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Nuclear and Electron Magnetic Resonance Spectroscopies of Atomically Precise Gold Nanoclusters
摘要： Atomically precise gold nanoclusters display properties that are unseen in larger nanoparticles. When the number of gold atoms is sufficiently small, the clusters exhibit molecular properties. Their study requires extensive use of classic molecular physical chemistry and, thus, methods such as theory and vibrational spectroscopies, electrochemistry, density functional molecular dynamics calculations, and of course nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopies. NMR and EPR studies have been mostly carried out on the benchmark, stable molecules Au25(SR)18, Au38(SR)24, Au102(SR)44, and Au144(SR)60 (where SR = thiolate). In this Account, we showcase examples primarily taken from our previous and ongoing NMR and EPR studies, which we hope will trigger further interest in the use of these sensitive, though often underutilized, techniques. Indeed, 1D and 2D NMR spectra of pure, atomically precise clusters can be very detailed and informative. Molecular clusters are molecules and, thus, have discrete energy levels and undergo stepwise oxidation or reduction. The effect of the charge state on the chemical shifts and line shapes is a function of the ligand type (ligands differ due to specific bonds with different Au atom types) and the position of the chemical group along the ligand backbone: for groups near the Au core, they can be very dramatic. Ligand-protected gold clusters are hard?soft molecules where a hard metal core is surrounded by a dynamic molecular layer. The latter provides a nanoenvironment that interfaces the cluster core with the surrounding environment and can be permeated by molecules and ions. NMR spectroscopy is especially useful to assess its structure. For example, the data show that whereas long alkanethiolates form bundles, shorter chains exhibit more conformational freedom and are quite folded. NMR spectroscopy allows studying diastereotopic effects and provides information on possible hydrogen bonds of ligands with sulfur or surface gold atoms. EPR spectroscopy is a very precise technique to check and characterize the magnetic state of gold clusters or clusters doped with foreign-metal atoms. Electron nuclear double resonance (ENDOR) provides a powerful tool to assess the interaction of an unpaired electron with nuclei, as we showed for 197Au and 1H. It can be used as a sensitive probe of the spin-density distribution in nanoclusters: for example, it showed that the singly occupied molecular orbital may span outside the Au core by nearly 6 ?. Solid-state EPR spectroscopy has provided compelling evidence that the specific ligands and the crystallinity degree are very important factors in determining the interactions between clusters in the solid state. Depending on the condition, paramagnetic, superparamagnetic, ferromagnetic, or antiferromagnetic behavior can be observed. Time-resolved EPR was successfully tested to determine the efficiency of singlet-oxygen generation via sensitization of Au25 clusters. This Account thus demonstrates some of the remarkable insights that can be gained into the properties of atomically precise clusters through detailed NMR and EPR studies.
关键词： EPR,gold nanoclusters,molecular properties,atomically precise,NMR
更新于2025-09-09 09:28:46
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DNA-Stabilized Silver Nanoclusters for Label-Free Fluorescence Imaging of Cell Surface Glycans and Fluorescence Guided Photothermal Therapy
摘要： A multifunctional nanoplatform that enables the integration of biological detection, imaging diagnosis, and synergistic therapy into a single nanostructure holds great promise for nanoscience and nanomedicine. Herein, a novel theranostic platform was presented for label-free imaging of cell surface glycans based on DNA/silver nanoclusters (AgNCs) via hybridization chain reaction (HCR) and fluorescence guided photothermal therapy (PTT). In this strategy, a dibenzocyclooctyne (DBCO)-functionalized DNA and two hairpin structures of DNA/AgNCs probes were involved. Following metabolic glycan labeling, the binding of DBCO-functionalized DNA to cell surface initiated HCR, and then cell surface glycans were specifically labeled by DNA/AgNCs fluorescent probes. Furthermore, this signal amplification strategy was adopted in quantitative analysis, and the detection limit could be achieved as low as 20 cells in 200 μL binding buffer. Moreover, the remarkable photothermal properties of DNA/AgNCs via HCR, led to efficient killing of cancer cell and inhibited the tumor growth under imaging guide. In this strategy, DNA/AgNCs were utilized to detect the cellular glycans, which aided in overcoming the high cost and instability of fluorescent dyes. Simultaneously, the HCR process avoided the introduction of excessive azido-sugars under the precondition of ensuring apparent fluorescence. These results indicated that the developed nanoplatform has great potential for specific cell surface glycans imaging and fluorescence guided PTT.
