Redox Titration Research Articles

Quantification of Iron(II) in Supplements Using Redox Titration and UV–Visible Spectroscopy

Quantification of Iron(II) in Supplements Using Redox Titration and UV–Visible Spectroscopy

Comparative Evaluation of Mediated Electrochemical Reduction and Chemical Redox Titration for Quantifying the Electron Accepting Capacities of Soils and Redox-Active Soil Constituents.

The electron accepting capacity (EAC) of soil plays a pivotal role in the biogeochemical cycling of nutrients and transformation of redox-labile contaminants. Prior EAC studies of soils and soil constituents utilized different methods, reductants, and mediators, making cross-study comparison difficult. This study was conducted to quantify and compare the EACs of two soil constituents (hematite and Leonardite humic acid) and 12 soils of diverse composition, using chemical redox titration (CRT) with dithionite as the reductant and mediated electrochemical reduction (MER) with diquat as the mediator. The EACs of hematite and humic acid measured by CRT (EACCRT) and MER (EACMER) are similar and close to the theoretical/reported values. For soils, EACCRT and EACMER increased with iron and organic carbon (TOC) contents, suggesting iron and carbon were the main contributors to soil EAC. EACCRT > EACMER for all soils, and their difference (ΔEAC = EACCRT - EACMER) increased with TOC, presumably due to the longer contact time in CRT and thus more complete reduction of carbonaceous redox moieties. We propose an equation that relates EACCRT to EACMER (ΔEAC = 1796fTOC + 32) and another that predicts EACCRT from dithionite-reducible Fe and TOC (EACCRT = 2705 μmol e-/g C × fTOC + 17907 μmol e-/g Fe × fFedithionite-reducible). Our results suggest that at least 10-15% of soil organic carbon contributed to EACCRT.

The experience of iron determination in technogenic materials with a high copper content by the redox titration method: case study of the waelz slag

Redox titration is one of the most common classical methods widely used in practice for the determination of total iron. A well-known procedure ISO 2597-1 (GOST 32517) includes the decomposition of a sample with dissolution, the reduction of Fe3+ to Fe2+ using a SnCl2 solution and its titration with a K2Cr2O7 solution in the presence of sodium or barium diphenylaminosulfonate as an indicator. We propose to use potassium tetrahydroborate KBH4 as a reducing agent for Fe3+ to Fe2+ instead of SnCl2 to modify a titrimetric method of total iron determination. The features of the well-known and considered methods are studied when using sintering for sample decomposition during the analysis of a large number of samples. Application of the developed method for the analysis of standard samples and technogenic materials with a high copper content, namely, Waelz slag showed a satisfactory accuracy and reproducibility of the obtained values of the total iron content. The results obtained indicate the possibility of the application of this method to the iron determination in the samples with a high copper content without an additional step of the iron separation from copper. A high productivity of the analysis (apart from the absence of the separation stage) is achieved due to the simplicity of the reduction process occurred at room temperature, no need for the control of the added amount of the reducing agent, and the possibility of holding the solutions for a long time before the titration. These advantages along with the no need for using toxic mercury compounds during the analysis make the method attractive for the analysis of a large number of samples.

Polar Interactions between Substrate and Flavin Control Iodotyrosine Deiodinase Function.

Flavin cofactors offer a wide range of chemical mechanisms to support a great diversity in catalytic function. As a corollary, such diversity necessitates careful control within each flavoprotein to limit its function to an appropriate subset of possible reactions and substrates. This task falls to the protein environment surrounding the flavin in most enzymes. For iodotyrosine deiodinase that catalyzes a reductive dehalogenation of halotyrosines, substrates can dictate the chemistry available to the flavin. Their ability to stabilize the necessary one-electron reduced semiquinone form of flavin strictly depends on a direct coordination between the flavin and α-ammonium and carboxylate groups of its substrates. While perturbations to the carboxylate group do not significantly affect binding to the resting oxidized form of the deiodinase, dehalogenation (kcat/Km) is suppressed by over 2000-fold. Lack of the α-ammonium group abolishes detectable binding and dehalogenation. Substitution of the ammonium group with a hydroxyl group does not restore measurable binding but does support dehalogenation with an efficiency greater than those of the carboxylate derivatives. Consistent with these observations, the flavin semiquinone does not accumulate during redox titration in the presence of inert substrate analogues lacking either the α-ammonium or carboxylate groups. As a complement, a nitroreductase activity based on hydride transfer is revealed for the appropriate substrates with perturbations to their zwitterion.

