Abstract
Amorphous forms are, by definition, non-crystalline materials which possess no long-range order. Their structure can be thought of as being similar to that of a frozen liquid with the thermal fluctuations present in a liquid frozen out, leaving only "static" structural disorder. The amorphous solids have always been an essential part of pharmaceutical research, but the current interest has been raised by two developments: a growing attention to pharmaceutical solids in general, especially polymorphs and solvates and a revived interest in the science of glasses and the glass transition. Amorphous substances may be formed both intentionally and unintentionally during normal pharmaceutical manufacturing operations. The properties of amorphous materials can be exploited to improve the performance of pharmaceutical dosage forms, but these properties can also give rise to unwanted effects that need to be understood and managed in order for the systems to perform as required.
Highlights
Amorphous forms are, by definition, non-crystalline materials which possess no long-range order
The amorphous solids have always been an essential part of pharmaceutical research, but the current interest [3,4,5] has been raised by two developments:
Studies of crystalline and amorphous solids are often so intertwined that it is natural to treat the two solids as "polymorphs" of each other. This view is harmonious with one definition of polymorphism [10], and with the "energy landscape"' model of solids [11], which regards crystalline and amorphous states as connected minima on a multi-dimensional potential energy surface corresponding to different molecular packing and conformations
Summary
Amorphous forms are, by definition, non-crystalline materials which possess no long-range order. Their structure can be thought of as being similar to that of a frozen liquid with the thermal fluctuations present in a liquid frozen out, leaving only "static" structural disorder [1]. The degree of crystallinity, according to the USP, depends on the fraction of crystalline material in the mixture, which is termed the two-state model. Another way of viewing this situation is that the crystallinity has a range from 100 percent for perfect crystals (zero entropy) to 0 percent (non-crystalline or amorphous); this is known as the onestate model [2]. This view is harmonious with one definition of polymorphism (any solids that share the same liquid state) [10], and with the "energy landscape"' model of solids [11], which regards crystalline and amorphous states as connected minima on a multi-dimensional potential energy surface corresponding to different molecular packing and conformations
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