The Contrasting Role of Water and Acid Within Organic Phase Amphiphile Aggregation

Hypothesis: Amphiphile self-assembly in non-polar media is often enhanced by polar co-solutes, as observed upon amphiphile mediated transport of water and acid into organic solution. Such co-extraction precludes understanding the individual roles of polar solutes upon self-assembly. Using this liquid-liquid extraction (LLE) system as a test-bed, we hypothesize that co-solute competition and hydrogen bond (HB) characteristics cause different size/shape distributions of assembled amphiphiles and alter self-assembly mechanisms in non-polar solvents. Experiments: Concentration dependent classical molecular dynamics simulation and intermolecular network analyses identified the correlating relationships between HB properties of H2O and HNO3 upon the aggregation of N,N,N,N-tetraoctyl-3-oxapentanediamide (TODGA), a prevalent LLE amphiphile extractant. Findings: Concentration dependent competition of hydrogen bonding fundamentally impacts amphiphile self-assembly in non-polar media. H2O bridges TODGA and enhances self-assembly, however as [H2O]org increases, preferential self-solvation leads to large (H2O)n clusters that cause TODGA clusters to sorb to the (H2O)n periphery and form extended aggregation. HNO3 restricts the (H2O)n size by disrupting the HB network. At large [H2O]org, HNO3 modulates TODGA self-assembly from extended to local aggregation. We attribute prior experimental observations to the role of water rather than co-extracted HNO3, thus providing valuable new insight into the means by which extractant aggregation can be tuned.

Photoluminescence and Electrochemiluminescence of Thermally Activated Delayed Fluorescence (TADF) Emitters Containing Diphenylphosphine Chalcogenide-Substituted Carbazole Donors

Aiming to develop efficient blue-emitting thermally activated delayed fluorescence (TADF) compounds, we have designed and synthesized derivatives of the well-known sky-blue emitter 2CzPN that contain electron-accepting phosphine chalcogenide groups to stabilize the HOMO level relative to the pristine compound, thus increasing the HOMO-LUMO gap and blue-shifting the emission wavelength. By cyclic voltammetry, photophysical data and quantum-chemical calculations, it was found that polar solvents and matrices validated the proposed concept, but these trends were not recovered in non-polar media. The suitability of these 2CzPN derivatives in polar matrices for optoelectronic applications was explored with electrochemiluminescence (ECL) by measuring emission delays, radical stability, emission stabilities, emission efficiencies and emission spectra. Some of the 2CzPN derivatives showed an unprecedented delayed onset of the ECL, and delayed rising time to the ECL maximum, as well as long ECL emission decay. All of these mentioned delay times suggest that these luminophores primarily emit via organic long-persistent electrochemiluminescence (OLECL) mechanisms. The derivatization of the donor groups of the emitters affected both the radical stability and the predominant emission mechanism, providing important insight into their potential as emitters in solid-state electroluminescent devices.

MANIFESTATION OF INTRAMOLECULAR VIBRATIONS IN THE FLUORESCENCE SPECTRA OF MOLECULES IN POLAR MEDIA

The effect of a low frequency intramolecular vibration on the nonstationary fluorescence spectrum of a molecule and the dynamics of the Stokes shift is analyzed in the framework of the nonstationary perturbation theory based on the operator of the interaction energy of the electric field of the exciting pump pulse with a dissolved molecule. Using a well-tested spin-boson model, which takes into account not only the reorganization of the relaxation polarization modes of the medium, but also intramolecular vibrations, an analytical expression for the time-resolved fluorescence signal is written, and the conditions under which the oscillations of the maximum of nonstationary fluorescence spectra can manifest themselves are analyzed. It is shown that the reorganization of the medium does not suppress the oscillations of the spectrum maximum.

Recent Advances of Taxol-Loaded Biocompatible Nanocarriers Embedded in Natural Polymer-Based Hydrogels

The discovery of paclitaxel (PTX) has been a milestone in anti-cancer therapy and has promoted the development and marketing of various formulations that have revolutionized the therapeutic approach towards several malignancies. Despite its peculiar anti-cancer activity, the physico-chemical properties of PTX compromise the administration of the compound in polar media. Because of this, since the development of the first Food and Drug Administration (FDA)-approved formulation (Taxol®), consistent efforts have been made to obtain suitable delivery systems able to preserve/increase PTX efficacy and to overcome the side effects correlated to the presence of some excipients. The exploitation of natural polymers as potential materials for drug delivery purposes has favored the modulation of the bioavailability and the pharmacokinetic profiles of the drug, and in this regard, several formulations have been developed that allow the controlled release of the active compound. In this mini-review, the recent advances concerning the design and applications of natural polymer-based hydrogels containing PTX-loaded biocompatible nanocarriers are discussed. The technological features of these formulations as well as the therapeutic outcome achieved following their administration will be described, demonstrating their potential role as innovative systems to be used in anti-tumor therapy.

Ionic effects on Supramolecular Hosts: Solvation and Counter-ion Binding in Polar Media

For the progress of synthetic supramolecular chemistry in aqueous solution the design of host molecules soluble in this medium is essential. A possible route is the introduction of ionic residues,...

Synthesis of well-defined diblock copolymer nano-objects by RAFT non-aqueous emulsion polymerization of N-(2-acryloyloxy)ethyl pyrrolidone in non-polar media

RAFT non-aqueous emulsion polymerization of N-(2-acryloyloxy)ethyl pyrrolidone in n-dodecane using a poly(stearyl methacrylate) precursor is used to prepare sterically-stabilized nanoparticles, which are evaluated as a putative Pickering emulsifier.

Ultrafast solid-liquid intercalation enabled by targeted microwave energy delivery

In chemical reactions, the breaking and formation of chemical bonds usually need external energy to overcome the activation barriers. Conventional energy delivery transfers energy from heating sources via various media, hence losing efficiency and inducing side reactions. In contrast, microwave (MW) heating is known to be highly energy efficient through dipole interaction with polar media, but how exactly it transmits energy to initiate chemical reactions has been unknown. Here, we report a rigorous determination of energy delivery mechanisms underlying MW-enabled rapid hydrothermal synthesis, by monitoring the structure and temperature of all the involved components as solid-liquid intercalation reaction occurs using in situ synchrotron techniques. We reveal a hitherto unknown direct energy transmission between MW irradiation source and the targeted reactants, leading to greatly reduced energy waste, and so the ultrafast kinetics at low temperature. These findings open up new horizons for designing material synthesis reactions of high efficiency and precision.