关键词： DNA-stabilized silver nanoclusters,fluorescence guided photothermal therapy,hybridization chain reaction,cell surface glycans,label-free fluorescence imaging
更新于2025-09-09 09:28:46
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Sensitive X-ray Absorption Near Edge Structure Analysis on the Bonding Properties of Au <sub/>30</sub> (SR) <sub/>18</sub> Nanoclusters
摘要： Au nanoclusters (NCs) with organothiolate protecting ligands are a field of great interest and X-ray absorption spectroscopy is a useful tool for the structure and property studies of these Au NCs. However, the Au NCs normally show broad and low-intensity features in the gold X-ray absorption near-edge structure (XANES) region, lowering the sensitivity of the technique and making it difficult to use for the analysis of Au NCs. In this work we report a sensitive gold L3-edge XANES study on the bonding properties of the newly discovered Au30(SR)18 NCs utilizing a combined approach of the first derivative XANES spectra and quantum simulations. First derivative XANES spectra are compared with the well-studied Au25(SR)18 with the aim of determining the unique features of Au30(SR)18. It is found that the early XANES region of the Au NCs is significantly influenced by the gold?gold bonding environment in the surface sites, as the varying surface Au?Au bond lengths in Au25(SR)18 and Au30(SR)18 result in pronounced difference in the first derivative XANES. These findings can be consistently explained using site-selective quantum simulations of the XANES spectra based on the Au NC structural models. The XANES method presented in this work offers a useful tool for the sensitive analysis on structure and bonding properties of Au NCs.
关键词： Au nanoclusters,bonding properties,quantum simulations,XANES,X-ray absorption spectroscopy
更新于2025-09-09 09:28:46
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Surface Dynamics and Ligand–Core Interactions of Quantum Sized Photoluminescent Gold Nanoclusters
摘要： Quantum-sized metallic clusters protected by biological ligands represent a new class of luminescent materials; yet the understanding of structural information and photoluminescence origin of these ultrasmall clusters remains a challenge. Herein we systematically study the surface ligand dynamics and ligand?metal core interactions of peptide-protected gold nanoclusters (AuNCs) with combined experimental characterizations and theoretical molecular simulations. We show that the peptide sequence plays an important role in determining the surface peptide structuring, interfacial water dynamics and ligand?Au core interaction, which can be tailored by controlling peptide acetylation, constituent amino acid electron donating/withdrawing capacity, aromaticity/hydrophobicity and by adjusting environmental pH. Specifically, emission enhancement is achieved through increasing the electron density of surface ligands in proximity to the Au core, discouraging photoinduced quenching, and by reducing the amount of surface-bound water molecules. These findings provide key design principles for understanding the surface dynamics of peptide-protected nanoparticles and maximizing the photoluminescence of metallic clusters through the exploitation of biologically relevant ligand properties.
关键词： gold nanoclusters,photoluminescence,surface dynamics,ligand-core interactions,peptide protection
更新于2025-09-09 09:28:46
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Determination of the activity of alkaline phosphatase based on?aggregation-induced quenching of the fluorescence of?copper nanoclusters
摘要： A rapid method is described for synthesis of copper nanoclusters (CuNCs) by utilizing L-histidine as the stabilizer and ascorbic acid (AA) as the reductant. The CuNCs display blue-green fluorescence with excitation/emission peaks at 390/485 nm. A sensitive fluorometric assay was worked out for determination of alkaline phosphatase (ALP) activity. If the ALP substrate p-nitrophenylphosphate (PNPP) is enzymatically hydrolyzed, it forms p-nitrophenol (PNP) which reduces the fluorescence of CuNCs because its absorption band at 410 nm overlaps the excitation peak of CuNCs at 390 nm. In addition, the amino groups and imidazole groups on the surface of CuNCs possibly form a complex with the phenol groups of PNP. This induces aggregation-induced quenching of the fluorescence of CuNCs. The fluorescent probe has a linear analytical range that extends from 0.5 mU·mL?1 to 40 mU·mL?1 and a detection limit of 45 μU·mL?1.
关键词： Alkaline phosphatase,Aggregation-induced quenching,Fluorometry,Inner filter effect,L-Histidine,Copper nanoclusters
更新于2025-09-04 15:30:14
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Aluminum(III) triggered aggregation-induced emission of glutathione-capped copper nanoclusters as a fluorescent probe for creatinine
摘要： Glutathione-capped copper nanoclusters (CuNCs) are presented that display aggregation-induced emission (AIE). This feature was exploited for selective and sensitive quantification of creatinine (CRN) which is an important diagnostic parameter. In the presence of Al3+ ions, such CuNCs rapidly aggregate, and this induces enhanced a red emission. The AIE nature of CuNCs was proven via TEM and fluorimetry. On addition of CRN, the coordination between CRN and Al3+ ions led to the quenching of fluorescence due to weakening the AIE. The best fluorescence intensity was measured at excitation/emission peaks of 360/585 nm. Quenched fluorescence intensity showed a linear dependence on the concentrations of CRN in the range of 2.5–34 μgL?1 with a detection limit of 0.63 μgL?1. The sensing mechanism of probe for CRN detection is discussed. The probe was applied to the determination of CRN in spiked human serum samples and gave satisfactory results.
