Braided peridotite sills and metasomatism in the Rum Layered Suite, Scotland.

The Rum Eastern Layered Intrusion (ELI; Scotland) is an open-system layered intrusion constructed of 16 macro-rhythmic units. Each of the macro-rhythmic units consists of a peridotite base and a troctolite (± gabbro) top, previously attributed to the fractional crystallisation of a single magma batch. This classic paradigm has been challenged, however, with evidence presented for the emplacement of peridotite sills in Units 9, 10, and 14, such as cross-cutting relationships, upward-oriented apophyses, and lateral discontinuities. To test whether the other major peridotites within the ELI represent sills, we have carried out new field, petrographic, and mineral chemical analyses of the peridotites in Units 7, 8 and 9. The peridotites display large- and small-scale cross-cutting relationships with the overlying troctolite, indicative of an intrusive relationship. The peridotites also show large-scale coalescence and lateral spatial discontinuities such that the ELI unit divisions become arbitrary. Harrisite layers and Cr-spinel seams found throughout Units 7, 8, and 9 suggest the peridotites were constructed incrementally via repeated injections of picritic magma. Our observations allow for distinct subtypes of peridotite to be defined, separated by intrusive contacts, allowing for their relative chronology to be determined. Older, poikilitic peridotite, rich in clinopyroxene, is truncated by younger, well-layered peridotite, containing abundant harrisite layers. In addition to the new peridotite subtypes defined in this study, we find strong evidence for laterally oriented metasomatism within clinopyroxene-rich wehrlites at the top of the Unit 8 peridotite. The wehrlites and surrounding peridotites record a complex series of metasomatic reactions that transformed thin picrite sills into clinopyroxene-rich wehrlites without any evidence for the sort of vertical melt movement typically posited in layered intrusions. The observations presented in this study from the ELI cannot be reconciled with the classic magma chamber paradigm and are better explained by the emplacement of composite sills into pre-existing feldspathic cumulate (gabbro or troctolite). The evidence for sill emplacement presented here suggests that the layered complex was constructed by a combination of sill emplacement and metasomatism, forming many of the unusual (often clinopyroxene-rich) lithologies that surround the sills. The broad-scale formation of the layered peridotites via incremental sill emplacement, suggested by the occurrence of upward-oriented apophyses, coalescence, and lateral discontinuity, could be applied to much larger ultramafic intrusions, which might have formed by similar mechanisms.

Application of inelastic neutron scattering to studies of CO2 reforming of methane over alumina-supported nickel and gold-doped nickel catalysts.

The methane reforming reaction with carbon dioxide as the oxidant over alumina-supported nickel and gold-doped nickel catalysts is studied using a variety of techniques such as reaction testing, vibrational spectroscopy (inelastic neutron scattering (INS), Raman scattering and infrared absorption), temperature-programmed oxidation (TPO), transmission electron microscopy and X-ray powder diffraction. The quantities of retained carbon and hydrogen are determined by TPO and INS, respectively. Minimal hydrogen retention indicates these catalysts to be very efficient at cycling hydrogen. The relative partitioning of hydrogen within the reaction media is used to formulate a qualitative description of the reaction kinetics. The presence of the gold modifier does not appear to provide any improvement in catalyst performance under the specified reaction conditions.

Characterization of C5 hydrocarbons relevant to catalysis.

A recent in situ infrared study on the selective hydrogenation of C5 dienes and monoenes over a Pd/Al(2)O(3) catalyst only reported incomplete vibrational assignments for some of the reagents, intermediates, and products encountered in that study. This work uses a combination of infrared absorption spectroscopy, Raman, and inelastic neutron scattering to characterize the vibrational spectra of pentane, 1-pentene, cis- and trans-2-pentene, cis- and trans-1,3-pentadiene, 1,4-pentadiene, cyclopentane, and cyclopentene. Ab initio calculations of the potential energy surface, geometry, and vibrational transition energies were performed and simulations of the vibrational spectra compared to the experimental data. Complete vibrational assignments for the majority of the molecules are presented. The potential for using gas-phase infrared measurements for studying heterogeneously catalyzed gas-phase reactions is also briefly considered.

Quantitative dual-energy CT as a nondestructive tool to identify indicators for fossilized bone in vertebrate paleontology.

