Andrey Yu. Chikishev

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.

Fourier Transform Infrared (FT-IR) Microspectroscopy of 20th Century Russian Oil Paintings: Problem of Dating

Analysis of the IR spectra of samples from 230 Russian oil paintings of the 20th century is used to propose a procedure for the threshold estimation of the age of paintings based on measured parameters (intensity ratios of spectral bands). The bands of compounds that are formed upon interaction of pigment (zinc white) with oil are used for dating.

Raman microspectroscopy of old paper samples with foxing.

Diagnostic methods and historical document and artwork (in particular, paper items) analysis using modern physical methods is a topical practical problem. Paper materials exhibit nonuniform degradation with the formation of foxing stains. Correct physico-chemical identification of the structure of foxed fragments depends on the efficiency of the experimental technique and offers guidelines for restoration. Raman spectroscopy makes it possible to characterize old paper samples; however, to our knowledge, a comprehensive Raman analysis of foxing has not been done. In this study, we demonstrate that Raman microspectroscopy allows the identification of spectral changes related to paper aging and foxing formation. The degree of degradation of the rag papers studied here is noticeably less than the degree of degradation of the wood-cellulose papers. The spectral differences among 19th-, 20th-, and 21st-century papers are revealed. The presence of lignin and gypsum filler in the 20th-century paper is demonstrated. Raman data indicate that the foxed fragments exhibit a stronger degradation of the paper. The spectral differences between the foxed and unfoxed fragments are discussed. The results can be used in the restoration of paper documents and artworks, in particular for identification of foxed fragments.

Effect of Laser Radiation on 19th Century Paper

Abstract The effect of laser radiation on a German geographic map printed in 1846 is investigated. The sample is irradiated with pulsed and continuous wave radiation (cw) at a wavelength of 532 nm and fluences of 5 and 3 kJ/cm2, respectively. A visible decrease in discoloration resulting from the pulsed irradiation is demonstrated. ATR FTIR and fluorescence spectroscopy are used for diagnostics. The discolouration of the laser irradiated map after five years and the corresponding spectral changes are discussed. Zusammenfassung Auswirkungen der Laserstrahlung auf Drucke aus dem 19. Jahrhundert Die Auswirkung von Laserstrahlung bei der Reinigung einer 1846 in Deutschland gedruckten Landkarte wird vorgestellt. Die Karte wurde gepulst und kontinuierlich mit einer Wellenlange von 530 nm mit einer Dosis von 5 und kJ/cm² bestrahlt. Dabei konnte die Verfarbung des Objektes reduziert werden. Die Folgen der Strahlungseinwirkung auf das Material wurden mit FTIR im ATR-Modus untersucht. Es wurde beobachtet, dass innerhalb von funf Jahren nach der Laserbestrahlung eine Wiederverfarbung des Objektes eintritt, deren Ursachen diskutiert werden. Résumé Influence de la radiation laser sur du papier datant du 19eme Siecle L’article a pour objectif de presenter l’effet d’une radiation laser sur une carte geograpique allemande imprimee en 1846. L’echantillon a ete irradie par rayonnement pulse et par rayonnement continu de longueur d’onde de 532 nm et une densite de flux de 5 et 3 kJ/cm² respectivement. On a pu demontrer une nette reduction de la decoloration de la carte a l’aide de l’irradiation impulsionnelle. L’echantillon a ete egalement passe au diagnostic de la spectroscopie ATR FTIR et de la spectroscopie fluorescente. On a pu observer que dans un intervalle de cinq annees apres l’irradiation au laser une nouvelle decoloration de l’objet a lieu dont on discutera des causes.

Picosecond time-resolved absorption spectroscopy of luciferin

Abstract We present the results of picosecond time-resolved absorption spectroscopy of luciferin, substrate of the bioluminescence reaction. Both absorption and emission from the excited states contribute to the detected signal. Time evolution of the differential optical density at different wavelengths is analyzed. Characteristic rate constants of the relaxation processes are determined. The possible relationship between the behavior of the luciferin molecule in the excited state and the properties of the luciferin–luciferase complex is discussed.

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.

Effect of thermal denaturation, inhibition, and cleavage of disulfide bonds on the low-frequency Raman and FTIR spectra of chymotrypsin and albumin.

Abstract. The analysis of the structure-function relationship is extremely important in the study of proteins. The importance of function-related motions of large parts or subglobules of protein molecules stimulates the spectroscopic study in the low-frequency (terahertz) domain. However, only tentative assignments are available and the spectroscopic data are insufficiently discussed in terms of structural changes. This work is aimed at the analysis of regularities of changes in the low-frequency (100 to 600  cm−1) FTIR and Raman spectra of proteins related to their structural modifications. We study the spectra of two proteins with substantially different structures (albumin and chymotrypsin) and the spectra of samples in which the structures of protein molecules are modified using inhibition, thermal denaturation, and cleavage of disulfide bonds. The results indicate that the low-frequency spectral interval can be used to characterize protein conformations. Correlated variations in the intensities of several low-frequency bands are revealed in the spectra of the modified proteins. The strongest spectral changes are caused by thermal denaturation of proteins, and the effect of cleavage of disulfide bonds is generally weaker. It is demonstrated that the inhibitor binding in the active site causes spectral changes that can be compared to the changes induced by thermal denaturation.

Raman microspectroscopy of nanodiamond-induced structural changes in albumin

Abstract. Nanodiamonds (NDs) are promising agents for theranostic applications due to reported low toxicity and high biocompatibility, which is still being extensively tested on cellular, tissue, and organism levels. It is presumed that for experimental and future clinical applications, NDs will be administered into the organism via the blood circulation system. In this regard, the interaction of NDs with blood components needs to be thoroughly studied. We studied the interaction of carboxylated NDs (cNDs) with albumin, one of the major proteins of blood plasma. After 2-h long in vitro incubation in an aqueous solution of the protein, 100-nm cNDs were dried and the dry samples were studied with the aid of Raman microspectroscopy. The spectroscopic data indicate significant conformational changes that can be due to cND–protein interaction. A possible decrease in the functional activity of albumin related to the conformational changes must be taken into account in the in vivo applications.

Low-frequency vibrational spectroscopy of proteins with different secondary structures

Abstract. Fourier transform infrared (FTIR) and Raman spectra of proteins with significantly different structures are measured in a spectral interval of 50 to 500  cm−1 and noticeable spectral differences are revealed. Intensities of several spectral bands correlate with contents of secondary structure elements. FTIR spectra of superhelical proteins exhibit developed spectral features that are absent in the spectra of globular proteins. Significant differences of the Raman spectra of proteins that are not directly related to the difference of the secondary structures can be due to differences of tertiary and/or quaternary structure of protein molecules.

Raman background photobleaching as a possible method of cancer diagnostics

Kinetics of photobleaching of background in Raman spectra of aqueous solutions of plant toxins ricin and ricin agglutinin, ricin binding subunit, and normal and malignant human blood serum were measured. For the excitation of the spectra cw and pulsed laser radiation were used. The spectra of Raman background change upon laser irradiation. Background intensity is lower for the samples with small molecular weight. The cyclization of amino acid residues in the toxin molecules as well as in human blood serum can be a reason of the Raman background. The model of the background photobleaching is proposed. The differences in photobleaching kinetics in the cases of cw and pulsed laser radiation are discussed. It is shown that Raman background photobleaching can be very informative for cancer diagnostics.