Steady-state electron paramagnetic resonance (EPR) spectroscopy is used to investigate the structure and stability of surfactant microbubbles made from distearoylphosphatidylcholine (DSPC) phospholipids and a polymeric stabilizer. The spin probe doxyl-5-stearic acid (5DSA) was incorporated into the phospholipid monolayer at an overall concentration of 3 × 10-7 M. The bubbles were characterized by optical microscopy and found to range in diameter from 0.6 to 10 μm. The EPR spectrum of the spin probe at room temperature exhibited slow motion and ordering. This behavior was simulated using the microscopic order-macroscopic disorder (MOMD) model through the EasySpin software package. During the course of 12 h in the EPR sample tube, a sharper fast-motion nitroxide spectrum appeared, indicating degradation of the bubbles over time. This is attributed to the typical process of microbubble degradation following gas exchange and interactions between the sample and capillary walls, leading to bubble collapse and the formation of a liquid phase with 5DSA incorporated into liposomes, micelles, or free molecules.

Organic molecules are being actively explored for use in logical devices, either as individual memory elements or as components embedded in small organic and polymeric materials. Conventional inorganic semiconductor devices are limited in terms of performance improvement owing to increased costs for device fabrication as well as physical limitations on minimum feature dimensions. Organic memory, however, is a possible substitute for both volatile and non-volatile memory devices. It has the advantages of facile tailoring through organic synthesis, simple device fabrication (even upon flexible substrates), and very low power consumption. Volatile organic memory is expected to be applied towards dynamic random access memory (DRAM), which typically requires a data refresh every few milliseconds, while non-volatile organic memory can be applied to read-only memory (ROM) and flash-type memory. Several types of organic and polymeric materials have been reported for this purpose, such as organic semiconductors, charge-transfer complexes (including redoxactive compounds), and metal-nanoparticle-dispersed thin films. Recently, a new type of organic memory has been added to this list, namely organic radical molecules (nitroxide radicals, NOC) that contain an unpaired electron that is capable of undergoing oxidation or reduction by applied bias voltages. Figure 1

In the present work, the sol-gel method was used to synthesize the Zn1-x-yErxCoyO system with different cations concentrations. The effect of dopant cations on the morphological, structural, and optical properties of particles, as well as their photocatalytic degradation of Yellow Eosin (YE) dye under UV irradiation, was investigated. X-ray diffraction (XRD) indicated excellent crystallinity of Wurtzite-like ZnO structures. Fourier Transform Infrared Spectroscopy showed characteristic absorption bands of ZnO. In addition, the dopant with different ions caused a decrease in the band gap energy compared to pure ZnO (3.16 eV), which is likely due to the defect levels formation. At higher Er3+ concentrations, the materials showed a slight reduction in the band gap (3.10 eV). However, for the samples with the highest Co2+ concentration, a lower band gap (3.0 eV) was observed, indicating that higher Co2+ concentrations favor the ZnO lattice distortion. In photocatalytic tests, the degradation rate of YE (similar to 48.7 %) was achieved using the ZEC23 sample (2 % of Er3+ and 3 % of Co2+), which is associated with the greater surface area found for this material. In a scavenger study, there was an increase in the rate of dye degradation (66.81 %) using ZEC23 when using an electron (e(-)) inhibitor reagent. In the presence of MetOH, a degradation rate of 44.0 % was observed, suggesting that the center dot OH radicals play a key role in the YE degradation.

The Feature highlights Electron Paramagnetic Resonance (EPR) spectroscopy as an indispensable tool to understand the excited state reactivity of organic molecules.

The study evaluates compatibility of stabilizers with dye doped liquid crystal (LC) scaffolds that are used in electronically dimmable materials. The photodegradation of the materials was investigated and suitable stabilizers were evaluated to slow the degradation process. Various types of benzotriazole-based stabilizers were evaluated for stabilizing the liquid crystals. Based on spin trapping experiments, radicals generated upon UV exposure is likely responsible for the degradation of the system. The radical generation is competitively inhibited by the addition of stabilizers.

