Sugar End-Capped Poly-d,l-lactides as Excipients in Oral Sustained Release Tablets

Sugar end-capped poly-d,l-lactide (SPDLA) polymers were investigated as a potential release controlling excipient in oral sustained release matrix tablets. The SPDLA polymers were obtained by a catalytic ring-opening polymerization technique using methyl α-d-gluco-pyranoside as a multifunctional initiator in the polymerization. Polymers of different molecular weights were synthesized by varying molar ratios of monomer/catalyst. The matrix tablets were prepared by direct compression technique from the binary mixtures of SPDLA and microcrystalline cellulose, and theophylline was used as a model drug. The tablet matrices showed in vitro reproducible drug release profiles with a zero-order or diffusion-based kinetic depending on the SPDLA polymer grade used. Further release from the tablet matrices was dependent on the molecular weight of the SPDLA polymer applied. The drug release was the fastest with the lowest molecular weight SPDLA grade, and the drug release followed zero-order rate. With the higher molecular weight SPDLAs, more prolonged dissolution profiles for the matrix tablets (up to 8–10 h) were obtained. Furthermore, the prolonged drug release was independent of the pH of the dissolution media. In conclusion, SPDLAs are a novel type of drug carrier polymers applicable in oral controlled drug delivery systems.     

Biotinylated glycopolymers synthesized by atom transfer radical polymerization

Biotinylated glycopolymers that bind to the protein streptavidin were synthesized by atom transfer radical polymerization (ATRP). Poly(methacrylate)s with pendent N-acetyl-d-glucosamines were prepared by polymerizing the protected monomer, followed by deprotection. Alternatively, the unprotected monomer was directly polymerized. Both paths provided well-defined glycopolymers with narrow molecular weight distributions (PDI = 1.07-1.23). The number-average molecular weights determined by gel permeation chromatography increased with increasing initial monomer-to-initiator ratios. The polymers were synthesized using a biotin-functionalized initiator for ATRP. Confirmation of the end group and binding to the protein streptavidin was achieved by (1)H NMR and surface plamon resonance.     

Supercritical carbon dioxide extraction of griseofulvin from the solid matrix obtained after solid-state fermentation

Globally there is an increasing concern to minimize the use of organic solvents, particularly the chlorinated ones because of their suspected human carcinogenicity. The use of ecofriendly carbon dioxide as an alternative to organic solvents would be appropriate in the perspective of green technology. Supercritical carbon dioxide (SC-CO(2)) extraction is suitable for extraction of nonpolar compound with molecular weights less than 400. Griseofulvin is an antifungal antibiotic having a molecular weight of 353, making it amenable to SC-CO(2) extraction. This work brings out the potential of supercritical carbon dioxide extraction (SCFE) for downstream processing of griseofulvin from the solid matrix obtained after solid-state fermentation (SSF). The optimized conditions for SCFE of griseofulvin from dried media after SSF were a flow rate of 0.4 L/min, temperature of 60 degrees C, and contact time of 90 min (30 min static + 60 min dynamic) at a pressure of 450-455 bar.     

Effects of culture conditions on molecular weights of poly(3-hydroxyalkanoates) produced byPseudomonas putida from octanoate

Summary Time-dependent changes in the molecular weights of poly(3-hydroxyalkanoates) (P(3HA)) produced byPseudomonas putida from octanoate were investigated. The mole ratio of carbon to nitrogen sources (C/N), incubation temperature, concentration of octanoate, and pH of culture solution were varied to study the effects of culture conditions on the yield and molecular weights of P(3HA). The molecular weights of P(3HA) decreased with time to reach a constant value during incubation. When the incubation temperature and the concentration of octanoate were low, P(3HA) polymers of high molecular weights were produced.     

Polysaccharide hydrolysis accelerated by adding carbon dioxide under hydrothermal conditions

Polysaccharides such as agar, guar gum, starch, and xylan were hydrolyzed to produce mono- and oligosaccharides under hydrothermal conditions with and without carbon dioxide in a small batch reactor. The molecular weight distributions of the polysaccharide hydrolyzates shifted to lower molecular weights by increasing the carbon dioxide load, corresponding to higher pressures of carbon dioxide. For example, the yield of glucose produced from the hydrolysis of starch at 200 degrees C was increased significantly from 3.7% to 53.0% (on a carbon weight basis) of the initial polysaccharide by increasing carbon dioxide load in a reaction time of 15 min. Carbonic acid generated from water and carbon dioxide appeared to lower the pH of high-temperature and high-pressure water. Polysaccharide hydrolysis under hydrothermal conditions in the presence of carbon dioxide is an environmentally benign method to produce mono- and oligosaccharides because the process does not require the use of conventional acids and bases followed by neutralization and separation.     

