ABSTRACT
Tetraphenylhexaazaanthracene (TPHA), a fluorescent zwitterionic biscyanine with a closed-shell singlet ground state, on treatment with manganese dioxide or phenyliodine bis(trifluoroacetate) (PIFA), undergoes oxidative dimerization to give a near-zero dipole scissor 5,5'-dimer DI-TPHA. Both acene components of the new dimer DI-TPHA maintain their biscyanine closed-shell singlet ground state motifs, as judged by analysis of both single crystal X-ray crystallographic and density functional theory computational studies; however, unlike TPHA, DI-TPHA is only very weakly fluorescent.
ABSTRACT
The 11-residue peptide fragment from transthyretin (TTR(105-115)) has been investigated using UV resonance Raman spectroscopy. Excitation at 239.5 nm reveals selective enhancement of scattering from two Tyr residues. The titrating behavior of the tyrosines is followed through the change in the Y8a band (1617 cm(-1)) frequency as a function of pH, and a pK(a) = 10.2 +/- 0.2 is obtained. This is compared to the value of 9.1 +/- 0.2 for the pK(a) of aqueous Tyr also obtained in the present study. The pK(a) difference observed here, along with observations in the nu(OH) region, suggest that the two Tyr residues in the peptide probe two distinct microenvironments.
