Koordinacijske spojine elagitaninov z železovimi(II) ioni: vpliv strukture in pH

magistrsko delo

Franjo Frešer (Author), Urban Bren (Mentor), Gregor Hostnik (Co-mentor)

Abstract

V magistrskem delu smo proučevali vpliv strukture elagitaninov in pH-ja na stehiometrijo in konstante formacije koordinacijskih spojin elagitaninov in železovih(II) ionov. Za to smo izbrali tri elagitanine: veskalin, kastalin in kastalagin. Veskalin in kastalin smo najprej izolirali iz vodnega ekstrakta kostanjevega lesa z uporabo preparativne tekočinske kromatografije visoke ločljivosti. Po končani izolaciji in karakterizaciji smo pokazali, da so izbrani elagitanini stabilni pri pH-jih nižjih od 7,39. Z uporabo UV/Vis-spektroskopije smo spremljali spreminjanje vrednosti absorbanc elagitaninov v odvisnosti od pH-ja medija ter s tem določili njihove konstante disociacije. Za vsako od proučevanih spojin smo v pH območju 3,50–5,51 pomerili UV/Vis-spektre pri različnih razmerjih med množinskimi koncentracijami elagitanina in Fe(II) ionov ter z uporabo Jobove metode določili stehiometrijo nastalih koordinacijskih spojin (1:2 pri reakciji veskalina ali kastalina s Fe(II) ioni ter 1:3 pri reakciji kastalagina s Fe(II) ioni). Pri vseh reakcijah se je pH medija nekoliko znižal, kar nakazuje, da pri tvorbi koordinacijskih spojin pride do deprotonacije fenolnih hidroksilnih skupin. Predpostavili smo dva modela, ki smo ju globalno prilegali eksperimentalnim točkam Jobovih diagramov. Pri modelu A smo predpostavili zaporedno ravnotežno reakcijo elagitanina s Fe(II) ioni, medtem ko smo pri modelu B v enako reakcijo vključili protolitsko ravnotežje elagitanina, ki smo ga določili s spremljanjem njegovih kislinsko-bazičnih lastnosti. S prileganjem modelnih funkcij k eksperimentalnim rezultatom smo določili molarne absorpcijske koeficiente, konstante formacije koordinacijskih spojin in iz njih standardne reakcijske Gibbsove proste energije. Z modeli smo izračunali množinske deleže tvorjenih koordinacijskih spojin ter ravnotežne množinske deleže elagitaninov in Fe(II) ionov. S primerjavo pridobljenih rezultatov smo pokazali, da kastalagin kelira največ Fe(II) ionov iz pripravljenih raztopin, medtem ko jih veskalin in kastalin manj, pri čemer so njune vrednosti podobne.

Keywords

elagitanini;železovi(II) ioni;koordinacijske spojine;Jobova metoda;UV/Vis-spektroskopija;modeliranje;magistrske naloge;

Data

Language:	Slovenian
Year of publishing:	2022
Typology:	2.09 - Master's Thesis
Organization:	UM FKKT - Faculty of Chemistry and Chemical Engineering
Publisher:	[F. Frešer]
UDC:	544.142.3:[547.98+546.72-11](043.2)
COBISS:	130940419
Views:	103
Downloads:	24
Average score:	0 (0 votes)
Metadata:

Other data

Secondary language:	English
Secondary title:	Coordination compounds of ellagitannins with Fe(ii) ions: Effects of structure and pH
Secondary abstract:	In the master's thesis, we studied the influence of the structure of ellagitannins and of the pH on the stoichiometry and formation constants of coordination compounds of ellagitannins and iron(II) ions. For this, we chose three ellagitannins: vescalin, castalin and castalagin. Vescalin and castalin were first isolated from an aqueous extract of chestnut wood using preparative high-performance liquid chromatography. After isolation and characterization, we showed that the selected ellagitannins are stable at pH values that are lower than 7,39. Using UV/Vis spectroscopy, we monitored changes in the absorbance values of ellagitannins depending on the pH of the medium, thereby determining their dissociation constants. For each of the studied compounds, UV/Vis spectra were measured in the pH range 3,50–5,51 at different ratios between the molar concentrations of ellagitannin and Fe(II) ions. Using Job's method, the stoichiometry of the resulting coordination compounds was determined (1:2 for the reaction of vescalin or castalin with Fe(II) ions and 1:3 for the reaction of castalagin with Fe(II) ions). In all reactions, the pH of the medium decreased slightly, which indicates that deprotonation of phenolic hydroxyl groups occurs prior to the formation of coordination compounds. We hypothesized two models, which we globally fitted to the experimental values of the Job plots. In model A, we assumed a sequential equilibrium reaction of ellagitannin with Fe(II) ions, while in model B, we included the protolytic equilibrium of ellagitannin in the same reaction, which was determined by monitoring their acid-base properties. By fitting the model functions to the experimental values, we determined the molar absorption coefficients, formation constants of coordination compounds, and from them the standard reaction Gibbs free energies. Using the models, we also calculated the molar fractions of the formed coordination compounds as well as the equilibrium molar fractions of ellagitannins and Fe(II) ions. By comparing the obtained results, we have shown that castalagin chelates the most Fe(II) ions from the prepared solutions, while vescalin and castalin chelate less Fe(II) ions (their values are similar).
Secondary keywords:	ellagitannins;iron(II) ions;coordination compounds;Job’s method;UV/Vis spectroscopy;modelling;
Type (COBISS):	Master's thesis/paper
Thesis comment:	Univ. v Mariboru, Fak. za kemijo in kemijsko tehnologijo
Pages:	1 spletni vir (1 datoteka PDF (XIV, 100 f.))
ID:	16254942