Redox Titration Research Articles

PHYTOCONSTITUENTS AND IN VITRO ANTI-UROLITHIATIC ACTIVITY OF VARIOUS HYDROPHILIC EXTRACTS OF TERMINALIA CATAPPA LEAVES ON CALCIUM OXALATE CRYSTAL

Background: Medicinal plants play an important role in the alternative or complement therapy to manage of urinary stones at this time. Terminalia genus was proved anti-urolithiatic activity via in vitro inhibition of calcium oxalate formation. Among the samples, Terminalia catappa showed as a potential plants for this activity in India. Moreover, they were a common plant species in Vietnam and there was no research on this topic in our country. Objectives: To evaluate in vitro antiurolithiatic activity of Terminalia catappa leaves in Vietnam, through inhibition of calcium oxalate formation. In addition, moisture value, preliminary screening of the chemical composition and determination of tanninoid content of aqueous extract also were conducted. Materials and methods: Moisture content of herbs was conducted according to guidelines of 5th Vietnam pharmacopoeia, appendix 9.6. Qualitation of the phytochemical constituents of aqueous extract with appropriate reagents to confirm the presence of natural compounds via chemical reactions. Determination of tanninoid content of aqueous extract was evaluated by using oxidation-reduction titration method (Lowenthal assay) and skin powder method in instructing of appendix 12.6 from 5th Vietnam pharmacopoeia. Inhibitory effect of calcium oxalate formation of three hydrophilic extracts (45% ethanol, 96% ethanol and aqueous extracts) was confirmed by nucleation assay with cystone as a positive control. Results: Moisture content of medicinal plant was 11.625%. Terminalia catappa leaves contain the major phytochemical constituents such as flavonoids, tanninoids and saponins. The tanninoid content according to Lowenthal method and skin powder method were 10.88% and 10.70%, respectively. Therefore, the average tannin content was confirmed to be approximately 10.79%. Among the investigated samples, aqueous extract showed the best inhibitory activity of calcium oxalate crystal formation with an IC50 of 602.67 μg/mL when compared to cystone with IC50 423.05 μg/mL. Conclusions: The aqueous extract from Terminalia catappa leaves has been shown to be a promising source for anti-calcium oxalate crystals formation activity on experimental model. The anti-urolithic potential of Terminalia catappa leaves may be related to its major phytoconstituents.

Mutant Cytochrome C as a Potential Detector of Superoxide Generation: Effect of Mutations on the Function and Properties.

Cytochrome c (CytC) is a single-electron carrier between complex bc1 and cytochrome c-oxidase (CcO) in the electron transport chain (ETC). It is also known as a good radical scavenger but its participation in electron flow through the ETC makes it impossible to use CytC as a radical sensor. To solve this problem, a series of mutants were constructed with substitutions of Lys residues in the universal binding site (UBS) which interact electrostatically with negatively charged Asp and Glu residues at the binding sites of CytC partners, bc1 complex and CcO. The aim of this study was to select a mutant that had lost its function as an electron carrier in the ETC, retaining the structure and ability to quench radicals. It was shown that a mutant CytC with substitutions of five (8Mut) and four (5Mut) Lys residues in the UBS was almost inactive toward CcO. However, all mutant proteins kept their antioxidant activity sufficiently with respect to the superoxide radical. Mutations shifted the dipole moment of the CytC molecule due to seriously changed electrostatics on the surface of the protein. In addition, a decrease in the redox potential of the protein as revealed by the redox titrations of 8Mut was detected. Nevertheless, the CD spectrum and dynamic light scattering suggested no significant changes in the secondary structure or aggregation of the molecules of CytC 8Mut. Thus, a variant 8Mut with multiple mutations in the UBS which lost its ability to electron transfer and saved most of its physico-chemical properties can be effectively used as a detector of superoxide generation both in mitochondria and in other systems.

