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sitivity limit their use for high-throughput analysis of chi- ... molecules can precisely self-assemble to form high geo- ... In contrast, Au(III) rea...
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Self-Assembled Chiral Gold Supramolecules with Efficient Laser Absorption for Enantiospecific Recognition of Carnitine Yu-Ting Tseng, Hsiang-Yu Chang, Scott G. Harroun, Chien-Wei Wu, Shih-Chun Wei, Zhiqin Yuan, Hung-Lung Chou, Ching-Hsiang Chen, Chih-Ching Huang, and Huan-Tsung Chang Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.8b00490 • Publication Date (Web): 22 May 2018 Downloaded from http://pubs.acs.org on May 22, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

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Analytical Chemistry

sitivity limit their use for high-throughput analysis of chiral molecules at low concentrations. In recent years, many nanomaterial-based optical and electrochemical approaches have been developed for sensing of chiral molecules.7−10 Through specific binding of the surface recognition elements with the chiral molecules, the nanomaterials either aggregates or deaggregates, leading to changes in their optical or electrochemical properties and thus selective detection of the analytes. For example, chiral cysteine-capped semiconductor (CdSe/ZnS) quantum dots (QDs) have been used for selective quantitation of L/D-carnitine (β-hydroxy-γ-Ntrimethylaminobutyric acid) through analyte induced fluorescence quenching.11 Similarly, CdSe/ZnS QDs modified with methyl ester N-acetyl-L-cysteine allow sensing of chiral drugs, namely, ketoprofen and flurbiprofen.12 LTartaric acid-modified gold nanoparticles (Au NPs) can selectively detect L-mandelic acid by monitoring the changes in their color and surface plasmon absorption as a result of aggregation.13 Glassy carbon electrodes modified with L-tryptophan-functionalized graphene supported with platinum nanoparticles show stronger enantiospecificity toward D-3,4-dihydroxyphenylalanine (DDOPA) than toward L-DOPA through differential pulse voltammetry measurements.14 Recently, satellite Au NPs networks modified with L-cysteine have been used to detect L/D-carnitine by monitoring the tunneling current.15 These nanoparticle-based sensing methods exhibit simple and fast optical or electrochemical responses through specific recognition of the functional nanoparticles toward the analytes.11−15 However, most of them suffer from matrix interferences when applied to the analysis of real samples, as nonspecific binding may cause false positive signal responses. In addition, changes in the structure of the surface recognition elements may occur, leading to loss in their specific recognition. Moreover, the targeted enantiomers mostly induce slight differences in the optical or electrochemical changes (responses) of the nanoparticles. Thus, development of highly specific, sensitive and high-throughput screening assays for detection of chiral molecules in real samples remains an attractive challenge. Functional biopolymers in nature and artificial supramolecules can precisely self-assemble to form high geometric structures, including nucleic acids, proteins, carbohydrates and lipids.16,17 The constructions of programmed artificial supramolecular architectures are highly dependent on the sequences, positions, and interactions of the building blocks in their self-assemblies.18 Controllable aggregation of gold(I) compounds (complexes) is an intriguing area due to their self-assembled aggregates

