Selective Recognition of Uracil and Its Derivatives Using a DNA Repair Enzyme Structural Mimic

Two Highly Stable Luminescent Lead Phosphonates Based on Mixed Ligands: Highly Selective and Sensitive Sensing for Thymine Molecule and VO3 - Anion

Two luminescent lead phosphonates with two-dimensional (2D) layer and three-dimensional (3D) framework structure, namely, Pb₃[(L₁)₂(Hssc)(H₂O)₂] (1) and [Pb₂(L₂)_0.5(bts)(H₂O)₂]·H₂O (2) (H₂L₁ = O(CH₂CH₂)₂NCH₂PO₃H₂, H₄L₂ = H₂PO₃CH₂NH(C₂H₄)₂NHCH₂PO₃H₂, H₃ssc = 5-sulfosalicylic acid, NaH₂bts = 5-sulfoisophthalic acid sodium) have been prepared via hydrothermal techniques. The two compounds not only show excellent thermal stability but also remain intact in aqueous solution within an extensive pH range. Moreover, the atomic absorption spectroscopy analysis experiment indicates that there does not exist the leaching of Pb²⁺ ions from the lead phosphonates, which show they are nontoxic in aqueous solution. In compound 1, the Pb(1)O₄, Pb(2)O₇, Pb(3)O₄, and CPO₃ polyhedra are interlinked into a one-dimensional chain, which is further connected to adjacent chain by sharing the Hssc^2- to form a 2D layer. Interestingly, compound 1 as a highly selective and sensitive luminescent material can be used to detect the thymine molecule with a very low detection limit of 8.26 × 10^-7 M. In compound 2, the Pb(1)O₆ and Pb(2)O₅ polyhedra are interlinked into a dimer via edge sharing, which is further connected to adjacent dimer to form a tetramer via corner sharing, and such a tetramer is then interlinked into a 2D layer through bts^3- ligands; the adjacent 2D layers are finally constructed to a 3D structure by sharing the L₂ ^4- ligand. Compound 2 can be applied as an excellent luminescent sensor for sensing of VO₃ ^- anion. Furthermore, the probable fluorescent quenching mechanisms of the two compounds have also been studied.

Remarkable influence of 'phane effect' on the excited-state properties of cofacially oriented coumarins

A comprehensive investigation of the photophysics of a cofacially oriented bis-coumarin based on naphthalene, i.e., Cou-Nap, designed and synthesized to examine the influence of π-electronic communication between the two fluorophores, reveals exceptional excited-state properties. While the anticipated [2 + 2] photocycloaddition is not observed despite the fact that the two reactive coumarin units are at a distance of 3.8 Å, the fluorescence quantum yields and singlet lifetimes in different solvents are found to be remarkably higher when compared to those of the parent coumarin and a mono-coumarin model system, i.e., Cou-Dur. In addition to large solvent-induced Stokes shifts, Cou-Nap displays intriguing temperature-dependent emission in a nonpolar solvent such as cyclohexane. The observed photophysical properties are reconciled based on the so-called 'phane effect' that is operative in cyclophanes. In the latter, an effective π-π interaction between the aromatic rings modifies the attributes of the chromophore in such a manner that the observed properties cannot be associated with the individual aromatic rings. The temperature-dependent emission is proposed to arise as a consequence of thermally activated ISC from the singlet-excited state to one of the higher energy triplet states. The results constitute, for the first time, the demonstration of modification of the excited-state properties of a fluorophore in a non-cyclophane system by 'phane effect'.

Fluorescent supramolecular polypseudorotaxane architectures with Ru(ii)/tri(bipyridine) centers as multifunctional DNA reagents

A water-soluble supramolecular polypseudorotaxane was prepared via the host–guest interaction of cucurbit[8]uril and the Ru(bpy)₃ complex with bis-naphthalene groups.

Crystal structure of 1,8-dibenzoyl-2,7-di-phen-oxy-naphthalene

In the title compound, C36H24O4, the benzene rings of the benzoyl and phen-oxy groups make dihedral angles of 75.01 (4), 75.78 (4), 83.17 (5) and 80.84 (5)° with the naphthalene ring system. In the crystal, two types of C-H⋯π inter-actions between the benzene rings of the benzoyl groups and the naphthalene unit, and two kinds of π-π inter-actions between the benzene rings, with centroid-centroid distances of 3.879 (1) and 3.696 (1) Å, are observed.

