The thermal behaviour of the aminosalicylic acids is compared with the behaviour of their 1:1 molar ratio physical and kneaded
mixtures with each of three different cyclodextrins (b-, hydroxypropyl-b-, and g-cyclodextrin), using differential scanning
calorimetry and thermogravimetry coupled with evolved gas analysis by Fourier transform infrared spectroscopy. X-ray powder
diffraction and infrared spectroscopy provided complementary information. Comparison of the effects of the different cyclodextrins
on the behaviour of the individual aminosalicylic acid isomers shows that hydroxypropyl-b-cyclodextrin has the greatest interaction
with 3-aminosalicylic acid and 5-aminosalicylic acid, followed by g-cyclodextrin, while b-cyclodextrin generally shows the
least interaction. For 4-aminosalicylic acid, the effect of g-cyclodextrin seems to be more marked than for 3-aminosalicylic
acid and 5-aminosalicylic acid.
The effect on the stability of the isomers of aminosalicylic acid of formation of their sodium salts has been studied by use
of differential scanning calorimetry and thermogravimetry, coupled with evolved gas analysis by Fourier transform infrared
spectroscopy. X-ray powder diffraction and infrared spectroscopy provided complementary information. The DSC curves for the
sodium salts of all of the isomers showed complex dehydration/decomposition endotherms. From the initial mass losses of the
TG curves, the amounts of water per mole of salt were estimated as 0.5, 2.4 and 1.4 moles for the sodium salts of 3-aminosalicylic
acid, 4-aminosalicylic acid and 5-aminosalicylic acid, respectively. TG-FTIR results for the sodium salt of 3-aminosalicylic
acid showed the evolution of carbon dioxide in three stages: below 150C, between 200 and 300C and continuous formation up
to 500C. This behaviour differs from that of 3-aminosalicylic acid itself, which forms CO2 between 225 and 290C. For the sodium salt of 4-aminosalicylic acid, the formation of carbon dioxide starts from 250C and
is still being formed at about 650C. 4-aminosalicylic acid decarboxylates above 150C. 5-aminosalicylic acid and its sodium
salt showed no evolution of carbon dioxide below 600C.
Triprolidine hydrochloride, C19H22N2HClH2O (TPH) is a well-known antihistamine drug, which is reported as being photosensitive. Solid-state photostability studies
of TPH were undertaken by irradiating TPH and its binary mixtures with β-cyclodextrin (BCD) and glucose, using an Atlas Suntest
CPS+ irradiation chamber and conditions according to the guidelines of the International Committee on Harmonization (ICH). HPLC
analysis was used to determine the extent of photodegradation. XRD results showed that changes in the TPH crystal structure
had occurred during irradiation and that these changes increased with the time of irradiation. Although the potential for
isomerization under the influence of UV-light to the pharmaceutically inactive Z-isomer exists, results have proved that this
transformation for solid-state TPH would require more extreme light conditions. The results of this study thus illustrate
the general light stability of TPH in the solid-state.
Nifedipine complexes with β-cyclodextrin (β-CD), γ-cyclodextrin (γ-CD), 2-hydroxypropyl-β-cyclodextrin (2HP-β-CD), randomly
methylated-β-cyclodextrin (RM-β-CD) and heptakis(2,6-O-dimethyl)-β-cyclodextrin (DM-β-CD) have been prepared by both kneading and heating methods and their behaviour studied by
differential scanning calorimetry (DSC), diffuse reflectance mid-infrared spectroscopy (FTIR) and X-ray diffractometry (XRD).
DSC revealed the nifedipine melting endotherm with onset at approximately 171°C for the kneaded mixtures with β-CD, γ-CD and
2HP-β-CD, thus confirming the presence of nifedipine in the crystalline state, while some decrease in crystallinity was observed
in the DM-β-CD kneaded mixture. With RM-β-CD, however, broadening and shifting of the nifedipine endotherm and reduction in
its intensity suggested that the kneading could have produced an amorphous inclusion complex. These differing extents of interaction
of nifedipine with the cyclodextrins were confirmed by FTIR and XRD studies.
Triprolidine hydrochloride (C19H22N2·HCl·H2O) (TPH) is a well-known antihistamine drug which is reported as being photosensitive. The thermal stabilities of TPH and
of 1:1 molar and 1:1 mass ratio physical mixtures of TPH with β-cyclodextrin (BCD) and with glucose have been examined using
DSC, TG and TG-FTIR, complemented by X-ray powder diffraction (XRD) and infrared spectroscopic (IR) studies. Thermal studies
of the solid TPH/BCD mixtures indicated that interaction between the components occurs and it is possible that the TPH molecule
may be least partially accommodated in the cavity of the BCD host molecule. XRD results support this indication of inclusion.
The results of molecular modelling suggest that TPH is most likely to be accommodated in the BCD cavity as a neutral triprolidine
molecule with the toluene portion of the molecule preferentially included in the cavity. The results obtained illustrate the
general stability of TPH. The study has also shown TPH to be compatible with both glucose and BCD, which are potential excipients
both in solid and liquid dosage forms. The presence of these excipients in dosage forms will thus not adversely affect the
stability and the therapeutic efficacy of TPH.
The thermal behaviour of benzoic and salicylic acids is compared with the behaviour of 1:1 molar ratio physical and kneaded
mixtures of these acids with each of three different cyclodextrins (b-, hydroxypropyl-b-, and g-cyclodextrin). Differential
scanning calorimetry and thermogravimetry coupled with evolved gas analysis by Fourier transform infrared spectroscopy were
used for the thermal studies and X-ray powder diffraction and infrared spectroscopy provided complementary information. Thermal
studies of benzoic acid with the cyclodextrins showed significant interactions in both physical and kneaded mixtures of benzoic
acid/b-cyclodextrin and benzoic acid/hydroxypropyl-b-cyclodextrin. Interactions in the kneaded benzoic acid/g-cyclodextrin
mixtures were the most extensive as might be expected for the cyclodextrin with the largest molecular cavity. The results
for the salicylic acid/b-cyclodextrin and salicylic acid/hydroxypropyl-b-cyclodextrin mixtures were similar to those for benzoic
acid/b-cyclodextrin and benzoic acid/hydroxypropyl-b-cyclodextrin. Again, the kneaded salicylic acid/g-cyclodextrin mixture
showed the most interaction.
Authors:S. Agotonovic-Kustrin, B. Glass, M. Brown, and M. Rotich
The application of classical QSAR and molecular modelling to the inclusion complexation of natural and modified cyclodextrins
(CDs) with carboxylic acid derivatives as guest molecules was examined. Information was available on the thermal behaviour,
in the solid-state of benzoic acid (BA), salicylic acid (SA), and various substituted aminosalicylic acids (3-aminosalicylic
acid, 3-ASA, 4-aminosalicylic acid, 4-ASA and 5-aminosalicylic acid, 5-ASA), as well as on the thermal behaviour of 1:1 molar
ratio physical and kneaded mixtures of these acids with each of three different cyclodextrins, β-, (BCD) 2-hydroxypropyl-β-,
(HPBCD) and γ-cyclodextrin (GCD). The thermal behaviour of the binary (1:1 stoichiometry) mixtures was modelled using stepwise
multiple regression (SMR). Two models for the prediction of the percentage mass loss and enthalpy of dehydration of the physical
mixtures were established with correlation coefficients (r) of 0.79 and 0.92, respectively. Decreased correlation in the thermal behaviour of kneaded mixtures indicated significant
interaction and possible formation of inclusion complexes.