Synthesis of monofunctionalized gold nanoparticles by fmoc solid-phase reactions

In this communication, solid-phase reactions for the synthesis of Lys-monofunctionalized gold nanoparticles are described. A controlled and selective fabrication of linear nanoparticle arrays can be achieved through peptide linkage systems, and therefore it is essential to prepare Fmoc amino acid nanoparticle building blocks susceptible to Fmoc solid-phase peptide synthesis. Gold nanoparticles containing carboxylic acids (2) in the organic shell were covalently ligated to Lys on solid supports through amide bond coupling reactions. We employed Fmoc-Lys-substituted polymer resins such as Fmoc-Lys-Wang or Fmoc-Lys-HMPA-PEGA. The low density of Lys on the matrix enabled 2 nm-sized gold nanoparticles to react with Lys in a 1:1 ratio. Subsequent cleavage reactions using 60% TFA reagent resulted in Lys transfer from the solid matrix to gold nanoparticles, and the Fmoc-Lys-monofunctionalized gold nanoparticles (5) were obtained with 3-15% yield. Synthesis using HMPA-PEGA resin increased productivity due to the superior swelling properties of PEGA resin in DMF. Monofunctionalization of nanoparticles was microscopically characterized using TEM for the ethylenediamine-bridged nanoparticle dimers (6). By counting the number of 6, we found that at least 60% of cleaved nanoparticles were monofunctionalized by Lys. This method is highly selective and efficient for the preparation of monofunctionalized nanoparticles.     

A facile synthesis of aliphatic thiol surfactant with tunable length as a stabilizer of gold nanoparticles in organic solvents

Three new aliphatic thiol surfactants were synthesized by reacting alkyl bromide with hexamethyldisilathiane under a mild condition. This approach provides an easy access for the direct synthesis of various different length thiol surfactants which play a crucial role in tuning the properties of gold nanoparticles. Gold nanoparticles encapsulated with one of our synthetic thiols were prepared and well characterized by H NMR, UV-vis, FT-IR, and TEM. The hybrid nanoparticles are very stable in both organic solvents and the solid state.     

Dendronized Anionic Gold Nanoparticles: Synthesis,Characterization, and Antiviral Activity

Anionic carbosilane dendrons decorated with sulfonate functions and one thiol moiety at the focal point have been used to synthesize water‐soluble gold nanoparticles (AuNPs) through the direct reaction of dendrons, gold precursor, and reducing agent in water, and also through a place‐exchange reaction. These nanoparticles have been characterized by NMR spectroscopy, TEM, thermogravimetric analysis, X‐ray photoelectron spectroscopy (XPS), UV/Vis spectroscopy, elemental analysis, and zeta‐potential measurements. The interacting ability of the anionic sulfonate functions was investigated by EPR spectroscopy with copper(II) as a probe. Different structures and conformations of the AuNPs modulate the availability of sulfonate and thiol groups for complexation by copper(II). Toxicity assays of AuNPs showed that those produced through direct reaction were less toxic than those obtained by ligand exchange. Inhibition of HIV‐1 infection was higher in the case of dendronized AuNPs than in dendrons.     

Preparation and characterization of gold nanoparticles capped by peptide-biphenyl hybrids

Gold nanoparticles were prepared using peptide-biphenyl hybrids (PBHs) as capping agents. AuNPs were characterized by different techniques including UV-Vis, TEM, EDX, FT-IR, elemental analysis, (1)H NMR and (13)C CP/MAS NMR spectroscopy. TEM analysis showed that AuNPs present diameters in the range of 1.8-3.7 nm, depending on the structure and the amount of the capping PBH used. FT-IR spectroscopy and solid-state (13)C NMR revealed that the carboxylic group of PBHs, especially in the case of the acid ligands, interacts with the gold surface (in the form of carboxylate). The results confirm that PBHs are excellent stabilizers of AuNPs, being one of the first examples on the use of peptidomimetics-gold hybrid materials.     

