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Metal-phenolic networks (MPNs) are amorphous materials that can be used to engineer functional films and particles. A fundamental understanding of the heat-driven structural reorganization of MPNs can offer opportunities to rationally tune their properties (ie/i.ig/i., size, permeability, wettability, hydrophobicity) for applications such as drug delivery, sensing, and tissue engineering. Herein, we use a combination of single-molecule localization microscopy, theoretical electronic structure calculations, and all-atom molecular dynamics simulations to demonstrate that MPN plasticity is governed by both the inherent flexibility of the metal (FesupIII/sup)-phenolic coordination center and the conformational elasticity of the phenolic building blocks (tannic acid, TA) that make up the metal-organic coordination complex. Thermal treatment (heating to 150 °C) of the flexible TA/FesupIII/supnetworks induces a considerable increase in the number of aromatic π-π interactions formed among TA moieties and leads to the formation of hydrophobic domains. In the case of MPN capsules, 15 min of heating induces structural rearrangements that cause the capsules to shrink (from ∼4 to ∼3 μm), resulting in a thicker (3-fold), less porous, and higher protein (ie.g./i, bovine serum albumin) affinity MPN shell. In contrast, when a simple polyphenol such as gallic acid is complexed with FesupIII/supto form MPNs, rigid materials that are insensitive to temperature changes are obtained, and negligible structural rearrangement is observed upon heating. These findings are expected to facilitate the rational engineering of versatile TA-based MPN materials with tunable physiochemical properties for diverse applications.

Coordination states of metal-organic materials are known to dictate their physicochemical properties and applications in various fields. However, understanding and controlling coordination sites in metal-organic systems is challenging. Herein, we report the synthesis of site-selective coordinated metal-phenolic networks (MPNs) using flavonoids as coordination modulators. The site-selective coordination was systematically investigated experimentally and computationally using ligands with one, two, and multiple different coordination sites. Tuning the multimodal Fe coordination with catechol, carbonyl, and hydroxyl groups within the MPNs enabled the facile engineering of diverse physicochemical properties including size, selective permeability (20-2000 kDa), and pH-dependent degradability. This study expands our understanding of metal-phenolic chemistry and provides new routes for the rational design of structurally tailorable coordination-based materials.

Although inorganic and metallic materials have demonstrated great success in energy storage, increasing concerns on resource depletion and potential environmental consequences associated with ore mining and processing have driven the search for sustainable and environmental-friendly alternatives. Organic redox molecules exhibiting multi-electron storage and fast electron transfer kinetics are ideal compounds for sustainable high-energy storage devices with high-power output. Nitroxide radical polymers (NRPs) are the representative materials that could achieve these functions. Nevertheless, most NRP batteries only demonstrated one-electron storage via the redox couple (I) NO+/NO˙. Two-electron storage through successive redox couple (I) NO+/NO˙ and (II) NO˙/NO− has been observed rarely only under specific electrode and electrolyte conditions with no mechanism presented. Here, we realize two-electron storage in a NRP/Li battery by using polyether-based NRP gel with a common battery condition from which we unravel electron transfer kinetics and the ion transport process in the battery condition. Electrochemical analysis reveals a ten-fold higher heterogeneous electron transfer rate constant (k0) for the redox couple (I) NO+/NO˙ in comparison to (II) NO˙/NO−, which agree with the value from Ab initio calculations and the Marcus–Hush theory's prediction. We find out that the high reorganization energy and slow diffusion of Li+ for redox couple NO˙/NO− are major causes for its sluggish or absent electron transfer process, which could be improved by altering the chemical composition of NRPs. Our findings imply how the molecular design of polymer electrode materials facilitates high-energy and high-power density storage.

