Synthesis of 1-aryl-3H-[1,2,5]triazepino[5,4-a]benzimidazol-4(5H)-ones and quantum chemical investigation of the rotamers of the Boc-protected hydrazide key intermediate

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Simple Method for the Preparation of 1,3-Dithiol-2-one and 1,3-Dithiol-2-thione

Abstract

The reaction of diisopropyl xanthogen and thio-diisopropyl xanthogen disulfide with alkynes furnished 1,3-dithiol-2-one and 1,3-dithiol-2-thione.     

Size-Exclusion Chromatography of Asphaltenes: An Experimental Comparison of Commonly Used Approaches

Asphaltenes, the heaviest and most polar fraction of crude oil, are responsible for the clogging of oil pipelines and of underground reservoir rocks. Asphaltenes are defined as a solubility class (toluene- or benzene-soluble, n-alkane insoluble), and a consensus is still lacking on the molar mass (M) averages, distribution, and range of these materials. Size-exclusion chromatography (SEC) is among the most widely employed methods for characterizing the M averages and distributions of both natural and synthetic polymers and, as such, has seen widespread application in the study of asphaltenes. SEC analysis of asphaltenes presents a number of challenges, however, some inherent to all low-M materials and some unique to these particular analytes. Here, we have experimentally compared several of the most commonly used approaches to SEC of asphaltenes, in hope of both demonstrating the influence of experimental conditions upon the results obtained as well as to determine optimal conditions of analysis. In the end, while the former goal was met, the latter one remains an open challenge in the field.     

Fractionation of the human plasma proteome for monoclonal antibody proteomics‐based biomarker discovery 2: Antigen identification by dot‐blot array screening

Immunization with complex mixtures, like the human plasma resulted in the generation of cloned mAb libraries (PlasmaScan? and QuantiPlasma? libraries, with >1000 individual mAbs) reacting with a nonredundant set of antigenic epitopes. mAb proteomics refers to quasi‐hypothesis‐free profiling of plasma samples with nascent or cloned mAb libraries for the discovery of disease‐specific biomarkers. Once mAbs with biomarker potential have been identified, the next task is the determination of cognate antigens recognized by the respective mAbs. To determine the cognate protein antigen corresponding to each individual mAbs in the cloned mAb libraries, we have separated human plasma by consecutive steps of desalting and various chromatography procedures. The process resulted in 783 fractions, which we termed “Analyte Library” (AL). The AL represents the human plasma proteome in relatively low‐protein complexity fractions. Here, to determine the utility of the AL, we selected ten plasma proteins and checked for their presence in the fractions. Among the ten cases, the distribution of four selected plasma proteins matched expectations, as these proteins were present only in a few fractions corresponding to their physical, chemical, and biochemical properties. However, in six cases, we observed “smear” ‐like distribution or complete absence of the proteins, suggesting that protein–protein interactions or protein variants may alter the observed plasma distribution profiles. Nevertheless, we conclude that the AL is an efficient, high throughput tool to complement the mAb biomarker discovery process with cognate protein antigen identification for each mAbs.     

Crosslinked penicillin acylase aggregates for synthesis of β-lactam antibiotics in organic medium

Crosslinked enzyme aggregates (CLEAs) of a partially purified penicillin acylase from a recombinant Escherichia coli strain have been produced as a novel type of biocatalysts well endowed to perform in organic media. Different protein precipitants were studied and glutaraldehyde was used as the crosslinking agent. Precipitation curves were obtained for all precipitants to determine the concentrations at which all the protein precipitated out of the solution. The effect of the glutaraldehyde-to-protein ratio was studied with respect to process recovery and the specific activity and stability of the biocatalyst. Recovery of penicillin acylase activity was moderately high, about 50%; major losses of enzyme activity were produced at the precipitation step. Specific activities of all CLEAs were very high, which is one of the advantages of using nonsupported biocatalysts. Ammonium sulfate and tert-butyl alcohol were the best precipitants at a glutaraldehyde-protein mass ratio of 2 and were selected to perform the kinetically controlled synthesis of ampicillin in 60% (v/v) ethylene glycol medium. At comparable conversion yields, volumetric and specific antibiotic productivity were much higher for CLEAs than for carrier-bound penicillin acylases.     

Nearly zero ultraflattened dispersion in photonic crystal fibers

We present a procedure for achieving photonic crystal fibers with nearly zero ultraflattened group-velocity dispersion. Systematic knowledge of the special guiding properties of these fibers permits the achievement of qualitatively novel dispersion curves. Unlike the behavior of conventional fibers, this new type of dispersion behavior permits remarkably improved suppression of third-order dispersion, particularly in the low-dispersion domain.     

Towards relativistic ECP / DFT description of chemical bonding in E112 compounds: spin-orbit and correlation effects in E112X versus HgX (X=H, Au)

The relativistic effective core potential (RECP) approach combined with the spin-orbit DFT electron correlation treatment was applied to the study of the bonding of eka-mercury (E112) and mercury with hydrogen and gold atoms. Highly accurate small-core shape-consistent RECPs derived from Hartree-Fock-Dirac-Breit atomic calculations with Fermi nuclear model were employed. The accuracy of the DFT correlation treatment was checked by comparing the results in the scalar-relativistic (spin-orbit-free) limit with those of high level scalar-relativistic correlation calculations within the same RECP model. E112H was predicted to be slightly more stable than its lighter homologue (HgH). The E112-Au bond energy is expected to be ca. 25–30 % weaker than that of Hg-Au. The role of correlations and magnetic (spin-dependent) interactions in E112-X and Hg-X (X=H, Au) bonding is discussed. The present computational procedure can be readily applied to much larger systems and seems to be a promising tool for simulating E112 adsorption on metal surfaces.     

A Practical General Method for the Preparation of Long Acenes

The field of long acenes, the narrowest of the zig-zag graphene nanoribbons, has been an area of significant interest in the past decade because of its potential applications in organic electronics, spintronics and plasmonics. However the low solubility and high reactivity of these compounds has so far hindered their preparation on large scales. We report here a concise strategy for the synthesis of higher acenes through Diels–Alder condensation of arynes with a protected tetraene ketone. After deprotection by cleavage of the ketal, the obtained monoketone precursors cleanly yield the corresponding acenes through quantitative cheletropic thermal decarbonylation in the solid state, at moderate temperatures of 155 to 205 °C. This approach allows the preparation of heptacene, benzo[a]hexacene, cis- and trans-dibenzopentacene and offers a valuable new method for the synthesis of even larger acenes.