A.Y. Chikishev

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.

Polarization sensitive coherent anti-Stokes Raman scattering spectroscopy of the amide I band of proteins in solutions

Polarization sensitive coherent anti-Stokes Raman scattering (PCARS) spectroscopy is a fruitful technique to study Raman vibrations of diluted molecules under off-electron resonant conditions. We apply PCARS as a direct spectroscopic method to investigate the broad amide I band of proteins in heavy water. In spontaneous Raman spectroscopy, this band is not well resolved. We fit a number of spectra taken of each protein under different polarization conditions, with a single set of parameters. It then appears that some substructure is observed in the amide I band. From this substructure, we determine the percentage of alpha-helix, beta-sheet, and random coil for the proteins lysozyme, albumin, ribonuclease A, and alpha-chymotrypsin.

Localization study of co‐phthalocyanines in cells by Raman micro(spectro)scopy

An investigation of intracellular localization of Co-phthalocyanines is reported. The Raman images of K562 cells stained with phthalocyanine were acquired. To understand the peculiarities of the Raman images, measurements were performed at different z-axis positions. The intracellular concentration of phthalocyanine was estimated. A colocalization study was carried out using the fluorescence probes FITC-dextran and acridine orange by means of Raman and fluorescence microscopy. Partial colocalization with both probes was revealed.

Computer simulation of the decay of nonlinear subglobular oscillations in aqueous solutions of protein molecules

The efficiency of the molecular machines can be determined by the Q-factor of oscillations in the selected degrees of freedom. In particular, the quasi-harmonic oscillations of chymotrypsin decrease the threshold for the diffusion limitation of its functioning as molecular scissors. It was demonstrated by the methods of molecular dynamics that the Q-factor of the subglobular oscillations of proteins in water at the frequencies (omega) about 1012 Hz can reach 10, although the Raman bands in the corresponding spectral range were found only in crystal samples. Q quadratically increases with (omega) . The earlier hypothesis regarding the catalytic importance of the Fermi resonance for the oscillations of ligands and atomic groups in the enzyme- substrate complexes was not proved in experiments with simple models. The Fermi resonance can be observed if the Q- factor of the selected degree of freedom exceeds 100.

Are the subglobular oscillations of protein molecule in water overdamped

Raman spectra of crystalline subglobular proteins exhibit peaks in the low-frequency spectral range. These peaks can be related to resonance oscillations of subglobules and possibly play an important role in the catalytic act. The low-frequency spectral features were not observed in aqueous solutions. According to the hydrodynamics, the corresponding oscillations must be overdamped. The results obtained by the methods of molecular dynamics how that the Q-factor of subglobular oscillations can be larger than 10, which stimulated further experimental studies of solutions of proteins.

Background photobleaching in raman spectra of aqueous solutions of plant toxins

Kinetics of background photobleaching in Raman spectra of aqueous solutions of ricin, ricin agglutinin and ricin binding subunit were measured. It was found that the spectrum of Raman background changes upon laser irradiation. Background intensity is lower for the samples with lower molecular weight. Photobleaching is characterized by oscillations in the multi exponentially decaying intensity.

Kinetics of photobleaching of aqueous solutions of ricin agglutinin in the presence of guanidine chloride

Kinetics of background decay in Raman spectra of aqueous solutions of ricin agglutinin in the presence of guanidine chloride were measured. The differences in the kinetics of photobleaching are discussed.

Time- and space-correlated single-photon counting system for fluorescence microspectroscopy of biological specimens

It is well known that fluorescence microspectroscopy is a powerful tool in the study of biological objects. Fluorescence lifetime imaging is one of the modern and promising techniques applied in these studies. The method implies the detection of not only spectral parameters of some molecules and molecular structures but also the fluorescence lifetimes. Thus, one can easily distinguish between two fluorophores with similar spectral properties but having different fluorescence lifetimes. Additional possibilities are offered by the method for stray light rejection and detection of Raman scattering because of the difference in time-correlation of the excitation, fluorescence, and Raman photons. We suggest the application of an original position-sensitive micro-channel plate photomultiplier as a key element of a newly developed fluorescence microspectrometer designated for the study of biological objects (cells, subcellular structures and organells). We present the first results of the experiments with the test objects. The results obtained clearly show that the new system is rather promising in the studies of living cells and tissues.

Systems of digital optical memory based on two-photon amplitude data writing in three-dimensional photosensitive media with the using femtosecond laser pulses: comparison of phase and amplitude approaches to the problem of 3D optical memory

The prospects for creating digital optical-memory systems based on two-photon amplitude data writing with the use of femtosecond light pulses and fluorescent data reading are analyzed. Phase and amplitude approaches to the implementation of 3D optical-memory devices are compared. The main results of investigations carried out at the International Laser Center of Moscow State University in 1996 are presented.

Stochastic cluster dynamics of macromolecules

The issues about the behavior of variant test particles (TP) in 2D potential field with complex relief are studied. The cases with time-dependent parameters of potential field are considered. In particular the mathematical models that are discussed in this paper can describe either the process of penetration of TP (ligand) in active site of the enzyme or protons transition from one potential pit to another.