Judith Mihály

Enhanced stability of polyacrylate-coated magnetite nanoparticles in biorelevant media.

Magnetite nanoparticles (MNPs) were prepared by alkaline hydrolysis of Fe(II) and Fe(III) chlorides. Adsorption of polyacrylic acid (PAA) on MNPs was measured at pH=6.5±0.3 and I=0.01 M (NaCl) to find the optimal PAA amount for MNP stabilization under physiological conditions. We detected an H-bond formation between magnetite surface groups and PAA by ATR-FTIR measurements, but bonds of metal ion-carboxylate complexes, generally cited in literature, were not identified at the given pH and ionic strength. The dependence of the electrokinetic potential and the aggregation state on the amount of added PAA at various pHs was measured by electrophoretic mobility and dynamic light-scattering methods. The electrokinetic potential of the naked MNPs was low at near physiological pH, but PAA adsorption overcharged the particles. Highly negatively charged, well-stabilized carboxylated MNPs formed via adsorption of PAA in an amount of approximately ten times of that necessary to compensate the original positive charge of the magnetite. Coagulation kinetics experiments revealed gradual enhancement of salt tolerance at physiological pH from ~0.001 M at no added PAA up to ~0.5 M at 1.12 mmol/g PAA. The PAA-coated MNPs exert no substantial effect on the proliferation of malignant (HeLa) or non-cancerous fibroblast cells (MRC-5) as determined by means of MTT assays.

Silver- and sulfadiazine-loaded nanostructured silica materials as potential replacement of silver sulfadiazine

Silver sulfadiazine (AgSD) is the leading topical antibacterial agent for the treatment of burn wound infections. Antibacterial effect of AgSD is limited by its poor aqueous solubility, and antibacterial activity develops only by decomposition of AgSD to silver ions and sulfadiazine. In this study, it is for the first time that application of silver-modified nanoporous silica carriers (MCM-41 or SBA-15) loaded with sulfadiazine (SD), instead of silver sulfadiazine, overcoming the abovementioned disadvantages has been demonstrated. By direct or post synthesis methods, 5-15 nm sized silver nanoparticles can be stabilized in the channels or on the outer surface of nanoporous silica supports; moreover, the empty channels can be loaded by SD molecules. The SD-loaded, silver-modified materials show sustained release properties and similar or even better antimicrobial properties than AgSD. Adsorption of AgSD on nanoporous silica particles significantly improves its water solubility.

Infrared spectroscopic investigation of CO adsorption on SBA-15- and KIT-6-supported nickel phosphide hydrotreating catalysts.

The infrared (IR) spectra of CO adsorbed on 10, 20, and 30 wt % nickel phosphide-containing reduced SBA-15 and KIT-6 mesoporous silica-supported catalysts have been studied at 300-473 K. On the catalysts containing a stoichiometric amount of phosphorus with 20 wt % loading, the most intense IR absorption band was observed at 2097-2099 cm(-1), which was assigned to CO terminally bonded to coordinatively unsaturated Ni(delta+) (0 < delta < 1) sites. The frequency of this band was 15 cm(-1), higher than that in the spectrum of a reduced Ni2P/SiO2 catalyst, indicating a modified Ni-P charge distribution. This band shifted to lower wavenumbers, and its intensity decreased, while the relative intensity of another band at 2191-2194 cm(-1) assigned to CO terminally bonded to P increased going to catalytically less active, excess-P-containing SBA-15-supported catalysts. CO also adsorbed as a bridged carbonyl (1910 cm(-1)) and as Ni(CO)4 (2050 cm(-1)) species, and the formation of surface carbonates was also identified. The nature of the surface acidity was studied by temperature-programmed desorption of ammonia (NH3-TPD). Weak and strong acid sites were revealed, and the high excess-P-containing catalyst released the highest amount of ammonia, indicating that a high concentration of strong acidity can be disadvantageous for reaching high hydrotreating catalytic activity. The modified Ni-P charge distribution, the mode of CO adsorption on surface nickel phosphide sites, as well as the acidity can be directly connected to the catalytic activity of these mesoporous silica-supported catalysts.