Dual-energy computed tomography (DECT) is an imaging technique that combines nondestructive morphological cross-sectional imaging of objects and the quantification of their chemical composition. However, its potential to assist investigations in paleontology has not yet been explored. This study investigates quantitative DECT for the nondestructive density- and element-based material decomposition of fossilized bones. Specifically, DECT was developed and validated for imaging-based calcium and fluorine quantification in bones of five fossil vertebrates from different geological time periods and of one extant vertebrate. The analysis shows that DECT material maps can differentiate bone from surrounding sediment and reveals fluorine as an imaging marker for fossilized bone and a reliable indicator of the age of terrestrial fossils. Moreover, the jaw bone mass of Tyrannosaurus rex showed areas of particularly high fluorine concentrations on DECT, while conventional CT imaging features supported the diagnosis of chronic osteomyelitis. These findings highlight the relevance of radiological imaging techniques in the natural sciences by introducing quantitative DECT imaging as a nondestructive approach for material decomposition in fossilized objects, thereby potentially adding to the toolbox of paleontological studies.

Determination of the helical screw sense and side-group chirality of a synthetic chiral polymer from Raman optical activity.

Splitting it up: excellent agreement between the experimental and the quantum-chemically simulated Raman optical activity (ROA) spectrum of (+)-poly(trityl methacrylate) shows that the polymer backbone adopts a left-handed helical conformation while the trityl side groups display a left-handed propeller conformation. Thus ROA can be used to determine the complete structure of synthetic chiral polymers in solution.

Poly(L-proline) II helix propensities in poly(L-lysine) dendrigraft generations from vibrational Raman optical activity.

Vibrational Raman optical activity (ROA), measured as small circularly polarized components in Raman scattering from chiral molecules, was applied to study the backbone conformations of the first five generations of poly(L-lysine) dendrigrafts (DGLs) in water. Generation 1 was found to support predominantly the poly(L-proline) II (PPII) conformation, the amount of which steadily decreased with increasing generation, with a concomitant increase in other backbone conformations. This behavior may be due to increasing crowding of the lysine side chains, together with suppression of backbone hydration, with increasing branching. In contrast, the ROA spectra of a series of linear poly(L-lysine)s in water show little change with increasing molecular weight. Our results may have implications for the nonimmunogenic properties of DGLs.

Identification of a human estrogen receptor alpha-derived antiestrogenic peptide that adopts a polyproline II conformation.

Polyproline II (PPII) helix is an extended secondary structure present in a number of proteins. PPII-containing sequences mediate specific protein-protein interactions with partners containing appropriate cognate domains called PPII-recognizing domains (PRDs) and are involved in the activation of intracellular signaling pathways. Thus, the identification of PPII structures in proteins is of great interest, not only to explore molecular and physiological mechanisms, but also to elaborate new potential drugs. By revisiting X-ray crystal structures of liganded alpha-type human estrogen receptor (ERalpha), we have identified an 11-residue PPII-helical sequence (D(321)AEPPILYSEY(331)) in the ligand-binding domain of the receptor. The data recorded by far-ultraviolet circular dichroism (far-UV CD), vibrational Raman optical activity (ROA) and differential scanning calorimetry (DSC) show that the corresponding peptide (Ac-DAEPPILYSEY-NH(2)) is particularly well structured in PPII, with the same proportion of PPII as observed from X-ray structures (approximately 85%). In addition, studies carried out on ERalpha-negative Evsa-T breast cancer cells transiently co-transfected with a pcDNA3-ERalpha plasmid and a Vit-tk-Luc reporter gene revealed that the peptide antagonizes the estradiol-induced transcription providing perspectives for researching new molecules with antagonistic properties.

Vibrational Raman optical activity of 1-phenylethanol and 1-phenylethylamine: revisiting old friends.

The samples used for the first observations of vibrational Raman optical activity (ROA) in 1972, namely both enantiomers of 1-phenylethanol and 1-phenylethylamine, have been revisited using a modern commercial ROA instrument together with state-of-the-art ab initio calculations. The simulated ROA spectra reveal for the first time the vibrational origins of the first reported ROA signals, which comprised similar couplets in the alcohol and amine in the spectral range approximately 280-400 cm(-1). The results demonstrate how easy and routine ROA measurements have become, and how current ab initio quantum-chemical calculations are capable of simulating experimental ROA spectra quite closely provided sufficient averaging over accessible conformations is included. Assignment of absolute configuration is, inter alia, completely secure from results of this quality. Anharmonic corrections provided small improvements in the simulated Raman and ROA spectra. The importance of conformational averaging emphasized by this and previous related work provides the underlying theoretical background to ROA studies of dynamic aspects of chiral molecular and biomolecular structure and behavior.

Residual structure in disordered peptides and unfolded proteins from multivariate analysis and ab initio simulation of Raman optical activity data.

