Publications by authors named "J Fraser Stoddart"

637 Publications

Single-Molecule Charge Transport through Positively Charged Electrostatic Anchors.

J Am Chem Soc 2021 Feb 12;143(7):2886-2895. Epub 2021 Feb 12.

Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.

The charge transport in single-molecule junctions depends critically on the chemical identity of the anchor groups that are used to connect the molecular wires to the electrodes. In this research, we report a new anchoring strategy, called the electrostatic anchor, formed through the efficient Coulombic interaction between the gold electrodes and the positively charged pyridinium terminal groups. Our results show that these pyridinium groups serve as efficient electrostatic anchors forming robust gold-molecule-gold junctions. We have also observed binary switching in dicationic viologen molecular junctions, demonstrating an electron injection-induced redox switching in single-molecule junctions. We attribute the difference in low- and high-conductance states to a dicationic ground state and a radical cationic metastable state, respectively. Overall, this anchoring strategy and redox-switching mechanism could constitute the basis for a new class of redox-activated single-molecule switches.
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http://dx.doi.org/10.1021/jacs.0c12664DOI Listing
February 2021

Radical-Pairing Interactions in a Molecular Switch Evidenced by Ion Mobility Spectrometry and Infrared Ion Spectroscopy.

Angew Chem Int Ed Engl 2021 Feb 9. Epub 2021 Feb 9.

University of Liege: Universite de Liege, UR Molsys, Allee du Six Aout, 11 - Quartier Agora, 4000, Liege, BELGIUM.

The digital revolution sets a milestone in the progressive miniaturization of working devices and in the underlying advent of molecular machines. Foldamers involving mechanically entangled components with modular secondary structures are among the most promising designs for molecular switch-based applications. Characterizing the nature and dynamics of their intramolecular network following the application of a stimulus is the key to their performance. Here, we use non-dissociative electron transfers as a reductive stimulus in the gas phase and probe the consecutive co-conformational transitions of a donor-acceptor oligorotaxane foldamer using electrospray mass spectrometry interfaced with ion mobility and infrared ion spectroscopy. The comparison of collision cross section distributions for analogous closed-shell and radical molecular ions sheds light on their respective formation energetics while variations in their respective infrared absorption bands evidence different intramolecular organizations as the foldamer gets compact. These differences are compatible with the advent of radical-pairing interactions.
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http://dx.doi.org/10.1002/anie.202014728DOI Listing
February 2021

Cyclodextrin Metal-Organic Frameworks and Their Applications.

Acc Chem Res 2021 Feb 1. Epub 2021 Feb 1.

Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States.

ConspectusCyclodextrin-based metal-organic frameworks (CD-MOFs), derived from γ-cyclodextrin (γ-CD) and alkali metal cations, constitute a class of porous, renewable, and edible MOFs that can be synthesized from a naturally occurring carbohydrate on a large scale. γ-CD is a -symmetrical cyclic oligosaccharide composed of eight asymmetric α-1,4-linked d-glucopyranosyl residues that possesses a bucket-shaped cavity with an inner diameter of ∼1 nm and a depth of ∼0.8 nm. Upon combination of 1 equiv of γ-CD with 8 equiv of potassium hydroxide in an aqueous solution, followed by vapor diffusion of MeOH (or EtOH) into this solution during several days, CD-MOF-1 is obtained as cubic crystals. This carbohydrate-based MOF, which was discovered serendipitously in 2010, was the first highly crystalline CD-MOF to be obtained. X-ray crystallography of a single crystal reveals that it adopts the space group 432 with unit cell dimensions of approximately 31 × 31 × 31 Å. Other CD-MOFs, namely, CD-MOF-2 and CD-MOF-3, can be obtained when potassium ions are replaced by rubidium and cesium ions, respectively. CD-MOFs comprise extended body-centered frameworks of (γ-CD) cubic units, which contain spherical pores that reside at the center of the cubes, interconnected by alkali metal cations, forming both cylindrical and triangular channels.During the past decade, CD-MOFs have emerged as a useful class of multifunctional materials based on porous frameworks with extended structures displaying robust crystallinity, permanent porosity, and excellent biocompatibility. The family of CD-MOFs has been joined by a growing collection of metal nodes involving alkali metal cations (Li, Na, K, Rb, Cs) and γ-CD as well as its derivatives. As a result of the ability of their extended porous frameworks to absorb guest molecules, including gases, drugs, metal-based nanoclusters, and nanoparticles, CD-MOFs have potential applications in areas as disparate as templating syntheses of metal-based nanoparticles and gels, adsorption and separation, trapping highly reactive intermediates, catalyst supports, sensing, electrical memory, and drug delivery.In this Account, we tell the story of CD-MOFs, a scientific discovery made in our research laboratory at Northwestern University, and the opportunities to use these environmentally friendly porous materials across different fields of science and technology. The story includes representative synthetic protocols for the preparation of CD-MOFs, along with an overview of their structural features, functionalization, and chemical modification aimed at increasing their stabilities in aqueous environments, and finally, a summary of their applications. The examples we will discuss, however, are only illustrative, and there is a significant body of additional findings emanating from our laboratory and others, especially in the realm of developing new synthetic strategies, tuning the framework stabilities, and exploring the guest inclusion and emergent properties of CD-MOFs. We refer readers to the original communications, papers, and reviews cited herein. We hope that, in the telling of the story of CD-MOFs, this Account may promote new scientific discoveries and further development of CD-MOF-based technologies in the future.
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http://dx.doi.org/10.1021/acs.accounts.0c00695DOI Listing
February 2021

A Diverse View of Science to Catalyse Change.

