Charged Counterparts Research Articles

Mechanisms of nanoparticle internalization and transport across an intestinal epithelial cell model: effect of size and surface charge.

This study investigated the effect of nanoparticle size (50 and 100 nm) and surface charge on their interaction with Caco-2 monolayers as a model of the intestinal epithelium, including cell internalization pathways and the level of transepithelial transport. Initially, toxicity assays showed that cell viability and cell membrane integrity were dependent on the surface charge and applied mass, number, and total surface area of nanoparticles, as tested in two epithelial cell lines, colon carcinoma Caco-2 and airway Calu-3. This also identified suitable nanoparticle concentrations for subsequent cell uptake experiments. Nanoparticle application at doses below half maximal effective concentration (EC₅₀) revealed that the transport efficiency (ratio of transport to cell uptake) across Caco-2 cell monolayers is significantly higher for negatively charged nanoparticles compared to their positively charged counterparts (of similar size), despite the higher level of internalization of positively charged systems. Cell internalization pathways were hence probed using a panel of pharmacological inhibitors aiming to establish whether the discrepancy in transport efficiency is due to different uptake and transport pathways. Vesicular trans-monolayer transport for both positively and negatively charged nanoparticles was confirmed via inhibition of dynamin (by dynasore) and microtubule network (via nocodazole), which significantly reduced the transport of both nanoparticle systems. For positively charged nanoparticles a significant decrease in internalization and transport (46% and 37%, respectively) occurred in the presence of a clathrin pathway inhibitor (chlorpromazine), macropinocytosis inhibition (42%; achieved by 5-(N-ethyl-N-isopropyi)-amiloride), and under cholesterol depletion (38%; via methyl-β-cyclodextrin), but remained unaffected by the inhibition of lipid raft associated uptake (caveolae) by genistein. On the contrary, the most prominent reduction in internalization and transport of negatively charged nanoparticles (51% and 48%, respectively) followed the inhibition of lipid raft-associated pathway (caveolae inhibition by genistein) but was not significantly affected by the inhibition of clathrin pathway.

Hypervalence in monoxides and dioxides of superalkali clusters.

F2Li3, a superalkali cluster, is characterized as having a lower adiabatic ionization energy than its elemental alkali counterpart and, coupled with the presence of complex molecular orbitals, suggests promise for novel bonding possibilities. CBS-QB3 composite method was used to study three distinct cluster isomers, as well as their cationic (+1) and anionic (-1) species, to identify energetic trends and observe geometric changes. Oxides were then generated from these clusters, of which three distinct monoxides and nine dioxides were obtained upon structure optimization. Identical calculations were performed for the oxide species and their charged counterparts. Some of the most stable oxides produced appear to possess hypervalent lithium and oxygen atoms, forming unique structures with exceptional stability.

Valley and spin thermoelectric transport in ferromagnetic silicene junctions

We have investigated the valley and spin resolved thermoelectric transport in a normal/ferromagnetic/normal silicene junction. Due to the coupling between the valley and spin degrees of freedom, thermally induced pure valley and spin currents can be demonstrated. The magnitude and sign of these currents can be manipulated by adjusting the ferromagnetic exchange field and local external electric field, thus the currents are controllable. We also find fully valley and/or spin polarized currents. Similar to the currents, owing to the band structure symmetry, tunable pure spin and/or valley thermopowers with zero charge counterpart are generated. The results obtained here suggest a feasible way of generating a pure valley (spin) current and thermopower in silicene.

