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Mars Science Laboratory's Sample Analysis at Mars (SAM) investigation has measured all of the stable isotopes of the heavy noble gases krypton and xenon in the martian atmosphere, in situ, from the Curiosity Rover at Gale Crater, Mars. Previous knowledge of martian atmospheric krypton and xenon isotope ratios has been based upon a combination of the Viking mission's krypton and xenon detections and measurements of noble gas isotope ratios in martian meteorites. However, the meteorite measurements reveal an impure mixture of atmospheric, mantle, and spallation contributions. The xenon and krypton isotopic measurements reported here include the complete set of stable isotopes, unmeasured by Viking. The new results generally agree with Mars meteorite measurements but also provide a unique opportunity to identify various non-atmospheric heavy noble gas components in the meteorites. Kr isotopic measurements define a solar-like atmospheric composition, but deviating from the solar wind pattern at 80Kr and 82Kr in a manner consistent with contributions originating from neutron capture in Br. The Xe measurements suggest an intriguing possibility that isotopes lighter than 132Xe have been enriched to varying degrees by spallation and neutron capture products degassed to the atmosphere from the regolith, and a model is constructed to explore this possibility. Such a spallation component, however, is not apparent in atmospheric Xe trapped in the glassy phases of martian meteorites.

[Figure][1] Spinel is a very important rock-forming mineral that is found in basalts from Earth, Mars, the Earth’s Moon, and basaltic meteorites. Spinel can be used as a sensitive indicator of petrologic and geochemical processes that occur in its host rock. This paper highlights the role of increasing f O2 (from IW-1 to FMQ+2) in converting a >90% normal spinel to an ~25% magnetite (inverse) spinel, the trajectory of D Vspinel/melt as it relates to the ratio of V3+/V4+ in the melt, and the crystal chemical attributes of the spinel that control the intrinsic compatibility of both V3+ and V4+. This work examines the nuances of the V partitioning and provides a crystal chemical basis for understanding Fe3+, Cr, and V substitution into the octahedral sites of spinel. Understanding this interplay is critical for using spinels as both indicators of planetary parentage and reconstructing the redox history of magmatic systems on the terrestrial planets. Three potential examples for this use are provided. In addition, this work helps explain the ubiquitous miscibility gap between spinels with changing ulvospinel contents. [1]: pending:yes

In this work we present a series of experiments that examine the relationship between oxygen fugacity and Cr valence ratio in olivine grown from a basaltic liquid. These experiments are specifically targeted for an olivine-rich martian basalt composition that was modeled after the bulk chemistry of the meteorite Yamato 980459 (i.e., Y-98). The chromium valence ratio in the olivine crystals was measured with X-ray absorption near edge spectroscopy (XANES) at the Advanced Photon Source, Argonne National Laboratory. Results from the XANES measurements indicate that the ratio of divalent to trivalent Cr in the olivine is not only systematically correlated with f O 2 , but is also reflective of the molar Cr 3+ /Cr 2+ in the silicate liquid from which it grew. In this way, measurements of Cr valence in olivine phenocrysts can yield important information about the oxygen fugacity and molar Cr 3+ /Cr 2+ of its parental liquid in the absence of a quenched melt phase. Although the results from the experiments presented in this work specifically apply to the Y-98 parental melt, the concepts and XANES analytical techniques discussed within the text present a novel, generalized methodology that may be applicable to any olivine-bearing basalt. Furthermore, the XANES-based measurements are made on a micrometer-scale, thus potential changes of the Cr 3+ /Cr 2+ in the melt during crystallization could be examined with a great deal of spatial detail.

[1] The Sample Analysis at Mars (SAM) instrument suite on the Mars Science Laboratory (MSL) measured a Mars atmospheric14N/15N ratio of 173 ± 11 on sol 341 of the mission, agreeing with Viking's measurement of 168 ± 17. The MSL/SAM value was based on Quadrupole Mass Spectrometer measurements of an enriched atmospheric sample, with CO2 and H2O removed. Doubly ionized nitrogen data at m/z 14 and 14.5 had the highest signal/background ratio, with results confirmed by m/z 28 and 29 data. Gases in SNC meteorite glasses have been interpreted as mixtures containing a Martian atmospheric component, based partly on distinctive14N/15N and40Ar/14N ratios. Recent MSL/SAM measurements of the40Ar/14N ratio (0.51 ± 0.01) are incompatible with the Viking ratio (0.35 ± 0.08). The meteorite mixing line is more consistent with the atmospheric composition measured by Viking than by MSL.

A spiked (with REE, V, Sc) martian basalt Yamato 980459 (Y98) composition was used to synthesize olivine, spinel, and pyroxene at 1200 °C at five oxygen fugacities: IW−1, IW, IW+1, IW+2, and QFM. These run products were analyzed by electron microprobe, ion microprobe, and X-ray absorption near-edge spectroscopy to establish four oxybarometers based on vanadium partitioning behavior between the following pairs of phases: V spinel-melt, V/(Cr+Al) spinel-melt, olivine-melt, and spinel-olivine. The results for the spinel-melt, olivine-melt, and V/(Cr+Al) spinel-melt are applicable for the entire oxygen fugacity range while the spinel-olivine oxybarometer is only applicable between IW−1 and IW+1. The oxybarometer based on V partitioning between spinel-olivine is restricted to basalts that crystallized under low oxygen fugacities, some martian, all lunar, as well as samples from 4 Vesta. The true potential and power of the new spinel-olivine oxybarometer is that it does not require samples representative of a melt composition or samples with some remnant of quenched melt present. It just requires that the spinel-olivine pairs were in equilibrium when the partitioning of V occurred. We have applied the V spinel-olivine oxybarometer to the Y98 meteorite as a test of the method.

