bluuebunny/crossref_metadata_2025 huggingface dataset:
Automated analysis of microplastics based on vibrational spectroscopy: Are we measuring the same metrics?
Authors: Dong Mingtan , She Zhenbing , Xiong Xiong , Luo Zejiao
Published: February 2022

The traditional manual analysis of microplastics has been criticized because it is labor intensive, inaccurate for identifying very small microplastics, and difficult to standardize or compare. There are already three automated analysis strategies for microplastics based on vibrational spectroscopy, laser direct infrared (LDIR)-based particle analysis, Raman-based particle analysis, and focal plane array-Fourier transform infrared (FPA-FTIR) imaging. We compared the performances of these strategies in terms of their quantification, detection limit, size measurement, and material identification accuracy and analysis speed by analyzing the same standard and environmental samples. Unfortunately, the automated analysis strategies are not consistent in terms of the quantification and material identification results. The number of particles smaller than 60 μm recognized by Raman-based particle analysis is far greater than that recognized by LDIR-based particle analysis. Raman-based particle analysis has a submicrometer detection limit but should not be used in the automated analysis of microplastics in environmental samples because of the strong fluorescence interference. LDIR-based particle analysis provides the fastest analysis speed, but we suggest using a reliable detection limit of approximately 60 μm and considering the material identification results and reference database used because the wavenumbers LDIR spectra are in the range of 975-1800 cm-1. FPA-FTIR imaging provides relatively reliable quantification and material identification for microplastics in environmental samples but might provide an imprecise description of the particle shapes. Optical photothermal infrared (O-PTIR) spectroscopy can detect submicron-sized microplastics (0.5-5 μm) but has not been automated. As a technological advancement, automated analysis of microplastics should be encouraged, but we need to foster the strengths and circumvent the weaknesses of different strategies. The automated analysis of microplastics should be further validated and standardized.
Deep Learning for the Automation of Particle Analysis in Catalyst Layers for Polymer Electrolyte Fuel Cells
Authors: Colliard-Granero André , Batool Mariah , Jankovic Jasna , Jitsev Jenia , Eikerling Michael H. , Malek Kourosh , Eslamibidgoli Mohammad Javad
Published: February 2022

The rapidly growing use of imaging infrastructure in the energy materials domain drives significant data accumulation in terms of their amount and complexity. The applications of routine techniques for image processing in materials research are often \textit{ad hoc}, indiscriminate, and empirical, which renders the crucial task of obtaining reliable metrics for quantifications obscure. Moreover, these techniques are expensive, slow, and often involve several preprocessing steps. This paper presents a novel deep learning-based approach for the high-throughput analysis of the particle size distributions from transmission electron microscopy (TEM) images of carbon-supported catalysts for polymer electrolyte fuel cells. Our approach employs training an instance segmentation model, called StarDist [Schmidt et al. Medical Image Computing and Computer-Assisted Intervention – MICCAI 2018, Lecture Notes in Computer Science, vol 11071. Springer, Cham], which resolves the main challenge in the pixel-wise localization of nanoparticles in TEM images: the overlapping particles. The segmentation maps outperform models reported in the literature, and the results on particle size analyses agree well with manual particle size measurements, albeit at a significantly lower cost.
Low-Cost Temperature Transition Mixtures (TTM) Based on Ethylene Glycol/potassium Hydroxide as Reversible CO2 Sorbents
Authors: Costamagna Marcello , Micheli Eleonora , Canale Valentino , Ciulla Michele , Siani Gabriella , Di Profio Pietro , Tiecco Matteo , Ciancaleoni Gianluca
Published: February 2022

A low-cost Transition Temperature Mixture (TTM) has been synthesized by mixing ethylene glycol and potassium hydroxide as a new non-aqueous CO2 sorbent. Boric acid has been added to ensure the reversibility of the system and a small amount of water to modulate the viscosity and optimize the performances. The resulting mixtures have been characterized in terms of viscosity, conductivity and density over temperature (therefore ionicity via Walden plots) and the effect of temperature, pressure and the kinetics of the absorption have been evaluated. Under optimized conditions, the four-component mixture EG/KOH/BA/H2O 3:1:1:3 can absorb 24 gCO2/kgsorbent in 30 minutes at 35°C at 1 atm (59 after 4 h) and 60 gCO2/kgsorbent in 30 minutes at high pressure (10 and 20 atm, 80 gCO2/kgsorbent after 50 min), while the desorption is quantitative after 30 minutes at only 60°C under a gentle N2 flow. The system is robust enough to ensure multiple absorption/desorption cycles.
Boosting the Efficiency and Stability of Blue TADF Emitters by Deuteration
Authors: Huang Tianyu , Zhang Dongdong , Zhan Ge , Wang Qi , Li Guomeng , Hong Xiangchen , Liu Ziyang , Duan Lian
Published: February 2022

