Reaction of derivatives of 1,4-dihydropyridine with the peroxynitrite anion

The reaction of derivatives of 1,4-dihydropyridine (1,4-DHP) with peroxynitrite anion is an oxidation reaction; no products of nitration were detected. It was found that some 1,4-DHP increase the lifetime of the peroxynitrite anion and the yield of hydroxyl radical in decomposition of the peroxynitrite anion.Latvian Institute of Organic Synthesis, Riga LV-1006. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 355–357, March, 1998.     

Vibrational spectroscopy at high pressure of the permanganate anion trapped in potassium bromide and potassium perchlorate matrices

The effect of high pressure on the resonance Raman spectra of the permanganate ion isolated in potassium bromide and potassium perchlorate matrices has been investigated at room temperature for pressures up to 50 kbar. The pressure dependences of the anharmonicity constants and harmonic frequencies have been determined from the overtones of the totally symmetric nu1(A1) mode of the permanganate ion. For both matrices, as the pressure increases, the anharmonicity constants decrease slightly, while the harmonic frequencies increase steadily. The effect of the potassium bromide phase transition from a face-centered to a body-centered structure was observed on the permanganate ion Raman spectrum at approximately 24 kbar. The perchlorate matrix does not exhibit any phase transition under the experimental conditions used in this study.     

Homolysis of N-alkoxyamines: a computational study.

During nitroxide-mediated polymerization (NMP) in the presence of a nitroxide R2(R1)NO*, the reversible formation of N-alkoxyamines [P-ON(R1)R2] reduces significantly the concentration of polymer radicals (P*) and their involvement in termination reactions. The control of the livingness and polydispersity of the resulting polymer depends strongly on the magnitude of the bond dissociation energy (BDE) of the C-ON(R1)R2 bond. In this study, theoretical BDEs of a large series of model N-alkoxyamines are calculated with the PM3 method. In order to provide a predictive tool, correlations between the calculated BDEs and the cleavage temperature (Tc), and the dissociation rate constant (k(d)), of the N-alkoxyamines are established. The homolytic cleavage of the N-OC bond is also investigated at the B3P86/6-311++G(d,p)//B3LYP/6-31G(d), level. Furthermore, a natural bond orbital analysis is carried out for some N-alkoxyamines with a O-C-ON(R1)R2 fragment, and the strengthening of their C-ON(R1)R2 bond is interpreted in terms of stabilizing anomeric interactions.     

Nitration reaction of lutein with peroxynitrite

The in vitro reactivity of lutein toward peroxynitrite was investigated, and the reaction products produced by scavenging with peroxynitrite were analyzed. A novel lutein-6H-1,2-oxazine (1) along with 14-s-cis-15-nitirolutein (2) and 14′-s-cis-15′-nitrolutein (3) was isolated from the products of the reaction of lutein with peroxynitrite. These results indicate that lutein is able to capture peroxynitrite and nitrogen dioxide radicals from their molecules to form oxazine or nitrocarotenoids.     

Oxidations with potassium permanganate in the presence of fluoride

Summary Trivalent chromium and quadrivalent vanadium can be determined with fair accuracy by a method consisting in mixing either with an excess of KMnO₄ in the presence of 0.3 to 1.8 M alkali hydroxide. After leaving the mixture for 5 min, the solution is acidified with sulphuric acid and mixed with 50 to 75 ml of 2% NaF solution. An excess of monovalent mercury Hg₂ ²⁺ solution is then added, the solution heated to 40° C and then titrated with KMnO₄ solution in the presence of Cu²⁺ ions to conceal the pink manganic fluoride colour.Part II: Issa, I. M., and M. Hamdy: Z. analyt. Chem. 172, 162 (1960).     

