Cation Exchange Interaction Research Articles

Transport of a PAH-degrading bacterium in saturated limestone media under various physicochemical conditions: Common and unexpected retention and remobilization behaviors.

Laboratory saturated columns packed with granular limestone grains were used to explore the retention and remobilization of functional bacteria FA1 under various physicochemical conditions. The unique surface properties of limestone and FA1 caused some unexpected phenomena. Solution IS, cation type, temperature and surface biological property all affected FA1 retention in the columns. The IS effect was temperature dependent and initial solution pH showed little influence due to the strong buffering ability of limestone. Perturbations of solution IS caused slight release of previously retained bacteria in some columns with NaCl as the background electrolyte, while increase in flow rate caused no release at all. When CaCl2 was the background, bacterial remobilization only occurred following both cation exchange and IS reduction. DLVO forces incorporating with surface roughness calculation were determined to assist with interpretation of interaction mechanisms. All the experimental evidences suggest the importance of cation bridging, cation exchange, surface roughness, and hydrophobic interaction in controlling bacterium transport in saturated limestone porous media.

An efficient adsorbent: Simultaneous activated and magnetic ZnO doped biochar derived from camphor leaves for ciprofloxacin adsorption

In this work, a novel magnetic biochar of camphor leaf with large micropore area was prepared for ciprofloxacin removal. Biochar show the advantage of resource utilization, as an adsorbent in pollutant removal, but limited by its relatively low specific surface area and poor adsorption capacity. An efficient method was formulated to prepare ZnO nanoparticle modified magnetic biochar to adsorb ciprofloxacin. The biochar with ZnCl2/biochar mass ratio of 2 at the calcination temperature of 650 °C was a typical microporous material with huge surface area (915 m2 g−1). The maximum ciprofloxacin adsorption capacity of the biochar reached 449.40 mg L−1. The adsorption mechanism was discussed in terms of physical adsorption and chemisorption involving intense π-π stacking interaction, electrostatic interaction, cation exchange interaction etc. The adsorption capacity of biochar did not decline adsorption capacity significantly after 3 times regeneration. It provides a recycle and reuse way for camphor leaves resource disposal.

Au and Ag nanoparticle-embedded calcium alginate fibers with laminated structure fabricated by molecule-directed self-assembly and cation exchange

Hyperbranched poly(amideamine) (HBPAA)-capped Au and Ag nanoparticles (NPs) were synthesized by hydrothermal reduction and then embedded into calcium alginate fibers (CAFs) by HBPAA-directed self-assembly and cation exchange between Ca2+ and HBPAA in aqueous solution to produce an Ag/Au-embedded coating inside the fiber surface. Transmission electron microscopy tests showed that as-prepared Au and Ag NPs possessed positive zeta potential (+34 and +13.5 mV) and had a regular spherical structure with an average particle size of 11.1 and 10.8 nm, respectively. Dual-coated CAFs were fabricated by successive or one-step impregnation of fibers with solutions of HBPAA-capped Au and Ag NPs, respectively, or with their mixed solution. As-prepared dual-coated CAFs have a Ca2+ outer coating and an Ag/Au internal coating. Upon strong electrostatic and hydrogen bonding interactions between HBPAA and alginate and the cation exchange interaction between amino-terminated HBPAAs and Ca2+ in CAFs, HBPAA-capped NPs were nearly completely exchanged to CAF surfaces at room temperature. It was noted that the dissociative Ca2+ can resorb to HBPAA, thereby forming a Ca2+ outer layer on NPs. This interesting structure may serve as a protective layer, avoiding direct contact with the human body and re-dissolution of NPs.