with particular morphologies that can be monitored via the change in their electronic, optical, and electrochemical properties.19 Synergistic aurophilic and electrostatic interactions, as well as hydrogen bonding of gold(I) compounds, can lead to the formation of fascinating supramolecular architectures with intriguing electronic, optical, and catalytic properties.19 The most interesting property of the polymers and supramolecules (self-assembled polymers) fabricated from gold(I)-thiolate complexes is their particular photoluminescence (PL) properties.20 The inter- and/or intramolecular Au(I)…Au(I) interactions coupled with ligand-ligand interactions in the gold(I)thiolate polymer chains could significantly alter goldcentered transitions and ligand-to-gold (S→Au) charge transfer and thus to enhance their transition probability, to reduce their energy gaps, and to minimize PL quenching.21,22 Although the intermediation of aurophilic Au…Au interactions in gold(I) compounds have been employed in many chemo-sensing applications by host-guest recognitions,23 chiral gold(I)-thiolate-based supramolecules are rarely prepared,24 especially for sensor development. Here, we demonstrated the structural and optical properties of Au(I)-based supramolecules that are highly dependent on the chirality of the protecting thiolated ligands. We have prepared self-assembled Cys−Au(I) supramolecules through a simple reaction of tetrachloroaurate(III) with cysteine (Cys) in aqueous solution. Gold ions (Au(III)) reacted with D-Cys and L-Cys to selfassemble to form −[D-Cys−Au(I)]n− and −[L-Cys−Au(I)]n− supramolecules, respectively in solution with pH values ≤ 7 (Scheme 1A and 1B). In contrast, Au(III) reacted with a mixture of the same concentration of D-Cys and L-Cys to form spindle-shaped −[D/L-Cys−Au(I)]n− supramolecules (Scheme 1C). After reaction with NaBH4, photoluminescent gold nanoclusters (Au NCs) were formed and embedded in the −[D-Cys−Au(I)]n− or −[L-Cys−Au(I)]n− supramolecules. In other words, only −[D-Cys−Au(I)]n− or −[L-Cys−Au(I)]n− supramolecules containing Au NCs (Au NCs/−[Cys−Au(I)]n−) exhibit distinctive PL properties. In our previous study, we demonstrated that the structures and optical properties of Au(I)-thiolate supramolecules were highly dependent on the types of thiol ligands and the concentration ratio of thiol ligands to Au(III) used in the synthesis.25 Here, we focus on the investigation of the effect of ligand-ligand interactions of chiral cysteine on the structures of Au NCs/−[Cys−Au(I)]n−, as well as their optical properties, by conducting a series of spectroscopic and microscopic characterizations and density functional theory (DFT) simulations.

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Scheme 1. Schematic representation of the synthesis of (A) Au NCs/−[D-Cys−Au(I)]n−, (B) Au NCs/−[L-Cys−Au(I)]n− supramolecules, and (C) −[D/L-Cys−Au(I)]n− supramolecules and their use in the analysis of chiral carnitine via LDI-MS. Atoms are shown in different colors: yellow, Au; lilac, S; blue, N; red, O; gray, C; white, H.

We also demonstrated that the chiral Au NCs/−[DCys−Au(I)]n− and Au NCs/−[L-Cys−Au(I)]n− supramolecules exhibit high enantiospecificity toward Lcarnitine and D-carnitine, respectively. Carnitine exists in two isomers, D-carnitine and L-carnitine, due to the asymmetric secondary carbon. L-Carnitine has some indispensable roles in the intermediary metabolism, such as transporting long-chain fatty acids through the mitochondrial inner membrane for β-oxidation, modulation of the acyl-CoA/CoA ratio, and reducing the intracellular accumulation of toxic metabolites under ischemic conditions, while conversely, D-carnitine is toxic because it inhibits the function of L-carnitine.26 Furthermore, taking L-carnitine supplements is needed for a patient with a genetic disorder who can not 26 endogenously synthesizes enough L-carnitine. Therefore, it is crucial to distinguish L-carnitine and Dcarnitine in biological and medicinal studies.27 Our asprepared Au NCs/−[D-Cys−Au(I)]n− supramolecules acted as a substrate for enantiospecific enriching of L-carnitine to facilitate surface-assisted laser desorption/ionization mass spectrometry (LDI-MS) analysis of L-carnitine. The Au NCs/−[D-Cys−Au(I)]n− coupled with the LDI-MS detection system allows quantitation of L-carnitine in the micromolar regime in supplements. EXPERIMENTAL METHODS Materials. D-carnitine, L-carnitine, sodium borohydride (NaBH4), sodium phosphate dibasic, sodium phosphate monobasic dihydrate, nitric acid (HNO3), sodium hydroxide (NaOH), ammonium hydroxide, and acetic acid were purchased from Sigma-Aldrich (St. Louis, MO, USA). Hydrogen tetrachloroaurate(III) trihydrate (HAuCl4·3H2O),

L-cysteine, and D-cysteine were purchased from Acros (Geel, Belgium). Ultrapure water (18.2 MΩ⋅cm) from a Milli-Q ultrapure water system (Millipore, Billerica, MA, USA) was used throughout for the experiments. All dietary supplements were purchased from a local health food store (Taipei, Taiwan).

