A Molecular Chameleon with Fluorescein and Rhodamine Spectroscopic Behaviors

A new class of fluorescein/rhodamine
hybrids with two spirolactone rings was reported to exhibit dual-output
fluorescent behaviors independently. Isolation and characterization
for two diastereomers, trans-RhOH and cis-RhOH, have been made and their X-ray crystal
structures determined. In a basic environment, the spirolactone ring
on the hydroxyl side will be opened to give a fluorescein-like optical
output with the lowest absorptions at 485 and 530 nm emission. On
the other hand, a rhodamine-like optical output, i.e., 528 nm absorption
and 575 nm emission, will be switched on by a H+ or a Hg2+ ion, attributed to the spirolactone ring opening on the
amino side. In a methanol−buffer system with different pH values,
the corresponding pKa values for the hydroxyl
and amino groups were determined as 5.7 and 2.3, respectively. Selective
Hg2+-sensing properties have also been discussed, and log Ks values of about 3.60 and 3.73 were determined.
Confocal microscopic images of Caenorhabditis elegans incubated with RhOH were found to show enhanced fluorescent
intensity with a Hg2+ ion, demonstrating the potential
application of RhOH for in vivo biological imaging.

报道了一种新型具有两个螺环的荧光素/罗丹明杂化物类别，该类别表现出独立的双输出荧光行为。已成功分离并表征了两种对映异构体，即顺式-RhOH和反式-RhOH，并确定了它们的X射线晶体结构。在碱性环境中，羟基侧的螺环将打开，产生类似荧光素的视觉效果，其最低吸收波长分别为485 nm和530 nm，并发出光子。另一方面，通过H+或Hg2+离子的作用，将激活类似罗丹明的视觉效果，即528 nm的吸收和575 nm的发射，这归因于氨基侧的螺环打开。在甲醇-缓冲液体系中，不同pH值下，羟基和氨基对应的pKa值分别为5.7和2.3。此外，还讨论了选择性Hg2+传感特性，并确定了约3.60和3.73的对数Ks值。使用共聚焦显微镜观察经RhOH孵育的秀丽隐杆线虫，发现其荧光强度在Hg2+离子存在下增强，这展示了RhOH在体内生物成像中的潜在应用。