Reversed-phase liquid chromatography system constant database over an extended mobile phase composition range for 25 siloxane-bonded silica-based columns

The solvation parameter model is used to characterize the retention properties of 25 siloxane-bonded type-B silica columns under typical reversed-phase liquid chromatography conditions with binary aqueous mobile phases containing 10–70% (v/v) methanol and acetonitrile. To further explore the affect of solvent type on column selectivity complementary information is presented for aqueous phases containing 10–70% (v/v) tetrahydrofuran for two columns. Columns were selected to include examples of all common column packing morphologies for small molecule separations (totally porous particles, superficially porous particles, organic–inorganic hybrid particles, and a monolith) and common topologies octadecylsiloxane-bonded (including phases with a polar-embedded group, mixed-mode phases with a short-chain siloxane-bonded polar functional group, sterically crowded, positive shield, and fluorine-containing phases); octylsiloxane-bonded; and various phenyl-containing stationary phases with different linker arms, pentafluorophenylalkyl and biphenyl groups. The column properties are reported as a system constant database and as system maps for the full range of mobile phase compositions. Selectivity differences are evaluated using principal component factor analysis to classify the columns into selectivity groups and correlation plots of the system constants for compared columns at all mobile phase compositions. The later is shown to be a suitable technique to identify (near) selectivity equivalent columns and varied columns suitable for method development. Contributions to retention from steric resistance and cation-exchange interactions not parameterized in the solvation parameter model are identified for columns and conditions where they may be important. It is shown that the interaction parameters employed in the hydrophobic-subtraction model have little overlap with those of the solvation parameter model and a quantitative comparison of column properties delineated by both models is not possible.

The multi-mechanisms and interlayer configurations of metoprolol uptake on montmorillonite

This study assessed the mechanisms using montmorillonite (MMT) for the uptake and removal of a β-blocker metoprolol (MTP) from aqueous solution. Uptake of MTP was fast and equilibrium could be reached in 15 min and 4 h under initial MTP tartrate concentrations of 800 and 4000 mg/L, respectively. The MTP uptake capacity was as high as 412 mg/g (corresponding to 1544 mmol/kg), suggesting that MMT was a good candidate for β-blocker removal. Equilibrium solution pH and ionic strength had strong influence on MTP uptake on MMT and MTP uptake was reduced under high pH and high ionic strength conditions. Desorption of exchangeable cations matched well with the amount of MTP uptake at low loading levels, suggesting cation exchange being responsible for the uptake of MTP. At higher MTP uptake levels, significant expansion of d001 spacing was observed, confirming extensive intercalation and changes in interlayer configuration of MTP. The decomposition temperature of MTP intercalated into the MMT increased in comparison to that of crystalline MTP as revealed by thermogravimetric analyses. Band shift in FTIR analyses indicated that hydrogen bonding besides cation exchange and ion-dipole interaction was responsible for the high MTP loading levels.

Biochemical characterization of Burkina red radish (<i>Raphanus sativus</i>) peroxidase

Objectives: Peroxidases (POX), isoenzymes were purified to homogeneity from bulbs of Raphanus sativus (Radish) grown in Burkina Faso and characterized for use as an alternative source of POX for biotechnological applications. Methodology and Results: The enzymes were purified using cation exchange, anion-exchange and hydrophobic interaction chromatography. Two isoperoxidases, cationic POX1 and anionic POX2, were isolated and purified 18.5 and 27.2 fold, respectively. Purified enzymes were found to be monomeric proteins with molecular masses of 70 kDa and 47 kDa for POX1 and POX2, respectively, as determined by SDS-PAGE. The effect of pH and temperature was done using guaicol as a substrate. The optimal pH of the both purified POX was 5.6 and 80 % of its activity was retained at pH values between 4.0–8.0 after incubation for 2 h, but POX2 appeared to be highly stable than POX1. POX1 and POX2 had optimum temperatures of activity at 35° and 40°C, respectively. Activities of these isoenzymes were determined using different phenolic substrates in the presence and absence of ionic effectors. The results show that both POX activities were activated by bivalent cations such as Mg 2+ and Ca 2+ but were inhibited by K + , Na + , Zn 2+ , EDTA and reducing compounds. While Ba 2+ is an activator for POX2, it had no effect on POX1. They oxidize all the phenolic compounds used. The greatest rate was obtained with ABTS and guaiacol, for POX1 and POX2, respectively. Conclusions and application of findings: POXs oxidize a wide range of phenolic substrates and have high stability at a wide range of pH. These properties make these enzymes potential biotechnological tools. They could be use in industrial applications to produce food dyes, phenolic resins from natural phenolic compounds or in the construction of biosensors and kits for analyses and diagnostics. They could play also an important role in the oxidation of phenolic compounds in polluted water. This is interesting because it could be useful in finding solutions to the thorny problem of recalcitrant phenolic compounds that resist to conventional methods for bioremediation. Keywords: peroxidase, purification, characterization, Raphanus sativus , phenolic compound

