PRACTICE OF CAD AND CAE DESIGN IN THE FIELD OF PLASMA TECHNOLOGIES

The effectiveness of automated plasma torch design methods can be improved by integrating design and engineering analysis technologies. The features of CAD and CAE technologies for designing plasma torches are considered. Shows examples of the design of plasma torches for cutting metals and waste treatment with the use of digital technologies.Эффективность автоматизированных методов проектирования плазмотронов можно повысить за счет интеграции технологий проектирования и инженерного анализа. Рассмотрены особенности CAD и CAE технологий проектирования плазмотронов. Показаны примеры проектирования плазмотронов для резки металлов и обезвреживания отходов с применением цифровых технологий

Conflicting Role of Water in the Activation of H₂O₂ and the Formation and Reactivity of Non-Heme Fe^III–OOH and Fe^III–O–Fe^III Complexes at Room Temperature

The formation of an Fe^III–OOH species by reaction of complex <b>1</b> ([(MeN3Py)­Fe^II(CH₃CN)₂]²⁺) with H₂O₂ at room temperature is reported and is studied by a combination of UV/vis absorption, EPR, and resonance Raman spectroscopies. The formation of the Fe^III–OOH species, and its subsequent conversion to relatively inert Fe^III–O–Fe^III species, is shown to be highly dependent on the concentration of water, with excess water favoring the formation of the latter species, which is studied by UV/vis absorption spectroelectrochemistry also. The presence of acetic acid increases the rate and extent of oxidation of <b>1</b> to its iron­(III) state and inhibits the wasteful decomposition of H₂O₂ but does not affect significantly the spectroscopic properties of the Fe^III–OOH species formed

Effect of Immobilization on Gold on the Temperature Dependence of Photochromic Switching of Dithienylethenes

We report the properties and switching characteristics of a series of dithienylethene photochromic switches immobilized on gold. Self-assembled monolayers (SAMs) of three structurally related dithienylethenes were formed on roughened gold bead substrates and studied by surface-enhanced Raman spectroscopy (SERS). These data were compared to SERS spectra obtained by aggregation of colloidal gold, solid state Raman spectra, and Raman spectra calculated using density functional theory (DFT). Two of the dithienylethenes studied have an “asymmetric” design, which was demonstrated earlier to lower the thermal barrier for photochemical ring opening in solution. Herein, we show that, when immobilized on a gold surface, the asymmetric dithienylethenes in fact display a higher thermal barrier than that of their symmetric counterparts. In addition, we show that photochemical ring closing of asymmetric dithienylethenes is inhibited when immobilized on gold

Mechanically Induced Gel Formation

Mechanical triggering of gelation of an organic solution by a carbazole-based bisurea organogelator is described. Both the duration of the mechanical stimulation and the gelator concentration control the gelation process and the characteristics of the gel obtained

Electrochemical Write and Read Functionality through Oxidative Dimerization of Spiropyran Self-Assembled Monolayers on Gold

In contrast to their photochromism, the electrochemistry of spiropyrans in self-assembled monolayers has attracted only modest attention in recent years. In this contribution the electrochemical oxidation of self-assembled monolayers (SAMs) of 6-nitro-BIPS spiropyran (SP) prepared on polycrystalline gold surfaces is described. The SAMs were characterized with cyclic voltammetry, X-ray photoelectron spectroscopy (XPS), surface-enhanced Raman scattering (SERS), and UV/vis absorption spectroelectrochemistry. The electrochemical oxidation of spiropyrans in solution results in aryl C–C coupling of the indole units and thereby the formation of a symmetric spiropyran dimer. Comparison of spectroscopic data obtained for electrochemically oxidized spiropyran dimers in solution with data from monolayers confirms that a similar oxidative coupling occurs in the SAMs on gold also. The dimer formed can be oxidized electrochemically to monocationic and dicationic states and shows remarkably good stability in UHV and ambient conditions in all three redox states. In addition, the dimerized spiropyran self-assembled monolayer show photochromism, which was characterized by XPS and SERS spectroscopy

UV/Vis and NIR Light-Responsive Spiropyran Self-Assembled Monolayers

Self-assembled monolayers of a 6-nitro BIPS spiropyran (SP) modified with a disulfide-terminated aliphatic chain were prepared on polycrystalline gold surfaces and characterized by UV/vis absorption, surface-enhanced Raman scattering (SERS), and X-ray photoelectron spectroscopies (XPS). The SAMs obtained are composed of the ring-closed form (i.e., spiropyran) only. Irradiation with UV light results in conversion of the monolayer to the merocyanine form (MC), manifested in the appearance of an N⁺ contribution in the N 1s region of the XPS spectrum of the SAMs, the characteristic absorption band of the MC form in the visible region at 555 nm, and the C–O stretching band in the SERS spectrum. Recovery of the initial state of the monolayer was observed both thermally and after irradiation with visible light. Several switching cycles were performed and monitored by SERS spectroscopy, demonstrating the stability of the SAMs during repeated switching between SP and MC states. A key finding in the present study is that ring-opening of the surface-immobilized spiropyrans can be induced by irradiation with continuous wave NIR (785 nm) light as well as by irradiation with UV light. We demonstrate that ring-opening by irradiation at 785 nm proceeds by a two-photon absorption pathway both in the SAMs and in the solid state. Hence, spiropyran SAMs on gold can undergo reversible photochemical switching from the SP to the MC form with both UV and NIR and the reverse reaction induced by irradiation with visible light or heating. Furthermore, the observation of NIR-induced switching with a continuous wave source holds important consequences in the study of photochromic switches on surfaces using SERS and emphasizes the importance of the use of multiple complementary techniques in characterizing photoresponsive SAMs

