A series of silver coordination polymers constructed from flexible bis(benzimidazole) ligands and different carboxylates

In this article, eight new silver coordination polymers constructed from two structurally related ligands, 1,1′-(1,4-butanediyl)bis(2-methylbenzimidazole) (bbmb) and 1,1′-(1,4-butanediyl)bis(2-ethylbenzimedazole) (bbeb), have been synthesized: [Ag(L1)(bbmb)]·C₂H₅OH·H₂O (1), [Ag(L2)(bbmb)]·C₂H₅OH (2), [Ag(L3)(bbmb)] (3), [Ag₂(L4)(bbmb)₂]·C₂H₅OH (4), [Ag(L2)(bbeb)]·C₂H₅OH (5), [Ag(L5)(bbeb)]·CH₃OH (6), [Ag₂(L6)₂(bbeb)]·H₂O (7), and [Ag₂(L7)(bbeb)₂]·4(H₂O) (8), where L1 = benzoate anion, L2 = p-methoxybenzoate anion, L3 = 2-amino-benzoate anion, L4 = oxalate anion, L5 = cinnamate ainon, L6 = 3-amino-benzoate anion, and L7 = fumaric anion. In 1-3, 5 and 6, the bidentate N-donor ligands (bbmb and bbeb) in trans conformations bridge neighboring silver centers to form 1D single chain structures. The carboxylate anions are attached on both sides of the chains. Moreover, 1 and 3 are extended into 2D layers, while 2 and 6 are extended into 3D frameworks through π-π interactions. In 4, the bbmb ligands bridge adjacent Ag(I) centers to form -Ag-bbmb-Ag- chains, which are further connected by L4 anions to form a 2D layer. The resulting layers are extended into 3D frameworks through strong π-π interactions. In 7, the N-donor ligands (bbeb) in trans conformations bridge two silver centers to generate a [Ag₂(bbeb)]²⁺ unit. The adjacent [Ag₂(bbeb)]²⁺ units are further connected via the L6 anions to form a 1D ladder chain. Moreover, the structure of compound 7 is extended into a 3D framework through hydrogen bonding and π-π interactions. In 8, two Ag(I) cations are bridged by two bbeb ligands in cis conformations to form a [Ag₂(bbeb)₂]²⁺ ring, which are further linked by L7 anions to generate a 1D string chain. Furthermore, the hydrogen bonding and π-π interactions link L7 anions to form a 2D supramolecular sheet. Additionally, the luminescent properties of these compounds were also studied.     

Spectroscopic, thermal and structural studies of cocrystal of 2,2′-diamino-4,4′-bis(1,3-thiazole) with 4,4′-bipyridine, 1,2-bis(4-pyridyl)ethylene and 1,3-bis(4-pyridyl)propane

Three new cocrystals based upon 2,2′-diamino-4,4′-bis(1,3-thiazole) (DABTZ) with 4,4′-bipyridine (4,4′-bipy), 1,2-bis(4-pyridyl)ethylene (bpe) and 1,3-bis(4-pyridyl)propane (bpp): [(DABTZ) (4,4′-bipy)], [(DABTZ) (bpe)] and [(DABTZ) (bpp)] have been synthesized and characterized by elemental analysis, IR-, ¹H NMR-, ¹³C NMR spectroscopy and studied by thermal and X-ray crystallography. Self-assembly of these compounds in the solid state is likely caused by both hydrogen bonding, and π-π stacking.     

Study on the new fluorescence enhancement system of Tb-1,10-bis(2′-carboxylphenyl)-1,4,7,10-tetraoxadecane in silver chloride collosol and its analytical application

A new salicylic-based open-chain crown ether ligand, 1,10-bis(2′-carboxylphenyl)-1,4,7,10-tetraoxadecane (BCPTD) was synthesized. Solutions of its complex with Tb³⁺ can emit the intrinsic fluorescence of Tb³⁺. The fluorescence intensity of the complex in KCl solution was enhanced by the addition of silver(I), leading to a new fluorescence enhancement phenomenon. The spectrofluorimetric determination of traces of silver(I) based on the above phenomenon was carried out. The excitation and emission wavelengths are 298 and 545 nm, respectively. Under optimal conditions, the differential value of fluorescence intensity in the absence and presence of Ag⁺ was proportional to the concentration of silver(I) in the range 0.5-20 μg ml⁻¹. The method was applied to the determination of silver(I) in a standard ore sample. The analytical performance is investigated in detail by using common aromatic carboxylic acids or synthetic analogues of BCPTD as ligands to replace BCPTD. It was found that Tb-aromatic acid complexes did not result in fluorescence enhancement of Tb³⁺ in AgCl collosol. The phenomenon was only observed in Tb(III) with BCPTD or its open-chain crown ether analogues solutions.In addition, the enhancement of the fluorescence intensity of terbium(III) in these complexes depends on the extent of formation of the AgCl collosol.     