Vibrational Raman optical activity (ROA), measured as a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light, or as the intensity of a small circularly polarized component in the scattered light, is a powerful probe of the aqueous solution structure of proteins. The large number of structure-sensitive bands in protein ROA spectra makes multivariate analysis techniques such as nonlinear mapping (NLM) especially favorable for determining structural relationships between different proteins. We have previously used NLM to map a large dataset of peptide, protein, and virus ROA spectra into a readily visualizable two-dimensional space in which points close to or distant from each other, respectively, represent similar or dissimilar structures. As well as folded proteins, our dataset contains ROA spectra from many natively unfolded proteins, proteins containing both folded and unfolded domains, denatured partially structured molten globule and reduced protein states, together with folded proteins containing little or no alpha-helix or beta-sheet. In this article, the relative positions of these systems in the NLM plot are used to obtain information about any residual structure that they may contain. The striking differences between the structural propensities of proteins that are unfolded in their native states and those that are unfolded due to denaturation may be responsible for their often very different behavior, especially with regard to aggregation. An ab initio simulation of the Raman and ROA spectra of an alanine oligopeptide in the poly(L-proline) II-helical conformation confirms previous suggestions that this conformation is a significant structural element in disordered peptides and natively unfolded proteins. The use of ROA to identify and characterize proteins containing significant amounts of unfolded structure will, inter alia, be valuable in structural genomics/proteomics since unfolded sequences often inhibit crystallization.

Enantiomerically pure quaternary ammonium salts with a chiral alkyl chain N(CH3)(n-C3H7)2(sec-C4H9)I: synthesis and physical studies.

A pair of enantiomerically pure quaternary ammonium salts with a chiral side chain, methyl-(R)-(1-methylpropyl)di(n-propyl)ammonium iodide 1 and methyl-(S)-(1-methylpropyl)di(n-propyl)ammonium iodide 2, and the related racemate, methyl-(rac)-(1-methylpropyl)di(n-propyl)ammonium iodide 3, were synthesized through a reductive alkylation procedure, starting from enantiomerically pure and, also, racemic forms of (rac)-(1-methylpropyl)amine. A spectroscopic chiroptical signature in solution was provided by the Raman optical activity spectra of compounds 1 and 2. The crystallographic structures of 1, 2, and 3 were examined by single crystal X-ray diffraction. 1 crystallizes in the tetragonal space group P4(3)2(1)2 (no. 96), a = b = 12.826 (2) A, c = 17.730 (2) A, V = 2916.9 (5) A(3), Z = 8, Flack coefficient 0.04 (2). 2 crystallizes in the tetragonal space group P4(1)2(1)2 (no. 92), a = b = 12.842 (1) A, c = 17.749 (2) A, V = 2927.0 (5) A(3), Z = 8, Flack coefficient 0.05 (2). The crystal structures and space groups for 1 and 2 are enantiomorphs and the crystallographic investigation confirmed the absolute configuration of the stereocenter in both compounds. 3 crystallizes in the monoclinic space group P2(1)/n(no. 14), a = 8.178 (1) A, b = 14.309 (2) A, c = 12.328 (2) A, beta = 96.811 (6) degrees, V = 1432.4 (2) A(3), Z = 4.

Delineation of protein structure classes from multivariate analysis of protein Raman optical activity data.

Vibrational Raman optical activity (ROA), measured as a small difference in the intensity of Raman scattering from chiral molecules in right and left-circularly polarized incident light, or as the intensity of a small circularly polarized component in the scattered light, is a powerful probe of the aqueous solution structure of proteins. On account of the large number of structure-sensitive bands in protein ROA spectra, multivariate analysis techniques such as non-linear mapping (NLM) are especially favourable for determining structural relationships between different proteins. Here NLM is used to map a dataset of 80 polypeptide, protein and virus ROA spectra, considered as points in a multidimensional space with axes representing the digitized wavenumbers, into readily visualizable two and three-dimensional spaces in which points close to or distant from each other, respectively, represent similar or dissimilar structures. Discrete clusters are observed which correspond to the seven structure classes all alpha, mainly alpha, alphabeta, mainly beta, all beta, mainly disordered/irregular and all disordered/irregular. The average standardised ROA spectra of the proteins falling within each structure class have distinct features characteristic of each class. A distinct cluster containing the wheat protein A-gliadin and the plant viruses potato virus X, narcissus mosaic virus, papaya mosaic virus and tobacco rattle virus, all of which appear in the mainly alpha cluster in the two-dimensional representation, becomes clearly separated in the direction of increasing disorder in the three-dimensional representation. This suggests that the corresponding five proteins, none of which to date has yielded high-resolution X-ray structures, consist mainly of alpha-helix and disordered structure with little or no beta-sheet. This combination of structural elements may have functional significance, such as facilitating disorder-to-order transitions (and vice versa) and suppressing aggregation, in these proteins and also in sequences within other proteins. The use of ROA to identify proteins containing significant amounts of disordered structure will, inter alia, be valuable in structural genomics/proteomics since disordered regions often inhibit crystallization.

Raman optical activity: a tool for protein structure analysis.

