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Biomimetic Synthesis of Gelatin Polypeptide-Assisted Noble-Metal Nanoparticles and Their Interaction Study

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ABSTRACT

Herein, the generation of gold, silver, and silver–gold (Ag–Au) bimetallic nanoparticles was carried out in collagen (gelatin) solution. It first showed that the major ingredient in gelatin polypeptide, glutamic acid, acted as reducing agent to biomimetically synthesize noble metal nanoparticles at 80°C. The size of nanoparticles can be controlled not only by the mass ratio of gelatin to gold ion but also by pH of gelatin solution. Interaction between noble-metal nanoparticles and polypeptide has been investigated by TEM, UV–visible, fluorescence spectroscopy, and HNMR. This study testified that the degradation of gelatin protein could not alter the morphology of nanoparticles, but it made nanoparticles aggregated clusters array (opposing three-dimensional α-helix folding structure) into isolated nanoparticles stabilized by gelatin residues. This is a promising merit of gelatin to apply in the synthesis of nanoparticles. Therefore, gelatin protein is an excellent template for biomimetic synthesis of noble metal/bimetallic nanoparticle growth to form nanometer-sized device.

No MeSH data available.


a TEM image of gelatin; b TEM image of AuNPs (dark dots) loaded by gelatin (gray plates) synthesized at 80°C (Cgelatin: 0.4%); c The magnified TEM images of b; d UV–vis of the Gelatin-AuNPs synthesized with 0.1, 0.15, 0.25, 0.5, 0.75, 1, and 2% gelatin solutions. The inset is the corresponding optical images of gelatin-AuNPs colloids (the gelatin concentration increasing from left to right).
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Figure 1: a TEM image of gelatin; b TEM image of AuNPs (dark dots) loaded by gelatin (gray plates) synthesized at 80°C (Cgelatin: 0.4%); c The magnified TEM images of b; d UV–vis of the Gelatin-AuNPs synthesized with 0.1, 0.15, 0.25, 0.5, 0.75, 1, and 2% gelatin solutions. The inset is the corresponding optical images of gelatin-AuNPs colloids (the gelatin concentration increasing from left to right).

Mentions: In the synthesis of AuNPs, classical reducers such as mercaptoundecanoic acid [19] and macromolecular containing end amino units such as (i.e. PVP-NH2) [20] are the most important type of stabilizing and reducing molecule to gold nanoparticles of any size. The functional group of gelatin such as –NH2, –SH and –COOH endow it as reducing and stabilizing agent to reduce Au(III) to form gold colloid. As observed in Figure 1, well-dispersed gelatin stabilized gold nanoparticles were prepared according to the synthetic procedure in "Generation of Gold Nanoparticles". Gelatin polypeptide chains with predominately coil conformation are freely soluble in water at elevated temperature (>35°C). However, gelatin molecules linked together to form aggregates when gelatin solution and gelatin-AuNPs colloid were gradually cooled to room temperature (see Figure 1a, b). This is because of protein properties. Proteins are marginally stable because the beneficial interactions that govern the native structure are counterbalanced by a large entropy loss associated with going from a large ensemble of states to a more restricted set of conformations, as well as by the repulsive electrostatic interactions present in the native state [21]. The blank zone in Figure 1a and 1b showed there is some free water in gelatin gel because of the gelatin semi-liquid state at the gelatin concentration of 1% or less [22]. Figure 1b showed that it created a AuNP-loaded gelatin microstructure that all AuNPs embedded in gelatin polypeptide templates instead of gold nanoparticle clusters coated with gelatin or isolated AuNPs clusters departed form aggregated polypeptide. Therefore, AuNPs is not only stabilized by gelatin polypeptides chains but also joined in the self-assembling activities of gelatin polypeptides upon cooling to room temperature. Figure 1d showed the typical absorption band of gold nanoparticles and gelatin was at about 500–550 nm and around 230–300 nm, respectively. When the gelatin concentration is above 0.25%, there is an obvious red shift of the absorption band edge of gelatin residue. This is due to the interaction of gold nanoparticle and gelatin residues.


