Unique Hydrogen Bonds between 9-Anthracenyl Hydrogen and Anions

Anion Recognition by Benzoxaborole

The binding types (H-bonding or coordinate) and stability constants for complexes of 11 mono- and di-anions with benzoxaborole (1) were determined by ¹H and ¹¹B NMR titrations in DMSO or MeCN. Compared to phenylboronic acid (PBA), 1 is a stronger Lewis acid and a poorer H-bond donor with only one B-OH group, which is expected therefore to recognize anions mostly through the coordinate bonding. This is the case however only with F^-, HPO₄^2-, and PhPO₃^2- anions, which are coordinately bonded to 1, and partially with SO₄^2-, which forms only the H-bonded complex with PBA, but both H-bonded and coordinate complexes with 1. The majority of tested anions (AcO^-, PhPO₃H^-, (PhO)₂PO₂^-, Cl^-, and Br^-) form H-bonded complexes with both 1 and PBA, whereas H₂PO₄^- changes the binding mode from coordinate for PBA to H-bonded for 1. The preferable binding type for each anion is confirmed by calculations of DFT-optimized structures of the anion complexes of 1. The preferable binding type can be rationalized considering the effects of the steric hindrance, more significant for the coordinate bonding, and of increased anion basicity, which is favorable for both binding types, but enhances the strength of coordinate bonding more significantly than the strength of H-bonding.

Allosteric binding properties of a 1,3-alternate thiacalix[4]arene-based receptor having phenylthiourea and 2-pyridylmethyl moieties on opposite faces

Thiacalix[4]arene receptors with two thiourea moieties and two 2-pyridyl moieties exhibited a heteroditopic dinuclear receptor with F− and Ag+ ions by a positive allosteric effect.

Fluoride anion sensing mechanism of a BODIPY-linked hydrogen-bonding probe

The sensing mechanism of a fluoride-anion probe BODIPY-amidothiourea (1c) has been elucidated through the density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations. The theoretical study indicates that in the DMSO/water mixtures the fluorescent sensing has been regulated by the fluoride complex that formed between the probe 1c/two water molecules and the fluoride anion, and the excited-state intermolecular hydrogen bond (H-B) plays an important role in the fluoride sensing mechanism. In the first excited state, the H-Bs of the fluoride complex 1cFH₂ are overall strengthened, which induces the weak fluorescence emission. In addition, molecular orbital analysis demonstrates that 1cFH₂ has more obvious intramolecular charge transfer (ICT) character in the S₁ state than 1cH₂ formed between the probe 1c and two water molecules, which also gives reason to the weaker fluorescence intensity of 1cFH₂ . Further, our calculated UV-vis absorbance and fluorescence spectra are in accordance with the experimental measurements. © 2018 Wiley Periodicals, Inc.

Anthracene Bisureas as Powerful and Accessible Anion Carriers

Synthetic anion carriers (anionophores) have potential as biomedical research tools and as treatments for conditions arising from defective natural transport systems (notably cystic fibrosis). Highly active anionophores that are readily accessible and easily deliverable are especially valuable. Previous work has resulted in steroid and trans-decalin based anionophores with exceptional activity for chloride/nitrate exchange in vesicles, but poor accessibility and deliverability. This work shows that anthracene 1,8-bisureas can fulfil all three criteria. In particular, a bis-nitrophenyl derivative is prepared in two steps from commercial starting materials, yet shows comparable transport activity to the best currently known. Moreover, unlike earlier highly active systems, it does not need to be preincorporated in test vesicles but can be introduced subsequent to vesicle formation. This transporter also shows the ability to transfer between vesicles, and is therefore uniquely effective for anion transport at low transporter loadings. The results suggest that anthracene bisureas are promising candidates for application in biological research and medicine.