Aryl-maleimides undergo a novel [2+4]-photodimerization instead of the expected [2+2]-photodimerization under both direct irradiation with visible light and under sensitized energy transfer conditions. This new excited state reactivity in aryl-maleimides is deciphered through photochemical, photophysical, and spectroscopic studies. The stereochemistry of the photodimer depends on the type of non-bonding interactions prevalent during photodimerization which is in turn dictated by the substituents on the maleimide ring. More importantly, the stereochemistry of the photodimer formed is complementary to the product observed under thermal conditions.

Our laboratory has a long-standing interest in the structure, reactivity, and dynamics of free radicals in both homogeneous and heterogeneous media.In this presentation, the basic tenets of steady-state and time-resolved (CW) electron paramagnetic resonance spectroscopy (SSEPR and TREPR) are explained, and their use in understanding the physical and chemical behavior of free radicals is outlined.Examples to be presented include the use of stable nitroxide spin probes to investigate the drying and curing of architectural coatings, and to probe the physical properties of structured (non-Newtonian) fluids at the molecular level.Chemical reactivity involving free radicals can be studied directly using TREPR, for example in the study of the mechanism for the light-struck flavor (so-called "skunking") of beer.Reactivity can also be investigated using spin trapping techniques.Two different trapping methods will be presented: nitrones can be used to confirm the mechanism of action of biocompatible polymer initiators, and the reaction of hindered amines with singlet oxygen can be used to quantify the kinetics and topology of such reactions in confined media.Finally, the application of EPR spectroscopy to study two aspects of polymer chain dynamics in liquid solution will be presented: 1) main chain radicals of acrylic polymers studied as a function of polymer structure and temperature, and 2) long-range radical-triplet state pair interactions in acrylic polymers.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The optoelectronic properties of colloidal semiconductor nanocrystals (NCs) can be manipulated by changing their geometric shape. The precise synthetic control over particle morphologies, however, has remained elusive. Conventional growth techniques rely on the kinetic assembly of atomic units, where supersaturation and precipitation processes can lead to a broad distribution of particle shapes. In this paper, we demonstrate that replacing atomic precursors with small-size nanocrystals as building blocks for larger colloids offers an easier, more predictive control over nanoparticle shape evolution. The reported growth strategy is illustrated via shape-selective syntheses of CdSe and CdS NC cubes, spheres, rods, as well as unprecedented "donut" and ring-like structures. Different particle morphologies were obtained through a thermodynamically driven growth, using a distinct combination of coordinating compounds that minimize the surface free energy. The demonstrated aggregative growth is explained using a thermodynamic model for interacting viscous colloids.

The spin dynamics of radical pairs from ion-pair complexes between viologen and tetraarylborate compounds have been investigated in the presence of microwave (μw) radiation, using steady-state electron paramagnetic resonance to follow the radical pair dynamics.

An investigation of spin and conformational dynamics in a series of symmetric Cu-Cu porphyrin dimer solutions is presented using electron paramagnetic resonance (EPR) spectroscopy. Previous spectral simulations focused on the isotropic exchange interaction (J(avg)) between the Cu centers. In this work, an additional line broadening parameter (J(mod)) is explored in detail via variable temperature X-band EPR in liquid solution for several different structures. The J(mod) phenomenon is due to fluctuations in the spin exchange interaction caused by conformational motion of the porphyrin planes. The J(mod) parameter scales with the inverse of the rotational barriers that determine the Boltzmann-weighted torsional angle distribution between neighboring porphyrin planes. Arrhenius plots allow for extraction of the activation energies for rotation, which are 5.77, 2.84, and 5.31 kJ/mol for ethyne-bridged (porphinato)copper(II)-(porphinato)copper(II), butadiyne-bridged (porphinato)copper(II)-(porphinato)copper(II), and ethyne-bridged (porphinato)copper(II)-(porphinato)zinc(II)-(porphinato)copper(II) complexes, respectively. DFT calculations of these torsional barriers match well with the experimental results. This is the first report of a J(mod) analysis within a highly anisotropic hyperfine field and demonstrates the utility of the theory for extraction of dynamic information.

