The structure, topology and orientation of membrane-bound antibiotic alamethicin were studied using solid state nuclear magnetic resonance (NMR) spectroscopy. (13)C chemical shift interaction was observed in [1-(13)C]-labeled alamethicin. The isotropic chemical shift values indicated that alamethicin forms a helical structure in the entire region. The chemical shift anisotropy of the carbonyl carbon of isotopically labeled alamethicin was also analyzed with the assumption that alamethicin molecules rotate rapidly about the bilayer normal of the phospholipid bilayers. It is considered that the adjacent peptide planes form an angle of 100° or 120° when it forms α-helix or 310-helix, respectively. These properties lead to an oscillation of the chemical shift anisotropy with respect to the phase angle of the peptide plane. Anisotropic data were acquired for the 4 and 7 sites of the N- and C-termini, respectively. The results indicated that the helical axes for the N- and C-termini were tilted 17° and 32° to the bilayer normal, respectively. The chemical shift oscillation curves indicate that the N- and C-termini form the α-helix and 310-helix, respectively. The C-terminal 310-helix of alamethicin in the bilayer was experimentally observed and the unique bending structure of alamethicin was further confirmed by measuring the internuclear distances of [1-(13)C] and [(15)N] doubly-labeled alamethicin. Molecular dynamics simulation of alamethicin embedded into dimyristoyl phophatidylcholine (DMPC) bilayers indicates that the helical axes for α-helical N- and 310-helical C-termini are tilted 12° and 32° to the bilayer normal, respectively, which is in good agreement with the solid state NMR results.
Bombolitin II (BLT2) is one of the hemolytic heptadecapeptides originally isolated from the venom of a bumblebee. Structure and orientation of BLT2 bound to 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) membranes were determined by solid-state (31)P and (13)C NMR spectroscopy. (31)P NMR spectra showed that BLT2-DPPC membranes were disrupted into small particles below the gel-to-liquid crystalline phase transition temperature (T(c)) and fused to form a magnetically oriented vesicle system where the membrane surface is parallel to the magnetic fields above the T(c). (13)C NMR spectra of site-specifically (13)C-labeled BLT2 at the carbonyl carbons were observed and the chemical shift anisotropies were analyzed to determine the dynamic structure of BLT2 bound to the magnetically oriented vesicle system. It was revealed that the membrane-bound BLT2 adopted an α-helical structure, rotating around the membrane normal with the tilt angle of the helical axis at 33°. Interatomic distances obtained from rotational-echo double-resonance experiments further showed that BLT2 adopted a straight α-helical structure. Molecular dynamics simulation performed in the BLT2-DPPC membrane system showed that the BLT2 formed a straight α-helix and that the C-terminus was inserted into the membrane. The α-helical axis is tilted 30° to the membrane normal, which is almost the same as the value obtained from solid-state NMR. These results suggest that the membrane disruption induced by BLT2 is attributed to insertion of BLT2 into the lipid bilayers.
Melittin is a venom peptide that disrupts lipid bilayers at temperatures below the liquid-crystalline to gel phase transition temperature (T). Notably, the ability of melittin to disrupt acidic dimyristoylphosphatidylglycerol (DMPG) bilayers was weaker than its ability to disrupt neutral dimyristoylphosphatidylcholine bilayers. The structure and orientation of melittin bound to DMPG bilayers were revealed by analyzing the C chemical shift anisotropy of [1-C]-labeled melittin obtained from solid-state C NMR spectra.C chemical shift anisotropy showed oscillatory shifts with the index number of residues. Analysis of the chemical shift oscillation properties indicated that melittin bound to a DMPG membrane adopts a bent α-helical structure with tilt angles for the N- and C-terminal helices of -32 and +30°, respectively. The transmembrane melittin in DMPG bilayers indicates that the peptide protrudes toward the C-terminal direction from the core region of the lipid bilayer to show a pseudotransmembrane bent α-helix. Molecular dynamics simulation was performed to characterize the structure and interaction of melittin with lipid molecules in DMPG bilayers. The simulation results indicate that basic amino acid residues in melittin interact strongly with lipid head groups to generate a pseudo-transmembrane alignment. The N-terminus is located within the lipid core region and disturbs the lower surface of the lipid bilayer.
