Nanozymes, as enzyme-mimicking nanomaterials, have emerged as attractive alternatives to natural enzymes due to their high stability, low cost and easy preparation [
1–
5]. Though extensive studies have focused on enhancing the catalytic efficiency of nanozymes, their enantioselective capabilities remain largely underexplored [
6–
8]. Moreover, precise enantioselective control in nanozymes presents a significant challenge due to their predominantly achiral nature [
9–
11].
Among various strategies to construct chiral nanozymes, integrating supramolecular chiral architectures with catalytic centers has been proven to be highly effective [
12–
14]. In this context, polyaniline (PANI)-based supramolecular scaffolds have drawn considerable attention because of their superior chemical stability and versatile supramolecular assembly properties [
15–
18]. The PANI supramolecular chiral scaffolds have been employed in combination with catalytic centers including Fe
3O
4, Au and transition metal ions (
e.g., Cu
2+, Zn
2+) to construct chiral nanozymes capable of enantioselective catalysis of 3,4-dihydroxy-
S/
R-phenylalanine (
S/
R-DOPA) [
19–
21]. Nevertheless, current research on PANI-based supramolecular chiral nanozymes primarily focuses on improving their enantioselective performance. To the best of our knowledge, regulating catalytic efficiency and enantioselectivity through compositional control have not been reported yet, but it is essential for the comprehensive understanding of chirality transfer effects and the origin of enantioselectivity. Among various nanozymes, alloy nanoparticles, such as platinum-nickel nanoparticles (Pt-Ni
x NPs), have garnered significant attention due to their superior catalytic activity, which stems from their small size, high surface area and abundant active sites [
22–
24]. Previous studies have demonstrated that precise compositional tuning of these nanoparticles can effectively modulate their geometric and electronic structures, thereby optimizing their catalytic performance [
25,
26].
Herein, we engineered a series of supramolecular chiral nanozymes, P/M-PANI@Pt-Nix (where x represents the Pt/Ni atomic ratio of Pt-Nix NPs), by integrating supramolecular chiral scaffolds (P/M-PANI) with Pt-Nix NPs. The resulting P-PANI@Pt-Nix nanozymes exhibited remarkable enantioselective catalytic activity toward S-DOPA oxidation, while M-PANI@Pt-Nix nanozymes preferentially catalyzed the oxidation of R-DOPA. Furthermore, systematic adjustment of the Pt/Ni atomic ratio effectively modulated the interface interactions and chiral transfer effects between the P/M-PANI scaffolds and the Pt-Nix NPs, thereby enabling precise control over enantioselectivity. Density functional theory (DFT) calculations further revealed the distinct adsorption behaviors of DOPA and its oxidation products on various Pt-Nix interfaces, providing mechanistic insights into the observed differences in catalytic efficiency of P/M-PANI@Pt-Nix nanozymes. This study, for the first time, demonstrated that tailoring the composition of the catalytic center can simultaneously regulate both catalytic efficiency and enantioselectivity, offering an innovative strategy for the controllable design of supramolecular chiral nanozymes.
In a typical synthesis procedure, equimolar amounts of Pt(Ⅱ) acetylacetonate and Ni(Ⅱ) acetylacetonate were co-reduced in benzyl ether, which functioned as the reaction medium and reducing agent. Oleic acid, oleylamine and tetradecanediol were employed as surface stabilizers. To render the resulting nanoparticles hydrophilic, a ligand exchange process was performed using 3,4-dihydroxyphenylacetic acid. Inductively coupled plasma atomic emission spectrometry (ICP-AES) analysis indicated the atomic ratio of Pt to Ni in the resulting Pt-Ni NPs is ~1:1, consistent with the stoichiometric ratio of the Pt/Ni precursors introduced during the synthesis (Table S1 in Supporting information). In addition, nanoparticles with different Pt/Ni atomic ratios, specifically Pt-Ni0.5 NPs and Pt-Ni2 NPs, were synthesized by adjusting the precursor ratios. ICP-AES analysis further confirmed that the atomic ratios of Pt-Ni0.5 NPs and Pt-Ni2 NPs closely matched the intended molar ratios of the Pt/Ni precursors.