Synthesis of Au NCs/− −[Cys− −Au(I)]n− Supramolecules. Cys (25 mM) and HAuCl4 (50 mM) solutions were prepared and adjusted using HNO3 and NaOH solutions, respectively, to the required pH values (3−9). For the synthesis of Au NCs/−[Cys−Au(I)]n− supramolecules, ultrapure water (155 μL), sodium phosphate buffer solution (100 µL, 125.5 mM; pH 3−9), Cys (500 μL, 25 mM), and HAuCl4 (500 μL, 3.75 mM) were added sequentially into a 7 mL screw-top vial. The mixture solution was shaken through a strong vortex for 1 h, followed by rapid addition of a freshly prepared solution of NaBH4 (1245 μL, 1.5 mM) in 100 mM sodium phosphate solution (pH 8). The mixture was then left to react in the dark at room temperature for 4 h to form the photoluminescent Au NCs/−[Cys−Au(I)]n− supramolecules. Characterization of Au NCs/− −[Cys− −Au(I)]n− Supramolecules. UV-Vis absorption and PL spectra of the −[Cys−Au(I)]n− supramolecules and Au NCs/−[Cys−Au(I)]n− supramolecules were recorded using a Cintra 10e double-beam UV–Vis spectrophotometer (GBC, Victoria, Australia) and a Cary Eclipse PL spectrophotometer (Varian, CA, USA), respectively. We conducted optical characterizations of the 10-fold dilution of −[Cys−Au(I)]n− supramolecules and Au NCs/−[Cys−Au(I)]n− supramolecules in sodium phosphate buffer (50 mM, pH = 8), and all the supramolecules are well-suspended in solution during the measurements.

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Figure 1. TEM images of the products from the reactions of HAuCl4 (0.7 mM) with (A) L-Cys (5.0 mM), (B) D-Cys (5.0 mM), and (C) the mixture of L-Cys (2.5 mM) and D-Cys (2.5 mM) for 1 h in sodium phosphate solutions (10 mM) at pH values of (a) 3, (b) 5, (c) 7, and (d) 9. (D) Optimized complex structures of (a) −[D-Cys−Au(I)−D-Cys−Au(I)]2−/−[D-Cys−Au(I)−DCys−Au(I)]2− and (b) −[D-Cys−Au(I)−L-Cys−Au(I)]2−/−[D-Cys−Au(I)−L-Cys−Au(I)]2−.

The light scattering from the supramolecules did not significantly affect the optical spectroscopy measurements due to the low concentration of the supramolecules (10folded diluted) and intrinsic weak scattering intensity from polymer-based aggregates (supramolecules). Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) images were recorded using FEI TecnaiG2-F20 TEM (Philips/FEI, Hillsboro, Oregon, USA); each sample was deposited onto a TEM grid coated with a thin layer of carbon. The PL lifetimes of the Au NCs/−[Cys−Au(I)]n− supramolecules were recorded using a F900 Spectrometer system (Edinburgh Instruments, Livingston, England) and 450 W ozone free xenon arc lamp as the light source. Detection of Carnitine Through Au NCs/− −[Cys− −Au(I)]n− Supramolecules Coupled with LDI-MS. D-carnitine or L-carnitine (0–10 μM) was preincubated at room temperature with 10-fold diluted Au NCs/−[Cys−Au(I)]n− supramolecules (Au NCs/−[DCys−Au(I)]n−, Au NCs/−[L-Cys−Au(I)]n− or −[D/LCys−Au(I)]n− supramolecules) in 10 mM ammonium acetate buffer (pH 3.0) solution for 1 h. After incubation and centrifugation (RCF 3000 g; 10 min) to remove unbound carnitine, the pellets (1.0 µL) and 0.1 % formic acid (1.0 µL) were dipped and mixed onto a 384-well matrixassisted LDI (MALDI) plate prior to LDI-MS measurement. MS experiments were performed in the reflectron positive-ion mode using an Autoflex speed MALDI timeof-flight (TOF)/TOF mass spectrometer (Bruker Daltonics, Bremen, Germany). The samples were irradiated with a SmartBeam laser (Nd:YAG, 355 nm, pulse width 6 ns,