Head-to-tail square-shaped cyclic hydrogen bonds leading to dimeric aggregates: 1,8-dibenzoyl-2,7-dihydroxynaphthalene and a comparison with its analogous benzoylnaphthalene

The title compound, C24H16O4, crystallized with two independent molecules in the asymmetric unit. Both carbonyl groups in these molecules form intramolecular O—H...O=C hydrogen bonds with neighbouring hydroxy groups, affording six-membered cyclic structures. In the crystal, dimeric aggregates arise from two intermolecular O—H...O=C hydrogen bonds between both independent molecules, forming head-to-tail square-shaped cyclic ...O...H...O...H... hydrogen bonds. These dimeric aggregates are connected into layers in thebcplane by intermolecular (naphthalene)C—H...O=C interactions. On the other hand, the analogous compound bearing methoxy groups at the 2- and 7-positions of the naphthalene ring, namely 1,8-dibenzoyl-2,7-dimethoxynaphthalene [Nakaemaet al.(2008).Acta Cryst.E64, o807], forms a three-dimensional molecular networkviaC—H...O=C and π–π interactions between the benzoyl groups. These results show that the intramolecular O—H...O=C hydrogen bonds in the title compound control the orientations of the benzoyl groups and thus promote the formation of the cyclic intermolecular O—H...O=C interactions involving the same donor and acceptor groups in pairs of molecules.

A specific molecular beacon probe for the detection of human prostate cancer cells

The small-molecule, water-soluble molecular beacon probe 1 is hydrolyzed by the lysate and living cells of human prostate cancer cell lines (LNCaP), resulting in strong green fluorescence. In contrast, probe 1 does not undergo significant hydrolysis in either the lysate or living cells of human nontumorigenic prostate cells (RWPE-1). These results, corroborated by UV-Vis spectroscopy and fluorescent microscopy, reveal that probe 1 is a sensitive and specific fluorogenic and chromogenic sensor for the detection of human prostate cancer cells among nontumorigenic prostate cells and that carboxylesterase activity is a specific biomarker for human prostate cancer cells.

Facile Aza-Michael Additions of Uracil Derivatives to Acrylates

24 Aza-Michael adducts were synthesised in moderate to excellent yields by the addition of 5-substituted uracils to acrylates with ethylamine as a catalyst. Many of the adducts were obtained in almost quantitive yield without column chromatography. The procedure provideded an efficient approach to the synthesis of N-1 uracil adducts using acrylates as acceptors. The structures of the compounds were determined by 1H NMR, 13C NMR, mass spectra and X-ray crystallography analyses. The uracil unit is present in DNA and related natural products and has a broad spectrum of biological activity.

A systems approach to controlling supramolecular architecture and emergent solution properties via host-guest complexation in water

The assembly behavior of aryl/alkyl imidazolium ionic liquid salts in aqueous solution has been investigated. These salts undergo self-assembly into one-dimensional stacks via hydrophobic and π-π interactions upon increasing concentration, which led to a substantial increase in the solution viscosity in water. Addition of the macrocyclic host molecules cucurbit[n]urils (CB[n]) were found to effectively alter the supramolecular assemblies, as evidenced from the dramatic increase (by CB[7]) and decrease (by CB[8]) in solution viscosity and aggregation size in water, on account of the different binding stoichiometries, 1:1 complexation with CB[7] and 2:1 complexation with CB[8]. Furthermore, the aggregate architectures were controllably modified by competitive guests for the CB[n] hosts. This complex supramolecular systems approach has tremendous implications in the fields of molecular sensor design, nonlinear viscosity modification, and controlled release of target molecules from a defined supramolecular scaffold in water.

A fluorescein-containing, small-molecule, water-soluble receptor for cytosine free bases

In this study, we synthesized small-molecule, water-soluble, fluorescein-containing ureido compounds 6 and 8 as target receptors for cytosine free bases and then investigated the binding of cytosine free bases with the receptors using (15)N NMR spectroscopy and partially labeled cytosine-2,4-(13)C-1,3,4-(15)N-cytosine. Binding with the receptor 6a (the disodium form of 6) caused the chemical shift of the nitrogen atom of the amino group of cytosine to move downfield; binding of the receptor 8a (the disodium form of 8), which is possessing no corresponding aryl nitrogen atom, had no effect on this signal. Fluorescence spectroscopy revealed that binding of cytosine and its derivatives led to quenching of the fluorescence of receptor 6a; in contrast, the quenching of receptor 8a was only slightly affected by cytosine. Because the fluorescence of 6a was not quenched by either deoxycytidine or uracil, it appears that this receptor is a specific for cytosine among the DNA bases. We used the fluorescence of 6a to measure the apparent binding constants for various cytosine derivatives, including the anticancer prodrug 5-fluorocytosine. Receptor 6a is the first small-molecule, water-soluble fluorescent receptor for the specific binding of cytosine free bases in aqueous solution.