Melting temperature of the samples was determined by differential
scanning calorimetry (DSC) (Perkin Elmer Diamond DSC,
USA). The sample (8–10 mg) was accurately weighed into aluminum
pans and sealed. The procedure was as follow: heating from
−10 ◦C to 200 ◦C at 10 ◦C min−1, isotherm 5 min, cooling from 200 ◦C
to −10 ◦C and heating from −10 ◦C to 200 ◦C at 10 ◦C min−1. The
second scan curve was used to determine the melting temperature
(Tm) of the sample i.e. the maximum temperature (peak) of the
endotherm. All of the experiments were performed under nitrogen
atmosphere.