Hydrogen-bonded Supramolecular Rosette Ribbon Constructed from Melamine with Isophthalic Acid

The new complex of melamine （MA） with isophthalic acid （H2IA）, [（HMA^＋）- （HIA^-）]·2H2O, has been prepared and its structure was characterized by X-ray crystallography. The crystal is of triclinic, space group P^-1 with a = 7.0228（6）, b = 9.1706（8）, c = 12.170（1） A, α = 95.337（2）, β = 105.247（2）, γ = 97.813（2）^o, V = 742.3（1） A ^3, Mr= 328.30, Z = 2, Dc = 1.469 g/cm^3, ;λ = 0.71073 A,μ（MoKa） = 0.121 mm^-1 and F（000） = 344. The structure was refined to R = 0.0389 and wR = 0.1093 for 2513 observed reflections with I 〉 2σ（I）. Melamine dimer and isophthalic acid anion are interlinked by N-H…N and N-H…O hydrogen bonds, resulting in a 1D rosette ribbon in which water molecules and amino groups are self-assembled into quasihexagonal patterns.     

Determination of phytosiderophores by anion-exchange chromatography with pulsed amperometric detection

Phytosiderophores of the mugineic acid family are separated by anion-exchange HPLC using NaOH gradient elution. Separation of mugineic acid (MA), 2'-deoxymugineic acid (DMA), 3-hydroxymugineic acid (HMA) and 3-epi-hydroxymugineic acid (epi-HMA) is obtained within 15 min. Detection of the underivatised phytosiderophores is performed using pulsed amperometric detection (PAD) at pH 13. The sensitivity of the detection increases in the order DMA < MA < HMA < epi-HMA and respective detection limits of 5 microM (DMA), 1 microM (MA) and < 0.5 microM (HMA, epi-HMA) are achieved. PAD is discussed in comparison with the well-established fluorimetric detection method after post-column derivatisation with ortho-phthaldialdehyde. The main advantage of PAD is the simplicity of the method (no derivatisation) and the high sensitivity for hydroxylated mugineic acids. The method is used for the determination of phytosiderophores in root washings of iron-deficient and non-deficient wheat and barley plants.     

Excited-State Hydrogen Bonding Dynamics of Hydrogen-Bonded Clusters Formed by of Coumarin Derivatives in Aqueous Solution: A Time-Dependent Density Functional Theory Study

The time-dependent density functional theory and the density functional theory are used to investigate the nature of hydrogen bonds formed by the derivative of the coumarin (TFKC) and the water molecules. The ground-state geometry optimizations, electronic excited energies and corresponding oscillation strengths for the TFKC monomer, the hydrogen-bonded TFKC–Water (HBA) dimer, TFKC–Water (HBB) dimer and TFKC–2Water complex are calculated. We find that, upon photoexcitation, the weaker hydrogen bond in the ground state will be affected by the relatively large impact for TFKC in the water. For better understanding the properties of the hydrogen bonds in the excited states, the frontier molecular orbitals of the S0 and S1 states are shown, and we find the obvious electron density transitions form the water molecules to the TFKC monomer. The electron transfer is expected to be the reason the hydrogen bond dynamics happens.     

Synthesis of metal-hydrazone complexes and vapochromic behavior of their hydrogen-bonded proton-transfer assemblies

We synthesized and investigated a new series of metal-hydrazone complexes, including deprotonated [MX(mtbhp)] and protonated forms [MX(Hmtbhp)](ClO(4)) (M = Pd(2+), Pt(2+); X = Cl(-), Br(-); Hmtbhp = 2-(2-(2-(methylthio)benzylidene)hydrazinyl)pyridine) and hydrogen-bonded proton-transfer (HBPT) assemblies containing [PdBr(mtbhp)] and bromanilic acid (H(2)BA). The mtbhp hydrazone ligand acts as a tridentate SNN ligand and provides a high proton affinity. UV-vis spectroscopy revealed that these metal-hydrazone complexes follow a reversible protonation-deprotonation reaction ([MX(mtbhp)] + H(+) ? [MX(Hmtbhp)](+)), resulting in a remarkable color change from red to yellow. Reactions between proton acceptor [PdBr(mtbhp)] (A) and proton donor H(2)BA (D) afforded four types of HBPT assemblies with different D/A ratios: for D/A = 1:1, {[PdBr(Hmtbhp)](HBA)·Acetone} and {[PdBr(Hmtbhp)](HBA)·2(1,4-dioxane)}; for D/A = 1:2, [PdBr(Hmtbhp)](2)(BA); and for D/A = 3:2, {[PdBr(Hmtbhp)](2)(HBA)(2)(H(2)BA)·2Acetonitrile}. The proton donor gave at least one proton to the acceptor to form the hydrogen bonded A···D pair of [PdBr(Hmtbhp)](+)···HBA(-). The strength of the hydrogen bond in the pair depends on the kind of molecule bound to the free monoanionic bromanilate OH group. Low-temperature IR spectra (T < 150 K) showed that the hydrogen bond distance between [PdBr(Hmtbhp)](+) and bromanilate was short enough (ca. 2.58 ?) to induce proton migration in the [PdBr(Hmtbhp)](2)(BA) assembly in the solid state. The hydrogen bonds formed not only between [PdBr(Hmtbhp)](+) and HBA(-) but also between HBA(-) and neutral H(2)BA molecules in the {[PdBr(Hmtbhp)](2)(HBA)(2)(H(2)BA)·2Acetonitrile} assembly. The H(2)BA-based flexible hydrogen bond network and strong acidic host structure result in an interesting vapor adsorption ability and vapochromic behavior in this assembly because the vapor-induced rearrangement of the hydrogen bond network, accompanied by changes in π-π stacking interactions, provides a recognition ability of proton donating and accepting properties of the vapor molecule.     

