Development ofN-Benzamidothioureas as a New Generation of Thiourea-Based Receptors for Anion Recognition and Sensing

Thiourea- and Amino-Substituted Benzoxadiazole Dyes with Large Stokes Shifts as Red-Emitting Probe Monomers for Imprinted Polymer Layers Targeting Carboxylate-Containing Antibiotics

Bifunctional fluorescent molecular oxoanion probes based on the benzoxadiazole (BD) chromophore are described which integrate a thiourea binding motif and a polymerizable 2-aminoethyl methacrylate unit in the 4,7-positions of the BD core. Concerted charge transfer in this electron donor-acceptor-donor architecture endows the dyes with strongly Stokes shifted (up to >250 nm) absorption and fluorescence. Binding of electron-rich carboxylate guests at the thiourea receptor leads to further analyte-induced red-shifts of the emission, shifting the fluorescence maximum of the complexes to ≥700 nm. Association constants for acetate are ranging from 1-5×105  M-1 in acetonitrile. Integration of one of the fluorescent probes through its polymerizable moiety into molecularly imprinted polymers (MIPs) grafted from the surface of submicron silica cores yielded fluorescent MIP-coated particle probes for the selective detection of antibiotics containing aliphatic carboxylate groups such as enoxacin (ENOX) at micromolar concentrations in highly polar solvents like acetonitrile.

Synthesis of novel hybrid pharmacophore of N-((4-sulfamoylphenyl)carbamothioyl)alkanamides as potent carbonic anhydrase-II and 15-lipoxygenase inhibitors

A series of N-((4-sulfamoylphenyl)carbamothioyl)alkanamides (5a-j) were synthesized by the reaction of sulphanilamide in dry acetone with freshly prepared alkyl and acyl isothiocyanates (5a-j). The structures of products were confirmed by IR, ¹ H, and ¹³ C NMR. The synthesized compounds were screened as inhibitors of the bovine erythrocyte carbonic anhydrase isoform II (bCA II) and 15-lipoxygenase enzyme (15-LOX). Most of the derivatives showed significant activity against bCA-II while only few compounds were found active against 15-LOX. Molecular docking studies of most active compounds were carried out against bCA II as well as 15-LOX to rationalize the binding mode and interactions of compound in the active sites. Additionally, the pharmacokinetic properties of the compounds were predicted through computational tools, which reflect that these compounds possess acceptable pharmacokinetic profile and good drug-likeness.

Synthesis of Potent Anticancer Substituted 5-Benzimidazol-2-amino Thiazoles Controlled by Bifunctional Hydrogen Bonding under Microwave Irradiations

Benzimidazol-amino thiazoles are synthesized under microwave irradiations using benzimidazole phenyl thiourea and 2-bromoacetophenone. Bifunctional hydrogen bonding plays an important role in chemical conversion. The reaction was carried out by C-C bond formation, followed by C-N bond cleavage and simultaneous migration of the benzimidazole ring. This reaction is novel and efficient for the synthesis of benzimidazol-amino thiazoles in which microwaves were used as driving forces. Synthesis of the product was controlled by double hydrogen bonding which is practically confirmed by the synthesis of routine imino-thiazole as an alternative product in the simple acidic condition. The simple acidic condition is neither responsible nor sufficient for optimum conversion of the benzimidazole migrated product. The synthesized products benzimidazole amino thiazoles D4 (IC₅₀ = 4.207 μM) and D8 (IC₅₀ = 2.398 μM) show interesting anticancer activities for human lung cancer with reference to doxorubicin (IC₅₀ = 1.750 μM).

Supersensitive Detection of Anions in Pure Organic and Aqueous Media by Amino Acid Conjugated Ellman's Reagent

The last few decades witnessed a remarkable advancement in the field of molecular anion receptors. A variety of anion binding motifs have been discovered, and large number of designer molecular anion receptors with high selectivity are being reported. However, anion detection in an aqueous medium is still a formidable challenge as evident from only a miniscule of synthetic systems available in the literature. We, herein, report 5,5'-dithio-bis(2-nitrobenzoic acid) (Ellman's reagent) appended with amino acids as supersensitive anion sensors that can detect F^- and H₂PO₄^- ions in both aqueous as well as organic media. Interestingly, the sensors showed a dual response to anions, viz., chromogenic response in organic medium and electrochemical response in aqueous solutions. Various spectroscopic techniques such as UV-vis and ¹H NMR are used to investigate the binding studies in acetonitrile, whereas electrochemical methods such as cyclic voltammetry (CV) and differential pulse voltammetry (DPV) are employed to explore the anion binding in water. The host-guest complex stoichiometry and binding constants are calculated using the BindFit software. The geometry of host-guest complex has been optimized by the density functional theory (DFT) method. These molecules are versatile sensors since these function in both water and acetonitrile with extremely low limit of detection (LOD) up to 0.07 fM and limit of quantification (LOQ) up to 0.23 fM. To our knowledge, the present system is the first example of a sensor that can detect the lowest concentration of anions in water quantitatively. The minimalistic design strategy presented here opens up the innumerable possibilities for designing dual anion sensors in a one fell swoop.

