MOLECULAR DYNAMICS SIMULATION OF STRUCTURE STABILITY OF SILVER NANOCLUSTERS

The structures of Ag clusters with sizes n=13 to 1157 are studied by tight binding molecular dynamics simulation. It is found that the stable structures of Ag clusters follow the sequence amorphous-crystalline-amorphous-crystalline with the cluster size increasing from 13 to 1157. Furthermore, all the shells of Ag clusters are different from the structure of the corresponding bulk Ag.

Alkynyl-anchored silver nanoclusters in lanthanide metal-organic framework for luminescent thermometer and CO_(2) cycloaddition

In this study,an alkynyl-modified aromatic dicarboxylic acid bifunctional ligand was selected to construct lanthanide compound{[Eu_(4)(ebdc)_(6)(4,4-bpy)_(0.5)(H_(2)O)_(4.5)]·(C_(2)H_(5)OH)_(1.25)(H_(2)O)}_(n)(Eu-MOF,H_(2)ebdc=5-ethynyl-isophthalic acid,4,4-bpy=4,4-bipyridine,MOF=metal-organic framework),of which the uncoordinated alkynyl group would be used to anchor silver nanoclusters(Ag NCs).The Eu-MOF exhibits double emission peaks,located at 492 and 611 nm,respectively,in which the high-energy blue emission is associated with alkynyl-modified ligand while the low-energy red emission belongs to characteristic emission of Eu3+,indicating that ligands can effectively sensitize Eu3+luminescence.The intensity ratio of the dual emission fluorescence peaks of Eu-MOF displays a good linear relationship with temperature,which realizes the detection function in the low temperature region of 75–275 K,the thermal sensitivity reaches 1.5398%·K^(−1).After anchoring the Ag NCs,the high-energy blue emission is significantly quenched,indicating that the Ag NCs are indeed confined into the framework and interact with the alkynyl group,and thus change the overall electronic distribution.This is the first case of anchoring Ag NCs by a luminescent Eu-MOF and studying nanocluster loading by using spectroscopic properties.In addition,the Ag NCs@Eu-MOF also shows a good catalytic activity for cycloaddition reaction from CO_(2)and epoxides.This study not only provides ideas for exploring the changes in optical properties of luminescent MOFs and Ag NCs caused by confinement effect,but also expands their potential applications in various fields.

Host molecule enhanced aggregation induced emission of chiral silver nanoclusters for achieving highly efficient circularly polarized electroluminescence

Chiral metal nanoclusters(MNCs)are competitive candidates for fabricating circularly polarized light-emitting diodes(CPLEDs),but the device performance is greatly limited by the poor emission of MNCs in solid thin films.Herein,host molecule enhanced aggregation induced emission(AIE)of MNCs is demonstrated for fabricating highly efficient CPLEDs.Namely,on the basis of the AIE effect of atomically precise enantiomeric(R/S)-4-phenylthiazolidine-2-thione capped silver(R/S-Ag_(6)(PTLT)_(6))NCs in solid thin films,1,3-bis(carbazol-9-yl)benzene(mCP)is introduced as a host molecule to control the orientation and packing arrangements of R/S-Ag_(6)(PTLT)_(6) NCs throughπ–πinteractions with the R/S-Ag_(6)(PTLT)_(6) NCs and further enhance the AIE.The as-fabricated Ag_(6)(PTLT)_(6) NC/mCP hybrid solid thin film shows a high photoluminescence quantum yield of 71.0%close to that of Ag_(6)(PTLT)_(6) NC single crystal.As the hybrid films are employed as the active emission layers of CPLEDs,mCP also suppresses the triplettriplet annihilation and balances the charge transport.Thus,the CPLEDs exhibit a maximum brightness of 3,906 cd/m^(2),peak external quantum efficiency of 10.0%,electroluminescence dissymmetry factors of−5.3×10^(−3)and 4.7×10^(−3).

