Surface Bernal

At this point we should also recall another application of the already mentioned Bernal model of amorphous surface. Namely, Cascarini de Torre and Bottani [106] have used it to generate a mesoporous amorphous carbonaceous surface, with the help of computer simulation and for further application to the computer simulation study of adsorption. They have added a new component to the usual Bernal model by introducing the possibility of the deletion of atoms, or rather groups of atoms, from the surface according to some rules. Depending on the particular choice of those rules, surfaces of different porosity and structure can be obtained. In particular, they have shown examples of mono- as well as pohdispersed porous surfaces... 

More than 50 years ago, the English physical chemist J. D. Bernal (1901-1971) suggested that clay minerals may have played a key role in synthetic processes taking place on the primordial Earth he was referring to the adsorption and concentration of organic substances at the surface of such minerals. 

Water molecules are oriented at the surfaces of macromolecules as well as at solid surfaces. For example, Bernal (1965) refers to a regular formation of ice surrounding most protein molecules, although by ice he does not mean free water ice. Bound water in hydration shells surrounding macromolecules in aqueous solutions is sometimes denoted as lattice-ordered or ice-like and has been taken into account in interpreting the dielectric functions of such solutions (Buchanan et al., 1952 Jacobson, 1955 Pennock and Schwan, 1969). 

J. D. Bernal (London) In my opinion many, if not all, so-called oxide covered surfaces are, at ordinary and even under high temperature conditions, effectively hydroxyl-covered. I would like to recall in connection an observation many years ago by Farkas. He was filling an evacuated and baked out silica apparatus with pure Da gas and noted after pumping out that the gas was contaminated with Ha. On repeating the same process with pure R2 he found a smaller Da contamination. The simplest explanation was that the surface of silica is normally covered by OH groups from which the hydrogen is not driven even at red heat, but which can exchange easily with Da to form OD and HD. Other x-ray evidence on finely divided quartz shows that the hydroxide layer may be thicker than monomolecular. 

Concentration of the organic reactants on surfaces or in the pores of clay materials prior to reaction has been suggested by Bernal [219] and Cairns-Smith [220]. Pores of different sizes might have operated as prebiotic reactors for asymmetric synthesis, since within their confined environment one may find chiral catalytic sites as well as chiral surfaces. One could envisage that such pores might have provided a plausible environment for the formation of diastereoisomeric self-assemblies of the types described in this review and as required for the stochastic mirror symmetry breaking scenarios. In addition, within such pores the chiral material once formed would be protected from racemization that could have been induced by impact with heavy bodies or by intense cosmic radiation. 

One of the most interesting is the theory of surface metabolism, an approach that was proposed, in different forms, by John Bernal in 1951, by Graham Cairns-Smith in 1982 and by Gunter Wachters-hauser in 1998. The central idea of this theory is based on solid thermodynamic arguments. The formation of a peptide bond is not favoured in solution because it increases the entropy of the system, but on a surface the same process takes place with a decrease of entropy, and is therefore favoured. And this is true not only for peptide bonding but for many other types of polymerisation. A great number of enzymatic reactions require a collision of three molecules, an event which is highly unlikely in space but much more probable on a surface. 

Bernal and Cairns-Smith proposed that the first metabolic surfaces were provided by crystals of clay, and therefore that life did literally originate in mud, because clays can adsorb a vast range of organic... 

M. J. Nozal, J. L. Bernal, J. J. Jimenez, M. T. Martin, and F. J. Diez, Development and validation of a liquid chromatographic method for determination of lacidip-ine residues on surfaces in the manufacture of pharmaceuticals, /. Chromatogr. A... 

We consider first the simulation of the atomic structure of vitreous silica because the majority of the simulations of amorphous oxides were done for this material. Some of these have simulated the formation of the vitreous silica surface in a very detailed fashion. Furthermore, the methods developed for the simulation of vitreous silica and its surface may be used with some modifications for other amorphous oxides. Subsequently, we consider less detailed methods of simulation of amorphous oxide surfaces which are not limited to Si02 but can be applied to various oxides. Finally the least detailed but the most general model - the Bernal surface (BS) - represents the atomic arrangement at the surface of any amorphous oxide (most important for physical adsorption) by the dense random packing of hard spheres. 

An even more general and correspondingly less detailed atomic model of amorphous oxide surfaces has been called the Bernal surface (BS)[3, 21]. It is based upon the fact that many oxides and halides can be regarded as close-packed arrays of large anions with much smaller cations occupying interstitial (usually tetrahedral or octahedral) positions (see., e.g. Ref. [4]). In line with this point of view, the BS is a surface of a collection of dense randomly packed hard spheres, a sphere representing an oxide anion. The cations in interstitial positions between hard spheres are excluded from the simulation since they do not attract adsorbed molecules due to their small polarizability. Thus only the atomic structure of the oxide ions is considered. This is called the Bernal structure and has been used for modelling simple liquids and amorphous metals [15]. 

The computer simulation of the Bernal atomic structure with a flat (on average) surface was carried out with the help of algorithm described in Refs. [3, 22]. The coordination number of hard spheres in this structure is about 8 which may be compared with the 0-0... 

Henry s Law constants for Ar on the surface of amorphous oxide modeled as a Bernal surface (cf. Fig.l) have been considered in Ref. [39]. The Henry s Law constant may be calculated as... 

Bernal S., Baker R. T., Burrows A., Calvino J. J., Kiely C. J., Lopez-Cartes C., Perez-Omil J. A. and Rodriguez-Izquierdo J. M., Surface and Interface Analysis 19 2Qm),4n-42. ... 

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