Macromolecular Ions Research Articles

Testing continuous spontaneous localization model with charged macromolecules

Abstract In the last decade, a growing interest has been devoted to models of spontaneous collapse of the wavefunction, known also as collapse models. They coherently solve the well-known quantum measurement problem by suitably modifying the Schrödinger evolution. Quantum experiments are now finally within the reach of testing such models (and thus testing the limits of quantum theory). Here, we propose a method based on a two-ions confined in a linear Paul trap to possibly enhance the testing capabilities of such experiments. The combination of an atomic and a macromolecular ion provide a good match for the cooling of the motional degrees of freedom and a non-negligible insight in the collapse mechanism, respectively.

An experimental investigation of rundown of the L-type calcium current

Background L-type calcium channels (LCCs) are multi-protein macro-molecular ion channel complexes that are involved in several critical functions in cardiac, skeletal, neuronal, smooth muscle, and endocrine cells. Like other ion channels, LCCs can be selectively over-expressed in a host cell line and studied using voltage-clamp patch-clamp experiments. However, L-type calcium current (ICaL) recordings commonly exhibit a reduction in current magnitude over time, commonly termed ‘rundown’. Previous studies have shown the effect of phosphorylation on rundown, here we provide evidence that accumulation of Ca2+ inside the cell also contributes towards ICaL rundown. Methods We generated experimental conditions that should promote the accumulation of sub-membrane Ca2+ in a CHO expression system, by increasing calcium import or decreasing export. These interventions took the form of: a decrease in inter-pulse duration between sweeps, block of the sodium-calcium exchanger, and increased temperature. Results On average, we found that current reduced to 63% of its initial value within 325 seconds. This reduction of current with time was found to follow two main patterns: linear or saturating decay. Additionally, current magnitude in some cells increased before stabilising or decaying. Conclusions This study shows that the rundown of ICaL in patch-clamp experiments can be reduced by modifying the experimental conditions, and implies that reduced accumulation of Ca2+ inside the cell membrane reduces calcium-dependent inactivation of ICaL.

Orbitrap-Based Mass and Charge Analysis of Single Molecules.

Native mass spectrometry is nowadays widely used for determining the mass of intact proteins and their noncovalent biomolecular assemblies. While this technology performs well in the mass determination of monodisperse protein assemblies, more real-life heterogeneous protein complexes can pose a significant challenge. Factors such as co-occurring stoichiometries, subcomplexes, and/or post-translational modifications, may especially hamper mass analysis by obfuscating the charge state inferencing that is fundamental to the technique. Moreover, these mass analyses typically require measurement of several million molecules to generate an analyzable mass spectrum, limiting its sensitivity. In 2012, we introduced an Orbitrap-based mass analyzer with extended mass range (EMR) and demonstrated that it could be used to obtain not only high-resolution mass spectra of large protein macromolecular assemblies, but we also showed that single ions generated from these assemblies provided sufficient image current to induce a measurable charge-related signal. Based on these observations, we and others further optimized the experimental conditions necessary for single ion measurements, which led in 2020 to the introduction of single-molecule Orbitrap-based charge detection mass spectrometry (Orbitrap-based CDMS). The introduction of these single molecule approaches has led to the fruition of various innovative lines of research. For example, tracking the behavior of individual macromolecular ions inside the Orbitrap mass analyzer provides unique, fundamental insights into mechanisms of ion dephasing and demonstrated the (astonishingly high) stability of high mass ions. Such fundamental information will help to further optimize the Orbitrap mass analyzer. As another example, the circumvention of traditional charge state inferencing enables Orbitrap-based CDMS to extract mass information from even extremely heterogeneous proteins and protein assemblies (e.g., glycoprotein assemblies, cargo-containing nanoparticles) via single molecule detection, reaching beyond the capabilities of earlier approaches. We so far demonstrated the power of Orbitrap-based CDMS applied to a variety of fascinating systems, assessing for instance the cargo load of recombinant AAV-based gene delivery vectors, the buildup of immune-complexes involved in complement activation, and quite accurate masses of highly glycosylated proteins, such as the SARS-CoV-2 spike trimer proteins. With such widespread applications, the next objective is to make Orbitrap-based CDMS more mainstream, whereby we still will seek to further advance the boundaries in sensitivity and mass resolving power.

