An ordering phase transition, short hydrogen bonds and high Z' in the structure of Ni(Hpydc)2·3H2O.

The structure of Ni(Hpydc)2·3H2O (H2pydc = pyridine-2,6-dicarboxylic acid, also known as dipicolinic acid) has been reinvestigated at variable temperatures. At room temperature, it matches the known structure in the space group P21/c, but at 180 K it undergoes a phase transformation to a twinned structure in Cc. By 120 K, the structure is ordered and twinned with Z' = 4, and shows interesting short hydrogen-bonding interactions that include the formation of hydroxonium species.

Surface-Renewable AgNPs/CNT/rGO Nanocomposites as Bifunctional Impedimetric Sensors.

ABSTRACT: In this study, glassy carbon electrode modified by silver nanoparticles/carbon nanotube/reduced graphene oxide (AgNPs/CNT/rGO) composite has been utilized as a platform to immobilize cis-dioxomolybdenum (VI)-salicylaldehyde-histidine (MoO2/Sal-His). The modified electrode shows two reversible redox couples for MoO2/Sal-His. Electrocatalytic oxidation of cysteine (CySH) and electrocatalytic reduction of iodate on the surface of the modified electrode were investigated with cyclic voltammetry and electrochemical impedance spectroscopy methods. The presence of MoO2/Sal-His on AgNPs/CNT/rGO shifted the catalytic current of iodate reduction to a more positive potential and the catalytic current of cysteine oxidation to a more negative potential. The change of interfacial charge transfer resistance (R ct) recorded by the modified electrode was monitored for sensitive quantitative detection of CySH and iodate. Moreover, the sensor has a good stability, and it can be renewed easily and repeatedly through a mechanical or electrochemical process.

Bifunctional impedimetric sensors based on azodicarboxamide supported on modified graphene nanosheets.

Herein, gold-coated graphene oxide nanosheets hybrid material (GO/AuNPs) with exceptional physical and chemical properties has been utilized as a novel platform for electrode modification. The synthetic method of GO/AuNPs involves anon-covalent functionalization of exfoliated GO with AuNPs based on the reduction of the Au(III) complex by sodium citrate. The prepared GO/AuNPs hybrid exhibits the dispersion of high density AuNPs which were densely decorated on the large surface area of GO. The GO/AuNPs modified glassy carbon (GC) electrode was employed as a sensing platform to immobilize azodicarboxamide (ACA). The morphology, structure and electrochemical performance of the sensor were characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results indicate that the modified electrode has a notable bifunctional catalytic activity. Electrocatalytic oxidations of cysteine and electrocatalytic reduction of iodate at the surface of modified electrode were investigated with different technique.

A label-free aptasensor based on polyethyleneimine wrapped carbon nanotubes in situ formed gold nanoparticles as signal probe for highly sensitive detection of dopamine.

Herein, a highly sensitive and selective aptamer biosensor for quantitative detection of a model target, dopamine (DA), was developed by using a gold (Au) electrode modified with highly dispersed gold nanoparticles (AuNPs) and acid-oxidized carbon nanotubes (CNTs-COOH) functionalized with polyethyleneimine (PEI). Amine-terminated12-mercaptureprobe (ssDNA1) as a capture probe and specific DA-aptamer (ssDNA2) as a detection probe was immobilized on the surface of a modified electrode via the formation of covalent amide bond and hybridization, respectively. Methylene blue (MB) was used as the redox probe, which was intercalated into the aptamer through the specific interaction with its guanine bases. In the presence of DA, the interaction between aptamer and DA displaced the MB from the electrode surface, rendering a lowered electrochemical signal attributed to decreased amount of adsorbed MB. The developed electrochemical DA aptasensor showed a good linear response to DA from 5 to 300nM with detection limit of 2.1nM. The biosensor also exhibited satisfactory selectivity and could be successfully used to detect DA in blood serum sample.

A novel impedimetric aptasensor, based on functionalized carbon nanotubes and prussian blue as labels.