The pKa value of protonated Jeffamine (bis(3-aminopropyl) terminated polyethylene glycol) in solution and attached as a monolayer to graphite surfaces has been determined using potentiometric titration. The protonated Jeffamine was found to have a pKa value of 9.7 in solution at 25 degrees C, whereas this value decreases to 7.1 when it is attached to a graphite surface. Potentiometric titrations from 25 to 40 degrees C allowed us to determine the surface pKa of the protonated Jeffamine at each temperature studied and hence to determine the enthalpy, entropy and Gibbs energy changes associated with the deprotonation of the amino-terminated surface bound Jeffamine groups. It was found that the enthalpic contribution is negligibly small and the evaluation of these thermodynamic parameters controlling the shift in surface pKa value indicates that this process is controlled by entropic contribution arising from the ordering/disordering of solvent molecules at the carbon-water interface. This suggests that the long chain Jeffamine molecules are oriented on the carbon surface rather than existing in the bulk solution.

A strategy has been established for the synthesis of peptidomimetics derived from unsaturated carbohydrates, and exemplified by the use of methyl 2,6-anhydro-7-azido-3,7-deoxy-4,5-O-isopropylidene-D-lyxo-hept-2-enonate 9 as a dipeptide ‘monomer’ which can be elaborated from either end. Selective reduction of 9 gives a protected pseudodipeptide ester suitable for use as an amino component, and saponification gives an azido acid suitable for use as a carboxyl component. The ‘dimer’ product of coupling these two components with TBTU can be similarly elaborated at either end to give a ‘trimer’, and a further cycle of selective reduction and coupling gave a ‘tetramer’, 17, a pseudo-octapeptide. Copyright © 2003 European Peptide Society and John Wiley & Sons, Ltd.

The thermodynamics of and the kinetic parameters controlling the sequestration of the toxic heavy-metal ion Cd(II) from aqueous media by using a novel material consisting of glassy carbon microspheres (10-20 microm in diameter) chemically modified with L-cysteine methyl ester are presented. In an effort to reduce the cost and increase the efficiency of toxic-metal-ion removal, this modification strategy was expanded to attach L-cysteine methyl chemically ester to less-expensive graphite powders (2-20 microm in diameter), and the thermodynamic and kinetic parameters of the sequestration of Cd(II), Cu(II), and As(III) toxic metal ions are presented. It was found that the use of chemically modified graphite powder greatly increased both the rate and the amount of metal ions removed from aqueous media. This work has important potential applications to filtration of drinking water and environmental remediation.

L-Cysteine methyl ester modified glassy carbon powder (CysOMe-GC) has been shown to have potential for the removal of toxic heavy metal ions, such as copper(II), cadmium(II) and arsenic(III), from “real” water samples. To develop this material for environmental applications we must develop an understanding of the thermodynamic parameters controlling the uptake of metal ions by the modified carbon powder. Here we characterise the material using X-ray photoelectron spectroscopy (XPS), before investigating the effect of varying the solution pH, the concentration of copper(II) ions and the mass of CysOMe-GC powder added to the solution using square wave voltammetry (SWV). This data allows us to understand the thermodynamics controlling the copper(II) ion uptake and elucidate that the adsorption of copper(II) onto the CysOMe modified surface is controlled by a Freundlich isotherm.

"Bamboo-like" multiwalled (b-MWCNT), "hollow-tube" multiwalled (h-MWCNT) and single-walled carbon nanotubes (SWCNT), chemically modified with 1-anthraquinonyl (AQ) or 4-nitrophenyl (NP) groups, are characterized using voltammetric, electron microscopic and Raman spectroscopic techniques. The pKa values of the AQ-modified CNTs are found to be shifted by greater than three units when compared to the pKa values of anthrahydroquinone (AHQ, the reduced form of AQ) in aqueous solution to beyond pH 14. These large changes in the surface pKa values of the modified CNTs are explored further by comparing the pKa values of CNTs modified with an anthraquinonyl-2-carboxylic acid group. These groups are attached to the CNT surface via the formation of an amide bond with an aminophenyl "spacer" unit derived from the chemical reduction of NP modified CNTs. The location of reactive sites on the CNT surface is investigated and their influence on the pKa of the modified materials is discussed. Comparison with modified pyrolytic graphite electrodes exposing pure edge-plane or pure basal-plane crystal faces indicates that the modifying aryl groups are predominantly located on edge-plane like defects at the tube ends of MWCNTs. The effect of polymer formation on electron transfer kinetics of b-MWCNTs and h-MWCNTs is also discussed. In contrast SWCNTs show both significant side-wall functionalisation and fast electron transfer kinetics which is attributed to their different electronic structure. This journal is © The Royal Society of Chemistry.

Quinone groups on the surface of edge-plane and basal-plane pyrolytic graphite electrodes, and, for the first time, "bamboo-like" multi-walled carbon nanotubes (b-MWCNTs), are labelled with a voltammetric "tag", namely 2,4-dinitrophenylhydrazine (2,4-DNPH). The voltammetric response of these materials is studied in both aqueous and non-aqueous electrolyte solutions, and mechanisms are proposed for each media involving the voltammetrically controlled cleavage of the 2,4-DNPH adduct. Thus, these materials can be used for potentiometrically controlled chemical release, and as such may find application in, for example, drug delivery systems. In aqueous media, this cleavage results in the conversion of the surface quinonyl groups into surface arylnitroso species. This conversion is confirmed by studying the voltammetric response of the arylnitroso/arylhydroxylamine redox couple, formed after cleavage of the 2,4-DNPH adduct in the presence of l-glutathione, which has been shown in our previous work to react with arylnitroso species on the surface of graphitic carbon materials. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.

