Carvajal M Teresa, Staniforth John N
Department of Industrial and Physical Pharmacy, Purdue University, West Lafayette, IN 47907-1336, USA.
Int J Pharm. 2006 Jan 13;307(2):216-24. doi: 10.1016/j.ijpharm.2005.10.006. Epub 2005 Nov 18.
The purpose of this study is to investigate the interactions of water adsorption on the surfaces of different crystal forms of the same drug. The energy of interaction between water vapor and the surfaces of the two crystal polymorphs has been investigated as a function of temperature and water activity. One of the adsorbents, the metastable form of the monotropically related pair used here, showed greater adsorptive capacity in terms of both the amount of water uptake as well the integral heat of adsorption. However, the specific heat of adsorption values revealed that even though the surface of the thermodynamically stable crystal adsorbs less water, water molecules are actually more strongly bound when adsorbed on the surface of the stable crystal form. This means that the metastable crystal form adsorbs a greater amount of more weakly bound water. Conversely, the thermodynamically stable form, presents on its surface a smaller number of stronger adsorption sites for water. This study also shows that the crystalline character of the surfaces of the two polymorphs, shown as quantifiable differences in their surface interactions, is maintained despite the presence of any crystal defects incorporated upon milling.
本研究的目的是探究同一药物不同晶型表面上的水吸附相互作用。研究了水蒸气与两种晶体多晶型物表面之间的相互作用能随温度和水分活度的变化情况。其中一种吸附剂，即此处使用的单向相关对中的亚稳形式，在吸水量和吸附积分热方面均表现出更大的吸附容量。然而，吸附比热数值表明，尽管热力学稳定晶体的表面吸附的水较少，但水分子吸附在稳定晶型表面时实际上结合得更强。这意味着亚稳晶型吸附了大量结合较弱的水。相反，热力学稳定形式在其表面上呈现出数量较少但对水具有更强吸附作用的位点。本研究还表明，尽管研磨时引入了任何晶体缺陷，但两种多晶型物表面的晶体特性（表现为其表面相互作用的可量化差异）仍然得以保持。
