Phosphates Sensing: Two Polyamino-Phenolic Zinc Receptors Able to Discriminate and Signal Phosphates in Water

Two Zn(II)-dinuclear systems were studied as receptors for phosphates; they were obtained by using the two polyamino-phenolic ligands 3,3′-bis[N,N-bis(2-aminoethyl)aminomethyl]-2,2′-dihydroxybiphenyl (L1) and 2,6-bis[N,N-bis(2-aminoethyl)aminomethyl]phenol (L2) in which the difference lies in the spacers between the two dien units, biphenol or phenol in L1 and L2, respectively. The metallo-receptors obtained are able to selectively discriminate phosphate (Pi) from pyrophosphate (PPi) and vice versa in aqueous solution in a wide range of pH (6 < pH < 10). The L1 receptor system shows selectivity toward PPi over Pi, and on the contrary the L2 system exhibits opposite selectivity. This different selectivity is ascribed to the different Zn(II)−Zn(II) distances between the two metal centers which, showing a similar coordination requirement and binding phosphate in a bridge disposition, fit in a different way with the different guests. Furthermore, NMR studies supported the model of interaction proposed between guests and receptors, highlighting that they are also able to bind biological phosphates such as G6P and ATP at physiological pH. Fluorescence studies showed that the receptor system based on L1 is able to signal the presence in solution of Pi and PPi at physiological pH; the presence of Pi is detected by a quenching of the emission, that of PPi by an enhancement of it. With the aid of an external colored sensor (PCV), the receptors were then used to produce simple signaling systems for phosphates based on the displacement method; the two chemosensors obtained are able to signal and quantify these anions at physiological pH, preserving the selectivity between phosphate and pyrophosphate and extending it to G6P and ATP.

本研究选取了两种锌(II)双核系统作为磷酸的受体进行研究；这两种系统分别由两种多胺酚配体3,3'-双[双(2-氨基乙基)氨基甲基]-2,2'-二羟基联苯（L1）和2,6-双[双(2-氨基乙基)氨基甲基]苯酚（L2）合成，其中两种配体的区别在于二烯单元之间的间隔基团，L1中为双酚，L2中为酚。所获得的金属受体能够在广泛的pH值范围内（6 < pH < 10）对水溶液中的磷酸（Pi）和焦磷酸（PPi）进行选择性区分，反之亦然。L1受体系统对PPi的选择性高于Pi，而L2系统则表现出相反的选择性。这种不同的选择性归因于两个金属中心之间不同的Zn(II)-Zn(II)距离，尽管它们表现出相似的配位需求和以桥连方式结合磷酸，但与不同客体的适配方式不同。此外，核磁共振（NMR）研究支持了客人与受体之间相互作用模型的提出，强调了它们在生理pH值下也能结合生物磷酸如G6P和ATP。荧光研究表明，基于L1的受体系统能够在生理pH值下对Pi和PPi的存在进行信号标记；Pi的存在通过发射淬灭被检测到，而PPi的存在则通过发射增强被检测到。借助外部有色传感器（PCV），这些受体随后被用于基于位移法的简单磷酸信号系统的生产；这两种化学传感器能够在生理pH值下对磷酸阴离子进行信号和量化，保持了磷酸与焦磷酸之间的选择性，并将这种选择性扩展到了G6P和ATP。