Elucidating the binding mode of carboxylate-containing ligands to gold nanoparticles (AuNPs) is crucial to understand their stabilizing role. A detailed picture of the three-dimensional structure and coordination modes of citrate, acetate, succinate and glutarate to AuNPs is obtained by ¹³C and ²³Na solid-state NMR in combination with computational modelling and electron microscopy. The binding between the carboxylates and the AuNP surface is found to occur in three different modes. These three modes are simultaneously present at low citrate to gold ratios, while a monocarboxylate monodentate (1κO¹) mode is favoured at high citrate:gold ratios. The surface AuNP atoms are found to be predominantly in the zero oxidation state after citrate coordination, although trace amounts of Au^δ+ are observed. ²³Na NMR experiments show that Na⁺ ions are present near the gold surface, indicating that carboxylate binding occurs as a 2e⁻ L-type interaction for each oxygen atom involved. This approach has broad potential to probe the binding of a variety of ligands to metal nanoparticles.

中文翻译：

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柠檬酸盐在金纳米粒子稳定过程中的结构和结合方式

阐明含羧酸盐的配体与金纳米颗粒（AuNPs）的结合方式对于理解其稳定作用至关重要。通过¹³ C和²³ Na固态NMR结合计算模型和电子显微镜，获得了柠檬酸盐，乙酸盐，琥珀酸盐和戊二酸盐与AuNPs的三维结构和配位模式的详细图片。发现羧酸盐和AuNP表面之间的结合以三种不同的方式发生。这三种模式中同时存在在低柠檬酸黄金比率，而一元羧酸的单齿（1 κO ¹柠檬酸：金比例高时更适合）模式。表面的AuNP原子被认为是主要在柠檬酸协调后的零氧化态，尽管微量的Au ^{δ +}观察。²³ Na NMR实验表明，Na ⁺离子存在于金表面附近，表明羧酸根结合以2e ^- L型相互作用的形式存在于所涉及的每个氧原子上。这种方法具有探测多种配体与金属纳米颗粒结合的广泛潜力。