Chemical warfare simulant-responsive polymer nanocomposites: Synthesis and evaluation

Nanomaterials that undergo a physical change upon chemical warfare agent (CWA) exposure can potentially be used in detectors to warn soldiers of their presence or in fabrics to provide on‐demand protection. In this study, hybrid nanoparticles (NPs) were prepared by grafting a CWA‐responsive polymer from a silicon dioxide (SiO₂) surface using ring opening metathesis polymerization; the covalent functionalization of the polymers on the NP surface was confirmed by gel permeation chromatography, dynamic light scattering, and transmission electron microscopy analysis. The polymer‐grafted SiO₂ NPs were found to undergo a pronounced decrease (approximately 200 nm) in their hydrodynamic radius upon exposure to CWA simulants trifluoroacetic acid and diethyl chlorophosphate in toluene. This decrease in hydrodynamic radius is attributed to the electrophile‐mediated ionization of the triarylmethanol responsive unit and represents a rare example of polycation formation leading to polymer chain collapse. We have ascribed this ionization‐induced collapse to the formation of a favorable stacking interaction between the planar triarylcations. These studies have important implications for the development of breathable fabrics that can provide on‐demand protection for soldiers in combat situations. Keywords: nanocomposites; stimuli-responsive; ROMP; organophosphates; triarylmethanolsDefense Threat Reduction Agency (DTRA) (Contract BA12PHM123

Catalytic strategies for asymmetric nucleophilic fluorination using a latent HF source: development and mechanistic investigations

Fluorinated organic molecules display broad utility as pharmaceuticals, radiotracers, performance materials, and agrochemicals. In particular, the development of new synthetic methods for C–F bond formation furthers the discovery of bioactive small molecules and PET tracers necessary to study, diagnose, and treat human disease. While catalytic asymmetric methods using electrophilic "F+" equivalents have been identified, complementary strategies for enantioselective C–F bond formation using abundant, inexpensive nucleophilic fluoride sources are scarce. We have developed catalytic methods for the synthesis of β-fluoroamines and alcohols using benzoyl fluoride as a soluble, latent source of fluoride anion. The combination of benzoyl fluoride and an alcohol generates HF in situ, allowing catalyst-controlled C–F bond formation. Under Lewis base catalysis, an amine–HF reagent is generated that shows excellent reactivity and broad substrate scope in aziridine hydrofluorination. The use of a chiral auxiliary enables the practical asymmetric synthesis of enantioenriched fluoroamines. This latent HF source has also been applied to the asymmetric catalytic ring opening of epoxides to provide β-fluoroalcohols. Both the desymmetrization of meso epoxides and the kinetic resolution of terminal epoxides were achieved under mild conditions. A dual-catalyst system, consisting of a chiral Lewis acid and an amine, was found to be optimal; cooperative effects between the cocatalysts were observed. Detailed mechanistic studies have shed light on the origin of cooperativity and enabled synthetic improvements. Additionally, these studies revealed that the active nucleophilic species is a chiral transition-metal fluoride formed from the Lewis acid catalyst and the latent HF source. To demonstrate the utility of this nucleophilic fluoride source in other asymmetric transformations, we developed an enantioselective heterobimetallic fluoride ring opening of aziridines

Synthesis of Miktoarm Branched Conjugated Copolymers by ROMPing In and Out

Architecture represents an underutilized yet promising control element in polymer design due to the challenging synthesis of compositionally varied branched copolymers. We report the one-pot synthesis of miktoarm branched polymers by ring-opening metathesis polymerization. In this work, we graft to and from telechelic poly(3-hexylthiophene), which is end-capped by oxime click chemistry, using various norbornene monomers. The self-assembly of the resulting miktoarm Hshaped conjugated polymers is studied in solution and in the solid state. A dual stimuli-responsive miktoarm polymer is prepared which displays pH-switchable lower critical solution temperature and fluorescence.United States. Army Research Office. Institute for Soldier Nanotechnologies (Contract W911NF-13-D-0001)United States. Air Force Office of Scientific Research (Grant (FA9550-14-1-0226)National Institutes of Health (U.S.). Ruth L. Kirschstein National Research Service Award (Fellowships Award GM106550

