Yuling Xu

Mono-, bi- and multi-nuclear silver complexes constructed from bis(benzimidazole)-2-oxapropane ligands and methacrylate: syntheses, crystal structures, DNA-binding properties and antioxidant activities

The reactions of AgNO3 with sodium methacrylate and three structurally related ligands in the absence of light gave three new silver coordination complexes, namely, [Ag2(methacrylate)2(Etobb)2]·CH3CN 1, [Ag(methacrylate)(Bobb)] 2 and [Ag2(methacrylate)2(Aobb)]n 3, where Etobb = 1,3-bis(1-ethylbenzimidazol-2-yl)-2-oxapropane, Bobb = 1,3-bis(1-benzylbenzimidazol-2-yl)-2-oxapropane, Aobb = 1,3-bis(1-allylbenzimidazol-2-yl)-2-oxapropane. All three complexes have been characterized by elemental analysis, UV-visible and infrared spectroscopy, and single-crystal X-ray diffraction. Complex 1 is binuclear and tri-coordinated by two N atoms to two Etobb ligands, while complex 2 is mononuclear. Complex 3 is a unique metal–organic compound that has a diamond-like multinuclear silver center, with each Ag bridged by two Aobb ligands and two methacrylate ions to form 1-D single-coordination polymer chain structures that extend into 2-D frameworks through π–π interactions. The X-ray structures show a wide range of Ag–Ag distances in the polymers, which are dependent on the conformation of the bridging ligand. The DNA-binding properties of the three Ag(I) complexes have been investigated by electronic absorption, fluorescence, and viscosity measurements. The results suggest that the three complexes bind to DNA via an intercalative mode, and their binding affinity for DNA follows the order 1 > 2 > 3. Moreover, the antioxidant activity experiment shows that complex 2 has the potential ability to scavenge hydroxyl radicals in in vitro studies.

Synthesis, crystal structures, and DNA-binding studies of two silver(I) complexes with 1,3-bis(1-ethylbenzimidazol-2-yl)-2-thiapropane

Abstract Two new silver(I) complexes, [Ag(bebt)(methacrylate)] (1) and [Ag2(bebt)2](pic)2 (2) (bebt = 1,3-bis(1-ethylbenzimidazol-2-yl)-2-thiapropane, pic = picrate), have been synthesized and characterized by physico-chemical and spectroscopic methods. Single-crystal X-ray diffraction revealed that the structure of 1 was four-coordinate in a distorted tetrahedral geometry, while in 2, it may be described as a 2 + 1 coordinated silver(I) compound with a nearly linear N–Ag–N backbone and a weak Ag–S interaction. Two ligands are arranged in a face-to-face syn conformation to coordinate to two Ag(I) ions from opposite directions in 2, generating a U-type double layer structure around the metal ions. Experimental studies of the DNA-binding properties indicated that free bebt and both complexes bind to DNA via intercalation, and the order of the binding affinity is 2 > 1 > bebt.

A highly selective fluorescent chemosensor based on naphthalimide and Schiff base units for Cu2+ detection in aqueous medium

Abstract A new Schiff base, 4-allylamine-N-(N-5-methylsalicylidene)-1,8-naphthalimide (1), has been designed and synthesized by combining a 1,8-naphthalimide moiety as a fluorophore and a Schiff base as a recognition group. Its photophysical properties were investigated by absorption and fluorescence spectroscopy, and this sensor exhibits a high fluorescence quantum yield of 0.75–0.91 inorganic solvents of different polarity. It also shows high selectivity for Cu2+ over other ions with fluorescence quenching in aqueous medium (pH=7.2). The reason for this phenomenon (fluorescence quenching) is attributed to the formation of a 1:1 complex between 1 and Cu2+ according to the Job plot and fluorescence titration. The sensor can be applied to the quantification of Cu2+ in a linear fashion from 0.5 to 5 μM with a detection limit of 0.23 μM. Additionally, the association constant (Ka) between Cu2+ and 1 is 1.328×106 M− 1 in aqueous media.

A three-coordinate Ag(I) complex based on the V-shaped ligand 1,3-bis(1-ethylbenzimidazol-2-yl)-2-thiapropane: synthesis, crystal structure and DNA-binding properties

The complex [Ag(bebt)(cinnamate)] [bebt = 1,3-bis(1-ethylbenzimidazol-2-yl)-2-thiapropane], has been synthesised and characterised by physico-chemical and spectroscopic methods. Single-crystal X-ray diffraction revealed that the coordination environment of the Ag(I) complex can be described as trigonal planar, and the Ag(I) atom is coordinated by one oxygen atom from a cinnamate anion and two nitrogen atoms from ligand bebt. Experimental studies of the DNA-binding properties indicated that the free ligand and the complex bind to DNA via the intercalation mode, and the binding affinity of the complex was found to be greater than that of just bebt.

Synthesis, crystal structures, and biological properties of a new naphthalimide Schiff base and its copper(II) complex

Abstract A new naphthalimide Schiff base N-allylamine-4-(ethylenediamine-3-methoxysalicylidene)-1,8-naphthalimide (HL) and its copper(II) complex {N-allylamine-4-(ethylenediamine-3-methoxysalicylidene)-1,8-naphthalimide copper(II)} (CuL2) have been synthesized and characterized. The crystal structure of CuL2 has been determined by X-ray single crystal diffraction. The central Cu(II) ion is four-coordinate with an N2O2 donor set which is afforded by two L ligands, forming a slightly distorted square planar geometry. The interactions of HL and CuL2 with calf thymus DNA were investigated using electronic absorption titration, fluorescence titration, and viscosity measurements. The results indicate that free HL and CuL2 bind to DNA in an intercalation mode, and their binding affinity for DNA takes the order CuL2 > HL. Moreover, the antioxidant assay in vitro also shows that HL and CuL2 possess significant antioxidant activities and CuL2 is more effective than free HL.