A method of constructing a "designer interface" consisting of either monolayers or multilayers of chemically modified microbeads is reported, whereby the shape of the interface as well as the interfacial chemistry imparts "diffusional protection" to the underlying surface material. © The Royal Society of Chemistry 2006.

Further studies on the use in peptide synthesis of N(π)-phenacyl protection for histidine side chains have shown that whilst this prevents the side chain-induced racemisation which can occur if there is a lone pair of electrons available at the π-nitrogen, there are concomitant drawbacks. As an alternative approach to the racemisation problem, the effect of halogenation of the heterocyclic ring carbons (to diminish the availability of the π-nitrogen lone pair) has been investigated. This gives derivatives which are convenient in both classical and solid-phase applications, the halogen modifying groups being removed at the last stage by catalytic hydrogenolysis over a rhodium catalyst. Racemisation is suppressed as expected, but it is not eliminated completely: direct blockade of the π-nitrogen appears to be indispensable for its complete prohibition. Protection of the π-nitrogen with a benzyloxymethyl group has now been found to be much more satisfactory than the use of the phenacyl group for this purpose. A π-benzyloxymethyl substituent not only prohibits side chain-induced racemisation but also gives derivatives with convenient physical properties which can be incorporated into well established classical and solid-phase strategies without the need for any novel or additional operations or changes in protocol. The protecting group is stable to basic conditions, to trifluoroacetic acid, and to aqueous solutions of carboxylic acids, but is cleaved cleanly and rapidly by hydrogen bromide in trifluoroacetic acid or by catalytic hydrogenolysis. N(α)-t-Butoxycarbonyl-N(π)-benzyloxymethyl-L-histidine has been prepared in good yield by a simple procedure from an easily accessible intermediate and isolated as a crystalline solid; its use has been demonstrated by a number of exercises including a solid-phase synthesis of 5-isoleucine-angiotensin II and a classical synthesis of trihistidine.

International audience; The Highly Siderophile Elements (HSE) are powerful tracers of planetary differentiation. Despite the importance of their partitioning between silicate and metal for the understanding of planetary core formation, especially for the Earth and Mars, there is still a huge discrepancy between conclusions based on different high temperature (HT) experimental studies. These disagreements may be due to the presence of HSE micro and nanonuggets in HT experiments. The formation of these nuggets is still interpreted in different ways. One hypothesis is that these HSE nuggets formed during the quench of the silicate melt, while another hypothesis supposes that these nuggets formed before the quench and represented artefacts of HT experiments. The goal of this work is to clarify whether the presence of HSE nuggets in silicate melts is linked to a quench effect or not. Understanding the formation of these HSE nuggets represents thus a necessary step towards the resolution of the Earth's core formation scenarios. We performed new HT experiments (1275–2000 • C) at different oxygen fugacities (fO 2), between ambient air up to ∼5 log units below the Iron-Wüstite buffer [IW-5], for two different silicate compositions (synthetic martian and terrestrial basalts) mixed with a metallic mixture of Pt–Au– Pd–Ru. Our 1275–1600 • C experiments were contained in either olivine, diopside or graphite crucible; experiments at 2000 • C were performed using a levitation method, so no capsule was necessary. Our samples contained quenched silicate melts, minerals (olivine, pyroxene, spinel depending on the run), a two-phase metallic bead and nano and micro-nuggets of HSE. Our samples underwent fine textural, structural and analytical characterizations. The distribution of the nuggets was not homogeneous throughout the quenched silicate melt. HSE nuggets were present within crystals. Dendritic textures from the quenched silicate melt formed around HSE nuggets, which could be crystallized, showing that the nuggets acted as nucleation sites during the quench. Thus they predated the quench. Finally, these nuggets also had strong heterogeneities suggesting at least a two-stage formation process under reducing conditions. Consequently, our observations clearly show that these HSE nuggets formed before the quench in the silicate melt. Our results agreed with previous studies, which concluded that HSE abundances in the Earth's mantle require the late accretion of chondritic material subsequent to core formation. However, the effects of metallic Si, O, H, or the effect of pressure on the HSE partitioning are still not fully understood. Further work to constrain these effects is to be encouraged to understand the Earth's core formation.

article i nfo Article history: Solid metal/liquid metal partitioning experiments were conducted at 9 GPa and 1323-1873 K in the Fe-S system. Analysis of the experimental charges by in situ laser ablation inductively coupled plasma mass spectrometry enabled partitioning results to be obtained for a total of 21 trace elements (Co, Ni, Cu, Ga, Ge, As, Mo, Ru, Rh, Pd, Ag, Sn, Sb, W, Re, Os, Ir, Pt, Au, Pb, and Bi). This new, elevated pressure dataset for the Fe-S system allows a direct comparison to the extensive data available at 0.1 MPa and permits evaluation of the effect of pressure on partitioning in this system. The majority of the elements studied exhibit different solid metal/liquid metal partitioning behaviors at 9 GPa than at 0.1 MPa. Additionally, the nature of these differences varies significantly between the 21 trace elements studied, spanning the range of behaviors of partitioning from more strongly into solid metal, to less strongly into solid metal, and to becoming insensitive to the metallic liquid composition. We conclude that pressure affects solid metal/liquid metal partitioning behavior in the Fe-S system and discuss the implications for fractionations due to Earth's core solidification and for planetary differentiation models.

