The work studies the spatial and electronic structure of the Cys-His dipeptide taking into account the isomerization of the histidine residue responsible for the selectivity in bind-ing of the modified Cys-T7 peptide to the transferrin receptor. Interest in this dipeptide stems from its cysteine residue, the thiol group of which is responsible for binding to the drug during its delivery to brain tumor cells. It has also been established that histi-dine ensures specific receptor recognition and sensitivity to changes in environmental acidity, which is important for drug release. Using semi-empirical methods of molecular mechanics and ab initio quantum chemistry method, the effect of L- and D-histidine on the conformational states of the Cys-His dipeptide fragment was studied. A comparative analysis of the obtained results was conducted depending on the methods used, taking into account the parameterization of potential functions. The spatial and electronic structure of the compound under study was defined.