An Acylhydrazone-Based Fluorescent Sensor for Sequential Recognition of Al3+ and H2PO4−

A novel acylhydrazone-based fluorescent sensor NATB was designed and synthesized for consecutive sensing of Al3+ and H2PO4−. NATB displayed fluorometric sensing to Al3+ and could sequentially detect H2PO4− by fluorescence quenching. The limits of detection for Al3+ and H2PO4− were determined to be 0.83 and 1.7 μM, respectively. The binding ratios of NATB to Al3+ and NATB-Al3+ to H2PO4− were found to be 1:1. The sequential recognition of Al3+ and H2PO4− by NATB could be repeated consecutively. In addition, the practicality of NATB was confirmed with the application of test strips. The sensing mechanisms of Al3+ and H2PO4− by NATB were investigated through fluorescence and UV–Visible spectroscopy, Job plot, ESI-MS, 1H NMR titration, and DFT calculations.

Azide Decomposition as a Pathway to Intramolecularly Upper Rim-Bridged Calix[4]arenes

Proximally single-atom bridged calix[4]arenes possess a rigidified cavity and, thus, unusual complexation properties. Here, we report on the synthesis of the first such heteroatom-bridged compound: amine-bridged calix[4]arene. This compound, prepared by thermal decomposition of 4-azidocalix[4]arene, was obtained alongside very interesting rearranged inherently chiral 10H-azepino[1,2-a]indole derivatives. NMR titration confirmed the suitability of amine cavity for the complexation of methylamonnium cations; moreover, the -NH- bridge function enables its further derivatization.

An Indole-Based Fluorescent Chemosensor for Detecting Zn2+ in Aqueous Media and Zebrafish

An indole-based fluorescent chemosensor IH-Sal was synthesized to detect Zn2+. IH-Sal displayed a marked fluorescence increment with Zn2+. The detection limit (0.41 μM) of IH-Sal for Zn2+ was greatly below that suggested by the World Health Organization. IH-Sal can quantify Zn2+ in real water samples. More significantly, IH-Sal could determine and depict the presence of Zn2+ in zebrafish. The detecting mechanism of IH-Sal toward Zn2+ was illustrated by fluorescence and UV–visible spectroscopy, DFT calculations, 1H NMR titration and ESI mass.

Solvent Controlled Colorimetric And Fluorometric Detection of Fe2+ and Cu2+ Ions By Naphthaldimine-Glucofuranose Conjugate

The sensing properties of naphthaldimine-glucofuranose conjugates 1 and 2 towards metal ions were investigated by 1H NMR titration, FTIR, absorbance, and fluorescence spectroscopic methods. The absorbance and fluorescence studies indicated that compound 1 formed coordination with Fe2+ and Cu2+ ions in DMSO through color changes yellow to brown and colorless, respectively. The Job's plots using absorbance data showed metal-ligand binding ratio is 1:1 for both cases. The formation of 1-Fe2+ and 1-Cu2+ complexes have been analyzed by absorption and emission spectroscopy, high-resolution mass spectrometry (HRMS) data, FTIR, 1H NMR titration experiment, and DFT calculations. The detection limits of naphthaldimine sugar conjugate 1 towards Fe2+/Cu2+ were calculated from UV-vis and fluorescence data according to the standard method. The sugar-naphthaldimine conjugate 2 has been used to establish the binding mode of 1 with Fe2+ or Cu2+ ions in DMSO.

A CH-Controlled Colorimetric Probe Based on Anthracene Carboximide for the Near-Infrared Detection of Cyanide

A novel CH-controlled colorimetric probe based on anthracene carboximide was developed for the near-infrared detection of cyanide. The probe was constructed by attachment of a CHCN binding site to anthracene carboximide fluorophore, and it showed a significant visual change from yellow-green (535 nm) to deep violet (825 nm) with a larger redshift (≈290 nm) when interacting with cyanide. The C-H deprotonation sensing mechanism was confirmed by 1H NMR titration. Additionally, colorimetric test paper was conveniently used to detect cyanide in aqueous solutions. The near-infrared detection of cyanide by CH-controlled probes was founded for the first time.

