Ambidextrous Catalysis for Control of Polymer Tacticity

纽约大学的James Canary教授获得了大分子、超分子和纳米化学项目的这一奖项，他正在开发可再生和可生物降解的塑料，这些塑料可以在医疗领域找到用途，比如植入物和开发将药物或药物输送到体内更精确位置的新手段。目前使用的最重要的可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、包装和其他常见材料，但它在制造医疗植入物和药物输送系统中也起着关键作用。聚乳酸的一个特别有用的特征是沿着分子主干排列的基团的相对取向。当这些相对方向发生变化时，所得到的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聚乳酸结构中基团取向的专用催化剂，从而控制其性能。这项工作正在对医学领域中各种用途的新材料的开发产生更广泛的影响。通过生产新的可生物降解塑料，以及用于制造聚乳酸的起始材料通常来自回收材料，它正在对环境产生进一步的广泛影响。这项工作还对下一代科学家的培训产生了影响，因为各级学生，甚至高中生都参与了这项研究。该小组正在进一步扩大他们研究的影响，帮助他们为当地博物馆纽约科学馆准备教育模块。该项目的重点是开发具有电化学开关能力的催化剂，从而在有机反应中逆转对映选择性或非对映选择性。这种特殊的性质，在其他体系中基本上是未知的，正在通过d，l-丙交酯（通常从回收材料中获得）的聚合反应来测试，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，甲基在聚合物背景上的相对取向，即所谓的弹性，是可以改变的。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构。一个有趣的系统，由l -蛋氨酸合成，导致在化学或电化学氧化或还原络合物的螺旋反转。非对映体铜(I)和铜（II）配合物的整体形状几乎是镜像的右旋和左旋螺旋桨结构。在最近的工作中，催化二苯脲基团被附着在可逆氧化还原开关的外围，为不对称反应创造了一种新的催化剂。右手催化剂（Cu（II）氧化态）主要生成(S)-绝对构型产物，而左手Cu(I)催化剂主要生成(R)构型产物。对照实验表明，催化剂的螺旋度决定了反应的立体化学结果。这种双灵巧催化剂方法的独特之处在于，当反应正在进行时，有机会实时切换对映体选择性。催化剂的这种动态特性正被应用于聚乳酸的合成，从而允许对产品的立体化学和这种重要聚合物的最终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.