Addition Of Metal Ions Research Articles

Synthesis, Characterization, and Antibacterial Studies of New Cu(II) and Pd(II) Complexes with 6-Methyl-2-Thiouracil and 6-Propyl-2-Thiouracil

The aim of the present study is to synthesize new metal complexes of 6-methyl-2-thiouracil and 6-propyl-2-thiouracil, elucidate their structures, and investigate their biological properties. All metal complexes were obtained after mixing water solutions of the corresponding metal salts and the ligand dissolved in DMSO and water solutions of NaOH in a metal-to-ligand ratio of 1:4:2. The structures of the new compounds are discussed based on melting point analysis (MP-AES) for Cu and Pd, UV-Vis, IR, ATR, 1H NMR, 13C NMR, and Raman spectroscopy. The interpretation of complex spectra is assisted by the data for 6-methyl-2-thiouracil and 6-propyl-2-thiouracil obtained from 1H-1H COSY, DEPT-135, HMBC and HMQC spectra. In addition, the antimicrobial activity of these complexes and the free ligands are assessed against both Gram-positive and Gram-negative bacteria, as well as yeasts. In general, the addition of metal ions improved the antimicrobial activity of both 6-methyl-2-thiouracil and 6-propyl-2-thiouracil. The Cu(II) complex with 6-methyl-2-thiouracil and the Pd(II) complex with 6-propyl-2-thiouracil exhibited the highest activity against the test microorganisms.

Optical Response of Various Heavy Metal Ions-Based Carbon Dots Photoluminescent Quenching Effect

Carbon nanodots (Cdots) are a type of semiconductor carbon-based nanomaterial that is gaining popularity due to its excellent characteristics (e.g., biocompatibility, unique optical properties, low cost, eco-friendly, and high stability). In terms of physicochemical properties for an environmentally friendly sensor application, this material also has an excellent ability to detect heavy metal ions in the biosphere. In this study, we proposed a comprehensive optical characterization to examine the sensitivity of the Cdots probe for three heavy metal ions (i.e., Mn, Pb, and Cr ions) and compare the performance. The results of the experiment revealed that each heavy metal ion reacted differently to the physical properties of Cdots. With the addition of Cr, Mn, and Pb metal ions from the original Cdot solution, which is only 1.45 ns, the lifetime of quenched Cdots is 2.55 ns, 3.15 ns, and 2.15 ns, respectively, according to the TRPL experiments. With additional Cr, Mn, and Pb discovered, the intensity of PL dropped by 5.7%, 14.2%, and 21.4%, respectively. Among these various heavy metal ions, Pb ions show the most affected by the quenching effect in Cdots-based photoluminescence, FTIR, and ultraviolet-visible light absorption characterization. Based on the results of three heavy metal ion experiments, this study can be implemented as the heavy metal ion sensor-based luminescence quenching effect of Cdots.

Phytase Production by Lactobacillus plantarum A1-E in Submerged and Solid-State Fermentation

Enzyme activity is influenced by several important factors, including the amount and type of substrate, solvent type, pH, temperature, presence of inhibitory and activating ions, and concentration of enzymes. Therefore, this research aimed to evaluate phytase production from Lactobacillus plantarum A1-E using submerged (SmF) and solid-state fermentation (SSF). Phytase production was determined using SmF with fructose and sucrose as the primary carbon sources at concentrations of 4.5%, 6%, and 7.5%. Additionally, SSF was conducted using three distinct substrates, including soybean Meal, rice Bran, and pollard. The results indicated that the highest phytase activity was achieved through SSF when rice bran was used as a substrate (88.48 U/mL or 4.65 U/mg). The use of 4.5% sucrose as a carbon source in the SmF technique showed the highest specific phytase activity (4.38 U/mg) compared to other carbon sources at various concentrations. The addition of metal ions showed that Fe 2+ , Mn 2+ , and Co 2+ at concentrations of 1-5 mM, Mg 2+ and Zn 2+ at concentrations of 3-5 mM, and Ca 2+ at a concentration of 3 mM acted as activators that increased phytase activity compared to control. Meanwhile, Mg 2+ and Zn 2+ at concentrations 1-2 mM were inhibitors.

