Kinetics of hydrogen bonding between anthracene urea derivatives and anions in the excited state

Urea compounds are useful anion sensors due to their hydrogen-bonding capabilities. We investigated the emissive properties of complexes consisting of urea-anthracene (nPUA, n = 1, 2) host compounds and acetate anions held as guests through intermolecular hydrogen bonding. The kinetics of a new emission band formed by conformational changes in the excited singlet state were revealed. The new band is thought to arise from a charge-transfer interaction between the anthracene and urea moieties after intermolecular hydrogen-bond reconfiguration in the excited state, with rate constants of 2.4 × 10(9) and 4.0 × 10(7) s(-1) for 1PUA and 2PUA, respectively.     

Fluorescence spectroscopic evidence for hydrogen bonding and deprotonation equilibrium between fluoride and a thiourea derivative

Interaction of anions with thiourea-linked acridinedione fluorophore was studied by absorption, (1)H NMR, steady-state and time-resolved fluorescence techniques. Addition of AcO(-) and H(2)PO(4)(-) shows a genuine H-bonded complex with thiourea receptor; whereas, F(-) shows stepwise H-bonding and deprotonation of thiourea NH as confirmed by (1)H NMR titration. Free receptor 1 shows emission maximum at 418 nm; whereas, H-bonded complex of 1·F(-) shows a new redshifted emission maximum at 473 nm and the deprotonated 1 exhibits an emission peak at 502 nm. Presence of these three different emitting species was probed by 3D emission spectroscopic studies. Equilibrium between the free receptor 1, 1·F(-) H-bonded complex and deprotonated 1 was confirmed by time-resolved fluorescence studies. Time-resolved area normalised emission spectra (TRANES) of 1 in the presence of F(-) shows two isoemissive points at 456 and 479 nm between time delays of 0-0.5 ns and 1-20 ns, respectively, due to the existence of three emitting species in equilibrium. Observation of such an equilibrium based on fluorescence spectroscopic studies further proves the earlier reported absorption and (1)H NMR spectroscopic studies of H-bonding and deprotonation processes and also illustrates the dynamics of anion-receptor interactions.     

Anion receptor based on thiourea: via hydrogen bonding interaction and efficient deprotonation

A new thiourea-based receptor through Schiff-based condensation of 8-hydroxyqui nolino-7-aldehyde and a phenylthiosemicarbazide was easily obtained. This novel sensor shows strong binding affinity for acetate, fluoride and phosphate ions through efficient deprotonation. We make an in-depth investigation on its anion binding prosperities and deprotonation process through Fluorescence, UV–vis and ¹H NMR titration experiments. Moreover, we propose the anion recognition process by assuming the existence of three-step equilibria.     

Excited-state hydrogen bonding and deprotonation of esculetin in solution: a DFT/TDDFT study

The combined density functional theory (DFT) and time-dependent density functional theory (TDDFT) method was used to study the electronic spectral properties of different deprotonated forms of esculetin. By comparing the experimental absorption and fluorescence bands with the calculated electronic spectra, it is evidently demonstrated that the minor absorption and fluorescence bands observed at slightly longer wavelengths than the principal bands in experiments are predominantly from the de-H3 form of the esculetin monomer. Furthermore, we clarified the relationship between electronic spectral shifts and electronic excited-state intramolecular hydrogen bonding changes: the strengthening of intramolecular hydrogen bond can induce an electronic spectral blueshift while the intramolecular hydrogen bond weakening can result in an electronic spectral redshift.     

A density functional study towards the preferential binding of anions to urea and thiourea

A DFT study predicted the trend towards binding of anions with simple urea/thiourea receptor units, which has been found to be in good agreement with experimentally observed results. Our results provide a trend for the interaction of anions of different shapes with urea/thiourea receptor molecules, which do not always follow the basicity scale of anions.     

DFT方法研究基于脲及硫脲衍生物的阴离子受体

采用密度泛函理论(DFT)模拟了两个基于脲和硫脲衍生物的受体分子对卤素阴离子的识别过程.结构优化表明基于脲衍生物的受体分子1最稳定构象为"反反"构象,分子内部形成稳定的C~α-H…O=C分子内氢键;而基于硫脲衍生物的受体分子2,不能形成分子内氢键,最稳定构象为"反顺"构象.受体1、2与卤素阴离子F~-、Cl~-可形成稳定的双氢键复合物,在此过程中,受体2经历了由"反顺"构象到"反反"构象的异构化过程.结构和能量分析表明,1、2受体分子与F~-离子间的氢键强度远大于其与Cl~-离子间的氢键;另一方面,受体2与阴离子间的氢键明显强于受体1,这是由于硫脲基N-H键具有更强的酸性.此外,对受体分子、氢键复合物及去质子化产物的吸收光谱计算结果表明,受体与F~-离子作用可产生明显的吸收光谱红移,而与Cl~-离子的作用对光谱影响较小.     

Colorimetric sensing of anions in aqueous solution using a charge neutral, cleft-like, amidothiourea receptor: tilting the balance between hydrogen bonding and deprotonation in anion recognition

The design, synthesis and physical evaluation of 1, a visible colorimetric 'naked eye' pyridyl based bis-amidothiourea sensor for anions, is described. This charge neutral sensor gives rise to significant changes in the absorption spectra upon interactions with several important biological anions such as AMP and ADP in 4:1 DMSO-H(2)O solution, while ATP was not detected. These colorimetric changes are due to the formation, or the combination of hydrogen bonding complexes and/or deprotonation between these anions and 1.     

