21 research outputs found
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 H<sub>2</sub>O<sub>2</sub> and the Formation and Reactivity of Non-Heme Fe<sup>III</sup>–OOH and Fe<sup>III</sup>–O–Fe<sup>III</sup> Complexes at Room Temperature
The
formation of an Fe<sup>III</sup>–OOH species by reaction of
complex <b>1</b> ([(MeN3Py)Fe<sup>II</sup>(CH<sub>3</sub>CN)<sub>2</sub>]<sup>2+</sup>) with H<sub>2</sub>O<sub>2</sub> 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<sup>III</sup>–OOH species, and its subsequent conversion to relatively
inert Fe<sup>III</sup>–O–Fe<sup>III</sup> 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
H<sub>2</sub>O<sub>2</sub> but does not affect significantly the spectroscopic
properties of the Fe<sup>III</sup>–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<sup>+</sup> 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 O<sub>2</sub> 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 O<sub>2</sub> without ligand degradation.
Under mildly basic conditions, however, highly selective base catalyzed
ligand degradation with O<sub>2</sub>, to form a well-defined pyridyl-imine
iron(II) complex and an iron(III) picolinate complex, is accelerated
photochemically. Specifically, a pyridyl-CH<sub>2</sub> moiety is
lost from the ligand, yielding a potentially N4 coordinating ligand
containing an imine motif. The involvement of reactive oxygen species
other than O<sub>2</sub> 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 H<sub>2</sub>O<sub>2</sub> 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