Constant K1 Research Articles

Identification of structural and optical properties and adsorption performance of (Cd0.4Ni0.4Mn0.2)Fe2-xRuxO4 nanoparticles for the removal of Congo red dye

In the field of industrial wastewater treatment, the application of highly efficient methods such as adsorption is crucial for effectively eliminating dangerous pollutants before effluent discharge. Ferrite nanoparticles (NPs) have emerged as promising candidates for the efficient and sustainable removal of dyes from wastewater. Therefore, the synthesis, characterization, and application of (Cd0.4Ni0.4Mn0.2)Fe2-xRuxO4 (0 ≤ x ≤ 0.04) NPs as adsorbents for the removal of Congo Red (CR) dye, is reported in this study. The X-ray powder diffraction (XRD) analysis has confirmed the purity of the samples with a very small amount of hematite phase. The prepared NPs have pseudo-spherical morphology and average particle size in the range of 12–17 nm. Furthermore, the elemental compositions, estimated from the energy dispersive x-ray (EDX) measurements, indicate the homogenous distribution of elements and the substitution of the Fe3+ host ions by the Ru3+ dopant. As the Ru content increases from 0.00 to 0.04, SBET increases from 52.39 to 78.34 m2/g, respectively. Furthermore, the pore diameter, ranging between 12.71 and 18.38 nm, reveals the mesoporous nature of the prepared samples. The direct and indirect bandgap energy, calculated from UV–vis spectroscopy analysis, is in the range of 3.049–3.232 eV and 1.894–2.642 eV, respectively. The adsorption performance of the prepared NPs for the removal of CR dye solution was investigated by varying the contact time, adsorbent amount, pH, and reaction temperature. The adsorption process follows a second-order kinetic model and the NPs with x = 0.015 revealed the highest adsorption rate with a rate constant k2 = 2.7 × 10−3 g.mg−1.min−1. The optimum experimental conditions, achieved in the presence of 80 mg of (Cd0.4Ni0.4Mn0.2)Fe1.985Ru0.015O4 NPs at 308 K and in the acidic medium at pH = 3.45, result in the removal of 87.5 % of CR dye after 60 min. After applying several non-linear adsorption isotherm models, mainly Langmuir, Freundlich, and Temkin isotherms, the experimental data were well-fitted with the Temkin isotherm model. The strong interactive force between CR and (Cd0.4Ni0.4Mn0.2)Fe1.985Ru0.015O4 nanoparticles is revealed from the high value of bT knowing that bT = 182.91 J.mol−1.

Nucleophilicity of 4-(Alkylthio)-3-imidazoline Derived Enamines.

Imidazolidine-4-thiones (ITOs) are cyclic, secondary amines that were considered as potential prebiotic organocatalysts for light-driven α-alkylations of aldehydes by bromoacetonitrile (BAN). Recent studies showed that the initially supplied ITOs represent the pre-catalyst because they undergo S-alkylation with BAN to give 4-(alkylthio)-3-imidazolines (TIMs). Given that the same reagent mix that undergoes light-driven α-alkylations is also effective in the dark, we synthesized ten ITO- or TIM-derived enamines of aldehydes and characterized their nucleophilic reactivities by kinetic studies in acetonitrile. The experimental second-order rate constants k2 for reactions of enamines with benzhydrylium ions (reference electrophiles) were evaluated by the Mayr-Patz equation, lg k2 (20 °C)=sN (N+E). The determined nucleophilicities N (and sN ) reveal the reactivity profiles of these enamines under prebiotically relevant conditions as well as their potential for use in organocatalytic synthesis.

