- The association of an ionic surfactants with β-cyclodextrin. An isothermal titration calorimeter study
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The association of a series of anionic surfactants (CnH2n+1SO4Na, n = 6, 8, 10, 12, 14) with β-cyclodextrin was studied by means of the isothermal titration calorimeter (i.t.c.) at T = 298.15 K. For these types of inclusion complexes, the results agreed well with a 1:1 association mode. Apparent values for the association constants, and changes in the standard molar Gibbs energies, enthalpies, and entropies were derived for the association process. The results indicated that the association of surfactants with β-cyclodextrin is characterized by both favourable enthalpy and favourable entropy changes. The results also demonstrated that the longer the alkyl chain of the anionic surfactant, the greater the association constant with β-cyclodextrin.
- Eli, Wumanjiang,Chen, Wenhai,Xue, Qunji
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- API ionic liquids: Probing the effect of counterion structure on physical form and lipid solubility
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Lipid based formulations (LBFs) are extensively utilised as an enabling technology in drug delivery. The use of ionic liquids (ILs) or lipophilic salts (LS) in drug delivery has also garnered considerable interest due to unique solubility properties. Conversion of active pharmaceutical ingredients (API) to ILs by pairing with an appropriately lipophilic counterion has been shown to decrease melting point of the salt complex and improve solubility in LBFs. However, the relationship between the structure of the counterion, the physicochemical properties of the resulting salts and solubility in LBFs has not been systematically explored. This study investigates the relationship between alkyl sulfate counterion structure and melting temperature (Tm or Tg) in addition to LBF solubility, utilizing cinnarizine and lumefantrine as model weakly basic APIs. Three series of structurally diverse alkyl sulfate counterions were chosen to probe this relationship. Pairing cinnarizine and lumefantrine with a majority of these alkyl sulfate counterions resulted in a reduction in melting temperature and enhanced solubility in model medium chain and long chain LBFs. The chain length of the alkyl sulfate plays a crucial role in performance, and consistently branched alkyl sulfate counterions perform better than straight chain alkyl sulfate counterions, as predicted. Most interestingly, trends in counterion performance were found to be consistent across two APIs with disparate chemical structures. The findings from this study will facilitate the design of counterions which enhance solubility of ionisable drugs and unlock the potential to develop compounds previously restrained by poor solubility.
- Benameur, Hassan,Ford, Leigh,Nguyen, Tri-Hung,Porter, Christopher J. H.,Scammells, Peter J.,Tay, Erin,Williams, Hywel D.
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p. 12788 - 12799
(2020/04/22)
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- Influence of Chain Length on the Sphere-to-Rod Transition in Alkyl Sulfate Micelles
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Using Quasielastic light scattering spectroscopy (QLS) we have deduced the mean hydrodynamic radius (Rh) of alkyl sulfate micelles as functions of chain length (number of carbons nc = 8-16), temperature (0-85 deg C), detergent concentration (0.01-4g/dL), and NaCl concentration (0.1-2 M).In the region of low chain length (nc h values (extrapolated to the cmc) increase approximately linearly with the chain length.These results combained with Huisman's aggregation numbers (nw(cmc)) are consistent with a micellar shape that is close to spherical (axial ratio less than 2).Under conditions of high NaCl concentrations of high NaCl concentration the micelles exhibit a temperature-dependent growth from small spherical aggregates into long spherocylindrical micelles at concentrations above the cmc.With increasing chain length the temperature dependence of Rh becomes stronger and the NaCl and detergent concentrations needed for micellar growth become smaller.Light scattering intensity measurements confirm a rodlike growth for these micelles at all chain lengths.From these Rh measurements, values of the thermodynamic parameter K governing the sphere-to-rod transition are determined by using an extension of our previous thermodynamic model (Missel et al., J.Phys.Chem., 84, 1044 (1980)).A quantitative analysis of the dependence of K on chain length, temperature, and NaCl concentration provides new insights into energetic factors which govern the structure and growth of micelles.
- Missel, Paul J.,Mazer, Norman A.,Benedek, George B.,Carey, Martin C.
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p. 1264 - 1277
(2007/10/02)
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