Mathematical Model and Numerical Simulation of Conductometric Biosensor of Urea

In this article, a mathematical model was developed to describe and optimize the configuration of the urea biosensor. The biosensor is based on interdigitated gold microelectrodes modified with a urease enzyme membrane. The model presented here focuses on the enzymatic reaction and/or diffusion phenomena that occur in the enzyme membrane and in the diffusion layer. Numerical resolution of differential equations was performed using the finite difference technique. The mathematical model was validated using experimental biosensor data. The responses of the biosensor to various conditions were simulated to guide experiments, improve analytical performance, and reduce development costs.     

Water-Assisted Concerted Proton-Electron Transfer at Co(II)-Aquo Sites in Polyoxotungstates With Photogenerated RuIII(bpy)33+ Oxidant

The cobalt substituted polyoxotungstate [Co₆(H₂O)₂(α-B-PW₉O₃₄)₂(PW₆O₂₆)]¹⁷⁻ ( Co6 ) displays fast electron transfer (ET) kinetics to photogenerated Ru^III(bpy)₃³⁺, 4 to 5 orders of magnitude faster than the corresponding ET observed for cobalt oxide nanoparticles. Mechanistic evidence has been acquired indicating that: (i) the one-electron oxidation of Co6 involves Co(II) aquo or Co(II) hydroxo groups (abbreviated as Co6(II) −OH ₂ and Co6(II) −OH, respectively, whose speciation in aqueous solution is associated to a pK_a of 7.6), and generates a Co(III)−OH moiety ( Co6(III) −OH), as proven by transient absorption spectroscopy; (ii) at pH>pK_a, the Co6(II) −OH→Ru^III(bpy)₃³⁺ ET occurs via bimolecular kinetics, with a rate constant k close to the diffusion limit and dependent on the ionic strength of the medium, consistent with reaction between charged species; (iii) at pH <pK_a, the process involves Co6(II) − OH₂ → Co6(III)−OH transformation and proceeds via a multiple-site, concerted proton electron transfer (CPET) where water assists the transfer of the proton, as proven by the absence of effect of buffer base concentrations on the rate of the ET and by a H/D kinetic isotope in a range of 1.2–1.4. The reactivity of water is ascribed to its organization on the surface of the polyanionic scaffold through hydrogen bond networking involving the Co(II)−OH₂ group.     

Exploring Charged Polymeric Cyclodextrins for Biomedical Applications

Over the years, cyclodextrin uses have been widely reviewed and their proprieties provide a very attractive approach in different biomedical applications. Cyclodextrins, due to their characteristics, are used to transport drugs and have also been studied as molecular chaperones with potential application in protein misfolding diseases. In this study, we designed cyclodextrin polymers containing different contents of β- or γ-cyclodextrin, and a different number of guanidinium positive charges. This allowed exploration of the influence of the charge in delivering a drug and the effect in the protein anti-aggregant ability. The polymers inhibit Amiloid β peptide aggregation; such an ability is modulated by both the type of CyD cavity and the number of charges. We also explored the effect of the new polymers as drug carriers. We tested the Doxorubicin toxicity in different cell lines, A2780, A549, MDA-MB-231 in the presence of the polymers. Data show that the polymers based on γ-cyclodextrin modified the cytotoxicity of doxorubicin in the A2780 cell line.     

Study on the Correlation between the Protein Profile of Lupin Milk and Its Cheese Production Compared with Cow’s Milk

