Selfassembly of α,ω‐dithiols on surfaces and metal dithiol heterostructures

α,ω‐Dithiols present an interesting case of molecules with two reactive terminal ‐SH groups (HS‐R‐SH) that allow their use as binders between different metallic entities. They have thus been used in molecular electronics conduction measurements, in “nanogap” electrodes of interest in plasmonics, as building blocks of more complex structures such as metal intercalated superlattices and in the formation of metalized organic thin films, including doped graphene type films. There exist however many problems, because the molecules may end up in undesirable configurations with both thiol terminals bound to the same metal particle/substrate or link with other molecules to produce “multi‐molecule” or “multilayer” structures. This report discusses various key questions on dithiol linking with metal surfaces and the quest of protocols of making problem free dithiol metal structures. It then describes the use of dithiols and their SAMs to produce various metal organic heterostructures useful for molecular electronics and formation of doped metalized organic thin films. We discuss the build up of these structures by self assembly and lithography, their chemical composition and functional properties.

     

Selective pyrolysis of bifunctional compounds: gas-phase elimination of carbonate-ester functionalities

Compounds containing both carbonate and ester functionalities were synthesized and then subjected to online-GC gas-phase pyrolysis. The carbonate groups were cleaved selectively in all elimination reactions. The end products of the reaction were found to be affected by the nature of the substrate. The presence of hydrogen and carbonyl substituents on the carbon β to the carbonate group resulted in further product decomposition through a concerted six-membered transition state. Results from flash vacuum pyrolysis (FVP) and analysis of the GC data indicate that the cleavage of the carbonate group is fast, and that the slower secondary decomposition reactions are independent of the presence of the carbonate group. Spectroscopic analyses of the products are reported.     

On-line monitoring of composite nanoparticles synthesized in a pre-industrial laser pyrolysis reactor using Laser-Induced Breakdown Spectroscopy

Laser-Induced Breakdown Spectroscopy (LIBS) was employed for on-line and real time process monitoring during nanoparticle production by laser pyrolysis. Laser pyrolysis has proved to be a reliable and versatile method for nanoparticle production. However, an on-line and real time monitoring system could greatly enhance the process optimization and accordingly improve its performances. For this purpose, experiments aiming at demonstrating the feasibility of an on-line monitoring system for silicon carbide nanoparticle production using the LIBS technique were carried out. Nanosecond laser pulses were focused into a cell through which part of the nanoparticle flux diverted from the production process was flowed for LIBS analysis purposes. The nanoparticles were vaporized within the laser-induced plasma created in argon used as background gas in the process. Temporally-resolved emission spectroscopy measurements were performed in order to monitor nanoparticle stoichiometry. Promising results were obtained and on-line Si/C_x stoichiometry was successfully observed. These results put forward the possibility of real time correction of the nanoparticle stoichiometry during the production process.     

Preparation and infrared/raman classification of 630 spectroscopically encoded styrene copolymers

The barcoded resins (BCRs) were introduced recently as a platform for encoded combinatorial chemistry. One of the main challenges yet to be overcome is the demonstration that a large number of BCRs could be generated and classified with high confidence. Here, we describe the synthesis and classification of 630 polystyrene-based copolymers prepared from the combinatorial association of 15 spectroscopically active styrene monomers. Each of the 630 copolymers displayed a unique vibrational fingerprint (infrared and Raman), which was converted into a spectral vector. To each of the 630 copolymers, a vector of the known (reference) composition was assigned. Unknown (prediction) vectors were decoded using multivariate data analysis. From the inner product of the reference and prediction vectors, a correlation map comparing 396 900 copolymer pairs (630 x 630) was generated. In 100% of the cases, the highest correlation was obtained for polymer pairs in which the reference and prediction vectors correspond to copolymers prepared from identical styrene monomers, thus demonstrating the high reliability of this encoding strategy. We have also established that the spectroscopic barcodes generated from the Raman and infrared spectra are independent of the copolymers' morphology (beaded versus bulk polymers). Besides the demonstration of the generality of the polymer barcoding strategy, the analytical methods developed here could in principle be extended to the investigation of the composition and purity of any other synthetic polymer and biopolymer library, or even scaffold-based combinatorial libraries.     