Computational chemistry at the G3(MP2)-RAD//M06-2X/6-31+G(d,p)//SMD level of theory was used to study the oxidation of a test set of methyl adducts of nitroxide radicals and methyl adducts of Blatter's radical, a Kuhn verdazyl and two oxo-verdazyls. The barriers and the reaction energies of the S

Photoactivation of tetrazoles to form nitrile imines primed for 1,3-dipolar cycloaddition reactions is of widespread utility in chemistry. In contrast, the corresponding thermal reactions usually possess prohibitively high barriers and have garnered significantly less attention. Here, computational chemistry at the M06-2X/6-31+G(d,p) level of theory with SMD solvent corrections is used to show that these thermal activation barriers can be significantly reduced through the use of nonconjugated charged functional groups (CFGs). For 2,5-dimethyl-tetrazole, a positive CFG on the

Controlled degradation of polypropylene (PP) is used industrially to improve the properties of crude PP. While this degradation is traditionally initiated by organic peroxides, N-acyloxyamines are ...

Oriented electrostatic fields can exert catalytic effects upon both the kinetics and the thermodynamics of chemical reactions; however, the vast majority of studies thus far have focused upon groun...

Atom transfer radical polymerization (ATRP) is the most commonly utilized technique in controlled radical polymerization. However, the identification of more active catalysts could further increase its scope, both for polymerization and small-molecule synthesis more generally. To this end, a series of novel ligands were designed on the basis of two strategies: replacing nitrogen-based ligands with their phosphorus equivalents and rigidifying the ligand cap of nitrogen-based ligands so as to enforce short Cu-cap distances. Each ligand was assessed using accurate computational chemistry, which was used to compute the thermodynamics and, in selected cases, kinetics of an ATRP reaction with a model methyl methacrylate propagating radical. In principle, the use of phosphorus ligand caps was found to be a powerful strategy for increasing catalyst activity. Unfortunately, in practice, speciation issues sacrificed much of their advantage. In contrast, cap rigidification increases the activity of nitrogen-based ligands, well beyond existing ATRP ligands such as TPMANMe2. The effectiveness of these ligands was further demonstrated for hard-to-activate initiating systems based on ethylene, vinyl chloride, and vinyl acetate polymerization. Several of these improved ligands are synthetically accessible, with rigid piperidine or quinuclidine analogues of TPMANMe2 possessing improved thermodynamic and kinetic activity by 2 to 3 orders of magnitude.

Respiring mitochondria establish a proton gradient across the mitochondrial inner membrane (MIM) that is used to generate ATP. Protein-independent mitochondrial uncouplers collapse the proton gradient and disrupt ATP production by shuttling protons back across the MIM in a protonophoric cycle. Continued cycling relies on the formation of MIM-permeable anionic species that can return to the intermembrane space after deprotonation in the mitochondrial matrix. Previously described protonophores contain acidic groups that are part of delocalised π-systems that provide large surfaces for charge delocalisation and facilitate anion permeation across the MIM. Here we present a new class of protonophoric uncoupler based on aryl-urea substituted fatty acids in which an acidic group and a π-system are separated by a long alkyl chain. The aryl-urea group in these molecules acts as a synthetic anion receptor that forms intermolecular hydrogen bonds with the fatty acid carboxylate after deprotonation. Dispersal of the negative charge across the aryl-urea system produces lipophilic dimeric complexes that can permeate the MIM and facilitate repeated cycling. Substitution of the aryl-urea group with lipophilic electron withdrawing groups is critical to complex lipophilicity and uncoupling activity. The aryl-urea substituted fatty acids represent the first biological example of mitochondrial uncoupling mediated by the interaction of a fatty acid and an anion receptor moiety, via self-assembly., A new mitochondrial uncoupler that forms membrane permeable dimers through interactions of remote acidic and anion receptor groups.

Bench- and air-stable 1-methoxy-2,2,6,6-tetramethylpiperidine (TEMPO-Me) is relatively unreactive at ambient temperature in the absence of an electrochemical stimulus. In this report, we demonstrate that the one-electron electrochemical oxidation of TEMPO-Me produces a powerful electrophilic methylating agent in situ. Our computational and experimental studies are consistent with methylation proceeding via a SN2 mechanism, with a strength comparable to the trimethyloxonium cation. A protocol is developed for the electrochemical methylation of aromatic acids using TEMPO-Me.