Luminescent silver nanoclusters for efficient detection of adenosine triphosphate in a wide range of pH values

In this work,polymethacrylic acid(PMAA)-templated silver nanoclusters(Ag NCs)were developed as the fluorescent probe for the efficient and sensitive detection of adenosine triphosphate(ATP)in a wide range of pH values.The fluorescence intensity of the Ag NCs could keep stable with pH values ranging from2.5 to 9.3.The detection of ATP was based on the quenching of the fluorescent Ag NCs in the presence of ATP.The fluorescence quenching of the Ag NCs with increasing ATP concentration was studied at pH 2.5,4.5,7.0 and 8.5 which involved a wide pH environment in body fluids.The limit of detection(LOD)for ATP was as low as 0.1 mmol/L in an acidic environment with pH of 2.5 and all the linear correlation coefficients were satisfactory under wide-span pH values from 2.5 to 8.5.In addition,the sensitive determination of ATP was also achieved by adding copper ions(Cu^2+).The high selectivity and rapid detection process proved that the fluorescent probe had great potential to detect ATP in biological samples under different pH conditions.

How G-quadruplex topology and loop sequences affect optical properties of DNA-templated silver nanoclusters

In the study of the fabrication of DNA-templated silver nanoclusters （DNA-Ag NCs）, how templates affect the fluorescence of the nanoclusters remains undear, and it has been a challenge to understand the correlation between the properties of the DNA template and the Ag NCs. In this respect, based on the rational design of a series of structurally defined intramolecular G-quadruplexes, we prepared G-quadruplex-templated Ag NCs with a defined G-tetrad-to-silver ratio of 1：2. We evaluated the effect of G-quadruplex topology and loop sequences on the fluorescence of DNA-Ag NCs using circular dichroism, and extinction and emission spectroscopy. G-quadruplex templates with an anti-parallel topology were found to produce Ag NCs with stronger fluorescence compared with parallel and hybrid configurations. Loop bases adjacent to G-tetrads have a more significant impact on the fluorescence of Ag NCs compared with those in the middle of the loop, with adenine largely exhibiting an enhancement effect and thymine being detrimental. Generally, G-quadruplexes having an anti-parallel topology with adenine in the loop adjacent to the G-tetrad would be good templates for producing highly fluorescent Ag NCs. This is the first study to focus on the correlation between G-quadruplex topology/sequence and the optical properties of Ag NCs. We hope that the results of this study will facilitate a more in-depth understanding of correlation between G-quadruplex templates and Ag NCs, and help to understand and utilize their unique attributes.

Converting ultrafine silver nanoclusters to monodisperse silver sulfide nanoparticles via a reversible phase transfer protocol

To achieve better control of the formation of silver sulfide （Ag2S） nanoparticles, ultrasmall Ag nanoclusters protected by thiolate ligands （Ag44（SR）30 and Agla（GSH）9） are used as precursors, which, via delicate chemistry, can be readily converted to monodisperse Ag2S nanoparticles with controllable sizes （4-16 nm） and switchable solvent affinity （between aqueous and organic solvents）. This new synthetic protocol makes use of the atomic monodispersity and rich surface chemistry of Ag nanoclusters and a novel two-phase protocol design, which results in a well-controlled reaction environment for the formation of Ag2S nanopartides.

Ratiometric fluorescence detection of bleomycin based on proximity-dependent fluorescence conversion of DNA-templated silver nanoclusters

We design a ratiometric fluo rescent sensing platform for bleomycin(BLM) by using proximity-dependent DNA-templated silver nanoclusters(DNA-AgNCs) probe.This ratiometric sensing system is constructed with DNA-AgNCs as single fluorophore.The proposed strategy is based on the two following facts:(1) a covert DNA can approach and transform the DNA-AgNCs with green emission(G-DNA-AgNCs) into red emission through hybridization reaction.(2) The specific cleavage of the convert DNA by BLM in the presence of Fe(Ⅱ) inhibits the discoloration of G-DNA-AgNCs.Thus,benefiting from the specific recognition of BLM and unique properties of G-DNA-AgNCs,a hignly-sensitive ratiometric sensor for BLM has been successfully developed.The detection limit is as low as 30 pmol/L.This label-free fluorescence probe possesses advantages of convenient synthetic process and low cost.Moreover,this ratiometric method has been applied to the detection of BLM in human serum samples,illustrating a promising tool for analysis of BLM in cancer therapy.

