Improved ion optics for introduction of ions into a 9.4‐T Fourier transform ion cyclotron resonance mass spectrometer

Enhancements to the ion source and transfer optics of our 9.4 T Fourier transform ion cyclotron resonance (ICR) mass spectrometer have resulted in improved ion transmission efficiency for more sensitive mass measurement of complex mixtures at the MS and MS/MS levels. The tube lens/skimmer has been replaced by a dual ion funnel and the following octopole by a quadrupole for reduced ion cloud radial expansion before transmission into a mass‐selective quadrupole. The number of ions that reach the ICR cell is increased by an order of magnitude for the funnel/quadrupole relative to the tube lens/skimmer/octopole. Copyright © 2015 John Wiley & Sons, Ltd.     

Front-End Electron Transfer Dissociation Coupled to a 21 Tesla FT-ICR Mass Spectrometer for Intact Protein Sequence Analysis

High resolution mass spectrometry is a key technology for in-depth protein characterization. High-field Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) enables high-level interrogation of intact proteins in the most detail to date. However, an appropriate complement of fragmentation technologies must be paired with FTMS to provide comprehensive sequence coverage, as well as characterization of sequence variants, and post-translational modifications. Here we describe the integration of front-end electron transfer dissociation (FETD) with a custom-built 21 tesla FT-ICR mass spectrometer, which yields unprecedented sequence coverage for proteins ranging from 2.8 to 29 kDa, without the need for extensive spectral averaging (e.g., ~60% sequence coverage for apo-myoglobin with four averaged acquisitions). The system is equipped with a multipole storage device separate from the ETD reaction device, which allows accumulation of multiple ETD fragment ion fills. Consequently, an optimally large product ion population is accumulated prior to transfer to the ICR cell for mass analysis, which improves mass spectral signal-to-noise ratio, dynamic range, and scan rate. We find a linear relationship between protein molecular weight and minimum number of ETD reaction fills to achieve optimum sequence coverage, thereby enabling more efficient use of instrument data acquisition time. Finally, real-time scaling of the number of ETD reactions fills during method-based acquisition is shown, and the implications for LC-MS/MS top-down analysis are discussed.

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An experimental study of the effect of free-stream turbulence on a trailing vortex

A study of turbulence evolution and spectra within and just outside the core of a trailing vortex is performed. The vortex is generated by a vortex generator consisting of four blades positioned orthogonally to each other with the same angle of attack and placed in a low-speed wind tunnel. A grid is placed upstream of the vortex generator to produce free-stream turbulence, which wraps around and interacts with the columnar vortex. Instantaneous measurements of the three velocity components are obtained using a miniature four-sensor hot-wire probe. The study focuses on the distribution of turbulence energy and Reynolds stress among the different spectral components of the flow at different positions across the vortex core and different axial positions along the tunnel. The effect of background grid turbulence on the spectral energy distribution of the vortex is examined in comparison to the vortex alone.     

Circumference and Pathwidth of Highly Connected Graphs

Birmele [J Graph Theory 2003] proved that every graph with circumference t has treewidth at most . Under the additional assumption of 2‐connectivity, such graphs have bounded pathwidth, which is a qualitatively stronger conclusion. Birmele's theorem was extended by Birmele et al. [Combinatorica 2007] who showed that every graph without k disjoint cycles of length at least t has treewidth . Our main result states that, under the additional assumption of ‐connectivity, such graphs have bounded pathwidth. In fact, they have pathwidth . Moreover, examples show that ‐connectivity is required for bounded pathwidth to hold. These results suggest the following general question: for which values of k and graphs H does every k‐connected H‐minor‐free graph have bounded pathwidth? We discuss this question and provide a few observations.     

Surface-confined nickel mediated cross-coupling reactions: characterization of initiator environment in Kumada catalyst-transfer polycondensation

Kumada catalyst-transfer polycondensation (KCTP) has proven to be an excellent strategy toward the synthesis of well-defined conjugated polymers. In this report, Ni(0) species are reacted with surface-bound aryl bromides to yield KCTP initiators of structure (aryl)Ni(II)-Br. Surface-confined Kumada reactions are carried out with a ferrocene functionalized Grignard reagent to quantify initiator coverage, ligand exchange, and Kumada reaction kinetics. In addition, surface-initiated Kumada catalyst-transfer polycondensation (SI-KCTP) is carried out from the fabricated initiators to modify SiO(2) and ITO surfaces. Uniform poly(3-methylthiophene) films with thicknesses between 40 and 65 nm were characterized using a variety of spectroscopic and electrochemical techniques.     