A facile method for the direct cross-annulation of unfunctionalized tetracene is reported. The one-pot oxidative crossdehydrogenative coupling (CDC) between tetracene and aromatic compounds, such as benzene or 2-methylthiophene, furnished annulated products with an extended π-network. Moreover, relative to the benzoannulated tetracenes, thieno-annulated tetracenes exhibited notably improved photooxidative stability. This behavior stands in sharp contrast with that of tetracene and its derivatives, such as rubrene, which readily engage in photoinduced oxidation reactions.
Electrochemical double-layer capacitors (EDLCs) are devices that store enormous amounts of charge electrostatically when a potential is applied between electrodes of very high surface area (typically made of porous carbon) and an electrolyte. Wider commercialization of this technology has been held back by the lack of ultralow-cost electrode materials. We demonstrate that used coffee grounds can be processed to form low-cost electrodes. The surface and electrochemical characteristics of microporous activated carbons from used coffee grounds (CGCs) were measured. First, optimal times and temperatures for carbonization and activation were identified on the basis of Brunauer-Emmett-Teller (BET) surface area, pore volume, and pore size distribution. Second, CGCs were used as polarized electrodes in EDLCs, whose capacitances were evaluated using cyclic voltammetry. The results show that carbonization for 1 h at 600 • C with a heating rate of 300 • C/h, followed by CO 2 activation for 2 h at 1000 • C, affords the highest BET surface area (1867 m 2 /g) compared to other works. The produced CGCs have many micropores of less than 2 nm across, which contribute to the formation of an electric double layer. Capacitors made using these CGCs show the highest capacitance (103 F/g) in 0.8 M (C 2 H 5 ) 4 NBF 4 /PC as an organic electrolyte, which is much higher than the ∼80 F/g typically used in organic-electrolyte-based commercial EDLCs, suggesting that coffee grounds are a useful electrode material.
Antimicrobial peptides (AMPs) are part of the immune response of all classes of life and have gained attention as promising alternative treatments for infectious bacteria resistant to conventional antibiotics. AMPs kill bacteria through two known mechanisms of action. Some AMPs, such as parasin and magainin II, kill bacteria by inducing membrane permeabilization. Other AMPs, such as buforin II (BF2) and DesHDAP1, readily translocate across the membrane and interact with intracellular components including nucleic acids. In recent years, there has been increased interest in developing hybrid AMPs that combine two distinct AMPs into a single peptide. These hybrid AMPs have been shown to be more potent than their individual AMP components. To date, few studied hybrid have combined AMPs that follow different mechanisms. Here, we focus on using a variety of cellular assays and confocal imaging to characterize the activity and mechanisms of action of hybrid AMPs that combine one permeabilizing AMP (parasin or magainin II) with one translocating AMP (BF2 or DesHDAP1) in different orientations and with different linkers. We show that these hybrid AMPs are generally more potent than their individual AMP components and that the permeabilizing peptide (parasin or magainin II) dominates the mechanism of action when combined with the translocating peptide (BF2 or DesHDAP1). These observations of 16 hybrid peptides have elucidated trends that will promote the rational design of AMPs with enhanced activity.
A domino-type multiple C–H
functionalization of tetracene
with molecular benzene is reported. Under the typical conditions of
the Scholl reaction, a domino reaction occurs between tetracene and
six molecules of benzene in one pot to furnish an aromatic compound
with a curved π-system. This reaction sequence involves oxidative
cross-dehydrogenative coupling/annulation and Friedel–Crafts-type
reactions. Eight C–C bonds are formed via this intermolecular
domino reaction without mediation by a metal or the assistance of
a specific substituent.
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