Simple synthesis of silver nanocluster composites AgNCs@PE-g-PAA by irradiation method and fluorescence detection of Cr^(3+)

Silver nanoclusters(AgNCs)are a new type of nanomaterials with similar properties to molecules and unique applications.The applications of AgNCs can be significantly expanded by combining them with different matrix materials to obtain AgNC composites.Using irradiation techniques,we developed a simple two-step method for preparing silver nanocluster composites.First,polyacrylic acid(PAA)chains were grafted onto the surface of a PE film as templates(PE-g-PAA).Subsequently,silver ions were reduced in situ on the surface of the template material to obtain the AgNC composites(AgNCs@PE-g-PAA).The degree of AgNC loading on the composite film was easily controlled by adjusting the reaction conditions.The loaded AgNCs were anchored to the carboxyl groups of the PAA and wrapped in the graft chain.The particle size of the AgNCs was only 4.38±0.85 nm,with a very uniform particle size distribution.The AgNCs@PE-g-PAA exhibited fluorescence characteristics derived from the AgNCs.The fluorescence of the AgNCs@PE-g-PAA was easily quenched by Cr^(3+)ions.The composite can be used as a fluorescence test paper to realize visual detection of Cr^(3+).

Fluorescent bovine serum albumin-silver nanoclusters loaded with paclitaxel can traverse the blood-brain barrier to inhibit the migration of glioma

Objective::Glioma is the most common and aggressive primary brain tumor. Here, we aimed to establish a nano-drug carrier system to traverse the blood-brain barrier for the treatment and inhibition of glioma migration.Methods::The synthesis of bovine serum albumin protected-silver nanoclusters (BSA-AgNCs) was performed using chemical reduction. The drug paclitaxel (PTX) can be loaded into BSA-AgNCs through electrostatic and hydrophobic interactions to formulate spherical BSA-AgNC-PTX nanoparticles (BSA-AgNC-PTX NPs). A glioma mouse model was established by injecting U251-GFP-Luc cells into the mouse striatum, and all surgical procedures were approved by the Animal Ethics Committee of Nanchang University (SYXK2019-0003) on December 29, 2019.Results::The BSA-AgNC-PTX NPs were able to efficiently pass through the blood-brain barrier, both in vitro and in vivo, to deliver the drug to the tumor site. The in vivo assessment of BSA-AgNC-PTX NPs in glioblastoma multiforme-bearing mice revealed the significant inhibition of tumor growth and migration, prolonging the survival of the mice.Conclusion::These results indicated that BSA-AgNCs might represent an ideal nanocarrier for the treatment of glioma and has the potential to be used in the treatment of a variety of central nervous system diseases.

