[Various properties of erythromycin basicity]. / Onekotorykh osobennostiakh osnovnosti éritromitsina.

Erythromycin (Er) as a weak base showed some specific properties when dissolved in aqueous solutions. The basic ability of Er had a tendency to become weaker during storage in the room settings and especially at high temperatures. The temperature gradient within the ranges of 10 to 25 degrees C was dpH/dt = -0.03 (for 2 x 10(-3) M Er solution). However, the basic properties of the Er base partly renewed when Lewis' bases such as dimethyl carboxide, dimethylformamide and dimethyl sulfoxide were added to Er aqueous solutions previously stored for days or weeks. In chloroform solutions, either the thermodynamics or the kinetics of Er protonization showed no abnormalities as compared to nitric bases. It was supposed that in aqueous solutions of Er base there was transformation linked with intramolecular or extramolecular interactions which provoked shielding of the tertiary basic atom of nitrogen due to formation of the nitrogen linkage.

[Hydrogen bond and acid-base interactions in erythromycin solutions]. / Vodorodnaia sviaz' i kislotno-osnovnye vzaimodeistviia v rastvorakh éritromitsina.

The association and conformational structure of the molecule of erythromycin in solutions of CCl4, C2Cl4 and CHCl3 were studied by the IR spectra in the region of v OH and vC = O. The analysis of the concentration and temperature changes showed that the erythromycin association was accounted for by the hydrogen linkage of OH ... O = C to the ester group. In the monomer molecule of erythromycin, all hydroxyl groups participated in the intramolecular hydrogen linkage. Band 3513 cm-1 belonged to the OH group in the five-membered cycles of OH ... O. Components 3500, 3530 and 3560 cm-1 of the wide band vOH were assigned to the cycles with OH ... N and OH ... O linkages of a larger size. The association was due to a break in a part of the intramolecular hydrogen linkages. Addition of strong acceptors of proton-hexamethanol and trioctylphosphinoxide to the solution resulted in attenuation of these bands and appearance of a strong band vOH of the erythromycin-acceptor complexes. In the presence of monochloroacetic acid in the solution of CHCl3 stoichiometric protonization of erythromycin was observed. The total acid was in the form of anion (vaCO-2 1610 cm-1) up to a ratio of 1:1. The protonization proceeded according to the nitrogen atom since the antibiotic spectrum in the region of vC=O did not change. Propionic acid titrated erythromycin in methanol solution and in mixtures of water and methanol up to a ratio of 1:5 (v/v). However, in the solution of CHCl3 equilibrium between the neutral and ionized molecules of the acid was seen.