ESPT of 2-(2'-pyridyl)benzimidazole at the Micelle-Water interface: selective enhancement and slow dynamics with sodium dodecyl sulfate

The effect of micellar environment on the excited state proton transfer (ESPT) of 2-(2'-pyridyl)benzimidazole (2PBI) has been investigated by steady state and time resolved fluorescence spectroscopy. The ESPT, which occurs to a rather small extent at pH 7, is found to be enhanced remarkably at the interface of sodium dodecyl sulfate (SDS) micelles and water. Such an enhancement is not observed for the cationic cetyl trimethyl ammonium bromide (CTAB) or neutral Triton X-100 micelles. This selective enhancement is explained in the light of a modification of pK(a) and a more acidic local pH in the micelle-water interface. A rise time of about 890 ps is observed in the region of tautomer emission. The origin of this rise time is explored, considering three factors, namely, diffusion controlled protonation of the normal form of 2PBI, slow and possibly incomplete solvation of the transition state, leading to a slowing down of the proton transfer process and a similar slow dynamics of the tautomeric excited state.     

Foldable semi-ladder polymers: novel aggregation behavior and high-performance solution-processed organic light-emitting transistors

A critical issue in developing high-performance organic light-emitting transistors (OLETs) is to balance the trade-off between charge transport and light emission in a semiconducting material. Although traditional materials for organic light-emitting diodes (OLEDs) or organic field-effect transistors (OFETs) have shown modest performance in OLET devices, design strategies towards high-performance OLET materials and the crucial structure–performance relationship remain unclear. Our research effort in developing cross-conjugated weak acceptor-weak donor copolymers for luminescent properties lead us to an unintentional discovery that these copolymers form coiled foldamers with intramolecular H-aggregation, leading to their exceptional OLET properties. An impressive external quantum efficiency (EQE) of 6.9% in solution-processed multi-layer OLET devices was achieved.

Coiled foldamers with intramolecular H-aggregation in semi-ladder copolymers lead towards the highest EQE of 6.9% in solution-processed multi-layer OLETs.     

On relativistic models of strange stars

The superdense stars with mass-to-size ratio exceeding 0.3 are expected to be made of strange matter. Assuming that the 3-space of the interior space-time of a strange star is that of a three-paraboloid immersed in a four-dimensional Euclidean space, we obtain a two-parameter family of their physically viable relativistic models. This ansatz determines density distribution of the interior self-gravitating matter up to one unknown parameter. The Einstein’s field equations determine the fluid pressure and the remaining geometrical variables. The information about mass-to-size ratio together with the conventional boundary conditions lead to the determination of total mass, radius and other parameters of the stellar configuration.      

Preparation,characterization and Mössbauer spectra of the iron(III) complexes of some dihydroxamic acids and amino monohydroxamic acids

Summary Fe^III complexes have been prepared from the dihydroxamic acids (CH₂)_n[CON(R)OH]₂ (n=2, 3, 4, 6, 8; R=H, Ph,o-tolyl,p-tolyl) (H₂L) and the amino monohydroxamic acids H₂NCH(R)CONHOH (R=H, Me) (HL) and XC₆H₄CONHOH (X=o-NH₂,p-NH₂) (HL). Based on elemental analyses, molecular weight data, and electronic and i.r. spectra, the complexes have been formulated as Fe₂(LH)₂L₂, Fe₂L₂O and Fe₂L₃ for the dihydroxamic acids, and Fe(OH)₄L₂(H₂O)₂ and FeL₃ for the amino monohydroxamic acids. The⁵⁷Fe Mossbauer spectra are discussed.The author is née Bose     

Broad band laser polarization rotator for high power applications in the IR

A device is described that rotates the polarization of a laser beam by 90° using successive reflections from four mirrors. The device can handle large incident powers and has a wide spectral range.     

Synthesis, anticancer and antibacterial activity of some novel mononuclear Ru(II) complexes

In search of potential anticancer drug candidates in ruthenium complexes, a series of mononuclear ruthenium complexes of the type [Ru(phen)(2)(nmit)]Cl(2) (Ru1), [Ru(bpy)(2)(nmit)]Cl(2) (Ru2), [Ru(phen)(2)(icpl)]Cl(2) (Ru3), Ru(bpy)(2)(icpl)]Cl(2) (Ru4) (phen=1,10-phenanthroline; bpy=2,2'-bipyridine; nmit=N-methyl-isatin-3-thiosemicarbazone, icpl=isatin-3-(4-Cl-phenyl)thiosemicarbazone) and [Ru(phen)(2)(aze)]Cl(2) (Ru5), [Ru(bpy)(2)(aze)]Cl(2) (Ru6) (aze=acetazolamide) and [Ru(phen)(2)(R-tsc)](ClO(4))(2) (R=methyl (Ru7), ethyl (Ru8), cyclohexyl (Ru9), 4-Cl-phenyl (10), 4-Br-phenyl (Ru11), and 4-EtO-phenyl (Ru12), tsc=thiosemicarbazone) were prepared and characterized by elemental analysis, FTIR, (1)H-NMR and FAB-MS. Effect of these complexes on the growth of a transplantable murine tumor cell line (Ehrlich Ascites Carcinoma) and their antibacterial activity were studied. In cancer study the effect of hematological profile of the tumor hosts have also been studied. In the cancer study, the complexes Ru1-Ru4, Ru10 and Ru11 have remarkably decreased the tumor volume and viable ascitic cell count as indicated by trypan blue dye exclusion test (p<0.05). Treatment with the ruthenium complexes prolonged the lifespan of Ehrlich Ascites Carcinoma (EAC) bearing mice. Tumor inhibition by the ruthenium chelates was followed by improvements in hemoglobin, RBC and WBC values. All the complexes showed antibacterial activity, except Ru5 and Ru6. Thus, the results suggest that these ruthenium complexes have significant antitumor property and antibacterial activity. The results also reflect that the drug does not adversely affect the hematological profiles as compared to that of cisplatin on the host.     

