A highly selective and sensitive fluorescence chemosensor based on optically active polybinaphthyls for Hg

The chiral polymer was synthesized by the polymerization of 4,7-diethynylbenzo[2,1,3]-thiadiazole (M-1) with (R)-6,6′-dibutyl-3,3′-diiodo-2,2′-bis(diethylaminoethoxy)-1,1′-binaphthyl (R-M-1) via Pd-catalyzed Sonogashira reaction. The chiral polymer has orange fluorescence due to the extended π-electronic structure between binaphthyl unit and benzo[2,1,3]thiadiazole (BT) group via ethynyl bridge. The responsive optical properties of the polymer on various metal ions were investigated by fluorescence spectra. The fluorescence of the chiral polymer can produce the pronounced enhancement as high as 1.8-fold upon addition of 1:2 molar ratio of Hg²⁺. Compared with other cations, such as K⁺, Mg²⁺, Pb²⁺, Co²⁺, Ni²⁺, Ag⁺, Cd²⁺, Cu²⁺, Zn²⁺, Mn²⁺ and Fe³⁺, Hg²⁺ can produce the pronounced fluorescence response of the polymer. The result indicates this kind of chiral polybinaphthyls incorporating diethylamino and benzo[2,1,3]thiadiazole (BT) moieties as receptors exhibits highly sensitive and selective behavior for Hg²⁺ detection.     

Ferrocene clicked polypyrrole derivatives: effect of spacer group on electrochemical properties and post-polymerization functionalization

In this study, novel ferrocene-functionalized N-alkyl substituted pyrrole derivatives, namely 4-ferrocenyl-1-[3-(pyrrol-1-yl)propyl]-1H-1,2,3-triazole (Py3Fc), 4-ferrocenyl-1-[4-(pyrrol-1-yl)butyl]-1H-1,2,3-triazole (Py4Fc), and 4-ferrocenyl-1-[6-(pyrrol-1-yl)hexyl]-1H-1,2,3-triazole (Py6Fc), were synthesized via click reaction and the monomers were characterized by ¹H NMR, ¹³C NMR, FTIR, and HRMS techniques. Redox properties of the monomers were investigated by cyclic voltammetry (CV) studies. Contrary to general literature, both Py4Fc and Py6Fc were electrochemically polymerized without loss in redox activity of ferrocene group. Moreover, click chemistry was utilized in post-polymerization functionalization. For this purpose, three azide-containing polypyrroles, P(Py3N₃), P(Py4N₃), and P(Py6N₃) were electrochemically synthesized and subjected to click reaction in the presence of ethynylferrocene. CV studies of the post-polymerization functionalized polymers revealed quasi-reversible waves, while only P(Py6-post-Fc) showed the characteristic redox behavior of both polypyrrole and ferrocene. Thus, in this study preparation of a conducting homopolymers of pyrrole having covalently bonded ferrocene units was demonstrated and effect of spacer group is investigated.     

Biparental Endowment of Endogenous Defensive Alkaloids in <Emphasis Type="Italic">Epilachna paenulata</Emphasis>

Coccinellid beetles contain a variety of defensive alkaloids that render them unpalatable to predators. Epilachna paenulata (Coleoptera: Coccinellidae) is a South American ladybird beetle that feeds on plants of the Cucurbitaceae family. The defensive chemistry of E. paenulata has been characterized as a mixture of systemic piperidine, homotropane, and pyrrolidine alkaloids. Whole body extracts of adult beetles contain four major alkaloids: 2-(2′-oxopropyl)-6-methylpiperidine (1); 1-(6-methyl-2,3,4,5-tetrahydro-pyridin-2-yl)-propan-2-one (2); 1-methyl-9-azabicyclo[3.3.1]nonan-3-one (3); and 1-(2″-hydroxyethyl)-2-(12′-aminotridecyl)-pyrrolidine (4). Comparative studies of the defensive chemistry of eggs, larvae, pupae, and adults showed differences in alkaloid composition and concentration among life stages. While adults contained mainly the homotropane 1-methyl-9-azabicyclo[3.3.1]nonan-3-one (3), eggs showed the highest concentration of the piperidine 2-(2′-oxopropyl)-6-methylpiperidine (1). We studied the origin of this alkaloid in the eggs by feeding newly emerged, virgin adult beetles with [2-¹³C]-labeled acetate, and by performing crosses between ¹³C-fed and unlabeled males and females. GC-MS analysis of alkaloids from ¹³C-fed males and females showed high incorporation of ¹³C into the alkaloids, as evidenced from a 20–30% increase of isotopic peaks in diagnostic fragment ions, confirming the expected endogenous origin of these alkaloids. In addition, analyses of eggs from different crosses showed that labeled alkaloids from both parents are incorporated into eggs, indicating that E. paenulata males transfer alkaloids to the females at mating. Biparental endowment of chemical defenses into eggs has been shown previously in insects that acquire defensive compounds from dietary sources. To our knowledge, this is the first report of biparental egg endowment of endogenous defenses. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Voltammetric characterization of selective potassium ion transfer across micro-water/1,2-dichloroethane interface facilitated by a novel calix[4]arene derivative

