Complexation and conformation of lead ion with poly-γ-glutamic acid in soluble state

Abstract

Complexation of microbial polymer in soluble state could impact the solubility, mobility, and bioavailability of heavy metals in the environment. The complexation of a bacterial exopolymer, poly-γ-glutamic acid (γ-PGA), with Pb2+ was studied using the polarographic method and circular dichroism measurement in soluble state. The number of available binding sites was determined based on the Chau’s method and was found to be 0.04, 1.12, 3.56 and 4.51 mmol/(g dry weight of γ-PGA) at pH 3.4, 4.2, 5.0 and 6.2, respectively. Further, the number of binding sites was determined based on the Ruzic’s method and was found to be 3.60 and 4.41 mmol/(g dry weight of γ-PGA) for pH 5.0 and 6.2, respectively. The constant (expressed as log K) values were 5.8 and 6.0 at pH 5.0 and 6.2. Compared to biopolymers secreted by other microorganisms, such as extracellular polymeric substances extraction from activated sludge, γ-PGA was a more efficient Pb2+ carrier from pH 5.0 to 6.2. The secondary structure of γ-PGA varied significantly when Pb2+ added. Ca2+ or Mg2+ replace a portion of the adsorbed Pb2+. However, the portion of Pb2+ involved in changing the γ-PGA conformation was not easily replaced by Ca2+ and Mg2+.

Effective Removal of Different Heavy Metals Ion (Cu, Pb, and Cd) from Aqueous Solutions by Various Molecular Weight and Salt Types of Poly-γ-Glutamic Acid

“…Specifically, at a γ-PGA concentration of 0.5%, the adsorption rates for Pb ions were observed to be 1.07 and 1.19 times greater than those for Cu and Cd ions, respectively. This pattern of adsorption behavior is consistent with previous research, which suggests that the biosorption capacity of γ-PGA is significantly influenced by its coordination mode and conformation changes upon metal ion complexation [ 48 ]. A critical aspect of this observation is the role of structural modifications in γ-PGA that occur upon complexation with Pb 2+ ions.…”

“…As previously discussed, these mechanisms include ion exchange processes and chemical interactions that are influenced by the specific properties of the metal ions, such as their electronegativities and tendencies to form complexes. The preferential adsorption of Pb ions over Cd ions may be due to a more favorable interaction between Pb ions and the functional groups present in Na-γ-PGA-HM [ 48 ].…”

“…This can be attributed to two main reasons: the higher electronegativity of Pb 2+ , which enhances its affinity towards the carboxylate (COO-) groups of γ-PGA [ 31 ], and its tendency to form coordination complexes with a larger number of water molecules compared to other ions [ 49 ]. The latter results in a larger hydrated radius, potentially disrupting hydrogen bonds within the γ-PGA molecule and leading to significant conformational changes [ 48 , 50 ]. These findings underscore the complexity of the adsorption process in multi-metal environments and highlight the need for comprehensive studies to better understand the interactions between γ-PGA and mixed heavy metal ions.…”

Development of Sustainable Vegan Pea Protein-Zinc Complex: Characterization, In Vitro Cellular Mineral Uptake, and Application in Functional Biscuit Production

“…Tis could be attributed due to the saturation of binding sites, altered protein conformation, competitive binding with other ions, pH and ionic changes, solubility limits, and potential protein aggregation. Additionally, elevated zinc sulfate concentrations could facilitate protein-protein interactions, impacting site accessibility and binding efciency [43]. Our study aligns with Shilpashree et al [44], who found maximum zincbinding capacity at 2 mM Zn concentration.…”

Bioremediation of environmental wastes: the role of microorganisms

“…Xiao et al (2019) reported the removal of copper (II) oxide and hexavalent chromium from wastewater using biochar in a mechanism which includes complexation. The organisms that have been reported to be involved in complexation include Rhodobacter blasticus (Bai et al, 2019) and B.lichenformisis (Wang et al, 2019).…”