Cytosol-mimetic chemistry: kinetics of the trypsin-catalyzed hydrolysis of p-nitrophenyl acetate upon addition of polyethylene glycol and N-tert-butyl acetoacetamide

The sensitivity of an enzyme to its environment has provoked much interest both for its immediate relevance to biochemistry and for the use of enzymes in chemical synthesis. The intercellular or extracellular environment in which an enzyme naturally operates is crowded with macromolecular, small-molecule, and ionic solutes and hence is markedly different from the dilute aqueous buffer solutions commonly cited for comparisons of biochemical processes. We report the results of a kinetic study into the effects of such a crowded solution on the rate of an enzyme-mediated process-the trypsin-catalyzed hydrolysis of a nonnatural substrate ester. The catalytic rate constant decreases linearly with solvent polarity, but substrate binding is independent of the concentration of added crowding agent up to 395 g/L.     

Synthesis and Structure Determination of Some New N‐Glycosides of 4,5‐Disubstituted‐1,2,4‐Triazole‐3‐Thiones

Some new N‐glycosides of 4‐(2‐phenylethyl)‐5‐pyridyl‐1,2,4‐triazole‐3‐thiones were synthesised by the coupling reaction of halo sugar with 4,5‐disubstituted 3H‐1,2,4‐triazole‐3‐thiones in the presence of mercuric cyanide and dry nitromethane as solvent, followed by deprotection using dry ammonia in methanol. All of the above compounds were fully characterized by means of infrared, ¹H NMR spectroscopy, mass spectroscopy and elemental analysis.     

Ketoconazol‐Triiodide Ion Pair Complex as a Suitable Carrier in an Iodide Selective Membrane Electrode

A novel membrane sensor for selective monitoring of iodide, consisting of a triiodide‐ketoconazole ion pair complex dispersed in a PVC matrix, plasticized with a mixture of 2‐nitrophenyl octyl ether and dioctylphtalate with unique selectivity toward iodide ions, is described. The influence of membrane composition, pH of test solution and foreign ions on the electrode performance were investigated. The optimized membrane demonstrates a near‐Nernstian response for iodide ions over a wide linear range from 1.0 × 10^?2 to 1.0 × 10^?5 M, at 25 ± 1 °C. The electrode could be used over a wide pH range 3–10 and has the advantages of high selectivity, fast response time and good lifetime (over 4 months). It was successfully used as indicator electrode in potentiometric titrations and direct potentiometric assay of iodide ions.     

Nickel(II) complexes of 3-acetyl-4,5-dihydro-1,2,4-triazole hydrazones

3-Acetyl-1,2,4-triazole hydrazones (3b,c) and methylhydrazone (4d) were prepared by reacting triazoles (1b–d) with an excess of hydrazines at room temperature. Square planar nickel(II) complexes (8b,c) of (3b,c) were obtained from their reaction with Ni(OAc)₂ in a 2:1 mol ratio in EtOH at room temperature. The spectral data suggest structures (8b,c) for the obtained complexes, which result from ring opening of the triazole ring followed by recyclization to give the 5-arylhydrazono-2,3-dihydro-4H-1,2,4-triazine ligand (7b,c). The reaction of triazole methylhydrazone (4d) with Ni(OAc)₂ in EtOH resulted, however, in the formation of the starting triazole (1d). All new compounds were characterized by elemental analysis, i.r., ¹H-n.m.r. ¹³C-n.m.r. and hrms.     

Mn12O12(OMe)2(O2CPh)16(H2O)2]2- single-molecule magnets and other manganese compounds from a reductive aggregation procedure