Frequency chasing of individual megadalton ions in an Orbitrap analyser improves precision of analysis in single-molecule mass spectrometry

To enhance the performance of charge-detection mass spectrometry, we investigated the behaviour of macromolecular single ions on their paths towards and within the Orbitrap analyser. Ions with a mass beyond one megadalton reach a plateau of stability and can be successfully trapped for seconds, travelling a path length of multiple kilometres, thereby enabling precise mass analysis with an effective resolution of greater than 100,000 at a mass-to-charge ratio of 35,000. Through monitoring the frequency of individual ions, we show that these high-mass ions, rather than being lost from the trap, can gradually lose residual solvent molecules and, in rare cases, a single elementary charge. We also demonstrate that the frequency drift of single ions due to desolvation and charge stripping can be corrected, which improves the effective ion sampling 23-fold and gives a twofold improvement in mass precision and resolution.

Toward understanded the electrochemical capacitance mechanism of MXene by intercalation of inorganic ions and organic macromolecular ions

Interlayer ion modification of MXene is one of the effective ways to improve the pseudocapacitance performance. However, the origin of electrochemical capacitance mechanism still remains elusive due to the effect of different kinds of ion interlayer modification. In this work, interlayer modification of MXene (Ti3C2Cl2) with inorganic ions (NaCl) and organic macromolecular ions (cetyl trimethyl ammonium bromide cation, CTAB) were carried out by ion ultrasonic intercalation and the electrochemical capacitance mechanism was investigated. It was found that MXene- CTAB has higher specific capacitance (258.28F g−1 Vs 225.55F g−1) and better cycle stability (93% retention Vs 85% retention after 3000 cycles) than MXene-NaCl. Such a large difference in electrochemical energy storage performance is mainly due to two points : (1) Organic macromolecular CTAB can effectively expand the layer spacing of MXene, which is conducive to the storage of electrolyte ions. (2) Compared with inorganic ions, organic macromolecular ions not only have redox reaction with interlayer ions of MXene, but also can adsorb counter ions in the electrolyte, thus providing additional pseudocapacitance. This work opens up a new way for the development of high-performance MXene based electrode materials.

On the aggregation of bovine serum albumin

In an attempt to elucidate the aggregation behaviour of bovine serum albumin and its modulation by salt ions, size-exclusion high-performance liquid chromatography was used and complemented by dynamic light scattering. The influence of the protein concentration, and type and concentration of inorganic salt on the aggregation of albumin in solution have been analyzed. Based on the observations herein reported an aggregation mechanism is proposed, according to which (i) some functional groups of albumin dissociate in solution forming macromolecular ions; (ii) the macromolecular ions bind with each other into large aggregates; and (iii) the salt ions establish chemical equilibria with the charges of opposing character present in the macromolecular ions’ backbone, promoting or preventing the aggregation. The present work shows that the aggregation behaviour of bovine serum albumin in solution and its modulation by salt ions can be explained by chemical concepts, with chemical equilibrium playing an essential role.

Simulation of the Drift of a Macromolecular Ion in a Gas under the Action of an Electric Field

Simulation of the Drift of a Macromolecular Ion in a Gas under the Action of an Electric Field

Direct observation of ion emission from charged aqueous nanodrops: effects on gaseous macromolecular charging.

Mechanistic information about how gaseous ions are formed from charged droplets has been difficult to establish because direct observation of nanodrops in a size range relevant to gaseous macromolecular ion formation by optical or traditional mass spectrometry methods is challenging owing to their small size and heterogeneity. Here, the mass and charge of individual aqueous nanodrops between 1–10 MDa (15–32 nm diameter) with ∼50–300 charges are dynamically monitored for 1 s using charge detection mass spectrometry. Discrete losses of minimally solvated singly charged ions occur, marking the first direct observation of ion emission from aqueous nanodrops in late stages of droplet evaporation relevant to macromolecular ion formation in native mass spectrometry. Nanodrop charge depends on the identity of constituent ions, with pure water nanodrops charged slightly above the Rayleigh limit and aqueous solutions containing alkali metal ions charged progressively below the Rayleigh limit with increasing cation size. MS2 capsid ions (∼3.5 MDa; ∼27 nm diameter) are more highly charged from aqueous ammonium acetate than from its biochemically preferred, 100 mM NaCl/10 mM Na phosphate solution, consistent with ion emission reducing the nanodrop and resulting capsid charge. The extent of charging indicates that the capsid partially collapses inside the nanodrops prior to the charging and formation of the dehydrated gaseous ions. These results demonstrate that ion emission can affect macromolecular charging and that conformational changes to macromolecular structure can occur in nanodrops prior to the formation of naked gaseous ions.

