Acceptor charge

The enantiophore query used in the search is derived from the CSP and directly built from a 3D structure model of the target CSP molecule, as it can be used today for the determination of new lead compounds [20, 21]. This procedure does not need an important modeling expertise. One can easily recognize the different center types in the receptor in question. These can be hydrogen-bond donors and acceptors, charged... 

In LiF (,1 1) ion-dipole complexes, donor-acceptor charge leakage from F to Li+ is apparent in each member of the series, but the incremental CT, expressed as a percentage of a full electronic charge, is progressively weakened with each added F ion,... 

Specific donor-acceptor charge transfer interactions can lead to a relatively large numerical value of the electronic matrix element, possibly attributable to an increase in V, and, thus, to larger rate constants than those predicted by distance variations alone. 

In this test the confined acceptor charge is separated from the Tetryl donor by a stack of plexiglas cards, the number of which is a measure of the gap thickness. 

Radical anions are produced in a number of ways from suitable reducing agents. Common methods of generation of radical anions using LFP involve photoinduced electron transfer (PET) by irradiation of donor-acceptor charge transfer complexes (equation 28) or by photoexcitation of a sensitizer substrate (S) in the presence of a suitable donor/acceptor partner (equations 29 and 30). Both techniques result in the formation of a cation radical/radical anion pair. Often the difficulty of overlapping absorption spectra of the cation radical and radical anion hinders detection of the radical anion by optical methods. Another complication in these methods is the efficient back electron transfer in the geminate cation radical/radical anion pair initially formed on ET, which often results in low yields of the free ions. In addition, direct irradiation of a substrate of interest often results in efficient photochemical processes from the excited state (S ) that compete with PET. 

Modified Influence (Propagation) Test. Gawthrop (Ref 1) and others used a modified gap test to determine the relative ability of a shielded donor charge to transfer detonation over an air gap to an acceptor charge. Clark (Ref 2) also used this method for the determination of the gap in the transmission of detonation from a small charge (0.5 to 2g) of HE to a cartridge of 40% straight dynamite... 

Initiation by Hot Fragments is probably the primary initiation mechanism in the so-called Halved Cartridge Gap Test (see Vol 1, p XV) and in other systems in which initiation occurs by transmission across an air gap from a donor to an acceptor charge. The hot fragments are products and reacting material thrown off by the donor see also Detonation by Influence in Vol 4, p 397-R... 

Geometry is the chief obstacle to reverse detonation. When the advancing shock front encounters the cone at the base of the cavity in which the acceptor charge is placed, the wave is transmitted normal to the surface of that juncture, and spatially dissipated away from the donor charge. It is therefore possible to place equivalent charges in proximity, while maintaining reliable go/no-go performance... 

It is also practical to invoke a one-electron approximation in the FCD method [41] when one estimates donor and acceptor charges. Thus, one approximates the fragment charges of the radical cations [(G C),(AT)] and [(GC),(A+T)] via the corresponding Mulliken populations of the HOMO and HOMO-1 of the neutral dimer. Then, the charge on fragment / in [(G+C),(AT)] is... 

Table 4 Sensitivity of the hole coupling matrix element Vda (in eV) between the two guanine units to structural fluctuations of the WCP dimer [(GC),(GC) as calculated by the FCD scheme. Also shown is the difference Aq of donor and acceptor charges (in e) ...

Bulk crystalline radical ion salts and electron donor-electron acceptor charge transfer complexes have been shown to have room temperature d.c. conductivities up to 500 Scm-1 [457, 720, 721]. Tetrathiafiilvalene (TTF), tetraselenoful-valene (TST), and bis-ethyldithiotetrathiafulvalene (BEDT-TTF) have been the most commonly used electron donors, while tetracyano p-quinodimethane (TCNQ) and nickel 4,5-dimercapto-l,3-dithiol-2-thione Ni(dmit)2 have been the most commonly utilized electron acceptors (see Table 8). Metallic behavior in charge transfer complexes is believed to originate in the facile electron movements in the partially filled bands and in the interaction of the electrons with the vibrations of the atomic lattice (phonons). Lowering the temperature causes fewer lattice vibrations and increases the intermolecular orbital overlap and, hence, the conductivity. The good correlation obtained between the position of the maximum of the charge transfer absorption band (proportional to... 

In this chapter, for space reasons, only a few paradigmatic examples of rotaxanes and catenanes based on donor-acceptor (charge transfer (CT)) and/or hydrogen bonding interactions (systems based on metal-ligand bonding are reviewed in another... 

The multiplier Rn in eqn. (37) can, in principle, lead to a further increase in the maximum value for the frequency factor. However, the role of this multiplier may not be so important due to the strong screening of the donor and acceptor charges in condensed media. This screening reveals itself in rather large values of es, and hence in rather small values of n ( 2Z n Z 1). 

The initiator in this instance is a length of detonating cord, donor and acceptor charges are both PETN, and the body is type 303S stainless steel with the bulkhead 0.075 " thick. This TBI was developed to initiate solid proplnt rocket motors that are used during stage separation to control the ullage in the main proplnt tanks and to provide retro thrust. The TBI ends are sealed so that the TBI will better withstand the temp environment (Ref 2)... 

The most prospective donors are those with ionization potentials of ID < 6.6 eV. Acceptors with electron affinities of EA > 2.6 eV are suitable. When / EA < 4 eV, donor-acceptor interaction leads to strong molecular complexes with a charge-transfer degree >0.5. Donor-acceptor charge transfer often results in the formation of ion radical salts having metallic conductivity. In terms of charge-transfer degree, ion radical salts have values >0.7. 

Conduction in weak donor-acceptor (charge-transfer) complexes 198... 

CONDUCTION IN WEAK DONOR-ACCEPTOR (CHARGE TRANSFER) COMPLEXES... 

Let us examine the structure of expression (16). The influence of the dielectric medium constant e0 affects the factor aroused from the long-range Coulomb s field of the donor and acceptor charges, (iexponential factor in g(rDA) is not yet examined. Note, the expression — (l/r )exp —differs from the Green s function of a free electron Go( D,r E) by the numeric factor l/2n only (see formula (6)). Therefore it will be considered that the influence of the medium on Green s function of a free electron does not interact with the donor and the acceptor. 

Pharmacophore keys are 3-D structural keys that are based on features of a molecule that are thought to have relevance for receptor binding. The features typically include hydrogen bond donors, hydrogen bond acceptors, charged centers, aromatic ring centers and hydrophobic centers. Pharmacophore keys are usually based on combinations of three or four pharmacophoric features and their associated distances. Flexibility can be taken into account by combining the keys for all distinct conformations of a molecule. 

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