A first-principles density-functional calculation of the electronic and vibrational structure of the key melanin monomers

We report first-principles density-functional calculations for hydroquinone (HQ), indolequinone (IQ), and semiquinone (SQ). These molecules are believed to be the basic building blocks of the eumelanins, a class of biomacromolecules with important biological functions (including photoprotection) and with the potential for certain bioengineering applications. We have used the difference of self-consistent fields method to study the energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, HL. We show that HL is similar in IQ and SQ, but approximately twice as large in HQ. This may have important implications for our understanding of the observed broadband optical absorption of the eumelanins. The possibility of using this difference in HL to molecularly engineer the electronic properties of eumelanins is discussed. We calculate the infrared and Raman spectra of the three redox forms from first principles. Each of the molecules have significantly different infrared and Raman signatures, and so these spectra could be used in situ to nondestructively identify the monomeric content of macromolecules. It is hoped that this may be a helpful analytical tool in determining the structure of eumelanin macromolecules and hence in helping to determine the structure-property-function relationships that control the behavior of the eumelanins.

Long-term quantification of the release of monomers from dental resin composites and a resin-modified glass ionomer cement

This study quantified the release of monomers from polymerized specimens of four commercially available resin composites and one glass ionomer cement immersed in water:ethanol solutions. Individual standard curves were prepared from five monomers: (1) triethylene glycol dimethacrylate (TEGDMA), (2) 2-hydroxy-ethyl methacrylate (HEMA), (3) urethane dimethacrylate (UDMA), (4) bisphenol A glycidyl dimethacrylate (BISGMA), and (5) bisphenol A. The concentration of the monomers was determined at Days 1, 7, 30, and 90 with the use of electrospray ionization/mass spectrometry. Data were expressed in mean mumol per mm(2) surface area of specimen and analyzed with Scheffe's test (P < 0.05). The following monomers were found in water: monomers (1) and (2) from Delton sealant, monomer (5) from ScotchBond Multipurpose Adhesive and Delton sealant, monomer (3) from Definite and monomer (4) from Fuji II LC, ScotchBond Multipurpose Adhesive, Synergy and Definite. All these monomers increased in concentration over time, with the exception of monomer (1) from Delton sealant. Monomers (3) and (5) were found in extracts of materials despite their absence from the manufacturer's published composition. All monomers were released in significantly higher concentrations in water:ethanol solutions than in water. The greatest release of monomers occurred in the first day. The effect of the measured concentrations of monomers (1-5) on human genes, cells, or tissues needs to be considered with the use of a biological model. (C) 2002 Wiley Periodicals, Inc.

The polar ionosphere at Zhongshan Station on May 11, 1999, the day the solar wind almost disappeared

The solar wind almost disappeared on May 11,1999: the solar wind plasma density and' dynamic pressure were less than 1 cm(-3) and 0.1 nPa respectively, while the interplanetary magnetic field was northward. The polar ionospheric data observed by the multi-instruments at Zhongshan Station in Antarctica on such special event day was compared with those of the control day (May 14). It was shown that geomagnetic activity was very quiet on May 11 at Zhongshan. The magnetic pulsation, which usually occurred at about magnetic noon, did not appear. The ionosphere was steady and stratified, and the F-2 layer spread very little. The critical frequency of dayside F-2 layer, f(0)F(2), was larger than that of control day, and the peak of f(0)F(2) appeared 2 hours earlier. The ionospheric drift velocity was less than usual. There were intensive auroral E-s appearing at magnetic noon. All this indicates that the polar ionosphere was extremely quiet and geomagnetic field was much more dipolar on May 11. There were some signatures of auroral substorm before midnight, such as the negative deviation of the geomagnetic H component, accompanied with auroral E-s and weak Pc3 pulsation.

Simultaneous FT-NIR and ESR analyses to yield propagation rate coefficients for polymerization of methyl methacrylate based monomers

A hyphenated instrumental approach has been used to obtain reliable values for the propagation rate coefficients as a function of conversion for polymerizations of methyl methacrylate (MMA) and a mixture of MMA and ethyleneglycol dimethacrylate (EGDMA) with a 1:1 concentration of double bonds, from near the onset of the Trommsdorf region into the glass region. ESR spectroscopy was used to measure the radical concentration while FT-NIR fibre-optic spectroscopy was employed to measure instantaneously the double-bond concentration within the temperature-controlled cavity of the ESR instrument during polymerization. The advantage of this approach to the measurement of the rate coefficient is that it is equally applicable to branching and linear polymerizations. For the polymerization of methyl methacrylate, the values of the rate coefficient at the lowest conversions at which reliable values could be obtained were in agreement with recently reported values obtained by the PLP-SEC method. For the lowest conversions, the values obtained were 403 1 mol(-1) s(-1) at 306 K for MMA and 5201 mol(-1) s(-1) at 310 K for a 1:1 mixture of MMA and EGDMA. (C) 2003 Society of Chemical Industry.

