A Rapid Electrochemical Method for Determining Rate Coefficients for Copper-Catalyzed Polymerizations

Macrocyclic Copper(II) Complexes as Catalysts for Electrochemically Mediated Atom Transfer

Copper-catalyzed electrochemical atom transfer radical addition (eATRA) is a new method for the creation of new C-C bonds under mild conditions. In this work, we have explored the reactivity of an analogous series of N4 macrocyclic CuII complexes as eATRA precatalysts, which are primed by reduction to their monovalent oxidation state. These complexes were fully characterized structurally, spectroscopically, and electrochemically. A spectrum of radical activation reactivity was found across the series [CuI(Me4cyclen)(NCMe)]+ (Me4cyclen = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane), [CuI(Me4cyclam)(NCMe)]+ (Me4cyclam = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), and [CuI(Me2py2clen)(NCMe)]+ (Me2py2clen = 3,7-dimethyl-3,7-diaza-1,5(2,6)-dipyridinacyclo-octaphane). The rate of radical production by [Cu(Me2py2clen)(NCMe)]+ was modest, but rapid radical capture to form the organocopper complex [CuI(Me2py2clen)(CH2CN)] led to a dramatic acceleration in catalysis, greater than seen in any comparable Cu complex, but this led to rapid radical self-termination instead of radical addition.

Electrochemically Mediated Surface-Initiated Atom Transfer Radical Polymerization by ppm of CuII/Tris(2-pyridylmethyl)amine

Atom transfer radical polymerization (ATRP) is one of the most widely used methods for modifying surfaces with functional polymer films and has received considerable attention in recent years. Here, we report an electrochemically mediated surface-initiated ATRP to graft polymer brushes onto solid substrates catalyzed by ppm amounts of CuII/TPMA in water/MeOH solution. We systematically investigated the type and concentrations of copper/ligand and applied potentials correlated to the polymerization kinetics and polymer brush thickness. Gradient polymer brushes and various types of polymer brushes are prepared. Block copolymerization of 2-hydroxyethyl methacrylate (HEMA) and 3-sulfopropyl methacrylate potassium salt (PSPMA) (poly(HEMA-b-SPMA)) with ultralow ppm eATRP indicates the remarkable preservation of chain end functionality and a pronounced "living" characteristic feature of ppm-level eATRP in aqueous solution for surface polymerization.

Design and optimization of sensitive analytical spectrophotometric method for micro determination of copper(II) from e-waste by using of novel chromogenic extractant

In this article, a novel spectrophotometric reagent 1-(pyrimidine)-4, 4, 6-trimethyl-1,4-dihydropyrimidine-2-thiol [PTPT] has been synthesized for liquid-liquid extraction and spectrophotometric determination of copper(II). The as-synthesized ligand has been selectively forms stable complex with copper(II) in basic medium (pH 9.0), in presence of mild pyridine the extraction and color stability has found to be synergistically enhanced. The equilibrium time is 10 min for effective extraction of copper(II) from organic phase and absorbance of colored organic complex in carbon tetrachloride is measured spectrophotometrically at λ_max 615 nm against reagent blank. The ternary complex of Cu(II)-PTPT-Py having molar ratio 1:2:2 (M:L:Py) showed green colored complex. The main factors influencing the achievement of synergistic extraction; i.e. pH, ligand concentration, type and volume of the dispersive organic solvents, equilibrium time, synergent concentration and foreign ions were investigated. The Beer's law was obeyed in the concentration range 1-20 μg mL^-1 of copper(II) and optimum concentration range is evaluated by Ringbom's plot and it is found that 2.5-25 μg mL^-1. In presence of pyridine, molar absorptivity and Sandell's sensitivity of copper(II)-PTPT complex is 2.80 × 10³ L mol^-1 cm^-1 and 0.226 μg cm^-2, respectively and in absence of pyridine, molar absorptivity and Sandell's sensitivity of copper(II)-PTPT complex is 1.35 × 10³ L mol^-1 cm^-1 and 0.469 μg cm^-2, respectively. The stoichiometry of the copper(II)-PTPT-pyridine complex was calculated by slope ratio method, mole ratio method and Job's method of continuous variation and it has been found as 1:2:2. No significant effects of potentially interfering species i.e. cations and anions were observed. The optimized method was applied for the determination of copper(II) in binary, synthetic mixtures and successfully applied for determination of copper(II) from e-waste samples. The standard deviation (R.S.D.) is 0.11% for n = 5 repetition. The reliability of the developed method is confirmed by comparison of experimental results with atomic absorption spectrophotometer.

