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At least 1,567 records · Page 87Linked to original sources
PubMed1994

Poly-DL-lactic acid: polyethylene glycol block copolymers. The influence of polyethylene glycol on the degradation of poly-DL-lactic acid.

ABA block copolymers of polyethylene glycol and poly-DL-lactic acid were prepared by ring-opening polymerization of DL-dilactide with alpha,omega-dihydroxy polyethylene glycol, Mn 1000 or 2000. The morphology of the resulting copolymers, with PEG:PLA ratios(mol/mol) of 1:2, 1:3 and 1:4, was characterized by DSC and ESR spectroscopy. The rate of water uptake was biphasic, reflecting the contribution of two processes: rapid diffusion of water into the initially miscible PEG and PLA blocks; then a slower rate of hydration possibly due to phase separation and hydrolytic cleavage of the PLA blocks. The rate of hydrolytic degradation of the block copolymers in DI water at 37 degrees C was measured by two methods: weight loss and colorimetric analysis of the carboxy end group concentration resulting from chain scission of PLA blocks. As a result of phase separation, the rate of scission of PLA blocks in the copolymers was similar to that of the PLA homopolymer. The more rapid onset of weight loss of the copolymers, relative to PLA, is attributed to the greater water solubility of PEG-PLA oligomers and their greater diffusivity in the more highly hydrated copolymers.

Biocompatible Materials↗
PubMed1994

Selective inhibition of gastrointestinal beta-glucuronidase by poly(vinylbenzyl D-glucaro(1,4)lactonate). Part 2. Poly(vinylbenzyl D-glucaro(1,4) lactonate) in vitro inhibition studies.

In vitro inhibition studies with beta-glucuronidase from purified E. coli and mouse intestinal contents indicated that the polymer, poly(vinylbenzyl D-glucaro(1,4)lactonate, is an effective beta-glucuronidase inhibitor. Purified E. coli beta-glucuronidase was inhibited by 99.6% with 177 mM D-glucaro(1,4)lactone using the polymer-inhibitor. Similarly, 95% inhibition of beta-glucuronidase activity of mouse intestinal contents was obtained with 177 mM and 50% inhibition was obtained with 31.5 mM D-glucaro(1,4)lactone based on the modified polymer. The structural requirements of an effective beta-glucuronidase inhibitor based on the structure of the polymer-inhibitor are also discussed.

Animals↗
PubMed2005

Biosynthesis of poly-gamma-glutamic acid in plants: transient expression of poly-gamma-glutamate synthetase complex in tobacco leaves.

Transient expression of genes coding for the poly-gamma-glutamate (gammaPGA) synthetase system (pgs) was investigated in tobacco plants. Three genes of the pgs, pgsA, pgsB and pgsC, were separately placed under the control of the CaMV 35S promoter and introduced into tobacco leaves via Agrobacterium infection. Synthesized gammaPGA in plant tissues was detected immunologically with mouse anti-gammaPGA antiserum which specifically reacts with gammaPGA on a nitrocellulose membrane. Confirmation of gammaPGA biosynthesis in the transient expression analysis in tobacco tissue indicates that subunits of pgs complex were expressed and reassembled in a functional form.

Genes, Plant↗
PubMed2003

Discrimination of poly(vinyl chloride) samples with different plasticizers and prediction of plasticizer contents in poly(vinyl chloride) using near-infrared spectroscopy and neural-network analysis.

In the recycling of poly(vinyl chloride) (PVC), it is required to discriminate every plasticizer for quality control. For this purpose, the near-infrared spectra were measured for 41 kinds of PVC samples with different plasticizers (DINP, DOP, DOA, TOTM and Polyester) and different plasticizer contents (0-49%). A neural-network analysis was applied to the near-infrared spectra pretreated by second-derivative processing. They were discriminated from one another. The neural-network analysis also allowed us to propose a calibration model which predicts the contents of plasticizers in PVC. The correlation coefficient (R) and the root-mean-square error of prediction (RMSEP) for the DINP calibration model were found to be 0.999 and 0.41 wt%, respectively. In comparison, a partial least-squares regression analysis was carried out. The R and RMSEP of the DINP calibration model were calculated to be 0.993 and 1.27 wt%, respectively. It is found that a near-infrared spectra measurement combined with a neural-network analysis is useful for plastic recycling.

Conservation of Natural Resources↗
PubMed1997

Chemical analysis of poly-gamma-glutamic acid produced by plasmid-free Bacillus subtilis (natto): Evidence that plasmids are not involved in poly-gamma-glutamic acid production.