A mechanistic view of lipid membrane disrupting effect of PAMAM dendrimers

The effect of 5th generation polyamidoamine (PAMAM G5) dendrimers on multilamellar dipalmitoylphosphocholine (DPPC) vesicles was investigated. PAMAM was added in two different concentrations to the lipids (10(-3) and 10(-2) dendrimer/lipid molar ratios). The thermal behavior of the evolved systems was characterized by DSC; while the structure and the morphology were investigated with small- and wide-angel X-ray scattering (SWAXS), freeze-fracture electron microscopy (FFTEM) and phosphorus-31 nuclear magnetic resonance ((31)P NMR) spectroscopy, respectively. IR spectroscopy was used to study the molecular interactions between PAMAM and DPPC. The obtained results show that the dendrimers added in 10(-3) molar ratio to the lipids generate minor perturbations in the multilamellar structure and thermal character of liposomes, while added in 10(-2) molar ratio dendrimers cause major disturbance in the vesicular system. The terminal amino groups of the dendrimers are in strong interaction with the phosphate headgroups and through this binding dendrimers disrupt the regular multilamellar structure of DPPC. Besides highly swollen, fragmented bilayers, small vesicles are formed.

Thermotropic and structural effects of poly(malic acid) on fully hydrated multilamellar DPPC–water systems

The thermotropic and structural effects of low molecular weight poly(malic acid) (PMLA) on fully hydrated multilamellar dipalmitoylphosphatidylcholine (DPPC)-water systems were investigated using differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), and freeze-fracture transmission electron microscopy (FFTEM). Systems of 20wt% DPPC concentration and 1 and 5wt% PMLA to lipid ratios were studied. The PMLA derivatives changed the thermal behavior of DPPC significantly and caused a drastic loss in correlation between lamellae in the three characteristic thermotropic states (i.e., in the gel, rippled gel and liquid crystalline phases). In the presence of PBS or NaCl, the perturbation was more moderate. The structural behavior on the atomic level was revealed by FTIR spectroscopy. The molecular interactions between DPPC and PMLA were simulated via modeling its measured infrared spectra, and their peculiar spectral features were interpreted. Through this interpretation, the poly(malic acid) is inferred to attach to the headgroups of the phospholipids through hydrogen bonds between the free hydroxil groups of PMLA and the phosphodiester groups of DPPC.

Inherently fluorescent and porous zirconia colloids: preparation, characterization and drug adsorption studies

Porous, fluorescent zirconia particles of nearly 380 nm diameter were prepared without template molecules or labeling dyes. The porous structure is the result of aggregation-induced particle formation. The inherent fluorescence is assigned to coordinatively unsaturated Zr4+ ions at the sol-gel derived ZrO2 surface. After physico-chemical characterization of the native zirconia particles carboxyl and/or amine bearing drug molecules (d,l-α-difluoromethylornithine - DFMO, ursolic acid - UA and doxorubicin - DOX) were adsorbed onto their surface, and the products were analyzed with Fourier-transform infrared spectroscopy (FTIR), thermogravimetry (TG), small-angle X-ray scattering (SAXS), fluorimetry and zeta potential vs. pH measurements. We have found that DOX complexes coordinatively unsaturated Zr4+ ions without dislocating them, while carboxyl-bearing drugs interact with basic surface Zr-OH sites eliminating some of the carbonate species. The adsorption of UA at the zirconia surface shifts considerably the isoelectric point of the surface and thus provides kinetic stability to the particles at physiological pH. An in vivo biodistribution study in two healthy dogs performed by SPECT/CT detection after 99mTc labeling of the nanocarriers has shown the possibility of drug delivery application.

