Authors: V. Sonois, P. Faller, W.S. Bacsa, N. Fazouan and A. Estève
Affilation: University Paul Sabatier, France
Pages: 37 - 40
Keywords: histamine, needle, Raman spectroscopy
Amino acids in aqueous solutions have low Raman signals and are difficult to detect at low concentrations. To increase Raman signals one often uses UV excitation. We find that nano-needels can be grown from droplets of aqueous histamine on silica substrates. We observe intense and narrow vibrational Raman bands of nanoscale needle shaped histamine using visible excitation sources. Scanning electron microscopy reveals a combined structure of folded flat leaves and regions with a dense array of needles with diameters in the 50-100nm range. The needles are formed mainly due to substrate heating, convection is found to be less important in their formation. The pH dependent measurements show their influence on the detected spectral bands. The observed spectral bands are compared with density functional calculations taking into account of the peptide bond formation with neighbouring molecules. The C-H stretching modes at high frequency are identified and attributed to modes of the imidiazole ring and the back bone. C-H stretching mode of the back bone is found to be strongly conformational dependent. We show that the growth method can be generalized to other amino acids and peptides.
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