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Defining Multiple Characteristic Raman Bands of α-Amino Acids as Biomarkers for Planetary Missions Using a Statistical Method.

Rolfe SM, Patel MR, Gilmour I, Olsson-Francis K, Ringrose TJ - Orig Life Evol Biosph (2016)

Bottom Line: Per amino acid, 240 spectra were recorded and compared using established statistical tests including ANOVA.The intensity of bands differed by up to six times when several points on the crystal sample were rotated through 360 °; to reduce this effect when defining characteristic bands for other molecules, we find that spectra should be recorded at a statistically significant number of points per sample to remove the effect of sample rotation.It is crucial that sets of characteristic Raman bands are defined for biomarkers that are targets for future planetary missions to ensure a positive identification can be made.

View Article: PubMed Central - PubMed

Affiliation: Planetary and Space Sciences, Department of Physical Sciences, The Open University, Robert Hooke Building, Walton Hall, Milton Keynes, MK7 6AA, UK. samantha.rolfe@open.ac.uk.

ABSTRACT
Biomarker molecules, such as amino acids, are key to discovering whether life exists elsewhere in the Solar System. Raman spectroscopy, a technique capable of detecting biomarkers, will be on board future planetary missions including the ExoMars rover. Generally, the position of the strongest band in the spectra of amino acids is reported as the identifying band. However, for an unknown sample, it is desirable to define multiple characteristic bands for molecules to avoid any ambiguous identification. To date, there has been no definition of multiple characteristic bands for amino acids of interest to astrobiology. This study examined L-alanine, L-aspartic acid, L-cysteine, L-glutamine and glycine and defined several Raman bands per molecule for reference as characteristic identifiers. Per amino acid, 240 spectra were recorded and compared using established statistical tests including ANOVA. The number of characteristic bands defined were 10, 12, 12, 14 and 19 for L-alanine (strongest intensity band: 832 cm(-1)), L-aspartic acid (938 cm(-1)), L-cysteine (679 cm(-1)), L-glutamine (1090 cm(-1)) and glycine (875 cm(-1)), respectively. The intensity of bands differed by up to six times when several points on the crystal sample were rotated through 360 °; to reduce this effect when defining characteristic bands for other molecules, we find that spectra should be recorded at a statistically significant number of points per sample to remove the effect of sample rotation. It is crucial that sets of characteristic Raman bands are defined for biomarkers that are targets for future planetary missions to ensure a positive identification can be made.

No MeSH data available.


The Raman spectra, averaged over the 16 points taken in map 1 using the 473 nm laser, of the amino acids in this study. The asterisks indicate the characteristic bands as described in the Tables 1 and 2
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Fig1: The Raman spectra, averaged over the 16 points taken in map 1 using the 473 nm laser, of the amino acids in this study. The asterisks indicate the characteristic bands as described in the Tables 1 and 2

Mentions: The Raman spectra for alanine, aspartic acid, cysteine, glutamine and glycine are presented in Fig. 1 as references for these amino acids. In the Figure, the characteristic bands, as described in the following sections, are marked with an asterisk. These spectra are an average of a 16 point map using the 473 nm laser, where each point is an average of five 15 s spectra acquisitions as described in Calibration and Data Collection. The baseline of the resulting spectra were corrected for background noise and other factors (described in Calibration and Data Collection) to provide a baseline for band intensity and allowed for more accurate band fitting by the fitting algorithm in LabSpec5. The spectral shapes of alanine, aspartic acid, glycine shown in Fig. 1 are in agreement with previously published data (Zhu et al. 2011), as well as that of glutamine (Dhamelincourt and Ramirez 1993). The cysteine spectra presented in Fig. 1 is consistent with that determined by Pawlukojć et al. (2005), except most of the bands recorded in this study are not as intense as the previously published bands.Fig. 1


Defining Multiple Characteristic Raman Bands of α-Amino Acids as Biomarkers for Planetary Missions Using a Statistical Method.

Rolfe SM, Patel MR, Gilmour I, Olsson-Francis K, Ringrose TJ - Orig Life Evol Biosph (2016)

The Raman spectra, averaged over the 16 points taken in map 1 using the 473 nm laser, of the amino acids in this study. The asterisks indicate the characteristic bands as described in the Tables 1 and 2
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4764629&req=5

Fig1: The Raman spectra, averaged over the 16 points taken in map 1 using the 473 nm laser, of the amino acids in this study. The asterisks indicate the characteristic bands as described in the Tables 1 and 2
Mentions: The Raman spectra for alanine, aspartic acid, cysteine, glutamine and glycine are presented in Fig. 1 as references for these amino acids. In the Figure, the characteristic bands, as described in the following sections, are marked with an asterisk. These spectra are an average of a 16 point map using the 473 nm laser, where each point is an average of five 15 s spectra acquisitions as described in Calibration and Data Collection. The baseline of the resulting spectra were corrected for background noise and other factors (described in Calibration and Data Collection) to provide a baseline for band intensity and allowed for more accurate band fitting by the fitting algorithm in LabSpec5. The spectral shapes of alanine, aspartic acid, glycine shown in Fig. 1 are in agreement with previously published data (Zhu et al. 2011), as well as that of glutamine (Dhamelincourt and Ramirez 1993). The cysteine spectra presented in Fig. 1 is consistent with that determined by Pawlukojć et al. (2005), except most of the bands recorded in this study are not as intense as the previously published bands.Fig. 1

Bottom Line: Per amino acid, 240 spectra were recorded and compared using established statistical tests including ANOVA.The intensity of bands differed by up to six times when several points on the crystal sample were rotated through 360 °; to reduce this effect when defining characteristic bands for other molecules, we find that spectra should be recorded at a statistically significant number of points per sample to remove the effect of sample rotation.It is crucial that sets of characteristic Raman bands are defined for biomarkers that are targets for future planetary missions to ensure a positive identification can be made.

View Article: PubMed Central - PubMed

Affiliation: Planetary and Space Sciences, Department of Physical Sciences, The Open University, Robert Hooke Building, Walton Hall, Milton Keynes, MK7 6AA, UK. samantha.rolfe@open.ac.uk.

ABSTRACT
Biomarker molecules, such as amino acids, are key to discovering whether life exists elsewhere in the Solar System. Raman spectroscopy, a technique capable of detecting biomarkers, will be on board future planetary missions including the ExoMars rover. Generally, the position of the strongest band in the spectra of amino acids is reported as the identifying band. However, for an unknown sample, it is desirable to define multiple characteristic bands for molecules to avoid any ambiguous identification. To date, there has been no definition of multiple characteristic bands for amino acids of interest to astrobiology. This study examined L-alanine, L-aspartic acid, L-cysteine, L-glutamine and glycine and defined several Raman bands per molecule for reference as characteristic identifiers. Per amino acid, 240 spectra were recorded and compared using established statistical tests including ANOVA. The number of characteristic bands defined were 10, 12, 12, 14 and 19 for L-alanine (strongest intensity band: 832 cm(-1)), L-aspartic acid (938 cm(-1)), L-cysteine (679 cm(-1)), L-glutamine (1090 cm(-1)) and glycine (875 cm(-1)), respectively. The intensity of bands differed by up to six times when several points on the crystal sample were rotated through 360 °; to reduce this effect when defining characteristic bands for other molecules, we find that spectra should be recorded at a statistically significant number of points per sample to remove the effect of sample rotation. It is crucial that sets of characteristic Raman bands are defined for biomarkers that are targets for future planetary missions to ensure a positive identification can be made.

No MeSH data available.