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1
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The Influence of Magnetic Particles on the Nematic Droplets Formation in Liquid Crystal

100%
Majorošová J., Gdovinová V., Tomašovičová N., Juríková A., Závišová V., Jadzyn J., Kopčanský P.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
955-957
EN
In this work the thermotropic nematic liquid crystal 4-trans-4'-n-hexyl-cyclohexyl-isothiocyanato-benzene (6CHBT) was dissolved in phenyl-isothiocyanate and doped with spherical magnetic particles with volume concentration ϕ₁=10¯⁴ and ϕ₂=10¯³. The influence of the volume concentration on the phase transitions from isotropic to nematic phase was studied by three experimental methods: optical microscopy, differential scanning calorimetry, and dielectric measurements. The obtained results confirmed the coexistence of isotropic and nematic phase, i.e. nematic or ferronematic droplets in isotropic phase in a wide temperature range between nematic and isotropic phase.
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The Structural Phase Transitions in 6CB-Based Ferronematics

100%
Tomašovičová N., Koneracká M., Kopčanský P., Timko M., Závišová V., Tomčo L., Jadżyn J.
Acta Physica Polonica A
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2009
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vol. 115
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issue 1
336-338
EN
The structural transitions in ferronematics based on the thermotropic nematic liquid crystal 4-cyano-4'-hexylbiphenyl were studied. The ferronematic samples were prepared by doping with magnetic suspension consisting of Fe_3O_4 particles (10 nm in diameter) coated with oleic acid as a surfactant with different volume concentrations of magnetic particles (from 10^{-5} to 10^{-3}). Freedericksz transitions were studied in combined electric and magnetic fields. The experimental results indicated soft anchoring with perpendicular initial orientation between the magnetic moment of the magnetic particles and director.
3
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Thermal Analysis of Magnetic Nanoparticles Modified with Dextran

100%
Juríková A., Csach K., Miškuf J., Koneracká M., Závišová V., Kubovčíková M., Kopčanský P.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1296-1298
EN
In the work the thermal behaviour of the magnetic nanoparticles modified with polysaccharide dextran of different weight ratios to the magnetite Fe_3O_4 was investigated using thermoanalytical methods - differential scanning calorimetry and thermogravimetric analysis. The adsorption of dextran on the magnetic nanoparticles was confirmed and the influence of the dextran amount in the modified magnetic fluid on the thermal decomposition of the complex system was studied. The results showed that magnetite catalyzed the thermal decomposition of dextran, the adsorbed dextran showed lower initial decomposition temperatures in comparison with the free one.
4
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Thermogravimetric Study of the Decomposition of BSA-Coated Magnetic Nanoparticles

100%
Csach K., Juríková A., Miškuf J., Koneracká M., Závišová V., Kubovčíková M., Kopčanský P.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1293-1295
EN
Magnetic nanoparticles used in biomedicine have to be biocompatible, which can be achieved by the modification of the magnetic particle surface with an appropriate biocompatible substance. In the work protein bovine serum albumin (BSA) was chosen to modify the surface of magnetic nanoparticles. The BSA-coated magnetic nanoparticles with different input weight ratios of BSA to the magnetite Fe_3O_4 were prepared and thermally characterized using thermogravimetric and differential scanning calorimetric analysis. The adsorption of BSA on the magnetic nanoparticles in wide range of concentration was confirmed. The activation energies of the thermal decomposition of the complex system were estimated.
5
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Magnetic Properties of Encapsulated Magnetite in PLGA Nanospheres

100%
Koneracká M., Závišová V., Timko M., Kopčanský P., Tomašovičová N., Csach K.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
595-598
EN
In this study, the biocompatible magnetic fluid was encapsulated in biodegradable polymer PLGA (poly D, L/lactide-co-glycolide acid) by the nanoprecipitation method. We characterized these spheres in terms of morphology, magnetite content and magnetic properties. The results showed good encapsulation with magnetite content 22wt% and magnetization 3.4 mT. The transmission electron microscopy and scanning electron microscopy images showed that magnetic particles have almost a spherical shape with approximate size 250 nm. Infrared spectroscopy and thermogravimetric analysis measurements were used to confirm incorporation of magnetic particles into the PLGA polymer.
6
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Structural Changes in Liquid Crystals Doped with Rod-Like Magnetic Particles Studied by Surface Acoustic Waves

