Publications
169 results found
Lapidot T, Heng JYY, 2016, Functionalized mesoporous silica for the control of crystallization fouling, Industrial & Engineering Chemistry Research, Vol: 55, Pages: 11475-11479, ISSN: 1520-5045
A seeding study to test the effectiveness of nanoparticles in mitigating crystallization fouling is reported. The effect of functionalized mesoporous silica particles on calcium sulfate crystallization was studied through a series of batch crystallization experiments. Tested surface chemistries include nonfunctionalized silica (hydrophilic), methyl (hydrophobic) propyl amine (basic), propyl sulfonic acid (acidic), and triaminetetraacitic acid (TAAcOH, chelating). Crystallization was tracked online using electrical conductivity to determine concentration as a function of time, which was used to calculate induction time and growth rate. At a loading of 0.1 mg/gsol, amine functionalized particles were found to be the most effective at reducing induction time, while TAAcOH particles were found to significantly increase induction time. The efficacy of TAAcOH particles was further tested at various loadings and was found to increase induction time 6-fold at a loading of 0.5 mg/gsol. Despite having a profound effect on induction time, growth rates remained relatively constant for all surface chemistries and loadings. Here, we show that the seed surface chemistry can play a major role in the control of calcium sulfate crystallization.
Parambil JV, Poornachary SK, Tan RBH, et al., 2016, Influence of solvent polarity and supersaturation on template-induced nucleation of carbamazepine crystal polymorphs, Journal of Crystal Growth, Vol: 469, Pages: 84-90, ISSN: 1873-5002
Studies on the use of template surfaces to induce heterogeneous crystal nucleation have gained momentum in recent years-with potential applications in selective crystallisation of polymorphs and in the generation of seed crystals in a continuous crystallisation process. In developing a template-assisted solution crystallisation process, the kinetics of homogeneous versus heterogeneous crystal nucleation could be influenced by solute-solvent, solute-template, and solvent-template interactions. In this study, we report the effect of solvents of varying polarity on the nucleation of carbamazepine (CBZ) crystal polymorphs, a model active pharmaceutical ingredient. The experimental results demonstrate that functionalised template surfaces are effective in promoting crystallisation of either the metastable (form II) or stable (form III) polymorphs of CBZ only in moderately (methanol, ethanol, isopropanol) and low polar (toluene) solvents. A solvent with high polarity (acetonitrile) is thought to mask the template effect on heterogeneous nucleation due to strong solute-solvent and solvent-template interactions. The current study highlights that a quality-by-design (QbD) approach-considering the synergistic effects of solute concentration, solvent type, solution temperature, and template surface chemistry on crystal nucleation-is critical to the development of a template-induced crystallisation process.
Smith RR, Shah UV, Parambil JV, et al., 2016, The effect of polymorphism on surface energetics of D-mannitol polymorphs, AAPS Journal, Vol: 19, Pages: 103-109, ISSN: 1550-7416
The aim of this work was to assess the effect of different crystalline polymorphism on surface energetics of D-mannitol using finite dilution inverse gas chromatography (FD-IGC). Pure α, β and δ polymorphs were prepared via solution crystallisation and characterised by powder X-ray diffraction (P-XRD). The dispersive surface energies were found to range from 43 to 34 mJ/m(2), 50 to 41 mJ/m(2), and 48 to 38 mJ/m(2) , for α, β, and δ, respectively, for surface coverage ranging from 0.006 to 0.095. A deconvolution modelling approach was employed to establish their energy sites. The primary sites corresponded to maxima in the dispersive surface energy of 37.1 and 33.5; 43.3 and 39.5; and 38.6, 38.4 and 33.0; for α, β, and δ, respectively. This methodology was also extended to an α-β polymorph mixture to estimate the amount of the constituent α and β components present in the sample. The dispersive surface energies of the α-β mixture were found to be in the range of 48 to 37 mJ/m(2) with 40.0, 42.4, 38.4 and 33.1 mJ/m(2) sites. The deconvolution modelling method extracted the energy contribution of each of the polymorphs from data for the polymorphic mixture. The mixture was found to have a β-polymorph surface content of ∼19%. This work shows the influence of polymorphism on surface energetics and demonstrates that FD-IGC coupled with a simple modelling approach to be a powerful tool for assessing the specific nature of this energetic distribution including the quantification of polymorphic content on the surface.
