1. Aim or purpose
Crystals of betulinic acid (BA) obtained in a recrystallization method from ethanol, isopropyl alcohol and 2-butanol from 1:1 solutions were characterised theoretically and experimentally by using FT-IR and FT-Raman spectroscopy, in conjunction with scanning electron microscopy (SEM) and X-ray powder diffraction (XRPD).
2. Materials and methods
Analytical purity of BA and the solvents (ethanol, isopropanol and 2 butanol) were acquired from Merck and Sigma Aldrich (Germany), respectively.
In each experiment BA was dissolved in the solvents close to the boiling temperature of each solvent and the mixture was stirred until BA was completely dissolved. The mixture was cooled down to room temperature and the crystals were obtained after a few days.
The morphology of the crystalline samples of betulinic acid in different solvatomorphs was investigated by scanning electron microscopy (SEM) (Hitachi S4700, Hitachi Scientific Ltd., Tokyo, Japan) at 10 kV.
The X-ray powder diffraction (XRPD) measurement was carried out with a BRUKER D8 Advance X-ray powder diffractometer with Cu Kα1 radiation (λ = 1.5406 Å) and a VÅNTEC-1 detector. The angular range was 3° to 40° at a step time of 0.1 s and a step size of 0.007°.
FT-IR spectra were recorded in mid-infrared 4000-400 cm-1 spectral range with a resolution of 2 cm-1 using a JASCO 670+ after KBr pelleting.
FT-Raman spectra of the powdered solid, polycrystalline solvatomorphs have been recorded with a Bruker Equinox 55 FT-IR spectrometer with an integrated FRA106S Raman module. Detection was accomplished with a Ge detector operating at the liquid nitrogen temperature. A Nd: YAG laser emitting the 1064 nm line was used for excitation. The output power was set to 350 mW and 500 scans were co-added.
3. Results
The SEM reveals the formations of soft agglomeratios with size of about 10-800 µm displayed as an iregular morphology in the form of the plates and bars slightly different from the needle shaped of pure BA crystals.
Obtained FT-IR and Raman experimental spectra for all three solvates of BA were compared with pure BA spectrum. Moreover, wave numbers of all normal modes for each molecule: BA (C30H48O3-237 normal modes); BA-EtOH (C30H48O3.C2H5OH-264 normal modes); BA-2BUT (C30H48O3.C4H9OH-282 normal modes); BA-IPA (C30H48O3.C3H7OH-273 normal modes) were calculated. The main experimental FT-IR and Raman harmonic wavenumbers, their corresponding calculated values, with tentative of their assignments, were given.
4. Conclusions
The X-ray analysis of solvatomorphs are in good agreement with the crystallographic structure and the space group. We established a good correlations betweencalculated and experimental data of the monosolvates betulinic acid. Also, we demonstrated that DFT calculations at BP86/TZVP level is a powerful tool for investigation of vibrational spectra for complex structures like BA and its derivatives. A lot of answers concerning vibrational modes for the low wavenumbers range in Raman Stokes and anti-Stokes region was given.

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