Synthesis and the crystal structures of N-(2-nitroxyethyl)isonicotinamide and its complexes with PdCl2 and PtCl2 as potential antitumor medicines

Previously unknown N-(2-nitroxyethyl)isonicotinamide was synthesized by the reaction of isonicotinoyl chloride with 2-nitroxyethylamine and was used as a ligand in the reactions with PdCl₂ and PtCl₂ to prepare new complexes, viz., trans-bis[(2-nitroxyethyl)isonicotinamide-N]dichloropalladium(ii) and cis-bis[(2-nitroxyethyl)isonicotinamide-N]dichloroplatinum(ii), respectively. The structures of the ligand and the resulting complexes were established by X-ray diffraction analysis.     

Synthesis and separation of the atropisomers of 2-(5-benzo[b]fluorenyl)-2′-hydroxy-1,1′-binaphthyl and related compounds

Several syn and anti atropisomers of 2-(5-benzo[b]fluorenyl)-2′-hydroxy-1,1′-binaphthyl and related compounds were synthesized from 1,1′-binaphthyl-2,2′-diol (BINOL). It was possible to separate the syn and anti atropisomers by silica gel column chromatography. The syn atropisomers are potential hetero-bidentate ligands for complex formation with metals. By starting from enantiomerically pure (R)-(+)-BINOL and (S)-(−)-BINOL, four optically active syn atropisomers and two anti atropisomers with high enantiomeric purity were obtained. The structures of two syn atropisomers and one anti atropisomer were established by X-ray structure analyses.     

Dinuclear copper(II) perchlorate complexes with 6-(benzylamino)purine derivatives: Synthesis,X-ray structure,magnetism and antiradical activity

The reactions of Cu(ClO₄)₂·6H₂O with 6-(benzylamino)purine derivatives in a stoichiometric 1:2 metal-to-ligand ratio led to the formation of penta-coordinated dinuclear complexes of the formula [Cu₂(μ-L^1–8)₄(ClO₄)₂](ClO₄)₂·nsolv, where L¹ = 6-(2-fluorobenzylamino)purine (complex 1), L² = 6-(3-fluorobenzylamino)purine (2), L³ = 6-(4-fluorobenzylamino)purine (3), L⁴ = 6-(2-chlorobenzylamino)purine (4), L⁵ = 6-(3-chlorobenzylamino)purine (5), L⁶ = 6-(4-chlorobenzylamino)purine (6), L⁷ = 6-(3-methoxybenzylamino)purine (7) and L⁸ = 6-(4-methoxybenzylamino)purine (8); n = 0–4 and solv = H₂O, EtOH or MeOH. All the complexes have been fully characterized by elemental analysis, FTIR, UV–Vis and EPR spectroscopy, and by magnetic and conductivity measurements. Variable temperature (80–300 K) magnetic susceptibility data of 1–8 showed the presence of a strong antiferromagnetic exchange interaction between two Cu(II) (S = 1/2) atoms with J ranging from −150.0(1) to −160.3(2) cm⁻¹. The compound 6·4EtOH·H₂O was structurally characterized by single crystal X-ray analysis. The Cu?Cu separation has been found to be 2.9092(8) Å. The antiradical activity of the prepared compounds was tested by in vitro SOD-mimic assay with IC₅₀ in the range 8.67–41.45 μM. The results of an in vivo antidiabetic activity assay were inconclusive and the glycaemia in pre-treated animals did not differ significantly from the positive control.     