Influence of Oxygen Vacancies in La0.4Sr0.6FeO3-δ Perovskite Oxide Nanoparticles for the Oxygen Evolution Reaction

Iron incorporation is one of the key factors to generate highly active NiFe(OH)x electrocatalysts for the oxygen evolution reaction (OER). However, it remains controversial whether Fe(IV) is present during OER and how the oxygen vacancies in Fe(IV)-containing metal oxides affect their activities. In this work, we develop a facile approach to control oxygen vacancy content, via an ozone treatment under ambient pressure during cooling for the synthesis of La1-x Sr x FeO3-δ (0 ≤ x ≤ 1, 0 ≤ δ ≤ 0.5x) perovskite oxides - an important class of energy-related materials that contain a rare Fe(IV) oxidation state. We have initially synthesized a series of La1-x Sr x FeO3-δ compounds using a polymerized complex method. The concentration of oxygen vacancies and Fe(IV) are determined by redox titration, and the crystal structures are derived by analyzing X-ray diffraction patterns using Rietveld refinement. Significant amounts of oxygen vacancies are found in the as-synthesized compounds with x ≥ 0.8: La0.2Sr0.8FeO3-δ (δ = 0.066) and SrFeO3-δ (δ = 0.195). A subsequent ambient-pressure ozone treatment approach is able to substantially reduce the amount of oxygen vacancies in these compounds to achieve levels near the ideal oxygen stoichiometry of 3 for La0.2Sr0.8FeO3-δ (δ = 0.006) and SrFeO3-δ (δ = 0.021). The oxygenation/deoxygenation kinetics can be tuned by the cooling rate after annealing. As the oxygen vacancy concentration decreases, the structure of SrFeO3-δ evolves from orthorhombic to cubic, demonstrating that the crystal structures in metal oxides can be highly sensitive to the number of oxygen vacancies. We have further conducted a systematic evaluation of the OER activity and stability of La1-x Sr x FeO3-δ perovskites in 1 M KOH. Their initial OER activity first increases with increasing Sr content (from x = 0 to 0.8), and then decreases when the Sr content is increased to 1. Their stability, as evaluated by monitoring element leaching from the electrodes show that La does not leach at a detectable rate, but Sr and Fe leach substantially. The leaching of Sr occurs at similar rates under open circuit potential (OCP) and OER potential, suggesting a nonelectrochemical dissolution process. The leaching of Fe is, however, strongly dependent on the electrode potential. More Fe leaching is observed at the OER potential than OCP. Additionally, the electrode with higher initial OER activity leaches more Fe. These results indicate that OER facilitates the dissolution of Fe from the electrode. The leaching of Fe, in turn, is considered responsible for the activity loss of La1- x Sr x FeO3- δ during OER. This study brings new insight into the degradation mechanism of La1- x Sr x FeO3- δ and related metal oxides during electro-oxidation processes.

The critical role of electron donating rate of pyrogenic carbon in mediating the degradation of phenols in the aquatic environment

Phenols are the widely detected contaminants in the aquatic environment. Pyrogenic carbon (PyC) can mediate phenols degradation, but the specific properties of PyC or phenols influencing this reaction remain unknown. The present study investigated the kinetic process and mechanism of removal of various phenols by different PyC in aqueous phase system. To avoid the impact of the accumulated degradation byproducts on the overall reaction, we conducted a short-term experiment, quantified adsorption and degradation, and obtained reaction rate constants using a two-compartment first-order kinetics model. The adsorption rate constants (ka) of phenols by PyC were 10–220 times higher than degradation rate constants (kd), and they were positively correlated. Interestingly, no correlation was found between kd and common PyC properties, including functional groups, electron transfer capacities, and surface properties. Phenols were primarily attacked by •OH in the adsorbed phase. But neither the instantly trapped •OH, nor the accumulated •OH could explain phenol degradation. Chemical redox titration revealed that the electron transfer parameters, such as the electron donating rate constant (kED) of PyC, correlated well with kd (r>0.87, P < 0.05) of phenols. Analysis of 13 phenols showed that Egap and ELUMO negatively correlated with their kd, confirming the importance of the electronic properties of phenols to their degradation kinetics. This study highlights the importance of PyC electron transfer kinetics parameters for phenols degradation and manipulation of PyC electron transfer rate may accelerate organic pollutant removal, which contributes to a deeper understanding of the environmental behavior and application of PyC systems.

