Achiral Sm(III)-Based Metal-Organic Framework as a Luminescence Sensor for Enantiodiscrimination of Quinine and Quinidine.

The effective discrimination and determination of the chiral antimalarial drugs quinine (QN) and quinidine (QD) are extremely important for human health. Herein, a 2D achiral Sm-based metal-organic framework (IMU-MOF1 = [Sm(tpba)(L)]n, where Htpba = 4-(2,2':6″,2'-terpyridin)-4'-ylbenzioc acid and H2L = 2,2'-biquinoline-4,4'-dicarboxylic acid) was successfully prepared by the solvothermal method. More importantly, IMU-MOF1 was designed as an ultrasensitive fluorescent probe for the identification of chiral enantiomer drugs. The limits of detection for QN and QD are 4.24 × 10-11 and 7.54 × 10-12 M, respectively. Furthermore, it was demonstrated that the stronger hydrogen-bonding interactions between IMU-MOF1 and quinine furnish a more efficient energy transfer to the ligands in the sensing process, resulting in a significant fluorescence enhancement of IMU-MOF1.

A Zn-coordination polymer as a multifunctional fluorescent probe for the detection of V2O74-, Fe3+, and p-nitrotoluene.

A transition metal coordination polymer, [Zn(tpba)(bqdbc)0.5]n (1), was successfully designed and synthesized based on 2,2'-biquinoline-4,4'-dicarboxylic acid (H2bqdc) and 4-(2,2';6',2'-terpyridin)-4'-yl)benzoic acid (Htpba). Compound 1 is initially constructed from the 1D chain of tpba- and bqdc2- and further connected by π⋯π interactions, forming a 2D layered structure. Notably, compound 1 showed good fluorescence stability ranging from pH 1 to 13 in an aqueous solution. It was found that compound 1 could not only detect V2O74- ions with high selectivity and recyclability but also serve as an excellent selective sensing material for Fe3+ among some cations. More crucially, it is the first time that a luminescent coordination polymer has been used to detect V2O74- ions in aqueous solution. The detection of nitrotoluene (p-NT) demonstrated that compound 1 could also behave as a functional probe with high selectivity, sensitivity, and recyclability; and the detection limit of p-NT was 50.9 nM. Meanwhile, the luminescence sensing mechanisms for different analytes were speculated in detail.

Identification of folic acid and sulfaquinoxaline using a heterometallic Zn-Eu MOF as a sensor.

A d-f heterometallic MOF using the 2,2'-bipyridine-4,4'-dicarboxylic acid ligand (H2LZ) was obtained by solvothermal synthesis, namely [EuZn(LZ)2(HCOO)(H2O)3]n (1). The structure analysis shows that compound 1 comprises heterometallic Zn2+ and Eu3+ ions, which are connected by LZ2- and HCOO- anions to form a three-dimensional framework. MOF 1 exhibited high stability of fluorescence intensity in the scope of pH 2-11 in an aqueous solution. Furthermore, MOF 1 served as an excellent selective sensing material for the detection of folic acid in the presence of some imitating materials of the human body and discerned sulfaquinoxaline in sulfonamide drugs with high sensitivity, selectivity, and reusability. Moreover, we designed and manufactured a sensor paper based on MOF 1 as a portable device for the visual detection of folic acid and sulfaquinoxaline. More crucially, this is the first example in which luminescent MOF is used to identify sulfaquinoxaline molecules in an aqueous solution. In addition, the luminescence sensing mechanisms of MOF 1 for the detection of the above analytes were explored in detail.

A water-stable terbium-MOF sensor for the selective, sensitive, and recyclable detection of Al3+ and CO32- ions.

A terbium metal-organic framework associated with mixed 4-(pyridin-3-yloxy)-phthalic acid (H2ppda) and oxalic acid (H2ox) has been synthesized under solvothermal conditions, namely [Tb(ppda)(ox)0.5(H2O)2]n (1). Compound 1 is constructed of 1D binuclear [Tb(ppda)]2 chains and is further connected by ox2- ligands, exhibiting a 2D layered structure. It is worth noting that compound 1 exhibits excellent fluorescence stability over a pH range from 2 to 13 in aqueous solution. Interestingly, compound 1 can detect Al3+ ions with high selectivity and sensitivity among diverse inorganic cations in aqueous solution. In addition, compound 1 is also a highly selective sensing material for CO32- ions without interference from other common anions. Therefore, compound 1 is a promising sensor with a fast response time and low limits of detection for simultaneously detecting Al3+ and CO32- ions, at 5.66 µM for Al3+ ions and 0.38 µM for CO32- ions. Compound 1 displays the lowest limit of detection for CO32- ions using a fluorescent MOF sensor reported to date. The luminescence quenching mechanisms for the different analytes are further explored in detail.

A water-stable europium-MOF as a multifunctional luminescent sensor for some trivalent metal ions (Fe3+, Cr3+, Al3+), PO43- ions, and nitroaromatic explosives.

A luminescent Eu-MOF, namely, [Eu2(ppda)2(npdc)(H2O)]·H2O (1) based on the mixed ligands 4-(pyridin-3-yloxy)-phthalic acid (H2ppda) and naphthalene-1,4-dicarboxylic acid (H2npdc) was synthesized under solvothermal conditions. Compound 1 was initially constructed from the 1D binuclear chains of [Ln(npdc)]2 and further connected by ppda2- ligands, forming a 2D layered structure. It is worth noting that compound 1 exhibited excellent fluorescence stability in the pH range of 2-13 in an aqueous solution. It was found that compound 1 could not only detect trivalent Fe3+, Cr3+ and Al3+ ions with high selectivity and recyclability but also serve as an excellent selective sensing material for PO43- ions among some anions. The detection of NACs demonstrated that compound 1 could also behave as a functional probe with high selectivity, sensitivity, and recyclability, and the detection limit of TNP was 2.97 × 10-6 M. Furthermore, the luminescent sensing mechanisms for different analytes were speculated.

Lanthanide-MOFs constructed from mixed dicarboxylate ligands as selective multi-responsive luminescent sensors.

Five novel Ln-MOFs associated with the mixed ligands of 4-(pyridin-3-yloxy)-phthalic acid (H2ppda) and terephthalic acid (H2bdc), namely, [Ln(ppda)(bdc)0.5(C2H5OH)(H2O)]n (Ln = Sm (1), Eu (2), Gd (3), Tb (4), and Dy (5)) were synthesized under the solvothermal conditions. Compounds 1-5 exhibit the isostructural 2D layered structures. The solid-state luminescence properties of compounds 1, 2, 4 and 5 were investigated in detail. It was found that compound 4 not only detected nitrobenzene derivatives-based explosives with high selectivity, sensitivity, and recyclability, but also served as an excellent selective sensing material for Fe3+ ion and Cr2O72- ion. In particular, it is worth noting that the detection limit of TNP can reach 3.0 × 10-8 M. It was found that the free oxygen atoms of the ether bond, which function as the Lewis basic sites in Ln-MOFs, might interact with metal ions. In addition, the sensing mechanisms of 4 for different analytes were explored further.