Studies on Tolfenamic Acid–Chitosan Intermolecular Interactions: Effect of pH, Polymer Concentration and Molecular Weight

Abstract

Solid-state properties of tolfenamic acid (TA) and its complexes with chitosan (CT) have been studied. Effect of medium pH, molecular weight of polymer and its different concentrations on these TA-CT complexes were studied in detail. Low and medium molecular weight CT have been used in different ratios at pH ranging from 4 to 6 and freeze-drying technique has been employed to modify the appearance of crystalline TA. Physical properties of the formed complexes have been studied by employing X-ray diffraction, differential scanning calorimetry and scanning electron microscopy; chemical structure has been studied using Fourier transform infrared spectroscopy. The results showed that both forms of the polymer exhibited complete conversion in 1:8 ratio at pH 4, 1:4 at pH 5 and 1:1 at pH 6 indicating a marked effect of pH on drug-polymer complexation. The percent crystallinity calculations indicated low molecular weight CT slightly more effective than the other form. No changes in the complexes have been observed during the 12 week storage under controlled conditions. Both forms of CT at different pH values indicated retardation of recrystallization in TA during cooling of the melt from 1:1 ratios exhibiting formation of strong intermolecular hydrogen bonding between the drug and the polymer.

Factors affecting formulation characteristics and stability of ascorbic acid in water‐in‐oil creams

“…FTIR spectrometry has been employed to observe any possible interaction between AA and CT at the molecular level. This technique can be used for the detection of any possible interaction or change from one polymorphic form to the other as a result of a shift or change in the intensity of absorption band height or area such as broadening of the peak .…”

“…FTIR spectrometry has been employed to observe any possible interaction between AA and CT at the molecular level. This technique can be used for the detection of any possible interaction or change from one polymorphic form to the other as a result of a shift or change in the intensity of absorption band height or area such as broadening of the peak [66,67]. AA is a six-carbon keto-lactone that contains four OH groups, of which two are attached to the lactone ring carbons (enolic OH groups) and the remaining two are on the side chain C atoms (Fig.…”

Development and Characterization of Novel Polyurethane Films Impregnated with Tolfenamic Acid for Therapeutic Applications

“…FTIR spectroscopy is considered as a valuable technique to study the degree of crystallinity based on the measurement of characteristic peak intensity for its particular polymorphic crystal state [30]. Infrared technique is also very useful to study the hydrogen bond formation of polymers with different drugs [29, 31, 33]. Therefore, FTIR spectroscopy was used in this study to identify the possible interaction and complexation between TA and PU.…”

“…However, one of its other polymorphic forms gives similar stretching vibrations at 3324–3315 cm −1 . Due to this reason, the spectral region between 3350 and 3300 cm −1 has been monitored for observing the spectral changes in the crystalline form of TA [31, 33, 40–42]. Similarly, PU is also known to exhibit its characteristic major NH peak at 3325 cm −1 (Figure 4(b)).…”

“…A number of methods have been reported to make drugs amorphous and hence more soluble and bioavailable [27–33]. But often it has been observed that the metastable amorphous forms have the tendency of recrystallization during storage, which is the major drawback in their preparation.…”