Chemical Sensing of Polyols with Shapeshifting Boronic Acids As a Self-Contained Sensor Array

Interdependent Dynamic Nitroaldol and Boronic Ester Reactions for Complex Dynamers of Different Topologies

Complex dynamic systems displaying interdependency between nitroaldol and boronic ester reactions have been demonstrated. Nitroalkane-1,3-diols, generated by the nitroaldol reaction, were susceptible to ester formation with different boronic acids in aprotic solvents, whereas hydrolysis of the esters occurred in the presence of water. The boronic ester formation led to significant stabilization of the nitroaldol adducts under basic conditions. The use of bifunctional building blocks was furthermore established, allowing for main chain nitroaldol-boronate dynamers as well as complex network dynamers with distinct topologies. The shape and rigidity of the resulting dynamers showed an apparent dependency on the configuration of the boronic acids.

Correlated shapeshifting and configurational isomerization

Herein we demonstrate that the rapid 'shapeshifting' constitutional isomerization of a substituted bullvalene is influenced by the E-to-Z configurational isomerization of a remote carbamate group, giving rise to correlated motion. We find that, while the E-configurational isomer of a bulky carbamate favors the β-bullvalene constitutional isomer, a noncovalent bonding interaction within the Z-carbamate tips the equilibrium toward the γ-bullvalene form. Using DFT modelling and NMR spectroscopy, this long-range interaction is identified as being between the bullvalene core and a pendant phenyl group connected to the carbamate. Coupling the constitutional changes of a bullvalene to a reciprocal configurational isomerization through a long-range interaction in this way will allow shapeshifting rearrangements to be exploited as part of collective motion in extended structures.

A guide to bullvalene stereodynamics

Here, we analyze the stereodynamic properties of bullvalenes using principal moments of inertia and exit vector plots to draw comparisons with commonly used ring systems in medicinal chemistry. To aid analyses, we first classify (i) the four elementary rearrangement steps available to substituted bullvalenes, which (ii) can be described by applying positional descriptors (α, β, γ, and δ) to the substituents. We also (iii) derive an intuitive equation to calculate the number of isomers for a given bullvalene system. Using DFT-modelled structures for di-, tri-, and tetrasubstituted bullvalenes, generated using a newly developed computational tool (bullviso), we show that their 3D shapes and the exit vectors available from the bullvalene scaffold make them comparable to other bioisosteres currently used to replace planar aromatic ring systems in drug discovery. Unlike conventional ring systems, the shapeshifting valence isomerism of bullvalenes gives rise to numerous shapes and substituent relationships attainable as a concentration-independent dynamic covalent library from a single compound. We visualize this property by applying population weightings to the principal moments of inertia and exit vector analyses to reflect the relative thermodynamic stabilities of the available isomers.

Molecular Ball Joints: Mechanochemical Perturbation of Bullvalene Hardy-Cope Rearrangements in Polymer Networks

The solution-state fluxional behavior of bullvalene has fascinated physical organic and supramolecular chemists alike. Little effort, however, has been put into investigating bullvalene applications in bulk, partially due to difficulties in characterizing such dynamic systems. To address this knowledge gap, we herein probe whether bullvalene Hardy-Cope rearrangements can be mechanically perturbed in bulk polymer networks. We use dynamic mechanical analysis to demonstrate that the activation barrier to the glass transition process is significantly elevated for bullvalene-containing materials relative to "static" control networks. Furthermore, bullvalene rearrangements can be mechanically perturbed at low temperatures in the glassy region; such behavior facilitates energy dissipation (i.e., increased hysteresis energy) and polymer chain alignment to stiffen the material (i.e., increased Young's modulus) under load. Computational simulations corroborate our work that showcases bullvalene as a reversible "low-force" covalent mechanophore in the modulation of viscoelastic behavior.

