The structure of liquid water at room temperature

Full details are given of a recent time-of-flight neutron diffraction experiment in which partial pair correlation functions for liquid water are extracted by isotope substitution. Measurements of differential cross sections of mixtures of heavy and light water are made, and by performing the experiment at the high neutron energies available at a pulsed neutron source (Los Alamos) the magnitude of dynamic corrections to the data is reduced. The problematic hydrogen incoherent scattering is removed by a subtraction technique which avoids reference to dynamic models of the liquid. The results, although they show good agreement with computer simulations, show serious qualitative differences with other neutron experiments on water, and it is suggested these discrepancies are a result of lack of attention to the unusual properties of hydrogen as a scatterer of neutrons.     

Measurements of differential capacitance in room temperature ionic liquid at mercury,glassy carbon and gold electrode interfaces

Differential capacitances were measured in 1-propyl-3-methylimidazolium tetrafluoroborate (PMIBF₄) ionic liquid at three different electrode substrates (Hg, GC (glassy carbon) and Au) as a function of potential. Essentially different capacitance–potential curves were obtained at different electrodes. From the parabolic electrocapillary curve measured at dropping Hg electrode in PMIBF_4, the potential of zero charge (PZC) was found to be −0.31 V vs. Ag/AgCl (wire). However, the capacitance–potential curve at Hg electrode was found not to show any valley related to the PZC, whereas at GC and Au electrodes a minimum was observed at 0.29 and −0.51 V, respectively. The results are in disagreement with the recent theoretical study which implies that the capacitance–potential curve should be of bell shape with the maximum value of capacitance at PZC. The parabolic capacitance–potential curve similar to those obtained in inorganic molten salts was also observed for the first time at GC electrode. Probable causes of the difference in their capacitance–potential curves were also discussed.     

Shear-induced lamellar phase of an ionic liquid crystal at room temperature

The phase behaviour of a number of N-alkylimidazolium salts was studied using polarizing optical microscopy, differential scanning calorimetry and X-ray diffraction. Two of these compounds exhibit lamellar mesophases at temperatures above 50°C. In these systems, the liquid crystalline behaviour may be induced at room temperature by shear. Sheared films of these materials, observed between crossed polarisers, have a morphology that is typical of (wet) liquid foams: they partition into dark domains separated by brighter (birefringent) walls, which are approximately arcs of circle and meet at “Plateau borders” with three or more sides. Where walls meet three at a time, they do so at approximately 120° angles. These patterns coarsen with time and both T1 and T2 processes have been observed, as in foams. The time evolution of domains is also consistent with von Neumann's law. We conjecture that the bright walls are regions of high concentration of defects produced by shear, and that the system is dominated by the interfacial tension between these walls and the uniform domains. The control of self-organised monodomains, as observed in these systems, is expected to play an important role in potential applications.     

Rapid and controllable covalent functionalization of single-walled carbon nanotubes at room temperature

We report a rapid and efficient procedure to functionalize SWNT where free radicals generated at room temperature by a redox reaction between reduced SWNT and diacyl peroxide derivatives were covalently attached to the SWNT wall.     

Direct electrocatalytic reduction of p-nitrophenol at room temperature ionic liquid modified electrode

Direct electrochemical reduction ofp-nitrophenol （PNP） was investigated on a room temperature ionic liquid N-butylpyridinium hexafluorophosphate （BPPF6） modified carbon paste electrode （CILE）. The cathodic peak potential was positively shifted and the peak currents were increased compared to that obtained on traditional carbon paste electrode （CPE）. The results indicated that the presence of ionic liquid BPPF6 on the electrode surface showed excellent catalytic ability to the electrochemical reduction of PNP. The electrochemical behaviors of PNP on the CILE were investigated by cyclic voltammetry and the conditions such as the scan rate, the buffer pH, the substrate concentration were optimized. The electrochemical parameters were further calculated with the results of the electron transfer number （n）, the charge-transfer coefficient （α） and the surface concentration （Гr） as 1.76, 0.37 and 2.47 × 10^-9 mol/cm^2, respectively, for the selected reductive peak. The results indicated that PNP showed an irreversible adsorption-controlled electrode process on the CILE.     

