The de Brécy Madonna and Child tondo painting: a Raman spectroscopic analysis

Raman spectra have been obtained from a Madonna and Child tondo painting, known as the de Brécy Tondo. Despite the provision of only a small number of microscopic samples, definitive spectra were obtained from mineral pigments. From one specimen, spectra of an organic binder enabled the consideration of several possibilities to be accomplished and a suggestion proposed for the medium. In another specimen the identification of the spectral signatures of Prussian blue, which was only synthesised some 200 years after the predicated date of execution of the painting, indicated that some unrecorded restoration had been undertaken later in the painting’s history. Research* carried out on this tondo from 1987 to 1991 indicated the probability that it is the work of Raphael, a conclusion supported by further research recently undertaken on the provenance. The stylistic similarity of the tondo to Raphael’s Sistine Madonna is very clear; the pigments identified in this analysis are consistent with a Renaissance attribution for the de Brécy Tondo. *Dr Murdoch Lothian, The Methods Employed to Provenance and to Attribute Putative Works by Raphael, Ph.D. Thesis, 1991.     

Raman spectroscopic analysis of human remains from a seventh century cist burial on Anglesey,UK

Specimens from human remains exhibiting unusual preservation excavated from a seventh century stone cist burial at Towyn y Capel in Anglesey, UK, have been analysed using Raman spectroscopy with near-infrared laser excitation at 1,064 and 785 nm. Specimens of hair and bone provided evidence for severe degradation and microbial colonisation. The deposits within the stone cist showed that some microbially mediated compounds had been formed. Analysis of crystals found at the interface between the hair and the skeletal neck vertebrae revealed a mixture of newberyite and haematite, associated with decomposition products of the hair and bone. An interesting differential degradation was noted in the specimens analysed which could be related to the air-void and the presence of plant root inclusions into the stone cist. This is the first time that Raman spectroscopy has been used in the forensic archaeological evaluation of burial remains in complex and dynamic environments.     

Analysis of gin essential oil mixtures by multidimensional and one-dimensional gas chromatography/mass spectrometry with spectral deconvolution

The composition of essential oils and their mixtures used to formulate gin is usually too complex to separate all sample components by standard capillary gas chromatography (GC). In particular, minor constituents that possess important organoleptic properties can be masked by co-elution with major sample components. A solution is provided that combines gas chromatography/mass spectrometry (GC/MS) with "interactive" spectral deconvolution software. Sequential two-dimensional (2D) GC/MS is used to produce a target compound library, with orthogonal GC-GC providing the separation power required to obtain peak retention times and the corresponding mass spectra needed for the deconvolution database. The combination of these two techniques, mass spectral deconvolution and automated sequential 2D-GC/MS, offers a very effective synergy for both identifying key constituents that determine the perception of flavor and aroma and the quality control needed to analyze mixtures of complex essential oils.     

The interaction between sodium alkyl sulfate surfactants and the oppositely charged polyelectrolyte, polyDMDAAC, at the air-water interface: the role of alkyl chain length and electrolyte and comparison with theoretical predictions

The effect of alkyl chain length and electrolyte on the adsorption of sodium alkyl sulfate surfactants and the oppositely charged polyelectrolyte, polyDMDAAC, at the air-water interface has been investigated by surface tension and neutron reflectivity. The variations in the patterns of adsorption and surface tension behavior with alkyl chain length and electrolyte are discussed in the context of the competition between the formation of surface active surfactant/polyelectrolyte complexes and polyelectrolyte/surfactant micelle complexes in solution. A theoretical approach based on the law of mass action has been used to predict the surface effects arising from the competition between the formation of polyelectrolyte/surfactant surface and solution complexes and the formation of free surfactant micelles. This relatively straightforward model is shown to reproduce the principal features of the experimental results.     

Intramolecular excimer formation and delayed fluorescence in sterically constrained pyrene dimers

The synthesis is described for a series of five molecular dyads comprising pyrene-based terminals covalently linked through a 1,3-disubstituted phenylene spacer. The extent of through-space communication between the pyrene units is modulated by steric interactions imposed by bulky moieties attached at the 6,8-positions of each pyrene unit. For the control compound, only hydrogen atoms occupy the 6,8 positions (DP1), whereas the remaining compounds incorporate ethynylene groups terminated with either triisopropylsilyl (DP2), 1-tert-butylbenzene (DP3), 2,6-di-tert-butylbenzene (DP4) or 1-tert-butyl-3,5-dimethylbenzene (DP5) units. Each compound shows a mixture of monomer and excimer fluorescence in fluid solution at room temperature, but only monomer emission in a glassy matrix at 77 K. The ratio of monomer to excimer fluorescence depends markedly on the molecular structure; DP1 is heavily biased in favour of the excimer and DP4 is enriched with monomer fluorescence. Photophysical properties, including laser induced and delayed fluorescence data, are reported for each compound. Delayed fluorescence occurs by both intramolecular and bimolecular steps, but these events take place on different timescales. The possibility is raised for using intramolecular triplet-triplet annihilation as a means of molecular imaging.     

