Dansyl-naphthalimide dyads as molecular probes: effect of spacer group on metal ion binding properties.
Dansyl-naphthalimide dyads as molecular probes: effect of spacer group on metal ion binding properties.
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DOI：
10.1021/jp207895y
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发表时间：
2011-10
期刊：
影响因子：
--
通讯作者：
B. H. Shankar;D. Ramaiah
中科院分区：
文献类型：
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作者：
B. H. Shankar;D. Ramaiah
通过吸收、荧光、NMR、等温量热法（ITC）和激光闪光光解技术研究了几种通过聚亚甲基间隔基团连接的丹磺酰萘酰亚胺共轭物1a-e与各种金属离子的相互作用。这些二联体的特征在于，它们表现出竞争性的单重态-单重态能量转移（SSET）和光诱导电子转移（PET）过程，这两者都随着间隔长度的增加而减少。取决于间隔基团，与其他一价和二价金属离子相比，这些二价体选择性地与二价Cu（2+）和Zn（2+）离子相互作用。Jobs作图分析表明，它们与Cu（2+）形成2：3的配合物，而与Zn（2+）形成1：1的配合物。测定了Zn（2+）和Cu（2+）配合物的缔合常数为10（3）-10（5）M（-1）。无论间隔基团的长度如何，这些二联体有趣地通过改变丹磺酰和萘酰亚胺发色团的发射强度来充当Cu（2+）离子的荧光比率分子探针。相比之下，只有萘酰亚胺的发色团的低级同系物（n = 1-3）的荧光强度被Zn（2+）离子改变。(1)H NMR和ITC测量证实了磺酰胺和二甲胺基团都参与了与Cu（2+）离子的络合，而只有后者参与了与Zn（2+）离子的络合。激光激发的二联体1a-e显示了瞬态吸收的形成，这可以归因于萘酰亚胺发色团的自由基阳离子，而只有三重激发态的二联体1a-e中观察到的Cu（2+）离子的存在下。独特的是，1a-e与Cu（2+）离子的络合作用同时影响PET和SSET过程，而Zn（2+）离子仅部分抑制了低浓度同系物（n = 1-3）的PET过程，而高浓度同系物的发射性质变化可忽略不计。我们的研究结果表明，这些新的共轭物的生物物理性质的间隔基长度依赖的变化，不仅能够选择性检测的Cu（2+）和Zn（2+）离子，但也有助于区分这两个生物重要的金属离子。
Interaction of a few dansyl-naphthalimide conjugates 1a-e linked through polymethylene spacer groups with various metal ions was investigated through absorption, fluorescence, NMR, isothermal calorimetric (ITC), and laser flash photolysis techniques. The characteristic feature of these dyads is that they exhibit competing singlet-singlet energy transfer (SSET) and photoinduced electron transfer (PET) processes, both of which decrease with the increase in spacer length. Depending on the spacer group, these dyads interact selectively with divalent Cu(2+) and Zn(2+) ions, as compared to other mono- and divalent metal ions. Jobs plot analysis showed that these dyads form 2:3 complexes with Cu(2+) ions, while 1:1 complexes were observed with Zn(2+) ions. The association constants for the Zn(2+) and Cu(2+) complexes were determined and are found to be in the order 10(3)-10(5) M(-1). Irrespective of the length of the spacer group, these dyads interestingly act as fluorescence ratiometric molecular probes for Cu(2+) ions by altering the emission intensity of both dansyl and naphthalimide chromophores. In contrast, only the fluorescence intensity of the naphthalimide chromophore of the lower homologues (n = 1-3) was altered by Zn(2+) ions. (1)H NMR and ITC measurements confirmed the involvement of both sulfonamide and dimethylamine groups in the complexation with Cu(2+) ions, while only the latter group was involved with Zn(2+) ions. Laser excitation of the dyads 1a-e showed formation of a transient absorption which can be attributed to the radical cation of the naphthalimide chromophore, whereas only the triplet excited state of the dyads 1a-e was observed in the presence of Cu(2+) ions. Uniquely, the complexation of 1a-e with Cu(2+) ions affects both PET and SSET processes, while only the PET process was partially inhibited by Zn(2+) ions in the lower homologues (n = 1-3) and the higher homologues exhibited negligible changes in their emission properties. Our results demonstrate that the spacer length dependent variations of the photophysical properties of these novel conjugates not only enable the selective detection of Cu(2+) and Zn(2+) ions but also aid in discriminating these two biologically important metal ions.