Deuteron spin lattice relaxation in amorphous ices

Temperature-dependent deuteron spin lattice relaxation times T(1) have been obtained from water in its three amorphous states at ambient pressure: low density amorphous (LDA), high density amorphous (HDA), and very high density amorphous (VHDA). It is found that in all of these states the magnetization recovery is essentially monoexponential and that T(1) of LDA is significantly longer than that of the higher density forms. Thus, T(1) can be used as a monitor parameter to study the kinetics of the transitions from HDA to LDA and from VHDA to LDA. During the transformation of VHDA to LDA an intermediate state is formed, which, according to its T(1) at low temperature, is clearly determined to be HDA-like. However, and most significantly, the transition from VHDA to this HDA-like state and further on to LDA occurs at temperatures significantly above the kinetic stability limit of native HDA produced at 77 K. These findings contribute to the current discussion on the nature of HDA and VHDA by strengthening the view that the annealing of VHDA at ambient pressure produces a relaxed HDA-like state.     

Direct transformation of ice VII′ to low-density amorphous ice

Vibrational spectra reveal that ice VII′ transforms to low-density amorphous ice (LDA) at low temperature on release of pressure to ambient pressure and low temperature. The measurements were obtained using in situ Raman spectroscopy of samples of ice VII′ as a function of pressure at 135 K. The observation of this direct decompression-induced VII′-LDA transition complements the previously observed pressure-induced reversible transition between LDA and high-density amorphous ice (HDA) at 120–140 K and the temperature-induced amorphization of metastable ice VII and ice VIII at 0.1 MPa.     

Water's polyamorphic transitions and amorphization of ice under pressure

Transformations of water's high density amorph (HDA) to low density amorph (LDA) and of LDA's to cubic ice (Ic) have been studied by in situ thermal conductivity kappa measurements at high pressures. The HDA to LDA transformation is unobservable at p of 0.07 GPa, indicating that, for a fixed heating rate, an increase in pressure increases the temperature of HDA to LDA transformation and decreases that of LDA to ice Ic, causing thereby the two transformations to merge, and HDA appears to convert directly to ice Ic. Thus either LDA forms but converts extremely rapidly to ice Ic, or LDA does not form. At a fixed p and T, in the range of pressure amorphization of hexagonal ice, kappa continues to decrease with time. Therefore, the amorphization of ice Ih is kinetically controlled. When HDA at 1 GPa was heated from 130 to 157 K and densified to very HDA, its kappa increased by 3%. Our findings and a scrutiny of earlier reports show that a reversible transition between HDA and LDA does not occur at approximately 135 K and approximately 0.2 GPa. Since there is no unique HDA, it is difficult to justify the conjecture for a second critical point for water.     

In situ Raman spectroscopy of low-temperature/high-pressure transformations of H2O

In situ Raman spectra of transformations of H2O as functions of pressure and temperature have been measured starting from high-density amorphous ice (HDA). Changes above Tx, the crystallization temperature of HDA, were observed. The spectra provide evidence for an abrupt, first-order-like, structural change that appears to be distinct from those associated with the transformation between low-density amorphous ice (LDA) and HDA. In separate experiments, in situ Raman spectra of ice XII transformed from HDA have been measured at various P-T regions, in order to improve the understanding of the stability limits of ice XII. The spectra of ices VI and XII differ in shape, but the vibrational frequencies are very close in the same P-T regimes. A metastable phase of ice found to form within the stability field of ice VI appears to be distinct from ice XII.     

Electronic structures and hydrogen bond network of high-density and very high-density amorphous ices

Electronic structures of hexagonal ice (ice Ih), high-density amorphous ice (HDA), and very high-density amorphous ice (VHDA) are investigated using ab initio density functional theory (DFT) at 77 K under a pressure of 0.1 MPa, focusing on band structure, density of states (DOS), partial density of states (PDOS), and electron density. It is found that the integration intensity of the O-2p bonding band in HDA is 1.53 eV wider than that in the VHDA. Because more 2p electrons in HDA participate the 2p-1s hybridization of O-H. The classical molecular dynamics (MD) method has further been carried out to analyze the hydrogen bond network of HDA and VHDA with larger numbers of water molecules under the same temperature, pressure, and boundary conditions used as those during the DFT calculation. MD results show that there exists some water molecules with five hydrogen bonds in both HDA (4.1 +/- 0.1%) and VHDA (2.8 +/- 0.1%), as compared with the LDA, being consistent with the integration intensity results of PDOS. This result can be used to interpret the physical nature of the similar transition temperature of HDA and VHDA to LDA with different heating rates.     