Optical visualization and quantification of enzyme activity using dynamic droplet lenses

In this paper, we describe an approach to measuring enzyme activity based on the reconfiguration of complex emulsions. Changes in the morphology of these complex emulsions, driven by enzyme-responsive surfactants, modulate the transmission of light through a sample. Through this method we demonstrate how simple photodetector measurements may be used to monitor enzyme kinetics. This approach is validated by quantitative measurements of enzyme activity for three different classes of enzymes (amylase, lipase, and sulfatase), relying on two distinct mechanisms for coupling droplet morphology to enzyme activity (host–guest interactions with uncaging and molecular cleavage).Massachusetts Institute of Technology. Institute for Soldier NanotechnologiesNational Institutes of Health (U.S.). Ruth L. Kirschstein National Research Service Award (Award GM106550)Tianjin University (Internship Program

Dynamically reconfigurable complex emulsions via tunable interfacial tensions

Emulsification is a powerful, well-known technique for mixing and dispersing immiscible components within a continuous liquid phase. Consequently, emulsions are central components of medicine, food and performance materials. Complex emulsions, including Janus droplets (that is, droplets with faces of differing chemistries) and multiple emulsions, are of increasing importance in pharmaceuticals and medical diagnostics, in the fabrication of microparticles and capsules for food, in chemical separations, in cosmetics, and in dynamic optics. Because complex emulsion properties and functions are related to the droplet geometry and composition, the development of rapid, simple fabrication approaches allowing precise control over the droplets’ physical and chemical characteristics is critical. Significant advances in the fabrication of complex emulsions have been made using a number of procedures, ranging from large-scale, less precise techniques that give compositional heterogeneity using high-shear mixers and membranes, to small-volume but more precise microfluidic methods. However, such approaches have yet to create droplet morphologies that can be controllably altered after emulsification. Reconfigurable complex liquids potentially have great utility as dynamically tunable materials. Here we describe an approach to the one-step fabrication of three- and four-phase complex emulsions with highly controllable and reconfigurable morphologies. The fabrication makes use of the temperature-sensitive miscibility of hydrocarbon, silicone and fluorocarbon liquids, and is applied to both the microfluidic and the scalable batch production of complex droplets. We demonstrate that droplet geometries can be alternated between encapsulated and Janus configurations by varying the interfacial tensions using hydrocarbon and fluorinated surfactants including stimuli-responsive and cleavable surfactants. This yields a generalizable strategy for the fabrication of multiphase emulsions with controllably reconfigurable morphologies and the potential to create a wide range of responsive materials.Eni S.p.A. (Firm) (Eni-MIT Alliance Solar Frontiers Program)Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (Contract W911NF-13-D-0001)National Institutes of Health (U.S.). Ruth L. Kirschstein National Research Service Fellowship (EB014682)National Institutes of Health (U.S.). Ruth L. Kirschstein National Research Service Fellowship (GM106550

Reconfigurable and responsive droplet-based compound micro-lenses

Micro-scale optical components play a crucial role in imaging and display technology, biosensing, beam shaping, optical switching, wavefront-analysis, and device miniaturization. Herein, we demonstrate liquid compound micro-lenses with dynamically tunable focal lengths. We employ bi-phase emulsion droplets fabricated from immiscible hydrocarbon and fluorocarbon liquids to form responsive micro-lenses that can be reconfigured to focus or scatter light, form real or virtual images, and display variable focal lengths. Experimental demonstrations of dynamic refractive control are complemented by theoretical analysis and wave-optical modelling. Additionally, we provide evidence of the micro-lenses’ functionality for two potential applications—integral micro-scale imaging devices and light field display technology—thereby demonstrating both the fundamental characteristics and the promising opportunities for fluid-based dynamic refractive micro-scale compound lenses.National Science Foundation (U.S.) (DMREF-1533985)Natural Sciences and Engineering Research Council of Canada (Graduate Fellowship)National Science Foundation (U.S.) (Grant DMR-1410718)Max Planck Society for the Advancement of ScienceMassachusetts Institute of Technology. Department of Mechanical Engineerin