Biological Inspirations: Iron Complexes Mimicking the Catechol Dioxygenases

Within the broad group of Fe non-heme oxidases, our attention was focused on the catechol 1,2- and 2,3-dioxygenases, which catalyze the oxidative cleavage of aromatic rings. A large group of Fe complexes with N/O ligands, ranging from N3 to N2O2S, was developed to mimic the activity of these enzymes. The Fe complexes discussed in this work can mimic the intradiol/extradiol catechol dioxygenase reaction mechanism. Electronic effects of the substituents in the ligand affect the Lewis acidity of the Fe center, increasing the ability to activate dioxygen and enhancing the catalytic activity of the discussed biomimetic complexes. The ligand architecture, the geometric isomers of the complexes, and the substituent steric effects significantly affect the ability to bind the substrate in a monodentate and bidentate manner. The substrate binding mode determines the preferred mechanism and, consequently, the main conversion products. The preferred mechanism of action can also be affected by the solvents and their ability to form the stable complexes with the Fe center. The electrostatic interactions of micellar media, similar to SDS, also control the intradiol/extradiol mechanisms of the catechol conversion by discussed biomimetics.

Bioinspired Mononuclear Mn Complexes for O2 Activation and Biologically Relevant Reactions

A general interest in harnessing the oxidizing power of dioxygen (O2) continues to motivate research efforts on bioinspired and biomimetic complexes to better understand how metalloenzymes mediate these reactions. The...

Kinetic study of catalytic CO 2 hydration by metal-substituted biomimetic carbonic anhydrase model complexes

The rapid rise of the CO 2 level in the atmosphere has spurred the development of CO 2 capture methods such as the use of biomimetic complexes that mimic carbonic anhydrase. In this study, model complexes with tris(2-pyridylmethyl)amine (TPA) were synthesized using various transition metals (Zn 2+ , Cu 2+ and Ni 2+ ) to control the intrinsic proton-donating ability. The pK a of the water coordinated to the metal, which indicates its proton-donating ability, was determined by potentiometric pH titration and found to increase in the order [(TPA)Cu(OH 2 )] 2+ < [(TPA)Ni(OH 2 )] 2+ < [(TPA)Zn(OH 2 )] 2+ . The effect of pK a on the CO 2 hydration rate was investigated by stopped-flow spectrophotometry. Because the water ligand in [(TPA)Zn(OH 2 )] 2+ had the highest pK a , it would be more difficult to deprotonate it than those coordinated to Cu 2+ and Ni 2+ . It was, therefore, expected that the complex would have the slowest rate for the reaction of the deprotonated water with CO 2 to form bicarbonate. However, it was confirmed that [(TPA)Zn(OH 2 )] 2+ had the fastest CO 2 hydration rate because the substitution of bicarbonate with water (bicarbonate release) occurred easily.

Outer Sphere Urea Hydrolysis by Bis-Nickel Complexes: Questioning the Urea Activation by the Urease Enzyme

Urease enzyme has a dinuclear nickel active centre that hydrolyze urea into carbon dioxide and ammonia. In this work, two bis-nickel urease models were synthesized, [Ni₂L(OAc)] and [Ni₂L(Cl)(Et₃N)₂], based on the Trost bis-Pro0Phenol ligand (L). Interestingly, both complexes produced ammonia from urea, in which the [Ni₂L(OAc)] complex was ten times slower than urease, whereas the more labile complex [Ni₂L(Cl)(Et₃N)₂],was only four times slower. The intermediates were evaluated both experimentally and theoretically, indicating that the [Ni₂L(H₂O)₂]⁺ intermediate is the most important to activate urea via an outersphere mechanism. Isocyanate was produced in a self-elimination mechanism. The reaction performed with different substrates indicated that the biomimetic complexes were able to hydrolyze isocyanate. The outersphere activation of urea by these complexes reals an alternative activation mechanism to be considered for the urease enzyme, not yet reported in the literature. . <br>

Outer Sphere Urea Hydrolysis by Bis-Nickel Complexes: Questioning the Urea Activation by the Urease Enzyme

Urease enzyme has a dinuclear nickel active centre that hydrolyze urea into carbon dioxide and ammonia. In this work, two bis-nickel urease models were synthesized, [Ni₂L(OAc)] and [Ni₂L(Cl)(Et₃N)₂], based on the Trost bis-Pro0Phenol ligand (L). Interestingly, both complexes produced ammonia from urea, in which the [Ni₂L(OAc)] complex was ten times slower than urease, whereas the more labile complex [Ni₂L(Cl)(Et₃N)₂],was only four times slower. The intermediates were evaluated both experimentally and theoretically, indicating that the [Ni₂L(H₂O)₂]⁺ intermediate is the most important to activate urea via an outersphere mechanism. Isocyanate was produced in a self-elimination mechanism. The reaction performed with different substrates indicated that the biomimetic complexes were able to hydrolyze isocyanate. The outersphere activation of urea by these complexes reals an alternative activation mechanism to be considered for the urease enzyme, not yet reported in the literature. . <br>