Formation of retinyl palmitate-loaded poly(l-lactide) nanoparticles using rapid expansion of supercritical solutions into liquid solvents (RESOLV)

Poly(l-lactide) (PLLA) nanoparticles loaded with retinyl palmitate (RP) were successfully prepared by rapid expansion of a supercritical carbon dioxide (CO₂) solution into an aqueous receiving solution containing a stabilizing agent (RESOLV). Three stabilizing agents, Pluronic F127, Pluronic F68, and sodium dodecyl sulfate (SDS) have been employed and the Pluronic F127 was found to be more effective for stabilizing PLLA/RP nanoparticles than Pluronic F68 and SDS, as RESOLV into a 0.1 wt% Pluronic F127 solution produced a stable nanosuspension consisting mainly of well-dispersed, individual nanoparticles. The effect of rapid expansion processing conditions (i.e., degree of saturation (S), pre-expansion temperature (T_pre), and concentrations of PLLA and RP (C_PLLA, C_RP)) on the particle size, form, and RP loading was systematically investigated. It was found that spherical PLLA/RP nanoparticles with an average size range of ∼40-110 nm and RP loadings of 0.9-6.2 wt% were consistently produced by RESOLV. The size of PLLA/RP nanoparticles increased from ∼30-80 to ∼30-160 nm as the solution degree of saturation changed from S < 1 to S > 1, independent of T_pre, C_PLLA, and C_RP. The entrapment capacity of RP in PLLA nanoparticles was predominantly determined by T_pre and C_RP. Increasing the T_pre from 70 to 100 °C and the C_RP from 0.05 to 0.15 wt% increased the encapsulated RP content at least twofold. Our results show that the technique with benign supercritical CO₂ should be generally applicable to nanoparticle fabrications of other important active ingredients, especially in liquid form, in polymeric nanoparticles.     

Influence of Growth Conditions on Magnetite Nanoparticles Electro-Crystallized in the Presence of Organic Molecules

Magnetite nanoparticles were synthesized by electrocrystallization in the presence of thiourea or sodium butanoate as an organic stabilizer. The synthesis was performed in a thermostatic electrochemical cell containing two iron electrodes with an aqueous solution of sodium sulfate as electrolyte. The effects of organic concentration, applied potential and growth temperature on particle size, morphology, structure and magnetic properties were investigated. The magnetite nanoparticles were characterized by X-ray diffraction, electron microscopy, magnetometry and Mössbauer spectrometry. When the synthesis is performed in the presence of sodium butanoate at 60 °C, a paramagnetic ferric salt is obtained as a second phase; it is possible to avoid formation of this phase, increase the specific magnetization and improve the structure of the oxide particles by tuning the growth conditions. Room-temperature magnetization values range from 45 to 90 Am²kg⁻¹, depending on the particle size, type of surfactant and synthesis conditions. Mössbauer spectra, which were recorded at 290 K for all the samples, are typical of nonstoichiometric Fe_3−δO₄, with a small excess of Fe³⁺, 0.05 ≤ δ ≤ 0.15.     

Ferromagnetism and optical properties of La1???x Al x FeO3 nanopowders

La_{1 − x} Al _x FeO₃ (x = 0.0, 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5) nanopowders were prepared by polymerization complex method. All prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), and UV-vis spectrophotometry (UV-vis). The magnetic properties were investigated using a vibrating sample magnetometer (VSM). The X-ray results of all samples show the formation of an orthorhombic phase with the second phase of α-Fe₂O₃ in doped samples. The crystallite sizes of nanoparticles decreased with increasing Al content, and they are found to be in the range of 58.45 ± 5.90 to 15.58 ± 4.64 nm. SEM and TEM images show the agglomeration of nanoparticles with average particle size in the range of 60 to 75 nm. The FT-IR spectra confirm the presence of metal oxygen bonds of O-Fe-O and Fe-O in the FeO₆ octahedra. The UV-vis spectra show strong absorption peaks at approximately 285 nm, and the calculated optical band gaps are found to be in the range of 2.05 to 2.09 eV with increasing Al content. The M-H loop of the pure sample is antiferromagnetic, whereas those of the doped samples tend to be ferromagnetic with increasing Al content. The magnetization, remanent magnetization, and coercive field of the Al-doped sample with x = 0.5 are enhanced to 1.665 emu/g, 0.623 emu/g, and 4,087.0 Oe, respectively.     

