Acid-Enhanced Photoiniferter Polymerization under Visible Light.

Photoiniferter (PI) is a promising polymerization methodology, often used to overcome restrictions posed by thermal reversible addition-fragmentation chain-transfer (RAFT) polymerization. However, in the overwhelming majority of reports, high energy UV irradiation is required to effectively trigger photolysis of RAFT agents and facilitate the polymerization, significantly limiting its potential, scope, and applicability. Although visible light PI has emerged as a highly attractive alternative, most current approaches are limited to the synthesis of lower molecular weight polymers (i.

Specific Adsorption of Alkaline Cations Enhances CO-CO Coupling in CO Electroreduction.

Electrolyte alkaline cations can significantly modulate the reaction selectivity of electrochemical CO reduction (eCOR), enhancing the yield of the valuable multicarbon (C) chemical feedstocks. However, the mechanism underlying this cation effect on the C-C coupling remains unclear. Herein, by performing constant-potential AIMD simulations, we studied the dynamic behavior of interfacial K ions over Cu surfaces during C-C coupling and the origin of the cation effect.

Investigating Competing Inner- and Outer-Sphere Electron-Transfer Pathways in Copper Photoredox-Catalyzed Atom-Transfer Radical Additions: Closing the Cycle.

This integrated computational and experimental study comprehensively examines the viability of competing inner-sphere electron transfer (ISET) and outer-sphere electron transfer (OSET) processes in [Cu(dap)]-mediated atom-transfer radical additions (ATRA) of olefins and CFSOCl that can deliver both R-SOCl and R-Cl products. Five sterically- and electronically-varied representative alkenes were selected from which to explore and reconcile a range of experimentally observed outcomes. Findings are consistent with photoexcited [Cu(dap)] initiating photoelectron transfer via ISET and the subsequent regeneration of the oxidized catalyst via ISET in the ground state to close the catalytic cycle and liberate products.

Maximizing Photon-to-Electron Conversion for Atom Efficient Photoredox Catalysis.

Photoredox catalysis is a powerful tool to access challenging and diverse syntheses. Absorption of visible light forms the excited state catalyst (*PC) but photons may be wasted if one of several unproductive pathways occur. Facile dissociation of the charge-separated encounter complex [PC:D], also known as (solvent) cage escape, is required for productive chemistry and directly governs availability of the critical PC intermediate.

Radical versus Non-Radical Reactivity in - and -Quinonedimethides and Implications for Cycloaddition Mechanisms.

The latent singlet diradical character of the parent -quinonedimethide (-QDM), as revealed by valence bond calculations, is demonstrated experimentally by trapping with the kinetically stable free radical TEMPO at room temperature. In the absence of TEMPO, the main pathway for decomposition at ambient temperature is not (as previously proposed in the literature) a radical reaction but instead a concerted Diels-Alder dimerization, which through ωB97X-D/aug-cc-pVTZ/SMD//M06-2X-D3/6-31+G(d,p)/SMD calculations is shown to proceed through an ambimodal bispericyclic transition state. The predominantly non-radical reactivity of -QDM at room temperature differs from that of its isomeric -quinonedimethide (-QDM) congener, which self-reacts through radical pathways.

Electrochemically Generated Carbocations in Organic Synthesis.

This Minireview examines a selection of case studies that showcase distinctive and enabling electrochemical approaches that have allowed for the generation and reaction of carbocation intermediates under mild conditions. Particular emphasis is placed on the progress that has been made in this area of organic synthesis and polymer chemistry over the past decade.

2-Cyanopropan-2-yl versus 1-Cyanocyclohex-1-yl Leaving Group: Comparing Reactivities of Symmetrical Trithiocarbonates in RAFT Polymerization.

This study introduces bis(1-cyanocyclohex-1-yl)trithiocarbonate (TTC-bCCH) as a novel trithiocarbonate chain transfer agent and compares its reactivity with the previously described bis(2-cyanopropan-2-yl)trithiocarbonate (TTC-bCP) for the reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene (St), n-butyl acrylate (nBA), and methyl methacrylate (MMA). Significant findings include the effective control of M and low dispersities from the onset of polymerization of St and nBA showing swift addition-fragmentation kinetics, leading to similar behaviors between the two RAFT agents. In contrast, a fourfold decrease of the chain transfer constant to MMA is established for TTC-bCCH over TTC-bCP.

