), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Because the low-energy PDMS phase dominates surfaces of this copolymer when solvent cast under air or vacuum conditions, attempts were made to explain surface restructuring and rearrangements induced in hydrated or aqueous environments that permit surface accessibility and bioactivity of heparin moieties. Based on comparisons with PDMS, PEO, and heparin homopolymers, PEO/heparin blends, and an unheparinized PDMS-PEO diblock copolymer, PDMS-PEO-heparin demonstrates both phase-mixed and phase-separated regions in DSC analysis. During annealing cycles above the Tg values of the copolymer constituents, phase-mixed regions become increasingly phase separated and PEO enriched. TGA analysis confirmed the presence block copolymer constituents and presented evidence of intermolecular segmental interactions, hence phase-mixing in the copolymers. ADESCA analysis indicates that the outer 5 A of both the PDMS-PEO and PDMS-PEO-Hep copolymers is essentially pure PDMS. However, significant amounts of PEO are detected 5 to 20 A below the surface. Static SIMS also detects the presence of PDMS at the surfaces of the PDMS-PEO and PDMS-PEO-Hep copolymers. Compositional models based on ADESCA, SIMS, and DSC data are presented for desiccated and hydrated copolymer surfaces.

Biocompatible Materials↗