Influence of Co content on the characterization and magnetic properties of magnetite

Preparation of nanosized Co_xFe_3−xO₄; 0.05 ≤ x ≤ 0.20 particles from metal nitrates solution through citrate–precursor method was performed. XRD pattern of all prepared systems showed single phase with cubic spinel structure. The crystallite size was determined from TEM and found to agree with that calculated from Sherrer's equation (60–76 nm) The magnetic constants such as molar magnetic susceptibility (χ_M), Curie temperature (T_C) and saturation magnetization (M_S) were measured and the results indicated that, at x = 0.2 the values of χ_M, M_S, remanent magnetization (M_r,) and coercive field (H_c) are 23 emu/g mol, 77.62 emu/g, 33.17 emu/g and 574.5 Oe, respectively_.     

Tangential Flow Ultrafiltration Allows Purification and Concentration of Lauric Acid-/Albumin-Coated Particles for Improved Magnetic Treatment

Superparamagnetic iron oxide nanoparticles (SPIONs) are frequently used for drug targeting, hyperthermia and other biomedical purposes. Recently, we have reported the synthesis of lauric acid-/albumin-coated iron oxide nanoparticles SEON^LA-BSA, which were synthesized using excess albumin. For optimization of magnetic treatment applications, SPION suspensions need to be purified of excess surfactant and concentrated. Conventional methods for the purification and concentration of such ferrofluids often involve high shear stress and low purification rates for macromolecules, like albumin. In this work, removal of albumin by low shear stress tangential ultrafiltration and its influence on SEON^LA-BSA particles was studied. Hydrodynamic size, surface properties and, consequently, colloidal stability of the nanoparticles remained unchanged by filtration or concentration up to four-fold (v/v). Thereby, the saturation magnetization of the suspension can be increased from 446.5 A/m up to 1667.9 A/m. In vitro analysis revealed that cellular uptake of SEON^LA-BSA changed only marginally. The specific absorption rate (SAR) was not greatly affected by concentration. In contrast, the maximum temperature T_max in magnetic hyperthermia is greatly enhanced from 44.4 °C up to 64.9 °C by the concentration of the particles up to 16.9 mg/mL total iron. Taken together, tangential ultrafiltration is feasible for purifying and concentrating complex hybrid coated SPION suspensions without negatively influencing specific particle characteristics. This enhances their potential for magnetic treatment.     

Chitosan-Coated Magnetic Nanoparticles Prepared in One Step by Reverse Microemulsion Precipitation

Chitosan-coated magnetic nanoparticles (CMNP) were obtained at 70 °C and 80 °C in a one-step method, which comprises precipitation in reverse microemulsion in the presence of low chitosan concentration in the aqueous phase. X-ray diffractometry showed that CMNP obtained at both temperatures contain a mixture of magnetite and maghemite nanoparticles with ≈4.5 nm in average diameter, determined by electron microscopy, which suggests that precipitation temperature does not affect the particle size. The chitosan coating on nanoparticles was inferred from Fourier transform infrared spectrometry measurements; furthermore, the carbon concentration in the nanoparticles allowed an estimation of chitosan content in CMNP of 6%–7%. CMNP exhibit a superparamagnetic behavior with relatively high final magnetization values (≈49–53 emu/g) at 20 kOe and room temperature, probably due to a higher magnetite content in the mixture of magnetic nanoparticles. In addition, a slight direct effect of precipitation temperature on magnetization was identified, which was ascribed to a possible higher degree of nanoparticles crystallinity as temperature at which they are obtained increases. Tested for Pb²⁺ removal from a Pb(NO₃)₂ aqueous solution, CMNP showed a recovery efficacy of 100%, which makes them attractive for using in heavy metals ion removal from waste water.     

