Programmed Enzyme-Mimic Hydrolysis of a Choline Carbonate by a Metal-Free 2-Aminobenzimidazole-Based Cavitand

Regiodivergent C-N Coupling of Quinazolinones Controlled by the Dipole Moments of Tautomers

Herein, we report that the dipole moments of tautomers can be the controlling factor for regiodivergent synthesis of either 14H-quinazolino[3,2-f]phenanthridin-14-ones or 6H-quinazolino[1,2-f]phenanthridin-6-ones, selectively, from unmasked 2-([1,1'-biphenyl]-2-yl)quinazolin-4(3H)-one. An intramolecular C(sp²)-NH coupling reaction mediated by PhI(OCOOCF₃)₂ could lead to two different regioisomers selectively at different temperatures when the dielectric constants of solvents like hexafluoroisopropanol and trifluoroacetic acid matched with the tautomer's dipole moments.

A Photochemical Intramolecular C-N Coupling Toward the Synthesis of Benzimidazole-Fused Phenanthridines

Herein, we report a direct photochemical dehydrogenative C-N coupling of unactivated C(sp²)-H and N(sp²)-H bonds. The catalysts or additive-free transformation of 2-([1,1'-biphenyl]-2-yl)-1H-benzo[d]imidazole to benzo[4,5]imidazo[1,2-f]phenanthridine was achieved at ∼350 nm of irradiation via ε-hydrogen abstraction. DFT calculations helped to understand that the N-H···π interaction was essential for the reaction to proceed at a lower energy than expected.

Selective Heavy Element Sensing with a Simple Host-Guest Fluorescent Array

A simple three component array of host-fluorophore complexes is capable of sensitive and selective discrimination of heavy metal ions, including lanthanide and actinide salts in aqueous solution. Instead of applying optical sensors that only use "single-mode" detection, i.e., coordination of the metal to a specific ligand and monitoring the change in emission of an appended fluorophore, we exploit a series of host-fluorophore complexes that are affected by the presence of small amounts of metal ions in aqueous solution in different ways. Variable host-metal and host-guest-metal interactions lead to both turn-on and turn-off fluorescence sensing mechanisms, enhancing the discriminatory properties of the array. The limit of detection for certain metals is as low as 70 nM, and highly similar metals such as lanthanides and actinides can be easily distinguished at low micromolar concentrations in complex salt mixtures.

Selective protein recognition in supported lipid bilayer arrays by tailored, dual-mode deep cavitand hosts

Self-folding deep cavitands with variably functionalized upper rims are able to selectively immobilize proteins at a biomimetic supported lipid bilayer surface. The immobilization process takes advantage of the dual-mode binding capabilities of the hosts, combining a defined binding pocket with upper rim charged/H-bonding groups. A variety of proteins can be selectively immobilized at the bilayer interface, either via complementary charge/H-bonding interactions, cavity-based molecular recognition, or a combination of both. The immobilization process can be used to bind unmodified native proteins, epitopes for bioadhesion, or proteins covalently modified with suitable RNMe3+ binding "handles" and charged groups that can either match or mismatch with the cavitand rim. The immobilization process can be monitored in real time using surface plasmon resonance (SPR) spectroscopy, and applied to the construction of cavitand:lipid arrays using the hosts and trehalose vitrified phospholipid vesicles. The selective, dual-mode protein recognition is maintained in the arrays, and can be visualized using SPR imaging.

Site selective reading of epigenetic markers by a dual-mode synthetic receptor array

Variably functionalized self-folding deep cavitands form an arrayed, fluorescent indicator displacement assay system for the detection of post-translationally modified (PTM) histone peptides. The hosts bind trimethyllysine (KMe3) groups, and use secondary upper rim interactions to provide more sensitive discrimination between targets with identical KMe3 binding handles. The sensor array uses multiple different recognition modes to distinguish between miniscule differences in target, such as identical lysine modifications at different sites of histone peptides. In addition, the sensor is affected by global changes in structure, so it is capable of discriminating between identical PTMs, at identical positions on amino acid fragments that vary only in peptide backbone length, and can be applied to detect non-methylation modifications such as acetylation and phosphorylations located multiple residues away from the targeted binding site. The synergistic application of multiple variables allows dual-mode deep cavitands to approach levels of recognition selectivity usually only seen with antibodies.

