Nanoporous Gold Catalyst for the Oxidative N-Dealkylation of Drug Molecules:A Method for Synthesis of N-Dealkylated Metabolites

A novel method for the selective catalytic N-dealkylation of drug molecules on a nanoporous gold (NPG) catalyst producing valuable N-dealkylated metabolites and intermediates is described. Drug metabolites are important chemical entities at every stage of drug discovery and development, from exploratory discovery to clinical development, providing the safety profiles and the ADME (adsorption, distribution, metabolism, and elimination) of new drug candidates. Synthesis was carried out in aqueous solution at 80 °C using air (oxygen source) as oxidant, in single step with good isolated yields. Different examples examined in this study showed that aerobic catalytic N-dealkylation of drug molecules on NPG has a broad scope supporting N-deethylation, N-deisopropylation and N-demethylation, converting either 3° amines to 2° amines, or 2° amines to 1° amines

Correlative Multiscale 3D Imaging of a Hierarchical Nanoporous Gold Catalyst by Electron, Ion and X-ray Nanotomography

Tomographic imaging of catalysts allows non‐invasive investigation of structural features and chemical properties by combining large fields of view, high spatial resolution, and the ability to probe multiple length scales. Three complementary nanotomography techniques, (i) electron tomography, (ii) focused ion beam—scanning electron microscopy, and (iii) synchrotron ptychographic X‐ray computed tomography, were applied to render the 3D structure of monolithic nanoporous gold doped with ceria, a catalytically active material with hierarchical porosity on the nm and μm scale. The resulting tomograms were used to directly measure volume fraction, surface area and pore size distribution, together with 3D pore network mapping. Each technique is critically assessed in terms of approximate spatial resolution, field of view, sample preparation and data processing requirements. Ptychographic X‐ray computed tomography produced 3D electron density maps with isotropic spatial resolution of 23 nm, the highest so far demonstrated for a catalyst material, and is highlighted as an emerging method with excellent potential in the field of catalysis

Measurement of local crystal lattice strain variations in dealloyed nanoporous gold

Reversible macroscopic length changes in nanoporous structures can be achieved by applying electric potentials or by exposing them to different gases or liquids. Thus, these materials are interesting candidates for applications as sensors or actuators. Macroscopic length changes originate from microscopic changes of crystal lattice parameters. In this report, we show spatially resolved measurements of crystal lattice strain in dealloyed nanoporous gold. The results confirm theory by indicating a compression of the lattice along the axis of cylindrically shaped ligaments and an expansion in radial direction. Furthermore, we show that curved npAu surfaces show inward relaxation of the surface layer. (Figure presented) IMPACT STATEMENT We show spatially resolved measurements of strain in nanoporous gold confirming theory: Crystal lattice is compressed along the axis of cylindrical ligaments and expanded in radial direction, surfaces relax inward

Influence of gas atmospheres and ceria on the stability of nanoporous gold studied by environmental electron microscopy and <em>In</em> <em>situ</em> ptychography

A novel complementary approach of electron microscopy/environmental TEM and in situ hard X-ray ptychography was used to study the thermally induced coarsening of nanoporous gold under different atmospheres, pressures and after ceria deposition. The temperature applied during ptychographic imaging was determined by IR thermography. While using elevated temperatures (room temperature – 400 °C) and realistic gas atmospheres (1 bar) we achieved for the first time a spatial resolution of about 20 nm during hard X-ray ptychography. The annealing of pure and ceria stabilized nanoporous gold in different atmospheres revealed that the conditions have a tremendous influence on the coarsening. The porous structure of the samples was stable up to approximately 800 °C in vacuum, whereas pronounced changes and coarsening were observed already at approximately 300 °C in oxygen containing atmospheres. A layer of ceria on the nanoporous gold led to an improvement of the stability, but did not alleviate the influence of the gas atmosphere. Different behaviors were observed, such as coarsening and even material loss or migration. The results suggest that additional mechanisms beyond surface diffusion need to be considered and that microscopic studies aimed at more realistic conditions are important to understand the behavior of such materials and catalysts

In Situ Ptychography of Heterogeneous Catalysts using Hard X-Rays: High Resolution Imaging at Ambient Pressure and Elevated Temperature