Deep-blue organic light-emitting diodes (OLEDs) with both high efficiency and stability remain exclusive in scientific literatures after decades of research. A key reason is the chemical bond dissociation through conical intersections between potential energy surfaces (PESs) of energetically-hot excited states and dissociative states. Here, we report a deuteration strategy to stabilize blue thermally activated delayed fluorescence (TADF) emitters. It is unveiled that deuteration would lower high-frequency vibrations to create shallower PESs in both ground and excited states, energetically retarding the cross of the conical intersection point in dissociative process and alleviate vibrational coupling to eliminate nonradiative decay. With a deuterated blue TADF compound, namely 2,3,4,5,6-pentakis(9H-carbazol-9-yl-d8) benzonitrile, as the sensitizer, a deep-blue OLED simultaneously achieves a peak external quantum efficiency of 30.3%, a Commission Internationale de L’Eclairage coordinate y value (CIEy) of 0.17, and a superb LT80 (time to 80% of initial luminance) of 227 h at 1000 cd/m2. And a blue OLED with a CIEy~0.19 shows an even longer LT80 of 456 h at 1000 cd/m2.
Nickel-Catalyzed Defluorinative Coupling of Aliphatic Aldehydes with Trifluoromethyl Styrenes
Authors: Xiao Jichao , Montgomery John
Published: February 2022

A simple procedure is reported for the nickel-catalyzed defluorinative alkylation of unactivated aliphatic aldehydes. The process involves the catalytic reductive union of trifluoromethyl styrenes with aldehydes using a nickel complex of a 6,6’-disubstituted bipyridine ligand with zinc metal as the terminal reductant. The protocol is distinguished by its broad substrate scope, mild conditions, and simple catalytic setup. Reaction outcomes are consistent with the intermediacy of an alpha-silyloxy(alkyl)nickel intermediate generated by a low-valent nickel catalyst, silyl electrophile, and the aldehyde substrate. Mechanistic findings with cyclopropanecarboxaldehyde provide insights into nature of the reactive intermediates and illustrate fundamental reactivity differences that are governed by subtle changes in ligand and substrate structure.
Orbital Exchange Calculations of Chemical Bonding in Some Molecules Containing Carbon
Authors: Merrithew Paul
Published: February 2022

The purpose of this paper is to extend the application of the orbital exchange method to a series of molecules containing carbon. The paper describes the calculation of bond length, bond strength and dipole moment in ethane, ethylene, acetylene, benzene, allene, hydrogen cyanide, formaldehyde, floromethane, tetrafloromethane and floromethylidyne (CF). This work explains how the s bonding orbital coefficients in such molecules as ethylene and acetylene are maximized to enable shorter and stronger carbon-carbon bonds. Pi orbital resonance of the form [C-C+,CC,C+C-] in ethylene, acetylene, and benzene is described and quantified. Pi orbital resonance in HCN [CN,C+N-] and H2CO [CO,C+O-] and sigma orbital resonance in H3CF [H3CF, H3C+F-], CF4 and CF is quantified. Except for HC bonds, calculated bond lengths are within 0.005Å of observed values. Calculated molecular energies are within 2%.
Observation of an Intermediate to H2 Binding in a Metal–organic Framework
Authors: Barnett Brandon R. , Evans Hayden A. , Su Gregory M. , Jiang Henry Z. H. , Chakraborty Romit , Banyeretse Didier , Hartman Tyler , Martinez Madison , Trump Benjamin A. , Tarver Jacob , Dods Matthew , Funke Lena M. , Börgel Jonas , Reimer Jeffrey A. , Drisdell Walter S. , Hurst Katherine , Gennett Thomas , FitzGerald Stephen A. , Brown Craig M. , Head-Gordon Martin , Long Jeffrey R.
Published: February 2022

Coordinatively-unsaturated metal sites within certain zeolites and metal–organic frameworks can strongly adsorb various molecules. While many classical examples involve electron-poor metal cations that interact with adsorbates largely through electrostatic interactions, unsaturated electron-rich metal centers housed within porous frameworks can often chemisorb guests amenable to redox activity or covalent bond formation. Despite the promise that materials bearing such sites hold in addressing myriad challenges in gas separations and storage, very few studies have directly interrogated mechanisms of chemisorption at open metal sites within porous frameworks. Here, we show that H2chemisorption at the trigonal pyramidal Cu+sites in the metal–organic framework CuI‑MFU-4l occurs via the intermediacy of a metastable physisorbed precursor species. This finding demonstrates that adsorption at framework metal sites does not always follow a concerted pathway and underscores the importance of probing kinetics in the design of next-generation adsorbents.
Uncertainty Quantification of Reactivity Scales
Authors: Proppe Jonny , Kircher Johannes
Published: February 2022

​According to Mayr, polar organic synthesis can be rationalized by a simple empirical relationship linking bimolecular rate constants to as few as three reactivity parameters. Here, we propose an extension to Mayr’s reactivity method that is rooted in uncertainty quantification and transforms the reactivity parameters into probability distributions. Through uncertainty propagation, these distributions can be transformed into uncertainty estimates for bimolecular rate constants. Chemists can exploit these virtual error bars to enhance synthesis planning and to decrease the ambiguity of conclusions drawn from experimental data. We demonstrate the above at the example of the reference data set released by Mayr and co-workers [J. Am. Chem. Soc. 2001, 123, 9500; J. Am. Chem. Soc. 2012, 134, 13902]. As by-product of the new approach, we obtain revised reactivity parameters for 36 π-nucleophiles and 32 benzhydrylium ions.
Boronic ester derivative-dependent activity of parthenolide analogues
Authors: Li Xingjian , Williams George , Quy Alex , Zhao Yiming , Male Louise , Anslyn Eric , Stankovic Tatjana , Leach Andrew , Agathanggelou Angelo , Fossey John
Published: February 2022