Biegaj K, Kwek JW, Lukas T, et al., 2016, Novel coupling of a capacitive probe with a dynamic vapor sorption (DVS) instrument for the electrostatic measurements of powders, Industrial & Engineering Chemistry Research, Vol: 55, Pages: 5585-5589, ISSN: 1520-5045
Powders may become electrostatically charged due to friction. This phenomenon may lead to unusual outcomes such as increased cohesion, adhesion, and poor flow. It is still a challenge to investigate the electrostatic properties of powders due to restrictions associated with existing methods. The objective is to present a novel coupling method with the dynamic vapor sorption (DVS) instrument using a capacitive probe to measure the electrostatic potential of powders. The critical factors affecting measurements are defined to aid experimental design. The method was tested with glass beads tribocharged after contact with stainless steel to assess the feasibility of the setup via analysis of the repeatability and reproducibility of the data generated. The results obtained show that electrostatic measurements can be performed with minimum noise interference, short equilibration time of 15 min, and high reproducibility based on 19 measurements. Stability of experimental conditions of ±0.1 °C and ±0.2% RH is achieved.
Yao Z, Wu D, Tang J, et al., 2016, A novel colored talc filler: preparation and surface property determination using two distinct methods, Chemometrics and Intelligent Laboratory Systems, Vol: 155, Pages: 54-61, ISSN: 1873-3239
Lapidot T, Sedransk Campbell KL, Heng JY, 2016, Model for interpreting surface crystallization using quartz crystal microbalance: theory and experiments, Analytical Chemistry, Vol: 88, Pages: 4886-4893, ISSN: 1086-4377
Surface crystallization of calcium sulfate was investigated using a dissipation crystal quartz microbalance (QCM-D) together with microscopy to understand the mechanical property changes occurring during the growth process. The use of optical microscopy and SEM revealed that needle-shaped crystals grow as clusters on the QCM sensor’s surface, not in uniform layers. As crystallization growth progressed, QCM-D revealed inversions between negative and positive frequency shifts. This behavior, a function of the growth of crystals in clusters, is not adequately predicted by existing models. As such, a new mass-to-frequency conversion model is proposed herein to explain the observed frequency inversions. This model is derived from a lumped element approach with point-contact loading and Mason equivalent circuit theory. Critically, the physical phenomena occurring form the basis of the model, particularly addressing the three sources of impedance. When a crystal nucleates and grows, its inertial impedance is considered along with a Kelvin–Voigt link with a hydration layer. A comparison between the proposed model and experimental data, of both frequency and dissipation data for the first four harmonics, shows good agreement for the supersaturations (S = C/C*) of S = 3.75, S = 3.48, and S = 3.22. Additionally, significant improvements over existing models for the case of surface crystallization are observed. The proposed model was therefore able to explain that frequency inversions are caused by a shift from inertia-dominated to elastic-dominated impedance, occurring as a result of crystal growth. Using the nucleation induction time and nucleation rates, determined with imaging, an additional understanding of the crystals’ mechanical properties (stiffness and dampening) was obtained.
Yao Z, Heng JYY, Lanceros-Méndez S, et al., 2016, Study on the surface properties of colored talc filler (CTF) and mechanical performance of CTF/acrylonitrile-butadiene-styrene composite, Journal of Alloys and Compounds, Vol: 676, Pages: 513-520, ISSN: 1873-4669
Hadjittofis E, Zhang GGZ, Heng J, 2016, Growing macroscopic hydrates using a bioinspired approach and investigating dehydration induced polymorphism, Pages: 960-962
Growing of macroscopic single crystals of organic materials is not necessarily a straight forward procedure. Carbamazepine dihydrate is one of these cases. Traditional approaches of crystallization of this, particular, compound using mixtures of alcohols with water lead to crystals with high aspect ratios (needle shaped or high aspect ratio plates)1. These crystals are not suitable for wettability or XPS measurements on individual facets2. In this work, a bioinspired crystallization method is employed for the growth of macroscopic carbamazepine dihydrate crystals.
