Manipulation of protein charge states through continuous flow-extractive desorption electrospray ionization: a new ambient ionization technique

Manipulation of protein charge states in electrospray ionization-mass spectrometry (ESI-MS) has implications for the study of intact proteins, protein-protein interactions, post-translational modifications, and protein sequencing. Control of these protein charge states is often difficult to achieve with conventional methods of analysis. A novel ambient ionization configuration, continuous flow-extractive desorption electrospray ionization (CF-EDESI), is presented as a means to control the charge state distribution of proteins. A key feature of the CF-EDESI technique is the continuous flow needle, which is a hypodermic needle presented orthogonal to the electrospray source and delivers a solvent flow containing analytes for extractive desorption ionization. With this source design, the successful manipulation of cytochrome c and lysozyme charge states with the use of different additives, such as acetic acid and sulfolane, was demonstrated. Results were compared to data obtained with conventional electrospray ionization. Good agreement with previously reported studies of cytochrome c unfolding/folding studies, performed by conventional ESI-MS, is evident. In addition to the protein analysis presented, the CF-EDESI-MS technique should be applicable for analyzing atypical analyte and solvent systems by mass spectrometry while maintaining optimal electrospray source conditions.     

The production of focused ion beams for surface and gas-phase collision studies

Factors limiting the performance of practical ion beam systems are discussed and include momentum dispersion, instabilities, space-charge repulsion and extraction optics. An approach to overall design is illustrated by an accelerator system employing low energy extraction and used for a range of working conditions and ion species.     

Tracking of single charge carriers in a conjugated polymer nanoparticle

The motion of individual charge carriers in organic nanostructures was tracked by fluorescence microscopy. A twinkling effect is observed in fluorescence microscopy of single conjugated polymer nanoparticles, that is, small displacements in the fluorescence spot of single nanoparticles of the conjugated polymer PFBT are observed over time. There is evidence that superquenching by the charge carrier induces a dark spot in the nanoparticle, which moves with the carrier, resulting in the observed displacements in the fluorescence. Zero-field mobilities of individual charge carriers consistent with highly trapped polarons were obtained from tracking experiments.     

Stark tuning of the charge states of a two-donor molecule in silicon

A singly ionized two-donor molecule in silicon is an interesting test-bed system for implementing a quantum bit using charge degrees of freedom at the atomic limit of device fabrication. The operating principles of such a device are based on wavefunction symmetries defined by charge localizations and energy gaps in the spectrum. The Stark-shifted electronic structure of a two-donor phosphorus molecule is investigated using a multi-million-atom tight-binding framework. The effects of surface (S) and barrier (B) gates are analyzed for various voltage regimes. It is found that gate control is smooth for any donor separation, although at certain donor orientations the S and B gates may alter in functionality. Effects such as interface ionization, saturation of the lowest energy gap, and sensitivity to donor and gate placements are also investigated. Excited molecular states of P(2) + are found to impose limits on the allowed donor separations and operating gate voltages for coherent operation. This work therefore outlines and analyzes the various issues that are of importance in the design and control of such donor molecular systems.     

Computer simulation of ion discrimination in mass and charge

This paper describes a method useful for apparatus designing or experiment preparation: the computer simulated identification, with a Fortran program, of light and medium heavy ions, using a detector telescope. The comparison with some experimental data is also presented.     

Modelling of the flow around a high-altitude ion concentration pickup

The results are presented for a study of the flow structure in the supersonic flow of air around a cylindrical body with an open and a blocked inner channel under the conditions of altitudes of 54–67 km. The studies were conducted on a low-density wind tunnel using the electron beam method of measurements.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 25, No. 1, pp. 111–115, July, 1973.     

Optical trapping of a single protein

We experimentally demonstrate the optical trapping of a single bovine serum albumin (BSA) molecule that has a hydrodynamic radius of 3.4 nm, using a double-nanohole in an Au film. The strong optical force in the trap not only stably traps the protein molecule but also unfolds it. The unfolding of the BSA is confirmed by experiments with changing optical power and with changing solution pH. The detection of the trapping event has a signal-to-noise ratio of 33, which shows that the setup is extremely sensitive to detect the presence of a protein, even at the single molecule level.     