Influence of Solute Charge and Pyrrolidinium Ionic Liquid Alkyl Chain Length on Probe Rotational Reorientation Dynamics

In recent years, the effect of molecular charge on the rotational dynamics of probe solutes in room-temperature ionic liquids (RTILs) has been a subject of growing interest. For the purpose of extending our understanding of charged solute behavior within RTILs, we have studied the rotational dynamics of three illustrative xanthene fluorescent probes within a series of N-alkylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([Cnmpyr][Tf2N]) RTILs with different n-alkyl chain lengths (n = 3, 4, 6, 8, or 10) using time-resolved fluorescence anisotropy decay. The rotational dynamics of the neutral probe rhodamine B (RhB) dye lies between the stick and slip boundary conditions due to the influence of specific hydrogen bonding interactions. The rotation of the negatively charged sulforhodamine 640 (SR640) is slower than that of its positively charged counterpart rhodamine 6G (R6G). An analysis based upon Stokes-Einstein-Debye hydrodynamics indicates that SR640 adheres to stick boundary conditions due to specific interactions, whereas the faster rotation of R6G is attributed to weaker electrostatic interactions. No significant dependence of the rotational dynamics on the solvent alkyl chain length was observed for any of the three dyes, suggesting that the specific interactions between dyes and RTILs are relatively independent of this solvent parameter.

An experimental and theoretical study on structural parameters and energetics in ionization and dissociation of cobalt tricarbonyl nitrosyl

In a combined theoretical and experimental study we calculate the geometrical parameters, dipole moments and rotational constants for the two lowest spin states of Co(CO)3NO, i.e., the 1A1 and 3A states of the neutral as well as their positively charged counterparts; the 2A′ and 4A″ states of [Co(CO)3NO]+. The geometrical parameters are also calculated for the two lowest spin states of all possible (Co containing) positively charged fragments, resulting from ligand loss through dissociative ionization (DI) of Co(CO)3NO. From the lowest total energies resulting from the geometrical optimizations, we calculate the ionization energy for Co(CO)3NO and the threshold energies for the two lowest spin states of all possible fragments, as well as the respective bond dissociation energies (BDE) describing the sequential ligand loss. Further, through electron bombardment, we determine the ionization energy for Co(CO)3NO, the appearance energies (AEs) of all DI products observed and the BDE for individual ligand loss. Finally, the theoretical and experimental IEs, AEs and BDEs derived are compared and discussed in context to earlier electron ionization and threshold photoelectron-photoion coincidence spectroscopy (TPEPICO) studies.

Charge Delocalization through Benzene, Naphthalene, and Anthracene Bridges in π-Conjugated Oligomers: An Experimental and Quantum Chemical Study

To understand the influence of orthogonal conjugation pathways fused directly to π-conjugated polymer backbones, we synthesized and studied three series of thiophene-based model compounds containing benzene, naphthalene, and anthracene peri-substituted central cores as representative acenes. These models were functionalized with methyl groups at the reactive thiophene positions in order to generate and observe oxidized species without complications from follow-up polymerization. The neutral monomers and their oxidized charged counterparts were subjected to cyclic voltammetry, spectroelectrochemistry, and EPR spectroscopy as appropriate, and these results were further corroborated with thorough density functional theory studies. This joint experimental and theoretical analysis allowed us to determine that benzene-based conjugated linkers led to more delocalized charge carriers on account of the quinoidal character maintained within the benzene core. In contrast, anthracene-based linkers displayed very localized carriers due to torsional strain between the adjacent aryl groups and to the local evolution of formal aromatic sextets on the benzo-fused rings orthogonal to the backbone in the quinoidal state. In some cases, the electronics of the thiophene-based substituent dominated the electronic properties of the oxidized species regardless of the nature of the central acene linker. These results highlight the dramatic influence that orthogonal conjugation pathways can exert on the electronic properties of π-conjugated materials.

Helical Structure Determines Different Susceptibilities of dsDNA, dsRNA, and tsDNA to Counterion-Induced Condensation

Recent studies of counterion-induced condensation of nucleic acid helices into aggregates produced several puzzling observations. For instance, trivalent cobalt hexamine ions condensed double-stranded (ds) DNA oligomers but not their more highly charged dsRNA counterparts. Divalent alkaline earth metal ions condensed triple-stranded (ts) DNA oligomers but not dsDNA. Here we show that these counterintuitive experimental results can be rationalized within the electrostatic zipper model of interactions between molecules with helical charge motifs. We report statistical mechanical calculations that reveal dramatic and nontrivial interplay between the effects of helical structure and thermal fluctuations on electrostatic interaction between oligomeric nucleic acids. Combining predictions for oligomeric and much longer helices, we also interpret recent experimental studies of the role of counterion charge, structure, and chemistry. We argue that an electrostatic zipper attraction might be a major or even dominant force in nucleic acid condensation.

