Correlated studies of photoluminescence, vibrational spectroscopy and mass spectrometry concerning the pantoprazole sodium photodegradation

Abstract

In this work, new optical evidences concerning the changes induced of the UV light on pantoprazole sodium (PS), in solid state and as aqueous solution, are reported by UV-VIS spectroscopy, photoluminescence (PL), Raman scattering and FTIR spectroscopy. New evidences concerning the products of the PS photodegradation pathways are reported by the correlated studies of thermogravimetry and mass spectrometry. The influence of the excipients and alkaline medium on the PS photodegradation is also studied. New aspects regarding the chemical mechanism of the PS photodegradation in the presence of the water vapor and oxygen form air and the alkaline medium are shown. Our results confirm that the PS photodegradation induced of the water vapors and oxygen from air leads to the generation of 5-difluoromethoxy-3H-benzimidazole-2-thione sodium, 5-difluoromethoxy-3H-benzimidazole sodium, 2-thiol methyl-3, 4-dimethoxypyridine and 2-hydroxymethyl-3, 4-dimethoxypyridine, while in the alkaline medium, compounds of the type of the 2-oxymethyl-3,4-dimethoxypyridine sodium salts are resulted.

Figure 1

PL (a₁ and a₂) and PLE (b) spectra of PS (1) and their evolution when the samples are exposed 300 min. to UV light. PL and PLE spectra were recorded at the excitation emission wavelengths of 335 nm and 425 nm, respectively. Red, green, and magenta curves in (a₁) and (a₂) correspond to the PL spectra of PS (1) sample prior and after 28 min and 300 min of UV light exposure, respectively, while black curves show PL spectra successively recorded.

Figure 2

PL (a) and PLE (b) spectra of the Controloc (4) drug and their evolution during of 300 min. exposure to UV light. PL and PLE spectra were recorded at the excitation and emission wavelengths of 335 nm and 425 nm, respectively. In Figure (a), the red and magenta curves correspond to the PL spectra of the Controloc (4) drug prior and after 300 min of UV light exposure, while the black curves show PL spectra successively recorded.

Figure 3

PL spectra of the aqueous solution of PS (1, a) and the Controloc drug (4, b), when the two samples are exposed to the UV light, for 300 min. The PS concentration in the two aqueous solutions was of 2 mg/ml. All PL spectra were recorded at the excitation wavelength of 335 nm. Red and magenta curves correspond to PL spectra of PS and Controloc, prior and after 300 min of UV light exposure, while the black curves show PL spectra successively recorded for the two compounds.

Figure 4

Raman (a) and IR (b) spectra of PS (1) in powder state prior (a₁, b₁) and after 300 min. exposure to UV light (a₂, b₂).

Scheme 1

The photodegradation reactions of PS (1) in the presence of the H₂O vapors and O₂ from air.

Figure 5

The dependence of the PL spectra of PS (1) depending on the pressure of environmental conditions (a) and the evolution of the PL spectra of PS (1) under vacuum conditions, when the pressure was equal to 2.5 × 10^–5 mbar and the sample was exposed to UV light, time of 28 min. (b). In Figure a, the black, red, green, blue, cyan, magenta and olive curves correspond to the PL spectra of PS when the sample is at a pressure equal to 1.013 × 10³ mbar, 10^–1 mbar, 10^–4 mbar, 4.5 × 10^–5 mbar, 3.4 × 10^–5 mbar, 3 × 10^–5 mbar and 2.5 × 10^–5 mbar, respectively. In Figure b, the black, red, green, blue, cyan, magenta, dark yellow, navy, purple and olive curves correspond to the exposure times of PS to UV light equal to 164 s, 328 s., 492 s, 656 s, 820 s, 984 s, 1148 s, 1312 s, 1476 s and 1680 s.

Figure 6

The PL spectra of PS (1; 2 mg/ml) in BP with the pH = 6 (a) and 8 (b) and their evolution during the 300 min. exposure to UV light. Red and magenta curves corresponds to PL spectra prior and after 300 min of UV light exposure, while the black curves show PL spectra successively recorded.

Figure 7

The UV–VIS spectra of the solution of PS (1; 2 mg/ml) in BP with the pH = 6 (a) and 8 (b) and their evolution during the 80 min. exposure to UV light. Black and red solid lines correspond to the UV–VIS spectra of the PS (1) solutions prior and after exposure to UV light, respectively, time of 80 min. Black dash lines correspond to the UV–VIS spectra of the PS (1) solution subsequently exposed for 2 min. to UV light.

Figure 8

The UV–VIS (a) and PL (b) spectra of the solution of PS (1; 2 mg/ml) in BP with the pH = 8 and their evolution after the storage time of 6 days. Black and red solid lines correspond to the UV–VIS and PL spectra of the PS (1) solutions prior and after the storage time of 6 days.

Figure 9

PL spectra of PS (1; 2 mg/ml) interacted with NaOH (0.3 M) when the volumetric ratio is equal to 2:1 (a), 1.5:1.5 (b) and 1:2 (c). Figure d shows the PL spectra of the Controloc (4) drug (having PS concentration of 2 mg/ml) interacted with the NaOH 0.3 M, when the volumetric ratio of the two solutions is of 2:1 and the sample is exposed to UV light, for 300 min. The red and magenta curves correspond to PL spectra of samples, prior and after to 300 min od UV light exposure, while the black curves show PL spectra successively recorded.

Figure 10

PL spectra of the sample resulted by the reaction of 1 ml PS (1) 2 mg/ml with 2 ml NaOH 0.3 M prior (a) and after the 300 min. exposure to UV light (b).

Figure 11

UV–VIS spectra of the PS (1; a, 0.02 mg/ml) and Controloc (4; b, the PS concentration is 0.02 mg/ml) and their evolution when the two samples are exposed 80 min. to UV light. Figure (c) shows UV–VIS spectra of the PS (1) interacted with NaOH 0.3 M. Black and red solid lines correspond to the UV–VIS spectra of the PS (1) and Controloc (4) solutions prior and after exposure to UV light, respectively, time of 80 min. Black dash lines correspond to the UV–VIS spectra of the PS (1) and Controloc (4) solutions subsequently exposed for 2 min. to UV light.

Scheme 2

The photodegradation reactions of NaOH-reacted PS (1).

Figure 12

Raman spectra, in the 100–3500 cm⁻¹ (a) and 1060–1100 cm⁻¹ (b) spectral ranges, of PS (1) (curve black) and NaOH-reacted PS (1), when the weight ratio between PS (1) and NaOH was of 1:1 (red curve) and 1:3 (blue curve).

Figure 13

FTIR spectra of NaOH-reacted PS (1), when the weight ratio between PS (1) and NaOH is of 1:1 (a) and 1:3 (b).

Figure 14

TG-DSC curves of PS in dark conditions (a) and the samples of PS (b) and NaOH-reacted PS (1) (c) after exposure to UV light.

Figure 15

MS curves of PS (1) in dark conditions (a) and after exposure to UV light of PS (1) (b) and NaOH-reacted PS (1) (c).