Monatshefte für Chemie / Chemical Monthly最新文献

Abstract

Green tea extract (GTE) is a supplement derived from the green tea plant which aids in weight loss along with other innumerable health. New analytical methods for determining GTE via its catechins using a design-assisted spectrophotometric methodologies are provided. The procedures are based on the formation of orange-colored products that are detectable at 473 or 455 nm, respectively, when catechins react with MBTH in the presence of FeCl₃ (method I) or K₂S₂O₈ (method II). Critical parameters were optimized using design of experiments (DOE). The absorbance-concentration plots were rectilinear over the ranges 4.0–20.0 or 4.0–40.0 µg cm⁻³ with limits of detection 0.393 or 0.493 µg cm⁻³ for methods I & II, respectively. Our methods were applied to pure catechins in GTE, namely (-)-epicatechin and (-)-epigallocatechin gallate. Moreover, the proposed methods were perfectly applied to the analysis of GTE in a commercial tablet. Good agreement between the collected data and those of the reported approach demonstrating that there were no significant variations. According to International Council for Harmonization (ICH) Guidelines, the procedures were validated.

Abstract

Due to the increasing demand for lithium-ion batteries, there is an urgent requirement for environmentally friendly and efficient means of recycling these batteries. Graphite, a readily available and cost-effective material, tends to be neglected compared to more expensive metals such as cobalt or nickel. To achieve the new European targets, it will be necessary to focus on recycling even less valuable materials, such as graphite. Direct recycling of graphite represents an environmentally and economically viable solution. However, the capacity of recycled graphite depends on several factors, with pressing pressure being a potential variable. Within this article, we have focused on the impact of pressing pressure of spent graphite anode. The recycling was performed on the battery sample with a known lifetime history. It was found that when optimized, it is possible to achieve high stability and high capacities exceeding 300 mAh/g.

In this work, a sensitive and reproducible voltammetric methodology using a modified carbon paste electrode has been established for the determination of the non-steroidal anti-inflammatory drug ibuprofen. MWCNTs-supported Ni electrocatalyst was applied as a bulk carbon paste modifier to fabricate the Ni-MWCNTs-CPE sensor, while square-wave voltammetry was utilized as an electroanalytical technique. Besides, cyclic voltammetry was used to study the electrochemical behavior of ibuprofen on the proposed sensor. Parameters of square-wave voltammetry were optimized using acetate buffer pH 4.5 as an optimal electrolyte. In addition, the sensitivity of the modified carbon paste electrode, as a sensing element, was compared to the unmodified one. Under optimized conditions, a wide linear range was obtained with LOD and LOQ values of 0.86 and 2.61 µM, and 0.13 and 0.39 µM, for bare CPE and Ni-MWCNTs-CPE, respectively. The presence of the modifier in the paste improved the sensitivity of the carbon paste electrode by almost 7 times. In addition, the newly fabricated Ni-MWCNTs-CPE sensor showed better results in terms of precision (RSD up to 2.49%). Finally, the validated voltammetric methodology was successfully applied for the determination of ibuprofen content in pharmaceutical formulations, without any complicated preliminary preparation steps, with recovery values between 94.4 and 98.1%.

Graphical abstract

MXene compound of Mn₇C₃ was successfully prepared using combined mechanical, thermal, and leaching processes. A mixture of MnO₂, Al, and black C with stoichiometric ratios 3:5:2 was mechanically activated in the ball mill for 5 h. Thermal treatment at 1000 °C was applied to this mixture. Magnetic separation was used to separate Mn₃AlC₂ from Al₂O₃. After that, Al was leached from Mn₃AlC₂ using 15% HF. SEM investigation indicated the formation of Mxene (Mn₇C₃) particles as aligned sheet-like structure and particle size distribution range of 110–145 nm. The obtained MXene compounds were used as an active material vs. lithium metal and assembled in a coin cell. The electrochemical assessment of this cell was carried out using galvanostatic cycling, electrochemical impedance spectroscopy, and cyclic voltammetry techniques. MXene (Mn₇C₃) cell showed better performance with charge capacity by preserving about 150 mAh g⁻¹ after 100 cycles. The coulombic efficiency of the cell is approaching 99.2% after long cycles.