Four parthenolide derived prodrugs, containing different boronic ester moieties, were synthesised, their drug-like properties were calculated and their activity against chronic lymphocytic leukaemia (CLL) MEC1 cells measured. Differences in the clogP, the propensity towards oxidation by hydrogen peroxide, the affinity of the associated diols to a model boronic acid and the biological activity against MEC1 cells were contrasted, and it was found that the propensity for oxidation correlated to biological activity.
indexGIXS – software for visualizing and interactive indexing of grazing-incidence scattering data
Authors: Smilgies Detlef-M. , Li Ruipeng
Published: February 2022

Grazing incidence small- and wide-angle scattering (GISAXS, GIWAXS) are widely applied for the study of organic thin films, be it for the characterization of nanostructured morphologies in block copolymers, nanocomposites, or nanoparticle assemblies, or the packing and orientation of small aromatic molecules and conjugated polymers. Organic thin films typically are uniaxial powders, with specific crystallographic planes oriented parallel to the substrate surface. The associated fiber texture scattering patterns are complicated by refraction corrections and multiple scattering. We present an interactive graphics tool to index such patterns.
Probing Chirality across the Electromagnetic Spectrum with the Full Semi-classical Light--Matter Interaction
Authors: van Horn Martin , Saue Trond , List Nanna
Published: February 2022

We present a formulation and implementation of anisotropic and isotropic electronic circular dichroism (ECD) using the full semi-classical light--matter interaction operator within a four-component relativistic framework. The account of both beyond-first-order light--matter interactions and relativistic effects allows us to investigate the ECD response across the electromagnetic spectrum from optical to X-ray wavelengths where relativistic selection rules and spatial field variations gain increasing importance. We consider the isotropic and oriented ECD across the valence, sulfur L- and K-edge transitions in the simplest disulfides, H2S2 and (CH3S)2, and evaluate the influence of the full interaction by comparing to a traditional truncated formulation in the Coulomb gauge (velocity representation). Additionally, we demonstrate that in the relativistic formalism it is possible to work in the velocity representation, hence keeping order-by-order gauge-origin invariance, contrary to multipolar gauge, yet being able to distinguish electric and magnetic multipole contributions. Going beyond a first-order treatment in the wave vector is mandatory in the higher-energy end of the soft X-ray region where the consequent intensity redistribution becomes significant. While the sulfur K-edge absorption spectrum is essentially unaffected by this redistribution, the signed differential counterpart is not: at least third-order contributions are required to describe the differential absorption profile that is otherwise overestimated by a factor of about two.
OS100: A Benchmark Set of 100 Digitized UV-Visible Spectra and Derived Experimental Oscillator Strengths
Authors: Tarleton Astrid , Garcia-Alvarez Jorge , Wynn Anah , Awbrey Cade , Roberts Tomas , Gozem Samer
Published: February 2022

The scientific method involves validating computational theories and methods against experimental results. However, the comparison between theory and experiments is not always straightforward; in UV-visible spectroscopy, experiments provide a plot of wavelength-dependent molar extinction/attenuation coefficients (ε) while computations typically provide single-valued excitation energies and oscillator strengths (ƒ) for each band. ε and ƒ are related, but this relation is complicated by various broadening and solvation effects. We describe a protocol to fit and integrate experimental UV-visible spectra to obtain ƒexp values for absorption bands and to estimate the uncertainty in the fitting. We apply this protocol to derive 164 ƒexp values from 100 organic molecules ranging in size from 6-34 atoms. The corresponding computed oscillator strengths (ƒcomp) are obtained with time-dependent density functional theory and a polarizable continuum solvent model. By expressing experimental and computed absorption strengths using a common quantity, we directly compare ƒcomp and ƒexp. While ƒcomp and ƒexp are well correlated (linear regression R2=0. 914), ƒcomp in most cases significantly overestimates ƒexp (regression slope=1.31). The agreement between absolute ƒcomp and ƒexp values is substantially improved by accounting for a solvent refractive index factor, as suggested in some derivations in the literature. The 100 digitized UV-visible spectra are included as plain text files in the supporting information to aid in benchmarking computational or machine-learning approaches that aim to simulate realistic UV-visible absorption spectra.
Copper-Catalyzed Difluoromethylation of Alkyl Halides Enabled by Aryl Radical Activation of Carbon–Halogen Bonds
Authors: Cai Aijie , Yan Wenhao , Liu Wei
Published: February 2022

The engagement of unactivated alkyl halides in copper-catalyzed cross-coupling reactions has been historically challenging, due to their low reduction potential and the slow oxidative addition of copper(I) catalysts. In this work, we report a novel strategy that leverages the halogen abstraction ability of aryl radicals, thereby engaging a diverse range of alkyl iodides in copper-catalyzed Negishi–type cross-coupling reactions at room temperature. Specifically, aryl radicals generated via copper catalysis efficiently initiate the cleavage of the carbon–iodide bonds of alkyl iodides. The alkyl radicals thus generated enter the copper catalytic cycles to couple with a difluoromethyl zinc reagent, thus furnishing the alkyl difluoromethane products. This unprecedented Negishi–type difluoromethylation approach has been applied to the late-stage modification of densely functionalized pharmaceutical agents and natural products.
Tandem electrocatalytic N2 fixation via concerted proton-electron transfer
Authors: Garrido-Barros Pablo , Derosa Joseph , Chalkley Matthew , Peters Jonas
Published: February 2022

