Aqueous-phase Size-exclusion Chromatography Research Articles

Cisplatin-Encapsulated Polymeric Nanoparticles with Molecular Geometry-Regulated Colloidal Properties and Controlled Drug Release

Encapsulation of chemotherapeutic agents inside a nanoscale delivery platform can provide an attractive therapeutic strategy with many pharmaceutical benefits, such as increased plasma solubility, prolonged in vivo circulation, and reduced acute toxicity. Given that the biological activities of polymeric nanoparticles are highly dependent on their colloidal structures, the molecular geometry-regulated programming of self-assembled nanoscale architecture is of great interest for chemical design of an ideal delivery platform. In this report, we demonstrate that the molecular geometry of block-copolymer excipients can govern the level of drug-loading capacity and core hydrophobicity of polymeric nanoparticles, which can eventually control the pH-sensitive drug-release property. Atom-transfer radical polymerization was employed as a controlled synthetic method for the copolymer excipients, which contain the metal-chelating poly(acrylic acid) block linked to either a small mPEG-grafted poly(methacrylate) to generate a bulky brush-like chains or a simple linear mPEG segment. During the coordination of cis-diammineplatinum(II) as an active pharmacophore of cisplatin, aqueous-phase size-exclusion chromatography analyses exhibited highly different self-association kinetic regimes prompted by versatile molecular geometry of copolymer excipients, which further allows us to explore the molecular geometry-colloidal property relationship.

The effect of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry instrumentation parameters on the matrix-assisted laser desorption/ionization simulated size exclusion chromatography number-mass, average-weight and polydispersity values of dextran against corresponding values obtained by size exclusion chromatography.

The matrix-assisted laser desorption/ionization simulated size exclusion chromatography (SECPC) average-number mass, weight average and polydispersity of dextran 1000 were determined by matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry. The instrument parameters were varied and the SECPC value determined via the Bruker XMASS software was compared to the value obtained from aqueous-phase size exclusion chromatography. The aqueous-phase size exclusion chromatography values for average-number mass, weight average and polydispersity were 1223 Da, 1500 Da and 1.23 (1010 Da, 1270 Da and 1.26 from manufacturer), whereas the SECPC value varied on the instrumental parameters. The factors that had the greatest effect on the average-number mass, weight average and polydispersity were: (most effect on SECPC value) laser attenuation > matrix-analyte molar concentration > matrix-analyte molar ratios > delay extraction time > solvent-system composition > detector delay (least effect on SECPC value). The oligosaccharide signal distribution as a function of laser attenuation indicate that two distinct regions exist in dextran 1000, where one corresponds to the higher mass oligosaccharides (hexasaccharide or greater), while another region corresponds to lower oligosaccharides (tetra-saccharide). This distribution depends upon the crystallization of the biopolymer and the efficiency of desorption/ionization, which yields the SECPC value. There was broad agreement between the SECPC values and size exclusion chromatography values for dextran, although the polydispersity indicated by SECPC was less than size exclusion chromatography (1.10 vs. 1.26). It can be shown that for narrow polydisperse biopolymers the instrumental conditions are less critical in the determination of average-number mass, weight average and polydispersity, although the SECPC Mn, and weight average values are often higher than the corresponding values obtained by aqueous-phase size exclusion chromatography.

Critically evaluated rate coefficients for free-radical polymerization Part 6: Propagation rate coefficient of methacrylic acid in aqueous solution (IUPAC Technical Report)

