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Investigation on humic substance and tetracycline interaction mechanism: biophysical and theoretical studies and assessing their effect on biological activity

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Abstract

Tetracycline (TC) is a widely used antibiotic, and evaluating its interaction with humic substances (HS) that act as a complexing agent in the environment is essential to understanding the availability of this contaminant in the environment. This study evaluated the interaction between HS and TC using different spectroscopic techniques, theoretical studies, and biological assays simulating environmental conditions. TC interacts with HS, preferably by electrostatic forces, with a binding constant of 9.2 × 103 M−1 (30 °C). This process induces conformational changes in the superstructure, preferably in the HS, like protein fraction. Besides, studies using the 8-anilino-1-naphthalene sulfonate (ANS) probe indicated that the antibiotic alters the hydrophobicity degree on HS’s surface. Synchronized fluorescence shows that the TC interaction occurs preferentially with the protein-like fraction of soil organic matter (KSV = 26.28 ± 1.03 M−1). The TC epitope was evaluated by 1H NMR and varied according to the pH (4.8 and 9.0) of the medium, as well as the main forces responsible for the stabilization of the HS-TC complex. The molecular docking studies showed that the formation of the HS-TC complex is carried out spontaneously (ΔG = −7.1 kcal mol−1) and is stabilized by hydrogen bonds and electrostatic interactions, as observed in the experimental spectroscopic results. Finally, biological assays indicated that HS influenced the antimicrobial activity of TC. Thus, this study contributed to understanding the dynamics and distribution of TC in the environment and HS’s potential in the remediation of antibiotics of this class in natural systems, as these can have adverse effects on ecosystems and human health.

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All data generated or analyzed during this study are included in this published article (and its supplementary information files).

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Acknowledgements

The authors are thankful to the Universidade Federal de Alagoas (UFAL), the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brazil (CAPES, Finance Code 001), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), and Fundação de Amparo à Pesquisa do Estado de Alagoas (FAPEAL). JCCS is the recipient of research fellowships from CNPq.

Funding

This work had financial support from CNPq (408590/2021-1, 313106/2022-3), CAPES (finance code 001), and FAPEAL (60030.0000002362/2022).

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Authors and Affiliations

Authors

Contributions

ALAN, SOS, ASG: investigation, writing-original draft. IMF: methodology, investigation. TAD: methodology, investigation. FSG: methodology, investigation. WGB: methodology, investigation, funding acquisition. JCCS: conceptualization, methodology, supervision, funding acquisition, writing-review and editing. All authors read and approved the final manuscript.

Corresponding author

Correspondence to Josué Carinhanha Caldas Santos.

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Not applicable for this study.

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Not applicable as the study did not include human subjects.

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All authors approve this submission.

Conflict of interest

The authors declare no competing interests.

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Responsible Editor: George Z. Kyzas

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Highlights

• Tetracycline (TC) is an antibiotic with an affinity for humic substances (HS) in environmental conditions.

• Potential use of HS in the remediation process of antibiotics in natural systems.

• The study of HS-TC interaction helps the understanding of the TC dynamics in the environment.

• HS may influence the antimicrobial activity of TC in real systems due to MIC change.

• The TC-HS interaction supramolecular model was suggested using theoretical studies.

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Nascimento, A.L.A., de Oliveira Souza, S., Guimarães, A.S. et al. Investigation on humic substance and tetracycline interaction mechanism: biophysical and theoretical studies and assessing their effect on biological activity. Environ Sci Pollut Res 31, 20172–20187 (2024). https://doi.org/10.1007/s11356-024-32168-6

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  • DOI: https://doi.org/10.1007/s11356-024-32168-6

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