A rapid and robust method for amino acid quantification using a simple N-hydroxysuccinimide ester derivatization and liquid chromatography-ion mobility-mass spectrometry.

The vast majority of mass spectrometry (MS)-based metabolomics studies employ reversed-phase liquid chromatography (RPLC) to separate analytes prior to MS detection. Highly polar metabolites, such as amino acids (AAs), are poorly retained by RPLC, making quantitation of these key species challenging across the broad concentration ranges typically observed in biological specimens, such as cell extracts. To improve the detection and quantitation of AAs in microglial cell extracts, the implementation of a 4-dimethylaminobenzoylamido acetic acid N-hydroxysuccinimide ester (DBAA-NHS) derivatization agent was explored for its ability to improve both analyte retention and detection limits in RPLC-MS. In addition to the introduction of the DBAA-NHS labeling reagent, a uniformly (U) 13C-labeled yeast extract was also introduced during the sample preparation workflow as an internal standard (IS) to eliminate artifacts and to enable targeted quantitation of AAs, as well as untargeted amine submetabolome profiling. To improve method sensitivity and selectivity, multiplexed drift-tube ion mobility (IM) was integrated into the LC-MS workflow, facilitating the separation of isomeric metabolites, and improving the structural identification of unknown metabolites. Implementation of the U-13C-labeled yeast extract during the multiplexed LC-IM-MS analysis enabled the quantitation of 19 of the 20 common AAs, supporting a linear dynamic range spanning up to three orders of magnitude in concentration for microglial cell extracts, in addition to reducing the required cell count for reliable quantitation from 10 to 5 million cells per sample.

Excitation-Wavelength-Dependent Photoinduced Electron Transfer in a π-Conjugated Diblock Oligomer.

Control of photoinduced electron transfer through selective excitation of a π-conjugated diblock oligomeric system featuring tetrathiophene (T4) and tetra(phenylene ethynylene) (PE4) donor blocks capped with a naphthalene diimide (NDI) acceptor (T4PE4NDI) is demonstrated. Each π-conjugated oligomeric segment has its own discrete ionization potential, electron affinity, and optical band gap which provides an absorption profile that has specific wavelengths that offer selective excitation of the PE4 and T4 blocks. Therefore, T4PE4NDI can be selectively excited to form a charge-separated state via ultrafast photoinduced electron transfer from the PE4 segment to NDI when excited at 370 nm, but it does not produce a charge-separated state when excited at 420 nm (T4). Picosecond transient absorption techniques were performed to probe the excited-state dynamics, revealing ultrafast charge separation (∼4 ps) occurring from the PE4 segment to NDI when excited at 370 nm, followed by delocalization of the hole over the T4 segment. On the contrary, electron transfer is suppressed with excitation at longer wavelengths (≥420 nm), where the spectrum is dominated by the T4 unit. The rate of electron transfer and charge recombination was investigated versus the length of the PE bridge unit in oligomers featuring zero and two PE units (T4NDI and T4PE2NDI). The rate of charge recombination decreases from 1.2 × 1011 to 1.0 × 109 s-1 with increasing bridge length between the T4 and NDI components (T4NDI to T4PE4NDI). Furthermore, wavelength-dependent photoinduced electron transfer was not observed in either T4NDI or T4PE2NDI due to an insufficient PEn bridge length. This work demonstrates the ability to use optical wavelength to control photoinduced electron transfer in a fully π-conjugated oligomer.

Fluorescent Charge-Transfer Excited States in Acceptor Derivatized Thiophene Oligomers.

A family of thiophene oligomers with lengths of 3, 4, 5, 6, and 8 units were synthesized and end-capped with a strongly coupled naphthalimide acceptor (TnNIF) which produces an emissive intramolecular charge-transfer state. A thorough photophysical study was performed on the oligomers including UV-vis absorption, fluorescence, and picosecond transient absorption spectroscopy to investigate the effect of thiophene oligomer length/donor strength and solvent polarity on the intramolecular charge-transfer properties. In hexane, the TnNIF compounds behave in a manner similar to that of oligothiophenes as fluorescence from a local singlet excited state and intersystem crossing to the triplet state dominates the excited-state dynamics. Interestingly, the excited-state dynamics become much more complicated with increasing solvent polarity, from ether to acetone, where emission from a charge-transfer state (δ+TnNIF-δ) and quenching from a charge-separated state (•+TnNIF-•) become competitive. A mechanism is proposed that consists of a four-state diagram including a locally excited singlet state (1TnNIF), a triplet state (3TnNIF), an emissive charge-transfer state, and a nonemissive charge-separated state. The population of each of these states is highly dependent on both the thiophene oligomer length and solvent polarity which results in a mixture of excited states.

