Investigation of the effects on proton relaxation times upon encapsulation in a water-soluble synthetic receptor.

Sequestration of small molecule guests in the cavity of a water-soluble deep cavitand host has a variety of effects on their NMR properties. The effects of encapsulation on the longitudinal (T1) and transverse (T2) relaxation times of the protons in variably sized guest molecules are analyzed here, using inversion recovery and spin-echo experiments. Sequestration of neutral organic species from the bulk solvent reduces the overall proton relaxation times, but the magnitude of this effect on different protons in the same molecule has a variety of contributors, from the motion of the guest when bound, to the position of the protons in the cavity and the magnetic anisotropy induced by the aromatic walls of the host. These subtle effects can have large consequences on the environment experienced by the bound guest, and this sheds light on the nature of small molecules in enclosed environments.

Using Flipped Classroom Modules to Facilitate Higher Order Learning in Undergraduate Organic Chemistry.

In an ongoing effort to incorporate active learning and promote higher order learning outcomes in undergraduate organic chemistry, a hybrid ("flipped") classroom structure has been used to facilitate a series of collaborative activities in the first two courses of the lower division organic chemistry sequence. An observational study of seven classes over a five-year period reveals there is a strong correlation between performance on the in-class activities and performance on the final exam across all classes; however, a significant number of students in these courses continue to struggle on both the in-class activities and final exam. The Activity Engagement Survey (AcES) was administered in the most recent course offering included in this study, and these preliminary data suggest that students who achieved lower scores on the in-class activities had lower levels of emotional and behavioral/cognitive engagement and were less likely to work in collaborative groups. In total, these findings suggest that if students can be guided to engage more successfully with the in-class activities, they are likely to be more successful in carrying out the higher order learning required on the final exam. In addition to the analyses of student performance and engagement in the in-class activities, the implementation of the flipped classroom structure and suggestions for how student engagement in higher order learning might be improved in future iterations of the class are described herein.

Selective recognition and discrimination of single isomeric changes in peptide strands with a host : guest sensing array.

An indirect competitive binding mechanism can be exploited to allow a combination of cationic fluorophores and water-soluble synthetic receptors to selectively recognize and discriminate peptide strands containing a single isomeric residue in the backbone. Peptide isomerization occurs in long-lived proteins and has been linked with diseases such as Alzheimer's, cataracts and cancer, so isomers are valuable yet underexplored targets for selective recognition. Planar cationic fluorophores can selectively bind hydrophobic, Trp-containing peptide strands in solution, and when paired with receptors that provide a competitive host for the fluorophore, can form a differential sensing array that enables selective discrimination of peptide isomers. Residue variations such as D- and L-Asp, D- and L-isoAsp, D-Ser and D-Glu can all be recognized, simply by their effects on the folded structure of the flexible peptide. Molecular dynamics simulations were applied to determine the most favorable conformation of the peptide : fluorophore conjugate, indicating that favorable π-stacking with internal tryptophan residues in a folded binding pocket enables micromolar binding affinity.

Selective Molecular Recognition and Indicator Displacement Sensing of Neurotransmitters in Cellular Environments.

Flexible, water-soluble hosts are capable of selective molecular recognition in cellular environments and can detect neurotransmitters such as choline in cells. Both cationic and anionic water-soluble self-folded deep cavitands can recognize suitable styrylpyridinium dyes in cellular interiors. The dyes selectively accumulate in nucleotide-rich regions of the cell nucleus and cytoplasm. The hosts bind the dyes and promote their relocation to the outer cell membrane: the lipophilic cavitands predominantly reside in membrane environments but are still capable of binding suitable targets in other cellular organelles. Incubating the cells with structurally similar biomarkers such as choline, cholamine, betaine, or butyrylcholine illustrates the selective recognition. Choline and butyrylcholine can be bound by the hosts, but minimal binding is seen with betaine or cholamine. Varying the dye allows control of the optical detection method, and both "turn-on" sensing and "turn-off" sensing are possible.

Selective anion sensing in high salt water via a remote indicator displacement assay.

Water-soluble deep cavitands with cationic functions at the lower rim can selectively bind iodide anions in purely aqueous solution. By pairing this lower rim recognition with an indicator dye that is bound in the host cavity, optical sensing of anions is possible. The selectivity for iodide is high enough that micromolar concentrations of iodide can be detected in the presence of molar chloride. Iodide binding at the "remote" lower rim causes a conformational change in the host, displacing the bound dye from the cavity and effecting a fluorescence response. The sensing is sensitive, selective, and works in complex environments, so will be important for optical anion detection in biorelevant media.

