Journal of Radioanalytical and Nuclear Chemistry, Vol. 253, No. 3 (2002) 369–373 Molar extinction coefficients in aqueous solutions of some amino acids Kulwant Singh, 1 * G. K. Sandhu, 1 Gagandeep Kaur, 1 B. S. Lark 2 1 Department of Physics, Guru Nanak Dev University, Amritsar-143005, India 2 Department of Chemistry, Guru Nanak Dev University, Amritsar-143005, India (Received June 26, 2001) Mass attenuation coefficients of amino acids viz. glycine (C 2 H 5 NO 2 ), l-Serine (C 3 H 7 NO 3 ), l-Theronine (C 4 H 9 NO 3 ), l-Proline (C 5 H 9 NO 2 ), l-Valine (C 5 H 11 NO 2 ) and l-Phenylalanine (C 9 H 11 NO 2 ) in aqueous solutions have been determined at 81, 356, 511, 662, 1173 and 1332 keV by the gamma- ray transmission method in a narrow beam good geometry setup. Precisely measured densities of these solutions were used for the determination of these coefficients which varied systematically with the corresponding changes in the concentrations (g/cm 3 ) of the solutions. Molar extinction coefficients of amino acids were then obtained at these energies and were found to be in good agreement with the theoretical results. In addition, total interaction cross sections of amino acids in aqueous solutions were also calculated. Introduction The present study of molar extinction coefficients of glycine (C 2 H 5 NO 2 ), l-Serine (C 3 H 7 NO 3 ), l-Theronine (C 4 H 9 NO 3 ), l-Proline (C 5 H 9 NO 2 ), l-Valine (C 5 H 11 NO 2 ) and l-Phenylalanine (C 9 H 11 NO 2 ) solutes in solutions covers the energy regions in which the influence of all photon interaction processes can be seen. The investigation is expected to yield a valuable information about the interaction of photons with hydrated rather than bare ions. Since radioactive sources are increasingly used in biological studies, radiation sterilization, and industry, 1,2 a thorough knowledge of the interaction of photons with biologically important substances is desirable. The study of attenuation coefficients is potentially useful in the development of semi-empirical formulations of high accuracy, possibly along the lines detailed by JACKSON and HAWKES. 1 Mass attenuation coefficients of gamma- rays in some compounds and mixtures of dosimetric and biological importance have been compiled by HUBBEL 3 in the energy range 1 keV to 20 MeV. An updated version of the attenuation coefficients for elements having atomic numbers from 1 to 92 and for 48 additional substances has also been compiled by HUBBEL and SELTZER. 4 GOPINATHAN et al. 5–8 have studied the total attenuation cross sections for several amino acids and sugars in the solid form for limited energies. Theory LAMBERT developed the equation for attenuation of a photon beam as a function of the thickness of a homogeneous medium. BEER developed the equation for the effect of concentration. According to Beer-Lambert law, the probability that a photon will be absorbed in a medium is directly proportional to the concentration of the absorbing molecule and to the thickness of the sample. Most of the previous studies for the determination of these coefficients have been concerned with crystalline samples in the solid form. TELI and co-workers 9–11 have determined gamma-ray attenuation coefficients in dilute solutions of some salts. GERWARD 12 determined linear and mass attenuation coefficients in the general case as well as in the limit of extreme dilution and developed the theory of X-ray and γ-ray attenuation in solutions. Recently SINGH et al. 13 determined attenuation coefficients of some solutes in water at different concentrations. Densities were determined experimentally as these are required for the estimation of mass attenuation coefficients. KAUR et al. 14 in a recent publication reported the molar extinction coefficient ε, a more useful quantity for alkali metal chlorides in aqueous solutions. This coefficient depends upon the optical-region photon wavelength and nature of the dissolved substance. The absorbance or radiation density (RD) of a solution is defined by: RD I I = log 0 (1) where I 0 is the intensity of the incident beam impinging on a cell containing the solution and I that of the transmitted beam. The radiation density is related to the concentration of the solution as: RD x c = (2) where x is the path length of the cell (cm) and c is the molar concentration (number of moles of the solute dissolved per litre of the solution) of the absorbing species in the solution. Molar extinction coefficient ε, depends upon the wavelength of the incident radiation and is greatest where the absorption is most intense. * E-mail: k_thind@yahoo.com 0236–5731/2002/USD 17.00 Akadémiai Kiadó, Budapest © 2002 Akadémiai Kiadó, Budapest Kluwer Academic Publishers, Dordrecht