The cationization of synthetic polymers in matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry: Investigations of the salt‐to‐analyte ratio

Matrix‐assisted laser desorption/ionization (MALDI) is a soft ionization technique that when used to analyze synthetic polymer analytes often requires the addition of a metal cationization agent (herein termed the “salt”). The choice of both the matrix and the cationization agent needs to be taken into account when considering the polymer under study; different polymers have shown different affinities toward different cationization agents, and their selectivity can change as the matrix changes. Salt‐to‐analyte ratio (S/A) plots are used in this work to investigate the effect of the quantity of cationization agent employed in the analysis of a poly (methylmethacrylate) (PMMA) analyte with different MALDI matrices. The point at which analyte signal stops increasing with the added cationization agent is termed the “cation saturation point,” and it was found to occur around a S/A of 1. When the analyte signal after this point remains constant, it is termed an “ideal case.” The “non‐ideal case” occurs when the analyte signal decreases after the cation saturation point. The amount of matrix present (measured as the matrix‐to‐analyte molar ratio, M/A) and the use of different counterions for the salt are also found to affect the intensity of the analyte signal. In non‐ideal cases, changes in the counterion or an increase in the M/A are found to increase the analyte signal, often converting an initially observed non‐ideal case into an ideal case. Several experiments attempting to uncover the reason for observation of the non‐ideal S/A behavior are also described.     

Nonreciprocal and directional wave propagation in a two-dimensional lattice with bilinear properties

Nonlinear Dynamics - A passive method of realizing nonreciprocal wave propagation in a two-dimensional (2D) lattice is proposed, using bilinear springs combined with the necessary spatial asymmetry...     

Electrical,structural, and thermal studies of antimony trioxide-doped poly(acrylic acid)-based composite polymer electrolytes

In this work, we investigate the electrical, structural, and thermal properties of composite polymer electrolytes (CPEs). Different mass fractions of antimony trioxide filler, Sb₂O₃, are added into poly(acrylic acid) (PAA)-based polymer electrolytes with N-lithiotrifluoromethane sulphonamide [LiN(SO₂CF₃)₂] (LiTFSI) as doping salt. Characteristics such as alternating current (AC)–impedance spectroscopy, attenuated total reflectance–Fourier transform infrared (ATR-FTIR), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) are analyzed. The highest ionic conductivity of (2.15?±?0.01)?×?10^?4 S cm^?1 is achieved at room temperature with addition of 6 wt% of fillers. The ionic transportation is further proven in a transference number study under DC polarization, whereas ATR-FTIR is employed to explore the complexation between PAA, LiTFSI, and Sb₂O₃. TGA reveals the improved thermal stability of CPEs. The glass transition temperature (T _g) is reduced upon addition of Sb₂O₃ as shown in DSC analysis.     

Confinement-Driven Photophysics in Hydrazone-Based Hierarchical Materials

Confinement-imposed photophysics was probed for novel stimuli-responsive hydrazone-based compounds demonstrating a conceptual difference in their behavior within 2D versus 3D porous matrices for the first time. The challenges associated with photoswitch isomerization arising from host interactions with photochromic compounds in 2D scaffolds could be overcome in 3D materials. Solution-like photoisomerization rate constants were realized for sterically demanding hydrazone derivatives in the solid state through their coordinative immobilization in 3D scaffolds. According to steady-state and time-resolved photophysical measurements and theoretical modeling, this approach provides access to hydrazone-based materials with fast photoisomerization kinetics in the solid state. Fast isomerization of integrated hydrazone derivatives allows for probing and tailoring resonance energy transfer (ET) processes as a function of excitation wavelength, providing a novel pathway for ET modulation.     

Uniform antibacterial cylindrical nanoparticles for enhancing the strength of nanocomposite hydrogels

Crystallization-driven self-assembly (CDSA) was employed for the preparation of monodisperse cationic cylindrical nanoparticles with controllable sizes, which were subsequently explored for their effect on antibacterial activity and the mechanical properties of nanocomposite hydrogels. Poly(ɛ-caprolactone)-block-poly(methyl methacrylate)-block-poly[2-(tert-butylamino) ethyl methacrylate] (PCL-b-PMMA-b-PTA) triblock copolymers were synthesized using combined ring-opening and RAFT polymerizations, and then self-assembled into polycationic cylindrical micelles with controllable lengths by epitaxial growth. The polycationic cylinders exhibited intrinsic cell-type-dependent antibacterial capabilities against gram-positive and gram-negative bacteria under physiological conditions, without quaternization or loading of any additional antibiotics. Furthermore, when the cylinders were combined into anionic alginate hydrogel networks, the mechanical response of the hydrogel composite was tunable and enhanced up to 51%, suggesting that cationic polymer fibers with controlled lengths are promising mimics of the fibrous structures in natural extracellular matrix to support scaffolds. Overall, this polymer fiber/hydrogel nanocomposite shows potential as an injectable antibacterial biomaterial, with possible application in implant materials as bacteriostatic agents or bactericides against various infections.     

