Distribution of copper, cobalt and nickel in ores and host-rocks, Ingladhal, Karnataka, India

Stratiform quartz-sulphide lodes in Ingladhal occur in a typical Precambrian green-stone-belt environment comprising metabasalts, tuff, chert and cherty iron-sulphide formation. Unusually high cobalt contents of metavolcanics and of sulphide minerals in orebodies suggest a consanguinity between ores and rocks. 90% of total nickel, 70% of total cobalt but only 30% of total copper in rocks occur in silicate phases and thus indicate an early separation of copper from cobalt and nickel. Unusually high non-sulphide copper in barren bedded cherts implies availability of Cu-rich solution prior to their lithification. Pyrite in sediments, in volcanics, and in orebodies is characterized by a distinctive pattern of Co-Ni distribution in each case. Partitioning of Co and Ni between coexisting sulphide pairs is complex, but gross equilibrium is indicated. Very high trace metal content of orebody pyrite sharply contrasts with very low such values in pyrite from adjacent sediments and points to a higher temperature of formation of orebodies

Geothermometry based on fractionation of Mn and Cd between coexisting sphalerite and galena from some carbonate-hosted sulfide deposits in India

Geothermometry based on the fractionation of Mn and Cd between coexisting sphalerite and galena from concordantly banded, strata-bound ores and younger vein ores of Rajpura-Dariba, Zawar, and Bandalamottu has been attempted. Different fractionation trends for the banded and vein ores in the same deposit at Rajpura-Dariba indicate different thermal regimes of final equilibration for the two varieties of ores. In contrast, a single trend incorporating both types of ores is suggestive of isothermal conditions of final equilibration for the banded and vein ores at Zawar. Unrealistically high temperatures obtained for the vein ores of Bandalamottu suggest equilibrium in the sphalerite-galena aggregates of this deposit was not attained. Thermometric data from Mn and Cd fractionation are compared with other independent geothermometric determinations obtained from fluid inclusion homogenization studies and based on phase equilibria. It has been found that, in general, the Cd-fractionation temperature (TCd) is a more reliable geothermometer than the Mn-fractionation temperature (TMn). This presumably may be due to the susceptibility of aqueous Mn species to subtle changes in fo2 in the ore fluid and consequent heterogeneity in Mn concentration in sphalerite, thus affecting the distribution coefficient. The investigation also suggests that TCd becomes increasingly more dependable when the ores are metamorphosed and reequilibrated at higher grades of metamorphism

Role of methylation on the thermochemistry of alkali metal cation complexes of amino acids: N-methyl proline

pre-printQuantitative thermodynamic information is obtained from the study of the gasphase interactions of the alkali metal cation complexes of N-methyl proline (NMP) with Xe using a guided ion beam tandem mass spectrometer (GIBMS). Absolute bond dissociation energies (BDEs) of M+ = Li+, Na+, K+, and Rb+ to NMP are determined experimentally from threshold collision-induced dissociation (TCID) measurements of the M+(NMP) complexes. Analysis of their kinetic energy cross sections provide the 0 K bond enthalpies after accounting for unimolecular decay rates, internal energy of reactant ions, and multiple ion-molecule collisions. Quantum chemical calculations of the M+(NMP) BDEs are found to be in good agreement with the experimental values, establishing that the zwitterionic form is the lowest energy structure for all the metal ion complexes. Compared to M+(Pro) BDEs, the metal binding in these zwitterions is slightly enhanced by the CH3 group on the ring nitrogen, presumably a result of an inductive effect and its higher polarizability. More profound consequences of the methyl group emerge in the charge-solvated conformers calculated for M+(NMP) where it directs multiple conformations of the pyrrolidine ring. This is unlike the ring puckering phenomenon seen in M+(Pro) complexes, where fewer conformations are found, apparently because inversion at the nitrogen center is more facile

