Department of Chemistry and Biochemistry, University of Detroit Mercy, 4001 West McNichols Road, Detroit, Michigan 48221, USA.
J Phys Chem A. 2010 Jun 3;114(21):6217-25. doi: 10.1021/jp100777u.
We present electron spin resonance (ESR) experiments that describe the interaction of beta-cyclodextrin (beta-CD) with spin adducts of three spin traps: 5,5-dimethyl-1-pyrroline N-oxide (DMPO), N-tert-butyl-alpha-phenylnitrone (PBN), and 2-methyl-2-nitrosopropane (MNP). The focus was on spin adducts of oxygen-centered radicals trapped by DMPO and PBN and on carbon-centered radical adducts trapped by MNP. The radicals were generated by reaction with hydroxyl radicals and the spin adducts studied were DMPO/OH and PBN/OH, MNP/CH(2)COOH generated in CH(3)COOH, and MNP/CF(2)COOH in CF(2)HCOOH. Di-tert-butyl nitroxide ((CH(3))(3)C)(2)NO (DTBN) was also detected in experiments with MNP as the spin trap. A range of interactions of the spin adducts and DTBN with beta-CD was identified. The presence of beta-CD led to significant stabilization of DMPO/OH and PBN/OH but to a negligible effect on the (14)N hyperfine splitting of the adducts, a(N), indicating that the N-O group is outside the beta-CD cavity. An increase of a(N) was detected for DTBN and MNP/CH(2)COOH in CH(3)COOH in the presence of beta-CD, a result we assigned to bonding at the rim of the host. Experiments with methylated beta-CD (Me beta-CD) provided support for this conclusion. A different type of complexation was detected for DTBN and MNP/CF(2)COOH in CF(2)HCOOH: for specific host concentrations both "in" and "out" species were detected. We suggest that the hydrophobicity of the fluorinated adduct leads to insertion of the adduct inside the host cavity. Calculation of the association constant K(a) indicated the competition between DTBN and the adduct for inclusion in the host. For MNP as spin trap, the two nitroxide radicals (adduct and DTBN) have the same type of interaction with the host: at the rim in acetic acid, and inside the host cavity in CF(2)HCOOH. Experiments with DTBN in the absence of the spin trap and of adducts illuminated the effect of the local polarity and of the pH on the hyperfine splittings and indicated that the presence of acetic acid encourages rim complexation.
我们展示了电子顺磁共振（ESR）实验，描述了β-环糊精（β-CD）与三种自旋捕获剂的自旋加合物的相互作用：5,5-二甲基-1-吡咯啉 N-氧化物（DMPO）、N-叔丁基-α-苯基硝酮（PBN）和 2-甲基-2-亚硝基丙烷（MNP）。重点是 DMPO 和 PBN 捕获的氧中心自由基的自旋加合物，以及 MNP 捕获的碳中心自由基加合物。自由基是通过与羟基反应生成的，研究的自旋加合物是在 CH3COOH 中生成的 DMPO/OH 和 PBN/OH、MNP/CH2COOH，以及在 CF2HCOOH 中生成的 MNP/CF2COOH。在 MNP 作为自旋捕获剂的实验中，还检测到二叔丁基氮氧化物（（CH3）3C）2NO（DTBN）。确定了一系列自旋加合物和 DTBN 与β-CD 的相互作用。β-CD 的存在导致 DMPO/OH 和 PBN/OH 的显著稳定，但对加合物的（14）N 超精细分裂 a（N）几乎没有影响，表明 N-O 基团在β-CD 腔外。在存在β-CD 的情况下，在 CH3COOH 中检测到 DTBN 和 MNP/CH2COOH 的 a（N）增加，我们将这一结果归因于主体边缘的键合。用甲基化的β-CD（Meβ-CD）进行的实验为这一结论提供了支持。对于 DTBN 和 MNP/CF2COOH 在 CF2HCOOH 中，检测到了一种不同类型的络合：对于特定的主体浓度，同时检测到“内”和“外”物种。我们认为，由于氟代加合物的疏水性，导致加合物插入主体腔中。通过计算缔合常数 K（a），表明了 DTBN 和加合物在包含在主体中的竞争。对于 MNP 作为自旋捕获剂，两个氮氧化物自由基（加合物和 DTBN）与主体的相互作用类型相同：在醋酸中的边缘，以及在 CF2HCOOH 中的主体腔内。用 DTBN 进行的没有自旋捕获剂和加合物的实验阐明了局部极性和 pH 值对超精细分裂的影响，并表明醋酸的存在促进了边缘络合。