A closer look at lithium-ion batteries in E-waste and the potential for a universal hydrometallurgical recycling process

The demand for lithium-ion batteries (LiBs) is rising, resulting in a growing need to recycle the critical raw materials (CRMs) which they contain. Typically, all spent LiBs from consumer electronics end up in a single waste stream that is processed to produce black mass (BM) for further recovery. It is desired to design a recycling process that can deal with a mixture of LiBs. Hence, this study investigates the structure and composition of battery modules in common appliances such as laptops, power banks, smart watches, wireless earphones and mobile phones. The battery cells in the module were disassembled into cell casing, cathode, anode and separator. Then, the cathode active materials (CAMs) were characterized in detail with XRD-, SEM-, EDX- and ICP-OES-analysis. No direct link was found between the chemistry of the active materials (NMC, LCO, LMO, LFP etc.) and the application. Various BM samples were submitted to a leaching procedure (2 M H2SO4, 50 °C, 2 h, 60 g BM/L) with varying concentration (0–4 vol%) of H2O2 to study the influence of their chemical composition on the dissolution of Li, Ni, Mn and Co. Only a part of the BMs dissolved completely at 4 vol% H2O2, which was attributed to the oxidation state of the transition metals (TMs). Exact determination of H2O2 consumption by redox titration confirmed this hypothesis.

Inquiry-based Investigation of the Influencing Factors on the Redox Titration Curves by Simulation

Inquiry-based Investigation of the Influencing Factors on the Redox Titration Curves by Simulation

A quantitative analysis of vitamin C in fruits, khat (Catha edulis), and pharmaceutical tablets using potassium iodate titration

Vitamin C, or ascorbic acid, is an essential antioxidant in various resources, such as pharmaceutical tablets, fruits, and vegetables. The human body cannot synthesize it by itself. This research aims to measure the vitamin C content in 29 commonly assessable compressed tablets, effervescent tablets, fruits, and khat (Catha edulis) leaves that are found in the Yemeni local markets. This study used a redox titration method with potassium iodate. These results reveal confirmed European and American standards and no significant difference between the measured vitamin C content in the commercial tablet (p &lt;0.05) and the amount stated on the product label, as well as the highest amount of vitamin C content in fruits in guava (111.21 mg/100 g), while the lowest amount of vitamin C is in apple (8.72 mg/100 g).

Influence of Conservation Methods on the sour cherry (Cerasus vulgaris Mill.) fruits quality