Citrinin revisited: from monomers to dimers and beyond

Detailed chemical analysis of the solid phase fermentation of an Australian Penicillium citrinum isolate has returned the known compounds citrinin (1), phenol A acid (6), dihydrocitrinone (7) and dihydrocitrinin (8), together with a novel cytotoxic dimer, dicitrinin A (5). Dicitrinin A (5) was determined to be a dimerised artefact of the major co-metabolite citrinin, and its structure solved by spectroscopic analysis and chemical modi. cation. Analysis of the products encountered during the controlled decomposition of citrinin led to the discovery of additional citrinin dimers and delineated a plausible mechanistic pathway linking all monomeric and dimeric citrinin degradation products.

Criteria for quantum coherent transfer of excitations between chromophores in a polar solvent

We show that the quantum decoherence of Forster resonant energy transfer between two optically active molecules can be described by a spin-boson model. This allows us to give quantitative criteria that are necessary for coherent quantum oscillations of excitations between the chromophores. Experimental tests of our results should be possible with flourescent resonant energy transfer (FRET) spectroscopy. Although we focus on the case of protein-pigment complexes our results are also relevant to quantum dots and organic molecules in a dielectric medium. (c) 2006 Elsevier B.V. All rights reserved.

Dual-symmetric Lagrangians in quantum electrodynamics: I. Conservation laws and multi-polar coupling

By using a complex field with a symmetric combination of electric and magnetic fields, a first-order covariant Lagrangian for Maxwell's equations is obtained, similar to the Lagrangian for the Dirac equation. This leads to a dual-symmetric quantum electrodynamic theory with an infinite set of local conservation laws. The dual symmetry is shown to correspond to a helical phase, conjugate to the conserved helicity. There is also a scaling symmetry, conjugate to the conserved entanglement. The results include a novel form of the photonic wavefunction, with a well-defined helicity number operator conjugate to the chiral phase, related to the fundamental dual symmetry. Interactions with charged particles can also be included. Transformations from minimal coupling to multi-polar or more general forms of coupling are particularly straightforward using this technique. The dual-symmetric version of quantum electrodynamics derived here has potential applications to nonlinear quantum optics and cavity quantum electrodynamics.

Production of triploid Kuruma shrimp, Marsupenaeus (Penaeus) japonicus (Bate) nauplii through inhibition of polar body I, or polar body I and II extrusion using 6-dimethylaminopurine

This study investigated the chromosome ploidy level of Marsupenaeus (Penaeus) japonicus (Bate) non-viable (unhatched) embryos and nauplii after exposure to 6-dimethylaminopurine (6-DMAP), timed to stop either polar body (PB) I, or PBI and II extrusion. Embryos from eight separate families or spawnings were exposed to 150 or 200 mu M 6-DMAP from 1- to 3-min post-spawning detection (psd) for a 4- to 5-min duration (timed to stop PBI extrusion). Separate aliquots of embryos from five of the same spawnings were also exposed to 200 mu M of 6-DMAP from 1- to 3-min psd for a 16-min duration (timed to stop both PBI and II extrusion). For one spawning, a third aliquot of embryos was exposed to 400 p M of 6-DMAP from 1- to 3-min psd for a 16-min duration (timed to stop both PBI and II extrusion). At 18-h psd, non-viable embryo and nauplii samples were taken separately for fluorescent activated cell sorting (FACS). FACS revealed that there were diploids and triploids among all treated non-viable embryos and nauplii. All control non-viable embryos and nauplii were diploid. Percentages of triploid induction for the 4- to 5-min and 16-min durations were not significantly different (P > 0.05). Additionally, no difference was found in the triploidy level of nonviable embryos compared to nauplii in these treatments. The percentage of triploid embryos and nauplii when exposed to 6-DMAP for a 4- to 5-min duration ranged from 29.57% to 99.23% (average 55.28 +/- 5.45%) and from 5.60% to 98.85% (average 46.70 +/- 7.20%), respectively. The percentage of triploid embryos and nauplii when exposed to 6-DMAP for a 16-min duration ranged from 11.71% to 98.96% (average 52.49 +/- 11.00%) and from 47.5% to 99.24% (average 79.38 +/- 5.24%), respectively. To our knowledge, this is the first documentation of successful PBI or PBI and II inhibition in shrimp. This study conclusively shows that treatment of M. japonicus embryos with 6-DMAP at 1- to 3-min pscl for either a 4- to 5-min duration (timed to stop PBl extrusion) or 16-min duration (timed to stop both PBI and II extrusion) results in viable triploid nauplii. (c) 2006 Elsevier B.V. All rights reserved.