Kinetic Control of Complexity in Multiple Dynamic Libraries

Multiple dynamic libraries of compounds are generated when more than one reversible reaction comes into play. Commonly, two or more orthogonal reversible reactions are used, leading to non-communicating dynamic libraries which share no building blocks. Only a few examples of communicating libraries have been reported, and in all those cases, building blocks are reversibly exchanged from one library to the other, constituting an antiparallel dynamic covalent system. Herein we report that communication between two different dynamic libraries through an irreversible process is also possible. Indeed, alkyl amines cancel the dynamic regime on the nucleophilic substitution of tetrazines, generating kinetically inert compounds. Interestingly, such amine can be part of another dynamic library, an imine-amine exchange. Thus, both libraries are interconnected with each other by an irreversible process which leads to kinetically inert structures that contain parts from both libraries, causing a collapse of the complexity. Additionally, a latent irreversible intercommunication could be developed. In such a way, a stable molecular system with specific host-guest and fluorescence properties, could be irreversibly transformed when the right stimulus was applied, triggering the cancellation of the original supramolecular and luminescent properties and the emergence of new ones.

Modular, Enantioselective Entry into Polysubstituted Shapeshifting Molecules

Dynamic, shapeshifting hydrocarbons have emerged as enabling frameworks across drug discovery, materials science, and catalysis. Their employment, however, is often hampered by a lack of efficient synthetic methods for their preparation. Herein, we report a unified, concise, and modular synthesis of enantioenriched shapeshifting hydrocarbons (barbaralones and bullvalones) and multisubstituted bullvalenes, leveraging mild photochemical and base-induced rearrangements.

Reversible Restrain and Release of the Dynamic Valence Isomerization in a Shape-shifting Bullvalene by Complex Formation

In search for structural features that enable the control of the valence isomerization of the fluxional bullvalene, a bullvalene-bis(harmane) conjugate is identified that acts as chelating ligand in complexes with metal ions. Spectrometric titrations show that this ligand forms 1 : 1 complexes with Ag+, Cu+, Cu2+, and Zn2+. Most importantly, detailed NMR-spectroscopic analysis at different temperatures reveals that the complexation with Ag+ strongly affects the dynamic isomerization of the bullvalene unit of the ligand such that only one predominant valence isomer is formed, even at 5 °C. Detailed 1H-NMR-spectroscopic studies disclose an increased barrier (~11 kJ mol-1) of the Cope rearrangement. Furthermore, the addition of hexacyclene displaces the Ag+ from the complex, so that the valence isomerization is accelerated and an equilibrium with two predominant isomers is formed. In turn, repeated addition of Ag+ regains the complex with the restrained isomerization of the bullvalene unit. This method to control the valence isomerism by straightforward chemical stimuli may be used to simplify structural analysis at elevated temperatures, i. e. a feature not available so far with bullvalenes, and it may be employed as functional element in dynamic supramolecular assemblies.

Boronic Acid-Decorated Carbon Dot-Based Semiselective Multichannel Sensor Array for Cytokine Discrimination and Oral Cancer Diagnosis

Cytokines are essential components of the immune system and are recognized as significant biomarkers. However, detection of a single cytokine is not precise and reliable enough to satisfy the requirements for diagnosis. Herein, we developed a pattern recognition-based method for the multiplexed sensing of cytokines, which involves three-color-emitting boronic acid-decorated carbon dots (BCDs) and arginine-modified titanium carbide (Ti3C2 MXenes) as the sensor array. Initially, the fluorescence signals of the three BCDs were quenched by Ti3C2 MXenes. In the presence of cytokines, the fluorescence intensity of the BCDs was restored or further quenched by different cytokines. The fluorescence response occurs in two steps: first, boronic acid interacts with cis-diol functional groups of cytokines, and second, arginine headgroup selectively interacts with glycans. By exploiting the different competing binding of the BCDs and the cytokines toward Ti3C2 MXenes, seven cytokines and their mixtures can be effectively discriminated at a concentration of 20 ng mL-1. Furthermore, our sensor array demonstrated an excellent performance in classifying human oral cancer saliva samples from healthy individuals with clinically relevant specificity. The noninvasive method offers a rapid approach to cytokine analysis, benefiting early and timely clinical diagnosis and treatment.

Modulating Escape Channels of Cycloheptatrienyl Rhodium Carbenes To Form Semibullvalene

We describe the various escape channels available to dirhodium carbene intermediates from cycloheptatrienyl diazo compounds located with density functional theory. An intramolecular cyclopropanation would, in principle, provide a new route to semibullvalenes (SBVs). A detailed exploration of the potential energy surface reveals that methylating carbon-7 suppresses a competing β-hydride migration pathway to heptafulvene products, giving SBV formation a reasonable chance. During our explorations, we additionally discovered unusual spirononatriene, spironorcaradiene, and metal-stabilized 9-barbaralyl cation structures as local minima.

