The following page (106) from the
inaugural dissertation with the subject INVESTIGATIONS TO
REACTIONS FROM DEHYDROASCORBIC AND DIKETOGULONIC ACID
WITH THE HELP OF CALCULATOR SUPPORTED INFRARED SPECTROSCOPY (German)
presented by Detlef Pagel from Hermannstein / Kreis Wetzlar, Germany
Giessen 1992
was typed and translated by and put into the world wide web with friendly approval of the author ©2010.106
5 Summary
In this dissertation, it was examined the oxidation and reduction of ascorbic acid and dehydroascorbic acid (redox system) as well as the alkaline hydrolysis of the dehydroascorbic acid (DHA) to the diketogulonic acid (DKG). With the help of the ascertained band parameters, standard and calibration spectra from the infrared measurements in substances, which contain H-O - and C=O - bond groups, the methodology to observe the reactions with infrared spectroscopy as well as the interpretation experienced an essential support.
In this connection, the problems of the keto-enol tautomerism were studied in acetylacetone and (iso-) ascorbic acids. It furthermore turned out, that the square root values of the integral extinction coefficient of the O=C-stretching vibration modes, which are proportional to the dipole moment changes, varied themselves comparably by the application of neighboring bond groups. It was able to pursue the phenomenon of the hydration of keto groups with infrared spectroscopy in a simple molecule (butanal). With the dehydroascorbic acids in solution the interpretation is still ambiguously because of several mutually effects of influence. However, clear differences arose in the H-O - and O=C - stretching vibration area between crystalline bis-DHA and the hydrated DHA form. Unambiguously the deuteration of the HO groups succeeded at bis-DHA. For the process of saponification of the DHA, there were determined functional coherencies of temperature and pH with an activation energy of 79.3 kJ/mol. With the help of the electronic data processing (EDP), up to three infrared standard spectra, namely of DHA, DKG, and another reductone-like substance, were able to be separated from D2O solutions. The pKa value of the soap making product (DKG), investigated by pH-titration and by infrared spectroscopy, corresponds to known pKa values of oxocarboxylic acids (oxocarbonic acids). The development of CO2 in spectra of pellets can be led back on the decarboxylating (decarboxylising, decarboxylizing) DKG. However, DKG is still quite stable in high concentrations in solution at 37°C. The DKG decomposition reactions were qualitatively examined, outgoing from DKG-stock solutions also in the neutral and alkaline pH area, except with the infrared spectroscopy, still with the spectral photometry, the fluorescence and also the electron paramagnetic resonance (EPR) spectroscopy. From DHA as well as from DKG it developed a ruby-red substance at high pH value. It is unstable against aerial influences and can be brought in connection with radicalic processes. One has found an EPR signal, which points at R-O• radicals.
It is problematic that reduction and oxidation are influenced by instabilities of DHA and DKG. Therefore equimolar NADH concentrations reduce only incompletely the DHA in the physiological pH area because of the additional DHA saponification. The same is valid with reductions by H-S-group containing substances for which an apparent reaction order similar to the DHA saponification was found. However, an intermediate state which the real reduction reaction of DHA follows, is infrared spectroscopically proved by reactions with H-S groups. Clear infrared spectroscopical differences were found at oxidation reactions between derivatives which are incapable or capable to form a C(6)-O-C(3) - ring.
5 Summary
In this dissertation, it was examined the oxidation and reduction of ascorbic acid and dehydroascorbic acid (redox system) as well as the alkaline hydrolysis of the dehydroascorbic acid (DHA) to the diketogulonic acid (DKG). With the help of the ascertained band parameters, standard and calibration spectra from the infrared measurements in substances, which contain H-O - and C=O - bond groups, the methodology to observe the reactions with infrared spectroscopy as well as the interpretation experienced an essential support.
In this connection, the problems of the keto-enol tautomerism were studied in acetylacetone and (iso-) ascorbic acids. It furthermore turned out, that the square root values of the integral extinction coefficient of the O=C-stretching vibration modes, which are proportional to the dipole moment changes, varied themselves comparably by the application of neighboring bond groups. It was able to pursue the phenomenon of the hydration of keto groups with infrared spectroscopy in a simple molecule (butanal). With the dehydroascorbic acids in solution the interpretation is still ambiguously because of several mutually effects of influence. However, clear differences arose in the H-O - and O=C - stretching vibration area between crystalline bis-DHA and the hydrated DHA form. Unambiguously the deuteration of the HO groups succeeded at bis-DHA. For the process of saponification of the DHA, there were determined functional coherencies of temperature and pH with an activation energy of 79.3 kJ/mol. With the help of the electronic data processing (EDP), up to three infrared standard spectra, namely of DHA, DKG, and another reductone-like substance, were able to be separated from D2O solutions. The pKa value of the soap making product (DKG), investigated by pH-titration and by infrared spectroscopy, corresponds to known pKa values of oxocarboxylic acids (oxocarbonic acids). The development of CO2 in spectra of pellets can be led back on the decarboxylating (decarboxylising, decarboxylizing) DKG. However, DKG is still quite stable in high concentrations in solution at 37°C. The DKG decomposition reactions were qualitatively examined, outgoing from DKG-stock solutions also in the neutral and alkaline pH area, except with the infrared spectroscopy, still with the spectral photometry, the fluorescence and also the electron paramagnetic resonance (EPR) spectroscopy. From DHA as well as from DKG it developed a ruby-red substance at high pH value. It is unstable against aerial influences and can be brought in connection with radicalic processes. One has found an EPR signal, which points at R-O• radicals.
It is problematic that reduction and oxidation are influenced by instabilities of DHA and DKG. Therefore equimolar NADH concentrations reduce only incompletely the DHA in the physiological pH area because of the additional DHA saponification. The same is valid with reductions by H-S-group containing substances for which an apparent reaction order similar to the DHA saponification was found. However, an intermediate state which the real reduction reaction of DHA follows, is infrared spectroscopically proved by reactions with H-S groups. Clear infrared spectroscopical differences were found at oxidation reactions between derivatives which are incapable or capable to form a C(6)-O-C(3) - ring.