We thank the Australian Research Council and the Institute of Advanced Studies for financial support. MLC acknowledges an ARC Laureate Fellowship, support from the ARC Centre of Excellence for Electromaterials Science and generous allocations of supercomputing time on the National Facility of the Australian National Computational Infrastructu

In this work, we show that the nature of the supporting electrolyte and solvent can dramatically alter the outcome of the electrochemically mediated cleavage of alkoxyamines. A combination of cycli...

A test set of 14 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO)-based alkoxyamines was studied via a combination of cyclic voltammetry and accurate quantum chemistry to assess the effect of substitue...

The authors gratefully acknowledge generous allocations of supercomputing time on the National Facility of the National Computational Infrastructure (NCI), and financial support from the Australian Research Council (ARC).

Predicting the conversion and selectivity of a photochemical experiment is a conceptually different challenge compared to thermally induced reactivity. Photochemical transformations do not currently have the same level of generalized analytical treatment due to the nature of light interaction with a photoreactive substrate. Herein, we bridge this critical gap by introducing a framework for the quantitative prediction of the time-dependent progress of photoreactions via common LEDs. A wavelength and concentration dependent reaction quantum yield map of a model photoligation, i.e., the reaction of thioether o-methylbenzaldehydes via o-quinodimethanes with N-ethylmaleimide, is initially determined with a tunable laser system. Combined with experimental parameters, the data are employed to predict LED-light induced conversion through a wavelength-resolved numerical simulation. The model is validated with experiments at varied wavelengths. Importantly, a second algorithm allows the assessment of competing photoreactions and enables the facile design of λ-orthogonal ligation systems based on substituted o-methylbenzaldehydes., Predicting the conversion and selectivity of a photochemical reactions is challenging. Here, the authors introduce a framework for the quantitative prediction of the time-dependent progress of a photoligation reaction and predict LED-light induced conversion through a wavelength-resolved numerical simulation.

Computational tools for modelling nitroxide radical chemistry are outlined and illustrated through a series of case studies. Different types of application raise different problems. Herein we outline and assess the computational methods available for modelling high-spin systems, predicting EPR hyperfine coupling constants, redox potentials, alkoxyamine dissociation equilibria and photochemical processes. While high-spin systems and excited states are best modelled with complex multireference methods incorporating static and dynamic correlation, there is a growing family of more economical approaches that can often achieve an acceptable level of accuracy. Redox potentials and alkoxyamine dissociation equilibria require only single reference methods, albeit at a high level of theory, but the accurate treatment of solvation remains an ongoing challenge. Modelling EPR requires a range of specialist techniques and basis sets to accurately capture core correlation. Through the case studies presented here we not only show that accurate and useful quantitative predictions are possible, but introduce a wide range of complementary tools for enhancing our qualitative understanding of structure–reactivity trends.

Controlled degradation of polypropylene (PP) is used industrially to improve the properties of crude PP. While this degradation is traditionally initiated by organic peroxides

Oriented electrostatic fields can exert catalytic effects upon both the kinetics and the thermodynamics of chemical reactions; however, the vast majority of studies thus far have focused upon ground-state chemistry and rarely consider any more than a single class of reaction. In the present study, we first use density functional theory (DFT) calculations to clarify the mechanism of CO

Organic electrosynthesis is going through its renaissance but its scope in surface science as a tool to introduce specific molecular signatures at an electrode/electrolyte interface is under explored. Here, we have investigated an electrochemical approach to generate in situ surface-tethered and highly-reactive carbocations. We have covalently attached an alkoxyamine derivative on an Si(100) electrode and used an anodic bias stimulus to trigger its fragmentation into a diffusive nitroxide (TEMPO) and a surface-confined carbocation. As a proof-of-principle we have used this reactive intermediate to trap a nucleophile dissolved in the electrolyte. The nucleophile was ferrocenemethanol and its presence and surface concentration after its reaction with the carbocation were assessed by cyclic voltammetry. The work expands the repertoire of available electrosynthetic methods and could in principle lay the foundation for a new form of electrochemical lithography.