关键词： Nanosensor,Renal biomarker,Serum analysis,Fluorescent nanomaterials,Metal nanoclusters,Nanoprobe,Paired t-test,Fluorometry,Real sample analysis
更新于2025-09-04 15:30:14
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Simultaneous Prediction of Atomic Structure and Stability of Nanoclusters in a Wide Area of Compositions
摘要： We present a universal method for the large-scale prediction of the atomic structure of clusters. Our algorithm performs the joint evolutionary search for all clusters in a given area of the compositional space and takes advantage of structural similarities frequently observed in clusters of close compositions. The resulting speedup is up to 50 times compared to current methods. This enables the first-principles studies of multi-component clusters with full coverage of a wide range of compositions. As an example, we report an unprecedented first-principles global optimization of 315 SinOm clusters with n ≤ 15 and m ≤ 20. The obtained map of Si-O cluster stability shows the existence of both expected (SiO2)n and unexpected (e.g. Si4O18) stable (magic) clusters, which can be important for miscellaneous applications.
关键词： atomic structure,nanoclusters,evolutionary algorithm,first-principles,stability
更新于2025-09-04 15:30:14
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[IEEE 2018 XXIIIrd International Seminar/Workshop on Direct and Inverse Problems of Electromagnetic and Acoustic Wave Theory (DIPED) - Tbilisi, Georgia (2018.9.24-2018.9.27)] 2018 XXIIIrd International Seminar/Workshop on Direct and Inverse Problems of Electromagnetic and Acoustic Wave Theory (DIPED) - Magnetometry and NMR Study of Carbon Nanopowders Doped with Cobalt Nanoclusters and Self-assembly of their Polymer Nanocomposites under Magnetic Field
摘要： The RF resonant magnetometry and NMR studies were carried out on carbon nanoparticles doped with magnetic cobalt clusters, which were synthesized by a technology combining of the hydrocarbon vapor pyrolysis and the chemical vapor deposition (CVD) process in a horizontal continuous reactor. The RF resonant magnetometry data show that the obtained carbon cobalt nanopowders are superparamagnetic at room temperatures and ferromagnetic at liquid nitrogen temperatures. The NMR study with the excitation by additional magnetic video-pulses of nanopowders obtained by using different hydrocarbons pyrolysis made it possible a fast assessment of their magnetic phase and hardness properties. The simple non-contact RF resonant magnetometry study of self-assembling processes in carbon cobalt polymer composite films synthesized using these nanopowders was made also.
关键词： magnetic nanoclusters,carbon nanopowder,core-shell structure,self-assembly,NMR,cobalt
更新于2025-09-04 15:30:14
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Synthesis of novel luminescent copper nanoclusters with substituent driven self-assembly and aggregation induced emission (AIE)
摘要： We demonstrate a novel strategy to synthesize highly stable luminescent mercaptoimidazole-capped copper nanoclusters (CuNCs). Herein we depict that a simple modification of substituents on the mercaptoimidazole ligand dictates the self-assembly and photophysical properties of the clusters. These CuNCs showed aggregation induced emission (AIE) with a large Stokes shift (Dk 4 200 nm), and the formation of clusters corresponding to Cu4L3 was confirmed by MALDI-TOF mass spectrometric analyses. Interestingly, these nanoclusters e?ectively internalize into mammalian cells while retaining their fluorescent properties and exhibit negligible toxicity.
关键词： mercaptoimidazole-capped,luminescent copper nanoclusters,AIE,aggregation induced emission,self-assembly
更新于2025-09-04 15:30:14
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A new approach to studying the luminescence spectra of free icosahedral and crystalline argon nanoclusters
摘要： We propose a new approach to analyzing the cathodoluminescence spectra of free argon nanoclusters, forming in a supersonic jet flowing into vacuum. Based on this approach, we conduct an analysis of the intensities of the luminescence bands of neutral and charged excimer complexes (Ar2)* and (Ar+4)*, measured for clusters with an average size ranging from 500 to 8900 atoms per cluster, and a diameter of 32–87 A? . It is shown that the concentration of the substance condensed into clusters, which determines the integrated intensity of the bands, is proportional to the logarithm of the average size of the clusters in the jet. An analysis of the normalized intensities of the (Ar2)* and (Ar+4)* bands for crystalline clusters with an fcc structure allowed us to establish that the luminescence of neutral (Ar2)* molecules comes from within the volume of the cluster, while the charged complexes (Ar+4)* emit from the subsurface layer. We highlighted an area of cluster dimensions at which the jet is dominated by quasi-crystalline clusters with an icosahedral structure, and it is shown that the transition from icosahedral clusters to fcc structures occurs when the average size of the cluster in the jet is (cid:2)N = (1000–1800) atoms/cluster.
关键词： cathodoluminescence,argon nanoclusters,luminescence spectra,excimer complexes,supersonic jet
更新于2025-09-04 15:30:14