Enhancement of electrochemical performance of SrFe0.5Co0.5O3-δ as air electrode for intermediate temperature solid oxide cells via Sb and Mo doping

Optimisation of the composition or rare-earth-free perovskites is of considerable interest for their application as air electrodes in intermediate temperature solid oxide cells (IT-SOCs). Herein, we report the effects of Mo and Sb doping (5 mol %) of SrFe0.5Co0.5O3-δ (SFC) on oxygen content, thermal behaviour, electrochemical properties and stability. Phase-pure, XRD-cubic perovskite is achieved on sintering powder derived from Pechini synthesis in the range 1000-1100 °C for SFC, SrFe0.475Co0.475Mo0.05O3-δ (SFCM) and SrFe0.475Co0.475Sb0.05O3-δ (SFCSb). Oxygen content determined by redox titration is greater for the Mo- and Sb-doped phases than for SFC, although oxygen loss occurring at > 350 °C is greatest for SFCSb. The higher total oxygen content of the Mo-doped phase is expected to increase the electron-hole content resulting in higher conductivity (σ = 340.5 S cm−1 at 300 °C in O2). In contrast, the greater oxygen-vacancy content with increasing temperature of the Sb-doped material is associated with the most competitive electrode-polarisation resistance (<0.1 Ω cm2 at 700 °C). The greater relative effect of cathodic and anodic polarisation on improving electrochemical performance at lower temperatures highlights the potential of the studied compositions as air electrodes in IT-SOCs.

Separating O-Redox and Mn-Redox Voltage Hysteresis in a Cation-Disordered Rock-Salt Cathode

Pronounced voltage hysteresis is commonly associated with oxygen redox in Li-excess cathode materials. However, they often involve coexisting transition-metal and oxygen redox, whose contributions to hysteresis are challenging to distinguish. In this work, a two-step aqueous redox titration was developed with the aid of mass spectrometry (MS) gas analyzer to quantify two coexisting solid-phase analytes, namely oxidized oxygen and Mn3+/4+ in a representative Li-excess cation-disordered rock salt (DRX) material. Two MS-countable gas molecules evolve from two separate titrant-analyte reactions, which allows decoupling Mn and O redox capacities. As incremental redox capacities are quantitatively decoupled, each redox voltage hysteresis can be further evaluated through deconvoluted energy efficiency and overvoltages. Overall, a low DRX operating efficiency arises not only from quasi-static voltage hysteresis of O redox, but also from asymmetric Mn-redox overvoltages. The results reveal that O redox is not always the only culprit for a low energy efficiency and slow kinetics, but instead discharging overvoltage, associated with transition-metal redox, can significantly drag down overall operating efficiency. This work further shows the potential of designing new analytical workflow to experimentally diagnose various DRX materials and inform improvement direction.

The Quantitative Determination of Oxacillin Using Kinetiс-Spectrophotometric and Redox Titration Methods

The search for new analytical reactions and finding out the optimal conditions for their course, which can be used as the basis for quantitative analytical determinations of penicillins, is a very urgent task.Aim. To develop methods for the quantitative determination of Oxacillin.Materials and methods. The study object was Oxacillin sodium salt powder in vials for preparing a solution for injections(0.5 g). Peroxomonosulfate acid as triple potassium salt 2КНSO5∙КНSO4∙K2SO4 (Oxone®) of “extra pure” grade was used as an oxidant. The methods of kinetic spectriphotometry and redox titration were used.Results and discussion. A simple procedure for the quantitative determination of the Oxacillin pure substance by the kinetic spectrophotometry and redox titration methods using potassium hydrogen peroxomonosulfate (KHSO5) has been developed. The results of the drug analysis obtained by newly developed and current methods are in good agreement with each other; δ (correctness) = (0.45 – 0.86) %.Conclusions. Using the methods of kinetic spectrophotometric and redox titration, two independent procedures for thequantitative determination of oxacillin in the substance and the drug product have been developed using potassium hydrogen peroxomonosulfate as an analytical reagent (KHSO5). A relative standard deviation RSD = (1.24 – 2.17) %.

Thermodynamic Two-Site Surface Reaction Model for Predicting Munition Constituent Reduction Kinetics with Iron (Oxyhydr)oxides.

