scholarly journals Stoichiometric active site modification observed by alkali ion titrations of Sn-Beta

2019 ◽  
Vol 9 (16) ◽  
pp. 4339-4346 ◽  
Author(s):  
Samuel G. Elliot ◽  
Irene Tosi ◽  
Sebastian Meier ◽  
Juan S. Martinez-Espin ◽  
Søren Tolborg ◽  
...  
Keyword(s):  
Active Site ◽  
Active Sites ◽  
Catalytic Properties ◽  
Alkali Ions ◽  
Functional Assays ◽  
Insight Into ◽  
Alkali Ion

Titrations and functional assays are combined to gain insight into the stoichiometric correlations for alkali ions and the tin active sites in Sn-Beta, and show that three different states with distinct catalytic properties exist.

Investigation of the Catalytic Properties of the Dysthrombin, Thrombin Quick

1979 ◽  
Author(s):  
R.A. Henriksen ◽  
W.G. Owen ◽  
M.E. Nesheim ◽  
K.G. Mann
Keyword(s):  
Active Site ◽  
Mayo Clinic ◽  
Active Sites ◽  
Fluorescence Enhancement ◽  
Catalytic Mechanism ◽  
Antithrombin Iii ◽  
Catalytic Properties ◽  
Inhibitor Binding ◽  
Equivalent Number ◽  
Aggregation Of Platelets

Thrombin Quick (TQ) may be isolated following treatment of Prothrombin Quick [Owen, et al, Mayo Clinic Proceedings, 53: 29-33, (1978)] with Taipan venom, phospholipid and Ca2+. The clotting activity of TQ with fibrinogen is 1/200 that of normal thrombin (T) The activation of Factors V and VIII, and the aggregation of platelets by TQ occurs with an effectiveness of about 1/50 that of thrombin. When incubated with antithrombin III, both T and TQ form inhibitor complexes as determined by dodecylsulfate gel electropheresis. Titration of T and TQ with the fluorescent inhibitor dansylarginine-4-ethylpiperidine amide indicates an equivalent number of active sites based on protein absorption at 280 nm. However, the two enzymes may be distinguished by the decreased fluorescence enhancement observed with TQ relative to T, indicating an increased polarity in the inhibitor binding site of TQ. With the substrate benzoylarginine ethylester, TQ has a Km = 4.5 x 10-5M and kcat - 6.93 compared to Km = 4.0 × 10-5M and kcat = 17.7 for T. This indicates that the defect in TQ esterase activity is in the catalytic mechanism itself and not in substrate binding. The rate of inhibition of TQ by diisopropylphosphofluoridate is decreased. Decreased acylation and deacylation rates for TQ relative to T are observed for tydrolysis of the active site titrant 4-methyumbel1 i feryl-p-guanidlnobenzoate.

scholarly journals Electrochemical insights into the mechanism of NiFe membrane-bound hydrogenases

2016 ◽  
Vol 44 (1) ◽  
pp. 315-328 ◽  
Author(s):  
Lindsey A. Flanagan ◽  
Alison Parkin
Keyword(s):  
Active Site ◽  
Precious Metal ◽  
Active Sites ◽  
Review Paper ◽  
Spectroscopic Studies ◽  
Electrochemical Studies ◽  
Control Centre ◽  
Catalytic Active Sites ◽  
Membrane Bound ◽  
Insight Into

Hydrogenases are enzymes of great biotechnological relevance because they catalyse the interconversion of H2, water (protons) and electricity using non-precious metal catalytic active sites. Electrochemical studies into the reactivity of NiFe membrane-bound hydrogenases (MBH) have provided a particularly detailed insight into the reactivity and mechanism of this group of enzymes. Significantly, the control centre for enabling O2 tolerance has been revealed as the electron-transfer relay of FeS clusters, rather than the NiFe bimetallic active site. The present review paper will discuss how electrochemistry results have complemented those obtained from structural and spectroscopic studies, to present a complete picture of our current understanding of NiFe MBH.

Investigation of the Catalytic Properties of the Dysthrombin, Thrombin Quick

1979 ◽  
Author(s):  
R Henriksen ◽  
W Owen ◽  
M Nesheim ◽  
K Mann
Keyword(s):  
Active Site ◽  
Active Sites ◽  
Fluorescence Enhancement ◽  
Catalytic Mechanism ◽  
Antithrombin Iii ◽  
Catalytic Properties ◽  
Inhibitor Binding ◽  
Equivalent Number ◽  
Hydrolysis Of ◽  
Aggregation Of Platelets

