UV-vis and fluorescence spectroscopic detection of anions by the conformational restriction of 2,2′-binaphthalene derivatives bearing thiourea groups through a methylene spacer

Novel fluorescence receptors, 2 and 3 based on 2,2′-binaphthalene possessing thiourea moieties via a methylene spacer have been synthesized. Hydrogen bonds of NH groups of thiourea moieties with acetate anion were confirmed by ¹H NMR study in MeCN-d₃. These receptors showed characteristic UV-vis spectral changes through isosbestic points on complexation with anions inspite of lacking conjugation between the chromophore and the binding sites in polar organic solvent such as acetonitrile. The UV-vis spectral changes arise from the conformational restriction of the 2,2′-binaphthyl skeleton on the complexation. The receptors exhibit high selectivities for AcO⁻ and F⁻. The fluorescence intensity of the receptors decreases with the increasing amount of the AcO⁻, however, addition of F⁻ induces a different change in its fluorescence spectrum, in which shorter emission of the receptors decreases with the increase in F⁻ concentration, while the longer emission of the receptors increases through an isoemissive point in MeCN. The results suggest that favorable dual-wavelength ratiometric fluorescence measurement can be conducted by the receptors for F⁻.     

Synthesis and anion recognition properties of 8,8′-dithioureido-2,2′-binaphthalene

A novel artificial receptor based on 2,2′-binaphthalene skeleton bearing two thiourea groups was prepared via nickel(II)-catalyzed homocoupling of the corresponding bromide. The receptor showed high binding ability for F⁻ and AcO⁻ in acetonitrile.     

Anthracene derivatives bearing two urea groups as fluorescent receptors for anions

For the recognition and sensing of anionic analytes, comparative studies were carried out on the anion bindings of pyrophosphate, H₂PO₄⁻, and dicarboxylates to the anthracene derivatives bearing two urea groups on the 1,8 and 9,10-positions as fluorescent chemosensors for anions. Their binding properties were compared using fluorescence and ¹H NMR, and the results were rationalized with an ab initio study.     

Synthesis and biological applications of some novel 8-Hydroxyquinoline urea and thiourea derivatives

A number of novel urea and thiourea derivatives of 8-hydroxyquinoline have been designed, synthesized and evaluated for their anticancer activities. The structures of the new compounds were established by spectroscopic techniques, ¹H NMR, ¹³C NMR, and mass spectrometry. The in vitro cytotoxicity against MCF7, and MDA-MB-231 cell lines were assessed by MTT assay. Six of the 11 compounds synthesized namely 5b, 5c, 5f, and 6b-d exhibited cytotoxicity with IC₅₀ values ranged between 0.5 and 42.4 µM. Apoptotic features of cells treated with 5b compound were observed via florescent microscopy using DAPI and ethidium bromide/acridine orange staining against MCF-7 cells. Molecular docking of these molecules against 16 potential breast cancer protein revealed that these compounds could interact with the active site of poly (ADP-ribose) polymerase-1 (PARP1), B-cell lymphoma-extra large (Bcl-xL) and PARP5A (Tankyrase 1) by forming hydrogen bonds, π-π interactions and hydrophobic interactions. The docked poses of these molecules were observed to be similar in the active site of each of these targets.     

Anion recognition by bisimidazolium and bisbenzimidazolium cholapods

Bile acid-based acyclic receptors bearing two imidazole and benzimidazole moieties have been synthesized. Anion binding studies using ¹H NMR revealed that imidazolium receptor exhibits high selectivity for chloride ion while benzimidazolium receptor showed selectivity for Y-shaped acetate ion through hydrogen bond interactions involving imidazolium C-2 and acetyl methylene hydrogens.     

Anion recognition by a disiloxane-1,3-diol in organic solvents

To explore the anion recognition ability of silanol derivatives, ESI-MS and ¹H NMR titrations of a 1,3-disiloxanediol 1 with anions were studied in CDCl₃ and MeCN-d₃. The results indicate that 1 showed strong binding to anions such as AcO⁻ and halides.     

Barium ion sensing by a 2,2′-binaphthalene derivative bearing two monoaza-15-crown-5 ethers

A novel fluoroionophore 1 based on 2,2′-binaphthalene bearing two monoaza-15-crown-5 ethers at 8- and 8′-positions was prepared. UV-vis and fluorescence responses of 1 upon the addition of alkali and alkaline earth metal cations were evaluated in 15% MeOH-MeCN. Receptor 1 showed unique response for Ba²⁺ due to the formation of an intramolecular sandwich complex.     