Supramolecular architecture in 1:1 cocrystal of N-carbamothioylacetamide and N,N'-thiocarbonyldiacetamide from the attempted synthesis of 1,3-diacetyl-2-thioxoimidazolidine-4,5-dione (a thioparabanic acid derivative)

An attempt to synthesize thioparabanic acid as precursor to other fused heterocyclic compounds, by a microwave assisted multistep one-pot reaction yielded a co-crystal of N-carbamothioylacetamide (NCTA) and N,N'-thiocarbonyldiacetamide (NNTCA) which is being reported in this paper. The structure of N-carbamothioylacetamide and N,N'-thiocarbonyldiacetamide from the attempted synthesis of 1,3-diacetyl-2-thioxoimidazolidine-4,5-dione, C₅H₈N₂O₂S.C₃H₆N₂OS, has triclinic (P-1) symmetry. It is of interest with respect to biological application. The structure displays inter- and intra-molecular hydrogen bonding through -C=O···H interactions. Similarly, -C=S···H hydrogen bonding interactions are present, providing additional intermolecular stability to the co-crystal. For application as a potential drug candidate, a density functional theory (DFT) simulation of the antioxidant activities of the co-crystal and its individual components (NCTA and NNTCA) has been performed. The computed redox potentials indicate that the study compounds show comparable antioxidant activities with ascorbic acid (AA) for a one electron transfer process. Meanwhile, for a two-electron process, AA showed significant antioxidant advantage over the titled compound.

Functional Single-Walled Carbon Nanotubes for Anion Sensing

We report an anion-sensing platform wherein conductance changes are triggered by chemical interactions between selectors and anions. The selector design incorporates both a cationic moiety (i.e., pyridinium) and a thiourea-based dual-hydrogen-bond donor. Anion binding by a model selector (2) was studied using ¹H NMR and UV-vis titrations, which reveal a binding strength toward acetate ions (AcO^-) followed by Cl^- > Br^- > NO₃^-. These studies reveal that selector 2 is deprotonated upon addition of AcO^-, whereas it undergoes hydrogen bonding associated with Cl^-, Br^-, and NO₃^-. The cationic pyridinium moiety improves anion binding affinity by lowering the pK_a value of selector 2 and enhancing the hydrogen-bond donor capability as confirmed by spectroscopic titrations and DFT calculations. The selector is covalently attached to poly(4-vinylpyridine) (P4VP), which wraps single-walled carbon nanotubes (SWCNTs) (i.e., P4VP-2-SWCNT) to transduce an electrical signal. As a result, continuous anion sensing was achieved with high sensitivity represented by a normalized resistance change of 101.9 ± 10.3% toward 16.7 mM AcO^-, whereas negligible sensitivity was observed toward Cl^-, Br^-, and NO₃^-. The sensitivity transition was attributed to the internal charge transfer of 2 by deprotonation of the thiourea proton upon addition of AcO^-.

Tuning Supramolecular Selectivity for Hydrosulfide: Linear Free Energy Relationships Reveal Preferential C-H Hydrogen Bond Interactions

Supramolecular anion receptors can be used to study the molecular recognition properties of the reactive yet biologically critical hydrochalcogenide anions (HCh^-). Achieving selectivity for HCh^- over the halides is challenging but necessary for not only developing future supramolecular probes for HCh^- binding and detection, but also for understanding the fundamental properties that govern these binding and recognition events. Here we demonstrate that linear free energy relationships (LFERs)-including Hammett and Swain-Lupton plots-reveal a clear difference in sensitivity to the polarity of an aryl C-H hydrogen bond (HB) donor for HS^- over other HCh^- and halides. Analysis using electrostatic potential maps highlights that this difference in sensitivity results from a preference of the aryl C-H HB donor for HS^- in this host scaffold. From this study, we demonstrate that LFERs are a powerful tool to gain interpretative insight into motif design for future anion-selective supramolecular receptors and highlight the importance of C-H HB donors for HS^- recognition. From our results, we suggest that aryl C-H HB donors should be investigated in the next generation of HS^- selective receptors based on the enhanced HS^- selectivity over other competing anions in this system.

