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5 Summary

In this dissertation, as well the oxidation and reduction of ascorbic acid and dehydroascorbic acid (redox system) as the alkaline hydrolysis from dehydroascorbic (DHA) to diketogulonic acid (DKG) were analyzed2) . With the help of the ascertained18)  band parameters, standard and calibration spectra from the infrared measurements in substances, which contain H–O- and C=O-bond groups, as well methodology for observing the reactions with infrared4)  spectroscopy as the interpretation experienced an essential support.

In this context, the problems of the keto-enol tautomerism were studied in acetylacetone and (iso-) ascorbic acids. Furthermore, it 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 comparatively through the substitution of neighboring bond groups14) . The phenomenon of the hydration of keto groups was able to be pursued with infrared spectroscopy in a simple molecule (butanal15) ). With the dehydroascorbic acids in solution, the interpretation is because of several effects of mutual influence still ambiguous. However, clear differences between crystalline bis-DHA and the hydrated DHA form resulted12)  from the H–O- and O=C-stretching vibration area. Unambiguously, the deuteration of the HO groups was successful for bis-DHA. For the process of saponification of the DHA, functional coherences of temperature and pH with an activation energy of 79.3 kJ/mol were determined. With the help of the electronic data processing (EDP), up to three infrared standard spectra, namely of DHA, DKG, and another one reductone-like substance, were able to be separated from D₂O solutions. The pK_a value of the soap making product (DKG), investigated by pH-titration and by infrared spectroscopy, corresponds to known pK_a values of oxocarboxylic acids (oxocarbonic acids). The evolution of CO₂ in spectra of pellets can be traced back to the decarboxylating3)  DKG. However, DKG is still quite stable in high concentrations in solution at 37°C. The DKG decomposition reactions were qualitatively examined, starting19)  from DKG-stock solutions also in the neutral and alkaline pH range, except with the infrared spectroscopy, still with the spectrophotometry, the fluorescence and also the electron paramagnetic resonance (EPR) spectroscopy. A ruby-red substance evolved16)  at high pH value from as well17)  DHA as DKG. It is unstable to aerial influences and can be associated with radicalic processes. It was found a R–O^• radicals indicating EPR signal.

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 range because of the additional DHA saponification. The same is valid13)  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 proven1)  by reactions with H–S groups. Clear infrared spectroscopic differences were found at oxidation reactions between derivatives, which are incapable or capable of C(6)–O–C(3) - cyclization.

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Nota:	English synonyms: Englische Synonyme:
1)	proven [Partizip Perfekt] proved [Partizip Perfekt; Imperfekt]
2)	analyzed analysed
3)	decarboxylating [often] decarboxylizing [rare] decarboxylising [very rare] decarboxylation doing [extremely rare]
4)	infrared ultrared ultra red
5)	substitution application
6)	deuteration deuteriation
7)	several a number of
8)	effects of mutual influence cross-influence effects
9)	development evolution
10)	instabilities unstablenesses
11)	cyclization cyclisation ring forming
12)	resulted from arose from
13)	is valid applies does apply
14)	neighboring bond groups neighbouring bond groups adjacent bond groups
15)	butanal butyraldehyde
16)	evolved developed itself
17)	from both, ... and ... from as well ... as ...
18)	ascertained determined found-out identified
19)	starting from beginning with