Carboxylate lability as a factor in the Rh2(carboxylate)4-catalysed cyclopropenation and cyclopropanation of alkynes and alkenes

The mechanism of Rh(2)(carboxylate)(4)-catalysed cyclopropenation and cyclopropanation via two different pathways has been investigated computationally. The two pathways either (a) conserve the Rh(2)O(8) framework, with initial coordination of CH(2)N(2) and further reaction occurring at an axial acceptor site, or (b) allow dechelation of carboxylate to liberate an equatorial site for activation of bound CH(2)N(2.) Calculations on the system in question [Rh(2)(formate)(4), CH(2)N(2), C(2)H(4) or C(2)H(2)] show that both pathways are equally favoured. The importance of coordinated solvent in determining the reaction pathway is demonstrated.     

Rapid identification of immunostimulatory alpha-galactosylceramides using synthetic combinatorial libraries

Two 60+-membered libraries of alpha-galactosylceramides have been prepared by reactions between activated ester resins and two core, fully deprotected galactosylated sphingoid bases. The libraries were evaluated for their ability to stimulate CD1d-restricted NKT cells, using in vitro stimulation of a murine NKT cell hybridoma line and for their ability to induce the expansion of NKT cells from peripheral blood mononuclear cells (PBMC) of a normal human subject. Our results showed that many compounds constructed on a C18-phytosphingosine base had significant stimulatory activity in both assays. Because no product purification was required, this approach is particularly attractive as a method for rapid synthesis of large libraries of potential immunomodulatory glycosylceramides.     

Coherent versus uncorrelated nanoscale heterogeneities in L1(0) solid solutions and their signatures from local and extended probes

The structural properties of the phase coexistence of chemically ordered L1(0) and chemically disordered structures within binary alloys are investigated, using the NiMn system as an example. Theoretical and numerical predictions of the signatures that one might expect in data from local and extended probes are presented in an attempt to explain the presence of antiferromagnetism in NiMn when no L1(0) signatures appear in diffraction data. Two scenarios are considered. In the first scenario, the tetragonal L1(0) structure and fcc chemically disordered structure are distributed evenly into uncorrelated domains of specified average diameter. The diffraction limit, below which the two structures can only be distinguished using a local probe, is quantified with respect to the domain diameter by applying straightforward diffraction analysis. In the second scenario, domains with chemical ordering oriented in different directions are required to maintain their atomic coherence with each other. A numerical treatment is used to illustrate the long-range strain that results from elastic energy considerations, and the effects on the structure factor (extended probe) and pair distribution function (local probe) are investigated.     

Aggregation properties of a polymeric anticancer therapeutic: a coarse-grained modeling study

The effects of paclitaxel (PTX) loading fraction and spatial PTX arrangement on poly(γ-glutamyl-glutamate) paclitaxel (PGG-PTX) aggregation were explored using coarse-grained molecular dynamics. Results show that the PTX loading fraction does not significantly impact aggregation, and the spatial PTX arrangement only affects aggregation at more concentrated PTX arrangements. Overall, the f(PTX) = 0.37 'ends' and f(PTX) = 0.18 'even' PGG-PTX systems exhibit the highest aggregation and the 'middle' and 'side' systems the lowest.     

The effect of inertial inhomogeneity on the flutter of a cantilevered flexible plate

We study the effect of adding discrete structural mass on the linear stability of an otherwise homogeneous cantilevered-free flexible plate immersed in uniform axial flow. The methods of Howell et al. that mixed numerical simulation with eigenvalue analysis are simply extended for the present study. An ideal two-dimensional flow is assumed wherein the rotationality of the boundary-layers is modelled by vortex elements on the solid-fluid interface and the imposition of the Kutta condition at the plate's trailing edge. The Euler-Bernoulli beam model is used for the structural dynamics. It is shown that addition of mass to the plate can be either stabilising or destabilising, depending upon the location of the added mass, and how its inclusion modifies the energy exchanges of the corresponding homogeneous structure. Our results therefore suggest a straightforward means by which the critical flow speed at which low-amplitude flutter sets in can be passively controlled in engineering applications.