Angew Chem Int Ed Engl 2020 10 17;59(42):18306-18310. Epub 2020 Aug 17.

State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, International Joint Research Laboratory of Nano-Micro Architecture Chemistry (NMAC), College of Chemistry, Jilin University, Changchun, 130012, People's Republic of China.

Valuing diversity leads to scientific excellence, the progress of science and most importantly, it is simply the right thing to do. We can value diversity not only in words, but also in actions.
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http://dx.doi.org/10.1002/anie.202009834DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7590070PMC
October 2020

Of numbers and movement - understanding transcription factor pathogenesis by advanced microscopy.

Dis Model Mech 2020 12 29;13(12). Epub 2020 Dec 29.

MRC Human Genetics Unit, University of Edinburgh, Edinburgh EH4 1XU, UK

Transcription factors (TFs) are life-sustaining and, therefore, the subject of intensive research. By regulating gene expression, TFs control a plethora of developmental and physiological processes, and their abnormal function commonly leads to various developmental defects and diseases in humans. Normal TF function often depends on gene dosage, which can be altered by copy-number variation or loss-of-function mutations. This explains why TF haploinsufficiency (HI) can lead to disease. Since aberrant TF numbers frequently result in pathogenic abnormalities of gene expression, quantitative analyses of TFs are a priority in the field. single-molecule methodologies have significantly aided the identification of links between TF gene dosage and transcriptional outcomes. Additionally, advances in quantitative microscopy have contributed mechanistic insights into normal and aberrant TF function. However, to understand TF biology, TF-chromatin interactions must be characterised , in a tissue-specific manner and in the context of both normal and altered TF numbers. Here, we summarise the advanced microscopy methodologies most frequently used to link TF abundance to function and dissect the molecular mechanisms underlying TF HIs. Increased application of advanced single-molecule and super-resolution microscopy modalities will improve our understanding of how TF HIs drive disease.
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http://dx.doi.org/10.1242/dmm.046516DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7790199PMC
December 2020

In vivo Validation of Bimolecular Fluorescence Complementation (BiFC) to Investigate Aggregate Formation in Amyotrophic Lateral Sclerosis (ALS).

Mol Neurobiol 2021 Jan 7. Epub 2021 Jan 7.

Centre for Motor Neuron Disease Research, Faculty of Medicine, Health and Human Sciences, Department of Biomedical Sciences, Macquarie University, Sydney, NSW, 2109, Australia.

Amyotrophic lateral sclerosis (ALS) is a form of motor neuron disease (MND) that is characterized by the progressive loss of motor neurons within the spinal cord, brainstem, and motor cortex. Although ALS clinically manifests as a heterogeneous disease, with varying disease onset and survival, a unifying feature is the presence of ubiquitinated cytoplasmic protein inclusion aggregates containing TDP-43. However, the precise mechanisms linking protein inclusions and aggregation to neuronal loss are currently poorly understood. Bimolecular fluorescence complementation (BiFC) takes advantage of the association of fluorophore fragments (non-fluorescent on their own) that are attached to an aggregation-prone protein of interest. Interaction of the proteins of interest allows for the fluorescent reporter protein to fold into its native state and emit a fluorescent signal. Here, we combined the power of BiFC with the advantages of the zebrafish system to validate, optimize, and visualize the formation of ALS-linked aggregates in real time in a vertebrate model. We further provide in vivo validation of the selectivity of this technique and demonstrate reduced spontaneous self-assembly of the non-fluorescent fragments in vivo by introducing a fluorophore mutation. Additionally, we report preliminary findings on the dynamic aggregation of the ALS-linked hallmark proteins Fus and TDP-43 in their corresponding nuclear and cytoplasmic compartments using BiFC. Overall, our data demonstrates the suitability of this BiFC approach to study and characterize ALS-linked aggregate formation in vivo. Importantly, the same principle can be applied in the context of other neurodegenerative diseases and has therefore critical implications to advance our understanding of pathologies that underlie aberrant protein aggregation.
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http://dx.doi.org/10.1007/s12035-020-02238-0DOI Listing
January 2021

Supramolecular Gold Stripping from Activated Carbon Using α-Cyclodextrin.

J Am Chem Soc 2021 Feb 30;143(4):1984-1992. Epub 2020 Dec 30.

Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.

We report the molecular recognition of the Au(CN) anion, a crucial intermediate in today's gold mining industry, by α-cyclodextrin. Three X-ray single-crystal superstructures-KAu(CN)⊂α-cyclodextrin, KAu(CN)⊂(α-cyclodextrin), and KAg(CN)⊂(α-cyclodextrin)-demonstrate that the binding cavity of α-cyclodextrin is a good fit for metal-coordination complexes, such as Au(CN) and Ag(CN) with linear geometries, while the K ions fulfill the role of linking α-cyclodextrin tori together as a result of [K···O] ion-dipole interactions. A 1:1 binding stoichiometry between Au(CN) and α-cyclodextrin in aqueous solution, revealed by H NMR titrations, has produced binding constants in the order of 10 M. Isothermal calorimetry titrations indicate that this molecular recognition is driven by a favorable enthalpy change overcoming a small entropic penalty. The adduct formation of KAu(CN)⊂α-cyclodextrin in aqueous solution is sustained by multiple [C-H···π] and [C-H···anion] interactions in addition to hydrophobic effects. The molecular recognition has also been investigated by DFT calculations, which suggest that the 2:1 binding stoichiometry between α-cyclodextrin and Au(CN) is favored in the presence of ethanol. We have demonstrated that this molecular recognition process between α-cyclodextrin and KAu(CN) can be applied to the stripping of gold from the surface of activated carbon at room temperature. Moreover, this stripping process is selective for Au(CN) in the presence of Ag(CN), which has a lower binding affinity toward α-cyclodextrin. This molecular recognition process could, in principle, be integrated into commercial gold-mining protocols and lead to significantly reduced costs, energy consumption, and environmental impact.
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http://dx.doi.org/10.1021/jacs.0c11769DOI Listing
February 2021

François N. Diederich: Pioneer of carbon allotropes and molecular recognition.

