Small anion binding to cycloamylose. Equilibrium constants

Wojcik, John F.; Rohrbach, Roger P.

doi:10.1021/j100588a010

Cited by 92 publications

(47 citation statements)

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“…This is most likely a reflection of the hydrophobic effect, which tends to squeeze DHA further into the hydrophobic HPβCD cavity as the S o for DHA decreases. The higher solubility of complexes prepared in acetate buffer than phosphate buffer at the same pH may be because phosphate buffer interferes with complexes of HPβCD and DHA, similar to sodium p-(4-hydroxy-1-naphthylazo) benzenesulfonate with β-CDs (Mochida et al, 1973); however, acetate ions do not interact with HPβCD (Wojcik and Rohrbach, 1975).…”

Section: Phase/equilibrium Solubilitymentioning

confidence: 99%

Dihydroartemisinin-cyclodextrin complexation: Solubility and stability

2009

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Dihydroartemisinin (DHA) is a major metabolite of artemisinin and its derivatives, including arteether, artemether, and artesunate. To improve the solubility and stability of poorly soluble DHA, we prepared inclusion complexes with hydroxypropyl-beta-cyclodextrin (HPbetaCD) and recrystalized DHA to study its thermal stability. The complexes were characterized by differential scanning calorimetery (DSC), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction patterns (XRD), thermal stability, phase, and equilibrium solubility studies. Pure DHA was crystalline and remained crystalline after recrystallization, but its unit cell dimensions changed as exhibited by XRD. DHA-HPbetaCD complexes showed a phase transitions towards amorphous in DSC thermograms, FTIR spectra, and XRD patterns. The phase solubility profiles of complexes prepared in water, acetate buffer, and phosphate buffers were classified as A(L)-type, indicating the formation of a 1:1 stoichiometric inclusion complex. The equilibrium solubility of DHA was enhanced as a function of HPbetaCD concentration. DHA-HPbetaCD complexes showed an 89-fold increase in solubility compared to DHA. Solubilities of complexes containing 275.1 mM HPbetaCD in water, acetate buffer (pH 3.0), and phosphate buffer (pH 3.0 and 7.4) were 10.04, 7.96, 6.30, and 11.61 mg/ml, respectively. Hydrogen bonding was found between DHA and HPbetaCD, and it was stronger in complexes prepared in water than in buffers. However, the AH values were higher in buffer than water. DHA-HPbetaCD complexes prepared using commercial (untreated) or recrystallized DHA (no detectable impurity) showed a 40% increase in thermal stability (50 degrees C) and a 29-fold decrease in hydrolysis rates compared with DHA. The rank order of stability constants (K(s)) was: water, acetate buffer (pH 3.0), phosphate buffer (pH 3.0), and phosphate buffer (pH 7.4). Thus, HPbetaCD complexation with recrystalized DHA increases DHA solubility and stability.

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Section: Phase/equilibrium Solubilitymentioning

confidence: 99%

Dihydroartemisinin-cyclodextrin complexation: Solubility and stability

2009

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“…This result is consistent with the D 1 mechanism, as identified by the TG and DTG analyses. It has been reported that the complexing process between cyclodextrins and guest molecules occurs at approximately the diffusion rate in solution [7]. The dissociation of [~-CD.CgI-IsO is dominated by a diffusion mechanism.…”

Section: Crystal Structure Analysismentioning

confidence: 99%

Kinetic studies on the thermal dissociation of the inclusion complex of β-cyclodextrin with cinnamic aldehyde

Zhang

et al. 1997

Journal of Thermal Analysis

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The stability of the inclusion complex of ~-CD with cinnamic aldehyde was investigated by means of TG and DSC. The mass loss takes place in three stages: dehydration occurs at 50-120~ dissociation of [~-CD-C9HsO proceeds in the range 200--260~ and decomposition of 13-CD begins at 280~ The kinetics of the dissociation of ~-CD.C9HsO was studied by means of thermogravimetry both at constant temperature and with linearly increasing temperature. The resuits demonstrate that the dissociation of ~-CD.C9H80 is dominated by a one-dimensional diffusion process. The activation energy E is 160 kJ tool -I, and the pre-exponential factor A is 5.8x1014 min -~. Scanning electron microscope observations and the results of crystal structure analysis are in good agreement with those of thermogravimetry.

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“…Preferable inclusion of Br -in comparison with Cl -, H 2 PO 4 -and SO 4 2-has been shown in our recent publication [20] as well as in the literature [21][22][23][24]. According to the NMR results [20,21], bromide is inserted into macrocyclic cavity and located near the inner protons H-5 of CDs.…”

Section: Resultsmentioning

confidence: 63%