- Effect of Sterical Shielding on the Redox Properties of Imidazoline and Imidazolidine Nitroxides
-
The oxidant properties of the series of 2,2,5,5-tetraalkyl imidazoline and imidazolidine nitroxides were investigated. An increase in the number of bulky alkyl substituents leads to a decrease in the rate of reduction with ascorbate, which makes the electrochemical reduction potential more negative and shifts the equilibrium in the mixture of nitroxide and reference hydroxylamine (3-carboxy-1-hydroxy-2,2,5,5-tetramethylpyrrolidine-1-oxyl-1-15N) toward the starting compounds. The effect of structural factors on these reactions was analyzed by means of multiple regression using the Fujita steric constant Es and the inductive Hammett constant σI. Satisfactory statistical outputs were obtained in all of the biparameter correlations, denoting that the oxidant properties of the nitroxides are determined by steric and electronic effects of the substituents. The data imply that bulky substituents can stabilize nitroxide and/or destabilize hydroxylamine.
- Kirilyuk, Igor A.,Bobko, Andrey A.,Semenov, Sergey V.,Komarov, Denis A.,Irtegova, Irina G.,Grigorev, Igor A.,Bagryanskaya, Elena
-
-
Read Online
- Mussel-inspired preparation of C60 nanoparticles as photo-driven DNA cleavage reagents
-
Designing and constructing favorable water-dispersible fullerenes and their derivatives are of huge importance for biological applications addressing DNA-cleavage and photodynamic therapy (PDT). In the present work, a mild, green and facile synthetic approach for the preparation of C60 nanoparticles was developed for the first time via the combination of mussel-inspired chemistry and the Michael addition reaction. The resultant C60-PDA-PEI nanoparticles were characterized by transmission electron microscopy (TEM), dynamic laser scattering (DLS), Fourier-transform infrared spectroscopy (FT-IR), Raman spectra, X-ray photoelectron spectra (XPS) and thermogravimetric analysis (TGA), demonstrating that the above two-step strategy allows easy access to the preparation of highly water-dispersible fullerene derivatives. Benefiting from their unique nanostructure, the versatile C60-PDA-PEI nanoparticles display a uniform hydrodynamic size of 160 nm in water and efficient 1O2 generation under irradiation. Furthermore, the good ability of cleaving DNA under visible light at a mass concentration of 62.5 ng μL-1 gives them high potential as PDT agents. The universal approach described in this work is capable of introducing many other functional molecules onto PDA-modified fullerenes, thus extending the possible applications of fullerene-based species in many fields of biotechnology and pharmaceutical chemistry.
- Ma, Yihan,Zhang, Xiaoyan,Cheng, Yinjia,Chen, Xiaosui,Li, Yong,Zhang, Aiqing
-
-
Read Online
- Kinetic analysis of nitroxide radical formation under oxygenated photolysis: Toward quantitative singlet oxygen topology
-
Reaction kinetics for two sterically hindered secondary amines with singlet oxygen have been studied in detail. A water soluble porphyrin sensitizer, 5,10,15,20-tetrakis-(4-sulfunatophenyl)-21,23H-porphyrin (TPPS), was irradiated in oxygenated aqueous solutions containing either 2,2,6,6-tetramethylpiperidin-4-one (TMPD) or 4-[N,N,N-trimethyl-ammonium]-2,2,6,6-tetramethylpiperidinyl chloride (N-TMPCl). The resulting sensitization reaction produced singlet oxygen in high yield, ultimately leading to the formation of the corresponding nitroxide free radicals (R2NO) which were detected using steady-state electron paramagnetic resonance (EPR) spectroscopy. Careful actinometry and EPR calibration curves, coupled with a detailed kinetic analysis, led to a simple and compact expression relating the nitroxide quantum yield ΦR2NO (from the doubly-integrated EPR signal intensity) to the initial amine concentration [R2NH]i. With all other parameters held constant, a plot of ΦR2NOvs. [R2NH]i gave a straight line with a slope proportional to the rate constant for nitroxide formation, kR2NO. This establishment of a rigorous quantitative relationship between the EPR signal and the rate constant provides a mechanism for quantifying singlet oxygen production as a function of its topology in heterogeneous media. Implications for in vivo assessment of singlet oxygen topology are briefly discussed. This journal is
- Zigler, David F.,Ding, Eva Chuheng,Jarocha, Lauren E.,Khatmullin, Renat R.,Dipasquale, Vanessa M.,Sykes, R. Brendan,Tarasov, Valery F.,Forbes, Malcolm D. E.
-
-
Read Online
- Novel 6-formylpterin derivatives: Chemical synthesis and O2 to ROS conversion activities
-
6-Formylpterin (6FP) has been demonstrated to have strong neuroprotective effects against transient ischemia-reperfusion injury in gerbils. Also it has been shown that in rats, 6FP protected retinal neurons even when it was administered after the ischemic insult. Since there is a significant need for such a compound that effectively suppresses the events caused by the lack of oxygen supply, 6FP has attracted further investigation. Unfortunately, however, 6FP is hardly soluble in water at neutral pH and in organic solvents because of its self-assembling ability. Although a several mM solution of 6FP is available in alkaline water, it is unstable. In the present study, a novel chemical derivatization of 6FP has been developed which maintains the formyl group on the 6-position of 6FP, which is essential for the physiological activities of 6FP, and increases solubility in water and organic solvents. In the method, the 2- and 3-positions of 6FP were modified by a three component coupling reaction: 6FP was subjected to the reaction with acid chloride and N,N-dimethylformamide. The derivatives synthesized here, 2-(N,N-dimethylaminomethyleneamino)-6-formyl-3- pivaloylpteridine-4-one 1, 2-(N,N-dimethylaminomethyleneamino)-6-formyl-3- isobutyrylpteridine-4-one 2, and 2-(N,N-dimethylaminomethyleneamino)-6-formyl-3- o-toluoylpteridine-4-one 3, showed high solubility in water (1.0-5.6 mM) and organic solvents. The O2 conversion property has also been determined for the derivative 1. Using an oxygen electrode, it has been found that O 2 is consumed in the presence of 1 and NADH at around pH 7.4 and that the rate of O2 consumption is enhanced by UV-A irradiation. Electron paramagnetic resonance (EPR) analysis coupled with DMPO spin trapping has also revealed that in the presence of NADH, 1 converts O2 to O 2-, which is further reduced to OH. By UV-A illumination in the analogous systems, 1O2 formation was observed. These results are similar to those reported previously for 6FP. The Royal Society of Chemistry 2006.