Preparation and characterization of PP/clay nanocomposites based on modified polypropylene and clay

X‐ray diffraction and differential scanning calorimeter (DSC) methods have been used to investigate the crystallization behavior and crystalline structure of hexamethylenediamine (HMDA)‐modified maleic‐anhydride‐grafted polypropylene/clay (PP‐g‐MA/clay) nanocomposites. These nanocomposites have been prepared by using HMDA to graft the PP‐g‐MA (designated as PP‐g‐HMA) and then mixing the PP‐g‐HMA polymer in hot xylene solution, with the organically modified montmorillonite. Both X‐ray diffraction data and transmission electron microscopy images of PP‐g‐HMA/clay nanocomposites indicate that most of the swellable silicate layers are exfoliated and randomly dispersed into PP‐g‐HMA matrix. DSC isothermal results revealed that introducing 5 wt % of clay into the PP‐g‐HMA structure causes strongly heterogeneous nucleation, which induced a change of the crystal growth process from a three‐dimensional crystal growth to a two‐dimensional spherulitic growth. Mechanical properties of PP‐g‐HMA/clay nanocomposites performed by dynamic mechanical analysis show significant improvements in the storage modulus when compared to neat PP‐g‐HMA. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3242–3254, 2005     

Configurational studies of complexes of various tea catechins and caffeine in crystal state

Crystals of the complexes of (+)-catechin (CA) of non-galloylated catechin and (-)-catechin-3-O-gallate (Cg) of galloylated catechin with caffeine were prepared, and their stereochemical structures and intermolecular interactions were determined by X-ray crystallographic analysis. CA formed a 1 : 1 complex with caffeine by intermolecular hydrogen bonds, whereas Cg formed a 1 : 2 complex with caffeine, which was formed by face-to-face and offset π-π interactions and intermolecular hydrogen bonds. A solution of two kinds of non-galloylated catechin, CA and (-)-epicatechin (EC), and caffeine (molar ratio 1 : 1 : 2) in water afforded a 1 : 1 : 2 complex, the crystal structure of which had two layers, one layer in which CA and caffeine formed alternate lines and an other layer in which EC and caffeine formed alternate lines. The 1 : 1 : 2 complex was formed by offset π-π and CH-π interactions and intermolecular hydrogen bonds.     

Supramolecular Structure of N,N-Bis(2-hydroxy-benzyl)alkylamine: From Hydrogen Bond Assembly to Coordination Network in Guest Acceptance

N,N-Bis(2-hydroxybenzyl)alkylamine ( HBA ) was described as a model to simplify the supramolecular system of polybenzoxazines. The single crystal X-ray analysis revealed that HBA forms a dimeric assembly based on its simultaneous inter- and intramolecular hydrogen bond network. When the HBA accepted the copper ion, the dimeric assembly HBA changed its primary hydrogen bond network to charge transfer coordination as clarified by the single crystal analysis as well as the superimposed structure based on DMol³ calculation. The supramolecular structure of HBA and copper also exhibited the role of solvent molecules in the packing structure which is a rare example showing the host accepts not only the metal ions but also the neutral molecules in the same time. The cyclization of HBA with esters or ethers to macrocyclic compounds was also an important model reaction to show how the backbone molecules self-stabilized with the hydrogen bond network initiate the simple, effective and efficient macrocyclic reaction.     

