Abstract In this paper we report on the Raman scattering of antimalarial artesunate, as a neutral species and as an anion in sodium salt, and on the surface-enhanced Raman scattering (SERS) of the anion adsorbed on silver nanoparticles. The vibrational assignment of the strongest Raman peaks of artesunate has been made with reference to the Raman data on artemisinin and by identifying peaks due to modes largely localized on the succinic side chain of artesunate. The structure of artesunate, as well as that of the anion, has been optimized by means of ab-initio calculations at the DFT/B3LYP/cc-pVDZ calculation level and found in good agreement with the experimental molecular geometry. The conformational minima of the flexible side chain both in the anion and in the anion complexed with Ag+ have been characterized by ab-initio methods at the same level of accuracy and eight pairs of conformers have been predicted. From these data the vibrational frequencies and Raman intensities have been obtained. This has allowed to assign the SERS spectrum of chemisorbed artesunate to conformers with nearly all-trans side chain. For these conformers the artemisinin core lies as far as ≈ 9 A from the silver ion and the active SERS modes are localized on the succinic fragment. Minor contributions to the SERS intensity are due to the di-silver complex and a more sterically hindered mono complex. It is a major conclusion of this study that the interaction of artesunate with the silver surface is exclusively through the side chain, leaving untouched the peroxide group responsible of the antimalarial activity.

中文翻译：

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抗疟药青蒿琥酯的光谱研究：青蒿琥酯在银纳米颗粒上的拉曼和表面增强拉曼散射和吸附几何结构

摘要 在本文中，我们报告了作为中性物质和钠盐中阴离子的抗疟药青蒿琥酯的拉曼散射，以及吸附在银纳米颗粒上的阴离子的表面增强拉曼散射 (SERS)。参照青蒿素的拉曼数据并通过识别主要位于青蒿琥酯琥珀酸侧链上的模式的峰，已经对青蒿琥酯的最强拉曼峰进行了振动分配。青蒿琥酯的结构以及阴离子的结构已通过 DFT/B3LYP/cc-pVDZ 计算级别的 ab-initio 计算进行了优化，并发现与实验分子几何结构非常吻合。阴离子和与 Ag+ 复合的阴离子中柔性侧链的构象最小值已通过 ab-initio 方法以相同的精度水平表征，并预测了八对构象异构体。从这些数据中获得了振动频率和拉曼强度。这允许将化学吸附的青蒿琥酯的 SERS 光谱分配给具有几乎全反式侧链的构象异构体。对于这些构象异构体，青蒿素核心距离银离子 ≈ 9 A，活性 SERS 模式位于琥珀片段上。对 SERS 强度的较小贡献是由于二银络合物和空间位阻更大的单络合物。本研究的一个主要结论是青蒿琥酯与银表面的相互作用完全通过侧链，