Objective: Sour cherry fruits (Cerasus vulgaris Mill.) belong to the Rosaceae family and are designed as a GRAS ingredient based on the FDA data. Animal experiments and clinical practice confirm that there are many positive pharmacological effects mainly related to anthocyanins. Development of standard regulations for this kind of medicinal plant raw materials is actual to introduce sour cherry fruits into official medical practice. In our research, we investigate macroscopic and microscopic properties and determine the content of tanning substances and anthocyanins in sour cherry fruits of various kinds of conservation. Materials and methods: Modern complex of physicochemical methods was used in pharmacognostical research. Microscopic analysis was performed on a LOMO Micmed-6 microscope with 10× eyepieces, 4×, 10×, 40× and 100× objectives, photographies were taken with a Sony Xperia Z3 compact digital camera. The content of total anthocyanins in terms of cyanidin-3-О-glucoside was determined by differential UV-spectrophotometry, total tannins content – by redox titration. Results and discussion: The anomocytic stomatal complex, fruits pulp druses, anthocyanins containing in the epidermis and fruits pulp cells, and vessels are typical signs for the sour cherry fruits anatomy structure. A conservation method has not to effect on visual representation of diagnostic signs. The contents of tanning substances are little; it is from 2.73±0.08% to 4.12±0.13% in terms of tannin. Maximal anthocyanin contents (in terms of cyanidin-3-glucoside and in absolutely dried raw material) were determined in fresh-frozen sour cherry fruits (after defrosting (with juice and without kernel) is 5.40±0.15% or in terms of moisture-containing raw materials (without kernel) – 0.690±0.019%. In the defrosted fruits without juice, the content of anthocyanins is two times lower in terms of completely dried raw material (without kernel), it is 2.77±0.12% or in terms of moisture-containing raw material (without kernel), it is 0.410±0.018%. In the juice released from cherry fruits after defrosting anthocyanin content in terms of cyanidin-3-glucoside is of 0.450±0.007% (g/100ml juice), in dried sour cherry fruits (without kernel) – 4.34±0.17%, which is lower than in fresh-frozen raw materials. It can be explained by the varietal features, as well by the conservation conditions; this matter is to be further studied. Contents of tanning substances in fresh-frozen and dried sour cherry fruits when storage during 4 months is insignificantly reduced, but it is established that contents of anthocyanin in terms of cyanidin-3-glucoside reduces 1.5 times in 4 months, if the raw material is frozen, and it reduces by 10% if the raw material is dried. Conclusion: Diagnostic signs of macroscopic and microscopic structures, contents of tanning substances and anthocyanins in terms of cyanidin 3-glycoside in sour cherry fruits were studied. The content of the main groups of biologically active substances decreases equally during storage of dried and frozen cherry fruits. When defrosting, it is necessary to carefully collect the juice, as it contains the bulk of the anthocyanins. It is promising to study various options for freezing and drying of cherry fruits with kernels in order to reduce the loss of fruits juice to a minimum. In this case, it is important to ensure that the kernels are whole (not destroyed), in order to avoid the ingress of cyanogenic glycosides into the medicinal plant material. The results will be used to develop normative documentation for sour cherry fruits.

Evaluation of Hypochlorite Concentration in Household Bleaches as Colour Removal Agent on Coloured Cotton Fabrics

Bleaches are known to remove stains from fabric. This study evaluates chlorine-based household bleaches as effective fabric colour removal agents and was conducted in the Chemistry and Textile laboratories of the Federal University of Agriculture, Abeokuta using experimental design. Five common household bleaches were collected from markets in study areas. The concentrations of Sodium hypochlorite in each bleach sample as indicated by the manufacturer were: A (3.85%), B (3.5%), C (not available), D (4.3%) and E (5.3%). To confirm the concentration of sodium hypochlorite in each bleach sample, Redox titration was conducted. One-minute Spot Test was used to determine the time taken for each bleach sample to remove colour (black, brown, navy blue, purple and army-green) from fabrics samples and similar test conducted with pure sodium hypochlorite (7.21% Chlorine) as control. The L*a*b* values for fabric colour change were obtained from images of the fabric samples using Fiji-Image J and Corel Photo-Paint 17. The laboratory analysis and evaluation revealed the concentration of hypochlorite in the bleaches samples as A: 0.36% (3.56 g/dm3), B: 3.5% (34.00g/dm3), C: 1.15% (11.48g/dm3), D: 4.29% (42.92g/dm3), and E: 0.06% (0.57g/dm3); therefore, established the information on bleaches B and D product package. The average time (seconds) to remove colour from fabric samples by bleach samples were A- 80.37; B- 19.60; C- 30.36; D- 20.10; E- no vivid colour change after 120.00 sec while colour change was obtained 7.00 sec by the control. Furthermore, Image J analysis and L*a*b* values show colour changes on fabric samples with Bleach B ((x ̅= 75.74) and D ((x) ̅= 61.22) most effective in colour removals. In conclusion, Chlorine base household bleaches containing above 1.0% V/v hypochlorite are suitable colour removal agents on coloured fabrics and not stain removals only. Consumers must be careful how to handle Chlorine household bleaches and coloured fabrics

Analysis of the electron transfer pathway in small laccase by EPR and UV–vis spectroscopy coupled with redox titration

