Acid-base activity, keto-enol tautomerism and complexing properties of 6beomoquercetin are investigated in water media at different conditions. The constants of dissociation (pKa) have been determined in pH region at various ionic strength. The analysis of protonation process is conducted in strongly acidic solutions of HCl. The complexation were studied with trivalent lanthanides. The stability constant of monocomplex species ML (M(III) =Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er, Tm, Yb, Lu) have been obtained. For interpretation and verification of received data the DFT calculations were implemented.
Abstract 22 23Acid-base activity, keto-enol tautomerism and complexing properties of 6-24 beomoquercetin are investigated in water media at different conditions. The constants of 25 dissociation (pKa) have been determined in pH region at various ionic strength. The analysis 26 of protonation process is conducted in strongly acidic solutions of HCl. The complexation were 27 studied with trivalent lanthanides. The stability constant of monocomplex species ML (M(III) 28 =Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er, Tm, Yb, Lu) have been obtained. For interpretation and 29 verification of received data the DFT calculations were implemented.30 31 32 33 34 Introduction 35 36 Being secondary metabolites, flavonoids exist ubiquitous in the plant world (Panche et 37 al. 2016). Quercetin or 5,7,3′,4′-flavon-3-ol is the most known and studied ligand from this 38 group of chemicals. The various qualities, such as anticancer (Le Marchand 2002), antibacterial 39 (Cushnie and Lamb, 2005) and antidiabetic (Vinayagam and Xu 2015) activities demonstrate a 40 multifaceted nature of quercetin. The numerous derivatives of quercetin are also show notable 41 biochemical characteristics (Kessler et al 2003; Sotnikova et al 2013; Manach et al 1998). The 42 complexes of flavonoids with all of groups of metals (Kasprzak et al. 2015; Samsonowicz and 43 Regulska 2017) are described in literature primarily for solid-state conditions. 44 The flavonoids exhibit medical and biological properties in water. Nevertheless, 45 the low solubility make them problematic objects for study of standard physical-chemical 46 methods. The solubility of quercetin in H2O at room temperature is about 10 -4 M (Srinivas et 47 al. 2010). In the same time, the necessary concentration for NMR-analysis or potentiometric 48 study is 10 -2 -10 -1 M. In all works where the issue of flavonoids in solution has been discussed 49 the water-ethanol mixtures or non-aqueous liquids were used as solvent. However, under such 50 conditions the behaviour of flavonoids is fundamentally different from biological media. The 51 spectrophotometric technique is one of the few methods that allow to research small amount of 52 sparingly soluble compounds and determine all equilibrium parameters in pure water with 53 concentration <10 -4 M. 54 ∆G aq. ). E zpe is calculated harmonic vibrational frequencies to estimate the zero point energy 104 correction. 105 106 Experimental 107 108 The UV-Vis spectra were m...