In this study, transfer reactions of alkali and alkaline-earth metal ions across a micro-water/1,2-dichloroethane (1,2-DCE) interface facilitated by a novel calix[4]arene derivative, 5,11,17,23-tetra-tert-butyl-25,27-bis(2′amino-methylpyridine)-26,28-dihydroxy calix[4]arene (APHC4), were investigated by cyclic and differential pulse voltammetry techniques. Well-defined voltammetric behavior was obtained only for K⁺ ion among the used metal ions. The electrochemical data were used to determine the stoichiometry and the appropriate association constant of the occurring complex between K⁺ ion and APHC4. The obtained steady-state voltammograms indicated that the facilitated transfer process occurs with a TIC/TID mechanism according to 1:1 stoichiometry. The logarithm of the association constant () of K(APHC4)⁺ complex in the DCE phase was calculated to be 6.32. Also, the availability of the facilitated transfer for the design of an amperometric screening sensor for K⁺ ion was evaluated in the range of 50–500 μmol dm⁻³.     

Polymerization of cyclic monomers 9. Synthesis and radical polymerization of spirocyclic 2-vinylcyclopropanes

Summary 6,6-Diethyl- (1a) and 6-methyl-6-propyl-5,7-dioxa-4,8-dioxo-1-vinylspiro[2.5]octane (1b) were synthesized by the acetalization of 2-vinylcyclopropane-1,1-dicarboxylic acid with 2- or 3-pentanone. The new monomers were characterized by IR, ¹H NMR and ¹³C NMR spectroscopy. The radical polymerization of the monomers 1a and 1b, in addition of 6,6-methyl-5,7-dioxa-4,8-dioxo-1-vinylspiro[2.5]octane (1c) and (exo/endo)-7-ethoxycarbonyl-2-oxo-7-vinyl-bicyclo[4.1.0]heptane (1d), was carried out in bulk with 2,2`-azoisobutyronitrile (AIBN) as the initiator. The polymer yield with 1d was only low. The polymerization of the monomers 1a and 1c resulted in cross-linked polymers, whereas in case of the polymerization of monomer 1b soluble polymers in a high yield were obtained. Received: 17 February 1999/Revised version: 7 July 1999/Accepted: 7 July 1999     

Effect of Coordination Modes of HL Ligand on the Molecular Architecture of Its Transition Metal Complexes (HL = 5-Methyl-2-Phenyl-4-[(2-<Emphasis Type="Italic">o</Emphasis>-Tolylamino)-Phenylmethylene]pyrazol-3(2H)-one)

Abstract  Two Ag⁺ complexes [Ag(HL)₂(PF₆)] (1) and [(AgL) _n  · n(CH₂Cl₂) · n(0.5H₂O)] (2) (HL = 5-methyl-2-phenyl-4-[(2-o-tolylamino)-phenylmethylene]pyrazol-3(2H)-one) were synthesized and structurally characterized by EA analysis, IR spectra and X-ray crystallography. The result shows that two expected coordination modes (Modes I and III in Scheme 1) of the HL ligand, can be observed in its Ag⁺ complexes, while not in other transition metal ions (Ni²⁺, Co²⁺ or Cu²⁺) complexes whether deprotonation or not for the HL ligand. Graphical Abstract  Three possible coordination modes (Modes I, II or III in Scheme 1) of the selected HL (HL = 5-methyl-2-phenyl-4-[(2-o-tolylamino)-phenylmethylene]pyrazol-3(2H)-one) ligand, can be adopted, in which Modes I and III can be observed in its two Ag⁺ complexes [Ag(HL)₂(PF₆)](1) and [(AgL) _n  · n(CH₂Cl₂) · n(0.5H₂O)] (2), while Mode II just observed in its transition metal ions (Cu²⁺, Ni²⁺, or Co²⁺) complexes, resulting from the deprotonatd form of the HL ligand and the coordination characters of transition metal ions.      

