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Relaxation Processes Related to Biomolecules

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Relaxation Processes in Exited Polyatomic Molecules in a Gas Phase as a Model of Fast Structural Changes of Biomolecules

Tech Area / Field

  • PHY-OPL/Optics and Lasers/Physics
  • BIO-CHM/Biochemistry/Biotechnology

Status
8 Project completed

Registration date
08.12.1999

Completion date
31.05.2005

Senior Project Manager
Malakhov Yu I

Leading Institute
National Academy of Sciences of the Republic of Belarus / Institute of Molecular and Atomic Physics, Belarus, Minsk

Project summary

As known, the processes of light-substance interaction as well as the fundamental processes of vital activity from the lowest one-cell organisms and plants to the higher mammals and man are realized on the molecular level. Perceiving the nature of phenomena and processes occurring on the molecular level is being performed more profitably by the spectroscopic methods and, as a rule, reflects the superposition both of the properties of inpidual molecules (as said, isolated) and of those caused by their interaction with an ambient medium. Thus, not elucidating the properties of isolated molecules, it is very difficult and often impossible to determine the role and place of real supramolecular and associative structures in physics, chemistry, biology and as a whole to approach the problems of life sciences.

The aim of the present Project is the experimental and theoretical studies of the dynamics of photophysical (electronic, vibrational, rotational) and photochemical (dissociation, electron transfer, conformational transformation) reactions that occur in electronically excited polyatomic molecules in high-temperature vapours and supersonic jet-cooled gases over the ranges from femto- to picoseconds.

The role of the proposed Project in the above-mentionted areas of science and technology is that the relaxation processes in isolated molecules important to occur biological processes should be considered as a primary model to elucidate the mechanisms of fast structural changes of organic compounds in the “pure” case. The main subjects of investigation will be DNA bases (triptophan and its analogs) and disulfide molecules as components of protein structure. The new subjects of spectroscopic studies will be steroid heteroanalogs which modulate the immune response of living organisms, as shown by the participants of the Project.

The statement of the problem is stipulated by the fact that the relaxation processes that are developing in polyatomic molecules after they have absorbed a light quantum are being most widely analyzed in condensed media. The distictive feature of the investigations of the Project authors is associated with studying intramolecular processes in electronically excited polyatomic molecules in a gas phase when no molecule collisions take place in the course of these reactions. Increasing a concentration of gas phase molecules allows us to follow the influence of the intermolecular interactions on the dynamics of the studied processes, while rising a pressure of foreign gases makes it possible to perform progressive conversion to condensed media. Solutions of organic compounds in this respect are considered as a limiting case.

The authors of the Project were the first who theoretically predicted and experimentally observed the anisotropy of an ensemble of electronically excited isolated molecules in a gas phase under optical excitation and electron impact. Owing to this, the main specific feature of the proposed Project investigations of fast relaxation processes in the electronically excited states of isolated molecules is a wide use of fluorescence anisotropy and absorption dichroism as the most sensitive characteristics conveying the earlier unknown information about photophysical and photochemical processes. The investigations of the Project are mainly focused on high-temperature vapours of organic compounds and supersonic jets of molecular systems.

The environmental influence on the relaxation processes will be elucidated both from investigations of bimolecular gas phase systems and from comparative studies of the relaxation process mechanisms for the same molecules in a gas phase, in liquid and solid solutions.

Highly skilled specialists in the field of optics, laser physics and physical chemistry who have earlier designed lasers for military purposes (powerful lasers, laser target indication systems, etc.) will participate in realizing the present Project. Among them are Academician of the National Academy of Sciences of Belarus and Russian Academy of Sciences N.A. Borisevich; Corresponding Member of the NASB Professor V.A. Tolkachev; Professor G.A. Zalesskaya; Professor G.B. Tolstorozhev as well as 1 Doctor, and 10 Candidates of Science (Phys.& Math.). Also of them are 2 Lenin Prize Winners (1980), 1 State Prize of USSR Winner (1973), and 4 State Prize of Belarus Winners (1998).

Expected Results. The following particular problems will be solved.

Femtosecond decay of optically induced anisotropy of isolated molecules of oxadiazole and disulfide type compounds in a gas phase will be investigated both theoretically and experimentally by analyzing the kinetics of polarized fluorescence and transient absorption dichroism. This will permit conclusions about the mechanisms for evolution of transient anisotropic ensembles, the rotational dynamics of asymmetric molecular rolls and their structures, and also about the characteristics of collision-induced anisotropy decay within the framework of different models for an angular momentum vector (J-, M-, E-diffusion).

Time evolution of photo-induced intramolecular charge transfer and redistribution of electron density in polyatomic molecules of alkylaminooxadiazole and 8-azasteroid type compounds both in a gas phase and in condensed media will be investigated. The dynamics and mechanisms for photodissociation of single chemical bonds in organic aminodisulfide molecules will be studied. Fast relaxation processes, including charge transfer in organic free radicals (fragments of dissociation), will be considered.

Fluorescence polarization characteristics of jet-cooled polyatomic molecules of indole and its analogs; Van der Waals and H-bond complexes and intermolecular exciplexes based on them will be analyzed from the rotational contour of the P-, Q-, R-branches. Conclusions about their structure, rotational dynamics and dissociation mechanisms will be made.