Waste tire upcycling for the efficient electrogeneration of H2O2 in advanced degradation of the antibiotic tinidazole by electro-Fenton process

The electrochemical production of H2O2 using small- and medium-size modular devices has emerged as an interesting approach for water treatment. In this work, waste tire-derived carbon (WTC) has been innovatively employed as a cheap and recycled electroactive material to manufacture a gas-diffusion cathode. It was found that acidification with HNO3 significantly enhanced the H2O2 production, attaining a concentration of up to 1161 mg/L with a current efficiency around 40 %–60 %. These results were superior to those obtained by treating the WTC with H2SO4 or KOH, being also better than the values reached with reported carbons. Liner and cyclic voltammetries informed about the oxygen reduction reaction profiles; transmission electron microscopy revealed the morphological features of the synthesized carbons, whereas other properties were obtained by Brunauer−Emmett−Teller analysis, Fourier transform infrared spectrometry and X-ray photoelectron spectroscopy. The cathode was further employed to degrade tinidazole (TNZ), a typical nitroimidazole antibiotic, in water by electro-Fenton at pH 3.0, producing more than 10 mM H2O2. The effect of solution pH, Fe2+ dosage and initial TNZ concentration was investigated. Under optimal conditions (0.5 mM Fe2+ and 20 mA/cm2), the treatment of solutions containing 20 mg/L TNZ at pH 3.0 yielded a pseudo-first-order constant (k1) of 0.449 min−1. Besides, the degradation pathways were proposed according to the 7 identified transformation products. This study demonstrates that waste tires can become a source of inexpensive carbon able to catalyze the in-situ H2O2 synthesis for water decontamination, in excellent agreement with new policies on circular economy.

Titanium dioxide/reduced graphene oxide nanocomposites as effective photocatalytic for hazardous 4-nitrophenol

Titanium dioxide/reduced graphene oxide nanocomposite (TiO2/rGO NCs) was prepared using various hydrothermal strategies as a highly efficient photocatalyst. The crystal structure, morphology, elemental distribution, chemical structure, optical properties, and electrical conductivity of TiO2/rGO NCs were studied to investigate the effect of the incorporation of rGO with TiO2NPs on these properties. The TiO2/rGO NCs surface exhibits thin sheets of rGO with TiO2NPs distributed on the sheets. The successful incorporation between rGO and TiO2NPs was confirmed by EDX maps, IR spectrum, and XRD patterns. Compared with TiO2NPs, a tiny reduction in the crystallite size and an increase in the microstrain was found; in addition, the TiO2/rGO NCs exhibit a low direct bandgap energy, a high electrical conductivity, and excellent photoconductivity. On the other hand, different amounts of 4-nitrophenol (4-NP) were used to investigate the photocatalyst degradation efficiency of TiO2NPs and TiO2/rGO NCs under UV irradiation. The higher degradation efficiency after 120 min was for TiO2/rGO NCs with 5 mg/L and 10 mg/L of 4-NP, with 94% and 91% values, respectively. The first-order kinetic constant (k1), the kinetic rate constant of the surface reaction (ks) and the adsorption equilibrium constant (KL) were evaluated. The KL of TiO2NPs and TiO2/rGO NCs is 0.003 and 0.182 (mgL−1)−1, and the ks is 2.53 and 0.21 mgL−1.min−1, respectively.

Heterogeneous electron transfer of ferrocene in acetonitrile-LiTFSI highly concentrated electrolyte

Highly concentrated electrolytes (HCE) are mixtures of equivalent or near-equivalent amounts of salt and solvent displaying a liquid phase at room temperature. HCE have intensively studied for application in energy storage devices with a particular focus on batteries since the demonstration of the lack of reactivity of lithium metal in an acetonitrile HCE. The lack of "free" solvent molecules in HCE is responsible for their stability. This feature also suggests that heterogeneous electron transfer (ET) in HCE could be different from conventional electrolytes because of the importance of solvent reorganization during ET. Thus, we investigated the heterogeneous electron transfer of the ferrocenium/ferrocene (Fc+/Fc) redox couple as a function of concentration of the salt Li bis(trifluoromethanesulfonyl)imide in acetonitrile, a model system for HCE. We show that while the diffusivity of Fc (Shoup-Szabo) follows the trend with viscosity (η) expected from the Stokes-Einstein relation over the entire concentration range, the ET rate constant (k0) variation with η on the other hand diverges from ideality. Using Raman spectroscopy in the solution and on the surface (EC-SERS), we show that the most likely cause for the difference in ET rate constant between dilute and highly concentrated electrolytes involves a strong coordination of the ferrocenium with the complexes found in HCE. This new knowledge highlights the importance of increasing fundamental research on the topic of electrochemistry in HCE.

