Estimated solubility determination of luteolin in water, nonpolar and polar solvents by applying infrared spectroscopic semi-quantitative method

V zadnjih letih so flavonoidi zaradi svojih številnih učinkov na zdravje človeka postali pogosto raziskovana tema v znanosti. Topnost flavonoidov ima velik pomen v farmacevtski, prehranski in kemijski industriji, zato je določitev ustreznih topil zelo pomembna. Spektrometrično analizo FTIR-ATR (angl. Fourier Transform Infrared – Attenuated Total Reflection) smo izvedli na nekaterih flavonoidih in fenolnih spojinah: luteolinu, hesperidinu, kvercetinu, naringeninu ter galni in taninski kislini. Kot modelno snov za podrobnejše raziskave smo izbrali luteolin ter določili korelacije med njegovo vsebnostjo in transmitanco v 12 topilih različne polarnosti. Na osnovi kalibracijskih krivulj smo določili ocene topnosti in jih primerjali z vrednostmi, določenimi s tekočinsko kromatografijo visoke ločljivosti (angl. High-Performance Liquid Chromatography – HPLC). Z obema uporabljenima metodama smo pridobili enak vrstni red topnosti luteolina. Kot najboljši topili sta se v obeh primerih izkazali dimetilsulfoksid (DMSO) in tetrahidrofuran (THF), nato pa je topnost luteolina v topilih upadala po naslednjem vrstnem redu: propanol > etanol > aceton > butanol > metanol > etil acetat > dietil eter > acetonitril > diklorometan > voda. Analiza s HPLC je pri vsebnosti luteolina 20 mg/mL pokazala, da se je celotna količina luteolina raztopila v topilih DMSO in THF, v propanolu je bila topnost 18,1 ± 0,001 mg/mL, v etanolu 18,0 ± 1,4 mg/mL, v acetonu 16,7 ± 2,3 mg/mL, v butanolu 15,9 ± 0,4 mg/mL, v metanolu 6,1 ± 1,0 mg/mL, v etil acetatu 2,9 ± 0,3 mg/mL, v dietil etru 0,7 ± 0,2 mg/mL, v acetonitrilu 0,6 ± 0,1 mg/mL, v diklorometanu 0,002 ± 0,0002 mg/mL in v vodi 0,004 ± 0,0002 mg/mL. Rezultati predstavljajo prikaz uporabe metode FTIR-ATR kot semikvantitativnega orodja za določitev ocene topnosti različnih spojin, ki omogoča prihranek velike količine topil in časa.In recent years, flavonoids have become a highly researched topic due to their health beneficial effects. Since flavonoids’ solubility plays a significant role in their use in pharmaceutical, food and chemical industry, the determination of suitable solvents is crucial. Fourier Transform Infrared – Attenuated Total Reflection (FTIR-ATR) analysis was used to characterize functional groups of several flavonoids and phenolic compounds, namely luteolin, hesperidin, quercetin, naringenin, gallic and tannic acid. Afterwards, luteolin was chosen as a model flavonoid, with its content correlated with transmittance using 12 solvents with different polarities. The solubility estimate was determined using calibration curves and compared with the values obtained by high-performance liquid chromatography (HPLC) analysis. By both methods, we obtained the same order of suitability of solvents for dissolving luteolin. DMSO and THF proved to be the most suitable solvents, followed by solvents in the following order: propanol > ethanol > acetone > butanol > methanol > ethyl acetate > diethyl ether > acetonitrile > dichloromethane > water. These results shed light on using FTIR-ATR as a semi-quantitative method for the initial screening of solvents and solubility determination of different compounds while saving time and solvents. HPLC analysis of luteolin dissolution of samples containing 20 mg luteolin in 1 mL of solvent, showed that the total amount of luteolin was dissolved in DMSO and THF, while the solubility in propanol was 18,1 ± 0,001 mg/mL, in ethanol 18,0 ± 1,4 mg/mL, in acetone 16,7 ± 2,3 mg/mL, in butanol 15,9 ± 0,4 mg/mL, in methanol 6,1 ± 1,0 mg/mL, in ethyl acetate 2,9 ± 0,3 mg/mL, in diethyl ether 0,7 ± 0,2 mg/mL, in acetonitrile 0,6 ± 0,1 mg/mL, in dichloromethane 0,002 ± 0,0002 mg/mL and in water 0,004 ± 0,0002 mg/mL. These results present a demonstration of the use of the FTIR-ATR method as a semi-quantitative tool for determining the solubility estimate of various compounds while saving large amounts of solvents and time