This study contributes to the sustained effort to unravel the chemical structure of graphite oxide (GO) by proposing a model based on elemental analysis, transmission electron microscopy, X-ray ...diffraction, 13C magic-angle spinning NMR, diffuse reflectance infrared Fourier transform spectroscopy, X-ray photoelectron spectroscopy, and electron spin resonance investigations. The model exhibits a carbon network consisting of two kinds of regions (of trans linked cyclohexane chairs and ribbons of flat hexagons with CC double bonds) and functional groups such as tertiary OH, 1,3-ether, ketone, quinone, and phenol (aromatic diol). The latter species give clear explanation for the observed planar acidity of GO, which could not be interpreted by the previous models. The above methods also confirmed the evolution of the surface functional groups upon successive oxidation steps.
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Encapsulation of hydrophilic and amphiphilic drugs in appropriate colloidal carrier systems for sustained release is an emerging problem. In general, hydrophobic bioactive substances tend to ...accumulate in water-immiscible polymeric domains, and the release process is controlled by their low aqueous solubility and limited diffusion from the nanocarrier matrix. Conversely, hydrophilic/amphiphilic drugs are typically water-soluble and insoluble in numerous polymers. Therefore, a core–shell approachnanocarriers comprising an internal core and external shell microenvironments of different propertiescan be exploited for hydrophilic/amphiphilic drugs. To produce colloidally stable poly(lactic-co-glycolic) (PLGA) nanoparticles for mitomycin C (MMC) delivery and controlled release, a unique class of amphiphilic polymershydrophobically functionalized polyelectrolyteswere utilized as shell-forming materials, comprising both stabilization via electrostatic repulsive forces and anchoring to the core via hydrophobic interactions. Undoubtedly, the use of these polymeric building blocks for the core–shell approach contributes to the enhancement of the payload chemical stability and sustained release profiles. The studied nanoparticles were prepared via nanoprecipitation of the PLGA polymer and were dissolved in acetone as a good solvent and in an aqueous solution containing hydrophobically functionalized poly(4-styrenesulfonic-co-maleic acid) and poly(acrylic acid) of differing hydrophilic–lipophilic balance values. The type of the hydrophobically functionalized polyelectrolyte (HF-PE) was crucial for the chemical stability of the payloadderivatives of poly(acrylic acid) were found to cause very rapid degradation (hydrolysis) of MMC, in contrast to poly(4-styrenesulfonic-co-maleic acid). The present contribution allowed us to gain crucial information about novel colloidal nanocarrier systems for MMC delivery, especially in the fields of optimal HF-PE concentrations, appropriate core and shell building materials, and the colloidal and chemical stability of the system.
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Herein we present the synthesis of a polymeric prodrug nanomaterial capable of spontaneous, self-assembled nanoparticle formation and of the conjugation (encapsulation) of drugs with amino and/or ...carboxyl and/or hydroxyl groups via ester and/or amide linkage. Mitomycin C (MMC) a versatile drug with antibiotic, antibacterial and antineoplastic properties, was used to prove this concept. The in vitro drug release experiments showed a fast release for the pure MMC (k = 49.59 h−n); however, a significantly lower MMC dissolution rate (k = 2.25, 1.46, and 1.35 h−n) was obtained for the nanoparticles with increased cross-link density (3, 10, 21%). The successful modification and conjugation reactions were confirmed using FTIR and EDX measurements, while the mucoadhesive properties of the self-assembled particles synthesized in a simple one-pot reaction were proved by rheological measurement. The prepared biocompatible polymeric prodrugs are very promising and applicable as a drug delivery system (DDS) and useful in the area of cancer treatment.