Coexistence of liquid and solid phases of Bmim-PF6 ionic liquid on mica surfaces at room temperature

In this communication, we report the coexistence of liquid and solid phases of room temperature ionic liquid (IL) [Bmim][PF6] on mica surfaces, observed by tapping mode atomic force microscopy (AFM) in air. Multilayers as well as drop-on-the-layer structures of the ionic liquid are revealed. The solid layers were very stable, and their orientations were affected by the mica lattice, indicating that the ionic liquid undergoes a template-induced ordering process. These results are helpful for advancing the understanding of interfacial structures of ILs on solid surfaces, the analogous structural patterns in both of its solid and liquid phases, and its heterogeneity.     

Kinetics of the metathetical reaction between carbon tetrachloride and toluene

A metathetical reaction between carbon tetrachloride and toluene to give benzyl chloride and chloroform occurs at temperatures above 200°C (k = 4.8 × 10¹⁰ e^?32,900/RT cc mole^?1sec^?1). The reaction does not involve free radicals, as is shown by the kinetic behavior of the system, by the lack of effect of added free-radical chain inhibitors, and by the absence of the expected chain termination product, hexachloroethane. The reaction is one of a general type between carbon tetrachloride and alkanes or alkylaromatics, but at the temperatures required it is often obscured by dehydrohalogenation of the product to the highly reactive olefin. At high temperatures, benzyl chloride reacts with toluene to give bibenzyl and hydrogen chloride, apparently also by a metathetical reaction. The transition state is postulated to be four-center, in which the carbon-chlorine and carbon–hydrogen bonds are broken and reformed: The experimental preexponential factor is in good agreement with that calculated from transition-state theory.     

High-pressure Raman study of liquid and molecular crystal at room temperature. 1,2-dibromoethane

Raman spectra of liquid and crystalline CH₂BrCH₂Br have been measured at hydrostatic pressures up to 120 kbar and at 300 K in a gasketed diamon     

High-pressure Raman study of liquid and molecular crystal at room temperature. Methylene chloride

Raman spectra of liquid and crystalline CH₂Cl₂ were measured at hydrostatic pressures up to 85 kbar and at room temperature. The pressure dependences of the internal modes (ν₄, ν₃, ν₉, ν₂ and ν₁) and the two external (lattice) modes are reported; the ν₄ symmetric CCl₂ bending mode is split into two major peaks at the liquid—solid phase transition point (at 11.3 kbar), and the discontinuities of the slopes for their peak frequencies against pressure suggest a second-order phase transition at ≈ 45 kbar. The pressure data are used to test the applicability of the vibrational scaling law proposed by Zallen for a molecular crystal.     

Computational studies of liquid water and diluted water in carbon tetrachloride

Molecular dynamics simulations were carried out to study solvent effects on the energetic and dynamical properties of water molecules in liquid water and in carbon tetrachloride (CCl4). In these studies, the free-energy profiles or potentials of mean force (PMF) for water dimers in both solvents were computed. The computed PMF results showed a stable minimum near 3 A for the O-O separation, with a minimum free energy of about -2.8 kcal/mol in CCl4, as compared to a value of -0.5 kcal/mol in liquid water. The difference in free energy in water as compared to that in CCl4 was expected and is the result of competition from surrounding water molecules that are capable of forming hydrogen bonds in the liquid water. This capability is absent in the diluted water found in CCl4. We found that the rotational motions of H2O/D2O were nonisotropic, with the out-of-plane vector correlation times in H2O/D2O varying from 5.6/5.8 ps at 250 K to 0.57/0.56 ps at 350 K and the corresponding OH/OD bond vectors varying from 6.5/7.7 ps to 0.75/0.75 ps. The results compare reasonably well to the available NMR experimental and computer simulation data on the same system (Farrar; Skinner; et al. J. Am. Chem. Soc. 2001, 123, 8047). For diluted water in CCl4, we found the computed rotational correlation times also were nonisotropic and much longer than the corresponding NMR experimental values at the same concentration (Farrar; et al. J. Phys. Chem. A 2007, 111, 6146). Upon analyzing the water hydrogen-bonding patterns as a function of water concentration, we conclude that the differences in the rotational correlation times mainly result from the formation of water hydrogen-bonding networks as the water concentration is increased in liquid CCl4. In addition, we found the rotational correlation times to be substantially faster in liquid CCl4 than in liquid water.     