Computational and experimental study of the mechanism of hydrogen generation from water by a molecular molybdenum-oxo electrocatalyst

We investigate the mechanism for the electrocatalytic generation of hydrogen from water by the molecular molybdenum-oxo complex, [(PY5Me(2))MoO](2+) (PY5Me(2) = 2,6-bis(1,1-bis(2-pyridyl)ethyl)pyridine). Computational and experimental evidence suggests that the electrocatalysis consists of three distinct electrochemical reductions, which precede the onset of catalysis. Cyclic voltammetry studies indicate that the first two reductions are accompanied by protonations to afford the Mo-aqua complex, [(PY5Me(2))Mo(OH(2))](+). Calculations support hydrogen evolution from this complex upon the third reduction, via the oxidative addition of a proton from the bound water to the metal center and finally an α-H abstraction to release hydrogen. Calculations further suggest that introducing electron-withdrawing substituents such as fluorides in the para positions of the pyridine rings can reduce the potential associated with the reductive steps, without substantially affecting the kinetics. After the third reduction, there are kinetic bottlenecks to the formation of the Mo-hydride and subsequent hydrogen release. Computational evidence also suggests an alternative to direct α-H abstraction as a mechanism for H(2) release which exhibits a lower barrier. The new mechanism is one in which a water acts as an intramolecular proton relay between the protons of the hydroxide and the hydride ligands. The calculated kinetics are in reasonable agreement with experimental measurements. Additionally, we propose a mechanism for the stoichiometric reaction of [(PY5Me(2))Mo(CF(3)SO(3))](+) with water to yield hydrogen and [(PY(5)Me(2))MoO](2+) along with the implications for the viability of an alternate catalytic cycle involving just two reductions to generate the active catalyst.     

Controlled Handedness of Twisted Lamellae in Banded Spherulites of Isotactic Poly(2‐vinylpyridine) as Induced by Chiral Dopants

Herein, we suggest a unique approach to control the handedness of twisted lamellae in banded spherulites of a stereoregular polymer, isotactic poly(2‐vinylpyridine) (iP2VP). When (R)‐ or (S)‐hexahydromandelic acid (HMA), which can associate with iP2VP, was introduced as a chiral dopant, mirror‐image CD spectra in the complex systems showed induced circular dichroism (ICD) of the iP2VP by chiral HMA. Banded spherulites resulting from lamellar twisting due to the imbalanced stresses at the opposite folding surfaces could be formed by crystallization of the iP2VP/HMA complexes, which had a crystalline structure similar to that of neat iP2VP. A preferential sense of the twisted crystalline lamellae was found in the iP2VP/HMA complex, thus suggesting homochiral evolution from conformational to hierarchical chirality.     

二苯并噻吩在分散型钼催化剂和原位产生的氢存在下的加氢脱硫 Ⅱ.原位氢和分子氢的比较

研究了水/甲苯乳化液中二苯并噻吩(硫芴)在分散型钼酸、磷钼酸和四硫钼酸铵催化剂存在下的加氢脱硫反应.反应在高压釜中于340℃及三种不同的气氛即H2,H2/H2O和CO/H2O(CO和H2O经水煤气转换反应(WGSR)产生原位氢)的存在下进行.用GC和GC-MS鉴定、分析了气体和液体产物的组成.结果表明:对硫芴的加氢脱硫反应,在分散型钼酸和磷钼酸存在下,原位产生的氢比加入的分子氢更为有效.动力学研究结果表明:WGSR反应比硫芴的加氢脱硫反应快5～10倍,说明在原位氢存在下硫芴的加氢脱硫反应是速度控制步骤.总之,试验结果证实,在分散型催化剂和原位氢存在下的加氢过程是重油乳状液改质和破乳的有效方法.     

Atomistic insights on the LCST behavior of PMEO2MA in water by molecular dynamics simulations

Fully atomistic molecular dynamics simulations of poly(2‐[2‐methoxyethoxy]ethyl methacrylate) (PMEO₂MA) in water at temperatures below and above its lower critical solution temperature (LCST) were performed to improve the understanding of its LCST behavior. Atomic trajectories were used to calculate various structural and dynamic properties. Simulation results show that PMEO₂MA undergo a distinct coil‐to‐globule transition above LCST. Detailed analyses of the number of first hydration shell water molecules around various atomic regions are revealed that the water solubility of PMEO₂MA below LCST is mainly provided by the hydrophobic hydration around the side chain carbon atoms. This is achieved by the cage‐like water network formations which are disrupted when the temperature is increased above LCST, accompanied by significant amount of water molecule release and local water‐ordering reduction, which leads to the LCST phase transition. Furthermore, other analyses such as the number of hydrogen bonds and hydrogen bond lifetimes suggest that intermolecular hydrogen bondings between polymer and water molecules have little effect on the phase transition. Our results will contribute to a better understanding on the LCST phase transition of oligo(ethylene glycol) methyl ether methacrylate (OEGMA)‐based homopolymers at atomistic level that will be useful when designing homo‐ and co‐polymers of OEGMAs with desired properties. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 429–441     