Proc Natl Acad Sci U S A 2020 12 21;117(52):32827-32829. Epub 2020 Dec 21.

Department of Chemistry, Northwestern University, Evanston, IL 60208.

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http://dx.doi.org/10.1073/pnas.2022550117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7776638PMC
December 2020

Discrete Open-Shell Tris(bipyridinium radical cationic) Inclusion Complexes in the Solid State.

J Am Chem Soc 2021 Jan 21;143(1):163-175. Epub 2020 Dec 21.

Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.

The solid-state properties of organic radicals depend on radical-radical interactions that are influenced by the superstructure of the crystalline phase. Here, we report the synthesis and characterization of a substituted tetracationic cyclophane, cyclobis(paraquat--1,4-dimethoxyphenylene), which associates in its bisradical dicationic redox state with the methyl viologen radical cation () to give a 1:1 inclusion complex. The (super)structures of the reduced cyclophane and this 1:1 complex in the solid state deviate from the analogous (super)structures observed for the reduced state of cyclobis(paraquat--phenylene) and that of its trisradical tricationic complex. Titration experiments reveal that the methoxy substituents on the -phenylene linkers do not influence binding of the cyclophane toward small neutral guests-such as dimethoxybenzene and tetrathiafulvalene-whereas binding of larger radical cationic guests such as by the reduced cyclophane decreases 10-fold. X-ray diffraction analysis reveals that the solid-state superstructure of the 1:1 complex constitutes a discrete entity with weak intermolecular orbital overlap between neighboring complexes. Transient nutation EPR experiments and DFT calculations confirm that the complex has a doublet spin configuration in the ground state as a result of the strong orbital overlap, while the quartet-state spin configuration is higher in energy and inaccessible at ambient temperature. Superconducting quantum interference device (SQUID) measurements reveal that the trisradical tricationic complexes interact antiferromagnetically and form a one-dimensional Heisenberg antiferromagnetic chain along the -axis of the crystal. These results offer insights into the design and synthesis of organic magnetic materials based on host-guest complexes.
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http://dx.doi.org/10.1021/jacs.0c07148DOI Listing
January 2021

The compartmental distribution of knee osteoarthritis - a systematic review and meta-analysis.

Osteoarthritis Cartilage 2020 Nov 27. Epub 2020 Nov 27.

Biomechanics Group, Department of Mechanical Engineering, Imperial College London, London, UK. Electronic address:

Objectives: For a population with knee osteoarthritis (OA), determine: 1) the prevalence of single compartmental, bicompartmental and tricompartmental OA, 2) the prevalence of isolated medial tibiofemoral, lateral tibiofemoral, or patellofemoral OA, and combinations thereof.

Methods: PubMed and Web of Science databases, and reference lists of identified studies, were searched to find studies which reported on the compartmental distribution and prevalence of knee OA. Two independent reviewers assessed studies against pre-defined inclusion criteria and prevalence data were extracted along with subject characteristics. The methodological quality of each included study was assessed. A random-effects model meta-analysis was performed for each OA category to estimate the relative prevalence of OA in the knee compartments amongst people with knee OA.

Results: 16 studies (3,786 knees) met the inclusion criteria. High heterogeneity was measured. Normalised for knees with OA, estimated prevalence rates (95% CI) were: single compartmental 50% (31.5-58.3%), bicompartmental 33% (23.1-37.2%) and tricompartmental only 17% (8.8-24.8%). Isolated medial tibiofemoral OA, isolated patellofemoral OA, and combined medial tibiofemoral and patellofemoral OA were more common than tricompartmental disease, occurring in 27% (15.2-31.1%), 18% (9.9-22.7%) and 23% (14.1-27.3%) of people respectively. Single/bicompartmental patterns of disease involving the lateral tibiofemoral compartment were less common, summing to 15% (8.5-18.7%).

Conclusion: Three-quarters of people with knee OA do not have tricompartmental disease. This is not reflected in the frequency with which partial and combined partial knee arthroplasties are currently used.

Trial Registration Number: PROSPERO systematic review protocol (CRD42019140345).
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http://dx.doi.org/10.1016/j.joca.2020.10.011DOI Listing
November 2020

Viologen Tweezers to Probe the Force of Individual Donor-Acceptor π-Interactions.

J Am Chem Soc 2020 12 23;142(50):21153-21159. Epub 2020 Nov 23.

Research Unit MolSys, NanoChem, University of Liege, Sart-Tilman, B6a, Liege 4000, Belgium.

