Interband regions

Nordheim A, Pardue ML, Lafer EM, MOller A, Stollar D, Rich A (1981) Antibodies to left-handed Z-DNA bind to interband regions of Drosophila polytene chromosomes. Nature (Lond) 294 417-422... 

Recent interpretations of wide-angle X-ray diffraction patterns have led to a three-chain structure for collagen, at least in the ordered interband regions. This strongly suggested that a three-stranded structure should exist in the collagen monomer as well. Several lines of evidence support this view ... 

The region near the plasma edge in Id conductors /any gap uj < interband region/ is known to approximately obey the Drude formula for the dielectric function ... 

Evidence that fibrils, when hydrated, lose to a certain extent the differentiation between band and interband regions is furnished also by electron optical experiments in which surface replicas of moist fibrils were compared with the same fibrils after drying, the latter remaining attached to the replicas (90). The distinctly corrugated appearance of the dry fibrils is not as evident in the replicas of the moist fibrils (Fig. 23). 

An important contribution to the theoretical model formation originates from the use of vacuum-ultraviolet radiation from a synchrotron source [6). It was shown that photostimulable centers in BaFBr Fu can be created by irradiation into the vacuum-ultraviolet region (> 6.7 eV), i.e. in the excitonic and interband region of the host lattice. 

Optical absorption experiments on the thin semitransparent t/ans-polyacetylene revealed essentially no absorption until the band gap of 1.4 eV was reached. The strong absorption beyond 1.4 eV in the interband region, is consistent with previous studies on undoped polyacetylene(lO). After n-doping with either Ca or Eu" 2 countercations, increased absorption is found in the midgap region (0.7 - 0.9 eV). 

The DNA sequences which code for proteins are located mainly in the interband regions of the polytene chromosome. According to Crick s calculations, the mean amount of DNA in the interband region in the Drosophila genome is enough to code for a protein with a molecular weight of 30,000-40,000. 

It is tempting to suggest that palindromes are located in the interbands because the number of palindromes in Drosophila is approximately equal to the number of interband regions in the polytene chromosomes. It is possible to illustrate polytene chromosome organization in Drosophila as follows ... 

The most interesting discovery that suggests the existence of Z-DNA in nature was made by Rich and co-workers (Lafer et al., 1981 Noidheim et al, 1981). These authors have successfully produced antibodies that are specific to the Z-DNA conformation, as proved by their binding in vitro to three different DNA polymers capable of forming Z-DNA. These antibodies are found to bind in vivo to the interband regions of polytene chromosomes of Drosophila as visualized by fluorescent staining, thus indi-... 

The main scheme is shown in Fig. 17. The photogenerated electron hole pairs transfer to the soliton-antisoliton pairs in 10 13s. Two kinks appeared in the polymer structure, which separates the degenerated regions. Due to the degeneration, two charged solitons may move without energy dissipation in the electric field and cause the photoconductivity. The size of the soliton was defined as 15 monomer links with the mass equal to the mass of the free electron. In the scheme in Fig. 17, the localized electron levels in the forbidden gap correspond to the free ( + ) and twice occupied ( — ) solitons. The theory shows the suppression of the interband transitions in the presence of the soliton. For cis-(CH)n the degeneration is absent, the soliton cannot be formed and photoconductivity practically does not exist. 

In summary the account of interband vibronic interactions in the doping-dependent electron spectmm of cuprates allows to explain the presence of two normal state pseudogaps at underdoping and the extent of the pseudogap behaviour to the whole doping region. Such results are far away from the basic Jahn-Teller effect framework and illustrate the brightness of the basic vibronic hybridization idea. 

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