Multifunctional Magnetic-Fluorescent Nanoparticle: Fabrication, Bioimaging, and Potential Antibacterial Applications

Magnetic-fluorescent nanoparticles integrating imaging and therapeutic capabilities have unparalleled advantages in the biomedical applications. Apart from the dual ability of unique biomolecular fluorescent recognition and magnetic modes, the nanoparticle also endows combined effective therapies with high physiological stability, long-term imaging, rapid response time, and excellent circulation ability. Herein, we developed a carboxyl-functionalized magnetic nanoparticle that was further functionalized by polydopamine (PDA) and Schiff base ligand (3-aminopyridine-2-carboxaldehyde N(4)-methylthiosemicarbazone, HL) to form multilayered coating single nanoparticles (Fe₃O₄@PDA@HL). Our work showed that the aggregation-induced emission (AIE) effect could be produced by embedding In³⁺ into the Fe₃O₄@PDA@HL nanostructure, which offered a new opportunity for utilization as a fluorescent detection and therapeutic platform. Cellular fluorescent imaging experiments provided bacterial cell biodistribution, demonstrating their excellent luminescent performance, magnetic aggregation, and separation capability. We simultaneously confirmed that the synergistic antibacterial effect was closely related to both Fe₃O₄@PDA@HL and In³⁺, leading to the disruption of membrane integrity and the leakage of intracellular components, thus inducing bacterial death. This approach presented in our work could promote the development of future bioimaging and clinical therapy applications.

Benzoylguanidines as Anion-Responsive Systems

A series of benzoylguanidinium salts was prepared and the changes in UV/Vis spectra, triggered by the presence of anions, were investigated. All compounds undergo deprotonation with basic anions like dihydrogenphosphate and acetate in acetonitrile. The most pronounced spectral changes were obtained by deprotonation of N¹ -benzoyl-N³ -(p-nitrophenyl) guanidinium chloride which shows the naked-eye visible color change from colorless to yellow. Measured pK_a (BH⁺ ) in acetonitrile ranges from 12-16, which is comparable to the pyridinium cations. The proton transfer equilibria were also tested in acetonitrile/water mixture where all but the most acidic derivatives showed pK_a (BH⁺ ) of 4-6 units which corresponds to apparent association constants of 10⁴ -10⁶  dm³  mol^-1 . UV/Vis spectra of neutral and protonated forms were modelled by the TD-DFT approach using CAM-B3LYP and PBE0 functionals and compared to CC2 results. In the case of CAM-B3LYP, a parameter ω, defining amount of long-range exchange correction, was varied to achieve the best agreement with the experimental spectra. The optimized ω parameters are 0.10 a₀ ^-1 for neutral benzoylguanidines and 0.20 a₀ ^-1 for neutral nitrobenzoyl and protonated systems. The larger ω parameter in the latter is ascribed to more pronounced charge transfer character of the HOMO-LUMO transition - the one responsible for the lowest energy absorption band.

A photo-stable fluorescent chiral thiourea probe for enantioselective discrimination of chiral guests

Herein, a chiral thiourea Schiff base derived from (1R,2R)-1,2-cyclohexanediamine and tetraphenylethylene (TPE) was applied as a highly effective chiral sensor for the enantioselective discrimination of various acids and aminesviaion-pair and hydrogen-bond interaction.

Comparison of halide receptors based on H, halogen, chalcogen, pnicogen, and tetrel bonds

A series of halide receptors are constructed and the geometries and energetics of their binding to F⁻, Cl⁻, and Br⁻assessed by quantum calculations. The dicationic receptors are based on a pair of imidazolium units, connectedviaa benzene spacer. The imidazoliums each donate a proton to a halide in a pair of H-bonds. Replacement of the two bonding protons by Br leads to bindingviaa pair of halogen bonds. Likewise, chalcogen, pnicogen, and tetrel bonds occur when the protons are replaced, respectively, by Se, As, and Ge. Regardless of the binding group considered, F⁻is bound much more strongly than are Cl⁻and Br⁻. With respect to the latter two halides, the binding energy is not very sensitive to the nature of the binding atom, whether H or some other atom. But there is a great deal of differentiation with respect to F⁻, where the order varies as tetrel > H ∼ pnicogen > halogen > chalcogen. The replacement of the various binding atoms by their analogues in the next row of the periodic table enhances the fluoride binding energy by 22–56%. The strongest fluoride binding agents utilize the tetrel bonds of the Sn atom, whereas it is I-halogen bonds that are preferred for Cl⁻and Br⁻. After incorporation of thermal and entropic effects, the halogen, chalcogen, and pnicogen bonding receptors do not represent much of an improvement over H-bonds with regard to this selectivity for F⁻, even I which binds quite strongly. In stark contrast, the tetrel-bonding derivatives, both Ge and Sn, show by far the greatest selectivity for F⁻over the other halides, as much as 10¹³, an enhancement of six orders of magnitude when compared to the H-bonding receptor.

