ABSTRACT
New bioorthogonal cycloaddition of 5-arylidene derivatives of 1,3-dimethylbarbituric acid as 1-oxa-1,3-butadienes and vinyl thioether as a dienophile has been applied to imaging inside living cells. The reaction is high yielding, selective, and fast in aqueous media. The proposed 1-oxa-1,3-butadiene derivative conjugated to a FITC fluorochrome selectively and rapidly labels the cancer cells pretreated with the dienophile-taxol. The second order rate constants k2 for various proposed bioorthogonal cycloadditions were estimated to be in the range from 0.9 × 10-2 M-1 s-1 to 1.4 M-1 s-1, which is much better than in the case of the first generation TQ-ligation (o-quinolinone quinone methide and vinyl thioether ligation, k2 = 1.5 × 10-3 M-1 s-1) and comparable or better to that for the second generation TQ-ligation (k2 = 2.8 × 10-2 M-1 s-1). The reaction rate constants k2 of proposed ligation reactions are in the range of the rate constants k2 for tetrazines and norbornenes or tetrazines and cyclopropenes. These findings indicate that this chemistry is suitable for in vitro imaging experiments.
Subject(s)
SulfidesABSTRACT
As an organic nanostructure, self-assembled monolayers (SAMs) play a central role in many aspects of nanotechnology, including molecular electronics. In this work, we show that SAMs based on N-heterocyclic carbenes on a Au(111) substrate offer a high level of crystallinity and also exhibit the highest possible packing density. As a result of this structural optimization, defect concentrations were reduced by 2-3 orders of magnitude and thermal stability was â¼100 K higher than those of any other SAMs on Au. The conductivity of these SAMs is â¼4 orders of magnitude lower than that of standard alkanethiols of comparable length, which together with very low defect concentration and high thermal stability makes them a highly interesting material for potential application in organic thin film transistors. The self-assembly of such dense, highly crystalline, and notably stable structures is associated with strong C-Au bonding and the rational design of assembled molecules, resulting in the high mobility of both adsorbate and substrate atoms, as confirmed by the size of the molecular domains and the adsorbate-driven modification of the Au(111) substrate, respectively.
ABSTRACT
The electron-irradiation-induced synthesis of carbon nanomembranes (CNMs) from aromatic thiol-based self-assembled monolayers (SAMs) on gold substrate is a well-established method to form molecular thin nanosheets. These molecular two-dimensional materials can be prepared with tunable properties; therefore, they find a variety of applications in nanotechnology ranging from ultrafiltration to nanobiosensors. However, no chemically inert CNM was fabricated up to now, as the reactive thiol group is present on the membrane surface even after transferring it to other substrates. Here, we study the electron irradiation of carboxylic acid-based SAMs on a silver substrate as an alternative route for CNM formation. Our analysis, based on a combination of X-ray photoelectron spectroscopy and scanning electron microscopy demonstrates that for this type of SAMs, purely carbonaceous CNMs with tunable porosity can be obtained.
ABSTRACT
Ion-induced desorption was successfully applied for the analysis of the stability of chemical bonds at the molecule-metal interface in the case of ionic bonding. The obtained experimental data combined with the results of the DFT calculations reveal the effect of positional oscillations in the stability of consecutive chemical bonds, which has general character in chemistry.