Mixed-ligand complexes of zinc(II), cobalt(II) and cadmium(II) with sulfur, nitrogen and oxygen ligands. Analysis of the solid state structure and solution behavior. Implications for metal ion substitution in alcohol dehydrogenase

In this paper we characterize new, mixed ligand complexes of zinc(II), cobalt(II) and cadmium(II) with tri-tert-butoxysilanethiolate and 2-(2′-hydroxyethyl)pyridine ligands. Due to the chelating versus non-chelating behavior of 2-(2′-hydroxyethyl)pyridine ligand we have obtained an interesting structural variety in the studied system. The presented coordination patterns together with the results of NMR studies have been used to illustrate a rapid chemical exchange undergoing in methanolic solutions of zinc(II) and cadmium(II) complexes. UV-Vis spectra of cobalt(II) species have also evidenced an exchange in the case of cobalt(II) complex. The relative strength of hydrogen bond formed by hydroxyl group bonded to Zn(II), Co(II) or Cd(II) was evaluated by analysis of structural parameters and position of the OH stretching vibrations in the FT-IR spectra of the complexes in solid state. The data were compared with the activity of zinc (native) alcohol dehydrogenase and alcohol dehydrogenase substituted with cobalt and cadmium ions. The enthalpies of proton abstraction in zinc and cobalt complexes were calculated and found to be very similar. The attempt to apply zinc tri-tert-butoxysilanethiolate as a catalyst in the biomimetic reaction of reduction of N-benzylnicotinamide chloride by ethanol was unsuccessful.     

Synthesis and gas transport properties of ODPA-TAP-ODA hyperbranched polyimides with various comonomer ratios

A series of hyperbranched copolyimides (HBPI)s based on commercially available monomers 4,4′-oxydiphthalic anhydride (ODPA), 2,4,6-triaminopyrimidine (TAP) and 4,4′-oxydianiline (ODA) were prepared. The synthesis involved the formation of hyperbranched polyamic acid (PAA) precursors in the first step and the thermal imidization of cast thin PAA films in the second step. Two basic types of HBPIs were prepared by controlling the molar ratio of ODPA and an amine mixture of TAP and ODA. When the molar ratio was 1:1, the amine-terminated HBPIs were obtained; with the molar ratio of 2:1 anhydride-terminated HBPIs were prepared. Degree of branching was estimated by ¹H and ¹³C NMR analysis. It was found that approximately 48% of TAP units presented in ODPA:TAP:ODA = 1:0.75:0.25 HBPI macromolecules create the branching unit. Amine-terminated HBPIs showed moderate weight-average molecular weights and these values rather higher than for the anhydride-terminated HBPIs. With increasing ODA comonomer content in amine-terminated HBPIs increased their molecular weight and thermal and mechanical stability, whereas in anhydride-terminated HBPIs these trends were opposite. Amine-terminated HBPIs generally exhibited higher thermal stability than the anhydride-terminated ones. Gas permeability coefficients of both HBPIs types increased with increasing content of ODA comonomer. Prepared membranes exhibited high separation performance and have a potential to be utilized in industrial gas separation applications.     

Fluorescent investigation of the interactions between N-(p-chlorophenyl)-N'-(1-naphthyl) thiourea and serum albumin: synchronous fluorescence determination of serum albumin

The interactions between N-(p-chlorophenyl)-N′-(1-naphthyl) thiourea and serum albumin were investigated by fluorescence spectroscopy and UV absorption spectrum under physiological conditions. The results of spectroscopic measurements suggested that N-(p-chlorophenyl)-N′-(1-naphthyl) thiourea should have a strong ability to quench the intrinsic fluorescence of both bovine serum albumin and human serum albumin through static quenching procedure, and the hydrophobic interaction was the predominant intermolecular force stabilizing the complex. Thermodynamic parameter enthalpy changes (ΔH) and entropy changes (ΔS) were calculated according to the Vant’Hoff equation. The binding distances between N-(p-chlorophenyl)-N′-(1-naphthyl) thiourea and the proteins were evaluated on the basis of the theory of Föster energy transfer. In addition, the effects of other ions on the binding constants of complexes were also discussed. Synchronous fluorescence technology was successfully applied to the determination of serum albumins added to the CPNT solution.     

Reducing the formation of six-membered ring ester during thermal degradation of biodegradable PHBV to enhance its thermal stability

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) has attracted the attention of academia and industry because of its biodegradability, biocompatibility, thermoplasticity and plastic-like properties. However, PHBV is unstable above 160 °C during melt processing at a temperature above the melting temperature, which restricts practical applications as a commodity material. It is widely believed that thermal degradation of PHBV occurs almost exclusively via a random chain scission mechanism involving a six-membered ring transition state. Here, 2,2′-bis(2-oxazoline) (BOX) was selected to modify PHBV to control the formation of six-membered ring ester during thermal degradation. The resulting hydroxyl-terminated PHBVs (HT-PHBVs) had improved thermal stability due to a decrease in the negative inductive effect of the neighboring group of methylene groups at the β-position to the ester oxygen, and a decrease in the electron-denoting effect of substituent group of carbon atoms at α-position to the ester oxygen. The optimal reaction temperature and time were determined to be 95 °C and 6 h, respectively. Compared with those of original PHBV, the temperature determined at 5% weight loss (T_5%), the initial decomposition temperature (T₀), the maximum decomposition temperature (T_max), the complete decomposition temperature (T_f) of HT-PHBV prepared under the optimal conditions increased by 31, 24, 19 and 19.1 °C, respectively.     

