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

大分子、超分子和纳米化学计划以及化学系的化学测量和成像计划支持福尔曼大学的Jeffrey T.Petty教授使用DNA链作为支架来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。这项研究影响了金属连接DNA结构的新兴领域，这些结构扩展了用于光学传感和成像应用的DNA的遗传密码。金属因其高导电性、延展性和反射性而被广泛应用于社会。当金属颗粒缩小到纳米尺寸，比人类头发的厚度小1000倍时，它们的电子就会重组，新的性质就会出现。例如，虽然大块银的反射率很高，但由几个原子组成的银原子团有不同的颜色，这取决于团簇的大小、形状和电荷。通过福尔曼大学的佩蒂教授和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-银团簇的原子分辨结构。纳米尺度结构的电子组织以激光的精度在纳秒到毫秒的时间尺度上被探测。该项目的教育影响更广泛，主要是通过全面的研究经验，对福尔曼大学的本科生进行指导和培训。福尔曼大学的本科生通过与佐治亚理工学院和明斯特大学等主要研究型大学的研究生和教职员工密切合作，领导他们的个人研究项目。在大分子、超分子和纳米化学计划以及化学测量和成像计划的支持下，弗曼大学的佩蒂教授的团队使用结构引导的方法开发了DNA-银簇发色团。具有~10个原子的银团簇由DNA链稳定，这些加合物的光谱和光物理通过DNA碱基编码。到目前为止，DNA-银团簇发色团已经被经验地开发用于特定的传感和成像应用。最近一个DNA-银簇合物的原子级结构确定了三个结构基序，显示了银和DNA是如何组织的。一个有两条A2C4链的DNA二聚体捕获了八个银原子，它们的排列方式与北斗七星中的一样。五个银原子的子集模仿北斗七星，因为它们有一个梯形。这些是由金属键距离分开的，很可能是绿色发光络合物的发色核心。另外三个银原子类似于勺柄，因为它们分散在成对的胞嘧啶之间，并连接到DNA链上。这三个键合基序是借用化学和生物化学的工具选择性地修饰的。这些修饰工具用于化学修饰碱基杂原子，酶法切除碱基，以及合成连接DNA链。所得团簇的电子环境通过稳态、时间分辨和手性光学光谱进行了全面的表征。具有独特光谱的DNA簇合物被用质谱学表征，以确定银原子在络合物中的数量和分布。然后使用广泛的溶液条件对这些物种进行筛选以形成晶体，并通过X射线衍射分析来建立DNA-银键和银团簇光谱之间的关系。这一奖项反映了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。

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.