Copper(II) and Cobalt(II) Complexes Based on Abietate Ligands from Pinus Resin: Synthesis, Characterization and Their Antibacterial and Antiviral Activity against SARS-CoV-2

Abstract

Co-abietate and Cu-abietate complexes were obtained by a low-cost and eco-friendly route. The synthesis process used Pinus elliottii resin and an aqueous solution of CuSO₄/CoSO₄ at a mild temperature (80 °C) without organic solvents. The obtained complexes are functional pigments for commercial architectural paints with antipathogenic activity. The pigments were characterized by Fourier-transform infrared spectroscopy (FTIR), mass spectrometry (MS), thermogravimetry (TG), near-edge X-ray absorption fine structure (NEXAFS), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and colorimetric analysis. In addition, the antibacterial efficiency was evaluated using the minimum inhibitory concentration (MIC) test, and the antiviral tests followed an adaptation of the ISO 21702:2019 guideline. Finally, virus inactivation was measured using the RT-PCR protocol using 10% (w/w) of abietate complex in commercial white paint. The Co-abietate and Cu-abietate showed inactivation of >4 log against SARS-CoV-2 and a MIC value of 4.50 µg·mL^-1 against both bacteria Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). The results suggest that the obtained Co-abietate and Cu-abietate complexes could be applied as pigments in architectural paints for healthcare centers, homes, and public places.

Keywords: SARS-CoV-2; abietic acid; antimicrobial pigments; antiviral surfaces; natural resin.

Figure 1

FTIR spectra of Na-abietate, the Co-abietate and Cu-abietate complexes.

Figure 2

Mass spectra of the Co-abietate. (A) peaks corresponding to the theoretical molecular mass of deprotonated abietic acid, the dimeric form of the abietic acid with three additional oxygen atoms corresponding to oxidations of three C=C bonds to its keto form; the formation of Co-abietate with three abietate ligands with three additional oxygen atoms; and the formation of the Co-abietate complex with four abietate ligands at m/z 301, m/z 649, m/z − 1008, m/z − 1270, respectively. (B) The dimeric form of the abietic acid with three additional oxygen atoms from consecutive oxidations of C=C bonds, resulting in a difference of m/z 16 between at m/z − 617; m/z − 633; m/z − 649. (C) The peak of m/z − 1008 corresponds to Co-abietate formation encompassing three abietate ligands, with three C=C bonds from the ligand oxidated to the keto form.

Figure 3

Mass spectra of the Cu-abietate. (A) The peaks corresponding to the molecular mass of deprotonated abietic acid (C₂₀H₂₉O₂)⁻; to the dimeric form of abietic acid; the molecular mass of copper bound to three abietate ligands [Cu(C₂₀H₂₉O₂)₃]⁻; and to the Cu-abietate complex constituted by four ligands (C₂₀H₂₉O₂)⁻, at corresponds to m/z − 301, m/z − 603, m/z − 966, and m/z − 1273, respectively. (B) Progressive oxidations of C=C bonds of the abietate ligand to the respective keto form, evidenced by the m/z difference of 16 units between the peaks.

Figure 4

(A) Na K-edge NEXAFS of Na-abietate. (B) Co L-edge of Co-abietate. (C) Cu-L-edge of Cu-abietate.

Figure 5

XPS spectra. (A) Survey spectrum of Co-abietate. (B) O1s spectrum of Co-abietate. (C) C1s spectrum of Co-abietate. (D) Survey spectrum of Cu-abietate. (E) O1s spectrum of Cu-abietate. (F) C1s spectrum of Cu-abietate.

Figure 6

SEM images and average particle sizes of the samples: (A,C) Co-abietate; (B,D) Cu-abietate.

Figure 7

(A) specimen painted with pigment Co-abietate dispersed in acrylic paint; (B) specimen painted with pigment Cu-abietate dispersed in acrylic paint; (C) Co-abietate powder; (D) Cu-abietate powder; (E) colorimetric parameters a* and b* of the pigments in powder according to CIE L*a*b*.

Figure 8

Thermal Decomposition of (A) Co-abietate, and (B) Cu-abietate samples by TG/DTG.