Bacterial small laccases (SLAC) are promising industrial biocatalysts due to their ability to oxidize a broad range of substrates with exceptional thermostability and tolerance for alkaline pH. Electron transfer between substrate, copper centers, and O2 is one of the key steps in the catalytic turnover of SLAC. However, limited research has been conducted on the electron transfer pathway of SLAC and SLAC-catalyzed reactions, hindering further engineering of SLAC to produce tunable biocatalysts for novel applications. Herein, the combinational use of electron paramagnetic resonance (EPR) and ultraviolet–visible (UV–vis) spectroscopic methods coupled with redox titration were employed to monitor the electron transfer processes and obtain further insights into the electron transfer pathway in SLAC. The reduction potentials for type 1 copper (T1Cu), type 2 copper (T2Cu) and type 3 copper (T3Cu) were determined to be 367 ± 2 mV, 378 ± 5 mV and 403 ± 2 mV, respectively. Moreover, the reduction potential of a selected substrate of SLAC, hydroquinone (HQ), was determined to be 288 mV using cyclic voltammetry (CV). In this way, an electron transfer pathway was identified based on the reduction potentials. Specifically, electrons are transferred from HQ to T1Cu, then to T2Cu and T3Cu, and finally to O2. Furthermore, superhyperfine splitting observed via EPR during redox titration indicated a modification in the covalency of T2Cu upon electron uptake, suggesting a conformational alteration in the protein environment surrounding the copper sites, which could potentially influence the reduction potential of the copper sites during catalytic processes. The results presented here not only provide a comprehensive method for analyzing the electron transfer pathway in metalloenzymes through reduction potential measurements, but also offer valuable insights for further engineering and directed evolution studies of SLAC in the aim for biotechnological and industrial applications.

Composition of biologically active substances of common cranberry fruits (Oxycoccus palustris Pers.) in various methods of preservation

Introduction. The study of common cranberry fruits is promising due to the wide variety of biologically active substances included in their composition, a wide range of therapeutic properties, as well as the ability of cranberry fruits for long-term storage and resistance to harsh environmental conditions. Fresh fruits contain the maximum amount of biologically active substances and, accordingly, have the most pronounced pharmacological effect. To preserve the composition and content of biologically active substances, preservation is used in pharmacy. Most often they resort to drying. Freezing can be considered a new and promising method for preserving the quality of medicinal plant materials. Purpose of the study. Study of the effect of freezing and drying on the qualitative composition and quantitative content of biologically active substances in common cranberry fruits. Material and methods. The object of the study was fresh, frozen, and dried common cranberry fruits collected in the Pskov and Novgorod regions in 2022 during the fruiting period. The study of the composition of biologically active substances (BAS) and quantitative assessment of the content were carried out according to pharmacopoeial methods, using analysis using thin layer chromatography (TLC), spectrophotometry and redox titration methods. Results. Using TLC analysis, organic acids (ascorbic, malic, citric, tartaric and succinic), flavonoids (rutin, quercetin), tannins (gallic acid) and anthocyanins were identified in the fruits. There were no differences in the qualitative composition of dried and frozen fruits. The content of organic acids, tannins, flavonoids and anthocyanins in cranberry fruits using different preservation methods was determined. It has been established that when fruits are dried, the content of all studied groups of biologically active substances decreases, on average by 40–60% of the initial content in fresh raw materials. Ascorbic acid is destroyed to a greater extent (90–92%). Exposure to low temperatures leads to a slight decrease in biologically active substances in common cranberry fruits (7–14%). Conclusion. The influence of preservation methods on the composition and content of biologically active substances in common cranberry fruits has been studied. The possibility of using frozen cranberry fruits as an alternative to fresh and dried raw materials in the manufacture of drugs in allopathy and homeopathy has been shown.

Treatment of chromium (VI) waste solutions with clay-based adsorbents after reduction with acid mine drainage

South Africa has one of the largest Cr-related industries in the world and generates large amounts of Cr-containing smelter dusts. It is normal practice to scrub Cr from the furnace off-gas in water, and to recover the Cr by adsorption, followed by recycling of the loaded adsorbent into the furnace. A study was conducted to find a low-cost adsorbent that is capable of removing sufficient Cr from the solutions generated by scrubbing. The test work focused on the evaluation of different clay minerals (attapulgite, bentonite, and kaolinite) as adsorbents for Cr. Cr(VI) could only be adsorbed after prereduction with e.g. ascorbic acid (ASA). An 80% removal of Cr(VI) could be achieved from a solution containing 20 mg/L Cr using bentonite clay after reduction with ASA. Attapulgite and kaolinite adsorbed less than 55% Cr after reduction with ASA. Both ASA and ferrous salts were found to be suitable reducing agents. The use of acid mine drainage (AMD) was also investigated as a low-cost alternative reducing agent, as AMD usually contains iron. The Cr(VI) reduction potential of the AMD was determined by redox titration against a solution containing 50 mg/L Cr(VI). Studies show that AMD can potentially be used as a reducing agent in a Cr removal process if it is available on site.