Donor-acceptor (DA) π-interactions are weak attractive forces that are exploited widely in molecular and supramolecular chemistry. They have been characterized extensively by ensemble techniques, providing values for their energies that are useful for the design of soft materials. For implementation of motions or operations based on these DA π-interactions in wholly synthetic molecular machines, the mechanical strength and force associated with their out-of-equilibrium performance are the key parameters, in addition to their energies obtained at thermodynamic equilibrium. In this context, we have used single-molecule force spectroscopy as a nonequilibrium technique to determine the mechanical strength of individual DA π-interactions in solution. We designed and synthesized a molecular tweezer that is able to encapsulate π-donors and also demonstrated a precise opening extension. The mechanical breaking of the noncovalent interactions between viologen units-π-acceptors commonly employed in mechanically interlocked molecules-and several π-donors afforded a characteristic force-distance signature, revealing the opening of individual viologen tweezers with an unambiguous extension. Single-tweezer host-exchange experiments performed demonstrated the sensitivity of the technique. This simple design could be exploited in quantifying the force of a large range of weak noncovalent bonding interactions as well as the potential work that molecular machines can generate at the single-molecule level.
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http://dx.doi.org/10.1021/jacs.0c10339DOI Listing
December 2020

Suit[3]ane.

J Am Chem Soc 2020 11 12;142(47):20152-20160. Epub 2020 Nov 12.

Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.

Suitanes are a class of mechanically interlocked molecules (MIMs) that consist of two components: a body with limbs protruding outward and a suit that fits appropriately around it, so that there is no easy way for the suit to be removed from the body. Herein, we report the synthesis and characterization of a suit[3]ane, which contains a benzotrithiophene derivative () with three protruding hexyl chains as the body and a 3-fold symmetric, extended pyridinium-based cage, namely, , as the suit. Central to its realization is effective templation, provided by during cage formation, an observation that has been supported by the strong binding constant between benzotrithiophene () and the empty cage. The solid-state structure of the suit[3]ane reveals that the body is confined within the suit's cavity with its alkyl chains protruding outward through the orifices in the cage. Notably, such a seemingly unstable molecule, having three flexible alkyl chains as its only protruding limbs, does not dissociate after prolonged heating in CDCN at 100 °C under pressure for 7 days. No evidence for guest exchange with the host was observed at this temperature in a 2:1 mixture of and in CDCN. The results indicate that flexible protruding limbs are sufficient for a suit[3]ane to remain mechanically stable even at high temperatures in solution.
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http://dx.doi.org/10.1021/jacs.0c09896DOI Listing
November 2020

MultiCon: A Semi-Supervised Approach for Predicting Drug Function from Chemical Structure Analysis.

J Chem Inf Model 2020 Dec 3;60(12):5995-6006. Epub 2020 Nov 3.

Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States.

Semi-supervised learning has proved its efficacy in utilizing extensive unlabeled data to alleviate the use of a large amount of supervised data and improve model performance. Despite its tremendous potential, semi-supervised learning has yet to be implemented in the field of drug discovery. Empirical testing of drugs and their classification is costly and time-consuming. In contrast, predicting therapeutic applications of drugs from their structural formulas using semi-supervised learning would reduce costs and time significantly. Herein, we employ a new multicontrastive-based semi-supervised learning algorithm-MultiCon-for classifying drugs into 12 categories, according to therapeutic applications, on the basis of image analyses of their structural formulas. By rational use of data balancing, online augmentations of the drug image data during training, and the combined use of multicontrastive loss with consistency regularization, MultiCon achieves better class prediction accuracies when compared with the state-of-the-art machine learning methods across a variety of existing semi-supervised learning benchmarks. In particular, it performs exceptionally well with a limited number of labeled examples. For instance, with just 5000 labeled drugs in a PubChem (D) data set, MultiCon achieved a class prediction accuracy of 97.74%.
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http://dx.doi.org/10.1021/acs.jcim.0c00801DOI Listing
December 2020

Post-Synthetically Elaborated BODIPY-Based Porous Organic Polymers (POPs) for the Photochemical Detoxification of a Sulfur Mustard Simulant.

J Am Chem Soc 2020 10 19;142(43):18554-18564. Epub 2020 Oct 19.

Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States.

Designing new materials for the effective detoxification of chemical warfare agents (CWAs) is of current interest given the recent use of CWAs. Although halogenated boron-dipyrromethene derivatives (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene or BDP or BODIPY) at the 2 and 6 positions have been extensively explored as efficient photosensitizers for generating singlet oxygen (O) in homogeneous media, their utilization in the design of porous organic polymers (POPs) has remained elusive due to the difficulty of controlling polymerization processes through cross-coupling synthesis pathways. Our approach to overcome these difficulties and prepare halogenated BODIPY-based porous organic polymers ( where X = Br or I) represents an attractive alternative through post-synthesis modification (PSM) of the parent hydrogenated polymer. Upon synthesis of both the parent polymer, , and its post-synthetically modified derivatives, and , the BET surface areas of all POPs have been measured and found to be 640, 430, and 400 mg, respectively. In addition, the insertion of heavy halogen atoms at the 2 and 6 positions of the BODIPY unit leads to the quenching of fluorescence (both polymer and solution-phase monomer forms) and the enhancement of phosphorescence (particularly for the iodo versions of the polymers and monomers), as a result of efficient intersystem crossing. The heterogeneous photocatalytic activities of both the parent POP and its derivatives for the detoxification of the sulfur mustard simulant, 2-chloroethyl ethyl sulfide (CEES), have been examined; the results show a significant enhancement in the generation of singlet oxygen (O). Both the bromination and iodination of served to shorten by 5-fold of the time needed for the selective and catalytic photo-oxidation of CEES to 2-chloroethyl ethyl sulfoxide (CEESO).
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http://dx.doi.org/10.1021/jacs.0c07784DOI Listing
October 2020

Evaluating lubricant performance to reduce COVID-19 PPE-related skin injury.