Alkoxyamines are heat-labile molecules, widely used as an in situ source of nitroxides in polymer and materials sciences. Here we show that the one-electron oxidation of an alkoxyamine leads to a cation radical intermediate that even at room temperature rapidly fragments, releasing a nitroxide and carbocation. Digital simulations of experimental voltammetry and current-time transients suggest that the unimolecular decomposition which yields the "unmasked" nitroxide (TEMPO) is exceedingly rapid and irreversible. High-level quantum computations indicate that the collapse of the alkoxyamine cation radical is likely to yield a neutral nitroxide radical and a secondary phenylethyl cation. However, this fragmentation is predicted to be slow and energetically very unfavorable. To attain qualitative agreement between the experimental kinetics and computational modeling for this fragmentation step, the explicit electrostatic environment within the double layer must be accounted for. Single-molecule break-junction experiments in a scanning tunneling microscope using solvent of low dielectric (STM-BJ technique) corroborate the role played by electrostatic forces on the lysis of the alkoxyamine C-ON bond. This work highlights the electrostatic aspects played by charged species in a chemical step that follows an electrochemical reaction, defines the magnitude of this catalytic effect by looking at an independent electrical technique in non-electrolyte systems (STM-BJ), and suggests a redox on/off switch to guide the cleavage of alkoxyamines at an electrified interface.

The oxidation potential of a test set of 21 nitroxide radicals, including a number of novel compounds, has been studied experimentally in acetonitrile and correlated with theoretical calculations. It was found that both Hammett constants (σp) of the substituents on the nitroxide radicals and hyperfine splitting constants of the respective nitrogen atoms (αN) were well correlated to their experimental oxidation potentials. Theoretical calculations, carried out at the G3(MP2,CC)(+)//M06-2X/6-31+G(d,p) level of theory with PCM solvation corrections, were shown to reproduce experiments to within a mean absolute deviation of 33 mV, with a maximum deviation of 64 mV. The oxidation potentials of the nitroxides examined varied over 400 mV, depending on ring size and substitution. This considerable variation can be rationalised by the ability of various substituents to electrostatically stabilize the oxidised oxoammonium cation. Importantly, this can be quantified by a simple predictive relationship involving the distance scaled dipole and quadrupole moments of the analogous cyclohexyl ring. This highlights the often-overlooked role of through-space electrostatic substituent effects, even in formally neutral compounds.

The synthesis of poly(vinyl chloride) (PVC) by nitroxide-mediated polymerization (NMP) using the SG1-based BlocBuilder alkoxyamine at low temperature (30 and 42 °C) is reported. The reaction system was studied regarding the nature of the solvent, the monomer-to-solvent ratio, the polymerization temperature, and the target molecular weight. First-order kinetics and linear evolutions of the molecular weight with vinyl chloride (VC) conversion were obtained in dichloromethane (DCM) and dimethyl sulfoxide (DMSO) together with decreasing dispersities (Đ) down to 1.59–1.47. The resulting PVC was fully characterized by 1H nuclear magnetic resonance spectroscopy (1H NMR), 31P NMR, and size exclusion chromatography (SEC). The 1H NMR and 31P NMR revealed the existence of very small content of structural defects and the presence of chain-end functional groups (∼91% SG1 chain-end functionality). Chain extension experiments were performed with VC, methyl methacrylate (MMA), and a mixture of monomers (90% of MMA and 10...

