An ultrastable conjugate of silver nanoparticles and protein formed through weak interactions

Abstract

In recent years, silver nanoparticles (AgNPs) have attracted significant attention owing to their unique physicochemical, optical, conductive and antimicrobial properties. One of the properties of AgNPs which is crucial for all applications is their stability. In the present study we unravel a mechanism through which silver nanoparticles are rendered ultrastable in an aqueous solution in complex with the protein ubiquitin (Ubq). This involves a dynamic and reversible association and dissociation of ubiquitin from the surface of AgNP. The exchange occurs at a rate much greater than 25 s(-1) implying a residence time of <40 ms for the protein. The AgNP-Ubq complex remains stable for months due to steric stabilization over a wide pH range compared to unconjugated AgNPs. NMR studies reveal that the protein molecules bind reversibly to AgNP with an approximate dissociation constant of 55 μM and undergo fast exchange. At pH > 4 the positively charged surface of the protein comes in contact with the citrate capped AgNP surface. Further, NMR relaxation-based experiments suggest that in addition to the dynamic exchange, a conformational rearrangement of the protein takes place upon binding to AgNP. The ultrastability of the AgNP-Ubq complex was found to be useful for its anti-microbial activity, which allowed the recycling of this complex multiple times without the loss of stability. Altogether, the study provides new insights into the mechanism of protein-silver nanoparticle interactions and opens up new avenues for its application in a wide range of systems.

Electrostatic Interactions and Protein Competition Reveal a Dynamic Surface in Gold Nanoparticle–Protein Adsorption

“…25 Moreover, the ubiquitin surface is similar to what was identified in earlier studies of ubiquitin-surface interactions. 43–46 Each cluster of ionizable residues experiences different p K a values depending on whether the protein is adsorbed on the AuNP surface or exposed to solution (Figure 3A). For simplicity, model-compound p K a values are used for the solution state, and each residue type is assigned an identical p K a shift.…”

Protein Interactions with Nanoparticle Surfaces: Highlighting Solution NMR Techniques

“…Brahmkhatri et al . demonstrated that a conjugate of AgNP with Ubq is highly stable over a wide range of pH values compared to the bare AgNP . Chemical shift perturbation was used to identify the Ubq residues responsible for binding with AgNP and the NMR titrations were carried out to measure the dissociation constant ( K D ) .…”

“…Generally, silver nanoparticles appear to have weaker protein binding compared to AuNPs, and AgNPs can gradually undergo oxidative dissolution in biological fluids, eventually dissolving while releasing soluble Ag + ions . This reduced stability appears to influence protein binding, leading to a more dynamic corona when observed by NMR …”

Some novel hexa‐coordinated cadmium Schiff base complexes: X‐ray structure, Hirshfeld surface analysis, antimicrobial and thermal analysis

“…Finally, the products were kept in a desiccator over silica gel. The physical and spectral data (IR and UV visible) of the compounds are collected in Tables 1 and 2 3.67(bs, 4H j,j' ), 2.87(bs, 6H h,h',i.i' ), 2.73(bs, 4H g,g' ) ppm. 13 C NMR (in DMSO): 167.32(C 7,7 0 ), 145.22(C 5,5 0 ), 135.05(C 4,4 0 ), 129.93(C 1,1 0 ), 128.86(C 2,2 0 ), 127.61(C 3,3 0), 126.39(C 6,6 0 ), 57.02(C 10,10 0), 48.05 (C 8,8 0), 46.02(C 9,9 0 ) ppm.…”

“…Antibacterial, antiviral, anti-flammatory, anti-oxidant activities, antifungal, analgesic and anti-tubercular are some notable properties of Schiff base complexes in biological field although they have extensive usage in other scientific fields. [1][2][3][4][5][6] In medical chemistry field, Schiff base complexes are known as new anti-cancer agent because of their abilities in cleavage of DNA strands and destruction of cancer cell. [7,8] Among many works on the Schiff base complexes, recently various researches on the cadmium Schiff base complexes and their applications have been reported.…”