Screening and Activity Analysis of α-Glucosidase Inhibitory Peptides Derived from Coix Seed Prolamins Using Bioinformatics and Molecular Docking.

Hydrolysates of coix seed prolamins (CHPs) have an excellent hypoglycemic effect and can effectively inhibit α-glucosidase, which is the therapeutic target enzyme for type 2 diabetes mellitus. However, its hypoglycemic components and molecular mechanisms remain unclear, and its stability in food processing needs to be explored. In this study, four potential α-glucosidase inhibitory peptides (LFPSNPLA, FPCNPLV, HLPFNPQ, LLPFYPN) were identified and screened from CHPs using LC-MS/MS and virtual screening techniques. The results of molecular docking showed that the four peptides mainly inhibited α-glucosidase activity through hydrogen bonding and hydrophobic interactions, with Pro and Leu in the peptides playing important roles. In addition, CHPs can maintain good activity under high temperatures (40~100 °C) and weakly acidic or weakly alkaline conditions (pH 6.0~8.0). The addition of glucose (at 100 °C) and NaCl increased the inhibitory activity of α-glucosidase in CHPs. The addition of metal ions significantly decreased the inhibitory activity of α-glucosidase by CHPs, and their effects varied in magnitude with Cu2+ having the largest effect followed by Zn2+, Fe3+, K+, Mg2+, and Ca2+. These results further highlight the potential of CHPs as a foodborne hypoglycemic ingredient, providing a theoretical basis for the application of CHPs in the healthy food industry.

Novel approach to supercritical fluid chromatography-mass spectrometry analysis of metal ions using EDTA complexation

BackgroundReliable methods enabling detection of metal ions, and especially heavy metals, in different matrices are necessary in various fields such as ecology, pharmaceuticals and toxicology. As some of the currently used methods suffer from spectral and chemical interferences, this study investigates the applicability of SFC-MS/MS for the determination of metal ions. ResultsEffective novel approaches for metal ion analysis using CO2-based mobile phase were developed using three ligands forming metal complexes. As metal-EDTA complexes are prepared by simple addition of EDTA to the solution containing metal ions, this approach to metal ion analysis does not require laborious synthesis and isolation of solid metal-complexes. Besides, two other approaches using diethyldithiocarbamate and acetylacetonate as ligands were compared. Metal complexes of Cu, Co, Cr, Fe, Al, Mn, and Zn with all 3 ligands were synthesized and their identity was confirmed by high-resolution mass spectrometry (HRMS). The suitability of the three developed UHPSFC-MS/MS methods was examined using the determination of calibration range and repeatability of injections. Moreover, the universality of the developed UHPSFC-MS/MS method for the determination of metal-EDTA complexes was proved by analyzing Ni, Bi and Pb as additional metal ions. Significance and noveltyThis study demonstrates the extended range of applicability for SFC based separations. For the first time, the possibility to analyze metal complexes with EDTA using a fast and reliable ultra-high performance supercritical fluid chromatography-tandem mass spectrometry (UHPSFC-MS/MS) method is reported. The three developed UHPSFC-MS/MS methods are able to separate DDC, acac, and EDTA complexes of various metals very efficiently (total cycle times of 5, 2, and 3 min, respectively). They offer a fast and green alternative to chromatographic methods commonly used for metal ion analysis.

A highly sensitive electrochemical sensor based on poly(3-aminobenzoic acid)/graphene oxide-gold nanoparticles modified screen printed carbon electrode for paraquat detection