Telescoped continuous flow generation of a library of highly substituted 3-thio-1,2,4-triazoles

An integrated continuous flow process for the synthesis of 3-thio-1,2,4-triazoles is reported. A small library of 18 compounds was prepared in just 48 minutes of residence time in moderate to excellent yields.

A colorimetric sensor based on thiourea–polyvinyl alcohol microspheres for the selective recognition of Hg2+ and Cu2+

A novel colorimetric sensor was proposed, and the sensor can be used to monitor Hg²⁺ and Cu²⁺ ions.

UV-visible and (1)H-(15)N NMR spectroscopic studies of colorimetric thiosemicarbazide anion sensors

Four model thiosemicarbazide anion chemosensors containing three N-H bonds, substituted with phenyl and/or 4-nitrophenyl units, were synthesised and studied for their anion binding abilities with hydroxide, fluoride, acetate, dihydrogen phosphate and chloride. The anion binding properties were studied in DMSO and 9 : 1 DMSO-H2O by UV-visible absorption and (1)H/(13)C/(15)N NMR spectroscopic techniques and corroborated with DFT studies. Significant changes were observed in the UV-visible absorption spectra with all anions, except for chloride, accompanied by dramatic colour changes visible to the naked eye. These changes were determined to be due to the deprotonation of the central N-H proton and not due to hydrogen bonding based on (1)H/(15)N NMR titration studies with acetate in DMSO-d6-0.5% water. Direct evidence for deprotonation was confirmed by the disappearance of the central thiourea proton and the formation of acetic acid. DFT and charge distribution calculations suggest that for all four compounds the central N-H proton is the most acidic. Hence, the anion chemosensors operate by a deprotonation mechanism of the central N-H proton rather than by hydrogen bonding as is often reported.

Solvent effect on neutral chiral supramolecular assemblies and their distinct receptor behaviour towards anions

We describe the distinct receptor behaviour of a neutral chiral Cu(ii) complex in dimethylsulfoxide or methanol towards anions, such as F(-), Cl(-), Br(-), I(-) or OAc(-), where F(-) and OAc(-) show the most colorimetric change, through various spectroscopic techniques. Further insights into this at the molecular level come from the single crystal X-ray structures of both dimethylsulfoxide and methanol solvates which show a solvent effect on their supramolecular network formation. Both chromogenic and fluorogenic sensing of the anions indicate a 2 : 1 receptor-anion formation via anion-π as well as hydrogen bonding interactions.

Substituent effects in hydrogen bonding: DFT and QTAIM studies on acids and carboxylates complexes with formamide

Four series of hydrogen bonded complexes of formamide and substituted benzoic acids and benzoates were studied in the light of substituent effect on intermolecular interactions. The analysis based on energy of interaction, geometry, QTAIM-derived properties of hydrogen bond critical point and energy of hydrogen bonds were made and discussed. The opposite effect of the substituent on hydrogen bond donor and acceptor in acid series was found and analyzed. The isodesmic reactions were used to further study the interaction preferences.

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Colorimetric anion sensor based on receptor having indole- and thiourea-binding sites

A new colorimetric sensor having nitro-substituted indole and bisthiocarbonohydrazone units for selective fluoride and acetate ions has been designed and synthesized.

Design, synthesis, molecular docking studies and in vitro screening of ethyl 4-(3-benzoylthioureido) benzoates as urease inhibitors

Thioureas are exceptionally versatile building blocks towards the synthesis of wide variety of heterocyclic systems, which also possess extensive range of pharmacological activities. The substituted benzoic acids were converted into corresponding acid chlorides, these acid chlorides were then treated with potassium thiocyanate in acetone and then the reaction mixture was refluxed for 1-2h afford ethyl 4-(3-benzoylthioureido)benzoates thioureas in good yields. All the newly synthesized compounds were evaluated for their urease inhibitory activities and were found to be potent inhibitors of urease enzyme. Compounds 1f and 1g were identified as the most potent urease inhibitors (IC50 0.21 and 0.13 μM, respectively), and was 100-fold more potent than the standard inhibitors. Further molecular docking studies were carried out using the crystal structure of urease to find out the binding mode of the inhibitors with the enzyme.