Negative thermal expansion of water in hydrophobic nanospaces

The density and intermolecular structure of water in carbon micropores (w = 1.36 nm) are investigated by small-angle X-ray scattering (SAXS) and X-ray diffraction (XRD) measurements between 20 K and 298 K. The SAXS results suggest that the density of the water in the micropores increased with increasing temperature over a wide temperature range (20-277 K). The density changed by 10%, which is comparable to the density change of 7% between bulk ice (I(c)) at 20 K and water at 277 K. The results of XRD at low temperatures (less than 200 K) show that the water forms the cubic ice (I(c)) structure, although its peak shape and radial distribution functions changed continuously to those of a liquid-like structure with increasing temperature. The SAXS and XRD results both showed that the water in the hydrophobic nanospaces had no phase transition point. The continuous structural change from ice I(c) to liquid with increasing temperature suggests that water shows negative thermal expansion over a wide temperature range in hydrophobic nanospaces. The combination of XRD and SAXS measurements makes it possible to describe confined systems in nanospaces with intermolecular structure and density of adsorbed molecular assemblies.ArticlePHYSICAL CHEMISTRY CHEMICAL PHYSICS. 14(2):981-986 (2012)journal articl

Direct determination of intermolecular structure of ethanol adsorbed in micropores using X-ray diffraction and reverse Monte Carlo analysis

The intermolecular structure of C(2)H(5)OH molecules confined in slit-shaped graphitic micropore of activated carbon fiber was investigated by in situ X-ray diffraction (XRD) measurement and reverse Monte Carlo (RMC) analysis. The pseudo-3-dimensional intermolecular structure Of C(2)H(5)OH adsorbed in the micropores was determined by applying the RMC analysis to XRD data, assuming a simple slit-shaped space composed of double graphene sheets. The results were consistent with conventional Monte Carlo simulation; e.g., bilayer structure formed by hydrogen bonds among C(2)H(5)OH adsorbed at low fractional filling. The RMC method based on experimental XRD data may be a useful tool to estimate the 3-dimensional structure of adsorbed phase confined in pores.ArticleCOLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS. 347(1-3):133-141 (2009)journal articl

Configurational evidence for antiferromagnetic interaction in disordered magnetic ionic liquids by X-ray scattering-aided hybrid reverse Monte Carlo simulation

Published online: 11 May 2020Magnetic ionic liquids (MIL) are a new type of ionic liquids that show paramagnetic response to magnetic fields. Here, we elucidate a plausible 3D liquid structure of the 1-ethyl-3-methyl-imidazolium tetrachloroferate (Emim[FeCl4]) and 1-butyl-3-methyl-imidazolium tetrachloroferate (Bmim[FeCl4]) MILs by X-ray scattering-aided hybrid reverse Monte Carlo simulations. Bmim[FeCl4] showed anomalously continuous structural changes over a wide temperature range (90–523 K) without crystallization, while Emim[FeCl4] displayed a melting point at 291 K with no glass transition.Conventional electron radial distribution function (ERDF) analysis provides misleading information about the structures of these MILs due to the mutual cancelation of the partial anion-anion and anion-cation ERDFs. Subsequent hybrid reverse Monte Carlo (HRMC) analysis revealed the precise coordination structures of both ionic liquids, and the alternating periodic arrangement of the anions and cations was visualized based on the HRMC simulation results. The results clearly revealed that the 1st coordination structure of the FeCl4 anion around the Bmim cation was widespread compared to that of the Emim cation, resulting in the absence of crystallization. In addition, we obtained new insights into the antiferromagnetic interaction between the FeCl4− ions of Bmim[FeCl4] even in the absence of the crystallization at low temperatures. Our results shed new light on the development of MILs not only for practical applications but also for the advancing the basic science of pure liquids with a high magnetic response.ArticleJournal of Molecular Liquids.311(1):113321(2020)journal articl