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The synthesis, characterization, and reactivity of several group 4 metal complexes featuring a central anionic pyrrole moiety connected via CH₂ linkers to two phosphine donors is described. Treatment of [P(NH)P-iPr] with [MCl₄(THF)₂] (M = Zr, Hf) in the presence of base yields the dimeric complexes [M(PNP^iPr)(μ-Cl)(Cl)₂]₂ featuring two bridging chloride ligands. These complexes react with sodium cyclopentadienyl and SiMe₃I to give the mononuclear complexes [M(PNP^iPr)(η⁵-Cp)(Cl)₂] and [M(PNP^iPr)(I)₃], respectively. The latter react with MeMgBr to form the trialkyl complexes [M(PNP^iPr)(Me)₃]. Upon treatment of [Ti(NMe₂)₄] with [P(NH)P-iPr] a complex with the general formula [Ti(PNP^iPr)(NMe₂)₃] is obtained. DFT calculations revealed that the most stable species is [Ti(κ¹N- PNP^iPr)(NMe₂)₃] featuring a κ¹N-bound PNP ligand. When [P(NH)P-iPr] is reacted with [Ti(NMe₂)₄] in CH₂Cl₂ complex [Ti(PNP^iPr)(Cl)₂(NMe₂)] is formed. Treatment of a solution of [P(NH)P-iPr] and [Zr(NMe₂)₄] with SiMe₃Br affords the anionic seven-coordinate tetrabromo complex [Zr(PNP^iPr)(Br)₄][H₂NMe₂]. The corresponding hafnium complex [Hf(PNP^iPr)(Br)₄][H₂NEt₂] is obtained in similar fashion by utilizing [Hf(NEt₂)₄] as metal precursor. All complexes are characterized by means of NMR spectroscopy. Representative complexes were also characterized by X-ray crystallography.

Graphical abstract

Electrochemical impedance spectroscopy (EIS) is a measurement method widely used for non-destructive analysis and diagnostics in various electrochemical fields. From the measured dependence of the battery impedance on the frequency, it is possible to determine the parameters of various equivalent electrical circuit models of the battery. The conventional method of battery measurement using single-sine EIS is currently one of the most widely used methods for the analysis of lithium-ion batteries. However, its most significant disadvantage is the relatively long measurement time. For this reason, there is a growing demand for faster methods using fast-Fourier transform or pseudo-random sequences. A description of various EIS methods applications is provided in this paper.

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Liquid and gel electrolytes based on common commercial and recently commercialized salts for application in lithium-ion (Li-ion) batteries are presented herein. Various solvent mixtures and electrolytes based on them are presented. Selected organic carbonates’ mixtures are chosen as the base for these electrolytes. LiTDI (lithium 4,5-dicyano-2-(trifluoromethyl)-imidazolide) and LiPF₆ (lithium hexafluorophosphate) are chosen to compare the behavior and the electrochemical properties of the investigated systems. The limited optimizations of electrolytes are presented for LiTDI salt. Results for LiPF₆ electrolytes are presented as a benchmark. The detailed comparison of lithium transference numbers is presented. All liquid electrolytes present quite high values of conductivity at room temperature and in some cases reach above 6 mS cm⁻¹ for LiTDI solutions. The base for gel electrolytes is PVdF-HFP co-polymer (poly(vinylidene difluoride-co-hexafluoropropylene)). The conductivity of gel electrolytes exceeds 1 mS cm⁻¹ in case of the LiTDI system. All presented electrolytes show relatively high stability vs. Li/Li⁺, up to 4.7 V in both liquid and gel systems.

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Abstract

In this work, the carbon paste electrode was electro-polymerized using l-phenylalanine in 0.2 M phosphate buffer solution of pH 8.0. This l-phenylalanine modified carbon paste electrode (PLPAMCPE) was used for the study of paracetamol (PCL). The modified electrode was characterized by cyclic voltammetry, differential pulse voltammetry (DPV), scanning electron microscopy, and electrochemical impedance spectroscopy. The PLPAMCPE showed an excellent current response towards the oxidation of PCL. During the pH study ranging from 5.0 to 8.0 pH, pH 6.0 showed high peak current hence considered as the optimum pH. The scan rate study showed that the reaction was adsorption-controlled reaction. Further study i.e., by varying concentration of PCL in the linear range of 1.2 µM to 12 µM, the current increases linearly. The limit of quantification of 18.2 μM and the limit of detection of 5.4 μM was obtained for the DPV method. The study also showed that the presence of different metal ions did not hinder the PCL analysis. The developed electrode showed good repeatability, stability, and reproducibility. Simultaneous study of PCL with dopamine shows good selectivity for PCL. This method is desirable due to its quickness, low cost, ease of handling, and its applicability to real sample.

Pyrazolines are among the heterocyclic compounds, a class that exhibit a range of applications in a wide diversity of fields. We report here, a novel approach to the pyrazoline scaffold featuring an unprecedented substitution pattern. This synthesis is carried out from a diazoester and promoted by the addition of a phosphinyl chloride through a putative cyclic phosphinazine. The pyrazoline has been fully spectroscopically characterized and the structure has been further assessed by X-ray diffraction, as the new compound crystallized from toluene in a monoclinic crystal lattice.

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A one-step procedure has been developed for the synthesis of new Hantzsch poly-substituted pyridines from a three-component reaction of N-(adamantan-1-yl)acetoacetamide, aldehyde derivatives, ammonium acetate in ethanol in the presence of montmorillonite K10 catalyst under reflux conditions. The presence of adamantyl moiety in adamantyl acetoacetamide as an active methylene component leads to a strong steric hindrance and accelerates the oxidation of 1,4-dihydropyridines to the pyridine derivatives. The use of montmorillonite catalyst leads to a simple procedure of synthesis and short reaction times. As a result, facile workup, simple reaction procedure, good yields, and economical process are advantages of this one-pot multicomponent reaction.

Graphical abstract