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ABSTRACT: A quartz crystal microbalance (QCM) technique is developed for the in situ analysis of the cooling crystallization processes of crystal nucleation and growth. In contrast to conventional techniques based on property changes in the solid or solution phase, the proposed QCM technique simultaneously exploits property changes in both the solid and solution phases, such as the solid mass and liquid viscosity, to analyze the crystallization processes. When initial cooling the solution, an increase in the solution viscosity is reflected in the QCM responses for the resonant frequency and resonant resistance. With further cooling, the resonant frequency and resonant resistance sharply change at the induction point of crystal nucleation, as the viscous liquid film on the sensor suddenly shifts to an elastic solid phase. Thereafter, the QCM responses are mainly controlled by the suspension viscosity due to simultaneous crystal nucleation and growth with further cooling. As a result, the QCM responses allow accurate measurement of the induction point and metastable zone width during the cooling crystallization. Additional mechanistic information on the crystallization, including molecular cluster formation, crystal nucleation, and crystal growth, is also extracted from a resonant frequency-resistance plot (F-R plot) of the QCM responses when varying the cooling conditions.
Analytical Chemistry 04/2013; · 5.86 Impact Factor
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ABSTRACT: The present study investigated the mechanism of the chiral recognition of the resolving agent (L-phenylalanine) to the chiral isomers (D/L-mandelic acid). According the NMR analysis, the distinctive chemical shifts of between two diastereomer crystals (L-mandelic acid-L-phenlyalanine and D-mandelic acid-L-phenylalanine) were observed even though there was no difference of the chemicals shift of the two diastereomer solutions. This result indicated that the chiral recognition of the resolving agent mainly occurred during the crystallization of the diastereomers in the solution. Then, the chiral recognition of the diastereomers was confirmed by using thermal analysis and AFM. The diastereomer crystal of L-mandelic acid-L-phenylalanine was much more thermally stable due to the higher lattice energy than the diastereomer crystals of D-mamdelic acid-L-phenylalanine. Also, the adhesive force measured with AFM exhibited a stronger molecular interaction between L-mandelic acid and 4-amino-L-phenylalanine than between D-mandelic acid and 4-amino-L-phenylalanine. Plus, the AFM results implied that the hydroxyl group abundance on the mandelic acid surface was a possible explanation for the different chiral selectivity of the L-phenylalanine.
Journal of Nanoscience and Nanotechnology 09/2012; 12(9):7139-47. · 1.56 Impact Factor
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ABSTRACT: This paper presents a direct interaction force measurement between histidine molecules using AFM force-distance curve measurement. AFM force-distance curves between the histidine-modified cantilever and substrate in the different conditions with or without intercalating Cu2+ ion were measured and interpreted via Gaussian curve fitting analyses. The adhesion force between histidine molecules was shown to be 110 pN under the presence of Cu2+. The result was compareable to the measured adhesion force about 0 pN, which was measured by the removal of Cu2+ ion with the addition of EDTA. The result indicated the direct histidine-histidie interaction was difficult without the role of the bridigible ionic component. From the results, the possibility of direct measurement on chemical affinities between biomolecules was suggested by using AFM force-distance curve analyses. Especially, the current approach showed the possible affinity measurement techniques that elucidate the role of bridge ions.
Journal of Nanoscience and Nanotechnology 07/2012; 12(7):5164-7. · 1.56 Impact Factor
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ABSTRACT: Aspartic acid (Asp) was employed as the organic template in inducing the nucleation and growth of calcium carbonate. Crystallization
experiments were carried out by the addition of Asp into the solution of sodium carbonate and calcium chloride. The effects
of reaction time, dropping velocity of Asp and Na2CO3 solution were tested. The CaCO3 crystals were analyzed by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) and Fourier transform
infrared spectrometry (FT-IR). Two kinds of crystals were identified by FT-IR spectrum. In the presence of Asp, formation
of vaterite is induced in crystallization solution. Also, under the initial condition of an excess amount of Asp, vaterite
morphology is the major one. Various morphologies of CaCO3 are made by changing dropping velocity of added Asp and Na2CO3.
