Specific Catalytic Effect Research Articles

Petal-by-petal tree-blossoming shaped bimetallic MOF-based material over SBA-15: Diverse designability, synergistic catalysis, and thermodynamics/kinetic analysis

Transition metal-based bimetallic MOF (CoMo-ZIF) with two different metal ions (Co/Mo) possess specific synergistic catalytic effect in olefins oxidation, but poor diffusion efficiency and less active areas limit its application. Herein, a novel CoMo-ZIF-based nanocomposite is fabricated via an in-situ solvothermal approach to break down active area or diffusion efficiency barrier of CoMo-ZIF via employing SBA-15 as the matrix and nanosacle polyoxometalate (POM) as external active species. Characterizations reveal that pristine rose-type CoMo-ZIF (∼350 nm diameter) alters to rambutan-like hollow sphere and eventually self-assembles into hierarchical petal-by-petal nanoflakes (ca. 20∼50 nm in thickness) after SBA-15 and POM introduction, respectively. POM@CoMo-ZIF@SBA-15 with super large pore size (10.44 nm) and increased active (Co2+ + Co3+)/satellite (1.92) exhibits excellent catalytic activity in cyclopentene (CPE) oxidation to glutaric acid (GAC) with 57.1 % CCPE, 61.6 % SGAC, and good reusability with 54.3∼57.1 % CCPE and 58.4∼63.2 % SGAC during 6 cycles. What's more, thermodynamic analysis indicates that CPE oxidation to GAC is a spontaneous reaction at 273.15∼373.15 K, and kinetic study shows that the key to develop CPE to GAC is to reduce activation energies of cyclopentene oxide ring-opening to 1,2-cyclopentanediol (73.8298 kJ⋅mol−1) and glutaradehyde (118.4571 kJ⋅mol−1). This study not only pioneers a promising strategy for oriented design of MOF-based materials, but also serves as a valuable reference for the computation of various chemical reactions.

Catalytic strategies for uniform monolayer MoSe2 growth in CVD processes

To facilitate the widespread utilization of devices based on two-dimensional transition metal dichalcogenide (TMDC) materials, addressing the challenge of producing large-area and uniform monolayers is crucial. In this study, we investigated the efficacy of various catalysts in promoting the growth of monolayer MoSe2 through chemical vapor deposition (CVD) as a potential solution to improve surface coverage and uniformity while maintaining the monolayer structure. Five distinct water-soluble catalysts (sodium chloride (NaCl), zinc chloride (ZnCl2), potassium hydroxide (KOH), potassium chloride (KCl), potassium oxalate (K2C2O4)) were employed in conjunction with a glass substrate for the CVD-based growth of monolayer MoSe2. We applied these catalyst solutions as thin layers onto SiO2/Si substrates to observe their specific catalytic effects on monolayer MoSe2 formation. MoSe2 was selected as the target material due to its promising characteristics within the TMDC family, particularly its high mobility. Our findings revealed that NaCl, ZnCl2, KCl, and K2C2O4 catalysts enhanced monolayer growth in the 2H phase on SiO2/Si substrates, while the glass substrate resulted in a hybrid 1T/2H MoSe2 structure, albeit with the highest surface coverage. Furthermore, the use of a catalyst allowed us to bypass the laborious transfer step by enabling direct growth of the MoSe2 flakes on the Si/SiO2 substrate, eliminating the risk of flake damage arising from the transfer process. Among the catalyst solutions, NaCl yielded the most homogeneous MoSe2 monolayer growth with relatively high coverage.

