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2 Biotechnology and Food Science

2 2018

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The DFT study on the electronic structure of boronic acid derivatives and its esters with fructose

Kur K., Kowalska-Baron A., Miller E.

Biotechnology and Food Science

2018

Vol. 82, nr 1

29--39

Theoretical investigations are carried out to examine the geometrical structure and parameters of electron transitions to the lowest excited states of two boronic acid derivatives: 3-aminophenylboronic acid and 3-(acetamidomethyl)phenyl boronic acid and its cycling esters with fructose, using the DFT based 6-31 G(d,p) method. The most stable ester isomer of each acid has been selected. Predicted excitation wavelength are shorter (less than 0.5 eV) than experimental ones, what is in a good agreement considering limitations of the DFT method. In case of almost every calculated molecule the analysis of electronic transitions shows that transition S0→S1 involves electron transfer mainly from the HOMO to LUMO orbital.

Optical properties of (3-(acetamidomethyl)phenyl)boronic acid and its interactions with selected sugars

Kur K., Przybyt M., Miller E.

Biotechnology and Food Science

2018

Vol. 82, nr 1

15--27

(3-(Acetamidomethyl)phenyl)boronic acid (3AAPBA)has at pH 7 absorbance maximum at 270 nm with molar absorbance coefficient 516 M-1cm-1. 3AAPBA exhibits weak fluorescence with maximum at 297 nm and quantum yield 0.062 ± 0.001. Fluorescence decay is monoexponential and the lifetime is 2.05 ± 0.01 ns. Interactions of 3AAPBA with selected sugars were studied by absorbance, steady-state and time-resolved fluorescence measurements. At pH 7 fluorescence of 3AAPBA is quenched only by fructose (with quenching constant 67.9 M-1) and to some extend by galactose. Addition of these two monosaccharides causes also changes of absorbance spectra of 3AAPBA. Acid-base dissociation of free 3AAPBA and its esters with sugars was studied by absorbance and steady-state fluorescence measurements in pH range from 4.5 to 11.00. Esterification of phenylboronic acid derivatives by sugars leads to increased acidity of them. In case of 3AAPBA the obtained values of pK indicate that affinity of studied sugars towards it can be ordered as follows: fructose > galactose > glucose > maltose > lactose > sucrose. At pHs higher than pK the fluorescence decays turn to biexponential with additional shorter component in lifetime which we propose to attribute to anionic form of 3AAPBA or its esters.