Herein, a modified screen printed carbon electrode (SPCE) based on a composite material, graphene oxide-gold nanoparticles (GO-AuNPs), and poly(3-aminobenzoic acid)(P3ABA) for the detection of paraquat (PQ) is introduced. The modified electrode was fabricated by drop casting of the GO-AuNPs, followed by electropolymerization of 3-aminobenzoic acid to achieve SPCE/GO-AuNPs/P3ABA. The morphology and microstructural characteristics of the modified electrodes were revealed by scanning electron microscopy (SEM) for each step of modification. The composite GO-AuNPs can provide high surface area and enhance electroconductivity of the electrode. In addition, the presence of negatively charged P3ABA notably improved PQ adsorption and electron transfer rate, which stimulate redox reaction on the modified electrode, thus improving the sensitivity of PQ analysis. The SPCE/GO-AuNPs/P3ABA offered a wide linear range of PQ determination (10−9–10−4 mol/L) and low limit of detection (LOD) of 0.45 × 10−9 mol/L or 0.116 µg/L, which is far below international safety regulations. The modified electrode showed minimum interference effect with percent recovery ranging from 96.5% to 116.1% after addition of other herbicides, pesticides, metal ions, and additives. The stability of the SPCE/GO-AuNPs/P3ABA was evaluated, and the results indicated negligible changes in the detection signal over 9 weeks. Moreover, this modified electrode was successfully implemented for PQ analysis in both natural and tapped water with high accuracy.

Functionalized Amphiphilic Block Copolymers and Complex Emulsions for Selective Sensing of Dissolved Metals at Liquid-Liquid Interfaces.

Increasing contamination in potable water supplies necessitates the development of sensing methods that provide the speed and selectivity necessary for safety. One promising method relies on recognition and detection at the liquid-liquid interface of dynamic complex emulsions. These all-liquid materials transduce changes in interfacial tensions into optical signals via the coupling of their chemical, physical, and optical properties. Thus, to introduce selectivity, it is necessary to modify the liquid-liquid interface with an interfacially stable and selective recognition unit. To this end, we report the synthesis and characterization of amphiphilic block copolymers modified with metal chelators to selectively measure the concentrations of dissolved metal ions. We find that significant reduction in interfacial tensions arises upon quantitative addition of metal ions with high affinity toward functionalized chelators. Furthermore, measurements from UV-vis spectroscopy reveal that complexation of the block copolymers with metal ions leads to an increase in surface excess and surfactant effectiveness. We also demonstrate selective detection of iron(III) cations (Fe3+) on the μM levels even through interference from other mono-, di-, or trivalent cations in complex matrices of synthetic groundwater. Our results provide a unique platform that couples selective recognition and modulation of interfacial behaviors and demonstrates a step forward in the development of the multiplexed sensing device needed to deconvolute the complicated array of contaminants that comprise real-world environmental samples.

A single fluorescent chemosensor for detecting Ag+ ion in DMF and common trivalent metal ions in ethanol

A fluorescent chemosensor PAOP based on pyrene formaldehyde and o-phenylenediamine was successfully synthesized, and its molecular structure was characterized by NMR and mass spectrometry. PAOP exhibits excellent fluorescence sensing ability for Ag+ in DMF with high selectivity and sensitivity. In addition, PAOP can selectively identify common trivalent metal ions (Al3+, Fe3+, Cr3+) in ethanol solution. After the addition of common trivalent metal ions, the fluorescence of PAOP ethanol solution changed from blue–violet to blue–green. The results of the reversible fluorescence change, mass spectra, FT-IR and DFT calculations proved that the selective fluorescence response towards the special metal ions was attributed to formation of stable 2:1 complex PAOP@Mn+. PAOP has good recovery in detection of Cr3+ in real water samples and shows great potential application as a chemosensor.

Metal-ion-tuned metal-organic frameworks for C2H2/CO2 separation

Adsorptive separation of acetylene (C2H2) from carbon dioxide (CO2) by adsorption is a viable method for producing high-purity C2H2 required for industrial applications. However, separating C2H2 and CO2 is challenging due to their extremely similar molecular sizes and physical properties. Metal-Organic Frameworks (MOFs), as a novel porous material with high specific surface area and tunable pore size, have shown great potential in the separation and purification of light hydrocarbons. Herein, we synthesized three isoreticular Al-MOFs (Al-TCPP, Al-TCPP(Co), and Al-TCPP(Fe)) by modulating metal ions at the porphyrin center, all of which can effectively separate C2H2/CO2. The addition of metal ions can regulate and improve the separation selectivity of C2H2/CO2. Compared with the parent Al-TCPP, the IAST selectivities of Al-TCPP(Co) and Al-TCPP(Fe) for equimolar C2H2/CO2 increased from 1.73 to 3.66 and 4.43, respectively. Breakthrough experiments validate their efficient separation of C2H2/CO2. Furthermore, they all exhibit excellent hydrothermal stability, laying the foundation for practical applications.

