Ambidextrous Catalysis for Control of Polymer Tacticity

纽约大学的詹姆斯·加纳利教授获得了大分子、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，这些塑料可能会在医疗领域找到用途，例如用于植入物和开发将药物或药物输送到体内更精确位置的新方法。今天使用的最重要的可生物降解塑料之一是聚乳酸，或称聚乳酸。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，但它也在医疗植入物和药物输送系统的制造中发挥关键作用。使其特别有用的特征之一是沿着分子主干连接的基团的相对取向。当这些相对取向不同时，所产生的塑料的硬度可以改变，其生物降解性也可以改变。该项目的目标是开发专门的催化剂，能够精确地控制聚乳酸结构中基团的取向，从而控制其性能。这项工作正在对医疗领域具有多种用途的新材料的开发产生更广泛的影响。它正在对环境产生更广泛的影响，既通过生产新的可生物降解塑料，也通过用于制造聚乳酸的原料通常从回收材料中获得这一事实。这项工作还通过各级学生，甚至是高中学生的参与，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，帮助为当地的博物馆纽约科学大厅准备他们工作的教育模块。这个项目专注于开发具有电化学切换能力的催化剂，从而逆转有机反应中的对映或非对映选择性。这种在其他系统中基本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，以形成聚乳酸(PLA)，这是一种可再生和可生物降解的聚合物。如果使用适当的催化剂，甲基在聚合物背景上的相对取向，即所谓的规整性，可以改变。该小组正在探索一系列铜络合物，这些络合物在中心铜原子氧化或还原时显示出有机配体的戏剧性重新配置。一个有趣的体系，由L-蛋氨酸合成，导致络合物的螺旋性在化学或电化学氧化或还原时发生反转。非对映异构体铜(I)和铜(II)络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，催化二苯基脲基团连接到可逆氧化还原开关的外围，创造了一种新的不对称反应催化剂。右旋催化剂(铜(II)氧化态)主要生成(S)-绝对构型产物，而左旋铜(I)催化剂主要生成(R)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，在反应进行时有机会实时切换对映体选择性。催化剂的这一动态特性正被应用于聚乳酸的合成，从而可以前所未有地控制产品的立体化学和由此产生的这种重要聚合物的性质。

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.