The peroxidase-like cleaning strategy for organic fouling of water treatment membranes based on MoS2 functional layers

Efficient cleaning strategies play a key role in implementing sustainable and economic membrane operations during water treatments and purification. We proposed in this paper to construct the functional layers on the surface of PES substate using MoS2 nanosheets synthesized by a hydrothermal method, namely MoS2/PES membrane. The membrane structure and properties were characterized by SEM, XRD, EDS and FTIR. This is then followed by an evaluation of the membrane fouling of the functional layers, and in turn exploring the membrane cleaning strategy. The specific catalytic effects between MoS2 nanosheets with peroxidase-like activity, and the cleaning agent (H2O2) was subtly combined to endow MoS2 functional layers with specific catalysis. Humic acid (HA, as a representative organic foulant) having the filtration efficiency (~91 %) of MoS2/PES membrane was ~6 % higher than that of the pristine PES membrane. The flux recovery rate of MoS2/PES membrane (~75 %) was significantly larger than the PES membrane (~16 %) under optimized conditions. Results of 7 cycles of consecutive membrane fouling and cleaning demonstrated MoS2 functional layers not only relieved membrane fouling but also exhibited higher water flux. The outstanding performance of MoS2 functional layers could be explained by their stacked honeycomb pore-like structure and the catalytic characteristics of MoS2-like peroxidases. H2O2 was used to trigger the in-situ catalytic function of MoS2 layers, generating strong ROS and oxygen for the enhanced removal of organic foulants. This study provides new insights into devising a novel membrane cleaning strategy using advanced functional nanomaterials.

Zeolitic imidazolate framework-8 encapsulating carbon nanodots and silver nanoparticles for fluorescent detection of H2O2 and glucose

In this study, a novel fluorescent biosensor is developed for the detection of H2O2 and glucose based on Zeolitic Imidazolate Framework-8 (ZIF-8) nanocomposites. ZIF-8 encapsulating carbon nanodot (CD) exhibits bright fluorescence emission. After further loading of AgNP, the fluorescence is quenched, which is mainly based on the excited electron transfer from CD to AgNP. Besides, the excitation wavelength of CD falls within the adsorption range of AgNP, which leads to efficient inhibition of the excitation energy. The as-prepared AgNP-CD-ZIF-8 nanocomposites can be utilized as a highly sensitive platform for the analysis of H2O2 and glucose. In the presence of glucose, H2O2 can be generated by the catalysis of glucose oxidase (GOD), which induces the etching of AgNP and subsequent recovery of CD-ZIF-8 fluorescence. This “turn on” biosensor can be applied for facile and convenient quantification of H2O2. It can also be further extended to detect glucose in real samples after combining specific catalytic effect of GOD. The analytical performances are excellent, which demonstrates great potential for practical utility.

Fast, Sensitive, and Highly Selective Room-Temperature Hydrogen Sensing of Defect-Rich Orthorhombic Nb2O5-x Nanobelts with an Abnormal p-Type Sensor Response.

The research and development of low-power-consumption and room-temperature hydrogen sensors are of great significance for the safe application of hydrogen energy. Herein, orthorhombic Nb2O5-x nanobelts are prepared through a combined procedure of hydrothermal, ion exchange, and annealing treatment in Ar. The topological transformation process results in the formation of abundant surface defects including chemical defects such as Nb4+, oxygen vacancies, and disordered microregions, which lead to the abnormal p-type conducting and hydrogen sensing behavior. Moreover, the orthorhombic Nb2O5-x nanobelts exhibit fast and sensitive room-temperature hydrogen sensing performance, which shows greater advancement than the monoclinic, tetragonal, and hexagonal Nb2O5 one-dimensional (1D) nanostructures. The response time and lowest limit of detection of the as-fabricated room-temperature sensor decrease to 28 s and 3.5 ppm, respectively. The sensor also exhibits a highly selective hydrogen response against CO, CH4, ethanol, H2S, and NH3. The hydrogen response of the Nb2O5-x nanobelts can be attributed to the redox reaction between hydrogen and preadsorbed oxygens. The defective surface structure and the prolonged dimension of the nanobelts give rise to the highly reactive surface and the suppression of the negative nanojunction effect, which greatly improves the sensing performance. The orthorhombic lattice structure can also promote gas adsorption and diffusion behavior due to its specific catalytic and pathway effect. The results of this work can be helpful for the rational design and defect engineering of the Nb2O5-based 1D nanostructures for room-temperature hydrogen sensing applications.