The title compound, [Cu 2 (C 19 H 23 N 7 O)(C 2 H 3 O 2 ) 4 ] n , was obtained via reaction of copper(II) acetate with the coordinating ligand, 6-ethoxy- N 2 , N 4 -bis[2-(pyridin-2-yl)ethyl]-1,3,5-triazine-2,4-diamine. The crystallized product adopts the monoclinic P 2 1 / c space group. The metal core exhibits a paddle-wheel structure typical for dicopper tetraacetate units, with triazine and pyridyl nitrogen atoms from different ligands coordinating to the two axial positions of the paddle wheel in an asymmetric manner. This forms a coordination polymer with the segments of the polymer created by the c -glide of the P 2 1 / c setting of the space group. The resulting chains running along the c -axis direction are held together by intramolecular N—H...O hydrogen bonding. These chains are further packed by dispersion forces, producing an extended three-dimensional structure.

Antibiotic-resistant superbug bacteria represent a global health problem with no imminent solutions. Here we demonstrate that the combination (termed AB569) of acidified nitrite (A-NO2-) and Na2-EDTA (disodium ethylenediaminetetraacetic acid) inhibited all Gram-negative and Gram-positive bacteria tested. AB569 was also efficacious at killing the model organism Pseudomonas aeruginosa in biofilms and in a murine chronic lung infection model. AB569 was not toxic to human cell lines at bactericidal concentrations using a basic viability assay. RNA-Seq analyses upon treatment of P. aeruginosa with AB569 revealed a catastrophic loss of the ability to support core pathways encompassing DNA, RNA, protein, ATP biosynthesis, and iron metabolism. Electrochemical analyses elucidated that AB569 produced more stable SNO proteins, potentially explaining one mechanism of bacterial killing. Our data implicate that AB569 is a safe and effective means to kill pathogenic bacteria, suggesting that simple strategies could be applied with highly advantageous therapeutic/toxicity index ratios to pathogens associated with a myriad of periepithelial infections and related disease scenarios.

Understanding factors that underpin the signs and magnitudes of electron spin-spin couplings in biradicaloids, especially those that are integrated into highly delocalized electronic structures, promises to inform the design of molecular spintronic systems. Using steady-state and variable temperature electron paramagnetic resonance (EPR) spectroscopy, we examine spin dynamics in symmetric, strongly π-conjugated bis[(porphinato)copper] (bis[PCu]) systems and probe the roles played by atom-specific macrocycle spin density, porphyrin-to-porphyrin linkage topology, and orbital symmetry on the magnitudes of electronic spin-spin couplings over substantial Cu-Cu distances. These studies examine the following: (i) meso-to-meso-linked bis[PCu] systems having oligoyne spacers, (ii) meso-to-meso-bridged bis[PCu] arrays in which the PCu centers are separated by a single ethynyl unit or multiple 5,15-diethynyl(porphinato)zinc(II) units, and (iii) the corresponding β-to-β-bridged bis[PCu] structures. EPR data show that, for β-to-β-bridged systems and meso-to-meso-linked bis[PCu] structures having oligoyne spacers, a through σ-bond coupling mechanism controls the average exchange interaction (Javg). In contrast, PCu centers separated by a single ethynyl or multiple 5,15-diethynyl(porphinato)zinc(II) units display a phenomenological decay of ln[Javg] versus Cu-Cu σ-bond separation number of ∼0.115 per bond, half as large as for these other compositions, congruent with the importance of π-mediated spin-spin coupling. These disparities derive from effects that trace their origin to the nature of the macrocycle-macrocycle linkage topology and the relative energy of the Cu dx2-y2 singly occupied molecular orbital within the frontier orbital manifold of these electronically delocalized structures. This work provides insight into approaches to tune the extent of spin exchange interactions and distance-dependent electronic spin-spin coupling magnitudes in rigid, highly conjugated biradicaloids.