Development of a focused high-energy macromolecular ion beam.

In this work, we report the development of a focused macromolecular ion beam with kinetic energy of up to 110 keV. The system consists of a quadrupole ion trap (QIT), einzel lens and linear accelerator (LINAC). Based on the combination of matrix-assisted laser desorption ionization (MALDI) and quadrupole ion trapping (QIT), ions were desorbed from the surface and trapped with an ion trap to form biomolecular ion packets. Positive- and negative-pulsed voltages were applied on each end-cap electrode of the QIT to extract the ion packets and form an ion beam that was subsequently focused via an einzel lens and accelerated by stepwise pulsed voltages. The tabletop instrument was designed and successfully demonstrated via measurements of molecular ions of insulin, cytochrome c and bovine serum albumin (BSA) with mass-to-charge ratios (m/z) ranging from ∼5.8 to 66.5 k. This is the first report of both a focused and high-kinetic-energy protein ion beam. In addition, both secondary ions and electrons were observed from the surface by hypervelocity ion beam bombardment. This focused macromolecular ion beam has demonstrated its potential in the study of interactions between large molecular ions with other molecules either in the gas phase or upon a surface.

Low-Field Differential Ion Mobility Spectrometry of Dipole-Aligned Macromolecules.

Ion mobility spectrometry (IMS) with mass spectrometry has grown into a powerful approach to simplify complex mixtures, disentangle isomers, and elucidate their geometries. Two established branches are linear IMS based on the absolute mobility K at moderate normalized electric field E/N and field asymmetric waveform IMS (FAIMS) relying on the evolution of K at high E/N causing strong ion heating. Here, we introduce low-field differential IMS (LODIMS), where the field is too weak for significant heating but suffices to lock the permanent macromolecular ion dipoles, producing novel separations based solely on their alignment. The method is demonstrated for a prototypical large protein-albumin. Its oligomers start separating at fields of just 1 kV/cm (4 Td), or ∼5% of those typical for FAIMS. Negligible ion heating at such fields allows preserving fragile species, in particular the noncovalent complexes up to pentamers (332 kDa) destroyed in FAIMS and not detected without it. The separation parameter (compensation field, EC) in this regime scales with the field linearly versus cubically in FAIMS. The dipole moments obtained from threshold fields for alignment and directional cross sections estimated from the slope of said linear EC dependence appear reasonable.

High-Pressure Electrospray Ionization Yields Supercharged Protein Complexes from Native Solutions While Preserving Noncovalent Interactions.

Increasing charge state of protein complexes from native solutions while preserving noncovalent interactions in native mass spectrometry (MS) offers great opportunity to gain deeper insights into gas-phase protein structures. Several previous studies have disclosed the possibility of high pressure in supercharging small proteins, whereas its capability to supercharge large protein assemblies under native conditions and how it might affect protein structures remain open questions. Herein, we demonstrated that the high-pressure-induced supercharging strategy affords unique advantages of supercharging protein complexes with the highest charge state surpassing the Rayleigh limit (ZR) and concurrently preserving native-like topology. By examining 32 proteins and protein complexes with molecular weights (MWs) ranging from 8.58 to 801 kDa, we demonstrated that the increased average charge states of macromolecular ions have a strong dependence on the surface areas of native protein conformations and MWs. Factors that might contribute to the high-pressure-induced supercharging capability toward macromolecular ions were discussed. Furthermore, using collision cross section (CCS) variation as a function of charge state, we investigate the effects of gas pressure and charge states on gas-phase structures of proteins and protein complexes. Smaller proteins have the largest CCS variations once supercharged, while macromolecular protein complexes are less affected. The results revealed that both surface density of charge and charged surface basic residues contribute to the observed CCS-charge disciplines for all the macromolecules investigated. Taken together, the results presented here indicate that increasing gas pressure in the ion source affords a rapid, simple, and controlled supercharging method, offering the potency of facilitating further applications of native top-down MS analysis with improved transmission, fragmentation, and detection efficiency.