In the present work, we examine the effects of zinc chloride (ZnCl2) and aluminium chloride (AlCl3) complexation on the photochemistry of two well-known type I photoinitiators, methyl-4′-(methylthio)-2-morpholinopropiophenone (MMMP) and 2,2-dimethoxy-2-phenylacetophenone (DMPA). High-level ab initio calculations and experimental results demonstrate that Lewis acid complexation has a significant effect on the individual processes that comprise radical photoinitiation. Theoretical calculations predict that ZnCl2 coordinates to MMMP and DMPA to form thermodynamically stable bidentate ketone–amine and ketone–ether chelates, respectively. Meanwhile, the AlCl2+ cation coordinates to MMMP and DMPA to form a tridentate ether–amine–ketone chelate and a bidentate ketone–ether chelate, respectively. We found that addition of ZnCl2 and AlCl3 to solutions containing MMMP significantly increase its molar extinction coefficient (e) between 350–360 nm. In contrast, the complexation of either ZnCl2 or AlCl3 to DMPA slightly reduces the value of e in the 350–360 nm range. Time dependent density functional theory (TD-DFT) calculations demonstrate that Lewis acid complexation blue shifts the nπ* excitations of both DMPA and MMMP, while concurrently red shifting the ππ* transitions. Complexation also significantly alters the stability and reactivity of the photoinitiator fragment radicals. Lewis acid complexation localizes and destabilizes acyl radicals, resulting in significantly increased reactivity towards methyl methacrylate (MMA). In contrast, complexation of Lewis acids dramatically reduces the reactivity of the morpholine substituted isopropyl radical and the dimethoxyphenyl radical towards MMA. Alternative complexation at the methyl ester side-chain of MMA has a beneficial effect on the reactivity of all fragments, increasing addition rate coefficients by 2–4 orders of magnitude. We discuss some of the important implications of these findings for pulsed laser polymerization (PLP), and acetophenone photochemistry more generally.

The fundamental influence of the structure and substitution of radical photoinitiators was investigated via a trifold combination of pulsed-laser polymerization with subsequent electrospray-ionization mass spectrometry (PLP-ESI-MS), femtosecond transient absorption (fs-TA) spectroscopy, and quantum chemistry. For the first time, a library of benzoin-derived photoinitiators with varied substitution patterns was synthesized. In the PLP-ESI-MS study, different photoinitiators were compared pairwise in so-called cocktail experiments, enabling the direct comparison of their initiation efficiency. In the fs-TA experiments, the transient response was observed after UV excitation in the visible spectral region, allowing for a description of excited state dynamics, which was analyzed with the aid of TD-DFT calculations. Ab initio calculations were undertaken to determine the reactivity of the radical fragments generated from these photoinitiators and to quantify the influence of various substituents on the rate of...

MLC gratefully acknowledges financial support from the Australian Research Council through an ARC Laureate Fellowship, and generous allocations of supercomputing time on the National Facility of the National Computational Infrastructure.

The wavelength-dependent conversion of two rapid photoinduced ligation reactions, i.e., the light activation of o-methylbenzaldehydes, leading to the formation of reactive o-quinodimethanes (photoenols), and the photolysis of 2,5-diphenyltetrazoles, affording highly reactive nitrile imines, is probed via a monochromatic wavelength scan at constant photon count. The transient species are trapped by cycloaddition with N-ethylmaleimide, and the reactions are traced by high resolution mass spectrometry and nuclear magnetic resonance spectroscopy. The resulting action plots are assessed in the context of Beer-Lambert's law and provide combined with time-dependent density functional theory and multireference calculations an in-depth understanding of the underpinning mechanistic processes, including conical intersections. The π → π* transition of the carbonyl group of the o-methylbenzaldehyde correlates with a highly efficient conversion to the cycloadduct, showing no significant wavelength dependence, while conversion following the n → π* transition proceeds markedly less efficient at longer wavelengths. The influence of absorbance and reactivity has critical consequences for an effective reaction design: At high concentrations of o-methylbenzaldehydes (c = 8 mmol L