Synthesis and structures of complexes ofN-2-nitroxyethylpicolinamide and 2-(2-pyridyl)-2-oxazoline with PdCl2

The reaction ofN,N′-bis(2-nitroxyethyl)pyridine-2,6-dicarboxamide with PdCl₂ afforded previously unknowncis-(N-2-nitroxyethylpicolinamide-N,N′)dichloropalladium(II) andcis-[2-(2-pyridyl)-2-oxazoline-N,N′]dichloropalladium(II), which were isolated as a cocrystallizate of the molecular compounds. Its structure was established by X-ray diffraction analysis. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1604–1606, August, 1999.     

Rapid synthesis of optically active poly(amide-imide)s by direct polycondensation of aromatic dicarboxylic acid with aromatic diamines

4,4^′-(Hexafluoroisopropylidene)-N,N^′-bis(phthaloyl-l-leucine-p-amidobenzoic acid) (2) was prepared from the reaction of 4,4^′-(hexafluoroisopropylidene)-N,N^′-bis(phthaloyl-l-leucine) diacid chloride with p-aminobenzoic acid. The direct polycondensation reaction of monomer (2) with p-phenylenediamine (2a), 4,4^′-diaminodiphenylsulfone (2b), 2,4-diaminotoluene (2c), 2,6-diaminopyridine (2d), m-phenylene diamine (2e), benzidine (2f), 4,4^′-diaminodiphenylether (2g) and 4,4^′-diaminodiphenyl methane (2h) was carried out in a medium consisting of triphenyl phosphite, N-methyl-2-pyrolidone, pyridine, and calcium chloride. The homogeneous mixture was heated at 220 °C for 1 min under nitrogen. The resulting poly(amide-imide)s (PAIs) having inherent viscosities 0.27-0.78 dl/g were obtained in high yield and are optically active and thermally stable. All of the above polymers were fully characterized by IR spectroscopy, elemental analyses and specific rotation. Some structural characterization and physical properties of this new optically active PAIs are reported.     

Liquid chromatography/tandem mass spectrometric method for the simultaneous determination of tobacco-specific nitrosamine NNK and its five metabolites

A sensitive and robust high-performance liquid chromatography-electrospray ionization tandem mass spectrometry method to analyze 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and its five metabolites in one passage was developed and validated. The method achieved excellent reproducibility and accuracy. Linearity was observed for all six compounds (R² = 0.999) with detection limits (S/N ≥ 3) ranging from 0.2 to 2.4 pg on column and 0.01-0.12 ng ml⁻¹ in samples injected. Average intra-day and inter-day variations (% R.S.D.) were 1.2 and 3.5%, respectively. A sample preparation method involving C8 and C18 solid phase extraction provided satisfactory recovery of the analytes in mouse urine. Each NNK metabolite was identified by its chromatographic retention time and specific fragmentation pattern. Since the carcinogenicity of NNK is related to its metabolism, the method described in this report should facilitate toxicological investigations into the carcinogenesis due to NNK exposure in the environment.     

Silica-bonded S-sulfonic acid: an efficient and recyclable solid acid catalyst for the synthesis of 4,4′-(arylmethylene)bis(1H-pyrazol-5-ols)

Silica-bonded S-sulfonic acid (SBSSA) is employed as a recyclable catalyst for the condensation reaction of aromatic aldehydes with 3-methyl-l-phenyl-5-pyrazolone. This condensation reaction was performed in ethanol under refluxing conditions giving 4,4′-alkylmethylene-bis(3-methyl-5-pyrazolones) in 75-90% yields.     

