Metamorphosis of caffeine hydrate and anhydrous caffeine

Molecular structure of caffeine as determined by gas electron diffraction aided by theoretical calculations

“…By using the diatomic approximation [29] and neglecting the centrifugal distortion term, the difference between the r g and r e distances can be approximated to be, r g -r e ≈ (3/2)al 2 , and by assuming the Morse parameter, a, to be 2.0 As mentioned in Introduction, no crystal structure has been reported for anhydrous caffeine. So the gas-phase structure of the present study is compared with the crystal structure of the monohydrated caffeine [8]. Disagreements are found for many structural parameters especially in bond lengths even with the difference between the definitions of the bond length (r g for electron diffraction and r α for X-ray diffraction) taken into account.…”

“…In Table 3, the structural parameters of caffeine monohydrate in the crystal [8] and the gas-phase structures of the related molecules, uracil [26] and imidazole [27,28] (see Fig. 1), are also listed.…”

“…Disagreements are found for many structural parameters especially in bond lengths even with the difference between the definitions of the bond length (r g for electron diffraction and r α for X-ray diffraction) taken into account. Monohydrated caffeine forms hydrogen bonded polymeric chains in the crystal, in which the N 9 atom accepts a hydrogen from the water molecule [8].…”

“…Although it is a common understanding that the above-mentioned effect of caffeine is brought about by its structural resemblance with adenosine and cyclic-AMP, no reliable experimental molecular structure even in the crystal has been reported. The crystal structures of caffeine hydrate have been reported [7,8], but the structural determination of pure anhydrous caffeine has not been successful because of the difficulty in preparing the fully ordered crystal [5,6].…”

Analytical study on irradiated methylxanthine derivatives

“…liquid (*236°C) phase transition also a change in the polymorphic form was noted at about 160°C. According to the literature on thermal investigation of methylxanthine derivatives [19], the course of their DSC curves is characteristic of anhydrous forms and the curve recorded for CF also implies that this derivative occurs in the polymorphic form a CF (form II), while the peak appearing at *160°C corresponds to the transition of CF into a new polymorphic form (form I). As a result of irradiation the character of the DSC curves recorded did not change and only slight changes in the values of T peak and T onset were noted ( Table 3).…”