Key wordsFeeding-Calcium Carbonate-Aspartic Acid
Korean Journal of Chemical Engineering 05/2012; 27(5):1532-1537. · 0.99 Impact Factor
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ABSTRACT: Separation of mandelic acid enantiomer was carried out by using laboratory simulated moving bed (SMB) chromatography. The
SMB process consists of four zones, with each zone having 1 column. The triangle theory was used to obtain the operating conditions
for SMB. Adsorption isotherms of the D-/L-mandelic acids were obtained by pulse input method, considering linear isotherms
of the two components. Flow rates of extract, raffinate, feed, and eluent streams were systematically changed to understand
the effects of operation flow rates of SMB. Simulation results and experimental data from the SMB chromatography showed good
agreements. Adjusting the flow rate in zone II increased the purity of D-mandelic acid from extract port. The highest purity
of D-mandelic acid in the extract was obtained as 94% under the operating flow rates of Qfeed = 0.1 mL/min, Qextract = 0.2 mL/min, Qraffinate = 0.8 mL/min, and Qeluent = 0.9 mL/min.
Keywordssimulated moving bed-mandelic acid-linear langmuir isotherm
Biotechnology and Bioprocess Engineering 04/2012; 15(1):103-109. · 1.28 Impact Factor
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ABSTRACT: Simulated moving bed (SMB) chromatography is very useful for the separation of binary systems such as chiral compounds. Because
loxoprofen racemate has four enantiomers owing to its two chiral centers, to gain pure enantiomer it is impossible with only
one step. To apply enrichment of loxoprofen using SMB, extract and raffinate should be separated as a binary mixture. In order
to enrich loxoprofen racemate as binary mixture among four mixtures and to characterize its enantiomer, we performed experiments
with two types of columns. When TBB® column was used as CSP, the mixture of (1′R,2S) and (1′S,2S) forms was eluted as a raffinate
and that of (1′R,2R) and (1′S,2R) forms was discharged as a extract under linear adsorption isotherm range. When the feed
flow rates were 0.1 and 0.3 mL/min, purities of raffinate and extract were 98 and 95%, respectively. In this case, productivity
of raffinate was 7.81 g/h·g-CSP and that of extract was 6.95 g/h·g-CSP
Korean Journal of Chemical Engineering 04/2012; 25(2):285-290. · 0.99 Impact Factor
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ABSTRACT: In this review, the basic principles and research trends of biosensors are briefly described and a nano-sensing system applying
QCM (quartz crystal micro-balance), nano-diagnosis methods by AFM (atomic force microscopy) and SNOAM (scanning near-field/atomic
force microscopy) is discussed intensively. The principle, construction, and applications of piezoelectric crystal sensors
as a universal sensor are reviewed. This review is focused mainly on liquid phase applications, such as immune-sensors, gelation
detecting sensors, and cultured cell monitoring sensors. The principle of nano-diagnosis based on the AFM or SNOAM techniques
is described in detail. Finally, the binding affinity of peptide probes to proteins using AFM and the visualizing of a hybridized
PNA probe on a DNA molecule using SNOAM are evaluated and discussed.
Key wordsBiosensors–Nano-sensor–Quartz Crystal Microbalance–Nano-diagnosis–Scanning Probe Microscopy
Korean Journal of Chemical Engineering 04/2012; 28(4):987-1008. · 0.99 Impact Factor
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ABSTRACT: This study demonstrates a new approach for the highly selective molecular recognition of chiral mandelic acid using an L-mandelic acid derivative with an optically active hydroxyl group as the selector. The proposed method is based on quartz crystal microbalance (QCM) detection combined with functional multilayer film techniques in a liquid environment. The present chiral recognition results suggest that the L-mandelic acid derivative is an excellent resolving agent for detecting chiral mandelic acid.