100%
Bury P., Veveričík M., Kúdelčík J., Kopčanský P., Timko M., Závišová V.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
913-915
EN
The effect of rod-like magnetic particles on liquid crystal (6CHBT) structural changes in electric and weak magnetic fields were studied by means of the attenuation of surface acoustic wave of frequency 30 MHz propagating along ferronematic liquid crystals. Three low volume concentrations (Φ=1×10¯⁵, 1×10¯⁴ and 1×10¯³) of rod-like magnetic particles were added to liquid crystal during its isotropic phase. Several measurements including the investigation of the effects of electrical and magnetic fields applied both separately and in conjunction as well as the influence of temperature on the surface acoustic wave attenuation were performed. The distinctive surface acoustic wave attenuation responses induced by both electric and magnetic fields in studied ferronematic liquid crystals have been observed suggesting both structural changes and the orientational coupling between magnetic moments of magnetic particles and the director of the liquid crystal. Obtained results confirmed the significant influence of the presence of magnetic particles on the structural properties and resulting behavior of 6CHBT liquid crystal.
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Thermal Analysis of Magnetic Polymer Nanospheres for Drug Targeting

100%
Juríková A., Csach K., Miškuf J., Koneracká M., Závišová V., Kopčanský P.
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issue 5
990-992
EN
Poly(D,L-lactic-co-glycolic) acid (PLGA) polymer nanospheres loaded with different input amounts of anticancer drug taxol were prepared by the modified nanoprecipitation method. Magnetite was incorporated into the polymer nanospheres to impart them superparamagnetic properties. Thermal properties of the drug loaded magnetic polymer nanospheres were characterized using differential scanning calorimetry and thermogravimetric analysis. The solid state solubility of taxol in PLGA nanospheres and the influence of external magnetic field on their thermal stability were estimated. The investigations have revealed that the samples of dried taxol loaded magnetic PLGA nanospheres undergo mass loss at three stages during heating.
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Preparation and Complex Characterization of Magnetic Nanoparticles in Magnetic Fluid

100%
Kubovčíková M., Antal I., Kováč J., Závišová V., Koneracká M., Kopčanský P.
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vol. 126
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issue 1
268-269
EN
This paper deals with the preparation and complex characterization of magnetite nanoparticles (MNPs), stabilized with sodium oleate (SO), by the routine methods such as infrared spectroscopy (FTIR), magnetic measurements, scanning electron microscopy (SEM) and dynamic light scattering (DLS). The FTIR spectra showed that SO molecules were linked to MNPs through chemical bonding. Magnetic measurements proved that the MNPs are superparamagnetic in nature. Four different methods were used to determine the size and size distribution of the MNPs: SEM, DLS, differential centrifugal sedimentation (DCS) and magnetic measurements. SEM analysis showed a relatively narrow size distribution of roughly spherical MNPs with a mean diameter of 61 nm. DLS analysis confirmed monodispersed MNPs production with hydrodynamic diameter of 75 nm. The size distribution determined by DCS was found to be 69 nm. Finally, the calculated magnetic core diameter obtained from magnetization curve was 10 nm. The obtained results demonstrate that SO coated MNPs fulfil the requirements for a useful drug delivery system.
9
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Temperature Effect on the Structure of Transformer Oil Based Magnetic Fluids Using Acoustic Spectroscopy

100%
Kúdelčík J., Bury P., Drga J., Kopčanský P., Závišová V., Timko M.
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EN
The changes in structural arrangement in transformer oil based magnetic fluids upon the effect of an external magnetic field and temperature were studied by acoustic spectroscopy. The attenuation of acoustic waves was measured as a function of an external magnetic field in the range of 0-300 mT, parallel to the direction of the field and as a function of temperature in the range of 15-35°C for various magnetic nanoparticles concentrations. The strong influence of the steeped magnetic field on the acoustic wave attenuation was detected and its hysteresis was observed, too. When a magnetic field is swept at a constant rate, the dominant interactions between the external magnetic field and the magnetic moment of the nanoparticles occur, leading to the aggregation of magnetic nanoparticles and clusters formation. However, the temperature of magnetic fluids has very important influence on the obtained dependences, where the mechanism of thermal motion acts against the cluster creation. The observed influences of magnetic field and temperature on the investigated magnetic liquids structure are discussed.
10
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Magnetic Field Induced Structural Transitions in 6CHBT-Based Ferronematics

