Spherical Silica Gel Particles Research Articles

Separation of chiral compounds using high performance liquid chromatography stationary phase based on covalent organic framework material TpPa-NH<sub>2</sub>-Glu

Covalent organic frameworks （COFs） are an emerging class of porous crystalline materials composed of multidentate organic units connected by covalent bonds. COFs have been demonstrated to exhibit great potential and research value in many fields， including gas storage and separation， photoelectric devices， fluorescence sensors， catalysis， drug delivery， dye and pollutant adsorption， and electronic devices， and so on. The COFs obtained by post-synthesis modification tend to exhibit high crystallinities and porosities， thereby rendering them suitable materials for use in the fields of chiral resolution， asymmetric catalysis， and chromatography. In this work， TpPa-NO2 was synthesized from 1，3，5-tricarbaldehyde phloroglucinol and 2-nitro-1，4-phenylenediamine， which was then reduced to TpPa-NH2. Subsequently， this material was modified with D-glucose via a post-synthesis modification strategy to obtain the TpPa-NH2-Glu. TpPa-NH2-Glu were characterized by nuclear magnetic resonance （NMR） spectroscopy， Fourier transform-infrared （FT-IR） spectroscopy， X-ray powder diffraction （XRD） analysis， etc. In the XRD pattern， the peaks observed at 4.7°， 8.1°， 11.1°， and 27° were attributed to the TpPa-NH2-Glu， and these peaks are consistent with previous reports， thereby confirming the successful synthesis of this derivative. In addition， circular dichroism experiments indicated that the TpPa-NH2-Glu exhibited a Cotton effect， further confirming the chiral COF was prepared. Subsequently， this material was immobilized on the surface of spherical silica gel particles via the net-wrapping method to prepare a stationary phase for high performance liquid chromatographic column. Using n-hexane-isopropanol （9∶1， v/v） or methanol-water （9∶1， v/v） as mobile phases at a flow rate of 0.5 mL/min， 16 racemates and two benzene-based positional isomers （o，m，p-nitroaniline and o，m，p-Iodoaniline） were successfully resolved by this chiral column. In addition， under methanol-water （9∶1， v/v） mobile phase conditions， five racemates were separated， among which propranolol hydrochloride， warfarin， and metoprolol reached baseline separation. Furthermore， under n-hexane-isopropanol （9∶1， v/v） mobile phase conditions， 11 racemates were resolved， among which ethyl 2-bromopropionate and 3-butyn-2-ol reached baseline separation. Meanwhile， the effect of temperature on the TpPa-NH2-Glu liquid chromatography column and the repeatability of the TpPa-NH2-Glu liquid chromatography column were also explored. The HPLC column prepared by TpPa-NH2-Glu had good repeatability， and its relative standard deviation （RSD） was 1.55% and 1.46%， respectively. It is demonstrated that the TpPa-NH2-Glu material has good resolution ability for chiral compounds.

Impact of particle morphology on abrasion, polishing and stain removal efficacy in a tooth cleaning model system

Toothbrushing with toothpaste is used for daily maintenance of oral hygiene, and aims to remove food debris, the dental plaque biofilm and dental stains from tooth surfaces. However, toothpastes can also cause tooth abrasion as different particle morphologies are known to exert differential cleaning and abrasivity. Consequently, silica and alumina particles with spherical and angular morphologies, at comparable size ranges and concentrations, were used to brush polished, partially roughened or stained bovine enamel specimens and their impact on tooth abrasion, surface polishing and stain removal in vitro, was determined. Spherical silica gel particles at concentrations as low as 0.5% (w/w) achieved greater dental stain removal and higher surface polishing compared with 15% (w/w) standard abrasive silica without producing significant increases in enamel wear. Comparable results were also found for alumina abrasive particles, whilst spherical alumina particles at concentrations as low as 0.25% (w/w) showed greater stain removal compared with 1% (w/w) angular alumina particles. Both particles achieved similar surface polishing and produced less enamel wear. These findings are important in underpinning the development of dentifrices which aim to achieve optimal cleaning whilst minimising dental hard tissue damage.

Preparation and Evaluation of HPLC Chiral Stationary Phases Based on Cationic/Basic Derivatives of Cyclofructan 6

The cyclofructan 6 (CF6) macrocyclic-oligosaccharide was derivatized with five different substituents able to bear positive charges: propyl imidazole, methyl benzimidazole, dimethyl aminopropyl, pyridine, and dimethyl aminophenyl. The derivatized cyclofructans were reacted with triethoxysilyl-propylisocyanate as a linker to bond them to 5 µm spherical silica gel particles and then used to prepare liquid chromatography columns. The bonded silica particles were analyzed to establish the bonding densities. A set of 34 chiral compounds including acids, neutral compounds, and bases was tested with nine different mobile phase compositions including two reverse phase (RP) acetonitrile/pH 4 buffer, three polar organic (PO) acetonitrile/methanol, and four normal phase (NP) heptane/ethanol mobile phases. No compounds could be separated in the RP mode. Eight compounds only could be enantioseparated in the PO mode and 21 compounds in the NP mode. The most effective chiral stationary phase was the propyl imidazole derivatized CF6 phase, provided no more than six imidazole substituents and two linkers are attached per CF6 unit.