Experimental Study of Surface Damage of Stainless Steel Subjected to Cavitation Collapse in Aqueous Environment

With the aim of understanding cavitation damage of stainless steel under the effect of cavitation collapse in an aqueous environment, morphology, phase, chemical state, electrochemical, and other properties after cavitation and erosion are methodically examined. The obtained results indicate that the addition of metal ions in pure water strengthens the dynamic effect of cavitation collapse. When the cavitation collapses, it is capable of releasing a high temperature and transferring it to the surface of the stainless steel in a short time. Then, through the rapid cooling of the pure water environment, the martensitic structure is generated, but the presence of a massive amount of metal ions leads to a decrease in the speed of heat conduction and absorption of some heat. After the collapse of the bubble, the passivation film on the surface of the stainless steel incorporates into the creation of initial micropores. A concentration difference and a growth of the current density at the bottom of the hole, as well as a reduction in the pH value are detectable. Compared with pure water, 3.5% NaCl solution contains more free ions and its local current density is higher, so its corrosion resistance is worse.

Effect of metal ions on gold adsorption onto activated carbon in the acidic thiourea solution: Experiment study and DFT calculation

Thiourea leaching has been regarded as a promising method to substitute cyanidation for gold recovery from ores or concentrates. Activated carbon used in traditional cyanide leaching solution can also be used for gold recovery from thiourea leaching solution. In this paper, the effect of metal ions including Cu2+, Ag+, Pb2+ and Zn2+ on gold adsorption onto activated carbon from acidic thiourea solution was studied for the first time. Results showed that the adsorption process of activated carbon for gold can be well described by the Freundlich isotherm model, and followed the Pseudo-second kinetic model. The adsorption of gold onto activated carbon in thiourea solution may be a ligand exchange reaction. The S of the activated carbon is the electron-accepting atoms, which can form the bond of Au-S with Au in Au[CS(NH2)2]2+. The presence of Pb2+ and Zn2+ did not interfere gold adsorption at gold concentration of 5 mg/L, but hindered gold adsorption at gold concentration of 100 mg/L. When Cu2+ and Ag+ were added in the whole studied concentration range, the gold adsorption could be significantly declined. The adsorption capacity of gold onto activated carbon in the presence of metal ions followed the sequence of Cu2+ < Ag+ < Pb2+ < Zn2+ < no addition of metal ions. Meanwhile, metal ions also adsorbed onto activated carbon, and their adsorption capacity on activated carbon obeyed the descending order of Cu2+ > Ag+ > Pb2+ > Zn2+, consistent with the complexing ability of metal ions with thiourea. The decrease of active site of activated carbon occupied by metal ions was responsible for the decrease of gold adsorption. Based on the DFT analysis, it can be inferred that the ability of metal ions to lose electrons caused the different influence of metal ions on gold adsorption.

Nanopore‐Based Metal Ion Detection and Metal Ion‐Mediated Nanopore Sensing†

Comprehensive SummaryWith the continuous development of nanotechnology, single‐molecule nanopore detection has become a popular research topic. In this review, we summarize the application of biological nanopores for metal ions detection as well as overview the function of metal ions in the ion‐mediated nanopore detection of different analytes in recent decades. According to the previous reports, biological nanopores utilize two strategies to detect metal ions. First, the specific binding sites are engineered in the nanopore to slow down the translocation rate of metal ions, resulting in the diverse specific current blockage signals. Secondly, the external molecule probes are added in the detection system to interact with metal ions, leading to the characteristic changes in the signals. At the same time, the external addition of metal ions into the nanopore detection systems enhances the sensitivity and selectivity through the changes of pore charges, the coordination with analytes or indirect detection. This review provides a summary on the role of metal ions in the application of nanopore detection technology.

