High spatial resolution analysis of ferromanganese concretions by LA-ICP-MS†

A procedure was developed for the determination of element distributions in cross-sections of ferromanganese concretions using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The effects of carrier flow rates, rf forward power, ablation energy, ablation spot size, repetition rate and number of shots per point on analyte intensity were studied. It is shown that different carrier gas flow rates are required in order to obtain maximum sensitivities for different groups of elements, thus complicating the optimisation of ICP parameters. On the contrary, LA parameters have very similar effects on almost all elements studied, thus providing a common optimum parameter set for the entire mass range. However, for selected LA parameters, the use of compromise conditions was necessary in order to compensate for relatively slow data acquisition by ICP-MS and maintain high spatial resolution without sacrificing the multielemental capabilities of the technique. Possible variations in ablation efficiency were corrected for mathematically using the sum of Fe and Mn intensities. Quantification by external calibration against matrix-matched standards was successfully used for more than 50 elements. These standards, in the form of pressed pellets (no binder), were prepared in-house using ferromanganese concentrates from a deep-sea nodule reference material as well as from shallow-marine concretions varying in size and having different proportions of three major phases: aluminosilicates, Fe- and Mn-oxyhydroxides. Element concentrations in each standard were determined by means of conventional solution nebulisation ICP-MS following acid digestion. Examples of selected inter-element correlations in distribution patterns along the cross-section of a concretion are given

Electron transfer to the active site of the bacterial nitric oxide reductase is controlled by ligand binding to heme b3

The active site of the bacterial nitric oxide reductase from Paracoccus denitrificans contains a dinuclear centre comprising heme b3 and non heme iron (FeB). These metal centres are shown to be at isopotential with midpoint reduction potentials of Em ˜ + 80 mV. The midpoint reduction potentials of the other two metal centres in the enzyme, heme c and heme b, are greater than the dinuclear centre suggesting that they act as an electron receiving/storage module. Reduction of the low-spin heme b causes structural changes at the dinuclear centre which allow access to substrate molecules. In the presence of the substrate analogue, CO, the midpoint reduction potential of heme b3 is raised to a region similar to that of heme c and heme b. This leads us to suggest that reduction of the electron transfer hemes leads to an opening of the active site which allows substrate to bind and in turn raises the reduction potential of the active site such that electrons are only delivered to the active site following substrate binding

PENGEMBANGAN MODEL PEMBELAJARAN PROBLEM BASED INSTRUCTION (PBI) PADA MATERI PENCEMARAN LINGKUNGAN UNTUK MENINGKATKAN PEMAHAMAN KONSEP SERTA SIKAP PEDULI DAN TINDAKAN TERHADAP LINGKUNGAN DI MADRASAH ALIYAH NEGERI DARUSSALAM KABUPATEN ACEH BESAR

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