Flow-injection extraction-spectrophotometric determination of permanganate with the triphenylsulphonium cation

Summary Permanganate can be determined spectrophotometrically at 548 nm after flow-injection extraction into chloroform of the ion-associate triphenylsulphonium permanganate. The carrier stream was a pH 6 buffer containing 10% (w/v) ammonium fluoride and the reagent stream was 0.10% (w/v) triphenylsulphonium chloride. The injection rate was 20 h^–1. The calibration graph is linear up to 40 g ml^–1 and the detection limit is 1.10 g ml^–1 Mn(VII), based on injection volumes of 250 l. The system has been applied to the determination of manganese in steels and a cupro-nickel alloy.     

Oxidations with potassium permanganate in the presence of fluoride

Summary The titration of ferrous iron in presence of fluoride ions in acid medium gives fleeting end points and erroneous results. A method is deviced to overcome this difficulty by oxidising the ferrous with an excess of KMnO₄ in alkaline medium. After mixing the reactants the excess of KMnO₄ is reduced by an excess of Hg₂ ²⁺ ions in presence of H₂SO₄ and fluoride. The remaining mercurous is then titrated with standard KMnO₄ solution.Part III: Issa, I. M., and M. Hamdy: Z. analyt. Chem. 174, 418 (1960).     

Oxidations with potassium permanganate in the presence of fluoride

Summary Quadrivalent selenium can be determined with fair accuracy by mixing with an excess of KMnO₄ in the presence of 25–75 ml of 2% NaF solution and 4–7 ml of 9 N sulfuric acid. After leaving the reaction mixture for 10–30 minutes the excess KMnO₄ is estimated by one of the following procedures: A) Titration of the excess KMnO₄ with monovalent mercury, B) Adding an excess of Hg₂ ²⁺ solution to react with the excess KMnO₄ followed by titrating the excess mercurous with KMnO₄ solution.Part I: Issa, I. M., and M. Hamdy, Z. analyt. Chem. 172, 94 (1980).     

Potentiometric titration of permanganate with resacetophenone oxime

Milligram amounts of permanganate can be titrated with resacetophenone oxime (4-acetylresorcinol oxime) as a reducing titrant in the presence of phosphoric acid (0.5 M). The stoichiometry between permanganate and the oxime is 3:1 (MnO₄^-:oxime). The titration is successful in the presence of large amounts of dichromate or vanadate or moderate amounts of cerium(IV).     

Oxidation of sulphides with alkaline potassium permanganate

Summary Sulphides are oxidised with potassium permanganate in alkaline medium to give dithionate. A method based upon this reaction is proposed for the determination of sulphides. The method consists in mixing the sulphide solution with an excess of permanganate in presence 1–2 M NaOH and 0.2 g telluric acid. The excess permanganate is then treated with ferrous ammonium sulphate in acid medium and the excess ferrous titrated with permanganate.     

Electronic structure of the permanganate ion

The electronic structure of the permanganate ion has been investigated, using a semiquantitative LCAO MO method without empirical parameters. The atomic orbital basis set for the central ion has been varied systematically, and the effect of symmetric changes of bond distances has also been examined. In addition, calculations have been performed in which the regions around the ligands have been made more attractive for electrons, to simulate the presence of cations in solution and in the crystalline state. The electronic absorption spectrum of MnO ₄ ^– has been tentatively assigned, on the basis of predicted band shapes and transition energies.

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Zusammenfassung Die Elektronenstruktur des Permanganations wurde mit einer halbquantitativen LCAO-MO Methode ohne empirische Parameter behandelt. Die Zustandsfunktionen des Zentralatoms wurden variiert und der Einflu\ symmetrische Änderungen der BindungsabstÄnde untersucht. Um die Gegenwart von Kationen in Lösung und im Kristall zu simulieren, wurden daneben auch Rechnungen durchgeführt, bei denen einer stÄrkeren Elektronenanziehung durch die Liganden Rechnung getragen wird. Ferner wurde versucht, das Absorptionsspektrum von MnO ₄ ^– auf Grund der vorausgesagten Bandenform und übergangsenergien zu deuten.

