Global Sampling of the Photochemical Reaction Paths of Bromoform by Ultrafast Deep-UV Through Near-IR Transient Absorption and ab initio Multiconfigurational Calculations

Ultrafast deep-ultraviolet through near infrared (210-950 nm) transient absorption spectroscopy complemented by ab initio multiconfigurational calculations offers a global description of the photochemical reaction pathways of bromoform following 255-nm excitation in methylcyclohexane and acetonitrile solutions. Photoexcitation of CHBr3 leads to the ground-state iso-CHBr3 product in a large quantum yield (∼35), formed through two different mechanisms: concerted excited-state isomerization and cage-induced isomerization through the recombination of the nascent radical pair. These two processes take place on different time scales of tens of femtoseconds and several picoseconds, respectively. The novel ultrafast direct isomerization pathway proposed herein is consistent with the occurrence of a conical intersection between the first excited singlet state of CHBr3 and the ground electronic state of iso-CHBr3. Complete active space self-consistent field calculations characterize this singularity in the vicinity of a second order saddle point on the ground state which connects the two isomer forms. For cage-induced isomerization, both the formation of the nascent radical pair and its subsequent collapse into ground-state iso-CHBr3 are directly monitored through the deep-ultraviolet absorption signatures of the radical species. In both mechanisms, the optically active (i.e., those with largest Franck-Condon factors) C-Br-Br bending and Br-Br stretching modes of ground-state iso-CHBr3 have the largest projection on the reaction coordinate, enabling us to trace the structural changes accompanying vibrational relaxation of the non-equilibrated isomers through transient absorption dynamics. The iso-CHBr3 photoproduct is stable in methylcyclohexane, but undergoes either facile thermal isomerization to the parent CHBr3 structure through a cyclic transition state stabilized by the polar acetonitrile medium (∼300-ps lifetime), and hydrolysis in the presence of water. © 2013 American Institute of Physics

Improving The Catalytic Activity Of Semiconductor Nanocrystals Through Selective Domain Etching

Colloidal chemistry offers an assortment of synthetic tools for tuning the shape of semiconductor nanocrystals. While many nanocrystal architectures can be obtained directly via colloidal growth, other nanoparticle morphologies require alternative processing strategies. Here, we show that chemical etching of colloidal nanoparticles can facilitate the realization of nanocrystal shapes that are topologically inaccessible by hot-injection techniques alone. The present methodology is demonstrated by synthesizing a two-component CdSe/CdS nanoparticle dimer, constructed in a way that both CdSe and CdS semiconductor domains are exposed to the external environment. This structural morphology is highly desirable for catalytic applications as it enables both reductive and oxidative reactions to occur simultaneously on dissimilar nanoparticle surfaces. Hydrogen production tests confirmed the improved catalytic activity of CdSe/CdS dimers, which was enhanced 3-4 times upon etching treatment. We expect that the demonstrated application of etching to shaping of colloidal heteronanocrystals can become a common methodology in the synthesis of charge-separating nanocrystals, leading to advanced nanoparticles architectures for applications in areas of photocatalysis, photovoltaics, and light detection

Bilateral pheochromocytoma and a tumor of the jejunum with neurofibromatosis of type 1

Neurofibromatosis type 1 (NF1) is a hereditary disease with the high frequency of neuroendocrine tumors. This article represents a clinical case of the diagnosed NF1 in a 40-year old patient with the history of bilateral pheocromocytoma and malignant gastrointestinal stromal tumor of the jejunum. Clinical diagnosis NF1 was suspected on the basis of the typical skin manifestations.The timely diagnosis of NF1 has practical significance as it enables physicians persistently search for neuroendocrine lesions in a such cohort of patients

Description of a new species of soil algae, Parietochloris grandis sp. nov., and study of its fatty acid profiles under different culturing conditions

© 2018 Elsevier B.V. The new species Parietochloris grandis sp. nov. is described from forest soil in the Dnipropetrovsk region, Ukraine. The description is based on morphological features and the phylogenetic analysis of partial SSU rDNA and rbcL genes. Phylogenetic analysis places P. grandis in the Parietochloris clade, within the family Trebouxiophyceae. The novel strain formed a strongly supported monophyletic lineage with the type species of Parietochloris, P. alveolaris. P. grandis differed from other species in the Parietochloris clade by the size and form of vegetative cells and the large number of zoospores in zoosporangia. A number of experiments with different phosphates and nitrates concentrations were conducted to evaluate changes in fatty acid profile and biomass. The dominant fatty acids during cultivation on standard BG-11 medium, as well as with the phosphates concentrations ranged from 0.22 to 2 mM, were linoleic acid (24–25%), palmitic acid (12–14%), linolenic acid (9–12%), and oleic acid (7–11%). The content of arachidonic acid and eicosapentaenoic acid ranged from 3.5 to 4.5% and 0.7% to 0.8%, respectively. The fatty acid profile and total fatty acids varied significantly under different nutrient deficiency. The greatest variation was found for oleic acid (9–46%) and linolenic acid (2–13%). The percentage of arachidonic acid was the highest with a standard nitrates concentration in the medium (5%) and the lowest in the absence of phosphates and nitrates (1.3–1.5%), but the absolute content in dry biomass was similar in all variants of the experiment (6.5–9.3 mg g−1 dry weight). The absence of nitrogen and both nitrogen and phosphorus led to a 3–fold increase in TFA in comparison with the control. Thus, this strain can be considered in biotechnological application as a potential producer of the essential linoleic acid or oleic acid

