Ye Libin, Larda Sacha Thierry, Frank Li Yi Feng, Manglik Aashish, Prosser R Scott
Department of Chemistry, University of Toronto, UTM, 3359 Mississauga Road North, Mississauga, ON, L5L 1C6, Canada.
J Biomol NMR. 2015 May;62(1):97-103. doi: 10.1007/s10858-015-9922-y. Epub 2015 Mar 27.
The elucidation of distinct protein conformers or states by fluorine ((19)F) NMR requires fluorinated moieties whose chemical shifts are most sensitive to subtle changes in the local dielectric and magnetic shielding environment. In this study we evaluate the effective chemical shift dispersion of a number of thiol-reactive trifluoromethyl probes [i.e. 2-bromo-N-(4-(trifluoromethyl)phenyl)acetamide (BTFMA), N-(4-bromo-3-(trifluoromethyl)phenyl)acetamide (3-BTFMA), 3-bromo-1,1,1-trifluoropropan-2-ol (BTFP), 1-bromo-3,3,4,4,4-pentafluorobutan-2-one (BPFB), 3-bromo-1,1,1-trifluoropropan-2-one (BTFA), and 2,2,2-trifluoroethyl-1-thiol (TFET)] under conditions of varying polarity. In considering the sensitivity of the (19)F NMR chemical shift to the local environment, a series of methanol/water mixtures were prepared, ranging from relatively non-polar (MeOH:H2O = 4) to polar (MeOH:H2O = 0.25). (19)F NMR spectra of the tripeptide, glutathione ((2S)-2-amino-4-{[(1R)-1-[(carboxymethyl)carbamoyl]-2-sulfanylethyl]carbamoyl}butanoic acid), conjugated to each of the above trifluoromethyl probes, revealed that the BTFMA tag exhibited a significantly greater range of chemical shift as a function of solvent polarity than did either BTFA or TFET. DFT calculations using the B3LYP hybrid functional and the 6-31G(d,p) basis set, confirmed the observed trend in chemical shift dispersion with solvent polarity.
通过氟（¹⁹F）核磁共振阐明不同的蛋白质构象或状态需要氟化部分，其化学位移对局部介电和磁屏蔽环境的细微变化最为敏感。在本研究中，我们评估了多种硫醇反应性三氟甲基探针[即2-溴-N-(4-(三氟甲基)苯基)乙酰胺（BTFMA）、N-(4-溴-3-(三氟甲基)苯基)乙酰胺（3-BTFMA）、3-溴-1,1,1-三氟丙-2-醇（BTFP）、1-溴-3,3,4,4,4-五氟丁-2-酮（BPFB）、3-溴-1,1,1-三氟丙-2-酮（BTFA）和2,2,2-三氟乙基-1-硫醇（TFET）]在不同极性条件下的有效化学位移分散情况。考虑到¹⁹F核磁共振化学位移对局部环境的敏感性，制备了一系列甲醇/水混合物，范围从相对非极性（甲醇:水 = 4）到极性（甲醇:水 = 0.25）。与上述每种三氟甲基探针共轭的三肽谷胱甘肽[（(2S)-2-氨基-4-{[(1R)-1-[(羧甲基)氨基甲酰基]-2-巯基乙基]氨基甲酰基}丁酸）]的¹⁹F核磁共振谱表明，与BTFA或TFET相比，BTFMA标签作为溶剂极性的函数表现出明显更大的化学位移范围。使用B3LYP杂化泛函和6-31G(d,p)基组的密度泛函理论计算证实了观察到的化学位移分散随溶剂极性的趋势。