The high average density and low surface FeO content of the planet Mercury are shown to be consistent with very low oxygen fugacity during core segregation, in the range 3–6 log units below the iron–wustite buffer. These low oxygen fugacities, and associated high metal content, are characteristic of high-iron enstatite (EH) and Bencubbinite (CB) chondrites, raising the possibility that such materials may have been important building blocks for this planet. With this idea in mind we have explored the internal structure of a Mercury sized planet of EH or CB bulk composition. Phase equilibria in the silicate mantle have been modeled using the thermodynamic calculator p-MELTS, and these simulations suggest that orthopyroxene will be the dominant mantle phase for both EH and CB compositions, with crystalline SiO 2 being an important minor phase at all pressures. Simulations for both compositions predict a plagioclase-bearing “crust” at low pressure, significant clinopyroxene also being calculated for the CB bulk composition. Concerning the core, comparison with recent high pressure and high temperature experiments relevant to the formation of enstatite meteorites, suggest that the core of Mercury may contain several wt.% silicon, in addition to sulfur. In light of the pressure of the core–mantle boundary on Mercury (∼7 GPa) and the pressure at which the immiscibility gap in the system Fe–S–Si closes (∼15 GPa) we suggest that Mercury’s core may have a complex shell structure comprising: (i) an outer layer of Fe–S liquid, poor in Si; (ii) a middle layer of Fe–Si liquid, poor in S; and (iii) an inner core of solid metal. The distribution of heat-producing elements between mantle and core, and within a layered core have been quantified. Available data for Th and K suggest that these elements will not enter the core in significant amounts. On the other hand, for the case of U both recently published metal/silicate partitioning data, as well as observations of U distribution in enstatite chondrites, suggest that this element behaves as a chalcophile element at low oxygen fugacity. Using these new data we predict that U will be concentrated in the outer layer of the mercurian core. Heat from the decay of U could thus act to maintain this part of Mercury’s core molten, potentially contributing to the origin of Mercury’s magnetic field. This result contrasts with the Earth where the radioactive decay of U represents a negligible contribution to core heating.

Syntheses of the sequential polypeptide elastin models poly-(Gly-Val-Gly-Val-Pro) and poly-(Gly-Val-Pro-Gly) are described.

In order to quantify possible fractionation of U and Pb into a metallic core, we have performed piston cylinder and multi-anvil press experiments at high pressure (up to 20 GPa) and high temperature (up to 2400 °C) and obtained the distribution coefficient Dmetal–silicate and the exchange partition coefficient Kmetal–silicate for these elements between metal and silicates (mineral or liquid). D Pb metal–silicate and D U metal–silicate depend strongly on the S content of the metallic phase, and also on the oxygen fugacity, in agreement with an effective valence state of 4 for U in silicates and 2 for Pb in silicates. K Pb d metal–silicate and K U d metal–silicate show no discernable pressure and temperature trend. U remains lithophile even at high pressure and high temperature but its lithophile nature decreases at very low oxygen fugacity. From our experimental data, it was possible to calculate the U and Pb contents of the cores of Mars and Earth under core-mantle equilibrium conditions at high pressure and high temperature. From the Dmetal–silicate of the present study, we obtained that: 0.008 ppm Our results suggest that the low concentration of Pb in the terrestrial mantle could not be explained by an early Pb sequestration in the Earth’s core even if S is the dominant light element of the core. If we assume a magma ocean scenario, U might produced a maximum value of 1.5% of the total heat budget of the core with a segregation occurring below ΔIW-3. The values found in the present study for U in the Martian core suggest that the magnetic field activity of Mars before ∼0.5 b.y. after its formation would be difficult to ascribe to the decay of U alone.

Of water and methane on Mars The Curiosity rover has been collecting data for the past 2 years, since its delivery to Mars (see the Perspective by Zahnle). Many studies now suggest that many millions of years ago, Mars was warmer and wetter than it is today. But those conditions required an atmosphere that seems to have vanished. Using the Curiosity rover, Mahaffy et al. measured the ratio of deuterium to hydrogen in clays that were formed 3.0 to 3.7 billion years ago. Hydrogen escapes more readily than deuterium, so this ratio offers a snapshot measure of the ancient atmosphere that can help constrain when and how it disappeared. Most methane on Earth has a biological origin, so planetary scientists have keenly pursued its detection in the martian atmosphere as well. Now, Webster et al. have precisely confirmed the presence of methane in the martian atmosphere with the instruments aboard the Curiosity rover at Gale crater. Science , this issue p. 412 , p. 415 ; see also p. 370

Carbon has been proposed as a potential light element in planetary cores, included in models of planetary core formation, and found in meteoritic samples and minerals. To better understand the effect of C on the partitioning behavior of elements, solid/liquid partition coefficients ( D = (solid metal)/(liquid metal)) were determined for 17 elements (As, Au, Co, Cr, Cu, Ga, Ge, Ir, Ni, Os, Pd, Pt, Re, Ru, Sb, Sn, and W) over a range of C contents in the Fe–Ni–C system at 1 atm. The partition coefficients for the majority of the elements increased as the C content of the liquid increased, an effect analogous to that of S for many of the elements. In contrast, three of the elements, Cr, Re, and W, were found to have anthracophile (C-loving) preferences, partitioning more strongly into the metallic liquid as the C content increased, resulting in decreases to their partition coefficients. For half of the elements examined, the prediction that partitioning in the Fe–Ni–S and Fe–Ni–C systems could be parameterized using a single set of variables was not supported. The effects of S and C on elemental partitioning behavior can be quite different; consequently, the presence of different non-metals can result in different fractionation patterns, and that uniqueness offers the opportunity to gain insight into the evolution of planetary bodies.

