Functionalisation of Graphene Sensor Surfaces for the Specific Detection of Biomarkers

We report on a controllable and specific functionalisation route for graphene field-effect transistors (GFETs) for the recognition of small physiologically active molecules. Key element is the noncovalent functionalisation of the graphene surface with perylene bisimide (PBI) molecules directly on the growth substrate. This Functional Layer Transfer enables the homogeneous self-assembly of PBI molecules on graphene, onto which antibodies are subsequently immobilised. The sensor surface was characterised by atomic force microscopy, Raman spectroscopy and electrical measurements, showing superior performance over conventional functionalisation after transfer. Specific sensing of small molecules was realised by monitoring the electrical property changes of functionalised GFET devices upon the application of methamphetamine and cortisol. The concentration dependent electrical response of our sensors was determined down to a concentration of 300 ng ml⁻¹ for methamphetamine.     

Self-assembly of surfactant-like peptides

Inspired by recent work describing surfactant-like peptides, we have carried out a systematic study on peptides with the underlying composition of V6D2, altering the absolute sequence to determine the importance of the surfactant-like structure. All of the peptides examined here formed self-assembled structures in water. However, in contrast to other reports, we have found a surprising diversity of structures including fibers, tapes, and twisted ribbons but an absence of the vesicles and nanotubes described previously. Further investigations demonstrated that peptide purity plays a significant role in the outcome of the self-assembly. Different batches behave very differently, which can be linked to the compositions of these batches. This work shows that there is a need for not only rational design but also ease of synthesis of the building blocks for self-assembled structures.     

Microsolvation and 13C-Li NMR coupling

The empirical expression (1)J(CLi) = L[n(a + d)](-1) is proposed; it claims a reciprocal dependence of the NMR coupling constant (1)J((13)C, Li) in a C-Li compound on two factors: (i) the number n of lithium nuclei in bonding contact with the observed carbanion center and (ii) the sum (a + d) of the numbers a of anions and d of donor ligands coordinated at the Li nucleus that generates the observed (1)J(CLi) value. The expression was derived from integrations of separate NMR resonances of coordinated and free monodentate donor ligands (t-BuOMe, Et2O, or THF) in toluene solutions of dimeric and monomeric 2-(alpha-aryl-alpha-lithiomethylidene)-1,1,3,3-tetramethylindan at moderately low temperatures. This unusually slow ligand interchange is ascribed to steric congestion in these compounds, which is further characterized by measurements of nuclear Overhauser correlations and by solid-state structures of the dimers bearing only one donor per lithium atom (d = 1). Increasing microsolvation numbers d are also accompanied by typical changes of the NMR chemical shifts delta (positive for the carbanionic (13)C(alpha), negative for C(para) and p-H). The aforementioned empirical expression for (1)J(CLi) appears to be applicable to other cases of solvated monomeric, dimeric, or tetrameric C-Li compounds (alkyl, alkenyl, alkynyl, and aryl) and even to unsolvated (d approximately 0) trimeric, tetrameric, or hexameric organolithium aggregates, indicating that (1)J(CLi) might serve as a tool for assessing unknown microsolvation numbers. The importance of obtaining evidence about the (13)C NMR C-Li multiplet splitting of both the nonfluxional and fluxional aggregates is emphasized.     

Synthesis and Conformational Analysis of Pentapeptides Containing Enantiomerically Pure 2,2‐Disubstituted Glycines

The synthesis and conformational analysis of model pentapeptides with the sequence Z‐Leu‐Aib‐Xaa‐Gln‐Valol is described. These peptides contain two 2,2‐disubstituted glycines (α,α‐disubstituted α‐amino acids), i.e., Aib (aminoisobutyric acid), and a series of unsymmetrically substituted, enantiomerically pure amino acids Xaa. These disubstituted amino acids were incorporated into the model peptides via the ‘azirine/oxazolone method’. Conformational analysis was performed in solution by means of NMR techniques and, in the solid state, by X‐ray crystallography. Both methods show that the backbones of these model peptides adopt helical conformations, as expected for 2,2‐disubstitued glycine‐containing peptides.     

Detection of coherent oceanic structures via transfer operators

Coherent nondispersive structures are known to play a crucial role in explaining transport in nonautonomous dynamical systems such as ocean flows. These structures are difficult to extract from model output as they are Lagrangian by nature and not revealed by the underlying Eulerian velocity fields. In the last few years heuristic concepts such as finite-time Lyapunov exponents have been used in an attempt to detect barriers to oceanic transport and thus identify regions that trap material such as nutrients and phytoplankton. In this Letter we pursue a novel, more direct approach to uncover coherent regions in the surface ocean using high-resolution model velocity data. Our method is based upon numerically constructing a transfer operator that controls the surface transport of particles over a short period. We apply our technique to the polar latitudes of the Southern Ocean.     

A convenient and general iron-catalyzed hydrosilylation of aldehydes

A general and highly chemoselective hydrosilylation of aldehydes using iron catalysts is reported. Fe(OAc)2 in the presence of tricyclohexylphosphine as ligand and polymethylhydrosiloxane (PMHS) as an economical hydride source forms an efficient catalyst system for the hydrosilylation of a variety of aldehydes. Aryl, heteroaryl, alkyl and alpha,beta-unsaturated aldehydes are successfully reduced to the corresponding primary alcohols. Broad substrate scope and high tolerance against several functional groups make the process synthetically useful.     

Stable carbon isotope ratios of methyl-branched fatty acids are different to those of straight-chain fatty acids in dairy products

Methyl-branched fatty acids (MBFAs) are the dominant form of fatty acid found in many bacteria. They are also found at low levels in a range of foodstuffs, where their presence has been linked to bacterial sources. In this study we evaluated the potential of compound-specific isotope analysis to obtain insights into the stable carbon isotope ratios (δ¹³C values in ‰) of individual MBFAs and to compare them to the stable carbon isotope ratios of straight-chain fatty acids in food. Due to their low abundance in foodstuffs, the MBFAs were enriched prior to gas chromatography coupled to isotope ratio mass spectrometric (GC–IRMS) analysis. After transesterification, urea complexation was used to suppress the 16:0 and 18:0 methyl esters that were dominant in the samples. Following that, silver-ion high performance liquid chromatography was used to separate the saturated from the unsaturated fatty acids. The resulting solutions of saturated fatty acids obtained from suet, goat’s milk, butter, and human milk were studied by GC–IRMS. The δ¹³C values of fatty acids with 12–17 carbons ranged from −25.4‰ to −37.6‰. In all samples, MBFAs were most depleted in carbon-13, followed by the odd-chain fatty acids 15:0 and 17:0. 14:0 and 16:0 contained the highest proportions of carbon-13. The results from this study illustrate that MBFAs have distinctive δ¹³C values and must originate from other sources and/or from very different substrates. These measurements support the initial hypothesis that δ¹³C values can be used to attribute MBFAs to particular sources.