Maximum Turnover Research Articles

Formic acid dehydrogenation using Ruthenium-POP pincer complexes in ionic liquids

Formic acid is one of the most promising candidates for the long-term storage of hydrogen in liquid form. Herein, we present a new collection of ruthenium pincer complexes of the general formula [RuHCl(POP)(PPh3)] using commercially available or easy-to-synthesize tridentate xantphos-type POP pincer ligands. We applied these complexes in the dehydrogenation of formic acid to CO2 and H2 using the ionic liquid BMIM OAc (1-butyl-3-methylimidazolium acetate) as solvent under mild, reflux-free conditions. The best performing catalyst with respect to maximum turnover frequency, the literature-known complex [RuHCl(xantphos)(PPh3)] Ru-1, produced a maximum turnover frequency of 4525 h−1 with 74% conversion after 10 min at 90 °C and complete conversion (> 98%) occurring within 3 h. On the other hand, the best overall performing catalyst, the novel complex [RuHCl(iPr-dbfphos)(PPh3)] Ru-2, facilitated full conversion within 1 h leading to an overall turnover frequency of 1009 h−1. Moreover, catalytic activity was observed at temperatures as low as 60 °C. Only CO2 and H2 are observed in the gas phase, with no CO detected. High-resolution mass spectrometry suggests the presence of N-heterocyclic carbene complexes in the reaction mixture.

Base-free aqueous Suzuki–Miyaura coupling reaction using recoverable bi-functional Pd supported nanocatalyst

A solid base catalyst comprising pyridine-palladium polyorganosiloxane framework was synthesized via a grafting method. The resulting organic–inorganic hybrid palladium nanomaterial was characterized by 13C CP-MAS NMR, 29Si CP-MAS NMR, XRD, EDX, TEM, TGA, and the BET measurements. The hybrid palladium nanomaterial exhibited high catalytic activity for the Suzuki–Miyaura cross-coupling reaction between aryl chlorides and phenylboronic acid under base-free and aerobic conditions. A maximum turnover number (TON) of 3150, with a 0.2 mol% Pd loading and a reaction temperature of 80 °C in aqueous solution. The catalyst demonstrated remarkable stability, maintaining its activity even after six cycles of reuse without significant loss of activity. TEM images showed that the catalyst retained its structure and high-order mesostructure after several uses. ICP-AES also confirmed the absence of palladium contamination in the final products. Leaching test studies further confirmed the true heterogeneous nature of the developed catalytic system.

Electronic Effects in Cobalt Phthalocyanine Catalysts Towards Noble-Metal-Free, Photocatalytic CO2-to-CO Reduction.

Noble-metal-free CO2 reduction systems based on cobalt phthalocyanine (CoPc) and its derivatives have demonstrated remarkable photocatalytic performances; however, their structure-activity relationship with electronic tuning remains unexplored. Herein, we now provide a systematic study to investigate the electron effects of substituents on the CoPc family in photocatalytic CO2 reduction, where a Cu(I) heteroleptic photosensitizer is utilized. The highest performance can be achieved using cobalt tetracarboxylphthalocyanine in light-driven CO2-to-CO reduction, with a maximum turnover number of 2950 at 450 nm and an outstanding apparent quantum yield of 63.5% at 425 nm, over ten times the activity with the tetra-dimethylamino-substituted CoPc derivative. The favorable electron-withdrawing effects have been further verified by DFT calculations and cyclic voltammetry, which reduces the overpotential required for CO2 reduction and decreases the Gibbs free energy of the catalyst active intermediates, particularly the CO-desorption energetics.

Chitosan pyrolysis in the presence of a ZnCl2/NaCl salts for carbons with electrocatalytic activity in oxygen reduction reaction in alkaline solutions.

