Spectroscopic polymer characterization without polymers: Benchmarking quantum chemistry in the gas phase
Final Report Abstract
Raman spectroscopy in supersonic jet expansions was used to unravel the conformational richness and gas phase dynamics of chain molecules as fragments of real polymers in the condensed phase. Important insights into the onset of folding in these chain molecules as a function of chain length were gained. Capping of a linear alkyl chain with a phenyl group greatly facilitates hairpin formation. By introducing a mid-chain ester group, folding of alkanes can be observed already for much shorter chains. For doubly methyl-capped polyethyleneglycol fragments, it was shown that two repeat units slightly prefer a stretched motif, whereas three units start to coil and the compactness of coiling increases substantially for the tetramer. Mechanical properties for a hypothetical stretched polymorph of polyethyleneoxide were obtained from chain extrapolation. For singly capped ethyleneglycol, aggregation and conformation were simultaneously monitored by a new double-detection scheme. Supramolecular trimers were investigated for three chain-aggregating hydrogen bond formers, namely N-methyl acetamide (the simplest model of a peptide bond), hexa uoroisopropanol (a conformation-controlling peptide co-solvent and uorous interaction model) and imidazole (a peptide side chain building block). In all three cases, the interplay between chain and ring trimers was quantitatively investigated and it was shown that London dispersion interaction tips the balance from chain to ring aggregation. To show this, the complementarity of infrared and Raman jet spectroscopy, a speciality of our research group, was key. We are now using the spatial mapping capability of Raman jet spectroscopy to explore possibilities for active conformational control by tailored supersonic ow patterns. All investigated systems provide rigorous benchmarks for the appropriate description of non-covalent interactions by theoretical methods. Due to a number of energetical neardegeneracies of qualitatively di erent structures uncovered in this work, only very accurate methods are expected to describe all chain folding phenomena correctly. The work thus provides a broad foundation for the new DFG research training group 2455 (BENCh) in Gottingen and perhaps it may even contribute to the testing of computational models for combinatorial polymer design.
Publications
- Correcting the record: The dimers and trimers of trans-N-methylacetamide, Phys. Chem. Chem. Phys. 19 (2017) 10727–10737
Thomas Forsting, Hannes C. Gottschalk, Beppo Hartwig, Michel Mons, Martin A. Suhm
(See online at https://doi.org/10.1039/c6cp07989j) - Identifying the first folded alkylbenzene via ultraviolet, infrared, and Raman spectroscopy of pentylbenzene through decylbenzene, Chem. Sci. 8 (2017) 5305–5318
Daniel M. Hewett, Sebastian Bocklitz, Daniel P. Tabor, Edwin L. Sibert III, Martin A. Suhm, Timothy S. Zwier
(See online at https://doi.org/10.1039/c7sc02027a) - Polymer segments at the folding limit: Raman scattering for the diglyme benchmark, ChemPhysChem 18 (2017) 3570–3575
Sebastian Bocklitz, Martin A. Suhm
(See online at https://doi.org/10.1002/cphc.201701169) - Conformational spectroscopy of flexible chain molecules near the folding limit, Dissertation, 2018, Universität Göttingen
Sebastian Bocklitz
- Strained hydrogen bonding in imidazole trimer: A combined infrared, Raman, and theory study, Phys. Chem. Chem. Phys. 21 (2019) 5989–5998
Thomas Forsting, Julia Zischang, Martin A. Suhm, Marco Eckhoff, Benjamin Schröder, Ricardo A. Mata
(See online at https://doi.org/10.1039/c9cp00399a) - The chiral trimer and a metastable chiral dimer of achiral hexafluoroisopropanol: A multi-messenger study, Angew. Chem. Int. Ed. 58 (2019) 5080–5084
Sönke Oswald, Nathan A. Seifert, Fabian Bohle, Maxim Gawrilow, Stefan Grimme, Wolfgang Jäger, Yunjie Xu, Martin A. Suhm
(See online at https://doi.org/10.1002/anie.201813881)