Selective Photo-Induced Oxidation with O₂ of a Non-Heme Iron(III) Complex to a Bis(imine-pyridyl)iron(II) Complex

Non-heme iron­(II) complexes of pentadentate N4Py (<i>N,N</i>-bis­(2-pyridylmethyl)-<i>N</i>-bis­(2-pyridyl)­methylamine) type ligands undergo visible light-driven oxidation to their iron­(III) state in the presence of O₂ without ligand degradation. Under mildly basic conditions, however, highly selective base catalyzed ligand degradation with O₂, to form a well-defined pyridyl-imine iron­(II) complex and an iron­(III) picolinate complex, is accelerated photochemically. Specifically, a pyridyl-CH₂ moiety is lost from the ligand, yielding a potentially N4 coordinating ligand containing an imine motif. The involvement of reactive oxygen species other than O₂ is excluded; instead, deprotonation at the benzylic positions to generate an amine radical is proposed as the rate determining step. The selective nature of the transformation holds implications for efforts to increase catalyst robustness through ligand design

Palladium-Catalyzed Anti-Markovnikov Oxidation of Allylic Amides to Protected β‑Amino Aldehydes

A general method for the preparation of N-protected β-amino aldehydes from allylic amines or linear allylic alcohols is described. Here the Pd­(II)-catalyzed oxidation of N-protected allylic amines with benzoquinone is achieved in tBuOH under ambient conditions with excellent selectivity toward the anti-Markovnikov aldehyde products and full retention of configuration at the allylic carbon. The method shows a wide substrate scope and is tolerant of a range of protecting groups. Furthermore, β-amino aldehydes can be obtained directly from protected allylic alcohols via palladium-catalyzed autotandem reactions, and the application of this method to the synthesis of β-peptide aldehydes is described. From a mechanistic perspective, we demonstrate that tBuOH acts as a nucleophile in the reaction and that the initially formed <i>tert</i>-butyl ether undergoes spontaneous loss of isobutene to yield the aldehyde product. Furthermore, tBuOH can be used stoichiometrically, thereby broadening the solvent scope of the reaction. Primary and secondary alcohols do not undergo elimination, allowing the isolation of acetals, which subsequently can be hydrolyzed to their corresponding aldehyde products

Mechanically Induced Gel Formation

Mechanical triggering of gelation of an organic solution by a carbazole-based bisurea organogelator is described. Both the duration of the mechanical stimulation and the gelator concentration control the gelation process and the characteristics of the gel obtained

Reversible Deactivation of Manganese Catalysts in Alkene Oxidation and H₂O₂ Disproportionation

Mononuclear MnII oxidation catalysts with aminopyridine-based ligands achieve high turnover-number (TON) enantioselective epoxidation of alkenes with H2O2. Structure reactivity relations indicate a dependence of enantioselectivity and maximum TON on the electronic effect of peripheral ligand substituents. Competing H2O2 disproportionation is reduced by carrying out reactions at low temperatures and with slow addition of H2O2, which improve TONs for alkene oxidation but mask the effect of substituents on turnover frequency (TOF). Here, in situ Raman spectroscopy provides the high time resolution needed to establish that the minimum TOFs are greater than 10 s–1 in the epoxidation of alkenes with the complexes [Mn(OTf)2(RPDP)] [where R = H (HPDP-Mn) and R = OMe (MeOPDP-Mn) and RPDP = N,N′-bis(2″-(4″-R-pyridylmethyl)-2,2′-bipyrrolidine)]. Simultaneous headspace monitoring by Raman spectroscopy reveals that H2O2 disproportionation proceeds concomitant with oxidation of the substrate and that the ratio of reactivity toward substrate oxidation and H2O2 disproportionation is ligand-dependent. Notably, the rates of substrate oxidation and H2O2 disproportionation both decrease over time under continuous addition of H2O2 due to progressive catalyst deactivation, which indicates that the same catalyst is responsible for both reactions. Electrochemistry, UV/vis absorption, and resonance Raman spectroscopy and spectroelectrochemistry establish that the MnII complexes undergo an increase in oxidation state within seconds of addition of H2O2 to form a dynamic mixture of MnIII and MnIV species, with the composition depending on temperature and the presence of alkene. However, it is the formation of these complexes (resting states), rather than ligand degradation, that is responsible for catalyst deactivation, especially at low temperatures, and hence, the intrinsic reactivity of the catalyst is greater than observed TOFs. These data show that interpretation of effects of ligand substituents on reaction efficiency (and conversion) with respect to the oxidant and maximum TONs needs to consider reversible deactivation of the catalyst and especially the relative importance of various reaction pathways