Fourier transform infrared measurement of solid-, liquid-, and gas-phase samples with a single photoacoustic cell

A photoacoustic detector based on the optical cantilever microphone has been built. The detector is capable of measuring solid-, liquid-, and gas-phase samples. Photoacoustic Fourier transform infrared (FT-IR) measurement with three samples in different phases was demonstrated. Example samples were polyethene, sunflower oil, and methane. The sensitivity of the cell was compared to a commercial photoacoustic FT-IR detector. With the standard carbon black sample the cantilever detector gave approximately five times higher signal-to-noise ratio than the reference detector. The sensitivity with methane was also compared to the DTGS detector of the FT-IR instrument corresponding to an absorption path of 6.3 cm. Simulation of the photoacoustic signal showed that a compromise has to be made in the cell design between sensitivity for solid- and gas-phase samples but it is possible to highly enhance the sensitivity for all types of samples by reducing cantilever dimensions.     

The cluster charge and size distribution during ion sputtering of metals

The process of elastic sputtering of a metal in the form of large neutral and charged clusters (with the number of atoms N≥5) during ion bombardment of the metal target was theoretically studied. The distribution is described by a simple analytical formula.     

Preparation and purification of synthetic protein nanoparticulates

The protein nanostructure used in this study (bovine serum albumin; BSA nanoparticles) were fabricated with an average nanoparticle diameter 150 nm based on the principle of coacervation. Practical recovery of nanoparticulate mimics, of products such as plasmid DNA and viruses as putative gene therapy vectors from model systems, has been studied. The adsorbents employed in this study for the recovery of nanoparticles had one of four discrete designs i.e. microporous (pore size <0.2 microm), macroporous (pore size >0.8 microm), solid phase (nonporous) and pellicular (pore size <0.5 microm). Soluble protein was included in the study to represent cellular components of complex feedstocks and the separation of assemblies from components, while particulate protein served as surrogate size and charge mimics of less easily sourced viral and plasmid gene therapy vectors. Candidate adsorbents were physically characterised to assess their suitability for fluidised-bed operation, biochemically characterised exploiting batch-binding experimentation and laser scanning confocal microscopy. The adsorptive capacity of nanoparticulate products was strongly influenced by the physical design of the adsorbents, and microporous adsorbents appeared to be less suited for the recovery of nanoparticulate products. The generic application of such adsorbents for the recovery of nanoparticulate bioproducts is discussed.     

Application of a SQUID to record magnetic ion concentration in maser crystals

A SQUID operated magnetometer is used to determine concentration deviations of low magnetic doping as a function of position. Experimental results are compared with computer calculations and some improvements are demonstrated.     

Mechanisms of formation and charge states of intrinsic defects in lead telluride films

A crystallochemical model of the vapor-phase epitaxy of lead telluride films is suggested. The model is based on the simultaneous formation of singly-and doubly-charged Frenkel defects in the cationic sublattice. The results of numerical calculations based on this model are in good agreement with the known experimental data.     

Nanopore translocation dynamics of a single DNA-bound protein

We study the translocation dynamics of a single protein molecule attached to a double-stranded DNA that is threaded through a solid-state nanopore by optical tweezers and an electric field (nanopore force spectroscopy). We find distinct asymmetric and retarded force signals that depend on the protein charge, the DNA elasticity and its counterionic screening in the buffer. A theoretical model where an isolated charge on an elastic, polyelectrolyte strand is experiencing an anharmonic nanopore potential was developed. Its results compare very well with the measured force curves and explain the experimental findings that the force depends linearly on the applied electric field and exhibits a small hysteresis during back and forth translocation cycles. Moreover, the translocation dynamics reflects the stochastic nature of the thermally activated hopping between two adjacent states in the nanopore that can be adequately described by Kramers rate theory.     

Electrostatic screening by self-consistent space charge,and the ion dynamics in a time-of-flight mass spectrometer

We construct a theory of an inertially dispersed collisionless plasma cloud in an external electric field F_ex. The solution of this problem is applied to the calculation of time-of-flight mass spectrometer.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 52, No. 4, pp. 553–562, April, 1987.     