- Nonogawa, Mitsuru,Arai, Toshiyuki,Endo, Nobuyuki,Pack, Seung Pil,Kodaki, Tsutomu,Makino, Keisuke
-
-
Read Online
- Oxidation of 4-substituted TEMPO derivatives reveals modifications at the 1- and 4-positions
-
Potenital pathways for the deactivation of hindered amine light stabilisers (HALS) have been investigated by observing reactions of model compounds - based on 4-substituted derivatives of 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) - with hydroxyl radicals. In these reactions, dilute aqueous suspensions of photocatalytic nanoparticulate titanium dioxide were irradiated with UV light in the presence of water-soluble TEMPO derivatives. Electron spin resonance (ESR) and electrospray ionisation mass-spectrometry (ESI-MS) data were acquired to provide complementary structural elucidation of the odd- and even-electron products of these reactions and both techniques show evidence for the formation of 4-oxo-TEMPO (TEMPONE). TEMPONE formation from the 4-substituted TEMPO compounds is proposed to be initiated by hydrogen abstraction at the 4-position by hydroxyl radical. High-level ab initio calculations reveal a thermodynamic preference for abstraction of this hydrogen but computed activation barriers indicate that, although viable, it is less favoured than hydrogen abstraction from elsewhere on the TEMPO scaffold. If a radical is formed at the 4-position however, calculations elucidate two reaction pathways leading to TEMPONE following combination with either a second hydroxyl radical or dioxygen. An alternate mechanism for conversion of TEMPOL to TEMPONE via an alkoxyl radical intermediate is also considered and found to be competitive with the other pathways. ESI-MS analysis also shows an increased abundance of analogous 4-substituted piperidines during the course of irradiation, suggesting competitive modification at the 1-position to produce a secondary amine. This modification is confirmed by characteristic fragmentation patterns of the ionised piperidines obtained by tandem mass spectrometry. The conclusions describe how reaction at the 4-position could be responsible for the gradual depletion of HALS in pigmented surface coatings and secondly, that modification at nitrogen to form the corresponding secondary amine species may play a greater role in the stabilisation mechanisms of HALS than previously considered. The Royal Society of Chemistry 2011.
- Marshall, David L.,Christian, Meganne L.,Gryn'ova, Ganna,Coote, Michelle L.,Barker, Philip J.,Blanksby, Stephen J.
-
-
Read Online
- Waste-derived bioorganic substances for light-induced generation of reactive oxygenated species
-
Urban waste-derived bioorganic substances (UW-BOS) have shown promise as chemical auxiliaries for a number of technological applications in the chemical industry and in environmental remediation. In this study, the application of these substances in the photodegradation of organic pollutants is addressed. The experimental work is specifically focused on the photolysis mechanism promoted by AC8, a UW-BOS isolated from a 2:1 w/w mixture of food and green residues, composted for 110 days, using 4-chlorophenol (4-CP) as probe molecule. The production of OH and the 1O2 is monitored by EPR spectroscopy. The correlation between radical species evolution and photodegradation of 4-CP is investigated. The effect of 1O 2 and OH scavengers on the 4-CP degradation process is also checked. The results suggest that the role of these species in the photodegradation of 4-CP depends on AC8 concentration. AC8 is thereby proven to be a photosensitizer for applications in environmental remediation. The results on AC8 further support the use of urban bio-waste as a versatile source of chemical auxiliaries of biological origin for use in diversified applications. An offer you can't refuse: A bioorganic substance isolated from a composted urban refuse (AC8) is applied as sensitizer in the photodegradation of 4-chlorophenol. Production of OH and 1O2 species is monitored by EPR spectroscopy and the data suggest that the role played by these species in the photodegradation process is strictly related to AC8 concentration. AC8 is thereby proven to be a photosensitizer for applications in environmental remediation.
- Bianco Prevot, Alessandra,Avetta, Paola,Fabbri, Debora,Laurenti, Enzo,Marchis, Tatiana,Perrone, Daniele G.,Montoneri, Enzo,Boffa, Vittorio
-
-
Read Online
- A new trick (hydroxyl radical generation) of an old vitamin (B2) for near-infrared-triggered photodynamic therapy
-
The photosensitizer has been supposed to be the key component in photodynamic therapy (PDT). Natural products and their intricate molecular frameworks are often used as starting points for drug discovery. Riboflavin (RF), also known as vitamin B2, has a unique conjugate structure of an isoalloxazine ring, and is a potential photosensitizer for use in the PDT of cancers. In this study, a novel near-infrared (NIR) mediated nanocomposite for PDT is presented, using this old vitamin (RF) as a PDT photosensitizer, integrated with the upconversion nanotechnology. Mesoporous silica coated sodium yttrium fluoride:ytterbium/thulium (NaYF4:Yb/Tm) nanoparticles were fabricated and used as drug carriers and photo-transducers. Chemical modification of RF was performed to obtain a photostable photosensitizer, 2′,3′,4′,5′-tetraacetylriboflavin (RTA). There is a good overlap between the fluorescence emission of NaYF4:Yb/Tm nanoparticles and the UV-visible absorption of RTA. The RTA molecules were incorporated into the mesoporous silica shell and the fluorescent emission from the NaYF4:Yb/Tm nanoparticles can be absorbed by RTA molecules under NIR irradiation. NIR-initiated reactive oxygen species generation was validated using electron paramagnetic resonance (EPR) spectroscopy combined with spin trapping. The results from the in vitro cell test show that this nanocomposite has good photodynamic efficacy. All the chemicals involved in this process are non-toxic, environmentally benign, and easily available. Thus, this nanocomposite has great potential in PDT applications.
- Xu, Fang,Li, Jin,Zhu, Ting-Ting,Yu, Sheng-Song,Zuo, Chong,Yao, Ri-Sheng,Qian, Hai-Sheng
-
p. 102647 - 102656
(2016)
-
Read Online
- Singlet oxygen generation properties of an inclusion complex of cyclic free-base porphyrin dimer and fullerene C60
-
To gain insight into the singlet oxygen (1O2) generation properties of supramolecular complexes of cyclic free-base porphyrin dimer with fullerene C60, we evaluated the 1O2 quantum yield (ΦΔ) and rate constant (Kobs) of 1O2 generation for a cyclic free-base porphyrin dimer (CPD) linked by butadiyne bearing four 4-pyridyl groups and its inclusion complex (C60?CPD) with C60. We demonstrate that CPD and C60?CPD possess the ability to generate 1O2 under visible light irradiation. Moreover, it was found that the ΦΔ value of C60?CPD is lower than that of CPD. Based on the kinetic and thermodynamic consideration concerning the electron transfer processes between the porphyrin dimer and C60, this work revealed that the lower ΦΔ value of the C60 inclusion complex would be attributed to the formation of the charge-separated state c60·?-CPD·+, leading to a low intersystem crossing (ISC) efficiency for the formation of the triplet excited state 3(CPD)*.
