Michal Kalina

Structural effects and nanoparticle size are essential for quantum dots–metallothionein complex formation

Interaction between semiconductor nanocrystals, cadmium telluride quantum dots (CdTe QDs) capped with mercaptosuccinic acid (MSA) and metallothionein (MT) was investigated. MSA-capped CdTe QDs were synthesized in aqueous solution. Mixture of MT and MSA-capped CdTe QDs has been investigated by various analytical methods as follows: tris-tricine gel electrophoresis, fluorescence evaluation and electrochemical detection of catalysed hydrogen evolution. The obtained results demonstrate that MSA-capped CdTe QDs and MT do not create firmly bound stabile complex. However, weak electrostatic interactions contribute to the interaction of MT with MSA-capped CdTeQDs. It can be concluded that QDs size influences the QDs and MT interaction. The smallest QDs had the highest affinity to MT and vice versa.

Composition, particle size, charge, and colloidal stability of pH-fractionated humic acids

PurposeThe purpose of this study was to divide humic acids into several fractions by means of their dissolving in buffers with different pH values and to characterize obtained humic fractions with respect to their composition, structure, particle size, and charge. Relationships between determined characteristics of fractionated humic acids and pH values of used buffer solutions and the method of fractionation was investigated.Materials and methodsHumic acids were fractionated by means of two different methods: the subsequent dissolution in buffers adjusted to different pH and the sequential dissolution in buffers with increasing pH values. Composition, structure, and properties of the obtained humic fractions were studied using elemental analysis, FT-IR spectroscopy, UV/VIS spectroscopy, and light scattering methods.Results and discussionAs expected, fractions obtained by subsequent dissolution were more heterogeneous than those prepared by sequential extraction. Fractions obtained at lower pH values contained higher amounts of aromatic and carboxylic groups, while those extracted at higher pH values were rich in aliphatic and/or peptide groups. Fractions extracted close to neutral pH region had some specific properties. Functional groups dissociated in a range of pH values depending on the chemical structure of the molecules. Weaker carboxylic groups could dissociate in less acidic solutions, and more aromatic fractions could be dissolved. Conformational changes and deaggregation process differed with the fractionation procedure and concentration of studied solutions. A bimodal distribution of particle sizes and higher values of polydispersity were obtained for some for less concentrated solutions of humic fractions.ConclusionsObtained humic fractions behave as anionic heterogeneous ligands with many carboxylic and phenolic groups of different strength, and present polyfunctional and polyelectrostatic effects due to different functional sites and net charged groups. Two main processes can affect their properties and behavior in aqueous solutions: dissociation of acidic functional groups and breaking of humic aggregates into smaller molecular associations or humic molecules. An important parameter affecting the spatial arrangement of obtained humic fractions is their concentration.

Characterization of the promising poly(3-hydroxybutyrate) producing halophilic bacterium Halomonas halophila

This work explores molecular, morphological as well as biotechnological features of the highly promising polyhydroxyalkanoates (PHA) producer Halomonas halophila. Unlike many other halophiles, this bacterium does not require expensive complex media components and it is capable to accumulate high intracellular poly(3-hydroxybutyrate) (PHB) fractions up to 82% of cell dry mass. Most remarkably, regulating the concentration of NaCl apart from PHB yields influences also the polymers molecular mass and polydispersity. The bacterium metabolizes various carbohydrates including sugars predominant in lignocelluloses and other inexpensive substrates. Therefore, the bacterium was employed for PHB production on hydrolysates of cheese whey, spent coffee grounds, sawdust and corn stover, which were hydrolyzed by HCl; required salinity of cultivation media was set up during neutralization by NaOH. The bacterium was capable to use all the tested hydrolysates as well as sugar beet molasses for PHB biosynthesis, indicating its potential for industrial PHB production.

On the role of humic acids’ carboxyl groups in the binding of charged organic compounds

Interactions of humic acids (HAs) with two cationic dyes (methylene blue and rhodamine 6G) were studied using a unique combination of diffusion and partitioning studies in HAs, containing hydrogels and batch sorption experiments. In order to investigate the involvement of carboxyl groups of HAs in these interactions, all experiments were performed for both, the original lignite HAs and HAs with selectively methylated carboxyls. The results of the diffusion experiments confirm that the interactions between the solute and humic substances have a strong impact on the rate of diffusion process. Surprisingly, the effect is almost equally approved for original and methylated HAs. On the other hand, the results of batch sorption experiments show strong improvement of the sorption capacity (methylated HAs), which is explained by changed morphology of alkylated HAs. The comparison of the results of diffusion and adsorption experiments shows that the diffusion experiments simulate the transport of solutes in natural humics containing environment more reasonably.

Long-term degradation study of hyaluronic acid in aqueous solutions without protection against microorganisms.

The degradation of hyaluronan (HA) of different molecular weights (Mw 14.3, 267.2 and 1160.6 kDa, measured for fresh solutions, before degradation) was studied in aqueous solutions by SEC-MALLS determination of molecular mass, polydispersity and conformation parameters. The solutions were stored either at laboratory or refrigerator temperatures for two months. After this period the weight average molecular weight decreased by 90% for 14.3 kDa, 95% for 267.2 kDa and 71% for 1160.6 kDa hyaluronan (room temperature) or 5.6% for 14.3 kDa, 6.2% for 267.2 kDa and 7.7% for 1160.6 kDa hyaluronan (refrigerator temperature). The hyaluronan aqueous solutions studied did not contain sodium azide or other protectants against microorganisms, because the aim of our study was to assess the degradation in solutions to be used in medicine or cosmetics (without any compounds that are poisonous or toxic for the human body). The solvent used to prepare the samples was pure water. The polydispersity of all the samples remained unaltered during the entire degradation at both temperatures. This indicates a non-random mechanism of degradation.