Comparative experimental studies of fluorescence anisotropy of aromatic and heterocyclic compounds under optical and monoenergetical electron beam excitation will be carried out. Based on the results obtained, the mechanisms for electron impact excitation of isolated molecules will be proposed.

Mechanisms of intermolecular vibrational energy transfer, triplet-triplet electronic energy transfer, photo-induced electron and hydrogen atom transfer in triplet-excited polyatomic molecules of heterocyclic compounds mixed with foreign gas molecules of different nature will be studied by the long-lived luminescence methods. The investigation is aimed at modelling relaxation processes in the intermediate case between isolated molecules and solvated ones in solution.

The expected results will be of fundamental significance and will make our knowledge of photophysics and photochemistry of isolated organic molecules more deep. New data on solving particular problems of modern molecular spectroscopy will be obtained: (1) dynamic behavior of transient anisotropic ensembles of polyatomic molecules in a gas phase; (2) specific exhibition of photo-induced intramolecular charge transfer in isolated molecules; (3) distinctive features of photodissociation of S-S bonds; (4) bimolecular complex structure; (5) mechanisms for interaction of fast electrons with molecules.

The practical importance of the results obtained is to a great extent bound up with a character and type of subjects of investigation of the Project. 8-azasteroid molecules and S-S- bond containing compounds serve important biological functions in real living organisms, particularly in proteins. Special attention will be paid to studying the cleavage of single S-S bonds in model molecular systems, allowing for the fact that when such a reaction occurs proteins can undergo fast folding. Information about the dynamics of such folding can shed light on the functioning mechanisms of proteins. Molecules of tryptophan and its analogs serve as fluorescence markers of proteins and will be also studied in this Project. Our synthesized 8-azasteroids are a new class of low-molecular agents that modulate the immune functions of man and animals. Studies of their spectroscopic properties are important, first, to establish an electron structure of these compounds and, second, to reveal possible correlations between their spectroscopic parameters and physiological action upon the cells of living organisms. This will find use in practical immunology.

The Project profitably realizes the main tasks of the ISTC: not to spread knowledge acquired in military studies; to develop fundamental and applied investigations; to encourage in every possible way international cooperation and integration of CIS scientists into world community; and, at last, to give the group of “weapon” scientists who have earlier designed lasers for military purposes (powerful lasers when acted upon materials, laser target indication systems, etc.) a chance to redirect their attention to solving peaceful and important for world community problems of fundamental science: establishing an electron structure of isolated biologically important molecules and mechanisms of photo-induced relaxation processes in them by methods of laser spectroscopy with superhigh temporal and spectral resolution.

Foreign collaborators will take part in discussing the obtained results and, if necessary, in correcting future plans of investigations. They will also receive exhaustive science and technology information about the results of Project investigations and will be able to use it in their work. It is planned to make joint correction of the used methods of femtosecond fluorescence spectroscopy and transient absorption spectroscopy (University of Tokyo), optimization of sub-50 fs laser spectrometer parameters (Tokyo Instruments, Inc.), joint analysis of mechanisms of ultrafast photo-induced processes in ethylene-containing organic compounds or in ethylene-containing heterosteroids (Centre National de la Recherche Scientifique, France), etc. Close cooperation between the authors of the Project and the Collaborators from Europe and Japan will be strengthened and broadened in the act of performing the Project in the interdisciplinary sciences.

The technical approaches and methodology underlying the Project are based on long-standing experience in designing and using lasers that emit ultrashort pulses (dynamics of fast processes over femto- and picosecond ranges), on the one hand side, and on using lasers with a narrow spectrum line (jet-cooled spectroscopy), on the other hand. In this respect, the Project investigations are related to the technology area: Physics: Optics and Lasers (PHY-OPL). Studies of an electronic structure of polyatomic molecules of organic compounds are the subject of Chemistry: Physical and Theoretical Chemistry (CHE-TEC). Since the main subjects of Project investigations are such molecules as bases of aminoacids and disulfide compounds that constitute the protein structure as well as heteroanalogs of steroids that modulate an immune response of living organisms, the proposed Project is directly bound up with: Biotechnology and Life Sciences: Biochemistry (BIO-BCH); Immunology (BIO-IMU).

In considering specific situations and in solving photobiological problems important in practice, experiments will be conducted on studying relaxation processes in the same molecular systems both in a gas phase and in condensed media. It is planned to widely use vector characteristics of molecular processes that manifest themselves in the polarized absorption and radiation emitted by isolated molecules and their fragments. It is also planned that with regard to the real conditions and the results of particular experiments, theoretical studies of the dynamics of transient molecular ensembles will overtake experimental ones. The inventions, patents and design documentation created by the authors of the Project both in developing laser technique and in carrying out the USSR military programs will be also utilized.

The present Project was submitted to the International Seminar “Conversion of Research Studies in Belarus within the framework of the ISTCs Activity” on the section “Physics” (Minsk, May 17-22, 1999) and published in the Proceedings of the Seminar in the paper “Relaxation Processes in Polyatomic Molecules”.


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