The redox states of volcanic and impact melts from the Earth, Moon, and Mars have been estimated from the valence state of V in basaltic glasses (Sutton et al. 2005). The V valence has been determined using synchrotron micro X-ray absorption near-edge structure spectroscopy (XANES) (Sutton et al. 2005), which allows for in situ measurements on samples with a micrometer spatial resolution and ~100 ppm elemental sensitivity. Here, we interpret those results for the natural samples and compare them to the literature. The results show that terrestrial melts are dominated by V 4+ , lunar samples by V 3+ , with Martian melts a mixture of both V 3+ and V 4+ . The f O 2 estimates derived from the V valence are consistent with those determined by other proven methods, whereby terrestrial basalts experience f O 2 conditions within 1 or 2 log units of the QFM buffer, lunar basalts equilibrate at 1 to 2 log units below the IW buffer, and Martian basalts fall somewhere between the QFM and IW buffer. The results illustrate the usefulness of this technique; i.e., a robust oxybarometer covering over six orders of magnitude, applicable to samples that record f O 2 conditions from reduced extraterrestrial bodies to the oxidized Earth.

A series of oxetane δ-amino acid scaffolds derived from L-rhamnose and D-xylose provide a new class of templated sugar amino acids (SAA), which can be considered as D/L-alanine-D-serine and glycine-L-serine dipeptide isosteres. © 2004 Elsevier Ltd. All rights reserved.

An efficient multigram ring contraction of a 1,4-lactone 2-O-triflate derived from l-rhamnose - with retention of configuration in the ring closure - is the key step in the preparation of a series of oxetanes, which are pseudoenantiomeric analogues of the naturally occurring antibiotic oxetin, an oxetane cis-β-amino acid. Subsequent nucleophilic displacements of the corresponding triflates by azide proceed in consistently excellent yields, without any elimination, to provide syntheses of scaffolds for analogues of the antibiotic. © 2004 Elsevier Ltd. All rights reserved.

Many solar system processes involve a metallic liquid, and the composition of the metallic liquid, such as the liquid's concentrations of S, P, and C, will influence the partitioning of elements during such processes. We present a method for parameterizing solid metal-liquid metal partition coefficients for siderophile (metal-loving) elements as a function of the metallic liquid composition. Our parameterization method is based on an older theory of Jones and Malvin (1990), which stated that the metallic liquid is composed of metal and non-metal-bearing domains, and the domains are the dominant influence on the partitioning behavior. By revising the means by which the metal domains are calculated, our revised parameterization method is able to match experimental partitioning data from the Fe-Ni-S, Fe-Ni-P, Fe-Ni-S-P, and Fe-Ni-C systems. Mathematical expressions were derived for the solid metal-liquid metal partitioning of 13 siderophile elements. Elements that are chalcophile (S-loving), P-loving, or C-loving prefer the non-metal-bearing domains in the metallic liquid and, consequently, aren't fit by the parameterization method presented here. Possible applications for our parameterization method include modeling the crystallization of iron meteorites, planetary differentiation, and the solidification of Earth's inner core.

Evidence is presented to show that the racemisation of N(alpha)-benzyloxycarbonyl-N(pi)-phenacyl-L-histidine which occurs on activation with dicyclohexylcarbodiimide in dimethylformamide takes place by action of the pi-nitrogen as an intramolecular base catalyst in the O-acylisourea adduct which is in reversible equilibrium with the reactants, rather than by formation of an optically labile heterocyclic intermediate.

An alternative synthesis of [7-(thiazolidine-4-carboxylic acid)]-oxytocin by a 6 + 3 route using a hexapeptide with a preformed disulphide bridge is outlined.

Details are given of a modified l-amino acid oxidase procedure for the estimation of racemisation of histidine residues in peptide synthesis.

[7-Methyltryptophan9]-beta-corticotropin-(1-24) has been synthesised. In an isolated adrenal cell bioassay, it has 2.7 times the steroidogenic activity of beta-corticotropin-(1-24) (Synacthen).

Previous investigators have shown that, at high pressure, Re is a good capsule material and that Fe loss to Re under these conditions is minimal (e.g., Herzberg and Zhang 1997). We present here the first systematic low-pressure study of Re loop stability and of Fe loss from silicate melts to Re loops as a function of f O2 . Experiments were performed at 1400 degrees C and one bar pressure over a range of f O2 . For f O2 values as low as QFM-2, Fe loss was found to be negligibly small, even for a charge/loop ratio of only about 2. According to our calculations, for the same conditions, Fe loss to a Pt loop could reach 70% of the initial FeO content. We have also estimated the diffusion coefficient of Fe in Re and found it to be very small ( nearly equal 10-12 cm 2 /s), which is an additional factor in preventing Fe loss. At values of f O2 near QFM, Re metal reacts to form volatile Re oxides. But at f O2 below QFM-1.7, Re loops were found to be stable for any reasonable experimental run duration at 1400 degrees C. At lower temperatures Re may be stable to even higher values of f O2 . These conditions are similar to or slightly more reducing than the accepted redox states for the mantles of the Earth and Mars. Consequently, for many experiments, Re may be a more convenient loop material than Pt.

Experimental details are presented for the introduction and application of pi-allyloxymethyl protection for histidine side-chains.