Selective oxidation of histamine H2-Receptor antagonists by peracetic Acid: Kinetics and mechanism

Peracetic acid (PAA) is an emerging substitutive oxidant to chlorine disinfectants owing to the low generation of harmful by-products. Herein, we report PAA-induced oxidation of histamine H2-receptor antagonists (HRAs) via non-radical participation for the first time. Results showed that PAA can selectively oxidize HRAs with high reactivity to ranitidine (RNTD), nizatidine (NZTD), cimetidine (CMTD), and famotidine (FMTD), but low reactivity to roxatidine (RXTD). PAA-induced HRAs oxidation followed the second-order kinetic reaction, the apparent second-order reaction rate constants (k2, app) of RNTD, FMTD, CMTD and NZTD were 18.78 ± (2.4), 37.22 ± (6.1), 36.53 ± (7.8), 30.04 ± (2.4) M−1•s−1, respectively. The value of k2, app decreased as pH increased. Scavenging experiments indicated that PAA-induced HRAs oxidation proceeded via a non-radical process. The theoretical calculation and product analysis further reveal that the reaction involves the double-electron transfer from thioether sulfur in HRAs to peroxide bond. HRAs oxidation by PAA was not affected by water matrices (Cl-, HCO3–, HA), which has good applicability in surface water (SW) and wastewater (WW). Toxicity assessment indicated ecotoxicity of oxidation products was much lower than that of HRAs. This work provided a facile and emerging technology to eliminate the HRAs and their toxicity in the wastewater.

Studi Kinetika Ekstraksi Pektin dari Kulit Buah Pisang Kepok

Pectin is one of the polysaccharides that located in plant cell walls along with cellulose, lignin, and hemicellulose. The method for obtaining pectin is extraction. During the extraction process, there is reaction kinetic occur. This study aims to determine the extraction kinetics of kepok banana peel including reaction rate constants and activation energy with variations in extraction time. Secondary data that is processed are 1; 1,5; and 2 of pH extraction, 80oC and 90oC of temperature extraction, time extraction 70, 80, 90, and 100 minutes, and yield of pectin. The result showed that the value of the degradation constant (k2) is smaller than the value of the extraction constant (k1) on all variables. The highest Yemax is 41,88% that was found at pH 1,5; 90oC and 80 minutes of extraction times. The lowest value of activation energy for pectin formation (Ea1) is 17,812 kJ/mol and the highest value of activation energy for pectin degradation (Ea2) is 3,787 kJ/mol, both of which are found at pH 1,5. The optimum conditions for extracting pectin from kepok banana peel were at pH extraction 1,5 and 90oC of temperature extraction taking into account the values of k1, k2, Yemax, tmax, and activation energy.

Sulfate encapsulation by hydrogen bonding in organic clefts based on biphenyl-bridged oligourea ligands

