bluuebunny/crossref_metadata_2025 huggingface dataset:
Supramolecular methods: the 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS) transport assay
Authors: Gilchrist Alexander , Wang Patrick , Carreira-Barral Israel , Alonso-Carrillo Daniel , Wu Xin , Quesada Roberto , Gale Philip Alan
Published: February 2022

The vesicular anion transport activity assay, which uses 8-hydroxypyrene-1,3,6-trisulfonic acid to monitor the internal pH of the vesicles (the HPTS assay), is a widely used technique for analysing the activity of anionophore facilitated transport across a phospholipid membrane. This methods paper describes the stepwise technique to conduct this transport assay, detailing both the perks and pitfalls of using this method to determine the activity of an anionophore and the transport mechanism.
Characterization of Cisplatin/Membrane Interactions by QM/MM Energy Decomposition Analysis
Authors: Cárdenas Gustavo , Pérez-Barcia Álvaro , Mandado Marcos , Nogueira Juan J.
Published: February 2022

The intermolecular interactions established between anticancer drugs and lipid membranes play a key role in the permeation mechanism of the drugs inside the cells. Herein we extend a quantum mechanical energy decomposition analysis scheme based on deformation electron densities to a hybrid multiscale quantum mechanics/molecular mechanics (QM/MM) framework, and apply it to characterize the interactions between the cisplatin drug and a dioleyl-phosphatidylcholine lipid membrane. The interaction energy decomposition into electrostatic, induction, dispersion and Pauli repulsion contributions is performed for ensembles of geometries taken from molecular dynamics simulations to account for conformational sampling and, thus, obtain a distribution of each of the energy components. Contrary to a previous energy decomposition using force fields, it is evidenced that the electrostatic component is predominant in both polar and non-polar regions of the bilayer, and the repulsive component is strong when considered quantum mechanically, while being largely underestimated by the force field
Investigation of the structure and properties of ceramic materials with a rigid system of microfiltration transport pores based on basalt fibers
Authors: Besarab Siarhei , Azarov Sergey , Sauka Justyna , Petyushik Evgeny , Azarova Tatyana , Drobysh Alexey
Published: February 2022

The report provides information on the formation of the structure of porous ceramic materials made of basalt fiber obtained by pressing with subsequent sintering. The phase composition, structure, and properties of ceramics are studied. The relationship between the structure, phase composition, and properties of the ceramic material is established.
A sensitive and compact optical detector based on lock-in amplification
Authors: Harvie Andrew J , Yadav Surendra K , de Mello John C
Published: February 2022

We report a sensitive, fixed-wavelength, lock-in-based optical detector built from a light-emitting diode, two colour filters, a photodetector, a small number of discrete analogue components, and a low-cost microcontroller development board. We describe the construction, operating principle, use and performance of the optical detector, which may be used for both absorption- and fluorescence- measurements in either a 10-mm pathlength cuvette or a low-volume (< 100 μl) flow-cell. For illustrative purposes the detector is applied here to a cholesterol assay based on the enzyme-mediated conversion of (non-emissive) Amplex Red into the fluorescent dye resorufin, providing a detection limit of ~200 nM – some four orders of magnitude lower than the typical concentration of cholesterol in human serum. (The resorufin molecule itself is detectable down to concentrations of ~20 nM). The system may be readily adapted to other biomolecules through a simple change of enzyme.
A preclinical biosensor for detecting phenylalanine photometrically in plasma and whole blood samples
Authors: Soto Rodriguez Paul Eduardo David , Valles Morgane , Romeo Agostino , Artuch Rafael , Sánchez Samuel
Published: February 2022

Phenylketonuria (PKU) is a metabolic disease resulting from a deficiency in the enzyme phenylalanine hydroxylase, increasing L-Phenylalanine (L-Phe) values in the blood and consequently in the brain. If untreated, PKU leads to neurological damage, which can be prevented by following a diet low in L-Phe. Thus, early detection of PKU in newborns is essential. The disease’s screening and monitoring are centralized in reference centers, which require specialized equipment. However, using these techniques, sample treatment is required before the analysis, and trained personnel must perform and interpret the results. In this work, we present an enzyme-based photometric strategy to measure blood L-Phe. An enzymatic mixture, selective for L-Phe, is immobilized on an UV transparent well, and the amount of consumed co-factor is monitored at 340 nm. Standard plasma and whole blood samples were chosen to pre-validate the sensor. The samples were spiked with an increasing amount of L-Phe, accurately discriminating between physiological and pathological L-Phe concentrations. The strategy can be easily extended to analyzing other samples, such as urine or sweat. The proposed photometric system allows to analyze up to 16 samples simultaneously within a matter of hours. The measurements are relatively fast, versatile, cost-effective, and easy to carry out.
Carbon Clusters: Thermochemistry and Electronic Structure at High Temperatures
Authors: Sharma Priyadarshini Maitreyee , Jaffe Richard , Panesi Marco
Published: February 2022