Mapping of the fibrinogen-binding site on the staphylocoagulase C-terminal repeat region

The N-terminus of S. aureus staphylocoagulase (SC) triggers activation of host prothrombin (ProT), and the SCProT* complex cleaves host fibrinogen (Fbg) to form fibrin (Fbn) deposits, a hallmark of SC-positive endocarditis. The C-terminal domain of the prototypical Newman D2 Tager 104 SC contains 1 pseudo-repeat (PR) and 7 repeats (R1R7) that bind Fbg/Fbn Fragment D (Frag D). This work defines affinities and stoichiometries of Frag D binding to single- and multi-repeat C-terminal constructs, using fluorescence equilibrium binding, NMR titration, Ala scanning, and native PAGE. Constructs containing PR and each single repeat bound Frag D with KD ~50 130 nM and a 1:1 stoichiometry, indicating a conserved binding site shared between PR and each repeat. NMR titration of PR-R7 with Frag D revealed that residues 22-49, bridging PR and R7, constituted the minimal peptide (MP) required for binding, corroborated by Ala scanning, and binding of labeled MP to Frag D. MP alignment with the PR-repeat and inter-repeat junctions identified conserved residues critical for binding. Labeled PR-(R1R7) bound Frag D with KD ~7 32 nM and stoichiometry of 1:5; and PR-R1R2R3, PR-R1R6R7, PR-R3R4R7, and PR-R3R6R7 competed with PR-(R1R7) for Frag D binding, with a 1:3 stoichiometry and KD ~7 42 nM. These findings are consistent with binding at the PR-R junctions with modest inter-repeat sequence variability. Circular dichroism of PR-R7 and PR-(R1R7) suggested a largely disordered structure and conformational flexibility, allowing binding of multiple fibrin(ogen) molecules. This property facilitates pathogen localization on host fibrin networks.

Synthesis and Coordination of a Neutral Phosphaguanidine and Comparison of its Basicity with a Guanidine

A phosphaguanidine [Me2NC(PPh2)=NiPr], the analogous guanidine [Me2NC(NPh2)=NiPr], and their hydrochloride (HCl) salts were prepared to study the influence of substituting a phosphorus atom for a nitrogen atom on the basicity of the two compounds and the bonding in their conjugate acids. The pKa values of both HCl salts were measured in acetonitrile by NMR titration. Surprisingly, the substitution of P for N has essentially no effect on basicity even though the geometry at that atom is changed. The presence of phenyl substituents in the protonated guanidine reduces the resonance in the CN3 core; while poor orbital overlap between P and C reduces the resonance in the N2CP core of the protonated phosphaguanidine. The neutral phosphaguanidine binds to a Cu(I) halide through both the Nimine and the P, which suggested that the basic N atom on the bound ligand may have little utility as a Brønsted base. Fortunately, however, a Cu(I) halide complex of the protonated phosphaguanidine is stable. Thus, the tendency of the basic N to bind to metals does not proscribe it serving as a metal-proximate Brønsted base.

Rigorous analysis of the interaction between proteins and low water-solubility drugs by qNMR-aided NMR titration experiments

Drugs are designed and validated based on physicochemical data on their interactions with target proteins. For low water- solubility drugs, however, quantitative analysis is practically impossible without accurate estimation of...

Enantioselective Michael Addition to Vinyl Phosphonates via Hydrogen Bond-Enhanced Halogen Bond Catalysis

An asymmetric Michael addition of malononitrile to vinyl phosphonates was accomplished by hydrogen bond-enhanced bifunctional halogen bond (XB) catalysis. 1H NMR titration experiments were used to demonstrate that halogen bonding,...

Chiral anion recognition using calix[4]arene-based ureido receptors in a 1,3-alternate conformation

The introduction of chiral alkyl substituents into the lower rim of calix[4]arene immobilised in the 1,3-alternate conformation led to a system possessing a preorganised ureido cavity hemmed with chiral alkyl units in the near proximity. As shown by the 1H NMR titration experiments, these compounds can be used as receptors for chiral anions in DMSO-d 6. The chiral recognition ability can be further strengthened by the introduction of another chiral moiety directly onto the urea N atoms. The systems with double chiral units being located around the binding ureido cavity showed better stereodiscrimination, with the highest selectivity factor being 3.33 (K L/K D) achieved for N-acetyl-ʟ-phenylalaninate. The structures of some receptors were confirmed by single crystal X-ray analysis.