Improved Peptide Retention Time Prediction in Liquid Chromatography through Deep Learning.

The accuracy of peptide retention time (RT) prediction model in liquid chromatography (LC) is still not sufficient for wider implementation in proteomics practice. Herein, we propose deep learning as an ideal tool to considerably improve this prediction. A new peptide RT prediction tool, DeepRT, was designed using a capsule network model, and the public data sets containing peptides separated by reverse-phase liquid chromatography were used to evaluate the DeepRT performance. Compared with other prevailing RT predictors, DeepRT attained overall improvement in the prediction of peptide RTs with an R2 of ∼0.994. Moreover, DeepRT was able to accommodate to the peptides that were separated by different types of LC, such as strong cation exchange (SCX) and hydrophilic interaction liquid chromatography (HILIC) and to reach the RT prediction with R2 values of ∼0.996 for SCX and ∼0.993 for HILIC, respectively. If a large peptide data set is available for one type of LC, DeepRT can be promoted to DeepRT(+) using transfer learning. Based on a large peptide data set gained from SWATH, DeepRT(+) further elevated the accuracy of RT prediction for peptides in a small data set and enabled a satisfactory prediction upon limited peptides approximating hundreds. Further, DeepRT automatically learns retention-related properties of amino acids under different separation mechanisms, which are well consistent with retention coefficients (Rc) of the amino acids. DeepRT was thus proven to be an improved RT predictor with high flexibility and efficiency. DeepRT is available at https://github.com/horsepurve/DeepRTplus .

Correlation between Structural, Magnetic and Spectroscopic Properties of Mg Substituted CoFe2O4

AbstractMg substituted cobalt ferrite spinel powder samples with the general formula MgxCO1-xFe2O4(x = 0 to 0.25) were synthesized chemically through sol-gel method and annealed at 1100 °C for 2 h. They were initially screened for the structural and morphological properties by X-ray diffraction and field emission scanning electron microscopy, respectively. Vibrational properties of the samples were studied by Raman and infrared spectroscopies. X-ray diffraction confirmed the formation of single pure or near-pure phase with cubic spinel structure for all the samples with expected occupancy values. The field emission scanning electron microscopy revealed a decrease in the particle size with an increase in Mg concentration. Both structural and magnetic properties of the samples were characterized using Mössbauer spectroscopy while the magnetic properties were studied using vibrating sample magnetometry. The changes in magnetic moment of ions, their coupling with neighboring ions and cation exchange interactions were confirmed from the Mössbauer spectroscopy analysis. Saturation magnetization and coercivity values can be explained based on the Slater-Pauling curve. The magnetometry results showed a decrease in saturation magnetization of the samples with increase in Mg concentration

Purification and Characterisation of a Thermostable β-Xylosidase from Aspergillus niger van Tieghem of Potential Application in Lignocellulosic Bioethanol Production.

