Disk aromaticity of the planar and fluxional anionic boron clusters B20(-/2-)

The presence of excess electrons modifies the structural landscape and tends to extend the planarity of boron clusters. While the neutral B(20) is tubular, both the anion and dianion B(20)(-/2-) become planar. Geometrical features of the stable anions suggest the existence of a new type of cluster that is planar and doubly cyclic with one atom located at the center (see figure), as well as being fluxional.     

Kinetics of the C-C bond beta scission reactions in alkyl radical reaction class

Kinetics of the β-scission in alkyl radical reaction class was studied using the reaction class transition state theory (RC-TST) combined with the linear energy relationship (LER) and the barrier height grouping (BHG) approach. All necessary parameters were derived from first-principle density functional calculations for a representative set of 21 reactions. Different error analyses and comparisons with available literature data were made. Direct comparison with available experimental data indicates that the RC-TST/LER, where only reaction energy is needed, can predict rate constants for any reaction in this reaction class with excellent accuracy. Specifically for this reaction class, the RC-TST/LER method has less than 60% systematic errors on average in the predicted rate constants when compared to explicit rate calculations.     

Study of the isomeric ratios in photonuclear reactions of natural Selenium induced by bremsstrahlungs with end-point energies in the giant dipole resonance region

We have determined the isomeric ratios in ⁷⁴Se(γ, n)^73m,gSe and ⁸²Se(γ, n)^81m,gSe photonuclear reactions of natural Selenium induced by bremsstrahlungs with end-point energies in the giant dipole resonance region. The investigated samples were irradiated at electron accelerator Microtron MT-25 of the Flerov Laboratory of Nuclear Reaction, Joint Institute for Nuclear Research, Dubna, Russia. The gamma spectra of the samples irradiated were measured with spectroscopic system consisting of 8,192 channel analyzer and high-energy resolution (180 keV at gamma ray 1,332 keV of ⁶⁰Co) HP(Ge) semiconductor detector Canberra. The GENIE2000 (Canberra) computer program was used for data processing. The results were discussed and compared with those of other authors.     

Kinetics of the hydrogen abstraction OH + alkane --> H2O + alkyl reaction class: an application of the reaction class transition state theory

This paper presents an application of the reaction class transition state theory (RC-TST) to predict thermal rate constants for hydrogen abstraction reactions of the type OH + alkane --> HOH + alkyl. We have derived all parameters for the RC-TST method for this reaction class from rate constants of 19 representative reactions, coupling with linear energy relationships (LERs), so that rate constants for any reaction in this class can be predicted from its reaction energy calculated at either the AM1 semiempirical or BH&HLYP/cc-pVDZ level of theory. The RC-TST/LER thermal rate constants for selected reactions are in good agreement with those available in the literature. Detailed analyses of the results show that the RC-TST/LER method is an efficient method for accurately estimating rate constants for a large number of reactions in this class. Analysis of the LERs leads to the discovery of the beta-carbon radical stabilization effect that stabilizes the transition state of any reaction in this class that yields products having one or more beta-carbons, and thus leads to the lower barrier for such a reaction.     

Multi-wall carbon nanotubes (MWCNTs)-doped polypyrrole DNA biosensor for label-free detection of genetically modified organisms by QCM and EIS

In this paper, we describe DNA electrochemical detection for genetically modified organism (GMO) based on multi-wall carbon nanotubes (MWCNTs)-doped polypyrrole (PPy). DNA hybridization is studied by quartz crystal microbalance (QCM) and electrochemical impedance spectroscopy (EIS). An increase in DNA complementary target concentration results in a decrease in the faradic charge transfer resistance (R_ct) and signifying “signal-on” behavior of MWCNTs-PPy-DNA system. QCM and EIS data indicated that the electroanalytical MWCNTs-PPy films were highly sensitive (as low as 4 pM of target can be detected with QCM technique). In principle, this system can be suitable not only for DNA but also for protein biosensor construction.     

The isomeric ratio of fragment 135Xe from photofission of 233U induced by 23.5 MeV bremsstrahlung

The ratio of the probabilities of population of the isomeric and ground states, so called the isomeric ratio is closely connected to the angular momentum of the initial fission fragments that is dissipated at the later stages of gamma ray cascade. This ratio also provides important information on the nuclear level structure as well as the nuclear reaction mechanism involved. In this work, the isomeric ratio in fission fragment ¹³⁵Xe from photofission of ²³³U induced by 23.5 MeV bremsstrahlung has been determined by the method that uses inert gaseous flow. The results have been discussed and compared with that of other authors.     

Necessary conditions for super minimizers in constrained multiobjective optimization

This paper concerns the study of the so-called super minimizers related to the concept of super efficiency in constrained problems of multiobjective optimization, where cost mappings are generally set-valued. We derive necessary conditions for super minimizers on the base of advanced tools of variational analysis and generalized differentiation that are new in both finite-dimensional and infinite-dimensional settings for problems with single-valued and set-valued objectives.      

Nonreciprocal behavior and switching in optical couplers with longitudinally varying coupling coefficient

We report the nonreciprocal behavior of an optical coupler consisting of two straight waveguides forming a small angle. An optical diode action is theoretically demonstrated when light is launched along opposite directions. The switching power is lower than the case of parallel waveguides with a constant coupling coefficient.     

Temporal Regulation of PET-RAFT Controlled Radical Depolymerization

A photocatalytic RAFT-controlled radical depolymerization method is introduced for precisely conferring temporal control under visible light irradiation. By regulating the deactivation of the depropagating chains and suppressing thermal initiation, an excellent temporal control was enabled, exemplified by several consecutive “on” and “off” cycles. Minimal, if any, depolymerization could be observed during the dark periods while the polymer chain-ends could be efficiently re-activated and continue to depropagate upon re-exposure to light. Notably, favoring deactivation resulted in the gradual unzipping of polymer chains and a stepwise decrease in molecular weight over time. This synthetic approach constitutes a simple methodology to modulate temporal control during the chemical recycling of RAFT-synthesized polymers while offering invaluable mechanistic insights.