4399-80-8Relevant articles and documents
Spin label studies of tropomyosin
Chao,Holtzer
, p. 2164 - 2170 (1975)
Studies are reported on nitroxide spin labeled tropomyosin. The labels attach to sulfhydryl groups and to amino groups. The amino spins are highly mobile, the sulfhydryl much less so. Spin count studies show an average of 0.5 labeled sulfhydryl/tropomyosin molecule and only 0.15 labeled amino group/molecule. The spectra ae used to study the denaturation of tropomyosin by guanidine hydrochloride. The information obtained reveals the course of denaturation at sites near the sulfhydryl group. It is found that these sites are more susceptible to guanidine than the bulk of the molecule; denaturation at the sulfhydryl sites is complete by 1.5 M guanidine, whereas optical studies indicate the molecule as a whole is not completely denatured until the concentration reaches 3.5 M. Spectra are also shown of tropomyosin fibers oriented variously with respect to the applied magnetic field. Strong orientation effects are seen and these indicate that the sulfhydryl attached spins (but not the amino attached spins) have a definite orientation in the fiber. Interpretation of the spectra reveals that the normal to the nitroxide plane is inclined to the fiber axis at an angle of 50°. Circular dichroism (CD) studies in the tyrosine region also reveal drastic changes wih guanidine denaturation, confirming the idea that denaturation produces pronounced increased in mobility at the β carbon (as in the sulfhydryl case). A strong negative band existing only in helical tropomyosin at pH's where the tyrosines are uncharged appears to be due to interaction of tyrosines with the helical backbone, whereas the appearance of a strong positive CD band at 250 nm at high pH (11) seems to be ascribable to interaction between the charged phenolic groups and the dissymmetric backbone α carbon atom.
Kinetics and thermodynamics of reversible disproportionation-comproportionation in redox triad oxoammonium cations - Nitroxyl radicals - Hydroxylamines
Sen, Vasily D.,Tikhonov, Ivan V.,Borodin, Leonid I.,Pliss, Evgeny M.,Golubev, Valery A.,Syroeshkin, Mikhail A.,Rusakov, Alexander I.
, p. 17 - 24 (2015/03/03)
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.
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
Zakrzewski, Jerzy,Hupko, Jarosllaw,Kryczka, Krzysztof
, p. 843 - 850 (2007/10/03)
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.
