Determination of binding strengths of a host-guest complex using resonance raman scattering

Edward H. Witlicki, Stinne W. Hansen, Martin Christensen, Thomas S. Hansen, Sune D. Nygaard, Jan O. Jeppesen, Eric W. Wong, Lasse Jensen, Amar H. Flood

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25 Scopus citations

Abstract

The detection of analyte-binding events by receptors is drawing together the fields of Raman spectroscopy and supramolecular chemistry. This study is intended to facilitate this cohering by examining a model system in the solution phase. The resonance Raman scattering (RRS) spectra of the complexation between tetrathiafulvalene (TTF) and cyclobis(paraquat-p-phenylene) (CBPQT 4+) has been used as the model to characterize the binding event of a host-guest system. RRS spectra are generated by excitation (λ exc = 785 nm) within the lowest-energy charge-transfer (CT) transition (λ max= 865 nm) of the TTFCCBPQT 4+ complex. The paired binding curves from the RRS and UV-vis-NIR titration data agrees with prior work, and a AG of -5.7 ± 0.6 kcal mol -1 (MeCN, 298 K) was obtained for the complexation of TTF with CBPQT4+. Computations on the complex and its components reproduce the energy shifts and resonance enhancements of the Raman band intensities, providing a basis to identify the structural and vibrational changes occurring upon complexation. The changes in bond lengths coincide with partial depopulation of a TTF-based HOMO and population of a CBPQT 4+-based LUMO through CT mixing in the ground state of 0.46e -. The structural changes upon complexation generally lead to lower wavenumber vibrations and to changes in the normal mode descriptions.

Original languageEnglish (US)
Pages (from-to)9450-9457
Number of pages8
JournalJournal of Physical Chemistry A
Volume113
Issue number34
DOIs
StatePublished - Aug 27 2009

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry

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