The one-step carbonization of low cost and abundant chitosan biopolymer in the presence of salt eutectics ZnCl2/NaCl results in nitrogen-doped carbon nanostructures(8.5 wt.% total nitrogen content). NaCl yields the spacious 3D structure, which allows external oxygen to easily reach the active sites for the oxygen reductionreaction (ORR) distinguished by their high onset potential and the maximum turnover frequency of 0.132 e site⁻1s⁻1. Data show that the presence of NaCl during the synthesis exhibits the formation of pores having large specific volumes and surface(specific surface area of 1217 m2g-1), and holds advantage by their pores characteristics such as their micro-size part, which provides a platform for mass transport distribution in three-dimensional N-doped catalysts for ORR. It holds benefit over sample pre-treated with LiCl in terms of the micropores specific volume and area, seen as their percentage rate, measured in the BET. Therefore, the average concentration of the active site on the surface is larger.

Revisiting the catalytic activity of single horseradish peroxidase clusters through electrochemical collision technique: Effect of electrolyte and substrate

Horseradish peroxidase (HRP) is a versatile biosensing label and signal reporter owing to its broad-spectrum catalytic ability. In present work, we characterized HRP's catalytic performance with various substrates using electrochemical collision technique and analyzed the associated electron transfer processes. Different electrolyte solutions greatly affected enzyme dispersibility and zeta potential, thereby impacting HRP collision dynamics in single H2O2 substrate system. The maximum turnover number (kcat) for single HRP molecules was calculated to be 3.611 ± 0.149 × 103 s−1 in 0.85 % NaCl and 2.967 ± 0.286 × 103 s−1 in 0.1 M PBS solution, reflecting differences in cluster size induced by the electrolyte conditions. More severe agglomeration of HRP molecules was observed in double-substrate systems, where the hydrophilic mediator (K4Fe(CN)6) and lipophilic mediator (ABTS) served as electron donors and signal reporters. The calculated kcat value of single HRP molecules in ABTS-H2O2 was 7.6 times higher than that in K4Fe(CN)6–H2O2. This difference is attributed to mediators' solubility, lipophilicity, and HRP's affinity for different substrates, with HRP demonstrated stronger affinity for ABTS-H2O2 substrates, which realized more efficient electron transfer and compensated for the low diffusion coefficient of ABTS. This work provides a comprehensive analysis of the effects of electrolytes and substrates on HRP collision and catalytic behavior, offering valuable insights for the advanced design of HRP-based biosensors and diagnostic platforms.

Analisis Penerapan Manajemen Strategi Budidaya Burung Kenari (Studi Kasus Pada Kenari Mcp Kota Mataram)

The purpose of this study was to determine and analyze how the implementation of canary cultivation strategy management at MCP Walnut Jl.Swakarya Raya Gg 2 No. 8 Pagesangan Mataram City. This research design is field research (Field Research). While the research approach is descriptive qualitative. Besides being researched with a qualitative descriptive approach, this research also uses the SWOT analysis method (Strenght, Weakness, Opportunity, Treath). SWOT analysis is used by researchers to analyze external factors, namely opportunities and threats, but also internal factors, namely strengths and weaknesses. Data collection was carried out using interview and documentation techniques. The data findings are described descriptively. The results of this study can be seen that this study has five strengths (Strenght), has three weaknesses (Weakness), has three opportunities (Opportunity), and has three threats (Threats). Based on the IFAS and EFAS Matrices, the strategies applied by MCP Kenari are SO, ST, WO, and WT strategies. Because this strategy signifies the state of canary cultivation that is strong and able to continue to grow by taking opportunities or opportunities that exist to achieve maximum turnover in increasing income.

Strong Enhancement in Cobalt(II)‐TPMA Aqueous Hydrogen Photosynthesis through Intramolecular Proton Relay

AbstractPhotosynthetic hydrogen generation by cobalt(II) tris(2‐pyridylmethyl)amine (TPMA) complexes is mainly limited by protonation kinetics and decomposition routes involving demetallation. In the present work we have explored the effects of both proton shuttles and improved rigidity on the catalytic ability of cobalt(II) TPMA complexes. Remarkably, we demonstrate that, while a small enhancement in the catalytic performance is attained in a rigid cage structure, the introduction of ammonium groups as proton transfer relays in close proximity to the cobalt center allows to reach a 4‐fold increase in the quantum efficiency of H2 formation, and a surprising 22‐fold gain in the maximum turnover number, at low catalyst concentration. The beneficial role of the ammonium relays in promoting faster intramolecular proton transfer to the reduced cobalt center is documented by transient absorption spectroscopy, showcasing the great relevance of tuning the catalyst periphery to achieve efficient catalysis of solar fuel formation.