Antimicrobial Properties of Polyelectrolyte–Amphiphilic Surfactant Complexes Containing Quaternary Ammonium Groups

Polymer-colloid complexes of polystyrenesulfonate and sodium polyacrylate with dimethyl-alkyl(С8-16)benzylammonium chlorides and polyvinylbenzyltrimethylammonium chloride with sodium dodecyl sulfate and laurate having similar structures of ion pairs macromolecular ion–counterion are synthesized. The composition of the resulting complexes is analyzed. Their antimicrobial properties are investigated. It is shown that the complexes in which quaternary ammonium groups serve as counterions and are bound to macromolecular chains via electrostatic interaction possess a higher antifungal activity than the complexes in which these groups are bound to macromolecular chains via covalent bonds. An important role of molecules of the ammonium compound containing a long-chain alkyl substituent which are involved in the form of associates in the composition of the complex in the antifungal activity of the complexes is demonstrated. A comparative analysis of the properties of film coatings based on the synthesized complexes is performed.

Conformation-dependent dynamics of macromolecular ions in the gas phase under an electrostatic field: A molecular dynamics simulation

Highly charged macromolecular ions exhibit various conformations in gas. Intramolecular charge-to-charge interaction induces a transformation from a globular structure into a stretched one. The cha...

Application of Nanotechnology in Wastewater Treatment

Because the current social water pollution is serious, and the conventional method cannot eff ectively manage alltypes of water pollution, and its single eff ect cannot be satisfactory, we must seek new and eff ective treatment. Thepaper is a comprehensive review of the best practices of the conventional wastewater treatment method with referenceto the experiments and research results of nanotechnology in sewage treatment. Comparison of nanotechnology canbe compared with conventional methods to make the particles have a special function, and some special performancejust in the sewage treatment medium to a good effect: the depth of the catalytic method can be effective in thedecomposition of many types of organic pollutants such as halogenated hydrocarbons Class, chlorinated phenols,cyanide, various organic acids and can handle metal particles; adsorption method for the water heavy metal pollutiontreatment costs less, simple and widely used, nanofi ltration membrane can replace the adsorption and electrochemicalmethods, Pulping and precipitation are one of the most eff ective methods for the treatment of colloidal wastewater. Itcan eff ectively reduce the turbidity and chroma of waste water, remove a variety of macromolecular organic matter andsome heavy metal ions ( Mercury and lead); organic / inorganic composite nanoparticles with its excellent inorganicmaterials, light, electricity, magnetic and other properties, organic materials, excellent processing performance,biocompatibility, for many diffi cult to deal with water pollution control, which has a corresponding method, can besimple and eff ective to solve the problem. The application of nanotechnology in water treatment has shown a broadprospect, but needs further research and improvement.

A Potentiostatic/Galvanostatic Study and Theoretical Description of Polypyrrole Film Electrodes: A Model of the Intracellular Matrix of Ectothermic Muscle Cells

AbstractPolypyrrole film electrodes are composed of macromolecular electrochemical machines, ions and water. They are considered here as a model of the intracellular matrix of ectothermic muscle cells. The oxidation/reduction responses to the working temperature in aqueous solutions were investigated herein by potential and current steps. Under potentiostatic conditions, rising temperatures stimulate deeper conformational movements of the polymeric chains leading to the exchange of more ions increasing the consumed charge, with the effect that the reaction charge responds and senses the working temperature. Under galvanostatic conditions and higher environmental thermal energies the material potential evolves at lower values during reactions consuming lower electrical energies. At any reaction time, both the consumed reaction energy and the material potential sense the working thermal conditions. Reactions involving molecular machines sense and respond to the working temperature. Similarities with energetic consumptions and sensing responses from muscles in cold‐blooded animals are discussed. A theoretical description is proposed.

Ion channels and ion selectivity.

