Fast time-resolved pair distribution function studies of supported gold nanoparticle formation

Fast time-resolved pair distribution function studies of supported gold nanoparticle formation

A method for detecting the time-resolved electron energy distribution function for periodically varying plasmas is proposed. The method is applied to detecting the time-resolved distribution function for ionization wave packets externally excited in the helium positive column. The distribution function shifts to a higher one with increasing wave amplitude, yielding the two-humped distribution in a certain duration of the negative phase of fluctuated electric field due to the increase in acceleration of electrons.

A dedicated apparatus has been developed for studying structural changes in amorphous and disordered crystalline materials substantially in real time. The apparatus, which can be set up on beamlines BL04B2 and BL08W at SPring-8, mainly consists of a large two-dimensional flat-panel detector and high-energy X-rays, enabling total scattering measurements to be carried out for time-resolved pair distribution function (PDF) analysis in the temperature range from room temperature to 873 K at pressures of up to 20 bar. For successful time-resolved analysis, a newly developed program was used that can monitor and process two-dimensional image data simultaneously with the data collection. The use of time-resolved hardware and software is of great importance for obtaining a detailed understanding of the structural changes in disordered materials, as exemplified by the results of commissioned measurements carried out on both beamlines. Benchmark results obtained using amorphous silica and demonstration results for the observation of sulfide glass crystallization upon annealing are introduced.

The application of a large-area (41 × 41 cm, 2048 × 2048 or 1024 × 1024 pixel) high-sensitivity (detective quantum efficiency > 65%) fast-readout (up to 7.5 or 30 Hz) flat-panel detector based on an amorphous silicon array system to the collection of high-energy X-ray scattering data for quantitative pair distribution function (PDF) analysis is evaluated and discussed. Data were collected over a range of exposure times (0.13 s–7 min) for benchmark PDF samples: crystalline nickel metal and amorphous silica (SiO2). The high real-space resolution of the resultant PDFs (withQmaxup to ∼40 Å−1) and the high quality of fits to data [RNi(0.13s)= 10.5%,RNi(1.3s)= 6.3%] obtained in short measurement times indicate that this detector is well suited to studies of materials disorder. Further applications of the detector to locate weakly scattering H2molecules within the porous Prussian blue system, {\rm Mn}^{\rm II}_{\,3}[CoIII(CN)6]2·xH2, and to follow thein situreduction of PtIVO2to Pt0at 30 Hz, confirm the high sensitivity of the detector and demonstrate a new potential for fast time-resolved studies.

Interactions of zeatin with gold ions and biomimetic formation of gold complexes and nanoparticles

Pair Distribution Function Obtained from Electron Diffraction: An Advanced Real-Space Structural Characterization Tool

The in situ formation of gold nanoparticles into the natural polymer chitosan is described upon pulsed laser irradiation. In particular, hydrogel-type films of chitosan get loaded with the gold precursor, chloroauric acid salt (HAuCl(4)), by immersion in its aqueous solution. After the irradiation of this system with increasing number of ultraviolet laser pulses, we observe the formation of gold nanoparticles with increasing density and decreasing size. Analytical studies using absorption measurements, atomic force microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy of the nanocomposite samples throughout the irradiation procedure reveal that under the specific irradiation conditions there are two competing mechanisms responsible for the nanoparticles production: the photoreduction of the precursor responsible for the rising growth of gold particles with increasing size and the subsequent photofragmentation of these particles into smaller ones. The described method allows the localized formation of gold nanoparticles into specific areas of the polymeric films, expanding its potential applications due to its patterning capability. The size and density control of the gold nanoparticles, obtained by the accurate increase of the laser irradiation time, is accompanied by the simultaneously controlled increase of the wettability of the obtained gold nanocomposite surfaces. The capability of tailoring the hydrophilicity of nanocomposite materials based on natural polymer and biocompatible gold nanoparticles provides new potentialities in microfluidics or lab on chip devices for blood analysis or drugs transport, as well as in scaffold development for preferential cells growth.

