Protein/lipid interactions in phospholipid monolayers containing the bacterial antenna protein B800-850

Studies on monomolecular layers of phospholipids containing the antenna protein B800-850 (LHCP) and in some cases additionally the reaction center of the photosynthetic bacterium Rhodopseudomonas sphaeroides are reported. Information on monolayer preparation as well as on protein /lipid and protein/protein interaction is obtained by means of fluorescence spectroscopy and microscopy at the air/water interface in combination with film balance experiments. It is shown that a homogeneous distribution of functional proteins can be achieved. This can be transformed into a regular pattern-like distribution by inducing a phospholipid phase transition. Although the LHCP preferentially partitions into the fluid lipid phase, it decreases the lateral pressure necessary to crystallize the lipid. This is probably due to an increase in order of the fluid phase. A pressure-induced conformation change of the LHCP is detected via a drastic change in fluorescence yield. A highly efficient energy transfer from LHCP to the reaction center is observed. This proves the quantitative reconstitution of both types of proteins and indicates protein aggregation also in the monolayer

Advances by the Marie Curie project TANGO in thermoacoustics

This paper gives an overview of the research performed by the project TANGO – an Initial Training Network (ITN) with an international consortium of seven academic and five industrial partners. TANGO is the acronym for ‘Thermoacoustic and Aeroacoustic Nonlinearities in Green combustors with Orifice structures’). The researchers in TANGO studied many of the intricate physical processes that are involved in thermoacoustic instabilities. The paper is structured in such a way that each section describes a topic investigated by one or more researchers. The topics include: - transition from combustion noise to thermoacoustic instability - development of an early-warning system by detecting the precursor of an instability - analytical flame models based on time-lags - Green's function approach for stability predictions from nonlinear flame models - intrinsic thermoacoustic modes - transport phenomena in swirl waves - model of the flame front as a moving discontinuity - development of efficient numerical codes for instability predictions - heat exchanger tubes inside a combustion chamber A substantial amount of valuable new insight was gained during this four-year project

Nanostructure and mechanics of mummified type I collagen from the 5300-year-old Tyrolean Iceman

Skin protects the body from pathogens and degradation. Mummified skin in particular is extremely resistant to decomposition. External influences or the action of micro-organisms, however, can degrade the connective tissue and lay the subjacent tissue open. To determine the degree of tissue preservation in mummified human skin and, in particular, the reason for its durability, we investigated the structural integrity of its main protein, type I collagen. We extracted samples from the Neolithic glacier mummy known as ‘the Iceman’. Atomic force microscopy (AFM) revealed collagen fibrils that had characteristic banding patterns of 69 ± 5 nm periodicity. Both the microstructure and the ultrastructure of dermal collagen bundles and fibrils were largely unaltered and extremely well preserved by the natural conservation process. Raman spectra of the ancient collagen indicated that there were no significant modifications in the molecular structure. However, AFM nanoindentation measurements showed slight changes in the mechanical behaviour of the fibrils. Young's modulus of single mummified fibrils was 4.1 ± 1.1 GPa, whereas the elasticity of recent collagen averages 3.2 ± 1.0 GPa. The excellent preservation of the collagen indicates that dehydration owing to freeze-drying of the collagen is the main process in mummification and that the influence of the degradation processes can be addressed, even after 5300 years

Initial coupling and reaction progression of directly deposited biradical graphene nanoribbon monomers on iodine-passivated versus pristine Ag(111)

