ASCORBIС ACID DEGRADATION IN N, N-DIMETHYLFORMAMIDE SOLUTIONS

Objective: Investigate the mechanisms of L-ascorbic acid transforтmation and formation of coloured enamines in N, N-dimethyl-formamide solutions. Methods: An automatic polarimeter Atago POL-1/2 was used for polarimetric investigation. Electronic spectra were recorded by UV-spectrometer Cary 60 (Agilent). The statistical analysis was carried out using the OriginPro 9.1 packages. Results: The Biot’s law violation was found in below 0.1% solutions of L-ascorbic acid (AA) in N, N-dimethylformamide (DMF). During the day, the specific rotation   of 1% AA solution varied from+37 to-1.0. Gradually, the solution acquired the red colour, and its intensity depended on the AA concentration. Spectrophotometrically, it was shown that after 15 min AA was absent in the n·10-3% solutions. The decomposition followed the first-order kinetics (k1=1.83·10-2с-1). At the same time, new absorption bands appeared at 273, 390, 533 nm. Model solutions containing dimethylamine (DMA) had a similar spectrum, and the intensity of the absorption bands increased in proportion to the concentration of DMA. Conclusion: The results show that the first step in the decomposition of ascorbic acid AA in DMF follows first-order kinetics. Numerous decomposition products are optically active compounds and reverse the sign of the optical rotation of the solution. The water resulting from the decomposition of AA is involved in the hydrolysis of the solvent. The hydrolysis product, the secondary amine DMA, interacts with the carbonyl groups of the AA decomposition products to form coloured enamines. Magnesium (II) accelerates the formation of coloured products

POLARIMETRIC RESEARCH OF PHARMACEUTICAL SUBSTANCES IN AQUEOUS SOLUTIONS WITH DIFFERENT WATER ISOTOPOLOGUES RATIO

Objective: Methodology development for quality control of optically active pharmaceutical substances based on water isotopologues. Methods: Solutions of L-ascorbic acid, glucose, galactose and valine stereoisomers were prepared using deuterium depleted water (DDW-«light» water, D/H=4 ppm), natural deionized high-ohmic water (BD, D/H=140 ppm), heavy water (99.9% D2O). The optical rotation was observed using an automatic polarimeter Atago POL-1/2. The size distribution of giant heterogeneous clusters (GHC) of water was recorded by low angle laser light scattering (LALLS) method. Results: The infringement of Biot's Law was found for solutions of ascorbic acid, expressed in the absence of a constant value of the specific optical rotation  at a concentration of below 0.1%, depends on the D/H ratio. The inequality was established in absolute values of optical rotation for L-and D-isomers of valine in solutions with different ratios of hydrogen isotopologues. The mutarotation of glucose confirmed the first-order kinetics, and the activation energies were statistically distinguishable for BD and DDW. The mutarotation of the natural galactose D-isomer proceeded with a lower energy consumption compared to the L-isomer. In heavy water, the mutarotation of monosaccharides had different kinetic mechanisms. Polarimetric results correlated with the number and size of GHC, which confirmed the possibility of chiral solvent structures induction by optically active pharmaceutical substances. Conclusion: In the optically active pharmaceutical substances quality control there should be considered the contribution of induced chiral GHC of water to the optical rotation value that depends on the isotopic D/H ratio, the substance nature and the form of its existence at a given pH

THE THE EFFECT OF THERMAL STERILIZATION AND EXCIPIENTS ON THE STABILITY OF ASCORBIC ACID IN AQUEOUS SOLUTIONS

Objective: To investigate the thermal stability of aqueous solutions of L-ascorbic acid (AA) and its reactions with excipients for the improvement of the injection forms technology. Methods: Solutions of L-ascorbic acid were prepared using deuterium depleted water (DDW-«light» water, D/H=4 ppm) and natural deionized high-ohmic water (BD, D/H=140 ppm). The optical rotation was observed using an automatic polarimeter Atago POL-1/2. Electrospray tandem mass spectra were recorded by Sciex X500R QTOF. Electronic spectra were recorded by UV-spectrometer Cary 60 (Agilent). Unicellular biosensor (Spirotox-test) was used for investigation of excipients influence on the AA biological activity. The statistical analysis was carried out using the OriginPro®9 packages. Results: The results demonstrate the thermal instability of AA. The optical activity of injection forms of AA differs from model solutions with the same concentration and pH value but without heat treatment. Monitoring of solutions by the LC-ESI-MS/MS method made it possible to characterize the nature of some thermal decomposition products. Thermodynamic calculations and evaluation of biological activity (Spirotox-test) indicate that AA interacts with sulfite-ion by redox mechanisms. Excipients in AA aqueous solutions decrease, but DDW increases the biological object lifetime. Conclusion: The use of the set of physicochemical and biological methods to study the effect of heat treatment of L-ascorbic acid solutions in the presence of sulfur (IV) compounds as excipients made it possible to identify decomposition products of the active pharmaceutical ingredient. The results indicate the need to exclude sterilization of the AA injection form by the thermal method and replace it with an alternative one, for example, with gamma radiation treatment