A simple and feasible electrochemical sensing protocol was developed for the detection of bisphenol A (BPA) by employing the gold nanoparticles (AuNPs), prussian blue (PB) and functionalized carbon nanotubes (AuNPs/PB/CNTs-COOH). An aminated complementary DNA as a capture probe and specific aptamer against BPA as a detection probe was immobilized on the surface of a modified glassy carbon (GC) electrode via the formation of covalent amide bond and hybridization, respectively. The proposed nanoaptasensor combined the advantages of the in situ formation of PB as a label, the deposition of neatly arranged AuNPs, and the covalent attachment of the capture probe to the surface of the modified electrode. Upon addition of target BPA, the analyte reacted with the aptamer and caused the steric/conformational restrictions on the sensing interface. The formation of BPA-aptamer complex at the electrode surface retarded the interfacial electron transfer reaction of the PB as a probe. Sensitive quantitative detection of BPA was carried out based on the variation of electron transfer resistance which relevant to the formation of BPA- aptamer complex at the modified electrode surface. Under the optimized conditions, the proposed aptasensor exhibited a high sensitivity, wide linearity to BPA and low detection limit. This aptasensor also displayed a satisfying electrochemical performance with good stability, selectivity and reproducibility.

An electrochemical dopamine aptasensor incorporating silver nanoparticle, functionalized carbon nanotubes and graphene oxide for signal amplification.

In this work, immobilization of a dopamine (DA) aptamer was performed at the surface of an amino functionalized silver nanoparticle-carbon nanotube graphene oxide (AgNPs/CNTs/GO) nanocomposite. A 58-mer DA-aptamer was immobilized through the formation of phosphoramidate bonds between the amino group of chitosan and the phosphate group of the aptamer at the 5' end. An AgNPs/CNTs/GO nanocomposite was employed as a highly catalytic label for electrochemical detection of DA based on electrocatalytic activity of the nanocomposite toward hydrogen peroxide (H2O2). Interaction of DA with the aptamer caused conformational changes of the aptamer which, in turn, decreased H2O2 oxidation and reduction peak currents. On the other hand, the presumed folding of the DA-aptamer complexes on the sensing interface inhibited the electrocatalytic activity of AgNPs/CNTs/GO toward H2O2. Sensitive quantitative detection of DA was carried out by monitoring the decrease of differential pulse voltammetric (DPV) responses of AgNPs/CNTs/GO nanocomposite toward H2O2 oxidation. The DPV signal linearly decreased with increased concentration of DA from 3 to 110nmolL(-1) with a detection limit of 700±19.23pmolL(-1). Simple preparation, low operation cost, speed and validity are the decisive factors of this method motivating its application to biosensing investigation.

Design of folding-based impedimetric aptasensor for determination of the nonsteroidal anti-inflammatory drug.

In this work, a novel sensing nanocomposite with highly dispersed platinum nanoparticles (PtNPs) on carbon nanotubes (CNTs) functionalized with polyethyleneimine (PEI) has been developed as a platform for immobilization of diclofenac (DIF) aptamer. PtNPs/PEI/CNTs nanocomposite provided abundant NH2 groups for the immobilization of DIF-specific aptamer. Attachment of DIF-aptamer at the surface of modified electrode was performed through the formation of phosphoramidate bonds between the amino group of PEI and the phosphate group of the aptamer at the 5' end. Nickel hexacyanoferrate (NiHCF) as signal probe was electrodeposited at the surface of nanocomposite by a simple electrodeposition method including two consecutive procedures. Under optimal conditions, DIF was detected by impedance spectroscopy (EIS) quantitatively. By adding DIF as the target at the surface of modified electrode, the aptamer specifically binds to DIF and its end folds into a DIF-binding junction, which leads to retarding the interfacial electron transfer of the probe at the surface of modified electrode. Sensitive quantitative detection of DIF was carried out by monitoring the increase of charge transfer resistance (Rct) by increasing the DIF concentration. The proposed aptasensor showed a good detection range from 10 to 200 nM with an unprecedented detection limit of 2.7 nM.

Design of ultrasensitive bisphenol A-aptamer based on platinum nanoparticles loading to polyethyleneimine-functionalized carbon nanotubes.

Here, a highly sensitive electrochemical aptasensor based on a novel signal amplification strategy for the determination of bisphenol A (BPA) was developed. Construction of the aptasensor began with the deposition of highly dispersed platinum nanoparticles (PtNPs)/acid-oxidized carbon nanotubes (CNTs-COOH) functionalized with polyethyleneimine (PEI) at the surface of glassy carbon (PtNPs/PEI/CNTs-COOH/GC) electrode. After immobilizing the amine-capped capture probe (ssDNA1) through the covalent amide bonds formed by the carboxyl groups on the nanotubes and the amino groups on the oligonucleotides, we employed a designed complementary BPA-aptamer (ssDNA2) as a detection probe to hybridize with the ssDNA1. By adding BPA as a target, the aptamer specifically bound to BPA and its end folded into a BPA-binding junction. Because of steric/conformational restrictions caused by aptamer-BPA complex formation at the surface of modified electrode, the interfacial electron transfer of [Fe(CN)6](3-/4-) as a probe was blocked. Sensitive quantitative detection of BPA was carried out by monitoring the decrease of differential pulse voltammetric responses of [Fe(CN)6](3-/4-) peak current with increasing BPA concentrations. The newly developed aptasensor embraced a number of attractive features such as ease of fabrication, low detection limit, excellent selectivity, good stability and a wide linear range with respect to BPA.

