I. INTRODUCTION
Loratadine (Figure 1), systematic name ethyl 4-(8-chloro-5,6-dihydro-11H-benzo[5,6]cyclohepta[1,2-b]pyridin-11-ylidene)-1-piperidinecarboxylate, is a second-generation H1 histamine antagonist drug used to treat allergies such as hay fever (allergic rhinitis), urticaria (hives), and other skin allergies (Haria et al., Reference Haria, Fitton and Peters1994). The oral loratadine is well absorbed from the gastrointestinal tract with rapid first-pass hepatic metabolism (Ghosal et al., Reference Ghosal, Gupta, Ramanathan, Yuan, Lu, Su, Alvarez, Zbaida, Chowdhury and Alton2009).
Figure 1. Structural formula of loratadine.
The single crystallographic data of loratadine [a = 28.299(3) Å, b = 4.993(1) Å, c = 29.137(3) Å, β = 109.189(9)°, unit-cell volume V = 3888.20 Å3, Z = 8, and space group C2/c] was obtained by Kaminski et al. (Reference Kaminski, Carruthers, Wong, Chan, Billah, Tozzi and McPhail1999). To date, the detailed X-ray powder diffraction data for loratadine have not been reported.
II. EXPERIMENTAL
A. Sample preparation
The title compound was purchased from J&K Chemical Co., Ltd., China and characterized by high-performance liquid chromatography (HPLC), UV and IR. It was recrystallized in methanol, then dried, and ground into powder.
B. Diffraction data collection and reduction
The diffraction pattern for the title compound was collected at room temperature using an X'Pert PRO diffractometer (PANalytical Co., Ltd., Netherlands) with an X'celerator detector and CuKα 1 radiation (λ = 1.54 056 Å, generator setting: 40 kV and 40 mA). The diffraction data were collected over the angular range from 5° to 50° 2θ with a step size of 0.01 313° 2θ and a counting time of 30 s/step. Data evaluation was performed using the software package Material Studio 4.2 (Accelrys Co., Ltd. USA).
The powder diffraction pattern was pre-treated by subtracting the background, smoothing, and eliminating the Kα 2 component. Indexing was carried out using peak positions obtained from the powder diffraction profiles by the X-Cell method. Then the best indexing results with 1094 for the value of figure-of-merit were refined using Pawley refinement (Pan et al., Reference Pan, Guo, Duan, Cheng and Li2012). In the indexing step, MC/SA search algorithm in the Powder Solve package (Engel et al., Reference Engel, Wilke, König, Harris and Leusen1999) was used to constantly adjust the conformation, position, and orientation of the trial model in a unit cell of loratadine. The result of Powder Solve (R wp = 6.74%) was refined by Rietveld refinement techniques based on the experimental X-ray powder diffraction pattern. In the Rietveld refinement (Young, Reference Young1993), variables defining the structural model and the powder diffraction profiles were adjusted by least-squares methods for obtaining an optimal fit between the experimental pattern and calculated pattern. After the Rietveld refinement, the final R wp was 8.94%.
III. RESULTS
The experimental powder diffraction pattern is depicted in Figure 2. Indexing results confirmed that loratadine is monoclinic with space group C2/c and unit-cell parameters after Pawley refinement: a = 28.302(18) Å, b = 4.996(3) Å, c = 29.154(19) Å, β = 109.158(2)°, unit-cell volume V = 3894.25 Å3, and Z = 8 (Table I). A comparison of unit-cell parameters from powder data and single-crystal data (Kaminski et al., Reference Kaminski, Carruthers, Wong, Chan, Billah, Tozzi and McPhail1999) displays a significantly consistency, and the deviations of the two methods were between 0.011 and 0.155%. All lines were indexed and are consistent with the C2/c space group.
Figure 2. X-ray powder diffraction pattern of the loratadine, using CuKα 1 radiation (λ = 1.54 056 Å).
Table I. Indexed X-ray powder diffraction data of loratadine (C22H23ClN2O2).
Only the peaks with I rel of 1 or greater are reported [a = 28.302(18) Å, b = 4.996(3) Å, c = 29.154(19) Å, β = 109.158(2)°, unit-cell volume V = 3894.25 Å3, Z = 8, and space group C2/c]. All measured lines were indexed and are consistent with the C2/c space group. The d-values were calculated using CuKα 1 radiation (λ = 1.54 056 Å).