Australian sweet lupin, the largest legume crop grown in Western Australia, is receiving global attention from the producers of new foods. To understand the effect of protein on cheese yield, lupin milk proteins were separated from the first, second, and third filtrations by cheesecloths. However, proteins from the first and second were analyzed using two-dimensional polyacrylamide gel electrophoresis; then, the isolated proteins associated with cheese production were identified. The research also focused on identifying the optimal method of cheese production based on the coagulation process, temperature, yield, and sensory evaluation. Lupin curds from the two cultivars, Mandelup and PBA Jurien, were produced using vinegar, lemon juice, starter culture, vegetable rennet enzyme as coagulant, as well as curd generated using starter culture and vegetable rennet enzyme. Cow’s milk was used as a control. The results indicated that first-time filtration produced better extraction and higher yield of lupin proteins and cheese than the second filtration. A sensory analysis indicated that lupin cheese produced from PBA Jurien lupin milk using vinegar, 7.80% expressed as acetic acid, and ground in 45 °C water, was the most acceptable. The cheeses were examined for their protein, carbohydrates, fat, ash, and moisture contents. The concentration of protein was approximately 27.3% and 20.6%, respectively, in the cheese from PBA Jurien and Mandelup. These results suggest that lupin milk can adequately supply the proteins needed in human diets and, thus, could be used in the production of many existing products that require animal milk as an input.     

Mixed‐Metal MIL‐100(Sc,M) (M=Al,Cr, Fe) for Lewis Acid Catalysis and Tandem CC Bond Formation and Alcohol Oxidation

The trivalent metal cations Al³⁺, Cr³⁺, and Fe³⁺ were each introduced, together with Sc³⁺, into MIL‐100(Sc,M) solid solutions (M=Al, Cr, Fe) by direct synthesis. The substitution has been confirmed by powder X‐ray diffraction (PXRD) and solid‐state NMR, UV/Vis, and X‐ray absorption (XAS) spectroscopy. Mixed Sc/Fe MIL‐100 samples were prepared in which part of the Fe is present as α‐Fe₂O₃ nanoparticles within the mesoporous cages of the MOF, as shown by XAS, TGA, and PXRD. The catalytic activity of the mixed‐metal catalysts in Lewis acid catalysed Friedel–Crafts additions increases with the amount of Sc present, with the attenuating effect of the second metal decreasing in the order Al>Fe>Cr. Mixed‐metal Sc,Fe materials give acceptable activity: 40 % Fe incorporation only results in a 20 % decrease in activity over the same reaction time and pure product can still be obtained and filtered off after extended reaction times. Supported α‐Fe₂O₃ nanoparticles were also active Lewis acid species, although less active than Sc³⁺ in trimer sites. The incorporation of Fe³⁺ into MIL‐100(Sc) imparts activity for oxidation catalysis and tandem catalytic processes (Lewis acid+oxidation) that make use of both catalytically active framework Sc³⁺ and Fe³⁺. A procedure for using these mixed‐metal heterogeneous catalysts has been developed for making ketones from (hetero)aromatics and a hemiacetal.     

Magnetic Coupling Constants of Self‐Assembled CuII [3×3] Grids: Alternative Spin Model from Theoretical Calculations

This paper reports a theoretical analysis of the electronic structure and magnetic properties of a ferromagnetic Cu^II [3×3] grid. A two‐step strategy, combining calculations on the whole grid and on binuclear fragments, has been employed to evaluate all the magnetic interactions in the grid. The calculations confirm an S=7/2 ground state, which is in accordance with the magnetisation versus field curve and the thermal dependence of the magnetic moment data. Only the first‐neighbour coupling terms present non‐negligible amplitudes, all of them in agreement with the structure and arrangement of the Cu 3d magnetic orbitals. The results indicate that the dominant interaction in the system is the antiferromagnetic coupling between the ring and the central Cu sites (J₃=J₄≈?31 cm^?1). In the ring two different interactions can be distinguished, J₁=4.6 cm^?1 and J₂=?0.1 cm^?1, in contrast to the single J model employed in the magnetic data fit. The calculated J values have been used to determine the energy level distribution of the Heisenberg magnetic states. The effective magnetic moment versus temperature plot resulting from this ab initio energy profile is in good agreement with the experimental curve and the fitting obtained with the simplified spin model, despite the differences between these two spin models. This study underlines the role that the theoretical evaluations of the coupling constants can play on the rationalisation of the magnetic properties of these complex polynuclear systems.     

