Endgroup determination of synthetic polymers by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

Electrospray ionization (ESI) was performed on a Fourier transform ion cyclotron resonance mass spectrometer for the endgroup and monomer mass determination of three poly(oxyalkylene)s in the mass range of 400–8000 Da. A combined use of the multiple charge states observed with ESI, leads to a threefold increase in accuracy of the endgroup and monomer determination. The improvement is attributed to the increased number of datapoints used for the regression procedure, yielding more accurate results. Endgroup masses are determined with a mass error better than 5 and 75 millimass units for the molecular weight range of 400–4200 and 6200–8000 Da, respectively. A mass error of better than 1 millimass unit was observed for all monomer mass determinations. With ESI, endgroup and monomer masses have been determined for poly(ethylene glycol) oligomers with a mass higher than 8000 Da. This is almost two times higher than observed with matrix-assisted laser desorption/ ionization on the same instrument.     

Facilitated phosphatidylserine (PS) flip-flop and thrombin activation using a synthetic PS scramblase

A cationic steroid with a hydrogen-bonding pocket that has an affinity for anionic phospholipid headgroups was synthesized and shown to strongly promote the translocation or flip-flop of a fluorescent, C(6)NBD-labeled phosphatidylserine probe (C(6)NBD-PS) across vesicle membranes. In addition, the synthetic PS scramblase increases the levels of endogenous PS on the surface of erythrocytes as monitored by flow cytometry analysis of annexin V-FITC binding. The PS scrambling effect is enhanced when the cells are pretreated with N-ethylmaleimide (NEM), an inhibitor of the endogenous aminophospholipid flippase. The combination of NEM and synthetic PS scramblase enhances the ability of erythrocytes to promote the conversion of prothrombin to thrombin by a factor of 4. An analogous cationic steroid with a smaller binding pocket has no measurable PS translocation activity, a result that is attributed to its inability to sufficiently diminish the hydrophilicity of the multiply charged PS headgroup.     

A comparison of protoporphyrin IX and protoporphyrin IX dimethyl ester as a photosensitizer in poorly differentiated human nasopharyngeal carcinoma cells

Protoporphyrin IX dimethyl ester (PME), a dimethyl esterification of protoporphyrin IX (PpIX), exhibits higher intracellular uptake into NPC/CNE2 cells, a poorly differentiated human nasopharyngeal carcinoma, than does PpIX. Phototoxicity studies reveal PME to be a more potent photosensitizer than is PpIX, at the early and late incubation time points. Correlating phototoxicity with subcellular localization indicates that PME is a more potent photosensitizer when its primary target of photodamage is mitochondria. Also, additional targeting of lysosome enhances phototoxicity.     

A Local Realistic Theory for Mermin’s EPR Experiment

As another counterexample to prevalent conventional belief, a realistic theory, which is local and reproduces all the probabilistic predictions of quantum theory, is presented for Mermin’s version of the Einstein-Podolsky-Rosen (EPR) experiment.     

Dynamics of Adsorbate Islands with Nanoscale Resolution

Surface catalytic processes produce, under certain conditions, small clusters of adsorbed atoms or groups, called islands which, after they have been formed, move as individual entities. Here we consider the catalytic reduction of NO with hydrogen on platinum. (i) Using video field ion microscopy, we observe the dynamic motion of small hydroxyl islands on the Pt(001) plane; despite changes in their morphology, the islands dimensions are confined to values corresponding to 10 to 30 Pt atoms suggesting cooperative effects to be in operation. (ii) We construct an automaton (or lattice Monte-Carlo) model on the basis of a set of elementary processes governing the microscopic dynamics. The agreement between the simulation results and the experimental observations suggests a possible mechanism for the formation and dynamics of hydroxyl islands.     