无长链席夫碱衍生物单分子膜和LB膜

在银离子的诱导下,两种含有苯并咪唑、没有长链取代基的席夫碱衍生物可以形成稳定的单分子膜,此单子分子膜可以用水平拉膜法转移到固体表面形成ＬＢ膜、ＬＢ膜的紫外吸收光谱和光电子能谱研究表明,Ａｇ（Ⅰ）离子被络合进行了单分子膜中。     

Structural, vibrational and quantum chemical investigations on 5-chloro-2-hydroxybenzamide and 5-chloro-2-hydroxybenzoic acid

The Fourier transform infrared (FTIR) and FT-Raman spectra of 5-chloro-2-hydroxybenzamide (5CBA) and 5-chloro-2-hydroxybenzoic acid (5C2HBA) have been recorded in the range 4000-400 and 4000-100 cm(-1), respectively. The complete vibrational fundamental modes of the compounds were assigned and analysed using the observed FTIR and FT-Raman data. The vibrational frequencies determined experimentally were compared with the theoretical wavenumbers calculated from ab initio HF and DFT-B3LYP gradient methods employing 6-31G** and 6-311++G** basis sets. The effect of halogen, hydroxyl groups and hydrogen bonding on the characteristic frequencies of the -COOH and -CONH2 group frequencies have been investigated. In 5CBA and 5C2HBA intramolecular hydrogen bond between a hydroxyl group and CO group makes a six membered ring, which causes the O?H interaction onto the resonance of the benzene ring. Comparison of the positions of the ν(OH) bands shows the ν(OH) band of 5CBA is located at considerably higher frequency which confirms a weaker hydrogen bond than in 5C2HBA.     

Equilibrium phase diagrams of aqueous mixtures of malonic acid and sulfate/ammonium salts

Tropospheric aerosols are usually complex mixtures of inorganic and organic components. Although the thermodynamic properties of inorganic aerosols have been widely studied, the effect of organics on such properties is still under discussion. In this study, solubility in water, water activity (a(w)) of aqueous solutions, deliquescence relative humidity (DRH), eutonic composition, and eutonic DRH were determined for bulk mixtures of malonic acid (MA) with ammonium sulfate (AS) and ammonium bisulfate (ABS) at 25 degrees C over the full range of composition (from 0 wt % to the solubility limit of the mixture components). The data were used to construct equilibrium phase diagrams, which show the phase of the mixtures as a function of total composition, dry mixture composition, water content, and ambient relative humidity (RH). This work complements previous reports on the thermodynamic properties of AS/MA mixtures because the range of concentrations investigated is larger than in any other published single study. On the other hand, this is the first report on the a(w), deliquescence, and water absorption of ABS/MA mixtures. The eutonic composition for AS/MA mixtures was found to be 66.8 MA dry wt % (MA dry wt % = MA mass x 100/(AS mass + MA mass) with a DRH of 0.437. The eutonic composition for the ABS/MA mixtures was lower than for the AS/MA mixtures: 20.9 MA dry wt % with a DRH of 0.327. Measured a(w) of liquid AS/MA and ABS/MA solutions is compared with an extended Zdanovskii-Stokes-Robinson expression, obtaining a good agreement (error < 5-6%). The expression was used to predict water uptake of mixtures and might be useful to interpret particle hygroscopic growth experiments. Comparison of the AS/MA and ABS/MA systems indicates that ABS reduces the DRH and enhances water uptake, relative to mixtures with AS. The results confirm that ambient particles containing sulfate and water-soluble organic compounds can remain liquid or partially liquid at very low ambient RH conditions, especially if the sulfate is not completely neutralized.     

