Zuzana Walterová

Quantification in MALDI-TOF mass spectrometry of modified polymers

MALDI-TOF mass spectrometry quantification is hampered by the poor reproducibility of the signal intensity and by molecular-mass and compositional discrimination. The addition of a suitable compound as an internal standard increases reproducibility and allows a calibration curve to be constructed. The concept was also verified with synthetic polymers but no instructions for practical implementation were given [H. Chen, M. He, J. Pei, H. He, Anal. Chem. 75 (2003) 6531-6535.], even though synthetic polymers are generally non-uniform with respect to molecular mass and composition and access to the polymer of the same molecular mass distribution and composition as that of the quantified one is thus the exception rather than rule. On the other hand, relative quantification of polymers e.g., the content of the precursor polymer in a batch of a modified polymer, is usually sought. In this particular case, the pure precursor is usually available and the modified polymer can serve as an internal standard. However, the calibration curve still cannot be constructed and the use of the internal standard has to be combined with the method of standard addition in which the precursor polymer is added directly to the analyzed sample. The experiments with simulated modified polymers, mixtures of poly(ethylene glycol) (PEG) and poly(ethylene glycol) monomethyl ether (MPEG) of similar molecular-mass distribution, revealed a power dependence of the PEG/MPEG signal-intensity ratio (MS ratio) on the PEG/MPEG concentrations ratio in the mixture (gravimetric ratio). The result was obtained using standard procedures and instrumentation, which means that the basic assumption of the standard-addition method, i.e., the proportionality of the MS and gravimetric ratios, generally cannot be taken for granted. Therefore, the multi-point combined internal-standard standard-addition method was developed and experimentally verified for the quantification of the precursor in modified polymers. In this method, the two parameters of the power-type calibration curve - the proportionality constant and the exponent-are assumed. If the exponent strongly deviates from unity the minority component can be significantly underrepresented in the spectrum. Therefore, the absence of the precursor polymer signals in the MALDI-TOF mass spectrum of a modified polymer sample does not prove the absence of the precursor in the sample. Such a conclusion has to be corroborated by the standard-addition method.

Novel thermosensitive telechelic PEGs with antioxidant activity: synthesis, molecular properties and conformational behaviour

We report on the synthesis and solution properties of novel tailor-made polymer conjugates, which are highly compelling for biomedical applications due to their antioxidant activity and the potential to fine-tune their thermosensitive properties. These conjugates consist of polyethylene glycol (PEG) polymers containing antioxidant moieties, namely 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate or 2-benzamido-3-(3,5-di-tert-butyl-4-hydroxyphenyl)acrylate, as end groups that differ in activity and hydrophobicity. It was shown that all of the synthesized conjugates have low critical solution temperatures (LCSTs) characteristic of type II polymers on a phase diagram. By simply varying the PEG molecular weight, the solution properties, including the LCST value, could be easily tuned across a broad temperature range of 20–90 °C, providing an ideal method for the creation of thermosensitive polymers. It was also established that the LCST value and the polymer conjugate conformation depend on the antioxidant structure. From dynamic light scattering and small-angle X-ray scattering data, we were able to construct a complete sequence diagram of the conformational phase behaviour of the polymers with increasing temperature. It was observed that the conjugate conformation changes are the result of water shifting from a thermodynamically favourable solvent to an unfavourable one. This process then leads to compaction of the conjugate, followed by its aggregation.

Influence of sol-gel conditions on the final structure of silica-based precursors

Abstract This work studied the solvent-free sol–gel process of (3-glycidyloxypropyl)trimethoxysilane using three different experimental setups and a ternary amine (DABCO) or a tin-based compound (DBTL) as the sol–gel catalysts, which allowed to prepare homogeneous liquid products and control their final microstructures. The aim was to synthesize epoxy-functionalized precursors for hybrid epoxy-based materials. The NMR spectroscopy, MALDI-TOF, DLS, FTIR and SEC were used to characterize the obtained sols and xerogels. The formed silica structures were primarily dependent on the type of catalyst used, but small cyclic structures were always present. Nevertheless, the DABCO-catalyzed system showed a higher tendency to create cage-like structures in contrast to the system that used DBTL catalyst in which larger ladder-like structures prevailed. The sols as well as the final xerogels with the higher condensation degree of alkoxysilane bonds were prepared under the basic (DABCO) conditions. All prepared liquid products (sols) were well miscible with epoxy pre-polymers and therefore can be considered as suitable epoxy-functionalized precursors for preparation of hybrid materials based on epoxy matrix.

