Development of non-lethal sampling of carbon and nitrogen stable isotope ratios in salmonids: effects of lipid and inorganic components of fins

The preferred tissue for analyses of fish stable isotope ratios for most researchers is muscle, the sampling of which typically requires the specimen to be sacrificed. The use of non-destructive methods in fish isotopic research has been increasing recently, but as yet is not a standard procedure. Previous studies have reported varying levels of success regarding the utility of non-lethally obtained stable isotope materials, e.g. fins, but none have accounted for the potential compounding effects of inorganic components of fin rays or lipids. Comparisons of carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotope ratios of muscle with adipose and caudal fin of two salmonids, Atlantic salmon (Salmo salar L.) and brown trout (Salmo trutta L.), revealed that caudal fin can be used as a non-destructive surrogate for muscle in stable isotope analysis, but that adipose fin, where available, is a better proxy. The use of a published model to inexpensively counteract the confounding effect of lipids, which are depleted in ¹³C, greatly improved the relationship between fish muscle and fins. However, efforts to account for the inorganic components of fin rays were counterproductive and required twice the biomass of fins clipped from each fish. As this experiment was conducted on wild fish, controlled laboratory studies are required to confirm these field observations.     

High-sensitivity vibrational imaging with frequency modulation coherent anti-Stokes Raman scattering (FM CARS) microscopy

We demonstrate a new approach to coherent anti-Stokes Raman scattering (CARS) microscopy that significantly increases the detection sensitivity. CARS signals are generated by collinearly overlapped, tightly focused, and raster scanned pump and Stokes laser beams, whose difference frequency is rapidly modulated. The resulting amplitude modulation of the CARS signal is detected through a lock-in amplifier. This scheme efficiently suppresses the nonresonant background and allows for the detection of far fewer vibrational oscillators than possible through existing CARS microscopy methods.     

Solid state solvation in amorphous organic thin films

The photoluminescence (PL) of the red laser dye DCM2, doped into blended thin films of polystyrene (PS) and the polar small molecule camphoric anhydride (CA), redshifts as the CA concentration increases. The DCM2 PL peaks at 2.20 eV (lambda=563 nm) for pure PS films and shifts to 2.05 eV (lambda=605 nm) for films with 24.5% CA (by mass). The capacitively measured electronic permittivity also increases from epsilon=2.4 to epsilon=5.6 with CA concentration. These results are consistent with the theory of solvatochromism developed for organic molecules in liquid solvents. To our knowledge, this work is the first application of a quantitative theory of solvation to organic molecules in amorphous thin films with continuously controllable permittivity, and demonstrates that "solid state solvation" can be used to predictably tune exciton energies in organic thin film structures.     

Synthesis, electrochemistry and metal binding properties of monosubstituted ferrocenoyl peptides with thioether-containing sidechains

Ferrocenoyl peptides incorporating thioether functionality respond more strongly to mercury(II) than to other heavy metal ions in solution. Compounds reported previously in this context are all 1,1′-disubstituted, and all include two or more sulfur-containing amino acids. To test whether two thioether groups are required for effective mercury binding by these systems, we have prepared a series of singly-substituted ferrocenoyl peptides from ferrocenecarboxylic acid and l-methionine, S-methyl-l-cysteine or S-trityl-l-cysteine, and tested them as electrochemical probes for mercury(II). Nine ferrocenoyl peptides have been synthesised using a Boc-protecting group strategy and HBTU-mediated peptide coupling. The electrochemical properties of these compounds have been determined using cyclic voltammetry, and all show fully reversible one electron oxidation steps. Forward sweep half wave peaks (E_F), reverse sweep half wave peaks (E_R), peak separations (ΔE_P) and half wave potentials (E_1/2) are reported. Changes in the potential of the iron(II)/iron(III) redox couple of the ferrocene core have been used to quantify heavy metal-peptide interactions, revealing that these monotopic systems also respond more strongly to mercury(II) than to zinc(II), cadmium(II), silver(I) and lead(II). NMR experiments to characterise the peptide-mercury interaction implicate the thioether sulfur as the site of mercury binding and indicate 1:1 stoichiometry. The crystal structure of ferrocenoyl-S-methyl-l-cysteine methyl ester is also reported. The greater responsiveness of these systems to mercury(II) makes them interesting leads for the development of biologically inspired sensors for this toxic heavy metal.     

Bottleable Neutral Analogues of [B2H5]− as Versatile and Strongly Binding η2 Donor Ligands

Herein we report the discovery that two bottleable, neutral, base‐stabilized diborane(5) compounds are able to bind strongly to a number of copper(I) complexes exclusively through their B?B bond. The resulting complexes represent the first known complexes containing unsupported, neutral σ_B?B diborane ligands. Single‐crystal X‐ray analyses of these complexes show that the X?Cu moiety (X=Cl, OTf, C₆F₅) lies opposite the bridging hydrogen atom of the diborane and is near perpendicular to the B?B bond, interacting almost equally with both boron atoms and causing a B?B bond elongation. DFT studies show that σ donation from and π backdonation to the pseudo‐π‐like B?B bond account for their formation. Astoundingly, these copper σ_B?B complexes are inert to ligand exchange with pyridine under either heating or photoirradiation.     

D3R grand challenge 4: blind prediction of protein–ligand poses,affinity rankings,and relative binding free energies

Journal of Computer-Aided Molecular Design - The Drug Design Data Resource (D3R) aims to identify best practice methods for computer aided drug design through blinded ligand pose prediction and...     

Oxime Side‐Chain Cross‐Links in an α‐Helical Coiled‐Coil Protein: Structure,Thermodynamics, and Folding‐Templated Synthesis of Bicyclic Species

Covalent side‐chain cross‐links are a versatile method to control peptide folding, particularly when α‐helical secondary structure is the target. Here, we examine the application of oxime bridges, formed by the chemoselective reaction between aminooxy and aldehyde side chains, for the stabilization of a helical peptide involved in a protein–protein complex. A series of sequence variants of the dimeric coiled coil GCN4‐p1 bearing oxime bridges at solvent‐exposed positions were prepared and biophysically characterized. Triggered unmasking of a side‐chain aldehyde in situ and subsequent cyclization proceed rapidly and cleanly at pH 7 in the folded protein complex. Comparison of folding thermodynamics among a series of different oxime bridges show that the cross links are consistently stabilizing to the coiled coil, with the extent of stabilization sensitive to the exact size and structure of the macrocycle. X‐ray crystallographic analysis of a coiled coil with the best cross link in place and a second structure of its linear precursor show how the bridge is accommodated into an α‐helix. Preparation of a bicyclic oligomer by simultaneous formation of two linkages in situ demonstrates the potential use of triggered oxime formation to both trap and stabilize a particular peptide folded conformation in the bound state.