In the present work we use accurate Pulsed Laser Polymerization (PLP) to measure the influence of various concentrations of lithium bis(trifluromethane)sulfonamide (LiNTf2) on the propagation rate coefficient of methyl methacrylate (MMA). We also perform 1H-NMR analysis to evaluate the effect of LiNTf2 on poly(MMA) stereochemistry. Additionally, we perform high-level quantum-chemical calculations to model the interactions between Li+ and the MMA monomer and propagating radical. Across a broad range of concentrations, LiNTf2 only slightly increases the isotacticity of the resultant poly(MMA). However, a significant increase in the propagation rate coefficient was noted upon addition of LiNTf2. The magnitude of this increase was found to be dependent on the LiNTf2 concentration and temperature. Theoretical calculations reveal the complexities associated with Lewis acid-mediated stereocontrol. On the basis of this theoretical work, we suggest that the potential stereocontrol afforded by Lewis acids is being hindered by their action as propagation catalysts though non-stereoselective binding modes.

Computational quantum chemistry can make valuable contributions to modelling and improving free radical polymerisation. At a microscopic level, it can assist in establishing reaction mechanisms and structure-reactivity trends; at a macroscopic level it can be used in the design and parameterisation of accurate kinetic models for process optimisation and control. This review outlines and critically evaluates various methodological approaches that have been employed in first principles prediction of rate coefficients in free radical polymerisation, examining in turn the choice of chemical model, electronic structure method, solvation modelling and the coupled issues of partition function evaluation and conformational analysis. It is shown that accurate and reliable predictions are possible but only if necessary precautions are taken into account. The practical value of accurate computational modelling of radical polymerisation kinetics is then illustrated through three representative case studies from the l...

This work demonstrates the effect of electrostatic interactions on the electroactivity of a persistent organic free radical. This was achieved by chemisorption of molecules of 4-azido-2,2,6,6-tetramethyl-1-piperdinyloxy (4-azido-TEMPO) onto monolayer-modified Si(100) electrodes using a two-step chemical procedure to preserve the open-shell state and hence the electroactivity of the nitroxide radical. Kinetic and thermodynamic parameters for the surface electrochemical reaction are investigated experimentally and analyzed with the aid of electrochemical digital simulations and quantum-chemical calculations of a theoretical model of the tethered TEMPO system. Interactions between the electrolyte anions and the TEMPO grafted on highly doped, i.e., metallic, electrodes can be tuned to predictably manipulate the oxidizing power of surface nitroxide/oxoammonium redox couple, hence showing the practical importance of the electrostatics on the electrolyte side of the radical monolayer. Conversely, for monolayers prepared on the poorly doped electrodes, the electrostatic interactions between the tethered TEMPO units and the semiconductor-side, i.e., space-charge, become dominant and result in drastic kinetic changes to the electroactivity of the radical monolayer as well as electrochemical nonidealities that can be explained as an increase in the self-interaction "a" parameter that leads to the Frumkin isotherm.

The regulation of stereochemistry in radical polymerization has thus far proved enormously challenging, being the subject of more than 50 years of intense and innovative research. The relatively recent development of living radical polymerization has revitalized interest in stereocontrol, as the lack of tacticity control is now the greatest obstacle to the synthesis of precisely controlled macromolecules by highly versatile and efficient radical-based processes. Lewis acids (LAs) have been employed in an attempt to overcome the relatively poor stereoselectivity of unmediated radical polymerization, although the level of stereocontrol achieved is highly variable and condition dependent. We examine the use of LAs in radical polymerization from a mechanistic perspective, considering the underlying mechanism of tacticity determination and the likely requirements for effective stereocontrol. Concurrently, we examine the use of LAs in synthetic radical transformations, where they can facilitate very high levels of diastereocontrol but similar variability and condition dependencies are also noted. This chapter outlines and assesses some of the key factors likely to underlie the success or failure LA-mediated isotactic control in radical polymerization.