Waterlike glass polyamorphism in a monoatomic isotropic Jagla model

We perform discrete-event molecular dynamics simulations of a system of particles interacting with a spherically-symmetric (isotropic) two-scale Jagla pair potential characterized by a hard inner core, a linear repulsion at intermediate separations, and a weak attractive interaction at larger separations. This model system has been extensively studied due to its ability to reproduce many thermodynamic, dynamic, and structural anomalies of liquid water. The model is also interesting because: (i) it is very simple, being composed of isotropically interacting particles, (ii) it exhibits polyamorphism in the liquid phase, and (iii) its slow crystallization kinetics facilitate the study of glassy states. There is interest in the degree to which the known polyamorphism in glassy water may have parallels in liquid water. Motivated by parallels between the properties of the Jagla potential and those of water in the liquid state, we study the metastable phase diagram in the glass state. Specifically, we perform the computational analog of the protocols followed in the experimental studies of glassy water. We find that the Jagla potential calculations reproduce three key experimental features of glassy water: (i) the crystal-to-high-density amorphous solid (HDA) transformation upon isothermal compression, (ii) the low-density amorphous solid (LDA)-to-HDA transformation upon isothermal compression, and (iii) the HDA-to-very-high-density amorphous solid (VHDA) transformation upon isobaric annealing at high pressure. In addition, the HDA-to-LDA transformation upon isobaric heating, observed in water experiments, can only be reproduced in the Jagla model if a free surface is introduced in the simulation box. The HDA configurations obtained in cases (i) and (ii) are structurally indistinguishable, suggesting that both processes result in the same glass. With the present parametrization, the evolution of density with pressure or temperature is remarkably similar to the corresponding experimental measurements on water. Our simulations also suggest that the Jagla potential may reproduce features of the HDA-VHDA transformations observed in glassy water upon compression and decompression. Snapshots of the system during the HDA-VHDA and HDA-LDA transformations reveal a clear segregation between LDA and HDA but not between HDA and VHDA, consistent with the possibility that LDA and HDA are separated by a first order transformation as found experimentally, whereas HDA and VHDA are not. Our results demonstrate that a system of particles with simple isotropic pair interactions, a Jagla potential with two characteristic length scales, can present polyamorphism in the glass state as well as reproducing many of the distinguishing properties of liquid water. While most isotropic pair potential models crystallize readily on simulation time scales at the low temperatures investigated here, the Jagla potential is an exception, and is therefore a promising model system for the study of glass phenomenology.     

Polarized Raman spectroscopic study on the solvent state of glassy LiCl aqueous solutions and the state of relaxed high-density amorphous ices

We measure polarized OH-stretching Raman spectra of the glassy lithium chloride aqueous solutions (LiClaq solutions) and the relaxed high-density amorphous ices (HDA). The totally OH symmetric vibrational mode around 3100 cm(-1) (g(1) mode) for the glassy LiClaq solutions of 14.3 mol% and the g(1) mode for the glassy LiClaq solution of 10.0 mol% seem to be similar to the g(1) mode for HDA at high pressure and the g(1) mode for HDA at 1 atm, respectively. This indicates that the solvent state of glassy LiClaq solution relates to the state of HDA and that the attenuation of the salt effect on water is equivalent to the attenuation of the pressure effect on water. This suggests a possibility that the hydration in electrolyte aqueous solution may relate to high-density liquid water.     

A photoluminescent switch based on the hybrid organized molecular films of decatungsteuropate and some amphiphiles

Hybrid organized molecular films composed of a polyoxometalate, decatungsteuropate (EuW(10)), and amphiphiles such as hexadecyltrimethylammonium bromide (CTAB), n-octadecylamine (ODA) and 4-hexadecylaniline (HDA) were fabricated by Langmuir-Blodgett (LB) technique and their photoluminescent properties were investigated. The hybrid films, which were formed through in situ complex formation at the air/water interface and subsequently transferred onto the solid substrate, were characterized by UV-vis, FT-IR, fluorescence, and AFM measurements. The transferred hybrid films showed red emission characteristic of the Eu(III) ion upon UV irradiation. The photoluminescence of the hybrid films was sensitive to the acid and base gases. When ODA/EuW(10) and HDA/EuW(10) hybrid films were exposed to HCl gas, their photoluminescence disappeared completely. Interestingly, the photoluminescence was recovered upon subsequent exposing the same film to NH(3) gas. Such process could be repeated many times and a switch based on these hybrid films was proposed. On the other hand, the photoluminescent intensity of CTAB/EuW(10) film decreased but never disappeared upon exposing to HCl gas. Similarly, the photoluminescence could also be partially recovered upon exposing to NH(3) gas. Detailed investigation on the spectral changes of the films revealed that the interaction between EuW(10) and CTAB and was different from EuW(10) with ODA or HDA, and protonation of amine group in ODA or HDA induced by HCl gas played an important role in realizing the "on" and "off" photoluminescence switch of the hybrid films.     