New electrochemical ammonia (NH3) synthesis technologies are of interest as a complementary route to the Haber-Bosch (HB) process for distributed fertilizer generation, and towards exploiting ammonia as a zero-carbon fuel produced via renewably-sourced electricity. Apropos of these goals is a surge of fundamental research targeting heterogeneous materials as electrocatalysts for the nitrogen reduction reaction (N2RR). These systems generally suffer from poor stability and NH3 selectivity; competitive hydrogen evolution reaction (HER) outcompetes N2RR. Molecular catalyst systems can be exquisitely tuned and offer an alternative strategy, but progress has thus far been thwarted by the same selectivity issue; HER dominates. Herein we describe a tandem catalysis strategy that offers a solution to this puzzle. A molecular complex that can mediate an N2 reduction cycle is partnered with a co-catalyst that interfaces the electrode and an acid to mediate concerted proton-electron transfer (CPET) steps, facilitating N−H bond formation at a favorable applied potential and overall thermodynamic efficiency. Without CPET, certain intermediates of the N2RR cycle would be unreactive via independent electron transfer (ET) or proton transfer (PT) steps, thereby shunting the system. Promisingly, complexes featuring several metals (W, Mo, Os, Fe) achieve N2RR electrocatalysis at the same applied potential in the presence of the CPET mediator, pointing to the generality of this tandem approach.
Ion-pairing chromatography and amine derivatization provide complementary approaches for the targeted UPLC-MS analysis of the polar metabolome
Authors: Sagi-Kiss Virag , Li Yufeng , Carey Matthew , Grover Sarah , Siems Karsten , Cirulli Francesca , Berry Alessandra , Musillo Chiara , Wilson Ian , Want Elizabeth , Bundy Jacob
Published: February 2022

Liquid chromatography coupled to mass spectrometry is a key metabolomics technology. Reversed-phase liquid chromatog-raphy (RPLC) is very widely used as a separation step, possessing excellent characteristics with respect to reproducibility and reliability, but typically has poor retention of highly polar metabolites. Here, we evaluated the combination of two alter-native methods for improving retention of polar metabolites based on 6-aminoquinoloyl-N-hydroxysuccinidimyl carbamate derivatization for amine groups, and ion-pairing chromatography (IPC) using tributylamine as an ion-pairing agent to retain acids. We compared both of these methods to RPLC and also to each other, for targeted analysis using a triple-quadrupole mass spectrometer, applied to a library of ca. 500 polar metabolites. IPC and derivatization were complementary in terms of their coverage: combined, they improved the proportion of metabolites with good retention to 91%, compared to just 39% for RPLC alone. We detected 132 metabolites for real biological samples (liver extracts) with good reproducibility (based on coefficients of variation in pooled biological quality control samples). Finally, we tested the combination of methods with real-world samples by analyzing a set of liver extracts from aged male and female mice that had been treated with the poly-phenol compound ampelopsin. Furthermore, we also compared the results of these LC-MS methods to 1H NMR spectrosco-py as an orthogonal method (also termed statistical heterospectroscopy (SHY)), and found a strong correlation between the results of these different analytical approaches. By these means, not only were a number of significantly changed metabolites detected, but also it could be shown that there was a clear interaction between ampelopsin treatment and sex, in that the di-rection of metabolite change was opposite for males and females.
Aluminium Mediated Isocyanide Insertion and Sequential Ring Opening Cyclization (SROC) Strategy: Synthesis of Azole Fused Benzimidazoquinazoline Skeletons
Authors: H. Shinde anand , Venkata Nagarjuna Babu , S. Punith , Sharada D. S.
Published: February 2022

A first report on transition-metal-free aluminium chloride mediated isocyanide insertion between two amine nucleophiles have been presented. Also, an unusual C-N bond cleavage allow for the further development of copper mediated ring open-ing cyclization (SROC) strategy for the synthesis of azole fused benzimidazoquinazoline scaffolds. The key features of this protocol are aluminium chloride as non-transition-metal based mediator, oxidant/base/ligand free isocyanide insertion, three new C-N and one C-C bond formations and simultaneous construction of multiprivileged azole fused benzimidazoquinazo-line in good yields.
Overcoming the Challenges Towards Selective C(6)-H Alkylation of 2- Pyridone with Maleimide through Mn(I)-Catalyzed C-H bond Activation: Zn assisted Unexpected Migration of Directing group
Authors: Mohanty Smruti Ranjan , Prusty Namrata , Banjare Shyam Kumar , Nanda Tanmayee , Ravikumar Ponneri C.
Published: February 2022

An earth-abundant and inexpensive Mn(I)-catalyzed alkylation of 2-pyridone with maleimide has been reported for the first time, in contrast to previously reported Diels-alder product. The directing group was easily removed after functionalization. Notably, unexpected migration of pyridine ring has been discovered in presence of zinc, and acetic acid conditions, which also provides a new route to quaternary carbon centers which contain two heterocycles. Furthermore, single crystal X-ray and HRMS revealed a five-membered manganacycle intermediate. This methodology tolerates a wide variety of functional groups delivering the alkylated products in moderate to excellent yields
Photosynthetic Reaction Center Variants Made via Genetic Code Expansion Show Tyr at M210 Tunes the Initial Electron Transfer Mechanism
Authors: Weaver Jared , Lin Chi-Yun , Faries Kaitlyn M. , Mathews Irimpan , Russi Silvia , Holten Dewey , Kirmaier Christine , Boxer Steven
Published: February 2022

