Principles of Fourier transform ion cyclotron resonance mass spectrometry and its application in structural biology

Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry has become increasingly significant within recent years. The inherently ultra-high resolution and mass accuracy allow unequivocal assignments of chemical formulae to be made and further structural elucidation can be conducted through the utilization of tandem mass spectrometry techniques. With the advent of electrospray ionization (ESI), FT-ICR mass spectrometry has become a powerful tool for the investigation of biological macromolecules, such as the study of non-covalent interactions of proteins. In this article, the basic principles are highlighted, some of the techniques employed are described and examples of applications are provided, with particular respect being paid to the field of characterization of biomolecules.     

Continuous molecular enrichment in microfluidic systems

Highly efficient molecular extractions in continuous flow microfluidic systems are demonstrated utilising the rapid mixing properties of biphasic segmented flow in conjunction with suspended micro-particulate adsorbents. A continuous flow technique providing potential for continual on-line sample enrichment, purification and clean-up in chemical synthesis, and sample preparation.     

Single molecule detection of double-stranded DNA in poly(methylmethacrylate) and polycarbonate microfluidic devices.

Single photon burst techniques were used to detect double-stranded DNA molecules in poly(methylmethacrylate) (PM MA) and polycarbonate (PC) microfluidic devices. A confocal epi-illumination detection system was constructed to monitor the fluorescence signature from single DNA molecules that were multiply labeled with the mono-intercalating dye, TOPRO-5, which possessed an absorption maximum at 765 nm allowing excitation with a solid-state diode laser and fluorescence monitoring in the near-infrared (IR). Near-IR excitation minimized autofluorescence produced from the polymer substrate, which was found to be significantly greater when excitation was provided in the visible range (488 nm). A solution containing lambda-DNA (48.5 kbp) was electrokinetically transported through the microfluidic devices at different applied voltages and solution pH values to investigate the effects of polymer substrate on the transport rate and detection efficiency of single molecular events. By applying an autocorrelation analysis to the data, we were able to obtain the molecular transit time of the individual molecules as they passed through the 7 microm laser beam. It was observed that the applied voltage for both devices affected the transport rate. However, solution pH did not alter the transit time for PM MA-based devices since the electroosmotic flow of PMMA was independent of solution pH. In addition, efforts were directed toward optimizing the sampling efficiency (number of molecules passing through the probe volume) by using either hydrodynamically focused flows from a sheath generated by electrokinetic pumping from side channels or reducing the channel width of the microfluidic device. Due to the low electroosmotic flows generated by both PMMA and PC, tight focusing of the sample stream was not possible. However, in PMMA devices, flow gating was observed by applying field strengths > -120 V/cm to the sheath flow channels. By narrowing the microchannel width, the number of molecular events detected per unit time was found to be four times higher in channels with 10 microm widths compared to those of 50 microm, indicating improved sampling efficiency for the narrower channels without significantly deteriorating detection efficiency. Attempts were made to do single molecule sizing of lambda-DNA, M13 (7.2 kbp) and pUC19 (2.7 kbp) using photon burst detection. While the average number of photons for each DNA type were different, the standard deviations were large due to the Gaussian intensity profile of the excitation beam. To demonstrate the sensitivity of single molecule analysis in the near-IR using polymer microfluidic devices, the near-IR chromophore, NN382, wasanalyzed using ourconfocal imager. A detection efficiency of 94% for single NN382 molecules was observed in the PC devices.     

Fabrication of Cobaltosic Oxide Nanoparticle-Doped 3 D MXene/Graphene Hybrid Porous Aerogels for All-Solid-State Supercapacitors

MXenes are a new family of 2 D transition metal carbides and nitrides, which have attracted enormous attention in electrochemical energy storage, sensing technology, and catalysis owing to their good conductivity, high specific surface area, and excellent electrochemical properties. In this work, a series of Co₃O₄-doped 3 D MXene/RGO hybrid porous aerogels is designed and prepared through a facile in situ reduction and thermal annealing process, in which the reduced graphene oxide (RGO) conductive network can electrically link the separated Co₃O₄-MXene composite nanosheets, leading to enhanced electronic conductivity. It is found that upon using the Co₃O₄-MXene/RGO hybrid porous aerogel prepared with a mass ratio of Co₃O₄-MXene/RGO of 3:1 (CMR31) as an electrode for a supercapacitor, a superior specific capacitance of 345 F g⁻¹ at the current density of 1 A g⁻¹ is achieved, which is significantly higher than those of Ti₃C₂T_x MXene, RGO, and MXene/RGO electrodes. In addition, a high capacitance retention (85 % of the initial capacitance after 10 000 cycles at a high current density of 3 A g⁻¹) and a low internal resistance R_s (0.44 Ω) can be achieved. An all-solid-state asymmetric supercapacitor (ASC) device is assembled using CMR31, and it has the ability to light up a blue LED indicator for 5 min if four ASCs are connected in series. Therefore, these novel Co₃O₄-MXene/RGO hybrid porous aerogels have potential practical applications in high-energy storage devices.     

Eta' photoproduction on the proton for photon energies from 1.527 to 2.227 GeV

Differential cross sections for the reaction gamma p --> eta' p have been measured with the CLAS spectrometer and a tagged photon beam with energies from 1.527 to 2.227 GeV. The results reported here possess much greater accuracy than previous measurements. Analyses of these data suggest for the first time the coupling of the eta'N channel to both the S11(1535) and P11(1710) resonances, known to couple strongly to the etaN channel in photoproduction on the proton, and the importance of J = 3/2 resonances in the process.