Organic nitrogen incorporated into geomacromolecules (e.g., humic substances, kerogen) represents a major reservoir of nitrogen on the earth's surface, accounting for more than 90% of the total nitrogen in soils, sediments, and aquatic environments. Its primary source is biochemical nitrogen from dead plant and animal residues (predominantly proteinaceous substances), which undergo a complex series of transformations, mediated by microbes and abiotic processes, ultimately resulting in the incorporation of the nonmineralized fraction into geomacromolecules. Simultaneously,the biochemical N is thought to be extensively altered structurally, forming more stable structures (such as heterocyclic forms), although the type of changes in chemical speciation, their timing, and mechanisms are not clear. It is important to have this knowledge because the type of N formed influences not only its reactivity and fate (e.g., the release of bioavailable N in soils) but also the physical and chemical characteristics of the associated macromolecular organic matter. We used nitrogen K-edge XANES spectroscopy (a selective, sensitive, and nondestructive method) to gain new insights into the speciation of this macromolecular nitrogen. Our results verified amide N as being the dominant type in humic substances and sediments but revealed that pyridinic N also is a significant component of the total N (approximately 20-30%), with a subfraction consisting of its oxidized derivatives. An unidentified form of highly oxidized N was present mainly in sediments. While amide N represents residues of original biochemical molecules, pyridinic N probably is generated abiotically. Our results imply that the abiotic formation of pyridinic N sets in during the early stages of organic matter transformations thereby stabilizing organic N, although such processes generating heterocyclic structures may continue much longer.

14Due to the central role of DNA, its interactions with inorganic salts and small organic molecules 15 are important for understanding various fundamental cellular processes in living systems, 16deciphering the mechanism of many diseases related to DNA damages, and discovering or 17 designing inhibitors and drugs targeting DNA. However, there is still a need for improved 18 sensitivity to detect these interactions, especially in situations where expensive sophisticated 19 equipment is not available. Here we report our development and demonstration of bent DNA bows 20 for amplifying, sensing, and detecting the interactions of 14 inorganic salts and small organic 21 molecules with DNA. With the bent DNA bows, these interactions were easily visualized and 22 quantified in gel electrophoresis, which were difficult to measure without bending. In addition, the 23 strength of the interactions of DNA with the various salts/molecules were quantified using the 24 modified Hill equation. This work highlights the amplification effects of the bending elastic energy 25 stored in the DNA bows and the potential use of the DNA bows for quantitatively measuring DNA 26interactions with small molecules as simple economic methods; it may also pave the way for 27 exploiting the bent DNA bows for other applications such as monitoring water quality and 28 screening DNA-targeting molecules and drugs. 29 30 31

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