Iron (oxyhydr)oxides comprise a significant portion of the redox-active fraction of soils and are key reductants for remediation of sites contaminated with munition constituents (MCs). Previous studies of MC reduction kinetics with iron oxides have focused on the concentration of sorbed Fe(II) as a key parameter. To build a reaction kinetic model, it is necessary to predict the concentration of sorbed Fe(II) as a function of system conditions and the redox state. A thermodynamic framework is formulated that includes a generalized double-layer model that utilizes surface acidity and surface complexation reactions to predict sorbed Fe(II) concentrations that are used for fitting MC reduction kinetics. Monodentate- and bidentate Fe(II)-binding sites are used with individual oxide sorption characteristics determined through data fitting. Results with four oxides (goethite, hematite, lepidocrocite, and ferrihydrite) and four nitro compounds (NB, CN-NB, Cl-NB, and NTO) from six separate studies have shown good agreement when comparing observed and predicted surface area-normalized rate constants. While both site types are required to reproduce the experimental redox titration, only the monodentate site concentration controls the MC reaction kinetics. This model represents a significant step toward predicting the timescales of MC degradation in the subsurface.

Diet typology as a factor of influence on environmental aspects of human life activity

Purpose. To analyze the influence of the typology of food of the population of a certain geographical region on the health and life expectancy of people in that region. To identify biologically active substances with a positive effect on the health in order to use them in the development of health food products. Methods. The antioxidant properties of red grape skin powder and its water-alcohol extract were studied. The moisture content of the obtained powder is no more than 6-7.5%. The powder of grape skins and its water-alcohol extract were introduced in the amount of 1% by mass into the model raw materials. Model raw materials are vegetable fats and oils. This raw material contains triglycerides of mono- and polyunsaturated higher carboxylic acids, which are subject to oxidation in air. This model raw were used to evaluate the antioxidant activity of the powder and water-alcohol extract of the powder of red grape skins. The antioxidant properties of the biologically active substances of the powder of the skins of red grape varieties were studied by the redox titration method. Results. The introduction of powder or water-alcohol extract of the skin of red grape varieties into the model raw material increases the resistance of the raw material to oxidation. The addition of a water-alcohol extract inhibits the oxidation process more effectively than the powder. Research in model conditions at temperature showed that the peroxide value of vegetable fat increases by 1.1 times when the extract is added, sunflower oil and olive oil - by 1.6 times. Under these conditions, the peroxide number of control samples without additives increased by 2.3 times for vegetable fat, and by 2.5 times for sunflower and olive oils. The skin of red grapes is a source of antioxidants. Antioxidant properties are preserved by the powder obtained from the skin of red grape varieties by drying, as well as by the water-alcohol extract of this powder. Conclusions. The skin of red grape varieties contains biologically active substances of the polyphenolic and stem series. These substances are powerful antioxidants. The skin of red grape varieties can be used in the technology of food for specific health purposes. This food to prevent heart diseases and gerontological purposes.

Enzymatic Birch Reduction via Hydrogen Atom Transfer at an Aqua-Tungsten-bis-Metallopterin Cofactor

The Birch reduction is a widely used synthetic tool to reduce arenes to 1,4-cyclohexadienes. Its harsh cryogenic reaction conditions and the dependence on alkali metals have motivated researchers to explore alternative approaches. In anaerobic aromatic compound degrading microbes, class II benzoyl-coenzyme A (CoA) reductases (BCRs) reduce benzoyl-CoA to the conjugated cyclohexa-1,5-diene-1-carboxyl-CoA (1,5-dienoyl-CoA) at a tungsten-bis-metallopterin (MPT) cofactor. Though previous structure-based computational studies were in favor of a Birch-like reduction via W(V)/radical intermediates, any experimental evidence for such a mechanism was lacking. Here, we combined freeze-quench and equilibrium electron paramagnetic resonance (EPR) spectroscopic analyses in H2O, D2O, and H217O with redox titrations using wild-type and molecular variants of the catalytic BamB subunit of class II BCR from the anaerobic bacterium Geobacter metallireducens. We provide spectroscopic evidence for a kinetically competent radical/W(V)–OH intermediate obtained after hydrogen atom transfer from the W-aqua-ligand to the aromatic ring and for an invariant histidine as a proton donor assisting the second electron transfer. Quantum mechanical/molecular mechanical calculations suggest that the unique tetrahydro state of both pyranopterins is essential for the reversibility of enzymatic Birch reduction. This work elucidates nature’s solution for the chemically demanding Birch reduction and demonstrates how the reactivity of MPT cofactors can be expanded to highly challenging radical chemistry at the negative limit of the biological redox window.

