Absorption and vibrational circular dichroism (VCD) spectra of six 1,1′-binaphthyl derivatives were measured and analyzed on the basis of ab initio modeling. The spectra of both enantiomers were recorded with a high signal-to-noise ratio. The BPW91/6-31G** density functional theory level and the gauge invariant atomic orbitals were used for the simulations of VCD intensities. The binaphthyl moiety behaves as a chiral chromophore with a strong VCD signal because the 1,1′-substitution hinders its rotation. Most of the VCD bands were assigned, and the contributions of the binaphthyl skeleton and the functional groups could be clearly distinguished. Distinct VCD characteristics were found for the compounds exhibiting C 2 and C 1 symmetry. A very good agreement between the calculated and experimental spectra was observed. Apart from indication of enantiomeric purity, the spectra contain readable information about molecular conformation. The dihedral angle between the naphthyls planes, equal to about 55°when naphthyl residues were connected with PO 4 covalent bridge, was found close to 90°for all the other derivatives.
The self-assembly of guanosine-5'-hydrazide G-1 in D(2)O, in the presence and absence of sodium cations, has been investigated by chiroptical techniques: electronic (ECD) and the newly introduced vibrational (VCD) circular dichroism spectroscopy. Using a combination of ECD and VCD with other methods such as IR, electron microscopy, and electrospray ionization mass spectrometry (ESI-MS) it was found that G-1 produces long-range chiral aggregates consisting of G-quartets, (G-1)(4), subsequently stacked into columns, [(G-1)(4)](n), induced by binding of metal cations between the (G-1)(4) species. This process, accompanied by gelation of the sample, is highly efficient in the presence of an excess of sodium cations, leading to aggregates with strong quartet-quartet interaction. Thermally induced conformational changes and conformational stability of guanosine-5'-hydrazide assemblies were studied by chiroptical techniques and the melting temperature of the hydrogels formed was obtained. The temperature-dependent experiments indicate that the long-range supramolecular aggregates are dissociated by increasing temperature into less ordered species, monomers, or other intermediates in equilibrium, as indicated by MS experiments.
Application of the finite impulse response (FIR) filtration technique for the removal of spectral noise and background broadband deformations from the Raman spectra is tested. Optimal parameters of FIR filters are found and their effectiveness is compared with the Savitzky-Golay (SG) smoothing procedure. The FIR filtration is found to be an effective procedure to treat the whole Raman spectra, but high computing power is needed.
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