Understanding the Mechanism of Mn-Promoted H2O Oxidation

受自然界光合作用对水的氧化作用的启发，清洁能源替代品需要了解重要的反应步骤。光合水（H2O）氧化产生氧气（O2）作为反应产物之一。这个过程中的关键步骤是形成O2中存在的氧-氧键。例如，基于人工光合作用的燃料电池受到其缓慢的H2O氧化速率的限制。这为理解自然界的催化剂是如何工作的提供了一个令人信服的动机。Kovacs教授的小组正在合成含有锰和钙的分子，这些元素是从水中自然光合形成氧气的重要成分。这项研究是（a）测试提出的光合O-O键形成机制，（B）提供证据，为什么钙是必不可少的。Kovacs教授是由华盛顿NSF资助的ADVANCE计划组织的女性教师指导小组的成员，并担任华盛顿和其他学术机构的女性教师，博士后和研究生的导师。她的研究生正在评判科学博览会（班布里奇小学科学博览会，华盛顿州科学与工程博览会），在海岸线STEM节上展示演示，并在太平洋科学中心做志愿者。这些活动使儿童（3-12岁）参与与科学有关的活动。 需要进行基础科学研究，以开发有效捕获阳光并将其能量转化为可储存燃料的方法。 大自然通过光合作用H2O氧化来实现这一点，将太阳能转化为电子和质子形式的化学键能，同时产生维持地球生命所必需的O2。 惰性H2O氧化催化剂限制了现有燃料电池的性能。 大自然有数十亿年的时间来优化其催化剂，其中包含Mn和Ca，这为了解大自然的催化剂如何工作提供了令人信服的动力。 形成过氧中间体的关键O-O键形成步骤的机制还不清楚。 Kovacs教授的研究小组正在合成旨在促进O-O键形成的位点差异化的异质结构MnCa复合物。 这些复合物在靠近锰的位置引入了Ca-OH部分，以便快速捕获通过连续氧化充电产生的MnV氧代中间体。 计算表明，合成目标中的Ca-Mn分离需要最小的重排以形成O-O键。 为了验证所设计的分子能够支持预期在O-O键形成后形成的过氧中间体，正在探索使用含有完整的预形成的O-O键的试剂（H2 O2）形成过氧的独立途径。 反应在低温下进行原位监测，使用电子吸收光谱和EPR，并以逐步的方式加入氧化剂，从而对O-O键形成步骤提供更多的控制。 科瓦奇教授是由UW NSF资助的ADVANCE计划组织的女教师指导小组的成员，并担任女教师，博士后和研究生的导师在UW和其他学术机构。 她的研究生判断当地的科学博览会（班布里奇小学科学博览会，华盛顿州科学和工程博览会在布雷默顿，华盛顿州），目前在海岸线干节示威，并在太平洋科学中心志愿者，从事儿童（3-12岁）在科学相关的活动。

Clean energy alternatives inspired by Nature's photosynthetic oxidation of water require an understanding of the important reaction steps. Photosynthetic water (H2O) oxidation produces oxygen (O2) as one of the reaction products. A key step in this process is the formation of the oxygen-oxygen bond present in O2. For example, fuel cells based on artificial photosynthesis are limited by their slow rates of H2O oxidation. This provides a compelling motivation to understand how Nature's catalyst works. Professor Kovacs' group is synthesizing molecules that contain both manganese and calcium, elements know to be important components in the natural photosynthetic formation of oxygen from water. This research is (a) testing proposed mechanisms for photosynthetic O-O bond formation, and (b) providing evidence as to why calcium is essential. Professor Kovacs is a member of a mentoring group for female faculty organized by the University of Washington NSF-funded ADVANCE program, and serves as a mentor to female faculty, post docs, and graduate students at Washington and other academic institutions. Her graduate students are judging science fairs (Bainbridge Elementary Science Fair, Washington State Science and Engineering Fair), presenting demonstrations at the Shoreline STEM Festival, and volunteering at the Pacific Science Center. These activities are engaging children (ages 3-12) in science-related activities. Fundamental scientific research is needed in order to develop methods for efficiently capturing sunlight, and converting its energy into storable fuels. Nature accomplishes this via photosynthetic H2O oxidation, which converts solar energy into chemical bond energy in the form of electrons and protons, and simultaneously produces the O2 necessary to sustain life on our planet. Sluggish H2O oxidation catalysts limit the performance of existing fuel cells. Nature had billions of years to optimize its catalyst, which incorporates both Mn and Ca, and this provides compelling motivation to understand how Nature's catalyst works. The mechanism of the key O-O bond-forming step to form a peroxo intermediate is not well-understood. Professor Kovacs' research group is synthesizing site-differentiated heterobimetallic MnCa complexes designed to promote O-O bond formation. These complexes incorporate a Ca-OH moiety in close proximity to Mn, in order to rapidly trap MnV oxo intermediates, generated via sequential oxidative charging. Calculations show that the Ca-Mn separations in the synthetic targets require minimal rearrangement for O-O bond formation to occur. In order to verify that the designed molecules are capable of supporting the peroxo intermediate expected to form following O-O bond formation, independent routes to peroxos are being explored, using a reagent (H2O2) containing an intact, preformed, O-O bond. Reactions are being monitored in situ at low T, using electronic absorption spectroscopy and EPR, and oxidants are added in a step-wise fashion, thereby providing more control over the O-O bond-forming step. Professor Kovacs is a member of a Mentoring group for female faculty organized by the UW NSF-funded ADVANCE program, and serves as a mentor to female faculty, post docs, and graduate students at the UW, and at other academic institutions. Her graduate students judge local Science Fairs (Bainbridge Elementary Science Fair, Washington State Science and Engineering Fair in Bremerton, WA), present demonstrations at the Shoreline STEM Festival, and volunteer at the Pacific Science Center, engaging children (ages 3-12) in science-related activities.