A rational attempt to prepare FmocHis(piTrt)OH regiospecifically gave in fact the well-known tau-trityl isomer, and experiments with model systems indicate that the prospects for access to pi-trityl histidine derivatives, which would be of great value for the racemization-free synthesis of histidine-containing peptides, are poor.

— Samples from a suite of Shergotty—Nakhla—Chassigny (SNC) meteorites were analyzed for their O isotopic ratios by a modified version of the laser fluorination technique. Measured isotopic ratios (17O/16O and 18O/16O) from bulk samples of the Shergottites, EETA79001, Shergotty and Zagami; the Nakhlite Lafayette; and Chassigny are similar to those reported in the literature, as are those from olivine and pyroxene mineral separates from Lafayette. Iddingsite, a preterrestrial alteration product of Lafayette, was measured for the first time as a separate phase. Oxygen isotopic ratios increase with the percentage of iddingsite in a sample to a maximum δ18O of 14.4% for a ∼90% separate. Based on these measurements, end-member iddingsite has a δ18O of 15.6%, which places it among other 18O-enriched secondary phases (carbonate and silica) observed in SNC meteorites. The relatively large difference in δ18O between iddingsite and the olivine and pyroxene it replaces (∼11%) is typical of low-temperature alteration products. A range of crustal fluid δ18O values can be interpreted from the δ18O for end-member iddingsite, assuming isotopic equilibrium was achieved during low-temperature hydrous alteration (

Two new cyclic oligomers, cyclo-tetra-[2,4-anhydro-3-O-tert- butyldimethylsilyl-5-deoxy-L-rhamnonamido-(N→5)] and the corresponding 6-deoxy-D-gulonate cyclic 'tetramer', have been synthesised from linear tetrameric oligomers, using TBTU- and pentafluorophenyl ester-based methodologies, respectively. These two compounds constitute a novel class of cyclic oligomers derived from oxetane-based sugar amino acids. Copyright © 2006 European Peptide Society and John Wiley and Sons, Ltd.

Mars' Atmosphere from Curiosity The Sample Analysis at Mars (SAM) instrument on the Curiosity rover that landed on Mars in August last year is designed to study the chemical and isotopic composition of the martian atmosphere. Mahaffy et al. (p. 263 ) present volume-mixing ratios of Mars' five major atmospheric constituents (CO 2 , Ar, N 2 , O 2 , and CO) and isotope measurements of 40 Ar/ 36 Ar and C and O in CO 2 , based on data from one of SAM's instruments, obtained between 31 August and 21 November 2012. Webster et al. (p. 260 ) used data from another of SAM's instruments obtained around the same period to determine isotope ratios of H, C, and O in atmospheric CO 2 and H 2 O. Agreement between the isotopic ratios measured by SAM with those of martian meteorites, measured in laboratories on Earth, confirms the origin of these meteorites and implies that the current atmospheric reservoirs of CO 2 and H 2 O were largely established after the period of early atmospheric loss some 4 billion years ago.

Experimental studies of the metal/silicate partitioning of Ir have produced two sets of results differing by a factor of 10 6 ( Jones and Drake, 1986 ; O'Neill et al., 1995 ). In an attempt to understand this discrepancy, we have performed instrumental neutron activation analyses of multiple glass chips from these siderophile element partitioning experiments. From seven to ten individual chips (~ 10–100 μ g each) were analyzed from each experimental glass. The major target was Ir, which was detected at concentrations ranging from 690 ppb (ng/g) to less than 1 ppb. Detection limits are less than 10 −13 grams Ir. Almost all of the run products appear to be homogeneous with respect to lithophile elements, but most vary considerably in their Ir concentrations. It appears that most of the experiments analyzed so far contain small amounts of metal in the glass separates. One experiment from Jones and Drake (1983) appears to be homogeneous, but in fact may not be. More recent experiments are definitely not homogeneous, and require the existence of a metallic phase distinctly different from the bulk solid metal or liquid metal/sulfide phases also present in the charges. Iridium contents of the glass in the stirred crucible experiment studied ( O'Neill et al., 1996 ) decreased continuously over a period of several months, even as the oxygen fugacity was increasing, suggesting that the experiment never achieved equilibrium. Iridium contents in multiple samples of the glasses varied over factors of 2 to 3x. Further subdivision of one low-Ir glass did not result in a reduction in the variation of Ir between aliquots. Thus, the variation in Ir concentration appears to remain fairly constant, irrespective of the scale of the sampling.

The melt portion of a parental magma, undergoing equilibrium olivine crystallization, passes through a succession of compositions unique to its initial composition. Because the succession of compositions follows uniquely from the parental magma's composition, a liquid line of descent model fit to several of the derivative-melt compositions can recover an estimate of the parental magma's composition. We have developed an algorithm to accomplish the model fitting and thus far equipped it to treat olivine fractionation including departures from perfect equilibrium crystallization. Here we report validation tests on the method, which we call “Derivative-Magma Analysis” (DMA), applied to computer-synthesized data and two instances of laboratory-synthesized data (one as a single-blind test). For the computer- and laboratory-synthesized data, DMA recovered the parental-magma compositions within common analytical accuracy. For the most difficult oxide to estimate, MgO, the recovered values deviated from the measured values by less than 0.5 wt% for the two laboratory-synthesized datasets. For other major-element oxides, recovered values typically deviate from nominal values by less than 0.2 wt%. DMA also reliably estimated the compositions of the olivines that coexisted with each derivative melt. Applied to the Kilauean summit eruption of 1959, DMA estimates a parental magma with Mg# = 73 (MgO ≈ 16 wt%). This value, while significantly higher than estimates from some authors who favor low-Mg parental magmas, rules out the extremely high-MgO parental magmas favored by other authors.

