Ligand Regiochemistry on Gold Nanoclusters

在化学系大分子、超分子和纳米化学计划(MSN)的支持下，科罗拉多州立大学的Christopher Ackerson教授正在结合化学合成和先进的化学分析工具，研究不同类型的分子如何竞争金原子簇表面的键位。这些表面可能是低对称性的，这意味着存在许多不同类型的键合位置。不同类型的分子偏爱不同类型的键位。有些分子会同时结合到两个位置。为了确定哪些分子更喜欢哪些结合位点，艾克森教授和他的学生制作了定义明确的金簇，例如AU25，它有18个分子结合位点。他们将AU25与其他分子混合，并使用先进的成像方法来查看分子结合的位置。从长远来看，他们希望制定规则，描述分子将在哪里与金属团簇结合。他们的发现可能导致制造目前无法合成的大分子的方法。这些分子可以用于催化，用作显微镜的标记，也可以用作药物。该奖项支持一个研讨会，该研讨会汇集了化学领域不同子专业的合成专家，并培训了不同的未来科学工作者。阿克森教授的目标是改变目前对金属纳米颗粒表面配体的区域化学控制的理解。所考察的特定体系是魔数金簇上的硫酸盐、乙炔和类似的配体。这些簇的对称性较低(例如，符合C2、I和相似的点群)，这意味着存在许多对称唯一的配体结合位点。总体目标是了解这种金纳米簇上单齿配体的区域化学，并从结构上确定双齿硫代配体如何与幻数金簇结合。讨论的问题包括：(1)什么反应机制可以获得具有长寿命的位置？(2)具有特殊或要求R-基团的硫醇酸盐是否根据其形状定位于特定的区域化学位置？(3)乙炔配体在环境条件下是否以缔合方式交换？(4)双齿硫醇配体结合的结构性质是什么？(5)在单齿配体继续交换的环境条件下，双齿配体能否实现有用的寿命(数天到数周)？(6)能否产生并结晶由双齿配体独占保护的幻数簇？这些问题是通过方法学方法解决的，包括确定配体交换程度的MALDI-MS，以及确定配体交换产品的区域化学的单晶X射线衍射或多维核磁共振光谱。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

With support from the Macromolecular, Supramolecular and Nanochemistry Program (MSN) in the Division of Chemistry, Professor Christopher Ackerson of Colorado State University is combining chemical synthesis and advanced chemical analysis tools to study how different types of molecules compete for bonding sites on the surfaces of clusters of gold atoms. These surfaces can be low-symmetry, meaning that many different types of bonding sites are present. Different types of molecules prefer different types of bonding sites. Some molecules will bond to two sites at the same time. To determine which molecules prefer which binding sites, Professor Ackerson and his students make well-defined gold clusters, such as Au25, which has 18 molecule binding sites. They mix Au25 with other molecules and use advanced imaging methods to see where the molecules bind. In the long term, they want to write rules that describe where molecules will bind to metal clusters. Their discoveries could lead to methods for making large molecules that cannot currently be synthesized. Those molecules could find use in catalysis, as labels in microscopy, and as medicines. The award supports a workshop that brings together synthetic experts from different sub-specialties in chemistry, as well as training the diverse future scientific workforce.Professor Ackerson aims to transform current understanding of regiochemical control of ligands on metal nanoparticle surfaces. The specific system examined is that of thiolate, acetylide, and similar ligands on magic number gold clusters. These clusters are of low symmetry (e.g., conforming to C2, i, and similar point groups), meaning that there are many symmetry-unique ligand binding sites. The overall goals are to understand the regiochemistry of monodentate ligands on such gold nanoclusters and to determine structurally how bidentate thiolate ligands bind to magic number gold clusters. Questions addressed include: (1) What reaction mechanisms access sites with long-term lifetimes? (2) Do thiolates with distinctive or demanding R-groups localize to specific regiochemical sites based on their shape? (3) Do acetylide ligands exchange associatively under ambient conditions? (4) What is the structural nature of bidentate thiol ligand binding? (5) Do bidentate ligands achieve useful lifetimes (days to weeks) in ambient conditions where monodentate ligands continue to exchange? (6) Can a magic-number cluster protected exclusively by bidentate ligands be produced and crystallized? These questions are addressed with methodological approaches including MALDI-MS to determine extent of ligand exchange, and either single crystal X-ray diffraction or multidimensional NMR spectroscopy to determine regiochemistry of ligand-exchange products.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.