As demonstrated by the transmission electron microscopy (TEM) images, Pt-Ni
0.5 NPs, Pt-Ni NPs and Pt-Ni
2 NPs all exhibited
quasi-spherical morphologies with average diameters of approximately 8 nm (
Figs. 1a-c, Fig. S1 in Supporting information). X-ray diffraction (XRD) patterns revealed that these nanoparticles possess a face-centered cubic (
fcc) crystal structure, characterized by the distinct (111) diffraction peak (Fig. S2 in Supporting information). Furthermore, the (111) diffraction peak position of Pt-Ni
x NPs lies intermediate between pure Pt (39.8°) and pure Ni (44.5°), providing clear evidence for successful alloy formation [
27,
28]. The high-resolution transmission electron microscopy (HRTEM) images of the Pt-Ni NPs clearly revealed lattice fringes with an interplanar spacing of 0.25 nm, which corresponded to the (111) crystal plane of the
fcc structure (
Fig. 1d).
Subsequently, based on previous reports, the polymerization of aniline was carried out using (
S/R)-camphor-10-sulfonic acid (
S/R-CSA) as the chiral inducing agent, leading to the formation of the
P/M-PANI-CSA precursor [
29]. As shown in Figs. S3a and b (Supporting information), the
P-PANI-CSA prepared with
S-CSA exhibited a right-handed twist, while
R-CSA induced the left-handed helical structure. Furthermore, the chiral structure of
P/
M-PANI-CSA was verified by ultraviolet-visible (UV-vis) and circular dichroism (CD) spectroscopy (Fig. S4 in Supporting information), with mirror imaged Cotton effects were observed in the CD spectra. The obtained
P/
M-PANI-CSA were subjected to a stepwise secondary doping process involving ammonia solution and thioglycolic acid, yielding the
P/
M-PANI supramolecular chiral scaffolds. Due to the molecular memory effect, the helical structure of
P/
M-PANI remained well-preserved after CSA removal (Figs. S3c and d in Supporting information). Finally, successful fabrication of
P/
M-PANI@Pt-Ni
x nanocomposites was achieved through the integration of synthesized Pt-Ni
x NPs with the
P/
M-PANI supramolecular chiral scaffolds. TEM and scanning electron microscopy (SEM) images displayed the uniform distribution of Pt-Ni
x NPs on the
P/
M-PANI surface, while the characteristic helical morphology was effectively retained (
Figs. 1e-g, Fig. S5 in Supporting information). In addition, XRD analysis revealed characteristic diffraction peaks corresponding to both
P-PANI and Pt-Ni
x NPs in
P-PANI@Pt-Ni
x (Fig. S6 in Supporting information). High-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) imaging combined with energy-dispersive X-ray spectroscopy (EDS) elemental mapping analysis of C, N, O, S, Ni and Pt in
P-PANI@Pt-Ni further demonstrated the successful integration of Pt-Ni NPs with the
P/
M-PANI scaffolds (
Figs. 1h-n).
To further clarify the chiroptical properties of the nanocomposites, the UV-vis and CD spectra were measured (
Fig. 2a). The UV-vis spectra indicated that
P/M-PANI@Pt-Ni
2,
P/
M-PANI@Pt-Ni and
P/
M-PANI@Pt-Ni
0.5 nanocomposites exhibited significantly enhanced absorption at 330 nm compared to
P/
M-PANI, which can be attributed to the successful integration of the
P/
M-PANI supramolecular chiral scaffolds with Pt-Ni
x NPs. As shown in CD spectra, no signals were observed in the 200-600 nm wavelength range for Pt-Ni
x NPs, indicating their achiral characteristics (Fig. S7a in Supporting information). Moreover, the strong opposite CD peaks at 450 nm were observed for
P-PANI and
M-PANI, confirming their distinct chiral environments. Upon the incorporation of Pt-Ni
x NPs, new peaks at 350 nm appeared of all these
P/
M-PANI@Pt-Ni
x nanocomposites. It is noteworthy that the CD spectra of
P/
M-PANI@Pt-Ni and
P/
M-PANI@Pt-Ni
2 featured a prominent peak at 350 nm alongside a smaller peak at 450 nm. In contrast, the
P/
M-PANI@Pt-Ni
0.5 predominantly exhibited a pronounced peak at 350 nm, with the original 450 nm signal nearly diminished. The CD peak intensities at 350 nm decreased in the order of
P/
M-PANI@Pt-Ni
0.5 >
P/M-PANI@Pt-Ni >
P/
M-PANI@Pt-Ni
2, indicating strongest chiral transfer effect between
P/
M-PANI scaffolds and Pt-Ni
0.5 NPs. Moreover, considering that Pt-Ni
0.5 NPs exhibited a characteristic absorption at 260 nm (Fig. S7b in Supporting information), the appearance of a new CD peak at 260 nm in
P/
M-PANI@Pt-Ni
0.5 suggests successful chiral transfer from the
P/
M-PANI supramolecular scaffolds to Pt-Ni
0.5 NPs. Additionally, high-resolution X-ray photoelectron spectroscopy (XPS) spectra of S 2p was obtained to further reveal the interface interactions. As indicated in
Fig. 2b, the binding energy of S 2p
3/2 (-SH) in
P/
M-PANI@Pt-Ni
x nanocomposites showed a noticeable negative shift compared with sole
P-PANI (164.14 eV), which clearly indicated a strong interface interaction between PANI and Pt-Ni
x NPs. Notably, the most pronounced negative shift was observed for
P-PANI@Pt-Ni
0.5, with the binding energy of S 2p
3/2 (-SH) decreasing to 163.82 eV. Moreover, as revealed in Fig. S8a (Supporting information), the XPS spectra of Pt 4f demonstrated that Pt species on the surface of Pt-Ni
x NPs primarily exist in the metallic Pt(0) state. Meanwhile, the XPS analysis of Ni 2p also revealed the compositional variations among the different Pt-Ni
x NPs (Fig. S8b in Supporting information). Based on above-mentioned results, it is safe to say that a series of
P/
M-PANI@Pt-Ni
x nanocomposites with chiral environment were successfully constructed.
