RUI: Crystallography-Guided Synthesis of DNA-Encapsulated Silver Clusters Chromophores

大分子、超分子和纳米化学项目以及化学部门的化学测量和成像项目支持弗曼大学的杰弗里·t·佩蒂教授控制和微调纳米级金属发色团（产生颜色的分子）的颜色和发射，使用DNA链作为支架。这项研究影响了金属链DNA构建的新兴领域，扩展了DNA的遗传密码，用于光学传感和成像应用。金属因其高导电性、延展性和反射率而广泛应用于社会。当金属颗粒缩小到纳米尺寸，比人类头发的厚度还小1000倍时，它们的电子就会重组，新的特性就会出现。例如，虽然大块的银具有很强的反射率，但由几个银原子组成的团簇根据团簇的大小、形状和电荷而具有不同的颜色。通过福尔曼大学的佩蒂教授与佐治亚理工学院的拉克尔·利伯曼教授和罗伯特·迪克森教授的联合专业知识，用x射线衍射测量了纳米级dna -银簇的原子分辨率结构。用激光精度在纳米到毫秒的时间尺度上探测纳米结构的电子组织。该项目更广泛的教育影响集中在通过全面的研究经验指导和培训弗曼大学（一个主要的本科院校）的本科生。弗曼大学的本科生通过与来自主要研究型大学（如佐治亚理工学院和明尼苏达大学）的研究生和教师密切合作，率先开展他们的个人研究项目。在大分子、超分子和纳米化学项目以及化学测量和成像项目的支持下，弗曼大学佩蒂教授的团队使用结构引导方法开发了dna -银簇发色团。含有~10个原子的银簇被DNA链稳定，这些加合物的光谱和光物理性质通过DNA核碱基编码。迄今为止，dna -银簇发色团已被经验开发用于特定的传感和成像应用。最近的DNA-银簇复合物的原子水平结构确定了三个结构基序，显示了银和DNA是如何组织的。带有两条A2C4链的DNA二聚体可以捕获8个银原子，它们的排列就像北斗七星一样。一个由五个银原子组成的子集模仿了勺子，因为它们具有梯形形状。它们被金属键距离隔开，很可能是绿色发光复合物的发色核心。另外三个银原子类似于勺子柄，因为它们分散在成对的胞嘧啶之间，并连接到DNA链上。这三个键基序通过借用化学和生物化学的工具进行选择性修饰。这些修饰工具用于化学修饰核碱基杂原子，酶切核碱基和合成连接DNA链。由此产生的团簇的电子环境是全面表征通过稳态，时间分辨，和手光谱学。具有独特光谱的dna -簇共轭物通过质谱法表征，以确定配合物中银原子的数量和分布。然后使用广泛的溶液条件筛选这些物种以形成晶体，并通过x射线衍射分析以建立dna -银键和银簇光谱之间的关系。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The Macromolecular, Supramolecular, and Nanochemistry Program along with the Chemical Measurement and Imaging Program in the Chemistry Division supports Professor Jeffrey T. Petty at Furman University to control and fine-tune the colors and emissions of nanoscale metal chromophores (color-producing molecules) using DNA strands as scaffolds. This research impacts the burgeoning area of metal-linked DNA constructs that expand the genetic code of DNA for optical sensing and imaging applications. Metals are widely used in society due to their high conductivity, malleability, and reflectivity. As metal particles shrink to nanometer dimensions of 1000 times smaller than the thickness of a human hair, their electrons reorganize and new properties emerge. For example, although bulk silver is highly reflective, clusters of a few-atoms of silver have diverse colors that depend on the cluster size, shape, and charge. Through the combined expertise of Professor Petty at Furman University along with Professors Raquel Lieberman and Robert Dickson at the Georgia Institute of Technology, atomic-resolution structures of nanoscale DNA-silver clusters are measured with X-ray diffraction. The electronic organization of the nanoscale structures are probed over nano- to milli-second time scales with laser-precision. The educational broader impact of the project centers on the mentoring and training of undergraduate students at Furman University, a primarily undergraduate institution, through a comprehensive research experience. Furman undergraduate students spearhead their individual research projects through close collaboration with graduate students and faculty from major research universities such as the Georgia Institute of Technology and the University of Münster.With this support from the Macromolecular, Supramolecular, and Nanochemistry Program and the Chemical Measurement and Imaging Program, Professor Petty’s team at Furman University develops DNA-silver cluster chromophores using a structure-guided approach. Silver clusters with ~10 atoms are stabilized by DNA strands, and the spectra and photophysics of these adducts are encoded via the DNA nucleobases. To date, DNA-silver cluster chromophores have been empirically developed for specific sensing and imaging applications. A recent atomic-level structure of a DNA-silver cluster complex identifies three structural motifs that show how the silvers and DNA are organized. A DNA dimer with two A2C4 strands traps eight silver atoms that are arranged as in the Big Dipper asterism. A subset of five silver atoms mimics the dipper because they have a trapezoid shape. These are separated by metallic bond distances and are likely the chromophoric core of the green-emitting complex. The three other silver atoms resemble the dipper handle because they disperse between pairs of cytosines and join the DNA strands. These three bonding motifs are selectively modified by borrowing tools from chemistry and biochemistry. The modification tools are for chemically modifying nucleobase heteroatoms, enzymatically excising nucleobases, and synthetically linking DNA strands. The electronic environment of the resulting clusters is comprehensively characterized via steady-state, time-resolved, and chirooptical spectroscopies. DNA-cluster conjugates with distinctive spectra are characterized by mass spectrometry to determine the numbers and distributions of silver atoms within the complex. These species are then screened using a wide range of solution conditions to form crystals and analyzed by X-ray diffraction to establish the relationship between the DNA-silver bonding and silver cluster spectra.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.