Polymers having stable radicals. II. Synthesis of nitroxyl polymers from 4-methacryloyl derivatives of 1-hydroxy-2,2,6,6-tetramethylpiperidine

Polymers having stable pendant . radicals were synthesized through their precursor polymers by oxidizing them in air or by H₂O₂–Na₂WO₄. Hydrochlorides and sulfates of 4-methacryloylamino- and 4-methacryloyloxy-1-hydroxy-2,2,6,6-tetramethylpiperidines were synthesized as precursor monomers and polymerized by using α,α′-azobisisobutyronitrile under appropriate conditions to precursor polymers of high molecular weight: poly-4-methacryloylamino-/oxy-1-hydroxy-2,2,6,6-tetramethylpiperidinehydrochlorides and sulfates. The precursor polymers were converted to polymers having nitroxyl stable radicals, i.e., poly-4-methacryloylamino-/oxy-2,2,6,6-tetramethylpiperidine-1-oxyls, by oxidation in air or with H₂O₂–Na₂WO₄ without any main-chain scission. The structure of the resultant stable radical polymers was determined by infrared, ultraviolet, and ESR spectroscopy. Based on the results of spectroscopic analysis and Kjeldahl analysis, the transformation from precursors to nitroxyl stable radical polymers was found to be quantitative. Investigations on the applicability of polymeric nitroxyl radicals to oxidation-reduction reactions were attempted by means of polarography; the reduction half-wave potential was found to be ?1.16 V for the mercury pool.     

The formation of nitroxyl radicals in reactions of dimethyldioxirane with 2,2,6,6-tetramethylpiperidine and 2,2,5,5-tetramethyl-3-imidazoline-3-oxide derivatives

The oxidation of secondary and tertiary amines, derivatives of 2,2,6,6-tetramethylpiperidine and 2,2,5,5-tetramethyl-3-imidazoline-3-oxide, by dimethyldioxirane results in the formation of nitroxyl radicals, which induce the decomposition of dimethyldioxirane. Chemiluminescence in the IR and visible regions during the reaction of dimethyldioxirane with 2,2,6,6-tetramethyl-4-hydroxypieeridine-1-oxyl was observed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2501–2503, December, 1998.     

Synthesis and polymerization of 4-o-vinylbenzyl-2,2,6,6-tetramethylpiperidine

Some hindered amine polymers containing 2,2,6,6-tetramethylpiperidine structure were synthesized. A new monomer, 4-O-vinylbenzyl-2,2,6,6-tetramethylpiperidine, was homopolymerized and copolymerized with some vinyl monomers in the presence of AIBN as an initiator. The obtained amine polymers were oxidized with hydrogen peroxide to obtain the polymers having nitroxyl radical moiety.     

Some derivatives of 4-(4-aminophenylamino)-2,2,6,6-tetramethylpiperidine

4-(4-Aminophenylamino)-2,2,6,6-tetramethylpiperidine was synthesized by alkylation of 4-aminotriacetoneamine with 4-chloronitrobenzene, followed by hydrogenation of the nitro derivative. Its reactions with acrylic, methacrylic, and itaconic acids were carried out. Transformations of the N-substituted amino acids to derivatives of 2-pyrrolidinone and dihydropyrimidinedione were studied.Kaunas Technological University, Kaunas LT-3028. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 629–631, May, 1997.     

Hypervalent iodine oxidation. Synthesis of spin labeled, 1-oxyl-2,2,6,6-tetramethylpiperidine derivatives

Oxidation of 1-oxyl-2,2,6,6-tetramethyl-4-piperidone ( 1 ) with [I,I-bis(acetoxy)iodo]benzene in methanolic potassium hydroxide yields 1-oxyl-4,4-dimethoxy-3-hydroxy-2,2,6,6-tetramethylpiperidine ( 2 ). Treatment of 2,2,6,6-tetramethyl-4-piperidone ( 3 ) with [I,I-bis(acetoxy)iodo]benzene in methanolic potassium hydroxide gave 3-methoxy-2,2,6,6-tetramethyl-4-piperidone ( 4 ) which on oxidation with 30% hydrogen peroxide and catalytic amount of sodium tungstate gave 1-oxyl-3-methoxy-2,2,6,6-tetramethyl-4-piperidone ( 5 ). The esr spectra of 1-oxyl-4,4-dimethoxy-3-hydroxy-2,2,6,6-tetramethylpiperidine ( 2 ) as well as 1-oxyl-3-methoxy-2,2,6,6-tetramethyl-4-piperidone ( 5 ) show three lines.     

New stable nitroxyl radicals from hydrogenated quinolines

Conclusions Syntheses were reported for 6-triphenylmethyl derivatives of 2,2,4-trimethyl-1,2-dihydroquinolines and 2,2,4-trimethyl-1,2,3,4-tetrahydroquinolines as well as 4-phenpl-1,2,3,4-tetrahydroquinoline. The oxidation of these compounds by H₂O₂ in the presence of Na₂WO₄ and also by m-chloroperbenzoic acid gave nitroxyl radicals, whose structures were supported by EPR spectroscopy.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimichesksya, No. 12, pp. 2870–2873, December, 1988.     