Journal of Nanoscience and Nanotechnology 09/2011; 11(9):7676-81. · 1.56 Impact Factor
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ABSTRACT: The phase transformation of guanosine 5-monophosphate (GMP) during drowning-out crystallization in a continuous Couette−Taylor (CT) crystallizer was studied experimentally and numerically. At a steady state, the phase transformation of the amorphous GMP into hydrate crystals was monitored along the axial direction of the CT crystallizer when varying the crystallization conditions, including the rotation speed of the inner cylinder of the crystallizer and the feed concentration. As a result, the phase transformation was significantly facilitated when increasing the rotation speed, due to the enhanced dissolution of the amorphous GMP, as well as the growth of the hydrate crystals. For the numerical modeling, simple material balances were derived for three kinds of GMP: the amorphous GMP, hydrate crystals, and GMP concentration in the solution, under the assumption of plug flow behavior for the fluid motion in the CT crystallizer. The simple model predictions matched well with the experimental profiles for the three kinds of GMP along the axial direction of the crystallizer, allowing estimates for the kinetics of the phase transformation, including the mass transfer coefficients for dissolution and growth. According to the model predictions, the rates of amorphous GMP dissolution and hydrate crystal growth were both competitive to control the phase transformation in the CT crystallizer, and about 10 times higher than those in a stirred tank crystallizer.
02/2011;
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ABSTRACT: This study uses quartz crystal microbalance (QCM) chiral recognition as a novel approach to predict the chiral recognizability of a chiral selector for a racemate. The chiral selector (l-phenylalanine, l-Phe) was immobilized on a QCM sensor surface using a two-step assembly procedure. The modification of the l-Phe on the sensor surface was then characterized using several techniques, including resonant frequency detection, the contact angle, and X-ray photoelectron spectroscopy measurements. When examining the chiral recognizability of the l-Phe-modified QCM sensor for l-mandelic acid (l-MA) using a vapor diffused molecular assembly reaction technique, the chiral discrimination factor between l- and d-MA was about 8. The practical diastereomeric crystallization resolution of a MA racemic compound was then carried out using l-Phe as the resolving agent. The different properties of the diastereomer crystals of l-Phe-l-MA and l-Phe-d-MA were confirmed using high performance liquid chromatography (HPLC) and differential scanning calorimetry (DSC) analysis, plus the factors influencing the chiral resolution, such as molar ratio of MA to l-Phe, agitation speed, pH, cooling rate, and crystallization temperature were examined. The results showed that the diastereomeric crystallization separation of racemate MA using l-Phe as the resolving agent matched well with the QCM chiral recognition results. Therefore, the proposed method using QCM chiral recognition offers a simple solution to the challenge of screening a resolving agent for diastereomeric crystallization.
12/2010;
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ABSTRACT: This study investigated the use of an ionic liquid for designing polymorphs of the active pharmaceutical ingredient adefovir dipivoxil (AD) in drowning-out crystallization. Because of the influence of 1-ally-3-ethylimidazolium tetrafluoroborate (AEImBF4) on the formation of the intermolecular interaction of AD in the solution, new anhydrous (N-II) and hemihydrate (N-I) crystals of AD were produced when varying the ionic liquid fraction and crystallization temperature. The polymorphic structure and number of hydrate crystals were determined using X-ray diffraction and thermogravimetric analysis, respectively. Also, AEImBF4 had a significant influence on the thermal stability of the AD molecules in the AEImBF4−water mixture, as there was no hydrolysis of the AD molecules up to a temperature of 90 °C. According to a differential scanning calorimetry thermal scan, the N-I and N-II crystals were uniquely transformed into other crystal phases in a solid state. That is, the N-I crystals underwent three polymorphic changes: N-I → amorphous → form-V → liquid, while the N-II crystals underwent two polymorphic changes: N-II → form-V → liquid.
06/2010;
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ABSTRACT: A continuous Couette−Taylor (CT) crystallizer exploiting a Taylor vortex was developed to promote the phase transformation of guanosine 5-monophosphate (GMP). In drowning-out crystallization, amorphous GMP is initially generated and then transformed into hydrate GMP crystals via the consecutive dissolution of the amorphous GMP and nucleation and growth of hydrate GMP crystals. Because of the intensive mixing of the Taylor vortex, the dissolution of the amorphous GMP and growth of the hydrate GMP crystals were both markedly promoted, allowing the phase transformation to be completed within a mean residence time of 5 min, even with a high GMP feed concentration of 150 g/L and moderate rotation speed of 300 rpm This result was at least 5 times faster than the phase transformation in a mixed suspension, mixed product removal (MSMPR) crystallizer under the same crystallization conditions. The phase transformation efficiency of the Taylor vortex over the turbulent eddy in the MSMPR crystallizer was explained in terms of the effectiveness of the turbulence for the mass transfer at the solid−liquid interface.
