Layered iron(II) spin crossover complex constructed by NH?Br hydrogen bonds with 2 K wide thermal hysteresis, [FeH3L]Br·CF3SO3 (H3L = tris[2-(((2-methylimidazol-4-yl)methylidene)amino)ethyl]amine)

A series of compounds [Fe^IIH₃L^Me]Br·Y·nMeOH ( (1), (2), (3), (4); n = 0 or 1) were synthesized, where H₃L^Me is a hexadentate N₆ tripodal ligand of the neutral form, tris[2-(((2-methylimidazol-4-yl)methylidene)amino)ethyl]amine, and their structures and magnetic properties were investigated. The compounds 1−3 with counter anions , , and contain methanol as a crystal solvent, and show no SCO behaviors, while the corresponding Cl⁻ compounds have no crystal solvent and show a variety of SCO behaviors. The compound [Fe^IIH₃L^Me]Br·CF₃SO₃ (4) has no crystal solvent and has isomorphous structure to the Cl⁻ compounds, and shows an abrupt spin transition between the HS (S = 2) and LS (S = 0) states with a hysteresis about 2 K and large frozen-in effect below 72 K. The T_1/2↑ and T_1/2↓ values are 98 and 96 K, whose values are higher than those of corresponding Cl⁻ compound about 15 K and the width of hysteresis is narrower than that of corresponding Cl⁻ compound about 2 K. The crystal structures of 4 were determined at 296 and 93 K, where the crystal system and space group showed no change between these temperatures. The structures at both temperatures have a same 2D layered structure, which is composed of NH?Br⁻ hydrogen bonds between the Br⁻ ion and the imidazole NH groups of three neighboring cations [Fe^IIH₃L^Me]²⁺. This network structure is the same as that of corresponding Cl⁻ compound. The 600 nm light irradiation at 5 K induced the LIESST effect.     

Coordination chemistry of the heterotopic 1,2-phenylenebis(thio)diacetic acid ligand: Rhodium(I), palladium(II) and nickel(II) complexes

Starting from the heterotopic multidentate ligand 1,2-phenylenebis(thio)diacetic acid (1), cis-rac-[PdCl₂{1,2-(HOOCCH₂S)₂C₆H₄-κ²S,S′}] (2), cis-rac-[Rh{1,2-(HOOCCH₂S)₂C₆H₄-κ²S,S′}(cod)]BF₄ (3) and cis-rac-[Ni{1,2-(OOCCH₂S)₂C₆H₄-κ⁴O,O′S,S′}{cis-(C₃H₄N₂)}₂] (4) were prepared and characterised by X-ray diffraction and conventional spectroscopic techniques. Compounds 1-4 show extensive hydrogen-bonded networks (XH?O, X = O, N) in the solid state.     

Selective inclusion of DMF molecules within non-covalent cavity

[Me₄P]₄[Cu₄(mnt)₄]·2CH₃CN (1), [Me₄P]₄[Cu₄(mnt)₄]·2CH₃NO₂ (2), [Me₄P]₄[Cu₄(mnt)₄]·2DMF (3) and [Me₄P]₄[Cu₄(mnt)₄]·2C₃H₃N (4) (mnt = maleonitriledithiolate, [S₂C₂(CN)₂]²⁻) clusters are readily synthesized in several solvents like acetonitrile, nitromethane, N,N-dimethylformamide and acrylonitrile to provide respective solvent as guest within the non-covalent cavity of the cluster ion. The guest species is accommodated within non-covalent cavity that is generated by two adjacent {Cu₄(mnt)₄} cores bridging with tetramethylphosphonium cation through hydrogen bonding. These hydrogen bonds are not strong and when mixed solvents were used selective DMF binding takes place to yield only complex 3 over other complexes.     

H NMR and X-ray studies on hydrogen bonding in alkyloxy ethanols and their MgCl2 adducts

Adducts of alkyloxy ethanols (2-isobutoxy ethanol, 2-isopropoxy ethanol, 2-ethoxy ethanol, and 2-methoxy ethanol) with MgCl₂ were prepared in the presence of excess alkyloxy ethanol in molar ratios 5:1-15:1. MgCl₂/2-isopropoxy ethanol and MgCl₂/2-isobutoxy ethanol adducts were successfully crystallized and their structures determined by single-crystal X-ray diffraction. Alkyloxy ethanol molecules bind to magnesium in 2:1 mol ratio through oxygens of the alcohol and ether groups forming a chelated structure. In the binuclear complexes [(ipe)₂MgCl₂Mg(ipe)₂][Cl]₂ and [(ibe)₂MgCl₂Mg(ibe)₂][Cl]₂ (structures 1 and 2), where ipe stands for 2-isopropoxy ethanol and ibe for 2-isobutoxy ethanol, the two magnesium centers are connected by two chlorine bridges. The mononuclear structure cis-[Mg(ibe)₂(H₂O)₂][Cl]₂ (structure 3) contains, besides two alkyloxy molecules, two water molecules bound to magnesium. Hydrogen bonding in the adducts, in liquid and solid states, was studied by ¹H NMR spectroscopy and X-ray diffraction, respectively. In liquid state, the sample concentration and temperature used in the measurements were observed to influence hydrogen bonding. All crystal structures show extensive hydrogen bonding from anionic chlorines to the OH hydrogen of alcohols or the water hydrogens.     