A new synthetic procedure has been developed in Mn cluster chemistry involving reductive aggregation of permanganate (MnO4-) ions in MeOH in the presence of benzoic acid, and the first products from its use are described. The reductive aggregation of NBu(n)4MnO4 in MeOH/benzoic acid gave the new 4Mn(IV), 8Mn(III) anion [Mn12O12(OMe)2(O2CPh)16(H2O)2]2-, which was isolated as a mixture of two crystal forms (NBu(n)4)2[Mn12O12(OMe)2(O2CPh)16(H2O)2].2H2O.4CH2Cl2 (1a) and (NBu(n)4)2[Mn12O12(OMe)2(O2CPh)16(H2O)2].2H2O.CH2Cl2 (1b). The anion of 1 contains a central [Mn(IV)4(mu3-O)2(mu-O)2(mu-OMe)2]6+ unit surrounded by a nonplanar ring of eight Mn(III) atoms that are connected to the central Mn4 unit by eight bridging mu3-O2- ions. This compound is very similar to the well-known [Mn12O12(O2CR)16(H2O)4] complexes (hereafter called "normal Mn12"), with the main difference being the structure of the central cores. Longer reaction times (approximately 2 weeks) led to isolation of polymeric [Mn(OMe)(O2CPh)2]n2, which contains a linear chain of repeating [Mn(III)(mu-O2CPh)2(mu-OMe)Mn(III)] units. The chains are parallel to each other and interact weakly through pi-stacking between the benzoate rings. When KMnO4 was used instead of NBu(n)4MnO4, two types of compounds were obtained, [Mn12O12(O2CPh)16(H2O)4] (3), a normal Mn12 complex, and [Mn4O2(O2CPh)8(MeOH)4].2MeOH (4.2MeOH), a new member of the Mn4 butterfly family. The cyclic voltammogram of 1 exhibits three irreversible processes, two reductions and one oxidation. One-electron reduction of 1 by treatment with 1 equiv of I- in CH2Cl2 gave (NBu(n)4[Mn12O12(O2CPh)16(H2O)3].6CH2Cl2 (5.6CH2Cl2), a normal Mn12 complex in a one-electron reduced state. The variable-temperature magnetic properties of 1, 2, and 5 were studied by both direct current (dc) and alternating current (ac) magnetic susceptibility measurements. Variable-temperature dc magnetic susceptibility studies revealed that (i) complex 1 possesses an S = 6 ground state, (ii) complex 2 contains antiferromagnetically coupled chains, and (iii) complex 5 is a typical [Mn12]- cluster with an S = 19/2 ground state. Variable-temperature ac susceptibility measurements suggested that 5 and both isomeric forms of 1 (1a,b) are single-molecule magnets (SMMs). This was confirmed by the observation of hysteresis loops in magnetization vs dc field scans. In addition, 1a,b, like normal Mn12 clusters, display both faster and slower relaxing magnetization dynamics that are assigned to the presence of Jahn-Teller isomerism.     

A simple colorimetric method for the assay of penicillin G salt and penicillamine by oxidation with iodate

A simple colorimetric procedure is described for determination of penicillin G salt and penicillamine. It is based on oxidation with potassium iodate at room temperature and measurement of the liberated iodine at 520 nm after extraction with carbon tetrachloride. Compared with other procedures, this method proved to be more rapid, highly reproducible and reasonably accurate. The relative standard deviation did not exceed 0.9% and 0.4% for penicillin and penicillamine, respectively. The procedure has been successfully applied to pharmaceutical preparations containing either of the two compounds.     

Preconcentration of metal ions using an immobilized dialkyldithiocarbamate in a flow system

Flow injection analysis with on-line preconcentration using a minicolumn loaded with dialkyldithiocarbamate immobilized on controlled pore glass is described for the determination of Rh(III), Co²⁺, Cu²⁺, Hg²⁺, and Hg₂²⁺. The detection limits range from 0.05 ng ml⁻¹ for Cu²⁺ to 50 ng ml⁻¹ for Hg²⁺ for 5- or 10-ml samples, improvement of 2–3 orders of magnitude compared with direct injection. The operating conditions are optimized and the effects of interferents are studied. The capacity of the collector varied from 0.9 mmol g⁻¹ for Rh(III) to ca 4 mmol g⁻¹ (Co²⁺, Cu²⁺, Hg²⁺).     

The kinetics of zinc dissolution in nitric acid

The dissolution of zinc in 0.48–1.49M HNO₃ was studied at 15–25°C, by following simultaneously the concentration changes of the reactants (Zn and HNO₃), intermediate (HNO₂) and product (Zn²⁺) with time. Explicit mechanisms were suggested for the dissolution of zinc in nitric acid. The kinetics of the dissolution process show that it is of the first-order with respect to [Zn] and [HNO₂]. The data obtained show that the dissolution process is diffusion-controlled. The mechanism of zinc dissolution is compared with the mechanism of copper dissolution.

