Effects of the host lattice and doping concentration on the colour of Tb3+ cation emission in Y2O2S:Tb3+ and Gd2O2S:Tb3+ nanometer sized phosphor particles.

Y2O2S and Gd2O2S phosphor lattices activated with a range of Tb(3+) concentrations have been successfully prepared as nanoparticles and their emission properties have been characterized using SEM, XRPD, photoluminescence spectroscopy and cathodoluminescence. (5)D3-(5)D4 cross relaxation processes between Tb(3+) cations were observed in both Y2O2S and Gd2O2S as a function of Tb(3+) concentration. In the Y2O2S host lattice, the predominant emission colour shifts from blue to green with increased Tb(3+) concentration. In contrast, green emission is always predominant in Gd2O2S at Tb(3+) concentrations from 0.1 mol% to 5 mol%. This finding is explained in accordance with previous reports on the bulk materials that found the Gd2O2S lattice has a lower charge transfer state than the Y2O2S host lattice.

Contrasting behaviour of the co-activators in the luminescence spectra of Y2O2S:Tb3+,Er3+ nanometre sized particles under UV and red light excitation.

Nanometre sized particles of terbium and erbium co-doped yttrium oxysulfide up-converting phosphors were prepared by a urea homogeneous-precipitation method. Results from X-ray powder diffraction (XRPD), scanning electron microscopy (SEM) and photoluminescence spectroscopy studies on the microstructure and luminescent properties of the materials are reported. Upconversion emission was observed from the Er(3+) cations when particles were excited with laser light of 632.8 nm wavelength. Under these conditions no interactions between the Er(3+) cations and the Tb(3+) cations were observed. In contrast there was evidence from the Stokes emission of the Er(3+) cations under 254 nm excitation for an interaction between the Er(3+) and Tb(3+) cations reducing intensity of the latter's blue and green emission bands by cross relaxation processes.

Vibrational spectra and structures of the anions of urazole and 4-methylurazole: DFT calculations of the normal modes and the influence of hydrogen bonding.

Solid state IR and Raman as well as aqueous solution state Raman spectra are reported for the anions of urazole and 4-methylurazole, and their N-deuterated derivatives. DFT calculations, at the B3-LYP/cc-pVTZ level, established that the structures and vibrational spectra of both anions can be interpreted using a model that incorporates hydrogen-bonded water molecules, in conjunction with the polarizable continuum solvation method. In the case of the urazole anion it is shown that deprotonation occurs primarily at N1 rather than N4, but there is also evidence for the second tautomer both in the solid state and in aqueous solution. The vibrational spectra were computed at the optimised molecular geometry in each case, enabling normal coordinate analysis, which yielded satisfactory agreement with the experimental IR and Raman data. Computed potential energy distributions of the normal modes provided detailed vibrational assignments.

Surface-enhanced Raman scattering studies of rhodanines: evidence for substrate surface-induced dimerization.

The surface-enhanced Raman scattering (SERS) spectra of rhodanine adsorbed on silver nanoparticles have been examined using 514.5 and 632.8 nm excitation. There is evidence that, under the experimental conditions used, rhodanine undergoes a nanoparticle surface-induced reaction resulting in the formation of a dimeric species via the active methylene group in a process which is analogous to the Knoevenagel reaction. The experimental observations are supported by DFT calculations at the B3-LYP/cc-pVDZ level. Calculated energies for the interaction of the E and Z isomers of the dimers of rhodanine with silver nanoparticles support a model in which the (intra-molecular hydrogen bonded) E isomer dimer is of lower energy than the Z isomer. A strong band, at 1566 cm(-1), in the SERS spectrum of rhodanine is assigned to the nu(C double bond C) mode of the dimer species.

Vibrational spectra of alpha-amino acids in the zwitterionic state in aqueous solution and the solid state: DFT calculations and the influence of hydrogen bonding.

The zwitterionic forms of the two simplest alpha-amino acids, glycine and l-alanine, in aqueous solution and the solid state have been modeled by DFT calculations. Calculations of the structures in the solid state, using PW91 or PBE functionals, are in good agreement with the reported crystal structures, and the vibrational spectra computed at the optimized geometries provide a good fit to the observed IR and Raman spectra in the solid state. DFT calculations of the structures and vibrational spectra of the zwitterions in aqueous solution at the B3-LYP/cc-pVDZ level were found to require both explicit and implicit solvation models. Explicit solvation was modeled by inclusion of five hydrogen-bonded water molecules attached to each of the five possible hydrogen-bonding sites in the zwitterion and the integration equation formalism polarizable continuum model (IEF-PCM) was employed, providing a satisfactory fit to observed IR and Raman spectra. Band assignments are reported in terms of potential-energy distributions, which differ in some respects to those previously reported for glycine and l-alanine.

