Charge stabilization via electron exchange: excited charge separation in symmetric, central triphenylamine derived, dimethylaminophenyl–tetracyanobutadiene donor–acceptor conjugates

The significance of electron exchange in stabilizing the charge-separated state is revealed in multi-modular donor–acceptor conjugates.

Spectral evidence for generic charge → acceptor interactions in carbamates and esters

NMR, FT-IR spectral correlations of the R–O–CO groups in carbamates and esters of homologous alcohols (R) reveal R-group-dependent negative charge stabilization at the carbonyl oxygen and its donation to generic acceptors at Cα of even alkyl R.

How Mg2+ stimulates DNA repair in prokaryotic (6-4) photolyases

Prokaryotic (6-4) photolyases branch at the base of the evolution of cryptochromes and photolyases. In the Agrobacterium (6-4) photolyase PhrB, the repair of DNA with UV-induced (6-4) pyrimidin dimers is stimulated by Mg2+. We show that Mg2+ is required for efficient lesion binding and for charge stabilization after electron transfer from the FADH- chromophore to the DNA lesion. Two highly conserved Asp residues close to the DNA binding site are essential for the Mg2+ effect. Simulations showed that two Mg2+ bind to the region around these residues. DNA repair by eukaryotic (6-4) photolyases is not increased by Mg2+. Here, the structurally overlapping region contains no Asp but positively charged Lys or Arg. During evolution, charge stabilization and DNA binding by Mg2+ was therefore replaced by a positive amino acid. We argue that this transition has evolved in a freshwater environment. Prokaryotic (6-4) photolyases usually contain an FeS cluster. DNA repair of a cyanobacterial member of this group which is missing the FeS cluster was also found to be stimulated by Mg2+.