Synthesis of hydrophobic derivatives of the G/\C base for rosette nanotube self-assembly in apolar media

Eleven self-complementary G/\C derivatives bearing hydrophobic moieties were synthesized and characterized. One representative derivative from this family was shown to self-assemble into rosette nanotubes in hexane and form Langmuir-Blodgett films at the air-water interface.     

A regioselective approach to trisubstituted 2 (or 6)-arylaminopyrimidine-5-carbaldehydes and their application in the synthesis of structurally and electronically unique GlambdaC base precursors

An efficient regioselective synthesis of trisubstituted 2(or 6)-arylaminopyrimidine-5-carbaldehydes has been developed via an S(N)Ar reaction of 2,4,6-trichloropyrimidine-5-carbaldehyde with aniline, methylamine, and alkoxide nucleophiles using a combination of phase-transfer catalysis and more traditional SNAr reaction conditions. We demonstrate that in a few synthetic steps, highly functionalized fused-bicyclic pyrimidine substrates can be accessed from the trisubstituted 2-arylaminopyrimidine-5-carbaldehydes. Furthermore, these fused-bicyclic compounds are readily derivatized using the Suzuki cross-coupling reaction to generate electronically and structurally unique GlambdaC base precursors.     

Proteomic Analysis of the Protein Expression Profile in the Mature <Emphasis Type="Italic">Nigella sativa</Emphasis> (Black Seed)

Nigella sativa (N. sativa) seed has been used as an important nutritional flavoring agent and in traditional medicine for treating many illnesses since ancient times. Understanding the proteomic component of the seed may lead to enhance the understanding of its structural and biological functional complexity. In this study, we have analyzed its proteome profile based on gel-based proteome mapping technique that includes one-dimensional gel electrophoresis followed by liquid chromatography and tandem mass spectrometry strategy. We have not come across any such studies that have been performed in N. sativa seeds up to date. A total of 277 proteins were identified, and their functional, metabolic, and location-wise annotations were carried out using the UniProt database. The majority of proteins identified in the proteome dataset based on their function were those involved in enzyme catalytic activity, nucleotide binding, and protein binding while the major cellular processes included regulation of biological process followed by regulation of secondary biological process, cell organization and biogenesis, protein metabolism, and transport. The identified proteome was localized mainly to the nucleus then to the cytoplasm, plasma membrane, mitochondria, plastid, and others. A majority of the proteins were involved in biochemical pathways involving carbohydrate metabolism, amino acid and shikimate pathway, lipid metabolism, nucleotide, cell organization and biogenesis, transport, and defense processes. The identified proteins in the dataset help to improve our understanding of the pathways involved in N. sativa seed metabolism and its biochemical features and detail out useful information that may help to utilize these proteins. This study could thus pave a way for future further high-throughput studies using a more targeted proteomic approach.     

A Stable Integrated Photoelectrochemical Reactor for H2 Production from Water Attains a Solar-to-Hydrogen Efficiency of 18 % at 15 Suns and 13 % at 207 Suns

The major challenge in solar water splitting to H₂ and O₂ is in making a stable and affordable system for large-scale applications. We have designed, fabricated, and tested a photoelectrochemical reactor characterized as follows: 1) it comprises an integrated device to reduce the balance of the system cost, 2) it utilizes concentrated sunlight to reduce the photoabsorber cost, and 3) it employs and alkaline electrolyte to reduce catalyst cost and eliminate external thermal management needs. The system consists of an III-V-based photovoltaic cell integrated with Ni foil as an O₂ evolution catalyst that also protects the cell from corrosion. At low light concentration, without the use of optical lenses, the solar-to-hydrogen (STH) efficiency was 18.3 %, while at high light concentration (up to 207 suns) with the use of optical lenses, the STH efficiency was 13 %. Catalytic tests conducted for over 100 hours at 100–200 suns showed no sign of degradation nor deviation from product stoichiometry (H₂/O₂=2). Further tests projected a system stability of years.