Conformational changes of ubiquitin during electrospray ionization as determined by in‐ESI source H/D exchange combined with high‐resolution MS and ECD fragmentation

In the paper, we have demonstrated the possibility of performing hydrogen/deuterium (H/D) exchange of proteins in the region of gas‐phase ion formation in an electrospray ion source by saturating the electrospray ionization source with vapors of a deuterating agent (D₂O or MeOD). In this region, charged droplets are shrinking and the protein ions transfer into the gas phase. As a model protein, we have used ubiquitin whose ion mobility spectrometry and gas‐phase H/D exchange in the vacuum part of a mass spectrometer demonstrated the presence of gas‐phase conformers with different cross sections and H/D exchange rates. In our experiments, we observed monomodal deuterium distributions for all solvents, charge states, desolvating capillary temperature and types of deuterating agent. Also, we found that the number of H/D exchanges increases with an increasing desolvating capillary temperature and decreasing charge state. We observed that solution composition (49 : 50 : 1 H₂O : MeOH : formic acid or 99 : 1 H₂O : formic acid) influences the charge‐state distribution but did not change the degree of H/D exchange for the same charge state. Electron‐capture dissociation fragmentation shows that higher charge states contain a segment that is protected from access by the deuterating agent. Copyright © 2014 John Wiley & Sons, Ltd.     

Chiral η6‐Arene/N‐Tosylethylenediamine–Ruthenium(II) Complexes: Solution Behavior and Catalytic Activity for Asymmetric Hydrogenation

Aromatic ketones are enantioseletively hydrogenated in alcohols containing [RuX{(S,S)‐Tsdpen}(η⁶‐p‐cymene)] (Tsdpen=TsNCH(C₆H₅)CH(C₆H₅)NH₂; X=TfO, Cl) as precatalysts. The corresponding Ru hydride (X=H) acts as a reducing species. The solution structures and complete spectral assignment of these complexes have been determined using 2D NMR (¹H‐¹H DQF‐COSY, ¹H‐¹³C HMQC, ¹H‐¹⁵N HSQC, and ¹H‐¹⁹F HOESY). Depending on the nature of the solvents and conditions, the precatalysts exist as a covalently bound complex, tight ion pair of [Ru⁺(Tsdpen)(cymene)] and X^?, solvent‐separated ion pair, or discrete free ions. Solvent effects on the NH₂ chemical shifts of the Ru complexes and the hydrodynamic radius and volume of the Ru⁺ and TfO^? ions elucidate the process of precatalyst activation for hydrogenation. Most notably, the Ru triflate possessing a high ionizability, substantiated by cyclic voltammetry, exists in alcoholic solvents largely as a solvent‐separated ion pair and/or free ions. Accordingly, its diffusion‐derived data in CD₃OD reflect the independent motion of [Ru⁺(Tsdpen)(cymene)] and TfO^?. In CDCl₃, the complex largely retains the covalent structure showing similar diffusion data for the cation and anion. The Ru triflate and chloride show similar but distinct solution behavior in various solvents. Conductivity measurements and catalytic behavior demonstrate that both complexes ionize in CH₃OH to generate a common [Ru⁺(Tsdpen)(cymene)] and X^?, although the extent is significantly greater for X=TfO^?. The activation of [RuX(Tsdpen)(cymene)] during catalytic hydrogenation in alcoholic solvent occurs by simple ionization to generate [Ru⁺(Tsdpen)(cymene)]. The catalytic activity is thus significantly influenced by the reaction conditions.     