Thrombin Quick (TQ) may be isolated following treatment of Prothrombin Quick [Owen, et al, Mayo Clinic Proceedings, 53: 29-33, (1978)] with Taipan venom, phospholipid and ca2+. The clotting activity of TQ with fibrinogen is 1/200 that of nornar thrombin (T). The activation of Factors V and VIII, and the aggregation of platelets by TQ occurs with an effectiveness of about 1/50 that of thrombin. when incubated with antithrombin III, both T ad TQ fom inhibitor complexes as determined by dodecylsulfate gel electropheresis. Titration of T and TQ with the fluorescent inhibitor dansylarginine-4-ethylpiperidine amide indicates an equivalent number of active sites based on protein absorption at 280 nm. However, the two enzymes may be distinquished by the decreased fluorescence enhancement observed with TQ relative to T, indicating an increased polarity in the inhibitor binding site of TQ. With the substrate benzoylarginine ethylester, TQ has a Km = 4.5 × 10-5M and kcat= 6.93 compared to Km = 4.0 × 10-5M and kcat= 17.7 for T. This indicates that the defect in TQ esterase activity is in the catalytic mechanism itself and not in substrate binding. The rate of inhibition of TQ by diisopropylphosphofluoridate is decreased. Decreased acylation and deacylation rates for TQ relative to T are observed for hydrolysis of the active site titrant 4-methykl-umbelliferyl-p-guanidinobenzoate

scholarly journals Structural and functional insight into pan-endopeptidase inhibition by α2-macroglobulins

2017 ◽  
Vol 398 (9) ◽  
pp. 975-994 ◽  
Author(s):  
Theodoros Goulas ◽  
Irene Garcia-Ferrer ◽  
Aniebrys Marrero ◽  
Laura Marino-Puertas ◽  
Stephane Duquerroy ◽  
...  
Keyword(s):  
Active Site ◽  
Active Sites ◽  
Large Cage ◽  
Covalent Linkage ◽  
Conformational Rearrangement ◽  
Bait Region ◽  
Active Site Cleft ◽  
Structural Details ◽  
Physical Entrapment ◽  
Insight Into

Abstract Peptidases must be exquisitely regulated to prevent erroneous cleavage and one control is provided by protein inhibitors. These are usually specific for particular peptidases or families and sterically block the active-site cleft of target enzymes using lock-and-key mechanisms. In contrast, members of the +1400-residue multi-domain α2-macroglobulin inhibitor family (α2Ms) are directed against a broad spectrum of endopeptidases of disparate specificities and catalytic types, and they inhibit their targets without disturbing their active sites. This is achieved by irreversible trap mechanisms resulting from large conformational rearrangement upon cleavage in a promiscuous bait region through the prey endopeptidase. After decades of research, high-resolution structural details of these mechanisms have begun to emerge for tetrameric and monomeric α2Ms, which use ‘Venus-flytrap’ and ‘snap-trap’ mechanisms, respectively. In the former, represented by archetypal human α2M, inhibition is exerted through physical entrapment in a large cage, in which preys are still active against small substrates and inhibitors that can enter the cage through several apertures. In the latter, represented by a bacterial α2M from Escherichia coli, covalent linkage and steric hindrance of the prey inhibit activity, but only against very large substrates.

scholarly journals A pyridinic Fe-N4 macrocycle models the active sites in Fe/N-doped carbon electrocatalysts

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Travis Marshall-Roth ◽  
Nicole J. Libretto ◽  
Alexandra T. Wrobel ◽  
Kevin J. Anderton ◽  
Michael L. Pegis ◽  
...  
Keyword(s):  
Active Site ◽  
Active Sites ◽  
Catalytic Properties ◽  
Molecular Model ◽  
Reduction Reaction ◽  
Electrochemical Studies ◽  
Onset Potential ◽  
Nitrogen Doped ◽  
Nitrogen Doped Carbon ◽  
Excellent Selectivity

Abstract Iron- and nitrogen-doped carbon (Fe-N-C) materials are leading candidates to replace platinum catalysts for the oxygen reduction reaction (ORR) in fuel cells; however, their active site structures remain poorly understood. A leading postulate is that the iron-containing active sites exist primarily in a pyridinic Fe-N4 ligation environment, yet, molecular model catalysts generally feature pyrrolic coordination. Herein, we report a molecular pyridinic hexaazacyclophane macrocycle, (phen2N2)Fe, and compare its spectroscopic, electrochemical, and catalytic properties for ORR to a typical Fe-N-C material and prototypical pyrrolic iron macrocycles. N 1s XPS and XAS signatures for (phen2N2)Fe are remarkably similar to those of Fe-N-C. Electrochemical studies reveal that (phen2N2)Fe has a relatively high Fe(III/II) potential with a correlated ORR onset potential within 150 mV of Fe-N-C. Unlike the pyrrolic macrocycles, (phen2N2)Fe displays excellent selectivity for four-electron ORR, comparable to Fe-N-C materials. The aggregate spectroscopic and electrochemical data demonstrate that (phen2N2)Fe is a more effective model of Fe-N-C active sites relative to the pyrrolic iron macrocycles, thereby establishing a new molecular platform that can aid understanding of this important class of catalytic materials.