Sulfate encapsulation faces great challenges due to the large hydration energy. Herein, a sulfate co-crystal [1, TBA4L(SO4)2, C104H174N16O20S2],was synthesized and characterized by 1H NMR, elemental analysis and Fourier transform infrared spectroscopy (FTIR). The X-ray single-crystal diffraction analysis showed that the sulfate anion was encapsulated by multiple hydrogen bonds in organic clefts containing biphenyl-bridged oligourea ligands. In the extended structure, a macrocycle including four ligands L and eight SO42- anions was constructed by N-H···O and C-H···O hydrogen bonds, which was further extended to two-dimensional hydrogen bonding network. DFT calculations showed that two sulfate anions were encapsulated by two clefts constructed by biphenyl bridged oligourea ligand, respectively, with the four corresponding tetrabutylammonium cations locating on both sides of the sulfate anions. This encapsulation mode is consistent with that of the crystal structure of the sulfate anion co-crystal 1. X-ray powder diffraction was used to study the phase purity of the bulk sample of co-crystal 1. In addition, the thermal stability of co-crystal 1 was explored by TG-DTG method, and the apparent activation energy Ea of co-crystal 1 was calculated during the main thermal decomposition process. Furthermore, the sulfate binding properties of L was investigated using UV/Vis spectroscopy method in CH3CN/DMSO solution. The binding ratio of ligand L to sulfate anion was derived as 1:2 by Job’s plot, with the binding constants K1 = 2.45 × 105 M−1 and K2 = 2.46 × 105 M−1, obtained by sulfate titration experiments. The study provides a new method for sulfate encapsulation and relative application.

Classification of semi-parallel hypersurfaces of the product of two spheres

It is known that Mendonça and Tojeiro (2013) [19] have established a complete classification of parallel submanifolds in the product manifold Qk1n1×Qk2n2, where Qk1n1 (resp. Qk2n2) is an n1-dimensional (resp. n2-dimensional) real space form with constant curvature k1 (resp. k2). In this paper, motivated by this result with considering further generalization, we study those semi-parallel hypersurfaces in case Qk1n1=Sk1n1 and Qk2n2=Sk2n2 with k1,k2>0. As the main result, we classify semi-parallel hypersurfaces of Sk1n1×Sk2n2 for n1,n2≥2.

Experimental and theoretic mechanism of successive adsorption of oppositely charged Cu(II) and Cr(VI) onto amine-rich cellulose adsorbent.

A novel layer-by-layer adsorption was proposed and used for adsorption of Cu(II) and Cr(VI) on the pre-bleached sawdust cellulose coated with polyethylenimine (PSC-PEI). It was found that PSC-PEI loaded with Cu(II) cations was favorable for Cr(VI) anions adsorption. The maximum adsorption capacities estimated by Langmuir model for Cu(II) and Cr(VI) were 80.0 and 93.5mg/g, respectively. The kinetic regression results, as fitted by the pseudo-second order model, revealed that the rate constant (k2) for Cr(VI) at 0.07g/mg/min is significantly greater than that observed for Cu(II) at 0.02g/mg/min, indicating that PSC-PEI exhibited a stronger affinity towards Cr(VI). The first-layer adsorption mechanism for Cu(II) involved the formation of copper-amine complex. Zeta potential and XPS results revealed that the second-layer adsorption of Cr(VI) mainly involved electrostatic attraction and redox reaction. The simulated results for dynamic column test showed good agreement between the theoretical values and the experimental values. The mass transfer mechanism indicated that Cu(II) adsorption was dependent on external mass transfer process, while the internal mass transfer is the rate-determining step for Cr(VI) adsorption. The saturated adsorbent was regenerated by washing with 5% NaOH and 5% H2SO4 solutions and the adsorption ability of more than 70% was sustained after three cycles of regeneration. This study demonstrated that the oppositely charged Cu(II) cations and Cr(VI) anions could be effectively removed by amine-rich cellulose adsorbent from wastewater through layer-by-layer adsorption.

Giant coercivity induced by perpendicular anisotropy in Mn2.42Fe0.58Sn single crystals

We report the discovery of a giant out-of-plane coercivity in the Fe-doped Mn3Sn single crystals. The compound of Mn2.42Fe0.58Sn exhibits a series of magnetic transitions accompanying with large magnetic anisotropy and electric transport properties. Compared with the ab-plane easy axis in Mn3Sn, it switches to the c-axis in Mn2.42Fe0.58Sn, producing a sufficiently large uniaxial anisotropy. At 2 K, a giant out-of-plane coercivity (Hc) up to 3 T was observed, which originates from the large uniaxial magnetocrystalline anisotropy. The modified Sucksmith-Thompson method was used to determine the values of the second-order and the fourth-order magnetocrystalline anisotropy constants K1 and K2, resulting in values of 6.0 × 104 J/m3 and 4.1 × 105 J/m3 at 2 K, respectively. Even though the Curie temperature (TC) of 200 K for Mn2.42Fe0.58Sn is not high enough for direct application, our research presents a valuable case study of a typical uniaxial anisotropy material.