Core engineering of paired core-shell silver nanoclusters

Unlike the facile modulation of surface structure through protecting ligands,the core shielded by outer shell of silver nanoclusters is still hard to be controlled.Ligand effects may seep into the incipient growth of silver core.However,the comparable cases to validate such hypothesis are currently lacking.Herein,we shed light on two core-shell silver nanoclusters,Ag_(7)S_(6)@Ag_(48)(SD/Ag55b,SD=SunDi)and Ag_(6)S_(6)@Ag_(48)(SD/Ag54b),differing in only one silver atom in the core which varies from a pentagon-bipyramidal Ag_(7)to an octahedral Ag_(6)while keeping the Ag_(48)shielding shell almost the same.Although no direct bonding between alkynes and silver core is observed in them,we propose that the ligand effect still exerts profound influences on the size and geometry of silver core.The solution behaviours and complete ligand-exchange reaction of SD/Ag55b in CH_(2)Cl_(2)are investigated using electrospray ionization mass spectrometry.Due to more and stronger argentophilic interactions,SD/Ag55b exhibits room-temperature phosphorescence with a 40 nm red-shift compared to that of SD/Ag54b in CH_(2)Cl_(2).This work not only presents effective fabrication of silver nanoclusters via synergism of dithiophosphate and alkyne ligands,but also provides us a pair of comparable examples to understand substitution group effect of protecting ligand on the core structures and properties.

Carbonate-Water Supramolecule Trapped in Silver Nanoclusters Encapsulating Unprecedented Ag_(11) Kernel

In the absence of inorganic anion templates and in high pH condition(pH∼14),an unprecedented carbonate-hydrate supramolecule,[(CO_(3))_(2)(H_(2)O)]^(4−),trapped from atmospheric CO_(2),found to play an anion templating role to support the architecture of two related silver(Ag)nanoclusters(SD/Ag54a and SD/Ag55a),which are coprotected by the same organic ligands but differ by one silver atom of the metallic frameworks.Two[(CO_(3))_(2)(H_(2)O)]^(4−)supramolecules are trapped into two Ag/tBuPhS/dppm pods,connected by a pair of face-shared silver pentagonal bipyramids(Ag_(11))into peanut-shaped silver nanoclusters.Interestingly,the equatorial Ag_(11) kernel represents a new embryonic ultrasmall silver nanocluster that is thought to follow a special facesharing growth fashion from pentagonal bipyramidal Ag7 subunit,which is also structurally elucidated in another new Ag44 nanocluster(SD/Ag44c)obtained in similar assembly system just changing tBuPhS−to iPrPhS−ligand.The isolation of SD/Ag54a and SD/Ag55a were associated with:(1)supramolecule induction and(2)reductive and carbonate-rich assembly system.First,this work brings a fresh perspective on the role of carbonate-water anion supramolecule in directing the assembly of silver nanoclusters.Second,it realizes the control of reduction kinetics and kernel growth using multiple weak reductants and thiolate ligands.Third,it provides a possible face-shared growth route for ultrasmall silver nanoclusters.

Angle-sensitive and fast photovoltage of silver nanocluster embeded ZnO thin films induced by 1.064-μm pulsed laser

Silver nanocluster embedded ZnO composite thin film was observed to have an angle-sensitive and fast photovoltaic effect in the angle range from -90° to 90° , its peak value and the polarity varied regularly with the angle of incidence of the 1.064-μm pulsed Nd：YAG laser radiation onto the ZnO surface. Meanwhile, for each photovoltaic signal, its rising time reached -2 ns with an open-circuit photovoltage of -2 ns full width at half-maximum. This angle-sensitive fast photovoltaic effect is expected to put this composite film a candidate for angle-sensitive and fast photodetector.

Preparation of antibacterial non-woven AgNCs@PP-g-PAA via radiation method

With the growing threat of airborne epidemics,there has been an increasing emphasis on personal protection.Masks serve as our primary external defense against bacteria and viruses that might enter the respiratory tract.Hence,it’s crucial to develop a polypropylene(PP)nonwoven fabric with quick antibacterial capabilities as a key component for masks.This study introduces silver nanoclusters(AgNCs)into non-woven PP using radiation technology to infuse antibacterial properties.Initially,a solid ligand(PP-g-PAA)was procured via radiation grafting of the ligand polyacrylic acid(PAA),which was incorporated into the nonwoven PP with the aid of a crosslinking agent at a lower absorbed dosage.Subsequently,AgNCs were synthesized in situ on PP-g-PAA via an interaction between PAA and AgNCs,leading directly to the formation of AgNCs@PP-g-PAA composites.Owing to the hydrophilicity of PAA,AgNCs@PP-g-PAA maintains good moisture permeability even when the voids are heavily saturated with PAA gel,preventing droplet aggregation by diffusing droplets on the surface of the material.This feature enhances the comfort of the masks.Most importantly,due to the incorporation of AgNCs,AgNCs@PP-g-PAA demonstrates outstanding antibacterial effects against Escherichia coli and Staphylococcus aureus,nearly achieving an instant“touch and kill”outcome.In conclusion,we synthesized a modified nonwoven fabric with significant antibacterial activity using a simple synthetic route,offering a promising material that provides improved personal protection.

