N.N. Brandt

Optimization of the Rolling-Circle Filter for Raman Background Subtraction

A procedure is proposed to optimize a high-pass filter enabling one to subtract the broadband background signals inherent in Raman spectra. A spectral approach is used to analyze the characteristics of the filter and the distortions in the processed spectra. Examples of the processing of real spectra are presented.

Photobleaching as a Method of Increasing the Accuracy in Measuring Carotenoid Concentration in Human Skin by Raman Spectroscopy

It was shown experimentally that the effect of photobleaching in noninvasive measurement of the Raman spectra of light used in determining the carotenoid concentration in human skin can be used to increase measurement accuracy. Increased accuracy occurs as a consequence of a decrease in the measurable Raman spectra of the wideband fluorescent background intensity when a sample is irradiated by laser radiation. Furthermore, it was demonstrated that, for the spectra of skin from nine volunteers, the fluorescent background intensity can be decreased on average by a factor of 1.4, which leads to an increase in the signal-to-noise ratio for Raman lines of skin carotenoids by a factor of 1.2 on average. The kinetics of photobleaching of humans can be described by biexponential decay with a correlation coefficient close to unity, which agrees with the presented theoretical calculations.

ATR-FTIR and FT Raman spectroscopy and laser cleaning of old paper samples with foxings

Samples of old paper are studied using ATR-FTIR and FT Raman spectroscopy. It is demonstrated that the methods of laser spectroscopy make it possible to distinguish between the foxing localization regions and the region of homogeneous aging (yellowing). A significant bleaching of old paper and an almost complete erasure of the foxing stains can be reached using laser irradiation.

Raman spectroscopy of tris-(hydroxymethyl)aminomethane as a model system for the studies of α-chymotrypsin activation by crown ether in organic solvents

Abstract Raman spectroscopy is employed to study tris-(hydroxymethyl)aminomethane and its complexes with 18-crown-6. The results obtained are used to interpret the known effect of α-chymotrypsin activation by crown ether in organic solvents. Raman spectra of the samples lyophilized from aqueous solutions at various pH values are measured in solid state, acetonitrile and cyclohexane.

Photoinduced formation of thiols in human hair

Raman, scanning electron, and optical microscopy of hair and spectrophotometry of soluble hair proteins are used to study the effect of UV-vis radiation on white hair. The samples of a healthy subject are irradiated using a mercury lamp and compared with non-irradiated (control) hair. The cuticle damage with partial exfoliation is revealed with the aid of SEM and optical microscopy of semifine sections. Gel filtration chromatography shows that the molecular weight of soluble proteins ranges from 5 to 7kDa. Absorption spectroscopy proves an increase in amount of thiols in a heavier fraction of the soluble proteins of irradiated samples under study. Raman data indicate a decrease in the amount of SS and CS bonds in cystines and an increase in the amount of SH bonds due to irradiation. Such changes are more pronounced in peripheral regions of hair. Conformational changes of hair keratins presumably related to the cleavage of disulfide bonds, follow from variations in amide I and low-frequency Raman bands. An increase in the content of thiols in proteins revealed by both photometric data on soluble proteins and Raman microspectroscopy of hair cuts can be used to develop a protocol of the analysis of photoinduced hair modification.

Optoacoustic measurements of the porosity of paper samples with foxings

The goal of this work is to investigate the porosity of old paper with foxings. Initially, paper samples are characterized using the conventional absorption and Fourier transform infrared spectroscopies. Optoacoustic method based on laser excitation of short ultrasound transients is used for porosity measurements. The paper porosity is calculated using the theory of two-component mixture with the experimentally determined sound speeds in paper samples saturated with liquids. An increase in the porosity in foxing stains on paper in comparison with the foxing-free fragments is clearly demonstrated.

CARS and Raman spectroscopy of function-related conformational changes of chymotrypsin

We report on the comparative analysis of the conformation-sensitive bands of free enzyme (chymotrypsin), liganded enzyme (chymotrypsin anthranilate) and enzyme complex with 18-crown-6. The studies were carried out by Raman scattering spectroscopy and polarization-sensitive coherent anti-Stokes Raman scattering spectroscopy (CARS). The bands of tyrosine and tryptophan residues, disulfide bridges and amide I and amide III were analyzed. It is concluded that the conformation of the enzyme changes much more in the case of liganding than in the case of the formation of a complex with the crown ether.

Laser Raman Spectroscopy of the Effect of Solvent on the Low-Frequency Oscillations of Organic Molecules

The effect of solvent on low-frequency oscillations is studied using an example of the 1,1,2,2-tetrachloroethane (TCE) and 1,1,2,2-tetrabromoethane (TBE) molecules, which exhibit torsional oscillations in the terahertz range. Dimethylsulfoxide (DMSO) and carbon tetrachloride (CTC) are used as solvents. It is demonstrated that a decrease in the concentration of the substance under study in the TBE/CTC, TCE/DMSO, and TCE/CTC mixtures leads to a frequency shift of the low-frequency oscillation. The shift is not observed in the TBE/DMSO mixture but a decrease in the TBE concentration causes significant broadening of the low-frequency line.

THz and IR Spectroscopy of Molecular Systems That Simulate Function-Related Structural Changes of Proteins

The activity of enzymes in organic solvents substantially increases in the presence of crown ethers. Tris(hydroxymethyl)aminomethane (tris) is chosen as a model compound to simulate the interaction of surface amino groups of proteins with crown ether. The methods of FTIR and time-domain THz spectroscopy are used to study the interaction of tris with 18-crown-6. The THz spectra of the complexes are measured for the first time.

BROADBAND BACKGROUND IN RAMAN SPECTRA OF PROTEINS: DETERMINISTIC SIGNAL OR NOISE?

The broadband background inherent in the Raman spectra of proteins is analyzed using a dual approach. Mathematical methods are used to eliminate the background signal that determines the noise contribution to the Raman spectra. Regularities in the time dependence of the background intensity and their relation to the protein structure are experimentally studied.