Molecular properties of hybrid macromolecular antioxidants: Dextran hydrophobically modified by sterically hindered phenols

The conformation properties of clinically relevant hybrid macromolecular antioxidants (dextran hydrophobically modified by sterically hindered phenols) in aqueous solution were characterized by a combination of dynamic light scattering (DLS), size exclusion chromatography (SEC), and small-angle neutron scattering (SANS). We were able to split and analyze separately two different types of polydispersity —polydispersity over molecular weights and the one over substitution degree. The properties of the hybrid macromolecules are determined by the number of hydrophobic antioxidants in a single molecule. An insertion of hydrophobic groups into a hydrophilic chain changes the conformation of a single conjugate macromolecule. We have established that with the increasing of a number of hydrophobic antioxidant groups, a conformational transition occurs where a single conjugate undergoes a transition from a Gaussian coil conformation to a more compact structure.

Potentiometric and viscometric study of the alkalization of latex dispersions of ethyl acrylate — methacrylic acid copolymers in the presence of salt

The behavior of latices of ethyl acrylate — methacrylic acid copolymers during alkalization was investigated using potentiometric titration and viscometry. In the presence of NaCl in dispersion medium pH and viscosity were lower compared to salt-free dispersions. Due to strong electrostatic interactions at low salt concentration the apparent dissociation constant of the carboxylic groups is small and the polymer segments bearing these groups are in extended conformations. The screening effect at higher salt concentration increases the apparent dissociation constant and decreases the extension of the polymer segments. The pH and viscosity of latex dispersions alkalized in the presence of salt are thus smaller.

Effect of cyclodextrins on pH-induced conformational transition of poly(methacrylic acid)

A pH-induced conformational transition of atactic poly(2-methylprop-2-enoic acid) (poly(methacrylic acid), PMMA) from the contracted to expanded conformation was investigated by viscometry, potentiometric titration, and anthracene solubilisation in the presence of low-molecular-mass non-ionogenic co-solutes-glucose, α-cyclodextrin (αCD), and γ-cyclodextrin (γCD), respectively. No effect of glucose and αCD on the conformational transition was observed with either of the methods used. On the other hand, the characteristic features of the conformational transition were absent in the presence of γCD. The different effects of the co-solutes indicate that the interaction between PMAA and γCD corresponds to the partial inclusion of the PMAA chain into the γCD cavity. The viscometry and anthracene solubilisation imply that γCD promotes the expanded conformation of PMAA at low pH. The potentiometric titration does not support this conclusion. Even though there is no break on the Henderson-Hasselbalch plot, a characteristic of the conformational transition, the potentiometric behaviour corresponds to that of the contracted PMMA conformation. Thus the results suggest the hierarchical picture of the PMAA conformation at low pH in which the local arrangement of the PMAA chain is a prerequisite for clustering on a larger scale.

Light scattering study of structure of dispersion particles based on ethyl acrylate-methacrylic acid copolymers

Abstract Structural changes of colloid particles of ethyl acrylate-methacrylic acid (0–70%) copolymers on addition of alkali (pH∼9) or methanol were investigated. In addition to the feeding time of the monomer mixture, the content of methacrylic acid in the copolymers has been shown to influence dissolution of dispersion particles prepared by semicontinuous emulsion copolymerization. The longer the feeding time leading to higher polymer solids and the lower the acid content in the copolymer, the more limited was dissolution of disperse particles. On the basis of consistency of the results obtained in both media, this behaviour was explained in terms of a crosslinked structure of the copolymer due to chain transfer reactions.

Multifunctional polypyrrole@maghemite@silver composites: synthesis, physico-chemical characterization and antibacterial properties

Maghemite (γ-Fe2O3) nanoparticles were synthesized by coprecipitation of ferrous and ferric salts with ammonia and oxidation with sodium hypochlorite. Polypyrrole (PPy) was obtained, by the chemical oxidative polymerization of pyrrole in an aqueous solution in the presence of iron oxide nanoparticles. The morphology of PPy was turned from globular to nanofibers by addition of dyes. The resulting PPy@γ-Fe2O3 hybrid composites were characterized by transmission electron microscopy, magnetic and electrical conductivity measurements and energy dispersive X-ray spectroscopy. Both the electrical conductivity and magnetic properties of the PPy@γ-Fe2O3 nanocomposites were controlled by the maghemite content due to the insulating properties of magnetic iron oxide nanoparticles added to the conducting polymer. Antibacterial activity of all materials was defined by determination of minimal inhibitory concentration. Antibacterial properties of native materials were improved by the reduction of silver ions from an aqueous solution to obtain PPy@γ-Fe2O3@silver composites. Due to the antibacterial properties of these composites, especially of those with silver particles, they can be considered for the applications where bacterial contamination can deteriorate the functionality of material.