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MECHANISMS OF THIOLS PHOTO-OXIDATION BY REACTIVE

SPECIES GENERATED IN THE PHTHALOCYANINES PHOTOSENSITISING

 

 

 PROJECT DURATION: 13.04.2009 – 30.11.2010

 

  PROJECT OBJECTIVES: The project aimed to contribute in the understanding of the interaction processes between the photo-generated reactive species (excited photosenzitizers, oxygen singlet) and biomolecules as proteins and their compounds.

 

 

   According with the initial project objectives, the following research activities and results were performed and obtained:

• The selection and identification studies regarding the compounds of interest in thiol photo-oxidation mechanisms, namely the proteins: BSA, HSA, Lysozime and the aminoacids: cysteine, tryptophan, tyrosine and on the other side the photosensitizers methylene blue and phthalocyanines with diamagnetic metals (Zn, Cu, Fe Co, Ni).
• The development of the experimental set-up for the time resolved measurements of oxygen singlet phosphorescence emission in the interaction with biomolecules aiming to elucidate the mechanism of thiols oxidation.

• The photophysical basic data as the quantum yields and the liftetime of the oxygen singlet generated by the studied phthalocyanines were obtained.
• The experimental study regarding the thiols photo-oxidation by oxygen singlet; the constant of the oxygen singlet quenching produced by the cysteine was determined. The photo-oxidation of cisteine to cistine by UV iradiation in the presence of the photosenzitizer Zn-phthalocianine, was emphasized using Raman spectroscopy.
• The intrinsec generation of oxygen singlet by the biological molecules as the aminoacids (triptophan, tyrosine) and the proteins ( human seric albumine, bovine seric albumine) was measured via the phosphorescence emission of oxygen at 1270nm. 
• The development of a Laser Raman Spectroscopy aparatus for the study of  the changes in biomelecule structures induced by photo-oxidation was performed at INFLPR site, by the guide and support of the french partner. The system was tested on biological samples as cysteine and cistine as solid and water solution samples and gave good results.

• The know-how transfer between the two teams in the complementary domains of Raman spectroscopy and the time resolved spectroscopy for oxygen singlet phosphorescence detection was made succesfully.
• The modifications in the conformational structures induced by UV irradiation on HSA, BSA, cysteine, tyrosine residue, was studied by Raman Spectroscopy.
• Studies of the photo-oxidation produced by the singlet oxygen generated by the laser excited methylene blue on the biological compounds, the proteins: BSA, lysozime, the amnioacids: triptophan, tyrosine, were performed. The oxygen singlet quenching constants by these compounds in heavy water solutions at different pD were determined. These parameters are important in establishing the protein conformational structure and the exposure level of the aminoacids present in proteins to the harmful UV radiation.
• The results of the actual project were presented at 3 international conferences and are the base of a paper in preparation for the submission to a peer-review journal.
• Due to the good and fruitful collaboration during the present project, they were envisaged and established the bases and the frame of an application for a cotutele doctorate in the annual programme « DOCTORAT EN CO-TUTELLE » of the French Embassy in Romania.