A locally isolated strain of Aspergillus niger van Tieghem was found to produce thermostable β-xylosidase activity. The enzyme was purified by cation and anion exchange and hydrophobic interaction chromatography. Maximum activity was observed at 70-75°C and pH 4.5. The enzyme was found to be thermostable retaining 91 and 87% of its original activity after incubation for 72h at 60 and 65°C, respectively, with 52% residual activity detected after 18h at 70°C. Available data indicates that the purified β-xylosidase is more thermostable over industrially relevant prolonged periods at high temperature than those reported from other A. niger strains. Maximum activity was observed on p-nitrophenyl-β-D-xylopyranoside and the enzyme also hydrolysed p-nitrophenyl β-D-glucopyranoside and p-nitrophenyl α-L-arabinofuranoside. The purified enzyme acted synergistically with A. niger endo-1,4-β-xylanase in the hydrolysis of beechwood xylan at 65°C. During hydrolysis of pretreated straw lignocellulose at 70°C using a commercial lignocellulosic enzyme cocktail, inclusion of the purified enzyme resulted in a 19-fold increase in the amount of xylose produced after 6h. The results observed indicate potential suitability for industrial application in the production of lignocellulosic bioethanol where thermostable β-xylosidase activity is of growing interest to maximise the enzymatic hydrolysis of lignocellulose.

Insights into the Retention Mechanism of Small Neutral Compounds on Octylsiloxane-Bonded and Diisobutyloctadecylsiloxane-Bonded Silica Stationary Phases in Reversed-Phase Liquid Chromatography

The system constants of the solvation parameter model are used to prepare system maps for the retention of small neutral compounds on an octylsiloxane-bonded (Kinetex C8) and diisobutyloctadecylsiloxane-bonded (Kinetex XB-C18) superficially porous silica stationary phases for aqueous mobile phases containing 10–70% (v/v) methanol or acetonitrile. Electrostatic interactions (cation-exchange) are important for the retention of weak bases with acetonitrile–water but not for methanol–water mobile phases. Compared with an octadecylsiloxane-bonded silica stationary phase (Kinetex C18) retention is reduced due to a less favorable phase ratio for both the octylsiloxane-bonded and diisobutyloctadecylsiloxane-bonded silica stationary phases while selectivity differences are small and solvent dependent. Selectivity differences for neutral compounds are larger for methanol–water but significantly suppressed for acetonitrile–water mobile phases. The selectivity differences arise from small changes in all system constants with solute size and hydrogen-bond basicity being the most important due to their dominant contribution to the retention mechanism. Exchanging the octadecylsiloxane-bonded silica column for either the octylsiloxane-bonded or diisobutyloctadecylsiloxane-bonded silica column affords little scope for extending the selectivity space and is restricted to fine tuning of separations, and in some cases, to obtain faster separations due to a more favorable phase ratio. For weak bases larger differences in relative retention are expected with acetonitrile–water mobile phases on account of the additional cation exchange interactions possible that are absent for the octadecylsiloxane-bonded silica stationary phase.

Ultrahigh selective adsorption of zwitterionic PPCPs both in the absence and presence of humic acid: Performance and mechanism

Since zwitterionic PPCPs could be combined with humic acid (HA) leading to certain contaminants residue in aqueous solution, adsorbents with much stronger binding with zwitterionic PPCPs were needed to avoid this phenomenon. Through comparison of serial magnetic carboxyl modified hypercrosslinked resins including MA10, MA30, MA40 and MA70, MA50 was found to exhibit ultrahigh selective adsorption of zwitterionic PPCPs including tetracycline and quinolone antibiotics due to the remarkable synergistic effects generated from cation exchange interaction and non-ion exchange interaction. To figure out the effect of HA, other five adsorbents including hypercrosslinked resin Q100, aminated hypercrosslinked resin GMA50, anion exchange resin MIEX, wood-based activated carbon F400D and coal-based activated carbon Norit were chosen as comparison to MA50 in adsorption performance of tetracycline (TC) and ciprofloxacin (CPX). It turned out that the percentage of CPX or TC combined with HA in aqueous solution varied greatly for studied adsorbents. There existed serious false-positive adsorption during the adsorption process by some commercial adsorbents such as MIEX and F400D, while MA50 exhibited relatively lower false-positive adsorption, ensuring the maximum safety of effluents. Breakthrough tests showed that MA50 had significant advantages in PPCPs removal at environment concentration, indicating its potential in application for real water.