- Ooyama, Yousuke,Enoki, Toshiaki,Ohshita, Joji,Kamimura, Takuya,Ozako, Shuwa,Koide, Taro,Tani, Fumito
-
-
Read Online
- Method for preparing hindered amine nitroxide free radical compound by alkaline heterogeneous catalysis system
-
The method comprises the following steps: dissolving a hindered amine compound in an organic solvent; adjusting pH by a carbonate aqueous solution; reacting with an aqueous hydrogen peroxide solution; and generating a hindered amine nitroxide free radical compound (IV). (V) Or (VI). The method is high in universality, and the hindered amine nitroxide free radical compound with various structures is prepared. The method is high in catalytic activity, short in reaction time, high in yield, simple in preparation process and convenient to operate; a high-purity target product can be obtained through simple phase separation, drying and concentration in the post-treatment process; meanwhile, the aqueous solution system and ethyl acetate can be recycled. Small by-products.
- -
-
Paragraph 0046-0049; 0058-0059
(2021/09/26)
-
- Spin-labeled naphthalimide oxygen-containing compound and application thereof
-
The invention belongs to the technical field of medical drugs, and relates to a spin-labeled naphthalimide compound containing an oxygen substituent and an application thereof, in particular to a stable nitroxide free radical labeled naphthalimide compound containing an oxygen substituent and an application thereof in preparation of anti-tumor drugs. According to the spin-labeled naphthalimide oxygen-containing compound and the application thereof, a stable nitroxide free radical is introduced into an oxygen-containing substituent naphthalimide parent to obtain the naphthalimide compound shown in the general formula I and pharmaceutically acceptable salt thereof, and the compound has good anti-tumor activity, shows lower toxicity to normal cells than a naphthalimide analogue containing a nitrogen substituent, and has very good development and application prospects.
- -
-
Paragraph 0030-0031
(2021/06/09)
-
- Preparation method for synthesizing polymerization inhibitor 702 from acetone and ammonia gas through one-pot method
-
The invention belongs to the technical field of polymerization inhibitor synthesis, and discloses a preparation method for synthesizing a polymerization inhibitor 702 from acetone and ammonia gas through a one-pot method. The preparation method comprises the following steps: adding acetone and a carrier catalyst into a reaction kettle, introducing ammonia gas, and conducting reacting at 50-60 DEG C for 2-6 hours; and then adding deionized water and hydrogen peroxide, conducting reacting at 15-40 DEG C for 1-3 hours, filtering the reaction solution, and carrying out reduced-pressure distillation on the obtained filtrate to obtain the polymerization inhibitor 702. According to the invention, reaction conditions are mild, the preparation method is simple and convenient, the carrier catalyst is easy to separate, and product yield is high.
- -
-
Paragraph 0036; 0038-0050
(2021/04/28)
-
- A class of stable nitroxide free radical modified naphthalimide compounds, and application thereof
-
The invention belongs to the technical field of medicines, and relates to a class of naphthalimide compounds modified by stable nitroxide free radicals, and application thereof, particularly to a class of naphthalimide compounds with stable nitroxide free radicals, and application of the naphthalimide compounds in preparation of antitumor medicines. According to the invention, stable nitroxide free radicals are introduced into a naphthalimide parent structure to obtain a naphthalimide compound represented by a general formula I or II, and a pharmaceutically acceptable salt, a solvate and a hydrate thereof, wherein R1, R2, R3 and R4 are defined in the claims and the specification.
- -
-
Paragraph 0066-0067
(2020/07/02)
-
- Ultrathin 2D Zirconium Metal–Organic Framework Nanosheets: Preparation and Application in Photocatalysis
-
Synthesizing ultrathin 2D metal–organic framework nanosheets in high yields has received increasing research interest but remains a great challenge. In this work, ultrathin zirconium-porphyrinic metal–organic framework (MOF) nanosheets with thickness down to ≈1.5 nm are synthesized through a pseudoassembly–disassembly strategy. Owing to the their unique properties originating from their ultrathin thickness and highly exposed active sites, the as-prepared ultrathin nanosheets exhibit far superior photocatalysis performance compared to the corresponding bulk MOF. This work highlights new opportunities in designing ultrathin MOF nanosheets and paves the way to expand the potential applications of MOFs.
- He, Ting,Ni, Bing,Zhang, Simin,Gong, Yue,Wang, Haiqing,Gu, Lin,Zhuang, Jing,Hu, Wenping,Wang, Xun
-
-
- Titanium-Carboxylate Metal-Organic Framework Based on an Unprecedented Ti-Oxo Chain Cluster
-
Titanium(IV)-based metal-organic frameworks (Ti-MOFs) have received significant attention in recent years due to their numerous photocatalytic applications. We herein prepare the single-crystalline Ti-carboxylate MOF (DGIST-1) composed of an unprecedented Ti-oxo chain cluster and the porphyrinic ligand, TCPP (tetrakis(4-carboxyphenyl)porphyrin). Preformed Ti-oxo clusters were used as Ti4+ sources to avoid the spontaneous hydrolysis and condensation reactions of traditional Ti-alkoxide precursors, thus, enabling the formation of the highly crystalline Ti-MOF. The successfully activated DGIST-1 exhibited a higher surface area (i.e., 1957.3 m2 g?1) than previously reported Ti-MOFs due to its high crystallinity. Furthermore, the visible-light-responsive photocatalytic activity of DGIST-1 was confirmed by the simultaneous generation of singlet oxygen (1O2) and superoxide (.O2?) species, in addition to the highly efficient and selective oxidation of benzyl alcohol to benzaldehyde.
- Keum, Yesub,Park, Seonghun,Chen, Ying-Pin,Park, Jinhee
-
supporting information
p. 14852 - 14856
(2018/10/20)
-
- Nickel-Catalyzed Aminoxylation of Inert Aliphatic C(sp3)-H Bonds with Stable Nitroxyl Radicals under Air: One-Pot Route to α-Formyl Acid Derivatives
-
Nickel-catalyzed aminoxylation of an unactivated C(sp3)-H bond with a stable nitroxyl radical has been accomplished for the first time to offer various N-alkoxyamine derivatives, which further enables a one-pot approach to α-formyl acid derivatives. The aminoxylation process reported also provides direct evidence for the oxidative addition of a cyclometallic intermediate with a free radical, which is helpful for the reaction-mechanism study in transition-metal-catalyzed functionalization of inert C(sp3)-H bonds.
- Wang, Chunxia,Zhang, Luoqiang,You, Jingsong
-
supporting information
p. 1690 - 1693
(2017/04/11)
-
- Synthesis and fluorescence properties of six fluorescein-nitroxide radical hybrid-compounds
-
Six fluorescein-nitroxide radical hybrid-compounds (2ab, 3ab, 4, and 5) were synthesized by the condensation of 5- or 6-carboxy-fluorescein and 4-amino-TEMPO (2ab), 5- or 6-aminofluorescein and 4-carboxy-TEMPO (3ab), and fluorescein and 4-carboxy-TEMPO (4), or by reaction of the 3-hydroxyl group of fluorescein with DPROXYL-3-ylmethyl methanesulfonate (5). Fluorescence intensities (around 520 nm) after reduction of the radical increased to 1.43-, 1.38-, and 1.61-folds for 2a, 2b and 3b respectively; 3a alone exhibited a decrease in intensity on reduction. Since 4 was readily solvolyzed in PBS or even methanol to afford fluorescein and 4-carboxy-TEMPO, its fluorescence change could not be measured. Hybrid compound 5 containing an ether-linkage between the fluorescein phenol and 3-hydroxymethyl-DPROXYL hydroxyl centers, was stable and on reduction, showed a maximum increase (3.21-fold) in relative fluorescence intensity in PBS (pH 5.0), despite its remarkably low absolute fluorescence intensity.
