Clay-porphyrin systems: Spectroscopic evidence of TMPyP protonation, non-planar distortion and meso substituent rotation
Clay-porphyrin systems: Spectroscopic evidence of TMPyP protonation, non-planar distortion and meso substituent rotation
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DOI：
10.1346/ccmn.2005.0530404
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发表时间：
2005-08-01
影响因子：
2.2
通讯作者：
Constantino, VRL
中科院分区：
文献类型：
--
作者：
Dias, PM;De Faria, DLA;Constantino, VRL
用拉曼光谱和紫外-可见光谱研究了水溶性5，10，15，20-四（1-甲基-4-吡啶基）-21 H，23 H卟啉（TMPyP）与不同2：1层状硅酸盐的相互作用。粘土样品用四价阳离子卟啉饱和并从水性悬浮液中分离。所有粘土-TMPyP体系的Soret谱带均发生红移，其顺序为蛭石< Laponite <云母-蒙皂石（Syn-1）<蒙脱石（SWy-2）。此外，在Sorel带（在-425、455和488 nm处）观察到三个分量。在457.9 nm、488.0 nm和514.5 nm激发的拉曼光谱表明卟啉质子化、非平面畸变和内消旋取代基的旋转发生。根据振动数据，提出了粘土的酸度标度：蛭石< Laponite < SWy-2 < Syn-1。质子化光谱的相对贡献在457.9 nm处大于在488.0 nm处，表明在455 nm处的峰对应于质子化物质。在Laponite中，在~ 1635 cm-1处的内消旋取代基谱带的相对强度表明，作为插层的结果，在非质子化卟啉中卟啉和甲基-吡啶基环之间形成的二面角减小。因此，拉曼数据与在457.9 nm处共振的至少两种卟啉物种的存在一致：质子化的和更平坦的非质子化的卟啉。在488.0 nm处，增强模式的数量增加，表明卟啉对称性降低。这使得以488 nm为中心的吸收带可以归属于非平面卟啉构象。
The interaction of the water-soluble 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21H,23Hporphine (TMPyP) with different 2:1 phyllosilicates was examined by Raman and UV-visible spectroscopies. The clay samples were saturated with the tetracationic porphyrin and isolated from the aqueous suspension. A red shift of the Soret band was observed for all the clay-TMPyP systems in the order vermiculite < Laponite < mica-smectite (Syn-1) < montmorillonite (SWy-2). Furthermore, three components were observed for the Sorel band (at -425, 455 and 488 nm). Raman spectra of the isolated solids excited at 457.9 nm, 488.0 nm and 514.5 nm suggest the occurrence of porphyrin protonation, nonplanar distortion and rotation of the meso substituent. Based on the vibrational data, an acidity scale was proposed for the clays: vermiculite < Laponite < SWy-2 < Syn-1. The relative contribution of the protonated spectra is larger at 457.9 nm than at 488.0 nm, suggesting that the peak at 455 nm corresponds to the protonated species. In Laponite, the relative intensity of the meso substituent band at -1635 cm-1 indicates that the dihedral angle formed between the porphyrin and the methyl-pyridyl rings decreased in the non-protonated porphyrin as a consequence of intercalation. Raman data are thus consistent with the presence of at least two porphyrin species in resonance at 457.9 nm: the protonated and a more planar nonprotonated porphyrin. At 488.0 nm the number of enhanced modes increases suggesting a decrease in the porphyrin symmetry. This allows assignment of the absorption band centered at 488 nm to a non-planar porphyrin conformation.