Pulsed neutron sources and third-generation synchrotron sources provide sufficiently high flux to acquire high wave momentum diffraction patterns suitable for pair distribution function (PDF) analysis in a matter of minutes to seconds, and even less. This allows for sequential data acquisition of a sample subjected to thermal, mechanical and even magnetic forces. Understanding the dynamics of the material's response to external stimuli will require new ways of analyzing the massive amounts of data collected during these time-resolved studies. The change in the PDF can be quickly evaluated using only the change in the measured intensities from an arbitrary initial state. With appropriate scaling factor, these can provide a quantitative measure of how the pairwise correlations change with external stimuli.

The unmatched properties of the element fluorine are reflected in organic fluorine compounds. The richness of modern fluorine chemistry allows for the regioselective introduction of this element at virtually every position of a given molecule.[1, 2] Thus the introduction of fluorine has been especially valuable in the process of drug discovery to fine tune many different target and off-target related properties.[3–6] For example, fluorine has been used to increase the binding affinity of small molecules to its target,[7] to tune the pKB and logD,[8] to improve target selectivity,[9] to improve oral absorption and exposure,[10] to prevent from metabolism[11] or to increase the antibacterial spectrum.[12] Not surprisingly, an estimated 20% of all pharmaceuticals contain fluorine.[4] Additionally, 18F is often used as a positron emission tomography (PET) active element to perform time and space resolved distribution studies of drugs in animals and humans.[13, 14] Last but not least, 19F is very useful in NMR of complex biological systems due to its high sensitivity and zero natural background.[15] Herein, we report the systematic F-scanning of a scaffold derived from the Ugi four-component reaction (Ugi-4CR) for the synthesis, optimization and biophysical characterization of potent p53-Mdm2 antagonists.

We report the effects of counterion species on the adsorption of cetyltrimetylammonium salts (C16TAX) onto gold surfaces and the subsequent formation of gold nanoparticles in the C16TAX surfactant solution. The surfactant adsorption onto gold surfaces was examined by using quartz crystal microbalance (QCM) and atomic force microscopy (AFM). The counterion species (X) examined in this study were as follows: X = Br-, Cl-, NO3-, F-, OH-, and SO42-. The adsorption onto the gold surface depended on the counterion species of C16TAXthe frequency shift of QCM decreased in the following order: X = Br- > NO3- ≈ SO42- > Cl- > F- > OH-. The chemical reduction of gold(III) in the surfactant solutions of C16TAX with use of 2,2‘-iminodiethanol as a mild reducing agent produced anisotropic gold nanoparticles, depending on the surfactant counterion. The high-affinity adsorption of Br-, NO3-, and Cl- on gold surfaces produced anisotropic gold nanoparticles, while only spherical gold nanoparticles were obtained for weakly bound counterions such as SO42-, F-, and OH-. In contrast, the chemical reduction with hydrazine proceeded rapidly such that the shape of the gold nanoparticles was uncontrollable; this resulted in the formation of spherical gold nanoparticles, irrespective of the surfactant counterion.

The local structural behavior of PbZr0.5Ti0.5O3 (PZT 50/50) ceramics during application of an electric field was investigated using pair distribution function (PDF) analysis. In situ synchrotron total scattering was conducted, and the PDFs were calculated from the Fourier transform of the total scattering data. The PDF refinement of the zero-field data suggests a local-structure model with [001] Ti-displacement and negligible Zr-displacement. The directional PDFs at different field amplitudes indicate the bond-length distribution of the nearest Pb-B (B = Zr/Ti) pair changes significantly with the field. The radial distribution functions (RDFs) of a model for polarization rotation were calculated. The calculated and the experimental RDFs are consistent. This result suggests the changes in Pb-B bond-length distribution could be dominantly caused by polarization rotation. Peak fitting of the experimental RDFs was also conducted. The peak position trends with increasing field are mostly in agreement with the calculation result of the polarization rotation model. The area ratio of the peaks in the experimental RDFs also changed with field amplitude, indicating that Zr atoms have a detectable displacement driven by the electric field. Our study provides an experimental observation of the behaviors of PZT 50/50 under field at a local scale which supports the polarization rotation mechanism.

