The breaking of bonds by catalytic electrons has gained prominence very recently but has been limited to cases where electrons from external sources have been used. Here, we show that upon photoexcitation, an electron of intramolecular origin is transferred from one part of a molecule to another followed by bond cleavage and then returns to its original moiety on completion of its catalytic function. By a proper assessment of the dramatic changes in aromaticity in excited-state intermediates along the photoreaction coordinate captured by the magnetically induced current density (MICD) technique, we show that in 5-phenyltetrazole, an excited electron, which migrates from the phenyl ring to the tetrazole ring, induces bond cleavage catalytically. Using the MICD technique, we establish for the first time a link between the phenomenon of excited-state electron/charge transfer among aromatic rings and the intricate interplay of aromatic, antiaromatic and non-aromatic states.
BackgroundSeasonal variation in the hospital admission due to cardiovascular disease (CVDs) has been widely reported. However, very limited data on Bangladesh is available regarding this matter. The aim of the current study was to investigate the effect of seasonal variation on hospital admission due to CVDs in a leading hospital of Bangladesh.MethodsOver a period of two years (from May 2010 to April 2012), the number of patients hospitalized due to various CVDs and number of death among these hospitalized patients were recorded on a day-to-day basis. The data were recorded according to the chief reason of hospital admission such as myocardial infarction or MI (acute, old and non-ST elevation), unstable angina (UA), exaggeration of stable angina, acute left ventricular failure (LVF), cardiomyopathy (ischemic and dilated) or heart failure, syncope and arrhythmia. The data were cumulated and analyzed on month-wise and season-wise manner.ResultsA total of 8371 patients were admitted over the study period (5909 male and 2462 female; M/F ratio - 2.4:1). The highest number of patients were admitted during winter (n = 2839, 33.9%) and lowest during summer (n = 1648, 19.7%). The hospital admission was also significantly higher in winter compared to other seasons (p-value versus summer, autumn and spring was 0.018, 0.020 and 0.023 respectively). Acute MI (n = 2374), Acute LVF (n = 1582) and UA (n = 1277) were the top three reasons for hospitalization. Number of death also significantly higher in winter compared to other seasons (p-value versus summer, winter and spring was 0.044, 0.050 and 0.014 respectively).ConclusionA seasonal variation in the hospital admission due to CVDs with a peak in winter was clearly demonstrated in the study. These data could be useful to improve causative prevention measures, therapeutic management, and educational strategies.
Atomic
layer deposition (ALD) of antimony selenide (Sb2Se3) is demonstrated using selenium dimethyldithiocarbamate
as a new chalcogen precursor with tris(dimethylamino) antimony as
a metal source at 150 °C. The ALD chemistry with this organic-selenide
precursor is explored as an alternative to highly toxic H2Se. The mechanistic facets of the reactions facilitating the deposition
are revealed through theoretical investigations using the density
functional theory. The findings from the theoretical study are in
good agreement with the experimental findings. The deposition mechanism
during the nucleation and linear growth regime is studied thoroughly
with an in situ quartz crystal microbalance illustrating a “substrate-enhanced
growth” during the initial deposition cycles. The saturated
growth rate of ∼0.28 Å per cycle is achieved. The as-grown
material is then investigated as the photon-absorber layer in the
sensitized solar cell application. The charge transfer processes are
studied using surface photovoltage studies under monochromatic light
and variable intensity white light using a vibrating Kelvin probe.
Photoremovable protecting groups (PPGs) provide spatial and temporal control over the release of various chemicals. Using surface hopping studies with multireference electronic structure methods we have unravelled the nuclear and the electronic events at play. Furthermore, the electronic changes along the reaction path were probed using excited state aromaticity quantifiers and orbital analysis. We find that upon irradiation with light of appropriate wavelength on the substituted coumarin system a π−π* electronic excitation occurs which is followed by an electron loss from the aromatic ring on gaining proper alignment between the π* and the C-LG (LG = leaving group) σ*. This alignment is brought about by a critical dihedral angle change in the molecule, which subsequently triggers C-LG bond cleavage. The sequence of events is indicative of an intramolecular electron catalyzed process which is established through investigations of changes in aromaticity of the phenyl ring which acts as an electron reservoir.
Realization
of practical hydrogen storage in adsorbent materials
is still elusive due to several insurmountable issues. In the case
of chemical hydrogen storage, the roadblock arises from the failure
to attain reversibility of hydrogenation/dehydrogenation under ambient
conditions. Herein we show with static and ab initio molecular dynamics
(aiMD) methods that the choice of a proper solvent can make monomeric
(BN)24, an experimentally known BN-fullerene, a viable
option for sustainable chemical hydrogen storage. A proper thermodynamic
and kinetic balance is attained, which prevents oligomerization of
monomeric (BN)24 and affords reversible hydrogenation of
the available tetragonal B2N2 rings to appreciable
rates and extents. Our calibrated static DFT and canonical (NVT) ensemble
aiMD studies indicate that the solvent–(BN)24 interactions
are adequately strong in nucleophilic solvents, while they are fairly
weak in electrophilic solvents. We show that hydrogenation of the
(micro)solvated monomeric fullerene can be achieved at reasonable
rates and to the desired extent in certain solvents using existing
metal-free hydrogenating agents. For hydrogenated (BN)24 the solvent–solute interactions are rather weak in both the
nucleophilic and electrophilic solvents, thus making the dehydrogenation
less challenging and allowing it to be achieved catalytically. Hence,
this endeavor provides the first-ever crucial understanding of the
solvation effect on sustainable hydrogenation/dehydrogenation involving
BN-fullerenes which is vital for attaining the magic target of over
5 wt % hydrogen storage under ambient conditions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.