Spectroscopy and Molecular Changes in Cancer Cells - Vibrational Spectroscopy for Tissue Analysis - page 19

structural characteristics of biological tissues and is only possible if the spec-
tral bands are precisely and accurately assigned to specific chemical bonds
and functional groups.
Peak Assignments of Biological Molecules
Huang et al. presented very useful information for interpreting the peak
intensities of the biological samples [10,11]. Table 2.1 summarizes the assign-
ments of the peaks investigated in these studies. It seems that these definitions
play a considerably important role in peak definitions of biological samples
done by other research groups [12-19]. As can be seen, proteins, lipids, nucleic
acids, and polysaccharides have distinct and definable peaks in Raman spectra.
Some of the Raman peaks can be interpreted more easily, as compared
to FTIR. This is because of the overlapping of the assignments, which can
be seen, for example, in peak intensities of 1445 cm −1 and 1302 cm −1 with
assignments due to both proteins and lipids. However, it was shown that
lung cancer tumours have higher amounts of proteins, decreased intensities
of phospholipids, and more widened and greater nucleic acid peaks.
However, there are differences among the definitions of some peaks. For
instance, it was concluded that a shoulder at 1121 cm −1 is due to the sym-
metric phosphodiester stretching band of nucleic acids, namely ribonucleic
acid (RNA). However, a shoulder at 1020 cm −1 was mentioned as being due to
deoxyribonucleic acid (DNA). The intensity ratio of 1121/1020 cm −1 was used
to grade the tumours, with increasing quantities for more developed malig-
nancies. Interestingly, Huleihel et al. [18] and Andrus [20] mention that same
intensity ratio, with the same interpretation. Furthermore, it was concluded
that possibly greater 1050-1080 cm −1 erosion indicated a greater degree of
oxidative damage to DNA.
Schultz and Baranska [21] made a detailed study of the characteristic peak
intensities of Raman spectroscopy (Table 2.2). Although this work is con-
centrated on plant samples, as almost all of these compounds and chemical
bands also exist in cells and tissues, the results and conclusions could be
successfully used in biological studies. Considering the significant amount
of information about the cellular molecules that can be obtained from these
tables, this article indicates the wide range of capacities of these techniques
in producing useful results in biological research.
Based on the information presented in Table 2.2, Andrus carried out an
interesting study on cancer grading of lymphoid tumours [20]. They also
used 1121 cm −1 (RNA band), 1053 cm −1 (DNA band), 1084 cm −1 (DNA and
RNA), 1650 cm −1 (protein), and 2800-3000 cm −1 (lipid and protein) in their
investigations, and believe that the protein:nucleic acid ratio could be
analysed through the 1650 cm −1 :1084 cm −1 ratio [20].