铜(Ⅱ)、铁(Ⅲ)与邻羟基苄胺固体配合物的研究

本文报道铜(Ⅰ)、铁(Ⅲ)与邻羟基苄胺(HBA)的固体配合物的合成及其溶解度、摩尔电导、磁性、红外光谱、热谱及绿色Cu(HBA)₂·1.5H₂O和棕色Cu(HBA)₂的相互转化的研究。在乙醇和水的混合溶剂中培养得绿色含水Cu(Ⅱ)-HBA配合物的单晶,在无水乙醇中培养,得棕色无水Cu(Ⅱ)-HBA配合物的单晶,测定了配合物的分子结构和晶体结构。     

尿素-富马酸根-水分子为主体晶格的四乙基铵离子包合物的合成与晶体结构

合成一种新的尿素-阴离子复合主体晶格包合物,(C₂H₅)₄N⁺[C₄H₂O₄^2-]1/2·CO(NH₂)₂·H₂O,并进行了X射线晶体结构分析.晶体为单斜晶系,C₂/_c(No.15)空间群,a=1.7909(5)nm,b=1.4431(4)nm,c=1.4443(3)nm,β=126.76(2)°,V=2.9905(13)nm³,Z=4,R₁=0.0647,_wR=0.0735.包合物中,两个尿素分子通过一对N-H…O氢键以通常的“肩并肩”方式连接起来,形成一个二聚体.这些二聚体沿c轴方向依次排列,每两个相邻二聚体间生成的氢键将它们连接成一个沿(001)方向延伸的锯齿形扭带.由c滑移面相关连的富马酸阴离子以水分子为桥,由O(W)-H…O氢键连成一条宽带,沿c轴方向延伸.这些富马酸根-水分子复合氢键宽带与尿素纽带交替平行排列,由此形成了一个平行于ac面的氢键层.四乙基铵离子层填充在b=1/4和b=3/4处的主体晶格的层间空隙处,构成“三明治”式夹层结构的包合物.     

Fluorescence study on a liquid‐crystalline polyester containing naphthoate mesogen units

Using fluorescence spectroscopy, we investigated intermolecular interaction between mesogenic units in a thermotropic main‐chain LC polyester, P(HBA73/HNA27), containing oxybenzoate (HBA) and oxynaphthoate (HNA) mesogenic units. It is known that P(HBA73/HNA27), which has a high molecular weight, shows second harmonic generation (SHG) activity. P(HBA73/HNA27) showed fluorescence at 410 nm and 430 nm, originating from two kinds of intermolecular interaction. Fluorescence with a peak at 410 nm comes from the ground‐state complex between partially overlapping naphthoate units or between naphthoate and oxybenzoate units whose interaction is weak. Fluorescence at 430 nm comes from the ground‐state complex between fully overlapping naphthoate units whose interaction is strong. The relative fluorescence intensity for 430 nm compared to 410 nm increases with increases in inherent viscosity, η_inh, of P(HBA73/HNA27), the composition ratio of HNA/HBA, and temperature. The fluorescence intensity ratio, I₄₃₀/I₄₁₀, of P(HBA73/HNA27) shows the same inherent‐viscosity dependence with its sudden increase at η_inh = 1.4 ∽ 2.2 dL/g as its SHG activity does, supporting the polar structure and uniformity of LC orientation of the present LC polyester. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2922–2928, 2000     

Mixed-mode retention mechanism for (-)-epigallocatechin gallate on a 12% cross-linked agarose gel media

The adsorption behaviour of (-)-epigallocatechin gallate (EGCG), the major polyphenolic substance in green tea extracts, on the cross-linked agarose gel Superose 12 HR 10/30, has been studied using a variety of solvent systems and shown to be based on a mixture of hydrogen bonding and hydrophobic interaction. The hydrogen bonding was studied in acetonitrile in the presence of different co-solvents possessing varying hydrogen bond donor (HBD) and/or hydrogen bond acceptor (HBA) characteristics. The HBA-value of the co-solvent had the highest effect whereas the HBD-value played a subordinate role. Retention due to hydrophobic interaction could be demonstrated when mobile phases containing high water content were applied. The retention of EGCG, and its analogues (-)-epigallocatechin (EGC) and (-)-catechin (C) were thus shown to be dependent on the polarity of the organic modifiers added. However, the elution order of EGC and C, was inversed to that observed in reversed phase chromatography, indicating that some hydrogen bonding was still in effect. The retardation of EGCG in the presence of a wide concentration range of acetonitrile in water confirmed the interpretation that the retention mechanism is of mixed-mode character based on both hydrogen bonding and hydrophobic interaction.     

Copolymerization of epichlorhydrin with maleic anhydride catalyzed by Zn(acac)2

Copolymerization of epichlorhydrin (ECH) with maleic anhydride (MA) was investigated under several conditions. Zinc acetylacetonate [Zn(acac)₂] was found to catalyze the alternate copolymerization of ECH with MA at a mild temperature, resulting in the formation of polyester, the structure of which was confirmed with the aid of infrared, NMR, and elemental analysis. From kinetic studies of copolymerization an apparent first order of reaction with respect to catalyst concentration and to monomer concentration with 1:1 mole mixture was established. A possible initiation mechanism was discussed, and Zn(acac)₂–MA complex was suggested to be an initiating species.