Quantum close-coupling calculations on conventional and coherence cross sections in Ca(4s4p,3P j=2←3P j=1) + RG inelastic collision

The quantum close-coupling studies of the ³P _j=2 ←³P _j=1 non-adiabatic transition in Ca colliding with He and Ar are presented. The multistructure cross sections are calculated using the pseudopotential curves of E. Czuchaj, M. Kro?nicki, H. Stoll, Chem. Phys. 101, 292 (2003). The conventional and coherence cross sections that can be measured in collisional experiments with atomic beams are expressed via generalized Grawert parameters, quantities dependent on dynamics only and independent of geometry. They allow us to obtain direct relationships between the average cross sections and the conventional and coherence cross sections. The possibility of experimental determination of reorientation, alignment and other non-adiabatic effects occuring during atomic collisions is discussed.     

Phosphonylated thiocarbonyl ylides from the reaction of aromatic thioketones with diethyl diazomethylphosphonates

The reaction of diazomethylphosphonates with aromatic thioketones at −65 °C to room temperature yields 2,5-dihydro-1,3,4-thiadiazole-2-phosphonates, which eliminates N₂ to give phosphonylated thiocarbonyl ylides as reactive intermediates. These sulfur-centered 1,3-dipoles undergo typical reactions of thiocarbonyl ylides, i.e., 1,3-dipolar cycloadditions, cyclodimerization, and electrocyclic ring closure, depending on the involved thioketone and, therefore, on the reaction conditions. In the case of the most reactive thiofluorenone, the phsophonylated thiocarbonyl methanide can be intercepted with thiobenzophenone, a phosphonodithioformate, and tetracyanoethylene. In the absence of such reactive dipolarophiles, cyclodimerization occurs to give the corresponding 1,4-dithiane.     

Assignment of the absolute configuration of hydroxy- and aminophosphonates by NMR spectroscopy

Phosphonate analogues of amino- and hydroxy acids have received considerable attention in bioorganic and medicinal chemistry due to their unique activities as peptidomimetics, being known as inhibitors of such enzymes as human renin, HIV protease and polymerase, leucine aminopeptidase and serine proteases. They have also been exploited as haptens for catalytic antibody research, herbicides, antibiotics, antiviral and anticancer agents and neuromodulators. Therefore, the demand for the asymmetric synthesis of hydroxy- and aminophosphonates should be accompanied by reliable methods for their absolute configuration assignment. NMR spectroscopy is one of the most commonly used techniques for the assignment of absolute configuration of different classes of compounds. This report describes the principles and practical aspects of applying chiral discriminating agents for the assignment of absolute configuration of 1- and 2-hydroxyphosphonates and 1- and 2-aminophosphonates by NMR spectroscopy. The report is organized in sections discussing the types of the chiral discriminating agents (including the models used for configuration assignment, if this was proposed) and the scope of their applications (with the list of all the examples of hydroxy- and aminophosphonates examined by this method). The application of the chiral derivatizing agents (CDA) and chiral solvating agents (CSA) used for these purposes, such as α-methoxy-α-(trifluoromethyl)phenylacetic acid (MTPA), α-methoxyphenylacetic acid (MPA), amino acids, diazaphospholidine, camphanic acid, naproxen, quinine and t-butylphenylphosphinothioic acid is discussed. Easy access to the selected values of the NMR chemical shifts observed for the diastereomeric species of the tested hydroxy- and aminophosphonates examined, will enable the reader to compare trends observed in spectra and subsequent absolute configuration assignment. In addition, any available complementary data confirming the configuration established by NMR (X-ray, chemical correlations, optical rotation) is also provided.     

DFT studies on the favored and rare tautomers of neutral and redox cytosine

The complete tautomeric mixture consisting of nine prototropic tautomers has been studied in the gas phase at the DFT(B3LYP)/6-311+G(d,p) level for neutral, oxidized, and reduced cytosine. Rotational isomerism of the exo –OH group and geometrical isomerism of the exo =NH group have also been considered. Tautomeric conversions possible for cytosine have been compared with those for its structural models, 4-amino- and 2-hydroxypyrimidine. Effects of intramolecular interactions between neighboring groups for cytosine are analogous to those observed for model compounds. Although they are not very strong, they are sufficient to influence tautomeric equilibria and relative stabilities of individual tautomers. One-electron oxidation and one-electron reduction change tautomeric preferences. Tautomers that are rare forms for neutral cytosine become favored ones for oxidized and reduced cytosine. Aromaticity is not the main factor that dictates the tautomeric preferences. Stability of functional groups seems to be more important than full electron delocalization.     

Bottom‐Up Fabrication of Nanopatterned Polymers on DNA Origami by In Situ Atom‐Transfer Radical Polymerization

Bottom‐up strategies to fabricate patterned polymers at the nanoscale represent an emerging field in the development of advanced nanodevices, such as biosensors, nanofluidics, and nanophotonics. DNA origami techniques provide access to distinct architectures of various sizes and shapes and present manifold opportunities for functionalization at the nanoscale with the highest precision. Herein, we conduct in situ atom‐transfer radical polymerization (ATRP) on DNA origami, yielding differently nanopatterned polymers of various heights. After cross‐linking, the grafted polymeric nanostructures can even stably exist in solution without the DNA origami template. This straightforward approach allows for the fabrication of patterned polymers with low nanometer resolution, which provides access to unique DNA‐based functional hybrid materials.     

The application of activated carbon modified by ozone treatment for energy storage

Activated carbon modified by ozone treatment was examined. The process was carried out in a glass reactor under a continuous flow of ozone through a bed of activated carbon for 15, 30, 60, 120, and 240 min. The modified and unmodified carbon materials were characterized by Raman spectroscopy and observed by scanning electron microscopy (SEM). Thermogravimetric analysis was used to estimate the presence of oxygen groups in the carbon structure. The surface area and pore size distribution were examined by nitrogen adsorption method at 77 K. Moreover, Fourier transform infrared (FTIR) spectroscopy was used to estimate the functional groups of modified activated carbon. The carbon content was estimated using the elemental analysis. The process of ozonation increases oxygen functionalities, thus the activated carbon was tested as electrodes for an electrochemical capacitor. The performance of an electrochemical capacitor was estimated by selected alternating (AC) and direct current (DC) methods in 1 M H₂SO₄, 1 M Na₂SO₄, and 6 M KOH electrolytes.

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Selenophen‐2‐yl‐Substituted Thiocarbonyl Ylides – at the Borderline of Dipolar and Biradical Reactivity

The reactions of aryl (selenophen‐2‐yl) thioketones with CH₂N₂ occur with spontaneous elimination of N₂, even at low temperature (?65°), to give regioselectively sterically crowded 4,4,5,5‐tetrasubstituted 1,3‐dithiolanes and/or a novel type of twelve‐membered dithia‐diselena heterocycles as dimers of the transient thiocarbonyl S‐methanides. The ratio of these products depends on the type of substituent located at C(4) of the phenyl ring. Whereas the formation of the 1,3‐dithiolanes corresponds to a [3+2] cycloaddition of an intermediate thiocarbonyl ylide with the starting thioketone, the twelve‐memberd ring has to be formed via dimerization of the ‘thiocarbonyl ylide’ with an extended biradical structure.