Hydrogen bonds/bonding water clusters

The chemical shift of the line at -0.1 ppm indicates a hydrogen-bonded water cluster, while the peak at -3.9 ppm results from monomers or small mul-timers. The authors suggested that the monomolecular species are in one of two sites, an octahedral void or a small vacancy left by a missing fullerene cage. The remaining signal at -0.1 ppm comes from large water clusters. Support for this conclusion comes from four observations ... 

The formation of clusters of hydrogen-bonded water molecules around different sizes of apolar molecules... 

Ludwig s (2001) review discusses water clusters and water cluster models. One of the water clusters discussed by Ludwig is the icosahedral cluster developed by Chaplin (1999). A fluctuating network of water molecules, with local icosahedral symmetry, was proposed by Chaplin (1999) it contains, when complete, 280 fully hydrogen-bonded water molecules. This structure allows explanation of a number of the anomalous properties of water, including its temperature-density and pressure-viscosity behaviors, the radial distribution pattern, the change in water properties on supercooling, and the solvation properties of ions, hydrophobic molecules, carbohydrates, and macromolecules (Chaplin, 1999, 2001, 2004). 

The situation for hydrated Nafion in the acid form, or as containing aqueous acids or strong bases, is more complex because protons and defect protons (i.e., OH ions), migrate according to a somewhat different mechanism. Proton transfer in either case occurs throughout and between clusters of hydrogen bonded water molecules to a degree that depends on the relative water content. 

In the absence of camphor the substrate binding site of the resting state 3 is occupied by a cluster of six hydrogen bonded water molecules. Surprisingly the iron(III) of the resting state 3 is predominantly 93% low spin (S = ) [18]. 

Stillinger (1980) suggested that disconnected icebergs should not be present, but that a more likely model is that of a random, three-dimensional network of hydrogen bonds, rather than long-lived clusters of molecules. Such networks of hydrogen-bonded water molecules and clusters are present when hydrates form or dissociate. These clusters are discussed relative to nucleation of hydrates in the following chapter. 

Water is considered to be supercooled when it exists as a liquid at lower temperatures than its melting point, for example, at less than 0°C at atmospheric pressure. In this state, the supercooled water is metastable. The properties of supercooled water have been examined in detail in excellent reviews by Angell (1982, 1983) and Debenedetti (1996, 2003). A brief review of the properties of supercooled pure liquid water and the different liquid water models are discussed in this section. These structures comprise hydrogen-bonded water networks and/or water clusters ( cages ) that are the starting points to hydrate formation. 

Oxtoby, N. S., Blake, A. J., Champness, N. R., Wilson, C., Water superstructures within organic arrays, Hydrogen-bonded water sheets, chains and clusters. Chem. Eur. J. 2005, 11, 4643-4654. 

S. Re and Y. Osamura, Size-dependent hydrogen bonds of cluster ions between phenol cation radicals and water molecules a molecular orbital study, J. Phys. Chem. A, 102 (1998) 3798-3812. 

This notion of co-operative build-up of a cluster of hydrogen-bonded water molecules is central to Frank and Wen s mixture model for water (p. 236). 

The V-structure of water then corresponds to clusters of water molecules separated by non-hydrogen bonded water molecules. With increase in temperature, so the proportion of (H20)d increases (cf. 

Fig. 2 Hydrogen-bonded water and water clusters in an interfacial zone formed by unordered peptide chains that separate the PB domains from the helical PBLG phase in films of PBLG-PB-PBLG triblock copolymers. (Reproduced with permission from [26]. Copyright 1979. The Society of Polymer Science, Japan)...

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