Showing papers by "Wolfgang Kiefer published in 2004"

Identification and characterization of pharmaceuticals using Raman and surface‐enhanced Raman scattering

Abstract: Many recent papers reflect ongoing research and development concerning pharmaceutical applications of Raman techniques. This short review highlights different Raman techniques (dispersive, Fourier transform, resonance Raman, SERS, SERRS, FT-SERS) employed in pharmaceutical investigations. Several Raman applications such as fundamental structural investigations, quantitative analysis, drug–excipient interaction, formulation, limit of detection, pH-dependent pharmaceutical species, adsorption geometry at a given surface and functional groups involved in adsorption for several widely used pharmaceutical compounds are presented. Copyright © 2004 John Wiley & Sons, Ltd.

Quantitative analysis of serum and serum ultrafiltrate by means of Raman spectroscopy

Abstract: The fast and reliable determination of concentrations of blood, plasma or serum constituents is a major requirement in clinical chemistry. We explored Raman spectroscopy as a reagent-free tool for predicting the concentrations of different parameters in serum and serum ultrafiltrate. In an investigation using samples from 247 blood donors (which we believe to be the largest study on Raman spectroscopy of serum so far) the concentrations of glucose, triglycerides, urea, total protein, cholesterol, high density lipoprotein, low density lipoprotein and uric acid were determined with an accuracy within the clinically interesting range. After training a multivariate algorithm for data analysis, using 148 samples, concentrations were predicted blindly for the remaining 99 serum samples based solely on the Raman spectra. Relative errors of prediction around 12% were obtained. Moreover, to the best of our knowledge, differentiation between HDL and LDL cholesterol as well as the quantification of uric acid was for the first time successfully accomplished for serum-based Raman spectroscopy. Finally, we showed that ultrafiltration can efficiently reduce fluorescent light background to improve prediction accuracy such that the relative coefficient of variation was reduced for glucose and urea in ultrafiltrate by more than a factor of 2 when compared to serum.

The application of a SERS fiber probe for the investigation of sensitive biological samples.

Abstract: The applicability of an etched and silver or gold coated SERS fiber probe in combination with a commercially available laboratory micro-Raman setup or a home built mobile micro-Raman setup to perform on-site field measurements was evaluated and successfully tested on different biological samples. The SERS fiber probe allows one to perform measurements with high spatial resolution. Simultaneously, the laser power used for Raman spectroscopy on biological samples as compared with conventional Raman experiments can be reduced by more than two orders of magnitude. This experimental arrangement was tested to investigate sensitive biological samples like mint plants (Bergamot mint, spear mint) and citrus fruits (kumquat). Furthermore, traces of fungicides on wine leaves were detected by means of such a SERS fiber probe setup.

Multimode pumped continuous-wave solid-state Raman laser.

Abstract: We demonstrate the continuous-wave operation of a solid-state Raman laser containing a barium nitrate crystal as the Raman medium. The Raman laser, which has a singly resonant cavity, is pumped by multimode radiation. The Raman oscillation threshold is reached at ∼2 W of pump power. As much as 500 kW/cm2 of Stokes power density at 60‐kW/cm2 pump power density is obtained in the cavity.

Identification of biotic and abiotic particles by using a combination of optical tweezers and in situ Raman spectroscopy.

Abstract: A highly versatile setup, which introduces an optical gradient trap into a Raman spectrometer, is presented. The particular configuration, which consists of two lasers, makes trapping independent from the Raman excitation laser and allows a separate adjustment of the trapping and excitation wavelengths. Thus, the excitation wavelength can be chosen according to the needs of the application. We describe the successful application of an optical gradient trap on transparent as well as on reflective, metal-coated microparticles. Raman spectra were recorded from optically trapped polystyrene beads and from single biological cells (e.g., erythrocytes, yeast cells). Also, metal-coated microparticles were trapped and used as surface enhanced Raman spectroscopy (SERS) substrates for tests on yeast cells. Furthermore, the optical gradient trap was combined with a SERS fiber probe. Raman spectra were recorded from trapped red blood cells using the SERS fiber probe for excitation.