Gasification of hydrolysis lignin with CO2 in the presence of Fe and Co compounds

The effect of the nature of the metal (Fe and Co) deposited on the surface of hydrolysis lignin, as well as the metal content (1, 3, 5 and 7 wt%), on the process of dry catalytic lignin reforming has been studied. The use of the catalyst led to a twofold increase in the conversion of carbon dioxide at temperatures of 500–800 °C, while both metals showed similar activity. The maximum specific catalytic effect is achieved when supporting 7 wt% of active metals.

Enhanced Combustion of Bituminous Coal and Semicoke Mixture by Ferric Oxide with Thermographic and Kinetic Analyses.

We study the specific catalytic effect of the catalyst on the combustion process of pulverized coal of increasing the proportion of semicoke in the mixture of semicoke and bituminous coal, and reducing the cost of blast-furnace coal injection. A combination of thermogravimetric and kinetic analyses were used to study the catalytic effect of Fe2O3 on semicoke and bituminous coal, and to improve the amount of semicoke in the mixed coal powder of bituminous coal and semicoke. Experimental results showed that Fe2O3 had a catalytic effect on both semicoke and bituminous coal, but there were differences in the catalytic stages of the same catalyst for different pulverized coal types. The addition of 2 wt % Fe2O3 to semicoke and bituminous coal each led to the ignition temperature and maximal burning rate temperature of the semicoke decreasing, indicating that the catalyst promoted the precipitation of a volatile fraction from the semicoke. The maximal burning rate temperature and burnout temperature of the bituminous coal decreased, and maximal weight loss rate increased, indicating that the catalyst promoted the combustion of the fixed carbon of bituminous coal. The optimal proportioning amount of semicoke in the mixed coal powder without the addition of a catalyst was 25%. After adding 2 wt % Fe2O3, the proportional amount of semicoke increased by 10%. The addition of the catalyst resulted in even lower activation energy for the same conversion rate. When the conversion rate was in the ranges of 0.1–0.2 and 0.5–0.7, the activation energy decreased by 22% and 26%, respectively, compared with that without a catalyst. Fe2O3 promoted the combustion of bituminous coal and semicoke. This enhanced the combustion performance of the pulverized coal mix and increased the proportion of semicoke in the mix, which has certain guiding significance in reducing the cost of blast-furnace iron making.

Electrochemical Biosensor Based on HRP/Ti3C2/Nafion Film for Determination of Hydrogen Peroxide in Serum Samples of Patients with Acute Myocardial Infarction.

Hydrogen peroxide (H2O2) has been reported to mediate a variety of physiological and pathological processes in living systems. In this work, a biosensor for determination of H2O2 was prepared by using an HRP/Ti3C2/Nafion film-modified glassy carbon electrode (GCE). Ti3C2 nanosheets with remarkable conductivity and high specific surface area were chosen as carriers for HRP. Moreover, this biosensor modified with HRP has a specific catalytic effect on H2O2. The difference in peak current could reflect the quantitative change of H2O2. The linear range of the biosensor is 5-8000 μM, and the detection limit is 1 μM (S/N = 3). This biosensor was used to detect H2O2 in clinical serum samples of normal controls and patients with acute myocardial infarction (AMI) before and after percutaneous coronary intervention (PCI). The results showed that the difference between normal controls and patients is significant (P < 0.05), as well as the difference for patients before and after PCI (P < 0.01), but no significant difference existed between postoperative patients and normal controls. This biosensor has the advantages of simple preparation, high sensitivity, and quick detection, showing potential application in clinical diagnosis.

Demethyltransferase AlkBH1 substrate diversity and relationship to human diseases.

