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Abstract Small organic molecules absorbing and emitting in the shortwave infrared (SWIR, 1000–2000 nm) region are desirable for biological imaging applications due to low auto‐fluorescence, reduce photon scattering, and good tissue penetration depth of photons which allows forin vivoimaging with high resolution and sensitivity. Si‐substituted xanthene‐based fluorophores with indolizine donors have demonstrated some of the longest wavelengths of absorption and emission from organic dyes. This work seeks to compare an indolizine heterocyclic nitrogen with dimethyl aniline nitrogen donors on otherwise identical Si‐substituted xanthene fluorophoresviaoptical spectroscopy, computational chemistry and electrochemistry. Three donors are compared including an indolizine donor, a ubiquitous dimethyl aniline donor, and a vinyl dimethyl aniline group that keeps the number of π‐bonds consistent with indolizine. Significantly higher quantum yields and molar absorptivity are observed in these studies for a dimethylamine‐based donor relative to a simple indolizine donor absorbing and emitting at similar wavelengths (~1312 nm emission). Substantially longer wavelengths are obtainable by appending aniline‐based groups to the indolizine donor (~1700 nm) indicating longer wavelengths can be accessed with indolizine donors while stronger emitters can be accessed with anilines in place of indolizine. 

Abstract Changes in the viscosity of intracellular microenvironments may indicate the onset of diseases like diabetes, blood‐based illnesses, hypertension, and Alzheimer's. To date, monitoring viscosity changes in the intracellular environment remains a challenge with prior work focusing primarily on visible light‐absorbing viscosity sensing fluorophores. Herein, a series of near‐infrared (NIR, 700–1000 nm) absorbing and emitting indolizine squaraine fluorophores (1PhSQ,2PhSQ,SO₃SQ,1DMASQ,7DMASQ, and1,7DMASQ) are synthesized and studied for NIR viscosity sensitivity.2PhSQexhibits a very high slope in its Forster‐Hoffmann plot at 0.75 which indicates this dye is a potent viscosity sensor. The properties of the squaraine fluorophores are studied computationallyviadensity functional theory (DFT) and time‐dependent (TD)‐DFT. Experimentally, both steady‐state and time‐resolved emission spectroscopy, absorption spectroscopy, and electrochemical characterization are conducted on the dyes. Precise photophysical tuning is observed within the series with emission maxima wavelengths as long as 881 nm for1,7DMASQand fluorescence quantum yields as high as 39.5 and 72.0 % for1PhSQin DCM and THF, respectively. The high tunability of this molecular scaffold renders indolizine squaraine fluorophores excellent prospects as viscosity‐sensitive biological imaging agents with2PhSQgiving a dramatically higher fluorescence quantum yield (from 0.3 to 37.1 %) as viscosity increases. 

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. 

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. 

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 Ni^IIaddition, 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 Ni^IIsite, towards the N‐termini, compared to below the Ni^IIsite towards the C‐termini. 

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. 

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. 

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. 

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. 

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.