Bi2O2CO3/g‐C3N4 Catalyst for Photocatalytic Coupling of Benzylamine under Mild Conditions

AbstractThe photocatalytic conversion of benzylamine into imine is promising for industrial production and environmental protection. To develop photocatalysts with desirable compositions and microstructures is key to achieve high activity and selectivity. Here we propose the immobilization of Bi2O2CO3 on g‐C3N4 for the photocatalytic conversion of benzylamine. The Bi2O2CO3/g‐C3N4 catalyst possesses improved light absorption capacity, electron transmission rate and reduced electron‐hole recombination than pure Bi2O2CO3. It can efficiently catalyze benzylamine coupling reaction under mild conditions, i. e., at room temperature, with air as oxidant and no additional oxidant involved. The maximum turnover frequency value of N‐benzylbenzaldimine reaches 1555.3 μmol g−1 h−1 under this condition. The Bi2O2CO3/g‐C3N4 catalyst has potential in other photocatalytic reactions.

Analisis SWOT Dalam Menentukan Strategi Kompetitif Sentra Batik Tulis Al-Barokah

The batik shop "Al-Barokah" is one of the major batik companies in Sumenep, which independently carries out production and marketing activities. As a high-medium scale batik company, “Al-Barokah” has several characteristics which are also internal strengths of the company, including the company's trademark that has been registered and officially in Desperindag, namely “Al-Barokah” which is located in the village of Pakandangan Tengah, Kec. Bluto Kab. Sumenep and using SWOT as a tool to compete and introduce 4P. Thus, the purpose of this study is to determine the strategy and method of Swot in determining the competitive strategy of Sentra Batik Tulis Shop. This type of research is qualitative with the research approach used is normative and sociological. The data sources of this research are primary data and secondary data. The data processing and analysis techniques were carried out using the Milles and Heubermen method with three stages, namely data reduction, data display and conclusion drawing. The research results show that the competitive strategy in the Al-Barokah Batik Tulis Center is more dominant and more specific to the development of the company, so that the 4P strategy is used as the main reference in competition, so that the competitive advantage is more dominant. In addition, the company views competitive strategy as the basis for developing its company. After a SWOT analysis, the business has great opportunities and strengths so that it can take advantage of existing opportunities. The strategy that must be applied in this condition is to support an aggressive growth policy (Growth Oriented Strategy). This strategy indicates that the company is strong and able to continue to grow by taking existing opportunities or opportunities to achieve maximum turnover. In this strategy, it can improve the competitiveness of written batik businesses in Pakandangan Tengah Village, Bluto District, Sumenep Regency.

Highly active nitrogen-doped biochar for catalytic reduction of 4-nitrophenol: Kinetic, thermodynamic and mechanism investigation

Biomass derived metal-free carbon catalysts are urgently needed in wastewater remediation and organic transformation, due to their environmental friendliness, low cost. In this respect, a series of nitrogen-doped hierarchically porous carbons (NHPCs) derived from cheap and abundant eggplant were fabricated via a one-pot strategy under different temperatures from 600 to 900°C, and employed as metal-free catalysts for the reduction of aromatic nitrophenols. Benefiting from the synergistic effects of the hierarchically porous structure, large specific surface area and abundant structural defects, NHPCs obtained from 800 °C has the highest reduction rate of 2.072 min−1 and maximal turnover frequency (TOF) for 4-nitrophenol of 1.23 × 10−2 mM·mg−1·min−1, which is superior to most of the reported metal-free catalysts. In addition, the NHPC-800 also exhibits satisfactory practicality and universality. The kinetic and thermodynamic studies were also conducted, finding that the obtained kinetics data over NHPC-800 fit well to L-H model with a low apparent activation energy (Ea = 18.96 kJ·mol−1). Furthermore, the mechanism was also elucidated by experimental investigation and theoretical calculations, which revealed that the pore creation and doping nitrogen can promote the adsorption of 4-NP and NaBH4 onto NHPC. This study make a significant contribution to the advancement of catalytic reduction of 4-NP by N-doped biochar catalysts.

