The Coordination Chemistry of Nanocrystal Surfaces: Understanding the Role of Val

描述(申请人提供)：半导体纳米晶体提供了许多技术机会，这些机会源于它们可调的光学和电学特性。纳米晶体具有优异的消光系数、荧光量子产率和对光漂白的稳定性，这使得许多研究人员开始研究纳米晶体作为生物荧光探针的问题。在这些努力面临的众多挑战中，通过配体交换来定制纳米晶体表面以满足期望的应用一直是一个问题。例如，将纳米晶体与生物分子接口的尝试一直难以合成具有紧凑的配位体壳层的充分发光的纳米晶体，这些配位体壳层容易与生物分子结合并在水条件下稳定。配体交换对新兴纳米晶体技术的重要性强调了对纳米晶体表面化学的总体描述的改进的必要性。通过关注这一主题，我们希望建立纳米晶体的分子描述，并改进它们的配位化学、表面结构和反应活性的模型。最终，这些基础研究将引导我们将这些非凡的发色团整合到传感应用中。目前对半导体纳米晶体表面的描述没有充分区分配位配体相互作用(L型结合)和与非化学计量比晶体平衡电荷的配体(X型结合)。为了解决这个问题，我们提出用多核磁共振波谱研究纳米晶体化学计量比与X型和L型表面配体交换的关系。我们的目标是测定配体的热力学结合常数，并研究它们交换的机理和动力学。使用具有明确结构的魔术大小的团簇将进一步允许我们获得关于晶体边、面和顶点上的配体交换的具体方面的细节。在这些研究的基础上，我们的目标是系统地设计锚定螯合剂(L，X型配体)，以不可逆地将水溶基团结合到纳米晶表面。然后，将使用高效液相色谱法对生物素偶联纳米晶的稳定性进行评估。我们还将使用传统的UV-Vis和光致发光测量来确定这些新的配体如何影响正在研究的纳米晶体的光学性质。阐明X-型配体对纳米晶体表面化学的重要性及其与化学计量学的关系可以对纳米晶体研究的所有途径产生重大影响。此外，通过研究X型配体交换，我们将获得精确定制纳米晶体表面的强有力的方法。我们对新的增水方法的研究将导致具有生物相关性的纳米晶体具有更好的尺寸、稳定性和溶解性能。这些方向在基础和技术层面上都是纳米科学的有希望的一步。 与公共健康相关：纳米技术提供了一种手段，使人类能够以以前无法获得的规模与物质进行接触。活着的生物体是由直径通常为微米的细胞组成，并充满了纳米级的机械，因此，纳米技术在细胞层面上询问和操纵生物学具有巨大的潜力。这项建议旨在更好地了解支配其结构和功能的纳米材料的基本性质，最终目标是改进纳米晶体的制备，用于生物探针、细胞标签和药物递送剂。

DESCRIPTION (provided by applicant): Semiconductor nanocrystals present numerous technological opportunities that stem from their tunable optical and electrical properties. Their extraordinary extinction coefficients, fluorescence quantum yields, and stability toward photobleaching have lead many researchers to investigate nanocrystals as fluorescent probes in biology. Among the many challenges facing these endeavors, tailoring nanocrystal surfaces to the desired application by ligand exchange has been persistently problematic. For example, attempts to interface nanocrystals with biological molecules have struggled to synthesize sufficiently luminescent nanocrystals with compact ligand shells that are easily conjugated to biomolecules and stable to aqueous conditions. The importance of ligand exchange to emergent nanocrystal technologies underscores the need for an improved description of nanocrystal surface chemistry in general. By focusing on this subject we hope to build a molecular description of nanocrystals, and to improve models of their coordination chemistry, surface structure and reactivity. Ultimately, these fundamental studies will lead us to integrate these extraordinary chromophores in sensing applications. Current descriptions of semiconductor nanocrystal surfaces do not adequately distinguish between dative ligand interactions (L-type binding) and ligands that balance their charge with nonstoichiometric crystals (X-type binding). To address this problem we propose to study the relationship between nanocrystal stoichiometry and the exchange of both X- and L-type surface ligands using multi-nuclear magnetic resonance spectroscopy. We aim to determine the thermodynamic binding constants of ligands and to study the mechanisms and kinetics of their exchange. The use of magic-sized clusters with a well defined structure will further allow us to obtain details about specific aspects of ligand exchange at crystal edges, faces, and vertices. Building upon these studies, we aim to systematically design anchoring chelators (L,X-type ligands) to bind water solubilizing groups irreversibly to the nanocrystal surface. Using HPLC methods the stability of biotin-conjugated nanocrystals will then be assessed. We will also determine, using traditional UV-Vis and photoluminescnece measurements, how these new ligands effect the optical properties of the nanocrystals under investigation. Clarifying the importance of X-type ligands to nanocrystal surface chemistry and its relationship to stoichiometry can have a dramatic influence on all avenues of nanocrystal research. Furthermore, by investigating X-type ligand exchange we stand to gain powerful methods to precisely tailor nanocrystal surfaces. Our studies on new water solubilization methods will lead to biologically relevant nanocrystals with improved size, stability, and solubility properties. These directions are a promising step for nanoscience, on both a fundamental and a technological level. PUBLIC HEALTH RELEVANCE: Nanotechnology has provided a means by which humans can interface with matter at a scale that was previously unobtainable. Living organisms are built of cells that are typically micrometers across and are filled with machinery on the nanometer scale, and thus, nanotechnology has great potential to interrogate and manipulate biology at the cellular level. This proposal aims to better understand the fundamental properties of nanomaterials that govern their structure and function with the ultimate goal of improving the fabrication of nanocrystals for use as biological probes, cellular labels, and drug delivery agents.