Analysis of the conversion of indigo into indigo carmine dye using SERRS.

In a novel application SERRS has been used, by employing a silver sol, to monitor and analyse the conversion of indigo into the indigo carmine dye.

A combination of both arginine- and lysine-specific gingipain activity of Porphyromonas gingivalis is necessary for the generation of the micro-oxo bishaem-containing pigment from haemoglobin.

The black pigment of Porphyromonas gingivalis is composed of the mu-oxo bishaem complex of Fe(III) protoporphyrin IX (mu-oxo oligomer, dimeric haem), namely [Fe(III)PPIX]2O. P. gingivalis W50 and Rgp (Arg-gingipain)- and Kgp (Lys-gingipain)-deficient mutants K1A, D7, E8 and W501 [Aduse-Opoku, Davies, Gallagher, Hashim, Evans, Rangarajan, Slaney and Curtis (2000) Microbiology 146, 1933-1940] were grown on horse blood/agar for 14 days and examined for the production of mu-oxo bishaem. Mu-oxo Bishaem was detected by UV-visible, Mössbauer and Raman spectroscopies in wild-type W50 and in the black-pigmented RgpA- and RgpB-deficient mutants (W501 and D7 respectively), whereas no haem species were detected in the straw-coloured colonies of Kgp-deficient strain K1A. The dark brown pigment of the double RgpA/RgpB knockout mutant (E8) was not composed of mu-oxo bishaem, but of a high-spin monomeric Fe(III) protoporphyrin IX species (possibly a haem-albumin complex). In vitro incubation of oxyhaemoglobin with cells of the W50 strain and the RgpA- and RgpB-deficient mutants (W501 and D7) resulted in the formation of mu-oxo bishaem via methaemoglobin as an intermediate. Although the Kgp-deficient strain K1A converted oxyhaemoglobin into methaemoglobin, this was not further degraded into mu-oxo bishaem. The double RgpA/RgpB knockout was also not capable of producing mu-oxo bishaem from oxyhaemoglobin, but instead generated a haemoglobin haemichrome. Inhibition of Arg-X protease activity of W50, W501, D7 and K1A with leupeptin, under conditions where Lys-X protease activity was unaffected, prevented the production of mu-oxo bishaem from oxyhaemoglobin, but resulted in the formation of a haemoglobin haemichrome. These results show that one or both of RgpA and RgpB gingipains, in addition to the lysine-specific gingipain, is necessary for the production of mu-oxo bishaem from haemoglobin by whole cells of P. gingivalis.

Two new cyclosporin folds observed in the structures of the immunosuppressant cyclosporin G and the formyl peptide receptor antagonist cyclosporin H at ultra-high resolution.

Cyclosporins are cyclic undecapeptides of fungal origin the best known of which, CsA, is a lead clinical immunosuppressant; CsG is a potential clinical immunosuppressant differing from CsA in residue 2 (L-alpha-amino-butyric acid in CsA, L-norvaline in CsG); and CsH is an inverse formyl peptide receptor agonist, differing from CsA in the chiral inversion of MeVal-11 from L to D. Crystal structure determinations of CsG and CsH were undertaken to identify structural and surface features important for biological activity and the future design of new cyclosporin derivatives. Ultra-high resolution X-ray structures (0.80 to 0.87 A resolution) determined for two crystal forms of both CsH and CsG in the presence and absence of Mg2+ are described. A major outcome of this study is the observation that the local change in chirality between CsA and CsH is associated with a major structural transformation from open beta-sheet in CsA to a highly convoluted conformation in CsH. CsG also possesses a completely novel cloverleaf motif with no H-bonded secondary structure features in spite of the minimal chemical difference with CsA. Unlike CsA, the structures of both CsH and CsG are heavily solvated. This study therefore shows that the chemical differences between the three cyclosporins, CsA, CsG and CsH can invoke unpredictably major differences in their 3D structures. The 9-11 cis-peptide bond in CsA moves to 11-1 in CsG, influencing the overall molecular conformation, while the peptide bonds in the highly convoluted loop conformation of CsH are all trans.

Raman spectra of carotenoids in natural products.

