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

知识价值。氮循环是一个涉及自然界中氮和含氮化合物转化的生物地球化学循环。氮对许多生物过程至关重要，对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（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和生态系统。N平衡。土壤或沉积物中的氮大部分是有机的。常规的15N交叉极化/魔角旋转技术已被广泛应用于土壤/沉积物有机质（SOM）中有机氮的研究，但该技术固有的缺点迄今为止对有机氮的结构提供了有限的了解。a)开发一种改进的先进固态方案来研究SOM中的有机N形式，b)研究不同有机N形式的分布，特别是SOM中杂环N的存在和丰度，以及可能的c)利用新的先进固态核磁共振技术来研究生物难熔N的形成机制。我们将主要关注（但不限于）两种样品，一种是IHSS Pony Lake （Antarctica）参考样品，另一种是gilsonite样品，这两种样品都含有较高的n。新的和改进的先进固态核磁共振技术将包括改进常规的15N交叉极化/魔角旋转（CP/MAS），通过使用适当的模型化合物来最大化交叉极化；开发了一些15N光谱编辑技术，以选择特定的官能团，并利用饱和脉冲诱导的偶极交换与重耦合分析共价结合的N。不同形式的有机氮的相对比例将使用这些改进的核磁共振技术进行检查。杂环N的存在和丰度可能被常规的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。新的或改进的核磁共振表征SOM中有机氮的技术将为SOM中有机氮的研究提供重要工具，为显著提高对氮生物地球化学的认识奠定基础。更广泛的影响。本项目将培养一名研究生在生物地球化学领域应用、改进和发展先进的固态核磁共振技术。它还将影响PI计划在大学和研究生一级进行的公共宣传和教育宣传的内容。更广泛的影响。本项目将培养一名研究生在生物地球化学领域应用、改进和发展先进的固态核磁共振技术。它还将影响PI计划在大学和研究生一级进行的公共宣传和教育宣传的内容。

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.