Shapeshifting bullvalene-linked vancomycin dimers as effective antibiotics against multidrug-resistant gram-positive bacteria

The alarming rise in superbugs that are resistant to drugs of last resort, including vancomycin-resistant enterococci and staphylococci, has become a significant global health hazard. Here, we report the click chemistry synthesis of an unprecedented class of shapeshifting vancomycin dimers (SVDs) that display potent activity against bacteria that are resistant to the parent drug, including the ESKAPE pathogens, vancomycin-resistant Enterococcus (VRE), methicillin-resistant Staphylococcus aureus (MRSA), as well as vancomycin-resistant S. aureus (VRSA). The shapeshifting modality of the dimers is powered by a triazole-linked bullvalene core, exploiting the dynamic covalent rearrangements of the fluxional carbon cage and creating ligands with the capacity to inhibit bacterial cell wall biosynthesis. The new shapeshifting antibiotics are not disadvantaged by the common mechanism of vancomycin resistance resulting from the alteration of the C-terminal dipeptide with the corresponding d-Ala-d-Lac depsipeptide. Further, evidence suggests that the shapeshifting ligands destabilize the complex formed between the flippase MurJ and lipid II, implying the potential for a new mode of action for polyvalent glycopeptides. The SVDs show little propensity for acquired resistance by enterococci, suggesting that this new class of shapeshifting antibiotic will display durable antimicrobial activity not prone to rapidly acquired clinical resistance.

Ratiometric Strategy Based on Intramolecular Internal Standard for Reproducible and Simultaneous Fingerprint Recognition of Diols via 19F NMR Spectroscopy

¹⁹F NMR spectroscopy has been widely used as a convenient and noninvasive analytical technique for understanding complex natural phenomena at the atomic level. However, current NMR referencing techniques are most optimized for ¹H NMR, which causes some limitations while referencing heteronuclear NMR. Despite its promising advantages, ¹⁹F NMR spectroscopy often exhibits large variations in experimental results and lacks consistency compared with ¹H NMR. Herein, we propose a new strategy to improve the consistency of ¹⁹F NMR referencing using an internal standard method. As a proof-of-concept, BA-Py-TFP was applied as a sensor for diols via ¹⁹F NMR spectroscopy. This strategy proved to be a robust and reproducible referencing method with acceptable deviation (Δδ_F = 43-58 ppb) across diverse NMR spectrometers at different institutions. In particular, this new strategy allows reliable fingerprint recognition for analytes and enables qualitative and quantitative analyses of mixtures of multiple analytes simultaneously. The high recovery rates for d-glucose in the human serum matrix suggest its potential suitability for a diverse range of applications, such as in diabetes-related diagnostics.

Toward Nanomolar Multi-Component Analysis by 19F NMR

The widespread application of nuclear magnetic resonance (NMR) spectroscopy in detection is currently hampered by its inherently low sensitivity and complications resulting from the undesired signal overlap. Here, we report a detection scheme to address these challenges, where analytes are recognized by ¹⁹F-labeled probes to induce characteristic shifts of ¹⁹F resonances that can be used as "chromatographic" signatures to pin down each low-concentration analyte in complex mixtures. This unique signal transduction mechanism allows detection sensitivity to be enhanced by using massive chemically equivalent ¹⁹F atoms, which was achieved through the proper installation of nonafluoro-tert-butoxy groups on probes of high structural symmetry. It is revealed that the binding of an analyte to the probe can be sensed by as many as 72 chemically equivalent ¹⁹F atoms, allowing the quantification of analytes at nanomolar concentrations to be routinely performed by NMR. Applications on the detection of trace amounts of prohibited drug molecules and water contaminants were demonstrated. The high sensitivity and robust resolving ability of this approach represent a first step toward extending the application of NMR to scenarios that are now governed by chromatographic and mass spectrometry techniques. The detection scheme also makes possible the highly sensitive non-invasive multi-component analysis that is difficult to achieve by other analytical methods.

