Thin‐Film Metal Hydrides

The goal of the medieval alchemist, the chemical transformation of common metals into nobel metals, will forever be a dream. However, key characteristics of metals, such as their electronic band structure and, consequently, their electric, magnetic and optical properties, can be tailored by controlled hydrogen doping. Due to their morphology and well‐defined geometry with flat, coplanar surfaces/interfaces, novel phenomena may be observed in thin films. Prominent examples are the eye‐catching hydrogen switchable mirror effect, the visualization of solid‐state diffusion and the formation of complex surface morphologies. Thin films do not suffer as much from embrittlement and/or decrepitation as bulk materials, allowing the study of cyclic absorption and desorption. Therefore, thin‐metal hydride films are used as model systems to study metal–insulator transitions, for high throughput combinatorial research or they may be used as indicator layers to study hydrogen diffusion. They can be found in technological applications as hydrogen sensors, in electrochromic and thermochromic devices. In this review, we discuss the effect of hydrogen loading of thin niobium and yttrium films as archetypical examples of a transition metal and a rare earth metal, respectively. Our focus thereby lies on the hydrogen induced changes of the electronic structure and the morphology of the thin films, their optical properties, the visualization and the control of hydrogen diffusion and on the study of surface phenomena and catalysis.     

Thin‐Film Infrared Spectroscopy of Acetonitrile

Acetonitrile and [D₃]acetonitrile in the vicinal region of a planar AgX fiber contain linear dipole–dipole linked oligomers as shown by 1) comparison of infrared band intensity ratios in the gaseous and condensed phases and 2) remarkable plots of absorbance (C? N stretch) versus time during evaporation from an AgX planar fiber element. The plots (CH₃CN 2252 cm^?1, CD₃CN 2262 cm^?1) reveal the presence of octamers, hexamers, tetramers, and dimers along with some heptamer, trimer, and monomer structures. A novel isotope effect arises from the somewhat smaller size of the CD₃CN resulting in an increase in the CN band intensity. The organized oligomers may be termed pseudocrystals and are the main components responsible for absorption intensity in the infrared spectrum of acetonitrile, on the AgX planar fiber or in an IR cell.     

Propargyl Amine Synthesis Catalysed by Gold and Copper Thin Films by Using Microwave‐Assisted Continuous‐Flow Organic Synthesis (MACOS)

An effective multi‐component reaction (MCR) protocol has been developed for the construction of propargyl amines from aldehydes, amines and terminal alkynes by using microwave‐assisted continuous‐flow organic synthesis (MACOS). The process is catalysed by thin films of either copper or gold that achieve temperatures in excess of 900 °C when irradiated with low levels of microwave power. The process works equally well for premixed solutions of the three starting materials, or as three separate streams, which improves the combinatorial efficiency of the method. The process tolerates a wide variety of functional groups and heterocycles, and conversion over these diverse substrates ranges from 70–90 %.     

Free‐Standing Gold‐Nanoparticle Monolayer Film Fabricated by Protein Self‐Assembly of α‐Synuclein

Free‐standing nanoparticle films are of great importance for developing future nano‐electronic devices. We introduce a protein‐based fabrication strategy of free‐standing nanoparticle monolayer films. α‐Synuclein, an amyloidogenic protein, was utilized to yield a tightly packed gold‐nanoparticle monolayer film interconnected by protein β‐sheet interactions. Owing to the stable protein–protein interaction, the film was successfully expanded to a 4‐inch diameter sheet, which has not been achieved with any other free‐standing nanoparticle monolayers. The film was flexible in solution, so it formed a conformal contact, surrounding even microspheres. Additionally, the monolayer film was readily patterned at micrometer‐scale and thus unprecedented double‐component nanoparticle films were fabricated. Therefore, the free‐floating gold‐nanoparticle monolayer sheets with these properties could make the film useful for the development of bio‐integrated nano‐devices and high‐performance sensors.     

First synthesis of α-aminophosphonates from natural porphyrin derivatives by the Kabachnik—Fields reaction

A preparative procedure is proposed for the synthesis of α-aminophosphonates of natural porphyrins by the microwave-assisted Kabachnik—Fields reaction.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 256–259, January, 2005.     