Structural, electrical and magnetic properties of carbon-nickel composite thin films

Carbon-nickel composite thin films (600 nm thick) were prepared by dc magnetron sputtering of Ni and C at several temperatures (25-800 °C) on oxidized silicon substrates. By transmission electron microscopy it was found that the composite consisted of Ni (or Ni₃C) nanoparticles embedded in a carbon matrix. The metallic nanoparticles were shaped in the form of globular grains or nanowires (of the aspect ratio as high as 1:60 in the sample prepared at 200 °C). The carbon matrix was amorphous, or graphite-like depending on deposition temperature. At low deposition temperatures T_S (25-400 °C) the Ni₃C nanoparticles were of hcp phase. Samples prepared at T_S ? 600 °C contained ferromagnetic fcc Ni nanoparticles. A correlation was found between the structural, electrical and magnetic properties of the composites. To characterise the films, dependences, such as resistivity vs. temperature, current vs. voltage, differential conductivity vs. bias voltage, and magnetoresistivity, were determined. For example, the tunneling effect was found in samples in which the metallic nanoparticles were separated by 2-3 nm thick amorphous carbon. When the metallic nanoparticles were connected by graphite-like carbon regions (having a metallic conductivity, in contrast to a-C), the temperature coefficient of the resistivity became slightly positive. An anisotropic magnetoresistivity of ∼0.1% was found in the sample that contained ferromagnetic columnar fcc Ni. Zero magnetoresistivity was found in the sample in which the metallic nanoparticles were of non-magnetic hcp phase.     

Enzymatic Synthesis of Magnetic Nanoparticles

We report the first in vitro enzymatic synthesis of paramagnetic and antiferromagnetic nanoparticles toward magnetic ELISA reporting. With our procedure, alkaline phosphatase catalyzes the dephosphorylation of l-ascorbic-2-phosphate, which then serves as a reducing agent for salts of iron, gadolinium, and holmium, forming magnetic precipitates of Fe_45±14Gd_5±2O_50±15 and Fe_42±4Ho_6±4O_52±5. The nanoparticles were found to be paramagnetic at 300 K and antiferromagnetic under 25 K. Although weakly magnetic at 300 K, the room-temperature magnetization of the nanoparticles found here is considerably greater than that of analogous chemically-synthesized Ln_xFe_yO_z (Ln = Gd, Ho) samples reported previously. At 5 K, the nanoparticles showed a significantly higher saturation magnetization of 45 and 30 emu/g for Fe_45±14Gd_5±2O_50±15 and Fe_42±4Ho_6±4O_52±5, respectively. Our approach of enzymatically synthesizing magnetic labels reduces the cost and avoids diffusional mass-transfer limitations associated with pre-synthesized magnetic reporter particles, while retaining the advantages of magnetic sensing.     

Ammonium fluoride-activated synthesis of cubic δ-TaN nanoparticles at low temperatures

Cubic delta-tantalum nitride (δ-TaN) nanoparticles were selectively prepared using a K₂TaF₇ + (5 + k) NaN₃ + kNH₄F reactive mixture (k being the number of moles of NH₄F) via a combustion process under a nitrogen pressure of 2.0 MPa. The combustion temperature, when plotted as a function of the number of moles of NH₄F used, was in the range of 850°C to 1,170°C. X-ray diffraction patterns revealed the formation of cubic δ-TaN nanoparticles at 850°C to 950°C when NH₄F is used in an amount of 2.0 mol (or greater) in the combustion experiment. Phase pure cubic δ-TaN synthesized at k = 4 exhibited a specific surface area of 30.59 m²/g and grain size of 5 to 10 nm, as estimated from the transmission electron microscopy micrograph. The role of NH₄F in the formation process of δ-TaN is discussed with regard to a hypothetical reaction mechanism.     

Facile molten salt synthesis of Li2NiTiO4 cathode material for Li-ion batteries

Well-crystallized Li₂NiTiO₄ nanoparticles are rapidly synthesized by a molten salt method using a mixture of NaCl and KCl salts. X-ray diffraction pattern and scanning electron microscopic image show that Li₂NiTiO₄ has a cubic rock salt structure with an average particle size of ca. 50 nm. Conductive carbon-coated Li₂NiTiO₄ is obtained by a facile ball milling method. As a novel 4 V positive cathode material for Li-ion batteries, the Li₂NiTiO₄/C delivers high discharge capacities of 115 mAh g^-1 at room temperature and 138 mAh g^-1 and 50°C, along with a superior cyclability.     