Photocurable biodegradable liquid copolymers: synthesis of acrylate-end-capped trimethylene carbonate-based prepolymers, photocuring, and hydrolysis

Various photocurable liquid biodegradable trimethylene carbonate (TMC)-based (co)oligomers were prepared by ring-opening (co)polymerization of TMC with or without L-lactide (LL) using low molecular weight poly(ethylene glycol) (PEG) (mol wt 200, 600, or 1000) or trimethylolpropane (TMP) as an initiator. Resultant (co)oligomers were pastes, viscous liquids, or liquids at room temperature, depending on the monomer composition and monomer/initiator ratio. Liquid (co)oligomers were subsequently end-capped with acrylate groups. Upon visible-light irradiation in the presence of camphorquinone as a radical generator, rapid liquid-to-solid transformation occurred to produce photocured solid. The photocuring yield increased with photoirradiation time, photointensity, and camphorquinone concentration. The photocured polymers derived from low molecular weight PEG (PEG200) and TMP exhibited much reduced hydrolysis potential compared with PEG1000-derived polymers in terms of weight loss, water uptake, and swelling depth. Force-distance curve measurements by nanoindentation using atomic force microscopy clearly showed that Young's moduli of the photocured polymer films decreased with increasing hydrolysis time. Their potential biomedical applications are discussed.     

Partition of proteins in aqueous polymer two-phase systems and the effect of molecular weight of the polymer

The partition of substances in aqueous polymer two-phase systems is influenced by the molecular weight of the phase-forming polymers. We investigate how the effect of the molecular weight of the polymers depends on the molecular weight of the partitioned protein. We show that the magnitude of change of the partition is very small for proteins of molecular weights around 10 000, but increases almost linearly up to molecular weights of 250 000.     

Synthesis of copolymers containing an active ester of methacrylic acid by RAFT: controlled molecular weight scaffolds for biofunctionalization

We report the controlled radical copolymerization of N-(2-hydroxypropyl)methacrylamide (HPMA) with a monomer containing an active ester, N-methacryloyloxysuccinimide (NMS), by reversible addition fragmentation chain transfer (RAFT). The large difference in the reactivity ratios of HPMA and NMS resulted in significant variations in copolymer composition with increasing conversion during batch copolymerization. The use of a semi-batch copolymerization method, involving the gradual addition of the more reactive NMS, allowed uniformity of copolymer composition to be maintained during the polymerization. We synthesized polymers in a wide range of molecular weights (M(n) = 3000-50,000 Da) with low polydispersities (1.1-1.3). The effect of the ratio of monomer to chain transfer agent (CTA) on the molecular weight of the polymer was investigated. Given the numerous applications of poly(HPMA)-based conjugates in designing polymeric therapeutics, these controlled molecular weight activated polymers represent attractive scaffolds for biofunctionalization. As a demonstration, we attached a peptide to the activated polymer backbone to synthesize a potent controlled molecular weight polyvalent inhibitor of anthrax toxin.     

Polymerization of propyl malolactonate in the presence of Candida rugosa lipase

To gain better insight into mechanistic features of enzyme-catalyzed malolactonate polymerization, reactions with propyl malolactonate were analyzed while varying enzyme concentration, reaction media composition, and reaction temperature. Monomer conversion and product molecular weights were characterized by (1)H NMR and MALDI-TOF MS, respectively. A high extent of thermal polymerization of propyl malolactonate was observed, while the polymer chain length in all reactions was controlled by the elimination of alpha-hydrogen from propyl malolactonate with formation of a new initiator and the new chains. The most efficient enzymatic catalysis occurred in toluene (2.11 M monomer) at 60 degrees C. Candida rugosa lipase (10 wt %) accelerated polymerization 25-fold over the rate of thermal polymerization. The maximum poly(propyl malate) number-average molecular weight obtained was 5000 Da at 20 wt % enzyme with a polydispersity of 1.15. These values compare with 1800 Da and 1.5, respectively, in the absence of enzyme.     

