Department of Analytical Chemistry, University of Chemistry and Technology, Technická 5, 166 28 Prague, Czech Republic.
Sensors (Basel). 2023 Apr 4;23(7):3727. doi: 10.3390/s23073727.
Vanillylmandelic acid (VMA) and homovanillic acid (HVA) are diagnostic markers of neuroblastoma. The purpose of this study was to understand the reason for the discrimination of structural analogues (VMA and HVA) onto a graphite electrode coated with an electrochemically oxidized urea derivative. Density functional theory calculations (DFT), FTIR spectroscopic measurements, and electrochemical impedance spectroscopic measurements were used in this work. Density functional theory calculations (DFT) were used to identify the most suitable binding sites of the urea derivative and to describe possible differences in its interaction with the studied analytes. The FTIR measurement indicated the enhancement and disappearance of NH vibrations on graphite and platinum surfaces, respectively, that could be connected to a different orientation and thus provide accessibility of the urea moiety for the discrimination of carboxylates. Additionally, the higher the basicity of the anion, the stronger the hydrogen-bonding interaction with -NH-groups of the urea moiety: VMA (pK = 10.6, K = (5.18 ± 1.95) × 10) and HVA (pK = 9.6, K = (4.78 ± 1.58) × 10). The differential pulse voltammetric method was applied to detect VMA and HVA as individual species and interferents. As individual analytes, both HVA and VMA can be detected at a concentration of 1.99 × 10 M (RSD ≤ 0.28, recovery 110-115%).
香草扁桃酸（VMA）和高香草酸（HVA）是神经母细胞瘤的诊断标志物。本研究旨在了解结构类似物（VMA 和 HVA）为何能被涂有电化学氧化尿素衍生物的石墨电极区分。本工作采用密度泛函理论计算（DFT）、傅里叶变换红外光谱测量和电化学阻抗谱测量。密度泛函理论计算（DFT）用于确定尿素衍生物的最适合结合位点，并描述其与研究分析物相互作用的可能差异。FTIR 测量表明 NH 振动在石墨和铂表面上的增强和消失，这可能与不同的取向有关，从而为羧酸根的区分提供脲部分的可及性。此外，阴离子的碱性越强，与尿素部分的-NH-基团的氢键相互作用越强：VMA（pK = 10.6，K =（5.18 ± 1.95）× 10）和 HVA（pK = 9.6，K =（4.78 ± 1.58）× 10）。差分脉冲伏安法被应用于检测 VMA 和 HVA 作为单一物质和干扰物。作为单一分析物，HVA 和 VMA 都可以在 1.99×10 M 的浓度下检测到（RSD≤0.28，回收率 110-115%）。
