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Issue 45, 2008
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Characterization of guanidiniocarbonyl pyrroles in water by pH-dependent UV Raman spectroscopy and component analysis

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Abstract

Guanidiniocarbonyl pyrroles are artificial receptors for the efficient complexation of carboxylates even in polar solvents such as water. Their carboxylate binding site (CBS) exhibits an electronic absorption maximum at ∼298 nm and 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 of 1 mM aqueous solutions with 275 nm laser excitation were recorded between pH 6 and 7. Within this small pH range near the pKa of 6.4, protonated and neutral CBS species are simultaneously present at similar concentrations (acid/base equilibrium). 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.

Graphical abstract: Characterization of guanidiniocarbonyl pyrroles in water by pH-dependent UV Raman spectroscopy and component analysis

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Publication details

The article was received on 26 Jun 2008, accepted on 22 Aug 2008 and first published on 03 Oct 2008


Article type: Paper
DOI: 10.1039/B810908G
Citation: Phys. Chem. Chem. Phys., 2008,10, 6770-6775
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    Characterization of guanidiniocarbonyl pyrroles in water by pH-dependent UV Raman spectroscopy and component analysis

    S. K. Srivastava, S. Niebling, B. Küstner, P. R. Wich, C. Schmuck and S. Schlücker, Phys. Chem. Chem. Phys., 2008, 10, 6770
    DOI: 10.1039/B810908G

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