Temperature-Responsive Poly(?-caprolactone) Cell Culture Platform with Dynamically Tunable Nano-Roughness and Elasticity for Control of Myoblast Morphology

We developed a dynamic cell culture platform with dynamically tunable nano-roughness and elasticity. Temperature-responsive poly(ɛ-caprolactone) (PCL) films were successfully prepared by crosslinking linear and tetra-branched PCL macromonomers. By optimizing the mixing ratios, the crystal-amorphous transition temperature (T_m) of the crosslinked film was adjusted to the biological relevant temperature (~33 °C). While the crosslinked films are relatively stiff (50 MPa) below the T_m, they suddenly become soft (1 MPa) above the T_m. Correspondingly, roughness of the surface was decreased from 63.4–12.4 nm. It is noted that the surface wettability was independent of temperature. To investigate the role of dynamic surface roughness and elasticity on cell adhesion, cells were seeded on PCL films at 32 °C. Interestingly, spread myoblasts on the film became rounded when temperature was suddenly increased to 37 °C, while significant changes in cell morphology were not observed for fibroblasts. These results indicate that cells can sense dynamic changes in the surrounding environment but the sensitivity depends on cell types.     

Synthesis and Characterization of Novel Quaternary Ammonium Urethane-Dimethacrylate Monomers—A Pilot Study

Six novel urethane-dimethacrylate analogues (QAUDMAs) were synthesized and characterized. They consisted of the 2,4,4,-trimethylhexamethylene diisocyanate (TMDI) core and two methacrylate-terminated wings containing quaternary ammonium groups substituted with alkyl chains of 8, 10, 12, 14, 16, or 18 carbon atoms. QAUDMAs, due to the presence of quaternary ammonium groups, may have possible antibacterial effects. Since they showed satisfactory physicochemical properties, they will be subjected to further research towards the development of dental composites with a capacity to reduce secondary caries. The synthesis of QAUDMAs included three stages: (i) transesterification of methyl methacrylate (MMA) with N-methyldiethanolamine (MDEA), (ii) N-alkylation of the tertiary amino group with alkyl bromide, and (iii) addition of TMDI to the intermediate achieved in the second stage. The formation of QAUDMAs was confirmed by ¹H and ¹³C NMR. They were characterized for density (d_m), viscosity (η), refractive index (RI), glass transition temperature (T_g), polymerization shrinkage (S), and degree of conversion (DC). QAUDMAs were yellow, viscous resins (the η values ranged from 1.28 × 10³ to 1.39 × 10⁴ Pa·s, at 50 °C). Their RI ranged from 1.50 to 1.52, T_g from −31 to −15 °C, DC from 53 to 78%, and S from 1.24 to 2.99%, which is appropriate for dental applications.     

Size-controllable synthesis and bandgap modulation of single-layered RF-sputtered bismuth nanoparticles

We here report a simple and efficient method to grow single-layer bismuth nanoparticles (BiNPs) with various sizes on glass substrates. Optimal conditions were found to be 200°C and 0.12 W/cm² at a growth rate of 6 Å/s, with the deposition time around 40 s. Scanning electron microscope (SEM) images were used to calculate the particle size distribution statistics, and high-resolution X-ray diffraction (XRD) patterns were used to examine the chemical interactions between BiNPs and the substrates. By measuring the transmission spectra within the range of 300 to 1,000 nm, we found that the optical bandgap can be modulated from 0.45 to 2.63 eV by controlling the size of these BiNPs. These interesting discoveries offer an insight to explore the dynamic nature of nanoparticles.     

Spin Polarization and Quantum Spins in Au Nanoparticles

The present study focuses on investigating the magnetic properties and the critical particle size for developing sizable spontaneous magnetic moment of bare Au nanoparticles. Seven sets of bare Au nanoparticle assemblies, with diameters from 3.5 to 17.5 nm, were fabricated with the gas condensation method. Line profiles of the X-ray diffraction peaks were used to determine the mean particle diameters and size distributions of the nanoparticle assemblies. The magnetization curves M(H_a) reveal Langevin field profiles. Magnetic hysteresis was clearly revealed in the low field regime even at 300 K. Contributions to the magnetization from different size particles in the nanoparticle assemblies were considered when analyzing the M(H_a) curves. The results show that the maximum particle moment will appear in 2.4 nm Au particles. A similar result of the maximum saturation magnetization appearing in 2.3 nm Au particles is also concluded through analysis of the dependency of the saturation magnetization M_P on particle size. The M_P(d) curve departs significantly from the 1/d dependence, but can be described by a log-normal function. Magnetization can be barely detected for Au particles larger than 27 nm. Magnetic field induced Zeeman magnetization from the quantum confined Kubo gap opening appears in Au nanoparticles smaller than 9.5 nm in diameter.     

