BOOK OF ABSTRACTS 29 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Monday, 24 August 2026 / Hall B+C Analysis and Characterization SL8 Exploring Aromatic Cluster Models and Superstructures in Humic Substances via Advanced Solid-State NMR Jingdong Mao1 1 Department of Chemistry and Biochemistry, Old Dominion University, Norfolk, VA 23529, USA The characteristics of Zook soil humic acid (HA) and prairie grass char were investigated in detail using advanced solid-state nuclear magnetic resonance (NMR) techniques. These techniques included quantitative direct polarization/ magic angle spinning (DP/MAS), dipolar dephasing, 13C chemical shift filter, 13C chemical shift filter with dipolar dephasing and short CP, C-H recoupled dipolar dephasing, and two-dimensional 1H-13C heteronuclear correlation NMR (2D HETCOR) with spin diffusion, as well as 2D HETCOR with regular 40ms and recoupled long-range dipolar dephasing. Advanced spectral-editing techniques identified specific functional groups in Zook soil HA and suggested significant oxidized chars in this sample. Reasonable aromatic cluster models were proposed based on the data from recoupled long-range dipolar dephasing and the fraction of edge carbons, c_edge, in the aromatics. It is estimated that Zook soil HA and prairie grass char contain at least 6 and 18 aromatic rings, respectively. The superstructure showing how the small aromatic clusters in Zook soil HA are incorporated into the other humic components in the material was investigated using long CP combined with 1H spin diffusion. The results indicated that the superstructure of Zook soil HA is most likely to be isolated stacks of aromatic clusters embedded in the humic matrix. References 1. Brewer, C. E.; Schmidt-Rohr, K.; Satrio, J. A.; Brown, R. C., Environ. Prog. Sustainable Energy 28 (2009) 386. 2. Mao, J. D.; Schmidt-Rohr, K., J. Magn. Reson. 162 (2003) 217.
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