A STUDY OF SELF-ASSOCIATION OF METHYLENE BLUE FROM PROTONATION EQUILIBRIA
A STUDY OF SELF-ASSOCIATION OF METHYLENE BLUE FROM PROTONATION EQUILIBRIA
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DOI：
10.1021/ja00725a005
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发表时间：
1970-01-01
影响因子：
15
通讯作者：
GHOSH, AK
中科院分区：
文献类型：
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作者：
GHOSH, AK
在研究亚甲基蓝质子化平衡的基础上，采用一种新的方法研究了亚甲基蓝的自缔合反应。在745 mju时，可以用分光光度法测定MBH2+的浓度。实验在0.200 Mhc1中进行。MBH2+的表观质子解离常数Kpdw，定义为B [H+]/[MBH2+]，其中B是所有非质子化染料的总当量浓度，变化系数为9，因为B从2.26 X 10-5变化到1.27 X 10-3 m。B= 0时的外推值a)给出了真正的质子解离常数Ktjd-r′，定义为¿>[H+]/[MBH2+]，其中B是染料单体的浓度。因此，比值Kvda)/kpdm等于Bjb， b可以作为b的函数得到。估计MB+与mbh2 +的关联导致一个小的校正。B (B)数据在质量上与使用“等萃取”方法获得的数据非常相似，并且可以用先前发现的对亚甲基蓝低离子强度满意的缔合模型很好地描述。因此，本方法为先前关于MB+自关联的结论提供了独立的证实。二聚化常数K>，比我们先前对其离子强度依赖性研究的长期外推所预期的要高一些。如果这种差异归因于二聚体与Cl-的离子配对，则推导出的离子配对平衡常数足够低，足以为我们在低离子强度研究中可以忽略反离子参与的假设提供强有力的支持。
The self-association of methylene blue (MB+) has been investigated by a new method based on the study of the protonation equilibrium of MB+. The concentration of MBH2+ can be estimated by spectrophotometry at 745 mju.. The experiments have been performed in 0.200 Mhc1. The apparent proton dissociation constant, Kpdw, of the species MBH2+, defined as B [H+]/[MBH2+], where B is the total equivalent concentration of all non-protonated dye species, varies by a factor of 9 as B varies from 2.26 X 10-5 to 1.27 X 10-3 M. The extrapolated value of A) at B= 0 gives the true proton dissociationconstant, Ktjd-r¡, defined as¿>[H+]/[MBH2+], where b is the concentration of dye monomers. The ratio Kvda)/kpdm thus equals Bjb, and b can be obtained as a function of B. The estimated association of MB+ withMBH2+ leads to a small correction. The B (b) data are qualitatively very similar to thoseobtained by using the “isoextraction” method and are described well by the association model previously found satisfactory for methylene blueat low ionic strengths. The present method thus provides independent confirmation of previous conclusions about the self-association of MB+. The dimerization constant, K>, is somewhat higher than expected on the basis of a long extrapolation from our previous study of its ionic strength dependence. If the difference is attributed to ion pairing of the dimer with Cl-, the derived equilibrium constant for ion pairing is low enough to provide strong supportfor the assumption of negligible counterion participation in our low-ionic-strength studies.