Solution Studies of Tris(2-aminoethyl)amine with Metal Ions of Biological Interest: The Electroanalytical Determination of the Phosphate Triester Hydrolysis

Complex formation of tris(2-aminoethyl)amine, Tren, with both Zn(II) and Cu(II) ions in aqueous solution was investigated spectroscopically by using ¹H NMR and UV-visible titrations as well as electrochemically by using cyclic voltammetry. Analysis of the titration data indicated that the aqua complexes [(Tren)Zn(OH₂)](ClO₄)₂ 1 and [(Tren)Cu(OH₂)](ClO₄)₂ 2 deprotonate at pH = 10.6 and 9.7, forming the dinuclear bridged hydroxo species {[(Tren)Zn]₂(μ-OH)}³⁺ 3 and {[(Tren)Cu]₂(μ-OH)}³⁺ 4, respectively. The catalytic hydrolysis of the activated phosphate ester tris(p-nitrophenyl)phosphate (TNPP) by using these model complexes was examined and the released phenolate anions were determined by using spectroscopic and electroanalytical techniques.     

Design,synthesis, antibacterial and antifungal activity of novel spiro-isoxazolyl bis-[5,5′]thiazolidin-4-ones and spiro-isoxazolyl thiazolidin-4-one-[5,5′]-1,2-4 oxdiazolines

The synthesis of novel isoxazolyl 1,6-dithia-4,9-diazaspiro[4.4]nonane-3,8-diones (4a–h) and isoxazolyl 1-oxa-6-thia-2,4,9-triazaspiro[4.4]non-2-ene-8-ones (5a–h) analogs is described. Reaction of N-1-\{3-methyl-5-[(E)-2-aryl-1-ethenyl]-4-isoxazolyl}-2-chloroacetamide (2) with aryl isothiocyanates yielded 3,3-methyl-5-[(E)-2-aryl-1-ethenyl]-4-isoxazolyl-2-(arylimino)-1,3-thiazolan-4-ones (3). Cyclocondensation of 3 with mercaptoacetic acid furnished novel isoxazolyl-1,6-dithia-4,9-diazaspiro[4.4]nonane-3,8-diones (4a–h). Cycloaddition of 3 with benzonitrile oxides afforded novel isoxazolyl 1-oxa-6-thia-2,4,9-triazaspiro[4.4]non-2-ene-8-ones (5a–h). Compounds 4a–h and 5a–h showed significant biological activity against all the standard strains.     

Novel conjugated alternating copolymer based on 2,7-carbazole and 2,1,3-benzoselenadiazole

A novel conjugated alternating copolymer (PCzDBSe) based on N-9′-heptadecanyl-2,7-carbazole and 5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzoselenadiazole) was synthesized by Suzuki polycondensation. The polymer reveals excellent thermal stabilities with the decomposition temperature (5% weight loss) of 390 °C and the glass-transition temperature of 140 °C. The absorption peaks of the polymer are located at 412 and 626 nm, respectively, while the absorption onset is extended to 716 nm, which is 56 nm red-shifted as compared with its analogue, poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT). The HOMO and LUMO levels of the polymer were estimated to be −5.28 and −3.55 eV, respectively, with an optical bandgap of 1.73 eV. The hole mobility of PCzDBSe as deduced from a solution-processed organic field effect transistor (OFET) was found to be 3.9 × 10⁻⁴ cm² V⁻¹ s⁻¹. Polymer solar cells (PSCs) based on the blends of PCzDBSe and [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM) with a weight ratio of 1:4 were fabricated. Under AM 1.5 (AM, air mass), 100 mW cm⁻² illumination, the devices were found to have an open-circuit (V_oc) of 0.75 V, a short-circuit current density (J_sc) of 7.23 mA cm⁻², a fill factor (FF) of 45% and a power conversion efficiency (PCE) of 2.58%. The primary results indicate that 5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzoselenadiazole) is a promising unit for low bandgap polymer for polymer solar cells.     

