Crystalline-water interactions

Scholze, H. (1988). Glass-water interactions. Journal of Non-Crystalline Solids 102 1-10. 

Crowley and Martini [48] reported on several studies evaluating the impact of unit process operations on hydrates. AU showed some level of dehydration liberating freed crystalline water to participate in moisture-mediated reactions. The authors speculated that such energetic processing conditions are likely to have a similar affect on hydrated excipients with a potential deleterious effect on moismre-sensitive APIs. They commented that classical excipient compatibility studies were ill-equipped to predict such moismre-mediated interactions and that compression, attrition and other energy-intensive unit operations were rarely mentioned as requiring investigations. 

Einspahr, H., and Bugg, C. E. (1980). The geometry of calcium-water interactions in crystalline hydrates. Acta Crystallogr. Sect. B 36, 264-271. 

Hydrogen bonds between water molecules provide the cohesive forces that make water a liquid at room temperature and that favor the extreme ordering of molecules that is typical of crystalline water (ice). Polar biomolecules dissolve readily in water because they can replace water-water interactions with more energetically favorable water-solute interactions. In contrast, nonpolar biomolecules interfere with water-water interactions but are unable to form water-solute interactions— consequently, nonpolar molecules are poorly soluble in water. In aqueous solutions, nonpolar molecules tend to cluster together. 

The liquid crystalline regions obey the general rules for the liquid phases, but only where the hydrocarbon content is high. Along the water-emulsifier axis the changes with temperature are small in the PIT range this indicates that the structure of the liquid crystalline phase depends mainly on short range emulsifier-water interactions, which limits the solubility of water into the emulsifier. 

In spite of the great importance of aqueous solubility in pharmaceutical chemistry, it is a very poorly understood phenomenon. Several attempts at predicting aqueous solubility from the chemical structure have been made [98.99] however, it is a quite complex process. The first step involves the removal of a molecule from the solid phase. The second step involves the creation of a hole or cavity in the solvent large enough to accept the molecule. The last step is the accommodation of the solute molecules in the cavity of the solvent. So we have to be able to estimate the entropy of mixing, the solute-water interactions and the interactions associated with lattice energy of crystalline solutes. The... 

Ivanovich M., Blomqvist R., and Frape S. K. (1992) Rock/ water interaction study in deep crystalline rocks using isotopic and uranium series radionuclide techniques. Radio-himica Acta 58/59, 401-408. 

Non-Ionics of the C E -type have a very typical solubility behaviour, which is related to the EO-water interaction, hydration for short. First, poly(ethylene oxide), (PEO)jj is fairly soluble in water at room temperature, but polylpropylene oxide) (PPO) is not (as expected), and neither is poly(methylene oxide) (PMO), (unexpected). This irregular trend reminds us that solubility is not only determined by hydration in solution, but also by the Gibbs energy in the crystalline phase, which will be related to the molecular packing therein. Based on this difference in solubility, and hence in adsorbability, surface active polymers of the PEO-PPO type have been synthesized [Pluronics]-, they have a wide scope of application. 

At an opposite extreme from crystalline water-containing polysaccharides are the mucopolysaccharides described by Ikada et al. [17]. In addition to the nonfreezing water that characterizes these polymers in the solid state, one to three thermal transitions measured on solutions suggest complex interactions with water. 

Hydrates of this type contain metal ion coordinated water, and the major concern with these is the effect of the metal-water interaction on the structure of crystalline hydrates. The metal-water interaction can be quite strong relative to the other bonding in a molecular crystal, so that dehydration takes place only at very high temperatures [13], Drugs with solubility, dissolution, or handling problems are most often recrystallized as Na(I), K(I), Ca(II), or Mg(II) salts and are often hygroscopic to some degree [16],... 

Regioselectively liinctionalized 2,3-O-hydroxyalkyl ethers are mentioned as an example of a detailed one- and two-dimensional C-NMR spectroscopic study of cellulose ethers. °° ° Tri-MC has also been flioroughly studied.While NMR spectro-seopy in solution clearly dominates fliis field, solid-state NMR has also been applied, but mainly for the analysis of crystallinity and interaction with plasticizers or water. 

Lipid-water interaction and liquid-crystalline phases... 

The water content (% w/w) in PLA versus relative humidity based on the value of K determined in MD simulations is presented in Figure 13.4 along with experimental results reported previously [46] for comparison. The agreement was within the error limits of the computational results. Previous studies have shown that for PLA, the L/D ratio and degree of crystallinity had little influence on the water sorption [51], which is generally less than 2% w/w within the 0-100% relative humidity range. This can be attributed to significantly weaker interactions between water and PLA compared to the water-water interactions in pure liquid water. 

Apart from the crystalline solids of clathrate hydrates, some cage structures in aqueous solutions around hydrophobic solutes have been observed by computer simulation [80-84], Therefore, it is important to investigate how the water-water interaction, and the tetrahedral hydrogen-bonded structure, is connected with the formation of clathrate hydrate structure when discussing the thermodynamic and structural properties of these aqueous solutions. 

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