Free Energy Dependence of Photoinduced Electron Transfer in Octathiophene-Diimide Dyads.

Donor-acceptor dyads consisting of octathiophene (T8) paired with three (di)imide acceptors (naphthalene diimide (NDI), benzene diimide (BDI), and naphthalimide (NI)) were synthesized and probed for their photoinduced forward electron transfer (ET) and charge recombination kinetics by using ultrafast transient absorption (TA) spectroscopy. The three acceptors have different electron affinities, leading to variation in the energy of the charge-separated state and the driving force (ΔG) for forward ET and charge recombination. Analysis of the TA spectra and kinetics allows assignment of rates for forward ET and charge recombination for each of the oligomers. Electrochemistry and photoluminescence spectroscopy are used to determine the ΔG values for the ET processes. For two of the oligomers (T8NDI and T8BDI), the rates for forward ET and charge recombination are very rapid (k > 3 × 1010 s-1). By contrast, for the third oligomer (T8NI), the rates for both processes are considerably slower (k < 5 × 109 s-1). Analysis of the rate/free energy correlation for the series of oligomers reveals generally good agreement with the Marcus semiclassical theory. In all of the oligomers, the ET reactions are nonadiabatic, in part, due to weak coupling caused by out-of-plane twisting of the phenylene spacer that lies between the T8 segment and the (di)imide acceptors. The rapid ET dynamics for T8NDI and T8BDI are explained as arising due to the processes occurring near the barrierless region (-ΔG ≈ λ) or slightly into the Marcus inverted region (-ΔG > λ). The slower dynamics for T8NI are explained as arising because the forward ET is weakly exothermic, whereas charge recombination is deep into the inverted region. This study is the first to produce experimental results that match a full Marcus bell-shaped curve with ET rates in the normal, barrrierless, and inverted regions in dyads based on a π-conjugated oligomer donor.

Drug Overdose, Loss of Consciousness, and Compartment Syndrome: A Life-Threatening Combination.

Acute extremity compartment syndrome is considered an orthopedic emergency that has serious consequences if a correct diagnosis is not made rapidly. Patients who lose consciousness due to a drug overdose are known to collapse onto their extremities. The limbs are compressed for hours, placing them at an increased risk for acute extremity compartment syndrome and its sequelae. Compartment syndrome due to a compression of a limb from loss of consciousness secondary to drug overdose, presents unique issues to health care providers. In the setting of overdose compartment syndrome, it is similar to the more common traumatic type of compartment syndrome with respect to the pathophysiology, diagnosis and treatment. However, it differs in relation to the muscles affected, physical assessment strategy, and accurately determining the amount of the time from onset of injury to the presentation of symptoms. The purpose of this article is to facilitate emergency department nurses' understanding of the complexities of overdose compartment syndrome, combined with the importance of early recognition of the condition. In addition, the authors review the pathophysiology, the traditional and innovative diagnostic techniques, and the current treatment options available for overdose compartment syndrome.

Photoinduced Electron Transfer in Naphthalene Diimide End-Capped Thiophene Oligomers.

A series of linear thiophene oligomers containing 4, 6, 8, 10, and 12 thienylene units were synthesized and end-capped with naphthalene diimide (NDI) acceptors with the objective to study the effect of oligomer length on the dynamics of photoinduced electron transfer and charge recombination. The synthetic work afforded a series of nonacceptor-substituted thiophene oligomers, Tn, and corresponding NDI end-capped series, TnNDI2 (where n is the number of thienylene repeat units). This paper reports a complete photophysical characterization study of the Tn and TnNDI2 series by using steady-state absorption, fluorescence, singlet oxygen sensitized emission, two-photon absorption, and nanosecond-microsecond transient absorption spectroscopy. The thermodynamics of photoinduced electron transfer and charge recombination in the TnNDI2 oligomers were determined by analysis of photophysical and electrochemical data. Excitation of the Tn oligomers gives rise to efficient fluorescence and intersystem crossing to a triplet excited state that is easily observed by nanosecond transient absorption spectroscopy. Bimolecular photoinduced electron transfer from the triplet states, 3Tn*, to N,N-dimethylviologen (MV2+) occurs, and by using microsecond transient absorption it is possible to assign the visible region absorption spectra for the one electron oxidized (polaron) states, Tn+•. The fluorescence of the TnNDI2 oligomers is quenched nearly quantitatively, and no long-lived transients are observed by nanosecond transient absorption. These findings suggest that rapid photoinduced electron transfer and charge recombination occurs, NDI-1(Tn)*-NDI → NDI-(Tn)+•-NDI-• → NDI-Tn-NDI. Preliminary femtosecond-picosecond transient absorption studies on T4NDI2 reveal that both forward electron transfer and charge recombination occur with k > 1011 s-1, consistent with both reactions being nearly activationless. Analysis with semiclassical electron transfer theory suggests that both reactions occur at near the optimum driving force where -ΔG ∼ λ.