84%
Tomašovičová N., Timko M., Koneracká M., Závišová V., Jadżyn J., Beaugnon E., Chaud X., Kopčanský P.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1276-1278
EN
Ferronematics are stable colloidal suspensions of magnetic particles in nematic liquid crystals. The presence of the magnetic particles enhances the magnetic susceptibility of ferronematics, in comparison with pure liquid crystals. In this work the thermotropic liquid crystal 4-(trans-4'-n-hexylcyclohexyl)-isothiocyanato-benzene (6CHBT) and 6CHBT dissolved in phenyl isothiocyanate were doped with spherical magnetic nanoparticles with aim to increase the sensitivity of the liquid crystal on an external magnetic field. The volume concentration of the magnetic particles was 5 × 10^{-4}. The phase transition temperature from isotropic to nematic phase in the external magnetic field up to 12 T was monitored by precise capacitance measurements in the capacitance cells filled with nematic sample as well as with the prepared ferronematic sample. There was no observable shift in the transition temperature in the case of pure 6CHBT, 6CHBT doped with spherical particles and 6CHBT dissolved in phenyl isothiocyanate while in the case of 6CHBT dissolved in phenyl isothiocyanate doped with spherical magnetic particles the shift in the temperature about 9C of the phase transition from isotropic to droplet state at the external magnetic field 12 T was observed.
11
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Kinetics of Nematic to Isotropic Phase Transition in Liquid Crystal Doped with Magnetic Nanoparticles

84%
Csach K., Juríková A., Miškuf J., Tomašovičová N., Gdovinová V., Závišová V., Kopčanský P., Éber N., Fodor-Csorba K., Vajda A.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
949-951
EN
A binary mixture of bent-core and rod-shaped liquid crystals was chosen as a model substance combining the properties of both types of liquid crystals. The mixture was doped with a small amount of spherical and rod-like magnetic nanoparticles. Differential scanning calorimetry experiments were performed for the pure as well as for the doped mixture at different heating rates ranging from 1 to 16°C/min. The addition of the magnetic nanoparticles lowered the phase transition temperature. This effect is more intensive in the case of the rod-like magnetic nanoparticles. The kinetics of the nematic to isotropic phase transition was evaluated in the framework of the differential isoconversional method. The calculated apparent activation energy showed non-monotonic behaviour and a sensitivity on the shape of added magnetic nanoparticles.
12
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Low Magnetic Field Response in Ferronematics

84%
Gdovinová V., Tomašovičová N., Závišová V., Éber N., Tóth-Katona T., Royer F., Jamon D., Jadzyn J., Kopčanský P.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
934-936
EN
In this work the 4-n-hexyl-4'-cyanobiphenyl liquid crystal was doped with differently shaped magnetite nanoparticles. The structural changes were observed by capacitance measurements. Influence of the shape of magnetic particles on magnetic Fréedericksz transition depends on the type of anchoring, which is characterized by the density of the anchoring energy and by the initial orientation between the liquid crystal molecules and the magnetic moment of the magnetic particles. It was observed that in the case of doping with spherical particles, the critical magnetic field is shifted to higher values with increase of volume concentration of the magnetic nanoparticles but decreases with increase of biasing voltage. In the case of doping with rod-like particles, the critical magnetic field is almost independent of the volume concentration of the magnetic nanoparticles.
13
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Magnetic Properties of Magnetite Formed by Biomineralization and Chemical Synthesis

84%
Timko M., Džarová A., Kopčanský P., Závišová V., Koneracká M., Kováč J., Šprincová A., Vaclavíková M., Ivaničová L., Vávra I.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
573-576
EN
In this work, the magnetic properties of biologically produced magnetite (magnetosomes) by biomineralization process were compared to those of chemically synthesized Fe_3O_4. The coercivity of 185 Oe in magnetosomes is connected with the fact that the mean diameter is larger than critical size for transition from superparamagnetic to ferromagnetic behavior. A sharp magnetic transition at 105 K (Verwey transition) is clearly present in magnetosomes while in opposite, this transition is missing in Fe_3O_4.
14
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The Anchoring Energy of Liquid Crystal Molecules to Magnetic Particles in HAB-Based Ferronematics

84%
Tomašovičová N., Koneracká M., Kopčanský P., Timko M., Závišová V., Vajda A., Fodor-Csorba K., Éber N., Tóth-Katona T., Jadzyn J.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
591-594
EN
In this work we describe the magnetic Freedericksz transition in HAB-based (4, 4'-di-n-heptylazoxybenzene) ferronematics. The ferronematic samples were prepared with two different volume concentrations of magnetic particles φ_1 = 2×10^{-5} and φ_2 = 2×10^{-4}. The liquid crystal HAB is nematic at the temperatures from ≈53°C to 70°C and smectic A at the temperatures under 53°C. The anisotropy of dielectric permitivity of HAB liquid crystal is positive in nematic phase and negative in smectic A phase. The magnetic Fredericksz transition was studied in nematic phase at temperature 60°C.
15
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Radiation Stability of the BSA Modified Biocompatible Magnetic Fluid