Resonance Raman spectra of naturally occurring carotenoids have been obtained from nautilus, periwinkle (Littorina littorea) and clam shells under 514.5 nm excitation and these spectra are compared with the resonance Raman spectra obtained in situ from tomatoes, carrots, red peppers and saffron. The tomatoes, carrots and red peppers gave rise to resonance Raman spectra exhibiting a nu1 band at ca. 1520 cm(-1), in keeping with its assignment to carotenoids with ca. nine conjugated carbon-carbon double bonds in their main chains, whereas the resonance Raman spectrum of saffron showed a nu1 band at 1537 cm(-1) which can be assigned to crocetin, having seven conjugated carbon-carbon double bonds. A correlation between nu1 wavenumber location and effective conjugated chain length has been used to interpret the data obtained from the shells, and the wavenumber position (1522 cm(-1)) of the nu1 band of the carotenoid in the orange clam shell suggests that it contains nine conjugated double bonds in the main chain. However, the black periwinkle and nautilus shells exhibit nu1 bands at 1504 and 1496 cm(-1), respectively. On the basis of the correlation between nu1 wavenumber location and effective conjugated chain length, this indicates that they contain carotenoids with longer conjugated chains, the former having ca. 11 double bonds and the latter ca. 13 or even more. Raman spectra of the nautilus, periwinkle and clam shells also exhibited a strong band at 1085 cm(-1) and a doublet with components at 701 and 705 cm(-1), which can be assigned to biogenic calcium carbonate in the aragonite crystallographic form.

The haem pigment of the oral anaerobes Prevotella nigrescens and Prevotella intermedia is composed of iron(III) protoporphyrin IX in the monomeric form.

The haem pigment of Porphyromonas gingivalis is composed of micro -oxo bishaem, [Fe(III)PPIX](2)O, but the nature of that generated by Prevotella species has not been established. Mössbauer, Raman and UV-visible spectrophotometry were used to characterize the haem pigment of Prevotella intermedia and Prevotella nigrescens. Mössbauer and Raman spectroscopy revealed the major haem species to be monomeric iron protoporphyrin IX, Fe(III)PPIX.OH (haematin). The terminal growth pH of both species on blood agar was between 5.8 and 6.0, which favours the formation and maintenance of monomeric Fe(III)PPIX.OH. Incubation of Pr. nigrescens and Pr. intermedia with oxyhaemoglobin at pH 6.5 resulted in formation of aquomethaemoglobin which was degraded to generate Fe(III)PPIX.OH which in turn became cell-associated, whilst incubation at pH 7.5 resulted in formation of [Fe(III)PPIX](2)O. It is concluded that both Prevotella species degrade oxyhaemoglobin to form [Fe(III)PPIX](2)O as an intermediate, which is converted to Fe(III)PPIX.OH through a depression in pH. The low pH encourages cell-surface deposition of insoluble Fe(III)PPIX.OH which would act as a barrier against oxygen and reactive oxygen species, and also protect against H(2)O(2) through its inherent catalase activity.

Infrared and Raman spectra of 3,5-diamino-6-(o-C6H4X)-1,2,4-triazines [X = F, Cl, Br, CH3].

Raman and infrared spectra of four substituted 3,5-diamino-6-(ortho-substituted phenyl)-1,2,4-triazines, having ortho-fluoro, -chloro, -bromo and -methyl groups on the phenyl ring, are reported and discussed. Bands due to substituent sensitive phenyl vibrations are observed in both the Raman and infrared spectra. The Raman spectra of all four compounds have strong bands near 770 and 1330 cm(-1) which are assigned to the ring breathing vibration of the 1,2,4-triazine ring and an asymmetric triazine C-NH2 stretching vibration, respectively. A medium/strong band near 800 cm(-1) in the infrared spectra is attributed to an out-of-plane bending vibration of the substituted 1,2,4-triazine ring.

Interactions of Porphyromonas gingivalis with oxyhaemoglobin and deoxyhaemoglobin.

When grown on blood-containing solid media, the anaerobic periodontal pathogen Porphyromonas gingivalis produces a haem pigment, the major component of which is the mu-oxo bishaem of iron protoporphyrin IX [Smalley, Silver, Marsh and Birss (1998) Biochem. J. 331, 681-685]. In this study, mu-oxo bishaem generation by P. gingivalis from oxy- and deoxyhaemoglobin was examined. Bacterial cells were shown to convert oxyhaemoglobin into methaemoglobin, which was degraded progressively, generating a mixture of both monomeric and mu-oxo dimeric iron protoporphyrin IX. The rate of methaemoglobin formation was accelerated in the presence of bacterial cells, but was inhibited by N-ethylmaleimide and tosyl-lysylchloromethylketone. Interaction of cells with deoxyhaemoglobin resulted in formation of an iron(III) haem species (Soret gamma(max), 393 nm), identified as pure mu-oxo bishaem.