Enhanced Lifetime Of Excitons In Nonepitaxial Au/cds Core/shell Nanocrystals

The ability of metal nanoparticles to capture light through plasmon excitations offers an opportunity for enhancing the optical absorption of plasmon-coupled semiconductor materials via energy transfer. This process, however, requires that the semiconductor component is electrically insulated to prevent a backward charge flow into metal and interfacial states, which causes a premature dissociation of excitons. Here we demonstrate that such an energy exchange can be achieved on the nanoscale by using nonepitaxial Au/CdS core/shell nanocomposites. These materials are fabricated via a multistep cation exchange reaction, which decouples metal and semiconductor phases leading to fewer interfacial defects. Ultrafast transient absorption measurements confirm that the lifetime of excitons in the CdS shell (tau approximate to 300 ps) is much longer than lifetimes of excitons in conventional, reduction-grown Au/CdS heteronanostructures. As a result, the energy of metal nanoparticles can be efficiently utilized by the semiconductor component without undergoing significant nonradiative energy losses, an important property for catalytic or photovoltaic applications. The reduced rate of exciton dissociation in the CdS domain of Au/CdS nanocomposites was attributed to the nonepitaxial nature of Au/CdS interfaces associated with low defect density and a high potential barrier of the interstitial phase

Ultrafast Photochemistry of Polyhalogenated Methanes and Non-Metals

A molecular level understanding of photodynamics in condensed media is one of the recent challenges to chemical physics. This is because of the intrinsic complexity of liquid-phase photophysical and photochemical singularities arising from competing intra- and intermolecular processes. Such processes often take place on a timescale of a few femtoseconds (10-15 s) to several tens of picoseconds (10-12 s). In this work, the model photochemical processes used to investigate ultrafast photo-induced reaction dynamics in solution. The model compounds are non-metal/metal polyhalogenated small molecules. The gas-phase photochemistry of these small molecules is thoroughly examined, which also enables to establish the connection between liquid and gas phase dynamics. Furthermore, contrary to the scrupulously investigated di- and triatomic molecular systems, more vibrational degrees of freedom are accessible both for the model parent molecules, nascent polyatomic radical species, and isomer photoproducts. Therefore, a detailed mapping of the photochemical reaction paths of these molecular systems can possibly reveal different couplings between the reactive modes and other dark states in a far-from-equilibrium situation. The complexity of the encountered ultrafast events requires the utilization of several experimental and computational approaches. Results of femtosecond transient absorption, picosecond transient resonance Raman, excited state ab initio calculations are discussed in this context

DIAGNOSTICS OF PSYCHOLOGICAL MATURITY OF THE PERSON

This article is devoted to the urgent problem of personality maturity and its diagnosis. The article analyzes the scientific views and the main maturity criteria, which are systematized by the author

THE LIFE CYCLE, THE CYTOLOGICAL AND CYTOCHEMICAL PECULIARITIES OF ADELINA GRYLLI, 1996 (APICOMPLEXA, EUCOCCIDIIDA, ADELEIDAE)

The peculiarities of the species have been examined thoroughly, the cytoenzymological investigation has been performed. For the first time, the population analysis of species of the parasitizing protozoya has been performed on the example of A. grylli. The degree of stability of the systematic signs of species, kin A. grylli and the composition of the kin have been analyzed. The phenomenon of self-regulation of the parasiters numbers in the host's organism on the different stages of the life cycle has been revealed. The technical ways of the work, easily reproduceable, with the coccidia of the invertebrates have been developed.Available from VNTIC / VNTIC - Scientific & Technical Information Centre of RussiaSIGLERURussian Federatio

Diagnostics of Psychological Maturity of the Person

This article is devoted to the urgent problem of personality maturity and its diagnosis. The article analyzes the scientific views and the main maturity criteria, which are systematized by the author