Preparative scale and convenient synthesis of a water-soluble, deep cavitand

Cavitands are established tools of supramolecular chemistry and molecular recognition, and they are finding increasing application in sensing and sequestration of physiologically relevant molecules in aqueous solution. The synthesis of a water-soluble, deep cavitand is described. The route comprises six (linear) steps from commercially available precursors, and it relies on the fourfold oligomeric cyclization reaction of resorcinol with 2,3-dihydrofuran that leads to the formation of a shallow resorcinarene framework; condensation with aromatic panels, which deepens the hydrophobic binding cavity; construction of rigid urea functionalities on the upper rim; and the introduction of the water-solubilizing methylimidazolium groups on the lower rim. Late intermediates of the synthesis can be used in the preparation of congener cavitands with different properties and applications, and a sample of such a synthetic procedure is included in this protocol. Emphasis is placed on scaled-up reactions and on purification procedures that afford materials in high yield and avoid chromatographic purification. This protocol provides improvements over previously described procedures, and it enables the preparation of sizable amounts of deep cavitands: 7 g of a water-soluble cavitand can be prepared from resorcinol in 13 working days.

Enhancing the Activity of Peptide-Based Artificial Hydrolase with Catalytic Ser/His/Asp Triad and Molecular Imprinting

In this study, an artificial hydrolase was developed by combining the catalytic Ser/His/Asp triad with N-fluorenylmethoxycarbonyl diphenylalanine (Fmoc-FF), followed by coassembly of the peptides into nanofibers (CoA-HSD). The peptide-based nanofibers provide an ideal supramolecular framework to support the functional groups. Compared with the self-assembled catalytic nanofibers (SA-H), which contain only the catalytic histidine residue, the highest activity of CoA-HSD occurs when histidine, serine, and aspartate residues are at a ratio of 40:1:1. This indicates that the well-ordered nanofiber structure and the synergistic effects of serine and aspartate residues contribute to the enhancement in activity. Additionally, for the first time, molecular imprinting was applied to further enhance the activity of the peptide-based artificial enzyme (CoA-HSD). p-NPA was used as the molecular template to arrange the catalytic Ser/His/Asp triad residues in the proper orientation. As a result, the activity of imprinted coassembled CoA-HSD nanofibers is 7.86 times greater than that of nonimprinted CoA-HSD and 13.48 times that of SA-H.

Synthesis and characterization of chiral aza-macrocycles and study of their enantiomer recognition ability for organo-phosphoric acid and phosphonic acid derivatives by 31P NMR and fluorescence spectroscopy

Two diastereomers of optically active N,O-containing new macrocycles with dual chirality were synthesized and evaluated for chiral discrimination of organo phosphoric and phosphonic acids by ³¹P NMR and fluorescence spectroscopy.

Engineering peptide-based biomimetic enzymes for enhanced catalysis

Herein, we reported a novel hydrolase model by integrating the supramolecular self-assembly of Fmoc-FFH and electrostatic complexation (with PEI) at an aqueous liquid–liquid interface for the synthesis of peptide–polymer hybrid capsules.

Protein-like proton exchange in a synthetic host cavity

The mechanism of proton exchange in a metal-ligand enzyme active site mimic (compound 1) is described through amide hydrogen-deuterium exchange kinetics. The type and ratio of cationic guest to host in solution affect the rate of isotope exchange, suggesting that the rate of exchange is driven by a host whose cavity is occupied by water. Rate constants for acid-, base-, and water-mediated proton exchange vary by orders of magnitude depending on the guest, and differ by up to 200 million-fold relative to an alanine polypeptide. These results suggest that the unusual microenvironment of the cavity of 1 can dramatically alter the reactivity of associated water by magnitudes comparable to that of enzymes.