Switching between blebbing and lamellipodia depends on the degree of non-muscle myosin II activity.

Cells can adopt both mesenchymal and amoeboid modes of migration through membrane protrusive activities, namely formation of lamellipodia and blebbing. How the molecular players control the transition between lamellipodia and blebs is yet to be explored. Here, we show that addition of the ROCK inhibitor Y27632 or low doses of blebbistatin, an inhibitor of non-muscle myosin II (NMII) ATPase activity and filament partitioning, induces blebbing to lamellipodia conversion (BLC), whereas addition of low doses of ML7, an inhibitor of myosin light chain kinase (MLCK), induces lamellipodia to blebbing conversion (LBC) in human MDA-MB-231 cells. Similarly, siRNA-mediated knockdown of ROCK and MLCK induces BLC and LBC, respectively. Interestingly, both blebs and lamellipodia membrane protrusions are able to maintain the ratio of phosphorylated to unphosphorylated regulatory light chain at cortices when MLCK and ROCK, respectively, are inhibited either pharmacologically or genetically, suggesting that MLCK and ROCK activities are interlinked in BLC and LBC. Such BLCs and LBCs are also inducible in other cell lines, including MCF7 and MCF10A. These studies reveal that the relative activity of ROCK and MLCK, which controls both the ATPase activity and filament-forming property of NMII, is a determining factor in whether a cell exhibits blebbing or lamellipodia.

Atomistic Simulations of Hydrated Sulfonated Polybenzophenone Block Copolymer Membranes.

We present a classical molecular dynamics simulations study on the nanostructures of the sulfonated polybenzophenone (SPK) block copolymer membranes at 300 K and 353 K. The results of the radial distribution function (RDF) show that the interactions of the sulfonate groups of the membrane with the hydronium ions are more significant than those of water due to the strong electrostatic attraction over the hydrogen bonding. However, the effect of temperatures on the RDF profile seems insignificant. Furthermore, the spatial distribution function (SDF) portrays that the sulfonate groups of the hydrophilic components are preferential binding sites for hydronium ions against the hydrophobic counterpart of the SPK membrane. The mobility of the H3 O+ ions at 300 K and 353 K is two (or three) times lower than that of Nafion/Aciplex. However, the diffusion coefficients for water molecules closely agree with Nafion/Aciplex. This study suggests that water clusters are more localized around the sulfonate groups in the SPK membranes. Thus, the molecular modeling study of SPK block copolymer membranes is warranted to design better-performing membrane electrolytes.

Insights into geometries, stabilities, electronic structures, reactivity descriptors, and magnetic properties of bimetallic Nim Cun-m (m = 1, 2; n = 3-13) clusters: Comparison with pure copper clusters.

A long-range corrected density functional theory (LC-DFT) was applied to study the geometric structures, relative stabilities, electronic structures, reactivity descriptors and magnetic properties of the bimetallic NiCun-1 and Ni2 Cun-2 (n = 3-13) clusters, obtained by doping one or two Ni atoms to the lowest energy structures of Cun , followed by geometry optimizations. The optimized geometries revealed that the lowest energy structures of the NiCun-1 and Ni2 Cun-2 clusters favor the Ni atom(s) situated at the most highly coordinated position of the host copper clusters. The averaged binding energy, the fragmentation energies and the second-order energy differences signified that the Ni doped clusters can continue to gain an energy during the growth process. The electronic structures revealed that the highest occupied molecular orbital and the lowest unoccupied molecular orbital energies of the LC-DFT are reliable and can be used to predict the vertical ionization potential and the vertical electron affinity of the systems. The reactivity descriptors such as the chemical potential, chemical hardness and electrophilic power, and the reactivity principle such as the minimum polarizability principle are operative for characterizing and rationalizing the electronic structures of these clusters. Moreover, doping of Ni atoms into the copper clusters carry most of the total spin magnetic moment. © 2018 Wiley Periodicals, Inc.

On low-lying excited states of extended nanographenes.