pulse duration 200 ns) at 100 Hz. Ions produced by laser desorption were stabilized energetically during a delayed extraction period of 30 ns and then accelerated through the TOF chamber prior to entering the mass analyzer. The available accelerating voltages ranged from +20 to −20 kV. The instrument was calibrated with Au clusters using their theoretical mass values ([Aun]+; n = 1−3). A total of 1000 pulsed laser shots were applied to accumulate signals from 10 MALDI target positions under a laser power density of 5.0 × 104 W cm−2. See the Supporting Information for the details on the extended X-ray absorption fine structure (EXAFS) and Xray absorption near edge structure (XANES) analysis, DFT calculations, and quantitation of L-carnitine in supplements by Au NCs/−[D-Cys−Au(I)]n−/LDI-MS and LC-MS. RESULTS AND DISCUSSION Self-Assembly of Chiral −[Cys− −Au(I)]n− Supramolecules. We prepared −[Cys−Au(I)]n− supramolecules through a simple reaction of HAuCl4 with D-Cys, L-Cys or D/L-Cys at various pH values (3−7). Cys is a mild reducing agent for the reduction of Au(III) ions to Au(I) ions, and subsequently complexes with Au(I) to form polymeric structures of −[Cys−Au(I)]n−.25 The −[Cys−Au(I)]n− polymers further self-assemble into supramolecular structures through inter- and intra-polymer chain interactions over the pH range of 3−7 (Figure 1 and Figure S1, Supporting Information). The Au(I)…Au(I) bond is estimated to have a bond energy around 4−10 kcal mol−1, which is comparable to a standard hydrogen bond.28 The −[D-Cys−Au(I)]n−

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or −[L-Cys−Au(I)]n− polymer aggregate into irregularly shaped supramolecules that are larger than 500 nm because of the inter-chain cooperative Au(I)…Au(I) aurophilic interactions and hydrogen bonding, as well as zwitterionic interactions from cysteine ligands.25,29−32 Therefore, aggregated (self-assembled) −[Cys−Au(I)]n− polymers could not be considered as pure polymers, and that it is denoted as supramolecules in this study. The −[DCys−Au(I)]n− and −[L-Cys−Au(I)]n− supramolecules are well dispersed in the solution. However, the degree of aggregation and molecular weight of such large-sized supramolecules are difficult to be determined. The strongly electrostatic repulsion of the Cys−Au(I) complex by their highly negative charges at pH 9 hinders the formation of −[Cys−Au(I)]n− polymers or aggregated supramolecules.25 The as-formed −[Cys−Au(I)]n− supramolecules at pH 3−7 exhibit a distinctive absorption band at 300−400 nm that is attributed to ligand-to-metal charge transfer (LMCT; S→Au) coupled with a ligand-tometal–metal charge transfer (LMMCT; S→Au…Au) from the densely stacked polynuclear Au(I) chains (Figure 2c).20−23,33,34 The much stronger circular dichroism (CD) signals of the −[D-Cys−Au(I)]n− or −[L-Cys−Au(I)]n− supramolecules synthesized under pH 3−7 conditions reveal the formation of a helically chiral structure.24,25,35−37 Free D-Cys or L-Cys shows a weak CD band at 210 nm; both their position and profile are similar to those of most