AlkBH1 is a member of the AlkB superfamily which are kinds of Fe (II) and α-ketoglutarate (α-KG)-dependent dioxygenases. At present, only demethyltransferases FTO and AlkBH5 have relatively clear substrate studies among these members, the types and mechanisms of substrates catalysis of other members are not clear, especially the demethyltransferase AlkBH1. AlkBH1, as a demethylase, has important functions of reversing DNA methylation and repairing DNA damage. And it has become a promising target for the treatment of many cancers, the regulation of neurological and genetic related diseases. Many scholars have made important discoveries in the diversity of AlkBH1 substrates, but there is no comprehensive summary, which affects the design inhibitor target of AlkBH1. Herein, We are absorbed in the latest progress in the study of AlkBH1 substrate diversity and its relationship with human diseases. Besides, we also discuss future research directions and suggest other studies to reveal the specific catalytic effect of AlkBH1 on cancer substrates.

Glucose and Hydrogen Peroxide Concentration Measurement using 1D Defective Phononic Crystal Sensor

The most of the present biosensors are concentrated on the electrochemical techniques. Here, a novel one-dimensional phononic crystal (1D PnCs) sensor, which is adequate for sensing biomaterials and solutions with the smallest difference in their acoustic properties, is developed. The sensor idea is particularly involved in measuring glucose and hydrogen peroxide (H2O2) concentrations based on the resonant mode frequencies. We have used the transfer matrix method (TMM) to obtain the transmittance spectra of glucose/H2O2 1D PnC sensor. The sensor structure is a defective 1D PnC design with a defect layer in the middle of alternating layers of glass and water. The sensor employed specific windows (transmitted peaks or resonant modes) for different concentrations of glucose and H2O2. The performance parameters and resonant peak frequency are calculated for the two solutions at very low and high concentrations of analytes. The sensor showed a high sensing performance for both glucose and H2O2 concentrations. We obtained high sensitivity (S), quality factor ( $$Q),$$ and figure of merit ( $$\mathrm{FOM}$$ ) values for both glucose and H2O2. The estimated values of S, $$Q$$ , and $$\mathrm{FOM}$$ for glucose (at concentration of 0.2%) are 100,000 Hz, 4867, and 1002, respectively. Similarly, the values of S, $$Q$$ , and $$\mathrm{FOM}$$ for H2O2 (at concentration of 0.2%) are 60,000 Hz, 4866, and 601, respectively. These results conclude that 1D PnC sensor is excellent choice for the detection of glucose and H2O2 owing to its sensitivity, performance, resolution, efficiency, and ease of fabrication at low cost. Moreover, without using a specific catalytic effect to produce glucose oxidase, the proposed sensor can successfully be utilized for the determination of glucose concentrations in the blood. On top of that, the sensor structure is stable under temperature variations due to the high stability of the acoustic properties of the constituent materials.

The effect of LaFeO3@MnO2 on the thermal behavior of energetic compounds: An efficient catalyst with core-shell structure

Large particle size and low specific surface area are two major factors of restricting metal oxides as combustion catalyst with high performance. The construction of three-dimensional (3D) heterojunction materials with synergistic effect is conducive to enhancing the catalytic activity. In this work, LaFeO3 were prepared by a facile solvo-thermal method and post-heat treament. However, the LaFeO3 with a large particle size shows poor specific surface area, resulting in a low catalytic activity. In order to improve its catalytic activity, a 3D core/shell heterostructured LaFeO3@MnO2 composite was constructed by coupling LaFeO3 with MnO2. The core-shell structured LaFeO3@MnO2 provides a larger specific surface area and high catalytic effect on the thermal decomposition of ammonium perchlorate (AP) with a reduced decomposition temperature from 403.73 °C to 281.38 °C, an enhanced energy release from 649.6 J·g−1 to 966.5 J·g−1, and a decreased apparent activation energy from 139.05 kJ·mol−1 to 110.88 kJ·mol−1. Additionally, LaFeO3@MnO2 also shows efficient catalytic effects on the thermal decomposition of hexanitrohexaazaisowurzitane (CL-20) and cyclotetramethylenetetranitramine (HMX).

