Hontz David, Hensley Jayden, Hiryak Kayla, Lee Jennifer, Luchetta Jared, Torsiello Maria, Venditto Michael, Lucent Del, Terzaghi William, Mencer Donald, Bommareddy Ajay, VanWert Adam L
Department of Chemistry & Biochemistry, College of Science and Engineering, Wilkes University, 84 W South St., Wilkes-Barre, Pennsylvania 18766, United States.
Department of Pharmaceutical Sciences, Nesbitt School of Pharmacy, Wilkes University, 84 W South St., Wilkes-Barre, Pennsylvania 18766, United States.
ACS Omega. 2020 Jul 27;5(31):19469-19477. doi: 10.1021/acsomega.0c01655. eCollection 2020 Aug 11.
Fluorescence sensing of oxalate has garnered some attention in the past two decades as a result of this anion's prominence and impact on society. Previous work on oxalate sensors and other divalent anion sensors has led to the conclusion that the sensors are selective for the anion under investigation. However, sensor selectivity is often determined by testing against a relatively small array of "guest" molecules or analytes and studies often exclude potentially interfering compounds. For example, studies on oxalate sensors have excluded compounds such as citrate and urate, which are anions in the biological matrices where oxalate is measured (., urine, blood, and bacterial lysate). In the present study, we reassessed the selectivity of a dinuclear copper(II) macrocycle (CuL) in an eosin Y displacement assay using biologically relevant anions. Although previously reported as selective for oxalate, we found greater indicator displacement (fluorescence response) for urate and oxaloacetate and a significant response to citrate. These anions are larger than oxalate and do not appear to fit into the putative binding pocket of CuL. Consistent with previous reports, CuL did not release eosin Y in the presence of several other dicarboxylates, including adipate, glutarate, malate (except at 10 mM), fumarate, succinate, or malonate (except at 10 mM), and the monocarboxylate acetate. This was demonstrated by the failure of the anions to reverse eosin Y quenching by CuL. We also assessed, for the first time, other monocarboxylates, including butyrate, pyruvate, lactate, propionate, and formate. None of these anions were able to displace eosin Y, indicating no interaction with CuL that interfered with the eosin Y binding site. Single-crystal X-ray crystallography revealed that nonselective binding of the anions is likely partly caused by readily accessible copper(II) ions on the external surface of CuL. In addition, π-π stacking of urate with the aromatic groups of CuL cannot be ruled out as a contributor to binding. We conclude that CuL is not suitable for oxalate sensing in a biological matrix unless interfering compounds are selectively removed or masked.
在过去二十年中，由于草酸根离子的显著地位及其对社会的影响，对草酸根离子的荧光传感研究受到了一定关注。先前关于草酸根传感器及其他二价阴离子传感器的研究得出结论，这些传感器对所研究的阴离子具有选择性。然而，传感器的选择性通常是通过针对相对较少的一系列“客体”分子或分析物进行测试来确定的，而且研究往往排除了潜在的干扰化合物。例如，关于草酸根传感器的研究排除了柠檬酸盐和尿酸盐等化合物，而在测量草酸根的生物基质（如尿液、血液和细菌裂解液）中，这些都是阴离子。在本研究中，我们使用与生物相关的阴离子，在曙红Y置换试验中重新评估了双核铜（II）大环化合物（CuL）的选择性。尽管之前报道该化合物对草酸根具有选择性，但我们发现尿酸盐和草酰乙酸盐导致更大的指示剂置换（荧光响应），并且对柠檬酸盐有显著响应。这些阴离子比草酸根大，似乎无法进入CuL假定的结合口袋。与先前报道一致，在几种其他二羧酸盐存在时，CuL不会释放曙红Y，这些二羧酸盐包括己二酸、戊二酸、苹果酸（10 mM时除外）、富马酸、琥珀酸或丙二酸（10 mM时除外），以及一元羧酸盐乙酸盐。阴离子无法使CuL对曙红Y的猝灭作用逆转，证明了这一点。我们还首次评估了其他一元羧酸盐，包括丁酸盐、丙酮酸盐、乳酸盐、丙酸盐和甲酸盐。这些阴离子均无法置换曙红Y，表明它们与CuL没有相互作用从而干扰曙红Y的结合位点。单晶X射线晶体学表明，阴离子的非选择性结合可能部分是由于CuL外表面易于接近的铜（II）离子所致。此外，不能排除尿酸盐与CuL芳香基团之间的π-π堆积作用对结合有贡献。我们得出结论，除非选择性地去除或掩盖干扰化合物，否则CuL不适用于生物基质中草酸根的传感。
