In this study, three profluorescent nitroxides 1,1,3,3-tetramethyldibenzo[e,g]isoindolin-2-yloxyl (TMDBIO), 1,1,3,3-tetramethyl-2,3-dihydro-2-azaphenalene-2-yloxyl (TMAO) and 5-[2-(4-methoxycarbonyl-phenyl)-ethenyl]1,1,3,3-tetramethylisoindoline-2-yloxyl (MeCSTMIO) were tested as probes for radical-mediated damage in polypropylene arising from both UV and thermally initiated sources. These nitroxides possess a very low fluorescence quantum yield due to quenching by the nitroxide group; however, when the free-radical moiety is removed by reaction with alkyl radicals (to give an alkoxyamine), strong fluorescence is observed. The results obtained from this profluorescent nitroxide trapping technique compare favourably with other methods of monitoring degradation, provided the appropriate probe is chosen for the conditions of oxidation, signalling an indication of damage well before other techniques show any response. The technique was also applied to the monitoring of crosslinked polyester coating resins. Differentiation in the oxidative stability of the resins was evident after as little as 200 min where other monitoring techniques require up to 300 h of accelerated degradation. This highlights the sensitivity of this method as well as demonstrating the scope of this technique to assess polymer stability. 相似文献
N‐(2‐Hydroxypropyl)methacrylamide (HPMA) copolymer‐linked nitroxides were synthesized as macromolecular contrast agents for MR imaging. Molar relaxivities of HPMA copolymer‐linked nitroxides increased linearly in proportion to the number of nitroxides attached per gram of copolymer. HPMA copolymer‐linked nitroxides with 15, 20 and 30 mol‐% nitroxide exhibited higher relaxivities than gadolinium diethylenetriaminepentaacetic acid (Gd‐DTPA). These results demonstrate the potential of HPMA copolymer‐linked nitroxides as MR contrast agents for solid tumors.
Structure of HPMA copolymer‐linked nitroxides. 相似文献
In recent decades, bicyclic nitroxyl radicals have caught chemists’ attention as selective catalysts for the oxidation of alcohols and amines and as additives and mediators in directed C-H oxidative transformations. In this regard, the design and development of synthetic approaches to new functional bicyclic nitroxides is a relevant and important issue. It has been reported that imidazo[1,2-b]isoxazoles formed during the condensation of acetylacetone with 2-hydroxyaminooximes having a secondary hydroxyamino group are recyclized under mild basic catalyzed conditions to 8-hydroxy-5-methyl-3-oxo-6,8-diazabicyclo[3.2.1]-6-octenes. The latter, containing a sterically hindered cyclic N-hydroxy group, upon oxidation with lead dioxide in acetone, virtually quantitatively form stable nitroxyl bicyclic radicals of a new class, which are derivatives of both 2,2,6,6-tetramethyl-4-oxopiperidine-1-oxyl (TEMPON) and 3-imidazolines. 相似文献
Some newly synthesized fluorinated nitroxides, such as t-butyl perfluoroalkyl nitroxides ButN(O) Rf (Rf=CF3, 5; C2F5, 6; n-C3F7, 7) and s-butyl perfluoroacyl nitroxides BusN(O) CORf (Rf=CF3, 9; n-C3F7, 10) have been employed as ESR probes of solvation in different common organic solvents. In aprotic solvents, the measured aN values for each of the nitroxyl probes show a linear correlation with the cybotactic polar solvent parameters ET (Dimroth) and Z (Kosowar), i.e. aN=bET+c, and aN=b′Z+c′. The physical significance for the slope (b or b′), the slope×ET or slope×Z, the extrapolated intercept on aN axis, c or c′, are linked, respectively, to the sensitivity of a specific nitroxide toward solvation, the magnitude of the overall solvation effect on the aN value, and the intrinsic aN value of each nitroxide in the ideal gaseous state. The intercept on the aN axis may also serve as a new measure of electronegativity for perfluoroalkyl groups, CF3, C2F5, n-C3F7, and perfluoroacyl groups, CF3CO, n-C3F7CO. In protic solvents, i.e. alcohols and carboxylic acids, however, aN values of all the probes, kept almost no change with the increase in ET and Z. Furthermore, the plots of aN versus non-cybotactic solvent constants, such as dipolar moment (μ) and dielectric constant (ε), all show random variations. 相似文献
New “Magic Blue” reagent, namely, the blue solution in F113 (CClF2CCl2F) containing H-abstracting agent bis[ω-fluorosulfonylperfluoroalkyl] nitroxide RFN(O)RF2 and ω-fluorosulfonylperfluoronitrosoalkane spin trap RFNO 3 both generated in the reaction of ω-fluorosulfonylperfluorodiacyl peroxide [FO2SCF2CF2OCF(CF3)CF2OCF(CF3)COO]21 with sodium nitrite in F113 (CClF2CCl2F) at room temperature, reacted with a series of p-substituted benzaldehydes 4 via regio-selective abstraction of the formyl hydrogen followed by spin trapping of the acyl radical intermediate 5, thus led to the formation of stable spin adducts ω-fluorosulfonylperfluoroalkyl p-substituted benzoyl nitroxides 6. The correlation analyses of aN values of nitroxides 6 with various substituent constants disclose that the polar effects are the major factors varying the spin density on the nitroxyl-nitrogen while the effect through spin-delocalization is felt slightly. 相似文献
