Trommel J S, Marzilli L G
Department of Chemistry, Emory University, Atlanta, Georgia 30322, USA.
Inorg Chem. 2001 Aug 13;40(17):4374-83. doi: 10.1021/ic010232e.
Organocobalt derivatives of tetracationic water-soluble porphyrins are difficult to prepare via the typical reductive alkylation of the Co(II)(por) (porH(2) = porphyrin ligand). None have been reported. The problem may arise because the porphyrin core is made relatively electron poor by the positively charged peripheral groups. We have circumvented this problem by using the Co(III)(NH(3))(5)CH(3) reagent, which inserts the Co(III)-CH(3) moiety directly into porH(2) in water under basic conditions. The method afforded two new CH(3)Co(por) derivatives, CH(3)CoTMpyP(4) and CH(3)CoTMAP, where TMpyP(4) and TMAP are the coordinated, NH-deprotonated forms of meso-tetrakis(N-methyl-4-pyridiniumyl)porphyrin and meso-tetrakis(N,N,N-trimethylaniliniumyl)porphyrin, respectively. The binding of the two new CH(3)Co(por) cations to DNA and to the synthetic DNA polymers poly(dA-dT) and poly(dG-dC) was studied. Using published criteria by which changes in DNA viscosity and in the visible and CD spectra in the Soret region can be used to assess DNA binding, we conclude that both are outside binders. A large hypochromicity of the Soret bands of the CH(3)Co(por) cations observed upon outside binding to DNA may indicate a high degree of self-stacking. The visible absorption and CD spectra of the CH(3)Co(por) cations in the presence of 1:1 mixtures of poly(dA-dT) and poly(dG-dC) are nearly identical to those with poly(dA-dT) alone and are very different from those of poly(dG-dC) alone. Thus, both cations show a high preference for outside binding at AT-rich over GC-rich DNA sites. Upon binding of each of the CH(3)Co(por) cations to all of the DNA polymers, the Soret bands exhibit blue shifts, whereas the Soret bands of the corresponding (H(2)O)(2)Co(por) cations exhibit red shifts. The blue shifts strongly suggest that the CH(3)Co(por) cations, particularly CH(3)CoTMAP, become five-coordinate forms to some extent on DNA binding; this result is the first good evidence for the presence at equilibrium of five-coordinate CH(3)Co(III)(N(4)) forms in water.
四价阳离子水溶性卟啉的有机钴衍生物很难通过典型的Co(II)(por)（porH₂ = 卟啉配体）还原烷基化反应来制备。尚无相关报道。问题可能源于带正电荷的外围基团使卟啉核心的电子相对匮乏。我们通过使用[Co(III)(NH₃)₅CH₃]²⁺试剂规避了这个问题，该试剂在碱性条件下能将Co(III)-CH₃部分直接插入水中的porH₂。该方法得到了两种新的[CH₃Co(por)]⁴⁺衍生物，[CH₃CoTMpyP(4)]⁴⁺和[CH₃CoTMAP]⁴⁺，其中[TMpyP(4)]⁴⁺和[TMAP]⁴⁺分别是中-四( N-甲基-4-吡啶基)卟啉和中-四( N,N,N-三甲基苯胺基)卟啉的配位、NH去质子化形式。研究了这两种新的[CH₃Co(por)]⁴⁺阳离子与DNA以及合成DNA聚合物[poly(dA-dT)]₂和[poly(dG-dC)]₂的结合情况。根据已发表的标准，DNA粘度以及Soret区域可见光谱和圆二色光谱的变化可用于评估DNA结合情况，我们得出结论，两者均为外部结合剂。[CH₃Co(por)]⁴⁺阳离子在外部与DNA结合时观察到的Soret带的大幅减色可能表明高度的自堆积。在[poly(dA-dT)]₂和[poly(dG-dC)]₂的1:1混合物存在下，[CH₃Co(por)]⁴⁺阳离子的可见吸收光谱和圆二色光谱与单独使用[poly(dA-dT)]₂时几乎相同，与单独使用[poly(dG-dC)]₂时的光谱非常不同。因此，两种阳离子在富含AT的DNA位点上对外部结合的偏好都高于富含GC的位点。当每种[CH₃Co(por)]⁴⁺阳离子与所有DNA聚合物结合时，Soret带会出现蓝移，而相应的[(H₂O)₂Co(por)]⁵⁺阳离子的Soret带会出现红移。蓝移强烈表明[CH₃Co(por)]⁴⁺阳离子，特别是[CH₃CoTMAP]⁴⁺，在与DNA结合时在一定程度上变成了五配位形式；这一结果首次有力证明了在水中五配位CH₃Co(III)(N₄)形式在平衡状态下的存在。