Determination of relative and absolute abundance of stable nitrogen isotopes by proton induced nuclear reactions

Thick-target yield of γ-rays emitted in the reactions¹⁴N(p,p′γ₁)¹⁴N and¹⁵N(p,αγ₁)¹²C were measured as a function of bombarding energy in order to select the conditions favoring the employment of these reactions in nitrogen isotopic analysis. The applicability of these reactions in the determination of relative as well as absolute nitrogen isotopic abundances was demonstrated at 4.3 MeV bombarding energy. Supported in part by the International Atomic Energy Agency, Vienna, Austria.     

An eco-safe approach to benzopyranopyrimidines and 4H-chromenes in ionic liquid at room temperature

An environmentally benign, ionic liquid promoted multicomponent protocol to benzopyrano(2,3-d)pyrimidines and 4H-chromenes has been developed at room temperature. Results of the reaction depend on the nature of the nucleophile used in the reaction. Secondary amines result in the formation of benzopyrano(2,3-d)pyrimidines, whereas thiols give rise to 4H-chromenes under the same set of reaction conditions.     

一种室温离子液体与水相互作用的密度泛函理论研究

采用量子化学计算中的密度泛函理论(DFT),在B3LYP/6-31+G(d,p)计算水平上研究了离子液体1-乙基-3-甲基咪唑四氟硼酸盐([Emim]BF4)及其与水分子形成的复合物的稳定构型和相互作用能;经振动频率分析得到了[Emim]BF4及其与水的复合物的红外光谱.计算结果表明,相对于水分子与阳离子的作用而言,水分子与阴离子的作用对离子液体结构的影响更大.与此同时,实验测得的[Emim]BF4的红外光谱与计算结果吻合.     

Metal-organic frameworks with exceptionally high capacity for storage of carbon dioxide at room temperature

Metal-organic frameworks (MOFs) show high CO2 storage capacity at room temperature. Gravimetric CO2 isotherms for MOF-2, MOF-505, Cu3(BTC)2, MOF-74, IRMOFs-11, -3, -6, and -1, and MOF-177 are reported up to 42 bar. Type I isotherms are found in all cases except for MOFs based on Zn4O(O2C)6 clusters, which reveal a sigmoidal isotherm (having a step). The various pressures of the isotherm steps correlate with increasing pore size, which indicates potential for gas separations. The amine functionality of the IRMOF-3 pore shows evidence of relatively increased affinity for CO2. Capacities qualitatively scale with surface area and range from 3.2 mmol/g for MOF-2 to 33.5 mmol/g (320 cm3(STP)/cm3, 147 wt %) for MOF-177, the highest CO2 capacity of any porous material reported.     

