Intrinsic and Environmental Effects in the Structure and Magnetic Properties of Glycine Radical in Aqueous Solution

Abstract

The electron spin resonance (ESR) spectrum of the radicals derived from glycine in aqueous solution has not been reproduced satisfactorily until now, even by refined quantum mechanical approaches. Here we will show that a recently developed computational tool provides, instead, results in remarkable agreement with experiment. The computational protocol is based on density functional calculations, on the simulation of the solvent with a continuous dielectric description, and on averaging over the most important vibrational motions. Both the direct polarization and the geometry relaxation induced by the solvent on the glycine radical are analyzed, and their effect on the ESR spectra is evaluated. The present procedure is able to separate the various intrinsic and environmental contributions and to provide useful insight to the structural study of large flexible radicals in solution.

Theoretical Interpretation of the Fragments Generated from a Glycine Radical Cation

“…Removing an R-H from the glycine radical cation requires overcoming a 30.1 kcal/mol energy barrier to generate the R-glycyl radical (I-H), which has C s symmetry, with all atoms coplanar. This does not concur with the results calculated by Rega et al 4 using the B3LYP/6-31G** method because that their calculated result shows that there are three H atoms ((N)H 2 and (C)H) of the glycyl radical that are out of the plane, but the geometrical parameters of our calculated result are similar to the results calculated by O'Hair et al 9 using the MP2(FC)/6-31+G* method. The R-glycyl cation can undergo further fragmentation reactions [5][6][7]9 to yield HCNH + (m/z 28) and some other fragments with low intensity.…”

Complete structural and magnetic characterization of biological radicals in solution by an integrated quantum mechanical approach: Glycyl radical as a case study

“…We just recall that, in contrast with the parent molecule, only planar ͑or nearly planar͒ conformations are accessible to the radical, due to the strong delocalization of the unpaired electron. 12,34,58,59 This planar arrangement ͑see Fig. 1͒ corresponds to the fully extended conformation typical of ␤ sheets, also known as C 5 structure ͑Ϸ180°, Ϸ180°͒.…”

“…In going from gas phase to aqueous solution ͑continuum͒ a shortening of the CN bonds and a lengthening of the CO bonds are observed due to the stabilization of ionic resonance structures by polar solvents. 58 At the same time, the intramolecular hydrogen bond is significantly weakened by the presence of a polar solvent. These effects are further enhanced by inclusion of the first solvent shell ͑seven water molecules͒, while negligible structural variations are found by further embedding this cluster in a continuum.…”

Dissociative electron attachment to gas-phase glycine

“…Thus a number of theoretical [13,14,15,16,17] and experimental [14,15,18,19,20] investigations on glycine have been published in recent years. For glycine and other amino acids a tautomeric equilibrium between neutral and zwitterionic forms exists that is of fundamental importance in biochemistry.…”