Bernhard Schrader

NIR FT Raman spectroscopy—a new tool in medical diagnostics

Abstract Raman spectroscopy may aid the development of new tools to make medical diagnostics more objective. By shifting the exciting radiation of Raman spectrometers from the visible to the NIR region, the competing fluorescence of normal cell components can be reduced. The fluorescence of organic molecules is virtually eliminated when excitation by the Nd: YAG laser radiation at 1064 nm is employed. In combination with optimized interferometers and remote probes, it is now possible to record Raman spectra in vivo in acceptable times. Software programs are developed which interpret the spectra to help in the identification of suspicious tissues and micro-organisms, and for establishing medical diagnosis. In each case, the information distributed over the whole spectrum has to be evaluated.

Quality control of food with near-infrared-excited Raman spectroscopy

SummaryThe former considerable handicap of Raman spectroscopy in the visible range, the disturbing fluorescence of impurities, has now been eliminated: Raman spectra are excited by light quanta of the near-infrared range; their energy, however, is too small to excite fluorescence spectra. Now Raman spectroscopy can be applied to many ‘real world samples’, to quality control of raw material, to production and product control. This paper gives examples of the application to food analysis. Many problems can be solved without a special sample preparation, even by using fibre bundles on-line at the sample site, in containers and in real time for production control. The configuration and amount of C=C bonds in lipids can be determined directly, also the nature and amount of proteins and carbohydrates, and the composition of food products. Natural and synthetic colours, flavours and vitamins can be detected on TLC plates, especially if Raman scattering is enhanced by resonance. Traces of distinct compounds can be detected by the SERS technique (the surface-enhanced Raman spectroscopy). The powerful new tool of analytical chemistry promises many useful applications and the replacement of time-consuming traditional methods.

Coupled calculation of vibrational frequencies and intensities

The combination of normal coordinate analysis with intensity calculations gives quantitative information about molecular force fields and the assignments of vibrational frequencies. Calculations of vibrational intensities by means of a standard CNDO/2 version give rise to satisfactory results for the IR intensities. However, the calculated Raman intensities often differ strongly from the experimental data. Inclusion of 2p-polarization functions on hydrogen in the usually used valence basis set is quite successful to obtain improved molecular polarizabilities as well as Raman intensities.

Monitoring of the polymerization of vinylacetate by near IR FT Raman spectroscopy

Abstract Emulsion polymerization of vinylacetate was studied to monitor the reaction on-line by the near infrared FT-Raman technique. The experimental conditions for monitoring the reaction by Raman spectroscopy were determined and discussed with regard to their applicability to industrial production of the polymer. The reaction goes to approximately 90% completion in 50 min and the polymerization can be succesfully monitored by taking full-scan measurements between 20–3500 cm −1 at every 8 min.

Coupled calculation of vibrational frequencies and intensities: Part VI. IR and Raman spectra of crotonaldehyde, methacrolein and methyl-vinylketone

Abstract The vibrational spectra of trans -crotonaldehyde, methacrolein and methylvinylketone have been reinvestigated and the bands assigned. Normal coordinate analyses of these molecules based on the given assignments have been carried out in the valence force field approximation. A transferable force field for α, β-unsaturated aldehydes and ketones was obtained leading to good agreement between observed and calculated frequencies. The relative cartesian displacements of the atoms given in the L matrices were used to compute the IR and Raman intensities of each mode by a modified CNDO/2 procedure. The intensity calculations confirm the assignments and support the calculated force constants.

Stokes Mueller Treatment of Artifacts in Natural Raman Optical Activity

A description of Raman scattering based on the theory by Barron and on Stokes Mueller formalism was developed into a uniform mathematical calculus such that Raman scattering can now be easily represented by a simple phenomenological matrix. This matrix, the Mueller matrix of a modulator driven by a square-wave voltage, and the matrix for a laser regarded as a fictitious polarizer are presented for the first time. With the use of these three matrices and the ones for the analyzer, the polarizer, the linearly birefringent sample cell, the circularly birefringent sample, and the partially polarizing detector, the main reasons for the appearance of artifacts in Raman optical activity have been identified. On the basis of a calculation for right-angle scattering of an isotropic solution of chiral molecules, sources of artifacts appear to be the linear birefringence of the cell walls and of the modulator material. Phase-sensitive detection is found to observe Raman optical activity with a minimal number of artifacts.

Coupled calculation of vibrational frequencies and intensities: Part V. IR and Raman spectra of glyoxal and acrolein

Abstract The normal coordinates of glyoxal and acrolein are calculated in the valence force field approximation. Reasonable force fields, transferable to other α,β-unsaturated aldehydes, are obtained. The derived L matrices are used to compute the infrared and Raman intensities of these molecules by a modified CNDO/2 method. The factors influencing the force fields and intensities are discussed.

Composition, constitution, and interaction of bone with hydroxyapatite coatings determined by FT Raman microscopy.

An optimized FT Raman microscope (inverted microscope with high throughput of radiation) was developed that allows minimal sample preparation and Raman spectroscopy without fluorescence. A quantitative determination of the mineralization of bone tissue and hydroxyapatite (HA) coatings of hip and knee prostheses was performed. The lateral resolution reached down to 10 microm. The distribution of the HA content in the coatings investigated was found to be similar all the time. This result was independent of the composition of the coatings and the history of the whole prosthesis. In the immediate vicinity of the prosthesis a large HA content could be observed that decreased to a minimum towards the periphery of the coating and increased at the site of the ongrown bone. For the interface between bone and HA coating a transitional zone was observed at a lateral distance of 30-40 microm to the implant.

Micro methods in infrared and Raman spectroscopy

SummaryEmploying the concept of the optical conductance [1–3] and taking into account the spectroscopic properties of the sample, firstly the features of sample arrangements are given, which are using minimal amounts of sample determined by the condition of complete illumination of the different types of spectrometers and using different techniques for infrared, near-infrared and Raman micro spectroscopy. Secondly, arrangements of a micro sample are discussed, the minimal size of which is determined by the laws of diffraction. In this case the spectrometers are usually not fully illuminated. The minimal amount of sample necessary is for infrared microscopy in the order of 1000 μm3 (1 pg), for Raman microscopy of the order 100 μm3 (0.1 pg). Examples demonstrate the state of the art and finally developments, which can be anticipated, are outlined.

Raman spectroscopic analysis of isomers of biliverdin dimethyl ester.

The constitutional isomers of biliverdin dimethyl ester, IX alpha and XIII alpha, were studied by resonance Raman spectroscopy. The far-reaching spectral similarities suggest that despite the different substitution patterns, the compositions of the normal modes are closely related. This conclusion does not hold only for the parent state (ZZZ, sss configuration) but also for the configurational isomers which were obtained upon double-bond photoisomerization. Based on a comparison of the resonance Raman spectra, a EZZ configuration is proposed for one of the two photoisomers of biliverdin dimethyl ester IX alpha, while a ZZE, ssa configuration has been assigned previously to the second isomer.