Biomedical subjects

Shun-Li Wang

Publications and source records attributed to Shun-Li Wang.

14 recordsLinked to original sources

PubMed2007

Estimating the blood velocity vector using aperture domain data.

Most conventional blood flow estimation methods measure only the axial component of the blood velocity vector. In this study, we developed a new method for two-dimensional (2-D) velocity vector estimation in which time shifts resulting from blood motion are calculated for the individual channels using aperture domain data. This allows the construction of a time-shift profile along the array direction as a function of channel index, which is approximated by a first-order polynomial whose zeroth-order and first-order terms can be used to determine the axial and lateral velocity components, respectively. The efficacy of the proposed method was verified by simulations and experiments in which the transducer array had 64 elements, an aperture size of 1.96 cm, and a center frequency of 5 MHz. The flow velocity ranged from 5 to 35 cm/s and the Doppler angle ranged from 0 degrees to 90 degrees. The experimental results show that the accuracy of axial velocity estimation is higher for the new method than for the autocorrelation-based conventional method when the signal-to-noise ratio is larger than 0 dB. The mean estimation error for the axial velocity component is 2.18% for the new method, compared to 4.51% for the conventional method. The mean estimation error for the lateral velocity component is 15%, which is comparable to existing methods.

Algorithms↗

PubMed2006

Thermal behavior and thermal decarboxylation of 10-hydroxycamptothecin in the solid state.

In order to investigate the thermal-related properties and thermal stability of 10-hydroxycamptothecin (10-HCPT) in the solid state, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and Fourier transform infrared (FT-IR) microspectroscopy were used. A novel combination of FT-IR microspectroscopy with thermal analyzer was applied simultaneously to monitor the dehydration and rehydration processes of the 10-HCPT sample. The thermal-induced decomposition of the 10-HCPT sample was also determined by using electrospray-ion trap mass spectrometry (ES-ITMS). The results indicated that the 10-HCPT sample used in this study was a monohydrate in structure, this form that can dehydrate to an anhydrate form if the temperature goes beyond 90 degrees C. The 10-HCPT anhydrate was first suggested to have two polymorphs, in which the form I might transform to form II when the 110 degrees C-preheated sample was cooled to 30 degrees C. The polymorphic transformation temperature was shown within 90-120 degrees C with 10.46 kcal/mol of enthalpy. The peak at 1723 cm(-1) found in the IR spectrum of 10-HCPT monohydrate might correspond to the hydrogen-bonded CO stretching vibration of lactone, which shifted to 1750 cm(-1) assigned to a free CO group of lactone after the destruction of hydrogen bonding via dehydration. This suggests that monohydrate seems to interact intramolecularly with 10-HCPT by hydrogen bonding. However, the rehydration process of the 10-HCPT anhydrate might cause it to return to being a monohydrate, depending on the storage condition. In addition, the thermal-induced decarboxylation of the solid-state 10-HCPT when the temperature is beyond 226 degrees C was proven by the appearance of a new IR peak at 1701 cm(-1) and one major mass spectral peak at m/z 321. This unique IR spectral peak at 1701 cm(-1) was due to the conjugated carbonyl group in the degraded product of 10-HCPT. The m/z 321 assigned to the decarboxylation of 10-HCPT was equal to the molecular weight loss of 44 from mass spectra; which was consistent with the weight loss of 11.9% (molecular weight of 43.3) from TGA curve of 10-HCPT anhydrate.

Antineoplastic Agents, Phytogenic↗

PubMed2006

Thermodynamic and kinetic characterization of polymorphic transformation of famotidine during grinding.

