Ambidextrous Catalysis for Control of Polymer Tacticity

凭借高分子、超分子和纳米化学项目的这一奖项，纽约大学的James Canary教授正在开发可再生和可生物降解的塑料，这些塑料可用于医疗领域，例如植入物和开发新方法，将药物或药物输送到体内更精确的位置。当今使用的最重要的生物降解塑料之一是聚乳酸或PLA。这种塑料在许多应用中用于制造容器，包装材料和其他常见材料，但它也在医疗植入物和药物输送系统的制造中发挥着关键作用。使PLA特别有用的特征之一是沿着分子主链沿着排列的基团的相对取向。当这些相对取向变化时，所得塑料的刚度可以改变，其生物降解性也可以改变。该项目的目标是开发能够精确控制PLA结构中基团取向的专用催化剂，从而控制其性能。这项工作对开发在医疗领域具有各种用途的新材料产生了更广泛的影响。它对环境产生了更广泛的影响，既通过生产新的可生物降解塑料，也通过用于制造PLA的起始材料通常从回收材料中获得。这项工作还通过各级学生，甚至高中学生参与研究，对下一代科学家的培训产生了影响。该小组正在进一步扩大他们的研究的影响，通过帮助准备教育模块，他们的工作，为当地的博物馆，纽约科学馆。该项目的重点是开发催化剂的能力，以电化学转换，并因此，在有机反应中的反对映体或非对映体选择性。这种在其他系统中基本上未知的特殊性质正在d，l-丙交酯（通常从回收材料中获得）的聚合反应中进行测试，以形成聚丙交酯（PLA），一种可再生和可生物降解的聚合物。如果使用合适的催化剂，甲基沿着聚合物背景的相对取向，即已知为立构规整度的性质可以变化。该小组正在探索一组铜配合物，这些配合物在中心铜原子氧化或还原时表现出有机配体的戏剧性重新配置。由L-甲硫氨酸合成的一个有趣的系统导致在化学或电化学氧化或还原时络合物的螺旋性反转。非对映体的铜（I）和铜（II）配合物的整体形状几乎是镜像左右手螺旋桨结构。在最近的工作中，催化二苯基脲基团被连接到可逆氧化还原开关的外围，创造了一种新的催化剂的不对称反应。右手催化剂（Cu（II）氧化态）主要生成（S）-绝对构型的产物，而左手Cu（I）催化剂主要生成（R）-绝对构型的产物。对照实验表明，催化剂的螺旋度控制反应的立体化学结果。这种双相催化剂方法的独特之处在于在反应进行的同时有机会在真实的时间内切换对映选择性。催化剂的这种动态特性正被应用于PLA的合成，从而允许对产物的立体化学和这种重要聚合物的所得性质进行前所未有的控制。

With this award from the Macromolecular, Supramolecular and Nanochemistry Program, Professor James Canary of New York University is developing renewable and biodegradable plastics that could find use in the medical field, such as in implants and the development of new means to deliver medicines or drugs to more precise locations in the body. One of the most important of the biodegradable plastics in use today is polylactic acid, or PLA. This plastic is used in many applications to make containers, wrappings and other common materials, but it also plays a key role in the manufacture of medical implants and drug delivery systems. One of the features of PLA that makes it particularly useful is the relative orientation of the groups that are strung along the backbone of the molecule. When these relative orientations are varied, the stiffness of the resulting plastic can be changed, as can its biodegradability. The goal of this project is to develop specialized catalysts that can precisely control the orientation of groups in the PLA structure, thus controlling its properties. This work is having a broader impact on the development of new materials with a variety of uses in the medical field. It is having a further broad impact on the environment, both through the production of new biodegradable plastics and through the fact that the starting material used to make PLA is typically obtained from recycled material. The work is also having an impact on the training of the next generation of scientists through the participation of students at all levels, even high school, in the research. The group is further expanding the impact of their research by helping to prepare educational modules on their work for a local museum, the New York Hall of Science.This project focuses on the development of catalysts with the capability to be switched electrochemically and, consequently, invert enantio- or diastereoselectivity in organic reactions. This special property, essentially unknown in other systems, is being tested in the polymerization reaction of d,l-lactide (normally obtained from recycled materials) to form polylactide (PLA), a renewable and biodegradable polymer. The relative orientation of the methyl groups along the polymer background, property known as tacticity, can be varied if appropriate catalysts are used. The group is exploring a set of copper complexes that exhibit dramatic reconfiguration of the organic ligand upon oxidation or reduction of a central copper atom. One interesting system, synthesized from L-methionine, results in the inversion of the helicity of the complex upon chemical or electrochemical oxidation or reduction. The overall shapes of the diastereomeric copper (I) and copper (II) complexes are nearly mirror image right- and left-handed propeller structures. In recent work, catalytic diphenylurea groups were attached to the periphery of the invertible redox switch, creating a new catalyst for asymmetric reactions. The right-handed catalyst (the Cu(II) oxidation state) gave mainly product of (S)-absolute configuration, while the left-handed Cu(I) catalyst produced mainly (R) product. Control experiments indicate that the helicity of the catalyst governs the stereochemical outcome of the reaction. The unique feature of this ambidextrous catalyst approach is the opportunity to switch enantioselectivity in real time while a reaction is underway. This dynamic feature of the catalyst is being applied to the synthesis of PLA, thus allowing unprecedented control over the stereochemistry of the product and the resulting properties of this important polymer.