84%
Tomašovičová N., Haysak I., Kováč J., Kubovčíková M., Závišová V., Timko M., Okunev A., Zorkovská A., Kopčanský P.
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vol. 126
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issue 1
262-263
EN
The aim of the presented work was to investigate the stability of biocompatible magnetic fluid, i.e. water-based magnetic fluid containing magnetite nanoparticles stabilized by surfactant sodium oleate and modified by bovine serum albumin (BSA) after electron irradiation. Samples with the same concentration of Fe_{3}O_{4} but different mass ratio BSA/Fe_{3}O_{4} (w/w=0.25, 1.0 and 2.5) were studied. The electron irradiation caused about 10% reduction of the saturation magnetization in the samples with w/w BSA/Fe_{3}O_{4} ratio of 0.25 and less than 5% in the samples with w/w BSA/Fe_{3}O_{4} ratio of 1 and 2.5.
16
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Thermal Stability of Bent-Core Liquid Crystals Doped with Magnetic Nanoparticles

69%
Juríková A., Csach K., Miškuf J., Tomašovičová N., Mitróová Z., Závišová V., Koneracká M., Kopčanský P., Timko M., Éber N., Fodor-Csorba K., Vajda A.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
638-640
EN
In the work phase transitions in bent-core liquid crystals were studied using differential scanning calorimetry. For the binary mixture of bent-core molecules with 50 wt% of rod-shaped compound, the nematic to smectic transition occured below 40°C and the crystallization temperature shifted to sub-ambient temperatures. The influence of doping of the bent-core liquid crystals with magnetic nanoparticles on the kinetics of observed phase transitions was studied. The phase transition temperatures were shifted depending on the nanoparticle type and changed with varying cooling rate for all studied liquid crystal samples.
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Magnetic Properties of Biocompatible Magnetic Fluid after Electron Irradiation

69%
Tomašovičová N., Haysak I., Koneracká M., Kováč J., Timko M., Závišová V., Okunev A., Parlag A., Fradkin A., Sakhno V., Kopčanský P.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1302-1304
EN
The magnetic particles in the water-based magnetic fluids were sterically stabilized by natrium oleate to prevent their agglomeration and consequently the adsorption of poly-ethylene-glycol (PEG) was carried out to improve the biocompatibility of the magnetic particles. Two sets of samples were prepared. The first set of the samples was with different molar weight of PEG (Mw = 400, 1000, 10000 and 20000) at the constant weight ratio of PEG/Fe_3O_4 = 0.25 and the second one was with different weight ratio of PEG/Fe_3O_4 and constant molar weight of PEG (Mw = 1000). The samples were irradiated with 20 Gy. The same reduction of saturated magnetization (about 10%) after electron irradiation with 20 Gy was observed for all prepared samples.
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Structural Phase Transition in Liquid Crystal Doped with Gold Nanoparticles

69%
Kopčanský P., Tomašovičová N., Koneracká M., Timko M., Mitróová Z., Závišová V., Éber N., Fodor-Csorba K., Tóth-Katona T., Vajda A., Jadzyn J., Beaugnon E., Chaud X.
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issue 5
988-989
EN
The influence of the inclusion of the dodecanethiol functionalized gold particles (with diameter 3-5 nm) on the structural transitions was investigated. The studied samples were based on the nematic liquid crystal 4-(trans-4'-n-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT). The volume concentration of the gold particles was ϕ_1 = 2 × 10^{-4} and ϕ_2 = 10^{-3}. The obtained results showed that the inclusion of the gold particles in the 6CHBT liquid crystal increases the sensitivity of such system on the external magnetic field.
19
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Characterization of Fe_3O_4 Magnetic Nanoparticles Modified with Dextran and Investigation of Their Interaction with Protein Amyloid Aggregates

69%
Koneracká M., Antošová A., Závišová V., Lancz G., Gažová Z., Šipošová K., Juríková A., Csach K., Kováč J., Tomašovičová N., Fabián M., Kopčanský P.
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issue 5
983-985
EN
Functionalised magnetic nanoparticles composed of Fe_3O_4 particles stabilised by sodium oleate and subsequently modified with dextran (MFDEX) were prepared by the co-precipitation method. Their morphology and particle size distribution were observed by scanning electron microscopy and photon cross correlation spectroscopy. In order to confirm the modification of magnetite surface with dextran physical techniques, including infrared spectroscopy, thermal analysis, and magnetic measurement, were used. Finally, the effect of MFDEX on amyloid fibrillar aggregates of human insulin and hen egg white lysozyme, typical amyloidogenic proteins, was investigated. In vitro interaction of MFDEX with protein amyloid fibrils resulted into destruction of amyloid aggregates. The anti-amyloid activity makes MFDEX of potential interest as therapeutic agent against amyloid-related diseases.
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