Design and characterization of electrochemical dopamine-aptamer as convenient and integrated sensing platform.

Here, an ultrasensitive label-free electrochemical aptasensor was developed for dopamine (DA) detection. Construction of the aptasensor was carried out by electrodeposition of gold-platinum nanoparticles (Au-PtNPs) on glassy carbon (GC) electrode modified with acid-oxidized carbon nanotubes (CNTs-COOH). A designed complementary amine-capped capture probe (ssDNA1) was immobilized at the surface of PtNPs/CNTs-COOH/GC electrode through the covalent amide bonds formed by the carboxyl groups on the nanotubes and the amino groups on the oligonucleotides. DA-specific aptamer was attached onto the electrode surface through hybridization with the ssDNA1. Methylene blue (MB) was used as an electrochemical indicator that was intercalated into the aptamer through the specific interaction with its guanine bases. In the presence of DA, the interaction between aptamer and DA displaced the MB from the electrode surface, rendering a lowered electrochemical signal attributed to a decreased amount of adsorbed MB. This phenomenon can be applied for DA detection. The peak current of probe (MB) linearly decreased over a DA concentration range of 1-30 nM with a detection limit of 0.22 nM.

Theoretical study of intermolecular interactions in CB4H8-HOX (X=F, Cl, Br, I) complexes.

The molecular aggregation based on intermolecular interactions between CB4H8 and HOX (X=F, Cl, Br and I) with particular emphasis on their bonding characteristics have been investigated using second order Moller-Plesset perturbation (MP2) method with aug-cc-pVDZ basis set. Different kinds of interactions including hydrogen bond (HB; H⋯O, XH; H⋯X), dihydrogen bond (DiHB; H⋯H) and non-classical B-B⋯H interactions were found between CB4H8 and HOX molecules. The structures of complexes have been analyzed using AIM and natural bond orbital methodologies. Good correlations have been found between the interaction energies (SE), the second-order perturbation energies E((2)), and the charge transfer qCT in the studied systems.

Immobilized organoruthenium(II) complexes onto polyethyleneimine-wrapped carbon nanotubes/in situ formed gold nanoparticles as a novel electrochemical sensing platform.

The polyethyleneimine (PEI) wrapped multi-walled carbon nanotubes functionalized with a carboxylic acid group (CNTs-COOH) gold nanoparticle (AuNP)-modified gold (Au) electrode has been utilized as a platform to immobilize organoruthenium(II) complexes (ORC). The surface structure and composition of the sensor were characterized by scanning electron microscopy (SEM). Electrocatalytic reduction of iodate and nitrite on the surface of modified electrode was investigated with cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and hydrodynamic voltammetry methods. The cyclic voltammetric results indicated the ability of AuNPs/PEI/CNT-COOH/ORC modified Au electrode to catalyze the reduction of this compound. AuNPs/PEI/CNTs-COOH nanocomposite combined the advantages of PEI-well dispersed CNTs-COOH and in situ formed AuNPs.

A new three-dimensional coordination polymer of Sr(II) based on dipicolinic acid, with different coordination environments for Sr(II).

A three-dimensional coordination polymer of Sr(II) based on dipicolinic acid (pydcH2) has been synthesized and characterized, namely poly[[diaquabis(µ3-6-carboxypyridine-2-carboxylato)bis(µ4-pyridine-2,6-dicarboxylato)tristrontium(II)] dihydrate], {[Sr3(C7H3NO4)2(C7H4NO4)2(H2O)2]·2H2O}n. The asymmetric unit consists of two unique Sr(II) centres (one of them situated on an inversion centre), two independent pydc(2-) ligands, and one coordinated and one uncoordinated water molecule. The two independent Sr(II) cations are surrounded by water and dipicolinate molecules in distorted square-antiprism and distorted tricapped trigonal prismatic geometries. The dipicolinate ligands adopt µ3- and µ4-bridging modes, linking the alkaline earth metal centres into a three-dimensional coordination framework. One dipicolinate ligand is doubly deprotonated, while the other is singly deprotonated.