This paper studies the thermochemistry and electronic structure of small carbon clusters and hydrocarbons which are major constituents of pyrolysis gases released into the boundary layer of ablating heat shields. Our focus lies on clusters of up to four carbon atoms including C3H and C4H. A study of electronically excited states of these molecules computed using the EOM-CCSD method has revealed C4 and C4H to be potential sources of radiation absorption in the boundary layer. We also study the effect of low-lying excited electronic states on the thermodynamics in the high temperature regime and show that neglecting these states records a difference of upto 12% in the computed Cp values. Finally, comparisons of the equilibrium mole fractions obtained using the thermodynamics computed in this paper with the existing state-of-the-art tables used for hypersonic applications (for example JANAF and Gurvich Tables) show an order of magnitude difference in the mixture compositions.
Regularized Second Order Møller-Plesset Theory: A More Accurate Alternative to Conventional MP2 for Noncovalent Interactions and Transition Metal Thermochemistry for the Same Compute Cost
Authors: Shee James , Loipersberger Matthias , Rettig Adam , Lee Joonho , Head-Gordon Martin
Published: February 2022

Second order Møller-Plesset theory provides a remarkably simple form for the electron correlation energy with many desirable properties, e.g. it is size-consistent, free of self-interaction error, and scales with the fifth power of system size. However, MP2 exhibits well-known shortcomings including an incomplete description of dispersion interactions and sizable failures for transition metal chemistry. Herein, we first explore multiple physically justified forms of single-parameter regularization and then demonstrate that with appropriate parameter choice, regularized MP2 with Hartree-Fock reference orbitals yields high and transferable accuracy across a wide variety of noncovalent interactions (S22, S66, XB40, A24, and L7 test sets) and (mostly closed-shell) transition metal thermochemistry (metal-carbonyl dissociations and a subset of MOR41). We find that, especially for systems with interacting pi systems relevant to dispersion interactions and dative bonding, regularization serves to damp overestimated pair-wise additive contributions to the first-order amplitudes that affect correlation energy and charge-density. The optimal parameter values for the noncovalent and transition metal sets are 1.1 and 0.4 for two regularizers, $\kappa$ and $\sigma^2$, respectively. These two regularizers slightly degrade the accuracy of conventional MP2 for some small-molecule test sets which are well-known to be sensitive to charge-density distribution (radical stabilization energies, barrier heights, dipole moments, and polarizabilities), most of which have relatively large gaps. Due to the relatively straightforward implementations of nuclear gradient and other properties, we recommend $\kappa$-MP2 with $\kappa$ = 1.1 as a more accurate alternative to conventional MP2 and other related variants. Our results suggest that appropriately regularized MP2 models represent promising forms for the nonlocal correlation part of double hybrid density functionals, at no additional cost over conventional MP2.
Zinc-Catalyzed β-Allylation of Cyclopropanols via Enolized Homoenolate
Authors: Yoshikai Naohiko , Sekiguchi Yoshiya
Published: February 2022

We report herein a zinc-catalyzed β-allylation of cyclopropanols with Morita–Baylis–Hillman (MBH) carbonates with retention of the cyclopropane ring. The reaction is promoted by a zinc aminoalkoxide catalyst generated from Et2Zn and a β-aminoalcohol, affording cyclopropyl-fused α-alkylidene-δ-valerolactone derivatives in moderate to good yields. A bicyclic 1,2-disubstituted cyclopropanols undergoes allylation at the sterically more hindered β-position. This observation, together with other mechanistic experiments, suggest that the present reaction does not proceed via direct β-C–H cleavage of the cyclopropanol, but rather involves zinc homoenolate and its enolization to generate a key bis- nucleophilic species. α-Allylation of this “enolized homoenolate” with MBH carbonate would be followed by regeneration of the cyclopropane ring and irreversible lactonization. A sequence of the present reaction and known cyclopropanol transformation provides an opportunity to transform a simple cyclopropanol into α,β- or β,β-difunctionalized ketones.
An [FeIII30] molecular metal oxide
Authors: Brechin Euan , Dearle Alice , Cutler Daniel , Coletta Marco , Lee Edward , Dey Sourav , Sanz Sergio , Fraser Hector , Nichol Gary , Rajaraman Gopalan , Schnack Juergen , Cronin Lee
Published: February 2022

Dissolution of FeBr3 in a mixture of acetonitrile and 3,4-lutidine in the presence of an amine results in the formation of an [Fe30] molecular metal oxide containing alternating layers of tetrahedral and octahedral FeIII ions. Mass spectrometry suggests the cluster is formed quickly and remains stable in solution, while magnetic measurements and DFT calculations reveal competing antiferromagnetic exchange interactions.
High-Resolution Ion-Flux Imaging of Proton Transport Through Graphene|Nafion Membranes
Authors: Bentley Cameron , Kang Minkyung , Bukola Saheed , Creager Stephen , Unwin Patrick
Published: February 2022