Microbiosensors based on DNA modified single-walled carbon nanotube and Pt black nanocomposites

Glucose and ATP biosensors have important applications in diagnostics and research. Biosensors based on conventional materials suffer from low sensitivity and low spatial resolution. Our previous work has shown that combining single-walled carbon nanotubes (SWCNTs) with Pt nanoparticles can significantly enhance the performance of electrochemical biosensors. The immobilization of SWCNTs on biosensors remains challenging due to the aqueous insolubility originating from van der Waals forces. In this study, we used single-stranded DNA (ssDNA) to modify SWCNTs to increase solubility in water. This allowed us to explore new schemes of combining ssDNA-SWCNT and Pt black in aqueous media systems. The result is a nanocomposite with enhanced biosensor performance. The surface morphology, electroactive surface area, and electrocatalytic performance of different fabrication protocols were studied and compared. The ssDNA-SWCNT/Pt black nanocomposite constructed by a layered scheme proved most effective in terms of biosensor activity. The key feature of this protocol is the exploitation of ssDNA-SWCNTs as molecular templates for Pt black electrodeposition. The glucose and ATP microbiosensors fabricated on this platform exhibited high sensitivity (817.3 nA/mM and 45.6 nA/mM, respectively), wide linear range (up to 7 mM and 510 μM), low limit of detection (1 μM and 2 μM) and desirable selectivity. This work is significant to biosensor development because this is the first demonstration of ssDNA-SWCNT/Pt black nanocomposite as a platform for constructing both single-enzyme and multi-enzyme biosensors for physiological applications.     

Tissue-Specific stem cell differentiation in an in vitro airway model

The respiratory tract is the primary site of exposure to airborne compounds, with the bronchial epithelium providing one of the first lines of defence. A growing need exists for an accurate in vitro model of the bronchial epithelium. Here, normal human bronchial epithelial (NHBE) cells cultured at an air/liquid interface create a fully differentiated, in-vivo-like model of the human bronchial epithelium. Developmental characterisation includes (i) trans-epithelial electrical resistance, (ii) morphology and (iii) bronchial cell specific stains/markers. It is concluded that the basal/progenitor cells create a pseudo-stratified, mucociliary NHBE model containing basal, serous, Clara, goblet and ciliated cells, reflective of the normal human bronchial epithelium (days 24-33 ALI culture).     

Ce(IV) complexes with donor-functionalized alkoxide ligands: improved precursors for chemical vapor deposition of CeO2

Thin films of ceria (CeO(2)) have many applications, and their synthesis by liquid-injection MOCVD (metal-organic chemical vapor deposition) or ALD (atomic layer deposition) requires volatile precursor compounds. Here we report the synthesis of a series of homoleptic and heteroleptic Ce(IV) complexes with donor-functionalized alkoxide ligands mmp (1-methoxy-2-methylpropan-2-olate), dmap (1-(dimethylamino)propan-2-olate), and dmop (2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)propan-2-olate) and their potential as precursors for MOCVD and ALD of CeO(2). New complexes were synthesized by alcohol exchange reactions with [Ce(OBu(t))(4)]. [Ce(mmp)(4)] and [Ce(dmap)(4)] were both found to be excellent precursors for liquid-injection MOCVD of CeO(2), depositing high purity thin films with very low carbon contamination, and both have a large temperature window for diffusion controlled growth (350-600 °C for [Ce(mmp)(4)]; 300-600 °C for [Ce(dmap)(4)]). [Ce(mmp)(4)] is also an excellent precursor for liquid-injection ALD of CeO(2) using H(2)O as oxygen source and demonstrates self-limiting growth from 150 to 350 °C. [Ce(dmap)(4)] has lower thermal stability than [Ce(mmp)(4)] and does not show self-limiting growth in ALD. Heteroleptic complexes show a tendency to undergo ligand redistribution reactions to form mixtures in solution and are unsuitable as precursors for liquid-injection CVD.     

Hematite and carbonaceous materials in geological samples: a cautionary tale

Over the last few decades Raman spectroscopy has been increasingly applied as an analytical tool in geoscience research. Raman spectroscopy is a powerful tool for geologists as it is non-destructive, requires little to no sample preparation, and can be undertaken in situ on various irreplaceable geological samples. Also, this technique is useful in the identification of minerals and geo-organic material. However, despite this ease of application, there are some facets of Raman spectroscopy data that can lead to erroneous interpretations. For instance, there is much confusion in the geological literature distinguishing the difference between the hematite vibrational mode at ca. 1320 cm(-1) and the disordered sp(2) carbonaceous material D band at 1340 cm(-1). Furthermore, geologists will often collect 2 spectra, one in the mineral finger print region (200-800 cm(-1)) and then a spectrum in the carbon first-order region (1000-1800 cm(-1)), rather than performing a full-region scan. This allows the misidentification of the hematite mode at 1320 cm(-1) as the D band from disordered carbonaceous material. Here we show that it is best practice for geologists to collect spectra between 200 and 1800 cm(-1) to better distinguish between hematite and disordered carbonaceous material, materials that often co-occur in geological samples.