Novel synthesis, characterization, and application of calcium ferrate (VI) in water treatment

Poor raw water quality has led science and technology research to explore more environmentally friendly water treatment methods, such as advanced oxidation processes. Ferrate (VI) salts have been regarded as a new green oxidant, cost-effective, and coagulant/flocculent in a single mixing and dosing unit in wastewater treatment. This research aimed to synthesize calcium ferrate (CaFeO4), a benign green chemical that can be utilized to treat water and wastewater through a facile wet oxidation process, with minimal increase in electrical conductivity. This study used the wet oxidation approach to synthesize stable aqueous calcium ferrate in an alkaline media using distilled water. During process optimization, CaFeO4 was synthesized and named 60-CaFeO4, 70-CaFeO4, 80-CaFeO4, and 90-CaFeO4, where the numbers represent the synthesis temperature. The prepared CaFeO4 was characterized using XRD, FT-IR, UV–Vis, TEM, SEM, Raman, and redox titration. FT-IR analysis confirmed the presence of the Fe–O stretching vibrations in all the freeze-dried CaFeO4 powders, signifying the successful preparation of the materials. The physicochemical characteristics of raw water, such as turbidity, color, COD, pH, EC, and TDS, were analyzed before and after treatment with CaFeO4. A jar test was performed to evaluate the reactivity and efficiency of the CaFeO4 toward wastewater treatment through coagulation/flocculation processes. After coagulation using CaFeO4, the pollutants levels were reduced COD (43.56–71.56%) and turbidity (97–99%), signifying the effectiveness of the as-prepared materials. CaFeO4 was successfully produced at various temperatures and was stable enough to be stored at room temperature for over six months without significantly decomposing.Graphical abstract

Redox potentials elucidate the electron transfer pathway of NAD+-dependent formate dehydrogenases

Metal-dependent, nicotine adenine dinucleotide (NAD+)-dependent formate dehydrogenases (FDHs) are complex metalloenzymes coupling biochemical transformations through intricate electron transfer pathways. Rhodobacter capsulatus FDH is a model enzyme for understanding coupled catalysis, in that reversible CO2 reduction and formate oxidation are linked to a flavin mononuclotide (FMN)-bound diaphorase module via seven iron-sulfur (FeS) clusters as a dimer of heterotetramers. Catalysis occurs at a bis-metal-binding pterin (Mo) binding two molybdopterin guanine dinucleotides (bis-MGD), a protein-based Cys residue and a participatory sulfido ligand. Insights regarding the proposed electron transfer mechanism between the bis-MGD and the FMN have been complicated by the discovery that an alternative pathway might occur via intersubunit electron transfer between two [4Fe4S] clusters within electron transfer distance. To clarify this difference, the redox potentials of the bis-MGD and the FeS clusters were determined via redox titration by EPR spectroscopy. Redox potentials for the bis-MGD cofactor and five of the seven FeS clusters could be assigned. Furthermore, substitution of the active site residue Lys295 with Ala resulted in altered enzyme kinetics, primarily due to a more negative redox potential of the A1 [4Fe4S] cluster. Finally, characterization of the monomeric FdsGBAD heterotetramer exhibited slightly decreased formate oxidation activity and similar iron-sulfur clusters reduced relative to the dimeric heterotetramer. Comparison of the measured redox potentials relative to structurally defined FeS clusters support a mechanism by which electron transfer occurs within a heterotetrameric unit, with the interfacial [4Fe4S] cluster serving as a structural component toward the integrity of the heterodimeric structure to drive efficient catalysis.

Thiol Redox Proteomics for Identifying Redox-Sensitive Cysteine Residues Within the Protein of Interest During Stress.

Redox modulation is a common posttranslational modification to regulate protein activity. The targets of oxidizing agents are cysteine residues(Cys), which have to be exposed at the surface of the proteins and are characterized by an environment that favors redox modulation. This includes their protonation state and the neighboring amino acids. The Cys redox state can be assessed experimentally by redox titrations to determine the midpoint redox potential in the protein. Exposed cysteine residues and putative intramolecular disulfide bonds can be predicted by alignments with structural data using dedicated software tools and information on conserved cysteine residues. Labeling with light and heavy reagents, such as N-ethylmaleimide (NEM), followed by mass spectrometric analysis, allows for the experimental determination of redox-responsive cysteine residues. This type of thiol redox proteomics is a powerful approach to assessing the redox state of the cell, e.g., in dependence on environmental conditions and, in particular, under abiotic stress.