Photosynthetic reaction centers (RCs) from Rhodobacter sphaeroides were engineered to vary the electronic properties of a key tyrosine close to an essential electron transfer component (M210) via its replacement with site-specific genetically encoded noncanonical amino acid tyrosine analogs. High fidelity of noncanonical amino acid incorporation was verified with mass spectrometry and x-ray crystallography and demonstrated that RC variants exhibit no significant structural alterations relative to wild-type. Ultrafast transient absorption spectroscopy indicates the excited primary electron donor, P*, decays via an approximately 4 ps and 20 ps population to produce the charge-separated state P+HA- in all variants. Global analysis indicates that in the 4 ps population P+HA- forms through a 2-step process P* –> P+BA– –> P+HA-, while in the 20 ps population it forms via a 1-step P* –> P+HA– superexchange mechanism. The percentage of P* population that decays via the superexchange route varies from approximately 25% to 45% among variants while in wild-type this percentage is approximately 15%. Increases in the P* population which decays via superexchange correlates with increases in free energy of the P+BA– intermediate caused by a given M210 tyrosine analog. This was experimentally estimated through resonance Stark spectroscopy, redox titrations, and near-infrared absorption measurements. As the most energetically perturbative variant, 3-nitrotyrosine at M210 creates an approximately 110 meV increase in the free energy of P+BA– along with a dramatic diminution of the 1030 nm transient absorption band indicative of P+BA– formation. Collectively this work indicates the tyrosine at M210 tunes the mechanism of primary electron transfer in the RC.
Temporally programmed polymer - solvent interactions using a chemical reaction network
Authors: Klemm Benjamin , Lewis Reece , Piergentili Irene , Eelkema Rienk
Published: February 2022

Chemical reaction networks (CRNs) that operate under constant influx of energy enable artificial materials to autonomously respond to their environment by activation and deactivation of intermolecular interactions. Generally, their activation can be driven by various energy sources, yet their deactivation to non-interacting building blocks remains largely limited to hydrolysis and internal pH change. To achieve control over deactivation, we developed a new CRN that enables reversible formation of positive charges on a tertiary amine substrate, which are removed using nucleophilic signals that control the deactivation kinetics. Incorporation of the CRN in a polymer material leads to a temporally programmed transition from collapsed and hydrophobic to solvated, hydrophilic polymer chains by controlling polymer-solvent interactions. Depending on the layout of the CRN, we can create stimuli-responsive or autonomously responding materials. This concept will not only offer new opportunities in molecular cargo delivery but also pave the way for next-generation interactive materials.
Molecular Alignment of a Meta-Aramid on Carbon Nanotubes by In-Situ Interfacial Polymerization.
Authors: Chazot Cécile , Damirchi Behzad , van Duin Adri , Hart John
Published: February 2022

Molecularly organized nanocomposites of polymers and carbon nanotubes (CNTs) have great promise as high-performance materials; in particular, conformal deposition of polymers can control interfacial properties for mechanical load transfer, electrical or thermal transport, or electro/chemical transduction. However, controllability of polymer-CNT interaction remains a challenge with common processing methods that combine CNTs and polymers in melt or in solution, often leading to non-uniform polymer distribution and/or aggregation of CNTs. Here, we demonstrate CNTs within net-shape sheets can be controllably coated with a thin, conformal coating of meta-aramid by simultaneous capillary infiltration and interfacial polymerization. We determine that π interaction between the polymer and CNTs results in chain alignment parallel to the CNT outer wall. Subsequent nucleation and growth of the precipitated aramid forms a smooth continuous layered sheath around the CNTs. These findings motivate future investigation of mechanical and interfacial properties of the resulting CNT composites, and adaptation of the in-situ polymerization method to other substrates.
Diindolocarbazole – Achieving Multiresonant Thermally Activated Delayed Fluorescence Without The Need for Acceptor Units
Authors: Hall David , Stavrou Kleitos , Duda EImantas , Danos Andrew , Bagnich Sergey , Warriner Stuart , Slawin Alexandra , Beljonne David , Koehler Anna , Monkman Andrew , Olivier Yoann , Zysman-Colman Eli
Published: February 2022

In this work we present a new multi-resonance thermally activated delayed fluorescence (MR-TADF) emitter paradigm, demonstrating that the structure need not require the presence of acceptor atoms. Based on an in-silico design, the compound DiICzMes4 possesses a red-shifted emission, enhanced photoluminescence quantum yield, and smaller ΔEST than the parent indolocarbazole that induces MR-TADF properties. Coupled cluster calculations accurately predict the magnitude of the singlet-triplet energy gap, ΔEST, when the optimized singlet and triplet geometries are used. Slow yet optically detectable reverse intersystem crossing contributes to low efficiency in organic light-emitting diodes using DiICzMes4 as then emitter. However, when used as a terminal emitter in combination with a TADF assistant dopant within a hyperfluorescence device architecture, maximum external quantum efficiencies of up to 16.9% were achieved at CIE (0.15,0.11). This represents one of the bluest hyperfluorescent devices reported to date. Simultaneously, recognising that MR-TADF emitters do not require acceptor atoms reveals an unexplored frontier in materials design, where yet greater performance may yet be discovered.
High-contrast Background-free Magnetic Resonance Molecular Imaging
Authors: Ray Sayoni , Hsu Chao-Hsiung , Li Zhao , Lin Fang-Chu , Lin Yung-Ya
Published: February 2022