Enolate Stabilization by Anion–π Interactions: Deuterium Exchange in Malonate Dilactones on π‐Acidic Surfaces

Of central importance in chemistry and biology, enolate chemistry is an attractive topic to elaborate on possible contributions of anion–π interactions to catalysis. To demonstrate the existence of such contributions, experimental evidence for the stabilization of not only anions but also anionic intermediates and transition states on π‐acidic aromatic surfaces is decisive. To tackle this challenge for enolate chemistry with maximal precision and minimal uncertainty, malonate dilactones are covalently positioned on the π‐acidic surface of naphthalenediimides (NDIs). Their presence is directly visible in the upfield shifts of the α‐protons in the ¹H NMR spectra. The reactivity of these protons on π‐acidic surfaces is measured by hydrogen–deuterium (H–D) exchange for 11 different examples, excluding controls. The velocity of H–D exchange increases with π acidity (NDI core substituents: SO₂R>SOR>H>OR>OR/NR₂>SR>NR₂). The H–D exchange kinetics vary with the structure of the enolate (malonates>methylmalonates, dilactones>dithiolactones). Moreover, they depend on the distance to the π surface (bridge length: 11–13 atoms). Most importantly, H–D exchange depends strongly on the chirality of the π surface (chiral sulfoxides as core substituents; the crystal structure of the enantiopure (R,R,P)‐macrocycle is reported). For maximal π acidity, transition‐state stabilizations up to ?18.8 kJ mol^?1 are obtained for H–D exchange. The Brønsted acidity of the enols increases strongly with π acidity of the aromatic surface, the lowest measured pK_a=10.9 calculates to a ΔpK_a=?5.5. Corresponding to the deprotonation of arginine residues in neutral water, considered as “impossible” in biology, the found enolate–π interactions are very important. The strong dependence of enolate stabilization on the unprecedented seven‐component π‐acidity gradient over almost 1 eV demonstrates quantitatively that such important anion–π activities can be expected only from strong enough π acids.     

二维多孔铜-间苯二腈配位聚合物用于阴离子交换及客体分子可逆吸附性的研究

The 2D porous copper（Ⅰ） complex with 1,3-dicyanobenzene （DCB）, [Cu（DCB）2]（PF6）（Me2CO） 1, exhibits channels along axis c, in which one molecule acetone and one anion PF6 per formula unit are included respectively. The reversible incorporation of guest acetone and acetonitrile, as well as the anion exchange from PF6^- to BF4^- or CF3SO3^-, was investigated by thermogravimetric （TG） analysis, ^1H NMR spectra and/or infrared absorption spectroscopy. Additionally, the incorporation of benzene and toluene into complex 1 was also discussed. Complex 1 exhibited size selectivity for guest inclusion or anion exchange.     

Online H/D exchange liquid chromatography as a support for the mass spectrometric identification of the oxidation products of melatonin

The hydrogen–deuterium exchange of protonated melatonin and its in vitro oxidation end‐products have been examined by liquid chromatography coupled with ion‐trap mass spectrometry. Specific H/D scrambling of protons in the C2 and C4 positions of the indole ring during gas‐phase fragmentation process was observed for both melatonin and its oxidation products. Collision‐induced dissociation spectra showed losses of variably deuterated NH₃, H₂O and CH₃CONH₂. In addition, a similar H/D scrambling behaviour was observed for the oxidation products, obtained from the opening of the indole ring by oxidative attack. Fragmentation pathways are proposed and H/D scrambling has been employed as a fingerprint, allowing identification of N¹‐acetyl‐5‐methoxykynurenin (AMK), N¹‐acetyl‐N²‐formyl‐5‐methoxykynurenin (AFMK), dehydro‐AFMK and hydroxymelatonin as the oxidation products of melatonin in vitro. Copyright © 2008 John Wiley & Sons, Ltd.     