Sensing Base Modifications in Non-Canonically Folded DNA with an Optimized Host:Guest Sensing Array.

An arrayed host:guest fluorescence sensor system can discriminate DNA G-quadruplex structures that differ only in the presence of single oxidation or methylation modification in the guanine base. These small modifications make subtle changes to G4 folding that are often not detectable by CD but induce differential fluorescence responses in the array. The sensing is functional in diluted serum and is capable of distinguishing individual modifications in DNA mixtures, providing a powerful method of detecting folding changes caused by DNA damage.

Enantioselective sensing of insect pheromones in water.

An arrayed combination of water-soluble deep cavitands and cationic dyes has been shown to optically sense insect pheromones at micromolar concentration in water. Machine learning approaches were used to optimize the most effective array components, which allows differentiation between small structural differences in targets, including between different diastereomers, even though the pheromones have no innate chromophore. When combined with chiral additives, enantiodiscrimination is possible, dependent on the size and shape of the pheromone.

Machine Learning Aids Classification and Discrimination of Noncanonical DNA Folding Motifs by an Arrayed Host:Guest Sensing System.

An arrayed host:guest fluorescence sensor system can discriminate among and classify multiple different noncanonical DNA structures by exploiting selective molecular recognition. The sensor is highly selective and can discriminate between folds as similar as native G-quadruplexes and those with bulges or vacancies. The host and guest can form heteroternary complexes with DNA strands, with the host acting as mediator between the DNA and dye, modulating the emission. By applying machine learning algorithms to the sensing data, prediction of the folding state of unknown DNA strands is possible with high fidelity.

Selective discrimination and classification of G-quadruplex structures with a host-guest sensing array.

The secondary structures of nucleic acids have an important influence on their cellular functions but can be difficult to identify and classify quickly. Here, we show that an arrayed suite of synthetic hosts and dyes is capable of fluorescence detection of oligonucleotide secondary structures. Multivariate analysis of different fluorescence enhancements-generated using cationic dyes that show affinity for both DNA G-quadruplexes and the synthetic hosts-enables discrimination between G-quadruplex structures of identical length and highly similar topological types. Different G-quadruplexes that display the same folding topology can also be easily differentiated by the number of G-quartets and sequence differences at the 3' or 5' ends. The array is capable of both differentiation and classification of the G-quadruplex structures at the same time. This simple non-invasive sensing method does not require the discovery and synthesis of specific G-quadruplex binding ligands, but employs a simple multicomponent approach to ensure wide applicability.

Selective sensing of THC and related metabolites in biofluids by host:guest arrays.

A water-soluble host molecule can bind tetrahydrocannabinol (Δ9-THC) and its metabolites in aqueous solution. By pairing this recognition event in a sensing array with fluorescent reporters and varying external mediators, pattern recognition-based detection is possible, which allows selective discrimination of the THC metabolites. The selective sensing can be performed in aqueous solution with micromolar sensitivity, as well as in biofluids such as urine and saliva. Metabolites as similar as Δ8- and Δ9-THC, differing only in the position of a double bond, can be distinguished.

Sensing of citrulline modifications in histone peptides by deep cavitand hosts.

Arrayed cavitand:fluorophore sensor complexes can selectively sense small citrulline modifications at arginine residues on post-translationally modified peptides. The sensor can differentiate between different numbers of citrulline modifications, and a simple two-fluorophore, 6-component array can effect cross-reactive discrimination between single modifications in aqueous solution.

Selective Array-Based Sensing of Anabolic Steroids in Aqueous Solution by Host-Guest Reporter Complexes.

Arrayed complexes of a water-soluble deep cavitand and two fluorescent indicators show selective sensing of anabolic-androgenic steroids in aqueous environments. By combining the host-guest complexes with small amounts of heavy metal ions, discrimination between steroids that vary in structure by only a single π bond is possible. The sensing occurs through a triggered aggregation mechanism, which can be mediated by both the presence of metal ions and the steroids. The use of both "turn-on" and "turn-off" fluorophores is essential for good discrimination. As low as 10 µm steroid can be detected, and the discrimination is selective in steroid samples spiked into human urine.