The development of widely applicable methods for the synthesis of C-C-bonded nanostructures on inert and insulating surfaces is a challenging yet rewarding milestone in the field of on-surface synthesis. This would enable studies of nearly unperturbed covalent nanostructures with unique electronic properties as graphene nanoribbons (GNR) and π-conjugated 2D polymers. The prevalent Ullmann-type couplings are almost exclusively carried out on metal surfaces to lower the temperature required for initial dehalogenation well below the desorption threshold. To overcome the necessity for the activation of monomers on the target surface, we employ a recently developed Radical Deposition Source (RaDeS) for the direct deposition of radicals onto inert surfaces for subsequent coupling by addition reactions. The radicals are generated en route by indirect deposition of halogenated precursors through a heated reactive tube, where the dehalogenation reaction proceeds. Here, we use the ditopic 6,11-diiodo-1,2,3,4-tetraphenyltriphenylene (DITTP) precursor that afforded chevron-like GNR on Au(111) via the usual two-staged reaction comprised of monomer-coupling into covalent polymers and subsequent formation of an extended GNR by intramolecular cyclodehydrogenation (CDH). As a model system for inert surfaces, we use Ag(111) passivated with a closed monolayer of chemisorbed iodine that behaves in an inert manner with respect to dehalogenation reactions and facilitates the progressive coupling of radicals into extended covalent structures. We deposit the DITTP-derived biradicals onto both iodine-passivated and pristine Ag(111) surfaces. While on the passivated surface, we directly observe the formation of covalent polymers, on pristine Ag(111) organometallic intermediates emerge instead. This has decisive consequences for the further progression of the reaction: heating the organometallic chain directly on Ag(111) results in complete desorption, whereas the covalent polymer on iodine-passivated Ag(111) can be transformed into the GNR. Yet, the respective CDH proceeds directly on Ag(111) after thermal desorption of the iodine passivation. Accordingly, future work is aimed at the further development of approaches for the complete synthesis of GNR on inert surfaces

Competitive metal‐coordination of hexaaminotriphenylene on Cu(111) by intrinsic copper versus extrinsic nickel adatoms

The interplay between self‐assembly and surface chemistry of 2,3,6,7,10,11‐hexaminotriphenylene (HATP) on Cu(111) was complementarily studied by high‐resolution Scanning‐Tunneling‐Microscopy (STM) and X‐ray Photoelectron Spectroscopy (XPS) under ultra‐high vacuum conditions. To shed light on competitive metal‐coordination, comparative experiments were carried out on pristine and nickel‐covered Cu(111). Directly after room temperature deposition of HATP onto pristine Cu(111) self‐assembled aggregates were observed by STM, while XPS indicated non‐deprotonated amino groups. Annealing up to 200 °C activated the progressive single deprotonation of all amino groups as indicated by chemical shifts of both N 1s and C 1s core levels in the XP spectra. This enabled the formation of topologically versatile π‐d conjugated coordination networks with intrinsic copper adatoms. The basic motif of these networks was a metal‐organic trimer, where three HATP molecules were coordinated by Cu3 clusters, as corroborated by accompanying Density Functional Theory (DFT) simulations. Additional deposition of more reactive nickel atoms resulted in both chemical and structural changes with deprotonation and formation of bis(diimino)‐Ni bonded networks already at room temperature. Even though fused hexagonal pores were observed, extended honeycomb networks remained elusive, as tentatively explained by a restricted reversibility of these metal‐organic bonds

Self-assembly of melem on Ag(111)—emergence of porous structures based on amino-heptazine hydrogen bonds

Self-assembly of melem on Ag(111) as studied by Scanning-Tunneling-Microscopy (STM) in ultra-high vacuum revealed a great structural variety. In total, five porous and two densely packed monolayer polymorphs were observed. All structures are stabilized by intermolecular hydrogen bonds, where melem–melem arrangements are based on very few basic motifs. Six out of seven polymorphs can be described by a unified concept

LRRML: a conformational database and an XML description of leucine-rich repeats (LRRs)

Background: Leucine-rich repeats (LRRs) are present in more than 6000 proteins. They are found in organisms ranging from viruses to eukaryotes and play an important role in protein-ligand interactions. To date, more than one hundred crystal structures of LRR containing proteins have been determined. This knowledge has increased our ability to use the crystal structures as templates to model LRR proteins with unknown structures. Since the individual three-dimensional LRR structures are not directly available from the established databases and since there are only a few detailed annotations for them, a conformational LRR database useful for homology modeling of LRR proteins is desirable. Description: We developed LRRML, a conformational database and an extensible markup language (XML) description of LRRs. The release 0.2 contains 1261 individual LRR structures, which were identified from 112 PDB structures and annotated manually. An XML structure was defined to exchange and store the LRRs. LRRML provides a source for homology modeling and structural analysis of LRR proteins. In order to demonstrate the capabilities of the database we modeled the mouse Toll-like receptor 3 (TLR3) by multiple templates homology modeling and compared the result with the crystal structure. Conclusion: LRRML is an information source for investigators involved in both theoretical and applied research on LRR proteins. It is available at http://zeus.krist.geo.uni-muenchen.de/similar to lrrml