Preparation of high selective molecularly imprinted polymers for tetracycline by precipitation polymerization

High selective molecularly imprinted polymers(MIPs) for tetracycline have been prepared by precipitation polymerization. Effects of monomer and solvent,the ratio of monomer and template and the characterization of the polymer were investigated by frontal chromatography and selectivity experiment.The results clearly indicated that the polymer,which had the highest molecular recognition abilities for tetracycline antibiotics,had been received.     

Stabilizer-free precipitation copolymerization of renewable bio-based α-methylene-γ-butyrolactone and styrene

Stabilizer-free precipitation copolymerization of α-methylene-γ-butyrolactone (MBL) and styrene (St) was carried out in isoamyl acetate with BPO as initiator at 80°C. The influence of monomer feed ratio, initiator concentration and reaction time on the size and morphology of the obtained polymer particle was investigated in details. It was found that the monomer feed ratio play an important role on the particle formation process. When the monomer feed ratio of MBL to St was 1:2, narrow size distributed spherical polymer particles were formed with number average diameters in the range of 785–2620 nm. The formation process of polymer particle was studied to get a deep insight into the polymerization process of this reaction system. It was found that the formation mechanism of the poly(MBL-co-St) particles was similar to that of conventional precipitation polymerization. After a short nucleation stage (10 min), the amount of polymer particles remained constant and the particle growth mainly came from the capturing of newly formed polymer chains. The chemical composition and thermal property of the poly(MBL-co-St) were fully characterized by FTIR, ¹H-NMR spectra, and DSC.     

Borate,lithium borate,and borophosphate powders by sol–gel precipitation

Borate, lithium borate and borophosphate powders were synthesized by the sol–gel method. Triethyl borate, lithium methoxide, and orthophosphoric acid were used as precursors for B₂O_3, Li₂O, and P₂O₅, respectively. Powders were characterized by FTIR, DTA, XRD and SEM techniques. Powders from the Li₂O–B₂O₃ system exhibited glassy features while borate and borophosphate powders contained mainly crystalline B₂O₃ according to XRD analysis. However, a 500 °C heat treatment transformed these crystalline powders into glass powders. Conversely, heat treatment of Li₂O–B₂O₃ powders transformed their structure from glassy to crystalline (Li₂B₄O₇). Chemical durability studies conducted in water at 60 °C showed that minor additions of P₂O₅ into borate and lithium borate powders improved their chemical durability significantly. Furthermore, Li₂O and P₂O₅ acted synergistically on the chemical durability when added simultaneously to borate compositions.     

Thermodynamic analysis of precipitation processes in Nb–Ti-microalloyed Si–Al TRIP steel

The work deals with the thermodynamic calculations of precipitation processes in austenite of the Nb–Ti-microalloyed steel with increased Si and Al content dedicated for the automotive industry. The analysis is based on the equilibrium precipitation of individual MX-type interstitial phases, as well as the effect of various Mn and Si additions is included. The solubility products and corresponding limits of the mutual solubility of microalloy and metalloid additions in austenite were calculated. The temperature sequence of the precipitation under equilibrium conditions was determined. The Dutta–Sellars model has been applied for determination of recrystallization stop temperature of austenite and time needed for Nb(C,N) precipitation. The calculations were verified by microstructure investigations including revealing prior austenite grain size as a function of austenitizing temperature and the identification of complex carbonitrides using transmission electron microscopy. The model calculations are in good agreement with experimental results.     

Synthesis of nanometric β-barium metaborate powder from different borate solutions by ultrasound-assisted precipitation

In this study, the synthesis of barium metaborate powder (BaB₂O₄) was carried out by ultrasound-assisted precipitation using different borate solutions. Different solutions such as borax (Na₂B₄O₇, BD), boric acid (H₃BO₃, BA), and sodium metaborate (NaBO₂, SMB) were used in the synthesis and an ultrasonic immersion horn probe was used as the major source of ultrasound. The effect of reaction temperature and time, pH, and crystallization time on the BaB₂O₄ yield (%) was investigated. The ultrasound-assisted synthesis up to 90 % yield could be achieved using a 0.2 M BD solution at 80 °C, reacting for 5 min at pH 13 followed by 2 h of crystallization. Following crystallization, the obtained powder was heated up to 140, 250, 650, and 750 °C for 2.5 h, and it was shown that β-BaB₂O₄ nanometric powders were obtained after the 750 °C heat treatment.     