Current-controlled ‘plug-and-play’ electrochemical atom transfer radical polymerization of acrylamides in water

Aqueous electrochemical atom transfer radical polymerisation (eATRP) can be challenging due to deleterious side reactions leading to the loss of the ω-chain end, increased rates of activation (k¬act) leading to...

Water-Borne Nanocoating for Rapid Inactivation of SARS-CoV-2 and Other Viruses

The rise in coronavirus variants has resulted in surges of the disease across the globe. The mutations in the spike protein on the surface of the virion membrane not only allow for greater transmission but also raise concerns about vaccine effectiveness. Preventing the spread of SARS-CoV-2, its variants, and other viruses from person to person via airborne or surface transmission requires effective inactivation of the virus. Here, we report a water-borne spray-on coating for the complete inactivation of viral particles and degradation of their RNA. Our nanoworms efficiently bind and, through subsequent large nanoscale conformational changes, rupture the viral membrane and subsequently bind and degrade its RNA. Our coating completely inactivated SARS-CoV-2 (VIC01) and an evolved SARS-CoV-2 variant of concern (B.1.1.7 (alpha)), influenza A, and a surrogate capsid pseudovirus expressing the influenza A virus attachment glycoprotein, hemagglutinin. The polygalactose functionality on the nanoworms targets the conserved S2 subunit on the SARS-CoV-2 virion surface spike glycoprotein for stronger binding, and the additional attachment of guanidine groups catalyze the degradation of its RNA genome. Coating surgical masks with our nanoworms resulted in complete inactivation of VIC01 and B.1.1.7, providing a powerful control measure for SARS-CoV-2 and its variants. Inactivation was further observed for the influenza A and an AAV-HA capsid pseudovirus, providing broad viral inactivation when using the nanoworm system. The technology described here represents an environmentally friendly coating with a proposed nanomechanical mechanism for inactivation of both enveloped and capsid viruses. The functional nanoworms can be easily modified to target viruses in future pandemics, and is compatible with large scale manufacturing processes.

Mapping the Pathway to Organocopper(II) Complexes Relevant to Atom Transfer Radical Polymerization

The rare organocopper(II) complex [Cu(Me₆tren)(CH₂CN)]⁺ (Me₆tren = tris(2-(dimethylamino)ethyl)amine) has emerged as an important model of potential byproducts in copper-catalyzed atom transfer radical polymerization. This complex has been generated by controlled potential electrolysis of [Cu(Me₆tren)(NCMe)]²⁺ in the presence of BrCH₂CN. Time-resolved UV-vis and continuous wave and pulse electron paramagnetic resonance (EPR) spectra identified [Cu(Me₆tren)Br]⁺ as an intermediate. Hyperfine sublevel correlation and electron nuclear double resonance spectroscopy of samples at different timepoints reveal signals that are assigned to a C-bound cyanomethylate ligand, with distinct ¹⁴N and ¹H hyperfine coupling constants in comparison with the corresponding N-bound acetonitrile and bromido complexes. The experimental EPR data are supported by density functional theory calculations to understand how the geometries of the species involved produce distinct spectroscopic signatures, and a clear picture of how this unusual organocopper(II) complex is formed has emerged.