Determination of critical parameters of drug substance influencing dissolution: a case study.

The purpose of this study was to specify critical parameters (physicochemical characteristics) of drug substance that can affect dissolution profile/dissolution rate of the final drug product manufactured by validated procedure from various batches of the same drug substance received from different suppliers. The target was to design a sufficiently robust drug substance specification allowing to obtain a satisfactory drug product. For this reason, five batches of the drug substance and five samples of the final peroral drug products were analysed with the use of solid state analysis methods on the bulk level. Besides polymorphism, particle size distribution, surface area, zeta potential, and water content were identified as important parameters, and the zeta potential and the particle size distribution of the drug substance seem to be critical quality attributes affecting the dissolution rate of the drug substance released from the final peroral drug formulation.

Silver Nanoparticles Stabilised by Cationic Gemini Surfactants with Variable Spacer Length

The present study is focused on the synthesis and investigation of the physicochemical and biological properties of silver nanoparticles stabilized with a series of cationic gemini surfactants having a polymethylene spacer of variable length. UV-VIS spectroscopy, dynamic light scattering, scanning electron microscopy and zeta potential measurements were applied to provide physicochemical characterization of the silver nanoparticles. The mean size values of the nanoparticles were found to be in the 50 to 115 nm range. From the nanoparticle size distributions and scanning electron microscopy images it results that a population of small nanoparticles with the size of several nanometers was confirmed if the nanoparticles were stabilized with gemini molecules with either a short methylene spacer (two or four −CH2− groups) or a long spacer (12 −CH2− groups). The average zeta potential value for silver nanoparticles stabilized with gemini molecules is roughly independent of gemini surfactant spacer length and is approx. +58 mV. An interaction model between silver nanoparticles and gemini molecules which reflects the gained experimental data, is suggested. Microbicidal activity determinations revealed that the silver nanoparticles stabilized with gemini surfactants are more efficient against Gram-negative bacteria and yeasts, which has a direct relation to the interaction mechanism of nanoparticles with the bacterial cell membrane and its structural composition.

Preparation and Characterisation of Highly Stable Iron Oxide Nanoparticles for Magnetic Resonance Imaging

Magnetic nanoparticles produced using aqueous coprecipitation usually exhibit wide particle size distribution. Synthesis of small and uniform magnetic nanoparticles has been the subject of extensive research over recent years. Sufficiently small superparamagnetic iron oxide nanoparticles easily permeate tissues and may enhance the contrast in magnetic resonance imaging. Furthermore, their unique small size also allows them to migrate into cells and other body compartments. To better control their synthesis, a chemical coprecipitation protocol was carefully optimised regarding the influence of the injection rate of base and incubation times. The citrate-stabilised particles were produced with a narrow average size range below 2źnm and excellent stability. The stability of nanoparticles was monitored by long-term measurement of zeta potentials and relaxivity. Biocompatibility was tested on the Caki-2 cells with good tolerance. The application of nanoparticles for magnetic resonance imaging (MRI) was then evaluated. The relaxivities (r1,r2) and r2/r1 ratio calculated from MR images of prepared phantoms indicate the nanoparticles as a promising T2-contrast probe.

Transport of Organic Compounds Through Porous Systems Containing Humic Acids

Soil pollution by the presence of different contaminants (e.g. heavy metal ions or pesticides) is one of the biggest problems worldwide. The positive affinity of natural humic acids towards these contaminants might contribute to the soil and ground water protection; therefore it is necessary to study the reactivity and barrier properties of humic acids. An original reactivity-mapping tool based on diffusion techniques designed to study the reactivity and barrier properties of polyelectrolytes was developed and tested on humic acids. The results of diffusion experiments demonstrate that the electrostatic interactions between humic acids functioning as a polyelectrolyte interpenetrated in a supporting hydrogel matrix (agarose) and cationic dye (methylene blue) as a model solute have a crucial impact on the rate of diffusion processes and on the barrier properties of hydrogels. The intensity of interactions was evaluated by fundamental diffusion parameters (effective diffusion coefficients and breakthrough time). The impact of modification of humic acids was also studied by means of diffusion experiments conducted on two types of standard humic acids (Leonardite 1S104H) and humic acids with selectively methylated carboxylic groups.

Reactivity-Mapping Tool Based on Diffusion Techniques for Characterization of Biocolloids

The universal reactivity-mapping tool was developed for characterization and study on barrier properties of selected biopolymers. The reactivity of biocolloids (humic acids) was studied by both diffusion techniques (break-through diffusion technique and non-stationary diffusion). The rate of reactivity of humic acids was compared by the interactions with basic cationic organic dye (Methylene Blue) because of the positive interactions among anionic supramolecular humic acids and cationic organic dyes were expected. The reactivity and barrier properties of biocolloids were compared by determination of fundamental diffusion parameters such as effective diffusion coefficient, sorption capacity, break-through time (the time needed for penetration of chosen organic dye through hydrogel porous barrier) or the concentration of organic dye on the interface hydrogel-solution. The original combination of simple diffusion experiments of suitable diffusion probe (organic dye) with the advantages of hydrogel porous media (simple preparation of hydrogels, the diffusion is undisturbed by convection, etc.) provides very valuable information about the reactivity of chosen biocolloids.