When Szent-Gyorgyi called water the “matrix of life”,1 he was echoing an old sentiment. Paracelsus in the 16th century said that “water was the matrix of the world and of all its creatures.”2 But Paracelsus’s notion of a matrixsan active substance imbued with fecund, life-giving propertiess was quite different from the picture that, until very recently, molecular biologists have tended to hold of water’s role in the chemistry of life. Although acknowledging that liquid water has some unusual and important physical and chemical propertiessits potency as a solvent, its ability to form hydrogen bonds, its amphoteric naturesbiologists have regarded it essentially as the backdrop on which life’s molecular components are arrayed. It used to be common practice, for example, to perform computer simulations of biomolecules in a vacuum. Partly this was because the computational intensity of simulating a polypeptide chain was challenging even without accounting for solvent molecules too, but it also reflected the prevailing notion that water does little more than temper or moderate the basic physicochemical interactions responsible for molecular biology. What Gerstein and Levitt said 9 years ago remains true today: “When scientists publish models of biological molecules in journals, they usually draw their models in bright colors and place them against a plain, black background”.3 Curiously, this neglect of water as an active component of the cell went hand in hand with the assumption that life could not exist without it. That was basically an empirical conclusion derived from our experience of life on Earth: environments without liquid water cannot sustain life, and special strategies are needed to cope with situations in which, because of extremes of either heat or cold, the liquid is scarce.4-6 The recent confirmation that there is at least one world rich in organic molecules on which rivers and perhaps shallow seas or bogs are filled with nonaqueous fluidsthe liquid hydrocarbons of Titan7smight now bring some focus, even urgency, to the question of whether water is indeed a * E-mail: p.ball@nature.com. Philip Ball is a science writer and a consultant editor for Nature, where he worked as an editor for physical sciences for more than 10 years. He holds a Ph.D. in physics from the University of Bristol, where he worked on the statistical mechanics of phase transitions in the liquid state. His book H2O: A Biography of Water (Weidenfeld & Nicolson, 1999) was a survey of the current state of knowledge about the behavior of water in situations ranging from planetary geomorphology to cell biology. He frequently writes about aspects of water science for both the popular and the technical media.

https://www.philipball.co.uk/images/stories/docs/pdf/ChemRev_final.pdf

Water as an Active Constituent in Cell Biology

A surface science perspective on TiO2 photocatalysis

Dang Sheng Su,*,†,‡ Siglinda Perathoner, and Gabriele Centi* †Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Science, 72 Wenhua Road, Shenyang 110006, China ‡Department of Inorganic Chemistry, Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany Dipartimento di Ingegneria Elettronica, Chimica ed Ingegneria Industriale, University of Messina and INSTM/CASPE (Laboratory of Catalysis for Sustainable Production and Energy), Viale Ferdinando Stagno, D’Alcontres 31, 98166 Messina, Italy

Nanocarbons for the Development of Advanced Catalysts

Heavy metal removal from aqueous solution by advanced carbon nanotubes: Critical review of adsorption applications

Carbon nanotubes as adsorbents in environmental pollution management: A review

We present the first experimental vibrational spectroscopy study providing direct evidence of a water phase inside single-walled carbon nanotubes that exhibits an unusual form of hydrogen-bonding due to confinement. Water adopts a stacked-ring structure inside nanotubes, forming intra- and inter-ring hydrogen bonds. The intra-ring hydrogen bonds are bulk-like while the inter-ring hydrogen bonds are relatively weak, having a distorted geometry that gives rise to a distinct OH stretching mode. The experimentally observed infrared mode at 3507 cm-1 is assigned to vibrations of the inter-ring OH-groups based on detailed atomic-level modeling. The direct observation of unusual hydrogen bonding in nanotubes has potential implications for water in other highly confined systems, such as biological channels and nanoporous media.

Unusual Hydrogen Bonding in Water-Filled Carbon Nanotubes

Infrared spectroscopy has been used to make the first experimental discrimination between molecules bound by physisorption on the exterior surface of carbon single-walled nanotubes (SWNTs) and molecules bound in the interior. In addition, the selective displacement of the internally bound molecules has been observed as a second adsorbate is added. SWNTs were opened by oxidative treatment with O3 at room temperature, followed by heating in a vacuum to 873 K. It was found that, at 133 K and 0.033 Torr, CF4 adsorbs on closed SWNTs, exhibiting its ν3 asymmetric stretching mode at 1267 cm-1 (red shift relative to the gas phase, 15 cm-1). Adsorption on the nanotube exterior is accompanied by adsorption in the interior in the case of opened SWNTs. Internally bound CF4 exhibits its ν3 mode at 1247 cm-1 (red shift relative to the gas phase, 35 cm-1). It was shown that, at 133 K, Xe preferentially displaces internally bound CF4 species, and this counterintuitive observation was confirmed by molecular simulations. T...