Tuning the Type 1 Reduction Potential of Multicopper Oxidases: Uncoupling the Effects of Electrostatics and H-Bonding to Histidine Ligands.

In multicopper oxidases (MCOs), the type 1 (T1) Cu accepts electrons from the substrate and transfers these to the trinuclear Cu cluster (TNC) where O2 is reduced to H2O. The T1 potential in MCOs varies from 340 to 780 mV, a range not explained by the existing literature. This study focused on the ∼350 mV difference in potential of the T1 center in Fet3p and Trametes versicolor laccase (TvL) that have the same 2His1Cys ligand set. A range of spectroscopies performed on the oxidized and reduced T1 sites in these MCOs shows that they have equivalent geometric and electronic structures. However, the two His ligands of the T1 Cu in Fet3p are H-bonded to carboxylate residues, while in TvL they are H-bonded to noncharged groups. Electron spin echo envelope modulation spectroscopy shows that there are significant differences in the second-sphere H-bonding interactions in the two T1 centers. Redox titrations on type 2-depleted derivatives of Fet3p and its D409A and E185A variants reveal that the two carboxylates (D409 and E185) lower the T1 potential by 110 and 255-285 mV, respectively. Density functional theory calculations uncouple the effects of the charge of the carboxylates and their difference in H-bonding interactions with the His ligands on the T1 potential, indicating 90-150 mV for anionic charge and ∼100 mV for a strong H-bond. Finally, this study provides an explanation for the generally low potentials of metallooxidases relative to the wide range of potentials of the organic oxidases in terms of different oxidized states of their TNCs involved in catalytic turnover.

Hole and Electron Doping Outcomes in Bi2YO4Cl.

Recognizing the deficiency in the hole and electron doping outcomes in layered bismuth-based oxyhalides intergrowths, the current study was addressed to the doping of Ca2+ and Zr4+ for Y3+ in Bi2YO4Cl. The samples were rapidly synthesized by a sol-gel auto combustion method and characterized extensively. Up to 30 mol % Y could be substituted with Ca in tetragonal symmetry and without the appearance of any additional phase. The unit cell parameters varied nonlinearly with the elongation of the Y-O bond. The Raman spectra supported the local site distortion. The calcium-substituted samples displayed selected area electron diffraction characteristics similar to those of Bi2YO4Cl. A blueshift of the absorption edge was noticed with increasing calcium content yielding optical band gap values in the 2.40-2.57 eV range. The creation of 10% Bi5+ in Bi2Y0.70Ca0.30O4Cl was established with the help of XPS measurements and redox titrations. The higher reactivity of Bi5+ in an aqueous solution has been demonstrated for the oxidation of As(III) to As(V). Electron doping through Zr4+ incorporation was possible up to 30 mol % in Bi2YO4Cl. The Y-O bonds are contracted, and the Bi-O bonds are elongated with increasing Zr4+ content. Zr4+'s incorporation induced a local distortion. The color of the sample changed from bright yellow to deep yellow with Zr inclusion, resulting in a progressive decrease in optical band gap values. The introduction of electrons caused the reduction of 13.6% of Bi(III) to Bi(0). These results have established the vulnerability of Bi2O2 chains to charge carriers in Bi2YO4Cl. Density functional theory (DFT) calculations were implemented to understand the electronic and optical properties of the pristine and doped compounds. From the band structure calculations, the chosen compounds were found to be indirect band gap semiconductors. The results of the DFT calculations were in good agreement with the experiment; however, for the doped cases, virtual crystal approximation has been used considering uniform doping at the Y-site.

A Refined Redox Titration Simulation Program for the Simple System

Commonly used methods to simulate the oxidation–reduction (redox) titration curves include the three-step method and the rigorous method. The simple three-step method simulates the redox titration curve with the assumption that the reaction is complete, which is widely used in undergraduate quantitative analysis courses. For the rigorous simulation method, the concentrations of the components are obtained throughout the titration by solving the equilibrium equation, and then the potential is obtained based on the Nernst equation. However, both methods have certain defects. In this work, a user-friendly program that uses an optimized rigorous algorithm to simulate the redox titration curve of a simple system with n1 = n2 = 1 at different potentials was built with LabVIEW. The program was then applied to the teaching of redox titration, and questionnaires from 15 students were used for evaluation. The results showed that the program improved students’ understanding of the principles of redox titration and deepened their graphical impression of Nernst equations.

