Specific and highly efficient condensation of GC and IC DNA by polyaza pyridinophane derivatives

Two bis-polyaza pyridinophane derivatives and their monomeric reference compounds revealed strong interactions with ds-DNA and RNA. The bis-derivatives show a specific condensation of GC- and IC-DNA, which is almost two orders of magnitude more efficient than the well-known condensation agent spermine. The type of condensed DNA was identified as psi-DNA, characterized by the exceptionally strong CD signals. At variance to the almost silent AT(U) polynucleotides, these strong CD signals allow the determination of GC-condensates at nanomolar nucleobase concentrations. Detailed thermodynamic characterisation by ITC reveals significant differences between the DNA binding of the bis- derivative compounds (enthalpy driven) and that of spermine and of their monomeric counterparts (entropy driven). Atomic force microscopy confirmed GC-DNA compaction by the bis-derivatives and the formation of toroid- and rod-like structures responsible for the psi-type pattern in the CD spectra

Conformational and structural studies of <i>N</i>-methylacetohydroxamic acid and of its mono- and bis-chelated uranium(VI) complexes

The thermodynamics and kinetics of the cis/trans isomerism of N-methylacetohydroxamic acid (NMAH) and its conjugated base (NMA−) have been reinvestigated in aqueous media by 1H NMR spectroscopy. Hindered rotation around the central C–N bond due to electronic delocalization becomes slow enough on the NMR time scale to observe both rotamers in equilibrium in D2O at room temperature. By properly assigning the methyl group resonances, evidence for the prevalence of the E over the Z form is unambiguously provided [K300 = [E] / [Z] = 2.86(2) and 9.63(5) for NMAH and NMA−, respectively], closing thereby a long-lasting dispute about the most stable conformer. To that end, calculations of the chemical shifts by density functional theory (DFT), which accurately reproduced the experimental data, turned out to be a much more reliable method than the direct computation of the relative energy for each conformer. The Z ⇌ E interconversion dynamics was probed at 300 K in D2O by 2D exchange-correlated spectroscopy (EXSY), affording the associated rate constants [kZE = 9.0(2) s− 1 and kEZ = 3.14(5) s− 1 for NMAH, kZE = 0.96(3) s− 1 and kEZ = 0.10(2) s− 1 for NMA−] and activation barriers at 300 K [ΔG≠ZE = 68.0 kJ mol− 1 and ΔG≠EZ = 70.6 kJ mol− 1 for NMAH, ΔG≠ZE = 73.6 kJ mol− 1 and ΔG≠EZ = 79.2 kJ mol− 1 for NMA−]. For the first time, mono- and bis-chelated uranium(VI) complexes of NMA− have been isolated. Crystals of [UO2(NMA)(NO3)(H2O)2] and [UO2(NMA)2(H2O)] have been characterized by X-ray diffractometry, infrared and Raman spectroscopies