- Sato, Shingo,Endo, Susumu,Kurokawa, Yusuke,Yamaguchi, Masaki,Nagai, Akio,Ito, Tomohiro,Ogata, Tateaki
-
supporting information
p. 66 - 71
(2016/07/06)
-
- Spin-labelled diketopiperazines and peptide-peptoid chimera by Ugi-multi-component-reactions
-
For the first time, spin-labelled coumpounds have been obtained by isonitrile-based multi component reactions (IMCRs). The typical IMCR Ugi-protocols offer a simple experimental setup allowing structural variety by which labelled diketopiperazines (DKPs) and peptide-peptoid chimera have been synthesized. The reaction keeps the paramagnetic spin label intact and offers a simple and versatile route to a large variety of new and chemically diverse spin labels.
- Sultani, Haider N.,Haeri, Haleh H.,Hinderberger, Dariush,Westermann, Bernhard
-
p. 11336 - 11341
(2016/12/18)
-
- EPR Studies of V-ATPase with Spin-Labeled Inhibitors DCC and Archazolid: Interaction Dynamics with Proton Translocating Subunit c
-
Vacuolar-type H+-ATPases (V-ATPases) have gained recent attention as highly promising anticancer drug targets, and therefore detailed structural analyses and studies of inhibitor interactions are very important research objectives. Spin labeling of the V-ATPase holoenzyme from the tobacco hornworm Manduca sexta and V-ATPase in isolated yeast (Saccharomyces cerevisiae) vacuoles was accomplished by two novel methods involving the covalent binding of a (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) derivative of N,N′-dicyclohexylcarbodiimide (DCC) to the essential glutamate residue in the active site and the noncovalent interaction of a radical analogue of the highly potent inhibitor archazolid, a natural product from myxobacteria. Both complexes were evaluated in detail by electron paramagnetic resonance (EPR) spectroscopic studies and double electron-electron resonance (DEER) measurements, revealing insight into the inhibitor binding mode, dynamics, and stoichiometry as well as into the structure of the central functional subunit c of these medicinally important hetero-multimeric proton-translocating proteins. This study also demonstrates the usefulness of natural product derived spin labels as tools in medicinal chemistry. Near and DEER: Electron paramagnetic resonance (EPR) and double electron-electron resonance (DEER) studies of V-ATPase in complex with spin-labeled inhibitors DCC and archazolid have enabled insight into the noncovalent binding dynamics and analysis of the enzyme′s key functional subunit c. These studies also demonstrate the general utility of natural product derived spin labels as innovative tools for chemical biology.
- G?lz, Jan Philipp,Bockelmann, Svenja,Mayer, Kerstin,Steinhoff, Heinz-Jürgen,Wieczorek, Helmut,Huss, Markus,Klare, Johann P.,Menche, Dirk
-
supporting information
p. 420 - 428
(2016/03/01)
-
- Design, Synthesis, EPR-Studies and Conformational Bias of Novel Spin-Labeled DCC-Analogues for the Highly Regioselective Labeling of Aliphatic and Aromatic Carboxylic Acids
-
Novel types of spin-labeled N,N′-dicyclohexylcarbodiimides (DCC) are reported that bear a 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO) residue on one side and different aromatic and aliphatic cyclohexyl analogues on the other side of the diimide core. These readily available novel reagents add efficiently to aliphatic and aromatic carboxylic acids, forming two possible spin-labeled amide derivatives with different radical distances of the resulting amide. The addition of aromatic DCC analogues proceeds with excellent selectivity, giving amides where the carboxylic acid is exclusively connected to the aromatic residue, while little or no selectivity was observed for the aliphatic congeners. The usefulness of these adducts in structural studies was demonstrated by EPR (electron paramagnetic resonance) measurements of biradical adducts of biphenyl-4,4′-dicarboxylic acids. These analyses also reveal high degrees of conformational bias for aromatic DCC derivatives, which further underlines the powerfulness of these novel reagents. This observation was further corroborated by quantum chemical calculations, giving a detailed understanding of the structural dynamics, while detailed information on the solid state structure of all novel reagents was obtained by X-ray structure analyses.
- G?lz, Jan Philipp,NejatyJahromy, Yaser,Bauer, Mirko,Muhammad, Ashraf,Schnakenburg, Gregor,Grimme, Stefan,Schiemann, Olav,Menche, Dirk
-
supporting information
p. 9591 - 9598
(2016/07/14)
-
- Kinetics and thermodynamics of reversible disproportionation-comproportionation in redox triad oxoammonium cations - Nitroxyl radicals - Hydroxylamines
-
Kinetics and equilibrium of the acid-catalyzed disproportionation of cyclic nitroxyl radicals R2NO· to oxoammonium cations R2NO+ and hydroxylamines R2NOH is defined by redox and acid-base properties of these compounds. In a recent work (J. Phys. Org. Chem. 2014, 27, 114-120), we showed that the kinetic stability of R2NO· in acidic media depends on the basicity of the nitroxyl group. Here, we examined the kinetics of the reverse comproportionation reaction of R2NO+ and R2NOH to R2NO· and found that increasing in -I-effects of substituents greatly reduces the overall equilibrium constant of the reaction K4. This occurs because of both the increase of acidity constants of hydroxyammonium cations K3H+ and the difference between the reduction potentials of oxoammonium cations ER2NO+/R2NO· and nitroxyl radicals ER2NO·/R2NOH. pH dependences of reduction potentials of nitroxyl radicals to hydroxylamines E1/3σ and bond dissociation energies D(O-H) for hydroxylamines R2NOH inwater were determined. For a wide variety of piperidine- and pyrrolidine-1-oxyls values of pK3H+ and ER2NO+/R2NO· correlate with each other, as well aswith the equilibriumconstants K4 and the inductive substituent constants ωI. The correlations obtained allowprediction of the acid-base and redox characteristics of redox triads R2NO·-R2NO+-R2NOH.
- Sen, Vasily D.,Tikhonov, Ivan V.,Borodin, Leonid I.,Pliss, Evgeny M.,Golubev, Valery A.,Syroeshkin, Mikhail A.,Rusakov, Alexander I.
-
-
- Visible light singlet oxygen production with tetra(4-carboxyphenyl) porphyrin/SiO2
-
The production of singlet oxygen with tetra(4-carboxyphenyl)porphyrin adsorbed on SiO2 irradiated with visible light (λ > 500 nm) was evidenced by EPR spectra of TEMPO formed by oxidation of 2,2,6,6-tetramethyl-4-piperidone(TEMP) with 1O2. The formation of singlet oxygen was also evidenced by the formation of anthraquinone and oxanthrone as oxidation products of anthracene with 1O 2. The absence of the EPR DMPO-O2- signal evidenced that superoxide anion was not present. No other oxygen radicals were detected. TCPP and TCPP/SiO2 were characterized with UV-vis, UV-vis diffuse reflectance and FT-IR spectroscopy.
