Ultrasonic absorption in aqueous solutions of amino acids at neutral pH
| Autor: | Sadakatsu Nishikawa, K. Yoshizuka, H. Huang, T. Ohno, F. Jordan |
|---|---|
| Rok vydání: | 2003 |
| Předmět: |
Materials science
Acoustics and Ultrasonics Phenylalanine Glycine Analytical chemistry Absorption Nuclear magnetic resonance Reaction rate constant Arts and Humanities (miscellaneous) Humans Molecule Histidine Ultrasonics Amino Acids Quantitative Biology::Biomolecules Range (particle radiation) Alanine Aqueous solution Imidazoles Tryptophan Hydrogen-Ion Concentration Solutions Wavelength Relaxation (physics) Ultrasonic sensor Absorption (chemistry) |
| Zdroj: | The Journal of the Acoustical Society of America. 113:2884-2888 |
| ISSN: | 0001-4966 |
| DOI: | 10.1121/1.1564012 |
| Popis: | Ultrasonic absorption coefficients in aqueous solutions of glycine, L-alanine, imidazole, L-phenylalanine, L-histidine and L-tryptophan at neutral pH were measured in the range from 0.8 to 220 MHz at 25 degrees C. A characteristic ultrasonic relaxation phenomenon was observed only in the solution of L-histidine with a relaxation frequency at around 2 MHz at neutral pH. It was proposed from the concentration independent relaxation frequency and the linear concentration dependence of the maximum absorption per wavelength that the relaxation mechanism was associated with a perturbation of the rotational isomeric equilibrium of the L-histidine molecule. The existence of two rotational isomeric forms of L-histidine in water was examined by semiempirical quantum chemical methods, in order to determine the free energy difference between the two states. The forward and backward rate constants were determined from the relaxation frequency and the energy change. Also, the standard volume change of the reaction was estimated from the concentration dependence of the maximum absorption per wavelength. It was speculated that L-histidine fulfills a specific function among amino acids because of the rotational motion in the molecule, in addition to its well-established acid-base properties. |
| Databáze: | OpenAIRE |
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