Figure 6 HR-XRD analysis. The Debye-Scherrer equation (D = 0.89λ/Wcosθ) was employed to estimate the particle diameter from the (111) peak, and the estimated diameter was approximately 16.6 nm. The definition of each term in the equation is as follows: λ is the wavelength of CuKα radiation (0.1541 nm), W is the full-width at half-maximum of the (111) peak, θ is the diffraction angle, and D is the particle diameter. Catalytic activity Selleck HIF inhibitor toward 4-nitrophenol reduction The catalytic activity of green-synthesized AuNPs has been evaluated by other researchers [19–24]. The biological entities used in these studies
were cyclodextrins and plant extracts (a glucan of an edible mushroom (Pleurotus florida), Trigonella foenum-graecum, ayurvedic arishtams, Anacardium occidentale, and Gnidia glauca). The merit of our method over these reports lies in its
energy-saving process, in which no input of external energy is used for the green synthesis of the catechin-AuNPs; in contrast, the other methods used elevated temperatures for the reactions. To evaluate the catalytic activity of the catechin-AuNPs, the reduction reaction of 4-NP to 4-AP in the presence of NaBH4 was studied. When NaBH4 was added to 4-NP, the color of the solution became yellow, which resulted in a peak at 400 nm in the UV-visible spectrum because of the formation of the 4-nitrophenolate anion. The reaction did not proceed any further in the C646 absence of the catechin-AuNP catalyst. Upon the addition of catechin-AuNPs, the appearance of 4-AP was monitored by the emergence of a peak at 300 nm with a concomitant decrease in the intensity of the peak at 400 nm (Figure 7A). The decreased intensity of the peak at 400 nm and the appearance of the peak at 300 nm were quantitatively monitored by UV-visible Methocarbamol spectrophotometry. The approximate time required for the completion of the reaction was 30 min. Figure 7 4-NP reduction by NaBH 4 in the presence of catechin-AuNPs catalyst. (A) UV-visible spectra and (B) a plot of ln(C t /C 0) as a function of time (min). The relationship between ln(C t /C 0) and time (min) revealed a linear correlation (y = −0.091x + 0.071,
r 2 = 0.981), where C 0 and C t are the 4-NP concentration at time 0 and time t, respectively (Figure 7B) [21]. The ratio of absorbance, A t /A 0, could be substituted for the ratio of concentration, C t /C 0 (i.e., C t /C 0 = A t /A 0) because the concentration of 4-NP is proportional to its absorbance [21]. On the basis of these results, we determined that the shell did not affect the catalytic activity of the catechin-AuNPs. Conclusions Catechin, which is a potent antioxidant, has been successfully utilized as a green reducing agent for the synthesis of AuNPs. No external energy was necessary during the 1 h reaction, which was simple, fast, energy-saving, and eco-friendly. Together with spherically shaped AuNPs, anisotropic AuNPs with diverse shapes were also observed.