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Die Kinetik der Auflösung von Zink in Salpetersäure

Zusammenfassung Die Auflösung von Zink in 0.48–1.49M HNO₃ wurde bei 15–25°C mittels gleichzeitiger Verfolgung der Konzentrationsänderungen der Reaktanden (Zn und HNO₃), des intermediären HNO₂ und des Produkts Zn²⁺ untersucht. Es wird ein Mechanismus vorgeschlagen. Die Kinetik der Auflösung ist erster Ordnung bezüglich [Zn] und [HNO₂]. Die Daten zeigen, daß der Auflösungsvorgang diffusionskontrolliert ist. Der Mechanismus der Auflösung von Zink wird mit dem der Kupferauflösung verglichen.

     

Effect of ZnO Nanofiller on Structural and Electrochemical Performance Improvement of Solid Polymer Electrolytes Based on Polyvinyl Alcohol–Cellulose Acetate–Potassium Carbonate Composites

In this study, a solution casting method was used to prepare solid polymer electrolytes (SPEs) based on a polymer blend comprising polyvinyl alcohol (PVA), cellulose acetate (CA), and potassium carbonate (K₂CO₃) as a conducting salt, and zinc oxide nanoparticles (ZnO-NPs) as a nanofiller. The prepared electrolytes were physicochemically and electrochemically characterized, and their semi-crystalline nature was established using XRD and FESEM. The addition of ZnO to the polymer–salt combination resulted in a substantial increase in ionic conductivity, which was investigated using impedance analysis. The size of the semicircles in the Cole–Cole plots shrank as the amount of nanofiller increased, showing a decrease in bulk resistance that might be ascribed to an increase in ions due to the strong action of the ZnO-NPs. The sample with 10 wt % ZnO-NPs was found to produce the highest ionic conductivity, potential window, and lowest activation energy (E_a) of 3.70 × 10^–3 Scm^–1, 3.24 V, and 6.08 × 10^–4 eV, respectively. The temperature–frequency dependence of conductivity was found to approximately follow the Arrhenius model, which established that the electrolytes in this study are thermally activated. Hence, it can be concluded that, based on the improved conductivity observed, SPEs based on a PVA-CA-K₂CO₃/ZnO-NPs composite could be applicable in all-solid-state energy storage devices.     

Determination of Chemical Compounds and Investigation of Biological Properties of Matricaria chamomilla Essential Oils,Honey, and Their Mixture

This exploratory investigation aimed to determine the chemical composition and evaluate some biological properties, such as antioxidant, anti-inflammatory, antidiabetic, and antimicrobial activities, of Matricaria chamomilla L. essential oils (EOs). EOs of M. chamomilla were obtained by hydrodistillation and phytochemical screening was performed by gas chromatography–mass spectrophotometry (GC-MS). The antimicrobial activities were tested against different pathogenic strains of microorganisms by using disc diffusion assay, the minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) methods. The antidiabetic activity was performed in vitro using the enzyme inhibition test. The antioxidant activity of EOs was tested using the free radical scavenging ability (DPPH method), ferrous ion chelating (FIC) ability, and β-carotene bleaching assay. The anti-inflammatory effects were tested in vivo using the carrageenan-induced paw edema method and in vitro using the inhibition of the lipoxygenase test. The analysis of the phytochemical composition by GC-MS revealed that camphor (16.42%) was the major compound of EOs, followed by 3-carene (9.95%), β-myrcene (8.01%), and chamazulene (6.54%). MCEO, honey, and their mixture exhibited antioxidant activity against the DPPH assay (IC₅₀ ranging from 533.89 ± 15.05 µg/mL to 1945.38 ± 12.71 µg/mL). The mixture exhibited the best radical scavenging activity, with an IC₅₀ of 533.89 ± 15.05 µg/mL. As antidiabetic effect, EO presented the best values against α-glucosidase (265.57 ± 0.03 μg/mL) and α-amylase (121.44 ± 0.05 μg/mL). The EOs and honey mixture at a dose of 100 mg/kg exhibited a high anti-inflammatory effect, with 63.75% edema inhibition after 3 h. The impact of EOs on the studied species showed an excellent antimicrobial (Staphylococcus aureus ATCC 29213 (22.97 ± 0.16 mm)), antifungal (Aspergillus niger (18.13 ± 0.18 mm)) and anti-yeast (Candida albicans (21.07 ± 0.24 mm) effect against all the tested strains. The results obtained indicate that the EOs of M. chamomilla could be a potential drug target against diabetes, inflammation and microbial infections; however, further investigations to assess their bioactive molecules individually and in combination are greatly required.