Low-lying excited states of planarly extended nanographenes are investigated using the long-range corrected (LC) density functional theory (DFT) and the spin-flip (SF) time-dependent density functional theory (TDDFT) by exploring the long-range exchange and double-excitation correlation effects on the excitation energies, band gaps, and exciton binding energies. Optimizing the geometries of the nanographenes indicates that the long-range exchange interaction significantly improves the CC bond lengths and amplify their bond length alternations with overall shortening the bond lengths. The calculated TDDFT excitation energies show that long-range exchange interaction is crucial to provide accurate excitation energies of small nanographenes and dominate the exciton binding energies in the excited states of nanographenes. It is, however, also found that the present long-range correction may cause the overestimation of the excitation energy for the infinitely wide graphene due to the discrepancy between the calculated band gaps and vertical ionization potential (IP) minus electron affinity (EA) values. Contrasting to the long-range exchange effects, the SF-TDDFT calculations show that the double-excitation correlation effects are negligible in the low-lying excitations of nanographenes, although this effect is large in the lowest excitation of benzene molecule. It is, therefore, concluded that long-range exchange interactions should be incorporated in TDDFT calculations to quantitatively investigate the excited states of graphenes, although TDDFT using a present LC functional may provide a considerable excitation energy for the infinitely wide graphene mainly due to the discrepancy between the calculated band gaps and IP-EA values. © 2017 Wiley Periodicals, Inc.

Relationship between orbital energy gaps and excitation energies for long-chain systems.

The difference between the excitation energies and corresponding orbital energy gaps, the exciton binding energy, is investigated based on time-dependent (TD) density functional theory (DFT) for long-chain systems: all-trans polyacetylenes and linear oligoacenes. The optimized geometries of these systems indicate that bond length alternations significantly depend on long-range exchange interactions. In TDDFT formalism, the exciton binding energy comes from the two-electron interactions between occupied and unoccupied orbitals through the Coulomb-exchange-correlation integral kernels. TDDFT calculations show that the exciton binding energy is significant when long-range exchange interactions are involved. Spin-flip (SF) TDDFT calculations are then carried out to clarify double-excitation effects in these excitation energies. The calculated SF-TDDFT results indicate that double-excitation effects significantly contribute to the excitations of long-chain systems. The discrepancies between the vertical ionization potential minus electron affinity (IP-EA) values and the HOMO-LUMO excitation energies are also evaluated for the infinitely long polyacetylene and oligoacene using the least-square fits to estimate the exciton binding energy of infinitely long systems. It is found that long-range exchange interactions are required to give the exciton binding energy of the infinitely long systems. Consequently, it is concluded that long-range exchange interactions neglected in many DFT calculations play a crucial role in the exciton binding energies of long-chain systems, while double-excitation correlation effects are also significant to hold the energy balance of the excitations. © 2016 Wiley Periodicals, Inc.

Reactivity index based on orbital energies.

This study shows that the chemical reactivities depend on the orbital energy gaps contributing to the reactions. In the process where a reaction only makes progress through charge transfer with the minimal structural transformation of the reactant, the orbital energy gap gradient (OEGG) between the electron-donating and electron-accepting orbitals is proven to be very low. Using this relation, a normalized reaction diagram is constructed by plotting the normalized orbital energy gap with respect to the normalized intrinsic reaction coordinate. Application of this reaction diagram to 43 fundamental reactions showed that the majority of the forward reactions provide small OEGGs in the initial stages, and therefore, the initial processes of the forward reactions are supposed to proceed only through charge transfer. Conversely, more than 60% of the backward reactions are found to give large OEGGs implying very slow reactions associated with considerable structural transformations. Focusing on the anti-activation-energy reactions, in which the forward reactions have higher barriers than those of the backward ones, most of these reactions are shown to give large OEGGs for the backward reactions. It is also found that the reactions providing large OEGGs in the forward directions inconsistent with the reaction rate constants are classified into SN 2, symmetric, and methyl radical reactions. Interestingly, several large-OEGG reactions are experimentally established to get around the optimum pathways. This indicates that the reactions can take significantly different pathways from the optimum ones provided no charge transfer proceeds spontaneously without the structural transformations of the reactants.

Reaction energetics on long-range corrected density functional theory: Diels-Alder reactions.