- Diaz-Uribe, Carlos E.,Daza, Martha C.,Páez-Mozo, Edgar A.,Martínez O., Fernando,Guedes, Carmen L.B.,Di Mauro, Eduardo
-
-
- Photoinduced oxidation of sterically hindered amines in acetonitrile solutions and titania suspensions (An EPR Study)
-
The reactions of sterically hindered amines (SHA) were investigated in acetonitrile solutions and TiO2 suspensions upon exposure to monochromatic radiation, λ = 365 nm, by means of in situ EPR spectroscopy. The formation of singlet oxygen, as one of the possible oxidation agents for SHA, in these systems is affected significantly by solvent used and the experimental conditions. Experiments in homogeneous media evidenced alternative pathways for the SHA oxidation with a variety reactive oxygen species involved. In anhydrous acetonitrile solutions containing KO2, the SHA oxidation was negligible not only in the dark but also on continuous exposure. However, the presence of water, even at low concentrations, led to the transformation of O2?- to singlet oxygen and hydrogen peroxide, which served as a source of hydroxyl radicals. These species participated in oxidation of SHA resulting in the generation of nitroxide radicals. To investigate the influence of different competitive reactions of SHA with other ROS formed upon TiO2 photoexcitation, a series of experiments using different additives (e.g. KO2, H2O 2, NaN3, dimethylsulfoxide, methanol as organic cosolvents) under air or argon were performed. The detailed analysis of paramagnetic intermediates formed upon the irradiation of the studied systems was accomplished using EPR spin trapping technique. The reactions of sterically hindered amines (SHA) were investigated in acetonitrile solutions and TiO 2 suspensions upon exposure to monochromatic radiation (λ = 365 nm) by in situ EPR spectroscopy. Experiments in homogeneous media using KO2 and H2O2 evidenced alternative pathways for the SHA oxidation with a variety reactive oxygen species (ROS) involved. The influence of competitive reactions of SHA with ROS formed upon TiO2 photoexcitation was investigated in a series of experiments using different additives (e.g. KO2, H2O2, NaN3, dimethylsulfoxide and methanol) under air or argon. The detailed analysis of paramagnetic intermediates formed upon the irradiation of the studied systems was accomplished using an EPR spin trapping technique. 2012 Wiley Periodicals, Inc. Photochemistry and Photobiology
- Barbierikova, Zuzana,Mihalikova, Maria,Brezova, Vlasta
-
p. 1442 - 1454
(2013/01/15)
-
- Mechanism of autoreduction of 2,2,6,6-tetramethyl-1,4-dioxopiperidinium cation in alkaline medium
-
Autoreduction of 2,2,6,6-tetramethyl-1,4-dioxopiperidinium ion to nitroxyl radical in alkaline medium involves a number of parallel and consecutive reactions. The primary products of the reaction of 2,2,6,6-tetramethyl-1,4- dioxopiperidinium with hydroxide ion are three nitroso compounds and N-hydroxy-2,2,6,6-tetramethylpiperidine N-oxide. Isomerization of the nitroso compounds and elimination of acetone from the N-oxide give cyclic hydroxylamines which reduce the initial cation to nitroxyl radical, being oxidized to nitrones. Pleiades Publishing, Ltd., 2011.
- Golubev,Sen
-
experimental part
p. 869 - 876
(2011/10/04)
-
- The synthesis and 1O2 photosensitization of halogenated asymmetric aniline-based squaraines
-
The halogenated (brominated or iodinated) squaraines have promising potential in the application of photodynamic therapy (PDT). Though aniline-based squaraines are the most classical squaraine dyes, no halogenated derivatives with the halogen atoms directly incorporated in the conjugation skeleton of the squaraine chromophore have been reported so far. In this work, a stepwise synthetic approach, i.e. by way of the halogenated semi-squaraines, was applied successfully to prepare halogenated asymmetric aniline-based squaraines. Such a structure makes iodine atoms be able to exert significant heavy atom effect on the intersystem crossing (ISC) efficiency of the squaraine dye. As a result, the iodinated asymmetric squaraine (SQ-OH-I) exhibits a singlet oxygen ( 1O2) quantum yield as high as 0.54. In contrast, the 1O2 quantum yield of the non-halogenated squaraine analogue (SQ-OH) is only 0.02. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011.
- Luo, Chao,Zhou, Qianxiong,Jiang, Guoyu,He, Liqing,Zhang, Baowen,Wang, Xuesong
-
body text
p. 1128 - 1132
(2011/07/08)
-
- Visible light superoxide radical anion generation by tetra(4-carboxyphenyl) porphyrin/TiO2: EPR characterization
-
The generation of superoxide radical anion O2- from tetra(4-carboxyphenyl)porphyrin (TCPP) adsorbed on TiO2 in DMSO and irradiated by visible light was studied using EPR spectroscopy and 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as spin trap. A chemical filter was used to remove light with wave lengths 2- and the second to the so-called nitroxide-like radical. Hyperfine coupling constants determined for the DMPO-O2 - adduct are: aN = 14.1 G, aHβ = 10.8 G and aHγ = 1.4 G, and for the nitroxide-like radical adduct aN = 14 G. An increased intensity of the EPR lines corresponding to the nitroxide-like radical adduct was observed under irradiation without chemical filter, which suggests a possible DMPO-O 2- decomposition. No singlet oxygen could be detected by EPR spectroscopy using 2,2,6,6-tetramethyl-4-piperidone (TEMP) as spin trap and by chemical trapping using anthracene as the trap.
- Diaz-Uribe, Carlos E.,Daza, Martha C.,Martínez, Fernando,Páez-Mozo, Edgar A.,Guedes, Carmen L.B.,Di Mauro, Eduardo
-
body text
p. 172 - 178
(2010/12/24)
-
- Mechanism of disproportionation of 2,2,6,6-tetramethyl-1,4- dioxopiperidinium perchlorate in acidic aqueous medium
-
The cation of 2,2,6,6-tetramethyl-1,4-dioxopiperidinium perchlorate disproportionates in acidic aqueous medium to give piperidinoxyl and/or 1-hydroxypiperidine, nitrone, and acetone. A mechanism of this reaction was proposed and the rate constants for its particular steps were calculated.
- Golubev,Sen
-
experimental part
p. 1824 - 1827
(2011/01/07)
-
- Nitroxyl radical plus hydroxylamine pseudo self-exchange reactions: Tunneling in hydrogen atom transfer
-
Bimolecular rate constants have been measured for reactions that involve hydrogen atom transfer (HAT) from hydroxylamines to nitroxyl radicals, using the stable radicals TEMPO· (2,2,6,6-tetramethylpiperidine-1-oxyl radical), 4-oxo-TEMPO·/
- Wu, Adam,Mader, Elizabeth A.,Datta, Ayan,Hrovat, David A.,Borden, Weston Thatcher,Mayer, James M.