Reports of percent level concentrations of normally lithophile elements such as Zr, Nb, and Ta in some refractory noble metal nuggets in CAIs raise important questions about the redox state of the early solar nebula. Consequently, we have determined the metal/silicate liquid partition coefficients for Zr, Nb, and Ti at 1548 K and solar oxygen fugacity (fo 2 ∼ 10 −16 bar). In most experiments, these elements formed intermetallic compounds with Pt-metal. Even though our partition coefficients for Zr (2.06–4.55) were substantially greater than previously determined values, they are still too small to account for percent levels of Zr in a refractory metal nugget from an average CAI. In addition, partition coefficient values obtained for Nb and Ti show an extremely strong affinity for the metal phase. Yet, Nb is rarely observed in refractory metal nuggets and Ti has never been observed. Given the abundance of Ti in CAIs, substantial concentrations of Ti should be present in refractory metal nuggets. This discrepancy is attributed to either: (1) the solarfo 2 was too oxidizing during condensation to form the predicted intermetallic compounds; or (2) the lithophile elements originally formed intermetallic compounds with Pt-metals during condensation in the solar nebula but were subsequently oxidized in a latter heating event. Whereas our experiments suggest that conditions were never reducing enough for Ti to alloy with Pt metal, other redox determinations (e.g.Ti 3+ /Ti 4+ ratios in CAI) imply approximately solar oxygen fugacities. Our experiments serve to emphasize the range in redox states implied by metal and silicate assemblages in CAI.

Liquid carbonate/ liquid silicate partition coefficients (D) for a suite of incompatible elements (Nb, Mo, Ba, Ce, Pb, Th, U) have been determined experimentally. For one experiment, D's for Ra and Pa were also determined. The partitioning behavior is shown to be a regular function of the ionic field strength (zr) of the partitioned elements. At constant temperature, increasing pressure from 7 to 20 kbar caused little change in the measured D. At constant pressure, increasing temperature causes all D's to approach unity, as the temperature nears the critical temperature and the two liquids become compositionally similar. Addition of P or F to the system enlarges the stability field of carbonate but does not affect the partitioning behavior of our suite of elements. However, both P and F are strongly partitioned into the carbonate liquid. Omphacite/carbonate liquid D's at 50–60 kbar have also been determined. Our results for DU and DTH are similar to those found previously for augite/silicate liquid. Thorium is more compatible than U in pyroxene, indicating that excesses of 230Th/238U found in MORB cannot be explained by fractionation between pyroxene and melt. The Soret effect in carbonate liquids is quite small, in contrast to the effect in silicate liquids. In general, we see no evidence for Soret separation in our experiments, implying that endmember Ca-, Na-, and Mg-carbonate liquids have simple speciations and mix nearly ideally. This observation suggests that the results of our liquid/liquid partitioning studies do not strongly depend on the exact composition of the carbonate. Our experimentally determined liquid-liquid partition coefficients can explain recent fractionations of 210T/238U and 226Ra/238U in carbonatitec lavas from the Oldoinyo Lengai volcano, but cannot explain similar fractionations in 230Th/238U. 210Pb has the shortest half-life of these nuclides, and is, therefore, the most sensitive to the exact timing and mechanism of fractionation. Because we can explain 210Pb/238U in terms of recent, instantaneous liquid immiscibility, we favor this model for the origin of the deviations of 210Pb/238U and 226Ra/238U from those expected under secular equilibrium. If our interpretation is correct, some other fractionation process(es) must have fractionated Th (and perhaps Pa) from U, Ra, and Pb in the Oldoinyo Lengai carbonatites.

The purpose of the study is to provide an alternative perspective on both the mass balance issue and on the issue of secular change in the Rb-Cs ratio in the earth mantle. In particular, it is argued that the apparent secular change in the Rb/Cs ratio may be simply an artifact of alteration of older rocks through weathering and/or metamorphism subsequent to formation. It is also shown that there is not necessarily a need for a hidden, undepleted reservoir, and the consistency of this result with other mass calculations is explored. New methods for estimating the Rb/Cs ratio of the bulk silicate earth are suggested.

Low-temperature metal-silicate partition coefficients are extrapolated to magma ocean temperatures. If the low-temperature chemistry data is found to be applicable at high temperatures, an important assumption, then the results indicate that high temperature alone cannot account for the excess siderophile element problem of the upper mantle. For most elements, a rise in temperature will result in a modest increase in siderophile behavior if an iron-wuestite redox buffer is paralleled. However, long-range extrapolation of experimental data is hazardous when the data contains even modest experimental errors. For a given element, extrapolated high-temperature partition coefficients can differ by orders of magnitude, even when data from independent studies is consistent within quoted errors. In order to accurately assess siderophile element behavior in a magma ocean, it will be necessary to obtain direct experimental measurements for at least some of the siderophile elements.

The N-alkylated deoxynojirimycin compound, N-(6'-(4''-azido-2''-nitrophenylamino)hexyl)-1-deoxynojirimycin (6) was synthesised as a potential photoaffinity probe for endoplasmic reticulum (ER) alpha-glucosidases I and II. Surprisingly this compound was a highly potent inhibitor of alpha-glucosidase I (IC(50), 17 nM) in an in vitro assay and proved equally effective at inhibiting cellular ER glucosidases, as determined by a free oligosaccharide (FOS) analysis. A modest library of compounds was synthesised to obtain structure-activity information by variation of the N-alkyl chain length and modifications to the azido-nitrophenyl group. All of these compounds failed to improve on the efficacy of compound 6, but most showed greater enzyme inhibitory potency than N-butyl-deoxynojirimycin (NB-DNJ), a pharmacological agent that has been evaluated for the treatment of several viruses for which infectivity is dependent on host cell glycosylation.

