The infrared spectrum of solid L-alanine: influence of pH-induced structural changes

The Journal of Physical Chemistry. a
Ana R GarciaLaura M Ilharco

Abstract

The influence of the pH on the infrared spectrum of L-alanine has been analyzed by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The amino acid was precipitated from aqueous solutions and dried at 36.5 degrees C, in order to stabilize cationic L-alanine or alaninium [CH3CH(NH3(+))COOH] at pH 1, the zwitterionic form [CH3CH(NH3(+))COO(-)] at pH 6, and anionic L-alanine or alaninate [CH3CH(NH2)COO(-)] at pH 13. New insight on the specific inter and intramolecular interactions in the different forms of L-alanine was reached by a novel methodological approach: an infrared technique not used before to analyze solid amino acid samples (DRIFTS), in combination with a detailed analysis based on spectral deconvolution. The frequency ranges of interest include the carbonyl/carboxyl stretching and amine deformation modes and the OH/NH stretching modes. It was shown that intermolecular hydrogen bonds between the NH3(+) and COO(-) groups are predominant in the zwitterionic form, whereas in cationic L-alanine, H bonds between the COOH groups are responsible for the formation of dimers. In anionic L-alanine, only strong electrostatic interactions between the COO(-) groups and Na(+) ions are proposed, evidencing the rele...Continue Reading

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Citations

Mar 25, 2010·The Journal of Chemical Physics·Aurélien TrivellaPetra Hellwig
Dec 19, 2016·Physical Chemistry Chemical Physics : PCCP·J ThøgersenS J Knak Jensen
Sep 17, 2010·Angewandte Chemie·Uwe J MeierhenrichSøren V Hoffmann
Jan 14, 2020·Physical Chemistry Chemical Physics : PCCP·Marlene Møller MadsenJan Thøgersen
Oct 18, 2012·Chemistry : a European Journal·Li-Wei ZhaoJing He
Aug 8, 2014·Dalton Transactions : an International Journal of Inorganic Chemistry·Roland SchnitterBerthold Kersting
May 13, 2021·Critical Reviews in Food Science and Nutrition·Magdi A A MousaMohammed Kamruzzaman
Dec 18, 2012·Journal of the American Chemical Society·Elizabeth C Griffith, Veronica Vaida
Apr 30, 2017·ACS Applied Materials & Interfaces·Chengchen GuoGregory P Holland

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