Improved performance and stability in CH3NH3PbI3/Si heterojunction photodetectors realized by ZIF-67 additive assisted Co ion doping

Lead halide perovskites have been regarded as promising materials for fabrication of high-performance photodetectors (PDs). However, spin-coated perovskite thin films generally have suffered from high-density grain boundaries and defect states, which severely deteriorated the performance and stability of resulting PDs. Fortunately, the above issues can be effectively solved via additive assisted metal ions doping. In this work, Co-based zeolite imidazole framework (ZIF-67) additive assisted Co ion doping has been proposed to prepare high-quality perovskite CH3NH3PbI3 (MAPbI3) thin films. Morphological, structural, optical, and electrical studies have shown that Co ion doping decreased grain boundaries as well as suppressed defect states, which greatly enhanced the performance and stability of MAPbI3/Si heterojunction PDs, including reducing dark current, increasing photocurrent, and increasing response speed. Finally, the mechanisms of suppression of defect states benefiting from Co ion doping were discussed based on density functional theory calculations. The results provided in this work will pave the way for development of high-performance and stable MAPbI3 PDs in the future.

Biochemical Characterization of Ketapang Lipase: Its Preference to Short-Chain Fatty Acids despite the Long-Chain Fatty Acids Dominant Content

Lipases are versatile enzymes with high specificity toward lipid substrate. They have many industrial applications, such as in food, pharmacy, and green fuel. So far, most explored lipases are from microbial and animal sources, whereas those from plants are less studied. The present study aims to characterize ketapang (Terminalia catappa Linn) lipase. The lipase was isolated from germinating ketapang seeds. The activity was determined by hydrolysis of virgin coconut oil (VCO). Biochemical characterization of ketapang lipase includes the optimum temperature, pH, kinetics, metal ions addition, and analysis of substrate specificity. It was shown that ketapang lipase has an optimum temperature of 45 oC, pH 7.5. Ca2+ increases the lipase activity, whereas Na+, K+, Mg2+, Zn2+, Fe2+, and Cu2+ inhibit ketapang lipase to various extents. A comparison of SDS-PAGE and native-PAGE analysis showed that ketapang lipase consists of several protein subunits. A further test by in-gel assay revealed that the 54 kDa, 35 kDa, two bands at ~16 kDa, and 12 kDa proteins showed lipolytic activity against a-naphthyl palmitate substrate. When tested on various chromogenic fatty acid substrates, ketapang lipase showed the highest specificity against short-chain fatty acids (C4 and C8), despite the fact that ketapang oil seed composes mainly of long fatty acid (C18). Since lipases that have high lipolytic activity toward short fatty acids are considered esterases, the esterase activity of ketapang lipase is yet to be determined.

Precipitation of Pt, Pd, Rh, and Ru Nanoparticles with Non-Precious Metals from Model and Real Multicomponent Solutions.

This article presents studies on the precipitation of Pt, Pd, Rh, and Ru nanoparticles (NPs) from model and real multicomponent solutions using sodium borohydride, ascorbic acid, sodium formate, and formic acid as reducing agents and polyvinylpyrrolidone as a stabilizing agent. As was expected, apart from PGMs, non-precious metals were coprecipitated. The influence of the addition of non-precious metal ions into the feed solution on the precipitation yield and catalytic properties of the obtained precipitates was studied. A strong reducing agent, NaBH4 precipitates Pt, Pd, Rh, Fe and Cu NPs in most cases with an efficiency greater than 80% from three- and four-component model solutions. The morphology of the PGMs nanoparticles was analyzed via SEM-EDS and TEM. The size of a single nanoparticle of each precipitated metal was not larger than 5 nm. The catalytic properties of the obtained nanomaterials were confirmed via the reaction of the reduction of 4-nitrophenol (NPh) to 4-aminophenol (NAf). Nanocatalysts containing Pt/Pd/Fe NPs obtained from a real solution (produced as a result of the leaching of spent automotive catalysts) showed high catalytic activity (86% NPh conversion after 30 min of reaction at pH 11 with 3 mg of the nanocatalyst).