Two polymorphs of famotidine were prepared by recrystallization from acetonitrile for form A and methanol for form B, respectively. The effect of grinding process on the polymorphic transformation of famotidine was investigated. Each famotidine sample ground for various grinding times in a ceramic mortar was determined by differential scanning calorimetry (DSC), conventional and thermal Fourier transform infrared (FT-IR) microspectroscopy. The results indicate that the raw material of famotidine was proved to be a form B. A unique IR absorption band at 3505 cm(-1) for famotidine form B gradually decreased its intensity with the grinding time, while two newer IR absorption bands at 3451 and 1671 cm(-1) for famotidine form A slowly appeared. The peak intensity ratio of 3451/350 5 cm(-1) was linearly (r=0.9901) increased with the grinding time, suggesting that the grinding process could induce the polymorphic transformation of famotidine from form B to form A by a zero-order process. The DSC endothermic peaks also confirmed this polymorphic transformation from famotidine form B (167 degrees C, DeltaH: 165J/g) to famotidine form A (174 degrees C, DeltaH: 148J/g) in which the values of enthalpy were linearly reduced with the increase of grinding time (r=0.9943). The phase transition temperature of the different ground famotidine samples could be easily and only evidenced by using thermal FT-IR microspectroscopy, rather than by DSC analysis. These phase transition temperatures of the famotidine form B ground for 5-20 min quickly reduced from 144 to 134 degrees C and maintained a constant at 134 degrees C even after 20-30 min grinding. The grinding process not only decreased the crystallinity of famotidine form B but also reduced the particle size of famotidine form B, resulting in easy induction of the polymorphic transformation of famotidine from form B to form A in ground famotidine sample.

Calorimetry, Differential Scanning↗

PubMed2004

Temperature effect on the structural stability, similarity, and reversibility of human serum albumin in different states.

In order to investigate the thermal stability of human serum albumin (HAS) in three different states (aqueous solution, cast film, and solid powder), Fourier transform infrared (FTIR) spectroscopy was applied to determine the protein secondary structural changes of these HSA samples under non-isothermal or isothermal condition. The structural similarity of HSA before and after thermal treatment was also studied to estimate the thermo-reversible property of the HSA in these different states. The results indicate that with the increase of temperature, the maximum peaks at 1652 and 1547 cm(-1) (alpha-helix) shifted to 1647 and 1542 cm(-1) (random coil), respectively. An additional peak at 1620 cm(-1) assigned to intermolecular beta-sheet structure clearly appeared with temperature. The alpha-helix content was found to be reduced in favor of the formation of intermolecular hydrogen-bonded antiparallel beta-sheet structure beyond 60 degrees C in the heating process. From the data of structural similarity, HSA sample whether in solid powder or cast film form exhibited a better thermo-reversible property than HSA in aqueous solution even heating to 200 degrees C.

Drug Stability↗

PubMed2004

Evidence of octacalcium phosphate and Type-B carbonated apatites deposited on the surface of explanted acrylic hydrogel intraocular lens.

Fourier-transform infrared (FTIR) microspectroscopy combining with attenuated total reflection (ATR) microsampling technique and micro-Raman spectrophotometer were used to detect the deposited materials on the surface of acrylic hydrogel intraocular lens (IOL) with or without ocular implantation. Surface morphology and the interface of this IOL were further examined by a confocal laser scanning microscope. The brand-new IOL exhibited a very smooth, transparent and featureless surface, but the explanted IOL had an irregular cerebriform-like opaque appearance. Both FTIR/ATR and Raman microspectroscopic analyses showed the deposits on the surface of acrylic hydrogel IOL after ocular implantation to consist of octacalcium phosphate (OCP) and Type B carbonated apatites, leading to the opalescence of acrylic hydrogel IOL. Both vibrational microspectroscopic examinations also confirmed the mineralization still in progress on the surface of acrylic hydrogel IOL after ocular implantation for 2 years.

Aged↗

PubMed2004

Factors determining pressure perturbation calorimetry measurements: evidence for the formation of metastable states at lipid phase transitions.

The factors that influence the application of pressure perturbation calorimetry in studying the volume change of the phase transition of lipids are discussed. These factors include a correction for the temperature-shift induced by perturbation, the kinetic irreversibility of the phase transition and the magnitude of the pressure perturbation. We take into account the fact that the dependence of the phase transition temperature on pressure will affect the temperature-shift induced by pressure. As a result, there is a discrepancy between the compression part of the cycle and the expansion. In addition, sequential cycles lead to a gradual loss in magnitude of the heat effect upon pressure perturbation. We suggest that these phenomena can be explained by the formation of a metastable glass-like state that converts to a stable phase at temperatures removed from the region of the phase transition.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed2004

Effect of ethanol or/and captopril on the secondary structure of human serum albumin before and after protein binding.