As nonmetals are added to the Fe-Ni system, segregation coefficients(k) of trace constituents change dramatically. For example, as the S content of the metallic liquid increases from 0 to ≈31 wt pct, the molar k(Ge) between solid and liquid metal increases from 0.6 to ~120. Little of this change can be ascribed to temperature. Also, these changes are not linear. In the case of the Fe-Ni-S system, the largest changes are seen between 20 and 30 wt pct S. Here we present a model for the interaction of nonmetals with other species in metallic systems. The model assumes that the nonmetal either repels or attracts tracers (E) in the metallic liquid, causing those tracers to either segregate strongly into the solid metal or to have enhanced solubility in the liquid. Examples of both types of behavior are given. The model predicts that the activity coefficient of the tracer (γE) should correlate linearly with (1 - αnXN @#@), where XN is the mole fraction of the nonmetal in the metallic liquid,n is a stoichiometry factor related to the speciation of N in the liquid, and a is a constant. Indeed, good linear correlations of n(k) vs n (1 -αnXN @#@) are found for all elements where there is a measurable effect. Thus, if the composition of the metallic liquid is known, a segregation coefficient of a trace constituent may be pre-dicted— even if the temperature, exact Fe/Ni ratio, and information about the activity coef-ficient in the solid phase are unknown. The nonmetal interaction model presented here can be related to more traditional methods of modeling activity coefficients(i.e., power law expan-sions) and can be shown to be a special case of this type of parameterization. Comparison of model predictions of first-order (sulfur-E) interaction coefficients (e) to measured values yields acceptable agreement for some elements, such as P and Ge, and all elements except Ni agree to within a factor of 3. The predictive model described above, based on equilibrium experi-ments, may be used to evaluate the segregation coefficients extracted from the dynamic (“plane front solidification”) experiments of Sellamuthu and Goldstein.[10,11] Contrary to claims, reliable segregation coefficients are not extractable from dynamic experiments.

A facile and rapid method of covalently modifying the surface of graphite powders with aminophenyl groups is described. This chemical modification strategy allows the production of bulk (gram) quantities of amino-modified carbon powder. 4-Nitrophenyl groups are covalently attached to graphite powder via the chemical reduction of the corresponding 4-nitrobenzenediazonium tetrafluoroborate salt using aqueous hypophosphorous acid. The 4-nitrophenyl groups on the carbon surface are then reduced to the corresponding 4-aminophenyl groups using alkaline iron(ii) ammonium sulfate solutions. Electrochemical and X-ray photoelectron spectroscopic characterisation is carried out at each stage of the synthesis. This journal is © The Royal Society of Chemistry.

Modifications of the noun peptide are explored and clarified; a few are condemned. Copyright © 2006 European Peptide Society and John Wiley & Sons, Ltd.

Conformational investigations have been undertaken on oligomers (dimers, tetramers, hexamers) of five closely related oxetane-based dipeptide isosteres. All the oligomers were subjected to a range of studies by NMR, FT-IR and CD spectroscopy. The oligomers derived from methyl 2,4-anhydro-5-azido-3-O-tert-butyldimethylsilyl-5-deoxy-L-rhamnonate ‘monomer’ all exhibited evidence of ordered conformations in chloroform and 2,2,2-trifluoroethanol (TFE) solution. 5-Acetamido and N -methylamide derivatives of the L-rhamnonate ‘monomer’, along with a ‘dimer’ lacking silyl protection at C-3, were synthesized to ascertain the \ud role of intramolecular interactions. This led to the conclusion that, for the L-rhamnonate oligomers, steric interactions govern the conformational preference observed. The equivalent silyl-protected D-lyxonate oligomers gave ordered CD spectra in TFE solution, but NMR and FT-IR spectroscopy in chloroform solution suggested an irregular, non-hydrogen bonded system. The remaining silyl-protected 6-deoxy-L-altronate, 6-deoxy-D-gulonate and D-fuconate oligomers appear to be characterized by their lack of ordered conformation in TFE and chloroform solution.

Routes to oligomers (dimers, tetramers, hexamers) of five oxetane-based dipeptide isosteres have been established. Methyl 2,4-anhydro-5-azido-5-deoxy-L-rhamnonate ‘monomer’ led, by coupling the corresponding carboxylic acid and amine, to a ‘dimer’. Reverse-aldol ring-opening occurred on attempted saponification of the dimer, so all further oligomerization was performed using TBDMS C-3 hydroxyl protection. The silyl protected L-rhamnonate monomer led in turn to the dimer (via the monomer acid and amine), the tetramer (via the dimer acid and amine) and finally the hexamer (via the tetramer acid and dimer amine). In each case the acids were obtained through saponification of the respective methyl esters and the amines were obtained by hydrogenation of the azides; coupling was TBTU-mediated. Essentially the same strategy was employed on equivalent D-lyxonate, 6-deoxy-L-altronate, 6-deoxy-D-gulonate and D-fuconate dipeptide isosteres to give the respective dimers, tetramers and hexamers. Copyright © 2004 European Peptide Society and John Wiley & Sons, Ltd.

The title compound, C7H11N3O4, was prepared from l-rhamnose as a conformationally restricted dipeptide isostere containing an oxetane ring. Its crystal structure was determined to confirm the synthetic product.