Water assisted growth of C₆₀ rods and tubes by liquid-liquid interfacial precipitation method

C?? nanorods with hexagonal cross sections are grown using a static liquid-liquid interfacial precipitation method in a system of C??/m-dichlorobenzene solution and ethanol. Adding water to the ethanol phase leads instead to C?? tubes where both length and diameter of the C?? tubes can be controlled by the water content in the ethanol. Based on our observations we find that the diameter of the rods/tubes strongly depends on the nucleation step. We propose a liquid-liquid interface growth model of C?? rods and tubes based on the diffusion rate of the good C?? containing solvent into the poor solvent as well as on the size of the crystal seeds formed at the interface between the two solvents. The grown rods and tubes exhibit a hexagonal solvate crystal structure with m-dichlorobenzene solvent molecules incorporated into the crystal structure, independent of the water content. An annealing step at 200 °C at a pressure < 1 kPa transforms the grown structures into a solvent-free face centered cubic structure. Both the hexagonal and the face centered cubic structures are very stable and neither morphology nor structure shows any signs of degradation after three months of storage.     

What drives the precipitation of long-chain calcium carboxylates (soaps) in aqueous solution?

The interaction of sodium octanoate, decanoate or dodecanoate with calcium(ii) in aqueous solutions has been studied using turbidity, conductivity and potentiometric measurements. These show a marked alkyl chain length dependence on the behaviour. At the calcium concentration used (1.0 mM), there is little interaction with the octanoate, the decanoate shows initially formation of a 1:1 complex, followed by precipitation, while the dodecanoate precipitates at low surfactant concentrations. The solid calcium carboxylates were prepared, and show lamellar, bilayer structures with planes of calcium(II) ions coordinated to carboxylate groups through bidentate chelate linkages. Thermogravimetry and elemental analyses indicate the presence of coordinated water with the calcium decanoate but not with longer chain carboxylates. The results of both the solution and solid state studies suggest that precipitation of long-chain carboxylates depends on a balance between hydration effects and hydrophobic (largely van der Waals') interactions. Electrostatic effects make little energetic contribution but play the important structural role of ordering the carboxylate anions before precipitation. Differences are observed in the interactions between calcium(II) and long chain alkylcarboxylates and alkylsulfates, and are interpreted in terms of stronger binding to the metal of the carboxylate group. A general mechanism is proposed for calcium carboxylate precipitation from aqueous solution based on this and previous studies.     

Rapid determination of Cl^- by light-absorption ratio variation approach using Cl^-eosin Y-Ag^＋ adsorptive precipitation

The adsorptive precipitation between eosin Y （EY） and AgCl colloids at pH 3.73 caused the sensitive color change of the solution. The reaction mechanism between EY and AgCl was analyzed and this reaction was used for determination of Cl^- in trace level by the light-absorption radio variation approach.     

Microstructure and hydrogen production activity of Pt–TiO2 prepared by precipitation–photodeposition

A series of Pt–TiO₂ photocatalysts were prepared by a facile precipitation–photoreduction method under different pH conditions, using H₂PtCl₆ as platinum precursor. The microstructure and chemical state of Pt loaded on the surface of TiO₂ were analyzed by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). It was revealed that the size and distribution of Pt nanoparticles on TiO₂ surface is closely related to the initial pH of H₂PtCl₆ solution. The optimal pH value for forming highly dispersed Pt nanoparticles is 12. The photocatalytic activities of the prepared samples were investigated in terms of hydrogen production. The results indicated that the Pt–TiO₂ sample prepared by precipitation–photodeposition method shows much higher activity than that prepared by traditional photodeposition method.     

Rapid determination of C1~- by light-absorption ratio variation approach using Cl~--eosin Y-Ag~ adsorptive precipitation

The adsorptive precipitation between eosin Y(EY)and AgCl colloids at pH 3.73 caused the sensitive color change of the solution.The reaction mechanism between EY and AgCl was analyzed and this reaction was used for determination of Cl~- in trace level by the light-absorption radio variation approach.     

