Showing papers by "Sebastian Schlücker published in 2004"

In vitro polarization‐resolved resonance Raman studies of the interaction of hematin with the antimalarial drug chloroquine

Abstract: Despite the public health impact of human malaria, the mechanism of hemozoin inhibition by antimalarial drugs such as chloroquine (CQ) is not yet fully understood. Polarization-resolved resonance Raman spectra of hematin and its complex with CQ were recorded under Q-band resonance conditions in order to monitor the binding of the 4-aminoquinoline drug to the heme macrocycle. Upon drug addition, only wavenumber shifts smaller than 2 cm−1 are detected, indicating a non-covalent interaction in the electronic ground state of the drug–target complex. The decreased resonance Raman intensity of the anomalously polarized mode ν19(a2g) in the perpendicular polarized spectrum of the complex suggests changes of the excited-state geometry along the corresponding normal coordinate. Copyright © 2004 John Wiley & Sons, Ltd.

Singlet-oxygen generation in the catalytic reaction of dioxiranes with nucleophilic anions.

Abstract: Nucleophilic anions such as Cl−, I−, Br−, t-BuO−, O2− and OH− efficiently catalyze the decomposition of dimethyldioxirane (DMD) and methyl(trifluoromethyl)dioxirane (TFD). Singlet oxygen (1O2) is formed in these catalytic reactions, as demonstrated by the characteristic infrared chemiluminescence (IR-CL) at 1268 nm. The yield of 1O2 generation, measured by the IR-CL method, lies in the range between 2 and 98%, which depends on the particular anion employed. For the bromide ion, the catalytic decomposition of the dioxirane is in competition with the oxidation of Br− to elemental bromine.

Vibrational Microspectroscopic Imaging: Spatial Resolution Enhancement

Abstract: We propose a methodology for enhancing the diffraction limited spatial resolution attained in Raman and Fourier transform infrared microspectroscopic imaging techniques. Near-field scanning optical microscopy (SNOM) and spectroscopy employ apertureless and aperture approaches to provide ultra-high spatially resolved images at the nanometer level. In contrast, we employ conventional spectral acquisition schemes modified by spatial oversampling with the subsequent application of deconvolution techniques. As an example, this methodology is applied to flat samples using point illumination. Simulated data, assuming idealized sample concentration profiles, are presented together with experimental Raman microspectroscopic data from chemically and morphologically well-defined test samples. Intensity profiles determined using conventional mapping and imaging techniques are compared to those obtained by the probe/deconvolution methodology.

Analysis of the symmetric and anti-symmetric N-H stretching modes of n-propylamine in binary mixtures with methanol: a concentration dependent Raman study and ab-initio calculations

Abstract: A polarization-resolved Raman spectroscopic analysis of neat n-propylamine and a series of binary mixtures with methanol is presented. The observed spectral changes for the symmetric and anti-symmetric N-H stretching modes are assigned to hydrogen bonding and compared with abinitio calculations on various hydrogen-bonded complexes of n-propylamine and methanol. The analysis of wavenumber shifts and vibrational line profiles in neat liquids and binary mixtures by Raman spectroscopy allows detailed studies of both interand intra-molecular interactions and molecular motions [1]. The wavenumber position of a Raman band, which relates essentially to the corresponding force constant, is influenced by molecular structure and electron density distribution. The Raman linewidth, however, contains information on dynamic aspects in molecular liquids and solids, for instance on vibrational relaxation (dephasing) and reorientational motions [2-3]. The possibility to separate out these effects by performing polarized Raman measurements is an obvious advantage over IR spectroscopy. The precise determination of the depolarization ratio by measurements of the parallel, I׀׀, and perpendicular, I⊥, components of the Raman scattered radiation, respectively, helps in ascertaining the symmetry of the vibration. For totally symmetric vibrations, the corresponding depolarization ratio is zero; deviations from zero observed upon solvent addition are attributed to intermolecular interactions. Polarization-resolved measurements also enable the determination of the isotropic part of the Raman scattered, which provides useful information on vibrational dephasing. Raman spectra of neat n-propylamine (C3H9N) and its binary mixtures with methanol (CH3OH) were acquired with the scanning multichannel detection technique (SMT). The III and I⊥ components of the Raman scattered radiation for n-propylamine mole fractions ranging from 0.1 to 0.9 were recorded in intervals of 0.1. The isotropic Raman spectra for neat n-propylamine and a 1:1 mixture with methanol are shown in Figure 1. The deconvolution of the asymmetric band shape observed for neat n-propylamine yields two peaks at ~ 3326 cm and ~ 3303 cm, which are assigned to the anti-symmetric and symmetric N-H stretching vibration, respectively. Upon dilution with methanol, these two bands exhibit significant changes in relative intensities, wavenumber positions and linewidths. The observed shift towards lower wavenumbers for both bands is assigned to hydrogen bond formation. The experimental results are compared with ab-initio calculations performed both earlier by others [4] as well as by us. Structures of various hydrogen bonded complexes calculated at the MP2 level are presented and correlated with the observed spectral changes.