Temperature-dependent chloride-mediated access to atom-precise silver thiolate nanoclusters

By using a unique temperature-dependent,chloride-mediated approach,two atom-precise silver nanoclusters[Cl@Ag_(14)(Tab)_(12)-(C_(5)H_(4)NCl)_(12)](PF_(6))_(13)(Cl@Ag_(14))and[Cl_(3)@Ag_(24)(Tab)_(20)(C_(5)H_(4)NCl)_(11)]Cl(PF_(6))_(20)(Cl_(3)@Ag_(24))(Tab=4-(trimethylammonio)benzenethiolate,C_(5)H_(4)NCl=3-chloropyridine)were obtained successfully.Notably,the number of chloride ions encapsulated inside the Ag-S shell could be regulated by the slow dissolution of almost insoluble KCl at various temperatures.The inclusion of additional core chloride ions results in the expansion of the surrounding Ag-S shell.This article provides a promising synthetic approach for controlling the number of Ag atoms that form a shell around the anionic core,in addition to offering a potential pathway for the introduction of other inorganic anions into silver clusters.More broadly,through the use of related ligands,the synthetic strategy offers scope for generating new families of silver thiolate clusters of varying size and composition.

一种快速响应的光致变色SCC-MOF用于光开关和信息加密

由于银硫簇的不稳定性和有限的刺激响应特性,构建新型的具有光开关性质的银-硫簇基金属有机框架(SCC-MOF)面临着重大挑战.基于此,本文设计并合成了一种新型光致变色的SCC-MOF(Ag_(12)-BMPTC),该材料利用二芳基乙烯配体和银硫簇前驱体通过溶剂缓慢挥发而得到.Ag_(12)-BMPTC在365和500 nm光照射下表现出优异的可逆光响应特性.此外,这种光开关性质为其在信息加密和手性开关方面提供了潜在应用.本研究不仅扩大了SCC-MOF的种类,而且为设计和合成新型光致变色材料提供了新的思路和潜在应用.

Multifunctional nano-herb based on tumor microenvironment for enhanced tumor therapy of gambogic acid

Multifunctional drug delivery systems(DDSs)have shown great prospects in overcoming the heterogeneous barrier of delivery drugs to the complex tumor microenvironment(TME).In this study,multifunctional AS/Ge-pNAB microgels with dual-active targeting,triple environment responsiveness,and fluorescence imaging capability were prepared through a straightforward procedure.This was aimed to improve the antitumor therapeutic application of gambogic acid(GA)based on the biological characteristics of TME.The microgels have a uniform double-layer structure with aptamer in the outer layer which helps in recognizing receptors on the tumor cells.The GA loaded nano-herb exhibited environment-responsive drug release profiles under acidic pH,reductant and high temperature.The nano-herb significantly improved the accumulation of GA in tumor sites through the synergistic combination of the enhanced permeability and retention effect and dual-ligand mediated internalization.Then,it accelerated intracellular drug release and killed tumor cells.Therefore,the nano-herb had specific therapeutic effects on the tumor in vitro and in vivo as they remarkably inhibited tumor growth while depicting optimal biosafety and lower levels of off-target toxicity.Overall,these findings demonstrate the great potential of the multifunctional AS/Ge-pNAB microgels for precisely targeted GA delivery and open a new avenue for the facile preparation of multifunctional DDSs.