Collision‐induced dissociation mass spectra of glucosinolate anions

Collision‐induced dissociation (CID) mass spectra of differently substituted glucosinolates were investigated under negative‐ion mode. Data obtained from several glucosinolates and their isotopologues (³⁴S and ²H) revealed that many peaks observed are independent of the nature of the substituent group. For example, all investigated glucosinolate anions fragment to produce a product ion observed at m/z 195 for the thioglucose anion, which further dissociates via an ion/neutral complex to give two peaks at m/z 75 and 119. The other product ions observed at m/z 80, 96 and 97 are characteristic for the sulfate moiety. The peaks at m/z 259 and 275 have been attributed previously to glucose 1‐sulfate anion and 1‐thioglucose 2‐sulfate anion, respectively. However, based on our tandem mass spectrometric experiments, we propose that the peak at m/z 275 represents the glucose 1‐thiosulfate anion. In addition to the common peaks, the spectrum of phenyl glucosinolate (β‐D ‐Glucopyranose, 1‐thio‐, 1‐[N‐(sulfooxy)benzenecarboximidate] shows a substituent‐group‐specific peak at m/z 152 for C₆H₅‐C(?NOH)S^?, the CID spectrum of which was indistinguishable from that of the anion of synthetic benzothiohydroxamic acid. Similarly, the m/z 201 peak in the spectrum of phenyl glucosinolate was attributed to C₆H₅‐C(?S)OSO₂^?. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis and Crystal Structure of the two Lithium Hypersilylcuprates LiCu2[Si(SiMe3)3]3 and [Li7(OtBu)6][Cu2{Si(SiMe3)3}3]

The two hypersilylcuprates LiCu₂Hyp₃ ( 2 ) and [Li₇(O^tBu)₆][Cu₂Hyp₃] ( 3 ) (Hyp = Si(SiMe₃)₃) were synthesized by reactions of unsolvated lithium hypersilanide, LiHyp with hypersilylcopper and CuO^tBu, respectively. Both contain the novel A‐frame trihypersilyldicuprate anion [Cu₂Hyp₃]^–. In the former case a molecular compound is produced containing intimate ion pairs. In the latter case the cuprate anion and the unique large [Li₇(O^tBu)₆]⁺ cation form a salt‐like compound, only sparingly soluble in unpolar solvents. According to NBO analyses the bonding within the trihypersilyldicuprate moiety is best described by interaction of a bridging lewis‐basic hypersilanide anion with two lewis‐acidic hypersilyl copper fragments.     

catena‐Poly­[[chloro(1,10‐phenanthroline‐κ2N,N′)copper(II)]‐μ‐imidazolato‐κ2N:N′]

In the polymeric title compound, [Cu(im)Cl(phen)]_n, where im is the imidazolate anion (C₃H₃N₂) and phen is 1,10‐phenanthroline (C₁₂H₈N₂), each Cu^II ion is five‐coordinated by four basal N atoms (two from two different im anions and two from one phen ligand) and one axial Cl atom, in a distorted square‐pyramidal coordination geometry. Moreover, each im anion bridges two identical {CuCl(phen)}⁺ cations through its two N atoms, resulting in a one‐dimensional zigzag chain along the crystallographic a axis. In addition, pairs of adjacent chains are staggered by π–π interactions, generating a two‐dimensional layer, and neighbouring layers are further linked by two different kinds of C—H⋯Cl interactions, producing a three‐dimensional network.     

Two polymorphs of 2‐(4‐chlorophenyl)‐4‐methylchromenium perchlorate

Crystallization (from ethyl acetate solution) of 2‐(4‐chlorophenyl)‐4‐methylchromenium perchlorate, C₁₆H₁₂ClO⁺·;ClO₄⁻, (I), yields two monoclinic polymorphs with the space groups P2₁/n [polymorph (Ia)] and P2₁/c [polymorph (Ib)]; in both cases, Z = 4. Cations and anions, disordered in polymorph (Ib), form ion pairs in both polymorphs as a result of Cl—O...π interactions. Related by a centre of symmetry, neighbouring ion pairs in polymorph (Ia) are linked viaπ–π interactions between cationic fragments, and the resulting dimers are linked through a network of C—H...O(perchlorate) interactions between adjacent cations and anions. The ion pairs in polymorph (Ib), arranged in pairs of columns along the a axis, are linked through a network of C—H...O(perchlorate), C—Cl...π, π–π and C—Cl...O(perchlorate) interactions. The aromatic skeletons in polymorph (Ia) are parallel in the cationic fragments involved in dimers, but nonparallel in adjacent ion pairs not constituting dimers. In polymorph (Ib), these skeletons are parallel in pairs of columns, but nonparallel in adjacent pairs of columns; this is visible as a herring‐bone pattern. Differences in the crystal structures of the polymorphs are most probably the cause of their different colours.     

