Elektronenstruktur und Solvatochromie von Betain B

[The vital staining of nuclear chromatin and the chromosomes of HeLa cells with the fluorochrome AMHA binding to DNA]

The fluorochrome AMHA (3-amino-6-methoxy-9-(2-hydroxyethylamino)acridine) stains the nuclear chromatin and the chromosomes of living HeLa cells. At relatively low dye concentrations CF less than or equal to 10(-4) M and short incubation periods tI less than or equal to 2 h cell growth is not affected by the drug. But at higher CF and longer tI the population doubling time of the cell cultures rapidly increases, and finally the cells die. In vital staining experiments the dye AMHA preferentially binds to the DNA of the nuclei and to the chromosomes of the cells, respectively. The dye binding to DNA has been proved by the absorption and emission microspectra of the stained cells, and by the comparison with authentic spectra of AMHA bound to DNA in aqueous solutions. Within the limits of experimental errors both types of spectra are identical. The spectra of DNA-bound AMHA show a characteristic gap of ca. 3500 cm-1 between the 0-0-transitions of the long wave length 1La absorption and the fluorescence. AMHA molecules dissolved in the polar solvent water have a gap of even 4100 cm-1. This energy gap shows that the electron distribution of AMHA is strongly changed by light absorption and emission. Finally, using absorption spectroscopy, we investigated the binding of AMHA to DNA in aqueous solutions over a wide range of concentrations of the dye, of nucleic acid (calf thymus), and of the competitor NaCl respectively. The Scatchard binding isotherms were determined. With the method of competitive salt effect three different bonds of AMHA to DNA can be distinguished even at low dye concentrations: The intercalation 1 of the fluorochrome F, binding constant KF1 = 1.1.10(5) M-1, binding parameter n1 = 0.15; the pre-intercalative or external binding 2, KF2 = 6.9.10(5) M-1, n2 = 0.21; the external binding 3, KF3 = 2.8.10(5) M-1, n3 = 0.55. Externally bound dye molecules 2 and 3 occupy two phosphodiester residues of the DNA. A detailed discussion of the data and the competitive salt effect shows that in living cells only intercalated and small amounts of pre-intercalatively bound molecules 1 and 2 exist. The binding constant KF1 = 1.1.10(5) M-1 of AMHA is unusual high in comparison with the constants of intercalation of other dyes, KF1 = (1-4).10(4) M-1.(ABSTRACT TRUNCATED AT 400 WORDS)

[Hydrophobic acridine dyes for fluorescence staining of mitochondria in living cells. 1. Thermodynamic and spectroscopic properties of 10-n-alkylacridine orange chlorides]

10-n-Alkyl-acridine-orange-chlorides (alkyl-AOs) are excellent dyes for fluorescence staining of mitochondria in living cells. The thermodynamic and spectroscopic properties of the series alkyl = methyl to nonyl have been investigated. The dyes form dimers in aqueous solution. The dimerisation is mainly a consequence of the hydrophobic interaction. The dissociation constant K respectively association constant K-1 of the dimers describes the hydrophobic interaction and therefore the hydrophobic properties of the dye cations. The dissociation constant K = K0 at the standard temperature T = 298 K has been determined spectroscopically in aqueous solution. It depends on the length of the alkyl residue n-CmH2m + 1 (m = 1 - 9) (Table 2). In addition the standard dissociation enthalpies (energies) delta H0 and dissociation entropies delta S0 have been determined from the temperature dependence of K (Table 2). With increasing chain length m the thermodynamic parameters K0, delta H0, delta S0 decrease. Therefore with growing m the dimers are stabilized. This stabilization is an entropic effect which is diminished by the energetic effect. The change of the thermodynamic parameters with m is in agreement with the concept of hydrophobic interaction and the stabilization of water structure in the surroundings of hydrophobic residues. As one would expect nonyl-AO is the most hydrophobic dye of the series. As an example the spectroscopic properties of nonyl-AO have been determined. We measured the absorption, luminescence and polarization spectra in rigid ethanol at 77 K. Under these conditions alkyl-AOs associate like dyes in Water at room temperature. The spectra depend on the concentration of the solution. In very dilute solution we observe mainly the spectra of the monomers M, in concentrated solution the spectra of the dimers D. The spectra of M and D are characteristically different. The monomers have one long wave length absorption M1 = 20.000 cm-1 with resonance fluorescence. In addition there is a long living phosphorescence at 16.600 cm-1. Its polarization is nearly perpendicular to the plane of the AO residue. The dimers have two long wave length absorption bands D1 = 18.700 and D2 = 21.200 cm-1 with very different intensities. D1 has very low intensity and is forbitten, D2 is allowed. D1 shows fluorescence. Phosphorescence has not been observed. D1, D2 and also M1 are polarized in the plane of the AO residue. At short wave length absorption and polarization spectra are very similar. From the spectra we constructed the energy level diagram of M and D (Fig. 9). The first excited state of M splits in D in two levels. The level splitting and the transition i