2 hydroxybenzaldehyde

Chemicals and reagents were purchased from commercial sources. 2-Hy­droxy­benzaldehyde, 2-meth­oxy­aniline and an­hydrous M^II halides, where M is Zn, Cd and Hg, were pur­chased from Sigma–Aldrich and Merck, and used as received. The Schiff base ligand 2-{[(2-meth­oxy­phen­yl)imino]­meth­yl}phenol (L) was prepared according to a previously reported method (Song et al., 2013 ▸ ). The IR spectra were recorded on a Nicolet FT–IR 100 spectrometer in the range 500–4000 cm⁻¹ using the KBr disk technique. Elemental analyses (C, H and N) were performed using an ECS 4010 CHN-O made in Costech, Italy. Melting points were measured by an Electrothermal 9100 melting-point apparatus and corrected. The measurements were carried out using 10 mg of a powdered sample sealed in aluminium pans with a mechanical crimp.

Analytical standards of 2,5-dihydroxybenzaldehyde (compound 2; 98% purity), m-cresol (3; 99% purity), 3-hydroxybenzyl alcohol (4; 99% purity), toluquinol (5; ≥98% purity), 3-hydroxybenzaldehyde (6; ≥99% purity), 3-hydroxybenzoic acid (7; 99% purity), 2,5-dihydroxybenzoic acid (8; 98% purity), 2,4-dihydroxybenzaldehyde (10; 98% purity), 3,4-dihydroxybenzaldehyde (11; 97% purity), 3,5-dihydroxybenzaldehyde (12; 98% purity), 2-hydroxybenzaldehyde (13; 98% purity), and 4-hydroxybenzaldehyde (14; 98% purity) were procured from Sigma-Aldrich, Seoul, Korea. Methanol, acetone, and water used for the following experiments were of high-performance liquid chromatography (HPLC) grade.

Low-molecular-weight chitosan (193 kDa, DD = 82%), 2-hydroxybenzaldehyde (98%), ethanol, acetic acid, phosphate buffer (PBS) (pH = 7.4), and diclofenac sodium salt (DCF) were procured from Sigma-Aldrich (St. Louis, MO, USA) and used as received.

All manipulations were performed under an inert atmosphere using Schlenk-line techniques (O₂ < 3 ppm) and a glove box (O₂ < 0.6 ppm) MBraun MB-20G (MBraun, Garching, Germany). Solvents were purified using an MBraun Solvent Purification System (MBraun, Garching, Germany). Deuterated solvents were degassed and stored in the glove box in the presence of molecular sieves (4 Å). Fluoroaniline compounds were purchased from Fluorochem (Fluorochem, Derbyshire, UK) and used as received. 2-hydroxybenzaldehyde and metallic precursors were purchased from Sigma-Aldrich (Merck, Darmstadt, Germany). NMR spectra were recorded with a Bruker 400 Ultrashield (Bruker, Karlsruhe, Germany) (¹H 400 MHz, ¹³C 101 MHz) at room temperature. All chemical shifts were determined using the residual signal of solvents and were reported versus SiMe₄. The assignment of the signal was carried out from 1D (¹H, ¹⁹F{¹H}, ¹³C{¹H}) and 2D (¹H-¹³C HSQC) NMR experiments. Elemental analyses were performed with a PerkinElmer 2400 CHNS/O analyzer Series II (PerkinElmer, Ohio, OH, USA) and were the average of at least two independent measurements.

All reagents used were of analytical reagent grade stated. Chitosan (CS) (with DDA 64% from IR chart) was extracted from shrimp shell were purchased from local market. Sodium hydroxide (NaOH, 97%) was purchased from Scharlau. Hydrochloric acid (HCl, 37%) and Glacial Acetic acid (CH₃COOH, 99.8%) were purchased from Merck. CuSO₄.5H₂O (99%) and ZnSO₄.7H₂O (99–100.5) were purchased from Sigma-Aldrich, Merck respectively. Cr₂(SO₄)₃.15H₂O (99%) and 3-dichloropropane (98%) were purchased from Riedel-De Haen AG. Na₂CO₃ (≥ 99.5%) and EDTA (99.4–100.6%) were purchased from BDH. absolute Ethanol and 2-hydroxybenzaldehyde were purchased from Sigma-Aldrich.

Photoacid was synthesized according to literature^{22 (link),23 (link)}. First, 2,3,3-trimethylindolenine (3.18 g, 20 mmol, 98%; Sigma-Aldrich) was mixed with 1,3-propanesultone (2.44 g, 20 mmol, >99%; Sigma-Aldrich) and then heated to 90 °C for 6 h under nitrogen protection. The product was collected as a purple solid by filtration and washed thoroughly with diethyl ether. The dried product (600 mg, 2.14 mmol) and 292 mg of 2-hydroxybenzaldehyde (2.4 mmol, >99.0%; Sigma-Aldrich) were then added to 12.0 mL of anhydrous ethanol, and the solution was refluxed overnight. The resulting orange solid was collected by filtration and rinsed thoroughly with ethanol (5 × 10 mL). The final product was dried in vacuum and stored in a freezer (−20 °C) under nitrogen protection. The pH of the photoacid solution was measured by a Mettler Toledo SevenExcellence pH meter.