Recognition of carboxylate and dicarboxylates by azophenol–thiourea derivatives: a theoretical host–guest investigation

Geometries of azophenol–thiourea derivative complexes with acetate, oxalate, malonate, succinate, glutarate, adipate, pimelate, suberate and azelate were carried out using the integrated MO:MO method. The binding and complexation energies of these complexes were derived from the ONIOM(B3LYP/6-31G(d):AM1) calculations. The relative stabilities of the complexes of azophenol–thiourea derivatives with carboxylate guests are reported. The binding interactions of the azophenol–thiourea receptor 1, 2 and carboxylate guests are described as multipoints hydrogen bonding, where the amine and phenolic hydrogen atoms of receptors act as hydrogen bond donors in complex with acetate and all amine-hydrogen and phenolic hydrogen atoms act as hydrogen bond donors in complex with dicarboxylate guests. Thermodynamic properties of binding interactions between receptors 1, 2 and their preorganizations and complexations are also reported.     

Anion recognition by 1,3-disiloxane-1,1,3,3-tetraols in organic solvents

Anion recognition by 1,3-disiloxane-1,1,3,3-tetraols has been elucidated by ¹H NMR titrations and ESI-MS in organic solvents. The association constants of the receptors for halide anions are larger than those of silanediol and 1,3-disiloxane-1,3-diol due to the cooperative hydrogen bonds by four silanol hydroxy groups of 1,3-disiloxane-1,1,3,3-tetraols.     

Unprecedented four-way-output molecular response system based on biphenyl-2,2′-diyldiacridiniums: induction of axial chirality through intramolecular hydrogen bonds between chiral amide groups

Upon the attachment of N-(R)-2-phenylethylamide moieties to the acridinium units of the title dication, intramolecular hydrogen bonds induce a diastereomeric preference in terms of axial chirality (70% de at −40 °C in CH₂Cl₂). Thus, external stimuli induce not only UV-vis and fluorescence spectra changes but also changes in the CD and fluorescence-detected CD (FDCD) spectra, realizing unprecedented four-way-output molecular response systems.     

Synthesis and anti-inflammatory and antimicrobial activities of some novel 2-methylquinazolin-4(3H)-one derivatives bearing urea,thiourea and sulphonamide functionalities

A variety of novel 2-methylquinazolin-4(3H)-one derivatives (1–29) bearing urea, thiourea and sulphonamide functionalities at position 3 of biological interest have been synthesized and screened for their anti-inflammatory (TNF-α and IL-6) and antimicrobial activities (antibacterial and antifungal). “Biological evaluation study revealed that the compounds 3, 4, 6, 9, 16 and 18 were found to have promising anti-inflammatory activity (up to 62–84% TNF-α and 73–92% IL-6 inhibitory activity) at concentration of 10 μM with reference to standard dexamethasone (75% TNF-α and 84% IL-6 inhibitory activities at 1 μM) and 7, 10, 12, 23, 25 and 28 have antimicrobial activity at MIC of 10–30 μg/mL against selected pathogenic bacteria and fungi.”     

Anion recognition by d-ribose-based receptors

Anion recognition properties of d-ribose-based receptors α- and β-1 were measured by ¹H NMR in CDCl₃ and MeCN-d₃. Receptor β-1 showed effective binding with anions by cooperative hydrogen bonds of cis-diol. The anomeric isomer α-1 is a less effective anion receptor which has similar cis-diol as a recognition site, indicating that the stereo configuration of the anomeric position is of significant influence on the anion recognition ability.     

Specific interactions in complexes formed by polythiophene derivatives bearing polar side groups and plasmid DNA

The interaction between plasmid DNA and polythiophene derivatives bearing substituents with polar groups has been examined using electrophoresis assays, and both UV-Vis and CD spectroscopies. Results clearly indicate that such conducting polymers form stable adducts with DNA, even although the interactions strongly depend on the chemical constitution of the polymers. Furthermore, digestion assays with EcoRI and BamHI evidence that the polymers form specific interactions with the DNA, protecting the target nucleotide sequences of these restriction enzymes. On the other hand, UV-Vis and CD spectra show that the interactions induce a fast and very significant exposition of the nitrogen bases, which is consequence of the structural alterations induced in the circular DNA. These results have been compared with those previously reported for polypyrrole, poly(3,4-ethylenedioxythiophene) and poly(3-methylthiophene). Finally, a model based on the intercalation of the conducting polymer between the two DNA strands has been proposed.     