-
scheme or table
p. 11985 - 11997
(2009/12/08)
-
- Light-fluorous TEMPO: reagent, spin trap and stable free radical
-
The synthesis of two light-fluorous TEMPO derivatives is reported, along with their fluorous-organic solvent partition coefficients and their ESR spectra. Applications of the fluorous-TEMPO reagents in oxidation reactions and as radical traps are discussed.
- Dobbs, Adrian P.,Jones, Peter,Penny, Mark J.,Rigby, Stephen E.
-
experimental part
p. 5271 - 5277
(2009/11/30)
-
- PROCESS FOR THE PREPARATION OF STERICALLY HINDERED NITROXYL ETHERS
-
The present invention relates to a novel process for the preparation of a sterically hindered nitroxyl ether from the corresponding sterically hindered nitroxyl radical by reacting it with a carbonyl compound and a hydroperoxide. The compounds prepared by this process are effective stabilizers for polymers against harmful effects of light, oxygen and/or heat, as flame-retardants for polymers and as polymerization regulators.
- -
-
Page/Page column 49
(2008/06/13)
-
- Synthesis of novel bicyclic nitroxides using partial favorskii rearrangement
-
3-Bromo-2,2,6,6-tetramethyl-4-oxopiperidine-1-oxyl was reacted with several C-nucleophiles to give novel bicyclic pyrrolidine nitroxides through partial Favorskii rearrangement. Further reduction with sodium borohydride gave spin probes with free hydroxyl groups and under harsh reduction conditions allowed the Favorskii rearrangement to proceed to completion. Georg Thieme Verlag Stuttgart.
- Babi?, Andrej,Pe?ar, Slavko
-
scheme or table
p. 1155 - 1158
(2009/04/07)
-
- Novel light-fluorous TEMPO reagents and their application in oxidation reactions
-
The synthesis of two light-fluorous TEMPO derivatives is reported, along with their application in oxidation reactions.
- Dobbs, Adrian P.,Penny, Mark J.,Jones, Peter
-
scheme or table
p. 6955 - 6958
(2009/04/07)
-
- The synthesis of EPR differentiable spinlabels and their coupling to uridine
-
For EPR measurements of RNA, DNA, or proteins, the occurrence of the paramagnetic species is necessary. The aim of this work is to improve the synthesis of two different EPR spinlabels 2,2,6,6-tetra methyl-3,4-dehydro- piperidin-N-oxyl-4-acetylene (TEMPA) 6 and 15N-labeled TEMPA 6* and their coupling to uridine. The yield of the synthesis of TEMPA could be increased to 40% and the second nitroxide 2,2,6,6-tetramethyl-3,4-dehydro-piperidin-15N-oxyl- 4-acetylene 6* could be synthesized with a yield of 11%. Copyright Taylor & Francis Group, LLC.
- Frolow, Olga,Bode, Bela E.,Engels, Joachim W.
-
p. 655 - 659
(2008/09/17)
-
- PROCESS FOR THE SYNTHESIS OF N-ALKOXYAMINES
-
The present invention relates to novel processes for the preparation of a sterically hindered amine ethers by the transformation of a corresponding oxo-piperidin to a hydroxy or animo substituted sterically hindered amine ether and the preparation of a N-propoxy or N- propenoxy substituted sterically hindered amine and some novel compounds obtainable by these processes. The compounds made by these processes are particularly effective in the stabilization of polymer compositions against harmful effects of light, oxyen and/or heat and as flame-retardants for polymers.
- -
-
Page/Page column 47-50
(2008/06/13)
-
- Process for the preparation of 4-substituted 2,2,6,6-tetramethyl-N-oxy and 2,2,6,6-tetramethyl-N-hydroxy piperidines
-
Preparation of 4-substituted-piperidine-N-oxy compounds (II) or mixture of (II) and 4-substituted-piperidin-N-hydroxy-compounds (III) comprises oxidation of 4-substituted-piperidine compound [I] with hydrogen peroxide in the presence of alkali and/or ammonium hydrogen carbonate and optionally in the presence of solvents, where the reaction is carried out under the addition of Bronsted acid. Preparation of 4-substituted 2,2,6,6-tetramethyl-piperidine-N-oxy compounds of formula (II) or mixture of (II) and 4-substituted 2,2,6,6-tetramethyl-piperidin-N-hydroxy-compounds of formula (III) comprises oxidation of 4-substituted 2,2,6,6-tetramethylpiperidine compounds of formula [I] by hydrogen peroxide in the presence of alkali and/or ammonium hydrogen carbonate and optionally in the presence of solvents, where the reaction is carried out under the addition of Bronsted acid that possess an acid strength higher than the hydrogen carbonate. X+Y : O, cyclic ketals (containing groups of O-(CH2)2-O, O-CH(CH3)-CH2-O, O-CH(CH2OH)-CH2-O, O-(CH2)3-O or O-CH2-C(CH3)2-CH2-O) or open chain ketal (where X is O-R and Y is O-Ra); and R, Ra : CH3, CH2-CH3, CH2-CH2-CH3, CH(CH3)-CH3, CH2-CH2-CH2-CH3 or CH2-CH(CH3)-CH3. An independent claim is also included for a method for preparing (II) or mixture of (II) and (III) comprising oxidation of (I) with hydrogen peroxide in the absence of hydrogen carbonate, where the reaction is carried out optionally in the presence of solvents and addition of alkali- and/or ammonium dihydrogen phosphate as catalysts. [Image].
- -
-
Page/Page column 9; 11
(2008/06/13)
-
- Process for preparing 4-substituted 2,2,6,6-tetramethylpiperidin-N-oxy and 2,2,6,6-tetramethylpiperidin-N-hydroxy compounds
-
A process for preparing 4-substituted 2,2,6,6-tetramethylpiperidin-N-oxy compounds (II) or mixtures of (II) and 4-substituted 2,2,6,6-tetramethylpiperidin-N-hydroxy compounds (III) where X+Y can be O or can represent a cyclic ketal with the radicals or can represent an open-chain ketal in which X═O—R and Y═O—R′, where R and R′ can be identical or different and can each be CH3, CH2—CH3, CH2—CH2—CH3, CH(CH3)—CH3, CH2—CH2—CH2—CH3 and CH2—CH(CH3)—CH3, by oxidizing corresponding 4-substituted 2,2,6,6-tetramethylpiperidines (I) with hydrogen peroxide in the presence of alkali metal hydrogencarbonate and/or ammonium hydrogencarbonate and in the presence or absence of a solvent, in which the reaction is carried out with the addition of Br?nsted acids which have an acid strength greater than that of the hydrogencarbonate.