Quantitative Decoupling of Oxygen‐Redox and Manganese‐Redox Voltage Hysteresis in a Cation‐Disordered Rock Salt Cathode

AbstractPronounced voltage hysteresis in Li‐excess cathode materials is commonly thought to be associated with oxygen redox. However, these materials often possess overlapping oxygen and transition‐metal redox, whose contributions to hysteresis between charge and discharge are challenging to distinguish. In this work, a two‐step aqueous redox titration is developed with the aid of mass spectrometry (MS) to quantify oxidized lattice oxygen and Mn3+ /4+ redox in a representative Li‐excess cation‐disordered rock salt—Li1.2Mn0.4Ti0.4O2 (LMTO). Two MS‐countable gas molecules evolve from two separate titrant‐analyte reactions, thereby allowing Mn and O redox capacities to be decoupled. The decoupled O and Mn redox coulombic efficiencies are close to 100% for the LMTO cathode, indicating high charge‐compensation reversibility. As incremental Mn and O redox capacities are quantitatively decoupled, each redox voltage hysteresis is further evaluated. Overall, LMTO voltage hysteresis arises not only from an intrinsic charge‐discharge voltage mismatch related to O redox, but also from asymmetric Mn‐redox overvoltages. The results reveal that O and Mn redox both contribute substantially to voltage hysteresis. This work further shows the potential of designing new analytical workflows to experimentally quantify key properties, even in a disordered material having complex local coordination environments.

English

The influence of aqueous extract of millet on the crystallization and the dissolution of calcium oxalate (CaOx) crystals were investigated in detail under supersaturated and artificial urinary circumstances in order to understand the effect of the water-soluble components of millet on CaOx kidney stones in humans. To investigate the inhibition effect, different volumes of millet extract were added separately to the combined supersaturated and artificial urinary solutions while the crystal deposition process was monitored by UV-Vis and conductivity measurements. The harvested crystals were characterized by FT-IR, SEM, TGA, XRD and redox titrations so as to determine the structure and the morphology of CaOx crystals formed. Our findings indicate that the crystals obtained from inhibition and dissolution experiments were mainly calcium oxalate monohydrate (COM), the thermodynamically more stable phase. Furthermore, the results show that the millet extract has a promising inhibition effect in the supersaturated solution and in artificial urinary circumstances showing ~34 and ~26% decrease in crystal deposition, respectively, with 50 mL of millet extract compared to control experiments. The dissolution effect of millet extract is far superior to that of the inhibition effect. One gram of COM crystals completely disappeared when the crystals were washed ten times with 300 mL millet extracts. Under the same conditions, the control experiment showed only ~44% dissolution of COM crystals. Further investigations conducted with actual kidney stones under artificial urinary circumstances showed approximately 20% dissolution when washings were carried out using 300-mL portions of millet over one week. This novel finding may shed the light on the possible use of millet as a potential natural antiurolithic remedy to treat CaOx kidney stones in humans. Key words: Calcium oxalate, kidney stones, millet, inhibition, dissolution effect.

A Comparative Analysis of Vitamin C Concentration in Fruits Consumed Commonly in Middle Region of Gujarat

In the several areas of Analytical chemistry such as biochemistry, pharmaceutical and food applications, the quantitative analysis of vitamin C has become an important subject. Vitamin C plays an important role in maintaining human health. During COVID -19 pandemic and current situation of various influenza viral infections Vitamin C possesses positive impacts on curing infection and it may play a protective role through improving the immune system. There are numerous methods for the determination of vitamin C in a variety of natural samples, biological fluids and pharmaceutical formulations. In the present work, it was aimed to determine and compare the Vitamin C concentration in some fresh fruits available in the middle region of Gujarat by using Titrimetric and UV spectrophotometric methods. It was found that vitamin C content of fruits commonly consumed at middle region of Gujarat; highest in Guava (108.50 mg/100gm by UV Spectrophotometric method and 157.38 mg/100gm by Redox titration method) and lowest in pineapple (16.24 mg/100gm by UV Spectrophotometric method and 20.53 mg/100gm by Redox titration method). These observations may serve as pointers on selection of fruits that can be consumed to match the requirement of vitamin C.

