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  1. Abstract

    De novo metalloprotein design involves the construction of proteins guided by specific repeat patterns of polar and apolar residues, which, upon self‐assembly, provide a suitable environment to bind metals and produce artificial metalloenzymes. While a wide range of functionalities have been realized in de novo designed metalloproteins, the functional repertoire of such constructs towards alternative energy‐relevant catalysis is currently limited. Here we show the application of de novo approach to design a functional H2evolving protein. The design involved the assembly of an amphiphilic peptide featuring cysteines at tandema/dsites of each helix. Intriguingly, upon NiIIaddition, the oligomers shift from a major trimeric assembly to a mix of dimers and trimers. The metalloprotein produced H2photocatalytically with a bell‐shape pH dependence, having a maximum activity at pH 5.5. Transient absorption spectroscopy is used to determine the timescales of electron transfer as a function of pH. Selective outer sphere mutations are made to probe how the local environment tunes activity. A preferential enhancement of activity is observed via steric modulation above the NiIIsite, towards the N‐termini, compared to below the NiIIsite towards the C‐termini.

    Free, publicly-accessible full text available November 28, 2023
  2. Abstract

    Shortwave infrared (SWIR) dyes are characterized by their ability to absorb light from 900 to 1400 nm, which is ideal for deep tissue imaging owing to minimized light scattering and interference from endogenous pigments. An approach to access such molecules is to tune the photophysical properties of known near‐infrared dyes. Herein, we report the development of a series of easily accessible (three steps) SWIR xanthene dyes based on a dibenzazepine donor conjugated to thiophene (SCR‐1), thienothiophene (SCR‐2), or bithiophene (SCR‐3). We leverage the fact thatSCR‐1undergoes a bathochromic shift when aggregated for in vivo studies by developing a ratiometric nanoparticle for NO (rNP‐NO), which we employed to successfully visualize pathological levels of nitric oxide in a drug‐induced liver injury model via deep tissue SWIR photoacoustic (PA) imaging. Our work demonstrates how easily this dye series can be utilized as a component in nanosensor designs for imaging studies.

    Free, publicly-accessible full text available February 1, 2024
  3. Abstract

    We report the formation of the cyclic methylphosphonic acid trimer [c‐(CH3PO2)3] through condensation reactions during thermal processing of low‐temperature methylphosphonic acid samples exploiting photoionization reflectron time‐of‐flight mass spectrometry (PI−ReTOF−MS) along with electronic structure calculations. Cyclic methylphosphonic acid trimers are formed in the solid state and detected together with its protonated species in the gas phase upon single photon ionization. Our studies provide an understanding of the preparation of phosphorus‐bearing potentially prebiotic molecules and the fundamental knowledge of low‐temperature phosphorus chemistry in extraterrestrial environments.

    Free, publicly-accessible full text available October 25, 2023
  4. Abstract

    Fluorescence resonance energy transfer (FRET) is a non‐invasive characterization method for studying molecular structures and dynamics, providing high spatial resolution at nanometer scale. Over the past decades, FRET‐based measurements are developed and widely implemented in synthetic polymer systems for understanding and detecting a variety of nanoscale phenomena, enabling significant advances in polymer science. In this review, the basic principles of fluorescence and FRET are briefly discussed. Several representative research areas are highlighted, where FRET spectroscopy and imaging can be employed to reveal polymer morphology and kinetics. These examples include understanding polymer micelle formation and stability, detecting guest molecule release from polymer host, characterizing supramolecular assembly, imaging composite interfaces, and determining polymer chain conformations and their diffusion kinetics. Finally, a perspective on the opportunities of FRET‐based measurements is provided for further allowing their greater contributions in this exciting area.

  5. Abstract

    Ionic liquids (ILs) have been shown to be effective transdermal penetrants of pharmaceutically active ingredients, including small molecules and proteins. The presence of water within ionic liquids has been demonstrated to play a critical role in  their structural organization on the molecular level. However, the impact of water on IL transdermal transport efficacy has yet to be investigated. Herein, a water concentration gradient (0%–100% v/v) is tested to evaluate  choline trans‐2‐octenoic (CA2OE)‐mediated transport of a hydrophilic model drug dextran (10000 Da) in an ex vivo porcine skin model.Compared to 2:1, 1:1, 1:4, and 1:5 ionic ratio formulations, 50% v/v CA2OE 1:2‐water evidences the greatest success at transporting dextran to the acceptor fluid. Physicochemical characterization (dynamic light scattering (DLS), scanning electron microscopy (SEM), optical density (O.D.), Fourier transform infrared spectroscopy (FTIR), fluorescent microscopy, and rheology) is conducted to test both bulk and nanoscale‐level CA2OE 1:2–water interactions. It is hypothesized that the presence of microemulsions in the CA2OE 1:2 75% v/v formulation accounted for the severely decreased transport compared to the 50%. It is thus critical to comprehensively consider interactions between IL components, co‐solvents, anddrug molecules when formulating ILs for transdermal transport applications.