Komparasi Metode Titrimetri Dengan Spektrofotometri UV-Vis pada Analisis Chemical Oxygen Demand (COD) Output IPAL Domestik Berdasarkan Linieritas, Akurasi dan Presisi

The method of a test must be evaluated and tested to ensure that the method is capable of producing valid data. So that validation needs to be done as a quality control that provides assurance that the measurements and results obtained are reliable. This study aims to determine the value and comparison of the values of linearity, accuracy, and precision of the titrimetric and spectrophotometric methods in COD analysis. Determination of the COD value for the titrimetric method was carried out by redox titration using a solution of Ferro Ammonium Sulphate (FAS). While the spectrophotometric method was carried out using UV-Vis spectrophotometry at a wavelength of 420 nm. The research results obtained a linear regression value for the titrimetric method of 0.9989, while the spectrophotometric method was 0.9991, this indicates that the linear regression value of the spectrophotometric method is better than the titrimetric method. The results of the accuracy analysis for the titrimetric method obtained a value of 111.48%, while for the spectrophotometric method it was 103.11%, this shows that the accuracy value of the spectrophotometric method is better than the titrimetric method. The precision analysis results for the titrimetric method obtained a value of 1.77%, while for the spectrophotometric method it was 1.55%, this shows that the spectrophotometric method has a better precision value than the titrimetric method. Based on the comparison of the results of statistical validation using the T-test, there was no significant difference in data between the titrimetric method and the spectrophotometric method.

Deductive approach to redox titration and kinetic-spectrophotometric methods for quantitative determination of ampicillin

The article considers the search for new analytical reactions that can be the basis of quantitative analytical determinations of penicillins. The optimal conditions for these reactions were determined. We developed two unified procedures have been and established the possibility of quantitative determination by the methods of kinetic-spectrophotometry and redox titration of ampicillin in a pure substance and drug by using potassium caroate. The scheme of the chemical transformation of ampicillin with the reaction of potassium caroate was proposed. The kinetics of the conjugated reactions of S-oxidation and perhydrolysis of ampicillin with potassium caroate in alkaline medium was studied by an increase in the light absorbance of the reaction product at 290 nm. The appearance of a new wave in kinetic-spectrophotometry created the possibility of developing a new procedure for the quantitative determination of ampicillin. The reaction rate was monitored spectrally and displayed in real time. A differential variation of the tangent method was used to process the kinetic data.

Increasing Reduction Potentials of Type 1 Copper Center and Catalytic Efficiency of Small Laccase from Streptomyces coelicolor through Secondary Coordination Sphere Mutations

AbstractThe key to type 1 copper (T1Cu) function lies in the fine tuning of the CuII/I reduction potential (E°′T1Cu) to match those of its redox partners, enabling efficient electron transfer in a wide range of biological systems. While the secondary coordination sphere (SCS) effects have been used to tune E°′T1Cu in azurin over a wide range, these principles are yet to be generalized to other T1Cu‐containing proteins to tune catalytic properties. To this end, we have examined the effects of Y229F, V290N and S292F mutations around the T1Cu of small laccase (SLAC) from Streptomyces coelicolor to match the high E°′T1Cu of fungal laccases. Using ultraviolet‐visible absorption and electron paramagnetic resonance spectroscopies, together with X‐ray crystallography and redox titrations, we have probed the influence of SCS mutations on the T1Cu and corresponding E°′T1Cu. While minimal and small E°′T1Cu increases are observed in Y229F‐ and S292F‐SLAC, the V290N mutant exhibits a major E°′T1Cu increase. Moreover, the influence of these mutations on E°′T1Cu is additive, culminating in a triple mutant Y229F/V290N/S292F‐SLAC with the highest E°′T1Cu of 556 mV vs. SHE reported to date. Further activity assays indicate that all mutants retain oxygen reduction reaction activity, and display improved catalytic efficiencies (kcat/KM) relative to WT‐SLAC.