One of the holy grails in cancer detection and therapy is to simultaneously image and deliver drugs to the tumor site using a safe nanoparticle. Liposomes are a well-known safe and stable nanoparticles that can be loaded with a drug and suitable contrast agent for magnetic resonance imaging (MRI). However, the loading of a contrast agent such as gadolinium in liposomes generally results in poor contrast and various artifacts in in vivo experiments, compared to free gadolinium chelate experiments. Current work demonstrates the effective filtering of artifacts and contrast enhancement to obtain high quality images of the tumor sites in mouse models using paramagnetic liposome nanoparticles as contrast agent, a novel pulse sequence in active-feedback MRI, and nonlinear fitting. Our results show a significant improvement in eliminating artifacts and increasing contrast compared to the standard MRI techniques, and a close correlation with histopathology and inductively coupled mass spectrometry results. This newly developed protocol could be used for any paramagnetic nanoparticle to improve detection sensitivity. We expect this methodology to produce similar improvements in human imaging, having the potential to significantly improve early tumor detection in clinical practice and opening up the possibility of its theranostic use.
Using pH dependence to understand mechanisms in electrochemical CO reduction
Authors: Kastlunger Georg , Wang Lei , Govindarajan Nitish , Heenen Hendrik H. , Ringe Stefan , Jaramillo Thomas , Hahn Christopher , Chan Karen
Published: February 2022

Electrochemical conversion of CO(2) into hydrocarbons and oxygenates is envisioned as a promising path towards closing the carbon cycle in modern technology. To this day, however, the reaction mechanisms towards the plethora of products are disputed, complicating the search for novel catalyst materials. In order to conclusively identify the rate-limiting steps in CO reduction on Cu, we analyzed the mechanisms on the basis of constant potential DFT kinetics and experiments at a wide range of pH values (3 - 13). We find that *CO dimerization is energetically favoured as the rate limiting step towards multi-carbon products. This finding is consistent with our experiments, where the reaction rate is nearly unchanged on an SHE potential scale, even under acidic conditions. For methane, both theory and experiments indicate a change in the rate-limiting step with electrolyte pH from the first protonation step in acidic/neutral conditions to a later one in alkaline conditions. We also show, through a detailed analysis of the microkinetics, that a surface combination of *CO and *H is inconsistent with the measured current densities and Tafel slopes. Finally, we discuss the implications of our understanding for future mechanistic studies and catalyst design.
MolAR: Bringing Chemical Structures to Life with Augmented Reality and Machine Learning
Authors: Sakshuwong Sukolsak , Weir Hayley , Raucci Umberto , Martínez Todd J.
Published: February 2022

Visualizing three-dimensional molecular structures is crucial to understanding and predicting their chemical behavior. Existing visualization software, however, can be cumbersome to use, and, for many, hand-drawn skeletal structures remain the preferred method of chemical communication. Although convenient, the static, two-dimensional nature of these drawings can be misleading in conveying the molecule’s 3D structure, not to mention that dynamic movement is completely disregarded. Here, we combine machine learning and augmented reality (AR) to develop MolAR, an immersive mobile application for visualizing molecules in real-world scenes. The application uses deep learning to recognize hand-drawn hydrocarbons structures which it converts into interactive 3D molecules in AR. Users can also “hunt” for chemicals in food and drink to uncover molecules in their real-life environment. A variety of interesting molecules are pre-loaded into the application, and users can visualize molecules in PubChem by providing their name or SMILES string and proteins in the Protein Data Bank by providing their PDB ID. MolAR was designed to be used in both research and education settings, providing an almost barrierless platform to visualize and interact with 3D molecular structures in a uniquely immersive way.
Efficient Dynamic Computational Strategy for Heterogeneous Catalysis Based on Neural Network Potential Energy Surface: A Case Study of Temperature-Dependent Thermodynamics and Kinetics for the Chemisorbed on-surface CO
Authors: Chen Jun , Jin Tan , Shen Tonghao , Yang Mingjun , Chen Zhe-Ning
Published: February 2022