Polarized Raman spectroscopic study of relaxed high density amorphous ices under pressure

We have made high density amorphous ice (HDA) by the pressure-induced amorphization of hexagonal ice at 77 K and measured the volume change on isobaric heating in a pressure range between 0.1 and 1.5 GPa. The volume of HDA on heating below ～0.35?GPa increases, while the volume of HDA on heating above ～0.35?GPa decreases. The polarized OH-stretching Raman spectra of the relaxed HDAs are compared with that of the unannealed HDA. The relaxed HDAs are prepared at 0.2 GPa at 130 K and 1.5 GPa at 160 K. It is found that the relatively strong totally symmetric OH-stretching vibration mode around 3100?cm(-1) exists in the depolarized reduced Raman spectrum χ(VH)(") of the unannealed HDA and that its intensity rapidly decreases by relaxation. The χ(VH)(") profiles of the relaxed HDA are similar to those of liquid water. These results indicate that the HDA reaches a nearly equilibrium state by annealing and the intrinsic state of HDA relates to a liquid state. The pressure-volume curve of the relaxed HDA at 140 K seems to be smooth in the pressure range below 1.5 GPa.     

2′-Lipid-modified oligonucleotides via a ‘Staudinger-Vilarrasa’ reaction

We report a new access to 2′-amido-2′-deoxyuridine via a Staudinger-Vilarrasa coupling reaction for the preparation of lipid-modified oligonucleotides. One or two lipidic moieties were inserted within the oligonucleotidic sequence (LONs) leading to a repertoire of original antagomir-like molecules targeting micro RNA (miRNA or miR). Melting temperature (Tm) experiments revealed that the stability of the duplexes depends on the lipid position and the number of lipid moieties inserted within the oligonucleotide sequence. Single lipid conjugations of positions 11 and 19 of LONs targeting miR-122 do not destabilize the duplexes.     

Hydrodistillation-adsorption method for the isolation of water-soluble, non-soluble and high volatile compounds from plant materials

Proposed method of hydrodistillation–adsorption (HDA) on activated carbon and hydrodistillation (HD) with solvent trap were compared for the isolation of water-soluble, non-soluble and high volatile compounds, such as acids, monoterpenes, isothiocyanates and others from carob (Certonia siliqua L.), rosemary (Rosmarinus officinalis L.) and rocket (Eruca sativa L.). Isolated volatiles were analyzed by GC and GC/MS. The main advantages of HDA method over ubiquitous HD method were higher yields of volatile compounds and their simultaneous separation in three fractions that enabled more detail analyses. This method is particularly suitable for the isolation and analysis of the plant volatiles with high amounts of water-soluble compounds. In distinction from previously published adsorption of remaining volatile compounds from distillation water on activated carbon, this method offers simultaneous hydrodistillation and adsorption in the same apparatus.     

Synthesis of fused uracils: pyrano[2,3-d]pyrimidines and 1,4-bis(pyrano[2,3-d]pyrimidinyl)benzenes by domino Knoevenagel/Diels-Alder reactions

Abstract  

Knoevenagel condensation of barbituric acids with aromatic aldehydes containing one or two formyl groups was carried out. 5-Arylidenebarbituric acids underwent smooth hetero-Diels-Alder (HDA) reactions with enol ethers to afford cis and trans diastereoisomers of pyrano[2,3-d]pyrimidine-2,4-diones and 5,5′-(1,4-phenylene)bis[2H-pyrano[2,3-d]pyrimidine-2,4(3H)-dione] derivatives in excellent yields (75–88 %). Syntheses were realized by Knoevenagel condensation and HDA reaction in four different reaction conditions: Knoevenagel condensation in water and Diels-Alder reaction in methylene chloride solution, Knoevenagel condensation in water and Diels-Alder reaction without solvent, three-component one-pot reaction in methylene chloride solution, or three-component one-pot reaction in water. All reactions were carried out without catalyst at room temperature. The reactions of malononitrile with Knoevenagel condensation products of barbituric acids and heteroaromatic aldehydes or terephthalaldehyde were examined and did not provide corresponding pyranopyrimidines.     