Electrical control of neutral and charged excitons in a monolayer semiconductor

Monolayer group-VI transition metal dichalcogenides have recently emerged as semiconducting alternatives to graphene in which the true two-dimensionality is expected to illuminate new semiconducting physics. Here we investigate excitons and trions (their singly charged counterparts), which have thus far been challenging to generate and control in the ultimate two-dimensional limit. Utilizing high-quality monolayer molybdenum diselenide, we report the unambiguous observation and electrostatic tunability of charging effects in positively charged (X(+)), neutral (X(o)) and negatively charged (X(-)) excitons in field-effect transistors via photoluminescence. The trion charging energy is large (30 meV), enhanced by strong confinement and heavy effective masses, whereas the linewidth is narrow (5 meV) at temperatures <55 K. This is greater spectral contrast than in any known quasi-two-dimensional system. We also find the charging energies for X(+) and X(-) to be nearly identical implying the same effective mass for electrons and holes.

Conjugation of Glutathione to Oxidized Tyrosine Residues in Peptides and Proteins

Tyrosine residues are sensitive to oxidation and can be converted to hydroperoxides either by superoxide reacting with the Tyr radical or by singlet oxygen. These hydroperoxides rearrange to bicyclic derivatives that are readily reduced to more stable hydroxides. The aromatic character of tyrosine is lost, but the product contains an α-β unsaturated carbonyl group and is, therefore, an electrophile. We have generated hydroxide derivatives of several Tyr-containing peptides and shown using liquid chromatography/mass spectrometry that they undergo Michael addition with GSH. For Tyr-Gly, rate constants of 9.2 and 11.8 m(-1)min(-1) were measured for the two chromatographically distinct isomers. Unusual for GSH addition to an electrophile, the reaction is reversible, with a half-life of many hours for the reverse reaction. These kinetics indicate that with a typical cellular concentration of 5 mm GSH, >95% Tyr-Gly hydroxide would become conjugated with a half-life of ∼15 min. Sperm whale myoglobin forms a hydroperoxide on Tyr-151 in a hydrogen peroxide/superoxide-dependent reaction. We show that its hydroxide derivative reacts with GSH to form a conjugate. Detection of the conjugate required stabilization by reduction; otherwise, the reverse reaction occurred during tryptic digestion and analysis. Our findings represent a novel mechanism for peptide or protein glutathionylation involving a carbon-sulfur cross-link between oxidized Tyr and Cys. As with other electrophiles, the oxidized Tyr should undergo a similar reaction with Cys residues in proteins to give intramolecular or intermolecular protein cross-links. This mechanism could give rise to protein cross-linking in conditions of oxidative stress.

Amine substitution into sulfuric acid – ammonia clusters

Abstract. The substitution of ammonia by dimethylamine in sulfuric acid – ammonia – dimethylamine clusters was studied using a collision and evaporation dynamics model. Quantum chemical formation free energies were computed using B3LYP/CBSB7 for geometries and frequencies and RI-CC2/aug-cc-pV(T+d)Z for electronic energies. We first demonstrate the good performance of our method by a comparison with an experimental study investigating base substitution in positively charged clusters, and then continue by simulating base exchange in neutral clusters, which cannot be measured directly. Collisions of a dimethylamine molecule with an ammonia containing positively charged cluster result in the instantaneous evaporation of an ammonia molecule, while the dimethylamine molecule remains in the cluster. According to our simulations, a similar base exchange can take place in neutral clusters, although the overall process is more complicated. Neutral sulfuric acid – ammonia clusters are significantly less stable than their positively charged counterparts, resulting in a competition between cluster evaporation and base exchange.

