1,721,019 research outputs found
New Poly(ester-carbonate) Block Copolymers Based on Poly(lactic-glycolic acid) and Poly(e-caprolactone) segments.
No full text
PEG-epirubicin conjugates with high drug loading
No full textPEG is a polymer extensively studied in drug delivery and some of its conjugates with proteins are already on the market. Studies are also focusing on PEG as polymeric carrier for low molecular weight drugs, but limitations arise from the possibility to link the drug at the level of the only one or two hydroxyl residues of the polymer. The synthesis of dendrimeric structure at the level of these groups may be a convenient solution to increase the polymer drug payload. The present report deals with the preparation of dendrimers, based on amino adipic acid or beta-glutamic acid as branching molecule, built on a PEG diol of MW 10,000 Da.
The polycyclic large drug epirubicin was chosen as a model to investigate the influence of the branching moiety structure in avoiding the drug steric hindrance during the coupling reaction. Several derivatives with increasing number of drug molecules linked to each PEG chain were synthesized and their physical, chemical and biological properties were studied. The study demonstrated that the use of proper amino bicarboxylic acid (amino adipic acid or β-glutamic acid), as branching moiety for the dendrimer synthesis, allows the linking of hindered molecule as epirubicin to multibranched PEG. It was found that the most drug loaded conjugates dissolve in water only following a pre-dissolution in DMSO. This solubility problem could be solved by adding a hydrophilic peptide linker between drug and polymer. The conjugates, synthesized in good yield and purity, showed higher stability than free epirubicin in buffers at different pHs and in plasma and a much prolonged residence time in blood. Dynamic light scattering investigation showed the high tendency of these products to aggregate forming stable micelles
Full characterization of a multiblock copolymer based on poly(2,6-dimethyl-1,4-phenylene oxide) and Poly(bisphenol-A carbonate)
No full textFull characterization, that is the true molar mass distribution and block sequence, of a multiblock copolymer based on poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and poly(bisphenol A carbonate) (PC) segments (PPO-b-PC), synthesized by polycondensation reaction of both diol-terminated PPO and PC samples with the bischloroformate of bisphenol A, is reported. The initial diol terminated PPO sample contains a few tetramethyl bisphenol A units in the backbone. The molar mass distribution of the starting PPO and PC homopolymers and the multiblock structure of the final PPO-b-PC copolymers were studied by light scattering and viscometry on-line with a SEC system, MALDI-TOF mass spectrometry, and NMR. In a previous study, we have demonstrated that homogeneous PPO-b-PC block copolymers having only one single T-g were obtained if low molar mass PPO and PC starting blocks were used. More important findings of this recent study are the following. MALDI-TOF analysis showed that the synthesized PPO-b-PC copolymers were composed of multiblock PPO-b-PC chains and also of some nonreacted PC oligomers terminated with methyl carbonate groups. Exhaustive and selective aminolysis of carbonate groups of the PC blocks has been also performed in order to determine the number of blocks and the average length of PPO blocks in the copolymers
Vinyl Polymers Based on L-Histidine Residues. Part 1. The Thermodynamics of Poly(ampholyte)s in the Free and in the Cross-Linked Gel Form
No full textAmphiphilic vinyl polymers (in the free and cross-linked forms), carrying carboxyl and imidazole groups, were prepared by a radical polymerization of the purposely synthesized N-acryloyl-L-histidine. The protonation thermodynamic studies (at 25 °C in 0.15 M NaCl) showed high polyelectrolyte character of the soluble polymer. Unlike the linear decreasing trend of the basicity constant, over the whole range of α (degree of protonation), the enthalpy changes for the protonation of the imidazole nitrogen in the polymer showed a decreasing pattern only at α > 0.5. This was ascribed to the formation of hydrogen bonds between protonated and free neighboring monomer units. Viscometric data revealed a minimum hydrodynamic volume of the polymer at its isoelectric point (pH 5), whereas at higher or lower pHs, the macromolecule expanded greatly as a consequence of the charged sites formation. This produced a preferential solvation of the protonated imidazole and carboxylate ions, the latter being surrounded by more water molecules in the hydration shell. The peculiar hydration behavior was confirmed in the cross-linked polymer. The hydrogel showed an equilibrium degree of swelling (EDS), strongly dependent on pH, in a similar manner as viscometric data of the soluble polymer. A linear relationship between the reduced viscosity and the EDS was found. The polymer was non toxic against the RAW264 cell line. © 2004 American Chemical Society
Synthesis, characterization and properties of a hyperbranched aromatic polyamide: poly(ABZAIA)
No full textSynthesis, characterisation and solution behaviour of thermo- and pH-responsive polymers bearing L-leucine residues in the side chains
No full textPolymers capable of responding to both temperature and pH changes were synthesised by radical copolymerisation of N-isopropylacrylamide (NIPAAm) and N-methacryloyl-l-leucine (MALEU) in different NIPAAm/MALEU molar ratios (15:1, 10:1, 2:1 and 1:1). The polymers were characterised by Size Exclusion Chromatography, acid–base titrations, FT-IR and 1H-NMR analyses. Their solution behaviour was studied in 0.1 M NaCl and in citrate buffers (pH 4.0, 4.5, 5.0 and 6.0). At pH 4.0 and 4.5 the cloud point temperature (TCP) of copolymers was depressed proportionally to their MALEU content. In contrast, at pH 5.0 and 6.0 the phase transition temperature increased linearly. The behaviour of the copolymers with NIPAAm/MALEU ratios 15:1 and 10:1 was investigated also between pH 3 and 11 in 0.1 M
NaCl. In both cases a sharp increase in TCP was observed around pH 4–5. The TCP vs. pH curve was linearised and the acidity constants were determined by the linearisation procedure. Furthermore, it was possible to demonstrate that the phase transition temperature increases linearly with the ionic content of the polymers
Sintesi e proprietà di nuovi polimeri termosensibili con residui di L-leucina in catena laterale.
No full textDegradation of high-molar-mass hyaluronan by an oxidative system comprising ascorbate, Cu(II), and hydrogen peroxide: Inhibitory action of antiinflammatory drugs-Naproxen and acetylsalicylic acid
No full textChanges in dynamic viscosity of the solutions of a high-molar-mass hyaluronan (HA) were monitored using a rotational viscometer. The degradative conditions generated in the HA solutions by a system comprising ascorbate plus Cu(II) plus H(2)O(2) were studied either in the presence or absence of a drug--naproxen or acetylsalicylic acid. Continual decrease of the dynamic viscosity of HA solution was indicative of the polymer degradation. Addition of the drug retarded/inhibited the HA degradation in a concentration-dependent manner. The characteristics of the fragmented polymers were investigated by FT-IR spectroscopy and by two different liquid chromatographic techniques, namely by size-exclusion chromatography equipped with a multi-angle light scattering photometric detector and by high-performance liquid chromatography connected on-line to a spectrofluorometer
- …