04/2010;
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ABSTRACT: This study presents a new approach for the highly selective recognition of chiral L/D-mandelic acid (MA) using a quartz crystal microbalance (QCM) with L-phenylalanine (L-Phe) as the selector. The immobilization of L-Phe on the gold surface of the QCM sensor was performed using a four steps layer-by-layer assembling procedure. The modification of the gold surface of the QCM sensor after each modification step was verified by the cyclic voltammetry, contact angle, FTIR, and QCM detection. The chiral recognition ability of L- and D-MA on the chiral surface was checked by sensing using the vapor diffused molecular assembly (VDMA) method with the QCM. The chiral discrimination factor between L- and D-MA, aplha(L-MA/D-MA), was found to be about 9. The L-Phe-modified QCM gold sensor also showed good stability and reusability. The high chiral discrimination ability of the modified surface might be the result of the different hydrogen bonding force between L- or D-MA and L-Phe.
Journal of Nanoscience and Nanotechnology 06/2009; 9(5):2937-43. · 1.56 Impact Factor
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ABSTRACT: This study presents a new method for the highly selective recognition of chiral mandelic acid (MA) using L-phenylalanine (L-Phe) as the selector. The proposed method is based on quartz crystal microbalance (QCM) detection, integrated with a vapor diffused molecular assembly (VDMA) reaction technique. The construction of the L-Phe-modified QCM sensor involved a two-step assembly procedure. The chiral recognizability of L- and D-MA on the L-Phe-modified surface was then examined using the VDMA method and QCM. The chiral discrimination factor between L- and D-MA detected by QCM, alpha(L-MA/D-MA), was found to be about 8. The VDMA selective sensing of L-MA on the L-Phe-modified surface was also confirmed by the contact angle measurements. The L-Phe-modified QCM sensor showed good stability and reusability. The present chiral recognition results suggest that L-phe is an excellent resolving agent for the resolution of chiral mandelic acid.
Biosensors & bioelectronics 03/2009; 24(9):2931-4. · 5.43 Impact Factor
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ABSTRACT: Chiral recognition is considered to be the most important, fundamental basis in the development of separation technology for chiral isomers in the pharmaceutical and biotechnology fields. However, the selective detection of individual enantiomers is still one of the most difficult analytical tasks because of the close similarity of the molecular configurations between chiral isomers. This study presents a versatile vapor-diffused molecular assembly (VDMA) reaction approach for chiral recognition by the quartz crystal microbalance (QCM). Chiral L/D-mandelic acid (MA) was used as the detection model, and L-phenylalanine (L-Phe) was used as the selector. The construction of the L-Phe-modified QCM sensor involved a four-step layer-by-layer assembly procedure. Each modification step was analyzed by cyclic voltammetry, the contact angle, and a resonance frequency measurement. The chiral recognizability of the L-Phe-modified QCM sensor to L-mandelic acid was then examined by resonance frequency measurement using the novel VDMA technique and also investigated by atomic force microscope (AFM) measurements. A chiral discrimination factor of up to approximately 9 between L- and d-MA on the L-Phe-modified QCM sensor was obtained by using this gaseous-phase reaction technique. AFM results also showed obvious selective aggregation of L-MA on the L-Phe-modified surface but no noticeable aggregation of D-MA during the VDMA reaction. Both of the QCM and AFM results confirmed the usefulness of this proposed VDMA technique for the study of chiral recognition. The main advantage of the proposed method is that it offers a universal simple application scheme for the QCM detection of small resonance frequency changes due to chiral molecular recognition by a chiral selector immobilized on the QCM sensor surface.