Wang Z, Shah UV, Olusanmi D, et al., 2015, Measuring the sticking of mefenamic acid powders on stainless steel surface, International Journal of Pharmaceutics, Vol: 496, Pages: 407-413, ISSN: 0378-5173
Al Nasser WN, Shah UV, Nikiforou K, et al., 2015, Effect of silica nanoparticles to prevent calcium carbonate scaling using an in situ turbidimetre, Chemical Engineering Research and Design, Vol: 110, Pages: 98-107, ISSN: 0263-8762
Scale minerals in the oil and gas industries are a major concern to reservoir and operations engineering. The main types of oilfield scales found are carbonate and sulfate scales. Calcium carbonate (CaCO3) is a major component of fouling in heat transfer surfaces across different sectors of industry, resulting in additional capital, maintenance and operating costs. Various techniques, including the use of chemical inhibitors, have been used to prevent the formation of scale. In the last decade, there have been considerable advances in the development of chemicals, effective in small concentrations for the control of scale deposits.The purpose of this study was to investigate the possibilities of utilizing nanoparticles as sacrificial surface for enhancement and control of the nucleation and crystallization of CaCO3, as a method for fouling mitigation. Here, the turbidity profile of the solution, using a light reflection technique, is used to monitor the process. The outcomes of this study will improve revenues by preventing the unscheduled shutdown of facilities and avoidance of using an excess of scale inhibitors. Silica nanoparticles of different size and surface functional groups were added to the solution. The results showed a reduction in the induction period, consequently indicating improved control over crystallization. Modified silica nanotemplates exhibited the highest reduction in induction time at room temperature. This resulted in preventing scale formation on the wall of the crystallizer. This conclusion is very significant, and further studies are proposed, which will attempt to understand the mechanisms of reactions between the nanoparticles and scaling ions.
Hedberg SHM, Heng JYY, Williams DR, et al., 2015, Micro scale self-interaction chromatography of proteins: a mAb case-study, Journal of Chromatography A, Vol: 1434, Pages: 57-63, ISSN: 0412-3425
Self-interaction chromatography is known to be a fast, automated and promising experimental technique for determination of B22, but with the primary disadvantage of needing a significant amount of protein (>50 mg). This requirement compromises its usage as a technique for the early screening of new biotherapeutic candidates. A new scaled down SIC method has been evaluated here using a number of micro LC columns of different diameters and lengths, using typically 10 times less stationary phase than traditional SIC. Scale-down was successfully accomplished using these micro-columns, where the SIC results for a range of differing columns sizes were in agreement, as reflected by k′, B22 and column volumes data. The results reported here demonstrate that a scaled down version of SIC can be easily implemented using conventional liquid chromatography system where the final amount of mAbs used was 10 times less than required by conventional SIC methodologies.
Shah UV, Wang Z, Olusanmi D, et al., 2015, Effect of milling temperatures on surface area, surface energy and cohesion of pharmaceutical powders, International Journal of Pharmaceutics, Vol: 495, Pages: 234-240, ISSN: 0378-5173
Cai X, Yang H, Heng JYY, 2015, Preface, POWDER TECHNOLOGY, Vol: 282, Pages: 1-1, ISSN: 0032-5910
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Hedberg SHM, Heng JYY, Williams DR, et al., 2015, Self-interaction chromatography of mAbs: accurate measurement of dead volumes, Pharmaceutical Research, Vol: 32, Pages: 3975-3985, ISSN: 1573-904X
Purpose: Measurement of the second virial coefficient B22 for proteins using self-interaction chromatography (SIC) is becoming an increasingly important technique for studying their solution behaviour. In common with all physicochemical chromatographic methods, measuring the dead volume of the SIC packed column is crucial for accurate retention data; this paper examines best practise for dead volume determination.Method: SIC type experiments using catalase, BSA, lysozyme and a mAb as model systems are reported, as well as a number of dead column measurements. Results: It was observed that lysozyme and mAb interacted specifically with Toyopearl AF-Formyl dead columns depending upon pH and [NaCl], invalidating their dead volume usage. Toyopearl AF-Amino packed dead columns showed no such problems and acted as suitable dead columns without any solution condition dependency. Dead volume determinations using dextran MW standards with protein immobilised SIC columns provided dead volume estimates close to those obtained using Toyopearl AF-Amino dead columns. Conclusion: It is concluded that specific interactions between proteins, including mAbs, and select SIC support phases can compromise the use of some standard approaches for estimating the dead volume of SIC columns. Two other methods were shown to provide good estimates for the dead volume.
