Electronic properties of polymethine systems. 10. Electron structure and absorption spectra of cyanine bases

Complex quantum-chemical and spectral studies of the features of the electron structure and absorption spectra of the bases' derivatives of the symmetrical cyanine dyes are performed. It is found that moving from cationic cyanines to their neutral bases is accompanied by a drastic increase in the bond length alternation, equalizing the electron densities at atoms in the chromophore and by sharp shifting up of the molecular levels. Spectral bands in the absorption spectra of the bases are essentially wider and lower intensive and hypsochromically shifted, what is suggested to be connected with different nature of the first electron transition in the cyanine dyes and their bases.     

Electronic energy levels and electron donor ability of γ-pyrylocyanines and their heteroanalogues

Investigation by spectral and polarographic measurement as well as quantum-chemical calculations were carried out in order to estimate the relative and absolute positions of the frontier energy levels of γ-pyrylocyanines and their heteroanalogues. Correlations between the theoretical energy levels and the redox potentials as well as between the calculated energy gaps and the transition energies have been established. A new parameter—electron donor ability Φ_o—has been used for the characterization of the relative position of the frontier MO.     

High-sensitivity ion mobility spectrometry/mass spectrometry using electrodynamic ion funnel interfaces

The utility of ion mobility spectrometry (IMS) for separation of mixtures and structural characterization of ions has been demonstrated extensively, including in biological and nanoscience contexts. A major attraction of IMS is its speed, several orders of magnitude greater than that of condensed-phase separations. Nonetheless, IMS combined with mass spectrometry (MS) has remained a niche technique, substantially because of limited sensitivity resulting from ion losses at the IMS-MS junction. We have developed a new electrospray ionization (ESI)-IMS-QTOF MS instrument that incorporates electrodynamic ion funnels at both front ESI-IMS and rear IMS-QTOF interfaces. The front funnel is of the novel "hourglass" design that efficiently accumulates ions and pulses them into the IMS drift tube. Even for drift tubes of 2-m length, ion transmission through IMS and on to QTOF is essentially lossless across the range of ion masses relevant to most applications. The rf ion focusing at the IMS terminus does not degrade IMS resolving power, which exceeds 100 (for singly charged ions) and is close to the theoretical limit. The overall sensitivity of the present ESI-IMS-MS system is comparable to that of commercial ESI-MS, which should make IMS-MS suitable for analyses of complex mixtures with ultrahigh sensitivity and exceptional throughput.