Ultraviolet visible spectrophotometer

The AP and AP-Nico crystals (10 mg, respectively) were determined by suspending them in 25 mL of distilled water and placing them in a 50-mL round bottom flask with glass stoppers. The suspensions were kept at different temperatures of 298 K and 310 K and stirred at 100 rpm using a magnetic stirrer. After 72 h, the sample concentration was measured at 342 nm by ultraviolet-visible spectrophotometer (Shimadzu Corporation of Japan), and the interference of suspension was filtered using a 0.22-μm microfiltration membrane.
Solubility studies: Solubility studies were undertaken on parent AP and AP-Nico pharmaceutical cocrystal in NaAc-HAc buffer and stirring the slurry in a thermostated (310 K) vessel, with a magnetic stir bat at 100 rpm. The suspension was sampled at specific time points (5, 10, 15, 20, 30, 45, 60, 90, 120, 150, 180, 240 min), and filtered using a 0.22-μm microfiltration membrane. The concentration of AP and Ap-Nico crystals was determined by ultraviolet-visible spectrophotometer (Shimadzu Company, Japan) from the slope of absorption and known concentration. Absorbance was measured at 342 nm where no interference of the conformer occurs. And the dissolution rate was obtained according to the cumulative release formula:

The flavonoid content of C. nutans was evaluated according to aluminum chloride assay [37 (link)]. The 1 mL of each extract was transferred into 10-mL volumetric flasks containing 4 mL of 80% methanol. Then, 0.3 mL of sodium nitrite (NaNO₂) solution (1:5, w/v) was added to the flasks and allowed to stand for 6 min at room temperature. Next, 0.3 mL of aluminum chloride (AlCl₃) solution (1:10, w/v) was added into the mixtures and kept for 6 min at room temperature. Finally, 2 mL of sodium hydroxide (NaOH) solution (1 M) was mixed and kept for 10 min at room temperature. The absorbance reading of yellow mixtures was measured at 510 nm by ultraviolet-visible (UV) spectrophotometer (Shimadzu, Kyoto, Japan). Quercetin was used as a standard for the calibration curve, and the samples were expressed as mg quercetin/g plant dry weight.

The content of phenolics, from the extract of C. nutans, was evaluated by using the Folin–Ciocalteau reagent-based assay, according to Barku [74 ] with slight modification. A 5 mL of Folin–Ciocalteau reagent was added to the 200 µL of samples, and the solutions were allowed to stand for 10 min at 25 °C. Later, 4 mL of sodium carbonate was added into the solutions, and the solutions were kept in total darkness for 20 min at room temperature. The absorbance reading of the blue color mixture was measured at 765 nm using an ultraviolet-visible (UV) spectrophotometer (Shimadzu, Kyoto, Japan). Gallic acid was used as a standard for the calibration curve, and the samples were expressed as mg GAE/g plant dry weight.