It has been postulated that the psf gene on a small plasmid, pUH1 (5.8 kb), regulates positively the synthesis of capsular poly-gamma-glutamic acid (gammaPGA) in Bacillus subtilis (natto) Asahikawa. We found that this strain harbored a second plasmid, named pNAGL1 (ca. 50 kb), in addition to pUH1. The growth conditions that cure pUH1 or pNAGL1 were established. The plasmid-free NAF4 strain derived from B. subtilis (natto) Asahikawa was found to produce gammaPGA which was the same as the parent strain in terms of quantity and chemical properties having the same molecular mass and content of D-glutamic acid. Furthermore, as in the case of the parent cells, the D-glutamic acid in gammaPGA, which is known to increase up to ca. 80% of the total glutamic acid as Mn(2+) ion concentration increases in growth medium, was found to make up 80% of the total glutamic acid of the gammaPGA produced by NAF4 cells grown in the presence of 0.1 mm MnCl(2). Thus, these results led us to conclude that the plasmids do not encode any gene important for gammaPGA production.

Journal Article↗
PubMedDate not supplied

Biodegradable poly(lactic acid) and poly(lactide-co-glycolide) microcapsules: problems associated with preparative techniques and release properties.

Poly(lactic acid) [PLA] and its co-polymers with glycolic acid [PLCG] have been known to be biodegradable and histocompatible for the past 20 years. Their physico-chemical and biological properties have been found suitable, in many instances, for sustaining drug release in vivo for days or months. Several dosage forms for parenteral administration have been investigated using these polymers and a microencapsulation technique is chosen frequently for its unique properties. There are a limited number of published papers concerning preparation and characterization of PLA or PLCG microcapsules, possibly because of commercial unavailability and difficulties in the synthesis of reproducible batches of these polymers. However, microcapsules can be made using different traditional and non-traditional techniques containing core materials ranging from biological proteins to synthetic drugs. An attempt is made here to review problems associated with the different microencapsulation techniques using PLA or PLCG. In vivo and in vitro drug release from these microcapsules is also reviewed.

Animals↗
PubMedDate not supplied

Properties and drug release behaviour of poly(3-hydroxybutyric acid) and various poly(3-hydroxybutyrate-hydroxyvalerate) copolymer microcapsules.

Microcapsules of poly(3-hydroxybutyric acid) [PHB] and its copolymers with hydroxyvalerate [HV] were prepared by the solvent evaporation technique and loaded with a model drug, 2,7-dichlorofluorescein. Microcapsules were also prepared from the same polymers by incorporating a polyphosphate-Ca+2 complex into the membrane. The morphology of the microcapsules varied by the change in the type of polymer used, by the introduction of drug and by the incorporation of the complex. Drug release behaviour, encapsulation efficiency and loading were all found to be influenced by the polymer type. The DSC results revealed that upon incorporation of valerate as the co-monomer, the crystallinity of the polymer decreased, leading to a material with more segmental mobility. This probably was the reason why the loading and encapsulation efficiency of the homopolymer were lower than those of the copolymers. DSC also indicated that the complex became an integral part of the membrane.

Calcium↗
PubMed1999

Interactions between a macrophage cell line (J774A1) and surface-modified poly (D,L-lactide) nanocapsules bearing poly(ethylene glycol).

The interactions of naked and surface-modified poly(D,L-lactic acid) (PLA) nanocapsules (NC), where polyethyleneglycol (PEG) was adsorbed or covalently attached, have been studied with a macrophage-like cell line. The fluorescent oil marker, DiD, was successfully encapsulated in NCs in order to follow their interactions with cells. The cell-associated fluorescence obtained with PEG-PLA NC was about 3- to 13-fold lower than that obtained with naked-PLA NC. The effects of PEG chain length, its content as a percentage of total polymer and NC concentration in the culture medium were evaluated. PEG-PLA NC showed dramatically reduced fluorescence association with cells during an 18 h incubation compared with naked-PLA NC, showing that covalent attachment of PEG is important for the persistence of low uptake. The best results in reducing cell-associated fluorescence were obtained with a surface-modified PEG-PLA NC bearing a chain with 20000 MW. Increasing the percentage of PEG produced a reduction in marker association for a given PEG chain length. Moreover, when the PEG-containing poloxamer was simply adsorbed, marker association was dependent on the extent of dilution and the type of serum in the culture medium. Serum proteins, especially immunoglobulins, increased cell-associated fluorescence for PEG-adsorbed NC, but had very little effect on PEG-PLA NC. Marker association was only partially inhibited in the presence of cytochalasin B. The mechanisms of cell-NC interaction depended on the characteristics of the NC surface in each formulation. When the NC was physically separated from cells no diffusion of fluorescent marker in aqueous medium occurred. Nevertheless, collision-mediated transfer of DiD from NC to J774 cells was a non-negligible route of marker transfer, mainly for naked NC. However, this collision-mediated transfer was reduced for the PEG-PLA NC probably due to the restricted contact between NC and cells afforded by PEG steric hindrance at the surface.