The attenuated total reflection/Fourier transform infrared technique has been utilized to characterize secondary structural changes in human serum albumin (HSA) before and after protein binding via incubation of HSA in different concentrations of ethanol, captopril or ethanol/captopril mixture. The results indicate that ethanol induced a transition from beta-sheet to an alpha-helical structure and promoted conversion of intramolecular hydrogen-bonded beta-sheet to intermolecular hydrogen-bonded beta-sheet. In contrast, captopril or captopril/ethanol mixture induced conversion of intramolecular hydrogen-bonded beta-sheet to intermolecular hydrogen-bonded beta-sheet and resulted in exposure of the aromatic side-chain groups in the unfolding conformation of HSA. Thus, protein binding between HSA and captopril or captopril/ethanol seems to play an important role in protein secondary structure.

Captopril↗

PubMed2004

Eudragit E accelerated the diketopiperazine formation of enalapril maleate determined by thermal FTIR microspectroscopic technique.

PURPOSE: Enalapril may undergo the thermal-induced intramolecular interaction to cause an enalapril diketopiperazine (DKP) formation. It is interesting to study the influence of Eudragit E, as a coating polymer, on the stability of enalapril maleate. The reaction kinetics of the solid-state degradation process of pure enalapril maleate and Eudragit E/enalapril maleate mixture with different weight ratios were examined. The mechanism of solid-state interaction between Eudragit E and enalapril maleate was also discussed. METHODS: The cast samples of pure enalapril maleate or Eudragit E/enalapril maleate mixture after evaporating the solvent were prepared on an aluminum foil and also determined by reflectance Fourier transform infrared (FTIR) microspectroscopy equipped with thermal analyzer. RESULTS: The result indicates that the interaction might occur between enalapril maleate and Eudragit E in the solid state after evaporating the solvent. The thermal-dependent FTIR spectra show that not only the formation of DKP but also the six-membered cyclic anhydride occurred in the enalapril maleate/Eudragit E mixture in the heating process. Two pathways for solid-sate interaction were proposed. The stability of enalapril maleate was dependent on the weight ratio of enalapril maleate and Eudragit E. The activation energy (n = 3) of DKP formation for pure enalapril maleate was about 141.2+/-0.7 kJ/mol, but it was reduced significantly to 86.7+/-0.8 kJ/mol after interaction with Eudragit E (weight ratio: 1:1), suggesting Eudragit E might exacerbate the degradation of enalapril maleate. However, the degradation accelerated by Eudragit E was reduced in high content of Eudragit E. CONCLUSIONS: When the weight ratio of both components was 1:1, Eudragit E might interact with the carboxyl group of maleic acid to exacerbate the degradation of enalapril maleate. However, the excess amount of Eudragit E might somewhat reduce the degradation of enalapril, due to the interaction that occurred between Eudragit E and carboxyl group of enalapril.

Algorithms↗

PubMed2003

Fourier transform IR attenuated total reflectance spectroscopy studies of cysteine-induced changes in secondary conformations of bovine serum albumin after UV-B irradiation.