Shape‐Shifting Molecules: Unveiling the Valence Tautomerism Phenomena in Bare Barbaralones

We report a state‐of‐the‐art spectroscopic study of an archetypical barbaralone, conclusively revealing the valence tautomerism phenomena for this bistable molecular system. The two distinct 1‐ and 5‐substituted valence tautomers have been isolated in a supersonic expansion for the first time and successfully characterized by high‐resolution rotational spectroscopy. This work provides irrefutable experimental evidence of the [3,3]‐rearrangement in barbaralones and highlights the use of rotational spectroscopy to analyze shape‐shifting mixtures. Moreover, this observation opens the window toward the characterization of new fluxional systems in the isolation conditions of the gas phase and should serve as a reference point in the general understanding of valence tautomerism.

Guest-Dependent Isomer Convergence of a Permanently Fluxional Coordination Cage

A fluxional bis-monodentate ligand, based on the archetypal shape-shifting molecule bullvalene, self-assembles with M2+ (M=Pd2+ or Pt2+ ) to produce a highly complex ensemble of permanently fluxional coordination cages. Metal-mediated self-assembly selects for an M2 L4 architecture while maintaining shape-shifting ligand complexity. A second level of simplification is achieved with guest-exchange; the binding of halides within the M2 L4 cage mixture results in a convergence to a cage species with all four ligands present as the "B isomer". Within this confine, the reaction graph of the bullvalene is greatly restricted, but gives rise to a mixture of 38 possible diastereoisomers in rapid exchange. X-ray crystallography reveals a preference for an achiral form consisting of both ligand enantiomers. Through a combination of NMR spectroscopy and DFT calculations, we elucidate the restricted isomerisation pathway of the permanently fluxional M2 L4 assembly.

Construction of vicinal 4°/3°-carbons via reductive Cope rearrangement

Herein reported is a strategy for constructing vicinal 4°/3° carbons via reductive Cope rearrangement. Substrates have been designed which exhibit Cope rearrangement kinetic barriers of ∼23 kcal mol⁻¹ with isoenergetic favorability (ΔG ∼ 0). These fluxional/shape-shifting molecules can be driven forward by chemoselective reduction to useful polyfunctionalized building blocks.

Herein reported is a strategy for constructing vicinal 4°/3° carbons via reductive Cope rearrangement.

Ambimodal Pericyclic Rearrangements of Dialkenyl-Bullvalenes Give Tetrahydro-1,8-ethenoheptalenes

The fluxional structure of bullvalene is expanded by the discovery of a [5,5]-sigmatropic rearrangement of dialkenyl substituted derivatives. This gives rise to tetrahydro-1,8-ethenoheptalenes (THEH), representing the first examples of this tricyclic scaffold. Variation of the substitution pattern alters the product distribution, including one thermodynamically balanced between THEH and bullvalene isomers. DFT calculations are used to explore the thermodynamic landscape and reaction mechanism revealing a pretransition state bifurcation leading to a concerted ambimodal rearrangement pathway.

Illustration of a computational pipeline for evaluating cyclodextrin host-guest complex formation through conformational capture of bullvalene

Cyclodextrins have a diverse range of applications, including as supramolecular hosts, as enzyme active-site analogs, in improving drug solubility and delivery, and in molecular selection. We have investigated their ability to form stable complexes with bullvalenes, unusual organic cage molecules that spontaneously interconvert between numerous degenerate isomers. The shape-shifting nature of substituted bullvalenes raises the potential for dynamic adaptive binding to biological targets. We tested whether β- and γ-cyclodextrins can capture particular bullvalene isomers and whether the preferred binding mode(s) differ between isomers. We first applied our computational host-guest interaction potential energy profiling to determine the best binding mode(s) of unsubstituted bullvalene and each isomer of methylenehydroxybullvalene to β- and γ-cyclodextrin. Subsequent molecular dynamics simulations of the predicted host-guest complexes showed that while unsubstituted bullvalene has a single, albeit ill-defined, binding mode with either cyclodextrin, each isomer of methylenehydroxybullvalene has two possible modes of binding to β-cyclodextrin but only a single, nebulous mode of binding to γ-cyclodextrin. Experimental determination of the binding free energy of each methylenehydroxybullvalene-cyclodextrin complex showed that methylenehydroxybullvalene is more likely to bind to β-cyclodextrin than to γ-cyclodextrin, despite its smaller cavity. Together, our results suggest that β-cyclodextrin, but not γ-cyclodextrin, shows promise for conformational capture of mono-substituted bullvalenes. More broadly, our computational pipeline should prove useful for rapid characterization of cyclodextrin host-guest complexes, avoiding the need for costly synthesis of guest molecules that are unlikely to bind stably, as well as providing detailed atomic-level insight into the nature of complexation.