Colorimetric anion sensors based on positional effect of nitro group for recognition of biologically relevant anions in organic and aqueous medium, insight real-life application and DFT studies

A new six colorimetric receptors A1-A6 were designed and synthesized, characterized by typical common spectroscopic techniques like FT-IR, UV-Visible, ¹H NMR, ¹³C NMR and ESI-MS. The receptor A1 and A2 exhibit a significant naked-eye response towards F^- and AcO^- ions in DMSO. Due to presences of the NO₂ group at para and ortho position with extended π-conjugation of naphthyl group carrying OH as a binding site. Compared to receptor A2, A1 is extremely capable of detecting F^- and AcO^- ions present in the form of sodium salts in an aqueous medium. This is owed to the occurrence of NO₂ group at para position induced in increasing the acidity of OH proton. Consequently, it easily gets deprotonated in aqueous media. The detection limit of receptor A1 was turned out to be 0.40 and 0.35ppm for F^- and AcO^- ions which is beneath WHO permission level (1.0ppm). Receptor A1 shows a solitary property of solvatochromism in different aprotic solvents in presence of AcO^- ion. Receptor A1 depicts high selectivity towards AcO^- ion in DMSO: HEPES buffer (9:1, v/v). Receptor A1 proved itself for real life application by detecting anion in solution and solid state. The binding mechanism of receptor A1 with AcO^- and F^- ions was monitored from ¹HNMR titration and DFT study.

β-Carboline–imidazopyridine hybrids: selective and sensitive optical sensors for copper and fluoride ions

Two rationally designed β-carboline–imidazopyridine hybrid chromofluorescent sensors S1 and S2 have been successfully synthesized and evaluated for the selective sensing of metal ions and anions.

Excited-state intermolecular proton transfer dependent on the substitution pattern of anthracene–diurea compounds involved in fluorescent ON1–OFF–ON2 response by the addition of acetate ions

Anthracene–diurea compounds exhibit different excited-state intermolecular proton transfer (ESIPT) reactions depending on the pattern of the substituents.

Fluorescent asymmetric bis-ureas for pyrophosphate recognition in pure water

Three fluorescent asymmetric bis-urea receptors (L1-L3) have been synthesised. The binding properties of L1-L3 towards different anions (fluoride, acetate, hydrogencarbonate, dihydrogen phosphate, and hydrogen pyrophosphate HPpi(3-)) have been studied by means of (1)H-NMR, UV-Vis and fluorescence spectroscopy, single crystal X-ray diffraction, and theoretical calculations. In particular, a remarkable affinity for HPpi(3-) has been observed in the case L1 (DMSO-d6/0.5% H2O) which also acts as a fluorimetric chemosensor for this anion. Interestingly, when L1 is included in cetyltrimethylammonium (CTAB) micelles, hydrogen pyrophosphate recognition can also be achieved in pure water.

The maiden report of a fluorescent-colorimetric sensor for expeditious detection of bifluoride ion in aqueous media

A fluorescent-colorimetric chemosensor L, for rapid detection of bifluoride ion has been developed based on a simple bis-Schiff base.

Curcumin based chemosensor for selective detection of fluoride and cyanide anions in aqueous media

The conjugate N,N-dimethyl curcumin analogue fluorophore dye 1 has been synthesized and its performance as a sensor was demonstrated.

Highly selective fluorescence sensors for the fluoride anion based on carboxylate-bridged diiron complexes

The diiron–sulfur clusters bearing urea and anthracene units showed rapid and selective recognition for the fluoride ion.

Anion recognition by oligo-(thio)urea-based receptors

Recent progress in the construction of metal-coordination-assisted and covalently connected oligourea receptors and their anion coordination chemistry is presented.

Coumarin functionalized thiocarbonohydrazones as a new class of chromofluorescent receptors for selective detection of fluoride ion

Thiocarbonohydrazone receptors selectively recognize fluoride ionsviaH-bond interactions and subsequent deprotonation to elicit a distinct visual and fluorescence colour change.

Fluoride responsive single nanochannel: click fabrication and highly selective sensing in aqueous solution

A F^– responsive nanochannel based on hydrogen-bonding interactions was designed to accomplish highly selective sensing in aqueous solution.

Fluoride is important to explore because it plays important roles in nature and biological processes. To accomplish selective F^– sensing in aqueous solution, a nanochannel modified with 1,3-dipropargylaza-p-tert-butyl calix[4]crown (C4CE) was designed on the basis of hydrogen-bonding interactions. The nanodevice not only exhibits high selectivity for F^–, even in serum, but also shows the useful property of recyclability.

