Simultaneous TR-SPIV and CH* chemiluminescence during precursor to LBO in a lean premixed swirl dump combustor

Blowout process in premixed swirl dump combustors is known to have temporary partial extinction followed by re-ignition events as precursors. This re-ignition process is investigated using high-speed CH* chemiluminescence and simultaneous TR-SPIV. It was found that during the extinction phase, the flame split into two zones, causing fresh mixture to enter the inner recirculation zone. The sudden loss of heat release causes the flow field to change such that the stagnation point moves further downstream, causing high negative velocity paths in the flow. The flame that was convected downstream, now uses these negative velocity paths to consume the fresh mixture that entered the IRZ. This is the re-ignition phase of the precursor event.     

Oxygen atom transfer promoted nitrate to nitric oxide transformation: a step-wise reduction of nitrate → nitrite → nitric oxide

Nitrate reductases (NRs) are molybdoenzymes that reduce nitrate (NO₃⁻) to nitrite (NO₂⁻) in both mammals and plants. In mammals, the salival microbes take part in the generation of the NO₂⁻ from NO₃⁻, which further produces nitric oxide (NO) either in acid-induced NO₂⁻ reduction or in the presence of nitrite reductases (NiRs). Here, we report a new approach of VCl₃ (V³⁺ ion source) induced step-wise reduction of NO₃⁻ in a Co^II-nitrato complex, [(12-TMC)Co^II(NO₃⁻)]⁺ (2,{Co^II–NO₃⁻}), to a Co^III–nitrosyl complex, [(12-TMC)Co^III(NO)]²⁺ (4,{CoNO}⁸), bearing an N-tetramethylated cyclam (TMC) ligand. The VCl₃ inspired reduction of NO₃⁻ to NO is believed to occur in two consecutive oxygen atom transfer (OAT) reactions, i.e., OAT-1 = NO₃⁻ → NO₂⁻ (r₁) and OAT-2 = NO₂⁻ → NO (r₂). In these OAT reactions, VCl₃ functions as an O-atom abstracting species, and the reaction of 2 with VCl₃ produces a Co^III-nitrosyl ({CoNO}⁸) with V^V-Oxo ({V^V O}³⁺) species, via a proposed Co^II-nitrito (3, {Co^II–NO₂⁻}) intermediate species. Further, in a separate experiment, we explored the reaction of isolated complex 3 with VCl₃, which showed the generation of 4 with V^V-Oxo, validating our proposed reaction sequences of OAT reactions. We ensured and characterized 3 using VCl₃ as a limiting reagent, as the second-order rate constant of OAT-2 (k₂^/) is found to be ∼1420 times faster than that of the OAT-1 (k₂) reaction. Binding constant (K_b) calculations also support our proposition of NO₃⁻ to NO transformation in two successive OAT reactions, as K_{b(Co^II–NO2⁻)} is higher than K_{b(Co^II–NO3⁻)}, hence the reaction moves in the forward direction (OAT-1). However, K_{b(Co^II–NO2⁻)} is comparable to K_b{CoNO}⁸, and therefore sequenced the second OAT reaction (OAT-2). Mechanistic investigations of these reactions using ¹⁵N-labeled-¹⁵NO₃⁻ and ¹⁵NO₂⁻ revealed that the N-atom in the {CoNO}⁸ is derived from NO₃⁻ ligand. This work highlights the first-ever report of VCl₃ induced step-wise NO₃⁻ reduction (NRs activity) followed by the OAT induced NO₂⁻ reduction and then the generation of Co-nitrosyl species {CoNO}⁸.

Single metal-induced reduction of NO₃⁻ → {NO₂⁻} → NO via oxygen atom transfer reaction.     

Ionizing radiation-induced XRCC4 phosphorylation is mediated through ATM in addition to DNA-PK

XRCC4 (X-ray cross-complementation group 4) is a protein associated with DNA ligase IV, which is thought to join two DNA ends at the final step of DNA double-strand break repair through non-homologous end-joining. It has been shown that, in response to irradiation or treatment with DNA damaging agents, XRCC4 undergoes phosphorylation, requiring DNA-PK. Here we explored possible role of ATM, which is structurally related to DNA-PK, in the regulation of XRCC4. The radiosensitizing effects of DNA-PK inhibitor and/or ATM inhibitor were dependent on XRCC4. DNA-PK inhibitor and ATM inhibitor did not affect the ionizing radiation-induced chromatin recruitment of XRCC4. Ionizing radiation-induced phosphorylation of XRCC4 in the chromatin-bound fraction was largely inhibited by DNA-PK inhibitor but further diminished by the combination with ATM inhibitor. The present results indicated that XRCC4 phosphorylation is mediated through ATM as well as DNA-PK, although DNA-PK plays the major role. We would propose a possible model that DNA-PK and ATM acts in parallel upstream of XRCC4, regulating through phosphorylation.     

