Bis‐4,9‐diazapyrenium dications: synthesis of the methylenedibenzyl‐analogue,interactions with nucleotides,DNA, RNA. The antitumour activity of all till now prepared analogues

Novel bis‐4,9‐diazapyrenium dication has shown reversible pH dependent formation of 4,9‐ diazapyrenium pseudobase in water characteristic for most 4,9‐diazapyrenium derivatives. The compound has formed non‐covalent complexes with nucleotides in water, whose stability is controlled dominantly by aromatic stacking interactions. No cooperativity between two 4,9‐diazapyrenium subunits was observed in binding of nucleotides. Novel bis‐4,9‐diazapyrenium dication formed mono‐intercalative complexes with studied double stranded DNA and RNA. Additional interactions of non‐intercalated part were found to depend significantly on the polynucleotide secondary structure, yielding strong DNA over RNA preference. Appearance of ICD band of 3 was found to be specific for DNA polynucleotides and together with observed destabilisation of double stranded RNA is attributed to the aggregation of compound in one of the RNA grooves. All bis‐4,9‐diazapyrenium dications prepared till now have shown considerable antiproliferative activity against five human tumour cell lines, which suggested mechanism of action by interacting with cell DNA. Copyright © 2007 John Wiley & Sons, Ltd.     

Synthesis and structure of a dimethyl(μ-hydrido)di-platinum(II) complex

The complex [Pt₂Me₂(μ-H)(μ-dppm)₂][PF₆] (I, dppm = Ph₂PCH₂PPh₂) has been prepared and characterised by ¹H and ³¹P NMR spectroscopy and by a full molecular structure determination by X-ray methods. The complex undergoes only slow reductive elimination of methane induced by added tertiary phosphine at 70°C.     

Correlation analysis of kinetic parameters of the free radical polymerization of alkylphenyl methacrylates

Data from previous articles on the initial polymerization rates of a series of monoalkyl substituted phenyl methacrylates were found to depend strongly on the size and position of the monoalkyl substituent in the phenyl ring. In order to investigate the possibility of correlation of all the rate data obtained, all those for phenyl methacrylate and ten other alkylphenyl substituted methacrylate monomers were fitted into empirical linear free energy relationships (LFER). Assuming steady-state kinetics and separating out the initiator decomposition contribution to the initial overall rate R_p, it was demonstrated that k′ = k_p/k_t^½ can be successfully correlated with LFER equations containing predominantly steric parameters. The steric influence is more pronounced in the o- than in the p-substitution, due to the proximity of the o-substituent to the reaction propagation site. The results are corroborated by the existence of an isokinetic relationship of ΔH? vs. ΔS?, providing the proportionality of electronic effects, however small, and the predominating steric effects. The treatment is based on the assumption that the initiator efficiency ? equals 1 and that the termination rate constants k_t are equal for monomers of similar structure, what might represent an approximation of the true situation in the system investigated. © John Wiley & Sons, Inc.     

The T-dual symmetries of a bosonic string

We investigate whether the symmetry transformations of a bosonic string are connected by T-duality. We start with a standard closed string theory. We continue with a modified open string theory, modified to preserve the symmetry transformations possessed by the closed string theory. Because the string theory is conformally invariant world-sheet field theory, in order to find the transformations which preserve the physics, one has to demand the isomorphism between the conformal field theories corresponding to the initial and the transformed field configurations. We find the symmetry transformations corresponding to the similarity transformation of the energy-momentum tensor, and find that their generators are T-dual. Particularly, we find that the general coordinate and local gauge transformations are T-dual, so we conclude that T-duality in addition to the well-known exchanges, transforms symmetries of the initial and its T-dual theory into each other.