Guanidinium hexa-aqua-zinc(II) bis[tris-(3-carb-oxy-pyridine-2-carboxyl-ato)zincate].

In the title mol-ecular salt, (CH(6)N(3))(1.30)[Zn(H(2)O)(6)](0.35)[Zn(C(7)H(4)NO(4))(3)](2), the Zn(II) atom (site symmetry 3) in the anion is coordinated by three N,O-bidentate 3-carb-oxy-pyridine-2-carboxyl-ate monoanions to generate a fac-ZnN(3)O(3) octa-hedral coordination geometry. The guanidinium cation (the C atom has site symmetry 3) and the octa-hedral hexa-aqua-zinc(II) dication (the Zn(2+) cation has site symmetry -3) are occupationally disordered in a 1.30:0.35 ratio. In the crystal, the components are linked by O-H⋯O and N-H⋯O hydrogen bonds to generate infinite (001) sheets. Weak aromatic π-π stacking [centroid-centroid distance = 3.797 (8) Å] is also observed in the crystal.

Bis(guanidinium) tris-(pyridine-2,6-dicarboxyl-ato-κ(3)O(2),N,O(6))zirconate(II) tetra-hydrate.

In the title complex, (CH(6)N(3))(2)[Zr(C(7)H(3)NO(4))(3)]·4H(2)O, the Zr(IV) ion lies on a twofold rotation axes and is coordinated by six O and three N atoms of three tridentate pyridine-2,6-dicarboxyl-ate ligands, forming a slightly distorted tricapped trigonal-prismatic geometry. In the crystal, O-H⋯O and N-H⋯O hydrogen bonds link the components into a three-dimensional network.

2,9-Dimethyl-1,10-phenanthrolin-1-ium (6-carb-oxy-4-hy-droxy-pyridine-2-carboxyl-ato-κO,N,O)(4-hy-droxy-pyridine-2,6-dicarboxyl-ato-κO,N,O)zincate(II) 2.35-hydrate: a proton-transfer compound.

In the title compound, (C(14)H(13)N(2))[Zn(C(7)H(3)NO(5))(C(7)H(4)NO(5))]·2.35H(2)O, the Zn(II) atom is coordinated by two N atoms and four O atoms from the carboxyl-ate groups of the 4-hy-droxy-pyridine-2,6-dicarboxyl-ate and 6-carb-oxy-4-hy-droxy-pyridine-2-carboxyl-ate ligands, forming a distored octa-hedral geometry. In the anion, the two pyridine rings are inclined to one another by 87.75 (13)°. Two types of robust O-H⋯O hydrogen bond synthons, viz. R(2) (2)(16) and R(6) (6)(42), link the anions to form a two-dimensional network parallel to the bc plane. Furthermore, O-H⋯O, N-H⋯O, N-H⋯N and weak C-H⋯O hydrogen bonds connect the two dimensional networks, forming a three-dimensional structure. In the crystal, there are also C-H⋯π and π-π inter-actions [centroid-centroid distances of 3.5554 (18) and 3.7681 (18) Å], and C=O⋯π inter-actions [O⋯centroid distance = 3.117 (2) Å] present. One of the three crystal water molecules shows an occupancy of 0.35.

Acridinium 6-carb-oxy-pyridine-2-carboxyl-ate monohydrate.

The title compound, C(13)H(10)N(+)·C(7)H(4)NO(4) (-)·H(2)O or (acrH)(+)(pydcH)(-)·H(2)O, is a monohydrate of acridinium cations and a mono-deprotonated pyridine-2,6-dicarb-oxy-lic acid. The structure contains a range of non-covalent inter-actions, such as O-H⋯O, O-H⋯N and N-H⋯O hydrogen bonds, as well as π-π stacking [range of centroid-centroid distances = 3.4783 (5)-3.8059 (5) Å]. The N-H⋯O hydrogen bond between the donor acridinium cation and the carboxyl-ate acceptor is particularly strong. The average separation between the π-stacked acridinium planes is 3.42 (3) Å.

Bis(9-amino-acridinium) bis-(pyridine-2,6-dicarboxyl-ato-κO,N,O)nickelate(II) trihydrate.

