Annihilation electrogenerated chemiluminescence of mixed metal chelates in solution: modulating emission colour by manipulating the energetics

We demonstrate the mixed annihilation electrogenerated chemiluminescence of tris(2,2′-bipyridine)ruthenium(ii) with various cyclometalated iridium(iii) chelates. Compared to mixed ECL systems comprising organic luminophores, the absence of T-route pathways enables effective predictions of the observed ECL based on simple estimations of the exergonicity of the reactions leading to excited state production. Moreover, the multiple, closely spaced reductions and oxidations of the metal chelates provide the ability to finely tune the energetics and therefore the observed emission colour. Distinct emissions from multiple luminophores in the same solution are observed in numerous systems. The relative intensity of these emissions and the overall emission colour are dependent on the particular oxidized and reduced species selected by the applied electrochemical potentials. Finally, these studies offer insights into the importance of electronic factors in the question of whether the reduced or oxidized partner becomes excited in annihilation ECL.     

Four‐Coordinate Copper Halonitrosyl {CuNO}10 Complexes

While copper nitrosyl complexes are implicated in numerous biological systems, isolable examples remain limited. In this report, we show that [Cl₃CuNO]^?, with a {CuNO}¹⁰ electron configuration, can be generated by nitrite reduction at a copper(I) dichloride anion or by nitric oxide addition to a copper(II) trichloride precursor. The bromide analogue, [Br₃CuNO]^? was synthesized analogously, and both copper halonitrosyl complexes were characterized by X‐ray diffraction and a variety of spectroscopic methods. Experimental data and multireference (CASSCF/NEVPT2) calculations provide strong evidence for a Cu^II–NO^. ground state. Both [Cl₃CuNO]^? and [Br₃CuNO]^? release and recapture NO^. reversibly, and exhibit nitrosative reactivities toward a wide range of biological nucleophiles, such as amines, alcohols, and thiols.     

Lantibiotics as surface active agents for biomedical applications

The unique physical structure of lantibiotics, (e.g. double bonds, thioethers rings, and unusual amino acid residues), makes these antimicrobial peptides highly reactive, and thus different in mode-of-action from clinical antibiotics. Members of the lantibiotic group have been successfully tested against pathogenic organisms for decades. Some lantibiotics have been studied for use in treating skin infections, and several have been characterized for their anti-viral activity. In addition to their antimicrobial capabilities, lantibiotics possess amphiphilic characteristics, making them potentially valuable as emulsifiers in drug formulations. The small size and surface activity of these peptides also may allow them to enhance the transport of therapeutic compounds across cell membranes. Over 30 lantibiotics are presently known, and more are being discovered each year. With the rising incidence of resistant bacteria, lantibiotics offer considerable potential as safe, antimicrobial barriers for use on synthetic material surfaces, as emulsifiers in formulation of hydrophobic drugs, and as absorption promoters for selected compounds across mucosal membranes. The major hindrance to research in this area is that lantibiotics are difficult to obtain. But with improved methods for production and purification of these unusual antimicrobial agents, the promise of cost-effective application of lantibiotics may eventually be realized.     

Inhibition of the proteolytic activity of anthrax lethal factor by aminoglycosides

The anthrax lethal factor (LF), a Zn-dependent endopeptidase, is considered the dominant virulence factor of anthrax. Because pharmacological inhibition of the catalytic activity of LF is considered a plausible mechanism for preventing the lethality of anthrax, a high-throughput screening experiment based on LF-catalyzed cleavage of a fluorescent substrate was performed to identify novel inhibitors of LF. The RNA-targeting antibiotics, neomycin B and some synthetic dimeric aminoglycosides, were found to be nanomolar active-site inhibitors of LF.     

The effect of sample environment on the room-temperature phosphorescence of several polynuclear aromatic hydrocarbons

Room-temperature phosphorescence (r.t.p.) of numerous molecules has been studied with emphasis on several polynuclear aromatic hydrocarbons (PAH). The heavy atom effect has led to a significant enhancement of r.t.p. signals for the PAH studied with the trend being Tl⁺ > Ag⁺ > Pb²⁺ > Hg²⁺. The Tl⁺ also resulted in enhanced spectral features of emission bands. R.t.p. could be induced from PAH on a sodium acetate sample support as well as on filter paper. A study of the effect of different gaseous environments provided anomalous results.     

Second harmonic generation from alkali metals

Nonlinear optical constants of the alkali metals, responsible for the second harmonic generation, are calculated using the Drude model. It is found that the electric quadrupole term of the nonlinear polarization is larger than that of a previous theory of Jha by a major factor of ω²_p/ω². By considering a more realstic electron density distribution, we also obtain an additional dipole term due to symmetry breakdown at the surface. The new nonlinear polarization gives the reflected second harmonic intensity in good agreement with experiments.     

Comparison of polarized fluorescence with polarized raman and infrared dichroism measures of orientation in uniaxially drawn poly(ethylene terephthalate)

In a number of previous papers the results of studies of molecular orientation in poly(ethylene terephthalate) (PET) by means of refractive index measurements and infrared, Raman and fluorescence spectroscopy have been presented. The present paper attempts to correlate the results of these studies and, in particular, to explain the observation that the fluorescent molecules appear to be more highly oriented than the polymer chains. Of the two explanations considered, that which assumes that the fluorescent molecules align themselves preferentially parallel to those segments of polymer chain in which the glycol residues are in the trans conformation is the more successful. It is also shown that the development of orientation in PET can be described well in terms of a simple modification of the rubber-network model even for large deformations.     

Heat transfer,development length,and friction factor correlations for the asymptotic region of a laminar arc constrictor

A rigorous equilibrium model is formulated for the laminar flow of plasma through the heating region of a constricted arc plasma generator. The resulting equations are solved for an argon gas using an implicit finite-difference scheme, and the wall shear stress and heat transfer are computed from momentum and energy balances for a wide range of flow rates and arc currents. Friction factors based on this method are in agreement with empirical values to within approximately 10 per cent, and heat transfer calculations agree with the orders of magnitude predicted by a simplified arc model. A dimensionless number peculiar to the constricted arc, the so-called Ohmic heating parameter, is used to correlate the mean Nusselt numbers in the asymptotic arc regime. When the fluid properties are based on the mean temperature, the product of friction factor and Reynolds number is found to be a constant for currents below 200 Amp and to vary with the Ohmic heating parameter for larger currents. Correlations are also presented for the thermal development length, and the agreement with experiment is good.