Conformational Stability of Poly (N-Isopropylacrylamide) Anchored on the Surface of Gold Nanoparticles

Abstract

To verify the temperature sensitive failure of poly (N-isopropylacrylamide) (PNIPAM) anchored on the surface of gold nanoparticles (AuNPs), the UV-Vis spectra with temperature variations of the following aqueous solutions respectively containing AuNPs-PNIPAM, Au-PNIPAM/PNIPAM, PNIPAM, in different media (including salt, ethanol, HCl and cetyltrimethylammoniumbromide (CTAB)), were systematically determined. The results indicated that the UV-Vis spectrum of AuNPs-PNIPAM suspension hardly changed even above the Lower Critical Solution Temperature (LCST) of PNIPAM, but that of Au-PNIPAM/PNIPAM sharply increased only in absorbance intensity. A possible mechanism of the failed temperature sensitivity of PNIPAM anchored on the surface of AuNPs was proposed. Being different from free PNIPAM molecules, a strong interaction exists among PNIPAM molecules anchored on the surface of AuNPs, restraining the change in conformation of PNIPAM. The temperature sensitivity of Au-PNIPAM/PNIPAM originates from the free PNIPAM molecules rather than the anchored PNIPAM one. The changing electrostatic interaction could effectively regulate the aggregation behavior of AuNPs-PNIPAM and enhance its sensitivity to temperature.

Smart Poly(N-Isopropylacrylamide)-Based Microgels Supplemented with Nanomaterials for Catalytic Reduction Reactions—A Review

“…The disadvantage of the catalyst being ineffective at higher temperatures was observed in the case of rigid core@polymeric shell HMGs, which was quite similar to the homogenous HMGs. Han et al [32], Minier et al [49], and Li et al [26] observed a similar trend of the reduction in the catalytic efficacy of HMGs owing to steric hindrance. The synthesis mechanism associated with the fabrication of the rigid core@polymeric shell is presented in Figure 11.…”

“…For instance, the polymerization techniques of reversible-addition chain-fragmentation transfer (RAFT) [24] and selective bond formation techniques [25] have been used alongside FEPol for the development of HMGs. Li et al [26] synthesized Au NPs using citrate reduction methodology and anchored two successive shells of PNIPAM layers (via FEPol) over these NPs by carrying out a polymerization reaction containing the dispersion of Au NPs in the reaction pot.…”

Identification of Proteins Using Supramolecular Gold Nanoparticle‐Dye Sensor Arrays

“…We hypothesized that the interactions between AuNPs and proteins can perturb the local environment of AuNP‐dye complexes, causing conformational changes in AuNPs and hence changing the signals of dyes. To support our hypothesis, we chose COOH−Py and incubated methanol with the complex, providing a model for dye release by protein binding [53,54] . Methanol can interact with AuNPs via hydrophobic interactions and hydrogen bonds, similar to proteins [55] .…”

“…To support our hypothesis, we chose COOHÀ Py and incubated methanol with the complex, providing a model for dye release by protein binding. [53,54] Methanol can interact with AuNPs via hydrophobic interactions and hydrogen bonds, similar to proteins. [55] Ultraviolet-visible spectroscopy (UV-Vis) is an effective method to detect effects of such environmental changes on AuNPs.…”

Aggregation of Gold Nanoparticles in Presence of the Thermoresponsive Cationic Diblock Copolymer PNIPAAM48-b-PAMPTMA6

“…For such a purpose, an interesting type of polymer is the temperature-sensitive poly( N -isopropylacrylamide), or PNIPAAM, because its structural features can be tuned by temperature [ 9 ]. It is well-known that high-molecular-weight PNIPAAM dissolved in water undergoes coil-to-globule transition when the temperature exceeds its lower critical solution temperature, LCST ≈ 32 °C [ 10 ].…”