Specific macromolecular transport systems, ion channels and pumps, provide the pathways to facilitate and control the passage of ions across the lipid membrane. Ion channels provide energetically favourable passage for ions to diffuse rapidly and passively according to their electrochemical potential. Selective ion channels are essential for the excitability of biological membranes: the action potential is a transient phenomenon that reflects the rapid opening and closing of voltage-dependent Na+-selective and K+-selective channels. One of the most critical functional aspects of K+ channels is their ability to remain highly selective for K+ over Na+ while allowing high-throughput ion conduction at a rate close to the diffusion limit. Permeation through the K+ channel selectivity filter is believed to proceed as a 'knockon' mechanism, in which 2-3 K+ ions interspersed by water molecules move in a single file. Permeation through the comparatively wider and less selective Na+ channels also proceeds via a loosely coupled knockon mechanism, although the ions do not need to be fully dehydrated. While simple structural concepts are often invoked to rationalize the mechanism of ion selectivity, a deeper analysis shows that subtle effects play an important role in these flexible dynamical structures.

Electron diffraction of CBr4 in superfluid helium droplets: A step towards single molecule diffraction.

We demonstrate the practicality of electron diffraction of single molecules inside superfluid helium droplets using CBr4 as a testing case. By reducing the background from pure undoped droplets via multiple doping, with small corrections for dimers and trimers, clearly resolved diffraction rings of CBr4 similar to those of gas phase molecules can be observed. The experimental data from CBr4 doped droplets are in agreement with both theoretical calculations and with experimental results of gaseous species. The abundance of monomers and clusters in the droplet beam also qualitatively agrees with the Poisson statistics. Possible extensions of this approach to macromolecular ions will also be discussed. This result marks the first step in building a molecular goniometer using superfluid helium droplet cooling and field induced orientation. The superior cooling effect of helium droplets is ideal for field induced orientation, but the diffraction background from helium is a concern. This work addresses this background issue and identifies a possible solution. Accumulation of diffraction images only becomes meaningful when all images are produced from molecules oriented in the same direction, and hence a molecular goniometer is a crucial technology for serial diffraction of single molecules.

Design and performance of an instrument for electron impact tandem mass spectrometry and action spectroscopy of mass/charge selected macromolecular ions stored in RF ion trap*

A new apparatus was designed, coupling an electron gun with a linear quadrupole ion trap mass spectrometer, to perform m/z (mass over charge) selected ion activation by electron impact for tandem mass spectrometry and action spectroscopy. We present in detail electron tracing simulations of a 300 eV electron beam inside the ion trap, design of the mechanical parts, electron optics and electronic circuits used in the experiment. We also report examples of electron impact activation tandem mass spectra for Ubiquitin protein, Substance P and Melittin peptides, at incident electron energies in the range from 280 eV to 300 eV.

Electron impact action spectroscopy of mass/charge selected macromolecular ions: Inner-shell excitation of ubiquitin protein

We have performed inner-shell electron impact action spectroscopy of mass and charge selected macromolecular ions. For this purpose, we have coupled a focusing electron gun with a linear quadrupole ion trap mass spectrometer. This experiment represents a proof of principle that an energy-tunable electron beam can be used in combination with radio frequency traps as an activation method in tandem mass spectrometry (MS2) and allows performing action spectroscopy. Electron impact MS2 spectra of multiply protonated ubiquitin protein ion have been recorded at incident electron energies around the carbon 1 s excitation. Both MS2 and single ionization energy dependence spectra are compared with literature data obtained using the soft X-ray activation conditions.

Experimental Evidence of a Strong Image Force between Highly Charged Electrosprayed Molecular Ions and a Metal Screen

ABSTRACTWe investigated the capturing mechanisms of highly charged macromolecular ions of polyethylene glycol electrosprayed onto a metal screen. Our experiments assessed how the charge state, size of the macromolecular ions, and filtration velocity affected the penetration of the ions through the metal screen. The single fiber efficiencies were plotted as functions of the Peclet number and image force parameter. Highly charged molecular ions had much higher collection efficiencies than neutralized macromolecules, suggesting the presence of a strong image force between the ions and metal surface. The single fiber efficiency by image force was proportional to the square root of an image force parameter predicted by theory. When using the prefactor of 9.7 proposed by Alonso et al. (2007), we found fair agreement between the experimental data and theoretical predictions on the collection efficiency of highly charged molecular ions with mobility diameters from 2.6 to 4.8 nm and numbers of electrical charges from 2 to 7. The experimental evidence from our study reveals that image force contributes strongly to the collection of multicharged macromolecular ions by a metal wire screen.