Structure and ion-dependent folding of k-junctions.

k-Junctions are elaborated forms of kink turns with an additional helix on the nonbulged strand, thus forming a three-way helical junction. Two were originally identified in the structures of Arabidopsis and Escherichia coli thiamine pyrophosphate (TPP) riboswitches, and another called DUF-3268 was tentatively identified from sequence information. In this work we show that the Arabidopsis and E. coli riboswitch k-junctions fold in response to the addition of magnesium or sodium ions, and that atomic mutations that should disrupt key hydrogen bonding interactions greatly impair folding. Using X-ray crystallography, we have determined the structure of the DUF-3268 RNA and thus confirmed that it is a k-junction. It also folds upon the addition of metal ions, though requiring a 40-fold lower concentration of either divalent or monovalent ions. The key difference between the DUF-3268 and riboswitch k-junctions is the lack of nucleotides inserted between G1b and A2b in the former. We show that this insertion is primarily responsible for the difference in folding properties. Finally, we show that the DUF-3268 can functionally substitute for the k-junction in the E. coli TPP riboswitch such that the chimera can bind the TPP ligand, although less avidly.

Synthesis of multicolor silver nanostructures for colorimetric sensing of metal ions (Cr3+, Hg2+ and K+) in industrial water and urine samples with different spectral characteristics

In this work, we have synthesized four different color (yellow, orange, green, and blue (multicolor)) silver nanostructures (AgNSs) by chemical reduction method where silver nitrate, sodium borohydride and hydrogen peroxide were used as reagents. The as-synthesized multicolor AgNSs were successfully functionalized with bovine serum albumin (BSA) and applied as a colorimetric sensor for the assaying of metal cations (Cr3+, Hg2+, and K+). The addition of metal ions (Cr3+, Hg2+, and K+) into BSA functionalized AgNSs (BSA-AgNSs) causes the aggregation of BSA-AgNSs, and are accompanied by visual color changes with red or blue shift in the surface plasmon resonance (SPR) band of BSA-AgNSs. The BSA-AgNSs show different SPR characteristic for each metal ions (Cr3+, Hg2+, and K+) with exhibiting different spectral shift and color change. The yellow color BSA-AgNSs (Y-BSA-AgNSs) act as a probe for sensing Cr3+, orange color BSA-AgNSs (O-BSA-AgNSs) act as probe for Hg2+ ion assay, green color BSA-AgNSs (G-BSA-AgNSs) act as a probe for the assaying of both K+ and Hg2+, and blue color BSA-AgNSs (B-BSA-AgNSs) act as a sensor for colorimetric detection of K+ ion. The detection limits were found to be 0.26 μM for Cr3+ (Y-BSA-AgNSs), 0.14 μM for Hg2+ (O-BSA-AgNSs), 0.05 μM for K+ (G-BSA-AgNSs), 0.17 μM for Hg2+ (G-BSA-AgNSs), and 0.08 μM for K+ (B-BSA-AgNSs), respectively. Furthermore, multicolor BSA-AgNSs were also applied for assaying of Cr3+, and Hg2+ in industrial water samples and K+ in urine sample.

Ligand-Directed Metalation of a Gold Pyrazolate Cluster.

Solid "[AuL]" (HL = 3-[pyrid-2-yl]-5-tertbutyl-1H-pyrazole) can be crystallized as cyclic [Au3(μ-L)3] and [Au4(μ-L)4] clusters from different solvents. The crystalline tetramer contains a square Au4 core with an HT:TH:TH:HT arrangement of ligand substituents, which preorganizes the cluster to chelate to additional metal ions via its pendant pyridyl groups. The addition of 0.5 equiv of AgBF4 to [AuL] yields [Ag2Au4(μ3-L)4][BF4]2, where two edges of the Au4 square are spanned by Ag+ ions via metallophilic Ag···Au contacts. Treatment of [AuL] with [Cu(NCMe)4]PF6 affords the metalloligand helicate [Cu2Au2(μ-L)4][PF6]2, via oxidation of the copper and partial fragmentation of the cluster.

Immobilization of Subtilisin Carlsberg and its use for transesterification of N-acetyl-L-phenylalanine ethyl ester in organic medium.