The possibility of quantitative reaction analysis on the orbital energies of long-range corrected density functional theory (LC-DFT) is presented. First, we calculated the Diels-Alder reaction enthalpies that have been poorly given by conventional functionals including B3LYP functional. As a result, it is found that the long-range correction drastically improves the reaction enthalpies. The barrier height energies were also computed for these reactions. Consequently, we found that dispersion correlation correction is also crucial to give accurate barrier height energies. It is, therefore, concluded that both long-range exchange interactions and dispersion correlations are essentially required in conventional functionals to investigate Diels-Alder reactions quantitatively. After confirming that LC-DFT accurately reproduces the orbital energies of the reactant and product molecules of the Diels-Alder reactions, the global hardness responses, the halves of highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy gaps, along the intrinsic reaction coordinates of two Diels-Alder reactions were computed. We noticed that LC-DFT results satisfy the maximum hardness rule for overall reaction paths while conventional functionals violate this rule on the reaction pathways. Furthermore, our results also show that the HOMO-LUMO gap variations are close to the reaction enthalpies for these Diels-Alder reactions. Based on these results, we foresee quantitative reaction analysis on the orbital energies.

Hydration, Prediction of the pK a, and Infrared Spectroscopic Study of Sulfonated Polybenzophenone (SPK) Block-Copolymer Hydrocarbon Membranes and Comparisons with Nafion.

We used long-range-corrected density functional theory to investigate the hydration, pK a values, and harmonic vibrational spectroscopy of sulfonated polybenzophenone (SPK) block-copolymer hydrocarbon membranes to ascertain the reasons why this gives comparable or higher proton conductivities against Nafion over a wide range of humidity. It was found that a minimum of three water molecules are required for proton dissociation in both membranes. From natural population analysis, it was noticed that the proton dissociation of SPK membranes is nearly comparable to Nafion at relatively low water content. Next, we explored the applicability of the appropriate treatment for pK a and proton's energy with a benchmark set (AKB) scheme to compute the pK a values for these membranes. These results indicate that the proton dissociative abilities of sulfonic acid groups of the SPK membrane are higher than those of Nafion. This could be one of the reasons for the SPK membrane to show higher proton conductivities at high relative humidity. Furthermore, the effect of hydration on the proton conductivity of membranes illustrates that asymmetric stretching of the SO3 - mode was in agreement with Nafion ones but opposite trends were found in the case of symmetric stretching of the SO3 - mode upon hydration.

Investigation of ethynylfurans using the electron propagator theory.

The first eleven vertical ionization energies of mono and diethynylfurans have been calculated using various electron propagator decouplings. Among all ethynylfurans, the pi-orbital interactions between ethynyl and furan moieties are found to be strongest in 2,5-diethynylfuran. Oxygen atom of the furan ring and carbon atoms of ethyne group play important role in stabilization/destabilization of HOMO/LUMO of ethynylfurans. Our results for energetic stability, dipole moment, HOMO-LUMO gap, ionization energies, and electron affinity indicate that 2-ethynylfuran among monoethynylfurans and 2,5-diethynylfuran among ethynylfurans may be useful precursors for the preparation of conducting polymers.

Nonmuscle myosin IIA and IIB differentially modulate migration and alter gene expression in primary mouse tumorigenic cells.

Though many cancers are known to show up-regulation of nonmuscle myosin (NM) IIA and IIB, the mechanism by which NMIIs aid in cancer development remains unexplored. Here we demonstrate that tumor-generating, fibroblast-like cells isolated from 3-methylcholanthrene (3MC)-induced murine tumor exhibit distinct phospho-dependent localization of NMIIA and NMIIB at the perinuclear area and tip of the filopodia and affect cell migration differentially. While NMIIA-KD affects protrusion dynamics and increases cell directionality, NMIIB-KD lowers migration speed and increases filopodial branching. Strategically located NMIIs at the perinuclear area colocalize with the linker of nucleoskeleton and cytoskeleton (LINC) protein Nesprin2 and maintain the integrity of the nuclear-actin cap. Interestingly, knockdown of NMIIs results in altered expression of genes involved in epithelial-to-mesenchymal transition, angiogenesis, and cellular senescence. NMIIB-KD cells display down-regulation of Gsc and Serpinb2, which is strikingly similar to Nesprin2-KD cells as assessed by quantitative PCR analysis. Further gene network analysis predicts that NMIIA and NMIIB may act on similar pathways but through different regulators. Concomitantly, knockdown of NMIIA or NMIIB lowers the growth rate and tumor volume of 3MC-induced tumor in vivo. Altogether, these results open a new window to further investigate the effect of LINC-associated perinuclear actomyosin complex on mechanoresponsive gene expression in the growing tumor.