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other α-amino acids.38 The −[L-Cys−Au(I)]n− and −[DCys−Au(I)]n− supramolecules exhibit a strong positive and negative CD band at ~350 nm, respectively, along with a broad band at a shorter wavelength. These CD bands are related to the LMCT and/or LMMCT transition of the polynuclear Au(I)-thiolate.33,34,39 The sulfur atoms are nearly sp3 hybridized, and have four different substituents in a tetrahedral coordination geometry in the supramolecules to render them as stereogenic centers. The strong chiroptical characteristics of the −[D-Cys−Au(I)]n− and −[L-Cys−Au(I)]n− supramolecules is mainly due to the synergetic interplay of the electrostatic and hydrogen bonding interactions among the −SR side chains and the Au(I)…Au(I) aurophilic bonds in the Cys−Au(I) polymeric backbone.24,40−42 In contrast to the irregularly shaped −[D-Cys−Au(I)]n− and −[L-Cys−Au(I)]n− supramolecules (Figure 1A and 1B), the −[D/L-Cys−Au(I)]n− self-assembles to form spindleshaped supramolecular structures (Figure 1C). In addition, the −[D/L-Cys−Au(I)]n− supramolecules exhibit relatively featureless absorption in the near-ultraviolet region, probably due to weak aurophilic Au(I)…Au(I) interaction that diminishes LMMCT transition. The DFT simulation of the interchain −[D-Cys−Au(I)−DCys−Au(I)]2−/−[D-Cys−Au(I)−D-Cys−Au(I)]2− and −[DCys−Au(I)−L-Cys−Au(I)]2−/−[D-Cys−Au(I)−L-Cys−Au(I)]2− interactions indicates the former has a stronger interac-

Figure 2. (a, b) CD spectra of (a) free Cys solutions and (b) their products from the reactions with HAuCl4 (0.7 mM) for 1 h. (c) UV–Vis absorption spectra of the products from the reactions of Cys and HAuCl4 (0.7 mM) for 1 h. (A) L-Cys (5.0 mM), (B) D-Cys (5.0 mM), and (C) L-Cys (2.5 mM) and D-Cys (2.5 mM) in sodium phosphate buffer solutions at (i) pH 3, (ii) pH 5, (iii) pH 7, and (iv) pH 9.

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tion energy (E(int); −1.421 vs. −1.274 eV) (Figure 1D). Their interaction energy difference of 0.137 eV (3.16 kcal mol−1) is close to that of hydrogen bonding of N−H···O=C (~5 kcal mol−1).43 The average aurophilic Au(I)−Au(I) bond length calculated by DFT simulation is 3.16 Å, which is consistent with most reports of polynuclear Au(I)-thiolate complexes (3.00−3.30 Å) and our EXAFS results.44−46 The bond lengths of N−H···O=C (2.21−2.26 Å) obtained from the simulation results of −[D-Cys−Au(I)−DCys−Au(I)]2−/−[D-Cys−Au(I)−D-Cys−Au(I)]2− and −[DCys−Au(I)−L-Cys−Au(I)]2−/−[D-Cys−Au(I)−L-Cys−Au(I)]2− are also consistent with that of supramolecular aggregates of Au(I) containing primary amide and carboxylic acid groups (2.10−2.30 Å).24,44,47,48 The stronger intensity of the N−H (1677 cm−1) and O=C (1566 cm−1) bands in the Fourier-transform infrared spec troscopy (FTIR) spectra of −[DCys−Au(I)]n− supramolecules relative to that of −[D/LCys−Au(I)]n− supramolecules further confirm more selfcomplementary hydrogen bonds formed in the −[DCys−Au(I)]n− supramolecules (Figure S2, Supporting Information).15 Furthermore, the Au L3-edge XANES spectra and Fourier transform (FT) EXAFS curves of −[DCys−Au(I)]n− or −[D/L-Cys−Au(I)]n− supramolecules show no obvious difference, revealing that the local structure of Au(I) in these supramolecules is very similar (Figure S3

