Analysis of host-assisted guest protonation exemplified for p-sulfonatocalix[4]arene -: Towards enzyme-mimetic pKa shifts
Analysis of host-assisted guest protonation exemplified for p-sulfonatocalix[4]arene -: Towards enzyme-mimetic pKa shifts
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DOI：
10.1002/chem.200501479
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发表时间：
2006-06-14
影响因子：
4.3
通讯作者：
Nau, Werner M.
中科院分区：
文献类型：
--
作者：
Bakirci, Hueseyin;Koner, Apurba L.;Nau, Werner M.
本文研究了对磺酸基杯[4]芳烃（CX_4）与偶氮烷烃2，3-二氮杂双环[2.2.1]庚-2-烯（1），2，3-二氮杂双环[2.2.2]辛-2-烯（2），2，3-二氮杂双环[2.2.3]壬-2-烯（3）和1-甲基-4-异丙基-2，3-二氮杂双环[2.2.2]辛-2-烯（4）在D_2O中络合作用的pD依赖性。依赖于PD的结合常数，通过H-1 NMR光谱测定，进行了分析，根据一个七态模型，其中包括CX 4四-和五-阴离子，质子化和非质子化形式的偶氮烷烃，相应的配合物，以及CX 4和氘代水合氢离子之间形成的配合物。紫外吸收光谱的变化，即质子化偶氮生色团的近紫外波段的蓝移，根据四态模型进行了分析。通过独立的方法进行的测量表明，通过CX 4的络合作用使客体分子的pK（a）值偏移约2个单位，从而建立了主体辅助客体质子化的情况。由于CX 4的阳离子-受体性质，pK（a）位移可以转化为质子化客体相对于其未质子化形式的结合改善（100倍）。在超分子催化活性的背景下讨论了结果，并比较了不同类型的大环主体诱导的pK（a）位移。
The pD dependence of the complexation of p-sulfonatocalix[4]arene (CX4) with the azoalkanes 2,3-diazabicyclo[2.2.1]hept-2-ene (1), 2,3-diazabicyclo[2.2.2]oct-2-ene (2), 2,3-diazabicyclo[2.2.3]non-2-ene (3), and 1-methyl-4-isopropyl-2,3-diazabicyclo- [2.2.2]oct-2-ene (4) in D2O has been studied. The pD-dependent binding constants, determined by H-1 NMR spectroscopy, were analyzed according to a seven-state model, which included the CX4 tetra- and penta-anions, the protonated and unprotonated forms of the azoalkanes, the corresponding complexes, as well as the complex formed between CX4 and the deuteriated hydronium ion. The variation of the UV absorption spectra, namely the hypsochromic shift in the near-UV band of the azo chromophore upon protonation, was analyzed according to a four-state model. Measurements by independent methods demonstrated that complexation by CX4 shifts the pK(a) values of the guest molecules by around 2 units, thereby establishing a case of host-assisted guest protonation. The pK(a) shift can be translated into improved binding (factor of 100) of the protonated guest relative to its unprotonated form as a result of the cation-receptor properties of CX4. The results are discussed in the context of supra-molecular catalytic activity and the pK(a) shifts induced by different types of macrocyclic hosts are compared.