The profluorescent nitroxide, 1,1,3,3-tetramethyldibenzo[e,g]isoindolin-2-yloxyl (TMDBIO) was investigated as a probe for the radical-mediated degradation of stabilised polypropylene. TMDBIO has been previously shown to be a sensitive probe for free-radical degradation during the thermo-oxidation of unstabilised polypropylene. Here we report on the effect that adding hindered phenol or phosphite stabilisers to polypropylene has on the free-radical sensing ability of TMDBIO during thermo-oxidation. In addition, novel dual-functional, hindered phenol containing profluorescent nitroxides, 5-[2-(4-hydroxy-3,5-di-tert-butylphenyl)ethenyl]-1,1,3,3-tetramethylisoindolin-2-yloxyl (HSTMIO) and its derivatives were investigated as probes for the radical-mediated degradation of polypropylene. These dual-functional probes were shown to be efficient stabilisers for polypropylene during thermo-oxidation at 150 °C in oxygen and sensors of thermo-oxidation during its early stages, in the so-called “induction period”. 相似文献
Two new nitronyl nitroxides with amido units L1 and L2 were synthesized and characterized. Reactions of L1 and L2 with M(hfac)2 [hfac=hexafluoroacetylacetonate, M=Co(II), Ni(II), Mn(II)] afforded five hetero-spin complexes LiCo(hfac)2, LlNi(hfac)2, L2Co(hfac)2, L2Ni(hfac)2 and L2Mn(hfac)2. The crystal structures and magnetic characterizations of L1, L2 and their metal complexes LM(hfac)2 were described and discussed. Crystal structural analysis shows that both the carbonyl oxygen and the nitroxide oxygen are coordinated to the metal ions. Strong antiferromagetic coupling between the nitronyl nitroxides and metal ions were observed for all the five LM(hfac)2 complexes. 相似文献
A new approach to the synthesis of polyfunctional pyrazolyl-substituted nitronyl nitroxides was developed based on the presynthesized
pyrazole derivatives prepared by 1,3-dipolar cycloaddition. The structures of the resulting mono-and biradicals were confirmed
by X-ray diffraction.
Dedicated to Academician A. L. Buchachenko on the occasion of his 70th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2105–2116, September, 2005. 相似文献
Sterically shielded nitroxides, which demonstrate high resistance to bioreduction, are the spin labels of choice for structural studies inside living cells using pulsed EPR and functional MRI and EPRI in vivo. To prepare new sterically shielded nitroxides, a reaction of cyclic nitrones, including various 1-pyrroline-1-oxides, 2,5-dihydroimidazole-3-oxide and 4H-imidazole-3-oxide with alkynylmagnesium bromide wereused. The reaction gave corresponding nitroxides with an alkynyl group adjacent to the N-O moiety. The hydrogenation of resulting 2-ethynyl-substituted nitroxides with subsequent re-oxidation of the N-OH group produced the corresponding sterically shielded tetraalkylnitroxides of pyrrolidine, imidazolidine and 2,5-dihydroimidazole series. EPR studies revealed large additional couplings up to 4 G in the spectra of pyrrolidine and imidazolidine nitroxides with substituents in 3- and/or 4-positions of the ring. 相似文献
The synthesis and evaluation of four C2-symmetric nitroxides are presented. The nitroxides were evaluated for their ability to mediate the oxidation of several alcohols and found to have good catalytic activity. One enantioenriched nitroxide was found to kinetically resolve selected secondary alcohols with very modest selectivities. 相似文献
Pyrrolidine nitroxides with four bulky alkyl substituents adjacent to N–O group are known for their high resistance to bioreduction. The 3,4-unsubstituted 2-tert-butyl-2-ethylpyrrolidine-1-oxyls were prepared from the corresponding 2-tert-butyl-1-pyrroline-1-oxides via either the addition of ethinylmagnesium bromide with subsequent hydrogenation or via treatment with ethyllithium. The new nitroxides showed excellent stability to reduction with ascorbate with no evidence for additional large hyperfine couplings in the EPR spectra. 相似文献
The synthesis and the full characterization of two new linear bisphosphonates (tetraethyl(N-tert-butyl-1-aminoethan-1,1-diyl)bisphosphonate and tetraethyl(N-sec-butyl-1-aminoethan-1,1-diyl)bisphosphonate), and the first analysis of the ESR spectra of the corresponding nitroxides is reported. The preliminary results of theoretical calculations on model compounds suggest a small B0 (in the McConnell equation). The results of bisphosphonate ester and bisphosphonic acid are similar. The discrepancies of P coupling for the diphosphorus compound stems from B2 that is different when the dihedral angle is larger than 90°. 相似文献
A new complex, [Cu(imme2py)2](ClO4) (imme2py?=?2-(2′-(6′-methylpyridyl))-4,4,5,5-tetramethyl-1H-imidazolyl-1-oxyl) has been synthesized and structurally characterized by X-ray diffraction methods. It crystallizes in the orthorhombic crystal system, space group P212121. The structure consists of [Cu(imme2py)2]+ cations and chloride anions. The coordination geometry about Cu(I) is tetrahedral with the four coordination sites being occupied by four nitrogen atoms. Magnetic measurements show intramolecular antiferromagnetic interactions between the imino nitroxides. 相似文献
The magnetic coupling in organic biradicals has been analyzed by means of ab initio wave function-based methods. Attention is focused on the coupling between the spin moments localized on the NO-groups in meta and para phenylene-bridged nitroxides, and bis(nitronyl) nitroxide and bis(imino) nitroxide biradicals. The leading mechanisms governing the coupling have been isolated by means of class-partitioned CI calculations. It was found that the mechanisms of the coupling in the para and meta phenylene-bridged nitroxides are similar to that found in transition metal complexes, while for the other biradicals the dominance of other mechanisms (like the spin polarization) imposes restrictions on the computational strategy to be followed to best estimate the coupling. 相似文献