PLoS One 2020 24;15(9):e0239363. Epub 2020 Sep 24.

Department of Mechanical Engineering, Imperial College London, London, United Kingdom.

Background: Healthcare workers around the world are experiencing skin injury due to the extended use of personal protective equipment (PPE) during the COVID-19 pandemic. These injuries are the result of high shear stresses acting on the skin, caused by friction with the PPE. This study aims to provide a practical lubricating solution for frontline medical staff working a 4+ hours shift wearing PPE.

Methods: A literature review into skin friction and skin lubrication was conducted to identify products and substances that can reduce friction. We evaluated the lubricating performance of commercially available products in vivo using a custom-built tribometer.

Findings: Most lubricants provide a strong initial friction reduction, but only few products provide lubrication that lasts for four hours. The response of skin to friction is a complex interplay between the lubricating properties and durability of the film deposited on the surface and the response of skin to the lubricating substance, which include epidermal absorption, occlusion, and water retention.

Interpretation: Talcum powder, a petrolatum-lanolin mixture, and a coconut oil-cocoa butter-beeswax mixture showed excellent long-lasting low friction. Moisturising the skin results in excessive friction, and the use of products that are aimed at 'moisturising without leaving a non-greasy feel' should be prevented. Most investigated dressings also demonstrate excellent performance.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0239363PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7514078PMC
October 2020

Two-photon excited deep-red and near-infrared emissive organic co-crystals.

Nat Commun 2020 Sep 15;11(1):4633. Epub 2020 Sep 15.

Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208, USA.

Two-photon excited near-infrared fluorescence materials have garnered considerable attention because of their superior optical penetration, higher spatial resolution, and lower optical scattering compared with other optical materials. Herein, a convenient and efficient supramolecular approach is used to synthesize a two-photon excited near-infrared emissive co-crystalline material. A naphthalenediimide-based triangular macrocycle and coronene form selectively two co-crystals. The triangle-shaped co-crystal emits deep-red fluorescence, while the quadrangle-shaped co-crystal displays deep-red and near-infrared emission centered on 668 nm, which represents a 162 nm red-shift compared with its precursors. Benefiting from intermolecular charge transfer interactions, the two co-crystals possess higher calculated two-photon absorption cross-sections than those of their individual constituents. Their two-photon absorption bands reach into the NIR-II region of the electromagnetic spectrum. The quadrangle-shaped co-crystal constitutes a unique material that exhibits two-photon absorption and near-infrared emission simultaneously. This co-crystallization strategy holds considerable promise for the future design and synthesis of more advanced optical materials.
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http://dx.doi.org/10.1038/s41467-020-18431-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7493989PMC
September 2020

Ring-in-Ring(s) Complexes Exhibiting Tunable Multicolor Photoluminescence.

J Am Chem Soc 2020 09 16;142(39):16849-16860. Epub 2020 Sep 16.

Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.

One ring threaded by two other rings to form a non-intertwined ternary ring-in-rings motif is a challenging task in noncovalent synthesis. Constructing multicolor photoluminescence systems with tunable properties is also a fundamental research goal, which can lead to applications in multidimensional biological imaging, visual displays, and encryption materials. Herein, we describe the design and synthesis of binary and ternary ring-in-ring(s) complexes, based on an extended tetracationic cyclophane and cucurbit[8]uril. The formation of these complexes is accompanied by tunable multicolor fluorescence outputs. On mixing equimolar amounts of the cyclophane and cucurbit[8]uril, a 1:1 ring-in-ring complex is formed as a result of hydrophobic interactions associated with a favorable change in entropy. With the addition of another equivalent of cucurbit[8]uril, a 1:2 ring-in-rings complex is formed, facilitated by additional ion-dipole interactions involving the pyridinium units in the cyclophane and the carbonyl groups in cucurbit[8]uril. Because of the narrowing in the energy gaps of the cyclophane within the rigid hydrophobic cavities of cucurbit[8]urils, the binary and ternary ring-in-ring(s) complexes emit green and bright yellow fluorescence, respectively. A series of color-tunable emissions, such as sky blue, cyan, green, and yellow with increased fluorescence lifetimes, can be achieved by simply adding cucurbit[8]uril to an aqueous solution of the cyclophane. Notably, the smaller cyclobis(paraquat--phenylene), which contains the same -xylylene linkers as the extended tetracationic cyclophane, does not form ring-in-ring(s) complexes with cucurbit[8]uril. The encapsulation of this extended tetracationic cyclophane by both one and two cucurbit[8]urils provides an incentive to design and synthesize more advanced supramolecular systems, as well as opening up a feasible approach toward achieving tunable multicolor photoluminescence with single chromophores.
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http://dx.doi.org/10.1021/jacs.0c07745DOI Listing
September 2020

Host-Guest Complexation-Mediated Supramolecular Photon Upconversion.

J Am Chem Soc 2020 09 17;142(39):16600-16609. Epub 2020 Sep 17.

Institute of Molecular Design and Synthesis, Tianjin University, 92 Weijin Road, Nankai District, Tianjin, 300072, China.

