SusChEM: Mechanisms of small molecule activation in constrained molecular environments

SusChEM：受限分子环境中小分子激活的机制

• 批准号: 1412909
• 负责人: Elena Rybak-Akimova
• 金额: $ 42万
• 依托单位: Tufts University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-08-15 至 2018-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1412909&HistoricalAwards=false
• 关键词: SusChEM; Mechanisms; small; molecule; activation

In the modern era of scarce resources, developing chemical processes that can eventually generate useful materials and fuels from readily available, cheap, renewable starting materials is of paramount importance. Small molecules (such as oxygen or its close relative, hydrogen peroxide) are ideal sources of oxygen atoms in synthetic applications. New strategies for utilizing oxygen in chemical synthesis and energy production may lead to environmentally clean oxidations that generate water as the only byproduct and rely on readily available reagents. Dr. Rybak-Akimova at Tufts University conducts research to gain a detailed understanding of the pathways in oxygen and peroxide binding and reactivity in selected examples of chemical systems. She aims to identify the "bottlenecks" of these reactions and gain fundamental knowledge important for informing the design of efficient and non-toxic reagents in synthetic applications. This research project provides opportunities for graduate and undergraduate students to be trained in high-level mechanistic studies while also participating in collaborative efforts to design, prepare, characterize, and apply new synthetic systems for small molecule activation. Dr. Rybak-Akimova plans to actively recruit female and minority students for the project through the Tufts Center for STEM Diversity. Outreach to high-school students from public schools in the area includes visits to and presentations at science fairs, field trips by groups of Medford and Somerville high school students to research laboratories at Tufts, and recruitment of high school students as summer researchers. The Macromolecular, Supramolecular and Nanochemistry Program and the Chemical Catalysis Program of the NSF Division of Chemistry jointly support the research group of Dr. Rybak-Akimova to study the role of secondary sphere effects, including hydrophobic interactions with sterically bulky substituents and hydrogen bonding, in selected chemical systems. More specifically, this project investigates: (1) O2 binding and activation at sterically protected metal centers capable of multi-electron oxidations (e.g. Pd(0)/Pd(II) or V(III)/V(V)), and the reactivity of thermally unstable end-on dioxygen adducts (metal-superoxo intermediates) compared to analogous stable side-on metal-peroxo species; (2) encapsulation of peroxide guest inside carboxamide cryptand host and the reactivity of this peroxocryptand with externally added oxidants or reductants; (3) generation and reactivity of metal-bound oxygen intermediates in amide-containing three-dimensional cages and analogous "open" tripodal or two-dimensional macrocyclic hosts; (4) anion recognition of high-valent peroxy anions (e.g. peroxyvanadates) with amide-containing tripods, macrocycles, and cages for selective substrate oxidations. This research aims to establish the mechanisms of stepwise coordination of dioxygen to low-valent metal centers supported by ligands with controlled level of steric bulk and/or the number and location of proton-donating groups at the periphery, measure the reactivity of these species with externally added substrates in direct double-mixing kinetic experiments, identify competent oxidants, examine steric and H-bonding modulation of peroxide reactivity encapsulated in metal-free hosts in reactions with external oxidants or reductants, and determine the mechanisms of electron transfer and atom transfer. Stopped-flow instrumentation and expertise in technically demanding kinetic measurements of rapid reactions developed at Tufts continues to have significant impact on the infrastructure for mechanistic research.

在资源稀缺的现代时代，开发化学工艺，最终能够从现成的、廉价的、可再生的起始材料中生产有用的材料和燃料，是至关重要的。小分子(如氧或其近亲过氧化氢)在合成应用中是氧原子的理想来源。在化学合成和能源生产中利用氧气的新策略可能会导致环境清洁的氧化反应，产生水作为唯一的副产品，并依赖于现成的试剂。塔夫茨大学的Rybak-Akimova博士进行研究，以详细了解选定的化学体系中氧和过氧化氢结合和反应的途径。她的目标是找出这些反应的“瓶颈”，并获得重要的基础知识，为在合成应用中设计高效无毒的试剂提供信息。这一研究项目为研究生和本科生提供了在高级机械研究方面接受培训的机会，同时还参与了设计、准备、表征和应用小分子激活的新合成系统的合作努力。Rybak-Akimova博士计划通过塔夫茨STEM多样性中心为该项目积极招募女性和少数族裔学生。面向该地区公立学校的高中生的宣传活动包括参观科学博览会并在会上发表演讲，梅德福德和萨默维尔的高中生团体到塔夫茨的研究实验室进行实地考察，以及招募高中生作为暑期研究人员。NSF化学部的大分子、超分子和纳米化学计划以及化学催化计划共同支持Rybak-Akimova博士的研究小组研究次级球效应在选定的化学体系中的作用，包括与空间大分子取代基的疏水相互作用和氢键。更具体地说，这个项目研究：(1)氧在能够进行多电子氧化的空间保护的金属中心(例如Pd(0)/Pd(II)或V(III)/V(V))上的结合和活化，以及与类似的稳定的侧面金属过氧基物种相比，热不稳定的端-端氧加成物(金属-超氧代中间体)的反应性；(2)过氧客体在氨基隐形化合物和主体内的包裹以及这种过氧物与外部添加的氧化剂或还原剂的反应性；(3)含酰胺的三维笼子和类似的“开放”三脚架或二维大环主体中金属结合氧中间体的生成和反应；(4)高价过氧阴离子(如过氧钒)与含酰胺的三脚架、大环和笼子的阴离子识别，用于选择性底物氧化。本研究旨在建立氧与低价金属中心的逐级配位机制，通过控制配位体和/或外围质子给电子基的数目和位置，在直接双混合动力学实验中测量这些物种与外部添加底物的反应性，识别合适的氧化剂，考察无金属主体中与外部氧化剂或还原剂反应中过氧化氢反应活性的空间和氢键调节，并确定电子转移和原子转移的机制。塔夫茨开发的停流仪器和在技术上要求苛刻的快速反应动力学测量方面的专门知识继续对机械研究的基础设施产生重大影响。