Shah UV, Amberg C, Diao Y, et al., 2015, Heterogeneous nucleants for crystallogenesis and bioseparation, CURRENT OPINION IN CHEMICAL ENGINEERING, Vol: 8, Pages: 69-75, ISSN: 2211-3398
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- Citations: 35
Lee K-Y, Blaker J, Murakami R, et al., 2015, Phase behavior of water-in-oil emulsions stabilised solely by hydrophobised bacterial cellulose nanofibrils, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Shah UV, Parambil JV, Williams DRM, et al., 2015, Preparation and characterisation of 3D nanotemplates for protein crystallisation, Powder Technology, Vol: 282, Pages: 10-18, ISSN: 0032-5910
Heterogeneous template nucleants are gaining pace as a favoured tool for crystallisation of proteins that may be otherwise difficult to crystallise. A systematic understanding on protein-nucleant interactions has to be developed to enable the development of nucleants for a wide spectrum of biological macromolecules. Thorough characterisation of the nucleants is the key starting point to achieve this aim. This report focuses on the method to produce and characterise functionalised 3D nanotemplates with controlled porosity in the range of 3-22. nm and surface chemistry that can vary from highly hydrophilic to highly hydrophobic in nature. BET and TEM are used to study porosity and pore size distribution while contact angle, XPS and zeta potential are used to investigate surface chemistry of the nucleants. These functionalised 3D nanotemplates are hereby reported to produce protein crystals (concanavalin A and catalase) of different habits without changing any other crystallisation parameters other than the surface chemistry of the templates. This emphasises the potential of 3D nanotemplates with well-ordered porosity and chemistry for further development in protein crystallisation experiments.
Shah UV, Olusanmi D, Narang AS, et al., 2015, Decoupling the Contribution of Surface Energy and Surface Area on the Cohesion of Pharmaceutical Powders, Pharmaceutical Research, Vol: 32, Pages: 248-259, ISSN: 1573-904X
PurposeSurface area and surface energy of pharmaceutical powders are affected by milling and may influence formulation, performance and handling. This study aims to decouple the contribution of surface area and surface energy, and to quantify each of these factors, on cohesion.MethodsMefenamic acid was processed by cryogenic milling. Surface energy heterogeneity was determined using a Surface Energy Analyser (SEA) and cohesion measured using a uniaxial compression test. To decouple the surface area and surface energy contributions, milled mefenamic acid was “normalised” by silanisation with methyl groups, confirmed using X-ray Photoelectron Spectroscopy.ResultsBoth dispersive and acid–base surface energies were found to increase with increasing milling time. Cohesion was also found to increase with increasing milling time. Silanised mefenamic acid possessed a homogenous surface with a surface energy of 33.1 ± 1.4 mJ/m2 , for all milled samples. The cohesion for silanised mefenamic acid was greatly reduced, and the difference in the cohesion can be attributed solely to the increase in surface area. For mefenamic acid, the contribution from surface energy and surface area on cohesion was quantified to be 57% and 43%, respectively.ConclusionsHere, we report an approach for decoupling and quantifying the contribution from surface area and surface energy on powder cohesion.