Biological synthesis of silver and gold nanoparticles using apiin as reducing agent

We report a novel strategy for the biological synthesis of anisotropic gold and quasi-spherical silver nanoparticles by using apiin as the reducing and stabilizing agent. The size and shape of the nanoparticles can be controlled by varying the ratio of metal salts to apiin compound in the reaction medium. The resultant nanoparticles were characterized by UV-vis-NIR, transmission electron microscopy (TEM), FT-IR spectroscopy, X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The interaction between nanoparticles with carbonyl group of apiin compound was confirmed by using FT-IR analysis. TEM photograph confirming the average size of the gold and silver nanoparticles were found to be at 21 and 39 nm. The NIR absorption of the gold nanotriangles is expected to be of application in hyperthermia of cancer cells and in IR-absorbing optical coatings.     

Synthesis, surface modification, and multilayer construction of mixed-monolayer-protected CdS nanoparticles

Herein, we describe a study aimed at synthesizing mixed-monolayer-protected CdS nanoparticles and investigating the reactivity of surface-bound functional groups in order to facilitate the immobilization of nanoparticles on a solid substrate as well as the construction of a three-dimensional nanocomposite. CdS nanoparticles initially prepared by the reverse micelle method were used to modify nanoparticle surfaces with 1-decanethiol molecules by ligand exchange. Subsequently, 11-mercapto-1-undecanol was partially incorporated by a place exchange reaction, thereby providing stable, mixed-monolayer-protected CdS nanoparticles. The nanoparticles obtained at each step were characterized by FT-IR and UV-vis spectroscopy, transmission electron microscopy, and elemental analysis. The reactivity of surface hydroxyl groups was verified by a reaction with isocyanate-bearing molecules that provide carbamate bonds in high yields at ambient temperature. The obtained mixed-monolayer-protected nanoparticles were also successfully immobilized on a glass substrate through a carbamate-bond-forming reaction that could be further utilized for multilayer construction in a layer-by-layer fashion.     

Microwave-induced synthesis of highly dispersed gold nanoparticles within the pore channels of mesoporous silica

Highly dispersed gold nanoparticles have been incorporated into the pore channels of SBA-15 mesoporous silica through a newly developed strategy assisted by microwave radiation (MR). The sizes of gold are effectively controlled attributed to the rapid and homogeneous nucleation, simultaneous propagation and termination of gold precursor by MR. Diol moieties with high dielectric and dielectric loss constants, and hence a high microwave activation, were firstly introduced to the pore channels of SBA-15 by a simple addition reaction between amino group and glycidiol and subsequently served as the reduction centers for gold nanoparticles. Extraction of the entrapped gold from the nanocomposite resulted in milligram quantities of gold nanoparticles with low dispersity. The successful assembly process of diol groups and formation of gold nanoparticles were monitored and tracked by solid-state NMR and UV-vis measurements. Characterization by small angle X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicated that the incorporation of gold nanoparticles would not breakup the structural integrity and long-range periodicity of SBA-15. The gold nanoparticles had a narrow size distribution with diameters in the size range of 5-10 nm through TEM observation. The average particles size is 7.9 nm via calculation by the Scherrer formula and TEM measurements. Nitrogen adsorption and desorption isotherms gave further evidence that the employed method was efficient and gold nanoparticles were successfully incorporated into the pore channels of SBA-15.     

Seedless synthesis of octahedral gold nanoparticles in condensed surfactant phase

We report a seedless synthetic method of gold octahedral nanoparticles in an aqueous phase. Eight facets with {111} crystalline structures of octahedral nanoparticles could be formed in an aqueous medium when the gold salt was reduced by ascorbic acid at room temperature in the presence of cetyltrimethylammonium bromide as a shape-inducing agent, and hydrogen peroxide as a reaction promoter. The growth kinetics and surface crystalline structures were characterized by UV-vis spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy.     