Novel dual fluorescence temperature-sensitive chameleon DNA-templated silver nanocluster pair for intracellular thermometry

For the first time, we are reporting a novel type of dual fluorescence temperaturesensitive DNA-templated silver nanocluster （AgNC） pair, which contains two pieces of single-stranded AgNC in proximity through hybridization. Both the chameleon AgNC pairs, A-NCP and B-NCP, possess two bright fluorescence peaks that achieve sensitive variations corresponding to temperature change from 15 to 45 ℃. With the increase in temperature, one of the fluorescence emissions of A-NCP （A-FL570） increases, while the other （A-FL640） decreases. However, both the emissions of B-NCP （B-FL685 and B-FL620） decrease simultaneously. Therefore, A-NCP shows a remarkable fluorescence color variation from orange to yellow, while the fluorescence color of B-NCP changes from orange to colorless, with increase in temperature. Moreover, the temperature responding linear range of A-NCP can be regulated by adjusting the structures and sequences of assistant DNA templates. It is assumed that the two single-stranded segmental AgNCs are integrated together as they are assembled into AgNC pairs, leading to a dramatic variation in fluorescence properties. The temperature-sensitive phenomenon is due to the dehybridization-induced separation of two pieces of segmental AgNC, caused by temperature increase. The temperature-sensitive AgNC pairs have been successful in indicating the temperature of living cells, showing the potential for a new application of silver nanocluster as a nanothermometer with adjustable response range, bringing novel insight into the regulatory mechanism of AgNC fluorescence variation.

Efficient silver nanocluster photocatalyst for simultaneous methyl orange/4-chlorophenol oxidation and Cr(Ⅵ) reduction

Metal nanoclusters have shown great potential in photocatalysis,while simultaneous removal of both inorganic and organic contaminants by metal nanoclusters under visible light is less explored.Here,we synthesized Agm(SR)n(SR represents 3-mercaptopropyltriethoxysilane ligand) nanoclusters(~1 nm) via a reduction of silver triphenylphosphine under ambient conditions in the presence of 3-mercaptopropyltriethoxysilane.The nanocluster was characterized by UV-vis spectroscopy,high resolution transmission electron microscopy(HRTEM),Fourier transform infrared spectrum(FTIR),and X-ray photoelectron spectroscopy(XPS).Under 5 W blue LED,the Agm(SR)n/P25 exhibits enhanced catalytic activity for simultaneous methyl orange(MO) oxidation and Cr(Ⅵ) reduction,and also for synchronous 4-chlorophenol oxidation and Cr(Ⅵ) reduction.Mechanism studies by electrochemical impedance spectroscopy(EIS),photoluminescence(PL),electron spin resonance(ESR) etc.and control experiments reveal that the unique structure of silver nanoclusters with thiolate ligands is vital to the high catalytic performance,and both the photo-generated holes and superoxide radicals are responsible for the decomposition of MO.

Solvent-driven reversible transformation between electrically neutral thiolate protected Ag_(25)and Ag_(26)clusters

Two atom-precise silver nanoclusters[Ag_(25)Cl_2(Tab)_(14)(Ph COO)_(11)(DMF)_4](PF_6)_(12)(Ag_(25),DMF=N,N-dimethylformamide)and[Ag_(26)Cl_2(Tab)_(14)(Ph COO)_(13)(DMAc)_4](PF_6)_(11)(Ag_(26),DMAc=N,N-dimethylacetamide)were synthesized based on the electrically neutral thiolate protective ligand,4-(trimethylammonio)benzenethiolate(Tab).The weak Ag–S interaction in Tab-protected silver nanoclusters allows to insert or leave a single silver atom in the Ag–S skeleton through solvent-trigger core fragmentation and re-arrangement,thereby realizing the reversible conversion of Ag_(25)and Ag_(26)for the first time.