On account of its sensitivity to chirality, Raman optical activity (ROA), measured here as the intensity of a small, circularly polarized component in the scattered light using unpolarized incident light, is a powerful probe of protein structure and behavior. Protein ROA spectra provide information on secondary and tertiary structures of polypeptide backbones, backbone hydration, and side chain conformations, and on structural elements present in unfolded states. This article describes the ROA technique and presents ROA spectra, recorded with a commercial instrument of novel design, of a selection of proteins to demonstrate how ROA may be used to readily distinguish between the main classes of protein structure. A principal component analysis illustrates how the many structure-sensitive bands in protein ROA spectra are favorable for applying pattern recognition techniques to determine structural relationships between different proteins.

Raman optical activity demonstrates poly(L-proline) II helix in the N-terminal region of the ovine prion protein: implications for function and misfunction.

The aqueous solution structure of the full-length recombinant ovine prion protein PrP(25-233), together with that of the N-terminal truncated version PrP(94-233), have been studied using vibrational Raman optical activity (ROA) and ultraviolet circular dichroism (UVCD). A sharp positive band at approximately 1315 cm(-1) characteristic of poly(L-proline) II (PPII) helix that is present in the ROA spectrum of the full-length protein is absent from that of the truncated protein, together with bands characteristic of beta-turns. Although it is not possible similarly to identify PPII helix in the full-length protein directly from its UVCD spectrum, subtraction of the UVCD spectrum of PrP(94-233) from that of PrP(25-233) yields a difference UVCD spectrum also characteristic of PPII structure and very similar to the UVCD spectrum of murine PrP(25-113). These results provide confirmation that a major conformational element in the N-terminal region is PPII helix, but in addition show that the PPII structure is interspersed with beta-turns and that little PPII structure is present in PrP(94-233). A principal component analysis of the ROA data indicates that the alpha-helix and beta-sheet content, located in the structured C-terminal domain, of the full-length and truncated proteins are similar. The flexibility imparted by the high PPII content of the N-terminal domain region may be an essential factor in the function and possibly also the misfunction of prion proteins.

Chiral discrimination within disordered adlayers on metal surfaces.

Using a novel non-linear optical technique enantiomeric excess within a translationally disordered overlayer on a metal surface has been monitored for the first time.

Raman spectral evidence of methyl rotation in liquid toluene.

In order to rationalize subtle details in the liquid phase toluene Raman backscattering spectra, an analysis was performed based on a quantum-mechanical Hamiltonian operator comprising rotation of the methyl group and the angular dependence of vibrational frequencies and polarizability derivatives. The separation of the methyl torsion from the other vibrational motions appears to be necessary in order to explain relative intensity ratios of several bands and an anomalous broadening of spectral intensity observed at 1440 cm(-1). These results suggest that the CH3 group in the liquid phase rotates almost freely, similarly as in the gaseous phase, and that the molecule consequently exhibits effectively C(2v) point group symmetry. A classical description and an adiabatic separation of the methyl rotation from other molecular motion previously used in peptide models is not applicable to toluene because of a strong coupling with other vibrational motions. Density functional computations, particularly the BPW91 functional, provide reasonable estimates of harmonic frequencies and spectral intensities, as well as qualitatively correct fourth-order anharmonic corrections to the vibrational potential.

Raman optical activity and circular dichroism reveal dramatic differences in the influence of divalent copper and manganese ions on prion protein folding.

The binding of divalent copper ions to the full-length recombinant murine prion protein PrP23-231 at neutral pH was studied using vibrational Raman optical activity (ROA) and ultraviolet circular dichroism (UV CD). The effect of the Cu2+ ions on PrP structure depends on whether they are added after refolding of the protein in water or are present during the refolding process. In the first case ROA reveals that the hydrated alpha-helix is lost, with UV CD revealing a drop from approximately 25% to approximately 18% in the total alpha-helix content. The lost alpha-helix could be that comprising residues 145-156, located within the region associated with scrapie PrP formation. In the second case, ROA reveals the protein's structure to be almost completely disordered/irregular, with UV CD revealing a drop in total alpha-helix content to approximately 5%. Hence, although Cu2+ binding takes place exclusively within the unfolded/disordered N-terminal region, it can profoundly affect the structure of the folded/alpha-helical C-terminal region. This is supported by the finding that refolding in the presence of Cu2+ of a mutant in which the first six histidines associated with copper binding to the N-terminal region are replaced by alanine has a similar alpha-helix content to the metal-free protein. In contrast, when the protein is refolded in the presence of divalent manganese ions, ROA indicates the alpha-helix is reinforced, with UV CD revealing an increase in total alpha-helix content to approximately 30%. The very different influence of Cu2+ and Mn2+ ions on prion protein structure may originate in the different stability constants and geometries of their complexes.