Measurement of the molecular weight distribution of debranched starch

Combining molecular weight distribution (MWD) data for linear chains of debranched starch from capillary electrophoresis and from size exclusion chromatography (SEC) with detection by differential refractive index and by multi-angle laser light scattering has enabled Mark-Houwink parameters to be determined for linear starch chains. For accurate results, it was found to be important to take SEC band broadening into account, and a methodology for implementing this is presented. This deconvolution technique can be used to reveal features such as maxima or shoulders in the MWD which have qualitative as well as quantitative significance. Remarkably, these data show that the empirical Mark-Houwink relation between molecular weight and hydrodynamic volume is, for linear debranched starch, valid for much lower molecular weights than synthetic polymers. This implies that these Mark-Houwink parameters can be used with "universal calibration" to enable SEC to be used with relative ease to provide MWDs for debranched starch for essentially any degree of polymerization.     

Synthesis and characterization of amphiphilic polyphosphates with hydrophilic graft chains and cholesteryl groups as nanocarriers

Amphiphilic polyphosphate graft copolymers with varied densities of cholesteryl esters and hydrophilic graft chains were prepared, and the solution properties of the graft copolymers were evaluated. Polyphosphates were synthesized as backbones by ring-opening polymerization of 2-isopropyl-2-oxo-1,3,2-dioxaphospholane (IPP), 2-(2-oxo-1,3,2-dioxaphosphoroyloxyethyl-2-bromoisobutyrate) (OPBB), and 2-choresteryl-2-oxo-1,3,2-dioxaphospholane (ChOP) using triisobutylaluminum as an initiator. Three types of polyphosphates (PIBr(x)Ch(y), x = number of OPBB units in a polymer; y = number of ChOP units in a polymer) such as PIBr4, PIBr6Ch1, and PIBr3Ch2 were obtained. The molecular weights of these polymers were 2.4 x 10(4), 2.4 x 10(4), and 2.6 x 10(4) g/mol, respectively. 2-Methacryloyloxyethyl phosphorylcholine (MPC) was grafted from the OPBB sites in PIBr(x)Ch(y) via atom transfer radical polymerization (ATRP) in EtOH. In each polymer system, the molecular weight of the graft polymer was linear with conversion. Furthermore, the polymer radical concentration remained constant during polymerization; that is, the molecular weights of the graft chains were easily controllable with polymerization time. The solution properties of amphiphilic PIBr(x)Ch(y)-g-PMPCs were investigated by the methods of surface tension measurement, light scattering, and fluorescence probe. The transition point (cmc) of the surface tension of the PIBr(x)Ch(y)-g-PMPCs aqueous solution decreased with an increase in the number of ChOP units in a graft polymer. Particularly, PIBr3Ch2-g-PMPC14.9K formed nanosized associates (R(h) = 7.5 nm) with 2.2 molecules above 0.1 wt %. v79 cells were used to evaluate the cytotoxicity of the graft polymers, but no cytotoxicity was observed. The graft polymers containing cholesteryl groups effectively enhanced the solubility of paclitaxel in an aqueous solution.     

Polymerization of gamma-benzyl-L-glutamate N-carboxyanhydride: effects of conditions of polymer precipitation on the molecular weight distribution

Poly-γ-berizyl-L -glutamate prepared by polymerization of γ-benzyl-L -glutamate NCA in dimethylformamide (DMF) with the use of diisopropylamine as the initiator was precipitated from the polymerization mixture under different conditions. A portion of the almost completely polymerized solution was treated with an excess of isopropylamine and then precipitated into diethyl ether (sample A). The remaining portion of the polymerization mixture was concentrated in a rotating evaporator, stored at room temperature for a few days, and then diluted with DMF and precipitated into diethyl ether (sample B). The molecular weight distributions of the two polymer samples were determined by the chromatographic procedure of Baker and Williams. The molecular weight of sample B is roughly three times that of sample A. However both samples have the “most probable” distribution of molecular weight. The results are interpreted according to Bamford's polymerization mechanism.     

