Amorphous compounds, stability

Solubility is extremely difficult to calculate. Dozens of methods exist, but none is reliable enough to be used in the entire chemical diversity space populated by infinite drug candidates. Experimental solubility errors are relatively high and frequent. Moreover, solubility can change dramatically with the purity of the compounds, stability, and time. Solubility of liquid substances differs from that of solid phase compounds. Solubility is thermodynamically affected by crystal packing, influencing the process of crystal lattice disruption and hence polymorphism, amorphous solid compounds lead to imprecise experimental measures. Finally, publically available databases of solubility values contain a lot of errors. 

P-aluminate amount is increased. The stabilizing effect of lanthanum was assumed to result from the formation of intermediate X-ray amorphous compounds with the transient AI2O3 forms [2],... 

If a lyophilized drug is amorphous, then knowledge of the glass transition temperature is important for stability reasons. Chemically, amorphous compounds are usually less stable than their crystalline counterparts. This is illustrated in Table 6.11, which shows some stability data for an amorphous compound (produced by lyophilization) and the crystalline hydrate... 

In order to get the benefit from high solubility and dissolution, the challenge of poor stability of amorphous compounds has to be addressed seriously. MPS with high surface area and pore volume can improve the stability of amorphous compounds. 

Numerous efforts are done to replace the lithium-cobalt oxide used in the first generation of commercial lithium-ion batteries by materials with low cost and environmental concerns. The development of new materials needs new synthesis procedure such as sol-gel processing, ion-exchange reaction, and hydrothermal reaction. The chemical and structural stabilities of the transition-metal oxide electrodes have been compared by studying bulk samples. In this respect, the various physicochemical techniques are welcome to design the best stmcture. Synthesis of amorphous compounds could help the knowledge of microstructures in this regard. 

If high impact resistance is required, the PA can be modified with rubber particles.11,15 The blends are usually made by reactive compounding from maleic-anhydride-modified rubbers, such as, EPDM, EPR, polybutadiene, or SEBS. Partial amorphous PA with a high Tg combines to give a high dimensional stability and good solvent resistance with transparency. 

Perspectives for fabrication of improved oxygen electrodes at a low cost have been offered by non-noble, transition metal catalysts, although their intrinsic catalytic activity and stability are lower in comparison with those of Pt and Pt-alloys. The vast majority of these materials comprise (1) macrocyclic metal transition complexes of the N4-type having Fe or Co as the central metal ion, i.e., porphyrins, phthalocyanines, and tetraazaannulenes [6-8] (2) transition metal carbides, nitrides, and oxides (e.g., FeCjc, TaOjcNy, MnOx) and (3) transition metal chalcogenide cluster compounds based on Chevrel phases, and Ru-based cluster/amorphous systems that contain chalcogen elements, mostly selenium. 

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