As a favorable alternative and complement of experimental techniques, computational tools on top of ab initio calculations have played an indispensable role in revealing the molecular details, thermodynamics and kinetics in catalytic reactions. The static computational strategy, which recovers the reaction thermodynamics and kinetics based on the calculations of a few stationary geometries at zero temperature and some ideal statistic mechanics models, is the most popular approach in theoretical catalysis due to its simplicity. In comparison, the ab initio molecular dynamics (AIMD) is a well-tested approach to provide more precise descriptions of catalytic processes, however, experiencing a significantly expensive computational cost in the direct ab initio calculation of potential energy and gradients. Here we proposed a highly efficient dynamic computational strategy for the calculation of thermodynamic and kinetic properties in heterogeneous catalysis on the basis of neural network potential energy surface (NN PES) and MD simulations. Taking CO adsorbate on Ru(0001) surface as the illustrative model catalytic system, we demonstrated that our NN-PES-based MD simulations can efficiently generate the reliable smooth two-dimensional potential-of-mean-force (2-D PMF) surfaces in a wide range of temperatures (from 300 to 900 K), and thus temperature-dependent thermodynamic properties can be obtained in a comprehensive investigation on the whole PMF surface rather than a rough estimation using ideal models based on a few optimized geometries. Moreover, MD simulations offer an effective way to describe the surface kinetics such as the CO adsorbate on-surface movement, which goes beyond the most popular static estimation based on calculated free energy barrier and transition state theory (TST). By comparing the results obtained in the dynamic and static approaches, we further revealed that the dynamic strategy significantly improves the predictions of both thermodynamic and kinetic properties as compared to the popular ideal statistic mechanics approaches such as harmonic analysis and TST. It is expected that this accurate yet efficient dynamic strategy can be a powerful tool in understanding reaction mechanisms and reactivity of a catalytic surface system, and further guides the rational design of heterogeneous catalysts.
Fourier-like Thermal Relaxation of Nanoscale Explosive Hot Spots
Authors: Kroonblawd Matthew , Hamilton Brenden , Strachan Alejandro
Published: February 2022

We develop here an approach to directly determine the thermal transport properties of explosive hot spots with realistic initial structures through a combination of molecular dynamics (MD) and diffusive heat equation (HEq) modeling. Effective thermal conductivity values are determined by fitting HEq models to MD predictions of long timescale hot spot relaxation. The approach is applied to model hot spots in the molecular crystalline explosive TATB for a range of shock strengths and two limiting cases for impact orientation. Conductivity is found to be a strong function of density, which parametrically captures dependence on temperature, pressure, and material state. The approach provides a convenient foundation for determining the effective thermal conductivity for hot spot problems in other explosives and directly yields information on reasonable approximations that might be taken in higher-level models for those materials.
Super-bridging Fibrous Materials for Water Treatment: Impacts on Removal of Plastic Particles, Phosphorus and Natural Organic Matter
Authors: Lapointe Mathieu , Jahandideh Heidi , Farner Jeffrey , Tufenkji Nathalie
Published: February 2022

To deal with issues of process sustainability, cost, and efficiency, we developed materials reengineered from fibers to serve as super-bridging agents, adsorbents, and ballast media. These sustainable fiber-based materials considerably increased the floc size (~6630 µm) compared to conventional physicochemical treatment using a coagulant and a flocculant (~520 µm). The materials also reduced coagulant usage (up to 40%) and flocculant usage (up to 60%). These materials could be used in synergy with coagulants and flocculants to improve settling in existing water treatment processes and allow facilities to reduce their capital and operating costs as well as their environmental footprint. Moreover, the super-sized flocs produced using fiber-based materials (up to ~13 times larger compared to conventional treatment) enabled easy floc removal by screening, eliminating the need for a settling tank, a large and costly process unit. The materials can be effective solutions at removing classical (e.g., natural organic matter (NOM) and phosphorus) and emerging contaminants (e.g., microplastics and nanoplastics). Due to their large size, Si- and Fe-grafted fiber-based materials can be easily recovered from sludge and reused multiple times.
Mechanistic Insights of Seeded Diamond Growth from Molecular Precursors
Authors: Ender Christopher P. , Liang Jiaxu , Friebel Jonas , Zapata Todd , Wagner Manfred , Ermakova Anna , Weil Tanja
Published: February 2022

We report mechanistic insights of the bottom-up synthesis of nanodiamonds (NDs) from adamantane derivatives as molecular precursors. Thermal cracking of tetracosane below the decomposition temperature of adamantane, 1-adamantylamine or 2-azaadamantane revealed the initial steps of seeded diamond growth mechanism based on pyrolysis studies.
Screening Of Zinc Database Against Streptococcal Cysteine Protease Enzyme For Identification Of Novel Group A Streptococcus Inhibitors
Authors: Bhowmik Ratul , Nath Ranajit , Roy Ratna
Published: February 2022

Inhibition of streptococcal cysteine protease has recently emerged as quite a promising target to treat severe cases of Group A Streptococcus infections. For the identification of streptococcal cysteine protease inhibitors, structure-based virtual screening (SBVS) of ZINC Database was performed. The docking protocol was performed with the help of AutoDock Tools and AutoDock Vina software. Based on binding affinity and similarity of interactions with our target receptor streptococcal cysteine protease, 4 hit compounds were identified, which were further subjected to ADMET (Adsorption, Distribution, Metabolism, Excretion, Toxicity) and Drug-likeness to identify the best hit compound. The most potent compound showed binding of -7.7 KJ/mol with receptor streptococcal cysteine protease. It also showed 6 similar amino acid interactions with the receptor’s native ligand along with good ADME and Drug-likeness properties. Furthermore, the molecular dynamics simulation analysis revealed that the complex formed between the protein streptococcal cysteine protease and the hit compound ZINC000205429716 had good structural stability. The current study reveals the successful use of in silico SBVS methods for the identification of novel and possible streptococcal cysteine protease inhibitors, with compound ZINC000205429716 serving as a potential lead for the creation of Group A Streptococcus inhibitors.
Semi-automated high-throughput substrate screening assay for nucleoside kinases
Authors: Hellendahl Katja , Fehlau Maryke , Hans Sebastian , Neubauer Peter , Kurreck Anke
Published: February 2022

