Журнал "Макрогетероциклы"

^aSyktyvkar State University, 167000 Syktyvkar, Russia

^bInstitute of Chemistry, Komi Science Centre, Ural Branch of the Russian Academy of Sciences, 167982 Syktyvkar, Russia

^@Corresponding author E-mail: belykh-dv@mail.ru

 

DOI: 10.6060/mhc180689b

Macroheterocycles 2018 11(4) 383-389

 

The proton exchange of deuteroporphyrin dimethyl ether internal NH protons with water molecules contained in deuterated chloroform was studied by DOSY. The solution components self-diffusion kinetics for bilateral chemical exchange was calculated in the fast diffusion approximation. It is shown that the measured self-diffusion coefficients of the components D with an increase in the diffusion observation time t_m (the interval between the gradient pulses in the DOSY method) exponentially approach the common limit. The limiting values of D depend on the molar ratios of the compounds participating in the exchange. The experimental data obtained for the coefficients of self-diffusion of NH protons and water protons (D_NH and D_W) in deuterated chloroform, firstly, confirm the observance of the fast exchange condition over the whole range of variation of t_m; secondly, the behavior of the measured D_NH and D_W as a function of t_m coincides with the calculated one. This proves that the effect observed is due to the exchange processes between the internal NH-groups of porphyrin and water molecules. The rate constants of the porphyrin internal NH-proton transfer to the water molecule and the inverse process were measured, respectively, k_NH≈4.5 sec^-1 and k_W≈16 sec^-1.