Redox-Responsive H-Bonding: Amplifying the Effect of Electron Transfer Using Proton-Coupled Electron Transfer

Unveiling the potential of machine learning in cost-effective degradation of pharmaceutically active compounds: A stirred photo-reactor study

In this study, neural networks and support vector regression (SVR) were employed to predict the degradation over three pharmaceutically active compounds (PhACs): Ibuprofen (IBP), diclofenac (DCF), and caffeine (CAF) within a stirred reactor featuring a flotation cell with two non-concentric ultraviolet lamps. A total of 438 datapoints were collected from published works and distributed into 70% training and 30% test datasets while cross-validation was utilized to assess the training reliability. The models incorporated 15 input variables concerning reaction kinetics, molecular properties, hydrodynamic information, presence of radiation, and catalytic properties. It was observed that the Support Vector Regression (SVR) presented a poor performance as the ε hyperparameter ignored large error over low concentration levels. Meanwhile, the Artificial Neural Networks (ANN) model was able to provide rough estimations on the expected degradation of the pollutants without requiring information regarding reaction rate constants. The multi-objective optimization analysis suggested a leading role due to ozone kinetic for a rapid degradation of the contaminants and most of the results required intensification with hydrogen peroxide and Fenton process. Although both models were affected by accuracy limitations, this work provided a lightweight model to evaluate different Advanced Oxidation Processes (AOPs) by providing general information regarding the process operational conditions as well as know molecular and catalytic properties.

Photoswitchable Quadruple Hydrogen-Bonding Motif

Multiple hydrogen-bonding motifs serve as important building blocks for molecular recognition and self-assembly. Herein, a photoswitchable quadruple hydrogen-bonding motif featuring near-complete, reversible, and thermostable conversion between DADA and AADD arrays associated with an alteration of their dimerization constants by over 3 orders of magnitude is reported. The system is based on a diarylethene featuring a ureidopyrimidin-4-ol moiety, which upon photoinduced ring closure and associated loss of aromaticity undergoes enol-keto tautomerization to a ureidopyrimidinone moiety. The latter causes a transformation of the hydrogen-bonding arrays and significantly weakens the free energy of dimerization in the case of the closed isomer. This photoswitchable quadruple hydrogen-bonding motif should allow us to spatially and temporarily direct self-assembly and supramolecular polymerization processes by light.

Long-Lived Multiple Charge Separation by Proton-Coupled Electron Transfer

Multiple charge separation has been successfully realized by a proton-coupled electron transfer reaction in an organic cocrystal. Benefiting from the adjustable electronic energy level of the electron donor and acceptor through thermal-induced proton migration, distinct optical absorption behaviors combined with color changes to blue or green are observed in these charge-separated states. It is of interest to note that such charge-separated states exhibit a longer lifetime of over a month as a result of the excellent coplanarity and π-π interaction of the electron acceptors. Moreover, the enhanced absorption toward longer wavelengths endows the charge-separated state with near-infrared (808 nm) photothermal conversion for imaging and bacterial inhibition, whereby the conversion performance can be controlled by the degree of proton migration.

Photo-Controlled Macroscopic Self-Assembly Based on Photo-Switchable Hetero-Complementary Quadruple Hydrogen Bonds

A photo-switchable hetero-complementary quadruple H-bonding array, which consists of an azobenzene-derived ureidopyrimidinone (UPy) module (Azo-UPy) and a nonphotoactive diamidonaphthyridine (DAN) derivative (Napy-1), is constructed based on a reversible photo-locking approach. Upon UV (390 nm)/Vis (460 nm) light irradiations, photo-switchable quadruple H-bonded dimerization between Azo-UPy and Napy-1 can be achieved with exhibiting 4.8×10⁴ -fold differences in binding strength (ON/OFF ratios). Furthermore, smart polymeric gels with unique photo-controlled macroscopic self-assembly behavior can be fabricated by introducing such quadruple H-bonding array as photo-regulable noncovalent interfacial connections.

Exploring the Role of H-Bonding in Organic Electrochemistry - From Supramolecular Applications to Mechanistic Investigations

H-bonds can exert a substantial impact on the course of organic electrode reactions due to their ability to stabilize charged intermediates and products formed during these reactions, as well as facilitate proton-coupled electron transfer (PCET) reactions. This has fundamental implications for the mechanism of organic electrode reactions, but also practical impact in supramolecular chemistry and potentially synthetic electrochemistry. My group's main focus has been on the supramolecular applications, using electron transfer to alter the strength of H-bonds to create highly redox-responsive H-bond dimers. Initially we sought to avoid proton transfer because we feared that would lead to irreversible electrochemistry. However, inevitably proton transfer did show up, but, to our surprise, did not lead to irreversible electrochemistry. To explain this, we developed a new mechanism, the "wedge scheme", that shows how H-bonding can facilitate reversible electron and proton transfer. This insight recently led us to a new PCET-based design strategy for the creation of our most highly redox-responsive H-bond dimers yet.

Towards photoswitchable quadruple hydrogen bonds via a reversible "photolocking" strategy for photocontrolled self-assembly

Developing new photoswitchable noncovalent interaction motifs with controllable bonding affinity is crucial for the construction of photoresponsive supramolecular systems and materials. Here we describe a unique "photolocking" strategy for realizing photoswitchable control of quadruple hydrogen-bonding interactions on the basis of modifying the ureidopyrimidinone (UPy) module with an ortho-ester substituted azobenzene unit as the "photo-lock". Upon light irradiation, the obtained Azo-UPy motif is capable of unlocking/locking the partial H-bonding sites of the UPy unit, leading to photoswitching between homo- and heteroquadruple hydrogen-bonded dimers, which has been further applied for the fabrication of novel tunable hydrogen bonded supramolecular systems. This "photolocking" strategy appears to be broadly applicable in the rational design and construction of other H-bonding motifs with sufficiently photoswitchable noncovalent interactions.