Dopant induced RTFM and enhancement of fluorescence efficiencies in spintronic ZnS:Ni nanoparticles

Diluted magnetic semiconducting (DMS) ZnS:Ni (Ni=0, 1, 3 and 5 at%) nanoparticles were synthesized by the refluxing technique at 80 °C. X-ray diffraction studies showed that undoped ZnS and Ni doped ZnS nanoparticles exhibited the expected zinc blende structure. X-ray photoelectron spectroscopy results revealed that the Ni ions existed in a +2 state in these nanoparticles. Reflectance measurements showed a decrease in band gap with increasing Ni concentration. Room temperature photoluminescence (PL) studies indicated that all the samples exhibited broad and asymmetric PL peaks covering a wide visible range. Gaussian fitting of PL data resulted in three deconvoluted peaks corresponding to blue and green emissions. Dramatic enhancement in fluorescence efficiency was observed in the doped ZnS nanoparticles indicating their possible applications in photoluminescent devices. Magnetic studies revealed that all the doped samples exhibited carrier mediated ferromagnetism at room temperature. Saturation magnetization (M_s) increased with increasing Ni content reaching a maximum for 3 at% Ni and decreased for samples of 5 at% Ni.     

Biocatalyzed Synthesis of Flavor Esters and Polyesters: A Design of Experiments (DoE) Approach

In the present work, different hydrolases were adsorbed onto polypropylene beads to investigate their activity both in short-esters and polyesters synthesis. The software MODDE^® Pro 13 (Sartorius) was used to develop a full-factorial design of experiments (DoE) to analyse the thermostability and selectivity of the immobilized enzyme towards alcohols and acids with different chain lengths in short-esters synthesis reactions. The temperature optima of Candida antarctica lipase B (CaLB), Humicola insolens cutinase (HiC), and Thermobifida cellulosilytica cutinase 1 (Thc_Cut1) were 85 °C, 70 °C, and 50 °C. CaLB and HiC preferred long-chain alcohols and acids as substrate in contrast to Thc_Cut1, which was more active on short-chain monomers. Polymerization of different esters as building blocks was carried out to confirm the applicability of the obtained model on larger macromolecules. The selectivity of both CaLB and HiC was investigated and best results were obtained for dimethyl sebacate (DMSe), leading to polyesters with a M_w of 18 kDa and 6 kDa. For the polymerization of dimethyl adipate (DMA) with BDO and ODO, higher molecular masses were obtained when using CaLB onto polypropylene beads (CaLB_PP) as compared with CaLB immobilized on macroporous acrylic resin beads (i.e., Novozym 435). Namely, for BDO the M_n were 7500 and 4300 Da and for ODO 8100 and 5000 Da for CaLB_PP and for the commercial enzymes, respectively. Thc_Cut1 led to polymers with lower molecular masses, with M_n < 1 kDa. This enzyme showed a temperature optimum of 50 °C with 63% of DMA and BDO when compared to 54% and 27%, at 70 °C and at 85 °C, respectively.     

Sol–gel auto combustion synthesis of CoFe2O4/1-methyl-2-pyrrolidone nanocomposite: Its magnetic characterization

