Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80210, USA.
Department of Pharmaceutical Sciences, School of Pharmacy & In Vivo Multifunctional Magnetic Resonance Center, West Virginia University, Morgantown, WV 26506, USA.
J Magn Reson. 2020 Sep;318:106797. doi: 10.1016/j.jmr.2020.106797. Epub 2020 Jul 28.
Electron spin relaxation times for perdeuterated Finland trityl 99% enriched in C at the central carbon (C-dFT) were measured in phosphate buffered saline (pH = 7.2) (PBS) solution at X-band. The anisotropic C hyperfine (A = A = 18 ± 2, A = 162 ± 1 MHz) and g values (2.0033, 2.0032, 2.00275) in a 9:1 trehalose:sucrose glass at 293 K and in 1:1 PBS:glycerol at 160 K were determined by simulation of spectra at X-band and Q-band. In PBS at room temperature the tumbling correlation time, τ, is 0.29 ± 0.02 ns. The linewidths are broadened by incomplete motional averaging of the hyperfine anisotropy and T is 0.13 ± 0.02 µs, which is shorter than the T ~ 3.8 µs for natural abundance dFT at low concentration in PBS. T for C-dFT in deoxygenated PBS is 5.9 ± 0.5 µs, which is shorter than for natural abundance dFT in PBS (16 µs) but much longer than in air-saturated solution (0.48 ± 0.04 µs). The tumbling dependence of T in PBS, 3:1 PBS:glycerol (τ = 0.80 ± 0.05 ns, T = 9.7 ± 0.7 µs) and 1:1 PBS:glycerol (τ = 3.4 ± 0.3 ns, T = 12.0 ± 1.0 µs) was modeled with contributions to the relaxation predominantly from modulation of hyperfine anisotropy and a local mode. The 1/T rate for the 1% C-dFT in the predominantly C labeled sample is about a factor of 6 more strongly concentration dependent than for natural abundance C-trityl, which reflects the importance of Heisenberg exchange with molecules with different resonance frequencies and faster relaxation rates. In glassy matrices at 160 K, T and T for C-dFT are in good agreement with previously reported values for C-dFT consistent with the expectation that modulation of nuclear hyperfine does not contribute to electron spin relaxation in a rigid lattice.
在 X 波段下，对在磷酸盐缓冲盐水（pH = 7.2）（PBS）溶液中，在中央碳原子（C-dFT）处 99%富集的氘代芬兰三芐基进行电子自旋弛豫时间的测量。在 293 K 下的 9:1 海藻糖：蔗糖玻璃和 160 K 下的 1:1 PBS：甘油中，通过在 X 波段和 Q 波段下对光谱进行模拟，确定了各向异性 C 超精细（A = A = 18 ± 2，A = 162 ± 1 MHz）和 g 值（2.0033、2.0032、2.00275）。在室温下的 PBS 中，翻滚相关时间 τ 为 0.29 ± 0.02 ns。线宽通过超精细各向异性的不完全运动平均而变宽，并且 T 为 0.13 ± 0.02 µs，这比低浓度 PBS 中天然丰度 dFT 的 T 〜 3.8 µs 短。在脱氧 PBS 中 C-dFT 的 T 为 5.9 ± 0.5 µs，这比 PBS 中的天然丰度 dFT（16 µs）短，但比空气饱和溶液（0.48 ± 0.04 µs）长得多。在 PBS 中，T 在 PBS 中的翻滚依赖性，3:1 PBS：甘油（τ = 0.80 ± 0.05 ns，T = 9.7 ± 0.7 µs）和 1:1 PBS：甘油（τ = 3.4 ± 0.3 ns，T = 12.0 ± 1.0 µs）通过主要来自超精细各向异性调制和局部模式的弛豫的贡献进行建模。在主要为 C 标记的样品中，1% C-dFT 的 1/T 速率比天然丰度 C-三芐基强约 6 倍，这反映了与不同共振频率和更快弛豫速率的分子的海森堡交换的重要性。在 160 K 的玻璃基质中，C-dFT 的 T 和 T 与先前报道的 C-dFT 值非常吻合，这与核超精细调制不会对刚性晶格中的电子自旋弛豫做出贡献的预期一致。