Hedberg S, Heng JYY, Williams DR, et al., 2015, Chromatographic tools to predict the stability of mAbs for faster identification of therapeutic candidates, Pages: 1150-1151
Protein-protein molecular interactions are known to be involved in protein solution aggregation behaviour and are a common issue for the manufacturing of therapeutic proteins such as mAbs. Much effort has been employed to gain a better understanding of aggregation, however the mechanisms leading to protein aggregation are still not fully understood. The osmotic second virial coefficient (B22) is a fundamental physiochemical property that describes protein-protein interactions solution, which can be a useful tool to predict aggregation propensity of proteins. One way of predicting aggregation propensity is self-interaction chromatography (SIC), which recently have shown to be a promising tool for better understanding of phase behaviour of proteins. Another technique, cross-interaction chromatography (CIC), has shown to be an even more high-throughput technique than its predecessor with possibly the same capabilities. This work consists of two experimental studies with therapeutic mAbs to improve SIC and CIC as a tool to predict protein aggregation. The first part includes a 10 times scale-down study of therapeutic mAbs from laboratory scale macro-columns to micro-scale columns, which will enable the determination of B22 for the individual protein as well as the cross-virial coefficient, B23, between two proteins. Micro SIC and CIC uses only a few milligrams of mAb in order to obtain a complete formulation study. The results from the first part of the study proved to give good comparable results between the micro and macro scales enabling the use of micro SIC for B22 determinations. The second part of this work presents an extensive formulation study of mAbs, varying pH and salt, as well as the presence of different stabilisers as well as different external factors known to induce aggregation. The B22 and B23 values determined from the formulation study are then correlated with aggregation data obtained from size-exclusion chromatography. It was shown that over all te
Wang D, Da Z, Zhang B, et al., 2015, Stability study of tubular DNA origami in the presence of protein crystallisation buffer, RSC ADVANCES, Vol: 5, Pages: 58734-58737, ISSN: 2046-2069
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- Citations: 26
Parambil JV, Poornachary SK, Hinder SJ, et al., 2015, Establishing template-induced polymorphic domains for API crystallisation: the case of carbamazepine, CRYSTENGCOMM, Vol: 17, Pages: 6384-6392, ISSN: 1466-8033
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- Citations: 32
Lee K-Y, Blaker JJ, Heng JYY, et al., 2014, pH-triggered phase inversion and separation of hydrophobised bacterial cellulose stabilised Pickering emulsions, REACTIVE & FUNCTIONAL POLYMERS, Vol: 85, Pages: 208-213, ISSN: 1381-5148
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- Citations: 18
Spathi C, Young N, Heng JYY, et al., 2014, A simple method for preparing super-hydrophobic powder from paper sludge ash, Materials Letters, Vol: 142, Pages: 80-83, ISSN: 1873-4979
Paper sludge ash (PSA) is a readily available waste material generated by the paper recycling industry. This work reports on the production of hydrophobic powders by dry milling PSA in the presence of a fatty acid surface functionalising agent. Optimum laboratory processing involves dry milling for 8 h with a 4 wt.% addition of stearic acid and this produced a super-hydrophobic powder with a water contact angle of 153°. Different chain length fatty acids were investigated but stearic acid produced the highest hydrophobicity. The super-hydrophobicity of PSA results from the micro-particulate texture induced by dry milling with simultaneous formation of calcium stearate self-assembling surface monolayers chemically bonded to fracture surfaces.
Shah UV, Olusanmi D, Narang AS, et al., 2014, Decoupling the contribution of dispersive and acid-base components of surface energy on the cohesion of pharmaceutical powders, International Journal of Pharmaceutics, Vol: 475, Pages: 592-596, ISSN: 1873-3476
This study reports an experimental approach to determine the contribution from two different components of surface energy on cohesion. A method to tailor the surface chemistry of mefenamic acid via silanization is established and the role of surface energy on cohesion is investigated. Silanization was used as a method to functionalize mefenamic acid surfaces with four different functional end groups resulting in an ascending order of the dispersive component of surface energy. Furthermore, four haloalkane functional end groups were grafted on to the surface of mefenamic acid, resulting in varying levels of acid-base component of surface energy, while maintaining constant dispersive component of surface energy. A proportional increase in cohesion was observed with increases in both dispersive as well as acid-base components of surface energy. Contributions from dispersive and acid-base surface energy on cohesion were determined using an iterative approach. Due to the contribution from acid-base surface energy, cohesion was found to increase ∼11.7× compared to the contribution from dispersive surface energy. Here, we provide an approach to deconvolute the contribution from two different components of surface energy on cohesion, which has the potential of predicting powder flow behavior and ultimately controlling powder cohesion.