Molecular Structure,Vibrational Spectra,and Hydrogen Bonding of the Ionic Liquid 1‐Ethyl‐3‐methyl‐1H‐imidazolium Tetrafluoroborate

The IR and Raman spectra and conformations of the ionic liquid 1‐ethyl‐3‐methyl‐1H‐imidazolium tetrafluoroborate, [EMIM] [BF₄] ( 6 ), were analyzed within the framework of scaled quantum mechanics (SQM). It was shown that SQM successfully reproduced the spectra of the ionic liquid. The computations revealed that normal modes of the EMIM⁺?BF ion pair closely resemble those of the isolated ions EMIM⁺ and BF , except for the antisymmetric BF stretching vibrations of the anion, and the out‐of‐plane and stretching vibrations of the H? C(2) moiety of the cation. The most plausible explanation for the pronounced changes of the latter vibrations upon ion‐pair formation is the H‐bonding between H? C(2) and BF . However, these weak H‐bonds are of minor importance compared with the Coulomb interactions between the ions that keep them closely associated even in dilute CD₂Cl₂ solutions. According to the ‘gas‐phase’ computations, in these associates, the BF anion is positioned over the imidazolium ring of the EMIM⁺ cation and has short contacts not only with the H? C(2) of the latter, but also with a proton of the Me? N(3) group.     

Ion‐Pair Complexation with a Cavitand Receptor

The capability of resorcinarenes to bind anions within the alkyl feet at the lower rim has been exploited as the starting point for developing a new cavitand able to engulf contact ion pairs of primary ammonium salts in chlorinated solvents with association constants (K_ass) in the range of 10³–10⁴ M ^?1. Methylene bridges were introduced into the upper rim to freeze the resorcinarene in the cone conformation with the four H_down protons converging in the lower pocket, thereby maximizing the CH–anion interactions responsible for the anion binding. Four additional phosphate moieties were introduced into the lower rim in close proximity to the anionic site to provide hydrogen‐bonding‐acceptor P?O groups and promote cation complexation at the bottom of the cavitand. The binding ability of the synthesized ligands was analyzed by ¹H NMR spectroscopy and, when possible, by isothermal titration calorimetry (ITC); the data were in agreement when complementary techniques were used.     

Highly alkaline stable anion exchange membranes from nonplanar polybenzimidazole with steric hindrance backbone

The anion exchange membranes (AEMs) with both high ionic conductivity and alkali stability are always the research focus of the AEM fuel cells. Here, a novel nonplanar polymer for AEMs manufacture, mPBI‐TP‐x‐R, with excellent hydroxide stability and satisfactory processability is reported for the first time. The serial mPBI‐TP‐x resins with steric hindrance were prepared by copolymerization among 3,3′,4,4′‐tetraaminobiphenyl, isophthalic acid and tetraphenyl‐terephthalic acid (TP) in different ratios under microwave condensation. The copolymers mPBI‐TP‐x were quaternized at N1/N3‐sites of benzimidazole unit in backbone with alkyl groups (R?CH₃, C₂H₅, n‐C₃H₇, or n‐C₄H₉) to prepare soluble ionomers, and the corresponding membranes in hydroxyl ion form were prepared by a solution casting method and subsequent ion‐exchange process. The chemical structure of all membranes was characterized using FTIR and ¹H NMR spectroscopy. The properties of ion exchange capacity, water uptake, swelling ratio, tensile strength, ionic conductivity, and alkaline stability were measured. Among the prepared membranes, the mPBI‐TP‐15%‐(n‐Bu) exhibited the excellent alkaline stability (only degradation ca. 5% under 1M NaOH aqueous solution at 60 °C for 800 h) and satisfactory OH^? conductivity (46.66 mS/cm at 80 °C). The current research provides a useful exploration to commercial application of alkaline fuel cell. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 1087–1096     

