Photophysics and dynamics of a β-carboline analogue in room temperature ionic liquids

Room temperature ionic liquids are rapidly emerging as a new class of media that are ideally suited for various applications including carrying out chemical reactions. In the present article, we report the photophysics of a β-carboline analogue, namely, 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ), in three room temperature ionic liquids (RTILs), 1-butyl-3-methylimidazolium methyl sulfate ([BMIM][MeSO(4)]), 1-butyl-3-methylimidazolium octyl sulfate ([BMIM][C(8)SO(4)]) and 1-ethyl-3-methylimidazolium methyl sulfate ([EMIM][MeSO(4)]). Out of these, [BMIM][C(8)SO(4)] is a typical RTIL that forms micellar aggregates above a critical micellar concentration (CMC). Steady state absorption, steady state and time resolved fluorescence techniques are used to probe the properties of these systems. The investigation reveals that the photophysics of AODIQ is modified significantly in the micelle-forming RTIL as compared to that in the other two. A comparative study with the fluorophore in [BMIM][C(8)SO(4)] and a conventional anionic surfactant of a similar hydrophobic chain length from the sodium-n-alkyl sulfate series, viz., sodium octyl sulfate (S(8)S), reveals that the fluorophore experiences a more constrained environment in the RTIL micelle as compared to the conventional anionic micelle.     

Multiple emissions of benzil at room temperature and 77 K and their assignments from ab initio quantum chemical calculations

Multiple emissions have been observed from benzil under different conditions in solutions at room temperature as well as in low temperature glass matrices at 77 K. Low temperature emission has been monitored in rigid matrices frozen under different conditions of illumination. Steady state and time-resolved results together with the ab initio quantum chemical calculations provide, for the first time, the assignments of the different fluorescence bands to the different geometries and∕or electronic states of the fluorophore molecule. It is revealed that the skew form of benzil emits from the first (S(1)) as well as the second excited singlet (S(2)) states depending on the excitation wavelength, while the relaxed transplanar conformer fluoresces only from the S(1) state. The yet unexplored emission band peaking at around 360 nm has been assigned to originate from the S(2) state. Ab initio calculations using the density functional theory at B3LYP∕6-31G?? level corroborate well with the experimental observations.     

Interaction of pyrene-end-capped poly(ethylene oxide) with bovine serum albumin and human serum albumin in aqueous buffer medium: a fluorometric study

The photophysical behavior of a hydrophobically tailored water-soluble polymer, pyrene-end-capped poly(ethylene oxide) (PYPY), has been studied in aqueous buffered bovine serum albumin (BSA) and human serum albumin (HSA) media. In buffered aqueous solution the polymer shows dual emission corresponding to the monomer and the excimer of pyrene moiety. The relative intensity of the monomer to the excimer emission shows interesting variation with the addition of BSA and HSA and is indicative of significant interaction of these albumin proteins with the polymer. The binding interaction has been shown to have a prominent role on the steady state fluorescence anisotropy of the two emission bands. Attempt has been made to determine the micropolarities of the protein microenvironments from a comparison of the variation of the monomer to excimer relative fluorescence intensities of the probe in water–dioxane mixtures with varying composition.     

Dramatic pressure-dependent quenching effects in supercritical CO2 assessed by the fluorescence of 4'-dimethylamino-3-hydroxyflavone. Thermodynamic versus kinetics control of excited-state intramolecular proton transfer

Steady-state fluorescence of 4'-dimethylamino-3-hydroxyflavone (DMA3HF) was observed in supercritical carbon dioxide (scCO(2)). Excited-state intramolecular proton transfer (ESIPT) occurs resulting in two well-separated emission bands corresponding to the normal and tautomer forms. As the scCO(2) density exceeds 0.7 g/mL, the relative intensity of the two bands tends to a constant value, comparable to that observed for organic solvents with ET(30) = 33.0 +/- 0.5 kcal/mol, such as toluene and di-n-butyl ether. At lower densities, the substantial decrease of the total fluorescence intensity (a 600-fold decrease as the pressure decreases from 100 to 80 bar) is accompanied by an even more accentuated decrease of the tautomer fluorescence. This can be explained by a shift in the equilibrium between normal and tautomer forms, concomitant with a more efficient quenching of the less solvated fluorophore, that may change the thermodynamic control of the relative population of the two emissive species to a kinetic control.     

A compton profile study of tantalum

We report the results of Compton profile study on polycrystalline tantalum. Measurements have been made using 59.54 keV gamma-rays. The results are compared with the APW band structure calculations of Papanicolaouet al and other available data. In contrast to the work of Changet al the overall agreement is better with the APW band structure which worsens on incorporating the electron correlation correction. Estimates of the errors due to the contribution from bremsstrahlung, non-validity of impulse-approximation and anomalous dispersion are also briefly discussed.     

Compton profile of molybdenum

In this paper we report the experimental Compton profile of polycrystalline molybdenum. The measurements have been made by scattering 59.54 keVγ-rays and are compared with the recent band structure calculation of Janiet al. [4]. These results have also been compared with our calculation based on the renormalized-free-atom model for different 4d-5s configurations. It is found that the present experimental data are relatively in good agreement with the band structure calculation.     

Stereoselective synthesis of 2-epi-jaspine B via base-catalyzed intramolecular oxy-Michael conjugate addition approach

2-epi-Jaspine B has been synthesized starting from (−)-diethyl tartrate in 12 simple steps and 26.6% overall yield. The key intermediate was obtained via stereoselective base-catalyzed intramolecular oxy-Michael conjugate addition followed by tandem hydrogenation/hydrogenolysis.     

Probability-one homotopy maps for mixed complementarity problems

Probability-one homotopy algorithms have strong convergence characteristics under mild assumptions. Such algorithms for mixed complementarity problems (MCPs) have potentially wide impact because MCPs are pervasive in science and engineering. A probability-one homotopy algorithm for MCPs was developed earlier by Billups and Watson based on the default homotopy mapping. This algorithm had guaranteed global convergence under some mild conditions, and was able to solve most of the MCPs from the MCPLIB test library. This paper extends that work by presenting some other homotopy mappings, enabling the solution of all the remaining problems from MCPLIB. The homotopy maps employed are the Newton homotopy and homotopy parameter embeddings.     

Photophysical studies on multichromophoric cyclotriphosphazenes. Trinuclear excimer formation in hexakis(2-naphthyloxy)cyclotriphosphazene

Hexakis(2-naphthyloxy)cyclotriphosphazene showed an interesting emission behavior between its monomer and excimer forms, the latter nearly completely dominating in water. Encapsulation studies with β-cyclodextrin in water partially revived the monomer emission.     

On a low intensity <Superscript>241</Superscript>Am Compton spectrometer for measurement of electron momentum density

In this paper, a new design and construction of a low intensity (100 mCi) ²⁴¹Am γ-ray Compton spectrometer is presented. The planar spectrometer is based on a small disc source with the shortest geometry. Measurement of the momentum density of polycrystalline Al is used to evaluate the performance of the new design. The measured profile is in good agreement with the existing theoretical data and our density functional calculations.