and S4, Supporting Information). The broad distribution of Au−Au/Au(I) −Au(I) bonds (interatomic distance (R) 2.8−3.3 Å) shown in the FT-EXAFS spectra (Figure S4) imply that complicated oxidation states of Au and aurophilic Au … Au bonds are present in the supramolecules.49 Overall, our results indicate that hydrogen bonding plays a crucial role in determining the structure of chiral −[Cys−Au(I)]n− supramolecules. The stronger hydrogen bonding interaction between the polymer chains of the −[D-Cys−Au(I)]n− or −[L-Cys−Au(I)]n− results in formation of larger supramolecules relative to −[D/LCys−Au(I)]n− supramolecules. Photoluminescent Au NCs/− −[Cys− −Au(I)]n− Supramolecules. Photoluminescent Au NCs/−[Cys−Au(I)]n− were synthesized by the NaBH4 (0.75 mM)-mediated reduction of −[D-Cys−Au(I)]n− or −[L-Cys−Au(I)]n− supramolecules (Figure 3 and Figure S5, Supporting Information). The absorption and PL spectra of Au NCs/−[DCys−Au(I)]n− and Au NCs/−[L-Cys−Au(I)]n− exhibit no statistically significant difference in terms of their absorbance and PL intensity (P>0.05, n = 5). HRTEM images show that the as-formed Au NCs are embedded in the supramolecules have a lattice constant (2.35 Å) corresponding to the d-spacing of the (111) crystal plane of a fcc structure (Insets in Figure S5A and S5B). NaBH4 reduced

Figure 3. (a) UV–Vis absorption spectra, (b) excitation and emission spectra, and (c) CD spectra of (A) −[L-Cys−Au(I)]n−, (B) −[D-Cys−Au(I)]n− and (C) −[D/L-Cys−Au(I)]n− supramolecules prepared from the reactions of HAuCl4 and Cys in sodium phosphate buffer at pH values of (i) pH 3, (ii) pH 5, (iii) pH 7, and (iv) pH 9, and after reaction with NaBH4 (0.75 mM) for 1 h. Inset to (b): photograph of the PL of the corresponding nanocomposite and/or polymer solutions upon excitation under a hand-held UV lamp (365 nm). The emission wavelength was set at 630 nm in (b) for collection of the excitation spectra. The PL intensities (IPL) excited at 365 nm are plotted in arbitrary units (a. u.). Other conditions are the same as those described in Fig. 2.