Nucleoside kinases (NKs) are key enzymes involved in the in vivo phosphorylation of nucleoside analogues used as drugs to treat cancer or viral infections. Having different specificities, the characterization of NKs is essential for drug design and the production of nucleotide analogues in an in vitro enzymatic process. Therefore, a fast and reliable substrate screening assay for NKs is of great importance. Here, we report the validation of a well-known luciferase-based assay for the detection of NK activity in 96-well plate format. The assay was semi-automated using a liquid handling robot. A good linearity was demonstrated (r² >0.98) in the range of 0 to 500 µM ATP, and it was shown that also alternative phosphate donors like dATP or CTP were accepted by the luciferase. The developed high-throughput assay revealed comparable results to HPLC analysis. The assay was exemplary used for the comparison of the substrate spectra of four nucleoside kinases using 20 (8 natural and 12 modified) substrates. The screening results correlated well with literature data and, additionally, previously unknown substrates were identified for three of the NKs studied. Our results demonstrate that the developed semi-automated high-throughput assay is suitable to identify best performing NKs for a wide range of substrates.
Enhanced visible light absorption in layered Cs3Bi2Br9 through mixed-valence Sn(II) / Sn(IV) doping
Authors: Krajewska Chantalle , Kavanagh Seán , Zhang Lina , Kubicki Dominik , Dey Krishanu , Gałkowski Krzysztof , Grey Clare , Stranks Samuel , Walsh Aron , Scanlon David , Palgrave Robert
Published: February 2022

Lead-free halides with perovskite-related structures, such as the vacancy-ordered perovskite Cs3Bi2Br9, are of interest for photovoltaic and optoelectronic applications. We find that addition of SnBr2 to the solution-phase synthesis of Cs3Bi2Br9 leads to substitution of up to 7% of the Bi(III) ions by equal quantities of Sn(II) and Sn(IV). The nature of the substitutional defects was studied by X-ray diffraction, 133Cs and 119Sn solid state NMR, X-ray photoelectron spectroscopy and density functional theory calculations. The resulting mixed-valence compounds show intense visible and near infrared absorption due to intervalence charge transfer, as well as electronic transitions to and from localised Sn-based states within the band gap. Sn(II) and Sn(IV) defects preferentially occupy neighbouring B-cation sites, forming a double-substitution complex. Unusually for a Sn(II) compound, the material shows minimal changes in optical and structural properties after 12 months storage in air. Our calculations suggest the stabilisation of Sn(II) within the double substitution complex contributes to this unusual stability. These results expand upon research on inorganic mixed-valent halides to a new, layered structure, and offer insights into the tuning, doping mechanisms, and structure-property relationships of lead-free vacancy-ordered perovskite structures.
In-situ characterization of discharge products of lithium-oxygen battery using Flow Electrochemical Atomic Force Microscopy
Authors: Cortés Páez Henry Andres , Corti Horacio
Published: February 2022

The increasing interest in lithium-oxygen batteries (LOB), having the highest theoretical energy densities among the advanced lithium batteries, has triggered the search for in-situ characterization techniques, including Electrochemical Atomic Force Microscopy (EC-AFM). In this work we addressed the characterization of the formation and decomposition of lithium peroxide (Li2O2) on a carbon cathode using a modified AFM technique, called Flow Electrochemical Atomic Force Microscopy (FE-AFM), where an oxygen-saturated solution of the non-aqueous lithium electrolyte is circulated through a liquid AFM cell. This novel technique does not require keeping the AFM equipment inside a glove-box, and it allows performing a number of experiments using the same substrate with different electrolytes without dissembling the cell. We study the morphology of Li2O2 on graphite carbon using lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) in dimethyl sulphoxide (DMSO) as electrolyte under different operational conditions and compare our results with those reported using other electrolytes and in-situ and ex-situ EC-AFM.
Pre-Nucleation Clusters Predict Crystal Structures in Models of Chiral Molecules
Authors: Carpenter John E. , Gruenwald Michael
Published: February 2022

Kinetics can play an important role in the crystallization of molecules and give rise to polymorphism, the prevalent ability of molecules to form more than one crystal structure. Current computational methods of crystal structure prediction, however, focus almost exclusively on identifying the thermodynamically stable polymorph. Kinetic factors of nucleation and growth are often neglected because the underlying microscopic processes are thought to be complex and accurate rate calculations are numerically cumbersome. In this work, we use molecular dynamics computer simulations to study a simple molecular model that reproduces the crystallization behavior of real chiral molecules, including the formation of enantiopure and racemic crystals, as well as polymorphism. We show that in many cases, the crystal that robustly forms in simulations is not the one with the lowest free energy. We demonstrate that at high supersaturation the prevailing polymorph can be accurately predicted by considering the similarities between prevalent oligomeric species in solution and molecular motifs in the crystal structure. For the case of racemic mixtures, we even find that knowledge of crystal free energies is not necessary and kinetic considerations are sufficient to determine if the system will undergo spontaneous chiral separation. Our results suggest conceptually simple ways of improving current crystal structure prediction methods.