In this study, inorganic-based carrier perlite (PER) and cyclodextrin-modified perlite (PER-CD) were used for Subtilisin Carlsberg (SC) immobilization. For enzyme immobilization, the supports aminated with 3-aminotriethoxysilane were first activated with glutaraldehyde (GA) and genipin (GE), and then, the immobilized enzymes (PER-SC and PER-CD-SC) were obtained. The reaction medium for SC immobilization consisted of 500mg carrier and 5ml (1mg/ml) enzyme solution. The immobilization conditions were pH 8.0, 25°C, and 2h incubation time. Free and immobilized SC were used for transesterification of N-acetyl-L-phenylalanine ethyl ester (APEE) with 1-propanol in tetrahydrofuran (THF). The transesterification activity of the enzyme and the yield of the transesterification reaction were determined by gas chromatography (GC). 50mg of immobilized or 2.5mg of free SC was added to the reaction medium, which was prepared as 1mmol APEE and 10mmol alcohol in 10mL of THF. The conditions for the transesterification reaction were 60°C and 24h of incubation. The structure and surface morphology of the prepared carriers were characterized using scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). Casein substrate was used in the optimization study. The optimum temperature and pH for SC activity were found to be 50°C and pH 8.0, respectively, for free and immobilized SC. The thermal stability of immobilized SC was found to be greater than that of free SC. At the end of 4h of exposure to high temperature, the immobilized enzyme maintained its activity at approximately 50%, while the free enzyme was maintained at approximately 20%. However, modification with cyclodextrin did not alter the thermal stability. The transesterification yield was found to be approximately 55% for the free enzyme, while it was found to be approximately 68% and 77% for PER-SC and PER-CD-SC, respectively. The effect of metal ions and salts on transesterification yield was examined. The results showed that the addition of metal ions decreased the percentage of transesterification by approximately 10% compared to the control group, whereas the addition of salt significantly decreased the percentage of transesterification by 60-80% compared to the control group.

Metal additives for boosting hydrogen production in anaerobic fermentation: Focus on the change of gene expression and cost analysis

Dark fermentation has emerged as a promising strategy for sustainable hydrogen production. However, the low hydrogen yield produced by anaerobic microbes continues to be a challenge. Although metal ion additives have been proposed to enhance hydrogen production, their entire impacts and underlying mechanisms are poorly understood. The present study aimed to examine the effects of Fe2+, Ni2+, Mg2+, and Mo6+ on dark fermentative hydrogen production, as well as their influences on microbial community analysis and gene expression in a batch system. The experiments were conducted under anaerobic conditions at 37 °C, utilizing 100 mM glucose as a substrate and an initial pH of 6.8. The results showed that Mo6+ at 0.015 mg-Mo6+/L significantly enhanced the hydrogen yield (2.21-fold increment) by upregulating nitrogenase gene expression (2.19-fold increment). Fe2+ at 50 mg-Fe2+/L was the second most effective metal ion, with a 1.81-fold increase in hydrogen yield and upregulation of ferredoxin (1.83-fold increment) and pyruvate formate-lyase gene (3.36-fold increment) expression. Mg2+ at 70 mg-Mg2+/L and Ni2+ at 25 mg-Ni2+/L also increased hydrogen yield by 1.51-fold and 1.31-fold, respectively, with upregulation of glyceraldehyde-3-phosphate dehydrogenase (1.02-fold and 1.81-fold increments, respectively) and ATP synthase (1.46-fold and 1.10-fold increments, respectively) expressions for both metal additives, pyruvate formate-lyase (2.77-fold increment) and pyruvate kinase (1.44-fold increment) gene expression for Mg2+. Regarding the mixed metal approach, it was observed that although certain combinations of mixed metals, such as Mg2++Mo6+, resulted in an enhancement of hydrogen yield by a factor of 1.37-fold, the increment was found to be lower than that of an individual metal. Therefore, the results of this study suggest that using a single metal would be more effective. Economic potential calculations further revealed that Mo6+ exhibited the highest economic feasibility, with the lowest expense of 2.02x10−5 $-metal/m3-H2, accounting for 0.002% of the average total production cost. This was followed by Mg2+, Fe2+, and Ni2+. Overall, our findings provide mechanistic insights into the use of metal ion additives for clean hydrogen production and offer a foundation for optimising their economic feasibility in large-scale hydrogen production.