Efficient Photocatalytic Reduction of CO2 Present in Seawater into Methanol over Cu/C-Co-Doped TiO2 Nanocatalyst Under UV and Natural Sunlight

Photocatalytic reduction of CO2 in seawater into chemical fuel, methanol (CH3OH), was achieved over Cu/C-co-doped TiO2 nanoparticles under UV and natural sunlight. Photocatalysts with different Cu loadings (0, 0.5, 1, 3, 5, and 7 wt%) were synthesized by the sol–gel method and were characterized by XRD, SEM, UV–Vis, FTIR, and XPS. Co-doping with C and Cu into TiO2 remarkably promoted the photocatalytic production of CH3OH. This improvement was attributed to lowering of bandgap energy, specific catalytic effect of Cu for CH3OH formation, and the minimization of photo-generated carrier recombination. Co-doped TiO2 with 3.0 wt% Cu was found to be the most active catalyst, giving a maximum methanol yield rate of 577 μmol g-cat−1 h−1 under illumination of UV light, which is 5.3-fold higher than the production rate over C-TiO2 and 7.4 times the amount produced using Degussa P25 TiO2. Under natural sunlight, the maximum rate of the photocatalytic production of CH3OH using 3.0 wt% Cu/C-TiO2 was found to be 188 μmol g-cat−1 h−1, which is 2.24 times higher than that of C-TiO2, whereas, no CH3OH was observed for P25.

Lanthanide Coordination Polymer Nanoparticles as an Excellent Artificial Peroxidase for Hydrogen Peroxide Detection

Lanthanide coordination polymer nanoparticles (Ln-CPNs) have been recently demonstrated as excellent platforms for biomolecule detection. In this work, we synthesized novel cerium coordination polymer nanoparticles ATP-Ce-Tris CPNs in a simple and quick way using ATP molecules as the biocompatible ligands to Ce(3+) ions in tris(hydroxymethyl)aminomethane hydrochloric (Tris-HCl) solution. In view of the excellent free radical scavenging property of cerium compounds, which is ascribed to the mixed valence state (Ce(3+), Ce(4+)) and the reversible switch from Ce(3+) to Ce(4+), the synthesized ATP-Ce-Tris CPNs was used as artificial peroxidase to selectively and sensitively detect H2O2. The sensing mechanism depends on the oxidation of the fluorescent ATP-Ce(III)-Tris CPNs to nonfluorescent ATP-Ce(IV)-Tris CPNs by H2O2. Compared with those inorganic cerium oxide sensors, this kind of fluoresence ATP-Ce-Tris CPNs sensor needs no additional organic redox dye, such as ABTS (2,20-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid), TMB (3,3,5,5-tetramethylbenzidine), or fluorescein as signal molecules. Moreover, such ATP-Ce-Tris CPNs sensor exhibited a more sensitive response to H2O2 with a detection limit down to 0.6 nM, which is 2 orders of magnitude lower than those of cerium oxide sensors. This sensing platform was further extended to the detection of glucose in combination with the specific catalytic effect of glucose oxidase (GOx) for the oxidation of glucose and formation of H2O2.

Achieving selectivity from the synergistic effect of Cr and Pt activated SnO2 thin film gas sensors

The enhanced selectivity due to the synergistic effect of Cr and Pt co-doping on gas sensing properties of SnO2 thin films, is reported. The undoped and Cr/Pt co-doped SnO2 thin films are deposited on the glass substrates by Ultrasonic Nebulized Spray Pyrolysis of Aqueous Combustion Mixture (UNSPACM). The as-deposited films are nanocrystalline in nature with crystallite size ∼3nm, as seen from x-ray diffraction and transmission electron microscopy (TEM). The chemical state of dopants is investigated using x-ray photoelectron spectroscopy. Further, the presence of separate Pt additives in SnO2 film is also confirmed using TEM studies. The gas sensing properties show that although Pt addition enhances the overall sensitivity, it does not improve the selectivity of the sensor. Nonetheless, Cr and Pt co-doped SnO2 films exhibit greater selectivity towards CO gas, while only Cr doped film exhibits selectivity towards NO2 gas at 275°C. The improved selectivity is attributed to the change in carrier concentration, oxygen stoichiometry and specific catalytic effect of the dopant ions.

