•Five sensors were formed from metal organic framework 1 with probe DNAs.•These sensors can be used for the detection of microRNAs.•Each sensor is selectively for the detection of its complementary microRNAs.•The detection limits are from 91 to 559 pM.We report herein five sensing platforms for the detection of five gastric cancer associated microRNAs (miRNAs). The sensing platforms are hybrids formed from a water-stable metal organic framework (MOF) {[Cu(dcbb)2(H2O)2]·10H2O}n (1, H2dcbbBr = 1-(3,5-dicarboxybenzyl)-4,4′-bipyridinium bromide), respectively with five carboxyfluorescein (FAM) labeled probe single-stranded DNA (probe ss-DNA, denoted as P-DNA). Within the hybrid, MOF 1 tightly interacts with the P-DNA through electrostatic and/or π-stacking interactions and results in fluorescence quenching of FAM via a photo-induced electron transfer (PET) process. In the presence of the complementary target miRNAs miR-185, miR-20a, miR-92b, miR-25 and miR-210, which are expressed abnormally in the plasma of gastric carcinoma patients, P-DNA is released from the surface of MOF 1 ascribed to the stronger base pair matching, leading to the FAM fluorescence recovery. Each P-DNA@1 system is effective and reliable for the detection of its complementary target miRNA with the detection limits from 91 to 559 pM, and is not interfered by other four miRNA sequences.Five sensing platforms were formed from MOF 1, respectively with five carboxyfluorescein labeled ss-DNA. These sensing platforms can be used for the detection of five type miRNAs, which are expressed abnormally in the plasma of gastric carcinoma patients. Each sensing system is effective and reliable for the detection of its complementary target miRNA with the detection limits from 91 to 559 pM, and is not interfered by the other four miRNA sequences.Download high-res image (271KB)Download full-size image

•Four water stable zwitterionic zinc carboxylate polymers are synthesized.•Compound 2 can interact with probe DNA to form an effective sensing system.•This system can be used as an effective sensing platform for the detection of HIV ds-DNA.•The detection limit is 7.4 nM.Four water-stable zwitterionic zinc-carboxylate polymers are prepared by reacting N-carboxymethyl-(3,5-dicarboxy)-pyridinium bromide (H3CmdcpBr) with zinc(II) nitrate in the presence of NaOH, through adjusting the solvents and ancillary ligands. With H2O as the solvent and the absence of an ancillary ligand, a two-dimensional (2D) polymer network [Zn(Cmdcp)(H2O)]n (1) is formed. In a mixed H2O/DMF solvent and with the presence of chelating ligands 2,2′-bipyridine (bipy), 1,10-phenanthroline (phen) and 2-(4-pyridyl)benzimidazole (pbz), a one-dimensional (1D) polymer of {[Zn2(Cmdcp)(bipy)2(H2O)5](NO3)2·3H2O}n (2), a mononuclear ionic species of [Zn(phen)(H2O)4][Cmdcp] (3), and a 2D polymer of {[Zn(Cmdcp)(pbz)][pbz]·7H2O}n (4) are accordingly formed. Compounds 1–4 are characterized by IR, elemental analyses and single crystal X-ray crystallography. Compound 2 strongly adsorbs single-stranded DNA (ss-DNA) probe (denoted as P-DNA) labeled with carboxyfluorescein (FAM) and quenches its fluorescence via a photo-induced electron transfer process. If, however, a double-stranded DNA (ds-DNA) of the human immunodeficiency virus 1 (HIV-1 ds-DNA) is further present, the P-DNA interacts with the major groove in HIV-1 ds-DNA via Hoogsteen hydrogen bonding to form a rigid triplex structure. This results in partial or complete fluorescence recovery depending on the concentration of HIV-1 ds-DNA. The findings are applied in fluorometric sensing of HIV-1 ds-DNA. The calibration plot is linear in the 0–60 nM target DNA concentration range, with a 7.4 nM detection limit (at a signal-to-noise ratio of 3). The assay is highly specific and not interfered by one base pair mutated for complementary target HIV-1 ds-DNA, complementary ss-DNA, single-base pair mutated for complementary ss-DNA, non-specific ss-DNA sequences, and higher-order dimeric G-quadruplexes.Four water stable zwitterionic zinc carboxylate polymers are synthesized. The one-dimensional compound with rigid and planar 2,2′-bipyridyl ancillary ligand can interact with carboxyfluorescein labeled DNA to form an effective sensing platform for the detection of HIV ds-DNA with a 7.4 nM detection limit.Download high-res image (216KB)Download full-size image

