Laser Flash Photolysis and CIDNP Studies of Steric Effects on Coupling Rate Constants of Imidazolidine Nitroxide with Carbon-Centered Radicals, Methyl Isobutyrate-2-yl and <i>tert</i>-Butyl Propionate-2-yl
作者:Dmitry Zubenko、Yuri Tsentalovich、Nataly Lebedeva、Igor Kirilyuk、Galina Roshchupkina、Irina Zhurko、Vladimir Reznikov、Sylvain R. A. Marque、Elena Bagryanskaya
DOI:10.1021/jo060787x
日期:2006.8.1
polarization (TR-CIDNP) and laser flashphotolysis (LFP) techniques have been used to measure rateconstants for coupling between acrylate-type radicals and a series of newly synthesized stable imidazolidine N-oxyl radicals. The carbon-centered radicals under investigation were generated by photolysis of their corresponding ketone precursors RC(O)R (R = C(CH3)2−C(O)OCH3 and CH(CH3)−C(O)−OtBu) in the presence
时间分辨化学诱导动态核极化(TR-CIDNP)和激光闪光光解(LFP)技术已被用于测量速率常数丙烯酸酯型基团和一系列新合成的稳定的咪唑之间的耦合ñ -氧基的基团。通过对其相应的酮前体RC(O)R(R = C(CH 3)2 -C(O)OCH 3和CH(CH 3)-C(O)-OtBu的光解产生了所研究的以碳为中心的自由基)在稳定的一氧化氮存在下。确定了用于氮氧化物介导的聚合反应(NMP)实验建模研究的偶联速率常数k c,以及空间和电子因素对通过使用哈米特线性自由能关系来解决k c值。通过双参数方程log(k c / M - 1 s - 1)=可以很好地描述由于取代基的空间(E s,n)和电子(σL ,n)变化而引起的k c的系统变化。3.52σL ,n + 0.47 E s,n + 10.62。因此,k c随着空间需求的增加而降低,并随着氮氧化物上取代基的吸电子特性的增加而增加。
Room-temperature electron spin relaxation of nitroxides immobilized in trehalose: Effect of substituents adjacent to NO-group
作者:Andrey A. Kuzhelev、Rodion K. Strizhakov、Olesya A. Krumkacheva、Yuliya F. Polienko、Denis A. Morozov、Georgiy Yu. Shevelev、Dmitrii V. Pyshnyi、Igor A. Kirilyuk、Matvey V. Fedin、Elena G. Bagryanskaya
DOI:10.1016/j.jmr.2016.02.014
日期:2016.5
Trehalose has been recently promoted as efficient immobilizer of biomolecules for room-temperature EPR studies, including distance measurements between attached nitroxide spin labels. Generally, the structure of nitroxide influences the electron spin relaxation times, being crucial parameters for room-temperature pulse EPR measurements. Therefore, in this work we investigated a series of nitroxides with different substituents adjacent to NO-moiety including spirocyclohexane, spirocyclopentane, tetraethyl and tetramethyl groups. Electron spin relaxation times (T-1, T-m) of these radicals immobilized in trehalose were measured at room temperature at X- and Q-bands (9/34 GHz). In addition, a comparison was made with the corresponding relaxation times in nitroxide-labeled DNA immobilized in trehalose. In all cases phase memory times T-m, were close to 700 ns and did not essentially depend on structure of substituents. Comparison of temperature dependences of T-m at T = 80-300 K shows that the benefit of spirocyclohexane substituents well-known at medium temperatures (similar to 100-180 K) becomes negligible at 300 K. Therefore, unless there are specific interactions between spin labels and biomolecules, the room temperature value of T-m in trehalose is weakly dependent on the structure of substituents adjacent to NO-moiety of nitroxide. The issues of specific interactions and stability of nitroxide labels in biological media might be more important for room temperature pulsed dipolar EPR than differences in intrinsic spin relaxation of radicals. (C) 2016 Elsevier Inc. All rights reserved.