A Raman spectroscopic study of the adsorption of fibronectin and fibrinogen on titanium dioxide nanoparticles

Abstract: The adsorption of proteins that contain the amino acid sequence Arg-Gly-Asp (RGD) plays a crucial role for the biocompatibility of implant materials. Detailed knowledge of the adsorption process is of great interest because it is a dominant factor that decides on the integration or rejection of an implant by the organism. We have studied the adsorption process on titanium dioxide nanoparticles via two proteins, namely fibrinogen and fibronectin. Bulk protein spectra are compared to spectra of proteins that were adsorbed on TiO2 nanoparticles (as an enlarged model surface for TiO2 implants). In the Raman spectra of the adsorbed proteins a characteristic band occurs that can be assigned to an interaction between TiO2 nanoparticles and the carboxylate groups of the protein. A moderate shift of the amide I band towards higher wavenumbers observed in the adsorbed fibrinogen spectrum in comparison to the bulk protein spectrum is due to conformational changes during the adsorption process. In the spectra of adsorbed fibrinogen the peak area of the multiplet of CH3 and CH2 deformation modes in relation to the amide I Raman peak area is decreased as compared to the spectra of bulk fibrinogen. These spectral features indicate an increasing content of β-sheet and a decrease of α-helical structure content for fibrinogen while for fibronectin an increase of β-sheet structure and a decreasing content of random coil structure was found. The adsorption takes place via the protein side-chains.

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.

In situ Raman investigation of single lipid droplets in the water‐conducting xylem of four woody plant species

Abstract: A micro-Raman spectroscopy approach was used for the direct in situ characterization of lipid bodies in the water-conducting branch xylem of an African resurrection plant and three deciduous European tree species. Because of average diameters of at least 1 microm, the lipid bodies of all investigated species proved to be easily accessible by this technique. All vesicle-forming xylem lipids were identified as fatty acid esters, which may correspond to phospholipids. Whereas in the resurrection plant saturated lipids were dominant, the lipid bodies of the European trees consisted of highly unsaturated fatty acids. A comparison of the spectra of lipid droplets of lime obtained in situ and from isolated xylem sap revealed slightly different signatures. This finding suggests that micro-Raman spectroscopy may be used to detect modifications of the chemical composition of biological substances as a result of the extraction mode.

Infrared absorption, Raman, and SERS investigations in conjunction with theoretical simulations on a phenothiazine derivative

Abstract: The vibrational characterization of the most stable conformer of 10-isopentyl-10H-phenothiazine-5,5-dioxide (10-I-10H-P-5,5-D) was performed by means of infrared absorption, Raman and surface-enhanced Raman spectroscopy (SERS). Hartree–Fock and density functional theory calculations were carried out to find the optimised structures and the computed vibrational wavenumbers of the title compound. The comparison of SER spectra obtained only in activated silver colloid with the corresponding Raman spectrum reveals small shifts and changes in the relative intensities proving the partial chemisorption of the molecules on the silver surface. The electromagnetic mechanism represents the main mechanism of the overall SERS enhancement. The changes observed in the SER spectra at different pH values were explained by considering the reorientation of the adsorbed molecule with respect to the metal surface.

Remote Raman spectroscopy as a prospective tool for planetary surfaces

Abstract: This paper summarizes the content of four Technical Notes that were established within a study contracted by the European Space Agency concerning the possibility of applying Raman spectroscopy in the field of remote imaging. An overview of the scientific demands and Raman spectroscopy from the user’s point of view is provided together with a few key aspects in the field of planetary research. Laboratory Raman experiments were used for establishing a basis for the subsequent extrapolation to remote Raman spectroscopy. A detailed numerical simulator was used to derive numbers concerning link budgets and overall remote Raman spectroscopy instrument performance for a number of different scenarios. A summary of subsystem technologies and criticalities is also presented together with the necessary R&D efforts. Copyright  2004 John Wiley & Sons, Ltd.

