We report, herein, the development of an easily synthesizable novel dansyl-based turn-on NO sensor L2. The UV-Vis titration data of L2 with Cu2+ display a gradual increase in absorbance at 418 nm with [Cu2+], which were analyzed by using a non-linear least-squares computer-fit program yielding K = (1.16 ± 0.36) × 106 M−1 and n = (1.28 ± 0.03) indicating a 1 : 1 complexation. The ground state geometries of L2 as well as its complex [Cu(L2)Cl]+ (1) were optimized by DFT calculations which showed that in complex 1 the central metal ion is in distorted tetrahedral geometry with bond distances very close to those found in analogous Cu2+ complexes. The fluorescence of L2 was dramatically quenched (∼60-fold) through complexation with paramagnetic Cu2+ to form [Cu(L2)Cl]+ in MeCN–H2O (9 : 1, v/v) at pH 7.2 in HEPES buffer, which on further treatment with Angeli's salt (Na2N2O3) restores its fluorescence property by ∼15-fold due to the reduction of Cu2+ to Cu+ by NO generated in solution from Na2N2O3. The lifetime measurements displayed a substantial decrease in the lifetime of free ligand L2 (τ0 = 12 ns) on complexation with Cu2+ (τ0 = 2.1 ns). The detection limit of NO calculated by the 3σ method gives a value of 1.6 nM. The NO induced fluorescence enhancement of [CuII(L2)Cl]+ was due to the reduction of [CuII(L2)Cl]+ (1) to [CuI(L2)]+ (2) and is supported by the disappearance of the d–d transition band at 850 nm as well as the X-band EPR signal of 1. The selective “turn on” fluorogenic behavior of L2 was examined on HeLa cells of human cervical cancer origin by fluorescence microscopy which showed very intense intracellular fluorescence that was strongly suppressed by the addition of Cu2+ but it regains its fluorescence property on further incubation with Angeli's salt (Na2N2O3). The existence of [CuII(L2)Cl]+ and [CuI(L2)]+ in solution was confirmed by ESI-MS+ (m/z) analysis. The effect of different biologically relevant cations and anions on the fluorescence property of L2 indicates that it was only the [CuII(L2)Cl]+ which displayed high selectivity for NO, indicating its suitability for intracellular application without much worry about its cytotoxicity in a specified dose.
本文报道了一种易于合成的新型丹磺酰基NO开启传感器
L2的开发。
L2与Cu2+的紫外-可见滴定数据显示,在波长418 nm处吸收逐渐增加,与Cu2+浓度相关,通过非线性最小二乘计算机拟合程序分析,得到K = (1.16 ± 0.36) × 106 M−1和n = (1.28 ± 0.03),表明形成了1:1的配合物。通过DFT计算优化了
L2及其配合物[Cu(
L2)Cl]+ (1)的基态几何结构,结果显示在配合物1中,中心
金属离子呈扭曲的四面体几何结构,键长与类似Cu2+配合物中发现的键长非常接近。
L2的荧光在甲腈-
水(9:1, v/v)中与顺磁性Cu2+形成[Cu(
L2)Cl]+时被显著淬灭(约60倍),在
HEPES缓冲液中pH 7.2下,进一步与Angeli盐(Na2N2O3)处理后恢复其荧光性质约15倍,这是由于溶液中由Na2N2O3生成的NO将Cu2+还原为Cu+。寿命测量显示,自由
配体L2(τ0 = 12 ns)与Cu2+结合后寿命显著减少(τ0 = 2.1 ns)。通过3σ方法计算的NO检测限为1.6 nM。[CuII(
L2)Cl]+的荧光增强是由NO诱导的[CuII(
L2)Cl]+ (1)还原为[CuI(
L2)]+ (2),这通过850 nm处d–d跃迁带的消失以及X波段EPR信号的消失得到支持。通过荧光显微镜在源自人类宫颈癌的HeLa细胞上检查了
L2的选择性“开启”荧光行为,结果显示强烈的细胞内荧光,在加入Cu2+后被强烈抑制,但在进一步与Angeli盐(Na2N2O3)孵育后恢复其荧光性质。通过ESI-MS+ (m/z)分析确认了溶液中[CuII(
L2)Cl]+和[CuI(
L2)]+的存在。不同
生物相关阳离子和阴离子对
L2荧光性质的影响表明,只有[CuII(
L2)Cl]+对NO显示出高选择性,表明其在特定剂量下适合细胞内应用,无需过多担心其细胞毒性。