Chicken-wire

Figure2-116. Graphical representations of molecular surfaces of phenylalanine a) dots b) mesh or chicken-wire c) solid d) semi-transparent,...

Depending on the application, models of molecular surfaces arc used to express molecular orbitals, clcaronic densities, van dor Waals radii, or other forms of display. An important definition of a molecular surface was laid down by Richards [182] with the solvent-accessible envelope. Normally the representation is a cloud of points, reticules (meshes or chicken-wire), or solid envelopes. The transparency of solid surfaces may also be indicated (Figure 2-116). 

To display properties on molecular surfaces, two different approaches are applied. One method assigns color codes to each grid point of the surface. The grid points are connected to lines chicken-wire) or to surfaces (solid sphere) and then the color values are interpolated onto a color gradient [200]. The second method projects colored textures onto the surface [202, 203] and is mostly used to display such properties as electrostatic potentials, polarizability, hydrophobidty, and spin density. 

Graphite, the most important component of the lead of pencils, is a black, lustrous, electrically conducting solid that vaporizes at 1700°C. It consists of flat sheets of sp2 hybridized carbon atoms bonded covalently into hexagons like chicken wire (Fig. 5.22). There are also weak bonds between the sheets. In the commercially available forms of graphite, there are many impurity atoms trapped between the sheets these atoms weaken the already weak intersheet bonds and let... 

The tubes were found to have a bonding structure similar to that of graphite. A nanotube can be thought of as a narrow sheer of a million or more carbon atoms linked together in six-membered benzenelike rings resembling chicken wire and rolled into a very long cylinder only 1-3 nm in diameter. 

The hardest of the transition-metal borides are the diborides. Their characteristic crystal structure (Figure 10.6) consists of plane layers of close-packed metal atoms separated by plane openly-patterned layers of boron atoms ( chicken-wire pattern). If the metal atoms in the hexagonal close-packed layer have a spacing, d, then the boron atoms have a spacing of d/V3. 

If you regularly make a leaf mold pile (see pp.44-45), you may well have an opossum sleeping in it for at least part of the year. Leave a gap in the chicken wire, or whatever supports your leaf heap, so that small animals can get in and out easily. 

In graphite, three ordinary electron-pair bonds link each C to its neighbors in a quasi-infinite tessellated hexagonal or chicken wire pattern, and the remaining valence electrons, one from each C, are delocalized in a n-orbital system extending across the entire chicken wire sheet, above and below. The three-dimensional structure consists of stacks of these sheets. The structure of the sheets is, in effect, one huge collection of fused benzene... 

Traditionally, the principal forms of carbon have (1) diamond, with its tetrahedral arrangement of atoms (2) graphite, whose structure resembles layers of chicken wire and sometimes (3) amorphous, a poorly defined... 

Generally speaking, we can distinguish two types of interactions between the chemical species and the sensor a surface interaction in which the species of interest is adsorbed at the surface, and a bulk interaction in which the species of interest partitions between the sample and the sensor and is absorbed. The classification of the interaction as either surface or bulk is relative with respect to the size of the species. It is the case of chicken and chicken wire. Obviously, a chicken wire fence is impervious to chickens, but presents no barrier whatsoever to mosquitoes. Similarly, large molecules, such as proteins, may adsorb at the surface of the sensor layer, whereas smaller ions can penetrate and absorb in the bulk. 

Singlewall nanotubes can be thought of as being made from rolled up chicken wire. 

Figure 8.43 (a) Chicken wire and (b) ladder motifs for saturated hydrogen bonded structures. The... 

Historically, the chemistry of layered intercalates began in 1840 with the report that graphite was able to intercalate sulfuric acid between successive layers of its chicken wire mesh. It was not until after the 1960s that serious interest was aroused by intercalates, following the realisation that guest intercalation may significantly alter the host s chemical, catalytic, electronic and optical properties. This is especially true when the host properties are dependent on its layered structure. In the case of graphite, for example, its use as a dry , low-temperature lubricant has come about because of the ease... 

A neutral macrocyclic receptor of nitrate was designed by a rational approach. [1] A hexagonal grid was constructed around the trigonal nitrate anion and the molecular frame was cut from the chicken wire pattern (Scheme 1). 

Scheme 1. Design of a neutral macrocyclic receptor using a chicken wire pattern...

Benzo(a)pyrene (Figure 1.14) is the most studied of the polycyclic aromatic hydrocarbons (PAHs), which are characterized by condensed ring systems ( chicken wire structures). These compounds are formed by the incomplete combustion of other hydrocarbons, a process that consumes hydrogen in preference to carbon. The carbon residue is left in the thermodynamically favored condensed aromatic ring system of the PAH compounds. 

Fig. 2 a The linear tape structure of terephthalic acid, b The zigzag tape structure of isophthalic acid, c The chicken wire sheet structure of trimesic acid [29]... 

From the reaction of Au with alkali metal polysulfide liquids, LiAuS and NaAuS were discovered. Both compounds contain infinite one-dimensional (AuS) chains, featuring alternating sulfide anions and linear coordinated Au centers. In LiAu8, the chains are zigzag and fully extended and they pack in mutually perpendicular sets. In NaAuS, the same chains coil in an unusual fashion so that they become interwoven to form layers reminiscent of chicken-wire (Figure 17). This novel coiling mode allows Au Au contacts to form, which help to stabilize the structure. 

Place samples in the evening, shortly before beavers emerge from their lodge. This way you minimize the risk that other herbivores, such as deer, will eat or sample the food first. (If that is a real possibility, the twigs have to be fenced off with high chicken wire, leaving 20 cm so open at the bottom for the beavers). 

---