Biomimetic Synthesis of Gelatin Polypeptide-Assisted Noble-Metal Nanoparticles and Their Interaction Study
a TEM image of gelatin; b TEM image of AuNPs (dark dots) loaded by gelatin (gray plates) synthesized at 80°C (Cgelatin: 0.4%); c The magnified TEM images of b; d UV–vis of the Gelatin-AuNPs synthesized with 0.1, 0.15, 0.25, 0.5, 0.75, 1, and 2% gelatin solutions. The inset is the corresponding optical images of gelatin-AuNPs colloids (the gelatin concentration increasing from left to right).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211277&req=5

Figure 1: a TEM image of gelatin; b TEM image of AuNPs (dark dots) loaded by gelatin (gray plates) synthesized at 80°C (Cgelatin: 0.4%); c The magnified TEM images of b; d UV–vis of the Gelatin-AuNPs synthesized with 0.1, 0.15, 0.25, 0.5, 0.75, 1, and 2% gelatin solutions. The inset is the corresponding optical images of gelatin-AuNPs colloids (the gelatin concentration increasing from left to right).
Mentions: In the synthesis of AuNPs, classical reducers such as mercaptoundecanoic acid [19] and macromolecular containing end amino units such as (i.e. PVP-NH2) [20] are the most important type of stabilizing and reducing molecule to gold nanoparticles of any size. The functional group of gelatin such as –NH2, –SH and –COOH endow it as reducing and stabilizing agent to reduce Au(III) to form gold colloid. As observed in Figure 1, well-dispersed gelatin stabilized gold nanoparticles were prepared according to the synthetic procedure in "Generation of Gold Nanoparticles". Gelatin polypeptide chains with predominately coil conformation are freely soluble in water at elevated temperature (>35°C). However, gelatin molecules linked together to form aggregates when gelatin solution and gelatin-AuNPs colloid were gradually cooled to room temperature (see Figure 1a, b). This is because of protein properties. Proteins are marginally stable because the beneficial interactions that govern the native structure are counterbalanced by a large entropy loss associated with going from a large ensemble of states to a more restricted set of conformations, as well as by the repulsive electrostatic interactions present in the native state [21]. The blank zone in Figure 1a and 1b showed there is some free water in gelatin gel because of the gelatin semi-liquid state at the gelatin concentration of 1% or less [22]. Figure 1b showed that it created a AuNP-loaded gelatin microstructure that all AuNPs embedded in gelatin polypeptide templates instead of gold nanoparticle clusters coated with gelatin or isolated AuNPs clusters departed form aggregated polypeptide. Therefore, AuNPs is not only stabilized by gelatin polypeptides chains but also joined in the self-assembling activities of gelatin polypeptides upon cooling to room temperature. Figure 1d showed the typical absorption band of gold nanoparticles and gelatin was at about 500–550 nm and around 230–300 nm, respectively. When the gelatin concentration is above 0.25%, there is an obvious red shift of the absorption band edge of gelatin residue. This is due to the interaction of gold nanoparticle and gelatin residues.

View Article: PubMed Central - HTML - PubMed

ABSTRACT

Herein, the generation of gold, silver, and silver–gold (Ag–Au) bimetallic nanoparticles was carried out in collagen (gelatin) solution. It first showed that the major ingredient in gelatin polypeptide, glutamic acid, acted as reducing agent to biomimetically synthesize noble metal nanoparticles at 80°C. The size of nanoparticles can be controlled not only by the mass ratio of gelatin to gold ion but also by pH of gelatin solution. Interaction between noble-metal nanoparticles and polypeptide has been investigated by TEM, UV–visible, fluorescence spectroscopy, and HNMR. This study testified that the degradation of gelatin protein could not alter the morphology of nanoparticles, but it made nanoparticles aggregated clusters array (opposing three-dimensional α-helix folding structure) into isolated nanoparticles stabilized by gelatin residues. This is a promising merit of gelatin to apply in the synthesis of nanoparticles. Therefore, gelatin protein is an excellent template for biomimetic synthesis of noble metal/bimetallic nanoparticle growth to form nanometer-sized device.

No MeSH data available.