The title compound, (C(13)H(11)N(2))(2)[Ni(C(7)H(3)NO(4))(2)]·3H(2)O, consists of a mononuclear anionic complex, two 9-amino-acridinium cations and three uncoordinated water mol-ecules. Two pyridine-2,6-dicarboxyl-ate (pydc) ligands are bound to the Ni(II) ion, giving an NiN(2)O(4) bonded set. The coordination geometry around the Ni(II) atom is distorted octa-hedral. There are two types of robust O-H⋯O hydrogen-bond synthons, namely R(6) (6)(24) and R(2) (4)(8), which link the complex anions and water mol-ecules to each other. N-H⋯O hydrogen bonds connect the stacks of anions and cations in the structure. Other inter-molecular inter-actions, including weak C-H⋯O hydrogen bonds, π-π [shortest centroid-centroid distance = 3.336 (7) Å] and C-O⋯π [O⋯centroid distance = 3.562 (10) Å] inter-actions, connect the various components.

Bis(9-amino-acridinium) bis-(pyridine-2,6-dicarboxyl-ato)cuprate(II) trihydrate.

The asymmetric unit of the title compound, (C(13)H(11)N(2))(2)[Cu(C(7)H(3)NO(4))(2)]·3H(2)O, consists of one [Cu(pydc)(2)](2-) dianion (pydc is pyridine-2,6-dicarboxyl-ate), two 9-amino-acridinum monocations and three uncoordinated water mol-ecules. The Cu(II) atom is coordinated by two pydc dianions acting as tridentate ligands, and forming five-membered chelate rings with copper(II) as the central atom. The Cu(II) atom is surrounded by four O atoms in the equatorial plane and two pyridine N atoms in axial positions, resulting in a distorted octa-hedral coordination geometry. In the crystal, there are two types of O-H⋯O and N-H⋯O hydrogen-bonding synthons linking the anionic and cationic fragments and the water mol-ecules, namely R(4) (4)(16), and R(4) (2)(8). There are also weak C-H⋯O hydrogen bonds, π-π stacking inter-actions [the shortest centroid-centroid distance is 3.350 (2) Å], and a C-O⋯π inter-action [O⋯centroid distance = 3.564 (2) Å], which connect the various components into a three-dimensional network.

2,9-Dimethyl-1,10-phenanthrolin-1-ium (6-carb-oxy-4-hy-droxy-pyridine-2-carboxyl-ato-κO,N,O)(4-hy-droxy-pyridine-2,6-dicarboxyl-ato-κO,N,O)nickelate(II) 2.35-hydrate: a proton-transfer compound.

The title proton-transfer compound, (C(14)H(13)N(2))[Ni(C(7)H(3)NO(5))(C(7)H(4)NO(5))]·2.35H(2)O, consists of an [Ni(hypydc)(hypydcH)](-) anion, a dmpH(+) cation and 2.35 uncoordinated water mol-ecules (where hypydcH(2) = 4-hy-droxy-pyridine-2,6-dicarb-oxy-lic acid and dmp = 2,9-dimethyl-1,10-phenanthroline). The Ni(II) atom is coordinated by two N atoms and four O atoms from the carboxyl-ate groups of the (hypydc)(2-) and (hypydcH)(-) ligands, forming a distorted octa-hedral environment. In the anion, the two pyridine rings are inclined to one another by 89.24 (10)°. In the crystal, cations are linked via O-H⋯O hydrogen bonds forming dimers, graph-set [R(2) (2)(16)], centered about inversion centers. These dimers are further linked by other cation O-H⋯O hydrogen bonds, graph-set [R(6) (6)(42)], forming a two-dimensional network in (011). Additional inter-molecular O-H⋯O, N-H⋯O, N-H⋯N, and weak C-H⋯O hydrogen bonds, and π-π inter-actions [shortest centroid-centroid distance = 3.5442 (14) Å], connect the two dimensional networks, forming a three-dimensional arrangement. The H atoms of one of the methyl groups are disordered over two sites with equal occupancy.

Acridinium 3-carb-oxy-pyrazine-2-carboxyl-ate.

The title ion pair, C(13)H(10)N(+)·C(6)H(3)N(2)O(4) (-), contains a protonated acridine cation and a 3-carb-oxy-pyrazine-2-carboxyl-ate monoanion, which are linked together through O-H⋯O, N-H⋯O and weak C-H⋯O hydrogen bonds. These hydrogen bonds generate a C(10) chain graph-set motif. The crystal structure is further stabilized by extensive π-π stacking inter-actions between nearly parallel [dihedral angle = 1.21(2)°] acridine systems. The shortest distance between the centroids of the six-membered rings within the cations is 3.6315 (8) Å. In addition, C-H⋯π edge-to-face inter-actions are present.