Introduction

Chloro benzoic acid is used as preservative for adhesive and paints, miticides, contrast media in urology, cholocystrographic examinations and in the manufacture of pharmaceuticals.[1]The 3-chlorobenzoic acid (3-CBA;Figure 1)  and its derivatives are used as antibacterial and antifungal agents against different bacterial and fungal species. Metallic zinc is a potential biocompatible and biodegradable material and important nutrient. Metallic zinc has many important biological functions including wound healing, cell division, development and sustenance of bone, DNA stabilization and replication.[2] 3-Chlorobenzoic acid was degraded and mineralized by these route of the ortho cleavage pathway, the modified ortho cleavage pathway, the meta-cleavage pathway, the gentisate pathway and the protocatechuate pathway under aerobic conditions. Reductive dechlorination is the main degradation pathway for most chlorinated aromatic compounds inanaerobic or anoxic environments. Under theaction of anaerobic microorganisms, 3-chlorobenzoic acid was first degraded to benzoic acid and then further degraded to acetic acid, H₂ and CO₂. In anoxic environments,denitrifying bacteria not only degraded 3-chlorobenzoic acid, but also used 4-CBA as an electron acceptor under denitrifying conditions.[3]

Antibacterial activity of 3-chlorobenzoic acid and its complexes

Raman spectroscopy is an effective tool for determining the antibacterial actitivites of organometallic compounds against different bacterial strains.The purpose of current study is to check the anibacterial activites of ligand (3-chlorobenzoicacid) and its respective zinc complex against gram positive and gram-negative bacterial strains by using surface enhanced Raman spectroscopy (SERS).The ligand (3-chlorobenzoic acid) and its respective zinc complex caused different biochemical changes in gram-positive and gram-negative bacterial strains such as lipid contents, DNA/RNA contents, proteins contents, peptidoglycan contents and bacterial spore contents which can be observed with different SERS spectral features. Surface enhanced Raman spectroscopy (SERS) has been employed for analyzing the antibiotic activities of 3-chlorobenzoic acid ligands and their respective zinc complexes against Escherichia coli (gram-negative) and Bacillus subtilis (gram-positive) bacterial strains. The bioactivity assay and SERS spectral results clearly show that the complex causes more degradation in both bacterial cells (E. coli and B. subtilis) as compared to ligand.Furthermore, PCA was employed for differentiating the mechanism of action of zinc complexes against gram-positive bacterial strain and gram-negative bacterial strain. SERS technique along with chemometric tools have successfully differentiated the antibiotic activities of 3-chlorobenzoic acid ligands and their respective zinc complexes against Escherichia coli (gram-negative) and Bacillus subtilis (gram-positive) bacterial strains.[2]

Degradation kinetics of 3-Chlorobenzoic acid in anoxic water

Degradation kinetics and mechanism of 3-chlorobenzoic acid (3-CBA) in anoxic water environmentusing graphene/TiO₂ (GR/TiO₂) as photocatalyst had been investigated. The results show that the residual concentration of 3-chlorobenzoic acid has a good linear relationship and its correlation coefficient R² are all greater than 0.985 by Langmuir–Hinshelwood (L–H) dynamic model under different photocatalytic degradation conditions. Photocatalytic oxidation and photocatalytic reduction reaction occur simultaneously when DO is in the range of 0.3–1.0mg/L. Some oxidative degradation products such as 3-chlorophenol, resorcinol, hydroxyquinol are generated, and some reductive degradation products such as 3-chlorobenzaldehyde, 3-hydroxybenzaldehyde, 3-hydroxybenzyl alcohol and cyclohexanediol are produced, and part of 3-chlorobenzoic acid is mineralized to generate CO₂ and H₂O. When the DO concentration is less than 0.29 mg/L, O₂ captures the photo-generated electrons no longer andelectrons directly attack 3-chlorobenzoic acid and other intermediates.Photocatalytic reduction mainly occurs, the concentration of Cl^? ion gradually increases, but TOC of thereaction solution remains almost unchanged.The results provide a theoretical basis for photocatalytic in situ remediation of pollutants in anoxic water environment.[3]

Biodegradation of 3?chlorobenzoic acid with electron shuttle systems

A synergy of biodegradation and electron shuttle systems is a promising strategy for eliminating pollutants including chlorinated aromatic compounds. The present work studies the degradation products of 3-chlorobenzoic acid by Pseudomonas putida in the presence of an electron shuttle system (ESS) composed of citrate and pyruvate as electron donors and the pollutant as an electron acceptor. Chromatographic results showed different pathways involved in the biodegradation process under the influence of electron shuttle systems. These routes depend on oxidation and reduction reactions for output byproducts to be easily mineralized by the bacterium under investigation. A nucleotide sequence with about 380 bp of a ton B gene was detected in P. putida and it resembles Escherichia coli Ton B. The relatedness tree of the selected gene reveals a high similarity and is comparable to P. aeruginosa (100%) and the highest variation with that of P. citronellolis (21.99%). Accordingly, in the presence of electron shuttle systems, the genes responsible for bacterial influx were activated to ease the biodegradation process. In an application model, the remediated-water samples were handled by two recycling processes using Scenedesmus obliquus and Trigonella foenum-graecum to evaluate the efficiency of this non-conventional treatment. In conclusion, this strategy succeeded in remediating the polluted water with chlorinated aromatic compounds for further applications.[4] 

References

[1] Ramalingam S, Babu PD, Periandy S, Fereyduni E. Vibrational investigation, molecular orbital studies and molecular electrostatic potential map analysis on 3-chlorobenzoic acid using hybrid computational calculations. Spectrochim Acta A Mol Biomol Spectrosc. 2011;84(1):210-220. doi:10.1016/j.saa.2011.09.030

[2] Ditta A, Majeed MI, Nawaz H, et al. Surface-enhanced Raman spectral investigation of antibacterial activity of zinc 3-chlorobenzoic acid complexes against Gram-positive and Gram-negative bacteria. Photodiagnosis Photodyn Ther. 2022;39:102941. doi:10.1016/j.pdpdt.2022.102941

[3] Huang Y, Wang H, Huang K, Huang D, Yin S, Guo Q. Degradation kinetics and mechanism of 3-Chlorobenzoic acid in anoxic water environment using graphene/TiO2 as photocatalyst. Environ Technol. 2020;41(17):2165-2179. doi:10.1080/09593330.2018.1556741

[4] Khalil OAA, Abu El-Naga MN, El-Bialy HA. Biodegradation of 3-chlorobenzoic acid with electron shuttle systems: pathways and molecular identification. Arch Microbiol. 2020;202(9):2471-2480. doi:10.1007/s00203-020-01965-1