Eco-friendly chitosan Schiff base as an efficient sensor for trace anion detection

Herein, a chitosan Schiff base sample (CSAN) was strategically designed and prepared via a two-step process. In the first step, an azo derivative of 1- naphthylamine namely, [2-hydroxy-5-(naphthalene-1-yldiazenyl) benzaldehyde] (HNDB) was synthesized as an aldehyde moiety. Then the condensation reaction of HNDB with chitosan afforded CSAN as the target product. Structural analyses of synthesized material were accomplished through FT-IR, ¹H NMR, UV-Vis, XRD, TGA, and SEM spectral methods. Meanwhile, the heterogeneous CSAN was able to detect the presence of hydrogen carbonate (HCO₃^-), acetate (AcO^-), and cyanide (CN^-) anions in semi-aqueous media (H₂O/DMSO; 10:90%, v/v). Moreover, the selectivity of CSAN towards CN^- anion was increased through variation in solvent mixture ratios. Thereupon, CSAN was explored as a promising sensor towards CN^- anion in an aqueous media through considerable color variation from colorless to pale yellow as well as quantitative chemical analysis. Overall, reliable CSAN chemosensor with high sensitivity for mentioned anions has a pivotal role in practical applications owing to it's reversibility ability.

Luminescent Rhenium(I)tricarbonyl Complexes Containing Different Pyrazoles and Their Successive Deprotonation Products: CO2 Reduction Electrocatalysts

Cationic fac-[Re(CO)₃(pz*H)(pypzH)]OTf (pz*H = pyrazole, pzH; 3,5-dimethylpyrazole, dmpzH; indazole, indzH; 3-(2-pyridyl)pyrazole, pypzH) were obtained from fac-[ReBr(CO)₃(pypzH)] by halide abstraction with AgOTf and subsequent addition of the corresponding pyrazole. Successive deprotonation with Na₂CO₃ and NaOH gave neutral fac-[Re(CO)₃(pz*H)(pypz)] and anionic Na{fac-[Re(CO)₃(pz*)(pypz)]} complexes, respectively. Cationic fac-[Re(CO)₃(pz*H)(pypzH)]OTf, neutral complexes fac-[Re(CO)₃(pz*H)(pypz)], and fac-[Re(CO)₃(pypz)₂Na] were subjected to photophysical and electrochemical studies. They exhibit phosphorescent decays from a prevalently ³MLCT excited state with quantum yields (Φ) in the range between 0.03 and 0.58 and long lifetimes (τ from 220 to 869 ns). The electrochemical behavior in Ar atmosphere of cationic and neutral complexes indicates that the oxidation processes assigned to Re^I → Re^II occurs at lower potentials for the neutral complex compared to cationic complex. The reduction processes occur at the ligands and do not depend on the charge of the complexes. The electrochemical behavior in CO₂ saturated media is consistent with CO₂ electrocatalyzed reduction, where the values of the catalytic activity [i_cat(CO₂)/i_cat(Ar)] ranged from 2.7 to 11.5 (compared to 8.1 for fac-[Re(CO)₃Cl(bipy)] studied as a reference). Controlled potential electrolysis for the pyrazole cationic (3a) and neutral (4a) complexes after 1 h affords CO in faraday yields of 61 and 89%, respectively. These values are higher for indazole complexes and may be related to the acidity of the coordinated pyrazole.