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•Surface reactivity of TiO2 and Ag–TiO2 nanohybrid films were tested by photooxidation.•Photocatalyst–bacteria interactions were defined by surface charge determination.•Higher ...surface charge induces stronger adhesion between the bacteria and the NPs.•Inactivation of GR+/GR− bacteria by hydroxyl radicals depends on cell wall structure.•The cell wall degradation of bacteria was proven with TEM and fluorescence studies
The aim of this study was to develop photoreactive surface coatings, possessing antibacterial properties and can be activated under visible light illumination (λmax=405nm) using LED-light source. The photocatalytically active titanium dioxide (TiO2) was functionalized with silver nanoparticles (Ag NPs) and immobilized in polyacrylate based nanohybrid thin film in order to facilitate visible light activity (λAg/TiO2,max=500nm). First, the photocatalytic activity was modelled by following ethanol vapor degradation. The plasmonic functionalization resulted in 15% enhancement of the activity compared to pure TiO2. The photoreactive antimicrobial (5log reduction of cfu in 2h) surface coatings are able to inactivate clinically relevant pathogen strains (methicillin resistant Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa) within short time (60–120min) due to the formed and quantified reactive oxygen species (ROS). The existence of electrostatic interactions between the negatively charged bacteria (from −0.89 to −3.19μeq/109 cfu) and positively charged photocatalyst particles (in the range of +0.38 and +12.3meq/100g) was also proven by charge titration measurements. The surface inactivation of the bacteria and the photocatalytic degradation of the cell wall component were also confirmed by fluorescence and transmission electron microscopic observations, respectively. According to the results an effective sterilizing system and prevention strategy can be developed and carried out against dangerous microorganisms in health care.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Antioxidant colloids were developed via controlled heteroaggregation of cerium oxide nanoparticles (CeO2 NPs) and sulfate-functionalized polystyrene latex (SL) beads. Positively charged CeO2 NPs were ...directly immobilized onto SL particles of opposite surface charge via electrostatic attraction (SL/Ce composite), while negatively charged CeO2 NPs were initially functionalized with poly(diallyldimethylammonium chloride) (PDADMAC) polyelectrolyte and then, aggregated with the SL particles (SPCe composite). The PDADMAC served to induce a charge reversal on CeO2 NPs, while the SL support prevented nanoparticle aggregation under conditions, where the dispersions of bare CeO2 NPs were unstable. Both SL/Ce and SPCe showed enhanced radical scavenging activity compared to bare CeO2 NPs and were found to mimic peroxidase enzymes. The results demonstrate that SL beads are suitable supports to formulate CeO2 particles and to achieve remarkable dispersion storage stability. The PDADMAC functionalization and immobilization of CeO2 NPs neither compromised the peroxidase-like activity nor the radical scavenging potential. The obtained SL/Ce and SPCe artificial enzymes are foreseen to be excellent antioxidant agents in various applications in the biomedical, food, and cosmetic industries.
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•CeO2 NPs were immobilized onto sulfate latex particles at two pH regimes.•Direct immobilization was achieved under acidic conditions.•Surface modification of CeO2 was required for immobilization at alkaline pH.•High stability of the composites was achieved by optimization of the mass ratio.•The formulated composites exhibited excellent antioxidant enzyme-like activity.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Synthesis of spherical (d = 3–5 mm) Fe(III)-alginate aerogel particles.•Detailed characterization of Fe(III)-alginate aerogel (including SAXS).•Impregnation of aerogel spheres with ibuprofen and ...ascorbic acid in sc. CO2.•Incorporated ascorbic acid markedly increases the rate of drug release.
Iron(III)-crosslinked alginate aerogel beads (d = 3–5 mm) were prepared and loaded with ibuprofen by using the technique of adsorptive deposition from supercritical CO2. Additional formulations were prepared where the aerogels were co-impregnated by ibuprofen and ascorbic acid. The release of ibuprofen from the Fe(III)-alginate is much faster in pH = 7.4 (PBS) than in pH = 2.0 (HCl), which can be explained by the faster dissolution and higher swelling of the alginate matrix in PBS. By decreasing the size of the beads and using a higher G content alginate the release rate could be slightly increased. A marked acceleration of drug release was achieved in both HCl and PBS by incorporating ascorbic acid into the Fe(III)-alginate aerogel preparations. The explanation is that in aqueous media ascorbic acid in situ reduces the crosslinking Fe(III) to Fe(II). The latter does not interact strongly with alginate, which promotes the hydration of the chains, thus the erosion and dissolution of the carrier matrix.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Microfibrous TiO2−sepiolite and TiO2/SiO2−sepiolite nanocomposites were prepared following a colloidal route based on the controlled hydrolysis of alkoxides in the presence of ...cetyltrimethylammonium−sepiolite gel. In this way, titanium(IV) isopropoxide and tetramethoxysilane were used as titania and silica precursors, respectively, being incorporated within the organophilic layer developed on the surface of the silicate microfibers and further hydrolyzed in this region. The hydrolysis of the precursor gives highly viscous colloidal systems leading to a spontaneous heterocoagulation process of the colloidal system. Drying and thermal treatments of the resulting gels ensure the elimination of water and organic matter, driving to the formation of TiO2 nanoparticles homogeneously distributed on the surface of the sepiolite microfibers. The nanocomposites were characterized by chemical analyses, transmission electron microscopy, field emission scanning electron microscopy, X-ray diffraction, thermogravimetric/differential thermal analysis, and N2 adsorption. They were tested as photocatalysts in the photo-oxidation of phenol in an aqueous medium, showing the efficiency of the anatase containing nanocomposites in the removal of this selected pollutant model molecule. Thiourea was incorporated to increase the TiO2 anatase phase stability, improving in this manner the photocatalytic activity of the TiO2−sepiolite nanocomposites. It has been shown that sepiolite has a positive synergistic effect on the TiO2 photocatalysis.