A magnetic nanocomposite was generated by the sol–gel auto-combustion method in the presence of 1-methyl-2-pyrrolidone, a functional solvent. The temperature-dependent magnetic properties of the CoFe₂O₄ nanoparticles have been extensively studied in the temperature range of 10–400 K and magnetic fields up to 80 kOe. Zero field cooled (ZFC) and field cooled (FC) curves indicate that the blocking temperature (T_B) of the CoFe₂O₄ nanoparticles is above 400 K. It was found from M–H curves that the low temperature saturation magnetization values are higher than bulk value of CoFe₂O₄. The saturation magnetization (M_s), remanence magnetization (M_r), reduced remanent magnetization (M_r/M_s) and coercive field (H_c) values decrease with increasing temperature. The M_r/M_s value of 0.75 at 10 K indicates that the CoFe₂O₄ nanoparticles used in this work have, as expected, cubic magnetocrystalline anisotropy according to the Stoner–Wohlfarth model. T^1/2 dependence of the coercive field was observed in the temperature range of 10–400 K according to Kneller's law. The extrapolated T_B and the zero-temperature coercive field values calculated according to Kneller's law are almost 427 K and 13.2 kOe, respectively. The room temperature H_c value is higher than that of the previously reported room temperature bulk values. The effective magnetic anisotropy constant (K_eff) was calculated as about 0.23×10⁶ erg/cm³ which is lower than that of the bulk value obtained due to disordered surface spins.     

Spark plasma sintering of Al2O3-cBN composites facilitated by Ni nanoparticle precipitation on cBN powder by rotary chemical vapor deposition

Al₂O₃-cBN/Ni composites were consolidated by spark plasma sintering (SPS) using α-Al₂O₃ and Ni nanoparticle precipitated cBN (cBN/Ni) powders. The Ni nanoparticles, 10-100 nm in diameter and 0.5-2.2 mass% in content, were precipitated on cBN powder by rotary chemical vapor deposition. The effect of sintering temperature (T_SPS) and Ni content (C_Ni) on the densification, phase transformation, microstructure and hardness of the Al₂O₃-cBN/Ni composites were investigated. The highest relative density of Al₂O₃-30 vol% cBN composite was 99% at T_SPS = 1573 K and C_Ni = 1.7 mass%. At T_SPS = 1673 K, the relative density decreased due to the phase transformation of cBN to hBN. The Vickers hardness of Al₂O₃-30 vol% cBN/Ni at T_SPS = 1573 K and C_Ni = 1.7 mass% showed the highest value of 27 GPa.     

Grain size dependence of dielectric relaxation in cerium oxide as high-k layer

Cerium oxide (CeO₂) thin films used liquid injection atomic layer deposition (ALD) for deposition and ALD procedures were run at substrate temperatures of 150°C, 200°C, 250°C, 300°C, and 350°C, respectively. CeO₂ were grown on n-Si(100) wafers. Variations in the grain sizes of the samples are governed by the deposition temperature and have been estimated using Scherrer analysis of the X-ray diffraction patterns. The changing grain size correlates with the changes seen in the Raman spectrum. Strong frequency dispersion is found in the capacitance-voltage measurement. Normalized dielectric constant measurement is quantitatively utilized to characterize the dielectric constant variation. The relationship extracted between grain size and dielectric relaxation for CeO₂ suggests that tuning properties for improved frequency dispersion can be achieved by controlling the grain size, hence the strain at the nanoscale dimensions.     

Organocatalytic Upgrading of Furfural and 5-Hydroxymethyl Furfural to C10 and C12 Furoins with Quantitative Yield and Atom-Efficiency

There is increasing interest in the upgrading of C₅ furfural (FF) and C₆ 5-hydroxymethyl furfural (HMF) into C₁₀ and C₁₂ furoins as higher energy-density intermediates for renewable chemicals, materials, and biofuels. This work utilizes the organocatalytic approach, using the in situ generated N,S-heterocyclic carbene catalyst derived from thiazolium ionic liquids (ILs), to achieve highly efficient self-coupling reactions of FF and HMF. Specifically, variations of the thiazolium IL structure have led to the most active and efficient catalyst system of the current series, which is derived from a new thiazolium IL carrying the electron-donating acetate group at the 5-ring position. For FF coupling by this IL (0.1 mol %, 60 °C, 1 h), when combined with Et₃N, furoin was obtained in >99% yield. A 97% yield of the C₁₂ furoin was also achieved from the HMF coupling by this catalyst system (10 mol % loading, 120 °C, 3 h). On the other hand, the thiazolium IL bearing the electron-withdrawing group at the 5-ring position is the least active and efficient catalyst. The mechanistic aspects of the coupling reaction by the thiazolium catalyst system have also been examined and a mechanism has been proposed.