Application of integrated molecular distillation-adsorption process for deacidification and recovery of vitamin E and carotenoids from palm oil

Palm oil is a natural source of phytonutrients such as vitamin E and carotenoids. However, these high-value compounds are lost during conventional refining. These phytonutrients can be separated and recovered from crude palm oil (CPO) through methods which prevents the degradation of these compounds. This study evaluated the integrated approach of molecular distillation and adsorption, with the aim of deacidifying and separating vitamin E and carotenoids from CPO, allowing their recovery. Wiped-film molecular distillation (WFMD) was used for deacidification and vitamin E enrichment, the best results were obtained at 200 °C and 21 mL/min. The distillate stream was enriched 937.8% in vitamin E, and the residue stream (named deacidified palm oil - DAPO), enriched in carotenoids, reached 0.1% free fatty acids (FFA). Integration with the adsorption process achieved a carotenoids removal of 79.4% from the DAPO stream. Moreover, the kinetic constant (k2) of adsorption increased by around 87% for DAPO, a result attributed to the absence of fat crystals on the adsorbent surface verified by scanning electron microscopy. Notably, the integrated process approach used is an innovative methodology for the vegetable oil industry presenting an alternative route that allows the preservation and recovery of phytonutrients, and the oil deacidification.

Parametric Imaging of P-Glycoprotein Function at the Blood-Brain Barrier Using kE,brain-maps Generated from [11C]Metoclopramide PET Data in Rats, Nonhuman Primates and Humans.

PET imaging using [11C]metoclopramide revealed the importance of P-glycoprotein (P-gp, ABCB1) in mediating the brain-to-blood efflux of substrates across the blood-brain barrier (BBB). In this work, the elimination rate constant from the brain (kE,brain), calculated from dynamic PET images without the need for arterial blood sampling, was evaluated as an outcome parameter for the interpretation of [11C]metoclopramide PET data. kE,brain parameter was obtained by linear regression of log-transformed brain time-activity curves (TACs). kE,brain values (h-1) obtained under baseline conditions were compared with values obtained after complete P-gp inhibition using tariquidar in rats (n = 4) and baboons (n = 4) or after partial inhibition using cyclosporine A in humans (n = 10). In baboons, the sensitivity of kE,brain to measure complete P-gp inhibition was compared with outcome parameters derived from kinetic modeling using a 1-tissue compartment model (1-TCM). Finally, kE,brain-maps were generated in each species using PMOD software. The linear part of the log-transformed brain TACs occurred from 10 to 30min after radiotracer injection in rats, from 15 to 60min in baboons, and from 20 to 60min in humans. P-gp inhibition significantly decreased kE,brain values by 39 ± 12% in rats (p < 0.01), by 32 ± 6% in baboons (p < 0.001), and by 37 ± 22% in humans (p < 0.001). In baboons, P-gp inhibition consistently decreased the brain-to-plasma efflux rate constant k2 (36 ± 9%, p < 0.01) leading to an increase in the total brain volume of distribution (VT, 101 ± 12%, p < 0.001). In all studied species, brain kE,brain-maps displayed decreased P-gp-mediated efflux across the BBB. kE,brain of [11C]metoclopramide provides a simple outcome parameter to describe P-gp function in the living brain when arterial input function data are unavailable, although less sensitive than VT. kE,brain-maps represent easy to compute parametric images reflecting the effect of P-gp on [11C]metoclopramide elimination from the brain.

