Pressure as a kinetic parameter in mechanistic studies of chemical reactions induced by flash photolysis and pulse radiolysis

Abstract A detailed outline is given of how pressure can be used as a mechanistic indicator in kinetic studies of chemical reactions in solution that are induced by flash photolysis and pulse radiolysis. These techniques have mainly been applied to tlie study of organometallic and bioinorganic reactions including processes such as ligand substitution, binding of small molecules, formation and breakage of metal-carbon bonds, 0-elimination and electron transfer. Typical examples are presented and an account of our most recent work in this area is given

Temperature- and pressure-dependent stopped-flow kinetic studies of jack bean urease : implications for the catalytic mechanism

Urease, a Ni-containing metalloenzyme, fea- tures an activity that has profound medical and agricultural implications. The mechanism of this activity, however, has not been as yet thoroughly established. Accordingly, to improve its understanding, in this study we analyzed the steady-state kinetic parameters of the enzyme (jack bean), K M and k cat , measured at different temperatures and pres- sures. Such an analysis is useful as it provides information on the molecular nature of the intermediate and transition states of the catalytic reaction. We measured the parame- ters in a noninteracting buffer using a stopped-flow tech- nique in the temperature range 15–35 ° C and in the pressure range 5–132 MPa, the pressure-dependent mea- surements being the first of their kind performed for urease. While temperature enhanced the activity of urease, pres- sure inhibited the enzyme; the inhibition was biphasic. Analyzing K M provided the characteristics of the formation of the ES complex, and analyzing k cat , the characteristics of the activation of ES. From the temperature-dependent measurements, the energetic parameters were derived, i.e. thermodynamic D H o and D S o for ES formation, and kinetic D H = and D S = for ES activation, while from the pressure- dependent measurements, the binding D V b and activation D V 6 ¼ cat volumes were determined. The thermodynamic and activation parameters obtained are discussed in terms of the current proposals for the mechanism of the urease reaction, and they are found to support the mechanism proposed by Benini et al. ( Structure 7:205–216; 1999), in which the Ni–Ni bridging hydroxide—not the terminal hydroxide—is the nucleophile in the catalytic reaction

Can a Nonorganometallic Ruthenium(II) Polypyridylamine Complex Catalyze Hydride Transfer? Mechanistic Insight from Solution Kinetics on the Reduction of Coenzyme NAD+ by Formate

Application of organometallic ruthenium(II) arene complexes has been successful for the modulation of cellular redox processes via their interaction with species such as formate to control the NAD+/NADH balance in cells. Here we present the first evidence that similar effects can be reached with the application of a nonorganometallic ruthenium(II) polypyridyl complex. Kinetic studies performed demonstrate the ability of [RuII(terpy)(en)(H2O/EtOH)]2+ in water/ethanol (1:9, v/v) solution, where terpy = 2,2′:6′,2″-terpyridine and en = ethylenediamine, to catalyze the reduction of the NAD+ coenzyme to NADH in the presence of formate as hydride transfer source. In this case, terpy instead of arene is responsible for the labilization of coordinated solvent. The suggested catalytic cycle begins with the fast anation of the [RuII(terpy)(en)(H2O/EtOH)]2+ complex by formate. This is followed by the rate-determining formate-catalyzed decarboxylation of the generated ruthenium(II) formato complex to form [RuII(terpy)(en)H]+. Rapid hydride transfer to NAD+ from [RuII(terpy)(en)H]+ to form NADH and to regenerate the starting ruthenium(II) solvato complex, closes the overall catalytic cycle

Influence of Krakow winter and summer dusts on the redox cycling of vitamin B12aB_{12a} in the presence of ascorbic acid

Air pollution remains a serious problem in Krakow, Poland. According to the European Environmental Agency, annual mean levels of both PM2.5 and PM10 recorded in Krakow are much higher than EU limit values. Thus, the influence of particulate matter (PM) on the function of living organisms, as well as different physiological processes, is an urgent subject to be studied. The reported research forms part of the multi-disciplinary project ‘Air Pollution versus Autoimmunity: Role of multiphase aqueous Inorganic Chemistry,’ which aims to demonstrate the PM effect on the immune system. The present studies focused on the role of dust collected in Krakow on the redox cycling of vitamin B12a in the presence of ascorbic acid. Dust samples collected during the winter 2019/2020 and summer 2020 months in the city center of Krakow were characterized using various analytical techniques. The influence of Krakow dusts on the kinetics of the reaction between nitrocobalamin and ascorbic acid was confirmed and discussed in terms of the composition of the samples. Possible reasons for the reported findings are provided

Electrochemistry of Ru(edta) complexes relevant to small molecule transformations: Catalytic implications and challenges

Electrochemistry of Ru(edta) complexes (edta4 = ethylenediaminetetraacetate) progressed over a period of several decades, with significant increase in understanding of the electro-catalytic processes involving the substrate coordinated to the metal center. While electrochemistry studies of many Ru(edta) complexes were published in several papers, no attempt has been made to provide a comprehensive and systematic overview of its electrochemical properties, evaluating its application to catalytic electrochemical transformation of small molecules. In this article, results of the electrochemical studies of both mononuclear and binuclear complexes of Ru(edta) are reviewed with regard to electron-transfer reaction mechanism and activity. Their potential to act as redox mediators or catalysts in electrochemical transformations of small molecules and enzymatic reactions, are highlighted. This review aims to contribute to the mechanistic understanding of Ru(edta) complexes in catalysis of such electrochemical transformations

Nitrosyl- versus nitroxyl-cobalamin?

The Commentary is in answer to the comment of a reader that objected against the use of the term ‘nitroxylcobalamin’ in two recent reports in JBC from our group. We use this opportunity to explain to the reader where this terminology originated from

Physicochemical analysis of water extracts of particulate matter from polluted air in the area of Kraków, Poland

Solubility of transition metal compounds plays a significant role in adverse health effects because that is one of the most important factors of particulate matter bioavailability in the body. In this study, we focus on the chemical analysis of particulate matter (PM) collected at different locations in the area of Kraków, one of the most polluted cities in Poland, and compare them with Standard Reference Material (SRM) 1648a from NIST. The content of four elements (carbon, hydrogen, nitrogen, and sulfur) was determined by elemental analysis, and the ratio between organic and inorganic carbon in PM extracts was confirmed by Total Organic Carbon analysis. Among the most concentrated elements found there are calcium, magnesium, sulfur, silicon, and zinc, whereas copper, iron, and manganese were present in lower concentrations. SEM-EDS analysis showed a similar morphology of the SRM and PM collected in the urban area of Kraków, while PM collected in the industrial area has smaller particles with a smooth surface. The reported analyses are significant for the APARIC project (“Air Pollution versus Autoimmunity: Role of multiphase aqueous Inorganic Chemistry”), which aims to identify the main inorganic components of PM and to understand how they affect the development of immunological diseases

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