We herein report a water-stable 3D dysprosium-based metal–organic framework (MOF) that can non-covalently interact with probe ss-DNA. The formed system can serve as an effective fluorescence sensing platform for the detection of complementary Ebolavirus RNA sequences with the detection limit of 160 pM.

•Six water-stable zinc(II) zwitterionic carboxylate compounds with 1D chain, 2D and 3D networks were synthesized.•Compound 2 can interact with the probe DNA through noncovalent bonds to form P-DNA@2 system.•A Zinc(II)-based MOF can interact with the probe DNA to form a system, which can be used for the detection of HIV ds-DNA.Coordination reaction of a known three-dimensional (3D) polymer precursor {Na3[Na9(Cbdcp)6(H2O)18]}n (A, Cbdcp = N-(4-carboxybenzyl)-(3,5-dicarboxyl)pyridinium) with Zn(NO3)2·6H2O in H2O or H2O/DMF at 100 °C and in the presence of aspirin, 5-fluorouracil (5-FU) as modulators, trans-1,2-bis(4-pyridyl)ethylene (bpe) or 1,2-bis(4-pyridyl)ethane (bpea) as ancillary ligands afforded six novel Zn(II)-based metal-organic frameworks (MOFs), that is, {[Zn(Cbdcp)(H2O)3]·H2O}n (1, 1D zigzag chain), {[Zn(HCbdcp)2]·H2O}n (2, 2D sheet), {[Zn(Cbdcp)(bpe)1/2]·2H2O}n (3, 3D polymer), {[Zn(Cbdcp)(bpe)1/2]·2H2O}n (4, 2D network), {[Zn(Cbdcp)(bpea)1/2]·2H2O}n (5, 3D polymer) and {[Zn(Cbdcp)(bpea)1/2]·2H2O}n (6, 2D network). Among them, compound 2 contains aromatic rings, positively charged pyridinium, Zn2+ cation centers and carboxylic acid groups lined up on the 2D sheet structure with a certain extended surface exposure. The unique structure of 2 facilitates effective association with carboxyfluorescein (FAM) labeled probe single stranded DNA (probe ss-DNA, delineates as P-DNA) to yield a P-DNA@2 system, and leads to fluorescence quenching of FAM via a photoinduced electron transfer process. The P-DNA@2 system is effective and reliable for the detection of human immunodeficiency virus 1 ds-DNA (HIV ds-DNA) sequences and capable of distinguishing complementary HIV ds-DNA from mismatched target sequences with the detection limit as low as 10 pM (S/N = 3).Six water-stable zinc(II) zwitterionic carboxylate compounds with 1D chain, 2D and 3D networks were synthesized. Compound 2 can interact with the probe DNA through noncovalent bonds to form P-DNA@2 system. This system can be used as an effective, fluorescent sensing platform for the detection of HIV ds-DNA with the detection limit as low as 10 pM.

We herein report a water-stable three-dimensional Cu-based metal–organic framework (MOF) 1 supported by a tritopic quaternized carboxylate and 4,4′-dipyridyl sulfide as an ancillary ligand. This MOF exhibits unique pore shapes with aromatic rings, positively charged pyridinium and unsaturated Cu(II) cation centers, free carboxylates, tessellating H2O, and coordinating SO42– on the pore surface. Compound 1 can interact with two carboxyfluorescein (FAM)-labeled single-stranded DNA sequences (probe ss-DNA, delineated as P-DNA) through electrostatic, π-stacking, and/or hydrogen-bonding interactions to form two P-DNA@1 systems, and thus quench the fluorescence of FAM via a photoinduced electron-transfer process. These P-DNA@1 systems can be used as effective fluorescent sensors for human immunodeficiency virus 1 double-stranded DNA and Sudan virus RNA sequences, respectively, with detection limits of 196 and 73 pM, respectively.