Experimental Confirmation of a Predicted Porous Hydrogen-Bonded Organic Framework

Hydrogen-bonded organic frameworks (HOFs) with low densities and high porosities are rare and challenging to design because most molecules have a strong energetic preference for close packing. Crystal structure prediction (CSP) can rank the crystal packings available to an organic molecule based on their relative lattice energies. This has become a powerful tool for the a priori design of porous molecular crystals. Previously, we combined CSP with structure-property predictions to generate energy-structure-function (ESF) maps for a series of triptycene-based molecules with quinoxaline groups. From these ESF maps, triptycene trisquinoxalinedione (TH5) was predicted to form a previously unknown low-energy HOF (TH5-A) with a remarkably low density of 0.374 g cm⁻³ and three-dimensional (3D) pores. Here, we demonstrate the reliability of those ESF maps by discovering this TH5-A polymorph experimentally. This material has a high accessible surface area of 3,284 m² g⁻¹, as measured by nitrogen adsorption, making it one of the most porous HOFs reported to date.     

Enantioselective Rhodium-Catalyzed Pauson–Khand Reactions of 1,6-Chloroenynes with 1,1-Disubstituted Olefins

An enantioselective rhodium(I)-catalyzed Pauson–Khand reaction (PKR) using 1,6-chloroenynes that contain challenging 1,1-disubstituted olefins is described. In contrast to the previous studies with these types of substrates, which are only suitable for a single type of tether and alkyne substituent, the new approach results in a more expansive substrate scope, including carbon and heteroatom tethers with polar and non-polar substituents on the alkene. DFT calculations provide critical insight into the role of the halide, which pre-polarizes the alkyne to lower the barrier for metallacycle formation and provides the proper steric profile to promote a favorable enantiodetermining interaction between substrate and chiral diphosphine ligand. Hence, the chloroalkyne enables the efficient and enantioselective PKR with 1,6-enynes that contain challenging 1,1-disubstituted olefins, thereby representing a new paradigm for enantioselective reactions involving 1,6-enynes.     

Quantitative Nanoscale Secondary Ion Mass Spectrometry (NanoSIMS) Imaging of Individual Vesicles to Investigate the Relation between Fraction of Chemical Release and Vesicle Size

We used correlative transmission electron microscopy (TEM) and nanoscale secondary ion mass spectrometry (NanoSIMS) imaging to quantify the contents of subvesicular compartments, and to measure the partial release fraction of ¹³C-dopamine in cellular nanovesicles as a function of size. Three modes of exocytosis comprise full release, kiss-and-run, and partial release. The latter has been subject to scientific debate, despite a growing amount of supporting literature. We tailored culturing procedures to alter vesicle size and definitively show no size correlation with the fraction of partial release. In NanoSIMS images, vesicle content was indicated by the presence of isotopic dopamine, while vesicles which underwent partial release were identified by the presence of an ¹²⁷I-labelled drug, to which they were exposed during exocytosis allowing entry into the open vesicle prior to its closing again. Demonstration of similar partial release fractions indicates that this mode of exocytosis is predominant across a wide range of vesicle sizes.     

Spatially Directed Pyrolysis via Thermally Morphing Surface Adducts

Combustion is often difficult to spatially direct or tune associated kinetics—hence a run-away reaction. Coupling pyrolytic chemical transformation to mass transport and reaction rates (Damköhler number), however, we spatially directed ignition with concomitant switch from combustion to pyrolysis (low oxidant). A ‘surface-then-core’ order in ignition, with concomitant change in burning rate,is therefore established. Herein, alkysilanes grafted onto cellulose fibers are pyrolyzed into non-flammable SiO₂ terminating surface ignition propagation, hence stalling flame propagating. Sustaining high temperatures, however, triggers ignition in the bulk of the fibers but under restricted gas flow (oxidant and/or waste) hence significantly low rate of ignition propagation and pyrolysis compared to open flame (Liñán's equation). This leads to inside-out thermal degradation and, with felicitous choice of conditions, formation of graphitic tubes. Given the temperature dependence, imbibing fibers with an exothermically oxidizing synthon (MnCl₂) or a heat sink (KCl) abets or inhibits pyrolysis leading to tuneable wall thickness. We apply this approach to create magnetic, paramagnetic, or oxide containing carbon fibers. Given the surface sensitivity, we illustrate fabrication of nm- and μm-diameter tubes from appropriately sized fibers.     

A General Strategy Toward pH-Resistant Phenolic Fluorophores for High-Fidelity Sensing and Bioimaging Applications

Aryl alcohol-type or phenolic fluorophores offer diverse opportunities for developing bioimaging agents and fluorescence probes. Due to the inherently acidic hydroxyl functionality, phenolic fluorophores provide pH-dependent emission signals. Therefore, except for developing pH probes, the pH-dependent nature of phenolic fluorophores should be considered in bioimaging applications but has been neglected. Here we show that a simple structural remedy converts conventional phenolic fluorophores into pH-resistant derivatives, which also offer “medium-resistant” emission properties. The structural modification involves a single-step introduction of a hydrogen-bonding acceptor such as morpholine nearby the phenolic hydroxyl group, which also leads to emission bathochromic shift, increased Stokes shift, enhanced photo-stability and stronger emission for several dyes. The strategy greatly expands the current fluorophores’ repertoire for reliable bioimaging applications, as demonstrated here with ratiometric imaging of cells and tissues.