Reactivity of a low-valent chromium dinitrogen complex

(Nn^iPrCr)₂(μ₂-κ²:κ²-N₂) (1, Nn^iPr = bis(2,6-diisopropylphenyl)pentane-2,4-ketiminato), formally a chromium(I) complex, was exposed to a variety of small molecules possessing hetero- or homo-atomic single, double, or triple bonds. Reaction of 1 with adamantyl azide yielded complexes in various higher oxidation states, such as (Nn^iPrCr^II)₂(μ₂-NAd) (2), Nn^iPrCr^III(κ²-N₄Ad₂) (3), or Nn^iPrCr^V(NAd)₂ (4). Compound 1 was found to reductively couple 3-pentanone to form Nn^iPrCr(κ²-O₂C₂Et₄) (5) and reductively couple benzylidene aniline to form both Nn^iPrCr^III(cis-κ²-C₂₈H₂₂N₂) (6a) an Nn^iPrCr^III(trans-κ²-C₂₈H₂₂N₂) (6b). Reaction with a stochiometric amount of benzylidene aniline yielded the imine complex Nn^iPrCr(η²-NPhCHPh) (7). Exposure of 1 to a bulky isocyanide formed the octahedral Nn^iPrCr^I[CN(C₆H₄(Me)₂]₄ (9). Complex 1 was also found to break the O-O, NO, and S-S bonds in various small molecules to form Nn^iPrCr^II(OCMe₃) (11), Nn^iPrCr^V(O)(NPh) (8), and [Nn^iPrCr^II(μ-SPh)]₂ (10).     

A new approach to coordination chemistry involving phosphorus-selenium based ligands. Ring opening, deselenation and phosphorus-phosphorus coupling of Woollins’ Reagent

The facile reaction of [CpCr(CO)₃]₂ (1) with an equivalent of 2,4-bis(phenyl)-1,3-diselenadiphosphetane-2,4-diselenide or Woollins’ Reagent (WR) at ambient temperature gave mainly [CpCr(CO)₂]₂Se (3) as the main product. A similar reaction with an excess of 1 gave 3 (58%) and trans-[CpCr(CO)₂(SePPh)]₂ (5, 25%). However reaction with an equivalent of the triply bonded congener Cp₂Cr₂(CO)₄ (2) at 60 °C took 3 h to complete and led to the isolation of trans-[CpCr(CO)₂(SePPh)]₂ (5, 3%), CpCr(CO)₂(SeP(H)Ph) (4, 18%) and [CpCr(Se₂P(O)Ph)]₂ (6, 2%). The ring-opening reaction of WR via an initial homolytic P-Se bond cleavage by CpCr(CO)_n· (n = 2 (2A) or 3 (1A)) depicts a new approach to coordination chemistry involving P-Se based ligands. A mechanistic pathway was proposed according to the evidences obtained from thermolysis, NMR and mass spectra studies. All the products of 4, 5 and 6 have been structurally characterized by single-crystal X-ray diffraction analysis.     

Carbohydrate liquid crystals: synthesis and characterisation of the methyl-6-O-(n-acyl)-α-D-glucopyranosides

Seven members of the methyl-6-O-(n-acyl)-α-d-glucopyranosides have been synthesised and their transitional properties determined. The undecanoyl and octadecanoyl members do not exhibit liquid crystallinity while the members having chain lengths between dodecanoyl and hexadecanoyl exhibit a monotropic smectic A phase. Variable temperature infrared spectroscopy reveals that the hydrogen bonding within the system shows a marked change at the melting point but apparently no change at the smectic A-isotropic transition. This observation is interpreted in terms of Goodby's model for the smectic A phase in which the carbohydrate moieties are located at the centre of the smectic bilayer and assuming that hydrogen bonded aggregates persist into the isotropic phase. Within this framework, the unusually low values of the entropy change associated with the smectic A-isotropic transition may also be accounted for.     

