Some Electronic Properties

The above-mentioned example of mellitin is a good illustration also for some electronic features which can be studied in proteinlike compounds. Melittin is an amphipathic peptide of 26 residues with a hydrophobic stretch of 19 amino acids followed by a cluster of four positively charged residues at the COOH terminus. 

Analysis of melittin-induced conductance fluctuations suggests perturbations of the lipid bilayer structure, and formation of structural channels. Addition of pronase to the trans-side in the presence of a trans-negatiwe membrane potential abolished the conductance as it did when added to the cis side. This implies that the conducting state of melittin requires a trans-membrane configuration. In a non-conducting absorbed state a hydrophobic loop, with the region from threonine-9 to proline-13 as the likely site of the turn, penetrates the lipid but does not extend across the membrane. In the conducting state the turn becomes extended as the peptide assumes a rra w-bilayer position. 

Energy calculations show that the membrane potential can supply sufficient energy for this transition. The membrane seems to be this structure at which energy transfer takes place through a low energy barrier, and where the uncontroUed diffusion of electrons is prevented by nonadiabatic behavior in the electron transfer process. The polar electronic structure of lipids and proteins holding vibrating ions is crucial here. 

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Quantitative structure-activity relationship studies are of great importance in modern chemistry. From their origin in the study of organic chemistry dating back to the 19th century, these studies have relied on some empirical and qualitative rules about the reactivity similarities of compounds with similar structures. The most significant development in QSARs occurred with the work of Louis Hammett (1894-1987), who correlated some electronic properties of organic acids and bases with their equilibrium constants and reactivity (Johnson, 1973). Hammett postulated that the effect... 

In this work, we use the confined atoms model, with hard walls, to estimate the pressure on confined Ca, Sr, and Ba atoms. With this approach, we will give an upper limit to the pressure, because it is well known that the Dirichlet boundary conditions give an overestimation to this quantity. By using this approach, we obtain the profiles of some electronic properties... 

Some Electronic Properties of Prototropic Tautomers of 8-Azapurine... 

The purpose of this chapter will be to review the fundamentals of ab initio MD. We will consider here Density Functional Theory based ab initio MD, in particular in its Car-Parrinello version. We will start by introducing the basics of Density Functional Theory and the Kohn-Sham method, as the method chosen to perform electronic structure calculation. This will be followed by a rapid discussion on plane wave basis sets to solve the Kohn-Sham equations, including pseudopotentials for the core electrons. Then we will discuss the critical point of ab initio MD, i.e. coupling the electronic structure calculation to the ionic dynamics, using either the Born-Oppenheimer or the Car-Parrinello schemes. Finally, we will extend this presentation to the calculation of some electronic properties, in particular polarization through the modern theory of polarization in periodic systems. 

Fig. 4.25. Schematic plot illustrating the development of some electronic properties (type of ground state, spontaneous magnetic moment and ordering temperature and the value of the coefficient y of the specific heat) through the UTX series with a special emphasis on magnetism. Data are compiled from the different literature sources quoted in the text.

Another heuristic value of the proteinoids would be to use membranes and compare them to known electronic devices such as, for instance, tunnel diode or unijunction transistor. Some electronic properties of membranes made of proteinoids highly resemble the respective characteristics of these electronic devices. Here we closely approach the domain of the next step in computer technology. As yet predominantly, if not only, theoretical and conceptual attempts are described in the literature (e.g.. Ref. 57) including the patent literature. 

These products were used in order to investigate the influence of the end groups upon some electronic properties of conjugated polymers (electrical, photo-electrical and luminescent properties) [26]. 

Freeman AJ, Desclaux JP (1979) Dirac-Fock studies of some electronic properties of rare-earth ions. J Magn Magn Mater 12(1) 11-21... 

The liquids discussed in the preceding chapters form different kinds of solid phases single crystals, polycrystalline solids, or glasses. Their electronic properties are influenced by the crystal structure, the presence of traps, and by the electrode/sample interface. In the following three sections, we shall discuss some electronic properties of nonpolar solids which are related to the corresponding liquid phase. The book concludes with a brief section on polymeric liquids. 

As a consequence, this procedure relies on a reduced number of empirical parameters, including, in particular, the sphere radii, which depend, at least, on the atomic number of the corresponding atom. Optimization of these parameters can be based on experimental solvation energies [172-174] or on the solvent shifts of some electronic properties [175], the second approach often providing better results for computational spectroscopy studies [176]. 

Some electronic properties of the quantum system along the trajectory in Figure 7 are shown in Figure 8. One may note that the Mulliken charge on the forming bromide anion oscillates between -0.6 and -0.3 in the CTC and decreases rapidly near the TS, where the formation of the bromide anion is almost achieved. The Br-Br and C-C bond orders follow closely the oscillations of this Mulliken charge. Note,... 

While the lanthanide series is due to the successive filling of the 4f orbitals, it is generally assumed that they do not contribute significantly to bonding due to their limited radial extension and the shielding from the valence shell by the filled 5s and 5p orbitals. However, these f-orbitals (filled or empty) should be able to modulate some electronic properties of the metal center. In the ubiquitous oxidation state 3+, the lanthanide ions reach an inert gas core configuration by the loss of one 4f electron. It is for this reason that yttrium and scandium complexes are included in discussions of lanthanide chemistry i.e., in their predominant 3+ oxidation states, these elements have an inert gas core configuration ([Kr] and [Ar], respectively) and empty d orbitals. Indeed, due to the lanthanide contraction, the size of Y + falls between Ho and Er +, whereas scandium is considerably smaller than the lanthanides. 

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