Animals↗
PubMed1999

Supramolecular Organometallic Polymer Chemistry: Self-Assembly of a Novel Poly(ferrocene)-b-polysiloxane-b-poly(ferrocene) Triblock Copolymer in Solution.

Micelles with unprecedented flowerlike arrangements of the poly(ferrocene) cores (shown in the TEM image) are among the supramolecular architectures generated in the self-assembly of a novel organometallic triblock copolymer from silicon-bridged [1]ferrocenophane monomers and [Me(2)SiO](3) in hexane, a solvent selective for the central polysiloxane block.

Journal Article↗
PubMed1986

Induction of differentiation of Friend murine erythroleukemia cells by poly-L-lysine and daunorubicin-poly-L-lysine conjugate.

The ability of the synthetic cationic polypeptide poly-L-lysine (PLL) to induce differentiation of Friend murine erythroleukemia cells was examined with the use of polymers of different molecular weights. Like other membrane-interacting agents (polar solvents), all the polymers tested were effective in inducing cell differentiation. This effect was found to be molecular weight dependent, as already reported for other membrane-related actions of these polymers. Since anthracyclines also exert direct effects on the cell membrane, the activity of the daunorubicin-PLL conjugate was also examined. The covalent linking of the drug to the polyamino acid somewhat reduced the differentiation-inducing activity in this system. Indeed, free daunorubicin was found to inhibit the maturational process. Although the inducing effect was observed when the free PLL or daunorubicin-linked PLL was added alone, polymers enhanced differentiation produced by suboptimal concentrations of dimethyl sulfoxide (DMSO). Since PLL was inactive as an initiator of the maturation of a DMSO-resistant line, it is likely that some events (presumably membrane-related effects) involved in the multistep stimulation process are common to polar-planar solvents and the polycationic polymer.

Animals↗
PubMed1997

Poly(L-lysine)-graft-dextran copolymer is a novel stabilizer of triplex DNA (I): stabilization of poly(dA).2poly(dT) triplex.

Comb-type polylysine copolymer having grafted hydrophilic side chains was newly designed as a novel stabilizer of triplex DNAs. The comb-type copolymer elevated melting temperature of poly(dA).2poly(dT) triplex by 50 degrees C without affecting reversibility, melting and reassociation, of the triplex in buffer with physiological salt concentrations. The stabilizing effect of the copolymer was greater than spermine. Our results indicate that the molecular designing of polycation with comb-type structure is a successful strategy for creating an effective triplex stabilizer.

Biocompatible Materials↗
PubMed1993

Detection of poly (U) hybridization using azido modified poly (A) coated piezoelectric crystals.

A technique has been developed which uses AT-cut, 9 MHz piezoelectric crystals for the immobilization of single stranded nucleic acids and the subsequent hybridization reactions. This hybridization technique is based on detecting small changes in mass on the surface of a piezoelectric crystal which occur upon immobilizing azido containing probe nucleic acid on the surface and hybridizing complementary target nucleic acid to previously immobilized probe. The immobilized probe could be used for repeated hybridization tests. The hybridization assays were performed in solution and the frequency measurements were performed in the dry state.

Azides↗
PubMed1999

Flexibility of single-stranded DNA: use of gapped duplex helices to determine the persistence lengths of poly(dT) and poly(dA).

The forces responsible for the formation and stabilization of secondary and higher-order nucleic acid structure can be more fully understood once the sequence-dependent properties (e.g. intrinsic rigidity, effective rise) of the component single-stranded species are well-defined. Knowledge of the conformations of the single-stranded polymers is also important for the development of better polyelectrolyte models for various structural or strand-dissociation reactions. However, there is at present little quantitative information regarding the sequence dependence of either rise or rigidity in single-stranded DNA or RNA polymers. To address this issue, we describe a form of transient electric birefringence (TEB) measurement in which the rotational decay times (taugap) of DNA molecules possessing central, single-stranded regions (gaps) are compared with the corresponding times (taudplx) for duplex control molecules of the same length (in nucleotides per strand) as the continuous strand in the "gapped duplex". For magnesium ion concentrations above 1-2 mM, the tau ratios ( identical withtaugap/taudplx) for the gapped duplexes reach plateau values, above which no further change in tau ratio is observed; values for the persistence length (P) and internucleotide spacing (h) of the gap sequences are obtained from the experimental tau ratios. For dTn, the permissible ranges of P and h are 20-30 A and 5-7 A per nucleotide (nt), respectively, with optimal values of 31 A (P) and 5. 2 A/nt (h). For dAn, the persistence length for the low temperature (4 degreesC), stacked form is 78 (+/-8) A for a helix rise of 3.2 A/nt. One significant advantage of the current method over previous approaches is the use of short (80-100 nt) molecules, thus facilitating the production of various gap sequences through synthetic means.

Base Sequence↗