abstract amino acids are building blocks of proteins, and play a vital role in living beings existence and their functionality. the interaction of these compounds with metal ions is of great importance to biochemists, and chemists, because their functions can be utilized as a model in understanding enzymes mechanism for transport of metal ions to tissues. among twenty essential amino acids we chose the reactions of cyclic amino acids in non-aqueous solutions which have high similarity to metal ion transport systems in our body. in this research stability constants of complexes of the amino acid of tryptophan with metal ions of co(ii), ni(ii), cu(ii), zn(ii), pb(ii), and fe(iii) have been determined in mixture of 50-50% water-dioxane (µ= 0.1 nano3) in four different temperatures of 20, 30, 35, 40 °c by potentiometry using modified bjerrum,s method and grc-beta software. the results show that the order of stability of these complexes is as follows: kf zn+2 –trp < kf co+2 –trp < kf pb+2 –trp < kf ni+2 –trp kf cu+2 –trp < kf fe+3–trp also it is found out that the values of complexes formation constants have been increased with elevating temperature and in going from aqueous solvent to non-aqueous solvent. in continuation of our work, using thermodynamic relations gibbs free energy (?g), standard enthalpy of formation (?h), and entropy (?s) for each of these complexes in four different temperatures were calculated and in general the following data were obtained. ?g zn+2 –trp ? ?g co+2 –trp < ?g pb+2 –trp < ?g ni+2 –trp < ?g cu+2 –trp < ?g fe+3–trp moreover, the activation energy (ea) and the rate of reaction for each of these complexes were estimated. k zn+2 –trp < k co+2 –trp < k pb+2 –trp < k ni+2 –trp < k cu+2 –trp < k fe+3–trp finally, quantum mechanical calculations were performed in order to determine the most stable configuration of tryptophan in gaseous and liquid state. all calculations were conducted by using gaussian 98 software and structural parameters in level of hf utilizing base function of 6-31g??. the results indicate that among 22 tryptophan configurations, the most stable configuration in gas phase and aqueous phase is t4.