- Influence of chemical structure on nitroxyl spin magnetic relaxation characteristics
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An attampt was made to develop guidelines for the design of new contrast agents using nitroxyl spin labels (NSL).The structural parameters of ring size and of substituents were correlated with the stability towards reduction and the relaxation effectiveness using 5 piperidine and 5 pyrrolidine nitroxyls containing the same substituents.The susceptibility of NSL to reduction was assessed by EPR spectroscopy.The relaxation effectiveness of NSL on proton in buffer and plasma solution was measured on a NMR spectrometer.The ring size and substituents has a decisive effect on the stability of NSL, whereby the ring size effect was dominant.In the case of spin-lattice relaxivities (R1) and spin-spin relaxivities (R2), the ring size and the substition effect were marginal in buffer solution, while in plasma these effects were more pronounced.A number of guidelines were proposed for the design of suitable NSL contrast agents for MRI.
- Brasch, Robert C.,McNamara, Michael T.,Ehman, Richard L.,Couet, Williams R.,Tozer, Thomas N.,et.al.
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- Synthesis of Isoselenocyanates
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Isoselenocyanates were synthesized by two methods under phase-transfer conditions (50% aq NaOH, CH2Cl2, Aliquat 336); the first started from isocyanides and selenium and gave isoselenocyanates in 61-89% yields, while the second started from amines and used chloroform and selenium, by applying sequentially the Hofmann isonitrile synthesis and the addition of selenium, in 4-70% yields.
- Zakrzewski, Jerzy,Huras, Bogumi?a,Kie?czewska, Anna
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- Synthesis and spectral properties of polymethine-cyanine dye-nitroxide radical hybrid compounds for use as fluorescence probes to monitor reducing species and radicals
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Various hybrid compounds comprised of two types of nitroxide radicals and either a pentamethine (Cy5) or trimethine cyanine (Cy3) were synthesized. The nitroxide radicals were linked either via an ester-bond to one or two N-alkyl carboxyl-terminated groups of Cy5, or via two amido-bonds (aminocarbonyl or carbonylamino group) to the 5-position of the indolenine moieties of Cy5 and Cy3. Changes in fluorescence and ESR intensities of the hybrid compounds were measured before and after addition of Na ascorbate in PBS (pH 7.0) to reduce the radicals. Among the hybrid compounds synthesized, those that linked the nitroxide radicals via an aminocarbonyl residue at the 5-position of the indolenine moieties on Cy5 and Cy3 exhibited a 1.8- and 5.1-fold increase in fluorescence intensity with the reduction of the nitroxide segment by the addition of Na ascorbate, respectively. In contrast, fluorescence intensity was not enhanced in the other hybrid compounds. Thus, the hybrid compounds which exhibited an increase in fluorescent intensity with radical reduction can be used in the quantitative measurement of reducing species such as Fe2+ and ascorbic acid, and hydroxyl radicals. Because these hybrid compounds have the advantage of fluorescing at longer wavelengths-661 (Cy5) or 568 (Cy3) nm, respectively, they can be used to measure radical-reducing species or radicals either in solution or in vivo.
- Sato, Shingo,Tsunoda, Minoru,Suzuki, Minoru,Kutsuna, Masahiro,Takido-uchi, Kiyomi,Shindo, Mitsuru,Mizuguchi, Hitoshi,Obara, Heitaro,Ohya, Hiroaki
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experimental part
p. 2030 - 2039
(2009/03/12)
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- Reaction of Nitroxides with Sulfur Containing Compounds II [1]. Preparation of Nitroxides Bearing an Isothiocyanate Substituent in View of the Nitroxyl Group Reduction with Thiophosgene
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The reaction of thiophosgene with 2,2,6,6-tetramethylpiperidine-1-oxyl (used as a model nitroxyl radical) was examined. 2,2,6,6-Tetramethylpiperidine and 2,2,6,6-tetramethyl-1-hydroxypiperidine were identified as products. The reaction is not competitive with the reaction of thiophosgene with an amino group. Thus, three nitroxides with an isothiocyanate group were synthesized from thiophosgene and the nitroxides containing the amino substituent.
- Zakrzewski, Jerzy,Hupko, Jarosllaw,Kryczka, Krzysztof
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p. 843 - 850
(2007/10/03)
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- INFLUENCE OF CHEMICAL STRUCTURE OF NITROXYL SPIN LABELS ON THEIR REDUCTION BY ASCORBIC ACID
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The influence of structure on the reduction of nitroxyl spin labels by ascorbic acid was examined using both piperidine and pyrrolidine nitroxyls.A five-fold molar excess of ascorbic acid and pH of 7.4 were used.The nitroxyl concentration was measured by electron spin resonance spectrometry.The five-membered (pyrrolidine) nitroxyls were more stable than the six-membered derivatives.Ring substituents also influenced the reaction.The anionic derivatives were more stable than the unionized compounds which, in turn, were more stable than the amines (cations at pH 7.4).
- Couet, W. R.,Brasch, R. C.,Sosnovsky, G.,Lukszo, J.,Prakash, I.,et. al.
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p. 1165 - 1172
(2007/10/02)
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