Department of Physics and Astronomy, Georgia State University, Atlanta, Georgia 30302-4106, United States.
J Phys Chem A. 2011 Oct 27;115(42):11566-78. doi: 10.1021/jp2015963. Epub 2011 Sep 29.
With K-band EPR (Electron Paramagnetic Resonance), ENDOR (Electron-Nuclear DOuble Resonance), and EIE (ENDOR-induced EPR) techniques, three free radicals (RI-RIII) in L-lysine hydrochloride dihydrate single crystals X-irradiated at 298 K were detected at 298 K, and six radicals (R1, R1', R2-R5) were detected if the temperature was lowered to 66 K from 298 K. R1 and RI dominated the central portion of the EPR at 66 and 298 K, respectively, and were identified as main chain deamination radicals, (-)OOCĊH(CH(2))(4)(NH(3))(+). R1' was identified as a main chain deamination radical with the different configuration from R1 at 66 K, and it probably formed during cooling the temperature from 298 to 66 K. The configurations of R1, R1', and RI were analyzed with their coupling tensors. R2 and R3 each contain one α- and four β-proton couplings and have very similar EIEs at three crystallographic axes. The two-layer ONIOM calculations (at B3LYP/6-31G(d,p):PM3) support that R2 and R3 are from different radicals: dehydrogenation at C4, (-)OOCCH(NH(3))(+)CH(2)ĊH(CH(2))(2)(NH(3))(+), and dehydrogenation at C5, (-)OOCCH(NH(3))(+)(CH(2))(2)ĊHCH(2)(NH(3))(+), respectively. The comparisons of the coupling tensors indicated that R2 (66 K) is the same radical as RII (298 K), and R3 is the same as RIII. Thus, RII and RIII also are the radicals of C4 and C5 dehydrogenation. R4 and R5 are minority radicals and were observed only when temperature was lowered to 66 K. R4 and R5 were only tentatively assigned as the side chain deamination radical, (-)OOCCH (NH(3))(+)(CH(2))(3)ĊH(2), and the radical dehydrogenation at C3, (-)OOCCH(NH(3))(+)ĊH(CH(2))(3)(NH(3))(+), respectively, although the evidence was indirect. From simulation of the EPR (B//a, 66 K), the concentrations of R1, R1', and R2-R5 were estimated as: R1, 50%; R1', 11%; R2, 14%; R3, 16%; R4, 6%; R5, 3%.
在 298 K 下用 K 波段电子顺磁共振（EPR）、电子-核双共振（ENDOR）和 EIE（ENDOR 诱导的 EPR）技术，在 L-赖氨酸盐酸盐二水合物单晶中检测到 3 个自由基（RI-RIII），如果将温度从 298 K 降低到 66 K，则可以检测到 6 个自由基（R1、R1'、R2-R5）。R1 和 RI 分别在 66 K 和 298 K 时主导 EPR 的中心部分，被鉴定为主链脱氨自由基，（-）OOCĊH（CH（2））（4）（NH（3））（+）。R1'在 66 K 时被鉴定为与 R1 不同构型的主链脱氨自由基，可能是在将温度从 298 降至 66 K 的过程中形成的。通过它们的耦合张量分析了 R1、R1'和 RI 的构型。R2 和 R3 各包含一个α-和四个β-质子耦合，在三个晶体学轴上具有非常相似的 EIE。两层 ONIOM 计算（在 B3LYP/6-31G（dp）：PM3 上）支持 R2 和 R3 来自不同的自由基：C4 脱氢，（-）OOCCH（NH（3））（+）CH（2）ĊH（CH（2））（2）（NH（3））（+），和 C5 脱氢，（-）OOCCH（NH（3））（+）（CH（2））（2）ĊHCH（2）（NH（3））（+）。耦合张量的比较表明，R2（66 K）与 RII（298 K）是相同的自由基，而 R3 与 RIII 相同。因此，RII 和 RIII 也是 C4 和 C5 脱氢的自由基。R4 和 R5 是少数自由基，仅在温度降低到 66 K 时观察到。R4 和 R5 仅被暂时分配为侧链脱氨自由基，（-）OOCCH（NH（3））（+）（CH（2））（3）ĊH（2），和 C3 脱氢自由基，（-）OOCCH（NH（3））（+）ĊH（CH（2））（3）（NH（3））（+），尽管证据间接。通过 EPR（B//a，66 K）的模拟，估计了 R1、R1'和 R2-R5 的浓度：R1，50%；R1'，11%；R2，14%；R3，16%；R4，6%；R5，3%。
