IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 BOOK OF ABSTRACTS 20 Analysis and Characterization Monday, 24 August 2026 / Hall B+C identified endmembers, we examined whether bulk compositional data could reveal recurring “endmember” motifs suitable for guiding molecular model representations. Using an HS dataset of the International Humic Substances Society, single- and multiblock nonnegative multivariate curve resolution-alternating least squares (MCR-ALS) decompositions were performed to integrate ¹³C NMR spectra with elemental composition and acidic functional group contents data [3]. Multiblock MCR-ALS analysis constrains the compositional space, contributing to the identification of unique, chemically meaningful components. Across diverse samples, two chemically distinct and nearly unique components representing an aromatic-rich and an aliphatic-rich motif, similarly hydrophilic in terms of contents of carboxylic and phenolic groups, consistently emerged, together explaining ~97–98% of the total variance while exhibiting minimal residual rotational ambiguity and pointing to the unique character of decomposition. Taken together, these results suggest a pathway in which data-driven compositional analysis informs molecular simulations. The MCRderived compositional endmembers offer chemically grounded ensemble descriptors that can serve as inputs for constructing more realistic molecular models. Bridging these approaches, we suggest a strategy in which experimentally derived endmembers guide the generation and testing of HS structures in silico, potentially improving the interpretability and predictive power of molecular modeling of HS and natural organic matter, in particular, helping to identify extreme behaviors within the compositional space defined by the data. Incorporating additional constraints into molecular models, such as the contents of carboxylic and phenolic groups or specific elemental ratios, may enable the development of even more realistic representations of the molecular HS ensembles. References 1. M. Borisover, D. Petrov, C. Oostenbrink, E. Galicia-Andrés, Colloids and Surfaces A: Physicochemical and Engineering Aspects 704 (2025) 135507. 2. A.C. García, T.A., van Tol de Castro, L.A. Santos, O.C.H. Tavares, R.N. Castro, R.L.L. Berbara, J.M. García-Mina, Journal of Environmental Quality 48 (2019) 1622. 3. M. Borisover, M. Lado, Minerals 16 (2026) 228.
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