Five water-soluble zwitterionic copper-carboxylate polymers were prepared from the reaction of N-carboxymethyl-(3,5-dicarboxyl)pyridinium bromide (H3CmdcpBr) with Cu(NO3)2 in the presence of NaOH by modulating the temperature, solvent and ancillary dipyridyl ligands. These complexes include a 1D ladder-shaped polymer {[Cu3(Cmdcp)2(OH)2(H2O)2]·H2O}n (1) formed in H2O at room temperature, and a 2D network polymer {[Cu(Cmdcp) (H2O)2]·2H2O}n (2) isolated in H2O at 135 °C. At 100 °C in H2O/DMF, the same reaction in the presence of an additional 2,2′-bipyridine (bipy) gave a 2D zwitterionic complex {[Cu(Cmdcp)(bipy)]·3H2O}n (3) together with a 1D double-stranded polymer {[Cu(Cmdcp)(H2O)2]·H2O}n (4) as a minor product. The replacement of bipy with phenanthroline (phen) afforded a 1D zigzag polymer chain {[Cu(Cmdcp)(phen)(H2O)]2·9H2O}5 (5). All these complexes were characterized by IR, elemental analyses and single crystal X-ray crystallography. Agarose gel electrophoresis (GE) and ethidium bromide (EB) displacement experiments indicated that complex 5 exhibited the highest pBR322 DNA cleaving ability with the catalytic efficiency (kmax/KM) of 14.80 h−1 mM−1 and the highest binding affinity toward calf-thymus DNA. The MTT assay indicated that complex 5 showed significant inhibitory activity toward the proliferation of several tumor cells. Its IC50 value was at micromolar level and lower than those of cisplatin and complexes 1–4, especially toward resistant lung adenocarcinoma cell A549.

A variety of network structures have been prepared by transmetalation of a polymer {Na3[Na9(Cbdcp)6(H2O)18]}n (1) (Cbdcp = N-(4-carboxybenzyl)-(3,5-dicarboxyl)pyridinium) containing dodecahedral Na9 aggregate secondary building units with Cu(II) by modulating the temperature, solvent, and pH. These complexes include a large, zwitterionic hexa-cuprometallocycle [Cu6(Cbdcp)6(H2O)18] (2) formed in H2O at room temperature, two three-dimensional polymers [Cu3(Cbdcp)2(OH)2(H2O)2]n (3) and {[Cu3(Cbdcp)2(OH)2]·2H2O}n (4) isolated from H2O and DMF/H2O at 135 °C, and a mononuclear complex [Cu(HCbdcp)2(H2O)3]·H2O (5) from H2O at 100 °C and pH = 6. All the complexes are robust and water stable. The crystal framework of macrocycle 2 is stable up to 100 °C under vacuum and selectively adsorbs CO2.