Synthesis of boronate-functionalized organic-inorganic hybrid monolithic column for the separation of cis-diol containing compounds at low pH.

In this work, an organic-inorganic hybrid boronate affinity monolithic column was prepared via "one-pot" process using 4-vinylphenylboronic acid as organic monomer and divinylbenzene as cross-linker. The effects of reaction temperature, solvents and composition of organic monomers on the column properties (e.g. morphology, permeability, and mechanical stability) were investigated. A series of test compounds including small neutral molecules, aromatic amines, and cis-diol compounds were used to evaluate the retention behaviors of the prepared hybrid monolithic column. The results demonstrated that the prepared hybrid monolith exhibited mixed-interactions including hydrophilicity, cation exchange, and boronate affinity interaction. The run-to-run, day-to-day and batch-to-batch reproducibilities of the prepared hybrid monolith for thiourea's retention time were satisfactory with the relative standard deviations (RSDs) less than 0.09, 1.45 and 4.05% (n=3), respectively, indicating the effectiveness and practicability of the proposed method.

Effect of acid-assisted hydrothermal carbonization (HTC) process of tree branches using nitric acid on cadmium adsorption

Application of acid in HTC process has been confirmed to have effect on hydrochar properties related to its adsorption capacity. Woody materials (tree branches) were used to investigate the relation of nitric acid addition in HTC process on the hydrochar surface properties and its adsorption mechanism toward cadmium in water solution. Tree branches were processed at 200-260 °C mixed with water and nitric acid (HNO3) at ratio 0-50% to hydrochar mass and held for holding time of 30, 105 and 180 minutes. Batch adsorption test was conducted by mixing the hydrochars with cadmium solution at 100 ppm and shaken for 24 hours at room temperature. The BET surface area, oxygen functional group (OFG) and the exchanged cations were analysed to investigate the effect of HTC process condition, nitric acid addition, and adsorption mechanism of cadmium. Tree branches treated at 200°C for 30 minutes and acid ratio of 50% showed the best adsorption result. Analysis on the surface properties also showed the best condition for cadmium adsorption. Thus hydrothermal treatment condition at low temperature, short time and high acid ratio usage could be effective in removing cadmium from water. The cadmium adsorption by cation exchange interaction might be the major adsorption mechanism as shown by consistency of trend of the exchanged cation concentration with cadmium adsorption capacit

Dielectric, magnetic, ferroelectric, and Mossbauer properties of bismuth substituted nanosized cobalt ferrites through glycine nitrate synthesis method

CoFe2-xBixO4 nanoferrites with x = 0, 0.05, 0.1, 0.5, and 1.0 have been synthesized by the glycine nitrate process. The present study investigates the effect of Bi3+ substitution on the microstructural, dielectric, ferroelectric, magnetic, and Mossbauer properties of CoFe2O4 nanoparticles. The X-ray diffraction technique was used to confirm the phase purity and estimate the crystallite size which revealed the formation of a secondary phase when Bi3+ concentration exceeds x = 0.5. Transmission electron microscopy indicated the formation of grains by aggregation of small crystallites with a reduction in grain size to 20 nm with an increase in Bi3+ content and also divulged the lattice parameter value to be 8.378 Å, confirming the crystalline nature of the synthesised sample. Dielectric properties performed in the frequency range of 100 Hz to 1 MHz determined that the dielectric behavior is attributed to the Maxwell-Wagner polarization and the activation energy of the specimens is calculated from the dielectric measurements. The hysteresis curve indicated the ferrimagnetic nature of the samples. The samples also exhibited a well saturated P-E loop with gradual lowering in remenant polarization, coercive field, and saturation polarization with an increase in bismuth concentration. Mössbauer spectroscopy analysis confirmed the changes in magnetic moment of ions, their coupling with neighbouring ions, and cation exchange interactions. Owing to the high physical, thermal, and chemical stabilities, these magnetic ceramics, CoFe2-xBixO4, possesses tremendous potential in major understanding of magnetism and in magnetic recording applications for high density information storage.

