Calculation of Clathrate‐Like Water Clusters Including H₂O‐Buckminsterfullerene

Abstract

The concept of buckminsterfullerene-like topology as a molecular-level structural motif has a long history in water cluster chemistry.[1] While carbon-based analogues have a well-established experimental foundation, "bucky-water" clusters remain largely conjectural species in the theoretical descriptions of pure water. Fullerene-like topologies are distinguished by the pattern of tricoordinate vertices in pentagonal and hexagonal facets that close to a convex polyhedron in three dimensions. They require exactly 12 pentagons and any number n hex of hexagons to form a polyhedron of 2n hex + 20 vertices. While pentagonal and hexagonal facets are well-known structural elements of all known crystalline forms of ice, [2] the intact Bucky-water polyhedra are principally recognized as elements in certain clathrate-type hydrates, such as the pentagonal dodecahedral (H 2 O) 20 (n hex = 0) and tetrakaidecahedral (H 2 O) 24 units (n hex = 2) of chlorine hydrate. [3] Today, gas hydrates are among the most well-known clathrate structures. These nonstoichiometric, crystalline compounds are found in natural-gas pipelines, on the ocean floor, and in permafrost environments, [4,5] deep ice cores, [6] rock inclusions, [7] comets, and certain outer planets. [8] There are three known types of natural-gas hydrates: the two cubic structures I and II, [9] and a hexagonal structure H.[ Recently, we extended a quantum statistical model of liquid water to include larger ice-like clusters, such as tetrahedral and fullerene-like clusters with up to 26 water molecules.[11] A low-energy tetrakaidecahedral (H 2 O) 24 cluster leads to a new low-temperature phase that bounds both liquid and vapor regions in first-order transition lines and gives rise to a true triple point. We characterized the microstructural composition and macroscopic properties of this "Bucky-ice" phase. Although it differs significantly from physical ice I h (for example, the melting point is 20 K too high and the molar volume is 5 % too low), it manifests qualitatively correct thermodynamic features of true ice polymorphs, which suggests an important role of voluminous clusters in the liquid/solid transition region. Thus understanding the structure and stability of such water clusters is of crucial importance for studying clathrate hydrates and hydration phenomena.The aim of this work is to investigate properties of larger water clusters including up to 60 water molecules. Some key questions will be addressed: Which of the calculated water clusters present minimum structures? How important are cooperative effects with increasing cluster size? Can hydrophobic guest molecules promote structure formation? Are larger clathrate structures than those known experimentally reasonable based on energetic considerations?The calculated bucky-water clusters having between 20 and 60 water molecules are shown in Figure 1. The variety of water cage structures comprises the dodecahedral (H 2 O) 20 cluster (n hex = 0), the tetrakaidecahedral (H 2 O) 24 cluster (n hex = 2), the hexakaidecahed...

Experimental nanocalorimetry of protonated and deprotonated water clusters

“…It is of fundamental interest to investigate the properties of water in the molecular size range: On the one hand, it is a unique benchmark to put to the test the descriptions of water molecules in interaction; on the other hand, knowing the properties of small water clusters is intrinsically useful since they are expected to play a crucial role in ubiquitous physical phenomena, from droplets nucleation [1,2,3] to liquid/solid transition in the bulk phase [4].…”

Substrate-induced cooperative effects in water adsorption from density functional calculations

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Facile Generation of Fullerene Nanoparticles by Hand‐Grinding

“…[9,11,12] Striking similarities in the surface characteristics between the C 60 nanoparticles obtained by hand-grinding and solution processes indicate that the surface characteristics arise from the surface properties of the C 60 nanoparticles, such as charge-transfer interaction between the C 60 molecules on the surface and the water molecules. [9,11,12,17] Recently, cytotoxicity of C 60 nanoparticles has been reported for fish, [18] human cells, [19] and microorganisms. [9] However, many aspects of the cytotoxicity of the C 60 nanoparticles remain to be clarified by further investigations.…”