Time-resolved electron paramagnetic resonance (TREPR) spectroscopy has been used to study the proton coupled electron transfer (PCET) reaction between a Ruthenium complex (Ru(bpz)(bpy)2) and several substituted hydroquinones (HQ).

The power of chemistry to prepare new molecules and materials has driven the quest for new approaches to solve problems having global societal impact, such as in renewable energy, healthcare and information science. In the latter case, the intrinsic quantum nature of the electronic, nuclear and spin degrees of freedom in molecules offers intriguing new possibilities to advance the emerging field of quantum information science. In this Perspective, which resulted from discussions by the co-authors at a US Department of Energy workshop held in November 2018, we discuss how chemical systems and reactions can impact quantum computing, communication and sensing. Hierarchical molecular design and synthesis, from small molecules to supramolecular assemblies, combined with new spectroscopic probes of quantum coherence and theoretical modelling of complex systems, offer a broad range of possibilities to realize practical quantum information science applications.

The creation of ordered arrays of qubits that can be interfaced from the macroscopic world is an essential challenge for the development of quantum information science (QIS) currently being explored by chemists and physicists. Recently, porous metal-organic frameworks (MOFs) have arisen as a promising solution to this challenge as they allow for atomic-level spatial control of the molecular subunits that comprise their structures. To date, no organic qubit candidates have been installed in MOFs despite their structural variability and promise for creating systems with adjustable properties. With this in mind, we report the development of a pillared-paddlewheel-type MOF structure that contains 4,7-bis(2-(4-pyridyl)-ethynyl) isoindoline N-oxide and 1,4-bis(2-(4-pyridyl)-ethynyl)-benzene pillars that connect 2D sheets of 9,10-dicarboxytriptycene struts and Zn-2(CO2), secondary binding units. The design allows for the formation of ordered arrays of reorienting isoindoline nitroxide spin centers with variable concentrations through the use of mixed crystals containing the secondary 1,4-phenylene pillar. While solvent removal causes decomposition of the MOF, magnetometry measurements of the MOF containing only N-oxide pillars demonstrated magnetic interactions with changes in magnetic moment as a function of temperature between 150 and 5 K. Variable-temperature electron paramagnetic resonance (EPR) experiments show that the nitroxides couple to one another at distances as long as 2 nm, but act independently at distances of 10 nm or more. We also use a specially designed resonance microwave cavity to measure the face-dependent EPR spectra of the crystal, demonstrating that it has anisotropic interactions with impingent electromagnetic radiation.

Substituted triphenylamine (TPA) radical cations show great potential as oxidants and as spin-containing units in polymer magnets. Their properties can be further tuned by supramolecular assembly. Here, we examine how the properties of photogenerated radical cations, intrinsic to TPA macrocycles, are altered upon their self-assembly into one-dimensional columns. These macrocycles consist of two TPAs and two methylene ureas, which drive the assembly into porous organic materials. Advantageously, upon activation the crystals can undergo guest exchange in a single-crystal-to-single-crystal transformation generating a series of isoskeletal host-guest complexes whose properties can be directly compared. Photoinduced electron transfer, initiated using 365 nm light-emitting diodes, affords radicals at room temperature as observed by electron paramagnetic resonance (EPR) spectroscopy. The line shape of the EPR spectra and the quantity of radicals can be modulated by both polarity and heavy atom inclusion of the encapsulated guest. These photogenerated radicals are persistent, with half-lives between 1 and 7 d and display no degradation upon radical decay. Re-irradiation of the samples can restore the radical concentration back to a similar maximum concentration, a feature that is reproducible over several cycles. EPR simulations of a representative spectrum indicate two species, one containing two N hyperfine interactions and an additional broad signal with no resolvable hyperfine interaction. Intriguingly, TPA analogues without bromine substitution also exhibit similar quantities of photogenerated radicals, suggesting that supramolecular strategies can enable more flexibility in stable TPA radical structures. These studies will help guide the development of new photoactive materials.