The Role of Ion Pairs in the Second‐Order NLO Response of 4‐X‐1‐Methylpiridinium Salts

A series of 4‐X‐1‐methylpyridinium cationic nonlinear optical (NLO) chromophores (X=(E)‐CH?CHC₆H₅; (E)‐CH?CHC₆H₄‐4′‐C(CH₃)₃; (E)‐CH?CHC₆H₄‐4′‐N(CH₃)₂; (E)‐CH?CHC₆H₄‐4′‐N(C₄H₉)₂; (E,E)‐(CH?CH)₂C₆H₄‐4′‐N(CH₃)₂) with various organic (CF₃SO₃^?, p‐CH₃C₆H₄SO₃^?), inorganic (I^?, ClO₄^?, SCN^?, [Hg₂I₆]^2?) and organometallic (cis‐[Ir(CO)₂I₂]^?) counter anions are studied with the aim of investigating the role of ion pairing and of ionic dissociation or aggregation of ion pairs in controlling their second‐order NLO response in anhydrous chloroform solution. The combined use of electronic absorption spectra, conductimetric measurements and pulsed field gradient spin echo (PGSE) NMR experiments show that the second‐order NLO response, investigated by the electric‐field‐induced second harmonic generation (EFISH) technique, of the salts of the cationic NLO chromophores strongly depends upon the nature of the counter anion and concentration. The ion pairs are the major species at concentration around 10^?3 M , and their dipole moments were determined. Generally, below 5×10^?4 M , ion pairs start to dissociate into ions with parallel increase of the second‐order NLO response, due to the increased concentration of purely cationic NLO chromophores with improved NLO response. At concentration higher than 10^?3 M , some multipolar aggregates, probably of H type, are formed, with parallel slight decrease of the second‐order NLO response. Ion pairing is dependent upon the nature of the counter anion and on the electronic structure of the cationic NLO chromophore. It is very strong for the thiocyanate anion in particular and, albeit to a lesser extent, for the sulfonated anions. The latter show increased tendency to self‐aggregate.     

N‐Methyl­pyridinium 3‐cyano‐4‐(di­cyano­methyl­ene)‐5‐oxo‐4,5‐di­hydro‐1H‐pyrrol‐2‐olate

The crystal structure of the title compound, C₆H₈N⁺·C₈HN₄O₂⁻, is characterized by three independent ion pairs (A, B and C) in the asymmetric unit. Each ion pair consists of an anion and a cation, and the three ion pairs have similar geometric parameters. All the anions are arranged as dianion dimers via two N—H⋯O hydrogen bonds and the dimers form one‐dimensional columns parallel to the b axis as a result of π–π interactions. The cations are also stacked, in two different ways: one type of stacking consists of alternating A and B cations, while the other type consists of C cations only. Each dianion dimer stack is surrounded by eight stacks of cations and is not connected directly to other dianion stacks.     

含氰基基团的以C为中心的不对称阴离子离子液体的合成、表征及应用

首次通过不对称阴离子的钠盐/钾盐和不同的季胺化的咪唑,吡咯溴盐/氯盐进行离子交换,合成了一系列含氰基官能团的不对称阴离子功能化离子液体。通过红外、核磁共振、质谱和元素分析对离子液体的结构进行表征;通过TGA对离子液体的热稳定性进行测定,结果发现不对称功能化离子液体具有良好的热稳定性,其分解温度在219-319℃范围内。将功能化离子液体[Bmim][C(CN)2COCH3]作为弱配体应用于模型的Suzuki偶联反应,发现在反应中加入功能化离子液体[Bmim][C(CN)2COCH3]可以使反应收率提高10-15%。     

Mononuclear nickel(II) and zinc(II) complexes with deprotonated forms of the tripodal hexadentate ligand 1,3‐bis(2‐hydroxybenzylidene)‐2‐(2‐hydroxybenzylideneaminomethyl)‐2‐methylpropane‐1,3‐diamine