High temperature liquid chromatography and liquid chromatography-mass spectroscopy analysis of octylphenol ethoxylates on different stationary phases

Temperature was investigated as active parameter in the liquid chromatography (LC) analysis of octylphenol ethoxylates. Significant differences in selectivity were observed when the oligomers were analyzed by reversed phase LC (RPLC) on silica-, zirconia- and polystyrene/divinylbenzene based stationary phases at low (ambient), medium and elevated temperature with acetonitrile/water as mobile phase. As ascertained by LC-mass spectroscopy (MS), in most cases the elution order of the oligomers was completely reversed comparing ambient and high temperature separations. On a graphitized carbon type column, the selectivity remained unchanged, regardless the analysis temperature. Also in normal phase LC, the elution order remained unaffected by temperature variations both for acetonitrile/water and methanol/water mixtures as mobile phase. Surprisingly, when reversed phase LC on a octadecylsilicagel column at different temperatures was repeated with methanol instead of acetonitrile as mobile phase ingredient, the reversal of elution order did not take place. Results are evaluated in terms of thermodynamic parameters.     

扩链剂对脂肪族聚氨酯脲和聚脲弹性体结构与性能的影响

用异佛尔酮二胺(IPDA)、乙二胺(EDA)和己二胺(HDA)三种扩链剂合成了不同结构的脂肪族聚氨酯脲和聚脲, 并考察了扩链剂对聚氨酯脲和聚脲形态结构与性能的影响. 研究结果表明, 与EDA和HDA扩链的聚氨酯脲和聚脲相比, IPDA扩链的聚氨酯脲和聚脲中脲羰基的氢键化程度较低, 软段和硬段间的相混合程度较好; 同时它们具有更好的拉伸强度、硬度和撕裂强度, 但断裂伸长率较低. EDA和HDA扩链的聚氨酯脲和聚脲相比, 两者性能相差不大. 聚氨酯脲的脲羰基较完善氢键化程度以及整个氢键化程度都比聚脲的要低, 同时聚氨酯脲的吸水率也较低.     

Evolution of the structure of amorphous ice: from low-density amorphous through high-density amorphous to very high-density amorphous ice

We report results of molecular dynamics simulations of amorphous ice for pressures up to 22.5 kbar. The high-density amorphous ice (HDA) as prepared by pressure-induced amorphization of I(h) ice at T=80 K is annealed to T=170 K at various pressures to allow for relaxation. Upon increase of pressure, relaxed amorphous ice undergoes a pronounced change of structure, ranging from the low-density amorphous ice at p=0, through a continuum of HDA states to the limiting very high-density amorphous ice (VHDA) regime above 10 kbar. The main part of the overall structural change takes place within the HDA megabasin, which includes a variety of structures with quite different local and medium-range order as well as network topology and spans a broad range of densities. The VHDA represents the limit to densification by adapting the hydrogen-bonded network topology, without creating interpenetrating networks. The connection between structure and metastability of various forms upon decompression and heating is studied and discussed. We also discuss the analogy with amorphous and crystalline silica. Finally, some conclusions concerning the relation between amorphous ice and supercooled water are drawn.     

Chromatographic determination of amines in biological fluids with special reference to the biological monitoring of isocyanates and amines. IV. Determination of 1,6-hexamethylenediamine in human urine using capillary gas chromatography and selective ion monitoring

A capillary gas chromatographic (GC) method was developed for the determination of 1,6-hexamethylenediamine (HDA) in hydrolysed human urine. The method was based on a derivatization procedure with heptafluorobutyric anhydride. The amides formed were determined using capillary GC with selected ion monitoring in the chemical ionization mode with ammonia as reagent gas. The overall recovery was 34% for a concentration of 100 micrograms/l of HDA in urine. The minimum detectable concentration in urine was below 0.5 microgram/l. The precision of the method was 5% (n = 9). Deuterium-labelled HDA [H2NC2H2(CH2)4C2H2NH2] was used as the internal standard. A male subject was exposed to hexamethylene diisocyanate (HDI) for 7.5 h in a test chamber. The average air concentration of HDI was ca. 30 micrograms/m3, which corresponds to ca. 85% of the threshold limit value in Sweden (35 micrograms/m3). The half time of urinary levels of HDA was ca. 1.4 h and more than 90% of the urinary elimination was completed within 4 h after the exposure. The amount of HDA excreted in urine was ca. 10 micrograms, corresponding to ca. 10% of the estimated inhaled dose of HDI.     

