Desrochers Patrick J, Duong Davis S, Marshall Ariel S, Lelievre Stacey A, Hong Bonnie, Brown Josh R, Tarkka Richard M, Manion Jerald M, Holman Garen, Merkert Jon W, Vicic David A
Department of Chemistry, University of Central Arkansas, Conway, AR 72035, USA.
Inorg Chem. 2007 Oct 29;46(22):9221-33. doi: 10.1021/ic701150q. Epub 2007 Sep 14.
The effect of chelating phosphines was tested on the structure and pH-dependent stability of nickel-cysteine binding. (1,2-Bis(diphenylphosphino)ethane (dppe) and 1,1,1-tris[(diphenylphosphino)methyl]ethane (triphos) were used with three different cysteine derivatives (L-cysteine, Cys; L-cysteine ethyl ester, CysEt; cystamine, CysAm) to prepare complexes of the form (dppe)NiCysR(n+) and (triphos)NiCysR(n+) (n = 0 for Cys; n = 1 for CysEt and CysAm). Similar 31P {1H} NMR spectra for all (dppe)NiCysRn+ confirmed their square-planar P2NiSN coordination spheres. The structure of [(dppe)NiCysAm]PF6 was also confirmed by single-crystal X-ray diffraction methods. The (triphos)NiCysAm+ and (triphos)NiCysEt+ complexes were fluxional at room temperature by 31P NMR. Upon cooling to -80 degrees C, all gave spectra consistent with a P2NiSN coordination sphere with the third phosphorus uncoordinated. Temperature-dependent 31P NMR spectra showed that a trans P-Ni-S pi interaction controlled the scrambling of the coordinated triphos. In aqueous media, (dppe)NiCys was protonated at pH approximately 4-5, leading to possible formation of a nickel-cysteinethiol and eventual cysteine loss at pH < 3. The importance of N-terminus cysteine in such complexes was demonstrated by preparing (dppe)NiCys-bead and trigonal-bipyramidal TpNiCys-bead complexes, where Cys-bead represents cysteine anchored to polystyrene synthesis beads and Tp- = hydrotris(3,5-dimethylpyrazolyl)borate. Importantly, results with these heterogeneous systems demonstrated the selectivity of these nickel centers for cysteine over methionine and serine and most specifically for N-terminus cysteine. The role of Ni-S pi bonding in nickel-cysteine geometries will be discussed, including how these results suggest a mechanism for the movement of electron density from nickel onto the backbone of coordinated cysteine.
测试了螯合膦对镍 - 半胱氨酸结合的结构和pH依赖性稳定性的影响。使用1,2 - 双（二苯基膦基）乙烷（dppe）和1,1,1 - 三[（二苯基膦基）甲基]乙烷（triphos）与三种不同的半胱氨酸衍生物（L - 半胱氨酸，Cys；L - 半胱氨酸乙酯，CysEt；胱胺，CysAm）制备形式为（dppe）NiCysR(n+)和（triphos）NiCysR(n+)的配合物（对于Cys，n = 0；对于CysEt和CysAm，n = 1）。所有（dppe）NiCysRn+的类似31P{1H} NMR光谱证实了它们的平面正方形P2NiSN配位球。[(dppe)NiCysAm]PF6的结构也通过单晶X射线衍射方法得到证实。（triphos）NiCysAm+和（triphos）NiCysEt+配合物在室温下通过31P NMR是动态的。冷却至 - 80℃时，所有光谱均与具有未配位的第三个磷的P2NiSN配位球一致。温度依赖性31P NMR光谱表明，反式P - Ni - S π相互作用控制了配位triphos的重排。在水性介质中，（dppe）NiCys在pH约为4 - 5时质子化，导致可能形成镍 - 半胱氨酸硫醇，并最终在pH < 3时失去半胱氨酸。通过制备（dppe）NiCys - 珠和三角双锥TpNiCys - 珠配合物证明了此类配合物中N端半胱氨酸的重要性，其中Cys - 珠表示锚定在聚苯乙烯合成珠上的半胱氨酸，Tp- = 氢三（3,5 - 二甲基吡唑基）硼酸酯。重要的是，这些非均相体系的结果证明了这些镍中心对半胱氨酸比对甲硫氨酸和丝氨酸具有选择性，并且最特别的是对N端半胱氨酸具有选择性。将讨论Ni - S π键在镍 - 半胱氨酸几何结构中的作用，包括这些结果如何暗示电子密度从镍转移到配位半胱氨酸主链上的机制。
