In continuation of our work on Wanzlick/Arduengo carbenes containing redox-active ferrocenyl substituents we report on the synthesis of N,N‘-diferrocenyl imidazol(in)ium salts as precursors of imidazol(in)-2-ylidenes. The necessary starting material for this chemistry is aminoferrocene, which was prepared by an improved and large-scale synthesis by the sequence solid lithioferrocene, iodoferrocene, N-ferrocenylphthalimide, aminoferrocene. The preparation of N,N‘-diferrocenyl heterocycles involves condensation of aminoferrocene with glyoxal to afford N,N‘-diferrocenyldiazabutadiene [Fc-DAB], reduction, condensation with formaldehyde, and oxidation with trityl salts to yield N,N‘-diferrocenylimidazol(in)ium salts. In situ deprotonation and trapping with electrophiles yielded the expected metal complexes and derivatives in some cases [Ag+ or S8], but attempted reaction with other transition metals [e.g., Pd(II)] failed to give the corresponding complexes, due to (i) steric hindrance by the two N-ferrocenyl substituents, (ii) reduced acidity of the imidazol(in)ium precursors, and (iii) inaccessibility of the free carbenes. Spectroscopic [IR, Raman, UV−vis, MS, NMR (1H, 13C, 109Ag)], structural [X-ray], and electrochemical [CV] properties are reported and compared to those of other N-heterocyclic carbene derivatives.

Conformational substates of B-DNA had been observed so far in synthetic oligonucleotides but not in naturally occurring highly polymeric B-DNA. Our low-temperature experiments show that native B-DNA from salmon testes and the d(CGCGAATTCGCG)2 dodecamer have the same BI and BII substates. Nonequilibrium distribution of conformer population was generated by quenching hydrated unoriented films to 200 K, and isothermal structural relaxation toward equilibrium by interconversion of substates was followed by Fourier transform infrared spectroscopy. BI interconverts into BII on isothermal relaxation at 200 K, whereas on slow cooling from ambient temperature, BII interconverts into BI. Our estimation of the dodecamer's BI-to-BII conformer substate population by curve resolution of the symmetrical stretching vibration of the ionic phosphate is 2.4 +/- 0.5 to 1 at 200 K, and it is 1.3 +/- 0.5 to 1 between 270 and 290 K. Pronounced spectral changes upon BI-to-BII interconversion are consistent with base destacking coupled with migration of water from ionic phosphate toward the phosphodiester and sugar moieties. Nonspecific interaction of proteins with the DNA backbone could become specific by induced-fit-type interactions with either BI or BII backbone conformations. This suggests that the BI-to-BII substate interconversion could be a major contributor to the protein recognition process.

Aqueous D2O solutions of lithium (0.5, 1, and 3 M) and sodium (1 and 3 M) perchlorate have been studied by FT-IR spectroscopy in their glassy states at 80 K, and their IR spectra compared with those of 1.0 M D2O solutions recorded from 300 to 235 K. Evidence for strongly increasing contact-ion pairing in going from ambient temperature to the glassy state is based on the development of a second band in the ν1 band region centered at high frequency of the band from “free” perchlorate and complete loss of degeneracy in the ν3 and ν4 band region. On the basis of curve resolution of the ν1 band region, increasing contact-ion pairing is much more pronounced for sodium than for lithium perchlorate. The spectral features of contact-ion paired perchlorate are consistent with at most C 2 v symmetry with bidentate binding. Anomalous increase in contact-ion pairing on hyperquenching into the glassy state is attributed to water's density maximum and the anomalies of supercooled water and “dilute” aqueous solutions. Spectral features of ion-pairing are weakly observable already at 300 K in the ν1 and ν3 band region and become more pronounced on cooling to 235 K. Significance of the results is discussed with respect to (i) differences in local geometry of contact-ion pairs in aprotic donor solvents, (ii) vapor-deposited alkali metal perchlorates isolated in a water matrix, (iii) thermodynamic continuity of states between vapor-deposited amorphous water, hyperquenched glassy water and normal supercooled water, and (iv) cryofixation of polyelectrolyte-type biomolecules such as nucleic acid sodium salts.