MaxKinEff: A Collision Theory-Based Approach for Analyzing Turnover Frequency and Turnover Number in Catalytic Processes.

The efficiency of catalysts relies on comprehending the underlying kinetics that govern their performance. Under the steady-state regime, the "rate" is referred to as the turnover frequency, where the reaction rate is first order with respect to catalysts. Here, we introduce the Maximum Kinetic Efficiency (MaxKinEff) model, grounded in collision theory, to predict efficiency based on maximum turnover frequency, and maximum turnover number, . The model was applied to molecular water oxidation using twenty-six transition metal catalysts from the first (3d), second (4d), and third (5d) rows. A thorough investigation reveals that [Ru(pda)(Br-py)2] (pda=1,10-phenanthroline-2,9-dicarboxylate; Py=pyridinophane) exhibits a notable of 1176.87×10-5 s-1 due to its larger collision diameter (σRC) and lower activation energy (Ea). Importantly, the trend in the computed values aligns with experimental TON, validating the model's accuracy. For instance, [Cp*Ir(κ2-N,O)NO3] is identified by MaxKinEff as a standout performer, with the normalized maximum computed TON, resembling the experimental TON, =2000.

Unveiling the Reactivity of Part Per Million Levels of Cobalt-Salen Complexes in Hydrosilylation of Ketones.

A series of air-stable cobalt(III)salen complexes Co-1 to Co-4 have been synthesized and employed in the hydrosilylation of ketones. Notably, the most intricately tailored Co-3 pre-catalyst exhibited exceptional catalytic activity under mild reaction conditions. The developed catalytic hydrosilylation protocol proceeded with an unusual ppm level (5 ppm) catalyst loading of Co-3 and achieved a maximum turnover number (TON) of 200,000. A wide variety of aromatic, aliphatic, and heterocyclic ketones encompassing both electron-donating and electron-withdrawing substituents were successfully transformed into the desired silyl ethers or secondary alcohols in moderate to excellent yields.

Strong Enhancement in Cobalt(II)-TPMA Aqueous Hydrogen Photosynthesis through Intramolecular Proton Relay.

Photosynthetic hydrogen generation by cobalt(II) tris(2-pyridylmethyl)amine (TPMA) complexes is mainly limited by protonation kinetics and decomposition routes involving demetallation. In the present work we have explored the effects of both proton shuttles and improved rigidity on the catalytic ability of cobalt(II) TPMA complexes. Remarkably, we demonstrate that, while a small enhancement in the catalytic performance is attained in a rigid cage structure, the introduction of ammonium groups as proton transfer relays in close proximity to the cobalt center allows to reach a 4-fold increase in the quantum efficiency of H2 formation, and a surprising 22-fold gain in the maximum turnover number, at low catalyst concentration. The beneficial role of the ammonium relays in promoting faster intramolecular proton transfer to the reduced cobalt center is documented by transient absorption spectroscopy, showcasing the great relevance of tuning the catalyst periphery to achieve efficient catalysis of solar fuel formation.

A research on the Italian fiscal shell companies turnover

Purpose The purpose of this paper is to study the turnover of Italian shell companies (SCs)/missing traders used for tax crimes, a predicate offence of money laundering. This research could be useful for Italian obliged entities to the Anti-Money Laundering Law to detect and report SCs, as soon as possible, to the Financial Intelligence Unit for Italy. Design/methodology/approach The author uses a sample of 32 SCs that are present in the Third Penal Section of the Italian Supreme Court in the period 2018–2020, involved in tax crimes and that have presented their balance sheets for two or more years. For SCs, the author computes the averages for: the turnover growth rate from first and the maximum turnover; the years between these two values; and the years in which SCs are active. Moreover, the author verifies if SCs are similar in terms of turnover by studying the relationship between the turnover growth rate and the first turnover and the reduction of turnover standard deviations. Findings SCs growth is very high and they reach, on average, their peak in less than three years; SCs are active, on average, for about four years; eventually, SCs exhibit a convergence process in turnover levels. Originality/value To the best of the author’s knowledge, there are no studies that analyse the SC turnover.