Intraparticle Mass Transfer in Adsorption Heat Pumps: Limitations of the Linear Driving Force Approximation

Adsorption heat pumps and chillers (ADHPCs) can utilize solar or waste heat to provide space conditioning, process heating or cooling, or energy storage. In these devices, intraparticle diffusion is shown to present a significant mass transfer resistance compared with interparticle permeation. Therefore, accurate modeling of intraparticle adsorbate mass transfer is essential for the accurate prediction of overall ADHPC performance. The linear driving force (LDF) approximation is often used to model intraparticle mass transfer in place of more detailed equations because of its computational simplicity. This paper directly compares the adsorbate contents predicted using the LDF and Fickian diffusion (FD) equations for cylindrical and spherical geometries. These geometries are typical of adsorbents commonly used in adsorption refrigeration such as cylindrical activated carbon fibers (ACFs) and spherical silica gel particles. In addition to the conventional LDF approximation, an empirical LDF approximation proposed by El-Sharkawy et al. (2006, “A Study on the Kinetics of Ethanol-Activated Carbon Fiber: Theory and Experiments,” Int. J. Heat Mass Transfer, 49(17–18), pp. 3104–3110) for ACF-ethanol (cylindrical geometry) is compared with the FD solution. By analyzing the relative error of the LDF approximation compared with the FD solution for an isothermal step-change boundary condition, the conditions under which the LDF approximation agrees with the FD equation are evaluated. It is shown that for a given working pair, agreement between the LDF and FD equations is affected by diffusivity, particle radius, half-cycle time, initial adsorbate content, and equilibrium adsorbate content. A step change in surface adsorbate content for an isothermal particle is shown to be the boundary condition that yields the maximum LDF error, and therefore provides a conservative bound for the LDF error under nonisothermal conditions. The trends exhibited by the ACF-ethanol and silica gel-water working pairs are generalized through dimensionless time and dimensionless driving adsorbate content, and LDF error is mapped using these two variables. This map may be used to determine ranges of applicability of the LDF approximation in an ADHPC model.

Preparation of Porous Diopside Microspheres from Spherical Silica Gels Impregnated with Ca(NO3)2 and MgCl2

Porous diopside microspheres, CaO·MgO·2SiO2, were prepared by heat treatment, at various temperatures, of spherical silica gel particles impregnated with Ca(NO3)2 and MgCl2. Spherical silica gel particles were prepared by the sol-gel method in an O/W emulsion using tetraethyl orthosilicate. When the silica gel particles containing Ca(NO3)2 and MgCl2 were heated at temperatures above 900°C, the results of X-ray powder diffractionmetry (XRD) and Fourier transform infrared spectroscopy (FT-IR) showed that the silica gels were crystallized into diopside, and scanning electron microscopy (SEM) observation revealed that a uniform porous structure was formed in the particles. The porosity in the diopside is believed to be caused by the mutual adhesion of smaller pores in the silica gel particles during the viscous sintering process.

Numerical study on adsorption enhancement of rectangular adsorption bed

The present paper has dealt with the one-sidewall cooling effect of spherical adsorbent particles packed in a rectangular bed on water vapor adsorption characteristics by a 2-dimensional numerical analysis. The analysis model was considered that one-sidewall of a rectangular packed bed with homogeneous spherical silica gel particles was cooled and another walls were adiabatic. The moist air flowed into the rectangular adsorption bed packed with spherical adsorbent particles. Fuji Sylsia silica gel B was selected as a suitable adsorbent with high adsorption ability over high relative humidity. Numerical results revealed the effects of moist air inlet humidity, airflow velocity, size of spherical silica gel particles, width of the rectangular packed bed, and the side-wall cooling temperature on the amount of water vapor adsorption.

Adorption Enhancement of Rectangular Packed Bed with Spherical Adonrbent by Side Wall Cooling in a Forced Convection Flow

The present paper has dealt with the one-sidewall cooling effect of spherical adsorbent paticles packed in a rectangular bed on water vapor adsorption characteristics by a 2-dimensional numerical analysis. The analysis model was considered that one-sidewall of a rectangular packed bed with the homogeneous spherical silica-gel particles was cooled and another walls were adiabatic. The moist air flowed into the rectangular packed bed with spherical adsorbent particles. The silica-gel B with high adsorption ability over high relative humidity was selected as a suitable adsorbent. Numerical results revealed the effects of moist air inlet humidity and airflow velocity, size of spherical silica-gel particles and width of the rectangular packed bed and the sidewall cooling terperature on the amount of water vapor adsorption.