Chiral molecules are widely recognized for their crucial roles in biological systems. A notable example is the differential biological activities of DOPA enantiomers:
S-DOPA is clinically effective in treating Parkinson's disease, whereas its enantiomer
R-DOPA exhibits toxicity in humans [
9]. Thus, the enantioselective catalytic capability of
P/
M-PANI@Pt-Ni
x nanocomposites was evaluated using
S/
R-DOPA as the model substrate. The reaction kinetics were followed by measuring the UV-vis absorption at 475 nm, corresponding to the formation of dopachrome, the distinctive oxidation product of DOPA. As illustrated in Fig. S9 (Supporting information), all
P-PANI@Pt-Ni
x nanozymes exhibited significantly higher catalytic efficiency toward
S-DOPA than
R-DOPA. In contrast, the
M-PANI@Pt-Ni
x nanozymes displayed superior catalytic efficiency for
R-DOPA. To further quantify the catalytic efficiency and enantioselectivity of the synthesized
P/
M-PANI@Pt-Ni
x nanozymes, steady-state kinetic assays were conducted. The typical Michaelis-Menten kinetics, determined by measuring initial reaction rates as a function of
S/
R-DOPA concentrations, are illustrated in
Figs. 3a-f. It is evident that the
P-PANI@Pt-Ni
x preferentially catalyzed
S-DOPA, whereas all
M-PANI@Pt-Ni
x showed the catalytic selectivity toward
R-DOPA.
The enzymatic kinetic parameters, specifically the turnover number (
kcat) and the Michaelis constant (
Km), were derived from the Michaelis-Menten curves and are summarized in Tables S2 and S3 (Supporting information). Meanwhile, the overall catalytic efficiency, expressed as the ratio
kcat/
Km, was calculated and presented in
Fig. 3g. Notably, the catalytic efficiency (
kcat/
Km) of
P/M-PANI@Pt-Ni
x nanozymes exhibited a positive correlation with the Ni content in the surface-loaded Pt-Ni
x NPs, which is consistent with the analysis of
kcat. Among these nanozymes,
P/M-PANI@Pt-Ni
2 exhibited the highest catalytic efficiency, while
P/M-PANI@Pt-Ni
0.5 displayed the lowest. This trend can be primarily attributed to differences in the intrinsic catalytic activity of various Pt-Ni
x NPs. To further evaluate the enantioselective performance of these nanozymes, the select factor, expressed as the ratio of
kcat/
Km toward
S- and
R-DOPA enantiomers (> 1), was calculated.
P-PANI@Pt-Ni
0.5 and
M-PANI@Pt-Ni
0.5 achieved the highest select factors of 2.15 and 2.26 (
Fig. 3h), outperforming most reported chiral nanozymes (Table S4 in Supporting information). In addition, the select factors of
P/
M-PANI@Pt-Ni
x increased in the order of
P/M-PANI@Pt-Ni
2 <
P/
M-PANI@Pt-Ni <
P/
M-PANI@Pt-Ni
0.5, a trend that strongly correlated with the degree of chiral transfer and the strength of interface interactions. The activation energy (
Ea) was determined by linear regression analysis of the logarithmic reaction rate versus the inverse reaction temperature, following the Arrhenius equation (
Fig. 3i, Figs. S10 and S11 in Supporting information). The
Ea for
S/R-DOPA oxidation catalyzed by
P/
M-PANI@Pt-Ni
x nanozymes were consistently lower compared to those for
R/
S-DOPA oxidation, providing additional evidence for the enantioselective catalytic behavior. It is noteworthy that
P/
M-PANI@Pt-Ni
2 exhibited the lowest
Ea for DOPA oxidation among these nanozymes, which is consistent with their highest catalytic efficiency.