In 2014, it was reported that hydrated protons are able to traverse nominally pristine monolayer graphene (and hexagonal boron nitride, h-BN) films under ambient conditions. This “intrinsic proton conductivity” of the one-atom-thick crystals, with proposed through-plane conduction, challenged the notion that graphene is impermeable to atoms, ions and molecules. More recent evidence points to a defect-facilitated transport mechanism, analogous to transport through conventional ion-selective membranes based on graphene and h-BN. To clarify the nature of proton transmission through graphene, local ion-flux imaging is performed herein on graphene|Nafion membranes using a new “electrochemical ion (proton) pump cell” mode of scanning electrochemical cell microscopy (SECCM). Targeting regions of the graphene|Nafion membranes that are free from visible macroscopic defects (e.g., cracks, holes etc.), and assessing hundreds to thousands of different sites across the graphene surfaces in a typical experiment, most of the graphene membrane is impermeable to proton transport, with transmission typically occurring at only ≈20 – 60 localized sites across a ≈0.003 mm2 area of membrane (>5000 measurements, total). When localized proton transport occurs, it can be a highly dynamic process, with new transmission sites “opening” and a small number of sites “closing” under an applied electric field, on the seconds timescale. Applying a simple equivalent circuit model of ion-transport through a cylindrical nanopore, the local transmission sites are estimated to possess dimensions (radii) on the (sub)nanometer-scale, implying that rare atomic defects are responsible for proton conductance through monolayer graphene. Overall, this work reinforces SECCM as a premier tool for the structure−property mapping of microscopically complex (electro)materials, with the new configuration reported herein opening up exciting new possibilities in functional membrane characterization, as well as any other application where reactive ion-flux is a highly localized phenomenon, e.g., for diagnosing failure mechanisms in protective surface coatings.
Comparing Transfer Learning to Feature Optimization in Microstructure Classification
Authors: Banerjee Debanshu , Sparks Taylor D.
Published: February 2022

Human analysis of research data is slow and inefficient. In recent years machine learning tools have advanced our capability to perform tasks normally carried out by humans, such as image segmentation and classification. In this work, we seek to further improve binary classification models for high throughput identification of different microstructural morphologies. We utilize a dataset with limited observations (133 dendritic structures, 444 non-dendritic) and employ data augmentation via rotation and translation to enhance the dataset six-fold. Then, transfer learning is carried out using pre-trained networks VGG16, InceptionV3, and Xception achieving only moderate F1 scores (0.801 to 0.822). We hypothesize that feature engineering could yield better results than transfer learning alone. To test this, we employ a new nature-inspired feature optimization algorithm, the Binary Red Deer Algorithm (BRDA), to carry out binary classification and observe F1 scores above 0.93.
Size-induced amorphous structure in tungsten oxide nanoparticles
Authors: Juelsholt Mikkel , Anker Andy Sode , Lindahl Christiansen Troels , Ry Jørgensen Mads , Kantor Innokenty , Risskov Sørensen Daniel , Jensen Kirsten Marie Ørnsbjerg
Published: February 2022

The properties of functional materials are intrinsically linked to their atomic structure. When going to the nanoscale, size-induced structural changes in atomic structure often occur, however these are rarely well-understood. Here, we systematically investigate the atomic structure of tungsten oxide nanoparticles as a function of the nanoparticle size and observe drastic changes when the particles are smaller than 5 nm, where the particles are amorphous. The tungsten oxide nanoparticles are synthesized by thermal decomposition of ammonium metatungstate hydrate in oleylamine and by varying the ammonium metatungstate hydrate concentration, the nanoparticle size, shape and structure can be controlled. At low concentrations, nanoparticles with a diameter of 2-4 nm form and adopt an amorphous structure that locally resembles the structure of polyoxometalate clusters. When the concentration is increased the nanoparticles become elongated and form nanocrystalline rods up to 50 nm in length. The study thus reveals a size-dependent amorphous structure when going to the nanoscale and provides further knowledge on how metal oxide crystal structures changes at extreme length scales.
Exploring graph traversal algorithms in graph-based molecular generation
Authors: Mercado Rocío , Bjerrum Esben , Engkvist Ola
Published: February 2022

Here we explore the impact of different graph traversal algorithms on molecular graph generation. We do this by training a graph-based deep molecular generative model to build structures using a node order determined via either a breadth- or depth-first search algorithm. What we observe is that using a breadth-first traversal leads to better coverage of training data features compared to a depth-first traversal. We have quantified these differences using a variety of metrics on a dataset of natural products. These metrics include: percent validity, molecular coverage, and molecular shape. We also observe that using either a breadth- or depth-first traversal it is possible to over-train the generative models, at which point the results with the graph traversal algorithm are identical
C-N triple bond cleavage via trans-membrane hydrogenation
Authors: Zhang Yuxuan , Kornienko Nikolay
Published: February 2022

