Dresden 2009 – wissenschaftliches Programm
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DF: Fachverband Dielektrische Festkörper
DF 2: Dielectric Spectroscopy & Microscopy
DF 2.7: Vortrag
Montag, 23. März 2009, 12:40–13:00, WIL A317
Characterization of guanidiniocarbonyl pyrroles in water by pH-dependent UV Raman spectroscopy and component analysis — Sunil Kumar Srivastava1, •Stephan Niebling1, Bernd Küstner1, Peter Richard Wich2, Carsten Schmuck2, and Sebastian Schlücker1 — 1Fachbereich Physik, Universität Osnabrück, Barbarastr. 7, 49076 Osnabrück. — 2Institut für Organische Chemie, Universität Duisburg-Essen, Universitätsstr. 5, 45141 Essen.
Guanidiniocarbonyl pyrroles are artificial receptors for the efficient complexation of peptides even in polar solvents such as water. Their carboxylate binding site (CBS) can be probed selectively by ultraviolet resonance Raman (UV RR) scattering. We present a pH-dependent UV RR spectroscopic investigation of two guanidiniocarbonyl pyrroles in water: the model receptor CBS-NH2 and the peptide receptor CBS-Lys-Lys-Phe-NH2. UV RR spectra with 275 nm laser excitation were recorded between pH 6 and pH 7. Within this small pH range near the pKa of 6.4, protonated and neutral CBS species are simultaneously present in an acid/base equilibrium. By using non-negative matrix factorization (NMF), the individual UV RR component spectra of these distinct CBS species were determined without any a priori knowledge. The pH-dependent UV RR spectra of the small model receptor CBS-NH2 and the larger peptide receptor CBS-Lys-Lys-Phe-NH2 can both be described as linear combinations of only two components. Control experiments at pH 2 and pH 10 show an excellent agreement with the derived NMF component spectra and confirm their assignment to the protonated and neutral CBS species, respectively.