Establishing the Kinetics of Aqueous Reactions at Fe(III) Molecules and Minerals

建立 Fe(III) 分子和矿物质的水反应动力学

• 批准号: 0814242
• 负责人: William Casey
• 金额: $ 38.31万
• 依托单位: University of California-Davis
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-09-01 至 2012-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0814242&HistoricalAwards=false
• 关键词: Establishing; Kinetics; Aqueous; Reactions; Fe

Investigators propose to establish a linear-free-energy relation (LFER) to predict rates of ligand substitution on Fe(III)-oxide minerals from the FeIII-OH2 bond lengths, which can either be calculated or measured. In the last funding period we showed experimentally that such a LFER probably exists between FeIII-OH2 bond lengths and rates of solvent exchanges. They also used similar data on nanometer-size Al(III) ions to establish a LFER for aluminous surface structures. They coupled 'rare event' simulation methods to experimental data on rates of water-exchanges from Al(III) metals in large nanometersize clusters. This work showed, for the first time, that the rates at the surfaces are extraordinarily and surprisingly rapid.Investigators now want to extend the work to Fe(III) (hydr)oxide materials. They use aqueous complexes with particularly useful FeIII-OH2 bond lengths and aqueous stabilities to establish an experimental scale of rates and bond lengths. In the last funding period, they mastered a 17O-NMR line-broadening method for paramagnetic metals like Fe(III). This method is new to geochemistry, but otherwise well understood and dependable. Once the experimental scale is established, they repeat their 'rare-event' simulations to estimate rates for Fe(III)-(hydr)oxide surface structures that are experimentally inaccessible.For bridging oxygens, and to complement the 17O-NMR measurements, they employ a new ElectroSpray-Ionization Mass-Spectrometry (ESI-MS) method that allows to follow the rates of oxygen-isotope exchanges in the dissolved molecules. With ESI-MS, we follow reactions at oxo bridges and the carboxylate oxygens in a bonded organic ligand. With this method, geochemists can study an enormous range of compounds that were previously impossible, such as the Mn(IV,III)-oxo clusters. In this sense, and in others, this research is both pioneering and transformative to geochemistry.This research is also Transformative because water-exchange rates are the most fundamental timescale for describing aqueous reactions---slow loss of these bound waters precedes most ligand substitutions ('adsorptions') and many electron exchanges. In soils, these reactions are usually part of a complex network, but these elementary reactions control the essential step. This research is Transformative because reactions are also at the appropriate scale to improve methods of simulation, which will be heavily employed by geochemists for cases where experiments are impossible. They are trying to make aqueous geochemistry quantitative at the molecule scale.The Intellectual Merit is fundamental research in aqueous reactivity where they answer questions such as: 'What are the most promising types of computationally inexpensive methods that can yield hidden reaction pathways in systems that are sufficiently large to be geochemically relevant?' The research also ties to the increased awareness about nanometer-size clusters in natural water chemistry, in transporting toxicants or as toxicants themselves, and as the fundamental building block for amorphous materials.The Broader Impacts extend well beyond Earth science because this research is used by many disciplines, including colloid chemistry, nanoscience, materials science and medicine (metalloproteins such as ferritin and enzymes such as the purple-acid phosphatases resemble these clusters). Also, enrollment at UCD draws disproportionately from the high population of new immigrants to the United States and lures them into Chemistry and Geochemistry. These funds bring nontraditional but highly talented students into the Earth Sciences, which comprise the population of UCD.

研究人员建议建立线性自由能关系 (LFER)，根据 FeIII-OH2 键长预测 Fe(III)-氧化物矿物上的配体取代率，该键长可以计算或测量。在上一个资助期间，我们通过实验表明，FeIII-OH2 键长和溶剂交换率之间可能存在这种 LFER。 他们还使用纳米级 Al(III) 离子的类似数据来建立铝表面结构的 LFER。他们将“罕见事件”模拟方法与大型纳米簇中 Al(III) 金属水交换速率的实验数据结合起来。这项工作首次表明，表面的速率异常快得令人惊讶。研究人员现在希望将工作扩展到 Fe(III) (Hydr)Oxide 材料。他们使用具有特别有用的 FeIII-OH2 键长和水稳定性的水性络合物来建立速率和键长的实验规模。在上一个资助期间，他们掌握了 Fe(III) 等顺磁性金属的 17O-NMR 谱线展宽方法。这种方法对于地球化学来说是新方法，但在其他方面很容易理解且可靠。一旦建立了实验规模，他们就会重复“罕见事件”模拟，以估计实验中无法达到的 Fe(III)-（氢）氧化物表面结构的速率。为了桥接氧，并补充 17O-NMR 测量，他们采用了一种新的电喷雾电离质谱 (ESI-MS) 方法，该方法允许跟踪氧同位素交换速率 溶解的分子。通过 ESI-MS，我们跟踪氧桥和键合有机配体中的羧酸氧的反应。通过这种方法，地球化学家可以研究以前不可能的大量化合物，例如 Mn(IV,III)-氧簇。从这个意义上说，从其他意义上说，这项研究对地球化学来说既是开创性的，也是变革性的。这项研究也是变革性的，因为水交换率是描述水反应最基本的时间尺度——这些结合水的缓慢损失先于大多数配体取代（“吸附”）和许多电子交换。在土壤中，这些反应通常是复杂网络的一部分，但这些基本反应控制着关键步骤。这项研究是变革性的，因为反应也处于适当的规模，以改进模拟方法，地球化学家将在无法进行实验的情况下大量使用模拟方法。他们正试图在分子尺度上定量水地球化学。智力价值是水反应性的基础研究，他们回答了这样的问题：“最有前途的计算成本低廉的方法是什么类型，可以在足够大的系统中产生隐藏的反应路径，以与地球化学相关？”这项研究还与人们对天然水化学中纳米级簇、有毒物质运输或有毒物质本身以及作为无定形材料的基本组成部分的认识的提高有关。更广泛的影响远远超出了地球科学，因为这项研究被许多学科所使用，包括胶体化学、纳米科学、材料科学和医学（铁蛋白等金属蛋白和紫酸等酶） 磷酸酶类似于这些簇）。此外，都柏林大学的入学人数不成比例地吸引了大量美国新移民，并吸引他们学习化学和地球化学。这些资金将非传统但才华横溢的学生带入地球科学领域，这些学生构成了都柏林大学的人口。