scholarly journals Insight into the active site nature of zeolite H-BEA for liquid phase etherification of isobutylene with ethanol

RSC Advances ◽  
2019 ◽  
Vol 9 (62) ◽  
pp. 35957-35968 ◽  
Author(s):  
Nina V. Vlasenko ◽  
Yuri N. Kochkin ◽  
German M. Telbiz ◽  
Oleksiy V. Shvets ◽  
Peter E. Strizhak
Keyword(s):  
Liquid Phase ◽  
Active Site ◽  
Active Sites ◽  
Acid Sites ◽  
Bronsted Acid ◽  
Brønsted Acid Sites ◽  
Silanol Groups ◽  
Etbe Synthesis ◽  
Brönsted Acid ◽  
Insight Into

The active sites of H-BEA zeolites for ETBE synthesis are the weak Brønsted acid sites representing internal silanol groups.

Active Sites of Iron Catalysts for Oxidation Reactions - H2O Oxidation and H2O2 Decomposition

1996 ◽  
Vol 454 ◽  
Author(s):  
V. L. Kuznetsov ◽  
G. L. Elizarova ◽  
A. N. Usoltseva ◽  
L. G. Matvienko ◽  
O. I. Shchegolikhina
Keyword(s):  
Active Site ◽  
Active Sites ◽  
Heterogeneous Catalysts ◽  
Catalytic Properties ◽  
Iron Catalysts ◽  
Structural Factors ◽  
Oxidation Reactions ◽  
H2o2 Decomposition ◽  
The Comparative Study ◽  
Selective Oxidation Catalysts

ABSTRACTSystems containing metal ions stabilized in Si-O matrix are perspective for the development of new selective oxidation catalysts. The comparative study of the following catalysts were performed to elucidate the influence of structural factors on the catalytic properties of iron systems in the reactions H2O oxidation, H2O2 decomposition, N2O decomposition and 16O2 ⇔ O18O2 exchange. The following catalysts were used: A) carbon-supported polyhedral silsesquioxanes (PhSiO1.5)12(MO)nL ((MO)n = (FeO)6, Fe2Ni4O6, (NiO)6; L=ROH, H2O); B) Fe-containing zeolites ZSM-5 (0.1−3.5 wt.% Fe); C) hydroxocomplexes Fe4(OH)10SO4 and NaFe3(OH)6(SO4)2). Fe silsesquoxanes in contrast to Fe-ZSM5 do not activate N2O decomposition and isotopie oxygen exchange. However, they are active in H2O oxidation and H2O2 decomposition. It was found that both reactions proceed via nonradical mechanism in the presence of Fe heterogeneous catalysts. For H2O oxidation active site contains at least two Fe atoms situated at appropriate distance from each other. H2O2 decomposition can proceed with participation either one and two metal active sites.

A Pyridinic Fe-N4 Macrocycle Effectively Models the Active Sites in Fe/N-Doped Carbon Electrocatalysts

2020 ◽  
Author(s):  
Travis Marshall-Roth ◽  
Nicole J. Libretto ◽  
Alexandra T. Wrobel ◽  
Kevin Anderton ◽  
Nathan D. Ricke ◽  
...  
Keyword(s):  
Oxygen Reduction ◽  
Active Sites ◽  
Catalytic Properties ◽  
Reduction Reaction ◽  
Iron Phthalocyanine ◽  
Electrochemical Studies ◽  
Onset Potential ◽  
Nitrogen Doped Carbon ◽  
Iron Active Sites