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A systematic investigation of single particle inductively coupled plasma mass spectrometry (spICP-MS) signal profiles recorded with normal (ms-range) and high (μs-range) temporal resolution for ...spherical and rod-shaped gold nanoparticles was performed. The experiments with nanorods were carried out on hemispherically capped cylindrical particles synthesized in the aspect ratio range from 1.5 to 4.5. A comparison of NP signals and time profiles for spherical and rod-shaped NPs revealed that (i) the volume of the particles can be assessed by conventional spICP-MS measurements using a joint, linear calibration plot; and (ii) the shape of signal time profiles and transit times for equal-volume spherical and rod-shaped NPs are different, based on which the aspect ratio can be calculated. By using the statistical evaluation of the high resolution signal time profiles, an analytical method was developed for the discrimination and dimensional analysis of nanorod-shaped NPs. The method is based on observing the shortest and longest transit times for nanoparticles. In the case of spherical NPs, these transit times are very similar, whereas in the case of nanorods, the shortest and longest transit times correlate with the characteristic width and length of the particles, respectively. This method is the first nanorod dimensional characterization method in the literature, which is based solely on ICP-MS measurements. It was shown that the accuracy of the method is very good – the characteristic length and width of the particles could be determined with less than 6% error.
In this paper, a rapid optical method for characterizing plasmonic (gold) nanoparticle (AuNP) adhesion is presented. Two different methods were used for AuNP preparation: the well-known Turkevich ...method resulted in particles with negative surface charge; for preparing AuNPs with positive surface charge, stainless steel was used as reducing agent. The solid surface for adhesion was provided by a column packed with pristine or surface-modified glass beads. The size of the nanoparticles was studied by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS); the surface charge of the components was determined by streaming potential measurements. The characterization of adhesion was performed in a flow system by UV-Vis spectroscopy. During the adhesion experiments, the role of the surface charge, the particle size, and the pH were studied, as well as the adhered amount of gold nanoparticles and the surface coverage values. The latter was estimated by theoretical calculations and defined by the quotient of the measured and the maximal adhered amount of nanoparticles, which could be determined by the cross-sectional area of the NPs and the specific surface area of the glass beads. The results are verified by the polarization reflectometric interference spectroscopy (PRIfS) method: silica nanoparticles with diameters of a few hundred (
d
~450) nanometers were immobilized on the surface of glass substrate by the Langmuir–Blodgett method, the surface was modified similar to the 3D (continuous flow packed column) system, and gold nanoparticles from different pH solutions were adhered during the measurements. These kinds of modified surfaces allow the investigation of biomolecule adsorption in the same reflectometric setup.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Anionic surfactants, such as sodium linear alkylbenzene sulfonates (NaLAS), are utilized in various fields, including industry, household, and agriculture. The efficiency of their use in aqueous ...environments is significantly affected by the presence of cations, Ca2+ and Mg2+ in particular, as they can decrease the concentration of the surfactant due to precipitation. To understand cation–sulfonate interactions better, we study both NaLAS colloidal solutions in the presence of CaCl2 and precipitates forming at higher salt concentrations. Upon addition of CaCl2, we find the surface tension and critical micelle concentration of NaLAS to decrease significantly, in line with earlier findings for alkylbenzylsulfonates in the presence of divalent cations. Strikingly, an increase in the surface tension is discernible above 0.6 g L–1 NaLAS, accompanied by the decrease of apparent micelle sizes, which in turn gives rise to transparent systems. Thus, there appears to be a second critical concentration indicating another micellar equilibrium. Furthermore, the maximum salt tolerance of the surfactant is 0.1 g L–1 Ca2+, above which rapid precipitation occurs yielding sparingly soluble CaLAS2∙2H2O.
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