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Experimental and theoretical approaches for the surface interaction between copper and activated sludge microorganisms at molecular scale.

Luo HW, Chen JJ, Sheng GP, Su JH, Wei SQ, Yu HQ - Sci Rep (2014)

Bottom Line: The complexing structure of Cu(II) on microbial surface was revealed by X-ray absorption fine structure (XAFS) and electron paramagnetic resonance (EPR) analysis.XAFS analysis further suggested that the surface complexation between Cu(II) and microbial cells was the distorted inner-sphere coordinated octahedra containing four short equatorial bonds and two elongated axial bonds.To further validate the results obtained from the XAFS and EPR analysis, density functional theory calculations were carried out to explore the structural geometry of the Cu complexes.

View Article: PubMed Central - PubMed

Affiliation: CAS Key Laboratory of Urban Pollutant Conversion, Department of Chemistry.

ABSTRACT
Interactions between metals and activated sludge microorganisms substantially affect the speciation, immobilization, transport, and bioavailability of trace heavy metals in biological wastewater treatment plants. In this study, the interaction of Cu(II), a typical heavy metal, onto activated sludge microorganisms was studied in-depth using a multi-technique approach. The complexing structure of Cu(II) on microbial surface was revealed by X-ray absorption fine structure (XAFS) and electron paramagnetic resonance (EPR) analysis. EPR spectra indicated that Cu(II) was held in inner-sphere surface complexes of octahedral coordination with tetragonal distortion of axial elongation. XAFS analysis further suggested that the surface complexation between Cu(II) and microbial cells was the distorted inner-sphere coordinated octahedra containing four short equatorial bonds and two elongated axial bonds. To further validate the results obtained from the XAFS and EPR analysis, density functional theory calculations were carried out to explore the structural geometry of the Cu complexes. These results are useful to better understand the speciation, immobilization, transport, and bioavailability of metals in biological wastewater treatment plants.

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(a) RSF obtained by Fourier transformation of the EXAFS spectrum; and (b) first-shell fit of the EXAFS function of the Cu(II)- activated sludge complex, nonlinear least-squares fits (solid lines) and experimental data (open circles).
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f4: (a) RSF obtained by Fourier transformation of the EXAFS spectrum; and (b) first-shell fit of the EXAFS function of the Cu(II)- activated sludge complex, nonlinear least-squares fits (solid lines) and experimental data (open circles).

Mentions: To gain more insight into the molecular structure of the Cu complexing with activated sludge, the EXAFS spectra were fitted according to the standard model of Cu(NO3)2. The first-shell fit of the EXAFS spectra of the Cu complexes and its corresponding radial structure function (RSF) derived from Fourier transformations, are illustrated in Fig. 4. The position of the peaks in the RSF corresponds to the relative distance (uncorrected for phase shift) between Cu(II) and complexing atoms in local coordination shells. The strongest peak, which appears between 1.44 and 1.50 Å in Fig. 4a, corresponded to the first-shell O atoms. Within the framework of the single scattering approach, the EXAFS spectra fitted well by Levenberg-Marquardt fitting (Fig. 4b), and the results are listed in Table 1. The results show that Cu(II) ions were surrounded by four equatorial oxygen atoms and two axial oxygen atoms. The average Cu-Oeq bond length was 1.95 ± 0.01 Å, and the Cu-Oax one was equal to 2.43 ± 0.50 Å. These data are consistent with those obtained from the EPR results and the XANES spectra: distorted octahedra containing four short equatorial bonds and two elongated axial bonds. Also, this agrees with previous studies, in which bond distance for Cu-Oeq first shell has been reported to range from 1.92 to 1.97 Å272829, while the second shell Cu–O/C ranged from 2.29 to 2.41 Å30.


Experimental and theoretical approaches for the surface interaction between copper and activated sludge microorganisms at molecular scale.

Luo HW, Chen JJ, Sheng GP, Su JH, Wei SQ, Yu HQ - Sci Rep (2014)

(a) RSF obtained by Fourier transformation of the EXAFS spectrum; and (b) first-shell fit of the EXAFS function of the Cu(II)- activated sludge complex, nonlinear least-squares fits (solid lines) and experimental data (open circles).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4233339&req=5

f4: (a) RSF obtained by Fourier transformation of the EXAFS spectrum; and (b) first-shell fit of the EXAFS function of the Cu(II)- activated sludge complex, nonlinear least-squares fits (solid lines) and experimental data (open circles).
Mentions: To gain more insight into the molecular structure of the Cu complexing with activated sludge, the EXAFS spectra were fitted according to the standard model of Cu(NO3)2. The first-shell fit of the EXAFS spectra of the Cu complexes and its corresponding radial structure function (RSF) derived from Fourier transformations, are illustrated in Fig. 4. The position of the peaks in the RSF corresponds to the relative distance (uncorrected for phase shift) between Cu(II) and complexing atoms in local coordination shells. The strongest peak, which appears between 1.44 and 1.50 Å in Fig. 4a, corresponded to the first-shell O atoms. Within the framework of the single scattering approach, the EXAFS spectra fitted well by Levenberg-Marquardt fitting (Fig. 4b), and the results are listed in Table 1. The results show that Cu(II) ions were surrounded by four equatorial oxygen atoms and two axial oxygen atoms. The average Cu-Oeq bond length was 1.95 ± 0.01 Å, and the Cu-Oax one was equal to 2.43 ± 0.50 Å. These data are consistent with those obtained from the EPR results and the XANES spectra: distorted octahedra containing four short equatorial bonds and two elongated axial bonds. Also, this agrees with previous studies, in which bond distance for Cu-Oeq first shell has been reported to range from 1.92 to 1.97 Å272829, while the second shell Cu–O/C ranged from 2.29 to 2.41 Å30.

Bottom Line: The complexing structure of Cu(II) on microbial surface was revealed by X-ray absorption fine structure (XAFS) and electron paramagnetic resonance (EPR) analysis.XAFS analysis further suggested that the surface complexation between Cu(II) and microbial cells was the distorted inner-sphere coordinated octahedra containing four short equatorial bonds and two elongated axial bonds.To further validate the results obtained from the XAFS and EPR analysis, density functional theory calculations were carried out to explore the structural geometry of the Cu complexes.

View Article: PubMed Central - PubMed

Affiliation: CAS Key Laboratory of Urban Pollutant Conversion, Department of Chemistry.

ABSTRACT
Interactions between metals and activated sludge microorganisms substantially affect the speciation, immobilization, transport, and bioavailability of trace heavy metals in biological wastewater treatment plants. In this study, the interaction of Cu(II), a typical heavy metal, onto activated sludge microorganisms was studied in-depth using a multi-technique approach. The complexing structure of Cu(II) on microbial surface was revealed by X-ray absorption fine structure (XAFS) and electron paramagnetic resonance (EPR) analysis. EPR spectra indicated that Cu(II) was held in inner-sphere surface complexes of octahedral coordination with tetragonal distortion of axial elongation. XAFS analysis further suggested that the surface complexation between Cu(II) and microbial cells was the distorted inner-sphere coordinated octahedra containing four short equatorial bonds and two elongated axial bonds. To further validate the results obtained from the XAFS and EPR analysis, density functional theory calculations were carried out to explore the structural geometry of the Cu complexes. These results are useful to better understand the speciation, immobilization, transport, and bioavailability of metals in biological wastewater treatment plants.

Show MeSH
Related in: MedlinePlus