Synthesis and characterization of poly(1-sila-cis-pent-3-enes) substituted with pendant pyridinyl groups

Poly[1-methyl-1-[3-(3-pyridinyl)propyl]-1-sila-cis-pent-3-ene], poly[1-phenyl-1-[3-(3-pyridinyl)propyl)-1-sila-cis-pent-3-ene], and poly[1-phenyl-1-(4-pyridinyl)-1-sila-cis-pent-3-ene] were synthesized by the anionic ring-opening polymerization of 1-methyl-1-[3-(3-pyridinyl)propyl]-1-silacyclopent-3-ene, 1-phenyl-1-[3-(3-pyridinyl)propyl]-1-silacyclopent-3-ene, and 1-phenyl-1-(4-pyridinyl)-1-silacyclopent-3-ene, respectively. These are the first polycarbosilanes which contain heterocyclic pyridine units as side-chain substituents. These polymers were characterized by¹H,¹³C, and²⁹Si NMR as well as by IR and UV spectroscopy. The molecular weight distributions were determined by gel permeation chromatography, glass transition temperatures, by differential seanning calorimetry: (DSC) and thermal behavior, by thermogravimetric analysis. (TGA).     

Über neue Pyrazolverbindungen. IV Darstellung und Cyclisierungsverhalten einiger akzeptorsubstituierter N-(Pyrazol-3-yl)-thioharnstoffe

New Pyrazol Derivatives. IV. Preparation and Cyclization of Some Acceptor-Substituted N-(Pyrazol-3-yl)-thioureas . 3-Aminopyrazol-4-carboxylic acid derivatives ( 1 , 2 ) were transformed by reaction with different isothiocyanates R²NCS to N-(pyrazol-3-yl)-N^. -substituted thioureas ( 5 , 6 ). Ethyl 3-amino-1-benzylpyrazol-4-carboxylate reacts with CSCl₂ to form ethyl 1-benzyl-3-isothiocyanatopyrazol-4-carboxylate ( 3 ) which yields with amines the corresponding N-(pyrazol-3-yl)-N^. -substituted thioureas ( 5 ). As a byproduct in the reaction with CSCl₂ N,N^. -di-(pyrazol-3-yl)-thiourea ( 4 ) is formed. With hydrazine or phenylhydrazine N-(pyrazol-3-yl)-thiosemicarbazides ( 7a , b ) are obtained. The thioureas ( 5 , 6 ) can be cyclized in basic solution to 4,5,6,7-tetrahydropyrazolo[3,4-d]pyrimidin-4-on-6-thiones ( 8 ) which on alkylation form 6-alkylthio-4,5-dihydropyrazolo[3,4-d]pyrimidin-4-ones ( 9 ). Methyl-N-(pyrazol-3-yl)-N^.-benzoylisothiourea ( 10 ) reacts with ethylamine to form N-benzoyl-N^. -ethyl-N^‥-(pyrazol-3-yl)-guanidine derivative ( 11 ) which on treatment with NaH in dimethylformamide yields 6-benzoylamino-5-ethyl-4,5-dihydropyrazolo[3,4-d]pyrimidin-4-one ( 12 ). By treatment with sulfuric acid the N-(pyrazol-3-yl)-thiourea derivatives ( 5 , 6 ) form new 6-amino substituted pyrazolo[3,4-d][1,3]thiazin-4-ones ( 13 ).     

Allgemeine Synthesen und rationelle Strukturparameter isomerer Derivate von [3,4]-kondensierten Pyrazolen

General Syntheses and Rational Parameters for Structural Assignment of Isomeric Derivatives of [3,4]-fused Pyrazoles 4 isomeric 1- or 2-methyl-, and 1- or 2-benzyl-pyrazolo[3,4-b]pyridones, i.e. the 4-oxo-types 17a, b or 11a, b and the 6-oxo-types 16a, b or 10a, b , are synthesized unambiguously. Cyclisation of 1-substituted 3- or 5-(1-methyl-2-ethoxycarbonyl-vinylamino)-pyrazoles 9a, b or. 15a, b , which were synthesized from 1-substituted 3- or 5-amino-pyrazoles and ethyl acetoacetate yields 11a, b or 17a, b in downtherm, but 10a, b or 16a, b in presence of acidic catalysts. The acidic cyclisation is preceded by a new rearrangement of 9 or 15 into 1- substituted 3- 27 or 5-amino-4-(1-methyl-2-ethoxycarbonyl-vinyl)-pyrazoles 30 ; mechanism and concurring reactions are explained. Because of their higher electron densities at C-4 it is easier to cyclise derivatives of 5-amino-pyrazoles compared to 3-amino-pyrazoles. All isomeric 1- or 2-substituted 4(6)-chloro-6(4)-methyl-pyrazolo-[3,4-b]pyridines are formed with POCl₃ from the corresponding oxo-compounds. The position of a substituent at N-1 or N-2 of [3,4]-fused pyrazoles can be assigned using the significant ¹H-n.m.r.-parameter Δ = δ — − δ_HMPT (conc. HC—3). If solvent influences are considered, δ(C  O) is a useful ¹³C-n.m.r.-parameter to distinguish the 4-oxo-types ( 11a, b; 17a, b ) from the 6-oxo-types ( 10a, b; 16a, b ) of pyrazolo[3,4-b]pyridones. Further own and lit. dates conc. structural assignment (n.m.r., i.r., u.v.) are discussed critically.     