Theoretical study of thiourea derivatives as chemosensors for fluoride and acetate anions

The different interactions between a chemosensor,1-(naphthalen-2-yl)-3-(6-nitrobenzothiazol-2-yl)-thiourea(1),and F-,acetate(AcO-),Cl-,and Br-anions have been investigated theoretically at the B3LYP/6-31+G(d,p) level with the basis set superposition error(BSSE) correction.It was found that the high selectivity of compound 1 for F-can be ascribed to the ability of the anion to deprotonate the N-H fragment of the host sensor,while the chemosensor also has a strong affinity for AcO-by virtue of the formation of a hydrogen-bonded complex.Intramolecular charge transfer(ICT) causes the colorimetric signaling of compound 1 after interaction with F-/AcO-.A study of substituent effects suggested that the O/NH-and O/S-substituted derivatives are also expected to be promising candidates for chromogenic F-/AcO-chemosensors.     

On differences between hydrogen bonding and improper blue-shifting hydrogen bonding.

Twenty two hydrogen-bonded and improper blue-shifting hydrogen-bonded complexes were studied by means of the HF, MP2 and B3LYP methods using the 6-31G(d,p) and 6--311 ++G(d,p) basis sets. In contrast to the standard H bonding, the origin of the improper blue-shifting H bonding is still not fully understood. Contrary to a frequently presented idea, the electric field of the proton acceptor cannot solely explain the different behavior of the H-bonded and improper blue-shifting H-bonded complexes. Compression of the hydrogen bond due to different attractive forces-dispersion or electrostatics--makes an important contribution as well. The symmetry-adapted perturbation theory (SAPT) has been utilized to decompose the total interaction energy into physically meaningful contributions. In the red-shifting complexes, the induction energy is mostly larger than the dispersion energy while, in the case of blue-shifting complexes, the situation is opposite. Dispersion as an attractive force increases the blue shift in the blue-shifting complexes as it compresses the H bond and, therefore, it increases the Pauli repulsion. On the other hand, dispersion in the red-shifting complexes increases their red shift.     

Unique hydrogen bonds between 9-anthracenyl hydrogen and anions

Unique hydrogen bonds of the 9-H of anthracene moieties in hosts 1 and 2 with fluoride and pyrophosphate ions were observed on the basis of the (1)H NMR experiments. Furthermore, hosts 1 and 2 act as a colorimetric sensor and a fluorescent chemosensor for the recognition of fluoride ion, respectively.     

Intramolecular hydrogen bonding studies in mono-, bis and poly-[N-formyl-N'-aryl(alkyl) substituted thiourea] ferrocene derivatives

For several years, we have been engaged in the synthesis and coordination chemistry of ferrocenyl-containing acyl thiourea derivatives[1-2].The existence of intramolecular hydrogen bond is another interesting problem to be investigated. A series of ferrocene derivatives containing N-formyl-N'-aryl (alkyl) thiourea side chains were synthesized by treating mono- or bis ferrocenoyl isothiocyanate with various amines. It was found that intramolecular hydrogen bond between the carbonyl oxygen and the hydrogen atom on N' is common in this kind of compound. The introduction of a ferrocene fragment into the molecule often leads to its better crystallizability.     

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.     

Synthesis and evaluation of urea and thiourea derivatives of oxazolidinones as antibacterial agents

Urea and thiourea derivatives of oxazolidinones were synthesized and their inhibitory activity (MIC) was determined on the bacterial strains which includes clinical isolates and quality control organisms. The structure activity relationships were studied and a 3D-QSAR model was built using Genetic Function Approximation. Interestingly found that electron withdrawing groups at the ortho position of the phenyl ring enhances the activity.     

Anion sensing by Phenazine-based urea/thiourea receptors

The novel colorimetric receptors 2,3-bis-N-(9,10-diaza-anthracen-1-yl)-N′-phenylurea and 2,3-bis-N-(9,10-diaza-anthracen-1-yl)-N′-phenylthiourea have been prepared by the reaction of 2,3-diaminophenazine with phenylisocyanate and phenylisothiocyanate, respectively, in quantitative yields. The interaction and colorimetric sensing properties of receptor = 2 and 3 with different anions were investigated by naked eye, UV-vis and fluorescence spectroscopy in DMSO. The receptors effectively and selectively recognized biologically important F⁻, CH₃COO⁻, H₂P in the presence of other anions, such as Cl⁻, Br⁻, I⁻ and HS in DMSO.     

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.     

Phase equilibria of supercritical C02-ethanol-stearic acid ternary system and hydrogen bonding between ethanol and stearic acid

Solubility of stearic acid in supercritical C0₂ with ethanol cosolvent was determined at 308.15 K in the pressure range from 8 to 16 MPa, and the cosolvent concentration ranges from 0 mol% to 4 mo1%. The corresponding densities of the fluid phases were also measured. It was observed that ethanol enhances the solubility significantly. The solubility increases with pressure noticeably at lower pressure, especially at lower cosolvent concentrations. The effect of pressure on the solubility is very limited at higher pressures or higher cosolvent concentrations. The hydrogen bonding between ethanol and stearic acid in supercritical C0₂ was also studied using FTIR in order to understand the mechanism of the solubility enhancement by ethanol. Project supported by the National Natural Science Foundation of China (Grant No. 29633020).     

Phase equilibria of supercritical CO_2-ethanol-stearic acid ternary system and hydrogen bonding between ethanol and stearic acid

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