Stereomutation of Substituted Bullvalenes

The stereomutation of substituted bullvalenes is an inevitable consequence of the valence isomerism that automerizes this unique fluxional hydrocarbon. The introduction of external stereogenicity in the substituents expands the reaction graphs and leads to a wealth of complex diastereochemical relationships. In this communication, we explore these possibilities and prepare a range of stereochemically rich substituted bullvalenes. This includes a series of disubstituted bullvalenes with two external stereocenters as a platform for fluxional, shape-diverse compound libraries. We also prepare a tethered bisbullvalene with central stereogenicity in the tether as an ensemble of 900 unique isomers that are completely stereomutable.

Tailoring Sensors and Solvents for Optimal Analysis of Complex Mixtures Via Discriminative 19F NMR Chemosensing

Separation-free analytic techniques capable of providing precise and real-time component information are in high demand. ¹⁹F NMR-based chemosensing, where the reversible binding between analytes and a ¹⁹F-labeled sensor produces chromatogram-like output, has emerged as a valuable tool for the rapid analysis of complex mixtures. However, the potential overlap of the ¹⁹F NMR signals still limits the number of analytes that can be effectively differentiated. In this study, we systematically investigated the influence of the sensor structure and NMR solvents on the resolution of structurally similar analytes. The substituents adjacent and distal to the ¹⁹F labels are both important to the resolving ability of the ¹⁹F-labeled sensors. More pronounced separation between ¹⁹F NMR peaks was observed in nonpolar and aromatic solvents. By using a proper sensor and solvent combination, more than 20 biologically relevant analytes can be simultaneously identified.

Recent Progress in Small Spirocyclic, Xanthene-Based Fluorescent Probes

The use of fluorescent probes in a multitude of applications is still an expanding field. This review covers the recent progress made in small molecular, spirocyclic xanthene-based probes containing different heteroatoms (e.g., oxygen, silicon, carbon) in position 10'. After a short introduction, we will focus on applications like the interaction of probes with enzymes and targeted labeling of organelles and proteins, detection of small molecules, as well as their use in therapeutics or diagnostics and super-resolution microscopy. Furthermore, the last part will summarize recent advances in the synthesis and understanding of their structure-behavior relationship including novel computational approaches.

Simultaneous detection of small molecule thiols with a simple 19F NMR platform

Thiols play critical roles in regulating biological functions and have wide applications in pharmaceutical and biomedical industries. However, we still lack a general approach for the simultaneous detection of various thiols, especially in complex systems. Herein, we establish a ¹⁹F NMR platform where thiols are selectively fused into a novelly designed fluorinated receptor that has two sets of environmentally different ¹⁹F atoms with fast kinetics (k ₂ = 0.73 mM^-1 min^-1), allowing us to generate unique two-dimensional codes for about 20 thiols. We demonstrate the feasibility of the approach by reliably quantifying thiol drug content in tablets, discriminating thiols in living cells, and for the first time monitoring the thiol related metabolism pathway at the atomic level. Moreover, the method can be easily extended to detect the activity of thiol related enzymes such as γ-glutamyl transpeptidase. We envision that the versatile platform will be a useful tool for detecting thiols and elucidating thiol-related processes in complex systems.

An Inexpensive Paper-Based Photoluminescent Sensor for Gallate Derived Green Tea Polyphenols

This work describes a terbium luminescence-based protocol to selectively detect gallate-derived green tea polyphenols on a supramolecular gel immobilised paper platform for the first time. This user-friendly, inexpensive (€ 0.0015) approach requires very low sample volumes for the analysis. The developed strategy enables simultaneous detection of gallate polyphenols in multiple tea samples with the potential for practical applications.

