Experimental and theoretical mass spectrometric quantification of diffusion parameters and 3D structural determination of ions of L-tryptophyl-l-tryptophan in electrospray ionization conditions in positive operation mode

Abstract

The issue of this work focuses on development of quantitative model equations connecting experimental mass spectrometric (MS) parameters, for instance, MS intensity, of analyte peaks with thermodynamic, kinetic and diffusion parameters of the corresponding ions with their 3D molecular and electronic structures. Our more recent contribution to this field has convincingly argued that equation D=1.3194.10−17.A.I2¯−(I¯)2(I−I¯)2, obtained on the base on stochastic dynamics, is applicable to electrospray ionization (ESI), collision induced dissociation (CID) and matrix–assisted laser desorption/ionization (MALDI) mass spectrometric (MS) methods, respectively. It connects MS diffusion parameters of ions with the intensities of their peaks in the MS spectrum. There has been evidenced, that experimental diffusion parameters correspond quantitatively to theoretical quantum chemical diffusion coefficients, obtained on the base on Arrhenius' formalism. If next research effort continues to confirm the validity of the shown above quantitative relation to the behavior of the MS intensity of the analyte, with respect to time, this might imply that the mass spectrometry represents not only an irreplaceable method for quantification in the analytical practice, but it provides exact experimental information about the 3D structure of the analytes. According to the latter line of research, the first aspect of this study is an experimental and theoretical MS quantification of diffusion parameters and 3D structural determination of ions of L-tryptophyl–l–tryptophan (H–Trp–Trp–OH) under ESI(+)–MS conditions. Another issue details experimentally and theoretically the process of molecular cyclization of H–Trp–Trp–OH. This aspect of the chemical reactivity of the dipeptide has provided very important insights into major reaction paths, yielding to permuted oxazolone. Taking a step into a broad application of our model relationship stated above to different areas of science, we should underline that, no doubt, the paper contributes significantly to methodological development of mass spectrometric based methods for 3D structural analysis, exploiting herein a nontrivial case of MS fragment behavior of the peptide H–Trp–Trp–OH under ESI–MS conditions.