Evaluation of 5H-Thiazolo[3,2-α]pyrimidin-5-ones as Potential GluN2A PET Tracers

We describe here our efforts to develop a PET tracer for imaging GluN2A-containing NMDA receptors, based on a 5H-thiazolo[3,2-α]pyrimidin-5-one scaffold. The metabolic stability and overall properties could be optimized satisfactorily, although binding affinities remained a limiting factor for in vivo imaging. We nevertheless identified 7-(((2-fluoroethyl)(3-fluorophenyl)amino)-methyl)-3-(2-(hydroxymethyl)cyclopropyl)-2-methyl-5H-thiazolo-[3,2-α]pyrimidin-5-one ([¹⁸F] 7b ) as a radioligand providing good-quality images in autoradiographic studies, as well as a tritiated derivative, 2-(7-(((2-fluoroethyl)(4-fluorophenyl)amino)methyl)-2-methyl-5-oxo-5H-thiazolo[3,2-α]pyrimidin-3-yl)cyclopropane-1-carbonitrile ([³H₂] 15b ), which was used for the successful development of a radioligand binding assay. These are valuable new tools for the study of GluN2A-containing NMDA receptors, and for the optimization of allosteric modulators binding to the pharmacophore located at the dimer interface of the GluN1-GluN2A ligand-binding domain.     

A highly selective fluorescent sensor for Hg based on the water-soluble poly(p-phenyleneethynylene)

The conjugated polymer P-1 could be synthesized by the polymerization of 4,7-diethynyl-benzo[2,1,3]thiadiazole (M-1) and 1,4-bis[3′-(N,N-diethylamino)-1′-oxapropyl]-2,5-diiodobenzene (M-2) via Pd-catalyzed Sonogashira reaction. The water-soluble conjugated polyelectrolyte P-2 could be obtained by the reaction of P-1 with ethyl bromide. Both P-1 and P-2 can emit orange fluorescence. The responsive optical properties of P-1 and P-2 on Hg²⁺ were investigated by fluorescence spectra. Hg²⁺ can lead to nearly complete fluorescence quenching of P-1. On the contrary, Hg²⁺ can show the most pronounced fluorescence enhancement response of P-2 in aqueous solution without interference from those coexistent ions, such as K⁺, Mg²⁺, Pb²⁺, Co²⁺, Ni²⁺, Ag⁺, Cd²⁺, Cu²⁺, Fe³⁺ and Zn²⁺. The results also exhibit that this kind of water-soluble conjugated polyelectrolyte can be used as a highly sensitive and selective fluorescence sensor for Hg²⁺ detection in water.     

Synthesis,Structural Characterization,Spectroscopic Properties,and Theoretical Investigations of Aminoacridine Derivatives

Synthesis of four N-(heterocyclic)-9-aminoacridine derivatives was investigated. The synthesized compounds, N-thiazolyl-9-aminoacridine (AC1), N-(1,3,4-thiadiazolyl)-9-aminoacridine (AC2), N-(5-methyl-1,3,4-thiadiazolyl)-9-aminoacridine (AC3), and N-(5-phenyl-1,3,4-thiadiazolyl)-9-aminoacridine (AC4) were characterized by FT-IR, ¹H NMR, mass-spectral, and elemental analysis. Amine-imine tautomerism was suggested by density functional theory (DFT) calculations. The optimized structures were obtained using B3LYP/6–311++G(d,p) level of theory. The UV–Vis absorption spectra were measured in various organic solvents. The synthesized compounds AC1–AC4 exhibit absorption spectra characteristic of typical donor–acceptor compounds. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) analysis have been used to explain the internal charge transfer (ICT) phenomena within the molecules. Also, simulated UV spectra were calculated using TD-DFT (B3LYP/6–311++G(d,p) and the results were compared with the experimental values.     

