Synthesis and Spectrophotometric Activity of Phthalocyanine Conjugated to Metal Nanoparticles and Evaluation of their Antibacterial Properties
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Date
2021
Authors
Nyamu, N. Samuel
Journal Title
Journal ISSN
Volume Title
Publisher
Kenyatta University
Abstract
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.
Description
A Thesis Submitted in Partial Fulfillment of the Requirements for the Award of the Degree of Doctor of Philosophy (Chemistry) in the School of Pure and Applied Sciences of Kenyatta University, Nobember, 2021
Keywords
Synthesis, Spectrophotometric Activity, Phthalocyanine Conjugated, Metal Nanoparticles, Evaluation, Antibacterial Properties