Hemocompatibility of siRNA loaded dextran nanogels

Although the behavior of nanoscopic delivery systems in blood is an important parameter when contemplating their intravenous injection, this aspect is often poorly investigated when advancing from in vitro to in vivo experiments. In this paper, the behavior of siRNA loaded dextran nanogels in human plasma and blood is examined using fluorescence fluctuation spectroscopy, platelet aggregometry, flow cytometry and single particle tracking. Our results show that, in contrast to their negatively charged counterparts, positively charged siRNA loaded dextran nanogels cause platelet aggregation and show increased binding to human blood cells. Although PEGylating the nanogels did not have a significant effect on their interaction with blood cells, single particle tracking revealed that it is necessary to prevent their aggregation in human plasma. We therefore conclude that PEGylated negatively charged dextran nanogels are the most suited for further in vivo studies as they do not aggregate in human plasma and exhibit minimal interactions with blood cells.

Mass Spectrometry Analysis of 2-Nitrophenylhydrazine Carboxy Derivatized Peptides

Peptides with two or more basic residues, including those with post-translational modifications (PTMs), such as methylation and phosphorylation, can be highly hydrophilic and, therefore, are often difficult to be retained on a reversed-phase (RP) column. In addition, these highly hydrophilic peptides may carry two or more positive charges, which often fragment poorly upon collisionally activated dissociation (CAD), resulting in few sequence-specific ions. C-terminal rearrangement may also occur during CAD. Furthermore, some PTMs are labile and tend to be lost when subjected to CAD as is the case with phosphorylation on serine or threonine. To overcome the difficulties of separation, detection, and fragmentation of highly hydrophilic peptides, we report here the effect of carboxy group derivatization with 2-nitrophenylhydrazine (this strategy will be called NPHylation for simplicity). NPHylation significantly increases the hydrophobicity of the peptides, eliminates C-terminal rearrangement in all cases, and offers enhanced sensitivity in some cases. In addition, the CAD spectra of the resulting NPHylated peptides carry more sequence-specific ions due to significant reduction of sequence scrambling as observed for peptide EHAGVISVL. Furthermore, the different carboxy derivatives of this peptide undergo sequence scrambling to varying degrees, which clearly demonstrates that the C-terminus has a profound effect on peptide fragmentation. Finally, sequence scrambling is a charge dependent phenomenon, which affects CAD of doubly charged peptides far more than their singly charged counterparts.

Structural, Electronic, and Magnetic Properties of Neutral and Charged Transition Metal–Bis(dicarbollide) Sandwich Clusters

Structural, electronic, and magnetic properties of transition metal (TM)–bis(dicarbollide) (TM(Dcb)2; TM = Sc–Mn, Dcb = dicarbollide) sandwich clusters and their charged counterparts (TM(Dcb)2+, TM(Dcb)2–) are systematically investigated by using all electron density functional theory approach. All TM(Dcb)2 sandwich clusters are highly stable because of the formation of ionic–covalent bonding. The Ti(Dcb)2 is the most stable, the Sc- and V(Dcb)2 are intermediate, and the Cr- and Mn(Dcb)2 are the least stable. The magnetic moment of TM(Dcb)2 exhibits a clear element-dependent variation with 1 μB for Sc(Dcb)2 and 0 μB for Ti(Dcb)2 and with a linear increased trend by 1 μB from Ti(Dcb)2 to Mn(Dcb)2. This element-dependent magnetic behavior can be well understood by electron transfer as well as spin density distribution. We further reveal that charging can induce the rotation of the ligands in the Sc-, V-, Cr-, and Mn(Dcb)2 clusters, which makes them promising candidates for molecular motors.