The phenomenon of photon upconversion, in which a system absorbs two or more photons of lower energy and emits a photon of higher energy, has been used in numerous applications, including non-destructive bioimaging, deep-penetrating photodynamic therapy, catalysis, and photovoltaic devices. To date, photon upconversion has been observed typically in inorganic nanocrystals, nanoparticles, metal-organic frameworks, supramolecular assemblies, and organic dyads. Herein, we demonstrate a new strategy for harnessing photon upconversion-supramolecular upconversion-based on host-guest chemistry. We have identified a box-like fluorescent tetracationic host incorporating a thiazolothiazole emitter, which can accommodate a guest-sensitizer, 5,15-diphenylporphyrin, inside its cavity, and demonstrated that the host-guest inclusion complex displays triplet-fusion upconversion when the guest is excited with low-energy light. The strategy of supramolecular upconversion has been employed successfully in two other host-guest complexes-with hosts comprised of anthracene emitters and a 5,15-diphenylporphyrin guest-corroborating the fact that this strategy is a general one and can be applied to the design of a new family of host-guest complexes for photon upconversion. More importantly, supramolecular upconversion is accessible in solution under dilute conditions (μM) compared to most of the existing approaches that require significantly higher concentrations (mM) of emitters and/or sensitizers. Transient absorption spectroscopy and density functional theory have been employed in order to confirm a triplet-fusion upconversion mechanism. Host-guest complexation-mediated supramolecular photon upconversion eliminates multiple issues in the existing systems related to high working concentrations, high incident laser power, and low optical penetration depths.
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http://dx.doi.org/10.1021/jacs.0c05445DOI Listing
September 2020

A diverse view of science to catalyse change.

Nat Chem 2020 09;12(9):773-776

State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, International Joint Research Laboratory of Nano-Micro Architecture Chemistry (NMAC), College of Chemistry, Jilin University, Changchun, People's Republic of China.

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http://dx.doi.org/10.1038/s41557-020-0529-xDOI Listing
September 2020

A Diverse View of Science to Catalyse Change.

J Am Chem Soc 2020 08 17;142(34):14393-14396. Epub 2020 Aug 17.

State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, International Joint Research Laboratory of Nano-Micro Architecture Chemistry (NMAC), College of Chemistry, Jilin University, Changchun, People's Republic of China.

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http://dx.doi.org/10.1021/jacs.0c07877DOI Listing
August 2020

Artificial Molecular Pump Operating in Response to Electricity and Light.

J Am Chem Soc 2020 08 12;142(34):14443-14449. Epub 2020 Aug 12.

Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.

The ability to control the relative motions of component parts in molecules is essential for the development of molecular nanotechnology. The advent of mechanically interlocked molecules (MIMs) has enhanced significantly the opportunities for chemists to harness such motions in artificial molecular machines (AMMs). Recently, we have developed artificial molecular pumps (AMPs) capable of producing highly energetic oligo- and polyrotaxanes with high precision. Here, we report the design, synthesis, and operation of an AMP incorporating a photocleavable stopper that allows for the use of orthogonal stimuli. Our approach employs a ratchet mechanism to pump a ring onto a collecting chain, forming an intermediate [2]rotaxane. At a subsequent time, application of light triggers the release of the ring back into the bulk solution with temporal control. This process is monitored by the quenching of the fluorescence of a naphthalene-based fluorophore. This design may find application in the fabrication of molecular transporting systems with on-demand functions.
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http://dx.doi.org/10.1021/jacs.0c06663DOI Listing
August 2020

"STRESSED OUT": The role of FUS and TDP-43 in amyotrophic lateral sclerosis.

Int J Biochem Cell Biol 2020 09 3;126:105821. Epub 2020 Aug 3.

Diabetes and Metabolism Division, Garvan Institute of Medical Research, Sydney, NSW, Australia; St Vincent's Clinical School, UNSW Sydney, Australia; Centenary Institute, The University of Sydney, NSW, 2006, Australia. Electronic address:

Mutations in fused-in-sarcoma (FUS) and TAR DNA binding protein-43 (TDP-43; TARDBP) are known to cause the severe adult-onset neurodegenerative disorder amyotrophic lateral sclerosis (ALS). Proteinopathy caused by cellular stresses such as endoplasmic reticulum (ER) stress, oxidative stress, mitochondrial stress and proteasomal stress and the formation of stress granules (SGs), cytoplasmic aggregates and inclusions is a hallmark of ALS. FUS and TDP-43, which are DNA/RNA binding proteins that regulate transcription, RNA homeostasis and protein translation are implicated in ALS proteinopathy. Disease-causing mutations in FUS and TDP-43 cause sequestration of these proteins and their interacting partners in the cytoplasm, which leads to aggregation. This mislocalization and formation of aggregates and SGs is cytotoxic and a contributor to neuronal death. We explore how loss-of-nuclear-function and gain-of-cytoplasmic function mechanisms that affect FUS and TPD-43 localization can generate a 'stressed out' neuronal pathology and proteinopathy that drives ALS progression.
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http://dx.doi.org/10.1016/j.biocel.2020.105821DOI Listing
September 2020

Dawning of the Age of Molecular Nanotopology.

Nano Lett 2020 08 14;20(8):5597-5600. Epub 2020 Jul 14.

Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.

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http://dx.doi.org/10.1021/acs.nanolett.0c02366DOI Listing
August 2020

High-Efficiency Gold Recovery Using Cucurbit[6]uril.

ACS Appl Mater Interfaces 2020 Aug 15;12(34):38768-38777. Epub 2020 Aug 15.

Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.