Chiral recognition of carboxylates by a static library of thiourea receptors with amino acid arms

Chiral recognition is based on a large network of very subtle interactions whose outcome is difficult to predict. A combinatorial approach is therefore the most suitable to search for the most efficient receptor and obtain a structure-enantioselectivity correlation. We synthesized a set of 12 receptors constructed with 1,9-diaminoantracene and α-amino acid esters, linked via thiourea groups. The association constants and enantioselectivities for the complexes with mandelate and N-acetylphenylalanine were determined by competitive NMR titrations. Association constants quite regularly depend on the substituents in the receptor structure, but the distribution of enantioselectivities across the library could not easily be rationalized.

Novel indole based dual responsive "turn-on" chemosensor for fluoride ion detection

An efficient new dual channel chemosensor 2,3-bis((E)-(1H-indole-3-yl)methyleneamino)maleonitrile (DN) which exhibits selective sensing of F(-) ions in DMSO, was synthesized by a facile one step condensation reaction of indole-3-carboxaldehyde with diaminomaleonitrile. The probe DN was characterized by elemental analysis, (1)H, (13)C-NMR, ESI-MS and IR spectral techniques. Upon addition of F(-), DN induces remarkable changes in both absorption and fluorescence spectra on the basis of charge transfer mechanism. The receptor DN serves for highly selective, sensitive detection of F(-) without the interference of other relevant anions. The Job's plot analysis indicates the binding stoichiometry to be 1:1 (host/guest).

A single probe for sensing both acetate and aluminum(iii): visible region detection, red fluorescence and human breast cancer cell imaging

A single probe (L) can recognise both AcO⁻ and Al³⁺ as prepared by coupling 2-hydroxy-1-naphthaldehyde with hydrazine. The probe allows both colorimetric and fluorescence detection of both the ions.

Positive and negative allosteric effects of thiacalix[4]arene-based receptors having urea and crown-ether moieties

Allosteric binding behaviors of heteroditopic receptors bearing the 1,3-alternate conformation based thiacalix[4]arene have been evaluated by absorption and ¹H NMR titration experiments.

An overlooked yet ubiquitous fluoride congenitor: binding bifluoride in triazolophanes using computer-aided design

Despite its ubiquity during the binding and sensing of fluoride, the role of bifluoride (HF2(-)) and its binding properties are almost always overlooked. Here, we give one of the first examinations of bifluoride recognition in which we use computer-aided design to modify the cavity shape of triazolophanes to better match with HF2(-). Computational investigation indicates that HF2(-) and Cl(-) should have similar binding affinities to the parent triazolophane in the gas phase. Evaluation of the binding geometries revealed a preference for binding of the linear HF2(-) along the north-south axis with a smaller Boltzmann weighted population aligned east-west and all states being accessed rapidly through in-plane precessional rotations of the anion. While the (1)H NMR spectroscopy studies are consistent with the calculated structural aspects, binding affinities in solution were determined to be significantly smaller for the bifluoride than the chloride. Computed geometries suggested that a 20° tilting of the bifluoride (stemming from the cavity size) could account for the 25-fold difference between the two binding affinities, HF2(-) < Cl(-). Structural variations to the triazolophane's geometry and electronic modifications to the network of hydrogen bond donors were subsequently screened in a stepwise manner using density functional theory calculations to yield a final design that eliminates the tilting. Correspondingly, the bifluoride's binding affinity (K ∼ 10(6) M(-1)) increased and was also found to remain equal to chloride in the gas and solution phases. The new oblate cavity appeared to hold the HF2(-) in a single east-west arrangement. Our findings demonstrate the promising ability of computer-aided design to fine-tune the structural and electronic match in anion receptors as a means to control the arrangement and binding strength of a desired guest.

A study of allosteric binding behaviour of a 1,3-alternate thiacalix[4]arene-based receptor using fluorescence signal

The allosteric binding behaviour of a receptor L bearing a 1,3-alternate conformation based thiacalix[4]arene has been evaluated by fluorescence and ¹H NMR titration experiments.