An approach for the surface functionalized gold nanoparticles with pH-responsive polymer by combination of RAFT and click chemistry

In this report, we demonstrated a novel efficient post-modification route for preparation of smart hybrid gold nanoparticles with poly(4-vinylpyridine) (P4VP) based on RAFT and click chemistry. A new azide terminated ligand was first synthesized to modify gold nanoparticles by ligand exchange reaction, and then click reaction was used to graft alkyne terminated P4VP which was prepared by RAFT onto the surface of gold nanoparticles. The functionalized hybrid gold nanoparticles were characterized by TEM, FTIR, and XPS etc. The results indicated that the P4VP was successfully grafted onto the surface of gold nanoparticles by click reaction. The surface grafting density was calculated to be about 6 chains/nm²_. In addition, the hybrid gold nanoparticles showed a pH responsive phenomenon as the pH value changed around 5.     

Gold nanoparticles with perfluorothiolate ligands

Two syntheses of gold nanoparticles with fluorinated alkyl and aryl thiolate ligands are reported. The fluorous Au nanoparticles are smaller than previous gold fluor-capped examples, and are in the 44-75 Au atom size range. Fluoroalkyl thiolate-protected (1H,1H,2H,2H-perfluorodecanethiolate) nanoparticles synthesized by a Brust reaction are a mixture of (mainly) approximately 8.5 kDa (ca. 44 core atoms) and approximately 14 kDa (ca. 75 core atoms) species, by MALDI-mass spectrometry. This composition is consistent with thermogravimetric analysis (TGA) results of the ligand shell composition. 19F NMR spectra display a progressive line broadening of resonances for fluorine sites closer to the Au core. A second synthetic route used a (ligand replacement) reaction of pentafluorobenzenethiol with Au55(PPh3)12Cl6. The exchange is (as previously observed for nonfluorinated thiols) accompanied by nanoparticle core size changes to produce a polydisperse mixture within which a Au75 core species could be electrochemically discerned by its characteristic 0.74 V electrochemical energy gap. Further characterization of the polydisperse nanoparticle product was done by HPLC, TEM, TGA, optical spectroscopy, and NMR data. Both varieties of fluorous nanoparticles exhibit solubilities typical of perfluorinated materials, as opposed to proteo versions.     

Aqueous-mixed ionic liquid system: phase transitions and synthesis of gold nanocrystals

Micelle-vesicle-micelle (MVM) transitions are observed in the aqueous-mixed ionic liquid (1-butyl-3-methylimidazolium octyl sulfate and 3-methyl-1-octylimidazolium chloride) system. The surface activity of mixed ILs, phase behavior, and solution structures in the system have been thoroughly characterized using conductometry, tensiometry, fluorimetry, dynamic light scattering (DLS), viscometry, turbidity, atomic force microscopy (AFM), transmission electron microscopy (TEM), and (1)H NMR techniques. Synergetic interactions between the two ILs in monolayers at the air/water interface and in micelles/vesicles have been determined using the regular solution approach, and the origins of spontaneous vesicle formation in this novel system are discussed. Using a photoreduction method, the formation of stable gold nanoparticles (GNPs) and microscale nanosheets of different shapes and sizes in the micellar and vesicle solutions has been reported. The studies show the potential of a mixed IL system in constructing stable micelles/supramolecular assemblies, such as bilayer vesicles, which are effective in the preparation of the desired nanomaterials.     

Synthesis and characterization of diazonium functionalized nanoparticles for deposition on metal surfaces

Silica nanoparticles were surface-functionalized with diazonium groups. The reaction steps leading to the formation of the diazonium functionality were followed with IR and XPS, and the structure of the diazonium-functionalized nanoparticle was confirmed with solid state NMR. Nanoparticle size distribution was determined with DLS, SEM, and TEM. The nanoparticles were then covalently bonded to gold and iron surfaces. Their spatial distribution over the metal surface was analyzed by SEM. Diazonium modification of nanoparticles represents a new method for the covalent attachment of nanoparticles to metal surfaces.     