    Free, publicly-accessible full text available November 3, 2023
  6. Abstract

    The design of bright, high quantum yield (QY) materials in the near‐infrared (NIR) spectral region in water remains a significant challenge. A series of cyanine and squaraine dyes varying water solubilizing groups and heterocycles are studied to probe the interactions of these groups with albumin in water. Unprecedented, ′ultra‐bright′ emission in water is observed for a sulfonate indolizine squaraine dye (61.1 % QY) and a sulfonate indolizine cyanine dye (46.7 % QY) at NIR wavelengths of >700 nm and >800 nm, respectively. The dyes presented herein have a lower limit of detection than the most sensitive dyes known in the NIR region for albumin detection by at least an order of magnitude, which enables more sensitive diagnostic testing. Additionally, biotinylated human serum albumin complexed with the dyes reported herein was observed to function as an immunohistochemical reagent enabling high resolution imaging of cellular α‐tubulin at low dye concentrations.

  7. Abstract

    Reversible addition‐fragmentation chain transfer (RAFT) polymerization has proven itself as a powerful polymerization technique affording facile control of molecular weight, molecular weight distribution, architecture, and chain end groups ‐ while maintaining a high level of tolerance for solvent and monomer functional groups. RAFT is highly suited to water as a polymerization solvent, with aqueous RAFT now utilized for applications such as controlled synthesis of ultra‐high molecular weight polymers, polymerization induced self‐assembly, and biocompatible polymerizations, among others. Water as a solvent represents a non‐toxic, cheap, and environmentally friendly alternative to organic solvents traditionally utilized for polymerizations. This, coupled with the benefits of RAFT polymerization, makes for a powerful combination in polymer science. This perspective provides a historical account of the initial developments of aqueous RAFT polymerization at the University of Southern Mississippi from the McCormick Research Group, details practical considerations for conducting aqueous RAFT polymerizations, and highlights some of the recent advances aqueous RAFT polymerization can provide. Finally, some of the future opportunities that this versatile polymerization technique in an aqueous environment can offer are discussed, and it is anticipated that the aqueous RAFT polymerization field will continue to realize these, and other exciting opportunities into the future.

  8. Abstract

    Poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is a popular hole transport material in perovskite solar cells (PSCs). However, the devices with PEDOT:PSS exhibit large open‐circuit voltage (Voc) loss and low efficiency, which is attributed to mismatched energy level alignment and the poor interface of PEDOT:PSS and perovskite. Here, three polymer analogues to polyaniline (PANI), PANI–carbazole (P1), PANI–phenoxazine (P2), and PANI–phenothiazine (P3) are designed with different energy levels to modify the interface between PEDOT:PSS and the perovskite layer and improve the device performance. The effects of the polymers on the device performance are demonstrated by evaluating the work function adjustment, perovskite growth control, and interface modification in MAPbI3‐based PSCs. Low bandgap Sn–Pb‐based PSCs are also fabricated to confirm the effects of the polymers. Three effects are evaluated through the comparison study of PEDOT:PSS‐based organic solar cells and MAPbI3 PSCs based on the PEDOT:PSS modified by P1, P2, and P3. The order of contribution for the three effects is work function adjustment > surface modification > perovskite growth control. MAPbI3 PSCs modified with P2 exhibit a highVocof 1.13 V and a high‐power conversion efficiency of 21.06%. This work provides the fundamental understanding of the interface passivation effects for PEDOT:PSS‐based optoelectronic devices.

    Free, publicly-accessible full text available October 7, 2023
  9. Abstract

    The morphological stability of an organic photovoltaic (OPV) device is greatly affected by the dynamics of donors and acceptors occurring near the device's operational temperature. These dynamics can be quantified by the glass transition temperature (Tg) of conjugated polymers (CPs). Because flexible side chains possess much faster dynamics, the cleavage of the alkyl side chains will reduce chain dynamics, leading to a higherTg. In this work, theTgs for CPs are systematically studied with controlled side chain cleavage. Isothermal annealing of polythiophenes featuring thermally cleavable side chains at 140 °C, is found to remove more than 95% of alkyl side chains in 24 h, and raise the backboneTgfrom 23 to 75 °C. Coarse grain molecular dynamics simulations are used to understand theTgdependence on side chain cleavage. X‐ray scattering indicates that the relative degree of crystallization remains constantduring isothermal annealing process. The effective conjugation length is not influenced by thermal cleavage; however, the density of chromophore is doubled after the complete removal of alkyl side chains. The combined effect of enhancingTgand conserving crystalline structures during the thermal cleavage process can provide a pathway to improving the stability of optoelectronic properties in future OPV devices.

  10. Abstract

    The Strecker Synthesis of (a)chiral α-amino acids from simple organic compounds, such as ammonia (NH3), aldehydes (RCHO), and hydrogen cyanide (HCN) has been recognized as a viable route to amino acids on primordial earth. However, preparation and isolation of the simplest hemiaminal intermediate – the aminomethanol (NH2CH2OH)– formed in the Strecker Synthesis to even the simplest amino acid glycine (H2NCH2COOH) has been elusive. Here, we report the identification of aminomethanol prepared in low-temperature methylamine (CH3NH2) – oxygen (O2) ices upon exposure to energetic electrons. Isomer-selective photoionization time-of-flight mass spectrometry (PI-ReTOF-MS) facilitated the gas phase detection of aminomethanol during the temperature program desorption (TPD) phase of the reaction products. The preparation and observation of the key transient aminomethanol changes our perception of the synthetic pathways to amino acids and the unexpected kinetic stability in extreme environments.