Metal-acid synergistic catalysis accelerates the hydrogen borrowing amination of alcohols by confining Ru sites in Beta zeolite

Direct hydrogen transfer amination of alcohols with amines is an environmentally friendly and atom-economical route for the synthesis of N-alkylamines. Noble metal species are highly catalytic active sites, but the exorbitant price makes the urgency to boost the atom efficiency with stable recyclability. Herein, we demonstrated that encapsulation of Ru nanoparticles (NPs) within BEA zeolite through direct hydrothermal approach greatly promoted the catalytic efficiency in the N-alkylation of aromatic alcohols and amines under additive- and solvent-free conditions, resulting in the high yield (∼93 %), maximum turnover number (TON) of 12,822 and turnover frequency (TOF) of 9012 h−1, with stable recyclability and extendable substrate scope. The kinetic studies and in-situ characterizations revealed that the synergy of confined Ru NPs and adjacent acid sites of BEA zeolite significantly promoted the C–H bond activation in the rate-determining step of alcohol dehydrogenation into aldehydes. Besides, the acid sites also accelerated the condensation of aldehyde intermediates and anilines to promote the kinetic equilibrium, while the moderate strength of the Ru–H bond resulting from the confined Ru NPs is advantageous to balance the dehydrogenation and hydrogenation steps to reach the fascinating H-transfer process.

Turnover Number in Photoinduced Molecular Catalysis of Hydrogen Evolution: a Benchmarking for Catalysts?

Development of devices for production of H2 using light and a sustainable source of electrons may require the design of molecular systems combining a molecular catalyst and a photosensitizer. Evaluation of the efficiency of hydrogen production is commonly performed in homogeneous solution with a sacrificial electron donor and the report of the maximal turnover number vs catalyst ( ). This figure of merit is strongly dependent on deactivation pathways and does not by itself provide a benchmarking for catalysts. In particular, when the photosensitizer degradation is the primary source of limitation, a kinetic model, rationalizing literature data, shows that a decrease of the catalyst concentration leads to an increase of . It indicates that exceptionally high obtained at very low catalyst concentration shall not be considered as an indication of an exceptional catalytic system. We advocate for a systematic kinetic analysis in order to get a quantitative measure of the competitive pathways leading to values and to provide keys for performance improvement.

Designing Degradable Polymers from Tricycloalkenes via Complete Cascade Metathesis Polymerization.

Cascade metathesis polymerization has been developed as a promising method to synthesize complex but well-defined polymers from monomers containing multiple reactive functional groups. However, this approach has been limited to the monomers involving simple alkene/alkyne moieties or produced mainly non-degradable polymers. In this study, we demonstrate a complete cascade ring-opening/ring-closing metathesis polymerization (RORCMP) using various tricycloalkenes and two strategies for the efficient degradation. Through rational design of tricycloalkene monomers, the structure and reactivity relationship was explored. For example, tricycloalkenes with trans configuration in the central ring enabled faster and better selective cascade RORCMP than the corresponding cis isomers. Also, a 4-substituted cyclopentene moiety in the monomers significantly enhanced the overall cascade RORCMP performance, with the maximum turnover number (TON) reaching almost 10,000 and molecular weight up to 170 kg/mol using an amide-containing monomer. Furthermore, we achieved one-shot cascade multiple olefin metathesis polymerization using tricycloalkenes and a diacrylate, to produce new highly A,B-alternating copolymers with full degradability. Lastly, we successfully designed xylose-based tricycloalkenes to give well-defined polymers that underwent ultra-fast and complete degradation under mild conditions.