Electroactive Anion Receptor with High Affinity for Arsenate

Herein, we present the synthesis and characterization of a macrocyclic polyamide cage that incorporates redox-active 1,4-dithiin units. UV/vis titration experiments with eight anions in acetonitrile revealed high affinity for H₂AsO₄^- (log β₂ = 10.4_-0.4^+0.4) and HCO₃^- (log β₂ = 8.3_-0.4^+0.3) over other common anionic guests, such as Cl^- (log K_1:1 = 3.20_-0.02^+0.03), HSO₄^- (log K_1:1 = 3.57_-0.03^+0.02), and H₂PO₄^- (log K_1:1 = 4.24_-0.04^+0.05), by the selective formation of HG₂ complexes. The recognition of arsenate over phosphate is rare among both proteins and synthetic receptors, and though the origin of selectivity is not known, exploiting the difference in the binding stoichiometry represents an underexplored avenue toward developing receptors that can differentiate between the two anions. Additional analysis by ¹H NMR in 1:3 CD₂Cl₂/MeCN-d₃ found a strong dependence of anion binding stoichiometry with the solvent employed. Finally, titration experiments with cyclic voltammetry provided varying and complex responses for each anion tested, though reaction between the anion and receptors was observed in most cases. These results implicate 1,4-dithiins as interesting recognition moieties in the construction of supramolecular receptors.

Shapeshifting molecules: the story so far and the shape of things to come

Shapeshifting molecules exhibit rapid constitutional dynamics while remaining stable, isolable molecules, making them promising artificial scaffolds from which to explore complex biological systems and create new functional materials. However, their structural complexity presents challenges for designing their syntheses and understanding their equilibria. This minireview showcases (1) recent applications of highly dynamic shapeshifting molecules in sensing and distinguishing complex small molecules and (2) detailed insights into the adaptation of tractable bistable systems to changes in their local environment. The current status of this field is summarised and its future prospects are discussed.

Network Analysis of Substituted Bullvalenes

Substituted bullvalenes are dynamic shape-shifting molecules that exist within complex reaction networks. Herein, we report the synthesis of di- and trisubstituted bullvalenes and investigate their dynamic properties. Trisubstituted bullvalenes share a common major isomer which shows kinetic metastability. A survey of the thermodynamic and kinetic landscapes through computational analysis together with kinetic simulation provides a map of the internal dynamics of these systems.

Poly(ionic liquid)s as a distinct receptor material to create a highly-integrated sensing platform for efficiently identifying numerous saccharides

A highly-integrated sphere-based sensing platform for directly identifying numerous saccharides very efficiently is developed.

Saccharides have strong hydrophilicities, and are complex molecular structures with subtle structure differences, and tremendous structural variations. The creation of one sensing platform capable of efficiently identifying such target systems presents a huge challenge. Using the integration of unique multiple noncovalent interactions simultaneously occurring in poly(ionic liquid)s (PILs) with multiple signaling channels, in this research an aggregation-induced emission (AIE)-doped photonic structured PIL sphere is constructed. It is found that such a sphere can serve as a highly integrated platform to provide abundant fingerprints for directly sensing numerous saccharides with an unprecedented efficiency. As a demonstration, 23 saccharides can be conveniently identified using only one sphere. More importantly, by using simple ion-exchanges of PIL receptors or/and increasing the AIE signaling channels, this platform is able to perform, on demand, different sensing tasks very efficiently. This is demonstrated by using it for the detection of difficult targets, such as greatly extended saccharides as well as mixed targets, in real-life examples on one or two spheres. The findings show that this new class of platform is very promising for addressing the challenges of identifying saccharides.

A chiral sensor for recognition of varied amines based on 19F NMR signals of newly designed rhodium complexes

A novel chiral octahedral rhodium complex containing fluorine has been developed to be an excellent chiral sensor for a variety of amines including diamines, monoamines, amino alcohols and amino acids, showing well distinguishable 19F NMR signals and an accurate measurement of enantiomeric determination.