Abstract Critically evaluated propagation rate coefficients, k p, for free-radical polymerization of methacrylic acid, MAA, in aqueous solution are presented. The underlying k p values are from two independent sources, which both used the IUPAC-recommended technique of pulsed-laser-initiated polymerization (PLP) in conjunction with molar mass distribution (MMD) analysis of the resulting polymer by size-exclusion chromatography (SEC). Different methods of measuring the MMD of the poly(MAA) samples have, however, been used: (i) direct analysis via aqueous-phase SEC and (ii) standard SEC with tetrahydrofuran as the eluent carried out on poly(methyl methacrylate) samples obtained by methylation of the poly(MAA) samples from PLP. Benchmark k p values for aqueous solutions containing 15 mass % MAA are presented for temperatures between 18 and 89 °C. The Arrhenius pre-exponential and activation energy of k p at 15 mass % MAA are 1.54 × 106 L mol-1 s-1 and 15.0 kJ mol-1, respectively. Also reported are critically evaluated k p values for 25 °C over the entire MAA concentration range from dilute aqueous solution to bulk polymerization.

Free-Radical Propagation Rate Coefficient of Nonionized Methacrylic Acid in Aqueous Solution from Low Monomer Concentrations to Bulk Polymerization

The propagation rate coefficient, kp, for free-radical polymerization of nonionized methacrylic acid (MAA) in aqueous solution has been studied via pulsed laser polymerization (PLP) in conjunction with aqueous-phase size-exclusion chromatography (SEC). The PLP−SEC experiments were carried out between 20 and 80 °C within the entire concentration range from dilute solution containing 1 wt % MAA up to bulk MAA polymerization. The kp values which are determined under the assumption that the relevant monomer concentration at the radical site is identical to the known overall MAA concentration decrease by about 1 order of magnitude between 1 and 100 wt % MAA. This significant lowering is almost entirely due to a reduction in the Arrhenius preexponential factor, A(kp), whereas the activation energy, EA(kp), stays essentially constant. The decrease in A(kp) is assigned to intermolecular interactions between the transition state (TS) structure for MAA propagation and an MAA environment being significantly stronger than the ones between this TS structure and an H2O environment. In an MAA-rich environment, the barrier to rotational motion of the relevant degrees of motion of the TS thus experiences enhanced friction, which is associated with a lowering of the preexponential factor and thus of kp.

Polymerization of guaiacol and a phenolic beta-O-4-substructure by Trametes hirsuta laccase in the presence of ABTS.

The reaction of the monomeric lignin model compound guaiacol and the beta-O-4-type dimer erol (1-(4-hydroxy-3-methoxyphenyl)-2(2-methoxyphenoxy)-propane-1,3-diol with laccase from Trametes hirsuta was studied in the presence of the mediator ABTS (2,2'-azino-di[3ethylbenzothiazoline-6-sulfonic acid]). The product mixtures were analyzed by means of aqueous-phase size exclusion chromatography (SEC) with 50 mM NaOH as eluent. Interestingly, in the laccase-catalyzed reaction with both substrates, the mediator not only functioned as an electron carrier but underwent coupling reactions with the substrate to give polymeric coupling products. The molecular weight of these copolymeric products was significantly higher than the molecular weight of products obtained without ABTS. After ultrafiltration, 33% and 21% of the initially applied ABTS could be found in the polymeric product fraction for the substrates guaiacol and erol, respectively, on the basis of nitrogen analysis. When ABTS was added to substrates after full laccase-catalyzed polymerization, the reaction proceeded toward higher molecular weights.

Investigations on the laccase-catalyzed polymerization of lignin model compounds using size-exclusion HPLC

The reaction of laccase from Trametes hirsuta with monomeric and dimeric lignin model compounds was studied with special attention to the formation of polymeric reaction products. Different HPLC techniques were evaluated for the analysis of the reaction products. Methods requiring a solvent change from aqueous to organic phase were found not to be adequate for the analysis of product mixtures since evaporation over nitrogen led to the polymerization of reactive monomers and extraction with dichloromethane was not quantitative in all cases. Therefore, aqueous phase size-exclusion chromatography (SEC) at high pH was used to characterize reaction product mixtures. The product molecular weight distribution (MWD) after reaction with laccase was observed to be highly dependent on the type of model compound whereas the enzyme concentration had only a limited impact.