Study of two-dimensional liquid chromatography with high temperature NPLC and room temperature RPLC

To overcome the peak band broadening and to increase the peak capacity and separation efficiency of a two-dimensional liquid chromatographic system, a high-temperature normal phase liquid chromatography (HTNPLC) was used as the first dimension (1^st-D), and a RPLC was used as the second dimension (2^nd-D). The sample was first separated on the 1^st-D CN column and the primary eluent stored in the sampling-loop system alternatively (in HTNPLC×RPLC mode) or selectively (in HTNPLC/RPLC mode) and was then transferred to 2^nd-D C₁₈ column for further separation. The resolution and separation efficiency of the systems were greatly improved. The systems were evaluated by analyzing several polycyclic aromatic hydrocarbons and Glycyrrhiza uralensis extract. __________ Translated from Journal of Instrumental Analysis, 2008, 27(1) (in Chinese)     

Stereoselective Negishi-like couplings between alkenyl and alkyl halides in water at room temperature

Mix in water and then stir. That is all that is required in this new approach to stereoselective sp(3)-sp(2) cross-couplings between an alkyl and alkenyl halide. Prior formation of organozinc reagents is not required.     

Rational tuning of melting entropies for designing luminescent lanthanide-containing thermotropic liquid crystals at room temperature

The connection of twelve peripheral and divergent dodecyloxy chains to a central tridentate aromatic binding unit provides the dodecacatenar ligand L11, for which room-temperature mesomorphism is detected. An enthalpically unbalanced large melting entropy (DeltaSmL11=226 J mol(-1) K(-1)) results from the programmed microsegregation induced in the crystalline phase, a phenomenon which is maintained in the associated lanthanide complexes [Ln(L11)(NO3)3] and [Ln(L11)(CF3CO2)3]2. Low-temperature melting processes (-43相似文献   

Determination of gastrodin and vanillyl alcohol in Gastrodia elata Blume by pressurized liquid extraction at room temperature

Pressurized liquid extraction (PLE) at room temperature with a laboratory-assembled system was applied for the extraction of gastrodin (GA) and vanillyl alcohol (VA) in Gastrodia elata Blume. The proposed system setup for this current work was simpler as no heating and backpressure regulator was required. Extraction with PLE was carried out dynamically at a flow rate of 1.5 mL/min, at room temperature, under an applied pressure of 10-20 bars with an extraction time of 40-50 min. The extraction efficiencies of the proposed method using 20% aqueous ethanol were compared with heating under reflux using organic solvents such as methanol and ethanol/water (20:80) for different batches of medicinal plant materials. For the determination of GA and VA in G. elata Blume, the extraction efficiencies of PLE at room temperature were observed to be comparable with heating under reflux. The method precision was found to vary from 1.6 to 8.6% (RSD, n = 6) on different days. The marker compounds present in the various medicinal plant extracts were determined by gradient elution HPLC and HPLC/MS/MS. Our work demonstrated the possibility of implementation of PLE at room temperature and the advantages of minimizing the use of organic solvents in the extraction process.     

Electrodeposition of lead on glassy carbon and mercury film electrodes from a distillable room temperature ionic liquid,DIMCARB

The electrochemical reduction of Pb²⁺ has been studied in the ‘distillable’ ionic liquid DIMCARB (a mixture of adducts of dimethylamine and carbon dioxide, comprising both neutral and ionic moieties). Voltammetric results show that Pb²⁺ is reduced in a single step to form Pb metal via a nucleation and growth mechanism on a glassy carbon electrode. Ex situ powder X-ray diffraction studies on deposited lead show the presence of both α- and β-PbO₂, as well as elemental lead, suggesting the finely deposited lead particles are in an active rather than passive state. Chronamperometric and scanning electron microscope measurements show that the nucleation and growth follows a progressive nucleation mechanism on glassy carbon. Large peak–peak separations for the Pb reduction and oxidation are consistent with this mechanism and do not suggest electrochemical reversibility. However, experiments with co-deposition of Hg show that this irreversibility is a result of deposition onto a solid glassy carbon surface rather than a solvent effect. The diffusion coefficient of Pb²⁺ in DIMCARB has been calculated to be 1.8±0.4×10⁻⁷ cm² s⁻¹. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users. This work is dedicated to Piero Zanello on the occasion of his 65th birthday in recognition of his numerous contributions to inorganic electrochemistry.