Synthesis of amphiphilic block copolymers bearing stable nitroxyl radicals

We present here the synthesis of two kinds of amphiphilic block copolymers, a diblock copolymer MPEG‐b‐PTAm and a triblock copolymer MPEG‐b‐PLA‐b‐PTAm, which can self‐assemble into micelles with nitroxyl radicals‐containing PTAm segment in the core. The structure of the block copolymers was characterized by ¹H NMR and GPC. Dynamic laser light scattering and transmission electron microscopy were used to study the micellar behavior of the two block copolymers in aqueous solution. The micelles carrying nitroxyl radicals in the core can generate electron paramagnetic resonance, which is stable for a period of time up to 8 min even in the presence of reducing reagent such as ascorbic acid. The enhanced stability against the reducing agent was ascribed to the inaccessibility of the nitroxyl radical core placed in the interior of the micelles. Combined with the biocompatibility, these micelles were promising to be used as the EPR probes for bioimaging in vivo. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Synthesis and structure of diastereomeric trans-3,4-diamino-2,2,6,6-tetramethylpiperidine1-oxyl derivatives

The reaction of 3,4-diamino-2,2,6,6-tetramethylpiperidine-1-oxyl with (1S)-(+)-camphor-10-sulfonyl chloride gives a mixture of diastereomeric 4-monosulfonylamino derivatives. The products of their acylation have been obtained. The 3,4-bis-[(1S)-camphor-10-sulfonylamino] derivative was synthesized and resolved to individual diastereomers. For one of them thetrans relationship of the 3- and 4-substituents and the absolute (3S,4R)-configuration were established by X-ray structural analysis.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 367–372, February, 1993.     

Electrochemical halogenation of 4-hydroximino-2,2,6,6-tetramethylpiperidine

Electrochemical chlorination and bromination of 4-hydroximino-2,2,6,6-tetramethylpiperidine were studied.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 11, 2004, pp. 1808–1810.Original Russian Text Copyright © 2004 by Kashparova, Kagan, Zhukova.     

Synthesis of bifunctional derivatives of nitroxyl radicals of imidazoline

3-Imidazoline derivatives that contain a substituent with a functional group in the 2 position of the heteroring were obtained by the reaction of 1,2-hydroxyamino ketones with functionally substituted ketones and ammonia. The use of the reactivity of the endocyclic imino group makes it possible to accomplish the synthesis of a number of bifunctional derivatives of nitroxyl radicals of imidazoline and imidazolidine.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 772–778, June, 1990.     

Diffusion of 2,2,6,6-tetramethylpiperidine 1-oxyl derivatives of variable hydrophobicity in tropocollagen I solution

Electrochemical time-of-flight was used to measure the diffusion coefficients of 2,2,6,6-tetramethylpiperidine 1-oxyl derivatives, C(n)TPA, (3 to 7 CH(2) groups), in tropocollagen I solution, as a function of the chain length and the cross-linking with glutaraldehyde. The values of the diffusion coefficient of C(n)TPA in pure aqueous electrolyte follow the Stokes-Einstein law, i.e. the diffusion coefficient is inversely proportional to the size of the redox probe. Different behavior is observed in 0.5% (w/v) tropocollagen solution where the molecules with longer alkyl chains show larger diffusion coefficients than the smaller molecules. This behavior is explained in terms of electrostatic interactions between tropocollagen chains and the C(n)TPA molecules. The measurements of the diffusion coefficients of C(n)TPA in 0.5% tropocollagen cross-linked with glutaraldehyde indicate that while the C(7)TPA and C(5)TPA probes exhibit lower diffusion coefficients upon addition of 0.05% GA and 0.1% (v/v) GA respectively, the other C(n)TPA molecules exhibit either unchanged or increased diffusion coefficients under the same conditions thus indicating the presence of hydrophobic pockets selectively interacting with C(n)TPAs. These results demonstrate the utility of electrochemical time-of-flight in measurements of diffusion coefficients in complex biopolymeric media.     

Synthesis of acetylenic carbinols of the 2,2,6,6-tetramethylpiperidine series

Conclusions A convenient method was proposed for the preparation of acetylenic carbinols of the 2,2,6,6-tetramethyl-piperidine series by the ethynylation of 2,2,6,6-tetramethyl-4-oxopiperidine in liquid ammonia in the presence of alcoholic alkali.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1680–1681, July, 1978.     

Conformation of the piperidine ring: Part IV. Investigations of 4-tert-butyl-4-hydroxy-2,2,6,6-tetramethylpiperidine derivatives*

Methods of synthesis of 4-tert-butyl-4-hydroxy-2,2,6,6-tetramethylpiperidine(1), 4-tert-butyl-4-hydroxy-1,2,2,6,6-pentamethylpiperidine (2) and 4-tert-butyl-4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl(3) are described. Interaction of the axial hydroxyl group with axial methyl groups in a chair form of these compounds causes a downfield shift of the methyl proton NMR signal of about 0.2 ppm. IR spectra of 1 and 2 indicate a considerable contribution in solution of non-chair forms stabilized by intramolecular hydrogen bonds. In 3 only intermolecular hydrogen bonds were found. The crystal and molecular structure of 2 have been determined by direct methods and refined to R = 0.0468. The molecules exist in the solid state in a chair conformation only. Van der Waals interactions of bulky substituents hinder a close approach of neighbouring molecules necessary for the formation of intermolecular hydrogen bonds.     

Synthesis of 2H-imidazole 1-oxides and stable nitroxyl radicals based on them

2H-Imidazole 1-oxides containing an aldonitrone group in the heterocyclic ring are obtained by the condensation of hydroximinomethyl ketones with ketones and ammonium acetate. Their oxidation with lead dioxide in methanol gives stable nitroxyl radicals — 5,5-dimethoxy-3-imidazoline-1-oxyls.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2113–2121, September, 1991.