Spectroscopic studies on the photoeffects on some metallocenes in the presence of chloroform molecules confined in poly(methyl methacrylate) thin films

The changes in the electronic absorption spectra (UV-Vis) (after photoexcitation) of poly(methyl methacrylate) (PMMA) thin films doped with a metallocene and containing chloroform molecules as impurities, have been studied as a function of photoexcitation wavelength (210-750 nm), photoexcitation time (duration), amount of metallocene in the film and amount of chloroform molecules present in the film. Photoeffects on the metallocenes have been observed, which depend significantly on the nature of the central metal atom of the metallocene and the results have been discussed on the basis of the electronic configuration of the metallocenes, which is under study.     

Diastereoselective construction of syn-α-oxyamines via three-component α-oxyaldehyde-dibenzylamine-alkyne coupling reaction: application in the synthesis of (+)-β-conhydrine and its analogues

A Cu(i)-catalyzed α-oxyaldehyde-dibenzylamine-alkyne coupling reaction was delineated for the construction of α-oxyamines with excellent yields and diastereoselectivity. Crystal structure analysis and theoretical calculations were also supportive of the formation of syn-α-oxyamines as the major products. Application of the methodology addresses the synthesis of (+)-β-conhydrine along with analogs having two different diversity features. A ring size variation allows construction of piperidine and pyrrolidine rings while a variation of side arm functionality is achieved by complete regioselective opening of epoxide by different organocopper ylides (Gilman reagents). A lactam-Cu(i) complexation motif is proposed which allows an intramolecular attack of ylides at the terminal epoxy carbon via the six-membered cyclic transition state. The present work features the synthesis of (+)-β-conhydrine over eight steps in 26% yield and its seven analogs in 21-28% yields.     

Nitryl chloride (ClNO2): UV/vis absorption spectrum between 210 and 296 K and O(3P) quantum yield at 193 and 248 nm

Recent studies have shown that the UV/vis photolysis of nitryl chloride (ClNO2) can be a major source of reactive chlorine in the troposphere. The present work reports measurements of the ClNO2 absorption spectrum and its temperature dependence between 210 and 296 K over the wavelength range 200–475 nm using diode array spectroscopy. The room temperature spectrum obtained in this work was found to be in good agreement with the results from Ganske et al. (J. Geophys. Res. 1992, 97, 7651) over the wavelength range common to both studies (200–370 nm) but differs systematically from the currently recommended spectrum for use in atmospheric models. The present results lead to a decrease in the calculated atmospheric ClNO2 photolysis rate by 30%. Including the temperature dependence of the ClNO2 spectrum decreases the calculated atmospheric photolysis rate at lower temperatures (higher altitudes) even further. A parametrization of the wavelength and temperature dependence of the ClNO2 spectrum is presented. O(3P) quantum yields, Φ(ClNO2)(O), in the photolysis of ClNO2 at 193 and 248 nm were measured at 296 K using pulsed laser photolysis combined with atomic resonance fluorescence detection of O(3P) atoms. Φ(ClNO2)(O)(λ) was found to be 0.67 ± 0.12 and 0.15 ± 0.03 (2σ error limits, including estimated systematic errors) at 193 and 248 nm, respectively, indicating that multiple dissociation channels are active in the photolysis of ClNO2 at these wavelengths. The Φ(ClNO2)(O)(λ) values obtained in this work are discussed in light of previous ClNO2 photodissociation studies and the differences are discussed.     

Variation of multiplicities of the secondary charged particles on the geometry of collision

The total charge of the projectile spectator fragments, Q_pf is taken as a measure of the degree of centrality of collision thus defining the collision geometry. In this paper the mean multiplicities of the different charged secondaries emitted in the interaction of ²⁴Mg-Em at 4.5A GeV have been investigated as a function of the total charge Q_pf of the projectile spectator fragments. It has been observed that the average number of the produced particles, 〈N^s〉 and the heavily ionizing particles, 〈N_h> decreases exponentially with the increase of Q_pf showing strong correlation with the geometry of the collision. An attempt has also been made to compare these results with ⁸⁴Kr-Em interaction at 0.95A GeV.     

Analysis of collimated radiation in participating media using the discrete transfer method

A general formulation of the discrete transfer method is provided to analyze radiative heat transfer problems in a participating medium subjected to collimated radiation. The formulation is validated by considering 1-D planar absorbing, emitting and anisotropically scattering gray medium in radiative equilibrium. Anisotropy of the medium is approximated by linear anisotropic phase function. For the purpose of comparison, the problem is also solved analytically. Results are obtained for different angles of incidence of the collimated radiation. At a given angle of incidence, results are obtained for forward, isotropic and backward scattering situations. Heat flux results are compared over a wide range of values of the extinction coefficient. Emissive power distributions in the medium are also obtained for some cases. The discrete transfer method results are found to compare very well with the analytic results.     

Low-Valent Titanium Mediated Reductive Deoxygenation of Carbonyls to Methylenes Via Carbon-Nitrogen Bond Cleavage in N-(Arylmethyl) Anilines

The reduction of aryl aldehydes and ketones in neutral medium, to the corresponding hydrocarbons via carbon-nitrogen bond cleavage of the intermediate N-(arylmethyl)anilines with low-valent titanium reagents is described. It provides a mild, convenient and selective pathway for deoxygenation of carbonyls without the production of any side product.     

