Browsing by Author "Matei, Adriana"

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Open Access
Optical investigations of biological samples in far infrared
(2005) Matei, Adriana; Dressel, Martin (Prof. Dr.)
The present work was performed in the frame of the EU project "Terahertz radiation in Biological Research, Investigations on Diagnostics and study of potential Genotoxic Effects". Amino acids, amino acid chains, proteins, and human blood serum have been investigated by means of Fourier transform infrared spectroscopy (FTIR) in the frequency range 10-650 cm-1. We looked for the properties of amino acids, those that they have in common, and those that make them different from each other. In this respect, we recorded transmission spectra and determined the relative absorption. A pattern in the absorption properties is repeated for each amino acid. There are specific vibrational frequencies that can be observed in most of the amino acids. The pattern is not always stable, and not all the samples display all the common features. Making a statistics for absorption frequencies, we can see that amino acids share common features, enough to make them a class of molecules. On the other hand, they exhibit enough differences, to make each of them an individual. Analyzing its far infrared spectra can unequivocally identify each amino acid. Their presence can be recognized in a sample as long as they are not bonded with other molecules. However, an amino acid is loosing its "identity" once is integrated in a protein. Already in a two amino acids-molecule is difficult to tell an amino acid from another. When the amino acids form oligomers, the absorption lines at low frequency shift and broaden to lower frequencies, as the oligomer chain is increasing. For a polymer, is rather impossible to distinguish from its spectrum only which amino acids are within. The spectrum of a polymer is broadening toward low frequencies in the same manner the water spectrum does. The overall behavior to be seen in this case is the hindered motion of the hydrogen bonds. The oligomers, from trimer up to the hexamer, show similarities in absorption pattern with PGI. Specific absorption bands show that they have the same secondary β structure as PGI. The spectrum of polyglycine spans a shorter frequency range than the spectra of glycine oligomers. This adds some difficulty in identifying the structure of PG. However, the presence of absorption peaks at 129 and 215 cm-1, similar with those previously seen in PG, can be used as an indication for β structure. Proteins have broad spectra, where the features of amino acids are not retained. Moreover, protein spectra differ from those of homopolymers. In our protein investigation, we used three proteins with a high content of α-helix. Two of them, acylase (142 and 221 cm-1) and lipase (131 cm-1 and 250 cm-1), that have a α-helix structure of 50%, show absorption frequencies that have been earlier associated with this type of secondary structure. We restrain ourselves from a straigthforward assumption that these modes indicate the presence of the α-helix. There are at least two reasons for doing this: (1)beta lactamase has no strong absorption at these values, in spite of its high helical content, (2) the α-helix has also other characteristics in the frequency range where we measured, that could not be observed. Due to the high water content (>90%) the differences between serum and water spectra are extremely small. We do not find any large deviations from the water spectrum and no sharp features. We can conclude that the optical properties of serum are governed by water, and that the effect of the radiation will manifest, first, in water.