Johari K, Saman N, Song ST, et al., 2014, Study of Hg( II) Removal From Aqueous Solution Using Lignocellulosic Coconut Fiber Biosorbents: Equilibrium and Kinetic Evaluation, CHEMICAL ENGINEERING COMMUNICATIONS, Vol: 201, Pages: 1198-1220, ISSN: 0098-6445
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Cole K, Buffler A, Cilliers JJ, et al., 2014, A surface coating method to modify tracers for positron emission particle tracking (PEPT) measurements of froth flotation, Powder Technology, Vol: 263, Pages: 26-30, ISSN: 0032-5910
Positron emission particle tracking (PEPT) is a technique by which particle behaviour can be measured in a system of flow. The quality of the measurement is related to the spatial and temporal precision of the PET scanner and the characteristics of the tracer, which must replicate physical and chemical properties of the system bulk. Tracer particles can be made from ion exchange resins which have a high capacity for the commonly used positron emitting radionuclides 18F or 68Ga. However, these resins have a polymer composition and are naturally hydrophilic, which limits their application in systems involving mineral particles. This work presents a method to modify ion exchange resins with a coating to change the physical properties of the tracer. Two types of tracer were fabricated in this way, with hydrophobic and hydrophilic surfaces, to investigate the behaviour of valuable and gangue minerals in froth flotation with PEPT. The PEPT data were used to determine the spatial occupancies of each tracer, showing that the hydrophobic tracer has the highest occupancy in the froth region and the hydrophilic tracer is rarely entrained.
Puncochova K, Heng JYY, Beranek J, et al., 2014, Investigation of drug-polymer interaction in solid dispersions by vapour sorption methods, INTERNATIONAL JOURNAL OF PHARMACEUTICS, Vol: 469, Pages: 159-167, ISSN: 0378-5173
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- Citations: 44
Smith RR, Williams DR, Burnett DJ, et al., 2014, A new method to determine dispersive surface energy site distributions by inverse gas chromatography, Langmuir: the ACS journal of surfaces and colloids, Vol: 30, Pages: 8029-8035, ISSN: 0743-7463
A computational model to predict the relative energy site contributions of a heterogeneous material from data collected by finite dilution–inverse gas chromatography (FD-IGC) is presented in this work. The methodology employed a multisolvent system site filling model utilizing Boltzmann statistics, expanding on previous efforts to calculate “experienced energies” at varying coverage, yielding a retention volume distribution allowing calculation of a surface free energy distribution. Surface free energy distributions were experimentally measured for racemic ibuprofen and β-mannitol powders, the energies of each were found in the ranges 43–52 and 40–55 mJ/m2, respectively, over a surface coverage range of 0–8%. The computed contributions to surface energy values were found to match closely with data collected on macroscopic crystals by alternative techniques (±<1.5 mJ/m2).
Shah UV, Olusanmi D, Narang AS, et al., 2014, Effect of crystal habits on the surface energy and cohesion of crystalline powders, International Journal of Pharmaceutics, Vol: 472, Pages: 140-147, ISSN: 1873-3476
The role of surface properties, influenced by particle processing, in particle–particle interactions (powder cohesion) is investigated in this study. Wetting behaviour of mefenamic acid was found to be anisotropic by sessile drop contact angle measurements on macroscopic (>1 cm) single crystals, with variations in contact angle of water from 56.3° to 92.0°. This is attributed to variations in surface chemical functionality at specific facets, and confirmed using X-ray photoelectron spectroscopy (XPS). Using a finite dilution inverse gas chromatography (FD-IGC) approach, the surface energy heterogeneity of powders was determined. The surface energy profile of different mefenamic acid crystal habits was directly related to the relative exposure of different crystal facets. Cohesion, determined by a uniaxial compression test, was also found to relate to surface energy of the powders. By employing a surface modification (silanisation) approach, the contribution from crystal shape from surface area and surface energy was decoupled. By “normalising” contribution from surface energy and surface area, needle shaped crystals were found to be ∼2.5× more cohesive compared to elongated plates or hexagonal cuboid shapes crystals.
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