High-Performance Wearable Organic Photodetectors by Molecular Design and Green Solvent Processing for Pulse Oximetry and Photoplethysmography.

White-light detection from the visible to the near-infrared region is central to many applications such as high-speed cameras, autonomous vehicles, and wearable electronics. While organic photodetectors (OPDs) are being developed for such applications, several challenges must be overcome to produce scalable high-detectivity OPDs. This includes issues associated with low responsivity, narrow absorption range, and environmentally friendly device fabrication. Here, an OPD system processed from 2-methyltetrahydrofuran (2-MeTHF) sets a record in light detectivity, which is also comparable with commercially available silicon-based photodiodes is reported. The newly designed OPD is employed in wearable devices to monitor heart rate and blood oxygen saturation using a flexible OPD-based finger pulse oximeter. In achieving this, a framework for a detailed understanding of the structure-processing-property relationship in these OPDs is also developed. The bulk heterojunction (BHJ) thin films processed from 2-MeTHF are characterized at different length scales with advanced techniques. The BHJ morphology exhibits optimal intermixing and phase separation of donor and acceptor moieties, which facilitates the charge generation and collection process. Benefitting from high charge carrier mobilities and a low shunt leakage current, the newly developed OPD exhibits a specific detectivity of above 1012  Jones over 400-900 nm, which is higher than those of reference devices processed from chlorobenzene and ortho-xylene.

Elucidating Design Rules toward Enhanced Solid-State Charge Transport in Oligoether-Functionalized Dioxythiophene-Based Alternating Copolymers.

This study investigates the solid-state charge transport properties of the oxidized forms of dioxythiophene-based alternating copolymers consisting of an oligoether-functionalized 3,4-propylenedioxythiophene (ProDOT) copolymerized with different aryl groups, dimethyl ProDOT (DMP), 3,4-ethylenedioxythiophene (EDOT), and 3,4-phenylenedioxythiophene (PheDOT), respectively, to yield copolymers P(OE3)-D, P(OE3)-E, and P(OE3)-Ph. At a dopant concentration of 5 mM FeTos3, the electrical conductivities of these copolymers vary significantly (ranging between 9 and 195 S cm-1) with the EDOT copolymer, P(OE3)-E, achieving the highest electrical conductivity. UV-vis-NIR and X-ray spectroscopies show differences in both susceptibility to oxidative doping and extent of oxidation for the P(OE3) series, with P(OE3)-E being the most doped. Wide-angle X-ray scattering measurements indicate that P(OE3)-E generally demonstrates the lowest paracrystallinity values in the series, as well as relatively small π-π stacking distances. The significant (i.e., order of magnitude) increase in electrical conductivity of doped P(OE3)-E films versus doped P(OE3)-D or P(OE3)-Ph films can therefore be attributed to P(OE3)-E exhibiting both the highest carrier ratios in the P(OE3) series, along with good π-π overlap and local ordering (low paracrystallinity values). Furthermore, these trends in the extent of doping and paracrystallinity are consistent with the reduced Fermi energy level and transport function prefactor parameters calculated using the semilocalized transport (SLoT) model. Observed differences in carrier ratios at the transport edge (ct) and reduced Fermi energies [η(c)] suggest a broader electronic band (better overlap and more delocalization) for the EDOT-incorporating P(OE3)-E polymer relative to P(OE3)-D and P(OE3)-Ph. Ultimately, we rationalize improvements in electrical conductivity due to microstructural and doping enhancements caused by EDOT incorporation, a structure-property relationship worth considering in the future design of highly electrically conductive systems.

Additive-free molecular acceptor organic solar cells processed from a biorenewable solvent approaching 15% efficiency.