Hydrogen bonded NHO chains formed by chloranilic acid (CLA) with 4,4′-di-t-butyl-2,2′-bipyridyl (dtBBP) in the solid state

In crystalline state 2,5-dichloro-3,6-dihydroxy-p-benzoquinone (chloranilic acid, CLA) forms with 4,4′-di-t-butyl-2,2′-bipyridyl (dtBBP) the hydrogen bonded chains along the b-axis. From one side of the CLA molecule the proton transfer takes place and the hydrogen bond length is very short (2.615 Å). A continuous infrared absorption is observed for dtBBP·CLA in the wavenumber range between 3100 and 800 cm⁻¹ also indicating the strong hydrogen bonds. The DSC measurements show a weak, close to continuous, phase transition at 414 K. The complex dielectric permittivity for a single crystal sample was measured in the temperature range 100-440 K and at frequencies between 200 Hz and 2 MHz. The dielectric response is a combination of semiconducting properties and a relaxation process most probably connected with the proton dynamics in the hydrogen bonds. The mechanism of the structural phase transition is discussed.     

Anion recognition and sensing in organic and aqueous media using luminescent and colorimetric sensors

This review article focuses primarily on the work carried in our laboratories over the last few years using luminescent and colorimetric sensors, where the anion recognition occurs through hydrogen bonding in organic or aqueous solvents. This review begins with the story of the discovery of fluorescent photoinduced electron transfer (PET) sensors for anions using charged neutral urea or thiourea receptors where both fluorescent and NMR spectroscopic methods monitored anion recognition. This work led to the development of dual luminescent and colorimetric anion sensors based on the use of the ICT based naphthalimide chromophore, where ions such as fluoride gave rise to changes in both the fluorescence and the absorption spectra of the sensors, but at different concentrations. Here, the former changes were due to hydrogen bonding interactions, whereas the latter was due to the deprotonation of acidic protons, giving rise to the formation of the bifluoride anion (HF₂⁻). Modification of the 4-amino-l,8-naphthalimide moiety has facilitated the formation of colorimetric anion sensors that work both in organic or aqueous solutions. Such charge neutral receptor motifs have also been incorporated into organic scaffolds with norbomyl and calixarene backbones, which have enabled us to produce anion directed self-assembled structures.     

Synthesis and characterization of polybinaphthalene incorporating chiral (R) or (S)-1,1′-binaphthalene and oxadiazole units by Heck reaction

Chiral conjugated polymers P-1 and P-2 were synthesized by the polymerization of (R)-3,3′-diiodo-2,2′-bisbutoxy-1,1′-binaphthalene ((R)-M-1) and (S)-3,3′-diiodo-2,2′-bisbutoxy-1,1′-binaphthalene ((S)-M-1) with 2,5-bis(4-vinylphenyl)-1,3,4-oxadiazole (M-2) under Pd-catalyzed Heck coupling reaction, respectively. Both monomers and polymers were analysed by NMR, MS, FT-IR, UV, DSC-TG, fluorescent spectroscopy, GPC and CD spectra. The chiral conjugated polymers exhibit strong Cotton effect in their circular dichroism (CD) spectra indicating a high rigidity of polymer backbone. CD spectra of polymers P-1 and P-2 are almost identical and have opposite signs for their position. These polymers have strong blue fluorescence.     

Fluorescence properties of (R)- and (S)-[1,1′-binaphthalene]-2,2′-diols solutions and their complexes with cyclodextrins in aqueous medium

Steady-state and time-resolved fluorescence techniques were used to study (R)- and (S)-[1,1′-binaphthalene]-2,2′-diol (1,1′-binaphthol or BINOL) dilute solutions of different polarity solvents, as well as their inclusion complexes with α- and βcyclodextrins (CDs) in water. BINOLs in dilute water solutions exhibited a surprisingly high fluorescence anisotropy that was explained as being due to the formation of fairly large order π–π stacking aggregates in aqueous polar media. Stoichiometries, formation constants and the changes of enthalpy and entropy upon inclusion were also obtained by measuring the variation of the fluorescence intensity with [CD] and temperature. Results agree with the formation of 1:1 stoichiometry complexes, but the association constants are rather low and very similar for both enantiomers. Molecular mechanic calculations in the presence of water were employed to study the formation of BINOL complexes with both α- and βCDs. For the most stable structures of any of the complexes only a small portion of the guests, in agreement with thermodynamics parameters and quenching experiments, penetrates inside the CD cavities. Driving forces for 1:1 inclusion processes may be dominated by non-bonded van der Waals host:guest interactions. The low guest:host binding constants and poor enantioselectivity of α- and βCDs for BINOLS may be a consequence of the BINOL aggregation in water.