Electrochemical Characterisation of Copper Thin‐Film Formation on Polycrystalline Platinum

Electrochemically formed thin films are vital for a broad range of applications in virtually every field of modern science and technology. Understanding the film formation process could provide a means to aid the characterisation and control of film properties. Herein, we present a fundamental approach that combines two well‐established analytical techniques (namely, electrochemical impedance spectroscopy and electrogravimetry) with a theoretical approach to provide physico‐chemical information on the electrode/electrolyte interface during film formation. This approach allows the monitoring of local and overall surface kinetic parameters with time to enable an evaluation of the different modes of film formation. This monitoring is independent of surface area and surface concentrations of electroactive species and so may allow current computational methods to calculate these parameters and provide a deeper physical understanding of the electrodeposition of new bulk phases. The ability of this method to characterise 3D phase growth in situ in more detail than that obtained by conventional approaches is demonstrated through the study of a model system, namely, Cu bulk‐phase deposition on a Pt electrode covered with a Cu atomic layer (Cu_ad/Pt).     

Surface Chemistry of tert‐Butylphosphine (TBP) on Si(001) in the Nucleation Phase of Thin‐Film Growth

We combine density functional theory calculations and scanning tunneling microscopy investigations to identify the relevant chemical species and reactions in the nucleation phase of chemical vapor deposition. tert‐Butylphosphine (TBP) was deposited on a silicon substrate under conditions typical for surface functionalization and growth of semiconductor materials. On the activated hydrogen‐covered surface H/Si(001) it forms a strong covalent P?Si bond without loss of the tert‐butyl group. Calculations show that site preference for multiple adsorption of TBP is influenced by steric repulsion of the adsorbate's bulky substituent. STM imaging furthermore revealed an anisotropic distribution of TBP with a preference for adsorption perpendicular to the surface dimer rows. The adsorption patterns found can be understood by a mechanism invoking stabilization of surface hydrogen vacancies through electron donation by an adsorbate. The now improved understanding of nucleation in thin‐film growth may help to optimize molecular precursors and experimental conditions and will ultimately lead to higher quality materials.     

Methylene Blue as a Photosensitizer and Redox Agent: Synthesis of 5‐Hydroxy‐1H‐pyrrol‐2(5H)‐ones from Furans

A highly efficient and general singlet‐oxygen‐initiated one‐pot transformation of readily accessible furans into 5‐hydroxy‐1H‐pyrrol‐2(5H)‐ones has been developed. The methodology was extended to the synthesis of other high‐value α,β‐unsaturated γ‐lactams. This useful set of transformations relies not only on the photosensitizing ability of methylene blue, but also on its redox properties: properties that have until now been virtually ignored in a synthetic context.     

Triphenylphosphine‐Mediated Reduction of Electron‐Deficient Propargyl Ethers to the Allylic Ethers

Semihydrogenation of α,β‐unsaturated ynoates and ‐ynones bearing a γ‐alkoxy group can be performed using triphenylphosphine and water. α,β‐Unsaturated ynoates were reduced to a mixture of cis and trans α,β‐unsaturated enoates, whereas, ynones were reduced to trans α,β‐unsaturated enones as the only products.     

Synthesis of Phenanthrene Derivatives through the Reaction of an α,α‐Dicyanoolefin with α,β‐Unsaturated Carbonyl Compounds

Phenanthrene derivatives were prepared by reacting an α,α‐dicyanoolefin with different α,β‐unsaturated carbonyl compounds resulting from Wittig reaction of ninhydrin and phosphanylidene or condensation of barbituric acid and an aldehyde. The easy procedure, mild and metal‐catalyst free, reaction conditions, good yields, and no need for chromatographic purifications are important features of this protocol. The structures of the product of type 3 and 5 were corroborated spectroscopically (IR, ¹H‐ and ¹³C‐NMR, and EI‐MS). A plausible mechanism for this type of reaction is proposed (Scheme 1).     

Biomineralization‐Inspired Preparation of Zinc Hydroxide Carbonate/Polymer Hybrids and Their Conversion into Zinc Oxide Thin‐Film Photocatalysts

The development of ZnO thin films has been achieved through the conversion of zinc hydroxide carbonate thin‐film crystals. Crystallization of this compound is induced by a biomineralization‐inspired method with polymer‐stabilized amorphous precursors. The crystals grow radially on polymer matrices, leading to the formation of zinc hydroxide carbonate/polymer thin‐film hybrids that fully cover the substrate. These hybrids are converted into ZnO and retain their thin‐film morphologies. The resultant ZnO thin films exhibit a preferential crystallographic orientation that is attributed to the alignment of zinc hydroxide carbonate crystals before conversion. In addition, a photocatalytic function of the ZnO thin films has been demonstrated by analyzing the oxidation reaction of 2‐propanol. The biomineralization‐inspired approach reported herein is a promising way to develop ZnO materials with controlled morphologies and structures for photocatalytic applications.     

