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PREDICTION OF MOLECULAR PROPERTIES WITH MID-INFRARED SPECTRA AND INTERFEROGRAMS
Citation:
Collette, T W. PREDICTION OF MOLECULAR PROPERTIES WITH MID-INFRARED SPECTRA AND INTERFEROGRAMS. APPLIED SPECTROSCOPY 55(6):1067-1078, (2001).
Impact/Purpose:
Elucidate and model the underlying processes (physical, chemical, enzymatic, biological, and geochemical) that describe the species-specific transformation and transport of organic contaminants and nutrients in environmental and biological systems. Develop and integrate chemical behavior parameterization models (e.g., SPARC), chemical-process models, and ecosystem-characterization models into reactive-transport models.
Description:
We have built infrared spectroscopy-based partial least squares (PLS) models for molecular polarizabilities using a 97 member training set and a 59 member independent prediction set. These 156 compounds span a very wide range of chemical structure. Our goal was to use this well defined chemical property to test the breadth of application of a method whose end use is aimed at predicting poorly defined, environmentally important properties and activity parameters (e.g., microbial transformation rate constants). Separate models were built using gas-phase mid-infrared spectra, and, alternatively, their Fourier transformations (i.e., interferograms). The optimum spectrum- and interferogram-based models produced approximately the same error (root mean square deviation divided by the parameter value range) for the independent prediction set, 9.53 and 9.92 %, respectively. With spectrum-based models, we found that de-resolving the spectra from a point spacing of 6 cm-1 to about 40 cm-1 produced much lower error (under leave-one-out, cross-validation) when all 156 compounds were included, but much higher error when a model was built using a structurally narrow subset of the compounds (namely, 38 alkanes). Qualitative interpretation of the first PLS weight-loading vector from the spectrum-based model provided important information on the relationship between chemical structure and molecular polarizability.