The renewable energy-driven valorization of excess feedstocks into commodity chemicals and societally useful products constitutes a longstanding push in energy and sustainability research. To this end, this work pushes to expand the scope of green electrosynthesis by innovating a new approach to convert acetonitrile, industrially generated in excess and burned off, to in-demand ammonia and acetaldehyde products. Success here was enabled through the use of a Pd-membrane based reactor which abstracted hydrogen atoms from water, which subsequently diffused through to a separate organic compartment in which they carried out the hydrogenation reaction. In this geometry, the reaction proceeded at 5.2 mA/cm2 partial current density and 60% Faradaic efficiency towards ammonia generation. Further, the transmembrane hydrogenation approach gave rise to an onset potential of 0.2VAg/AgCl, surpassing previous state-of-the-art systems by 0.7V. A customized infrared spectroelectrochemcal setup was built up to probe the mechanism of the reaction, which was shown to proceed through an imine hydrolysis like pathway, with the hydrogenation of the NHx species that remained being the rate-limiting steps in the process. This work establishes a new route in electrochemical nitrile hydrogenation and general opens up promising avenues in green electrosynthesis.
Synthesis of Bench-Stable N-Quaternized Ketene N,O-Acetals and Preliminary Evaluation as Reagents in Organic Synthesis
Authors: McConnell Danielle L. , Blades Alisha M. , Gomes Rodrigues Danielle , Keyes Phoebe V. , Sonberg Justin C. , Anthony Caitlin E. , Rachad Sofia , Simone Olivia M. , Sullivan Caroline F. , Shapiro Jonathan D. , Williams Christopher C. , Schafer Benjamin C. , Glanzer Amy , Hutchinson Holly , Thayaparan Ashley , Krevlin Zoe , Bote Isabella , Haffary Yasin , Bhandari Sambat , Goodman Jack A. , Majireck Max
Published: February 2022

N-Quaternized ketene N,O-acetals are typically an unstable, transient class of compounds most commonly observed as reactive intermediates. In this report, we describe a general synthetic approach to a variety of bench-stable N-quaternized ketene N,O-acetals via treatment of pyridine or aniline bases with acetylenic ethers and an appropriate Brønsted or Lewis acid (triflic acid, triflimide, or scandium(III) triflate). The resulting pyridinium and anilinium salts can be used as reagents or synthetic intermediates in multiple reaction types. For example, N-(1-ethoxyvinyl)pyridinium or anilinium salts can thermally release highly reactive O-ethyl ketenium ions for use in acid catalyst-free electrophilic aromatic substitutions. N-(1-Ethoxyvinyl)-2-halopyridinium salts can be employed in peptide couplings as a derivative of Mukaiyama reagents or react with amines in nucleophilic aromatic substitutions under mild conditions. These preliminary reactions illustrate the broad potential of these currently understudied compounds in organic synthesis.
A ruthenium-oligonucleotide bioconjugated photosensitizing aptamer for cancer cell specific photodynamic therapy
Authors: McKenzie Luke , Flamme Marie , Felder Patrick , Karges Johannes , Bonhomme Frédéric , Gandioso Albert , Malosse Christian , Gasser Gilles , Hollenstein Marcel
Published: February 2022

Ruthenium complexes have emerged as a promising class of compounds for use as photosensitizers (PSs) in photodynamic therapy (PDT) due to their attractive photophysical properties and relative ease of chemical alteration. While promising, they generally are not inherently targeting to disease sites and may therefore be prone to side effects and require higher doses. Aptamers are short oligonucleotides that bind specific targets with high affinity. One such aptamer is AS1411, a nucleolin targeting, G-quadruplex forming, DNA aptamer. Here we present the first example of direct conjugation of a Ru(II) polypyridyl complex-based PS to an aptamer and an assessment of its in vitro cancer cell specific photosensitization including discussion of the challenges faced.
Evaluation of an Internal Standard for Qualitative DART-MS Analysis of Seized Drugs
Authors: Sisco Edward , Burns Amber , Schneider Elizabeth , Ikpeama Ikenna
Published: February 2022

Rapid and accurate screening tools for seized drug analysis continue to be needed due to the complexities associated with the emerging drug landscape. Direct analysis in real-time mass spectrometry (DART-MS) is one technique that has been used for this purpose and is seeing increased implementation due to its ability to provide high-fidelity information rapidly. As with any analytical technique, ensuring data integrity with DART-MS results is critical. To further enhance data integrity and eliminate some of the challenges associated with qualitative analysis of seized drugs using DART-MS, the incorporation of an internal standard was investigated. After evaluating a number of candidate compounds, tetracaine was chosen because of its desirable characteristics. An appropriate concentration of tetracaine was established that provided similar sensitivity to GC-MS for a panel of drugs. The presence of tetracaine in a drug extract was found to cause a reduction in signal for some common drugs due to competitive ionization but did not cause complete suppression of signal at relevant concentrations. Evaluation of a set of 60 representative case samples with and without internal standard found that the presence of internal standard did not negatively impact the results and that its presence eliminated the false identification of noise peaks in negative samples. The use of an internal standard also provided within-sample mass calibration and analyte concentration checks. It also allowed for automated mass drift compensation, removing a time-consuming process for high resolution DART-MS data processing.
A Cocktail Approach Toward Tunable Organic Afterglow Systems
Authors: Ma Xiang , Ma Liangwei , Xu Qiangyang , Ding Bingbing , Huang Zizhao , Sun Siyu , Tian He
Published: February 2022