Adsorptive Properties of Fly Ash Zeolite Synthesized via Microwave and Ultrasonic Pretreatments

Being abundant and hazardous solid waste, the utilization of fly ash was sought. This study aimed to convert coal fly ash into zeolite using reflux method combined with microwave and ultrasonic pretreatments. Fly ash was reacted with NaOH 2 M, ultrasonicated for 30 minutes and irradiated using microwave for 45 minutes. The resulting solution was then refluxed for 24 hours. The zeolite formation was confirmed by FTIR and XRD analysis. The zeolite was then activated by 20% HCl for 2 hours. Fly ash, zeolites and activated zeolite were characterized for their adsorptive properties using a cationic dye via batch experiment. The maximum adsorption capacity (Qm) of fly ash, zeolite, and acid activated zeolite were 0.0003 mg g, 51 mg/g, and 101 mg/g, respectively. BET analyses indicated that the surface area of fly ash was 7 m2/g, while that for zeolite and acid activated zeolite were 82.4 m2g and 82.6 m2/g, respectively. The FTIR showed the Si-OH groups were significantly enhanced upon acid activation indicated by absorption peak at 960-1100 cm-1. It can be concluded that the chemisorption via cation-exchange or monolayer interaction played a major role in the adsorption mechanism of zeolite, supported by the allignment of the adsorption data plots to Langmuir isoterm adsorption model.

High-level expression and purification of a molluskan endoglucanase from Ampullaria crossean in Pichia pastoris

EG27I is an endogenous glucanase belonging to glycoside hydrolase family (GHF) 45 from the mollusk Ampullaria crossean. In this study, the mature EG27I peptide gene fused to the HFBII secretion signal of Trichoderma reesei was expressed under the GAP promoter of Pichia pastoris in SMD1163 strain. A bioactive EG27I with a molecular weight of 27 kDa was successfully expressed and secreted into our culture medium. The respective final OD600 and hydrolytic activity were 333 and 1.28 U/mL when high-cell-density fermentation of the recombinant P. pastoris was performed in a 7.5 L fermenter through a fed-batch strategy for 132 h. The recombinant protein concentration of the fermentation supernatant was 47.7 mg/L. EG27I was consecutively purified from the fermentation supernatant through ultrafiltration, cation exchange, and hydrophobic interaction. The specific activity of the recombinant EG27I was 26.8 U/mg, and the optimal pH and temperature of the enzyme were 5 and 50 °C, respectively. The half-life of the enzyme activity at 100 °C could reach 40 min. The N-terminal amino acid sequence analysis of the purified recombinant protein confirmed that the amino terminal sequence was consistent with the natural structure. The high quantity and purity of the EG27I provide a basis for future structural and functional studies.

One-pot preparation of an organic polymer monolith by thiol-ene click chemistry for capillary electrochromatography.

A novel organic monolith was successfully fabricated by a one-pot thiol-ene click reaction of triallyl isocyanurate with pentaerythritol tetrakis-(2-mercaptoacetate) and mercaptopropionic acid in the presence of porogens. We investigated the effects of the ratio of monomer and cross-linking agent, the type and ratio of porogen, and click reaction temperature on the permeability and morphology of the prepared poly triallyl isocyanurate-co-pentaerythritol tetrakis (2-mercaptoacetate) monoliths. The monolith was also characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. The results indicated that the monoliths had continuous porous framework, good permeability, and high mechanical stability. A series of analytes with different properties such as alkylbenzenes, polycyclic aromatic hydrocarbons, anilines, and phenols were used to evaluate the electrochromatographic performance of the prepared monoliths in pressurized capillary electrochromatography. The prepared polymer monolith showed typical reversed-phase electrochromatographic behavior for hydrophobic substances. Moreover, the prepared monolith showed a mix of reversed-phase and cation exchange interaction modes for basic aniline compounds. The minimum plate height of the monolith was 8.76μm (132100 plates/m) for propylbenzene. These results demonstrated that one-pot thiol-ene click chemistry can provide a simple and reliable method for the preparation of organic monoliths.