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Résumé La structure électronique de l'ion permanganate est étudiée à l'aide d'une méthode LCAO MO semi-quantitative sans paramètres empiriques. La base d'orbitales atomiques pour l'ion central a été systématiquement variée et l'effet de changements symétriques des longueurs de liaison a été aussi examiné. Pour simuler la présence des cations dans la solution et dans le cristal on a fait des calculs dans lesquels la région autour des ligands était rendue plus attractive pour les électrons. Le spectre d'absorption de MnO ₄ ^–1 est interprété à l'aide des prédictions sur les formes des bandes et les énergies de transition.

     

A generator of peroxynitrite activatable with red light

The generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) as “unconventional” therapeutics with precise spatiotemporal control by using light stimuli may open entirely new horizons for innovative therapeutic modalities. Among ROS and RNS, peroxynitrite (ONOO⁻) plays a dominant role in chemistry and biology in view of its potent oxidizing power and cytotoxic action. We have designed and synthesized a molecular hybrid based on benzophenothiazine as a red light-harvesting antenna joined to an N-nitroso appendage through a flexible spacer. Single photon red light excitation of this molecular construct triggers the release of nitric oxide (˙NO) and simultaneously produces superoxide anions (O₂˙⁻). The diffusion-controlled reaction between these two radical species generates ONOO⁻, as confirmed by the use of fluorescein-boronate as a highly selective chemical probe. Besides, the red fluorescence of the hybrid allows its tracking in different types of cancer cells where it is well-tolerated in the dark but induces remarkable cell mortality under irradiation with red light in a very low concentration range, with very low light doses (ca. 1 J cm⁻²). This ONOO⁻ generator activatable by highly biocompatible and tissue penetrating single photon red light can open up intriguing prospects in biomedical research, where precise and spatiotemporally controlled concentrations of ONOO⁻ are required.

Excitation of a molecular hybrid with highly biocompatible red light generates cytotoxic peroxynitrite, produces red fluorescence useful for cell tracking and induces remarkable cancer cell death at very low concentrations and very low light doses.     

Chemiluminescence accompanied by the reaction of gold nanoparticles with potassium permanganate

It was found that potassium permanganate (KMnO(4)) could react with gold nanoparticles in a strong acid medium to generate particle size-dependent chemiluminescence (CL). For gold nanoparticles with the size of 2.6 or 6.0 nm, the reaction was fast and could produce the excited state Mn(II) with light emission around 640 nm. For gold nanoparticles larger than 6.0 nm, no light emission was observed due to a much slower reaction rate. The CL intensity was found to increase linearly with the concentration of 2.6 nm gold nanoparticles. The effects of the acid medium, concentration of KMnO(4) and presence of N(2) and O(2) were investigated. UV-Vis absorption spectra and X-ray photoelectron spectra (XPS) measured before and after the CL reaction were analyzed. A CL mechanism has been proposed suggesting that the potassium permanganate was reduced by gold nanoparticles in the strong acid medium to the excited state Mn(II), yielding light emission. The results bestow new light on the size-dependent chemical reactivities of the gold nanoparticles and on nanoparticle-induced chemiluminescence. The CL reaction was considered to be of potential use for bioanalysis applications.     

Homolysis of the TL-C bond in hydrodethallation of alkylthallium(III) compounds with n-benzyl-1,4-dihydronicotinamide

Reduction of alkylthallium(III) compounds, RT1X₂ with N-benzyl-1,4-dihydronicotinamide to give high yields of RH compounds proceeds through homolysis of the Tl-C bond of an alkylthallium(II) intermediate formed by one-electron reduction of RT1X₂.     

Titrations with extractive end-points: The permanganate titration

A method for titrations with KMnO₄ in coloured solutions is recommended, in which the permanganate ion is extracted as Ph₃MeAsMnO₄ at the end-point. The procedure is satisfactory for titrations with $\text{N}\text{10}$, $\text{N}\text{50}$ and $\text{N}\text{100}$ KmnO₄, and for the back-titration of KmnO₄, in the presence of coloured ions of molar concentrations up to 400 times that of the substance titrated. A stable permanganate, Ph₃MeAsMnO₄.$\text{case1}\text{2}$H₂O, has been isolated.