ФИТОХИМИЧЕСКАЯ ХАРАКТЕРИСТИКА И АНТИОКСИДАНТНЫЕ СВОЙСТВА ТРАВЫ КЛЕВЕРА ЛУГОВОГО, ПРОИЗРАСТАЮЩЕГО НА ТЕРРИТОРИИ ОРЕНБУРГСКОЙ ОБЛАСТИ

Objective: to analyze the quantitative content and assess the severity of the total antioxidant activity of natural antioxidants of the herb of Trifolium pratense L., growing in the Orenburg region. Methodology: Herb of Trifolium pratense L. collected in Sakmarsky, Tyulgansky, Buzuluksky and Ponomarevsky districts of the Orenburg region was used as objects of research. The quantitative content of the sum of flavonoids and the sum of hydroxycinnamic acids was evaluated by differential UV spectrophotometry, the content of the sum of tannins and the sum of organic acids was found by titrimetry, the level of ascorbic acid was determined by redox titration. The severity of the total antioxidant activity of the studied plant raw materials was judged by the ability to inhibit the autoxidation of adrenaline. Statistical processing of primary data was carried out using the Microsoft Excel 2016 and Statistica 6.0 software package. Results. The analysis of the quantitative content of biologically active substances and the severity of the total antioxidant activity revealed the maximum accumulation of flavonoids, tannins, organic, hydroxycinnamic acids and the severity of the total antioxidant activity in the herb of meadow clover growing on the territory of the Ponomarevsky district, the largest accumulation of ascorbic acid – in the raw materials of meadow clover growing in the Tyulgansky district. Conclusion. The herb of Trifolium pratense L. which grows in the Orenburg region can be considered as a potential source of natural antioxidants (organic acids, phenolic compounds).

Application of Ideological and Political Education in Chemical Analysis Experiment under the Background of Emerging Engineering Education: Taking the Redox Titration Experiment as an Example

Application of Ideological and Political Education in Chemical Analysis Experiment under the Background of Emerging Engineering Education: Taking the Redox Titration Experiment as an Example

A novel method for Ion Exchange Capacity characterization applied to Anion Exchange Membranes for Water Electrolysers

Hydrogen production from water electrolysis, hydrogen fuel cells and redox flow batteries are the right approach for the renewable energy sector because the electricity generated by solar, wind, photovoltaic, hydroelectric can be managed with a carbon-free approach. These technologies all have in common one fundamental component: the membrane. Different types of membranes have been developed for both cationic and anionic exchange, and recently, research activity focalized on improving their performances is very fervent. One fundamental characteristic of a membrane is its Ion Exchange Capacity (IEC), i.e. the density of charged functionalizing groups. Within our research project NEMESI, funded by EU-PNRR (ID: RSH2B_000002), and dedicated to Anion Exchange Membrane Water Electrolysis, we studied and validated a novel alternative method to measure IEC. The present titration methods have limitations for the need of dedicated hardware or qualitative inspection of their color-turning endpoint. The proposed method, based on the redox titration of potassium ferricyanide with ascorbic acid, allows a quantitative and independent assessment based on both potentiometric and spectrophotometric measurements, along with the usually adopted visual observation, as the yellow-colored ferricyanide is reduced to colorless ferrocyanide. Moreover, if compared to the classical Mohr titration with silver nitrate, the new method can be carried out at variable ferricyanide concentrations during the addition of the ascorbic acid, so a complete curve of the redox reaction can be constructed: the initial ferricyanide ion load of the membrane (IEC) can thus be derived in a more precise way than with a single-point evaluation. Only one Ag/AgCl reference electrode and a platinum working electrode are required without any power supply/potentiostat. The proposed method was validated using Anion Exchange Membranes with known IEC.

Quantum Mechanical Calculations of Redox Potentials of the Metal Clusters in Nitrogenase.