Bioconcentration of carbamazepine, enalapril, and sildenafil in neotropical fish species.

Sewage effluents are the main source of entry of Human Pharmaceutical Active Ingredients (HPAIs) to surface water bodies. Carbamazepine (CBZ), psychiatric drug, enalapril (ENA) antihypertensive, and sildenafil (SIL), to treat erectile dysfunction, have been frequently detected in receiving wastewater and in wild fish species from Argentina. This study aimed to assess the bioconcentration of selected HPAIs in native fish species of the Del Plata Basin. In a first trial, the bioconcentration factors of CBZ, ENA, and SIL were obtained by exposing Cnesterodon decemmaculatus, respectively, to 135, 309, and 70μg/L during 96h. Then the bioconcentration kinetic of SIL was comparatively assessed in C. decemmaculatus and Piaractus mesopotamicus exposed, respectively, to 44.1 and 16.2μg/L during a one-week, followed by a four-day depuration phase. HPAIs concentrations in water and tissue were measured by HPLC-MS after 0.22μm filtration and direct injection or solid-liquid extraction, respectively. Bioconcentration factors obtained empirically (BCFe) for C. decemmaculatus were CBZ = 1.5, SIL = 1.4, and ENA = 0.007. Parameters estimated by the SIL bioconcentration kinetic model for C. decemmaculatus were: uptake rate constant (k1) = 5.5L/kg d, elimination rate constant during uptake phase (k2u) = 0.00175 d-1, maximum predicted tissue concentration (Ct(max)) = 138588μg/kg, estimated bioconcentration factor (BCFm) = 3143, lag time between the exposure and the first detection in tissue (tlag) = 0 d, elimination rate constant in the depuration phase (k2d) = 0.49 d-1 and half-life in the tissue (t1/2) = 1.4 d. The model parameters for P. mesopotamicus were k1: 7.3L/kg d, k2u: 0.0836 d-1, Ct(max): 1423μg/kg, BCFm: 88, tlag: 3.8 d in the uptake phase and k2d: 0.31 d-1 and t1/2: 2.3 d in the depuration phase. The reached conclusions were: 1) the bioconcentration capacity of CBZ and SIL are similar but around 200 times higher than ENA, 2) the time to reach the bioconcentration equilibrium for SIL is longer than 1week, then estimated BCFm are between 1 and 3 orders of magnitude higher than BCFe obtained after 96h exposure, but actual values need to be verified, 3) substantial differences (≈30 fold) were observed in the estimated BCF of SIL among species, indicating the need for further studies toward understanding such diversity to improve HPAIs ecological risk assessment worldwide.

Tris-Copper Nanozyme as a Novel Laccase Mimic for the Detection and Degradation of Phenolic Compounds.

Phenolic compounds are one of the main organic pollutants in the environment that can seriously affect ecosystems, even at very low concentrations. Due to the resistance of phenolic compounds to microorganisms, conventional biological treatment methods face challenges in effectively addressing this pollution problem. In this study, a novel laccase mimic (Tris-Cu nanozyme) is prepared using a simple and rapid synthesis strategy based on the coordination of copper ions and amino groups in Tris(hydroxymethyl)aminomethane (Tris). It is found that the Tris-Cu nanozyme exhibits good catalytic activity against a variety of phenolic compounds, the Km, Vmax and Kcat are determined to be 0.18 mM, 15.62 μM·min-1 and 1.57 × 107 min-1 using 2,4-dichlorophenol (2,4-DP) as the substrate, respectively. Then, based on the laccase-like activity of the Tris-Cu nanozyme, a novel colorimetric method for 2,4-DP (the limit of detection (LOD) = 2.4 μM, S/N = 3) detection in the range of 10-400 μM was established, and its accuracy was verified by analyzing tap and lake water samples. In addition, the Tris-Cu nanozyme shows excellent removal abilities for six phenolic compounds in experiments. The removal percentages for 2,4-DP, 2-chlorophenol (2-CP), phenol, resorcinol, 2,6-dimethoxyphenol (2,6-DOP), and bisphenol A (BPA) are 100%, 100%, 100%, 100%, 87%, and 81% at 1 h, respectively. In the simulated effluent, the Tris-Cu nanozyme maintains its efficient catalytic activity towards 2,4-DP, with a degradation percentage of 76.36% at 7 min and a reaction rate constant (k0) of 0.2304 min-1. Therefore, this metal-organic complex shows promise for applications in the monitoring and degrading of environmental pollutants.

