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Microstructural, spectroscopic, and antibacterial properties of silver-based hybrid nanostructures biosynthesized using extracts of coriander leaves and seeds

View Article: PubMed Central - PubMed

ABSTRACT

Coriander leaves and seeds have been highly appreciated since ancient times, not only due to their pleasant flavors but also due to their inhibitory activity on food degradation and their beneficial properties for health, both ascribed to their strong antioxidant activity. Recently, it has been shown that coriander leaf extracts can mediate the synthesis of metallic nanoparticles through oxidation/reduction reactions. In the present study, extracts of coriander leaves and seeds have been used as reaction media for the wet chemical synthesis of ultrafine silver nanoparticles and nanoparticle clusters, with urchin- and tree-like shapes, coated by biomolecules (mainly, proteins and polyphenols). In this greener route of nanostructure preparation, the active biocompounds of coriander simultaneously play the roles of reducing and stabilizing agents. The morphological and microstructural studies of the resulting biosynthesized silver nanostructures revealed that the nanostructures prepared with a small concentration of the precursor Ag salt (AgNO3 =5 mM) exhibit an ultrafine size and a narrow size distribution, whereas particles synthesized with high concentrations of the precursor Ag salt (AgNO3 =0.5 M) are polydisperse and formation of supramolecular structures occurs. Fourier transform infrared and Raman spectroscopy studies indicated that the bioreduction of the Ag− ions takes place through their interactions with free amines, carboxylate ions, and hydroxyl groups. As a consequence of such interactions, residues of proteins and polyphenols cap the biosynthesized Ag nanoparticles providing them a hybrid core/shell structure. In addition, these biosynthesized Ag nanomaterials exhibited size-dependent plasmon extinction bands and enhanced bactericidal activities against both Gram-positive and Gram-negative bacteria, displaying minimal inhibitory Ag concentrations lower than typical values reported in the literature for Ag nanoparticles, probably due to the synergy of the bactericidal activities of the Ag nanoparticle cores and their capping ligands.

No MeSH data available.


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TEM images of silver urchin- and tree-like structures.Notes: (A) TEM image of a silver urchin-like structure. The inset is the SAED pattern of the structure of panel A. (B) TEM image of a silver tree-like structure.Abbreviations: TEM, transmission electron microscope; SAED, selected-area electron diffraction.
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f6-ijn-11-4787: TEM images of silver urchin- and tree-like structures.Notes: (A) TEM image of a silver urchin-like structure. The inset is the SAED pattern of the structure of panel A. (B) TEM image of a silver tree-like structure.Abbreviations: TEM, transmission electron microscope; SAED, selected-area electron diffraction.

Mentions: Figure 4A is a representative SAED pattern of sample S-0.5M. This is constituted by spotty rings associated to the (111), (002), (022), (113), and (222) planes of the fcc metallic silver. Moreover, some spots related to the additional crystalline phase detected by X-ray diffraction were also found. This sample also showed a broad and asymmetric size distribution (Figure 4B and C). In fact, particles with different morphologies and crystalline properties were observed. In this regard, most of the particles of this sample exhibited faceted morphologies and twinning boundaries. Figure 4D shows an HRTEM micrograph of a typical particle with these features. The FFT images of different zones showed that this particle is constituted by two twinned crystals viewed along the (110) direction (Figure 4E and F). Also, monocrystalline nanoparticles with a circular disc-like shape (Figure 5A) or with a rounded triangular morphology (Figure 5B) were observed. The FFT images of the HRTEM micrographs of these nanoparticles showed that these particles were usually viewed along the same crystallographic directions: the circular nanodiscs viewed down the (211) zone axis (Figure 5C), and the rounded nanotriangles viewed down the (111) zone axis (Figure 5D). Interestingly, some spots observed in these FFT images were associated to 1/2(113) (Figure 5C) or 1/3(224) (Figure 5D) forbidden reflections. In fact, the exposed faces of the rounded nanotriangles were related to the 3× (224) superlattices (Figure 5B and D). These features are in agreement with a flattened morphology.17,30 In addition, a minor fraction of particles exhibited rod-like shapes (Figure 5E) characterized by the presence of (111) stacking faults (Figure 5F). Some micrometric urchin-like (Figure 6A) and tree-like (Figure 6B) structures formed by aggregated and coalesced particles were also observed. The SAED patterns of these structures displayed spots that form arcs of ~30° (shown in the inset of Figure 6A), suggesting that these structures grew by oriented attachment of particles.


