Dirhodium Tetracarboxylate Scaffolds as Reversible Fluorescence-Based Nitric Oxide Sensors

We report the synthesis and characterization of dirhodium tetracarboxylate complexes [Rh2(μ-O2CR)4(L)2], with R = Me and L = dansyl-imidazole (Ds-im) or dansyl-piperazine (Ds-pip). The fluorophores
coordinate to the axial sites of the dirhodium core through the imidazole or piperazine N-atom and emit
only weakly when excited at 365 or 345 nm for the Ds-im and Ds-pip complexes, respectively. These
fluorophore-containing complexes were investigated for their ability to elicit a fluorescence response in the
presence of NO. An immediate increase in fluorescence emission of greater than 15-fold occurs when NO
is admitted to solutions containing [Rh2(μ-O2CMe)4] and Ds-pip or Ds-im. In both systems, the fluorescence
response, which arises by NO-induced displacement of the axially coordinated fluorophore, is reversible
with a sensitivity of ∼4 μM. The related dinitrosyl complexes [Rh2(μ-O2CR)4(NO)2], where R = Me, Et, or
n-Pr, were prepared, structurally characterized, and found to be air-stable, losing NO upon standing in
solution. Sequestration of a methylene chloride solution of the Ds-pip complex from aqueous media by a
NO-permeable membrane allows for fluorescence detection of NO for potential applications in biological
fluids.

本工作报道了四羧酸二铑配合物[Rh₂(μ-O₂CR)₄(L)₂]的合成与表征，其中取代基R为甲基（Me），配体L为丹磺酰基咪唑（dansyl-imidazole，简写为Ds-im）或丹磺酰基哌嗪（dansyl-piperazine，简写为Ds-pip）。上述荧光团通过咪唑或哌嗪环上的氮原子配位至二铑核的轴向位点；对于Ds-im和Ds-pip配合物，分别在365 nm和345 nm波长激发时，其荧光发射信号极弱。本研究考察了这类含荧光团配合物与一氧化氮（NO）作用时诱发荧光响应的能力。当向含有[Rh₂(μ-O₂CMe)₄]与Ds-pip或Ds-im的溶液中通入NO时，荧光发射强度会立刻提升15倍以上。在两个体系中，该荧光响应源于NO诱导轴向配位荧光团的解离，且具有可逆性，检测灵敏度约为4 μM。我们还制备了相关的二亚硝酰配合物[Rh₂(μ-O₂CR)₄(NO)₂]，其中R为甲基（Me）、乙基（Et）或正丙基（n-Pr），并对其完成了结构表征；该类配合物在空气中稳定性良好，但在溶液中静置时会逐渐释放NO。通过透NO膜将Ds-pip配合物的二氯甲烷溶液与水相介质隔离，可实现对NO的荧光检测，该方法有望应用于生物体液中的NO检测场景。