In this work, a cocktail approach toward tunable organic long-lived luminescence materials in solid, solution, and gel states is proposed. The tunable long-lived luminescence (τ > 0.7 s) is realized by controlling the energy transfer via manipulating the photo-induced isomerization of the energy acceptor (5). The afterglow can be regulated between blue and yellow emission upon irradiation of UV or visible light. And the “apparent lifetime” for the long-lived fluorescence is the same as the lifetime of the energy donor. The function is relying on the simple radiative energy transfer (reabsorption) between a long-lived phosphorescence and a highly efficient fluorescent isomer (5b), rather than the complicated communication between the excited state of the molecules such as Förster resonance energy transfer or Dexter energy transfer. The simple working principle endows this strategy with huge universality, flexibility, and operability. This work offers an extremely simple, feasible, and universal way to construct tunable afterglow materials in solid, solution, and gel states.
Reducing the irreducible: Dispersed metal atoms facilitate reduction of irreducible oxides.
Authors: Korpelin Ville , Melander Marko M. , Honkala Karoliina
Published: February 2022

Oxide reducibility is a central concept quantifying the role of the support in catalysis. While reducible oxides are often considered catalytically active, irreducible oxides are seen as inert supports. Enhancing the reducibility of irreducible oxides has, however, emerged as an effective way to increase their catalytic activity while retaining their inherent thermal stability. In this work, we focus on the prospect of using single metal atoms to increase the reducibility of a prototypical irreducible oxide, zirconia. Based on extensive self-consistent DFT+U calculations, we demonstrate that single metal atoms significantly improve and tune the surface reducibility of zirconia. Detailed analysis of the observed single atom induced reducibility allows us to attribute the enhanced reducibility to strong interactions between the metal atom and the electrons trapped in the vacancy, and d-p orbital interactions between the metal atom and oxygen. This analysis enables transferring the obtained theoretical understanding to other irreducible oxides as well. The detailed understanding of how oxide reducibility can be tuned offers precise control over the catalytic properties of metal--oxides.
Insights from an information thermodynamics analysis of a synthetic molecular motor
Authors: Amano Shuntaro , Esposito Massimiliano , Kreidt Elisabeth , Leigh David A. , Penocchio Emanuele , Roberts Benjamin M. W.
Published: February 2022

Information is a physical quantity, the realisation of which transformed the physics of measurement and communication in the latter half of the 20th Century. However, the relationship and flow between information, energy and mechanics in chemical systems and mechanisms remains largely unexplored. Here we analyze a minimalist experimental example of an autonomous artificial chemically-driven molecular motor - a molecular information ratchet - in terms of information thermodynamics, a framework that quantitatively relates information to other thermodynamic parameters. This treatment reveals how directional motion is generated by free energy transfer from the chemical to the mechanical processes involving the motor. We find that the free energy transfer consists of two distinct contributions that can be considered as “energy flow” and “information flow”. We identify the efficiency with which the chemical fuel powers the free energy transfer and show that this is a useful quantity with which to compare and evaluate mechanisms of, and guide designs for, molecular machines. The study provides a thermodynamic level of understanding of molecular motors that is general, complements previous analyses based on kinetics, and has practical implications for designing and improving synthetic molecular machines, regardless of the particular type of machine or chemical structure. In particular, the study confirms that, in line with kinetic analysis, power strokes do not affect the directionality of chemically-driven molecular machines. However, we also find that under some conditions power strokes can modulate the molecular motor current (how fast the components rotate), efficiency with respect to how free energy is dissipated, and the number of fuel molecules consumed per cycle. This may help explain the role of such conformational changes in biomolecular machine mechanisms and illustrates the interplay between energy and information in chemical systems.
Accelerated Design of Near-Infrared-II Molecular Fluorophores via First-Principles Understanding and Machine Learning
Authors: Xu Shidang , Cai Pengfei , Li Jiali , Zhang Xianhe , Liu Xianglong , Wang Xiaonan , Liu Bin
Published: February 2022

Organic molecular fluorophores in the second near-infrared window (NIR-II) have attracted much attention in the recent decade due to their great potentials in both fundamental research and practical applications. This is especially true for biomedical research, owing to their deep light penetration depth and low bioluminescence background at the long wavelength. However, the fluorescence quantum yields (QY) of most NIR-II materials are very low, which are not ideal for practical applications. Although there is a growing need to discover new NIR-II fluorophores, most of them were designed based on experience, and the structures were limited to few molecular motifs. Herein, we report the design of high QY NIR-II fluorophores in solutions based on enhancing the rigidity of the conjugated backbones, which could be quantified by the Seminario method. A deep neural network was trained to predict the HOMO-LUMO energy gaps for a chemical library of NIR-II backbone structures. Hundreds of new NIR-II cores with low energy gap were discovered, and eight of them across different acceptor cores are found to have relatively rigid conjugated backbones. With further molecular processing or formulation, the proposed new fluorophores should boost the development of NIR-II materials for applications in a wide range of fields.
Second-order Phase Transition Behavior in a Polymer above the Glass Transition Temperature
Authors: Ishikawa Mitsuru , Takahashi Taihei , Hayashi Yu-ichiro , Akashi Maya , Uwada Takayuki
Published: February 2022