Characterization of a heavy oil–propane system in the presence or absence of asphaltene precipitation

When a light hydrocarbon solvent is injected into a heavy oil reservoir under a sufficiently high reservoir pressure, asphaltene precipitation occurs so that the heavy oil is in situ deasphalted during a hydrocarbon solvent-based heavy oil recovery process. The physicochemical properties of this in situ deasphalted heavy oil are rather different from those of the original crude oil in the heavy oil reservoir. In this paper, a heavy oil sample is saturated with a typical light hydrocarbon solvent (i.e., propane) under different saturation pressures in a see-through windowed high-pressure saturation cell. The heavy oil–propane system is characterized by measuring and comparing several important physicochemical properties of the propane-saturated heavy oil samples under different saturation pressures and the flashed-off heavy oil samples, such as the solubility, oil-swelling factor, density, viscosity, asphaltene content, hydrogen and carbon aromaticities. When the heavy oil is saturated with propane at P ≤ 780 kPa and T = 20.8 °C, there is no observable asphaltene precipitation and deposition under a microscope camera. The respective properties of the propane-saturated heavy oil samples taken from the upper and lower parts of the saturation cell are measured and found to be essentially the same within the experimental errors so that the entire system is considered to be almost homogeneous. If the saturation pressure is increased to P = 850 kPa, strong asphaltene precipitation occurs and some large asphaltene particles are deposited onto the bottom of the saturation cell. In this case, the heavy oil is deasphalted and the flashed-off heavy oil has lower density, viscosity, asphaltene content, hydrogen and carbon aromaticities than those of the original heavy crude oil.     

Visual chiral recognition of mandelic acid and α-amino acid derivatives by enantioselective gel formation and precipitation

Novel chiral receptors based on l-phenylalanine and l-valine have been synthesized and their chiral recognition properties toward mandelic acid and N-tosyl α-amino acids are studied. The phenylalanine-based receptor undergoes enantioselective gel formation with R-mandelic acid and N-tosyl-d-valine, whereas the valine-linked receptor in their presence results in the formation of precipitates.     

Tritium in surface waters, tap water and in precipitation in Poland during the 1994–1999 period

Concentrations of tritium in environmental waters (precipitation, rivers, lakes, tap water) have been determined using electrolytic enrichment and liquid scintillation counting. In waters of big rivers (the Vistula and the Odra rivers), lakes and tap water the annual average concentrations were similar to each other being from 1.4 to 1.9 Bq·dm^-3. These concentrations were similar to those in the precipitation in which they ranged from 1.7 to 2.2 Bq·dm^-3. The lowest tritium concentrations were found in waters of the Seashore Region rivers (average for 1994–1999 was 1.1 Bq·dm^-3). The tritium concentrations in surface waters and in precipitation are still higher than that of natural level. The data obtained show that tritium concentration in the water of rivers might depend on the size of drainage area. The observed seasonal variations of tritium concentration in the precipitation collected in Warsaw and at the Mount Sniezka indicate the stratospheric source of tritium. It was found that about 30% of tritium deposited with precipitation is removed to the Baltic Sea with river waters.     

Modeling the first stages of Cu precipitation in α-Fe using a hybrid atomistic kinetic Monte Carlo approach

We simulate the coherent stage of Cu precipitation in α-Fe with an atomistic kinetic Monte Carlo (AKMC) model. The vacancy migration energy as a function of the local chemical environment is provided on-the-fly by a neural network, trained with high precision on values calculated with the nudged elastic band method, using a suitable interatomic potential. To speed up the simulation, however, we modify the standard AKMC algorithm by treating large Cu clusters as objects, similarly to object kinetic Monte Carlo approaches. Seamless matching between the fully atomistic and the coarse-grained approach is achieved again by using a neural network, that provides all stability and mobility parameters for large Cu clusters, after training on atomistically informed results. The resulting hybrid algorithm allows long thermal annealing experiments to be simulated, within a reasonable CPU time. The results obtained are in very good agreement with several series of experimental data available from the literature, spanning over different conditions of temperature and alloy composition. We deduce from these results and relevant parametric studies that the mobility of Cu clusters containing one vacancy plays a central role in the precipitation mechanism.     

DSC analysis of phase transformations during precipitation hardening in Al–Zn–Mg alloy (7020)

The hardening of the Al–Zn–Mg alloys during ageing process is based on very complex phase transformations. In order to contribute to the comprehension of these phenomena, we proceed to study the phase transformations of 7020 alloy using differential scanning calorimetry and X-ray diffraction analysis. The results confirm the formation of hardening phase GP zones, intermediate hardening metastable phase η′ and the equilibrium phase η. The calorimetric and X-ray diffraction results are in good agreement and confirm the successive precipitation/dissolution sequence. The dissolution of the precipitates is accompanied by the increase in the crystallographic lattice parameter due to the increase in solid solution concentration and by the softening of the material. On the contrary, the precipitation produces a lower concentration of the Zn/Mg solutes in the Al matrix, which generates a decrease in the lattice parameter value. These precipitates produce the hardening of the alloy. The sequence of phase formation and dissolution explains the evolution of the 7020 hardness as a function of the ageing temperature.

