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

4. Structure of Ionic Hydration Shells 1351 4.1. Results from Diffraction Experiments 1351 4.1.1. X-ray Diffraction 1351 4.1.2. Neutron Diffraction 1351 4.2. Results from Computer Simulations 1352 4.3. Results from Spectroscopic Measurements 1354 4.3.1. Vibrational Spectroscopic Measurements 1354 4.3.2. EXAFS Spectroscopy 1354 4.3.3. NMR Relaxation Studies 1355 4.3.4. Dielectric Relaxation Studies 1355 4.4. Summary of the Structure of Ionic Hydration Shells 1355

Effect of ions on the structure of water: structure making and breaking.

We have developed a new technique, based on the standard Monte Carlo simulation method with Markov chain sampling, in which a set of three dimensional particle configurations are generated that are consistent with the experimentally measured structure factor. A(Q), and radial distribution function, g(r), of a liquid or other disordered system. Consistency is determined by a standard χ2 test using the experimental errors. No input potential is required, we present initial results for liquid argon. Since the technique can work directly from the structure factor it promises to be useful for modelling the structures of glasses or amorphous materials. It also has other advantages in multicomponent systems and as a tool for experimental data analysis.

Reverse Monte Carlo Simulation: A New Technique for the Determination of Disordered Structures

1 The ion-selective and ion transport properties of glycine receptor (GlyR) and gamma-aminobutyric acid receptor (GABAR) channels in the soma membrane of mouse spinal cord neurones were investigated using the whole-cell, cell-attached and outside-out patch versions of the patch-clamp technique 2 Current-voltage (I-V) relations of transmitter-activated currents obtained from whole-cell measurements with 145 mM-Cl- intracellularly and extracellularly, showed outward rectification In voltage-jump experiments, the instantaneous I-V relations were linear, and the steady-state I-V relations were rectifying outwardly indicating that the gating of GlyR and GABAR channels is voltage sensitive 3 The reversal potential of whole-cell currents shifted 56 mV per tenfold change in internal Cl- activity indicating activation of Cl(-)-selective channels The permeability ratio of K+ to Cl- (PK/PCl) was smaller than 005 for both channels 4 The permeability sequence for large polyatomic anions was formate greater than bicarbonate greater than acetate greater than phosphate greater than propionate for GABAR channels; phosphate and propionate were not measurably permeant in GlyR channels This indicates that open GlyR and GABAR channels have effective pore diameters of 52 and 56 A, respectively The sequence of relative permeabilities for small anions was SCN- greater than I- greater than Br- greater than Cl- greater than F- for both channels 5 GlyR and GABAR channels are multi-conductance-state channels In cell-attached patches the single-channel slope conductances close to 0 mV membrane potential were 29, 18 and 10 pS for glycine, and 28, 17 and 10 pS for GABA-activated channels The most frequently observed (main) conductance states were 29 and 17 pS for the GlyR and GABAR channel, respectively 6 In outside-out patches with equal extracellular and intracellular concentrations of 145 mM-Cl-, the conductance states were 46, 30, 20 and 12 pS for GlyR channels and 44, 30, 19 and 12 pS for GABAR channels The most frequently occurring main state was 46 pS for the GlyR and 30 pS for the GABAR channel 7 Single-channel conductances measured in equal 140 mM concentrations of small anions on both membrane faces revealed a conductance sequence of Cl- greater than Br- greater than I- greater than SCN- greater than F- for both channels This is nearly the inverse sequence of that found for the permeability of these ions indicating the presence of binding sites for ions in the channel(ABSTRACT TRUNCATED AT 400 WORDS)

Mechanism of anion permeation through channels gated by glycine and gamma-aminobutyric acid in mouse cultured spinal neurones.

Review of the structure and the electrochemistry of nickel hydroxides and oxy-hydroxides

Ions in water: characterizing the forces that control chemical processes and biological structure.

The structure of molten sodium chloride has been investigated by applying the technique of neutron diffraction to isotopically enriched samples. The three partial structure factors relating to Na-Na, Cl-Cl, and Na-Cl correlations have been successfully extracted from the data. Some general conclusions about the structure of molten sodium chloride are made and the relationship between the present work and earlier theoretical studies is discussed.

https://iopscience.iop.org/article/10.1088/0022-3719/8/21/018/pdf

The structure of molten sodium chloride

The nature of ionic hydration for the cations in NiCl2 solution and the anions in NaCl solution has been investigated by neutron diffraction experiments on samples which have been isotropically enriched. Well defined hydration numbers are found for both the Ni2+ ion and Cl- ion.

https://iopscience.iop.org/article/10.1088/0022-3719/10/11/014/pdf

A neutron diffraction study of hydration effects in aqueous solutions

The ion Ca2+ is common in nature and has an important role in many biochemical processes1. However, the way in which this ion behaves in aqueous solution is the subject of much controversy. There are two structural parameters which are necessary for a fuller understanding of Ca2+ in solution: the number of water molecules to which Ca2+ coordinates in solution, n, and the configuration which a water molecule adopts relative to it (defined by Φ, the angle between the plane of the water molecule and the Ca–O axis and rCaO, the Ca–O separation). The technique of neutron diffraction in conjunction with isotopic substitution has been successful in giving unambiguous information regarding, n, Φ and r for a variety of aqueous solutions2. Studies have been carried out on Li+, Ni2+ and Cl− at several concentrations3 and Ca2+ at one concentration4. We report here the results of a study of the structure of the Ca2+–D2O conformation as a function of concentration.

Environment of Ca 2+ ions in aqueous solvent

The coordination of water molecules around the metal ion in acidified 1 m DyCl3, 1.0 m Dy(ClO4)3, 0.3 m Dy(ClO4)3, and 1.0 m Yb(ClO4)3 solutions in D2O have been determined by the neutron diffraction difference technique. A coordination number of eight is found for the two ions, which depends neither on the counterion, nor on the concentration. The near metal–oxygen and metal–deuterium distances are, respectively, 2.39±0.02 and 3.03±0.02 A for dysprosium and 2.33±0.02 and 2.98±0.02 A for ytterbium. A general discussion concerning the hydration of the lanthanide ions is given.

John E. Enderby

Papers

Ions in water: characterizing the forces that control chemical processes and biological structure.

The structure of molten sodium chloride

A neutron diffraction study of hydration effects in aqueous solutions

Environment of Ca 2+ ions in aqueous solvent

The hydration of Dy3+ and Yb3+ in aqueous solution: A neutron scattering first order difference study