Fourier transform IR spectroscopy equipped with attenuated total reflection was used to investigate the cysteine-induced alteration of the protein secondary structure of bovine serum albumin (BSA) in aqueous solution before and after UV-B irradiation. Several amino acids were also studied. The results indicate the unchanged IR spectra of BSA coincubated with amino acids, except cysteine, did not change after 72-h UV-B irradiation. There was no difference in the IR spectrum of the unirradiated BSA coincubated with cysteine. A shoulder at 1620 cm(-1) attributed to the intermolecular beta-sheet structure was observed for the IR spectrum of BSA coincubated with cysteine after 72-h UV-B irradiation. Moreover, the peak intensity at 1303 cm(-1) that is due the alpha-helix structure was reduced, but the peak intensity at 1247 cm(-1) corresponding to beta-sheet structures was increased. Longer UV-B exposure for a BSA solution coincubated with cysteine changed the BSA solution from clear to viscous to gel form in which a transparent gel and another white gel were simultaneously observed. A gradual IR spectral alteration was found for BSA coincubated with cysteine and subjected to increased UV-B irradiation. The longer UV-B irradiation yielded increased intensity at 1620 cm(-1). The second-derivative IR peaks at 1655, 1631, and 1548 cm(-1) were shifted to 1650, 1620, and 1544 cm(-1), respectively, by the increase of UV-B irradiation, suggesting a progressive transformation from an alpha-helix to an intermolecular beta-sheet structure for BSA coincubated with cysteine. This strongly implies that longer UV-B exposure time for the BSA solution in the presence of cysteine did alter the protein secondary structures of BSA more, thus inducing gel formation by protein aggregation.

Amino Acids↗

PubMed2003

Excimer and intramolecular charge transfer chemiluminescence from electrogenerated ion radicals of donor-acceptor stilbenoids.

Electrongenerated chemiluminescence (ECL) of a series of intramolecular charge transfer (ICT) donor acceptor stilbenoid systems (2-9) bearing N,N-dimethylamino group as donor and pyridine, thiophene, quinoline or aryl groups as acceptors are studied. Most of the compounds (3-9) show ICT ECL through direct annihilation of the radical ions. For the weaker ICT compound (2), excimer ECL is observed instead.

Journal Article↗

PubMed2002

Hydration-induced proton transfer in the solid state of norfloxacin.

Norfloxacin is a special compound. Its hydrate form seems to be more soluble in water than in the anhydrate form. To investigate the hydration behavior of norfloxacin, the moisture-sorption analysis of anhydrous norfloxacin in different humidities was determined by using differential scanning calorimetry and thermogravimetric analysis. The contents of free water and bound water in the moisture-equilibrated norfloxacin were estimated quantitatively by using a curve-fitting program. Fourier transform infrared microspectroscopy with or without thermal analyzer was used to examine the structural change and dehydration process of norfloxacin in different humidities. The result indicates that the water content sorbed to anhydrous norfloxacin changed lightly below 51% relative humidity (RH) but increased markedly beyond 51% RH. The content of free water in the moisture-equilibrated norfloxacin was nearly to zero below 55% RH, but increased dramatically in high humidity. The content of bound water also enhanced gradually with the external humidity and reached to a constant of one unit after > 75% RH. When norfloxacin anhydrate transformed to its hydrate, the infrared peak intensity at 1732 and 1253 cm(-1) assigned to the C=O and C-O groups of carboxylic acid decreased gradually with the increase of water content, but the infrared peak intensity at 1584 and 1339 cm(-1) corresponding to asymmetric and symmetric carboxylates increased. Furthermore, the peak at 2553 cm(-1) assigned to the NH(+)(2) also appeared clearly and shifted from 2558 cm(-1) in higher water content and humidity. The main functional groups of norfloxacin changed from COOH to COO(-) and NH to NH(+)(2), attributable to the proton transfer from COOH group to NH group. This suggests that the hydration can induce the interaction between norfloxacin molecules from hydrogen bonding to ionic bonding by a proton-transfer process in the solid state.

Anti-Infective Agents↗

PubMed2002

Intramolecular cyclization of diketopiperazine formation in solid-state enalapril maleate studied by thermal FT-IR microscopic system.

