Temperature dependence of strain energy and thermodynamic properties of V2O5‐based single‐walled nanotubes: Zone‐folding approach

A zone‐folding approach is applied to estimate the thermodynamic properties of V₂O₅‐based nanotubes. The results obtained are compared with those from the direct calculations. It is shown that the zone‐folding approximation allows an accurate estimation of nanotube thermodynamic properties and gives a gain in computation time compared to their direct calculations. Both approaches show that temperature effects do not change the relative stability of V₂O₅ free layers and nanotubes derived from the α‐ and γ‐phase. The internal energy thermal contributions into the strain energy of nanotubes are small and can be ignored. © 2016 Wiley Periodicals, Inc.     

Theoretical Study of α‐V2O5‐Based Double‐Wall Nanotubes

First‐principles calculations of the atomic and electronic structure of double‐wall nanotubes (DWNTs) of α‐V₂O₅ are performed. Relaxation of the DWNT structure leads to the formation of two types of local regions: 1) bulk‐type regions and 2) puckering regions. Calculated total density of states (DOS) of DWNTs considerably differ from that of single‐wall nanotubes and the single layer, as well as from the DOS of the bulk and double layer. Small shoulders that appear on edges of valence and conduction bands result in a considerable decrease in the band gaps of the DWNTs (up to 1 eV relative to the single‐layer gaps). The main reason for this effect is the shift of the inner‐ and outer‐wall DOS in opposite directions on the energetic scale. The electron density corresponding to shoulders at the conduction‐band edges is localized on vanadium atoms of the bulk‐type regions, whereas the electron density corresponding to shoulders at the valence‐band edges belongs to oxygen atoms of both regions.     

Biocompatible Ir(III) Complexes as Oxygen Sensors for Phosphorescence Lifetime Imaging

Synthesis of biocompatible near infrared phosphorescent complexes and their application in bioimaging as triplet oxygen sensors in live systems are still challenging areas of organometallic chemistry. We have designed and synthetized four novel iridium [Ir(N^C)₂(N^N)]⁺ complexes (N^C–benzothienyl-phenanthridine based cyclometalated ligand; N^N–pyridin-phenanthroimidazol diimine chelate), decorated with oligo(ethylene glycol) groups to impart these emitters’ solubility in aqueous media, biocompatibility, and to shield them from interaction with bio-environment. These substances were fully characterized using NMR spectroscopy and ESI mass-spectrometry. The complexes exhibited excitation close to the biological “window of transparency”, NIR emission at 730 nm, and quantum yields up to 12% in water. The compounds with higher degree of the chromophore shielding possess low toxicity, bleaching stability, absence of sensitivity to variations of pH, serum, and complex concentrations. The properties of these probes as oxygen sensors for biological systems have been studied by using phosphorescence lifetime imaging experiments in different cell cultures. The results showed essential lifetime response onto variations in oxygen concentration (2.0–2.3 μs under normoxia and 2.8–3.0 μs under hypoxia conditions) in complete agreement with the calibration curves obtained “in cuvette”. The data obtained indicate that these emitters can be used as semi-quantitative oxygen sensors in biological systems.     

High-accuracy calculation of 6s --> 7s parity-nonconserving amplitude in Cs

We calculated the parity-nonconserving (PNC) 6s-->7s amplitude in Cs. In the Dirac-Coulomb approximation our result is in good agreement with other calculations. Breit corrections to the PNC amplitude and to the Stark-induced amplitude beta are found to be -0.4% and -1%, respectively. The weak charge of 133Cs is Q(W) = -72.5+/-0.7 in agreement with the standard model.     

Utility of the tandem Pauson-Khand reaction in the construction of tetracycles

The scope of the tandem Pauson-Khand reaction has been explored for the regiospecific construction of [5.5.5.5]- and [5.6.6.5]tetracyclic systems via the photolytic method of Livinghouse. The rapid regiospecific entry into the two dicyclopentapentanoid systems 17 and 29 was accomplished from the key diene-diynes 11 and 19b. A photochemically mediated catalytic tandem Pauson-Khand cyclization was employed to prepare the parent ring systems of dicyclopenta[a,e]pentalene (from 19b) and dicyclopenta[a,f]pentalene (from 11) in regiospecific fashion in a one-pot process. Under these conditions, conversion of acyclic diene-diyne 16 into tetracyclic system 17 was achieved in 74% yield, while a similar process was employed to convert 28 into tetracycle 29 in 90% yield. This is much improved over the previous conditions that employed NMO. Six carbon-carbon bonds were generated in this process constituting up to 98% yield for each carbon-carbon bond so formed. Furthermore, tetracyclic [5.6.6.5] systems such as dicyclopenta[b,g]decalins 37, 38, and 40 were prepared from similar diene-diyne precursors via the tandem Pauson-Khand cyclization. Importantly, acetal 36 provided the desired cis-fused [5.6.6.5] system 38a (via 40a/b) in stereospecific fashion. This reaction is unique in that it provides a cis-decalin ring system; moreover, the yield of each of the six carbon-carbon bonds formed in this process was at least 89%. The structure of cis diol 38a was confirmed by X-ray crystallography.