Reactions of the aquapentacyanoferrate(II) ion with 2-nitroso-1-naphthol and 2-nitroso-1-naphthol-4-sulphonic acid

Spectrophotometric Studies of Reactions of the Aquapentacyanoferrate(II) Ion with Ketones. Kinetics and Mechanism of the Substitution Reaction of the Aquapentacyanoferrate(II) Ion with 1-Benzoylethylpyridinium Chloride

The carbonyl group of compounds of the phenacyl- and benzoylethyl-pyridinium type is recognized as a potential σ donor ligand which can produce complexes with the aquapentacyanoferrate(II) ion. Its reactive form is the ionized one i.e. the enolate ion. A detailed spectrophotometric investigation has been made for the reaction of the aquapentacyanoferrate(II) ion with 1-benzoylethylpyridinium chloride. The equilibrium constant of the produced complex was derived using two literatury available additional types of processing the molar ratio method’s experimental data which were not found to be applied to this type of complexes. The kinetics of this substitution reaction were studied in buffered solutions at pH = 8.0 and I = 0.05 M. The obtained results are consistent with a dissociative mechanism.

Kinetics and Mechanism of Uncatalysed Substitution of Cyanide in Hexacyanoferrate(Ii) by Isoniazid

The kinetics and mechanism of the uncatalysed ligand substitution reaction between potassium ferrocyanide, K4[Fe(CN)6] and isoniazid (INH) in aqueous medium has been investigated spectrophotometrically at 435 nm, i.e. the Λmax of the golden yellow complex, [Fe(CN)5(INH)]3-, as a function of [Fe(CN)64-] and [INH] under the conditions: pH = 3.5 ± 0.02, temperature = 30 ± 0.1°C and ionic strength, I = 0.05 mol/l (KNO3). The reaction is first order each in [Fe(CN)64-] and isoniazid (INH) at low [INH]. The initial rate of reaction is determined from the slopes of absorbance versus time plots. As [INH] increases, the rate of reaction increases, passes through a maximum and then falls, suggesting that the course of the reaction is different at low and high [INH]. A tentative mechanism has been proposed, which is further supported by the results of studies, such as variation in [Fe(CN)64-], effect of temperature and pH of the reaction medium. The composition of the complex formed in the present reaction has been established to be 1:1 by the mole ratio and slope ratio methods. A repetitive spectral scan is also provided in support of the exchange of coordinated cyanide ions by isoniazid in hexacyanoferrate(II).

Inhibition of acetylcholinesterase by three new pyridinium compounds and their effect on phosphonylation of the enzyme

Three new mono-pyridinium compounds were prepared: 1-phenacyl-2-methylpyridinium chloride (1), 1-benzoylethylpyridinium chloride (2) and 1-benzoylethylpyridinium-4-aldoxime chloride (3) and assayed in vitro for their inhibitory effect on human blood acetylcholinesterase (EC 3.1.1.7, AChE). All the three compounds inhibited AChE reversibly; their binding affinity for the enzyme was compared with their protective effect (PI) on AChE phosphonylation by soman and VX. Compound 1 was found to bind to both the catalytic and the allosteric (substrate inhibition) sites of the enzyme with estimated dissociation constants of 6.9 microM (Kcat) and 27 microM (Kall), respectively. Compound 2 bound to the catalytic site with Kcat = 59 microM and compound 3 only to the allosteric site with Kall = 328 microM. PI was evaluated from phosphonylation measured in the absence and in presence of the compounds applied in a concentration corresponding to their Kcat or Kall value, and was also calculated from theoretical equations deduced from the reversible inhibition of the enzyme. Compounds 1 and 3 protected the enzyme from phosphonylation by soman and VX, whereas no protection was observed in the presence of compound 2 under the same conditions. Irrespective of the binding sites to AChE, PI for compounds 1 and 3 evaluated from phosphonylation agreed with PI calculated from reversible inhibition. Compound 3 was found to be a weak reactivator of methylphosphonylated AChE with Kr = 1.1 x 10(2) L mol-1 min-1.