Photophysical and in vitro photoinactivation of Escherichia coli using cationic 5,10,15,20-tetra(pyridin-3-yl) porphyrin and Zn(II) derivative conjugated to graphene quantum dots

Pathogenic microorganisms may continue causing infection through the transfer of antibiotic resistance genes. As a result, the efficacy of pharmaceuticals in microbial inactivation is deteriorating. The present study was con-ducted to investigate the antimicrobial activity of neutral and quaternized free base and Zn 5,10,15,20-tetra(pyr-idin-3-yl) porphyrins on Escherichia coli (E. coli), a gram-negative bacterium that causes cholecystitis, pneumonia and urinary tract infections. Conjugation of the porphyrin to graphene quantum dots (GQDs) was implemented to enhance photocatalysis and reactive oxygen species generation. Density functional theory (DFT) geometry op-timizations for free base and Zn porphyrin based on the B3LYP (Becke 3-Parameter (Exchange), Lee, Yang and Parr) functional of the Gaussian09 program package and Time-dependent density-functional theory (TD-DFT) calculations of the associated UV-visible absorption spectra are reported to analyse the electronic structure and optical properties of the porphyrins. The TD-DFT calculations showed that for both porphyrins the value of highest occupied molecular orbital (Delta HOMO) is greater than that of lowest unoccupied molecular orbital (Delta LUMO) which tells that there is no unusual splitting of (LUMO) orbitals which may be caused by systematic error in TD-DFT calculations. Due to the red shift in the spectrum of ZnT(3-Py)P and the Delta LUMO being higher, the HOMO-LUMO gap was expected to be lower than that of H2T(3-Py)P. The photophysical properties and Photodynamic antimicrobial chemotherapy activities of these nanoconjugates were investigated. The highest phi Delta was that of Q-ZnT(3-Py)P-GDQs at 0.69 with the log reduction of 9.42.

Automated summary

Pathogenic microorganisms can cause infection by transferring antibiotic resistance genes. This study investigated the antimicrobial activity of different types of porphyrins on E. coli and found that conjugating porphyrins to graphene quantum dots enhances their effectiveness. The electronic structure and optical properties of the porphyrins were analyzed using density functional theory calculations.