Unusual pH-dependent polarity changes in PAMAM dendrimers: Evidence for pH-responsive conformational changes
Unusual pH-dependent polarity changes in PAMAM dendrimers: Evidence for pH-responsive conformational changes
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DOI：
10.1021/ma000791p
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发表时间：
2000-12-12
期刊：
影响因子：
5.5
通讯作者：
Thomas, JL
中科院分区：
文献类型：
--
作者：
Chen, W;Tomalia, DA;Thomas, JL
结果通过在固定pH值下向2 μM DNS水溶液中加入递增量的树枝状聚合物，研究DNS与PAMAM第6代（G6）的结合。在pH 8（图1，正方形）下，DNS显示荧光强度增加，最大发射峰蓝移，与树枝状聚合物结合DNS的环境极性降低一致。荧光在约100nm处饱和。20 μM G6，这意味着荧光团的结合完成。然后，发射强度的增加和发射最大值的蓝移指示结合染料的环境。在pH 8时最大荧光增加约为1.5。30%，而最大蓝移为9 nm，表明环境的极性比水稍低，但比甲醇极性大得多，其中DNS发射蓝移40 nm。在1M NaCl存在下，DNS在具有类似G6浓度的情况下在发射强度或发射最大值方面均未显示任何显著变化（结果未显示），这表明在高离子强度下不存在结合，并证实了静电相互作用在带负电荷的DNS与带正电荷的树枝状聚合物的结合中的作用。
Results. The binding of DNS to PAMAM generation 6 (G6) was investigated by adding increasing amounts of dendrimers into 2 μM aqueous DNS solution at fixed pH. At pH 8 (Figure 1, squares), DNS showed an increase in the fluorescence intensity and a blue shift in the emission maximum, consistent with a reduced environmental polarity for dendrimer-bound DNS. The fluorescence changes saturated at ca. 20 μM G6, implying that binding of the fluorophore was complete. The increase in emission intensity and blue shift in emission maximum are then indicative of the environment of the bound dye. The maximum fluorescence increase at pH 8 was ca. 30%, while the maximum blue shift was 9 nm, indicating an environment somewhat less polar than water but considerably more polar than methanol, in which DNS emission is blue-shifted 40 nm. In the presence of 1 M NaCl, DNS did not show any significant changes in either the emission intensity or the emission maximum with similar G6 concentration (results not shown), which indicated the absence of binding at high ionic strength and confirmed the role of electrostatic interactions in binding of the negatively charged DNS to the positively charged dendrimers.