We have calculated redox potentials of the two metal clusters in Mo-nitrogenase with quantum mechanical (QM) calculations. We employ an approach calibrated for iron-sulfur clusters with 1-4 Fe ions, involving QM-cluster calculations in continuum solvent and large QM systems (400-500 atoms), based on structures from combined QM and molecular mechanics (QM/MM) geometry optimisations. Calculations on the P-cluster show that we can reproduce the experimental redox potentials within 0.33 V. This is similar to the accuracy obtained for the smaller clusters, although two of the redox reactions involve also proton transfer. The calculated P1+/PN redox potential is nearly the same independently of whether P1+ is protonated or deprotonated, explaining why redox titrations do not show any pH dependence. For the FeMo cluster, the calculations clearly show that the formal oxidation state of the cluster in the resting E0 state is MoIIIFe3IIFe4III , in agreement with previous experimental studies and QM calculations. Moreover, the redox potentials of the first five E0-E4 states are nearly constant, as is expected if the electrons are delivered by the same site (the P-cluster). However, the redox potentials are insensitive to the formal oxidation states of the Fe ion (i.e., whether the added protons bind to sulfide or Fe ions). Finally, we show that the later (E4-E8) states of the reaction mechanism have redox potential that are more positive (i.e., more exothermic) than that of the E0/E1 couple.

Effect of Different Cooking Methods on the Concentration of Vitamin C in Cowpea Vegetable (Vigna unguiculata)

Background: Vitamin C is a water-soluble vitamin widely distributed in nature, mostly rich in fresh fruits and green leafy vegetables. The amount of Vitamin C in a given food depends on soil condition, climate in their area of growth, storage condition after harvest, and methods of preparation. Much amount of Vitamin C in vegetables is lost during cooking and there are still limited information on the impact of different cooking methods on the vitamin C content in leafy vegetable like cowpea vegetable (Vigna unguiculata). It is upon this background that this study aimed to determine the concentration of Vitamin C in cowpea vegetable when cooked using different cooking methods.&#x0D; Methodology: Vitamin C concentration in a solution of cowpea vegetable cooked by different cooking methods (boiling, steaming and microwave methods) was determined by a redox titration using iodine in the presence of starch indicator. This was conducted at Busitema University, Faculty of Science and Education, Biology Laboratory in Uganda.&#x0D; Results: The study revealed that cooking cowpea vegetable using microwave yields the highest concentration of vitamin C (154.8 mg/L), followed by steaming (142.9 mg/L) and boiling yielding the least concentration of vitamin C (130.4 mg/L).&#x0D; Conclusion: The concentration of vitamin C obtained by the three methods of cooking cowpea vegetable has shown that microwaving method of cooking yields the highest concentration of vitamin C followed by steaming method and finally boiling. Further studies should be done to explain the variation of vitamin C concentration in cowpea vegetable when cooked using the above cooking methods. Similar studies should be conducted on other leafy vegetables which are potential sources of Vitamin C.

Mapping of well water and soil parameters in a selected grama niladhari division of Gampaha district

This study intends to fill an essential knowledge gap in the field of environmental information in Sri Lanka, by providing a reliable data bank supporting the information of existing chemical species of two important components, well water and soil. Further, this study would provide reference information for future work and aid in explaining the changes that would occur due to changes in the chemical composition of the environment. Thalawathuhenpita North Grama Niladhari division was selected as the initial site of study and sampling was done from 23 sites, where two representative samples of each soil and well water were collected from each site. This study investigates the well water quality parameters such as pH determined by a pH meter, hardness and Calcium content using complexometric titrations, nitrate content using a spectrometric analysis, Iron content using a colorimetric analysis, and soil quality parameters such as active pH using a pH meter, water-soluble and exchangeable cations(Na+,Ca2+,K+)using a flame photometer and complexometric titration, organic matter content using a redox titration, iron content and nitrate content as mentioned above. The readings were duplicated and reported as means ± standard deviation, and contour maps were produced using Surfer ® (Golden Software, LLC). Maps depict the scope of variation of the determined parameters within the selected area and highlight the point that it is crucial to monitor the environmental resources chemically in a regular manner to address the environmental problems that may occur in the future.