The procedure for investigation of the efficiency of purification of natural gases in a supersonic separator

A procedure is suggested for determining the field of application of supersonic separators. The formulation of the problem is given as regards the choice of optimal values of Mach number. The compositions of gas-liquid mixtures are determined as a function of the initial parameters (composition of gas, temperature, pressure, and Mach number). The results are given in the form of temperature, pressure, and Mach number dependences of the composition of the liquid phase of gas-liquid mixture. Primary estimation is made of the efficiency of purification of natural gases depending on their initial parameters.     

中空超滤在酶纯化浓缩中的应用

叙述了两种不同孔径的中空纤维超滤膜分别与微滤膜装置相结合,纯化、浓缩酶溶液的试验研究,开发出了一套兼有超滤、微滤、活性炭过滤器等装置于一体的工艺流程;并对该工艺进行了高倍数酶溶液浓缩的可行性探讨;分析了几种主要运行参数对整个工艺的影响．     

Study of single particle charge and Brownian motions with surface plasmon resonance

We demonstrated a method to accurately measure the zeta potentials and surface charges of individual particles by surface plasmon resonance microscopy (SPRM). The principle is based on the sensitive dependence of surface plasmons in a metal surface on the distance between a particle and the surface. By applying a periodic (ac) electric field to the metal surface, the charged particle oscillates, which is measured with SPRM, from which the zeta potential and the surface charge of the particle can be determined. The ac method reduces the electro-osmotic effect and noises induced by Brownian motions and allows for the rapid determination of the zeta potentials of individual particles.     

A family of exact eigenstates for a single trapped ion interacting with a laser field

Abstract

We show that, under certain combinations of the parameters governing the interaction of a harmonically trapped ion with a laser beam, it is possible to find one or more exact eigenstates of the Hamiltonian, with no approximations except the optical rotating-wave approximation. These are related via a unitary equivalence to exact eigenstates of the full Jaynes-Cummings model (including counter-rotating terms) supplemented by a static driving term.     

Impact resistance of a rectangular polycarbonate armor plate subjected to single and multiple impacts

In the present work the plastic deformation of a thin rectangular polycarbonate armor plate subjected to single and multiple impacts was investigated in detail. The impacts were conducted on a horizontal and diagonal path to explore the plate vulnerability against the in-coming single and multiple projectiles striking at various locations. Single impacts revealed the overall trend in plate dent sizes and thickness reductions on the horizontal and diagonal paths. Results were compared with previous research [Shah QH, Abakr YA. Effect of distance from the support on the penetration mechanism of clamped circular polycarbonate armor plates. International Journal of Impact Engineering 2008;35:1244–50] conducted on circular armor plate for validation purposes. The single impact data scatter necessitated to conduct repeated impact tests at reduced number of locations to search for a definite answer for the possible failure process in the vicinity of the clamped edges of the plate. An accelerated plastic deformation resulting in early perforation was found to occur in the diagonal plate corner compared to the plate center impact position or close to a straight clamped edge. Multiple impact results presented can be significantly helpful in designing rectangular shape polycarbonate armor plates to enhance safety. LSDYNA was used to simulate the impact event for the plate midpoint, the horizontal edge, and the diagonal edge. The results show a close agreement with the experimental work.     

Three-dimensional finite element analysis of the stress concentration at a single fibre break

A linear elastic analysis is performed of a single broken fibre surrounded by six equally spaced fibres. These fibres and the surrounding epoxy matrix are modelled separately whilst the rest of the composite is treated as a homogeneous, orthotropic material. The distance of the adjacent fibres is fixed based on an assumed fibre volume fraction of 0·60. The analysis shows that the stress concentration in the adjacent fibres is 1·058, much lower than the value of 1·104 predicted by Hedgepeth and van Dyke (J. Comp. Mater., 1 (1967) 294–309). The positively affected length where there is an increase in stress is only about half the ineffective length of the broken fibre. Further away from the break the axial stress in the adjacent fibres actually drops below the nominal axial stress. This results in a very small enhanced probability of failure in the adjacent fibres. Very close local fibre spacing around the broken fibre increases the maximum stress in the adjacent fibres by less than 3%.