Water-soluble gold nanoparticles protected by fluorinated amphiphilic thiolates

The preparation and the properties of gold nanoparticles (Au NPs) protected by perfluorinated amphiphiles are described. The thiols were devised to form a perfluorinated region close to the gold surface and to have a hydrophilic portion in contact with the bulk solvent to impart solubility in water. The monolayer protected clusters were prepared, in an homogeneous phase using sodium thiolates because of the low nucleophilicity of the alpha-perfluorinated thiols, and fully characterized with (1)H, (19)F NMR spectrometry, IR and UV-vis absorption spectroscopies, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). Au NPs with core diameters ranging from 1.6 to 2.9 nm, depending on the reaction conditions, were obtained. Water-soluble NPs (MPC-F8-PEGs) were obtained with the thiol HS-F8-PEG ending with a short poly(ethylene glycol) unit (PEG-OMe 550), whereas thiols with shorter PEG chains give rise to NPs insoluble in water. MPC-F8-PEGs undergo an exchange reaction with amphiphilic alkyl thiols. ESR investigations, using a hydrophobic radical probe, indicate that the MPC-F8-PEG monolayer shows a greater hydrophobicity compared to the analogous hydrogenated monolayer.     

Controlling the Spatial Organization of Liquid Crystalline Nanoparticles by Composition of the Organic Grafting Layer

Understanding how the spatial ordering of liquid crystalline nanoparticles can be controlled by different factors is of great importance in the further development of their photonic applications. In this paper, we report a new key parameter to control the mesogenic behavior of gold nanoparticles modified by rodlike thiols. An efficient method to control the spatial arrangement of hybrid nanoparticles in a condensed state is developed by changing the composition of the mesogenic grafting layer on the surface of the nanoparticles. The composition can be tuned by different conditions of the ligand exchange reaction. The thermal and optical behavior of the mesogenic and promesogenic ligands were investigated by using differential scanning calorimetry (DSC) and hot‐stage polarized optical microscopy. The chemical structure of the synthesized hybrid nanoparticles was characterized by ¹H NMR spectroscopy, thermogravimetric analysis (TGA), XPS, and elemental analysis, whereas the superstructures were examined by small‐angle X‐ray diffraction (SAXSRD) analysis. Structural studies showed that the organic sublayer made of mesogenic ligands is denser with an increasing the average ligand number, thereby separating the nanoparticles in the liquid crystalline phases, which changes the parameters of these phases.     

Preparation of core-shell carbon black nanoparticles and their crystallization-induced orientation

Core-shell carbon black nanoparticles were prepared by surface-initiated ring-opening polymerization of ε-caprolactone. ¹H NMR, ¹³C NMR, FT-IR, TGA, AFM, TEM and dynamic light scattering were used to characterize the core-shell carbon black nanoparticles (CB-g-PCL). TEM and AFM measurements showed that CB-g-PCL formed the core-shell structure with carbon black as the “core” and the PCL layer as the “shell”. TEM study also indicated that the core-shell carbon black nanoparticles could be homogeneously oriented in the PCL continuous phase under certain crystallization condition.     

Galvanic replacement of semiconductor phase I CuTCNQ microrods with KAuBr4 to fabricate CuTCNQ/Au nanocomposites with photocatalytic properties

In this study, the reaction of semiconductor microrods of phase I copper 7,7,8,8-tetracyanoquinodimethane (CuTCNQ) with KAuBr(4) in acetonitrile is reported. It was found that the reaction is redox in nature and proceeds via a galvanic replacement mechanism in which the surface of CuTCNQ is replaced with metallic gold nanoparticles. Given the slight solubility of CuTCNQ in acetonitrile, two competing reactions, namely CuTCNQ dissolution and the redox reaction with KAuBr(4), were found to operate in parallel. An increase in the surface coverage of CuTCNQ microrods with gold nanoparticles occurred with an increased KAuBr(4) concentration in acetonitrile, which also inhibited CuTCNQ dissolution. The reaction progress with time was monitored using UV-visible, FT-IR, and Raman spectroscopy as well as XRD and EDX analysis, and SEM imaging. The CuTCNQ/Au nanocomposites were investigated for their photocatalytic properties, wherein the destruction of Congo red, an organic dye, by simulated solar light was found dependent on the surface coverage of gold nanoparticles on the CuTCNQ microrods. This method of decorating CuTCNQ may open the possibility of modifying this and other metal-TCNQ charge transfer complexes with a host of other metals which may have significant applications.     

