Synthesis and Spectrophotometric Activity of Phthalocyanine Conjugated to Metal Nanoparticles and Evaluation of their Antibacterial Properties
Nyamu, N. Samuel
MetadataShow full item record
In recent times, microbial pathogens have increasingly shown multi-drug resistance leading to a growing concern. Analysis of 624 isolates from Kenya revealed 88% of isolates tested were multi-drug resistant. It is estimated that about 4,150,000 deaths will be attributed to antimicrobial resistance (AMR) in Africa by 2050. Therefore, current research is increasingly focusing on antimicrobial photodynamic therapy that utilizes non-toxic photosensitizer exhibiting visible light activity towards the generation of free radicals and singlet oxygen which kill pathogens. The photo-sensitizer may be conjugated to visible-light responsive nanoparticles to further increase their photochemical activities. Phthalocyanine (Pc) is one of the promising dyes that have shown notable photochemical stability, a high degree of aromaticity and ease of structural modification resulting in increased activities. Despite these attractive properties, its antibacterial properties remain under researched. Therefore, this study aimed to tuning the photodynamic antibacterial activity of Pc by using electron withdrawing and electron donating group, conjugating the obtained compounds to silver nanoparticles (AgNps) and zinc oxide nanoparticles (ZnO-Nps) and evaluating the activity of the resulting composites against drug resistant strains Escherichia coli, Staphylococcus aureus, Bacillus subtilis and Salmonella typhi. 2,9,16,23-tetra-iodo- 3,10,17,24-tetra-(3-methoxyprop-1-nyl) Pc (6) and 2,9,16,23-tetra-iodo-3,10,17,24-tetra ethylsulfonyl Pc (10) were synthesized respectively. The Pc derivatives were synthesized upon exposure to microwave radiation under solvent-free conditions. Both Pc 6 and 10 were β-form in nature with monoclinic structure confirmed by powder XRD. Pc (6) had two absorption bands between 345-364 nm for B-band and 660-680 nm for Q-band while Pc (10) indicated two major absorption bands between 354-360 nm for B-band and 685- 689 nm bands for Q-band of UV-Vis absorption in different solvents. FTIR confirmed the presence of attached substituent groups to the Pcs. Pc 6 and 10 showed singlet oxygen quantum yield (ΦΔ) values of 0.53 and 0.63 and fluorescence quantum yield (ΦF) value of 0.14 and 0.13 respectively. The Pc 10 exhibited zone of inhibition >23±0.12 μg/ml for all the strains, making it more effective as compared to Pc 6. In addition, all strains of tested bacteria were susceptible to Pc 10 at a concentration > 31.25 μg/ml. This implies that substituting Pc with electron withdrawing allows it to release more singlet oxygen in presence of light and which results to oxidation of the bacterial wall. AgNp and ZnO-Np were synthesized by microwave assisted extraction. The UV-Vis was used to confirm the formation of nanoparticles and also characterization done using FTIR, TEM and SEM. AgNps were of diameters ˂ 58.5 nm that easily conjugated to Pc while ZnO-Nps were of large grain size ˃ 95, the particles aggregated making it difficult to conjugate with Pcs. Conjugation of Pc 10 with AgNp ˂ 10 nm resulted to a more superior antibacterial as compared to unconjugated Pc 10. There was no significant different for zone of inhibition for Pc 10 conjugated to AgNp when compared to positive control ciprofloxacin at 500 μg/ml for all the strains except for B. subtilis. It had minimum inhibitory concentration (MIC) values of 3.91, 1.96, 1.96 and 15.63 μg/ml, for E. coli, S aureus, B. subtilis and S. typhi respectively. Both Pc showed no toxicity on Vero cells at concentration of 600 μg/ml. In overall, this work reports the successful tuning of the photo-chemical and antibacterial photodynamic properties of Pc using electron withdrawing and donating substituent. The Pc 10 with electron withdrawing group exhibit superior antibacterial activity which is further enhanced by conjugation with AgNp of ˂ 10 nm.
- PHD-Chemistry