Short Formal Syntheses of Lycorine and Congeners Using a 5/6 Radical Cyclization Sequence.

Here, we report a practical route to medicinally interesting lycorine congeners alongside formal syntheses of various lycorine-type natural products, including lycorine itself. The efficiency of our strategy derives from a back-to-back 5/6 radical cyclization sequence, which we systematically studied both experimentally and computationally. The results of our work will facilitate future development of urgently needed antiviral therapeutics based on lycorine.

Solvation Shifts the Band-Edge Position of Colloidal Quantum Dots by Nearly 1 eV.

The optoelectronic properties of colloidal quantum dots (cQDs) depend critically on the absolute energy of the conduction and valence band edges. It is well known these band-edge energies are sensitive to the ligands on the cQD surface, but it is much less clear how they depend on other experimental conditions, like solvation. Here, we experimentally determine the band-edge positions of thin films of PbS and ZnO cQDs via spectroelectrochemical measurements.

Photochemical Povarov-type Reactions: Electron Donor-Acceptor Photoactivation by Visible Light.

This report investigates the mechanism of photochemical Povarov-type reactions of ,-dialkylanilines and maleimides in polar solvents (DMF or dioxane) in the presence of light. Fundamental aspects of the electron donor-acceptor (EDA) photoactivation pathway proposed to underpin this chemistry are examined through integrated experimental and computational studies. This approach provided evidence supporting the involvement of an EDA complex in facilitating this chemistry via a reaction mechanism that does not involve a triplet manifold.

Utilising a Proton-Responsive 1,8-Naphthyridine Ligand for the Synthesis of Bimetallic Palladium and Platinum Complexes.

We present four proton-responsive palladium and platinum complexes, [MCl ( PONNHO)] (M=Pd, Pt; R= Pr, Bu) synthesised by complexation of PdCl or PtCl (COD) with the 1,8-naphthyridine ligand PONNHO. Deprotonation of [MCl ( PONNHO)] switches ligand coordination from mono- to dinucleating, offering a synthetic pathway to bimetallic Pd and Pt complexes [M Cl ( PONNO) ]. Two-electron reduction gives planar M -M complexes [M ( PONNO) ] (M=Pd, Pt) containing a metal-metal bond.

A one-pot reduction route to bimetallic manganese 1,8-naphthyridine complexes.

Reaction of the dinucleating ligand 2,7-bis(6-methyl-2-pyridyl)-1,8-naphthyridine (L) with the Mn and Mn precursors MnBr(CO) and MnCl resulted in the formation of the monometallic complexes [MnBr(CO)(L)] (1) and [MnCl(L)] (3). In both cases, formation of bimetallic manganese complexes could be achieved by reduction with KC, yielding the carbonyl-bridged complex [Mn(CO)(L)] (2) and the helicate complex [Mn(L)] (4), respectively. EPR results demonstrate that 4 represents a novel, weakly antiferromagnetically coupled homovalent dimer ( = -0.

Impact of a short online course on the accuracy of non-ophthalmic diabetic retinopathy graders in recognising glaucomatous optic nerves in Vietnam.

Purpose: To test an online training course for non-ophthalmic diabetic retinopathy (DR) graders for recognition of glaucomatous optic nerves in Vietnam.

Methods: This was an uncontrolled, experimental, before-and-after study in which 43 non-ophthalmic DR graders underwent baseline testing on a standard image set, completed a self-paced, online training course and were retested using the same photographs presented randomly. Twenty-nine local ophthalmologists completed the same test without the training course.

Air Tolerant Cadiot-Chodkiewicz and Sonogashira Cross-Couplings.

Cadiot-Chodkiewicz cross-couplings generate an unsymmetric buta-1,3-diyne by way of a Cu(I)-catalyzed coupling between a terminal alkyne and a 1-haloalkyne. Despite their widespread use, Cadiot-Chodkiewicz reactions are plagued by the generation of symmetric buta-1,3-diyne side products, formed through competing: (a) formal reductive homo-coupling of the 1-haloalkyne and (b) oxidative (Glaser-Hay/Eglinton) homo-coupling of the terminal alkyne. To overcome this issue, a large excess of one of the two reacting alkynes is commonly deployed, and difficult separations of cross- and homo-coupled products are often encountered.

