We observed the expression of human c-fos mRNA in a living transfected Cos7 cell under a fluorescence microscope by detecting hybrid formed with two fluorescently labeled oligodeoxynucleotides (oligoDNAs) and c-fos mRNA in the cytoplasm. Two fluorescent oligoDNAs were prepared, each labeled with a fluorescence molecule different from the other. When two oligoDNAs hybridized to an adjacent sequence on the target mRNA, the distance between the two fluorophores became very close and fluorescence resonance energy transfer (FRET) occurred, resulting in changes in fluorescence spectra. To find sequences of high accessibility of c-fos RNA to oligoDNAs, several sites that included loop structures on the simulated secondary structure were selected. Each site was divided into two halves, and the pair of fluorescent oligoDNAs complementary to the sequence was synthesized. Each site was examined for the efficiency of hybridization to c-fos RNA by measuring changes in fluorescence spectra when c-fos RNA was added to the pair of oligoDNAs in solution. A 40 mer specific site was found, and the pair of oligoDNAs for the site were microinjected into Cos7 cells that expressed c-fos mRNA. To block oligoDNAs from accumulating in the nucleus, oligoDNA was bound to a macromolecule (streptavidin) to prevent passage of nuclear pores. Hybridization of the pair of oligoDNAs to c-fos mRNA in the cytoplasm was detected in fluorescence images indicating FRET.

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We have made the first observations of the lyotropic cholesteric liquid crystal state of polyisocyanates, in which a synthetically controlled range of the dynamic excesses of one helical sense offer new opportunities for study in the area. In poly((R)-2,6-dimethylheptyl isocyanate) we have generated the cholesteric lyotropic state and studied the pitch as a function of solvent, temperature, and concentration. These data were broken down into entropic, Sq, and enthalpic, Hq, terms and were compared to theoretical predictions. The data for the polyisocyanate were compared to those already known for poly(7-benzyl L-glutamate) and schizophyllail. For all three helical polymers, the sign of S, agrees with Straley's screw model, allowing an absolute assignment of macromolecular helical sense from liquid crystal properties. The nematic phase of the dynamically racemic poly(n-hexyl isocyanate) was doped with a derivative of a steroid and of menthol, and the resulting cholesteric pitch was studied as a function of temperature and dope concentration. The failure to fit these data to theoretical expectations applicable to intrinsically chiral polymers may be due to a sensitivity of the helix sense ratio of the macromolecule to the chiral characteristics of the cholesteric phase.

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The 2pn*-3dn interaction in the excited state of aromatic silanes has been studied by means of absorption and emission spectroscopy. Broad and structureless fluorescence spectra of phenyldisilanes and naphthyldisilanes with large Stokes shifts have been observed and they have been attributed to the emissions from the intramolecular charge-transfer (c. t.) states with large dipole moments. Evidence that the c.t. emission originates from the l(2pn, 3dz) state produced by the 2pn* (aromatic ring) 3d7t (Si-Si bond) intramolecular charge transfer is given by the effect of steric twisting on the emission. It is shown that the fast formation (d 1 ns) of the c.t. state from the locally excited state I(n, n*) 'B, (or ' L b ) of phenyldisilanes takes place, followed by rapid decay (d 1 ns) of the intersystem crossing I(2pn, 3dn) + 3(7t, x*). However, no c. t. emission has been observed for aromatic monosilanes and polycyclic aromatic disilanes (aromatic rings 2 3) even in fluid polar solvents. The 2pn* -+ 3dn intramolecular c.t. mechanism is discussed in comparison with that of the twisted intramolecular charge-transfer (t.i.c.t.) state.