Theoretical Investigation of the H2O2-Induced Degradation Mechanism of Hydrated Nafion Membrane via Ether-Linkage Dissociation.

A H2O2-induced degradation mechanism is presented for the hydrated Nafion membrane proceeding through the dissociation of the ether linkages of the side chains. Although the durability of proton-exchange membrane fuel cells clearly depends on the degradation rate of the membrane, typically Nafion, the degradation mechanism still has not been resolved. It has often been assumed that the principal mode of degradation involves OH• radicals; in contrast, we show here that a H2O2-induced degradation mechanism is more likely. On the basis of state-of-the-art theoretical calculations and detailed comparison with experimental results, we present such a mechanism for the hydrated Nafion membrane, proceeding through the dissociation of the ether linkage of the side chains, with a relatively low activation energy. In this mechanism, (H2O)λHO3S-CF2-CF2-O-O-H (λ is the hydration number) is obtained as a key degradation fragment. Possible subsequent decomposition-reaction mechanisms are also elucidated for this fragment. The calculated vibrational spectra for the intermediates and products proposed in these mechanisms were found to be consistent with the experimental IR spectra. Further consideration of this H2O2-mediated degradation mechanism could greatly facilitate the search for ways to combat membrane degradation.

Differential role of nonmuscle myosin II isoforms during blebbing of MCF-7 cells.

Bleb formation has been correlated with nonmuscle myosin II (NM-II) activity. Whether three isoforms of NM-II (NM-IIA, -IIB and -IIC) have the same or differential roles in bleb formation is not well understood. Here we report that ectopically expressed, GFP-tagged NM-II isoforms exhibit different types of membrane protrusions, such as multiple blebs, lamellipodia, combinations of both, or absence of any such protrusions in MCF-7 cells. Quantification suggests that 50% of NM-IIA-GFP-, 29% of NM-IIB-GFP-, and 19% of NM-IIC1-GFP-expressing MCF-7 cells show multiple bleb formation, compared with 36% of cells expressing GFP alone. Of interest, NM-IIB has an almost 50% lower rate of dissociation from actin filament than NM-IIA and -IIC1 as determined by FRET analysis both at cell and bleb cortices. We induced bleb formation by disruption of the cortex and found that all three NM-II-GFP isoforms can reappear and form filaments but to different degrees in the growing bleb. NM-IIB-GFP can form filaments in blebs in 41% of NM-IIB-GFP-expressing cells, whereas filaments form in only 12 and 3% of cells expressing NM-IIA-GFP and NM-IIC1-GFP, respectively. These studies suggest that NM-II isoforms have differential roles in the bleb life cycle.

Tautomeric forms of azolide anions: vertical electron detachment energies and Dyson orbitals.

Several decouplings of the electron propagator, including the relatively new P3+ approximation for the self-energy, have been used to calculate vertical electron detachment energies of tautomeric forms of closed-shell, pentagonal, aromatic anions in which ring carbons without bonds to hydrogens appear. This study extends previous work in which the most stable forms of anionic, five-member rings with one to five nitrogens were considered. Whereas the lowest electron detachment energies sometimes are assigned by Koopmans's theorem results to pi orbital vacancies, electron propagator calculations always obtain sigma orbital vacancies for the ground states of the doublet radicals. Higher electron detachment energies that correspond to excited doublets with pi vacancies also are presented. The predicted transition energies are in good agreement with low-intensity peaks in recent anion photoelectron spectra that have been assigned to less stable, tautomeric forms of these anions.