Iron- and nitrogen-doped carbon (Fe-N-C) materials are leading candidates to replace platinum in fuel cells, but their active site structures are poorly understood. A leading postulate is that iron active sites in this class of materials exist in an Fe-N<sub>4</sub> pyridinic ligation environment. Yet, molecular Fe-based catalysts for the oxygen reduction reaction (ORR) generally feature pyrrolic coordination and pyridinic Fe-N<sub>4</sub> catalysts are, to the best of our knowledge, non-existent. We report the synthesis and characterization of a molecular pyridinic hexaazacyclophane macrocycle, (phen<sub>2</sub>N<sub>2</sub>)Fe, and compare its spectroscopic, electrochemical, and catalytic properties for oxygen reduction to a prototypical Fe-N-C material, as well as iron phthalocyanine, (Pc)Fe, and iron octaethylporphyrin, (OEP)Fe, prototypical pyrrolic iron macrocycles. N 1s XPS signatures for coordinated N atoms in (phen<sub>2</sub>N<sub>2</sub>)Fe are positively shifted relative to (Pc)Fe and (OEP)Fe, and overlay with those of Fe-N-C. Likewise, spectroscopic XAS signatures of (phen<sub>2</sub>N<sub>2</sub>)Fe are distinct from those of both (Pc)Fe and (OEP)Fe, and are remarkably similar to those of Fe-N-C with compressed Fe–N bond lengths of 1.97 Å in (phen<sub>2</sub>N<sub>2</sub>)Fe that are close to the average 1.94 Å length in Fe-N-C. Electrochemical studies establish that both (Pc)Fe and (phen<sub>2</sub>N<sub>2</sub>)Fe have relatively high Fe(III/II) potentials at ~0.6 V, ~300 mV positive of (OEP)Fe. The ORR onset potential is found to directly correlate with the Fe(III/II) potential leading to a ~300 mV positive shift in the onset of ORR for (Pc)Fe and (phen<sub>2</sub>N<sub>2</sub>)Fe relative to (OEP)Fe. Consequently, the ORR onset for (phen<sub>2</sub>N<sub>2</sub>)Fe and (Pc)Fe is within 150 mV of Fe-N-C. Unlike (OEP)Fe and (Pc)Fe, (phen<sub>2</sub>N<sub>2</sub>)Fe displays excellent selectivity for 4-electron ORR with <4% maximum H<sub>2</sub>O<sub>2</sub> production, comparable to Fe-N-C materials. The aggregate spectroscopic and electrochemical data establish (phen<sub>2</sub>N<sub>2</sub>)Fe as a pyridinic iron macrocycle that effectively models Fe-N-C active sites, thereby providing a rich molecular platform for understanding this important class of catalytic materials.<p><b></b></p>

Catalytic Resonance Theory: Parallel Reaction Pathway Control

2019 ◽  
Author(s):  
M. Alexander Ardagh ◽  
Manish Shetty ◽  
Anatoliy Kuznetsov ◽  
Qi Zhang ◽  
Phillip Christopher ◽  
...  
Keyword(s):  
Chemical Reactions ◽  
Active Site ◽  
Active Sites ◽  
Reaction Pathway ◽  
Control Strategies ◽  
Oscillation Amplitude ◽  
Catalytic Performance ◽  
Parallel Reaction ◽  
Resonance Theory ◽  
Static Conditions

Catalytic enhancement of chemical reactions via heterogeneous materials occurs through stabilization of transition states at designed active sites, but dramatically greater rate acceleration on that same active site is achieved when the surface intermediates oscillate in binding energy. The applied oscillation amplitude and frequency can accelerate reactions orders of magnitude above the catalytic rates of static systems, provided the active site dynamics are tuned to the natural frequencies of the surface chemistry. In this work, differences in the characteristics of parallel reactions are exploited via selective application of active site dynamics (0 < ΔU < 1.0 eV amplitude, 10<sup>-6</sup> < f < 10<sup>4</sup> Hz frequency) to control the extent of competing reactions occurring on the shared catalytic surface. Simulation of multiple parallel reaction systems with broad range of variation in chemical parameters revealed that parallel chemistries are highly tunable in selectivity between either pure product, even when specific products are not selectively produced under static conditions. Two mechanisms leading to dynamic selectivity control were identified: (i) surface thermodynamic control of one product species under strong binding conditions, or (ii) catalytic resonance of the kinetics of one reaction over the other. These dynamic parallel pathway control strategies applied to a host of chemical conditions indicate significant potential for improving the catalytic performance of many important industrial chemical reactions beyond their existing static performance.

Physicochemical and Catalytic Properties of Spinels Formed by Solid-Solid Interaction Between Fe2O3and V2O5

1996 ◽  
Vol 61 (8) ◽  
pp. 1131-1140 ◽  
Author(s):  
Abd El-Aziz Ahmed Said
Keyword(s):  
Vanadium Oxide ◽  
Active Sites ◽  
Catalyst Surface ◽  
Catalytic Properties ◽  
Flow System ◽  
Oxide Catalysts ◽  
X Ray Diffraction ◽  
Selective Catalyst ◽  
X Ray ◽  
Solid Catalysts

Vanadium oxide catalysts doped or mixed with 1-50 mole % Fe3+ ions were prepared. The structure of the original samples and those calcined from 200 up to 500 °C were characterized by TG, DTA, IR and X-ray diffraction. The SBET values and texture of the solid catalysts were investigated. The catalytic dehydration-dehydrogenation of isopropanol was carried out at 200 °C using a flow system. The results obtained showed an observable decrease in the activity of V2O5 on the addition of Fe3+ ions. Moreover, Fe2V4O13 is the more active and selective catalyst than FeVO4 spinels. The results were correlated with the active sites created on the catalyst surface.

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