Micro-Raman spectroscopy: a valuable tool for the investigation of extraterrestrial material

Abstract: The investigation of different samples of SNC (Shergotty-Nakhla-Chassigny) meteorites was chosen to test the ability of micro-Raman spectroscopy to cope with extraterrestrial material. The following SNC meteorites were investigated: Sayh al Uhaymir 060, Dar al Gani 735, Dar al Gani 476, Northwest Africa 856, Los Angeles, Northwest Africa 1068 and Zagami. Pyrite as a hitherto undescribed phase in the picritic (olivine-phyric) shergottite NWA 1068 and reduced carbon (e.g. graphite) and anatase in the shergottite Say al Uhaymir 060 are new findings for this class of meteorites.

Hydrogen-bonding and self association investigated in the binary mixture (C6H5CN + CH3OH)via concentration dependent Raman study of the CN stretching mode of benzonitrile (C6H5CN) and ab-initio calculations

Abstract: The Raman study of (C6H5CN + CH3OH) binary mixture has been presented. The isotropic part of the Raman spectra, Iiso are analyzed in the CN stretching region. For neat C6H5CN, the Iiso shows a double peak structure, which has been explained in terms of self association. A quantum chemical calculation on the optimized structures and wavenumbers of different modes of neat C6H5CN, self associated C6H5CN and the hydrogen-bonded C6H5CN⋯HOCH3 complex reveals that the wavenumber position of the CN stretching mode is blue shifted due to both the self association and the hydrogen-bonding with CH3OH. The Raman spectra of binary mixtures with different mole fractions of the reference system (C6H5CN), C = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, as well as neat liquid have been explained in terms of self association and hydrogen-bonding. A variation of intensity ratio of the peak assigned to the hydrogen-bonded complex to the main band with concentration exhibits a regular trend. The dephasing of the CN stretching mode in the free C6H5CN molecules seems to be governed predominantly by the concentration fluctuation model, but other effects like diffusion and motional narrowing may also have some small influence.

The Excited‐State Dynamics of Phycocyanobilin in Dependence on the Excitation Wavelength

Abstract: The primary light-induced processes of phycocyanobilin were studied by means of transient-grating spectroscopy, whereby the excitation wavelength was varied over the spectral region of the ground-state absorption. On the basis of the results obtained, both the rate of the photoreaction in phycocyanobilin and the ratio of the decay of different excited-state species via two decay channels depend on the excitation wavelength. Furthermore, the formation of the photoreaction product is also dependent on the pump color. These data support a recently established model for the primary photoprocesses in phycocyanobilin. In addition, phycocyanobilin protonated at the basic pyrrolenine-type nitrogen atom was included in the transient absorption study. The decay behavior was found to be almost unchanged when compared with the unprotonated form, and this suggests that protonation of the tetrapyrrole ring structure has no effect on the overall photochemistry.

Spectroscopic studies on the structure of vanadium tellurite glasses

Abstract: Glasses having the compositions x V 2 O 5 . (1-x) TeO 2 with x=0.04, 0.1, 0.18 and 0.25 were studied by means of optical absorption (UV-VIS-NIR), infrared, Raman and electron paramagnetic resonance spectroscopies. Accordingto the latter method the [V 4 + ]/([V 5 + ]+[V 4 + ]) ratio steadily decreases with increasing V 2 O 5 concentration from 9.0 to 2.4%. The UV- VIS spectra reveal a shift in cut-off to higher wavelength indicating structural changes. Infrared and Raman spectra show the occurrence of tellurium in this system as trigonal TeO 4 bipyramids, TeO 3 trigonal pyramids and TeO 3 + 1 polyhedra. By increasing the V 2 O 5 concentrations, a transformation of TeO 4 into TeO 3 + 1 polyhedra and TeO 3 units has been observed A high wavenumber band located around 910 cm - 1 which could be assigned to vibrations of short V-O bonds shows a blue shifted with increasing V 2 O 5 content revealing the presence of both VO 4 tetrahedra and VO 5 bipyramids.