Graphene Quantum Dots Assembled with Metalloporphyrins for "Turn on" Sensing of Hydrogen Peroxide and Glucose.

Noncovalent and multifunctional hybrids have been generated via π-π stacking and electrostatic interactions by combining the nanometer-scale graphene structure of graphene quantum dots (GQDs) with Fe(III) 5,10,15,20-tetrakis(1-methyl-4-pyridyl)porphine (FeTMPyP). The inner filter effect (IFE) of FeTMPyP on the GQDs results in substantial PL quenching of the GQDs. The quenched PL of GQDs by the FeTMPyP can be switched back "on" in response to the reaction between FeTMPyP and H2 O2 , which causes rupture of the cyclic tetrapyrrolic nucleus with consequential loss of iron from FeTMPyP, and then proceeds further to produce colorless dipyrroles and monopyrroles. This "turn on" system can be applied for simple and convenient H2 O2 sensing and can be further extended to the detection of glucose in combination with the specific catalytic effect of glucose oxidase (GOx) through the oxidation of glucose and formation of H2 O2 . Because of the inherent synthetic control available for the design of metalloporphyrins, the GQDs-based optical sensing approach described here has the potential to be highly versatile for other target analytes.

Sensitive and selective chemiluminescence assay for hydrogen peroxide in exhaled breath condensate using nanoparticle-based catalysis

The catalytic properties of cubiform Co3O4 nanoparticles, α-Fe2O3 nanorods, and NiO nanoparticles were studied using both microarray method and FI-CL method. These nanoarticles exhibit high specific catalytic effects on the chemiluminescence (CL) reaction of the luminol–H2O2 system in alkaline solution compared with other common catalysts. A reaction mechanism is described. It provides new insights into the application of nanoparticle materials. The CL method based on the use of the Co3O4 nanoparticles is ultrasensitive and particularly selective. Therefore, it was applied to the analysis of H2O2 which can be determined in the concentration range from 1.0nM to 1000nM, with a detection limit of 0.3nM. The relative standard deviation is 2.1% at 0.1μM of H2O2 (for n=11). The method was successfully applied to the determination of trace quantities of H2O2 in exhaled breath condensate (EBC) where it is a mediator of oxidative stress and a promising biomarker for diagnosing. The assay requires a small sample and no incubation time, and has an analytical runtime of <1min. It is timesaving and suitable for larger studies. The levels of H2O2 in EBC are found to be elevated in healthy subjects (average=0.54nM), rheum subjects (average=0.24nM), and feverish subjects (average=0.16nM). Our data suggested that the average H2O2 concentration of EBC from feverish subjects was significantly higher than healthy subjects and rheumatic subjects.

Fate of L-DOPA in the Presence of Inorganic Matrices: Vectorization or Composite Material Formation?

Novel bionanocomposite materials were successfully prepared using 2:1 phyllosilicates and an amino acid, L-DOPA. A systematic study of DOPA interactions with these smectites and with a nonporous amorphous silica (Aerosil) used for comparison was undertaken by combining macroscopic information, including XRD, thermogravimetric analysis, and proton relaxation times in the synthesis supensions, with microscopic observations and several spectroscopic techniques: vibrational (transmission mode IR and photoacoustic spectroscopies), solid-state 13C NMR, and XPS. A significant variety of behaviors is revealed. DOPA interacts very weakly with Aerosil, although it contributes to the structuring of the solution with the appearance of a population of bound water molecules. In contrast, the weakly basic conditions in smectite suspensions catalyze oxidation by dissolved O2 to indolic species and polymerization to pseudomelanin. With saponite, structural characterization reveals that L-DOPA zwitterions are accommodated vertically in the interlayer region as a monolayer of partially superimposed species. In addition, TEM indicates that lamellar deposits of pseudomelanin grow epitaxially on the saponite layers. With Laponite, the oxidation reactions seem to be somewhat modified by the specific catalytic effect of edge groups, and the organic species cause a strong structuring of the dispersion with gelification. The interesting chemistry taking place in these systems has implications for both DOPA vectorization and nanocomposite materials synthesis.