Small angle x-ray scattering of a supercritical electrolyte solution: the effect of density fluctuations on the hydration of ions

Synchrotron small angle x-ray scattering measurements on water and zinc bromide ZnBr2 aqueous solutions were carried out from ambient to supercritical conditions. For both systems several isobars (between 285 and 600 bars) were followed beyond the critical isochore. The data were analyzed through an Ornstein-Zernike formalism in terms of correlation length and null angle structure factor. The results for pure water are in agreement with previously published values. Solutions of different electrolyte concentrations were studied. In each case, the values of the correlation length and null angle structure factor are larger than those of pure water. This effect is more pronounced for higher concentrations and/or for pressure closer to the critical point of pure water. This is in agreement with the shift of the critical point determined in the literature for NaCl solutions. Comparing these results to previous x-ray absorption measurements carried out on identical samples we propose the following two step sequence for ionic hydration up to supercritical conditions: (1) from ambient to about 300 degrees C, an increase of ion pairing and formation of multi-ionic complexes which can be correlated to the decrease of the dielectric constant; (2) an enhancement of the local solvation shell of ions due to the onset of the thermal density fluctuations at high temperature, leading to a screening effect between ions and inhibiting the ion pairing processes.     

Stability studies of arsenate, monomethylarsonate, dimethylarsinate, arsenobetaine and arsenocholine in deionized water, urine and clean-up dry residue from urine samples and determination by liquid chromatography with microwave-assisted oxidation-hydride generation atomic absorption spectrometric detection

The stability of arsenate, monomethylarsonate, dimethylarsinate (DMA), arsenobetaine (AsB) and arsenocholine (AsC) at a concentration of 200 μg l⁻¹ in deionized water, urine and dry clean-up residue of urine, stored in dark at −20 °C, 4 °C and ambient temperature, without the addition of any stabilizer reagent was evaluated. The five species were determined independently by liquid chromatography with microwave-assisted oxidation-hydride generation atomic absorption spectrometric detection. At −20 °C, all species were stable in water and untreated urine; at 4 °C and ambient temperature, they were stable during the 67 days of testing in the urine dry residue after the clean-up procedure. In untreated urine samples at 4 °C and ambient temperature, AsC is unstable and easily transformed to the more oxidized species, AsB. In deionized water, AsB and AsC are transformed to other species such as DMA. The dry urine residue may be a good matrix as a reference material for As species.     

Dynamic deswelling studies of poly(N-vinyl-2-pyrrolidone/itaconic acid) hydrogels swollen in water and terbinafine hydrochloride solutions

Deswelling kinetics of water and terbinafine hydrochloride adsorbed poly(N-vinyl-2-pyrrolidone/itaconic acid) P(VP/IA) hydrogels were investigated. Hydrogels were prepared by irradiating the ternary mixture of VP/IA and cross-linking agent ethylene glycol dimethacrylate (EGDMA) in water by γ-rays at ambient temperature. Hydrogels swelled in pure water and terbinafine hydrochloride (TER-HCl) solutions at room temperature and deswelling or water loss were investigated between 4 and 45 °C temperature range and on human skin. The influence of IA content, % swelling, temperature and TER-HCl content on the water loss from gel matrix were investigated. Induction time for 80% water loss from hydrogel systems are found to increase from 9.6 to 21.2 h by increasing IA content in the gel system at 25 °C and decreased by 11 h with addition of TER-HCl in the gel system. Kinetic analyses had shown that the basic properties affecting the water loss behavior of these hydrogels are the IA and TER-HCl content and temperature of the medium.     

Asymmetric Diels–Alder and Inverse‐Electron‐Demand Hetero‐Diels–Alder Reactions of β,γ‐Unsaturated α‐Ketoesters with Cyclopentadiene Catalyzed by N,N′‐Dioxide Copper(II) Complex

Highly enantioselective Diels–Alder (DA) and inverse‐electron‐demand hetero‐Diels–Alder (HDA) reactions of β,γ‐unsaturated α‐ketoesters with cyclopentadiene catalyzed by chiral N,N′‐dioxide–Cu(OTf)₂ (Tf=triflate) complexes have been developed. Quantitative conversion of β,γ‐unsaturated α‐ketoesters and excellent diastereoselectivities (up to 99:1) and enantioselectivities (up to >99 % ee) were observed for a broad range of substrates. Both aromatic and aliphatic β,γ‐unsaturated α‐ketoesters were found to be suitable substrates for the reactions. Moreover, the chemoselectivity of the DA and HDA adducts were improved by regulating the reaction temperature. Good to high chemoselectivity (up to 94 %) of the DA adducts were obtained at room temperature, and moderate chemoselectivity (up to 65 %) of the HDA adducts were achieved at low temperature. The reaction also featured mild reaction conditions, a simple procedure, and remarkably low catalyst loading (0.1–1.5 mol %). A strong positive nonlinear effect was observed.