High Electric Fields on Water Microdroplets Catalyze Spontaneous and Fast Reactions in Halogen-Bond Complexes.

The use of external electric fields as green and efficient catalysts in synthetic chemistry has recently received significant attention for their ability to deliver remarkable control of reaction selectivity and acceleration of reaction rates. Technically, methods of generating high electric fields in the range of 1-10 V/nm are limited, as in-vacuo techniques have obvious scalability issues. The spontaneous high fields at various interfaces promise to solve this problem.

Oxidative Addition and β-Hydride Elimination by a Macrocyclic Dinickel Complex: Observing Bimetallic Elementary Reactions.

The dinickel(I) complex Ni ( PONNOPONNO), featuring a planar macrocyclic diphosphoranide ligand PONNOPONNO, offers a unique architectural platform for observing bimetallic elementary reactions. Oxidative addition reactions of alkyl halides produce dinickel(II) complexes of the type Ni (μ-R)(μ-X)( PONNOPONNO). However, when R=Et β-hydride elimination is observed to form a dinickel monohydride, with the rate dependent on the nature of X.

Deep Learning for Localized Detection of Optic Disc Hemorrhages.

Purpose: To develop an automated deep learning system for detecting the presence and location of disc hemorrhages in optic disc photographs.

Design: Development and testing of a deep learning algorithm.

Methods: Optic disc photos (597 images with at least 1 disc hemorrhage and 1075 images without any disc hemorrhage from 1562 eyes) from 5 institutions were classified by expert graders based on the presence or absence of disc hemorrhage.

Computational and Experimental Confirmation of the Diradical Character of -Quinonedimethide.

The ground-state structure of the parent -quinonedimethide (-QDM) molecule is generally represented in its closed shell form, i.e., as a cyclic, nonaromatic, through-conjugated/cross-conjugated hybrid comprising four C═C bonds.

Lewis Acid-Induced Reversible Disproportionation of TEMPO Enables Aqueous Aluminum Radical Batteries.

Nitroxide radicals, such as 2,2,6,6-tetramethylpiperidyl-1-oxy (TEMPO), are typical organic electrode materials featuring high redox potentials and fast electrochemical kinetics and have been widely used as cathode materials in multivalent metal-ion batteries. However, TEMPO and its derivatives have not been used in emerging rechargeable aluminum-ion batteries (AIBs) due to the known disproportionation and possible degradation of nitroxide radicals in acidic conditions. In this study, the (electro)chemical behavior of TEMPO is examined in organic and aqueous Lewis acid electrolytes.

Separating Convective from Diffusive Mass Transport Mechanisms in Ionic Liquids by Redox Pro-fluorescence Microscopy.

The study of electrochemical reactivity requires analytical techniques capable of probing the diffusion of reactants and products to and from electrified interfaces. Information on diffusion coefficients is often obtained indirectly by modeling current transients and cyclic voltammetry data, but such measurements lack spatial resolution and are accurate only if mass transport by convection is negligible. Detecting and accounting for adventitious convection in viscous and wet solvents, such as ionic liquids, is technically challenging.

Electrochemical Synthesis of Poly(trisulfides).

With increasing interest in high sulfur content polymers, there is a need to develop new methods for their synthesis that feature improved safety and control of structure. In this report, electrochemically initiated ring-opening polymerization of norbornene-based cyclic trisulfide monomers delivered well-defined, linear poly(trisulfides), which were solution processable. Electrochemistry provided a controlled initiation step that obviates the need for hazardous chemical initiators.

Accurate Prediction of Three-Body Intermolecular Interactions via Electron Deformation Density-Based Machine Learning.

This work extends the electron deformation density-based descriptor, originally developed in the electron deformation density-based interaction energy machine learning (EDDIE-ML) algorithm to predict dimer interaction energies, to the prediction of three-body interactions in trimers. Using a sequential learning process to select the training data, the resulting Gaussian process regression (GPR) model predicts the three-body interaction energy within 0.2 kcal mol of the SRS-MP2/cc-pVTZ reference values for the 3B69 and S22-3 trimer data sets.