Procedure for Fabricating Biofunctional Nanofibers

Electrospinning is an effective processing method for preparing nanofibers decorated with functional groups. Nanofibers decorated with functional groups may be utilized to study material-biomarker interactions i.e. act as biosensors with potential as single molecule detectors. We have developed an effective approach for preparing functional polymers where the functionality has the capacity of specifically binding with a model protein. In our model system, the functional group is 2,4-dinitrophenyl (DNP) and the protein is anti-DNP IgE (Immunoglobulin E). The functional polymer, α,ω-bi[2,4-dinitrophenyl caproic][poly(ethylene oxide)-b-poly(2-methoxystyrene)-b-poly(ethylene oxide)] (CDNP-PEO-P2MS-PEO-CDNP), is prepared by anionic living polymerization. The difunctional initiator utilized in the polymerization was prepared by electron transfer reaction of α-methylstyrene and potassium (mirror) metal. The 2-methoxystyrene monomer was added first to the initiator, followed by the addition of the second monomer, ethylene oxide, and finally the living polymer was terminated by methanol. The α,ω-dihydroxyl polymer [HO-PEO-P2MS-PEO-OH] was reacted with N-2,4-DNP-∈-amino caproic acid, by DCC coupling, resulting in the formation of α,ω-bi[2,4-dinitrophenylcaproic][poly(ethyleneoxide)-b-poly(2-methoxystyrene)-b-poly(ethylene oxide)] (CDNP-PEO-P2MS-PEO-CDNP). The polymers were characterized by FT-IR, ¹H NMR and Gel Permeation Chromatography (GPC). The molecular weight distributions of the polymers were narrow (1.1-1.2) and polymers with molecular weights greater than 50,000 was used in this study. The polymers were yellow powders and soluble in tetrahydrofuran. A water soluble CDNP-PEO-P2MS-PEO-CDNP/ DMEG (dimethoxyethylene glycol) complex binds and achieves steady state binding with solution IgE within a few seconds. Higher molecular weight (water insoluble i.e. around 50,000) CDNP-PEO-P2MS-PEO-CDNP polymers, containing 1% single wall carbon nanotubes (SWCNT) were processed into electroactive nanofibers (100 nm to 500 nm in diameter) on silicon substrate. Fluorescence spectroscopy shows that anti-DNP IgE interacts with the nanofibers by binding with the DNP functional groups decorating the fibers. These observations suggest that appropriately functionalized nanofibers hold promise for developing biomarker detection device.     

Steric control in the polymerization of 1,2-anhydro-3,4,6-tri-O-benzyl-beta-D-mannopyranose

Polymerization of 1,2-anhydro-3,4,6-tri-O-benzyl-beta-D-mannopyranose under acid catalysis has led to a series of polymers varying in anomeric configuration from approximately 90% alpha to 70% beta. Optical rotations follow 13C-n.m.r. estimates of anomeric composition linearly over this range. Low-temperature polymerization with trifluoromethanesulfonic anhydride as initiator favors mainly cis-opening of the anhydro ring, presumably through the intermediary of a macroester. These results are compared with related glycosylation and polymerization reactions on 1,2-anhydro sugar derivatives, and some mechanistic conclusions are proposed.     

Organocatalytic ring opening polymerization of trimethylene carbonate

A variety of organocatalysts has been surveyed in the ring opening polymerization of trimethylene carbonate. Excellent control was found for several of these catalysts yielding well-defined polycarbonates with molecular weights up to 50,000 g mol(-1), polydispersities below 1.08, and high end-group fidelity. Melt or bulk polymerization was accomplished without loss of control of molecular weight or polydispersity, and random ester-carbonate bulk polymerizations were also demonstrated. Furthermore, by combining disparate polymerization techniques using bifunctional initiators, the mild polymerization conditions allow for the preparation of new block copolymers. Hydrogen-bond activation of monomer and initiator/propagating species is proposed as the underlying mechanism, which can be tuned to mitigate adverse side reactions.     

Polymerization of protamine sulphate by carbodiimide and interaction of isolated protamine polymers with human red blood cells.

A method using a water-soluble carbodiimide to polymerize protamine sulphate is described. The behaviour of polymerized protamine in Sephadex chromatography and in polyacrylamide gel electrophoresis indicates that protamine has been polymerized into aggregates with defined molecular weights. Turbidimetrical titrations of the isolated protamine polymers with dextran sulphate show that the cationic charge density has been conserved after polymerization. The binding characteristics of the protamine polymers to human red blood cells as measured by cell electrophoresis indicate increased affinity with increased molecular weight of the polymer.     

Continuous lipase-catalyzed production of fatty acid ethyl esters from soybean oil in compressed fluids

This work investigates the continuous production of fatty acid ethyl esters from soybean oil in compressed fluids, namely carbon dioxide, propane and n-butane, using immobilized Novozym 435 as catalyst. The experiments were performed in a packed-bed bioreactor evaluating the effects of temperature in the range of 30–70 °C, from 50 to 150 bar, oil to ethanol molar ratio of 1:6–1:18 and solvent to substrates mass ratio of 4:1–10:1. In contrast to the use of carbon dioxide and n-butane, results showed that lipase-catalyzed alcoholysis in a continuous tubular reactor in compressed propane might be a potential route to biodiesel production as high reaction conversions were achieved at mild temperature (70 °C) and pressure (60 bar) conditions in short reaction times.     