Agglomeration,colloidal stability,and magnetic separation of magnetic nanoparticles: collective influences on environmental engineering applications

Magnetic nanoparticles (MNPs) which exhibit magnetic and catalytic bifunctionalities have been widely accepted as one of the most promising nanoagents used in water purification processes. However, due to the magnetic dipole-dipole interaction, MNPs can easily lose their colloidal stability and tend to agglomerate. Thus, it is necessary to enhance their colloidal stability in order to maintain the desired high specific surface area. Meanwhile, in order to successfully utilize MNPs for environmental engineering applications, an effective magnetic separation technology has to be developed. This step is to ensure the MNPs that have been used for pollutant removal can be fully reharvested back. Unfortunately, it was recently highlighted that there exists a conflicting role between colloidal stability and magnetic separability of the MNPs, whereby the more colloidally stable the particle is, the harder for it to be magnetically separated. In other words, attaining a win-win scenario in which the MNPs possess both good colloidal stability and fast magnetic separation rate becomes challenging. Such phenomenon has to be thoroughly understood as the colloidal stability and the magnetic separability of MNPs play a pivotal role on affecting their effective implementation in water purification processes. Accordingly, it is the aim of this paper to provide reviews on (i) the colloidal stability and (ii) the magnetic separation of MNPs, as well as to provide insights on (iii) their conflicting relationship based on recent research findings.

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Graphical abstract Interrelationship of agglomeration, colloidal stability, and magnetic separability of nanoparticles

     

Enhanced Electroreduction of Carbon Dioxide to Methanol Using Zinc Dendrites Pulse‐Deposited on Silver Foam

The electrocatalytic CO₂ reduction reaction (CO₂RR) can dynamise the carbon cycle by lowering anthropogenic CO₂ emissions and sustainably producing valuable fuels and chemical feedstocks. Methanol is arguably the most desirable C₁ product of CO₂RR, although it typically forms in negligible amounts. In our search for efficient methanol‐producing CO₂RR catalysts, we have engineered Ag‐Zn catalysts by pulse‐depositing Zn dendrites onto Ag foams (PD‐Zn/Ag foam). By themselves, Zn and Ag cannot effectively reduce CO₂ to CH₃OH, while their alloys produce CH₃OH with Faradaic efficiencies of approximately 1 %. Interestingly, with nanostructuring PD‐Zn/Ag foam reduces CO₂ to CH₃OH with Faradaic efficiency and current density values reaching as high as 10.5 % and ?2.7 mA cm^?2, respectively. Control experiments and DFT calculations pinpoint strained undercoordinated Zn atoms as the active sites for CO₂RR to CH₃OH in a reaction pathway mediated by adsorbed CO and formaldehyde. Surprisingly, the stability of the *CHO intermediate does not influence the activity.     

Selective small molecule peptidomimetic ligands of TrkC and TrkA receptors afford discrete or complete neurotrophic activities

We designed a minilibrary of 55 small molecule peptidomimetics based on beta-turns of the neurotrophin growth factor polypeptides neurotrophin-3 (NT-3) and nerve growth factor (NGF). Direct binding, binding competition, and biological screens identified agonistic ligands of the ectodomain of the neurotrophin receptors TrkC and TrkA. Agonism is intrinsic to the peptidomimetic ligand (in the absence of neurotrophins), and/or can also be detected as potentiation of neurotrophin action. Remarkably, some peptidomimetics afford both neurotrophic activities of cell survival and neuronal differentiation, while others afford discrete signals leading to either survival or differentiation. The high rate of hits identified suggests that focused minilibraries may be desirable for developing bioactive ligands of cell surface receptors. Small, selective, proteolytically stable ligands with defined biological activity may have therapeutic potential.     

Investigation of possible structures of silicon nanotubes via density-functional tight-binding molecular dynamics simulations and ab initio calculations

We show, computationally, that single-walled silicon nanotubes (SiNTs) can adopt a number of distorted tubular structures, representing respective local energy minima, depending on the theory used and the initial models adopted. In particular, "gearlike" structures containing alternating sp(3)-like and sp(2)-like silicon local configurations have been found to be the dominant structural form for SiNTs via density-functional tight-binding molecular dynamics simulations (followed by geometrical optimization using Hartree-Fock or density function theory) at moderate temperatures (below 100 K). The gearlike structures of SiNTs deviate considerably from, and are energetically more stable than, the smooth-walled tubes (the silicon analogues of single-walled carbon nanotubes). They are, however, energetically less favorable than the "string-bean-like" SiNT structures previously derived from semiempirical molecular orbital calculations. The energetics and the structures of gearlike SiNTs are shown to depend primarily on the diameter of the tube, irrespective of the type (zigzag, armchair, or chiral). In contrast, the energy gap is very sensitive to both the diameter and the type of the nanotube.