Functionalization of gold nanoparticles as antidiabetic nanomaterial

Amines are used extensively as reductants and subsequent capping agents in the synthesis of metal nanoparticles, especially gold, due to its affinity to nitrogen. Taking 2-methyl aniline as an example, we show that metal reduction is followed by polymerization of the amine, while part of it covers the nanoparticle surface another fraction deposits in the solution. It is found that the oxidative polymerization of the amine goes in step with the formation of gold nanoparticles. The gold nanoparticles thus formed have a mean diameter of 20 nm. The polymerized amine encapsulates the gold nanoparticle forming a robust shell of about 5 nm thickness, making the gold core inert towards mineralizing agents such as chloroform, bromoform, sodium cyanide, benzylchloride, etc. which react with the naked gold nanoparticles. The deposited polymer is largely protonated, taking up protons from the medium during its formation. Similar results have been observed in the case of aniline also. The materials have been fully characterized by spectroscopy and microscopy.

Cationic gold nanoparticles modified with 2-aminoethanethiol, 8-amino-1-octanethiol, and 11-amino-1- undecanethiol were prepared by NaBH4 reduction of HAuCl4 in the presence of thiols in water or a water/ethanol mixture solvent. The formation of gold nanoparticles depended on the kind of solvent, and the concentration of NaBH4, HAuCl4, and thiols. A low concentration of HAuCl4 and a high concentration of NaBH4 facilitated the formation of gold nanoparticles. A high concentration of HAuCl4 solution resulted in aggregation and a low concentration of NaBH4 did not induce the formation of gold nanoparticles. The size of the gold nanoparticles increased with an increase of the concentration of the HAuCl4 solution, while it decreased with an increase of the concentration of the NaBH4 solution. When thiols were present, the HAuCl4/thiol ratio must be in the range of 1:1 to 1:2 for the formation of gold nanoparticles in both the water and water/ethanol mixture solvents. Modification with thiol molecules changed surface charge of the gold nanoparticles from negative to positive, and stabilized the gold nanoparticles. The cationic gold nanoparticles promoted gene transfection. A high ratio of gold nanoparticles to DNA increased transfection efficiency. However, the length of the alkyl groups had no evident effect.

The extensive and diversified applications of the well-known plasmonic nanoparticle systems along with their easy and environment-friendly synthesis strategies drive us to investigate in-depth this important research field. In the current scenario, our present study deals with an important plasmonic nanomaterial, i.e., globular protein, and human serum albumin (HSA)-conjugated gold nanoparticle (HSA-Au NP) system. The well-known chemical denaturants, urea and guanidine hydrochloride (GdnHCl or GnHCl), are investigated to show detrimental effects toward the formation of gold nanoparticles; however, the effect of GdnHCl is observed to be much prominent compared to that of urea. The synthesized nanoparticle system is found to be highly biocompatible from the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)-based cytotoxicity assay, and therefore, the applications of encapsulation of the well-known anticancer drug molecule, doxorubicin hydrochloride (Dox), in the nanoparticle system are further studied. In this drug encapsulation study, drug-metal complexation between Dox and HAuCl4·3H2O has been discussed elaborately. Similar to the nanoparticle formation, the effects of denaturants on drug encapsulation have also been discovered, and interestingly, it has been observed that urea plays a positive role, whereas GdnHCl plays a negative or detrimental role toward drug encapsulation in the synthesized gold nanoparticle system. The detailed photophysical mechanisms behind the drug encapsulation in the synthesized plasmonic nanosystem at every stage have also been explored. Overall, this study will conclusively explain the influences of the extensively used chemical denaturants on the synthesis and drug encapsulation behaviors of a well-known protein-conjugated gold nanoparticle, and as a consequence, it can be highly useful and acceptable to the biomedical and pharmaceutical research communities.