Designing Degradable Polymers from Tricycloalkenes via Complete Cascade Metathesis Polymerization

AbstractCascade metathesis polymerization has been developed as a promising method to synthesize complex but well‐defined polymers from monomers containing multiple reactive functional groups. However, this approach has been limited to the monomers involving simple alkene/alkyne moieties or produced mainly non‐degradable polymers. In this study, we demonstrate a complete cascade ring‐opening/ring‐closing metathesis polymerization (RORCMP) using various tricycloalkenes and two strategies for the efficient degradation. Through rational design of tricycloalkene monomers, the structure and reactivity relationship was explored. For example, tricycloalkenes with trans configuration in the central ring enabled faster and better selective cascade RORCMP than the corresponding cis isomers. Also, a 4‐substituted cyclopentene moiety in the monomers significantly enhanced the overall cascade RORCMP performance, with the maximum turnover number (TON) reaching almost 10,000 and molecular weight up to 170 kg/mol using an amide‐containing monomer. Furthermore, we achieved one‐shot cascade multiple olefin metathesis polymerization using tricycloalkenes and a diacrylate, to produce new highly A,B‐alternating copolymers with full degradability. Lastly, we successfully designed xylose‐based tricycloalkenes to give well‐defined polymers that underwent ultra‐fast and complete degradation under mild conditions.

Unveiling the Broad Substrate Specificity of Deoxynivalenol Oxidation Enzyme DepA and Its Role in Detoxifying Trichothecene Mycotoxins.

DepA, a pyrroloquinoline quinone (PQQ)-dependent enzyme isolated from Devosia mutans 17-2-E-8, exhibits versatility in oxidizing deoxynivalenol (DON) and its derivatives. This study explored DepA's substrate specificity and enzyme kinetics, focusing on DON and 15-acetyl-DON. Besides efficiently oxidizing DON, DepA also transforms 15-acetyl-DON into 15-acetyl-3-keto-DON, as identified via LC-MS/MS and NMR analysis. The kinetic parameters, including the maximum reaction rate, turnover number, and catalytic efficiency, were thoroughly evaluated. DepA-PQQ complex docking was deployed to rationalize the substrate specificity of DepA. This study further delves into the reduced toxicity of the transformation products, as demonstrated via enzyme homology modeling and in silico docking analysis with yeast 80S ribosomes, indicating a potential decrease in toxicity due to lower binding affinity. Utilizing the response surface methodology and central composite rotational design, mathematical models were developed to elucidate the relationship between the enzyme and cofactor concentrations, guiding the future development of detoxification systems for liquid feeds and grain processing. This comprehensive analysis underscores DepA's potential for use in mycotoxin detoxification, offering insights for future applications.

Computational Design of an Electro-Organocatalyst for Conversion of CO2 into Formaldehyde.

Density functional theory calculations employing a hybrid implicit/explicit solvation method were used to explore a new strategy for electrochemical conversion of CO2 using an electro-organocatalyst. A particular structural motif is identified that consists of an electron-rich vicinal enediamine (>N-C═C-N<) backbone, which is capable of activating CO2 by the formation of a C-C bond while subsequently facilitating the transfer of electrons from a chemically inert cathode to ultimately produce formaldehyde. Unlike transition metal-based electrocatalysts, the electro-organocatalyst is not constrained by scaling relations between the formation energies of activated CO2 and adsorbed CO, nor is it expected to be active for the competing hydrogen evolution reaction. The rate-limiting steps are found to occur during two proton-coupled electron transfer (PCET) sequences and are associated with the transfer of a proton from a proton transfer mediator to a carbon atom on the electro-organocatalyst. The difficulty of this step in the second PCET sequence necessitates an electrode potential of -0.85 V vs RHE to achieve the maximum turnover frequency. In addition, it is postulated that the electro-organocatalyst should also be capable of forming long-chain aldehydes by successively carrying out reductive aldol condensation to grow the alkyl chain one carbon at a time.