Glass transition was primarily considered to be not phase transition; however, it has similarity to the second-order phase transition. Recent single-molecule spectroscopy developments have prompted re-investigating glass transition at the microscopic scale, revealing that glass transition includes phenomena similar to second-order phase transition. They are characterized by microscopic collective polymer motion and discontinuous changes in temperature dependent relaxation times, later of which is similar to critical slowing down, within a temperature window that includes the polymer calorimetric glass transition temperature. Considering that collective motion and critical slowing down are accompaniments to critical phenomena, second-order phase transition behavior was identified in polymer glass transition.
Second-order Phase Transition Behavior behind Polymer Glass Transition
Authors: Ishikawa Mitsuru , Takahashi Taihei , Hayashi Yu-ichiro , Akashi Maya , Uwada Takayuki
Published: February 2022

Glass transition has similarity to the second-order phase transition in temperature dependent changes in entropy, non-Arrhenius viscosity, and heat capacity of glass forming materials. However, it has primarily been considered to be not phase transition. Recent single-molecule spectroscopy developments prompted re-investigating glass transition at the nanometer scale probing resolution, showing that glass transition includes phenomena similar to the second-order phase transition. They are characterized by microscopic collective polymer motion and discontinuous changes in temperature dependent relaxation times, the latter of which resembles the critical slowing down of second-order phase transitions, within a temperature window above the polymer calorimetric glass transition temperature. Simultaneous collective motion and critical slowing down occurrences disclose that the second-order phase transition hides behind polymer glass transition.
Sequential Storage and Release of Microdroplets for On and Off-chip Analysis
Authors: Toprakcioglu Zenon , Knowles Tuomas
Published: February 2022

Droplet microfluidic methods have opened up the possibility of studying a plethora of phenomena ranging from biological to physical or chemical processes at ultra-low volumes and high throughput. A key component of such approaches is the ability to trap droplets for observation, and many device architectures for achieving this objective have been developed. A challenge with such approaches is, however, recovering the droplets following their confinement for applications involving further analysis. Here, we present a device capable of generating, confining and releasing microdroplets in a sequential manner. Through a combination of experimental and computational simulations, we shed light on the key features required for successful droplet storage and retrieval. Moreover, we explore the effect of the ow rate of the continuous phase on droplet release, determining that a critical rate is needed to ensure complete droplet deformation through constrictions holding the droplets in place prior to release. Finally, we find that once released, droplets can be retrieved and collected off chip. The ability to generate, store and sequentially release droplets renders such a device particularly promising for future applications where reactions may not only be monitored on-chip, but droplets can be retrieved for further analysis, facilitating new exploratory avenues in the fields of analytical chemistry and biology.
Acridinone-based anion transporters
Authors: McNaughton Daniel , Macreadie Lauren , Gale Philip Alan
Published: February 2022

The arrangement of hydrogen bond donors around a central lipophilic scaffold has proven a successful strategy in the development of potent chloride transporters. In this work, we revisit an acridinone 1,9-bis(thio)urea motif which had previously shown promise as an anion sensor and expand the series of compounds by appending a variety of electron-withdrawing groups to the peripheral phenyl moieties. High levels of activity were achieved by the most effective compounds in the series, which facilitated strictly electroneutral transport.
Regioselective and Water-Promoted Surface Esterification of Never-Dried Cellulose Fibers Towards Nanofibers with Adjustable Surface Energy
Authors: Beaumont Marco , Otoni Caio G. , Mattos Bruno D. , Koso Tetyana V. , Abidnejad Roozbeh , Zhao Bin , Kondor Anett , W. T. King Alistair , Rojas Orlando J.
Published: February 2022

A new regioselective route is introduced for surface modification of biological colloids in the presence of water. Taking the case of cellulose nanofibers (CNFs), we demonstrate a site-specific (93% selective) reaction between the primary surface hydroxyl groups (C6-OH) of cellulose and acyl imidazoles. Cellulose nanofibers bearing C6-acetyl and C6-iso-butyl groups, with a degree of substitution of up to 1 mmol·g–1 are obtained upon surface esterification, affording CNFs of adjustable surface energy. The morphological and structural features of the nanofibers remain largely unaffected, but the regioselective surface reactions enable tailoring the interfacial interactions, as demonstrated in oil/water Pickering emulsions. Our method precludes the need for drying or exchange with organic solvents for surface esterification, otherwise needed in the synthesis of esterified colloids and polysaccharides. Moreover, the method is well suited for application at high-solid content, opening the possibility for implementation in reactive extrusion and compounding. The proposed acylation is introduced as a sustainable approach that benefits from the presence of water and affords a high chemical substitution selectivity.
Low-temperature ammonia synthesis on electron-rich [RuH6] catalytic centers
Authors: Pan Jaysree , Wang Qianru , Guo Jianping , Hansen Heine Anton , Chen Ping , Vegge Tejs
Published: February 2022