     

Influence of variation in the silicon content on the silicon precipitation in the Al–Si binary system

Ti-based amorphous alloys produced by ultra-rapid melt cooling represent an excellent option as biomaterials because of their mechanical properties and corrosion resistance. However, complete elimination of toxic elements is affecting the glass-forming ability and amorphous structure could be obtained only for thin ribbons or powders that are subsequently processed by powder metallurgy. Amorphous ribbons of special Ti₄₂Zr₄₀Ta₃Si₁₅ alloy, which is completely free of any toxic element, were produced by melt spinning, and the thermostability of resulting material was investigated in order to estimate its ability for further heat processing. Isochronal differential scanning calorimetry (DSC) was used to determine transformation points such as glass transition temperature T _g or crystallization temperature T _x. The activation energy for crystallization of amorphous phase was calculated based on Kissinger method, using heating rates ranging between 5 and 20 °C min^?1. Amorphous structure of resulting ribbon was evidenced by means of X-rays diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM). It was determined that amorphous Ti₄₂Zr₄₀Ta₃Si₁₅ alloy has a high activation energy for crystallization, similar to other Ti-based amorphous alloys, which provides good thermal stability for subsequent processing, especially by means of powder metallurgy techniques.     

Palladium metal electrode and its analytical application to precipitation and acid–base analysis in aqueous and non-aqueous media

Electrochemical characterization of palladium electrode has been reported. The investigated electrode showed a linear dynamic response for p-toluensulfonic acid and iodide ions in the concentrations range between 5?×?10^?1 and 1?×?10^?5 mol L^?1 with a Nernstian slope of 55 mV for p-toluensulfonic acid and 63 mV per decade for iodide ions in water, as well as 53 mV for p-toluensulfonic acid and 51 mV per decade for iodide ions in dioxane. The response time of the electrodes was less than 10 s in the used solvents. Some potential analytical applications of the sensors have been pointed. Palladium electrode for the potentiometric titrations of acids (citric, barbituric, and p-toluensulfonic acid), bases (N,N’-diphenylguanidine, tributylamine, and 2,2'–bipyridine), halides, and some real samples in aqueous and non-aqueous solutions were studied. Тetrabutylammonium hydroxide, perchloric acid, and silver nitrate proved to be very suitable titrating agents for these titrations. The standard deviation of the determination of the investigated compounds was less than 0.9 % from those obtained with a glass electrode, i.e., silver electrode.     

Synthesis of nanocrystalline γ-Al_2O_3 by sol-gel and precipitation methods for methanol dehydration to dimethyl ether

The capability of sol-gel and conventional precipitation techniques for the synthesis of nanocrystalline γ-alumina was investigated. These catalysts were used for vapor-phase dehydration of methanol to dimethyl ether in a fixed-bed reactor under the same operating conditions (T = 300 ?C, P = 1 bar, LHSV = 2.8, 11.7, 26.1 h?1) and characterized by means of N2 adsorption-desorption, NH3-TPD, XRD, TGA and SEM techniques. According to the experimental results, the catalysts prepared using sol-gel method in non-aqueous medium showed better performance compared with those prepared by other methods.     

A green protocol to prepare monodisperse poly(TMPTMA–styrene) microspheres by photoinitiated precipitation polymerization in low-toxicity solvent

To prepare monodisperse polymer microspheres under mild conditions, a green protocol is set up by means of photoinitiated precipitation polymerization. The work is carried out with three novel parameters, including: new type crosslinker of trifunctionality, low-toxicity solvent, and ambient temperature. Firstly, trihydroxymethyl propane triacrylate (TMPTMA) is selected as the most suitable crosslinker to prepare microspheres under ambient temperature, after comparing the morphology of its polymerization products with those of other two similar crosslinkers, i.e., trimethylolpropane triacrylate and ethoxylated trimethylolpropane triacrylate. In addition, as high as possible concentrations of TMPTMA and styrene are attempted to harvest the largest amounts of microspheres; however, a threshold of monomer concentration is found at 6 %. One kind of low-toxicity solvent, i.e., ethanol, is used as the reaction media to replace the commonly used toxic organic solvents, and it is proven to be the near Θ solvent for the present polymerization. Observation from scanning electron microscopy indicates that photoinitiation is an effective way to control the growth of microspheres, and highly monodisperse microspheres of 2.67 μm are achieved at polymerization time of 120 h. Finally, the reactive vinyl groups on microsphere surface are confirmed, which indicate that the microspheres from this green protocol is in favor of further functionalization and bio-medical application.