Adsorption of CF4 on the internal and external surfaces of opened single-walled carbon nanotubes: a vibrational spectroscopy study.

The oxidative etching of single walled carbon nanotubes (SWNTs) is useful for opening the end caps and the sidewalls of the nanotubes to provide access to the interior. We have studied the effect of successive treatment of SWNTs by 95% pure O3(g), which is a powerful and convenient oxidizing agent. The surface area of the SWNTs was measured following exposure to O3(g) at 300 K and also following heating to 1073 K in a vacuum to decompose the oxidized groups on the nanotubes, a procedure called etching. This O3-induced etching process was observed by scanning electron microscopy and by transmission electron microscopy, and the kinetics of the process was studied gravimetrically. It was found that O3 attack occurs preferentially on the outermost geometric surface of the conglomerate sample of the nanotubes as a result of the high efficiency of O3 to react in a few collisions with the nanotube surface. Ozone-induced etching causes the loss of pores in the 20 A diameter range as observed by nitrogen adsorptio...

Etching of carbon nanotubes by ozone--a surface area study.

The physical adsorption of NO on purified single-walled carbon nanotubes was investigated at low temperatures by means of transmission infrared spectroscopy. Ozone treatment followed by annealing was used as the method of opening the entry ports for adsorption into the interior of the nanotubes. The IR spectra show that the NO that is adsorbed inside nanotubes exists exclusively in its dimer form, with no infrared bands of the monomer visible at a sensitivity level of 5 mol % NO. The internally adsorbed NO dimer species observed is cis-(NO)2, with ν1(symmetric) = 1853 cm-1 and ν5(asymmetric) = 1754 cm-1. Introduction of Xe into the system leads to selective displacement of the internally bound cis-(NO)2 dimer. A large spectroscopic red shift of the symmetric (−0.80%) and the asymmetric (−1.96%) modes for cis-(NO)2 adsorbed inside nanotubes [relative to gas-phase cis-(NO)2] points to the strong interaction of the dimer with the nanotube interior. The enthalpy of dissociation of the adsorbed dimer molecule ...

Adsorption and Dimerization of NO Inside Single-Walled Carbon NanotubesAn Infrared Spectroscopic Study

We present theoretical and experimental evidence for CO(2) adsorption on different sites of single walled carbon nanotube (SWNT) bundles. We use local density approximation density functional theory (LDA-DFT) calculations to compute the adsorption energies and vibrational frequencies for CO(2) adsorbed on SWNT bundles. The LDA-DFT calculations give a range of shifts for the asymmetric stretching mode from about -6 to -20 cm(-1) for internally bound CO(2), and a range from -4 to -16 cm(-1) for externally bound CO(2) at low densities. The magnitude of the shift is larger for CO(2) adsorbed parallel to the SWNT surface; various perpendicular configurations yield much smaller theoretical shifts. The asymmetric stretching mode for CO(2) adsorbed in groove sites and interstitial sites exhibits calculated shifts of -22.2 and -23.8 cm(-1), respectively. The calculations show that vibrational mode softening is due to three effects: (1) dynamic image charges in the nanotube; (2) the confining effect of the adsorption potential; (3) dynamic dipole coupling with other adsorbate molecules. Infrared measurements indicate that two families of CO(2) adsorption sites are present. One family, exhibiting a shift of about -20 cm(-1) is assigned to internally bound CO(2) molecules in a parallel configuration. This type of CO(2) is readily displaced by Xe, a test for densely populated adsorbed species, which are expected to be present on the highest adsorption energy sites in the interior of the nanotubes. The second family exhibits a shift of about -7 cm(-1) and the site location and configuration for these species is ambiguous, based on comparison with the theoretical shifts. The population of the internally bound CO(2) may be enhanced by established etching procedures that open the entry ports for adsorption, namely, ozone oxidation followed by annealing in vacuum at 873 K. Xenon displacement experiments indicate that internally bound CO(2) is preferentially displaced relative to the -7 cm(-1) shifted species. The -7 cm(-1) shifted species is assigned to CO(2) adsorbed on the external surface based on results from etching and Xe displacement experiments.

Oleg Byl

Papers

Unusual Hydrogen Bonding in Water-Filled Carbon Nanotubes

Adsorption of CF4 on the internal and external surfaces of opened single-walled carbon nanotubes: a vibrational spectroscopy study.

Etching of carbon nanotubes by ozone--a surface area study.

Adsorption and Dimerization of NO Inside Single-Walled Carbon NanotubesAn Infrared Spectroscopic Study

Vibrational behavior of adsorbed CO2 on single-walled carbon nanotubes.