In this work, temperature-responsive poly(N-isopropylacrylamide) (PNIPAM) and the guanylthiourea (GLA) were used to modify chitosan (CS) to prepare a novel PNIPAM/GLA/CS adsorbent for Ag(I) ions. Temperature variations near the lower critical solution temperature (LCST) facilitate the adjustment of functional group distribution within the composite material, thereby influencing its adsorption performance for silver ions. The characteristics of this composite material were confirmed using a variety of techniques, including scanning electron microscopy (SEM), variable-temperature ultraviolet-visible near-infrared spectroscopy, Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Studies on the adsorption of Ag(I) ions by the PNIPAM/GLA/CS adsorbent indicated that the optimal pH for adsorption is 6.0. The adsorption kinetics were best described by the pseudo-second order kinetic model, while the equilibrium adsorption data aligned more closely with the Langmuir adsorption isotherm model, achieving a maximum adsorption capacity of 336.33 mg/g at 40°C. Experimental results demonstrated that higher adsorption amounts were observed above the LCST, while desorption of target ions was more favorable below the LCST. This research provides valuable insights for the design of new structural adsorbents.
In this study, the antityrosinase and antioxidant activities of four guanidine compounds (GCs), including guanylthiourea (GT), guanidine thiocyanate (GTC), phenylguanidine (PG), and phenethyldiguanide (PTDG), were investigated. The results showed that the GCs reduced the monophenolase and diphenolase activities of tyrosinase. The IC 50 values of GT, GTC, PG, and PTDG were 0.27, 3.53, 6.68, and 5.18 mM for monophenolase and 0.23, 3.24, 3.97 and 2.50 mM for diphenolase, respectively. The inhibition of diphenolase activity was reversible for the four GCs. The inhibition types of GT and PTDG were competitive, while those of GTC and PG were mixed. FRAP, ABTS, DPPH, and DNA damage protection assays revealed that only GT possessed significant antioxidant activity. Furthermore, GT was found to decrease the melanin content and expression of TYR, MITF and DCT in both B16F10 cells and zebrafish. Overall, our results indicated that GT can inhibit tyrosinase activity in vitro , which suggests that these GCs are potential candidates for novel small-molecule tyrosinase inhibitors and that GT could have broader application prospects.
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