Developing an extremely efficient and highly selective process for gold recovery is urgently desired for maintaining a sustainable ecological environment. Herein, we report a highly efficient gold-recovery protocol on the basis of the instantaneous assembly between cucurbit[6]uril (CB[6]) and [AuX] (X = Cl/Br) anions. Upon mixing CB[6] with the four gold-bearing salts MAuX (M = H/K, X = Cl/Br) in aqueous solutions, yellow or brown coprecipitates form immediately, as a result of multiple weak [Au-X···H-C] (X = Cl/Br) hydrogen-bonding and [Au-X···C=O] (X = Cl/Br) ion-dipole interactions. The gold-recovery efficiency, based on · coprecipitation, reaches 99.2% under optimized conditions. In the X-ray crystal superstructures, [AuCl] anions and CB[6] molecules adopt an alternating arrangement to form doubly connected supramolecular polymers, while [AuBr] anions are accommodated in the lattice between two-dimensional layered nanostructures composed of CB[6] molecules. DFT calculations have revealed that the binding energy (34.8 kcal mol) between CB[6] molecules and [AuCl] anions is higher than that (11.3-31.3 kcal mol) between CB[6] molecules and [AuBr] anions, leading to improved crystallinity and higher yields of · (M = H/K) coprecipitates. Additionally, a laboratory-scale gold-recovery protocol, aligned with an attractive strategy for the practical recovery of gold, was established based on the highly efficient coprecipitation of ·. The use of CB[6] as a gold extractant provides us with a new opportunity to develop more efficient processes for gold recovery.
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http://dx.doi.org/10.1021/acsami.0c09673DOI Listing
August 2020

Mixed-flow design for microfluidic printing of two-component polymer semiconductor systems.

Proc Natl Acad Sci U S A 2020 Jul 9;117(30):17551-17557. Epub 2020 Jul 9.

Department of Chemistry, Center for Light Energy Activated Redox Processes, Northwestern University, Evanston, IL 60208;

The rational creation of two-component conjugated polymer systems with high levels of phase purity in each component is challenging but crucial for realizing printed soft-matter electronics. Here, we report a mixed-flow microfluidic printing (MFMP) approach for two-component -polymer systems that significantly elevates phase purity in bulk-heterojunction solar cells and thin-film transistors. MFMP integrates laminar and extensional flows using a specially microstructured shear blade, designed with fluid flow simulation tools to tune the flow patterns and induce shear, stretch, and pushout effects. This optimizes polymer conformation and semiconducting blend order as assessed by atomic force microscopy (AFM), transmission electron microscopy (TEM), grazing incidence wide-angle X-ray scattering (GIWAXS), resonant soft X-ray scattering (R-SoXS), photovoltaic response, and field effect mobility. For printed all-polymer (poly[(5,6-difluoro-2-octyl-2H-benzotriazole-4,7-diyl)-2,5-thiophenediyl[4,8-bis[5-(2-hexyldecyl)-2-thienyl]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl]-2,5-thiophenediyl]) [J51]:(poly{[N,N'-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)}) [N2200]) solar cells, this approach enhances short-circuit currents and fill factors, with power conversion efficiency increasing from 5.20% for conventional blade coating to 7.80% for MFMP. Moreover, the performance of mixed polymer ambipolar [poly(3-hexylthiophene-2,5-diyl) (P3HT):N2200] and semiconducting:insulating polymer unipolar (N2200:polystyrene) transistors is similarly enhanced, underscoring versatility for two-component -polymer systems. Mixed-flow designs offer modalities for achieving high-performance organic optoelectronics via innovative printing methodologies.
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http://dx.doi.org/10.1073/pnas.2000398117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7395453PMC
July 2020

Identification of a localized nonsense-mediated decay pathway at the endoplasmic reticulum.

Genes Dev 2020 Aug 2;34(15-16):1075-1088. Epub 2020 Jul 2.

MRC Human Genetics Unit, Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh EH4 2XU, United Kingdom.

Nonsense-mediated decay (NMD) is a translation-dependent RNA quality control mechanism that occurs in the cytoplasm. However, it is unknown how NMD regulates the stability of RNAs translated at the endoplasmic reticulum (ER). Here, we identify a localized NMD pathway dedicated to ER-translated mRNAs. We previously identified NBAS, a component of the Syntaxin 18 complex involved in Golgi-to-ER trafficking, as a novel NMD factor. Furthermore, we show that NBAS fulfills an independent function in NMD. This ER-NMD pathway requires the interaction of NBAS with the core NMD factor UPF1, which is partially localized at the ER in the proximity of the translocon. NBAS and UPF1 coregulate the stability of ER-associated transcripts, in particular those associated with the cellular stress response. We propose a model where NBAS recruits UPF1 to the membrane of the ER and activates an ER-dedicated NMD pathway, thus providing an ER-protective function by ensuring quality control of ER-translated mRNAs.
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http://dx.doi.org/10.1101/gad.338061.120DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7397857PMC
August 2020

Supramolecular Porous Organic Nanocomposites for Heterogeneous Photocatalysis of a Sulfur Mustard Simulant.

Adv Mater 2020 Aug 29;32(32):e2001592. Epub 2020 Jun 29.

Department of Chemistry, Northwestern University, Evanston, IL, 60208, USA.

