Dynamics of DNA. A quantumchemical study

Abstract

Johan J . C. van Lier et al. /Dynamics of DNA. A quantumchemical study Recl. Trav. Chim. Pays-BasAbstract. On the basis of CNDO-2 and MNDO quantumchemical calculations we suggest that direct generation of Pv trigonal bipyramidal (TBP) intermediates, in pC and pT fragments of ds DNA with repetitive purine-pyrimidine sequences, results in the B + Z transition via a selective pathway. The calculations reveal that 5'-d(G,C), 5'-d(G,T), 5'-d(A,C) and 5'-d(A,T) fragments are selected to initiate the B + Z transition. We therefore suggest that the cooperative B + Z transition can only proceed in helices having repetitive GC, GT, AC or AT sequences.Abstract. Two epimeric steroidal allenes, 1 and 2, have been interconverted by reaction with Me,CuMgCI and Me,CuLi. MeCu could also be used, although in this case the isomerisation was much slower. The 1,4-disubstituted butatrienes 6 and 8 have also been isomerised by means of Me,CuMgCI and MeCu, while the trisubstituted butatriene 2-7 has been isomerised into its geometric isomer using Et,CuMgCI. The isomerisations are thought to proceed through radical anions. In the case of the butatriene series, it is assumed that the carbometallation of the inner double bond by the copper(1) reagents also proceeds through the proposed radical anion intermediates.