Synthesis and Characterization of Phosphorus-Containing Sorbent for Basic Dye Removal.

A new phosphorus-containing sorbent was prepared by copolymerizing ethylene glycol dimethacrylate (EGDMA) and trimethylvinyl silane (TMVS) with diphenylvinylphoshine oxide (DPVO). It was characterized and applied in the removal of cationic dyes such as C.I. Basic Yellow 2 (BY2), C.I. Basic Blue 3 (BB3) and C.I. Basic Red 46 (BR46) using the batch method. Spectroscopic analysis indicated that the phosphinoyl group was introduced into the sorbent structure. Equilibrium adsorption data were fitted to the Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models. The Freundlich model is the most suitable to describe the adsorption of BB3 (the Freundlich constant kF = 32.3 mg1-1/nL1/n/g) and BY2 on the sorbent (13.8 mg1-1/nL1/n/g), while the Langmuir model is the most adequate to describe the adsorption of BR46 (the monolayer capacity Q0 = 2.7 mg/g). The kinetics of the dye adsorption follows the assumptions of the pseudo-second-order (the rate constants k2 = 0.087 ÷ 0.738 g/mg min) model rather than pseudo-first-order or intraparticle diffusion. The presence of Na2SO4 and cationic surfactant in the aqueous solutions inhibited dye retention by the DPVO-EGDMA-TMVS. Adsorbent regeneration efficiency does not exceed 60% using 1 M NaCl and 1 M HCl solutions in the presence of 50% v/v methanol.

Reactivity and mechanism of the reactions of 4-methylbenzoquinone with amino acid residues in β-lactoglobulin: A kinetic and product investigation

Quinones, produced by the oxidation of phenolic compounds, covalently bind to nucleophilic groups on amino acids or proteins. In this study, the reactions of 4-methylbenzoquinone (4MBQ) with β-lactoglobulin (β-LG) and amino acids at neutral pH were investigated. LC-MS analysis revealed that Cys121 was likely the most modified residue in β-LG. Identification of reaction products by LC-MS/MS showed that Michael addition occurred in all reactions with amino acids tested. The formation of Schiff base and a di-adduct was found in His and Trp samples. Apparent second-order rate constants (k2) were determined at 25 °C and pH 7.0 by stopped-flow spectrophotometry. The rate of reactions decreased in the order: β-LG > His > Trp > Arg > Nα-acetyl His > Nα-acetyl Arg > Nα-acetyl Trp. The rate constants correlated with the pKa values of the amino acids, showing that the amount of unprotonated amine is the major factor determining the reactivity.

Amperometric flow injection analysis of hydroquinone in dermatological creams using a porous diamond-like carbon electrode

A porous diamond-like carbon film deposited on vertically aligned multi-walled carbon nanotubes (DLC:VAMWCNT) was evaluated as an electrode material in flow injection analysis (FIA) with amperometric detection. The redox behavior of hydroquinone (H2Q) was carried out as proof of concept. From cyclic voltammetry tests, H2Q gave a heterogeneous electron transfer rate constant (k0) of 4.9 × 10−3 cm s−1, which is comparable or better than those obtained with conventional electrodes. For the H2Q determination with the FIA-amperometry system, optimizations were performed regarding the supporting electrolyte, applied potential and FIA parameters (flow rate and sample injection volume). Under optimal conditions, the amperometric response of the DLC:VAMWCNT electrode was linear in the H2Q concentration range from 1.0 × 10−6 to 1.0 × 10−4 mol L−1, with a limit of detection (LOD) of 7.7 × 10−7 mol L−1. Interestingly, the DLC:VAMWCNT electrode displayed a very stable response under hydrodynamic conditions, with no memory effect while retaining accuracy towards the analysis of commercial H2Q-based dermatological creams. From these findings, DLC:VAMWCNT appears to be an outstanding candidate for flow injection analysis systems coupled to electrochemical detection.