Bioengineering functional copolymers. XXI. Synthesis of a novel end carboxyl-trithiocarbonate functionalized poly(maleic anhydride) and its interaction with cancer cells

A novel carboxyl-trithiocarbonate functionalized polymer with a highly selective antitumor activity was synthesized by a reversible addition-fragmentation chain transfer (RAFT) polymerization of maleic anhydride (MA) with benzoyl peroxide as an initiator and S-1-dodecyl-S-(α,α'-dimethyl-α″-acetic acid)trithiocarbonate as a RAFT agent with the aim to design and synthesize an effective anticancer agent with minimum side effects. The structure, molecular weights and composition of synthesized polymers were investigated by (1)H ((13)C) NMR, MALDI-TOF-MS and GPC analyzes. It was demonstrated that RAFT polymerization of MA was accompanied by a partially controlled decarboxylation of anhydride units and the formation of conjugated double bond fragments in backbone macromolecular chains. The mechanism of interaction of pristine RAFT agent and PMA-RAFT polymer with cancer (HeLa human cervix carcinoma) and normal (L929 Fibroblast) cells was investigated by using a combination of chemical, biochemical, statistical, spectroscopic (SEM and fluorescence inverted microscope) and real-time analysis (RTCA) methods. PMA-RAFT exhibited higher and selective cytotoxicity, apoptotic and necrotic effects toward HeLa cells at relatively low concentrations (around 7.5-75μgmL(-1), IC(50)=11.183μgmL(-1)) and toward Fibroblast cells at high concentrations (IC(50)>100μgmL(-1)). The observed highly selective antitumor activity render PMA-RAFT polymers as promising candidates for the utilization in cancer chemotherapy.     

Influence of polymer architecture and molecular weight of poly(2-(dimethylamino)ethyl methacrylate) polycations on transfection efficiency and cell viability in gene delivery

Nonviral gene delivery with the help of polycations has raised considerable interest in the scientific community over the past decades. Herein, we present a systematic study on the influence of the molecular weight and architecture of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) on the transfection efficiency and the cytotoxicity in CHO-K1 cells. A library of well-defined homopolymers with a linear and star-shaped topology (3- and 5-arm stars) was synthesized via atom transfer radical polymerization (ATRP). The molecular weights of the polycations ranged from 16 to 158 kDa. We found that the cytotoxicity at a given molecular weight decreased with increasing number of arms. For a successful transfection a minimum molecular weight was necessary, since the polymers with a number-average molecular weight, M(n), below 20 kDa showed negligible transfection efficiency at any of the tested polyelectrolyte complex compositions. From the combined analysis of cytotoxicity and transfection data, we propose that polymers with a branched architecture and an intermediate molecular weight are the most promising candidates for efficient gene delivery, since they combine low cytotoxicity with acceptable transfection results.     

Surface eroding, liquid injectable polymers based on 5-ethylene ketal ε-caprolactone

Liquid, injectable hydrophobic polymers are potentially useful as depot systems for localized drug delivery. Low molecular weight polymers of 5-ethylene ketal ε-caprolactone and copolymers of this monomer with D,L-lactide were prepared and their properties assessed with respect to their suitability for this purpose. The polymers were amorphous and of low viscosity, and the viscosity was adjustable by choice of initiator and/or by copolymerizing with D,L-lactide. Lower viscosity polymers were attained by using 350 Da methoxy poly(ethylene glycol) as an initiator in comparison to octan-1-ol, while copolymerization with D,L-lactide increased viscosity. The initiator used had no significant effect on the rate of mass loss in vitro, and copolymers with D,L-lactide (DLLA) degraded faster than 5-ethylene ketal ε-caprolactone (EKC) homopolymers. For the EKC-based polymers, a nearly constant degradation rate was observed. This finding was attributed to the hydrolytic susceptibility of the EKC-EKC ester linkage, which was comparable to that of DLLA-DLLA, coupled with a higher molecular weight of the water-soluble degradation product and the low initial molecular weight of the EKC-based polymers. Cytotoxicity of the hydrolyzed EKC monomer to 3T3 fibroblast cells was comparable to that of ε-caprolactone, suggesting that polymers prepared from EKC may be well tolerated upon in vivo implantation.