Kinetics of Cluster-Mediated Filling of Water Molecules into Carbon Micropores

Understanding the kinetics of water adsorption/desorption on activated carbon is significant for chemical applications in which competitive adsorption of water occurs. In this study, we investigated the water adsorption process by determining the adsorption rate constant using the novel pressure feedback method (PFM), which measures the rate of adsorption directly with high precision (∼10 nmol s^–1) by controlling the introducing and outgassing flow rates. The PFM was used to investigate water vapor adsorption kinetics on activated carbon fibers (ACFs) of different pore sizes and to obtain a correlation of rate constant with pore size. The systems show good agreement with the stretched exponential model. The adsorption rate constants were found to be lower for ACFs with a larger pore width (average pore width; <i>w</i> = 1.03 nm) as compared with those for smaller pore systems (<i>w</i> = 0.57, 0.72 nm)

Identification of a novel mammalian post-translational modification, phosphocholine, on placental secretory polypeptides

Placental neurokinin B appears to be post-translationally modified by phosphocholine (PC) attached to the aspartyl side chain at residue 4 of the mature peptide. Corticotrophin releasing factor (CRF) was found to be expressed by the rat placenta with the main secreted forms being phosphocholinated proCRF+/- one or two polysaccharide moieties. A combination of high-pressure liquid chromatography (HPLC) and two-site immunometric analysis suggested that PC was also attached to the placental precursors of adrenocorticotrophin, hemokinin, activin and follistatin. However, the fully processed forms of rat placental activin and CRF were free of PC. Formerly, the parasitic filarial nematodes have used PC as a post-translational modification, attached via the polysaccharicle moiety of certain secretory glycoproteins to attenuate the host immune system allowing parasite survival, but it is the PC group itself which endows the carrier with the biological activity. The fact that treatment of proCRF peptides with phospholipase C but not endoglycosidase destroyed PC immunoreactivity suggested a simpler mode of attachment of PC to placental peptides than that used by nematodes. Thus, it is possible that by analogy the placenta uses its secreted phosphocholinated hormones to modulate the mother's immune system and help protect the placenta from rejection

Organoclays in Water Cause Expansion That Facilitates Caffeine Adsorption

This study investigates the adsorption of caffeine in water on organically modified clays (a natural montmorillonite and synthetic saponite, which are smectite group of layered clay minerals). The organoclays were prepared by cation-exchange reactions of benzylammonium and neostigmine with interlayer exchangeable cations in the clay minerals. Although less caffeine was uptaken on neostigmine-modified clays than on raw clay minerals, uptake was increased by adding benzylammonium to the clays. The adsorption equilibrium constant was considerably higher on benzylammonium-modified saponite (containing small quantities of intercalated benzylammonium) than on its montmorillonite counterpart. These observations suggest that decreasing the size and number of intercalated cations enlarges the siloxane surface area available for caffeine adsorption. When the benzylammonium–smectite powders were immersed in water, the intercalated water molecules expanded the interlayer space. Addition of caffeine to the aqueous dispersion further expanded the benzylammonium–montmorillonite system but showed no effect on benzylammonium–saponite. We assume that intercalated water molecules were exchanged with caffeine molecules. By intercalating benzylammonium into smectites, we have potentially created an adaptable two-dimensional nanospace that sequesters caffeine from aqueous media

Vertically Oriented Propylene Carbonate Molecules and Tetraethyl Ammonium Ions in Carbon Slit Pores

We report the vertical alignment of propylene carbonate (PC) molecules interacting with Et₄N⁺ and BF₄^– which are confined in extremely narrow slit pores (<i>w</i> ∼ 0.7 nm) of carbide-derived carbon and pitch-based activated carbon fiber. On the basis of X-ray diffraction (XRD), electron radial distribution function analysis reveals that the nearest PC–PC distance is 0.05–0.06 nm shorter than that in the bulk solution, indicating dense packing of PC molecules in the pores. This confinement effect results from the vertically aligned PC molecules, which are indicated by the reverse Monte Carlo analysis. The ensemble structure of PC molecules in the subnanometer carbon pores will provide better understanding the supercapacitor function