Polymer Complexes XLIV. Potentiometric and Thermodynamic Studies of Monomeric and Polymeric Complexes Containing 2-Acrylamido-2-methylpropanesulfonic Acid

Proton-monomeric ligand dissociation and metal-monomeric ligand stability constants of 2-acrylamido-2-methyl-1-propanesulfonic acid with several metal ions were determined potentiometrically in water and 0.1 M KCl. In the presence of 2,2-azobisisobutyronitrile as an initiator, the dissociation and stability constants of AMS were determined for the polymeric form (PAMS). The influence of temperature on the dissociation of AMS and the stability constants of their complexes in monomeric and polymeric forms were studied. The vinyl group in the monomeric form decreases the electron density and hence reduces the N–H bond strength (lower pK^H ₂ value). The stability constants of the metal complexes in the polymeric form (better complexing agent) are larger than those of the monomeric form.     

Extreme sensitivity of grandisal to acids

Attempted purification of synthetic racemic grandisal1 by silica gel chromatography resulted in severe decomposition. The nature of this reaction was studied on silica gel and in an ether solution ofp-toluenesulfonic acid. The same products resulted from both reaction systems, although in different ratios. Five racemic, rearrangement products were isolated by preparative GC and identified as follows: (1RS, 3SR, 6RS)-1-methyl-5-methylenebicyclo[4.2.0]octan-3-ol (4); (1RS, 3RS, 6RS)-1-methyl-5-methylenebicyclo[4.2.0]octan-3-ol (5); (1RS,3RS,6RS)-1,5-dimethylbicyclo[4.2.0]oct-4-en-3-ol (6); (1RS,3SR,6RS)-1,5-dimethylbicyclo[4.2.0]oct-4-en-3-ol(7); and 3-methyl-7-methylenecyclooct-3-en-l-ol (8). The stereochemical assignments are based on our proposed mechanism, which also accounts for all products observed. The racemic bicyclic enone (3) was a by-product of grandisol (2) oxidation.     

Facile synthesis of novel 6-methyl-5-phenyl-2-sulfido-1,2,3,5-tetrahydro-4H[1,2] oxazolo[4′,5′:5,6]pyrano[2,3-d][1,3,2]diazaphosphinines

A number of 6-methyl-5-phenyl-2-sulfido-1,2,3,5-tetrahydro-4H[1,2]oxazolo[4′,5′: 5,6]pyrano[2,3-d][1,3,2]diazaphosphinines 4–11 were synthesized via an interaction of tetraphosphorus decasulfide and Lawesson’s reagent under different conditions with 6-amino-3-methyl-4-phenyl-4H-pyrano[3,2-d][1,2]oxazole-5-carbonitrile (3). The reaction mechanisms for these products were discussed. Structures of the newly synthesized products were established on the basis of elemental analysis and spectral data.     

A novel (3,4,8)-connected 3D topology framework based on [Gd2(bpdc)3(H2O)3] second building units

A new 3D coordination polymer {[Gd₂(bpdc)₃(H₂O)₃]·H₂O}_n(1) has been isolated from the reaction of 2,2′-bipyridine-4,4′-dicarboxylic acid (H₂bpdc) and Gd(III) salts under hydrothermal conditions. Single-crystal X-ray diffraction study shows that compound 1 is constructed from Gd₂-based second building units (SBUs) [Gd₂(bpdc)₃(H₂O)₃] and displays a 3D (3,4,8)-connected net with (4²·6)(3²·4²·5²)(3²·4⁵·5⁴·6¹¹·7⁶) topology. A thermogravimetric analysis of 1 shows a high thermal stability. The magnetic behavior of 1 reveals a weak antiferromagnetic interaction between Gd(III) ions.     

Stable, colourless and water-soluble electron-transfer mediators used in enzyme electrochemistry

Electron-transfer mediators are needed to transport charge between electrodes and enzymes, as enzymes hardly react on conventional electrode surfaces. Several complex ions were tested for their stability, absorbance and ability to work as electron-transfer mediators. A set of five stable mediators covering the potential range from 0 mV to +800 mV vs. SHE was established: [Fe-DCTA]^0/1+ (DCTA is 1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid), [Co-terpyridine₂]^2+/3+, [Fe(CN)₆]^4−/3−, [W(CN)₈]^4−/3− and [Mo(CN)₈]^4−/3−. These mediators are water-soluble, pH-independent and able to transfer one electron at a time. This set offers promising mediator candidates whenever indirect electrochemistry is needed, as is not restricted to any particular enzyme. It is especially useful for redox titrations and other enzyme research, where colourlessness is required. As all charge is consumed by the desired redox reactions, and not by degradation reactions, even amperometric and coulometric titrations are possible.