TITLE:
Metallated Schiff-Base Macromolecules as Alternative Metalloprotein Electron Transfer Intermediates
AUTHORS:
Al C. Farao, Rachel Fanelwa Ajayi, Meryck Ward, Priscilla GL Baker
KEYWORDS:
Cytochrome-C, Macromolecule, Metallated, Metalloproteins, Schiff-Base
JOURNAL NAME:
Journal of Surface Engineered Materials and Advanced Technology,
Vol.10 No.2,
April
30,
2020
ABSTRACT: In the construction of biosensors, enzymes function as mediators
converting biological signals generated by
specific biological processes, into electrochemical signals. The ideology of
bio-sensor design is retention of electron transfer activity of the enzyme
utilizing superior interfacial architecture. In this work a Schiff-base
macromolecule has been synthesized by reflux of 2, 3-diaminonaphthalene and
pyrrole-2-carboxaldehyde starting materials. The Schiff-base ligand was
subsequently complexed with FeCl2?4H2O under reflux,
to produce the Fe-Schiff-base complex. The Schiff-base ligand and
Fe-Schiff-base complex were characterized using nuclear magnetic resonance
(NMR) spectroscopy, Ultra Violet/Visible (UV/Vis) spectroscopy, Fourier
transfer infrared resonance (FTIR) and
electron energy loss spectroscopy (EELS) to confirm the structure of the
synthesis products. NMR spectroscopy confirmed the imide linkage of Schiff-base
formation as two symmetrical peaks at 8.1 and 7.7 ppm respectively. Comparison
of starting materials and product spectra by UV/Vis spectroscopy confirmed the
disappearance of the diaminonaphthalene peak at 250 nm as evidence of complete
conversion to product. FTIR spectroscopy of the Schiff-base ligand
confirmed the formation of the imine bond at 1595 cm-1. EELS spectra
comparing FeCl2?4H2O and the Fe-Schiff-base complex,
showed good agreement in the energy loss profiles associated with changes to
the electronic arrangement of Fe d-orbitals. EDS clearly identified a spectral
band for Fe (7 - 8 eV) in the Fe-Schiff-base complex. Electrochemical
evaluation of the Fe-Schiff-base complex was compared to the electrochemical
signature of denatured cytochrome-C using cyclic voltammetry and square wave
voltammetry. The Fe2+/Fe3+ quasi-reversible behavior for
iron in the metallated complex was observed at -0.430 V vs. Ag/AgCl, which is consistent with reference values
for iron in macromolecular structures.