Synthesis of oxidized guar gum by dry method and its application in reactive dye printing

The aim of this study was to prepare oxidized guar gum with a simple dry method, basing on guar gum, hydrogen peroxide and a small amount of solvent. To obtain a product with suitable viscosity for reactive dye printing, the effects of various factors such as the amount of oxidant and solvent, reaction temperature and time were studied with respect to the viscosity of reaction products. The product was characterized by Fourier transform infrared spectroscopy, size exclusion chromatography, scanning electron microscopy and differential scanning calorimetry. The hydrated rate of guar gum and oxidized guar gum was estimated through measuring the required time when their solutions (1%, w/v) reached the maximum viscosity. The effects of the salt concentration and pH on viscosity of the resultant product were studied. The mixed paste containing oxidized guar gum and carboxymethyl starch was prepared and its viscosity was determined by the viscometer. The rheological property of the mixed paste was appraised by the printing viscosity index. In addition, the applied effect of mixed paste in reactive dye printing was examined by assessing the fabric stiffness, color yield and sharp edge to the printed image in comparison with sodium alginate. And the results indicated that the mixed paste could partially replace sodium alginate as thickener in reactive dye printing. The study also showed that the method was low cost and eco-friendly and the product would have an extensive application in reactive dye printing.     

Hydrogen peroxide stimulates the epithelial sodium channel through a phosphatidylinositide 3-kinase-dependent pathway

Recent studies indicate that oxidative stress mediates salt-sensitive hypertension. To test the hypothesis that the renal epithelial sodium channel (ENaC) is a target of oxidative stress, patch clamp techniques were used to determine whether ENaC in A6 distal nephron cells is regulated by hydrogen peroxide (H(2)O(2)). In the cell-attached configuration, H(2)O(2) significantly increased ENaC open probability (P(o)) and single-channel current amplitude but not the unit conductance. High concentrations of exogenous H(2)O(2) are required to elevate intracellular H(2)O(2), probably because catalase, the enzyme that promotes the decomposition of H(2)O(2) to H(2)O and O(2), is highly expressed in A6 cells. The effect of H(2)O(2) on ENaC P(o) was enhanced by 3-aminotriazole, a catalase inhibitor, and abolished by overexpression of catalase, indicating that intracellular H(2)O(2) levels are critical to produce the effect. However, H(2)O(2) did not directly activate ENaC in inside-out patches. The effects of H(2)O(2) on ENaC P(o) and amiloride-sensitive Na(+) current were abolished by inhibition of phosphatidylinositide 3-kinase (PI3K). Confocal microscopy data showed that H(2)O(2) elevated phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P(3)) in the apical membrane by stimulating PI3K. Because ENaC is stimulated by PI(3,4,5)P(3), these data suggest that H(2)O(2) stimulates ENaC via PI3K-mediated increases in apical PI(3,4,5)P(3).     

Asparagine 175 of connexin32 is a critical residue for docking and forming functional heterotypic gap junction channels with connexin26

The gap junction channel is formed by proper docking of two hemichannels. Depending on the connexin(s) in the hemichannels, homotypic and heterotypic gap junction channels can be formed. Previous studies suggest that the extracellular loop 2 (E2) is an important molecular domain for heterotypic compatibility. Based on the crystal structure of the Cx26 gap junction channel and homology models of heterotypic channels, we analyzed docking selectivity for several hemichannel pairs and found that the hydrogen bonds between E2 domains are conserved in a group of heterotypically compatible hemichannels, including Cx26 and Cx32 hemichannels. According to our model analysis, Cx32N175Y mutant destroys three hydrogen bonds in the E2-E2 interactions due to steric hindrance at the heterotypic docking interface, which makes it unlikely to dock with the Cx26 hemichannel properly. Our experimental data showed that Cx26-red fluorescent protein (RFP) and Cx32-GFP were able to traffic to cell-cell interfaces forming gap junction plaques and functional channels in transfected HeLa/N2A cells. However, Cx32N175Y-GFP exhibited mostly intracellular distribution and was occasionally observed in cell-cell junctions. Double patch clamp analysis demonstrated that Cx32N175Y did not form functional homotypic channels, and dye uptake assay indicated that Cx32N175Y could form hemichannels on the cell surface similar to wild-type Cx32. When Cx32N175Y-GFP- and Cx26-RFP-transfected cells were co-cultured, no colocalization was found at the cell-cell junctions between Cx32N175Y-GFP- and Cx26-RFP-expressing cells; also, no functional Cx32N175Y-GFP/Cx26-RFP heterotypic channels were identified. Both our modeling and experimental data suggest that Asn(175) of Cx32 is a critical residue for heterotypic docking and functional gap junction channel formation between the Cx32 and Cx26 hemichannels.