Reference materials and representative test materials to develop nanoparticle characterization methods: the NanoChOp project case

This paper describes the production and characteristics of the nanoparticle test materials prepared for common use in the collaborative research project NanoChOp (Chemical and optical characterization of nanomaterials in biological systems), in casu suspensions of silica nanoparticles and CdSe/CdS/ZnS quantum dots (QDs). This paper is the first to illustrate how to assess whether nanoparticle test materials meet the requirements of a “reference material” (ISO Guide 30, 2015) or rather those of the recently defined category of “representative test material (RTM)” (ISO/TS 16195, 2013). The NanoChOp test materials were investigated with small-angle X-ray scattering (SAXS), dynamic light scattering (DLS), and centrifugal liquid sedimentation (CLS) to establish whether they complied with the required monomodal particle size distribution. The presence of impurities, aggregates, agglomerates, and viable microorganisms in the suspensions was investigated with DLS, CLS, optical and electron microscopy and via plating on nutrient agar. Suitability of surface functionalization was investigated with attenuated total reflection Fourier transform infrared spectrometry (ATR-FTIR) and via the capacity of the nanoparticles to be fluorescently labeled or to bind antibodies. Between-unit homogeneity and stability were investigated in terms of particle size and zeta potential. This paper shows that only based on the outcome of a detailed characterization process one can raise the status of a test material to RTM or reference material, and how this status depends on its intended use.

Controlled synthesis and characterization of biodegradable, stereomer co-polycondensates of l-malic acid

A one-pot synthesis of stereomer cross-linked copolymers of l-malic acid with tuned properties is reported. The β-cyclodextrin, as co-monomer with several OH groups, was applied to promote the polyester formation with higher, pre-defined molecular weight. The importance of the experimental conditions for preparation of polymers with tailor-made, optically active compositions is described, and their structures are characterized by different techniques such as thermogravimetry–differential scanning calorimetry−mass spectrometric evolved gas analysis, infrared spectroscopy and specific rotation. To our knowledge, first time was used the specific optical rotation for characterization of retention of the optical activity in the course of the synthesis.

Physicochemical characterization of artificial nanoerythrosomes derived from erythrocyte ghost membranes

Colloidal stabile nanoerythrosomes with 200 nm average diameter were formed from hemoglobin-free erythrocyte ghost membrane via sonication and membrane extrusion. The incorporation of extra lipid (1,2-dipalmitoyl-sn-glycero-3-phosphocholine, DPPC), added to the sonicated ghosts, caused significant changes in the thermotropic character of the original membranes. As a result of the increased DPPC ratio the chain melting of the hydrated DPPC system and the characteristic small angle X-ray scattering (SAXS) of the lipid bilayers appeared. Significant morphological changes were followed by transmission electron microscopy combined with freeze fracture method (FF-TEM). After the ultrasonic treatment the large entities of erythrocyte ghosts transformed into nearly spherical nanoerythrosomes with diameters between 100 and 300 nm and at the same time a great number of 10-30 nm large membrane proteins or protein clusters were dispersed in the aqueous medium. The infrared spectroscopy (FT-IR) pointed out, that the sonication did not cause changes in the secondary structures of the membrane proteins under our preparation conditions. About fivefold of extra lipid--compared to the lipid content of the original membrane--caused homogeneous dispersion of nanoerythrosomes however the shape of the vesicles was not uniform. After the addition of about tenfold of DPPC, monoform and monodisperse nanoerythrosomes became typical. The outer surfaces of these roughly spherical objects were frequently polygonal, consisting of a net of pentagons and hexagons.

Specific behavior of the p-aminothiophenol--silver sol system in their Ultra-Violet-Visible (UV-Visible) and Surface Enhanced Raman (SERS) spectra.

The UV-Visible and Surface Enhanced Raman Spectroscopy (SERS) behavior of silver sol (a typical SERS agent) were studied in the presence of different bifunctional thiols such as p-aminothiophenol, p-mercaptobenzoic acid, p-nitrothiophenol, p-aminothiophenol hydrochloride, and 2-mercaptoethylamine hydrochloride in diluted aqueous solution. Our results confirm that the p-aminothiophenol induced aggregation of citrate stabilized silver colloid originates from its electrostatic nature, as well as the azo-bridge formation cannot be the reason of the observed time dependent UV-Visible spectra. Based on our parallel SERS and electrospray ionization mass spectrometry measurements, we have concluded that certain amount of oxidized form of the probe molecule has to be present for the so-called b2-mode enhancement in the SERS spectrum of p-aminothiophenol. Our findings seem to support the idea that the azo-bridge formation is responsible for the b2-mode enhancement in the SERS spectrum of p-aminothiophenol.