In the crystal structures of both title compounds, [1,3‐bis(2‐hydroxybenzylidene)‐2‐methyl‐2‐(2‐oxidobenzylideneaminomethyl)propane‐1,3‐diamine]nickel(II) [2‐(2‐hydroxybenzylideneaminomethyl)‐2‐methyl‐1,3‐bis(2‐oxidobenzylidene)propane‐1,3‐diamine]nickel(II) chloride methanol disolvate, [Ni(C₂₆H_25.5N₃O₃)]₂Cl·2CH₄O, and [1,3‐bis(2‐hydroxybenzylidene)‐2‐methyl‐2‐(2‐oxidobenzylideneaminomethyl)propane‐1,3‐diamine]zinc(II) perchlorate [2‐(2‐hydroxybenzylideneaminomethyl)‐2‐methyl‐1,3‐bis(2‐oxidobenzylidene)propane‐1,3‐diamine]zinc(II) methanol trisolvate, [Zn(C₂₆H₂₅N₃O₃)]ClO₄·[Zn(C₂₆H₂₆N₃O₃)]·3CH₄O, the 3d metal ion is in an approximately octahedral environment composed of three facially coordinated imine N atoms and three phenol O atoms. The two mononuclear units are linked by three phenol–phenolate O—H...O hydrogen bonds to form a dimeric structure. In the Ni compound, the asymmetric unit consists of one mononuclear unit, one‐half of a chloride anion and a methanol solvent molecule. In the O—H...O hydrogen bonds, two H atoms are located near the centre of O...O and one H atom is disordered over two positions. The Ni^II compound is thus formulated as [Ni(H_1.5L)]₂Cl·2CH₃OH [H₃L is 1,3‐bis(2‐hydroxybenzylidene)‐2‐(2‐hydroxybenzylideneaminomethyl)‐2‐methylpropane‐1,3‐diamine]. In the analogous Zn^II compound, the asymmetric unit consists of two crystallographically independent mononuclear units, one perchlorate anion and three methanol solvent molecules. The mode of hydrogen bonding connecting the two mononuclear units is slightly different, and the formula can be written as [Zn(H₂L)]ClO₄·[Zn(HL)]·3CH₃OH. In both compounds, each mononuclear unit is chiral with either a Δ or a Λ configuration because of the screw coordination arrangement of the achiral tripodal ligand around the 3d metal ion. In the dimeric structure, molecules with Δ–Δ and Λ–Λ pairs co‐exist in the crystal structure to form a racemic crystal. A notable difference is observed between the M—O(phenol) and M—O(phenolate) bond lengths, the former being longer than the latter. In addition, as the ionic radius of the metal ion decreases, the M—O and M—N bond distances decrease.     

Carbon Dioxide Capture and Release by Anions with Solvent‐Dependent Behaviour: A Theoretical Study

Recently, Clyburne and co‐workers [Science, 2014 , 344, 75–78] reported the novel synthesis of the elusive cyanoformate anion, NCCO₂^?. The stability of this anion is dependent on the dielectric constant of the local environment (polarity‐switchable solvent): it is stable in low‐polarity media and unstable in high‐polarity solvents; hence, capturing and then releasing CO₂. The possibility of extending such behaviour to other anions is explored herein. Specifically, the CO₂ capture process is studied for 26 anions in the gas phase and 3 distinct solvents (water, tetrahydrofuran, and toluene) by using the polarisable continuum model. Calculations are performed with the M06‐2X and B3LYP‐D3 density functionals and the aug‐cc‐pVTZ basis set. The design of new CO₂ complexes with the anion, which can be formed or destroyed on demand by changing the solvent, is possible; the results for the alkoxylate and thiolate anions are especially promising. The nature of the substituents connected to the atom that bonds to CO₂ in the anion is crucial in modulating the relative stability of the products—a key point for reversibility in the CO₂ capture process. A moderate interaction for the anion–CO₂ adduct—about 10 kcal mol^?1 relative free energy with respect to the isolated reactants in the gas phase—and a relevant effect in the dielectric constant of the local environment are also key ingredients to achieve solvent dependency.     