- -
-
Page/Page column 6-7
(2008/06/13)
-
- PROCESS FOR THE OXIDATION OF SECONDARY AMINES INTO THE CORRESPONDING NITROXIDES
-
The invention relates to a process for the preparation of secondary nitroxide radicals from their corresponding secondary amines by oxidation with an organic peracid, comprising the steps a) adding to a reaction vessel a secondary amine, optionally together with an organic solvent and in one batch a base selected from the group consisting of alkali metal, alkaline earth metal or ammonium bicarbonates and alkaline earth metal or ammonium carbonates or mixtures thereof in the form of a solid together with water or as an aqueous slurry; b) dosing a peracid under stirring to the reaction mixture in an amount of 1,0 to 2,5 mol per mol of secondary amine; and c) isolating the organic phase.
- -
-
-
- New seven- and eight-membered cyclic alkoxyamines for the living free radical polymerization
-
A straightforward synthesis of new seven- and eight-membered cyclic alkoxyamines from the corresponding lower homologous keto-alkoxyamines via ring-enlargement using TMS-diazomethane is described. The use of these ring-enlarged cyclic alkoxyamines as regulators/initiators for the radical polymerization of styrene and n-butyl acrylate is presented. Efficient controlled and living styrene polymerization (molecular weight of up to 40 000) can be obtained using the seven- and eight-membered alkoxyamine initiators. The influence of the ring-enlargement on the quality of the polymerization process (polymerization time, livingness, PDI) is discussed. The rate constant of the C-O bond cleavage of these new alkoxyamines has been measured. In addition, the thermal decomposition of the alkoxyamines has been studied. Furthermore, EPR data of the corresponding new nitroxides are presented.
- Schulte, Tobias,Studer, Armido
-
p. 3078 - 3084
(2007/10/03)
-
- Singlet-oxygen reactions sensitized on solid surfaces of lignin or titanium dioxide: Product studies from hindered secondary amines and from lipid peroxidation
-
Product analyses and kinetic methods were used to determine the role of singlet oxygen in lignin-catalyzed oxidations of organic substrates. Method A used the ESR analysis of nitroxide radicals formed by singlet oxygen (Type II) on 2,2,6,6-tetramethylpiperidine, 1, or tetramethylpiperidone, 2. Method B used HPLC analysis of the 9- and 13-linoleate chain hydroperoxides formed on oxidation of methyl linoleate to distinguish free-radical peroxidation (Type I) from singlet-oxygen oxidation (Type II) on the basis of different cis,trans (kinetic) to trans,trans (thermodynamic) product ratios. Applications of method A to solid dispersions of lignin or titanium dioxide (TiO2, a known singlet-oxygen sensitizer) indicated singlet-oxygen reactions. In addition to the nitroxide triplet, irradiation of lignin produces a persistent broad signal in the solid attributed to phenoxyl radicals. Benzophenone and 3,5-di-tert-butyl-ortho-benzoquinone, 5, coated on silica gel were used as models to compare the effects of irradiating such compounds on the products and kinetics of methyl linoleate oxidation. Benzophenone acted as an initiator, giving free-radical peroxidation, whereas 5 or lignin coated with methyl linoleate acted as singlet-oxygen sensitizers, according to both product studies (method B) and the kinetic order in oxygen consumption during UV photolysis. Photolysis of phase-separated sensitizer (TiO2 or lignin) and substrate (methyl linoleate) resulted in typical singlet-oxygen products. These results indicate that singlet oxygen plays a significant role in the photo-yellowing of high-lignin-content wood pulps.
- Barclay,Basque,Vinqvist
-
p. 457 - 467
(2007/10/03)
-
- Spectroscopic studies and photodynamic actions of hypocrellin B in liposomes.
-
Hypocrellin B (HB), a lipid-soluble natural pigment of perylenequinone derivative, is considered as potential photosensitizer for photodynamic therapy. Liposomes loaded with HB can constitute a simple model system, appropriate for better understanding the photodynamic action of HB in vivo. The steady-state absorption and emission spectra, quantum yield and lifetime of fluorescence of HB incorporated into egg L-a-phosphatidyl-choline (EPC) liposome were examined. The photochemical properties (Type I and/or Type II) of HB have also been studied in aqueous dispersions of small unilamellar liposomes of EPC using electron paramagnetic resonance and spectrophotometric methods, respectively. The quantum yield of 1O2 generated by HB is ca 0.76 in chloroform solution and it did not change upon the incorporation of HB into liposomes of EPC. The superoxide anion radical was generated by the electron transfer from the anion radical of HB (HB.-) to oxygen. The disproportionation of O2.- can generate H2O2 and ultimately the highly reactive .OH via the Fenton reaction. It could be that the disproportionation proceeded too fast, so we could not detect O2.- directly in aqueous dispersions of liposome EPC. Moreover, the self-sensitized photooxygenation of HB embedded in liposomes was studied, and almost fully (87%) inhibiting this reaction of HB by p-benzoquinone (as the quencher of O2.-) in aqueous dispersion of liposome EPC indicated that the radical mechanism (Type I) might be mainly involved in this oxygenation. All these findings suggested that the photodynamic action of HB proceeded via both Type-I and -II mechanisms, but Type-I mechanism might play a more important role in the aqueous dispersion.
- Yu,Chen,Zhang,Shen
-
p. 482 - 488
(2007/10/03)
-
- The aluminium(III) complex of hypocrellin B as a PDT photosensitizer
-
The complex of hypocrellin B (HB) with aluminium was synthesized to improve the water solubility and red absorption of the parent pigment. The complexation of HB with Al3+ resulted in the formation of a complex with 1 : 1 Al(III) : HB stoichiometry (Al3+-HB) measured by molar ratio and continuous variation methods, respectively. The structure of this complex has been characterized by UV-Vis, IR, 1H NMR and elemental analysis data. Compared with HB, the complex possesses excellent solubility in water; in addition, the absorption wavelength of Al3+-HB shifts bathochromically into the phototherapeutic window (600-900 nm). The generation of active oxygen species, including the superoxide radical anion (O2·-) and singlet oxygen (1O2) by Al3+-HB photosensitization was observed. The efficiency of O2· generation by Al3+-HB was twice as much as that of HB. Under our experimental conditions, the rate of O2·-generation by Al3+-HB was about 2.3 μM min-1 measured by the cytochrome c reduction method using 578 nm light. The quantum yield of singlet oxygen (1O2) was 0.23 in DMSO determined by the 9,10-DPA (diphenylanthracene) photobleaching experiments. These results suggest that the new complex possesses an enhanced type I process but a decreased type II process as compared with hypocrellin B.
- Ma,Zhao,Jiang
-
p. 847 - 852
(2007/10/03)
-
- Inhibiting polymerization of vinyl aromatic monomers
-
When a nitroxyl compound is heated in an oxygen-free atmosphere with a vinyl aromatic monomer at 50-140 DEG C. for up to 60 days, it forms an activated inhibitor mixture which is superior to the nitroxyl compound itself in preventing the premature polymerization of a vinyl aromatic monomer during its processing and purification.
