RUI: Influence of Surface Interactions of Organic Ligand-Iron Oxide/Water Interfaces on Carbon and Iron Cycling Studied by Second Harmonic and Sum Frequency Generation Spectroscopy

在化学学部环境化学科学项目的支持下，阿曼达·米夫林博士和普吉特海湾大学的本科生研究人员正在利用表面特异性激光技术探测有机配体和氧化铁矿物表面之间的相互作用。他们的实验研究得到了与太平洋西北国家实验室（PNNL）分子科学计算小组的科学家合作进行的计算模型的补充。所研究的系统可以作为土壤中常见的地球化学系统的模型，对于理解元素（或其化合物）在生命系统和环境之间转移的过程具有重要意义。该项目特别考虑了植物、动物、土壤和溪流中铁和碳的转移。这项研究为本科生提供了发展关键技术和沟通技能的机会，为他们成功的职业生涯做好准备。他们在PNNL的经历为他们指明了通往政府实验室的职业道路。他们在地区场馆的演讲也有助于向公众宣传环境问题。在环境相关浓度下，金属-表面配合物的直接表面测量，特别是那些涉及有机配体表面络合机制的表面测量，很难研究。Mifflin小组正在利用二次谐波产生（SHG）和和频产生（SFG）探测矿物氧化物/水性有机体系，以获得金属配合物表面性质和结合过程的分子水平信息。研究人员试图更全面地了解这些系统在环境相关条件下的结合和氧化还原化学。具体来说，作为土壤中常见的有机-矿物地球化学系统的模型，研究了含水铁载体去铁胺- b （DFO-B）在赤铁矿/水界面上的吸附、解吸和溶解行为。计算研究有助于解释实验结果，针对其他矿物表面-有机配体相互作用的预测能力。实验提供了直接的光谱证据的表面覆盖，结构和动力学的络合和溶解，以及分子取向。这些关于生物地球化学铁和碳循环的信息可以反过来改进全球模型。

With support from the Environmental Chemical Sciences Program of the Division of Chemistry, Dr. Amanda Mifflin and undergraduate researchers at the University of Puget Sound are probing the interactions between organic ligands and the surfaces of iron oxide minerals using surface-specific laser techniques. Their experimental studies are complemented by computational modeling carried out in collaboration with scientists in the Molecular Science Computing group at Pacific Northwest National Laboratory (PNNL). The systems under study serve as models for geochemical systems commonly found in soils, and have important implications for understanding the process by which elements (or their chemical compounds) are transferred between living systems and the environment. This project specifically considers the transfer of iron and carbon from plants and animals and the soil and streams. The research provides undergraduate students with opportunities to develop critical technical and communication skills that prepare them for successful careers. Their time at PNNL shows them career paths to government laboratories. Their presentations in regional venues also help inform the general public about environmental issues.Direct surface measurements of metal-surface complexes at environmentally relevant concentrations, especially those involving the mechanisms of surface complexation with organic ligands, are difficult to study. The Mifflin group is probing mineral oxide/aqueous organic systems using second harmonic generation (SHG) and sum frequency generation (SFG) to gain molecular-level information of the surface properties and binding processes of metal complexes. The researchers seek a more complete understanding of the binding and redox chemistry of these systems under environmentally relevant conditions. Specifically, the adsorption, desorption and dissolution behavior of the aqueous siderophore desferrioxamine-B (DFO-B) at the hematite/water interface is being studied as a model for organic-mineral geochemical systems commonly found in soils. The computational studies aid in the interpretation of experimental results, targeting predictive capability for other mineral surface-organic ligand interactions. The experiments provide direct spectroscopic evidence of surface coverage, structure and kinetics of complexation and dissolution, and molecular orientation. This information about biogeochemical iron and carbon cycling can in turn lead to improved global models.