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

智力上的功绩。氮(N)循环是一种生物地球化学循环，涉及自然界中氮和含氮化合物的转化。氮是许多生物过程所必需的，对地球上的任何生命都是至关重要的。例如，氮是蛋白质和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的关键组成部分，如DNA和RNA。因此，N循环是生物地球化学研究中最重要的课题之一，了解N循环有助于控制两者的自然--S N平衡。土壤或沉积物中的大部分氮是有机的。虽然常规的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N的研究，但该技术的固有缺陷迄今对有机N的结构提供了有限的洞察力。该项目的目标是：a)开发一种改进的先进固态方法来研究SOM中有机N的形态，b)调查不同有机N形态的分布，特别是杂环N在SOM中的存在和丰度，以及c)使用新的和先进的固体核磁共振技术来研究生物难降解N形成的机理。我们将主要关注但不限于两个样品，一个是IHSS Pony Lake(南极洲)的参照物，另一个是含氮相对较高的绿柱石。新的和改进的先进固态核磁共振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的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；以及使用饱和脉冲诱导重新耦合偶极交换来分析共价结合的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。还将使用这些技术调查常规15N CP/MAS可能低估的杂环N的存在和丰度。该项目有望在理解土壤有机质中有机氮的性质方面取得重大进展。它将揭示不同形态有机氮相对比例的更准确信息。用于表征SOM中有机N的新的或改进的核磁共振技术将为研究SOM中的有机N提供关键工具，为显著提高对氮的生物地球化学的理解奠定基础。该项目将培训一名研究生应用、改进和开发先进的固体核磁共振生物地球化学技术。它还将影响PI在大学和研究生一级计划的公共宣传和教育宣传的内容。更广泛的影响。该项目将培训一名研究生应用、改进和开发先进的固体核磁共振生物地球化学技术。它还将影响PI在大学和研究生一级计划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.