Conformation and Hydrogen Bonding Properties of an Aziridinyl Peptide: X-ray Structure Analysis, Raman Spectroscopy and Theoretical Investigations

Abstract: The X-ray structure analysis of the aziridinyl peptide EtO-Azi-Gly-Gly-OBn indicates that the linear conformation adopted in the crystalline state is established by an intermolecular hydrogen bonding network. This is confirmed by force field computations. They show that the intermolecular interactions in the crystal are stronger than the intramolecular ones which for a single molecule would lead to a bent structure. As expected, the stabilization energies strongly decrease with increasing polarity of the environment. For medium polar environments, the intermolecular interactions are still stronger than the intramolecular ones which is in nice agreement with results from 1H NMR dilution studies in CDCl3. For very polar environments, the intramolecular interactions become stronger than the intermolecular ones, however, if the solvent is able to form stable hydrogen bonds, e.g., DMSO, the intramolecular hydrogen bonds are replaced by hydrogen bonds to the solvent molecules. Raman spectra of the crystalline c...

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.

DFT and HF Studies of the Geometry, Electronic Structure, and Vibrational Spectra of 2-Nitrotetraphenylporphyrin and Zinc 2-Nitrotetraphenylporphyrin

Abstract: The ground-state geometries and electronic structures of 2-nitrotetraphenylporphyrin (H 2 -2-NO 2 -TPP) and zinc 2-nitrotetraphenylporphyrin (Zn-2-NO 2 -TPP) with C s and C 1 symmetry have been determined from density functional theory, using the Becke-Lee-Yang-Parr composite exchange-correlation functional (B3-LYP) and ab initio RHF method and 6-31G(d) basis set. The optimized geometries are then compared with the crystallographic data of related compounds. The energy and electronic structures of different conformers are analyzed and compared with each other. The conformers with C 1 symmetry are found to be more stable than that of C s symmetry. The relative order of the highest occupied a 2 u and a 1 u orbitals determined by B3LYP (a 2 u > a 1 u ) is reversed by RHF (a 1 u > a 2 u ). The vibrational wavenumber, IR, and Raman intensities are also calculated at B3LYP/6-31G(d) optimized geometries. The calculated wavenumbers are scaled by a uniform scaling factor and compared with the experimental one. Most of the scaled modes are found to be in good agreement with the observed fundamentals. A single β-NO 2 substitution slightly changes the geometries, the vibrational wavenumbers, and the frontier orbitals energy level.

EXTENDED-MIRAS: The instrumental approach for the search of traces of extinct and extant life on Mars, instrument setup

Abstract: Whether there was or is life on Mars is a question of high interest to man. When looking for evidence of present or ancient life on Mars it might be not sufficient to disclose the chemical composition of the surface or subsurface material. Further information concerning for example the morphology of the sample under investigation or the spatial distribution of the observed chemicals or minerals is of similar relevance. So we need a reliable, automated, robust and miniaturized apparatus capable of resolving all the above mentioned problems in one effort. EXTENDED-MIRAS is an instrumental approach combining optical microscopy and micro-Raman spectroscopy with additional elementary characterization methods such as LIPS/LIBS (laser induced plasma spectrometry / laser induced breakdown spectrometry) or LMS (laser mass spectrometry).

Raman Investigation of the Low Temperature Phase Transitions in Monoclinic TlReO4

Abstract: The Raman spectrum of monoclinic TlReO4 is presented together with a factor group analysis and assignment of the bands. The phase transitions of monoclinic TlReO4 is investigated below room temperature, and two phase transitions were identified between room temperature and 90 K. The room temperature monoclinic phase was converted to the orthorhombic phase at 170 K upon cooling, and to the tetragonal phase at 150 K. Upon heating back to room temperature the tetragonal phase persisted until the orthorhombic phase could be identified at 210 K and 220 K. From 230 K to room temperature the monoclinic phase could again be observed. Raman-Untersuchung der Tieftemperatur-Phasenumwandlungen von monoklinem TlReO4 Das Raman-Spektrum von monoklinem TlReO4 wird mitgeteilt und die Zuordnung der Banden auf der Basis einer Faktorgruppenanalyse vorgenommen. Durch Abkuhlen auf 90 K lassen sich zwei Phasenubergange beobachten. Bei 170 K entsteht die orthorhombische Phase, bei 150 K die tetragonale Phase. Beim Anwarmen auf Raumtemperatur wird bei 210 und 220 K die orthorhombische Phase identifiziert, wahrend ab 230 K wieder die monokline Phase zuruckgebildet wird.