Electronic structures of Group 9 metallocorroles with axial ammines

The electronic structures of metallocorroles (tpfc)M(NH(3))(2) and (tfc)M(NH(3))(2) (tpfc is the trianion of 5,10,15-(tris)pentafluorophenylcorrole, tfc is the trianion of 5,10,15-trifluorocorrole, and M = Co, Rh, Ir) have been computed using first principles quantum mechanics [B3LYP flavor of Density Functional Theory (DFT) with Poisson-Boltzmann continuum solvation]. The geometry was optimized for both the neutral systems (formal M(III) oxidation state) and the one-electron oxidized systems (formally M(IV)). As expected, the M(III) systems have a closed shell d(6) configuration; for all three metals, the one-electron oxidation was calculated to occur from a ligand-based orbital (highest occupied molecular orbital (HOMO) of B(1) symmetry). The ground state of the formal M(IV) system has M(III)-Cπ character, indicating that the metal remains d(6), with the hole in the corrole π system. As a result the calculated M(IV/III) reduction potentials are quite similar (0.64, 0.67, and 0.56 V vs SCE for M = Ir, Rh and Co, respectively), whereas the differences would have been large for purely metal-based oxidations. Vertically excited states with substantial metal character are well separated from the ground state in one-electron-oxidized cobalt (0.27 eV) and rhodium (0.24 eV) corroles, but become closer in energy in the iridium (0.15 eV) analogues. The exact splittings depend on the chosen functional and basis set combination and vary by ~0.1 eV.     

A micro-convection model for thermal conductivity of nanofluids

Increase in the specific surface area as well as Brownian motion are supposed to be the most significant reasons for the anomalous enhancement in thermal conductivity of nanofluids. This work presents a semi-empirical approach for the same by emphasizing the above two effects through micro-convection. A new way of modeling thermal conductivity of nanofluids has been explored which is found to agree excellently with a wide range of experimental data obtained by the present authors as well as the data published in literature     

Influence of entrance channel properties on heavy-ion reaction dynamics

In the fusion of heavy nuclei, there is a distribution of fusion barrier energies resulting from coupling between intrinsic motion and internal degrees of freedom. Precise experimental measurements of excitation functions have allowed the extraction of the distributions by taking the second derivative using a point-difference method. In the case of statically deformed nuclei, experimental data shows that the different fusion barrier energies correspond to different physical configurations of the colliding nuclei, the latter affecting the subsequent dynamical trajectories over the potential energy surface, influencing the ultimate reaction products, as for example in quasi-fission. The fusion barrier distribution is also valuable in understanding the fusion of weakly bound nuclei, enabling a reliable prediction of the expected fusion cross-sections, and thus the determination of fusion suppression factors at above-barrier energies. Received: 1 May 2001 / Accepted: 4 December 2001     

Dual pole eikonal ands-channel singularities

Eikonalization of dual pole amplitudes, such as the Veneziano amplitude, is shown to lead to singularities in the impact parameter plane, which, in the eikonal approximation, may be interpreted as branch points in the direct channel angular momentum plane. This result is discussed in the light of dual absorption models.     

A chemiluminescence-based continuous flow aqueous ozone analyzer using photoactivated chromotropic acid

Ozone has become the oxidant of choice for water disinfection, especially in large water treatment facilities. This paper describes a fast and sensitive method for the determination of ozone content by reaction with photoactivated chromotropic acid (CA, 4,5-dihydroxynaphthalene-2,7-disulfonic acid), which results in intense chemiluminescence (CL). Freshly ozonated water from a recirculating ozonizer/reservoir is injected into a carrier stream of deionized water in the flow-injection mode. This flow mixes with a stream of photoactivated CA solution in a spiral cell placed directly on top of an inexpensive miniature (8 mm diameter active area) photomultiplier tube (PMT). Alkaline CA is photoactivated by passing it through a FEP-Teflon^® coil (residence time ∼ 50 s) wrapped around a 1 W UV lamp emitting at 254 nm; without photoactivation, the signal is ∼70-fold lower. The S/N = 3 limit of detection for aqueous ozone is 3 μg l⁻¹ and good response slope is obtained up to an ozone concentration of 1.4 mg l⁻¹, the highest that could be made in this study. The response obeyed a quadratic equation with r² = 0.9984. No interference from permanganate ion is observed. The proposed system was applied to the monitoring of ozonation status of a playa lake water that exhibited significant ozone demand.     

Head-group size or hydrophilicity of surfactants: the major regulator of lipase activity in cationic water-in-oil microemulsions

To determine the crucial role of surfactant head-group size in micellar enzymology, the activity of Chromobacterium Viscosum (CV) lipase was estimated in cationic water-in-oil (w/o) microemulsions of three different series of surfactants with varied head-group size and hydrophilicity. The different series were prepared by subsequent replacement of three methyl groups of cetyltrimethylammonium bromide (CTAB) with hydroxyethyl (1-3, series I), methoxyethyl (4-6, series II), and n-propyl (7-9, series III) groups. The hydrophilicity at the polar head was gradually reduced from series I to series III. Interestingly, the lipase activity was found to be markedly higher for series II surfactants relative to their more hydrophilic analogues in series I. Moreover, the activity remained almost comparable for complementary analogues of both series I and III, though the hydrophilicity was drastically different. Noticeably, the head-group area per surfactant is almost similar for comparable surfactants of both series I and III, but distinctly higher in case of series II surfactants. Thus the lipase activity was largely regulated by the surfactant head-group size, which plays the dominant role over the hydrophilicity. The increase in head-group size presumably allows the enzyme to attain a flexible conformation as well as increase in the local concentration of enzyme and substrate, leading to the higher efficiency of lipase. The lipase showed its best activity in the microemulsion of 6 probably because of its highest head-group size. Furthermore, the observed activity in 6 is 2-3-fold and 8-fold higher than sodium bis(2-ethyl-1-hexyl)sulfosuccinate (AOT) and CTAB-based microemulsions, respectively, and in fact highest ever in any w/o microemulsions.     

Transport in boundary layer of divertor tokamaks

Study of transport in the boundary layer of tokamak plasma in presence of magnetic divertors is extended to the second order in ion collision frequency. Numerical results for ion and energy losses to the collector plates are presented for toroidal and poloidal divertors. For the toroidal case, the Wiener-Hopf solution for the second order distribution function is obtained. An error occurring in an earlier first order calculation is pointed out and corrected first order fluxes are also given. For the poloidal divertor, asymmetry observed in ion and energy transport is found to persist in the second order result.