title: Determination of binding strengths of a host-guest complex using resonance Raman scattering.
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 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 system to characterize the binding event of a host-guest system. RRS spectra are generated by excitation (lambda(exc) = 785 nm) within the lowest-energy charge-transfer (CT) transition (lambda(max) = 865 nm) of the TTF subsetCBPQT(4+) complex. The paired binding curves from the RRS and UV-vis-NIR titration data agrees with prior work, and a DeltaG of -5.7 +/- 0.6 kcal mol(-1) (MeCN, 298 K) was obtained for the complexation of TTF with CBPQT(4+). 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.
authors: Chemistry Department, Indiana University, 800 East Kirkwood Avenue, Bloomington, Indiana 47405, USA.
authors: Edward H
authors: EH
authors: Witlicki
authors: Stinne W
authors: SW
authors: Hansen
authors: Martin
authors: M
authors: Christensen
authors: Thomas S
authors: TS
authors: Hansen
authors: Sune D
authors: SD
authors: Nygaard
authors: Jan O
authors: JO
authors: Jeppesen
authors: Eric W
authors: EW
authors: Wong
authors: Lasse
authors: L
authors: Jensen
authors: Amar H
authors: AH
authors: Flood