Electrochemical Exploration of Active Cu-Based Atom Transfer Radical Polymerization Catalysis through Ligand Modification

The intersection between Cu-catalyzed atom transfer radical polymerization (ATRP) and organometallic mediated radical polymerization (OMRP) has been recently shown to be a result of competition between the Cu^I and Cu^II complexes of polyamine ligands for the same organic free radical. The tetradentate ligands N,N'-bis-2'-pyridylmethyl-ethane-1,2-diamine (L¹) and N,N'-dimethyl-N,N'-bis-2'-pyridylmethyl-ethane-1,2-diamine (L²) form stable Cu complexes which, depending on their oxidation state, can either liberate or complex organic radicals. Herein, we show that this process may be affected by subtle changes to the ligand system. Switching from a tertiary amine (L²) to a secondary amine (L¹) retains ATRP and OMRP activity through a series of cyclic voltammetry measurements in the presence of the initiator bromoacetonitrile.

Electrochemistry for Atom Transfer Radical Polymerization

Atom Transfer Radical Polymerization (ATRP) is the most powerful and most employed technology of Controlled Radical Polymerization (CRP) to produce polymers with well-defined architecture, that is, composition, topology, and functionality. Several hundreds of papers are published every year on ATRP processes, mainly based on empiric experimental procedures. Electrochemistry powerfully entered in the field of ATRP about 10 years ago, providing important contributions both to the further development of the process and to a better understanding of its mechanism. Five main issues took advantage of electrochemistry and/or its synergism with ATRP: i) understanding the mechanism of ATRP activation; ii) determination of thermodynamic parameters; iii) determination of activation and deactivation rate constants; iv) the SARA ATRP vs SET-LRP dispute: the role of Cu⁰ ; v) electrochemically-mediated ATRP.

The fate of copper catalysts in atom transfer radical chemistry

The pathway of atom transfer radical polymerisation (ATRP) is influenced by the nature of the alkyl bromide initiator (RBr) to the extent that reactions between the radical R˙ and the original copper(i) catalyst can divert the reaction toward different products.

Synthesis and Characterization of the Most Active Copper ATRP Catalyst Based on Tris[(4-dimethylaminopyridyl)methyl]amine

The tris[(4-dimethylaminopyridyl)methyl]amine (TPMA^NMe2) as a ligand for copper-catalyzed atom transfer radical polymerization (ATRP) is reported. In solution, the [Cu^I(TPMA^NMe2)Br] complex shows fluxionality by variable-temperature NMR, indicating rapid ligand exchange. In the solid state, the [Cu^II(TPMA^NMe2)Br][Br] complex exhibits a slightly distorted trigonal bipyramidal geometry (τ = 0.89). The UV-vis spectrum of [Cu^II(TPMA^NMe2)Br]⁺ salts is similar to those of other pyridine-based ATRP catalysts. Electrochemical studies of [Cu(TPMA^NMe2)]²⁺ and [Cu(TPMA^NMe2)Br]⁺ showed highly negative redox potentials (E_1/2 = -302 and -554 mV vs SCE, respectively), suggesting unprecedented ATRP catalytic activity. Cyclic voltammetry (CV) in the presence of methyl 2-bromopropionate (MBrP; acrylate mimic) was used to determine activation rate constant k_a = 1.1 × 10⁶ M^-1 s^-1, confirming the extremely high catalyst reactivity. In the presence of the more active ethyl α-bromoisobutyrate (EBiB; methacrylate mimic), total catalysis was observed and an activation rate constant k_a = 7.2 × 10⁶ M^-1 s^-1 was calculated with values of K_ATRP ≈ 1. ATRP of methyl acrylate showed a well-controlled polymerization using as little as 10 ppm of catalyst relative to monomer, while side reactions such as Cu^I-catalyzed radical termination (CRT) could be suppressed due to the low concentration of L/Cu^I at a steady state.

Two-compartment kinetic Monte Carlo modelling of electrochemically mediated ATRP

Novel eATRP mechanistic insights are formulated, considering a two-compartment kinetic Monte Carlo model with catalyst concentration gradients accounted for.