Incorporation of Copper (II) Phtalocyanines as Model Dyes in Exponentially Growing Polyelectrolyte Multilayer Films: A Multiparametric Investigation

The incorporation of two different copper (II) phtalocyanines differing in their charged groups (sulfonato versus pyridino) in exponentially growing polyelectrolyte multilayer films (PEMs) made either from poly-l-lysine (PLL) and poly-l-glutamic acid (PGA) or from PLL and sodium hyaluronate (HA) has been investigated. The motivation of our study was to investigate the influence of different parameters on the ability of a molecule of constant size but differing in its charge to incorporate in and to be released from PEMs. The investigated parameters were: the nature of the last deposited polyelectrolyte, the ionic strength of the solution, and the nature of the polyanion present in the film (PGA versus HA). Complementarily, we have investigated the simultaneous or the consecutive incorporation of two anionic species, the anionic phtalocyanine and Ti(IV) (bislactato dihydroxyde) in (PLL−HA)n films: the incorporation of both species was possible only if they were put in competition during their incorporation in the film, but if the films were saturated by one of the species, the subsequent incorporation of the second one was not possible anymore. Overall our findings show that exponentially growing PEMs having a positive Donnan potential can be used to incorporate negatively charged copper phtalocyanines at very high concentrations, whereas the positively charged counterparts are totally excluded. In addition, our data show that the negatively charged phtalocyanines are not homogeneously incorporated through the whole thickness of the PEMs.

The influence of net charge and charge distribution on cellular uptake and cytosolic localization of arginine-rich peptides

Properties of different arginine-rich peptides, including net charge and charge distribution, were evaluated for their influence on surface binding, internalization, and intracellular localization. The peptides were radiolabeled and subsequently tested for surface binding and internalization in CHO-K1 cells. Subcellular fractionation assays were performed to separate the amount of peptides associated within vesicles from those inside the cytosol. Net neutral charged peptides, YGR6E6 and YG(RE)6, showed large decreases in both surface binding and cell uptake compared to their net positive charged counterparts, YGR6G6 and YG(RG)6. The peptides with clustered arginine residues, YGR6G6 and YGR6E6, exhibited significantly higher binding and uptake than those with alternating arginine and glycine/glutamate residues, YG(RG)6 and YG(RE)6. The intracellular distribution analysis for all of the peptides tested showed that, regardless of the net uptake, the arginine-rich peptides were preferentially localized in the cytosolic compartment of the cells. Both net positive charge and a clustered arginine sequence enhance the surface binding and internalization of peptides; however, the cytosolic versus vesicular intracellular distribution does not change. The results presented in this report provide important information regarding the specificity of binding and internalization of arginine-rich peptides, which is necessary for the future design of targeted drug delivery systems.

ChemInform Abstract: Neutralization-Reionization Mass Spectrometry Applied to Organometallic and Coordination Chemistry (Update: 1994-1998)

This review presents the results from the last 5 years on neutralization–reionization mass spectrometry (NRMS) studies of metal-containing ions. The results for silicon- and phosphorus-containing species are also discussed. The major aim of NRMS experiments is to generate (in the gas phase) neutrals that cannot be easily produced and/or detected in other experimental conditions. A variety of elusive complexes of coordinatively unsaturated and saturated metal(s), including important reaction intermediates, have been produced by collisional neutralization of their positively or negatively charged counterparts in the mass spectrometer. The detection of these species helps in understanding the mechanisms of reactions in the gas and condensed phases (interstellar chemistry, catalytic transformations, reactions on surfaces, etc.). The reviewed period of time has been characterized by the development of new experimental techniques. These techniques allow studying stability, electronic structure, and reactivity of selected molecules and radicals. The review provides a complete list of metal-, Si-, and P-containing ions that have been studied by using NRMS and related methods prior to 1999. © 1999 John Wiley & Sons, Inc., Mass Spec Rev 18: 87–118, 1999

The elliptic genus from split flows and Donaldson-Thomas invariants

We analyze a mixed ensemble of low charge D4-D2-D0 brane states on the quintic and show that these can be successfully enumerated using attractor flow tree techniques and Donaldson-Thomas invariants. In this low charge regime one needs to take into account worldsheet instanton corrections to the central charges, which is accomplished by making use of mirror symmetry. All the charges considered can be realized as fluxed D6-D2-D0 and anti-D6-D2-D0 pairs which we enumerate using DT invariants. Our procedure uses the low charge counterpart of the picture developed Denef and Moore. By establishing the existence of flow trees numerically and refining the index factorization scheme, we reproduce and improve some results obtained by Gaiotto, Strominger and Yin. Our results provide appealing evidence that the strong split flow tree conjecture holds and allows to compute exact results for an important sector of the theory. Our refined scheme for computing indices might shed some light on how to improve index computations for systems with larger charges.

