Boreal forests emit a large amount of monoterpenes into the atmosphere. Traditionally these emissions are assumed to originate as evaporation from large storage pools. Thus, their diurnal cycle would depend mostly on temperature. However, there is indication that a significant part of the monoterpene emission would originate directly from de novo synthesis. By applying 13 CO2 fumigation and analyzing the isotope fractions with proton transfer reaction mass spectrometry (PTR-MS) and classical GC-MS, we determined the fractions of monoterpene emissions originating from de novo biosynthesis in Pinus sylvestris (58%), Picea abies (33.5%), Larix decidua (9.8%) and Betula pendula (100%). Application of the observed split between de novo and pool emissions from P. sylvestris in a hybrid emission algorithm resulted in a better description of ecosystem scale monoterpene emissions from a boreal Scots pine forest stand.

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To understand how membrane-active peptides (MAPs) function in vivo, it is essential to obtain structural information about them in their membrane-bound state. Most biophysical approaches rely on the use of bilayers prepared from synthetic phospholipids, i.e. artificial model membranes. A particularly successful structural method is solid-state NMR, which makes use of macroscopically oriented lipid bilayers to study selectively isotope-labelled peptides. Native biomembranes, however, have a far more complex lipid composition and a significant non-lipidic content (protein and carbohydrate). Model membranes, therefore, are not really adequate to address questions concerning for example the selectivity of these membranolytic peptides against prokaryotic vs eukaryotic cells, their varying activities against different bacterial strains, or other related biological issues.Here, we discuss a solid-state (19)F-NMR approach that has been developed for structural studies of MAPs in lipid bilayers, and how this can be translated to measurements in native biomembranes. We review the essentials of the methodology and discuss key objectives in the practice of (19)F-labelling of peptides. Furthermore, the preparation of macroscopically oriented biomembranes on solid supports is discussed in the context of other membrane models. Two native biomembrane systems are presented as examples: human erythrocyte ghosts as representatives of eukaryotic cell membranes, and protoplasts from Micrococcus luteus as membranes from Gram-positive bacteria. Based on our latest experimental experience with the antimicrobial peptide gramicidin S, the benefits and some implicit drawbacks of using such supported native membranes in solid-state (19)F-NMR analysis are discussed.

(19)F NMR is a unique tool to examine the structure of fluorine-labeled peptides in their native cellular environment, due to an exquisite sensitivity and lack of natural abundance background. For solid-state NMR analysis, we isolated native membranes from erythrocyte ghosts and bacterial protoplasts and prepared them as macroscopically oriented samples. They showed a high purity and quality of alignment according to (31)P NMR, and the membrane-bound antimicrobial peptide PGLa could be detected by (19)F NMR. The characteristic fingerprint splitting of its (19)F reporter group indicated that the peptide helix binds to the native membranes in a surface alignment, albeit with a higher affinity in the prokaryotic than the eukaryotic system.

The synthesis and characterization of polyhedral boron hydrides [1] and boron subhalides, [2] originally regarded as curios, at a second glance have proved to be a lucky chance for progress in chemistry, as on this basis new concepts of chemical bonding were developed, e. g. the Wade-Mingos rules. [3][4][5][6][7] Two milestones in aluminum-organic chemistry with a polyhedral {Al n }-lattice are [Al 12 R 12 ] 2À (1 2À ) [8] and [Al 4 Cp* 4 ] (2; Cp* = C 5 Me 5 ) [9][10][11] (Figure 1). The polyhedral closo-cluster 1 2À is an exception compared to the common low-valent aluminum and gallium clusters which tend to be so-called metalloid clusters.[12] These are clusters mainly characterized by the fact that the topology of the "naked", that is, non-ligand bearing cluster atoms in the cluster core, in many cases reflects the topology of the atoms found in metals and elements, respectively. [13][14][15] Prior to presenting the results of quantum chemical calculations for some [M 12 X 12 ] and [M 13 X 12 ] (M = B, Al, Ga; X = halide) model compounds, we describe our most recent experimental findings which prompted us to start these investigations: [16] Mass spectrometric examinations of the structurally known metalloid-cluster anion [Ga 13 (GaR À (3 À ). [16][17][18] This anion formed during the stepwise reaction of chlorine in the gas phase and as a result of the cleavage of six GaCl moieties [Eq (1)]. The isomer 3 À , when generated from density functional theory (DFT) calculations is, with its octahedral {Ga 6 } core, 30 kJ mol À1 more stable than the icosahedral molecule with a {Ga 12 } core and 12 terminally bound ligands that would be expected according to Wades rules. Based on these surprising results [16, 19] we have performed DFT calculations to elaborate some fundamental differences between typical Wade clusters in boron chemistry and metalloid clusters in aluminum and gallium chemistry.We have examined neutral and dianionic compounds of the structure [M 12 Cl 12 ] 0,2À (M = B, Al, Ga) to determine which of the two structural patterns (icosahedral M 12 -units or clusters with an M 6 -core) is energetically favored for the particular element. For each species we calculated the isomer with an icosahedral structure and terminally bound ligands (ico) and the isomer with an octahedral core of "naked" metal atoms (hence the term "metalloid" (m)). For the metalloid clusters (m), a protecting shell results consisting of doubly oxidized MX 2 units; the bridging (M-X-M) unit contributes to the stabilization of the cluster. The energetic relations between all isomers are shown in Figure 2. Selected structural parameters of [B 12 Cl 12 ] (4), [B 12 The energy diagram (Figure 2) depicts the differences between boron-, aluminum-, and gallium clusters: The icosahedral species 4 (ico) and 4 2À (ico) are energetically favored by 600 kJ mol À1 and 918 kJ mol À1 , respectively, over the metalloid isomers 4 (m) and 4 2À (m). On the other hand, the neutral metalloid Al and Ga clusters 5 (m) and 6 (m) are,