Carbene‐Catalyzed Enantioselective Aldol Reaction: Post‐Aldol Stereochemistry Control and Formation of Quaternary Stereogenic Centers

The dominated approaches for asymmetric aldol reactions have primarily focused on the aldol carbon–carbon bond‐forming events. Here we postulate and develop a new catalytic strategy that seeks to modulate the reaction thermodynamics and control the product enantioselectivities via post‐aldol processes. Specifically, an NHC catalyst is used to activate a masked enolate substrate (vinyl carbonate) to promote the aldol reaction in a non‐enantioselective manner. This reversible aldol event is subsequently followed by an enantioselective acylative kinetic resolution that is mediated by the same (chiral) NHC catalyst without introducing any additional substance. This post‐aldol process takes care of the enantioselectivity issues and drives the otherwise reversible aldol reaction toward a complete conversion. The acylated aldol products bearing quaternary/tetrasubstituted carbon stereogenic centers are formed in good yields and high optical purities.     

Orientational control of liquid crystal molecules via carbon nanotubes and dichroic dye in polymer dispersed liquid crystal

Polymer dispersed liquid crystals (PDLCs) using nematic liquid crystal and photo-curable polymer (NOA 65) were prepared by polymerisation-induced phase separation technique, in equal ratio (1:1) of polymer and liquid crystal (LC). We demonstrate that doping of small amount (0.125%, wt./wt.) of multiwall carbon nanotubes (CNTs) and orange azo dichroic dye in PDLC generously controlled the molecular orientation, dynamics of LC in droplet and size of droplets. The effects of multiwall CNTs and dye on PDLCs were studied in terms of transition temperature, droplet morphology, transmittance characteristic, contrast ratio and response time. The results exhibited that the values of the threshold electric fields were reduced from 8 V/µm (pure PDLC) to 1.18 and 1.72 V/µm, doped with multiwall CNTs and dye, respectively. The CNTs-doped PDLC shows faster switching response as compared with pure PDLC and dye-doped PDLC. However, dye-doped PDLC shows much higher contrast among all PDLC samples. Further, the results also illustrate that the birefringence value of LC in PDLCs was changed with doping of CNTs and dye.     

Extensive enhancement in power conversion efficiency of dye-sensitized solar cell by using Al-doped TiO<Subscript>2</Subscript> photoanode

In this work, we have prepared Al-doped TiO₂ nanoparticles via a hydrothermal method and used it for making photoanode in dye-sensitized solar cell (DSSC). Material characterizations were done using XRD, AFM, SEM, TEM and EDAX. XPS results reveal that Al is introduced successfully into the structure of TiO₂ creating new impurity energy levels in the forbidden gap. This resulted in tuning of the conduction band of TiO₂ and reduced charge recombination which led to better current conversion efficiency of DSSC. Greater dye loading and enhanced surface area was obtained for Al-doped TiO₂ compared to un-doped TiO₂. I-V analysis, EIS and Bode plots are employed to evaluate photovoltaic performance. The short-circuit current density (J _sc) and efficiency (η) of cell employing Al-doped TiO₂ photoanode were extensively enhanced compared to the cell using un-doped TiO₂. The optical band gap (E _g) for Al-doped and un-doped TiO₂ was obtained as 2.8 and 3.2 eV, respectively. J _sc and η were 13.39 mAcm^?2 and 4.27%, respectively, under illumination of 100 mWcm^?2 light intensity when thin films of 1% Al-doped TiO₂ was employed as photoanode in DSSC using N719 as the sensitizer dye. With the use of un-doped TiO₂ as photoanode under similar conditions, J _sc 5.12 mAcm^?2 and η 1.06% only could be obtained. The maximum IPCE% obtained with Al-doped TiO₂ and un-doped TiO₂ was 67 and 38% respectively at the characteristic wavelength of dye (λ _max = 540 nm). The EIS analyses revealed resistive and capacitive elements that provided an insight into various interfacial processes in terms of the charge transport. It was observed that Al-doping reduced the interfacial resistance leading to better charge transport which has improved both photocurrent density and conversion efficiency. Higher electron mobility and fast diffusion resulting in greater charge collection efficiency was obtained for Al-doped TiO₂ compared to the un-doped TiO₂. Using the Mott–Schottky plot, the donor density was calculated for un-doped and Al-doped TiO₂. The work demonstrated that the Al-doped TiO₂ is potential photoanode material for low-cost and high-efficiency DSSC.