New cis-(1,2-azole)-aquo bis(2,2′-bipyridyl)ruthenium(II) (1,2-azole (az*H) = pzH (pyrazole), dmpzH (3,5-dimethylpyrazole), and indzH (indazole)) complexes are synthesized via chlorido abstraction from cis-[Ru(bipy)2Cl(az*H)]OTf. The latter are obtained from cis-[Ru(bipy)2Cl2] after the subsequent coordination of the 1,2-azole. All the compounds are characterized by 1H, 13C, 15N NMR spectroscopy as well as IR spectroscopy. Two chlorido complexes (pzH and indzH) and two aquo complexes (indzH and dmpzH) are also characterized by X-ray diffraction. Photophysical and electrochemical studies were carried out on all the complexes. The photophysical data support the phosphorescence of the complexes. The electrochemical behavior of all the complexes in an Ar atmosphere indicate that the oxidation processes assigned to Ru(II) → Ru(III) occurs at higher potentials in the aquo complexes. The reduction processes under Ar lead to several waves, indicating that the complexes undergo successive electron-transfer reductions that are centered in the bipy ligands. The first electron reduction is reversible. The electrochemical behavior in CO2 media is consistent with CO2 electrocatalyzed reduction, where the values of the catalytic activity [i cat(CO2)/i p(Ar)] ranged from 2.9 to 10.8. Controlled potential electrolysis of the chlorido and aquo complexes affords CO and formic acid, with the latter as the major product after 2 h. Photocatalytic experiments in MeCN with [Ru(bipy)3]Cl2 as the photosensitizer and TEOA as the electron donor, which were irradiated with >300 nm light for 24 h, led to CO and HCOOH as the main reduction products, achieving a combined turnover number (TONCO+HCOO– ) as high as 107 for 2c after 24 h of irradiation.
The interior of the living cell is highly concentrated and structured with molecules having different shapes and sizes. However, almost all experimental biochemical data have been obtained working in dilute solutions that do not reflect in vivo conditions. In this paper, we study in vitro the effect of macromolecular crowding on the reaction rates of the oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) by hydrogen peroxide (H 2 O 2 ) catalyzed by Horseradish Peroxidase (HRP), by adding Dextrans of various molecular weights to the reaction solutions as crowding agents. The results indicate that the volume occupied by the crowding agent, regardless its size, plays an important role in the rate of this reaction. Both Michaelis-Menten parameters, ݒ ௫ and ܭ , decrease when the Dextran concentration in the sample increases, which might be due to a crowding-induced effect in the catalytic constant, ݇ ௧ , of this enzymatic reaction. Thus, our results suggest that there is an activation control of the enzymatic reaction in this particular system. In our opinion, this work could facilitate the understanding of biomolecules behavior in vivo and be useful for biotechnology in vitro applications, since HRP is widely used in the development of biosensors.
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