Diagnostic di‐ and triphosphate cyclisation in the negative ion electrospray mass spectra of phosphoSer peptides

It has been shown previously that [M–H]^– anions of small peptides containing two phosphate residues undergo cyclisation of the phosphate groups, following collision‐induced dissociation (CID), to form a characteristic singly charged anion A (H₃P₂O₇^–, m/z 177). In the present study it is shown that the precursor anions derived from the diphosphopeptides of caerin 1.1 [GLLSVLGSVAKHVLPHVVPVIAEHL(NH₂)] and frenatin 3 [GLMSVLGHAVGNVLGGLFKPKS(OH)] also form the characteristic product anion A (m/z 177). Both of the precursor peptides show random structures in water, but partial helices in membrane‐mimicking solvents [e.g. in d₃‐trifluoroethanol/water (1:1)]. In both cases the diphosphopeptide precursor anions must have flexible conformations in order to allow approach of the phosphate groups with consequent formation of A: for example, the two pSer groups of 4,22‐diphosphofrenatin 3 are seventeen residues apart. Finally, CID tandem mass spectrometric (MS/MS) data from the [M–H]^– anion of the model triphosphoSer‐containing peptide GpSGLGpSGLGpSGL(OH) show the presence of both product anions A (m/z 177) and D (m/z 257, H₄P₃O₁₀^–). Ab initio calculations at the HF/6‐31+G(d)//AM1 level of theory suggest that cyclisation of the three phosphate groups occurs by a stepwise cascade mechanism in an energetically favourable reaction (ΔG = ?245 kJ mol^–1) with a maximum barrier of +123 kJ mol^–1. Copyright © 2011 John Wiley & Sons, Ltd.     

Poly[[μ‐(1‐azaniumylethane‐1,1‐diyl)bis(hydrogen phosphonato)]sodium]: a powder X‐ray diffraction study

The title two‐dimensional coordination polymer, [Na(C₂H₈NO₆P₂)]_n, was characterized using powder X‐ray diffraction data and its structure refined using the Rietveld method. The asymmetric unit contains one Na⁺ cation and one (1‐azaniumylethane‐1,1‐diyl)bis(hydrogen phosphonate) anion. The central Na⁺ cation exhibits distorted octahedral coordination geometry involving two deprotonated O atoms, two hydroxy O atoms and two double‐bonded O atoms of the bisphosphonate anion. Pairs of sodium‐centred octahedra share edges and the pairs are in turn connected to each other by the biphosphonate anion to form a two‐dimensional network parallel to the (001) plane. The polymeric layers are connected by strong O—H...O hydrogen bonding between the hydroxy group and one of the free O atoms of the bisphosphonate anion to generate a three‐dimensional network. Further stabilization of the crystal structure is achived by N—H...O and O—H...O hydrogen bonding.<!?tpb=18.7pt>     

Synthesis and specific solvatochromism of D–π–A type pyridinium dye

Donor–π–acceptor (D–π–A) type pyridinium dye bearing an iodide ion as the counter anion that has been newly synthesized showed specific solvatochromism, leading to large bathochromic shift of absorption band in halogenated solvents: the bathochromic shifts of the D–π–A type pyridinium dye in halogenated solvents are larger than those of the non-halogenated solvents of low ?_r values. Investigation of absorption spectral measurement, ¹H NMR measurements, and semi-empirical molecular calculations (AM1 and INDO/S using the SCRF Onsager Model) revealed that the intramolecular charge transfer (ICT) characteristics of the D–π–A type pyridinium dye became stronger in the halogenated solvents. On the basis of the experimental results and the theoretical calculations, the influences of halogenated solvent on the large bathochromic shift of D–π–A type pyridinium dye are discussed. ^©2012 Elsevier Science. All rights reserved.