Novel α-Aminophosphonates and α-Aminophosphonic Acids: Synthesis,Molecular Docking and Evaluation of Antifungal Activity against Scedosporium Species

The Scedosporium genus is an emerging pathogen with worldwide prevalence and high mortality rates that gives multidrug resistance to antifungals; therefore, pharmacological alternatives must be sought for the treatment of diseases caused by this fungus. In the present project, six new α-aminophosphates were synthesized by the Kabachnik–Fields multicomponent reaction by vortex agitation, and six new monohydrolyzed α-aminophosphonic acids were synthesized by an alkaline hydrolysis reaction. Antifungal activity was evaluated using the agar diffusion method as an initial screening to determine the most active compound compared to voriconazole; then it was evaluated against 23 strains of the genus Scedosporium following the M38-A2 protocol from CLSI (activity range: 648.76–700 µg/mL). Results showed that compound 5f exhibited the highest antifungal activity according to the agar diffusion method (≤1 mg/mL). Cytotoxicity against healthy COS-7 cells was also evaluated by the MTT assay and it was shown that compound 5f exhibits a lower toxicity in comparison to voriconazole at the same concentration (1000 µM). A docking study was conducted afterwards, showing that the possible mechanism of action of the compound is through the inhibition of allosteric 14-α-demethylase. Taking these results as a basis, 5f is presented as a compound with attractive properties for further studies.     

Single‐Step,Rapid, and Mild Synthesis of β‐Amino Acid N‐Carboxy Anhydrides Using Micro‐Flow Technology

β‐Amino acid N‐carboxy anhydrides (β‐NCAs) are rarely used in the synthesis of β‐peptides, which is due mainly to the poor availability of these potentially useful substrates. Herein, we describe the heretofore challenging synthesis of β‐NCAs via a single‐step, rapid, and mild formation using pH flash switching and flash dilution, which are aspects of micro‐flow technology. We synthesized 15 β‐NCAs in good to excellent yields that included acid‐labile β‐NCAs that cannot be readily synthesized using the conventional Leuchs approach. Scaled‐up synthesis using this process can be readily achieved via continuous operation.     

Pure Cubic‐Phase Hybrid Iodobismuthates AgBi2I7 for Thin‐Film Photovoltaics

Bismuth‐based hybrid perovskites are candidates for lead‐free and air‐stable photovoltaics, but poor surface morphologies and a high band‐gap energy have previously limited these hybrid perovskites. A new materials processing strategy to produce enhanced bismuth‐based thin‐film photovoltaic absorbers by incorporation of monovalent silver cations into iodobismuthates is presented. Solution‐processed AgBi₂I₇ thin films are prepared by spin‐coating silver and bismuth precursors dissolved in n‐butylamine and annealing under an N₂ atmosphere. X‐ray diffraction analysis reveals the pure cubic structure (Fd3m) with lattice parameters of a=b=c=12.223 Å. The resultant AgBi₂I₇ thin films exhibit dense and pinhole‐free surface morphologies with grains ranging in size from 200–800 nm and a low band gap of 1.87 eV suitable for photovoltaic applications. Initial studies produce solar power conversion efficiencies of 1.22 % and excellent stability over at least 10 days under ambient conditions.     

Continuous‐Flow Suzuki‐Miyaura and Mizoroki‐Heck Reactions under Microwave Heating Conditions

Microwave‐assisted continuous‐flow reactions have attracted significant interest from synthetic organic chemists, especially process chemists from practical points of view, due to a less complicated shift to large‐scale synthesis based on simple and continuous access to products with low energy requirements. In this personal account, we focused on the Suzuki‐Miyaura and Mizoroki‐Heck reactions, both of which are significantly important cross‐coupling reactions for the synthesis of various functional materials. Microwave power is effective for heating. Typical homogeneous palladium catalysts, such as PdCl₂(PPh₃)₂, Pd(PPh₃)₄, and Pd(OAc)₂, as well as heterogeneous palladium catalysts, such as Pd‐film, Pd/Al₂O₃, Pd/SiO₂, and Pd supported on polymers, can be used for these reactions.