We report on the use of molecular acceptors (MAs) and donor polymers processed with a biomass-derived solvent (2-methyltetrahydrofuran, 2-MeTHF) to facilitate bulk heterojunction (BHJ) organic photovoltaics (OPVs) with power conversion efficiency (PCE) approaching 15%. Our approach makes use of two newly designed donor polymers with an opened ring unit in their structures along with three molecular acceptors (MAs) where the backbone and sidechain were engineered to enhance the processability of BHJ OPVs using 2-MeTHF, as evaluated by an analysis of donor-acceptor (D-A) miscibility and interaction parameters. To understand the differences in the PCE values that ranged from 9-15% as a function of composition, the surface, bulk, and interfacial BHJ morphologies were characterized at different length scales using atomic force microscopy, grazing-incidence wide-angle X-ray scattering, resonant soft X-ray scattering, X-ray photoelectron spectroscopy, and 2D solid-state nuclear magnetic resonance spectroscopy. Our results indicate that the favorable D-A intermixing that occurs in the best performing BHJ film with an average domain size of ∼25 nm, high domain purity, uniform distribution and enhanced local packing interactions - facilitates charge generation and extraction while limiting the trap-assisted recombination process in the device, leading to high effective mobility and good performance.

Iron(III) Dopant Counterions Affect the Charge-Transport Properties of Poly(Thiophene) and Poly(Dialkoxythiophene) Derivatives.

This study investigates the charge-transport properties of poly(3-hexylthiophene-2,5-diyl) (P3HT) and poly(ProDOT-alt-biEDOT) (PE2) films doped with a set of iron(III)-based dopants and as a function of dopant concentration. X-ray photoelectron spectroscopy measurements show that doping P3HT with 12 mM iron(III) solutions leads to similar extents of oxidation, independent of the dopant anion; however, the electrical conductivities and Seebeck coefficients vary significantly (5 S cm-1 and + 82 µV K-1 with tosylate and 56 S cm-1 and +31 µV K-1 with perchlorate). In contrast, PE2 thermoelectric transport properties vary less with respect to the iron(III) anion chemistry, which is attributed to PE2 having a lower onset of oxidation than P3HT. Consequentially, PE2 doped with 12 mM iron(III) perchlorate obtained an electrical conductivity of 315 S cm-1 and a Seebeck coefficient of + 7 µV K-1. Modeling these thermoelectric properties with the semilocalized transport (SLoT) model suggests that tosylate-doped P3HT remains mostly in the localized transport regime, attributed to more disorder in the microstructure. In contrast perchlorate-doped P3HT and PE2 films exhibited thermally deactivated electrical conductivities and metal-like transport at high doping levels over limited temperature ranges. Finally, the SLoT model suggests that PE2 has the potential to be more electrically conductive than P3HT due to PE2's ability to achieve higher extents of oxidation and larger shifts in the reduced Fermi energy levels.

Importance of Electric-Field-Independent Mobilities in Thick-Film Organic Solar Cells.

In organic solar cells (OSCs), a thick active layer usually yields a higher photocurrent with broader optical absorption than a thin active layer. In fact, a ∼300 nm thick active layer is more compatible with large-area processing methods and theoretically should be a better spot for efficiency optimization. However, the bottleneck of developing high-efficiency thick-film OSCs is the loss in fill factor (FF). The origin of the FF loss is not clearly understood, and there a direct method to identify photoactive materials for high-efficiency thick-film OSCs is lacking. Here, we demonstrate that the mobility field-dependent coefficient is an important parameter directly determining the FF loss in thick-film OSCs. Simulation results based on the drift-diffusion model reveal that a mobility field-dependent coefficient smaller than 10-3 (V/cm)-1/2 is required to maintain a good FF in thick-film devices. To confirm our simulation results, we studied the performance of two ternary bulk heterojunction (BHJ) blends, PTQ10:N3:PC71BM and PM6:N3:PC71BM. We found that the PTQ10 blend film has weaker field-dependent mobilities, giving rise to a more balanced electron-hole transport at low fields. While both the PM6 blend and PTQ10 blend yield good performance in thin-film devices (∼100 nm), only the PTQ10 blend can retain a FF = 74% with an active layer thickness of up to 300 nm. Combining the benefits of a higher JSC in thick-film devices, we achieved a PCE of 16.8% in a 300 nm thick PTQ10:N3:PC71BM OSC. Such a high FF in the thick-film PTQ10 blend is also consistent with the observation of lower charge recombination from light-intensity-dependent measurements and lower energetic disorder observed in photothermal deflection spectroscopy.

Orbital Roof "Blow-in" Fracture: A Case Report and Review.

We report a relatively rare case of an essentially isolated orbital roof "blow-in" fracture in a pediatric patient. A 13-year-old male presented with headache and nausea following blunt facial trauma sustained during a skate boarding accident. CT head revealed soft tissue swelling and an abnormal bony density in the superior, posterior right orbital region. Follow-up CT orbits revealed a comminuted orbital roof "blow-in" fracture with involvement of the ethmoid air cells and two tiny foci of intracranial air. Expert consultation revealed normal ophthalmologic and neurologic examination; conservative management was recommended. The case report is followed by a brief overview of orbital fractures including pertinent radiographic considerations.