A new closed cell is presented for in situ X-ray ptychography which allows studies under gas flow and at elevated temperature. In order to gain complementary information by transmission and scanning electron microscopy, the cell makes use of a Protochips E-chipTM which contains a small, thin electron transparent window and allows heating. Two gold-based systems, 50 nm gold particles and nanoporous gold as a relevant catalyst sample, were used for studying the feasibility of the cell. Measurements showing a resolution around 40 nm have been achieved under a flow of synthetic air and during heating up to temperatures of 933 K. An elevated temperature exhibited little influence on image quality and resolution. With this study, the potential of in situ hard X-ray ptychography for investigating annealing processes of real catalyst samples is demonstrated. Furthermore, the possibility to use the same sample holder for ex situ electron microscopy before and after the in situ study underlines the unique possibilities available with this combination of electron microscopy and X-ray microscopy on the same sample

An overview of dealloyed nanoporous gold in bioelectrochemistry

peer-reviewedNanoporous gold (NPG) obtained via dealloying of Au alloys has potential applications in a range of fields, and in particular in bioelectrochemistry. NPG possesses a three dimensional bicontinuous network of interconnected pores with typical pore diameters of ca. 30-40 nm, features that are useful for the immobilisation of enzymes. This review describes the common routes of fabrication and characterization of NPG, the use of NPG as a support for oxidoreductases for applications in biosensors and biofuel cells together with recent progress in the use of NPG electrodes for applications in bioelectrochemistry

ALD Functionalized Nanoporous Gold: Thermal Stability, Mechanical Properties, and Catalytic Activity

Nanoporous metals have many technologically promising applications but their tendency to coarsen limits their long-term stability and excludes high temperature applications. Here, we demonstrate that atomic layer deposition (ALD) can be used to stabilize and functionalize nanoporous metals. Specifically, we studied the effect of nanometer-thick alumina and titania ALD films on thermal stability, mechanical properties, and catalytic activity of nanoporous gold (np-Au). Our results demonstrate that even only one-nm-thick oxide films can stabilize the nanoscale morphology of np-Au up to 1000 C, while simultaneously making the material stronger and stiffer. The catalytic activity of np-Au can be drastically increased by TiO{sub 2} ALD coatings. Our results open the door to high temperature sensor, actuator, and catalysis applications and functionalized electrodes for energy storage and harvesting applications

Nanoporöses Gold: Neuartige Anwendungen in der Katalyse und Aktuatorik

New materials are sought for applications in catalysis, sensing, optics, electronics and other emerging fields. With the event of nanotechnology, innovations greatly profit from the access to new nano-sized materials with novel properties of materials simply resulting from the reduction of size. In this dissertation nanoporous gold (np-Au) is investigated with respect to its surface mediated applications in catalysis and actuation technology. Additionally the influence of adsorbates on the stability of the nanostructure during annealing is investigated. The np-Au material is found to be highly active for the oxidation of CO at low temperatures as well as the highly selective oxidation of methanol. Although most of the catalytic performance can be assigned to the surface chemistry of gold, small Ag residues - leftovers from manufacturing procedure - are shown to facilitate the activation of molecular oxygen. In a further set of experiments it is shown that surface chemistry of high surface area materials such as np-Au can lead to a macroscopic strain response. By using ozone to efficiently oxidize the surface and CO as reducing agent np-Au cubes could be strained up to 0.5 %, a value comparable to that of commercial piezo ceramics

Nanoporous Gold: Novel Catalytic and Sensor Applications

New materials are sought for applications in catalysis, sensing, optics, electronics and other emerging fields. With the event of nanotechnology, innovations greatly profit from the access to new nano-sized materials with novel properties of materials simply resulting from the reduction of size. In this dissertation nanoporous gold (np-Au) is investigated with respect to its surface mediated applications in catalysis and actuation technology. Additionally the influence of adsorbates on the stability of the nanostructure during annealing is investigated. The np-Au material is found to be highly active for the oxidation of CO at low temperatures as well as the highly selective oxidation of methanol. Although most of the catalytic performance can be assigned to the surface chemistry of gold, small Ag residues - leftovers from manufacturing procedure - are shown to facilitate the activation of molecular oxygen. In a further set of experiments it is shown that surface chemistry of high surface area materials such as np-Au can lead to a macroscopic strain response. By using ozone to efficiently oxidize the surface and CO as reducing agent np-Au cubes could be strained up to 0.5 %, a value comparable to that of commercial piezo ceramics