Ab-initio molecular dynamics and hybrid explicit-implicit solvation model for aqueous and nonaqueous solvents: GFP chromophore in water and methanol solution as case study

Solute–solvent interactions are proxies for understanding how the electronic density of a chromophore interacts with the environment in a more exhaustive way. The subtle balance between polarization, electrostatic, and non-bonded interactions need to be accurately described to obtain good agreement between simulations and experiments. First principles approaches providing accurate configurational sampling through molecular dynamics may be a suitable choice to describe solvent effects on solute chemical–physical properties and spectroscopic features, such as optical absorption of dyes. In this context, accurate energy potentials, obtained by hybrid implicit/explicit solvation methods along with employing nonperiodic boundary conditions, are required to represent bulk solvent around a large solute–solvent cluster. In this work, a novel strategy to simulate methanol solutions is proposed combining ab initio molecular dynamics, a hybrid implicit/explicit flexible solvent model, nonperiodic boundary conditions, and time dependent density functional theory. As case study, the robustness of the proposed protocol has been gauged by investigating the microsolvation and electronic absorption of the anionic green fluorescent protein chromophore in methanol and aqueous solution. Satisfactory results are obtained, reproducing the microsolvation layout of the chromophore and, as a consequence, the experimental trends shown by the optical absorption in different solvents.     

Selective cytotoxicity of organotin(IV) compounds with 2,3-dihydroxybenzyldithiocarbazate Schiff bases

Research on Chemical Intermediates - A series of tridentate ONS Schiff bases were synthesised via condensation by reacting 2,3-dihydroxybenzaldehyde with S-2-methylbenzyldithiocarbazate (S2MBDTC)...     

Intelligence Way from Eco-friendly Synthesis Strategy of New Heterocyclic Pyrazolic Carboxylic α-Amino Esters

The α-amino acid derivatives constitute a class of compounds of particular medicinal and synthetic attention and considerable interest has been devoted to their synthesis in recent years. In the present work, we develop the computational study of the synthesis reaction of new pyrazolyl α-amino esters derivatives using the Gaussian 09 based on the DFT/B3LYP density functional theory method, with the base 6-31G(d, p) to ensure the possibility of carrying out these reactions within the laboratory of synthesis. Indeed, this research has encouraged us to establish an economical synthesis strategy of these products in overall yields of 73.5% to 87% to have access to new active biomolecule through the O-alkylation reaction between methyl α-azidoglycinate N-benzoylated and primary pyrazole alcohols[(3,5-dimethyl-1H-pyrazol-1-yl)methanol, (1H-pyrazol-1-yl)methanol and (3-ethoxy-5-methyl-1H-pyrazol-1-yl)methanol] under different operating conditions. The structure of the prepared heterocyclic systems was characterized by conventional spectroscopic techniques, like ¹H NMR, ¹³C NMR, and MS. The results revealed that the experimental study is in good correlation with the computational one.     

Mathematical Modelling of Glyphosate Molecularly Imprinted Polymer-Based Microsensor with Multiple Phenomena

The massive and careless use of glyphosate (GLY) in agricultural production raises many questions regarding environmental pollution and health risks, it is then important to develop simple methods to detect it. Electrochemical impedance spectroscopy (EIS) is an effective analytical tool for characterizing properties at the electrode/electrolyte interface. It is useful as an analytical procedure, but it can also help in the interpretation of the involved fundamental electrochemical and electronic processes. In this study, the impedance data obtained experimentally for a microsensor based on molecularly imprinted chitosan graft on 4-aminophenylacetic acid for the detection of glyphosate was analyzed using an exact mathematical model based on physical theories. The procedure for modeling experimental responses is well explained. The analysis of the observed impedance response leads to estimations of the microscopic parameters linked to the faradic and capacitive current. The interaction of glyphosate molecules with the imprinted sites of the CS-MIPs film is observed in the high frequency range. The relative variation of the charge transfer resistance is proportional to the log of the concentration of glyphosate. The capacitance decreases as the concentration of glyphosate increases, which is explained by the discharging of the charged imprinted sites when the glyphosate molecule interacts with the imprinted sites through electrostatic interactions. The phenomenon of adsorption of the ions in the CMA film is observed in the low frequency range, this phenomenon being balanced by the electrostatic interaction of glyphosate with the imprinted sites in the CS-MIPs film.