Heavy element topology

Plot of heavy element topology from 1978 showing some landing points for proposed reactions. New heavy element isotopes reported as of mid-2002 are indicated with symbols denoting the following half-life ranges + = 0.1 ms to 0.1 s o = 0.1 s to 5 min = >5 min... 

There are many other types of contact or weak bonding interaction that cannot always be decided on by distance criteria alone. These include weak dispersive interactions between heavy elements, interactions between aromatic units and hydrogen bonding. Other sources of information from spectroscopy, electron density topology or quantum mechanical calculations have to be used jointly to give a satisfactory chemical explanation. This should always be remembered when you see a crystal structure with a simple line drawn between two atoms. 

ZVS QR topologies appear to be the more popular of two methods of quasi-resonant technologies. This is mainly due to two reasons first, its typical variation in frequency over its input and load variations is 4 f as opposed to fO f for the ZCS topologies secondly, it has a better heavy load performance. Also, some of the more troublesome parasitic elements within the circuit can be more easily harnessed. 

In either construction, each element of the APH can be assigned a unique turn (/)10 and angular step ( -n) along the helical pathway, measured from the s-block origin that forms the natural spine of the spiral pattern (the heavy vertical line in Fig. B.3). For example, the element chromium (Cr) can be denoted as the t5/d4 element, to locate it at the d4 angular step (the fourth element of the d block) on the t5 tier of the helix. In this manner, the distinctive form, topology, and orientation of the APH effectively complement... 

The atomistic topological indices were proposed by Burden [Burden, 1996] as atom-type counts where each atom is classified by its element and the number of cormections, thus also accounting for atom hybridization. In particular, Np, N, Np primary, secondary, tertiary, and quaternary carbon atoms, respectively N, the numbers of sp, sp, and sp carbon atoms, respectively Nar the number of aromatic carbon atoms and Nxsp3, NxspZ, and Nxsp the numbers of sp, sp, and sp heavy atoms, respectively. 

The two considered atoms need not be directly connected and the separation can be the topological distance between them [Carhart, Smith et al., 1985] these descriptors are usually called topological atom pairs being based on the topological representation of the molecules. Atom type is defined by the element itself, the number of heavy-atom cormections and number of 7t electron pairs on each atom. 

Using the geometric distance in place of the topological distance between any pair of atom types, geometric atom pair descriptors were analogously defined [Sheridan, Nilakantan et al, 1989 Sheridan, Miller et al, 1996]. Atom types are defined here by the chemical element, number of heavy-atom cormections, number of n electron pairs, number of attached hydrogens, and formal charge. 

The concentration factors listed in Table 1 serve to indicate the topological sequence of specific element enrichment in the muscles of fish Zn>Cu>Pb>Cd = sequence of the heavy metal accumulation in the fish (muscles) in the Danube Delta lakes. 

---