In vitro evaluation of sol–gel processed spray dried silica gel microspheres as carrier in controlled drug delivery

The objective of this study was to evaluate sol–gel-derived spray dried silica gel microspheres as carrier material for dexmedetomidine HCl and toremifene citrate. The drug was dissolved in sol–gel processed silica sol before spray drying with Büchi laboratory scale equipment. Microspheres with a low specific surface area were spherical by shape with a smooth surface without pores on the external surface. The particle size distribution was quite narrow. The in vitro release of toremifene citrate and dexmedetomidine HCl showed a dose-dependent burst followed by a slower release phase, that was proportional to the drug concentration in the concentration range between 3.9 and 15.4 wt.%. The release period for toremifene citrate was approximately 10 days and for dexmedetomidine HCl between 7 and 50 days depending on drug concentration. Spray drying is a promising way to produce spherical silica gel particles with a narrow particle size range for controlled delivery of toremifene citrate and dexmedetomidine HCl.

回転容器内粒子偏析現象に及ぼす粒子浸透効果

In order to investigate the effect of particle-permeation on the segregation of solid mixture in a rotating vessel, radial and axial segregations of spherical binary solid mixture were observed by using a horizontal rotating cylinder and a horizontal rotating conical vessel. The binary mixture used was made by combining glass beads, spherical alumina particles and spherical silica-gel particles having various sizes and densities.As a result, it was obtained that radial and axial segregations of binary solid mixture in a rotating vessel were closely related to the permeation effect (xT/xB) measured in a moving bed. On the basis of the permeation effect (xT/xB), it was tried to estimate the segregation pattern, degree and direction of the mixture cascading in a vessel rotated at lower speed of rotation.

Einfluss der geometrischen verhältnisse der trägermaterialien auf die leistungsfähigkeit eines extraktions-chromatographischen systems I. Änderung der gesamtkapazität und des verteilungskoeffizienten von Eu 3+ in dem system HDEHP SiO 2HCl in abhängigkeit von der porengrösse der trägermaterialien (matrizen)

The distribution coefficient and the total capacity of Eu 3+ were studied as a function of the pore size or the solid support with the HDEHPHCl partition chromatography system. Spherical silica gel particles with an average diameter of 56 μm were investigated and found to have surfaces between 1 and 295 m 2/g and the median pore diameters in the range of 117–5500 Å. The coating of the silylated support material always was 10% (w/w). The experimental results can be interpreted in a way that one has to differentiate between four ranges of pore diameters with regard to the utilization of the extracting phase: (1) 0–15 Å: the stationary phase lies on the outer surface of the support sphere, the capacity is maximal, the stationary phase is mechanically unstable; (2) 15–90 Å: steric exclusion of the complex species in the pores, capacity low or not-existent; (3) 90–300 Å: decreasing steric exclusion of the complex species with increasing pore diameter, increasing capacity; (4) >300 Å: no steric exclusion, maximal capacity. The total capacities of supports with pore diameters 300–500 Å were found to be 0.28 mequiv. per g coated support material (15.7 mg Eu per g HDEHP). This value was in accordance with the capacity found by solvent extraction under the same conditions. The molar ratio Eu:HDEHP was 1:3. In the same manner the distribution coefficient increased with pore diameter and reached the upper limit ( K d = 8200) at a pore diameter ⩾ 1500 Å. This value is also in accordance with the distribution coefficient of a comparable solvent extraction. The silylation of the silica gel support does not affect the experimental results in any measurable way.

The Effect of the Speed of Rotation on Segregation of Particles in a Horizontal Rotary Conical Vessel

In order to discuss the axial segregation of solid mixture in a horizontal rotary vessel, the experiments were carried out by using a horizontal conical vessel of 12.5cm inside diameter of one end, where the diameter of the vessel is a minimum, 24.5cm in i. d. of the other end, where the diameter is the maximum, and 30cm in length. As materials, three kinds of mixtures were prepared.As the result of the experiments, the larger particles of silica sand mixture having size distribution move to the point of the maximum inside diameter, and the smaller particles segregate near the end of the maximum diameter of the conical vessel at lower speed of rotation (at 20≤n<80 r.p.m.). The smaller particles migrate toward the point of smaller diameter at 80<n≤100 r.p.m., and this tendency of the segregation is contrary to the result of the segregation at n<80 r.p.m.. Most of spherical silicagel particles of the binary solid mixture which consists of spherical and irregular silica gel of nearly the same size are segregated near the end of the minimum diameter at 15≤n<80 r.p.m. and the irregular particles are collected at the point of smaller diameter at 80<n≤100 r.p.m.. The irregular particles of the binary solid mixture, whose diameter is larger than that of the spherical particles in Weigels diameter, are segregated near the end of the minimum diameter of the vessel at n=15 r.p.m.. At about 80 r.p.m., the degree of these axial segregations decreases.These experimental results are discussed on the basis of a few characteristics of cascading particles in a rotary cylinder and the shape of the conical vessel.