As discussed above, the differences in catalytic efficiency among these nanozymes are likely associated with the intrinsic catalytic performance of catalytic centers loaded on the
P/
M-PANI surface. However, direct evidence elucidating the underlying mechanisms responsible for these variations remains limited. To further elucidate the origin of the excellent catalytic efficiency of Pt-Ni
2 NPs, DFT calculations were performed to investigate the oxidation of DOPA across different Pt-Ni
x surfaces. Three (111) slab models were constructed, each including four alloy layers of (ⅰ) Pt-Ni
0.5 (Pt/Ni = 2:1), (ⅱ) Pt-Ni (Pt/Ni = 1:1) and (ⅲ) Pt-Ni
2 (Pt/Ni = 1:2) to represent the catalytic surfaces of Pt-Ni
0.5 NPs, Pt-Ni NPs and Pt-Ni
2 NPs, respectively. Subsequently, the adsorption behaviors of DOPA and dopachrome on these catalytic surfaces were simulated. The adsorption energies of DOPA and dopachrome were calculated and employed as key descriptors to assess the adsorption strength. All possible adsorption configurations are presented in Figs. S12-S17 (Supporting information), with the most stable adsorption configurations summarized in
Figs. 4a-f. Among the three catalytic surfaces, Pt-Ni
2 exhibited the lowest adsorption energies for both DOPA and dopachrome, with values of -1.205 eV and -2.980 eV, respectively. In contrast, Pt-Ni
0.5 showed the highest adsorption energies for DOPA (-1.012 eV) and dopachrome (-1.617 eV). As illustrated in
Fig. 4g, the adsorption energies of DOPA and dopachrome decreased with decreasing Pt/Ni atomic ratio on the catalytic surface. These results provide a clear explanation for the observed trend in catalytic efficiency among these nanozymes:
P/
M-PANI@Pt-Ni
2 >
P/
M-PANI@Pt-Ni >
P/
M-PANI@Pt-Ni
0.5.
Moreover, the distinct enantioselectivity observed in
P/
M-PANI@Pt-Ni
0.5,
P/
M-PANI@Pt-Ni and
P/
M-PANI@Pt-Ni
2 nanozymes can be attributed to the varying degrees of chiral transfer between
P/
M-PANI scaffolds and Pt-Ni
x NPs with different Pt/Ni atom ratios. To gain deeper insights into the origins of the catalytic performance differences observed in
P/
M-PANI@Pt-Ni
x nanozymes, enantioselective adsorption experiments were conducted using
P-PANI@Pt-Ni
x as the representative nanozymes. Following 4h incubation of
P-PANI@Pt-Ni
x nanozymes with the racemic solution of DOPA, the filtrate was subjected to CD and UV-vis measurements. As displayed in Fig. S18 (Supporting information), the CD and UV-vis spectra revealed that
P-PANI@Pt-Ni
0.5 exhibited the weakest adsorption toward DOPA, yet displayed the highest enantioselectivity. In contrast,
P-PANI@Pt-Ni
2 demonstrated the strongest DOPA adsorption capacity but the lowest enantioselectivity. As illustrated in
Fig. 4h, this enantioselective adsorption behavior resulting in reduced catalytic efficiency but enhanced enantioselective performance for
P-PANI@Pt-Ni
0.5, while
P-PANI@Pt-Ni
2 exhibited superior catalytic efficiency and diminished enantioselectivity.
In conclusion, this study successfully developed a series of supramolecular chiral nanozymes, P/M-P@Pt-Nix, that integrate P/M-PANI supramolecular chiral scaffolds with Pt-Nix NPs. These nanozymes demonstrated significant enantioselectivity in the catalytic oxidation of S/R-DOPA. Moreover, the interface interaction and the chiral transfer effects were effectively modulated by tuning the composition of Pt-Nix NPs, enabling precise control over the enantioselectivity of the nanozymes. In addition, DFT calculations provided crucial insights into the mechanistic origins of the observed variations in catalytic efficiency among different nanozymes. This study not only established an innovative approach for the systematic design of chiral nanozymes but also highlighted the pivotal role of compositional tuning in optimizing catalytic performance. The findings offered essential guidelines for fabricating advanced supramolecular chiral nanozymes with tailored properties, demonstrating significant potential for applications in biocatalysis.
PDF
Full
59
34
关闭全屏
No. 86 Xueyuan South Road, Haidian District, Beijing
010-62662699(Operation and Technical Support)
qkjq@cast.org.cn