Microstructural, spectroscopic, and antibacterial properties of silver-based hybrid nanostructures biosynthesized using extracts of coriander leaves and seeds
TEM images of silver urchin- and tree-like structures.Notes: (A) TEM image of a silver urchin-like structure. The inset is the SAED pattern of the structure of panel A. (B) TEM image of a silver tree-like structure.Abbreviations: TEM, transmission electron microscope; SAED, selected-area electron diffraction.
© Copyright Policy
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC5036574&req=5

f6-ijn-11-4787: TEM images of silver urchin- and tree-like structures.Notes: (A) TEM image of a silver urchin-like structure. The inset is the SAED pattern of the structure of panel A. (B) TEM image of a silver tree-like structure.Abbreviations: TEM, transmission electron microscope; SAED, selected-area electron diffraction.
Mentions: Figure 4A is a representative SAED pattern of sample S-0.5M. This is constituted by spotty rings associated to the (111), (002), (022), (113), and (222) planes of the fcc metallic silver. Moreover, some spots related to the additional crystalline phase detected by X-ray diffraction were also found. This sample also showed a broad and asymmetric size distribution (Figure 4B and C). In fact, particles with different morphologies and crystalline properties were observed. In this regard, most of the particles of this sample exhibited faceted morphologies and twinning boundaries. Figure 4D shows an HRTEM micrograph of a typical particle with these features. The FFT images of different zones showed that this particle is constituted by two twinned crystals viewed along the (110) direction (Figure 4E and F). Also, monocrystalline nanoparticles with a circular disc-like shape (Figure 5A) or with a rounded triangular morphology (Figure 5B) were observed. The FFT images of the HRTEM micrographs of these nanoparticles showed that these particles were usually viewed along the same crystallographic directions: the circular nanodiscs viewed down the (211) zone axis (Figure 5C), and the rounded nanotriangles viewed down the (111) zone axis (Figure 5D). Interestingly, some spots observed in these FFT images were associated to 1/2(113) (Figure 5C) or 1/3(224) (Figure 5D) forbidden reflections. In fact, the exposed faces of the rounded nanotriangles were related to the 3× (224) superlattices (Figure 5B and D). These features are in agreement with a flattened morphology.17,30 In addition, a minor fraction of particles exhibited rod-like shapes (Figure 5E) characterized by the presence of (111) stacking faults (Figure 5F). Some micrometric urchin-like (Figure 6A) and tree-like (Figure 6B) structures formed by aggregated and coalesced particles were also observed. The SAED patterns of these structures displayed spots that form arcs of ~30° (shown in the inset of Figure 6A), suggesting that these structures grew by oriented attachment of particles.

View Article: PubMed Central - PubMed

ABSTRACT

Coriander leaves and seeds have been highly appreciated since ancient times, not only due to their pleasant flavors but also due to their inhibitory activity on food degradation and their beneficial properties for health, both ascribed to their strong antioxidant activity. Recently, it has been shown that coriander leaf extracts can mediate the synthesis of metallic nanoparticles through oxidation/reduction reactions. In the present study, extracts of coriander leaves and seeds have been used as reaction media for the wet chemical synthesis of ultrafine silver nanoparticles and nanoparticle clusters, with urchin- and tree-like shapes, coated by biomolecules (mainly, proteins and polyphenols). In this greener route of nanostructure preparation, the active biocompounds of coriander simultaneously play the roles of reducing and stabilizing agents. The morphological and microstructural studies of the resulting biosynthesized silver nanostructures revealed that the nanostructures prepared with a small concentration of the precursor Ag salt (AgNO3 =5 mM) exhibit an ultrafine size and a narrow size distribution, whereas particles synthesized with high concentrations of the precursor Ag salt (AgNO3 =0.5 M) are polydisperse and formation of supramolecular structures occurs. Fourier transform infrared and Raman spectroscopy studies indicated that the bioreduction of the Ag− ions takes place through their interactions with free amines, carboxylate ions, and hydroxyl groups. As a consequence of such interactions, residues of proteins and polyphenols cap the biosynthesized Ag nanoparticles providing them a hybrid core/shell structure. In addition, these biosynthesized Ag nanomaterials exhibited size-dependent plasmon extinction bands and enhanced bactericidal activities against both Gram-positive and Gram-negative bacteria, displaying minimal inhibitory Ag concentrations lower than typical values reported in the literature for Ag nanoparticles, probably due to the synergy of the bactericidal activities of the Ag nanoparticle cores and their capping ligands.

No MeSH data available.


Related in: MedlinePlus