Perfect pairing

In the perfectly paired double strand 22, the yield of product PGgg> which indicates the amount of charge that has reached the hole trap GGG, is 68%. But if the intermediate G C base pair is exchanged by a G T mismatch, the efficiency of the charge transport drops to 23%. With an abasic site (H) opposite to G the hole transport nearly stops at this mismatched site (Fig. 15). We have explained this influence of a mismatch on the efficiency of the charge transport by a proton transfer from the guanine radical cation (G2 +)... 

The classic HLSP-PP-VB (Heitler-London-Slater-Pauling perfect-pairing valence-bond) formalism and its chemical applications are described by L. Pauling, The Nature of the Chemical Bond. 3rd edn. (Ithaca, NY, Cornell University Press, 1960 G. W. Wheland, The Theory of Resonance (New York, John Wiley, 1944) and H. Eyring, J. Walter, and G. E. Kimball, Quantum Chemistry (New York, John Wiley, 1944). 

The number No of occupied valence SCF orbitals in a molecule is typically less than the total number Nmb of orbitals in the minimal valence basis sets of all atoms. The full valence MCSCF wavefunction is the optimal expansion in terms of all configurations that can be generated from N b molecular orbitals. Closely related is the full MCSCF wavefunction of all configurations that can be generated from Ne orbitals, where Nc is the number of valence electrons, i.e. each occupied valence orbital has a correlating orbital, as first postulated by Boys (48) and also presumed in perfect pairing models (49,50), We shall call these two types of frill spaces FORS 1 and FORS 2. In both, the inner shell remains closed. 

One of the most useful types of constraint is the restriction of the spin coupling to just a single mode. Many molecular systems are described rather well by the perfect pairing mode of spin coupling, for example. A useful alternative, especially when this is not the case, is to base the structure coefficients on the CASSCF wavefunction in the VB orbital basis ... 

Spin functions oo i and qo s are identical and define the perfect-pairing mode for a six-electron-singlet. 

The spin-coupling pattern go for the reordered orbital set is largely dominated by its perfect-pairing component [ qq-s = in the Kotani basis, see Eq. (5)], in... 

This term together with the first provides the two Rumer diagrams for the bonding scheme. That this has such a large coefficient indicates that electron pair bonds are not near perfect pairing. 

Nuclear spin-spin interactions between directly bonded nuclei also are considered to proceed primarily via the Fermi contact interaction mechanism. Here, however, there is no need to consider structures representing deviations from perfect pairing and indeed such have been ignored in calculations to date as of being of secondary importance. 

A somewhat similar structure appears to be present in the specialized eukaryotic lampbrush chromosomes (Fig. 27-6), which are observed during the meiotic prophase of oocytes. They have been studied intensively in amphibians such as Xenopus. A lampbrush chromosome is actually a homologous pair of chromosomes, each one in turn consisting of two closely associated chromatids. The chromosomes are highly expanded, and about 5% of the DNA is extended in the form of -4000 perfectly paired loops visible with an electron microscope. Each loop consists of - 50 pm or -150 kb of extended DNA. No evidence of any breaks in the DNA is seen, a fact that supports the... 

No matter whether calculated within the perfect pairing VB approach or by the spin-coupled VB approach, in both cases the CC hybrid orbital extends outside the three-membered ring as expected by the schematic representations in Figure 7, but also inside... 

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