Rapid Electron Transfer Self-Exchange in Conformationally Dynamic Copper Coordination Complexes.

We report the electron transfer (ET) self-exchange rate constants (k11) for a pair of CuII/I complexes utilizing dpaR (dpa = dipicolylaniline, R = OMe, SMe) ligands assessed by NMR line broadening experiments. These ligands afford copper complexes that are conformationally dynamic in one oxidation state. With R = OMe, the CuI complex is dynamic, while with R = SMe, the CuII complex is dynamic. Both complexes exhibit unexpectedly large k11 values of 2.48(6) × 105 and 2.21(9) × 106 M-1 s-1 for [CuCl(dpaOMe)]+/0 and [CuCl(dpaSMe)]+/0, respectively. Among the fastest reported molecular copper coordination complexes to date, that of [CuCl(dpaSMe)]+/0 exceeds all others by an order of magnitude and compares only with those observed in type 1 blue copper proteins. The dynamicity of these complexes establishes pre-steady-state conformational equilibria that minimize the inner-sphere reorganization energies to 0.71 and 0.62 eV for R = OMe and SMe, respectively. In contrast to the emphasis on rigidity in the formulation of entatic states applied to blue copper proteins, the success of these two systems highlights the relevance of conformational dynamicity in mediating rapid ET.

POTENTIAL HERB-DRUG INTERACTION OF DECALEPIS HAMILTONII VIA P-GP MEDIATED PHARMACOKINETIC INTERACTION WITH FEXOFENADINE IN RATS: AN IN SITU AND IN VIVO STUDY

Objective: The objective of this study was to investigate the influence of Decalepis hamiltonii (D. hamiltonii), a traditional plant used in herbal medicine, on the intestinal absorption and pharmacokinetics of fexofenadine, a substrate of P-glycoprotein (P-gp), in rats. Methods: In situ intestinal perfusion tests were conducted to assess the intestinal permeability of fexofenadine. P-gp ATPase activity was also evaluated to understand the modulatory effects of D. hamiltonii on P-gp. An in vivo pharmacokinetic investigation was performed by administering oral fexofenadine to rats. Results: The in situ study results revealed that the effective permeation (Peff) of fexofenadine was significantly diminished (p&lt;0.001***) in aqueous extract of D. hamiltonii (AREDH, 200 mg/kg p. o.) pretreated group compared to normal control indicating modulation in absorption. Further, there was significant augmentation (p&lt;0.01**) of P-gp ATPase activity in AREDH pretreated group (200 mg/kg p. o.) compared normal control indicating P-gp inductive potential of D. hamiltonii. Pharmacokinetic study results revealed that the peak plasma concentration (Cmax) and the area under the concentration-time curve (AUC) of fexofenadine was significantly downregulated (p&lt;0.001***) in AREDH pretreated group (200 mg/kg p. o.) compared to the normal control group indicating the compromised absorption and bioavailability. However, no significant changes were observed in fexofenadine half-life (T1/2 k10), time to reach peak plasma concentration (Tmax), or elimination rate constant (k10). Conclusion: In conclusion, D. hamiltonii significantly reduced the oral bioavailability of fexofenadine by promoting P-gp-mediated drug efflux during intestinal absorption. This suggests that the modulatory characteristics of D. hamiltonii may lead to herb-drug interactions when taken in combination with xenobiotics, emphasizing the importance of considering such interactions in clinical practice and further research.