321 research outputs found
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 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
Elucidation of inorganic reaction mechanisms in ionic liquids: the important role of solvent donor and acceptor properties
In this article, we focus on the important role of solvent donor and acceptor properties of ionic liquids in the elucidation of inorganic reaction mechanisms. For this purpose, mechanistic and structural studies on typical inorganic reactions, performed in ionic liquids, have been conducted. The presented systems range from simple complex-formation and ligand-substitution reactions to the activation of small molecules by catalytically active complexes. The data obtained for the reactions in ionic liquids are compared with those for the same reactions carried out in conventional solvents, and are discussed with respect to the donor and acceptor properties of the applied ionic liquids. The intention of this perspective is to gain more insight into the role of ILs as solvents and their interaction with metal ions and complexes in solution
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
Equilibrium Studies on Pd(II)–Amine Complexes with Bio-Relevant Ligands in Reference to Their Antitumor Activity
This review article presents an overview of the equilibrium studies on Pd-amine complexes with bio-relevant ligands in reference to their antitumor activity. Pd(II) complexes with amines of different functional groups, were synthesized and characterized in many studies. The complex formation equilibria of Pd(amine)2+ complexes with amino acids, peptides, dicarboxylic acids and DNA constituents, were extensively investigated. Such systems may be considered as one of the models for the possible reactions occurring with antitumor drugs in biological systems. The stability of the formed complexes depends on the structural parameters of the amines and the bio-relevant ligands. The evaluated speciation curves can help to provide a pictorial presentation of the reactions in solutions of different pH values. The stability data of complexes with sulfur donor ligands compared with those of DNA constituents, can reveal information regarding the deactivation caused by sulfur donors. The formation equilibria of binuclear complexes of Pd(II) with DNA constituents was investigated to support the biological significance of this class of complexes. Most of the Pd(amine)2+ complexes investigated were studied in a low dielectric constant medium, resembling that of a biological medium. Investigations of the thermodynamic parameters reveal that the formation of the Pd(amine)2+ complex species is exothermic
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