The pathway of diketopiperazine (DKP) formation of solid-state enalapril maleate has been studied by using a novel Fourier transform infrared microspectroscope equipped with a thermal analyzer (thermal FT-IR microscopic system). The thermogram of the conventional differential scanning calorimetry (DSC) method was also compared. The results show new evidence of IR peaks at 3250 cm(-1) (the broad O-H stretching mode of water), and at 1738 and 1672 cm(-1) (the carbonyl band of DKP), indicating DKP formation in enalapril maleate via intramolecular cyclization. Moreover, the disappearance of IR peaks from enalapril maleate at 3215 cm(-1) (the secondary amine), 1728 cm(-1) (the carbonyl group of carboxylic acid), and 1649 cm(-1) (the carbonyl stretching of tertiary amide) also confirmed the DKP formation. The thermal FT-IR microscopic system clearly evidenced that the DKP formation in enalapril maleate started from 129 degrees C, and reached a maximum at 137 degrees C. This result was also confirmed by the conventional DSC thermogram of the compressed mixture of KBr powder and enalapril maleate, in which an endothermic peak at 144 degrees C with an extrapolated onset temperature at 137 degrees C was observed. This strongly suggests that the thermal FT-IR microscopic system was able to qualitatively detect the formation of DKP derivatives in solid-state enalapril maleate via intramolecular cyclization.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed2002

Transformation of metastable forms of acetaminophen studied by thermal Fourier transform infrared (FT-IR) microspectroscopy.

A novel Fourier transform infrared (FT-IR) microspectroscopy equipped with a micro hot stage (thermal FT-IR microscopic system) was used to quickly study the phase transformation of acetaminophen polymorphs by a one-step process. Acetaminophen was sealed in KBr disc on the first and second heating processes under this system. The results indicate that the contour IR profile of form I acetaminophen in the first heating process changed dramatically only near 165 degrees C, but in the re-heating process exhibited a considerable alteration in peak intensity, band width and position near the temperatures at 85, 118 and 153 degrees C. A glassy form of acetaminophen was obtained after rapidly cooling the melted acetaminophen from 200 to 25 degrees C. The glassy acetaminophen was recrystallized at 85 degrees C to transform to the form III of acetaminophen in the reheating process, and then transformed to its form II near 118 degrees C. The thermal FT-IR microscopic system is a simple, quick and timesaving tool for investigation of the thermo-dependent molecular structure of acetaminophen polymorphs in the processes of recrystallization and polymorphic transition.

Acetaminophen↗

PubMed2002

PH-dependent coordination of metal-lisinopril complex investigated by attenuated total reflection/Fourier transform infrared spectroscopy.

In order to simulate the in vivo binding behavior of angiotensin-converting enzyme (ACE) inhibitors to the zinc-containing active center of ACE, the in vitro interaction between lisinopril and zinc or nickel ions was investigated in aqueous solutions of different pH by using attenuated total reflection (ATR)/Fourier transform infrared (FT-IR) spectroscopy with second-derivative IR spectral analysis. The results indicated that the lisinopril dissociation process occurred in a stepwise fashion during increase in pH. The IR peaks at 1642 cm(-1) (carbonyl stretching of tertiary amide) and at 1582 cm(-1) (asymmetric COO- stretching) for lisinopril in solution at pH 3.5 shifted to 1606 and 1586 cm(-1) after addition of Ni2+ ions, respectively, but there was no marked changes in IR spectra of lisinopril after addition of Zn2+ ions. When the Zn2+ ions were added to lisinopril solution at pH 5.0, the peak at 1642 cm(-1) also shifted to 1604 cm(-1) and the peak at 1582 cm(-1) shifted to 1586 cm(-1), similar to the changes at pH 3.5 after adding Ni2+ ions. However, the peaks at 1582 and 1642 cm(-1) both shifted to 1599 cm(-1) after addition of Ni2+ ions at pH 5.0 or at pH 7.3. The peak at 1576 cm(-1) also shifted to 1599 cm(-1) after addition of Zn2+ ions to lisinopril solution at pH 7.3. Different coordination sites or types (chelating, bridging or pseudounidentate complex) between lisinopril and Zn2+ or Ni2+ ions were proposed, based on the separation value between v(as) (COO-) and v(s) (COO-), and the shifting of carbonyl groups. Coordination of the secondary amine in lisinopril to metal ions was also evidenced.

Angiotensin-Converting Enzyme Inhibitors↗