Langmuir 01/2009; 25(2):648-52. · 4.19 Impact Factor
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Journal of Molecular Catalysis B Enzymatic 01/2009; 60:87. · 2.73 Impact Factor
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ABSTRACT: The present study used a mechanistic approach to control the phase transformation of guanosine 5'-monophosphate (GMP) via the operating conditions of agitation and feed concentration during drowning-out crystallization. First, Fourier transform infrared and UV/vis spectrophotometry were successfully applied to monitor the mass fraction of GMP polymorphs (amorphous and hydrate crystalline GMPs) and GMP supersaturation, respectively, during the crystallization. The phase transformation of amorphous GMP into hydrate crystals was significantly influenced by the agitation, which promoted the mass transfer of GMP dissolution and growth. Therefore, the phase transformation was quickly finished when increasing the agitation speed. However, a high agitation caused breakage of the hydrate crystals, resulting in a reduced crystal size with a bimodal distribution. The phase transformation was also influenced by the GMP feed concentration, as the crystal growth was promoted and the crystal size increased when increasing the feed concentration up to 61 g/l. However, a further increase in the feed concentration caused secondary nucleation due to the induction of a high supersaturation level during the phase transformation, leading to a small crystal size with a bimodal distribution. In addition, the rectangular-shaped hydrate GMP crystals exhibited a higher growth rate in the b direction rather than the a direction. Therefore, the crystal morphology shifted from a long rectangle to a square when increasing the feed concentration.
Applied biochemistry and biotechnology 12/2008; 160(2):561-73. · 1.94 Impact Factor
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ABSTRACT: We have fabricated polymer tips for atomic force microscopy in order to elucidate the effects of tip length and shape on cantilever vibration damping in liquids. The vibration damping is investigated by measuring the vibration amplitude of cantilevers as a function of tip-sample distance. The cantilever with a short tip provides a higher damping effect over long tip-sample distances. When the vibration amplitude was rescaled to show the effect of the cantilever width on oscillation damping, the vibration amplitude of cantilevers with various tip lengths was similarly obtained in a long distance range over 50 microm. This similarity is explained by an acoustic damping model in which an acoustic wave is generated by the cantilever. Finally, the results indicate a cantilever with a sufficiently long tip compared to the cantilever width can dramatically reduce the long-range damping effect in a liquid environment.
Analytica chimica acta 04/2008; 611(2):233-8. · 4.31 Impact Factor
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ABSTRACT: The feasibility of controlling the selective precipitation of pancreatic proteins was investigated using designed organic antisolvents in a drowning-out process. First, the solubility of pancreatin was measured in water−organic solutions when the organic species and their composition in the solution were varied. Due to the hydrophilicity of the proteins, solubility was rapidly reduced when the organic species fraction in the solution was increased. This reduced solubility was further amplified with a less polar organic species. Plus, the pancreatin solubility as a predictor was found to agree well with the solution polarity as a single parameter, expressed in terms of the Hildebrand solubility parameter. The precipitation of pancreatin was then carried out with various antisolvents composed of alcoholic and nonalcoholic species. The precipitation was promoted along with an antisolvent of a lower polarity, which was also functionally related to the solution polarity. The amylase, lipase, and protease proteins contained in the pancreatin displayed different precipitation behaviors depending on the polarity of the antisolvent. Thus, it was possible to selectively separate the proteins and control their composition in the precipitated pancreatin.
05/2007;
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ABSTRACT: We show a new atomic force microscopy technique for obtaining high-resolution topographic images of large bio-samples. To obtain high-resolution topographic images for the samples, we fabricated a long polymeric tip with a small protrusion using two-photon adsorbed photo-polymerization techniques. The obtained tip length was over 50 microm, and the tip was used directly to visualize COS-1 and 293 cells. Compared with commercial tips, the long tip made it easier to obtain topographic images of the large cells. In the magnified topographic images, the sub-100-nm resolution was confirmed with the long tips. This long probe tip is expected to broaden large sample-related studies and applications in the future.
Journal of Microscopy 12/2006; 224(Pt 2):146-51. · 1.63 Impact Factor
