Synthesis, spectroscopic and structural characterization of Co(II)-pullulan complexes by UV-Vis, ATR-FTIR, MALDI-TOF/TOF MS and XRD

Žarko Mitić; Goran M Nikolić; Milorad Cakić; Goran S Nikolić; Slavoljub Živanović; Sanja Mitić; Stevo Najman

doi:10.1016/j.carbpol.2018.07.032

Synthesis, spectroscopic and structural characterization of Co(II)-pullulan complexes by UV-Vis, ATR-FTIR, MALDI-TOF/TOF MS and XRD

Carbohydr Polym. 2018 Nov 15:200:25-34. doi: 10.1016/j.carbpol.2018.07.032. Epub 2018 Jul 27.

Authors

Žarko Mitić¹, Goran M Nikolić², Milorad Cakić³, Goran S Nikolić³, Slavoljub Živanović², Sanja Mitić³, Stevo Najman²

Affiliations

¹ University of Niš, Faculty of Medicine, RS-18000, Niš, Serbia. Electronic address: zarko.mitic@medfak.ni.ac.rs.
² University of Niš, Faculty of Medicine, RS-18000, Niš, Serbia.
³ University of Niš, Faculty of Technology, RS-16000, Leskovac, Serbia.

PMID: 30177164
DOI: 10.1016/j.carbpol.2018.07.032

Abstract

Complexes of Co(II) ion with reduced low-molar pullulan (RLMP) (M_w 6000 g/mol) were synthesized in aqueous solutions at boiling temperature in the pH range from 7.5 to 13.5. Obtained Co(II)-RLMP complexes, with cobalt content ∼2-8% (AAS), were characterized by UV-Vis spectrophotometry, FTIR spectroscopy (ATR-FTIR, FT-IRIS), MALDI-TOF/TOF MS, and XRD. Tetragonally distorted O_h coordination of Co(II) ions with O ligand atoms in synthesized complexes is suggested based on the spectrophotometric data. No influence of complexation process on the ⁴C₁ chair conformation of the d-glucopyranose units of pullulan was detected by ATR-FTIR measurements and FT-IRIS showed high homogeneity of synthesized complexes. Some additional depolymerization of pullulan during complex synthesis was indicated by MALDI-TOF/TOF MS but it also revealed good stability of complexes with much weaker binding of Co(II) ion in low molar mass fragments. Even in complexes with highest Co(II) ion content a low degree of crystallinity was detected by XRD analysis.

Keywords: ATR-FTIR; Co(II)-pullulan; MALDI-TOF/TOF MS; XRD.