Ammonia is a central vector in sustainable global growth, but the usage of fossil feedstocks and centralized Haber-Bosch synthesis conditions causes >1.4% of the global anthropogenic CO2 emissions. While nitrogenase enzymes convert atmospheric N2 to ammonia at ambient conditions, even the most active manmade inorganic catalysts fail due to low activity and parasitic hydrogen evolution at low temperatures. Here, we show the [RuH6] catalytic center in ternary ruthenium complex hydrides (Li4RuH6 and Ba2RuH6) activate N2 preferentially and avoid hydrogen over-saturation at low temperatures and near ambient pressure by delicately balancing H2 chemisorption and N2 activation. The active [RuH6] catalytic center is capable of achieving an unprecedented yield at low temperatures via a shift in the rate-determining reaction intermediates and transition states, where the reaction orders in hydrogen and ammonia change dramatically. Temperature-dependent atomic-scale understanding of this unique mechanism is obtained with synchronized experimental and density functional theory investigations.
Facile and Divergent Optimization of Chromazonarol Enabled the Identification of Simplified Drimane Meroterpenoids as Novel Pharmaceutical Leads
Authors: Wang Xia , Hu Nvdan , Kong Wenlong , Song Baoan , Li Shengkun
Published: February 2022

The coverage of drimane hydroquinones chemical space was expanded by the facile construction of the focused libraries of (+)-chromazonarol relevant natural products, isomers and analogues for advance as pharmaceutical leads. Through the synergistic interaction of the programmable synthesis and bioactivity-guided screening, the structure-activity relationship of (+)-chromazonarol relevant (non)-natural products was delineated. The first divergent derivatization of (+)-chromazonarol demonstrated that the phenolic hydroxyl group is one inviolable requirement for antifungal effect. Pin-point modification of (+)-yahazunol manifested the position of hydroxyl group was crucial for both antifungal and anti-tumor activities. (+)-Albaconol, (+)-neoalbaconol and two yahazunol isomers (24 and 25) were witnessed to be the novel pharmaceutical leads. The probable macromolecular targets were estimated to deliver new information about the biological potential resident in (+)-yahazunol relevant products. This work also featured the first synthesis of (+)-albaconol and (+)-neoalbaconol, the first biological exploration of (+)-dictyvaric acid and an improved preparation of (+)-8-epi-puupehedione and a promising pelorol analogue.
Simulation of Defects, Flexibility and Rupture in Biopolymer Networks
Authors: Bailey Matthew H. J. , Wilson Mark
Published: February 2022

Networks of biopolymers occur often in nature, and are vulnerable to damage over time. In this work, a coarse grained model of collagen IV molecules is applied in a 2D hexagonal network and the mechanisms by which these networks can rupture are explored. The networks are stretched linearly in order to study their structural limits and mechanism of rupture over timescale of up to 100 microseconds. Metrics are developed to track the damage networks suffer over time, and qualitatively analyse ruptures that occur. Further simulations repeatedly stretch the networks sinusoidally to mimic the in vivo strains. Defects of increasing levels of complexity are introduced into an ordered network, and their effect on the rupturing behaviour of the biopolymer networks studied. The effect of introducing holes of varying size in the network, as well as strips of finite width to mimic surgical damage are studied. These demonstrate the importance of the flexibility of the networks to preventing damage.
Fluorescent Silver-AIE Visualization of Neurons and Fibres in the Cleared Brain
Authors: Xie Sheng , Wong Alex Y. H. , Chuen Kam , Hermanson Ola , Ip Nancy , Tang Ben Zhong , Chen Sijie
Published: February 2022

Herein, we report a novel fluorogenic visualization method for mouse brain tissues by making use of a Ag+-specific aggregation-induced emission (AIE) strategy after silver impregnation. This novel fluorogenic silver-AIE method surpasses the chromogenic detection used by many conventional silver staining protocols, which have historically made revolutionary contributions to neuroanatomy. This fluorescent silver-based stain allows for analysis of images acquired using wide-field, confocal, SIMs, or light-sheet fluorescence microscopy. We validated the sensitivity, specificity, and versatility of the silver-AIE stain as compared to conventional silver stains and other neuron-specific ones. The silver-AIE stain is demonstrated to be highly compatible with immunofluorescence co-staining in paraffin sections and can be applied to hydrogel-based cleared tissue by the passive CLARITY method for image analysis of large tissue slices of 300 μm thick in this study. From this fluorogenic strategy, it is possible for vast types of classic silver staining methods to be modified and re-vitalized.
Computational studies of a DNA-based aptasensor: toward theory-driven transduction improvement.
Authors: Araujo-Rocha Mario , Piro Benoît , Noël Vincent , Barbault Florent
Published: February 2022