Excitonically Coupled Cyclic BF2 Arrays of Calix[8]‐ and Calix[16]phyrin as Near‐IR‐Chromophores

Two giant calix[n]phyrin derivatives namely calix[8]‐ ( 4 ) and calix[16]phyrin ( 5 ), involving two and four BF₂ units, respectively, were prepared through the condensation of the bis‐naphthobipyrrolylmethene‐BF₂ complex ( 3 ) with pentafluorobenzaldehyde. Calix[n]phyrins 4 and 5 display extremely high extinction coefficients (3.67 and 4.82×10⁵ m ^?1 cm^?1, respectively) in the near‐IR region, which was taken as initial evidence for strong excitonic coupling within these cyclic multi‐chromophoric systems. Detailed insights into the effect of excitonic coupling dynamics on the electronic structure and photophysical properties of the macrocycles came from fluorescence, time‐correlated single‐photon counting (TCSPC) and transient absorption (TA) measurements. Support for these experimental findings came from theoretical studies. Theory and experiment confirmed that the coupling between the excitons depends on the specifics of the calix[n]phyrin structure, not just its size.     

Enantioconvergent Biohydrolysis of Racemic Styrene Oxide to R-phenyl-1, 2-ethanediol by a Newly Isolated Filamentous Fungus Aspergillus tubingensis TF1

An effort was made to isolate biocatalysts hydrolyzing epoxides from various ecological niches of northeast India, a biodiversity hot spot zone of the world and screened for epoxide hydrolase activity to convert different racemic epoxides to the corresponding 1, 2-vicinal diols. Screening of a total of 450 microorganisms isolated was carried out using NBP colorimetric assay. One of the strains TF1, after internal transcribed spacer sequence analysis, identified as Aspergillus tubingensis, showed promising enantioconvergent epoxide hydrolase activity. The hydrolysis of unsubstituted styrene oxide (1) occurred to give 97 % ee of R-(?)-1-phenylethane-1, 2-diol (6) with more than 99 % conversion within 45 min incubation. It is shown to be a cheap and practical biocatalyst for one step asymmetric synthesis of chiral R-diol. The other representative substrates (2–5), although underwent hydrolysis with more than 99 % conversion beyond 15 h, exhibited poor enantioselectivity.     

Atmospheric chemistry of CF3CF═CH2 and (Z)-CF3CF═CHF: Cl and NO3 rate coefficients, Cl reaction product yields, and thermochemical calculations

Rate coefficients, k, for the gas-phase reactions of Cl atoms and NO(3) radicals with 2,3,3,3-tetrafluoropropene, CF(3)CF═CH(2) (HFO-1234yf), and 1,2,3,3,3-pentafluoropropene, (Z)-CF(3)CF═CHF (HFO-1225ye), are reported. Cl-atom rate coefficients were measured in the fall-off region as a function of temperature (220-380 K) and pressure (50-630 Torr; N(2), O(2), and synthetic air) using a relative rate method. The measured rate coefficients are well represented by the fall-off parameters k(0)(T) = 6.5 × 10(-28) (T/300)(-6.9) cm(6) molecule(-2) s(-1) and k(∞)(T) = 7.7 × 10(-11) (T/300)(-0.65) cm(3) molecule(-1) s(-1) for CF(3)CF═CH(2) and k(0)(T) = 3 × 10(-27) (T/300)(-6.5) cm(6) molecule(-2) s(-1) and k(∞)(T) = 4.15 × 10(-11) (T/300)(-0.5) cm(3) molecule(-1) s(-1) for (Z)-CF(3)C═CHF with F(c) = 0.6. Reaction product yields were measured in the presence of O(2) to be (98 ± 7)% for CF(3)C(O)F and (61 ± 4)% for HC(O)Cl in the CF(3)CF═CH(2) reaction and (108 ± 8)% for CF(3)C(O)F and (112 ± 8)% for HC(O)F in the (Z)-CF(3)CF═CHF reaction, where the quoted uncertainties are 2σ (95% confidence level) and include estimated systematic errors. NO(3) reaction rate coefficients were determined using absolute and relative rate methods. Absolute measurements yielded upper limits for both reactions between 233 and 353 K, while the relative rate measurements yielded k(3)(295 K) = (2.6 ± 0.25) × 10(-17) cm(3) molecule(-1) s(-1) and k(4)(295 K) = (4.2 ± 0.5) × 10(-18) cm(3) molecule(-1) s(-1) for CF(3)CF═CH(2) and (Z)-CF(3)CF═CHF, respectively. The Cl-atom reaction with CF(3)CF═CH(2) and (Z)-CF(3)CF═CHF leads to decreases in their atmospheric lifetimes and global warming potentials and formation of a chlorine-containing product, HC(O)Cl, for CF(3)CF═CH(2). The NO(3) reaction has been shown to have a negligible impact on the atmospheric lifetimes of CF(3)CF═CH(2) and (Z)-CF(3)CF═CHF. The energetics for the reaction of Cl, NO(3), and OH with CF(3)CF═CH(2) and (Z)-CF(3)CF═CHF in the presence of O(2) were investigated using density functional theory (DFT).     

A Sandwich Azobenzene–Diamide Dimer for Photoregulated Chloride Transport

There has been a tremendous evolution for artificial ion transport systems, especially gated synthetic systems, which closely mimic their natural congeners. Herein, we demonstrate a trans-azobenzene-based photoregulatory anionophoric system that transports chloride by forming a sandwich dimeric complex. Further studies confirmed a carrier-mediated chloride-anion antiport mechanism, and the supramolecular interactions involved in chloride recognition within the sandwich complex were revealed from theoretical studies. Reversible trans–cis photoisomerization of the azobenzene was achieved without any significant contribution from the thermal cis→trans isomerization at room temperature. Photoregulatory transport activity across the lipid bilayer membrane inferred an outstanding off-on response of the azobenzene photoswitch.