Efficient heterogeneous photosensitizing materials require both large accessible surface areas and excitons of suitable energies and with well-defined spin structures. Confinement of the tetracationic cyclophane (ExBox ) within a nonporous anionic polystyrene sulfonate (PSS) matrix leads to a surface area increase of up to 225 m g in ExBox•PSS. Efficient intersystem crossing is achieved by combining the spin-orbit coupling associated to Br heavy atoms in 1,3,5,8-tetrabromopyrene (TBP), and the photoinduced electron transfer in a TBP⊂ExBox supramolecular dyad. The TBP⊂ExBox complex displays a charge transfer band at 450 nm and an exciplex emission at 520 nm, indicating the formation of new mixed-electronic states. The lowest triplet state (T , 1.89 eV) is localized on the TBP and is close in energy with the charge separated state (CT, 2.14 eV). The homogeneous and heterogeneous photocatalytic activities of the TBP⊂ExBox , for the elimination of a sulfur mustard simulant, has proved to be significantly more efficient than TBP and ExBox , confirming the importance of the newly formed excited-state manifold in TBP⊂ExBox for the population of the low-lying T state. The high stability, facile preparation, and high performance of the TBP⊂ExBox•PSS nanocomposites augur well for the future development of new supramolecular heterogeneous photosensitizers using host-guest chemistry.
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http://dx.doi.org/10.1002/adma.202001592DOI Listing
August 2020

Precious metal recovery from electronic waste by a porous porphyrin polymer.

Proc Natl Acad Sci U S A 2020 07 22;117(28):16174-16180. Epub 2020 Jun 22.

Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST), Yuseong-gu, 34141 Daejeon, Korea;

Urban mining of precious metals from electronic waste, such as printed circuit boards (PCB), is not yet feasible because of the lengthy isolation process, health risks, and environmental impact. Although porous polymers are particularly effective toward the capture of metal contaminants, those with porphyrin linkers have not yet been considered for precious metal recovery, despite their potential. Here, we report a porous porphyrin polymer that captures precious metals quantitatively from PCB leachate even in the presence of 63 elements from the Periodic Table. The nanoporous polymer is synthesized in two steps from widely available monomers without the need for costly catalysts and can be scaled up without loss of activity. Through a reductive capture mechanism, gold is recovered with 10 times the theoretical limit, reaching a record 1.62 g/g. With 99% uptake taking place in the first 30 min, the metal adsorbed to the porous polymer can be desorbed rapidly and reused for repetitive batches. Density functional theory (DFT) calculations indicate that energetically favorable multinuclear-Au binding enhances adsorption as clusters, leading to rapid capture, while Pt capture remains predominantly at single porphyrin sites.
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http://dx.doi.org/10.1073/pnas.2000606117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7368251PMC
July 2020

A precise polyrotaxane synthesizer.

Science 2020 06 11;368(6496):1247-1253. Epub 2020 Jun 11.

Department of Chemistry, Northwestern University, Evanston, IL 60208, USA.

Mechanically interlocked molecules are likely candidates for the design and synthesis of artificial molecular machines. Although polyrotaxanes have already found niche applications in exotic materials with specialized mechanical properties, efficient synthetic protocols to produce them with precise numbers of rings encircling their polymer dumbbells are still lacking. We report the assembly line-like emergence of poly[]rotaxanes with increasingly higher energies by harnessing artificial molecular pumps to deliver rings in pairs by cyclical redox-driven processes. This programmable strategy leads to the precise incorporation of two, four, six, eight, and 10 rings carrying 8+, 16+, 24+, 32+, and 40+ charges, respectively, onto hexacationic polymer dumbbells. This strategy depends precisely on the number of redox cycles applied chemically or electrochemically, in both stepwise and one-pot manners.
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http://dx.doi.org/10.1126/science.abb3962DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7375334PMC
June 2020

Early recovery dynamics of turbid coral reefs after recurring bleaching events.

J Environ Manage 2020 Aug 14;268:110666. Epub 2020 May 14.

CSIRO Oceans & Atmosphere, Indian Ocean Marine Research Centre, Perth, WA, 6009, Australia.

The worlds' coral reefs are declining due to the combined effects of natural disturbances and anthropogenic pressures including thermal coral bleaching associated with global climate change. Nearshore corals are receiving increased anthropogenic stress from coastal development and nutrient run-off. Considering forecast increases in global temperatures, greater understanding of drivers of recovery on nearshore coral reefs following widespread bleaching events is required to inform management of local stressors. The west Pilbara coral reefs, with cross-shelf turbidity gradients coupled with a large nearby dredging program and recent history of repeated coral bleaching due to heat stress, represent an opportune location to study recovery from multiple disturbances. Mean coral cover at west Pilbara reefs was monitored from 2009 to 2018 and declined from 45% in 2009 to 5% in 2014 following three heat waves. Recruitment and juvenile abundance of corals were monitored from 2014 to 2018 and were combined with biological and physical data to identify which variables enhanced or hindered early-stage coral recovery of all hard corals and separately for the acroporids, the genera principally responsible for recovery in the short-term (<7 years). From 2014 to 2018, coral cover increased from 5 to 10% but recovery varied widely among sites (0-13%). Hard coral cover typically recovered most at shallower sites that had higher abundance of herbivorous fish, less macroalgae, and lower turbidity. Similarly, acroporid corals recovered most at sites with lower turbidity and macroalgal cover. Juvenile acroporid densities were a good indicator of recovery at least two years after they were recorded. However, recruitment to settlement tiles was not a good predictor of total coral or acroporid recovery. This study shows that coral recovery can be slower in areas of high turbidity and the rate may be reduced by local pressures, such as dredging. Management should focus on improving or maintaining local water quality to increase the likelihood of coral recovery under climate stress. Further, in turbid environments, juvenile coral density predicts early coral recovery better than recruits on tiles and may be a more cost-effective technique for monitoring recovery potential.
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http://dx.doi.org/10.1016/j.jenvman.2020.110666DOI Listing
August 2020