Hemoglobin−Silver Interaction and Bioconjugate Formation: A Spectroscopic Study

In this article, we report the results of the extent of interaction as well as the formation of a bioconjugate of human hemoglobin (Hb) with silver (Ag). The complexation process and conformational changes are characterized using different spectroscopic and microscopic techniques. The UV−vis study demonstrates the perturbation of the soret/heme band and generates conformational heterogeneity within the heme group in the presence of silver. A fluorescence study suggests that the Tryptophan (Trp) residues of Hb are in a more polar environment after conjugation. Initial fluorescence enhancement with addition of silver is due to metal-enhanced fluorescence. Moreover, the fluorescence quenching after the formation of the Hb−Ag bioconjugate follows the modified Stern−Volmer (S−V) plot. The S−V plot along with the time-resolved fluorescence study indicates the presence of both static and dynamic types of quenching. In addition, the reduction potential values of the entities (Hb−heme, Ag+, and Trp) indicate the possible electron transfer. The secondary structure calculation from CD and FTIR spectra indicate α-helix to β-sheet conversion, and unfolding of Hb is also responsible for the bioconjugate formation. In addition, FE-SEM, phase contrast inverted microscopy (PCIM) images demonstrate the formation of the silver−protein bioconjugate. The overall data show that there is a change in the secondary as well as the tertiary structure of Hb after conjugation with silver.