- -
-
-
- Application of 4-hydroxy-, 4-Oxo-, and 4-hydroxyimino derivatives of stable 2,2,6,6-tetramethylpiperidine N-oxyl radical for the measurements of lewis acidity of solvents
-
UV-VIS spectra of 2,2,6,6-tetramethylpiperidine N-oxyl (TMPNO) stable radical measured in 18 solvents were compared with the spectra of its derivatives functionalized in the 4 position (4-hydroxy-(h-TMPNO), 4-oxo-(o-TMPNO) and 4-hydroxyimino-(i-TMPNO)). The results obtained proved, that the λmax values corresponding to the n → π* transition in the N-O? chromophore are for all TMPNO derivatives intercorrelated, and they also correlate very well with other acidity parameters (Z, E"T" and AN). Thus, all these compounds could be used as standard bases for determination of the experimental acidity of solvents. Detailed analysis of the spectral characteristics of all compounds leads to the conclusion, that the molar absorptivities (ε) of TMPNO and h-TMPNO corresponding to the n → π* transition are of the order of 10 dm3 mol-1 cm-1, whereas those of the o-TMPNO and i-TMPNO are two times lower. In the case of the π → π* transition we observed an opposite behaviour - the molar absorptivities (ε) of TMPNO and h-TMPNO are close to 2×103 dm3 mol-1 cm-1, whereas those of the oxo and hydroxyimino derivatives are equal to ～4.4×103 dm3 mol-1 cm-1. The integral intensities of both bands behave accordingly. These differences were attributed to the formation of the head-to-tail dimers, in which the N-O? chromophore interacts with the exocyclic double bond in the 4-position of the piperidine.
- Glowacka,Szczepek,Wrona
-
p. 1341 - 1348
(2007/10/03)
-
- Polymerization inhibition of acrylates using blends of nitroxides
-
Ethylenically unsaturated carboxyl monomers, such as acrylic or methacrylic acid or their esters, are protected from premature polymerization during manufacture and storage in the presence or absence of water by the incorporation therein of an effective stabilizing amount of a blend two or more nitroxides. Some of these blends provide synergistic stabilization efficacy much superior to the stabilization results obtained by use of either nitroxide alone.
- -
-
-
- A novel steroidal spin label for membrane structure studies: Synthesis and applications
-
2,2,6,6-Tetramethyl piperidine-N-oxyl nitroxyls are known to partition between aqueous and lipid phases, thus serving as probes to study membrane dynamics. The synthesis of a novel steroidal spin label, 3α-hydroxycholan- 24-yl-(2'',2'',6'',6''-tetramethyl-N-oxyl)piperidyl butan-1',4'-dioate, containing 2,2,6,6-tetramethylpiperidine-N-oxyl moiety covalently bonded to the side chain in 3,24-caprostan-diol has been described. The localization of this spin label in model biomembranes has been studied by using electron spin resonance, differential scanning calorimetry, and 1H and 31P NMR spectroscopic techniques. Its applicability in studying the phase transition properties of model membrane L-α-dipalmitoyl phosphatidyl choline in the presence and absence of drugs has been described by using electron spin resonance. The label has also been used to study the permeability of epinephrine into membrane. The results have shown the applicability of the spin label as a potential spin probe in the study of biomembranes.
- Katoch, Rita,Trivedia, Girish K.,Phadke, Ratna S.
-
p. 849 - 855
(2007/10/03)
-
- The exchange reaction of hydrogen atoms in the system sterically hindered hydroxylamine - Nitroxyl radical
-
The rate constants of the direct and reverse exchange reactions of the hydrogen atom in the system sterically-hindered nitroxyl radical - hydroxylamine of the quinoline, imidazoline, pyrrolidine, and piperidine series as well as diarylhydroxylamine were determined. A scale of the reductive abilities of the hydroxylamines was established. A low value of the isotope effect is typical of the reactions of hydrogen exchange in the systems hydroxylamine - nitroxyl radical.
- Malievskii,Koroteev
-
p. 1287 - 1291
(2007/10/03)
-
- 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-hydroxypiperidine-1-oxyl was observed.
- Kabal'nova,Grabovsky,Shishlov,Shereshovets,Volodarskii,Tolstikov
-
p. 2419 - 2421
(2007/10/03)
-
- Method for inhibiting premature polymerization of vinyl aromatic monomers
-
Nitroxyl inhibitors in combination with some oxygen reduce the premature polymerization of vinyl aromatic monomers during the manufacturing processes for such monomers. Even small quantities of air used in combination with the nitroxyl inhibitors result in vastly prolonged inhibition times for said monomers.
- -
-
-
- α-helical versus 310-helical conformation of alanine-based peptides in aqueous solution: An electron spin resonance investigation
-
Due to the difficulties in experimentally differentiating between the α- and 310-helical conformations in solution, isolated helical peptides have been assumed to be in the α-helical conformation. However, recent electron spin resonance (ESR) studies have suggested that such peptides, in particular short alanine-based peptides, are 310-helical (Miick, S. M.; et al. Nature 1992, 359, 653-5). This result prompted us to further investigate the helical conformations of alanine-based peptides in solution using electron spin resonance spectroscopy. Unlike previous investigations with a flexible link connecting the spin-label to the peptide backbone, we used a conformationally constrained spin-label (4-amino-4-carboxy-2,2,6,6-tetramethylpiperidine-1-oxyl, Toac) that is rigidly attached to the peptide backbone. From a combination of molecular modeling and ESR spectroscopy investigations, it was concluded that these alanine-based peptides exist primarily in the α-helical conformation, and not the 310-form as previously suggested for an analogous set of peptides in aqueous environments. This discrepancy is thought to be due to the differences in flexibility of the spin-labels employed. The conformationally constrained spin-label Toac used in this study should accurately reflect the backbone conformation. Free energy surfaces, or potentials of mean force, for the conformational transition of the spin-label used in previous studies (Miick S. M.; et al. Nature 1992, 359, 653-5) suggest that this spin-label is too flexible to accurately distinguish between the α- and 310-helical conformations.
- Smythe, Mark L.,Nakaie, Clovis R.,Marshall, Garland R.
-
p. 10555 - 10562
(2007/10/03)
-
- Oxidation of Secondary Amines to Nitroxides with Oxone in Aqueous Buffered Solution
-
Under biphasic conditions (CH2Cl2/H2O) using acetone, oxone, buffer and phase-transfer catalyst Bu4NHSO4-, some secondary amines without α hydrogens are oxidized to their corresponding nitroxides in rapid and good yields.
- Brik, M. E.
-
p. 5519 - 5522
(2007/10/02)
-
- Inhibiting polymerization of vinyl aromatic monomers
-
The polymerization of a vinyl aromatic compound, such as styrene, during distillation or purification is very effectively inhibited by the presence of at least one stable nitroxyl compound together with at least one aromatic nitro compound.
- -
-
-