N-Oxides rescue Ru(v) in catalytic Griffith–Ley (TPAP) alcohol oxidations

Electrochemistry of tetrapropylammonium perruthenate (TPAP) reveals that an unstable Ru(v) complex is reoxidised by amine N-oxides in catalytic Griffith–Ley alcohol oxidations.

SET-LRP of NIPAM in water via in situ reduction of Cu(ii) to Cu(0) with NaBH4

The direct and quantitative reduction of the air-stable Cu(ii)Br₂/Me₆TREN to Cu(0) by NaBH₄ represents a new method for the aqueous single electron transfer-living radical polymerization (SET-LRP) of water soluble polymers.

Tapping the potential of polymer brushes through synthesis

CONSPECTUS: Polymer brushes are becoming increasing popular in the chemical literature, because scientists can control their chemical configuration, density, architecture, and thickness down to nanoscale precision with even simple laboratory setups. A polymer brush is made up of a layer of polymers attached to a substrate surface at one end with the other end dangling into a solvent. In a suitable solvent, the polymer chains stretch away from the surface due to both steric and osmotic repulsion between the chain segments. In an inadequate solvent, however, the polymer chains collapse due to enough interior free space after desolvation. This unique class of materials exhibit interesting physicochemical properties at interfaces and have numerous applications from sensing to surface/interface property control. Chemists have made recent advances in surface modification and specific application of polymer brushes, due to both profound mechanistic understanding and synthetic strategies. The commonly used synthetic strategies for generating polymer brushes are surface-initiated polymerizations (SIPs), which resemble planting rice. That is, the assembly of initiator on the surface is similar to transplanting rice seedlings, and the subsequent polymerizations are akin to rice growth. Among different SIP methods, researchers mostly use surface-initiated atom transfer radical polymerization (SI-ATRP) because it provides many advantages in the preparation of well-defined polymer brushes, including easy initiator synthesis, fair control over polymer growth, a "living" end for copolymer grafting, and polymerization in aqueous solution. However, chemists gradually realized that there still room for improvement in this method, since the conventional SI-ATRP method suffers several drawbacks. These include having limited availability on various materials surfaces, rigorous synthetic protocols, heavy consumption and waste of unreacted monomers, and limited ability to control a polymerization process. Moreover, applications of polymer brushes as model surfaces must benefit from the synergistic strategies and profound insights into the fundamental understanding of the polymerization. This is not only to optimize the SI-ATRP process but also to expand the range of monomers, simplify reaction setups, reduce the cost, and ultimately gain control of the synthesis of well-defined polymeric surfaces for material science and engineering. In this Account, we provide an overview of our and others' recent advances in the fabrication of polymer brushes by using SI-ATRP, to promote the widespread application of SI-ATRP and practical applications of the polymer brushes. We aim to provide fundamental mechanistic and synthetic features of SI-ATRP, while emphasizing the various externally applied stimuli mediated catalytic and initiation systems, including electrochemistry, chemical reducing agents, and photochemistry. In addition, we discuss how chemists can advantageously exploit these methods to synthesize functional polymeric surfaces in environmentally friendly media and facilitate in situ regulation of a dynamic polymerization process. We also discuss structural polymer brushes, such as block copolymers and patterned and gradient structures. Finally, we provide examples that highlight some practical applications of polymer brushes using SI-ATRP, especially the emerging polymerization methods. Overall, recently developed SI-ATRP systems overcome many limitations that permit less rigorous synthetic protocols and facilitate scientific community-wide access to surface modifications. By using these methodologies, chemists are tapping the potential of polymer brushes in surface/interface research areas.

Construction of a 3-Miktoarm Star from Cyclic Polymers

Cyclic polymers have intriguing physical properties, including those found in biological membranes for greater temperature, salt and acid stability. Although, many unique and complex synthetic cyclic structures have been prepared, there are no reports of ABC miktoarm stars constructed of three cyclic polymers with very different chemical compositions. We report such a structure in one pot at 25 °C by modulating the copper catalyst activity using combinations of solvents and ligands.