Nucleic acids Raman spectra

Infrared and Raman spectroscopy are in current use fo r elucidating the molecular structures of nucleic acids. The application of infrared spectroscopy to studies of the structure of nucleic acids has been reviewed,135 as well as of Raman spectroscopy.136 It was noted that the assignments are generally based on isotopic substitution, or on comparison of the spectrum of simple molecules that are considered to form a part of the polynucleotide chain to that of the nucleic acid. The vibrational spectra are generally believed to be a good complementary technique in the study of chemical reactions, as in the study76 of carbohydrate complexation with boric acid. In this study, the i.r. data demonstrated that only ribose forms a solid complex with undissociated H3B03, and that the complexes are polymeric. 

Raman optical activity (RO A) Due to molecular chirality there is a difference in the intensity of Raman scattered right and left circularly polarized light. Raman optical activity (ROA) is a vibrational spectroscopic technique that is reliant on this difference and the spectrum of intensity differences recorded over a range of wavenumbers reveals information about chiral centers within a sample molecule. It is a useful probe to study biomolecular structures and their behavior in aqueous solution especially those of proteins, nucleic acids, carbohydrates, and viruses. The information obtained is in realistic conditions... 

To obtain a Raman spectrum of a protein or nucleic acid, one places the sample at the focal point of a focused laser beam. Because a laser beam can be focused into a circle with a radius of approximately its wavelength, this allows for a spatial resolution of the order of a cubic micrometer. The light scattered from the DNA sample in the focused laser beam is collected by means of a lens system and directed through a suitable monochromator to a photon detector. The intensity of the scattered light is measured as a function of its frequency. A plot of the intensity of the scattered light (photons per square centimeter per second) as a function of the frequency difference, fi, between the incident laser frequency and the scattered light frequency, constitutes a Raman spectrum (i.e., H = wl - Ws). When a band appears in the Raman spectrum at a particular... 

We have demonstrated that Ag nanorod-based SERS is not only sensitive to purified virus, but also is able to sense the presence of virus after infection in biological media 49). To demonstrate this, we compared the SERS spectra of uninfected Vero cell lysate, RSV-infected cell lysate and purified RSV. The results show that major Raman bands can be assigned to different constituents of the cell lysate and the virus, such as nucleic acids, proteins, protein secondary structure units and amino acid residues present in the side chains and the backbone. However, our most significant result was that vibrational modes due to the virus could be unambiguously identified in the SERS spectrum of the Vero cell lysate after infection 49). 

E plots the Raman band and CARS signal at 1000 cm" that are assigned predominantly to proteins. A wider gap is similarly resolved here. Cluster analysis of the Raman image identifies three main groups of spectra that are displayed in Figure 3.5. The spectrum of the tissue (blue cluster) contains spectral contributions of proteins and nucleic acids, whereas lipid bands are weak. The intensities of lipid bands increase and the intensities of proteins and nucleic acids decrease in the spectra of the gaps. It can be concluded that the gap is filled with lipids of different density. The result of the underlying chemical composition can only be obtained by multivariate analysis of hyperspectral Raman data such as k-means cluster analysis. Similar observations were also made for brain tissue as described in the later section. 

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