Nedocromil sodium trihydrate

In the crystalline state of a substance, the molecules are arranged in a defined unit cell that is repeated in a three-dimensional lattice [1], Since the crystal lattice can act as a diffraction grating for X-rays, the X-ray diffraction pattern of a crystal consists of a number of sharp lines or peaks, often with baseline separation. Figure 1 shows the X-ray powder diffraction pattern of the crystalline and amorphous forms of nedocromil sodium trihydrate. 

Figure 1 X-ray powder diffractograms of the crystalline and amorphous forms of nedocromil sodium trihydrate. I is the intensity of the diffracted beam at a diffraction angle 9. (RK Khankari and DJW Grant, unpublished observations.)...

Clarke MJ, Tobyn MJ, Staniforth JN. The formulation of powder inhalation systems containing a high mass of nedocromil sodium trihydrate. J Phann Sci 2001 90(2) 213-223. 

When the solvate happens to be water, these are called hydrates, wherein water is entrapped through hydrogen bonding inside the crystal, and strengthens the crystal structure, thereby invariably reducing the dissolution rate (Table 4). The water molecules can reside in the crystal either as isolate lattice, where they are not in contact with each other as lattice channel water, where they fill space and metal coordinated water in salts of weak acids, where the metal ion coordinates with the water molecule. Metal ion coordinates may also fill channels, such as in the case of nedocromil sodium trihydrate. Crystalline hydrates have been classified by structural aspects into three classes isolated lattice sites, lattice channels, and metal-ion coordinated water. There are three classes, which are discernible by the commonly available analytical techniques. 

R Khankari, DJW Grant. Hydration-dehydration phenomena of nedocromil sodium trihydrate (PT 6195). Pharm Res 9(10) S-163, 1992. 

In some structures, both (2) and (3) can occur together. Nedocromil sodium trihydrate, for example, shows both metal co-ordinated water and channel water. 

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