Prismane

Butyne trimerizes in the presence of aluminum chloride to give hexamethyl Dewar-benzene (W. Schafer, 1967). Its irradiation leads not only to aromatization but also to hexa-methylprismane (D.M. Lemal, 1966). Highly substituted prlsmanes may also be obtained from the corresponding benzene derivatives by irradiation with 254 nm light. The rather stable prismane itself was synthesized via another hydrocarbon, namely benzvalene, a labile molecule (T. J. Katz, 1971, 1972). 

UV irradiafion of perfluoro o, m-, and p-xylenes in the gas phase gives a mixture of all possible Dewar benzene isomers Prismane valence bond isomers are proposed to be intermediates [148]... 

Here are the strongest predicted peaks for prismane and pentaprismane ... 

Figure 10.12 (a) Prismane structure of [Ge6 CH(SiMej)2)6l (for clarity only the ipso C atoms of the R groups are shown), (b) The tetracycio structure of [GegBugBrj] with only the ipso C atoms of the Bu groups shown, (c) The cubane structure of [Geg(CMeEt2>g] again with only the ipso C atoms of the t-hexyl groups shown. 

Bicyclo[2.2.0]hexadienes and prismanes are valence isomers of benzenes. These compiounds actually have the structures that were proposed for benzenes in the nineteenth century. Prismanes have the Ladenburg formula, and bicyclo[2.2.0]-hexadienes have the Dewar formula. Because of this bicyclo[2.2.0]hexadiene is often called Dewar benzene. On page 32 it was mentioned that Dewar formulas are canonical forms (though not very important) of benzenes. Yet, they also exist as separate compounds in which the positions of the nuclei are different from those of benzenes. 

II, Historical Discovery of Prismane Protein (Now Termed Fepr)... 

Subsequent studies provided a wealth of information that appeared to support the hypothesis that the Fepr protein was a genuine [6Fe-6S]-containing protein. In a biochemical study (10) the elemental analysis was meticulously repeated, and, based on an assumed molecular mass of 52 kDa, the prismane protein was found to contain 6.3 Fe atoms, averaged over as many as nine different preparations. Again, no other metals than Fe were detected, suggesting that all... 

MCD results more or less confirmed the conclusions drawn from previous EPR data (27). The shapes of the MCD spectra of the putative prismane protein in the 3+, 4+, and 5+ states had not been observed for any Fe-S protein. This was not surprising, since every single type of Fe-S cluster is considered to exhibit a unique MCD spectrum. Magnetization data confirmed the S = ground state of the 5-1- state, as well as the S = 4 ground state of the 4+ state. Unexpectedly, in addition to the S = 4 contribution, a considerable diamagnetic contribution was observed for the 4-1- state. The nature of the diamagnetic contribution was not understood a physical spin mixture was considered to be a possible explanation. 

Resonance Raman studies on the putative prismane protein would provide other important information. In the frequency region of 200-430 cm the putative prismane protein showed bands that at first sight seemed to be typical for Fe-S clusters, but at a closer look appeared to be broader than those observed in basic Fe-S proteins. Also, the resonance frequencies were slightly different from known Fe-S clusters, and it was contended that A prismane-type [6Fe-6S] core is clearly an excellent candidate in light of the available analytical and biophysical data [28]. 

Fe-S and Fe-Fe distances in [2Fe-2S], [3Fe-4S], and [4Fe-4S] clusters are all very similar 2.3 and 2.7 A, respectively. In the [6Fe-6S] prismane model cluster, however, there is an additional Fe-Fe distance at 3.7 A (Fig. 2). If a [6Fe-6S] cluster were present in the Fepr protein, then this longer Fe-Fe distance should he visible with extended X-ray absorption fine structure (EXAFS). As a consequence, EXAFS studies were carried out at the CCLRC Synchrotron Radiation facility in Daresbury, UK. The two Fepr proteins (those of D. vulgaris and D. desulfuricans), as well as a synthetic [6Fe-6S] cluster, were subjected to an EXAFS study. Low-temperature EXAFS... 

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