Aptamers are a class of bioreceptors used in analytical tools dedicated to molecular diagnostics due to their ability to perform structural reorganization upon target binding. However, there is a lack of methodologies allowing to rationalize their structure in order to improve their transduction efficiency. We chose here, a three-strand DNA structure as probe anchored on a gold surface and partially hybridized with an aptamer sequence sensitive to Ampicillin (AMP). Using a set of computational techniques, we investigated the structure change upon analyte binding, taking into account the grafting on the surface. Original analyses unveil a distinct pattern between both states which can be related to changes in capacitance of the interface between these states. To our knowledge, this work demonstrates for the first time the ability of computational investigations to drive, in-silico, the design of aptasensors.
Further synthesis and biological characterization of a series of 2-sulfonamidebenzamides as allosteric modulators of MrgX1
Authors: Sharma Swagat , Peng Qi , Vadukoot Anish , Aretz Christopher , Jensen Aaron , Wallick Alexander , Dong Xinzhong , Hopkins Corey
Published: February 2022

The present study describes our continued efforts in the discovery and characterization of a series of 2-sulfonamidebenzamides as allosteric modulators of MrgX1. MrgX1 has been shown to be an attractive target as a non-opioid receptor for the potential treatment of chronic pain. Working from our original compound, ML382, and utilizing iterative medicinal chemistry, we have identified key halogen substituents that improve MrgX1 potency by ~8-fold. In addition, we have evaluated the compounds in Tier 1 DMPK assays and have identified key compounds that impart improved potency and microsomal stability.
3D Printed Polymer Photonic Topological Insulators and their Robustness to Fabrication Disorder
Authors: Sabatini Mattei Michael , Liu Boyuan , Mazzei Capote Gerardo A. , Liu Zijie , Hacha Brandon G. , Osswald Tim A. , Yu Zongfu , Goldsmith Randall H.
Published: February 2022

Photonic topological insulators have emerged as an exciting new platform for backscatter-free waveguiding even in the presence of defects, with applications in robust long-range energy and quantum information transfer, spectroscopy and sensing, chiral quantum optics, and optoelectronics. We demonstrate a design for spin-Hall photonic topological insulators with remarkably low refractive index contrast, enabling the synthesis of photonic topological waveguides from polymeric materials for the first time. Our design is compatible with additive manufacturing methods, including fused filament fabrication for microwave frequencies, and constitutes the first demonstration of a 3D printed all-dielectric photonic topological insulator. We combine rapid device fabrication through 3D printing with high-speed FDTD simulation to quantify topological protection of transmission through “omega” shaped bent topological waveguides and find that one corner in the waveguide is 3-5 times more robust to disorder than the other. This dichotomy, a new empirical design rule for ℤ2 topological insulator devices, is shown to originate in the fundamental system symmetries and is illustrated via the distributions of Poynting vectors that describe energy flow through the waveguide. Taken together, our demonstration of 3D printed polymeric spin-Hall photonic topological insulators paired with quantification of robustness to disorder at bent topological interfaces provides a rapid, flexible scheme for engineering high-performance topological photonic devices across multiple frequency regimes from microwave to THz, to visible.
Metalation/De-metalation as a Post-Gelation Strategy to Tune the Mechanical Properties of Catenane-Crosslinked Gels
Authors: Nosiglia Mark A. , Colley Nathan D. , Palmquist Mark S. , Delawder Abigail O. , Tran Sheila L. , Harlan Gray H. , Barnes Jonathan C.
Published: February 2022

Mechanically interlocked molecules (MIMs) possess unique architectures and non-traditional degrees of freedom that arise from well-defined topologies that are achieved through precise mechanical bonding. Incorporation of MIMs into materials can thus provide an avenue to discover new and emergent macroscale properties. Here, the synthesis of a phenanthroline-based [2]catenane crosslinker and its incorporation into polyacrylate organogels is described. Specifically, Cu(I) metalation and de-metalation was used as a post-gelation strategy to tune the mechanical properties of a gel by controlling the conformational motions of integrated MIMs. The organogels were prepared via thermally initiated free radical polymerization, and Cu(I) metal was added in MeOH to pre-treated, swollen gels. De-metalation of the gels was achieved by adding cyanide salts and washing the gels. Changes in Young’s and shear moduli, as well as tensile strength, were quantified through oscillatory shear rheology and tensile testing. The reported approach provides a general method for post-gelation tuning of mechanical properties using metals and well-defined catenane topologies as part of a network architecture.
Light Directs Monomer Coordination in Catalyst-Free Grignard Photopolymerization
Authors: Woods Eliot , Berl Alexandra , Kantt Leanna , Eckdahl Christopher , Wasielewski Michael , Haines Brandon E. , Kalow Julia
Published: February 2022

π-Conjugated polymers can serve as active layers in flexible and lightweight electronics, and are conventionally synthesized by transition-metal-mediated polycondensation at elevated temperatures. We recently reported a photopolymerization of electron-deficient heteroaryl Grignard monomers that enables the catalyst-free synthesis of n-type π-conjugated polymers. Herein we provide an experimental and computational investigation of the mechanism of this photopolymerization. Spectroscopic studies performed in situ and after quenching reveal that the propagating species is a radical anion with halide end groups. DFT calculations for model oligomers suggest a Mg-templated SRN1-type coupling, in which Grignard monomer coordination to the radical anion chain avoids the formation of free sp2 radicals and enables C–C bond formation with very low barriers. We find that light plays an unusual role in the reaction, photoexciting the radical anion chain to shift electron density to the termini and thus favor productive monomer binding.