Postsynthesis racemization and place exchange reactions. Another step to unravel the origin of chirality for chiral ligand-capped gold nanoparticles

We examine how postsynthesis nanoparticle ligand shell modifications as a general approach can help in the understanding of currently proposed mechanisms for gold nanoparticle chirality. We compare the CD response of chirally decorated mixed-monolayer-protected gold nanoparticles synthesized in situ with quasi-identical gold nanoparticles either prepared by place exchange reactions or subjected to an aqueous base, resulting in partial hydrolysis and simultaneous partial racemization. We find that the CD response at wavelengths where the free chiral ligand does not absorb strongly depends on the preparation conditions, i.e., in situ synthesis vs place exchange, and that postsynthesis racemization of the chiral ligand produces racemic nanoparticles with no CD response, i.e., no induction of a chiral bias during reductive nanoparticle formation. Considering all experimental results for the described gold nanoparticle system with a C12H24 spacer between the nanoparticle surface and chiral center, the so-called "vicinal effect" with the formation of a supramolecular assembly of the chiral moieties seems to be active. Finally, we argue that postsynthesis nanoparticle ligand shell modifications such as racemization and/or place exchange reactions are very powerful tools to unravel contributions of the different gold nanoparticle chirality mechanisms.     

Crosslinking of poly(vinyl alcohol) using functionalized gold nanoparticles

We report on the preparation of a new class of polymer hydrogels obtained through the chemical crosslinking reaction of poly(vinyl alcohol) (PVA) and functionalized gold nanoparticles. Carboxylic group functionalized gold nanoparticles were synthesized, dispersed in a PVA matrix and allow to react with the hydroxyl groups of PVA at high temperature. FT-IR and swelling experiments carried out on the cross-linked samples confirmed that the crosslinking reaction took place. This is the first time, to our knowledge, that functionalized nanoparticles are used as chemical crosslinking agents.     

Preparation and characterization of gold nanoparticles and nanowires loaded into rod-shaped silica by a one-step procedure

Rod-shaped mesoporous silica nanoparticles (RMSN) with built-in gold nanoparticles or thin gold nanowires in the pore channels were in situ synthesized via a one-step procedure. The insertion of a hydrophobic gold precursor into the mesopores of RMSN was reached through a micellar solubilization mechanism and gold nanoparticles were achieved through a thermal reduction. The resulting RMSN and Au-RMSN samples were characterized by using X-ray diffraction, transmission and scanning microscopies (TEM and SEM), X-ray photoelectron spectroscopy (XPS), nitrogen physisorption and solid-state Nuclear Magnetic Resonance (NMR). The interaction of Au precursor (a carbene complex) with the thiol group at the silica surface was identified and found to play a crucial role in the dispersion of the uniform metal nanoparticles at the internal surface of RMSN. Moreover, TEM micrographs revealed the absence of large gold particles outside the mesopore network. The shape of Au nanoparticles and their loading amount in the mesoporous silica could be easily tuned by altering the concentration of gold precursor.     

Spectroscopic identification of S-Au interaction in cysteine capped gold nanoparticles

This study deals with the synthesis of cysteine capped gold nanoparticles with an average size of 12 nm by borohydride reduction and spectroscopic identification of SAu interaction. We have studied the interaction of thiol with gold nanoparticles in aqueous medium by employing UV-vis, Raman, NMR, and FT-IR spectroscopy. The shifting of gold plasmon resonance in the UV-vis spectra shows the stabilization of gold nanoparticles by cysteine. The disappearance of S-H stretching in both the IR and Raman spectra and the shifting of the NMR signals of the protons in close proximity to the metal center supported the existence of the S-Au interaction in cysteine capped gold nanoparticles. The TEM images shows cysteine capped gold nanoparticles as distinct and spherical entities as compared to free colloidal gold nanoparticles.