Six transition metal complexes, that is, {[Cu(Ccbp)2]·4H2O}n (1), [Ni(H2O)6](Ccbp)2·4H2O (2), [M(Ccbp)2(H2O)4]·2H2O·2MeOH (M = ZnII (3), CoII (4), MnII (5)), and [Cu(Cbp)2(H2O)2](NO3)2·4H2O (6) were synthesized from the reaction of 4-carboxy-1-(4-carboxybenzyl)pyridinium bromide (H2CcbpBr) and N-(4-carboxybenzyl)pyridinium bromide (HCbpBr) with the corresponding metal salts in the presence of NaOH, respectively. All these metal complexes were characterized by IR, elemental analyses and single crystal X-ray crystallography. In complex 1, every two Ccbp− ions bridge two Cu2+ ions through four terminal carboxylate ions in a monodentate coordination mode, thus forming a one-dimensional polymer structure. Complex 2 is an ionic metal complex consisting of isolated [M(H2O)6]2+ dications and Ccbp− anions. Complexes 3–5 have similar structures, in which the central metal atom in [M(Ccbp)2(H2O)4] unit adopts a slightly distorted octahedral geometry. In complex 6, the central Cu atom adopts a distorted tetrahedral coordination geometry that is formed from two unidentate Cbp ligands and two H2O molecules. Agarose gel electrophoresis studies on the cleavage of plasmid pBR322 DNA by complexes 1–6 indicated that only complex 1 was capable of efficiently cleaving DNA, most probably via an oxidative mechanism. Kinetic assay of complex 1 afforded the maximal catalytic rate constant kmax of 0.50 h−1 and Michaelis constant KM of 0.60 mM, respectively. Ethidium bromide displacement experiments indicated that complex 1 had a binding affinity of (3.10 ± 0.90) × 105 M−1 toward calf-thymus DNA, 10- to 55-fold higher than those shown by H2CcbpBr and complexes 2–5. The high cleaving efficacy of complex 1 is thought to be due to its polynuclear structure.Graphical abstractFive metal complexes of 4-carboxy-1-(4-carboxybenzyl)pyridinium bromide were synthesized and characterized. Among them, the copper(II) complex having polynuclear structure exhibited high DNA-binding affinity and oxidative DNA cleavage.Highlights► 4-Carboxy-1-(4-carboxybenzyl)pyridinium bromide (H2CcbpBr) and its five metal complexes were synthesized and fully characterized. ► Complexes 1, 2 and 3–5 formed a polynuclear structure, an ionic metal complex and mononuclear structures, respectively. ► Complex 1 was capable of efficiently cleaving DNA, most probably via an oxidative mechanism. ► Complex 1 exhibited the maximal catalytic rate constant kmax of 0.50 h−1 and Michaelis constant KM of 0.60 mM, respectively. ► The high cleaving efficacy of complex 1 is thought to be due to its polynuclear structure.

Five water-soluble zwitterionic copper-carboxylate polymers were prepared from the reaction of N-carboxymethyl-(3,5-dicarboxyl)pyridinium bromide (H3CmdcpBr) with Cu(NO3)2 in the presence of NaOH by modulating the temperature, solvent and ancillary dipyridyl ligands. These complexes include a 1D ladder-shaped polymer {[Cu3(Cmdcp)2(OH)2(H2O)2]·H2O}n (1) formed in H2O at room temperature, and a 2D network polymer {[Cu(Cmdcp) (H2O)2]·2H2O}n (2) isolated in H2O at 135 °C. At 100 °C in H2O/DMF, the same reaction in the presence of an additional 2,2′-bipyridine (bipy) gave a 2D zwitterionic complex {[Cu(Cmdcp)(bipy)]·3H2O}n (3) together with a 1D double-stranded polymer {[Cu(Cmdcp)(H2O)2]·H2O}n (4) as a minor product. The replacement of bipy with phenanthroline (phen) afforded a 1D zigzag polymer chain {[Cu(Cmdcp)(phen)(H2O)]2·9H2O}5 (5). All these complexes were characterized by IR, elemental analyses and single crystal X-ray crystallography. Agarose gel electrophoresis (GE) and ethidium bromide (EB) displacement experiments indicated that complex 5 exhibited the highest pBR322 DNA cleaving ability with the catalytic efficiency (kmax/KM) of 14.80 h−1 mM−1 and the highest binding affinity toward calf-thymus DNA. The MTT assay indicated that complex 5 showed significant inhibitory activity toward the proliferation of several tumor cells. Its IC50 value was at micromolar level and lower than those of cisplatin and complexes 1–4, especially toward resistant lung adenocarcinoma cell A549.

We herein report a water-stable 3D dysprosium-based metal–organic framework (MOF) that can non-covalently interact with probe ss-DNA. The formed system can serve as an effective fluorescence sensing platform for the detection of complementary Ebolavirus RNA sequences with the detection limit of 160 pM.