Stability of amorphous

Stabilization of amorphous calcium phosphate by Mg and ATP Calcified Tissue Research 23 245-250. 

Various attempts have been made to improve the stability of amorphous sulphur. Addition of small amounts of halogens, i.e., chlorine, bromine, iodine, treatment with sulphur monochloride or the addition of a terpene have some effect on the rate of conversion. As far as is known, none of the modified materials are commercially available. 

Zhou, D. G., G. Z. Zhang, D. Law, D. J. W. Grant, and E. A. Schmitt. 2002. Physical stability of amorphous pharmaceuticals Importance of con gurational thermodynamic quantities and molecular mobility. J Pharm Sc01 1863-1872. 

Burger, A. and Ratz, A.W. (1990). Physical and chemical stability of amorphous and crystalline tetracycline hydrochloride,Sci. Pharm., 58 69-75. 

Guo Y, Byrn SR, Zografi G. Effects of lyophilization on the physical characteristics and chemical stability of amorphous quinapril hydrochloride. Pharm Res 2000 17 930-935. 

Aso Y, Yoshioka S, Otsuka T, Kojima S. The physical stability of amorphous nifedipine determined by isothermal microcalorimetry. Chem Pharm Bull 1995 43(2) 300-303. 

Hatley and Blair [3.69] presented mean Tg data for anhydrous carbohydrates (Table 3.1), which vary in the literature owing to measurement and interpretation differences. Small amounts of water may depress the data substantially. The physical stability of amorphous formulations below Tg is generally accepted, and a collapse can be avoided. This does not always apply to the chemical stability. If the temperature is reduced below T, the configurational entropy diminishes until it reaches zero. This T0 (also shown in Table 3.1) is called the zero mobility temperature at which the molecular motion stops. The authors define three areas of chemical reactions above Tg, chemical reactions are generally possible at T, reactions such as aggregation, which require substantial molecular motion, stop and between Tg and T0, reactions involv-... 

Aizenberg, J. 1996. Stabilization of amorphous calcium carbonate by specialized macromolecules in biological and synthetic precipitates. Advanced Materials, 8 222-5. 

The chemical and physical stability of amorphous pharmaceutical materials is controlled by the same basic factors as for crystalline materials [i.e., molecular structure (chemistry), purity (absence of catalysts, chemical reactants, or nucleating agents), molecular orientation (physical form), and molecular mobility (related to temperature)]. For any sample of a given molecular structure and purity, there will be more possible molecular orientations that occur in an amorphous sample than in a crystalline sample. Thus... 

Pikal, M.J. Stability of amorphous solids dynamics, reactivity, and the glass transition. Proceedings of BioPharm, Cambridge, MA, 1993. 

Watanabe, T. Wakiyama, N. Usui, E. Ikeda, M. Isobe, T. Senna, M. Stability of amorphous indomethacin compounded with silica. Int. J. Pharm. 2001, 226, 81-91. 

Several excellent reviews have been published on the relevance, characteristics, significance, and stabilization of amorphous materials of pharmaceutical interest (12-15). 

How can differences in the thermodynamic stabilities of amorphous versus crystalline forms of Si02, A1(0H)3 and Fe(OH)j, affect their occurrence in soils and sediments, ... 

Though there have been significant advances in the sophistication of longterm stability predictions (i.e., beyond a simple Tg-based approach), the hydration limit continues to be an active area of research in our and others laboratories. The hydration limit may be related to the temperature of "zero mobility" and that the use of the temperature dependence of the hydration limit has shovm some promise as a quantitative approach to determine the effect of residual water on the long-term stability of amorphous solids. 

The stability problem seems to be receding as more glassy metals are examined under reaction conditions and some are found to be remarkably stable. However, too little information about the factors determining the stability of glassy materials under reaction conditions is still available. There are methods, however, suitable for improving the thermal stability of amorphous materials. Alloying of properly selected components can result in glassy alloys with improved thermal stability or increased activity, which permit low-temperature application. 

Hydroperoxide decomposition. Yet another reaction (number 48) was added to the basic mechanism scheme to allow for the stabilization of amorphous linear polyethylene by the harmless removal of the hydro-... 

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