MD-2-mediated Ionic Interactions between Lipid A and TLR4 Are Essential for Receptor Activation

Lipopolysaccharide (LPS) activates innate immune responses through TLR4.MD-2. LPS binds to the MD-2 hydrophobic pocket and bridges the dimerization of two TLR4.MD-2 complexes to activate intracellular signaling. However, exactly how lipid A, the endotoxic moiety of LPS, activates myeloid lineage cells remains unknown. Lipid IV(A), a tetra-acylated lipid A precursor, has been used widely as a model for lipid A activation. For unknown reasons, lipid IV(A) activates proinflammatory responses in rodent cells but inhibits the activity of LPS in human cells. Using stable TLR4-expressing cell lines and purified monomeric MD-2, as well as MD-2-deficient bone marrow-derived macrophages, we found that both mouse TLR4 and mouse MD-2 are required for lipid IV(A) activation. Computational studies suggested that unique ionic interactions exist between lipid IV(A) and TLR4 at the dimerization interface in the mouse complex only. The negatively charged 4'-phosphate on lipid IV(A) interacts with two positively charged residues on the opposing mouse, but not human, TLR4 (Lys(367) and Arg(434)) at the dimerization interface. When replaced with their negatively charged human counterparts Glu(369) and Gln(436), mouse TLR4 was no longer responsive to lipid IV(A). In contrast, human TLR4 gained lipid IV(A) responsiveness when ionic interactions were enabled by charge reversal at the dimerization interface, defining the basis of lipid IV(A) species specificity. Thus, using lipid IV(A) as a selective lipid A agonist, we successfully decoupled and coupled two sequential events required for intracellular signaling: receptor engagement and dimerization, underscoring the functional role of ionic interactions in receptor activation.

Thermal instability of Olivine-type LiMnPO 4 cathodes

The remarkable thermal stability of LiFePO 4 and its charged counterpart, FePO 4, have been instrumental in its commercialization as a lithium-ion battery cathode material. Despite the similarity in composition and structure, and despite the high thermal stability of the parent compound, LiMnPO 4, we find that the delithiated phase Li y MnPO 4 (which contains a small amount of residual lithium), is relatively unstable and reactive toward a lithium-ion electrolyte. The onset temperature for heat evolution in the presence of 1 M LiPF 6 in 1:1 ethylene carbonate/propylene carbonate is around 150 °C, and the total evolved heat is 884 J g −1, comparable to that produced under similar conditions by charged LiCoO 2 electrodes.

Influence of "Flexible" versus "Rigid" Nanoparticles on the Stability of Matrix Metalloproteinase-7

Matrix Metalloproteinase-7 (MMP-7) is invariably expressed in a variety of cancer cells, and exhibits the potentials to interact with differently charged macromolecular surfaces 1. To ascertain whether the nature of the charge carrying surfaces influences the stability as well as catalytic properties of the enzyme, we compared the effects of differently charged lipid (representative of "flexible") and gold ("rigid") nanoparticles. The experimental data revealed that the catalytic activity of MMP-7 is impaired only by the positively charged lipid nanoparticles, and it remains unaffected by their negatively charged or neutral counterparts. On the other hand, both positively and negatively charged gold nanoparticles impair the enzyme activity with nearly equal potency; no significant influence of neutral gold nanoparticles was noted on the enzyme activity. Unlike lipid nanoparticles, the charged gold nanoparticles mediated effects were found to be manifested partially via the inactivation of the enzyme. Arguments are presented that both the "rigidity" as well as the surface curvature of the lipid ("flexible") vis a vis the gold ("rigid") nanoparticles are responsible for eliciting differential influence on the catalytic activity as well as the stability of MMP-7.