The structure of clusters in ethanol–water binary solutions at xE (ethanol mole fraction) ≥ 0.2 was investigated by the mass-spectrometric analysis of clusters isolated from liquid droplets and X-ray diffraction measurements of the intact solution. The average number of water molecules (Na) of the ethanol m-mer hydrates (5 < m < 15) in the mixtures at 0.2 ≤ xE ≤ 0.8 was found to be expressed by a function of the water mole fraction (xw), Na = {(m/4.2) − 1}2 (xw + 0.85), suggesting that the fundamental structure of ethanol polymer-hydrates is invariable in this region. An inflection point of Na was found at xE ≈ 0.2. The radial distribution functions (RDFs) from X-ray measurements demonstrated a decrease of linear hydrogen bonds at 2.8 Å with increasing xE, while keeping the strongest peak at 4.8 Å for 0.4 ≤ xE ≤ 1.0. On the basis of a composition analysis of the mass spectra and the concentration dependence of RDFs, we propose the most likely model of ethanol–water binary clusters formed in the region 0.2 ≤ xE ≤ 0.8.

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The optimal prescription of transdermal preparations of prostaglandin E1 (PGE1) for treatment of peripheral vascular diseases has been investigated. The chemical stability of PGE1 in fatty alcohol/propylene glycol (FAPG) ointment was markedly improved by carboxymethyl-ethyl-beta-cyclodextrin (CME-beta-CyD). Application of a PGE1 ointment containing the penetration enhancer, 1-dodecylazacycloheptane-2-one (Azone) or 1-[2-(decylthio)ethyl]azacyclopentane-2-one (HPE-101), onto the skin of hairless mice showed the increase of blood flow in the skin due to the vasodilating action of PGE1. In particular, the ointment containing a PGE1-CME-beta-CyD complex supplemented with HPE-101 showed the most prominent increase of the blood flow. Compared with other ointments, this ointment was found to show significantly greater transfer of HPE-101 into in-vitro preparations of the skin of hairless mice. Transfer of PGE1 into the skin was thought to be facilitated by this increased transfer of HPE-101. These results suggest that a combination of CME-beta-CyD and HPE-101 is useful for designing PGE1 ointments for topical application with good chemical stability and percutaneous permeability.

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