Unraveling structural conundrum of organic nitrogen in soil and sediment organic matter using advanced solid-state NMR: insights into formation mechanisms of stabilized nitrogen

智力优点。氮（N）循环是涉及自然界中氮和含氮化合物转化的生物地球化学循环。氮对于许多生物过程至关重要，对于地球上的任何生命都至关重要。例如，氮是蛋白质、氨基酸的组成部分之一，也是构成所有生命遗传密码的碱基（例如 DNA 和 RNA）的关键组成部分。因此，氮循环是生物地球化学中最重要的课题之一，了解氮循环有助于控制自然界的氮平衡。土壤或沉积物中的大部分氮是有机的。虽然常规 15N 交叉极化/魔角旋转技术已广泛应用于土壤/沉积物有机质 (SOM) 中有机氮的研究，但该技术的固有缺点迄今为止对有机氮结构的了解有限。该项目的目标是：a) 开发一种改进的先进固态协议，用于研究 SOM 中的有机氮形态，b) 研究不同有机氮形态的分布，特别是 SOM 中杂环氮的存在和丰度，c)使用新型和先进的固态核磁共振技术研究生物难熔氮形成的机制。我们将主要关注但不限于两个样品，即 IHSS Pony Lake（南极洲）参考样品和硬沥青，这两个样品都含有相对较高的 N。新的和改进的先进固态 NMR 技术的工作将包括通过使用适当的模型化合物来最大化交叉极化来改进常规 15N 交叉极化/魔角旋转 (CP/MAS)；开发一些 15N 光谱编辑技术来选择特定的官能团，并使用饱和脉冲诱导偶极交换和重偶联来分析共价结合的 N。将使用这些改进的核磁共振技术检查不同形式的有机氮的相对比例。杂环氮的存在和丰度可能会被常规 15N CP/MAS 低估，也将使用这些技术进行研究。该项目有望在了解 SOM 中有机氮的性质方面取得重大进展。它将揭示有关不同形式有机氮相对比例的更准确信息。用于表征SOM中有机氮的新的或改进的NMR技术将为我们提供研究SOM中有机氮的关键工具，为显着提高对氮生物地球化学的理解奠定基础。更广泛的影响。该项目将培训一名研究生应用、改进和开发先进的生物地球化学固态核磁共振技术。它还将影响 PI 计划的大学和研究生级别的公共宣传和教育宣传内容。更广泛的影响。该项目将培训一名研究生应用、改进和开发先进的生物地球化学固态核磁共振技术。它还将影响 PI 计划的大学和研究生级别的公共宣传和教育宣传内容。

Intellectual Merit. The nitrogen (N) cycle is a biogeochemical cycle involving the transformation of nitrogen and nitrogen-containing compounds in nature. Nitrogen is essential for many biological processes and is crucial for any life on earth. For example, nitrogen is one of the building blocks of proteins, amino acids, and is a key component of the bases that make up the genetic code of all life, such as DNA and RNA. Therefore, N cycle is one of the most important topics in biogeochemistry and understanding the N cycle can help control both the nature?s N balance. Most of N in soils or sediments is organic. While routine 15N cross polarization/magic angle spinning technique has been extensively applied to the investigations of organic N in soil/sediment organic matter (SOM), the inherent drawbacks of this technique have so far provided limited insight into the structures of organic N. The objectives of the project are: a) to develop an improved advanced solid-state protocol for investigating organic N forms in SOM, b) to investigate the distributions of different organic N forms and in particular the presence and abundance of heterocyclic N in SOM, and possibly c) to investigate the mechanisms underlying the formation of biologically refractory N using the new and advanced solid-state NMR techniques. We will primarily focus on, but not are limited to, two samples, an IHSS Pony Lake (Antarctica) Reference and a gilsonite, both of which contain relatively high N.The work on the new and improved advanced solid-state NMR techniques will include improvement of routine 15N cross polarization/magic angle spinning (CP/MAS) by using appropriate model compounds to maximize cross polarization; development of some 15N spectral-editing techniques to select specific functional groups and analysis of covalently-bound N using saturation-pulse induced dipolar exchange with recoupling. The relative proportions of different forms of organic N will be examined using these improved NMR techniques. The presence and abundance of heterocyclic N, which could be underestimated by routine 15N CP/MAS, will also be investigated using these techniques. The project promises significant advances in understanding the nature of organic N in SOM. It will reveal more accurate information on the relative proportions of different forms of organic N. The new or improved NMR techniques for characterizing organic N in SOM will provide us with a critical tool for research on organic N in SOM, laying the foundations for a significantly improved understanding of nitrogen biogeochemistry.Broader Impacts. This project will train a graduate student in applying, improving and developing advanced solid-state NMR techniques for biogeochemistry. It will also influence the content of planned public outreach and educational outreach at the college and graduate levels by the PI. Broader Impacts. This project will train a graduate student in applying, improving and developing advanced solid-state NMR techniques for biogeochemistry. It will also influence the content of planned public outreach and educational outreach at the college and graduate levels by the PI.