当前位置: X-MOL 学术J. Am. Chem. Soc. › 论文详情
Our official English website, www.x-mol.net, welcomes your feedback! (Note: you will need to create a separate account there.)
Overhauser Dynamic Nuclear Polarization with Selectively Deuterated BDPA Radicals
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2021-11-23 , DOI: 10.1021/jacs.1c09406
Léo Delage-Laurin 1 , Ravi Shankar Palani , Natalie Golota , Michael Mardini , Yifu Ouyang , Kong Ooi Tan , Timothy M Swager 1 , Robert G Griffin
Affiliation  

The Overhauser effect (OE), commonly observed in NMR spectra of liquids and conducting solids, was recently discovered in insulating solids doped with the radical 1,3-bisdiphenylene-2-phenylallyl (BDPA). However, the mechanism of polarization transfer in OE-DNP in insulators is yet to be established, but hyperfine coupling of the radical to protons in BDPA has been proposed. In this paper we present a study that addresses the role of hyperfine couplings via the EPR and DNP measurements on some selectively deuterated BDPA radicals synthesized for this purpose. Newly developed synthetic routes enable selective deuteration at orthogonal positions or perdeuteration of the fluorene moieties with 2H incorporation of >93%. The fluorene moieties were subsequently used to synthesize two octadeuterated BDPA radicals, 1,3-[α,γ-d8]-BDPA and 1,3-[β,δ-d8]-BDPA, and a BDPA radical with perdeuterated fluorene moieties, 1,3-[α,β,γ,δ-d16]-BDPA. In contrast to the strong positive OE enhancement observed in degassed samples of fully protonated h21-BDPA (ε ∼ +70), perdeuteration of the fluorenes results in a negative enhancement (ε ∼ −13), while selective deuteration of α- and γ-positions (aiso ∼ 5.4 MHz) in BDPA results in a weak negative OE enhancement (ε ∼ −1). Furthermore, deuteration of β- and δ-positions (aiso ∼ 1.2 MHz) results in a positive OE enhancement (ε ∼ +36), albeit with a reduced magnitude relative to that observed in fully protonated BDPA. Our results clearly show the role of the hyperfine coupled α and γ 1H spins in the BDPA radical in determining the dominance of the zero and double-quantum cross-relaxation pathways and the polarization-transfer mechanism to the bulk matrix.

中文翻译:


选择性氘代 BDPA 自由基的 Overhauser 动态核极化



欧沃豪瑟效应 (OE) 通常在液体和导电固体的核磁共振谱中观察到,最近在掺杂 1,3-双二亚苯基-2-苯基烯丙基 (BDPA) 基团的绝缘固体中被发现。然而,绝缘体中OE-DNP的极化转移机制尚未建立,但已经提出了自由基与BDPA中质子的超精细耦合。在本文中,我们提出了一项研究,通过对为此目的合成的一些选择性氘代 BDPA 自由基进行 EPR 和 DNP 测量来解决超精细耦合的作用。新开发的合成路线能够在正交位置选择性氘化或芴部分全氘化, 2 H 掺入率为 >93%。随后使用芴部分合成两个八氘化 BDPA 自由基,1,3-[α,γ- d 8 ]-BDPA 和 1,3-[β,δ- d 8 ]-BDPA,以及具有全氘化芴的 BDPA 自由基部分,1,3-[α,β,γ,δ- d 16 ]-BDPA。与在完全质子化的h 21 -BDPA (ε ∼ +70) 脱气样品中观察到的强正 OE 增强相反,芴的全氘化导致负增强 (ε ∼ -13),而 α- 和 γ 的选择性氘化BDPA 中的 - 位置(iso 5.4 MHz)导致弱负 OE 增强(ε ∼ -1)。此外,β-和δ-位置( a iso ∼ 1.2 MHz)的氘化导致OE的正增强(ε ∼ +36),尽管相对于完全质子化的BDPA中观察到的幅度有所降低。 我们的结果清楚地表明了 BDPA 自由基中超精细耦合的 α 和 γ 1 H 自旋在确定零量子和双量子交叉弛豫路径的主导地位以及向体基质的极化转移机制中的作用。
更新日期:2021-12-08
down
wechat
bug