Polyoxometalate incorporated polymer monolith microextraction for highly selective extraction of antidepressants in undiluted urine

In this work, a polyoxometalate (POM) incorporated polymer monolith microextraction (PMME) was successfully proposed and employed in the selective extraction of basic antidepressants in undiluted urine sample. This hybrid monolith exhibited strong cation-exchange interaction (SCX) with positively charged antidepressants when pH was 3.0, because of the multiple ionizable moieties on polyanionic POM. As such, antidepressants in complex sample matrices were efficiently extracted by the monolith, and the matrix effect was significantly reduced. In addition, due to the high amount of anionic POM, the monolith exhibited remarkable extraction capacities for target antidepressants ranging from 4.7 to 5.8mg/g. Further, the POM incorporated PMME was coupled with high-performance liquid chromatography-ultraviolet (HPLC-UV). Thus, antidepressants in undiluted urine sample was efficiently extracted under optimized extraction conditions online. The limits of detection (LODs) for the target antidepressants ranged from 0.7 to 1.4ng/mL, and the linear range was 5–1000ng/mL with determination coefficients (R2) higher than 0.9960. The recoveries ranged from 86.8% to 104.0% with relative standard deviations (RSDs) of 0.4–10.1%. The proposed procedure was successfully applied to determine antidepressant in human urine. Taken together, the developed method presented a new strategy for the analysis of basic drugs in undiluted urine sample, which could be used for monitoring medicines in pharmacokinetic analysis.

Nano-level constitutive model for expansive clays

Expansive clayey soils, which are prevalent across the surface sediments of the earth, are considered problematic for the structures and infrastructure founded in them. These soils are also challenging for environmental engineers involved in the design and construction of municipal and nuclear waste liners, petroleum engineers dealing with shale oil and gas, and agricultural scientists. Because their overall behaviour is controlled by molecular-level processes and interactions, a behaviour model encompassing the contributions from these interactions is required to predict the behaviour of these soils. This interaction becomes increasingly complex for natural expansive clays where a complex composition of clay and non-clay minerals exists. Unfortunately, none of the existing constitutive models pertaining to expansive clays comprehensively incorporates all the factors contributing to volume change behaviour of naturally occurring expansive soils. This study led to the development of a nano-level constitutive model for natural expansive clays through a three-phase study consisting of macro-level swell potential testing on laboratory control and natural field samples, micro-investigation of the pre- and post-swell specimens, and molecular level modelling through molecular mechanics, molecular dynamics and Monte Carlo techniques. This swell potential behaviour model incorporates all the major contributing factors such as moisture content, density, cation exchange capacity, exchangeable cations and interaction of clay minerals with non-clay minerals. The developed models have been successfully validated through close prediction of the swell potential behaviour of the laboratory control samples and natural field samples.

Facile preparation of magnetic carbon nanotubes-immobilized lipase for highly efficient synthesis of 1,3-dioleoyl-2-palmitoylglycerol-rich human milk fat substitutes

In this study, Candida lipolytica lipase (CLL) was immobilized on magnetic multi-walled carbon nanotubes (mMWCNTs) via hydrophobic and cation-exchange interaction. The resultant immobilized CLL showed much better thermal stability, biocatalyst activity and easier recycling than the free form. A method for efficient enzymatic acidolysis of tripalmitin (PPP) with oleic acid (OA), to produce OPO-rich TAGs, was developed, using the immobilized CLL as the biocatalyst. Under optimized conditions (2% water, 20mg/ml enzyme, 1:6 PPP/OA, 50°C, 2h), the content of OPO in the final product reached 46.5%. CLL@mMWCNTs had a better activity and manipulative stability than commercial lipases. More importantly, the feasibility of CLL@mMWCNTs was also validated in the practical production of OPO-rich TAGs, using lard and restructured palm oil as the raw material. These results suggest that CLL@mMWCNTs is a promising biocatalyst for the OPO-rich TAGs production and will be helpful for the infant formula industry.