Y. Shaban

Reversible release of nitric oxide from an iron(II) nitrosyl complex containing a biomimetic S4N chelate. A facile release of nitric oxide

Abstract The release of NO by [Fe(NO)(Et2NpyS4)], where (Et2NpyS4)2− = 2,6-bis(2-mercaptophenylthiomethyl)-4-substituted pyridine(2-), has been studied in the absence and presence of a trapping agent. The results show that [Fe(NO)(Et2NpyS4)] releases NO spontaneously in solution with a slow rate, k-NO = 1.7 × 10−4 s−1 at 23 °C, in a reversible reaction. NO release becomes faster when the reaction intermediate [Fe(Et2 NpyS4)] was trapped by CO, thereby preventing the back reaction. The release of NO was studied as a function of CO concentration and temperature. The reported activation parameters, especially the positive activation entropy values for the release of NO, favor the operation of a dissociative interchange (Id) mechanism. Thus, [Fe(NO)(Et2NpyS4)] can serve as a NO deliverer.

Norfloxacin La(III)-based complex: synthesis, characterization, and DNA-binding studies

A La(III) complex, [LaIIICl2(NOR)2]Cl (2), containing norfloxacin (NOR) (1), a synthetic fluoroquinolone antibacterial agent, has been synthesized and characterized by elemental analysis, IR, UV–vis spectra and 1H NMR spectroscopy, and molar conductance measurements. The interaction between 2 and CT-DNA was investigated by steady-state absorption and fluorescence techniques in different pH media, and showed that 2 could bind to CT-DNA presumably via non-intercalative mode and the La(III) complex showed moderate ability to bind CT-DNA compared to other La(III) complexes. The binding site number n, and apparent binding constant KA, corresponding thermodynamic parameters ΔG#, ΔH#, ΔS# at different temperatures were calculated. The binding constant (KA) values are 0.23 ± 0.05, 0.56 ± 0.05, and 0.18 ± 0.08 × 105 L mol−1 for pH 4, 7, and 11, respectively. It was also found that the fluorescence quenching mechanism of CT-DNA by La(III) complex was a static quenching process. Graphical Abstract

Iron(II) complexes containing the 2,6-bis-iminopyridyl moiety. Synthesis, characterization, reactivity, and DNA binding

Two iron(II) complexes, [FeII(pytBuN3)2](FeCl4) (1) and [FeII(pytBuMe2N3)Cl2] (2), with sterically constrained pytBuN3 and pytBuMe2N3 chelate ligands (pytBuN3 = 2,6-bis-(aldiimino)pyridyl; pytBuMe2N3 = 2,6-bis-(ketimino)pyridyl), have been synthesized and characterized by elemental analysis, IR, UV–vis spectra, and preliminary X-ray single-crystal diffraction. The latter revealed that Fe(II) in 1 is six-coordinate by six nitrogen donors from two bisiminopyridines in a distorted octahedron. Complex 2 reacts with thiourea with a second-order rate constant k2 = (2.50 ± 0.05) × 10−3 M−1 s−1 at 296 K, and the reaction seemed to be slow. In a similar way, the interaction of 2 and DNA was studied by fluorescence and absorption spectroscopy. The results revealed that 2 caused fluorescence quenching of DNA through a dynamic quenching procedure. The binding constants KA, Kapp, and KSV as well as the number of binding sites between 2 and DNA were determined.

Oxidation of Ru-bound thiolate thioether and its NS4-ligand containing thiolate and thioether sulfur donors: synthesis, characterization, and X-ray structures

A ruthenium complex [Ru(H2O){Et2NpyS4(O3)2}] · (4) containing sulfinates, sulfenates S-donors, and water as co-ligand has been synthesized from oxidation of hydrazine complex [Ru(N2H4)(Et2NpyS4)] (3) and completely characterized with X-ray structural analysis [Et2Npy = 4-(diethylamino)-2,6-bis[(2-mercaptophenyl)thiomethyl]pyridine(2−)]. Complex 4 exhibits distorted octahedral coordination of the ruthenium center and the d [Ru–Ssulfinates] and d [Ru–Ssulfenates] are almost equivalent. The average d[S–Osulfinate] at 148.0 pm is ca 10 pm longer than the average d [S–Osulfenate] at 138.0 pm. The sulfinates IR(KBr) bands are located in the range 1132–1113 cm−1 as two band sets, ν(SO)asym and ν(SO)sym, whereas the sulfenates show a single absorbance at approximately 882 cm−1. The lower frequency of the ν(SO) stretches of the sulfenates as compared to that of their sulfinate rivals indicates a weaker S–O bond in the sulfenates and is consistent with X-ray crystal structure data (vide infra). Oxidation of the dithiol ligand Et2NpyS4–H2 (1) under the same condition afforded the disulfide, in this case forming a macrocyclic ligand S,S-Et2NpyS4 (2) as is evidenced by an X-ray crystal structure determination. Thus, the oxidation of 3 involves activation of either the oxygen or thiolate by the ruthenium center.