Threaded Rings that Swim in Excitable Media

Cardiac tissue and the Belousov-Zhabotinsky reaction provide two notable examples of excitable media that support scroll waves, in which a filament core is the source of spiral waves of excitation. Here we consider a novel topological configuration in which a closed filament loop, known as a scroll ring, is threaded by a pair of counterrotating filaments that are perpendicular to the plane of the ring and end on the boundary of a thin medium. We simulate the dynamics of this threaded ring (thring) in the photosensitive Belousov-Zhabotinsky excitable medium, using the modified Oregonator reaction-diffusion equations. These computations reveal that the threading topology induces an exotic motion in which the thring swims in the plane of the ring. We propose a light templating protocol to create a thring in the photosensitive Belousov-Zhabotinsky medium and provide experimental confirmation that this protocol indeed yields a thrin

Structural and thermodynamic analysis of a three-component assembly forming <i>ortho</i>-iminophenylboronate esters

Structural studies of a three-component assembly - a host and two distinct guests - were carried out using a combination of 11B and 1H NMR. In aprotic solvent, the imino group that forms ortho to the boronic acid or boronate ester group can form a dative N-B bond. In protic solvent, a molecule of solvent inserts between the nitrogen and boron atoms, partially ionizing the solvent molecule. Additionally, 11B NMR was used in combination with a seventh-order polynomial to calculate five binding constants for each of the individual steps in protic solvent. Comparison of these binding constants was used to establish positive cooperativity in the binding of the two guests.</p

The mechanisms of boronate ester formation and fluorescent turn-on in ortho-aminomethylphenylboronic acids

ortho-Aminomethylphenylboronic acids are used in receptors for carbohydrates and various other compounds containing vicinal diols. The presence of the o-aminomethyl group enhances the affinity towards diols at neutral pH, and the manner in which this group plays this role has been a topic of debate. Further, the aminomethyl group is believed to be involved in the turn-on of the emission properties of appended fluorophores upon diol binding. In this treatise, a uniform picture emerges for the role of this group: it primarily acts as an electron-withdrawing group that lowers the pK(a) of the neighbouring boronic acid thereby facilitating diol binding at neutral pH. The amine appears to play no role in the modulation of the fluorescence of appended fluorophores in the protic-solvent-inserted form of the boronic acid/boronate ester. Instead, fluorescence turn-on can be consistently tied to vibrational-coupled excited-state relaxation (a loose-bolt effect). Overall, this Review unifies and discusses the existing data as of 2019 whilst also highlighting why o-aminomethyl groups are so widely used, and the role they play in carbohydrate sensing using phenylboronic acids

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

The Bull–James assembly as a chiral auxiliary and shift reagent in kinetic resolution of alkyne amines by the CuAAC reaction

The Bull-James boronic acid assembly is used simultaneously as a chiral auxilary for kinetic resolution and as a chiral shift reagent for in situ enantiomeric excess (ee) determination by (1)H NMR spectroscopy. Chiral terminal alkyne-containing amines, and their corresponding chiral triazoles formed via CuAAC, were probed in situ. Selectivity factors of up to s = 4 were imparted and measured, accurate to within ±3% when compared to chiral GC

Modeling Boronic Acid Based Flourescent Saccharide Sensors: Computational Investigation of d-Fructose Binding to Dimethylaminomethylphenylboronic Acid (DMPBA)

Designing organic saccharide sensors for use in aqueous solution is a non-trivial endeavor. Incorporation of hydrogen bonding groups on a sensor’s receptor unit to target saccharides is an obvious strategy, but not one that is likely to ensure analyte-receptor interactions over analyte-solvent or receptor-solvent interactions. Phenylboronic acids are known to reversibly and covalently bind saccharides (diols in general) with highly selective affinity in aqueous solution. Therefore, recent work has sought to design such sensors and understand their mechanism for allowing fluorescence with bound saccharides. In past work, binding orientations of several saccharides were determined to dimethylaminomethylphenylboronic acid (DMPBA) receptors with an anthracene fluorophore, however the binding orientation of D-fructose to such a sensor could not be determined. In this work, we investigate the potential binding modes by generating 20 possible bidentate and six possible tridentate modes between fructose and DMPBA, a simplified receptor model. Gas phase and implicit solvent geometry optimizations, with a myriad functional/basis set pairs, were carried out to identify the lowest energy bidentate and tridentate binding modes of D-fructose to DMPBA. An interesting hydrogen transfer was observed during selected bidentate gas phase optimizations, this transfer suggests a strong sharing of the hydrogen atom between the boronate hydroxyl and amine nitrogen

Disaggregation is a Mechanism for Emission Turn-On of <i>ortho</i>-Aminomethylphenylboronic Acid-Based Saccharide Sensors

<i>ortho</i>-Aminomethylphenylboronic acid-based receptors with appended fluorophores are commonly used as molecular sensors for saccharides in aqueous media. The mechanism for fluorescence modulation in these sensors has been attributed to some form of photoinduced electron transfer (PET) quenching, which is diminished in the presence of saccharides. Using a well-known boronic acid-based saccharide sensor (<b>3</b>), this work reveals a new mechanism for fluorescence turn-on in these types of sensors. Compound <b>3</b> exhibits an excimer, and the associated ground-state aggregation is responsible for fluorescence modulation under certain conditions. When fructose was titrated into a solution of <b>3</b> in 2:1 water/methanol with NaCl, the fluorescence intensity increased. Yet, when the same titration was repeated in pure methanol, a solvent in which the sensor does not aggregate, no fluorescence response to fructose was observed. This reveals that the fluorescence increase is not fully associated with fructose binding, but instead disaggregation of the sensor in the presence of fructose. Further, an analogue of the sensor that does not contain a boronic acid (<b>4</b>) responded nearly identically to <b>3</b> in the presence of fructose, despite having no functional group with which to bind the saccharide. This further supports the claim that fluorescence modulation is not primarily a result of binding, but of disaggregation. Using an indicator displacement assay and isothermal titration calorimetry, it was confirmed that fructose does indeed bind to the sensor. Thus, our evidence reveals that while binding occurs with fructose in the aqueous solvent system used, it is not related to the majority of the fluorescence modulation. Instead, disaggregation dominates the signal turn-on, and is thus a mechanism that should be investigated in other <i>ortho</i>-aminomethylphenylboronic acid-based sensors

Rapid Determination of Enantiomeric Excess via NMR Spectroscopy: A Research-Informed Experiment

An undergraduate chemistry experiment that draws from primary research is described. The experiment exploits chiral supramolecular assemblies for the determination of enantiomeric excess by 1H NMR spectroscopy. This report describes the delivery of the experiment to a cohort of students, and as a result of feedback from those involved, an optimized protocol is presented. Particular care has been taken to facilitate ready adoption in other institutions by providing comprehensive teaching support materials as well as technical guidance for supporting the experiment