Photoregulated fluxional fluorophores for live-cell super-resolution microscopy with no apparent photobleaching

Photoswitchable molecules have multiple applications in the physical and life sciences because their properties can be modulated with light. Fluxional molecules, which undergo rapid degenerate rearrangements in the electronic ground state, also exhibit switching behavior. The stochastic nature of fluxional switching, however, has hampered its application in the development of functional molecules and materials. Here we combine photoswitching and fluxionality to develop a fluorophore that enables very long (>30 min) time-lapse single-molecule localization microscopy in living cells with minimal phototoxicity and no apparent photobleaching. These long time-lapse experiments allow us to track intracellular organelles with unprecedented spatiotemporal resolution, revealing new information of the three-dimensional compartmentalization of synaptic vesicle trafficking in live human neurons.

Super-resolution microscopy with spontaneously blinking dyes is dependent on pH and polarity of the medium. Here the authors introduce a photoactivatable fluxional fluorophore for live cell imaging that allows control over the fraction of spontaneously blinking molecules independently of medium properties.

Nonconjugated Hydrocarbons as Rigid-Linear Motifs: Isosteres for Material Sciences and Bioorganic and Medicinal Chemistry

Nonconjugated hydrocarbons, like bicyclo[1.1.1]pentane, bicyclo[2.2.2]octane, triptycene, and cubane are a unique class of rigid linkers. Due to their similarity in size and shape they are useful mimics of classic benzene moieties in drugs, so-called bioisosteres. Moreover, they also fulfill an important role in material sciences as linear linkers, in order to arrange various functionalities in a defined spatial manner. In this Review article, recent developments and usages of these special, rectilinear systems are discussed. Furthermore, we focus on covalently linked, nonconjugated linear arrangements and discuss the physical and chemical properties and differences of individual linkers, as well as their application in material and medicinal sciences.

Shape-selective crystallisation of fluxional carbon cages

Dynamic covalent rearrangements of fluxional carbon cages, such as bullvalenes and barbaralanes, impart 'shapeshifting' molecular properties. Here, a series of five barbaralanes each interconvert dynamically between two constitutional isomers in solution, but resolve to single isomers upon crystallisation. Unexpectedly, the minor solution-phase isomers are resolved in two instances. Through dynamic NMR, crystallographic and DFT analyses, we show that the isomer observed in the solid state is not a direct consequence of the equilibrium distribution in solution or any specific noncovalent interactions. Rather, the dynamic preferential crystallisation is dictated by differences in molecular size and shape.

Fluorescent Gold Nanocluster-Based Sensor Array for Nitrophenol Isomer Discrimination via an Integration of Host-Guest Interaction and Inner Filter Effect

The rapid discrimination of nitrophenol isomers has been a long-standing challenge because of the tiny structural differences among the isomers. In this study, a fluorescent sensor array based on three different-color emitting gold nanoclusters (Au NCs) that were functionalized with three different ligands and a cocapping ligand β-cyclodextrin (β-CD) has been constructed for the facile discrimination of three nitrophenol isomers via the linear discriminant analysis of isomer-induced fluorescence quenching patterns. The fluorescence quenching occurs in two steps: first, β-CDs adsorb nitrophenol isomers onto the surface of Au NCs via a host-guest interaction; second, each nitrophenol isomer quenches the fluorescence of a specific type of Au NCs through diverse inner filter effect. The different binding affinities between β-CD and each nitrophenol isomer, as well as the distinct quenching efficiencies of the isomers on the fluorescence of each Au NCs, enable an excellent discrimination of the three isomers at a concentration of 5 μM, when linear discriminant and hierarchical cluster analyses were smartly combined. In addition, even a mixture of two isomers could be distinguished with the proposed sensor array. The practicability of this developed sensor array is validated by a high accuracy (98.0%) examination of 51 unknown samples containing a single isomer or a mixture of two isomers.

Synthesis and Analysis of Substituted Bullvalenes

Herein we detail a practical synthesis of bullvalene and a variety of mono- and disubstituted analogues through cobalt-catalysed [6+2] cycloaddition of cyclooctatetraene to alkynes, followed by photochemical di-π-methane rearrangement. The application of isomer-network analysis, coupled with quantum-chemical calculations, provides a powerful automated tool for predicting the properties of bullvalene isomer networks.

Computational Chemistry: The Fate of Current Methods and Future Challenges

"Where do we go from here?" is the underlying question regarding the future (perhaps foreseeable) developments in computational chemistry. Although this young discipline has already permeated practically all of chemistry, it is likely to become even more powerful with the rapid development of computational hard- and software.