Oxovanadium(V) and cobalt(III) complexes of dithiocarbazate-based Schiff base ligands: formation of a thiadiazole ring by vanadium-induced cyclization of the coordinated ligand

S-Methyl 3-((2-hydroxyphenyl)methyl)dithiocarbazate (H(2)L(1)) and its bromo derivative (H(2)L(2)), which are traditionally biprotic tridentate (ONS) ligands, behave in an unprecedented manner when allowed to react with [VO(acac)(2)] under an oxidative environment in acetonitrile-water medium containing a catalytic amount of alkali metal ion. The products obtained are oxovanadium(V) compounds [VOL(L(cyclic))] (L = L(1), 1a, and L(2), 1b) that contain one molecule of ligand which undergoes metal-induced cyclization to form a thiadiazole ring. Compound 1a crystallizes in the triclinic space group P(-)1 with a = 9.1830(9) A, b = 9.4165(12) A, c = 12.700(2) A, alpha = 100.988(8)(o), beta = 100.195(7)(o), gamma = 78.774(8)(o), V = 1046.3(2) A(3), and Z = 2. With cobalt(III), however, the products [CoL(HL)].H(2)O (L = L(1), 2a, and L(2), 2b) have hydrogen-bonded dimeric structures with each ligand virtually carrying 1.5 units of negative charge as confirmed by X-ray crystal structure analysis of 2a. It also crystallizes in triclinic space group P(-)1 with a = 12.0842(8) A, b = 13.5251(9) A, c = 14.1960(10) A, alpha = 78.122(6)(o), beta = 73.888(6)(o), gamma = 78.255(6)(o), V = 2154.7(3) A(3), and Z = 4. In solution, 2a is a symmetric molecule as indicated by (1)H NMR, involving a characteristic hydrogen-bonded O-H-O broad feature in the downfield (at 14.5 ppm) connecting both monoprotonated (LH(-)) and deprotonated (L(2-)) forms of the ligand--a situation somewhat analogous to the classic H-F-H case as observed in bifluoride ion.     

Turbulent piloted partially-premixed flames with varying levels of O2/N2: stability limits and PDF calculations

This paper reports measured stability limits and PDF calculations of piloted, turbulent flames of compressed natural gas (CNG) partially-premixed with either pure oxygen, or with varying levels of O₂/N₂. Stability limits are presented for flames of CNG fuel premixed with up to 20% oxygen as well as CNG–O₂–N₂ fuel where the O₂ content is varied from 8 to 22% by volume. Calculations are presented for (i) Sydney flame B [Masri et al. 1988] which uses pure CNG as well as flames B15 to B25 where the CNG is partially-premixed with 15–25% oxygen by volume, respectively and (ii) Sandia methane–air (1:3 by volume) flame E [Barlow et al. 2005] as well as new flames E15 and E25 that are partially-premixed with ‘reconstituted air’ where the O₂ content in nitrogen is 15 and 25% by volume, respectively. The calculations solve a transported PDF of composition using a particle-based Monte Carlo method and employ the EMST mixing model as well as detailed chemical kinetics. The addition of oxygen to the fuel increases stability, shortens the flames, broadens the reaction zone, and shifts the stoichiometric mixture fraction towards the inner side of the jet. It is found that for pure CNG flames where the reaction zone is narrow (～0.1 in mixture fraction space), the PDF calculations fail to reproduce the correct level of local extinction on approach to blow-off. A broadening in the reaction zone up to about 0.25 in mixture fraction space is needed for the PDF/EMST approach to be able to capture these finite-rate chemistry effects. It is also found that for the same level of partial premixing, increasing the O₂/N₂ ratio increases the maximum levels of CO and NO but shifts the peak to richer mixture fractions. Over the range of oxygenation investigated here, stability limits have shown to improve almost linearly with increasing oxygen levels in the fuel and with increasing the contribution of release rate from the pilot.     

Induction of Apoptosis by Ribosome Inactivating Proteins

Apoptotic cell death is a fundamental process in the development and physiological homeostasis of multicellular organisms. It is associated with control of cell numbers in tissues and organs during development, with cell turnover, and with response to infection. Molecules that trigger this process in continuously proliferating cancer cells can be used as chemotherapeutic agents. Ribosome inactivating proteins (RIPs) that inhibit translation in a cell by depurinating (N-glycosidase activity) the 28S rRNA are known to serve as apoptosis inducers. However, the role of depurination activity of the RIPs in apoptosis induction is still controversial. Presently, there are three different hypotheses which propose that depurination is: (1) essential, (2) essential but not the sole factor, or (3) not essential for apoptosis induction. This article reviews various experimental outcomes on the importance of N-glycosidase activity of RIPs in the induction of apoptosis.