pH Dependence of Absorption and Emission Spectra of Ru(phen)2(phenOH)2+(PF6)2 Complex

A ruthenium complex of the 4-hydroxy- 1,10-phenanthroline ligand was synthesized, and the variation of its absorption and emission intensity and litetime with pH characterized. Excited state lifetime, luminescence intensity, and emission properties were determined.  The complex exhibits a maximum at 460nm, and a small red shift at higher pH. The spectra show a well defined isobestic point. Luminescence intensity exhibited a sigmoidal relationship with pH, a behaviour that is similar to those of other ruthenium complexes carrying protonable functional groups. This characteristic is suggestive of the suitability of this complex for pH sensor design for medical practices as well as industrial processes. pH dependence is more evident in the emission than the absorption spectra, a behaviour characteristic of higher pH dependence on the excited than the ground state of the complex. Emission lifetimes of 165.4ns and 3.08ns for the protonated and deprotonated states respectively, were determined and the pK*a value calculated as 3.68

Kinetics and Mechanism of Electron Transfer Reaction of an Adipato Bridged Iron(III)-Salen Complex with Dithionite Ion in Perchloric Acid Medium

Redox kinetics of the reaction of an adipato bridged iron(III)-salen complex, [(Fe(salen))2adi] with dithionite ion, S2O42–, was investigated in perchloric acid at I = 0.05 mol dm–3 (NaClO4) and T = 29 ± 1 °C. Spectrophotometric titrations indicated consumption of one mole of S2O42– per mole of [(Fe(salen))2adi] reduced. Under pseudo-first order conditions of [S2O42–] above ten-fold excess of concentration of [(Fe(salen))2adi], observed rates increased with increase in [S2O42–] and second order rate constants were fairly constant (0.285 ± 0.01 dm3 mol–1 s–1) indicating first order dependence of the rate on [(Fe(salen))2adi]. A plot of logkobs versus log[S2O42–] was linear and gave a slope of 1.0 indicating first order dependence of the rate on [S2O42–]. The reaction rate increased with increase in [H+] within 3 × 10–3 mol dm–3 ≤ [H+] ≤ 14 × 10–3 mol dm–3. The reaction was unaffected by variation of ionic strength and dielectric constant of the medium. Addition of anion and cation did not catalyze the reaction. The reaction has been analyzed on the basis of an inner-sphere mechanism mediated by proton transfer

Structure and Computational Studies of New Sulfonamide Compound: {(4-nitrophenyl)sulfonyl}tryptophan

Synthesis of sulfonamide through an indirect method that avoids contamination of the product with no need for purification has been carried out using the indirect process. Here, we report the synthesis of a novel sulfonamide compound, ({4-nitrophenyl}sulfonyl)tryptophan (DNSPA) from 4-nitrobenzenesulphonylchloride and L-tryptophan precursors. The slow evaporation method was used to form single crystals of the named compound from methanolic solution. The compound was characterized by X-ray crystallographic analysis and spectroscopic methods (NMR, IR, mass spectrometry, and UV-vis). The sulfonamide N-H NMR signal at 8.07–8.09 ppm and S-N stretching vibration at 931 cm−1 indicate the formation of the target compound. The compound crystallized in the monoclinic crystal system and P21 space group with four molecules of the compound in the asymmetric unit. Molecular aggregation in the crystal structure revealed a 12-molecule aggregate synthon sustained by O-H⋯O hydrogen bonds and stabilised by N-H⋯O intermolecular contacts. Experimental studies were complemented by DFT calculations at the B3LYP/6-311++G(d,p) level of theory. The computed structural and spectroscopic data are in good agreement with those obtained experimentally. The energies of interactions between the units making up the molecule were calculated. Molecular docking studies showed that DNSPA has a binding energy of −6.37 kcal/mol for E. coli DNA gyrase (5MMN) and −6.35 kcal/mol for COVID-19 main protease (6LU7)