Hapten synthesis and antibody production for the development of a melamine immunoassay

The incorporation of melamine into food products is banned but its misuse has been widely reported in both animal feeds and food. The development of a rapid screening immunoassay for monitoring of the substance is an urgent requirement. Two haptens of melamine were synthesized by introducing spacer arms of different lengths and structures on the triazine ring of the analyte molecular structure. 6-Aminocaproic acid and 3-mercaptopropionic acid were reacted with 2-chloro-4,6-diamino-1,3,5-triazine (CAAT) to produce hapten 1 [3-(4,6-diamino-1,6-dihydro-1,3,5-triazin-2-ylamino) hexanoic acid] and hapten 2 [3-(4,6-diamino-1,6-dihydro-1,3,5-triazin-2-ylthio) propanoic acid], respectively. The molecular structures of the two haptens were identified by ¹H nuclear magnetic resonance spectrometry, mass spectrometry and infrared spectrometry. An immunogen was prepared by coupling hapten 1 to bovine serum albumin (BSA). Two plate coating antigens were prepared by coupling both haptens to egg ovalbumin (OVA). A competitive indirect enzyme-linked immunosorbent assay (ciELISA) was developed to evaluate homogeneous and heterogeneous assay formats. The results showed that polyclonal antibodies with high titers were obtained, and the heterogeneous immunoassay format demonstrated a better performance with an IC₅₀ of 70.6 ng mL⁻¹, a LOD of 2.6 ng mL⁻¹ and a LOQ of 7.6 ng mL⁻¹. Except for cyromazine, no obvious cross-reactivity to common compounds was found. The data showed that the hapten synthesis was successful and the resultant antisera could be used in an immunoassay for the rapid and sensitive detection of this banned chemical.     

Study of the behavior of p-bis{3-[N,N-dialkyl-N-(4-hydroxybut-2-ynyl)ammonio]prop-2-ynyl}-benzene dichlorides in relation to aqueous alkali. Double intramolecular recyclization of benzo[5,6;5′,6′-a,c]di(2,2-dialkyl-4-hydroxymethyl)isoindolinium dichlorides

p-Bis{3-[N,N-dialkyl-N-(4-hydroxybut-2-ynyl)ammonio]prop-2-ynyl}benzene dichloride in the presence of catalytic amounts of aqueous alkali is subject to a double intramolecular cyclization forming benzo[5,6;5′,6′-a,c]di(2,2-dialkyl-4-hydroxymethyl)isoindolinium dichloride in 40–42% yield. Simultaneously an intramolecular recyclization takes place with the formation of dialkyl(6-dialkylaminomethyl-7,9,10,12-tetrahydro-8,11-dioxadicyclopenta[c,g]phenanthren-1-ylmethyl)amines in 7–9% yield. The same compounds are obtained in 70–72% yield by the recyclization of benzo[5,6;5′,6′-a,c]di(2,2-dialkyl-4-hydroxymethyl)isoindolinium dichlorides under conditions of aqueous alkaline degradation. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1329–1335, September, 2006.     

Design of single chain magnets through cyanide-bearing six-coordinate complexes

The design and preparation of stable cyanide-bearing six-coordinate complexes of formula [M^III(L)(CN)_x]^{(x + l − m)−} (M = trivalent transition metal ion and L = polydentate blocking ligand) are summarized here. Their use as ligands towards either fully hydrated metal ions or coordinatively unsaturated preformed species, to afford a wide variety of low-dimensional metal assemblies whose nuclearity, dimensionality and magnetic properties can be tuned, is also reviewed. Special emphasis is put on the appropriate choice of the end-cap ligand L whose denticity determines the number of coordinated cyanide groups in the mononuclear precursors. Among the different new spin topologies obtained through this rational synthetic strategy, ferromagnetically coupled 4,2-ribbon like bimetallic chains which exhibit slow magnetic relaxation and hysteresis effects (chain as magnets) are one of the most appealing and constitute the heart of the present contribution.     

Design of “smart” segmented polymers by incorporating random copolymers as building blocks

This article is dealing with the design of novel segmented polymers comprising homopolymer and random copolymer building blocks designated as block-random. This type of polymeric materials can be prepared through macromolecular engineering by using controlled polymerization methods. By replacing a homopolymer block with a random one, in block copolymer topologies, further tuning of the copolymer properties can be achieved. The present article highlights the recent developments on block-random segmented macromolecules, bearing building blocks of tunable properties (e.g. thermo-sensitivity (LCST), hydrophobicity) and exhibiting responsive behavior in aqueous environments. Furthermore, preliminary novel results regarding pH-sensitive segmented macromolecules of various topologies, bearing random polyampholyte blocks among others, are also demonstrated and discussed.