Candida antarctica lipase B-catalyzed the unprecedented three-component Hantzsch-type reaction of aldehyde with acetamide and 1,3-dicarbonyl compounds in non-aqueous solvent

A direct approach to 1,4-dihydropyridines by lipase-catalyzed unprecedented three-component Hantzsch-type reaction of aldehyde with 1,3-dicarbonyl compounds and acetamide in non-aqueous solvent has been developed. Some control experiments have been performed to demonstrate the specific catalytic effect of CAL-B. Acetamide was utilized as a novel ammonia source in the Hantzsch-type reaction for the first time. An array of 1,4-dihydropyridines was successfully synthesized through this methodology.

A cooperative and specific DNA-binding mode of HIV-1 integrase depends on the nature of the metallic cofactor and involves the zinc-containing N-terminal domain

HIV-1 integrase catalyzes the insertion of the viral genome into chromosomal DNA. We characterized the structural determinants of the 3′-processing reaction specificity—the first reaction of the integration process—at the DNA-binding level. We found that the integrase N-terminal domain, containing a pseudo zinc-finger motif, plays a key role, at least indirectly, in the formation of specific integrase–DNA contacts. This motif mediates a cooperative DNA binding of integrase that occurs only with the cognate/viral DNA sequence and the physiologically relevant Mg2+ cofactor. The DNA-binding was essentially non-cooperative with Mn2+ or using non-specific/random sequences, regardless of the metallic cofactor. 2,2′-Dithiobisbenzamide-1 induced zinc ejection from integrase by covalently targeting the zinc-finger motif, and significantly decreased the Hill coefficient of the Mg2+-mediated integrase–DNA interaction, without affecting the overall affinity. Concomitantly, 2,2′-dithiobisbenzamide-1 severely impaired 3′-processing (IC50 = 11–15 nM), suggesting that zinc ejection primarily perturbs the nature of the active integrase oligomer. A less specific and weaker catalytic effect of 2,2′-dithiobisbenzamide-1 is mediated by Cys 56 in the catalytic core and, notably, accounts for the weaker inhibition of the non-cooperative Mn2+-dependent 3′-processing. Our data show that the cooperative DNA-binding mode is strongly related to the sequence-specific DNA-binding, and depends on the simultaneous presence of the Mg2+ cofactor and the zinc effector.

Kinetic Study of the Hexacyanoferrate (III) Oxidation of Dihydroxyfumaric Acid in Acid Media

The kinetics of the hexacyanoferrate (III) oxidation of dihydroxyfumaric acid to hexacyanoferrate (II) and diketosuccinic acid was looked into within the 0.04 to 5.3 M HCl acidity range under different temperatures, ionic strengths, and solvent permittivity conditions. The kinetic effect of alkali metal ions, transition metal impurities, and substrate concentrations have also been analyzed. The observed inhibition effect brought about by addition of the reaction product, hexacyanoferrate (II), is a sign of a complex mechanism. The rate constants remained essentially unchanged up to 1 M HCl, diminished between 1.0 and 3.0 M HCl, and rose above 3.0 M HCl. Depending on the medium acidity, three mechanisms can be put forward, which involve different kinetically active forms. At low acidity, the rate-determining step involves a radical cation and both the neutral and the anion substrate forms are equally reactive ( k 1 = k 2 = 2.18 +/- 0.05 M (-1) s (-1), k -1 = 0.2 +/- 0.03). When the medium acidity is boosted, the rate-determining step involves the neutral dihydroxyfumaric acid and two hexacyanoferrate (III) forms. In the intermediate region the rate constant diminished with rising [H (+)] ( k' 1 = 0.141 +/- 0.01 and k' 2 = 6.80 +/- 0.05). Specific catalytic effect by binding of alkali metal ions to oxidant has not been observed. In all instances it was assessed that the substrate decomposition is slow compared to the redox reaction.