Theoretical investigation and reinterpretation of the decomposition of lithiated proline and N-Methyl Proline

pre-printLithium cation complexes of proline (Pro) and N-methyl proline (NMP) have been collisionally activated with xenon in a guided ion beam tandem mass spectrometer (GIBMS). In addition to the loss of the intact ligand, Pro and NMP, we observed two prominent fragmentation pathways involving the loss of (CO + LiOH) and (CO + H2O). Quantum chemical calculations at the B3LYP/6-311+G(d,p) level are used to explore the reaction mechanisms of these Li+(Pro) and Li+(NMP) fragmentations. Complete potential energy surfaces including all intermediates and transition states are elucidated for the two fragmentation processes in both systems. Theoretical molecular parameters for the rate-limiting transition states are then used to analyze the experimental data. The experimental threshold energies are compared with single point energies calculated at six different levels of theory. Reasonable agreement between experiment and some levels of theory indicate that loss of the intact amino acid competes with the loss of CO over a tight transition state in both Li+(Pro) and Li+(NMP) systems. Once CO is lost, efficient loss of H2O can occur at lower or comparable energy and is followed at somewhat higher energies by loss of LiOH, both proceeding by loose transition states. Overall, we find that MP2(full)/6-311+G(2d,2p) gives the best agreement with the experimental threshold energies and the qualitative characteristics of the competing reactions. This study refines the bond energy of Li+ to Pro by considering competition with CO loss and lowers the value previously published by 24 12 kJ/mol, with methylation of proline increasing the bond energy to Li+ by 9 15 kJ/mol

Antimicrobial host defence peptides: functions and clinical potential

Cationic host defence peptides (CHDP), also known as antimicrobial peptides, are naturally occurring peptides that can combat infections through their direct microbicidal properties and/or by influencing the host's immune responses. The unique ability of CHDP to control infections as well as resolve harmful inflammation has generated interest in harnessing the properties of these peptides to develop new therapies for infectious diseases, chronic inflammatory disorders and wound healing. Various strategies have been used to design synthetic optimized peptides, with negligible toxicity. Here, we focus on the progress made in understanding the scope of functions of CHDP and the emerging potential clinical applications of CHDP-based therapies

Complexity of Strong Implementability

We consider the question of implementability of a social choice function in a classical setting where the preferences of finitely many selfish individuals with private information have to be aggregated towards a social choice. This is one of the central questions in mechanism design. If the concept of weak implementation is considered, the Revelation Principle states that one can restrict attention to truthful implementations and direct revelation mechanisms, which implies that implementability of a social choice function is easy to check. For the concept of strong implementation, however, the Revelation Principle becomes invalid, and the complexity of deciding whether a given social choice function is strongly implementable has been open so far. In this paper, we show by using methods from polyhedral theory that strong implementability of a social choice function can be decided in polynomial space and that each of the payments needed for strong implementation can always be chosen to be of polynomial encoding length. Moreover, we show that strong implementability of a social choice function involving only a single selfish individual can be decided in polynomial time via linear programming

Low-temperature behaviour of ammonium ion in buddingtonite [N(D/H) 4 AlSi 3 O 8 ] from neutron powder diffraction

The structural response of buddingtonite [N(D/H) 4 AlSi 3 O 8 ] on cooling has been studied by neutron diffraction. Data have been collected from 280 K down to 11 K, and the crystal structure refined using the Rietveld method. Rigid-body constraints were applied to the ammonium ion to explore the structural properties of ammonium in the M-site cavities at low-temperature. Low-temperature saturation is observed for almost all the lattice parameters. From the present in situ low-temperature neutron diffraction studies, there is no strong evidence of orientational order–disorder of the ammonium ions in buddingtonite.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46909/1/269_2004_Article_425.pd

Chromatographic and spectral studies of jetsam and archived ambergris

<p>We describe determination of the dichloromethane-soluble components of 12 samples of the natural product, ambergris, using capillary gas chromatography–mass spectrometry (GC–MS). Ambergris is produced <i>in vivo</i> in about 1% of Sperm whales and is used in perfumery and for odour fixation. Whilst descriptions of ambergris chemistry appeared until about 40 years ago, few accounts of analyses of whole extracts of multiple samples of ambergris by GC–MS have been published before. As expected, our analyses revealed that the major component (up to 97% of the dichloromethane-soluble material) was ambrein, with co-occurring, variable proportions of steroids. Moreover, we report apparently for the first time, mass spectra and retention indices of derivatised ambrein. These data should now allow reliable, rapid confirmation of even small amounts of jetsam, archived museum and customs samples of ambergris and an assessment of ambergris ‘quality’.</p