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the Au(I) ions in the −[D-Cys−Au(I)]n− or −[LCys−Au(I)]n− supramolecules to form the Au(0)−Cys intermediates, and subsequently self-aggregated to form Au(0) core with a staple-like Au(I)–thiolate complex shell.50−52 The highly dense and rigid Cys−Au(I) complexes on the surface of the Au(0) core are the main contributors to the strong optical absorption and PL of the as-formed Au NCs/−[D-Cys−Au(I)]n− and Au NCs/−[L-Cys−Au(I)]n− supramolecules (Figure 3A and 3B (a, b)).50−56 These Au NCs/−[D-Cys−Au(I)]n− and Au NCs/−[L-Cys−Au(I)]n− supramolecules have a red emission (630 nm), large Stokes shift (>250 nm), and long PL lifetime (τavg> 500 ns; Figure S6, Supporting Information), supporting that the PL originates from the triplet metal centered −[Cys−Au(I)]n− shell on Au NCs. The LMMCT relative PL has been observed in number of polymeric gold-thiolate based complexes as well as in small sized core-shell Au NCs because the aurophilic coupled with ligand-ligand interactions confine the adjacent Au−Au distances are less than 3.6 Å.22,50,53−54,56 After the NaBH4-mediated the formation of Au NCs embedded in the −[Cys−Au(I)]n− supramolecules, compact −[Cys−Au(I)]n− motifs were capped on the Au core to form an interlocked shell. As a result, a densely polymeric −[Cys−Au(I)]n− ligand shell strongly stapled on the Au core can minimize the collision-induced PL quenching and restrain intramolecular vibration- and rotation-induced internal nonradiative relaxation pathways.53,56−58 The profiles of CD spectra of the Au NCs/−[DCys−Au(I)]n− and Au NCs/−[L-Cys−Au(I)]n− supramolecules (Figure 3c) are very different from that of −[DCys−Au(I)]n− and −[L-Cys−Au(I)]n− supramolecules (Figure 2b), further supporting that the interlocked polynuclear Au(I)-thiolate motifs capped on the Au core play a crucial role in their optical properties. Chiral nanostructures with CPL have attracted increasing attention in recent years for their promising applications in asymmetric photochemical synthesis, chiral biosignatures, 3D optical displays, and chiral photoelectric devices.59−61 Recently, some reports have demonstrated that semiconductor CdS and CdSe quantum dots (QDs), Ag nanoclusters (NCs), and perovskite CsPbBr3 nanocrystals capped with chiral small ligands or protein show chiral crystal structures and thus posse CPL activities.62−65 We therefore performed CPL spectroscopy to study the CPL activities of the as-prepared chiral supramolecules. Figure S7 displays that our photoluminescent Au NCs/−[D-Cys−Au(I)]n− and Au NCs/−[L-Cys−Au(I)]n− supramolecules did not exhibit CPL characteristics. Although chiral Au(I)–D-Cys or Au(I)–L-Cys staples on the Au NCs lead the supramolecules to show strong CD activities (Figure 3A(c) and 3B(c)), the achiral core of Au NCs with a chiral surface structure did not possess CPL emission.66 The CPL result further reveals that the optical activity of Au NCs/−[Cys−Au(I)]n− supramolecules originates not from the Au core but from the surface shell containing chiral cysteine capping molecules. The quantum yield (QY) of these Au NCs/−[Cys−Au(I)]n− photoluminescent supramolecules are ca. 10%, as determined by comparison with the QY of

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quinine (QY: 53%; in 0.1 M H2SO4). Although the absorbance of Au NCs/−[Cys−Au(I)]n− supramolecules (Figure 3A and 3B (a)) is only ca. 2.5-fold higher than that of −[Cys−Au(I)]n− supramolecules (Figure 2A and 2B (c)), the photoluminescent QY of Au NCs/−[Cys−Au(I)]n− are much higher (10% vs. 0.2%). This substantially higher photoluminescent QY of Au NCs/−[Cys−Au(I)]n− supramolecules compared to those of most other previously reported polynuclear Au(I) complexes, Au(I)-thiolate polymers, and supramolecules in water.20,41 Although the Au−thiolate NCs could be simply bottom-up prepared from the reaction of NaBH4-mediated reduction of Au(I)−thiolate complexes in water solution, the QY of the resulting Au−thiolate NCs with PL from blue to near-infrared region rarely exceeds 5%.68 Recently, some studies have revealed the charge, density, and rigidity of Au(I)–thiolate shell play a crucial role in determining the QY of Au−thiolate NCs. Those Au−thiolate NCs having highly dense thiolated ligands and QY>10% mostly are emitted at 600−700 nm,22,50,53−55,57,58 consisting with our Au NCs/−[Cys−Au(I)]n− supramolecules (630 nm). Compared to that employed organic solvent, mixed ligands, ligand exchange, host−guest recognition, ultrasound- or light irradiation-treatment to obtain dense thiolated ligands on Au NCs for boosting the QY of Au NCs,22,50,53−55,57,58 our one-pot synthesis of highly photoluminescent Au NCs/−[Cys−Au(I)]n− supramolecules is relatively simple and straightforward. In addition, good batch-to-batch reproducibility (relative standard deviations (RSD)