Tomas Kurucsev

Linear dichroism spectroscopy of nucleic acids.

This review will consider solution studies of structure and interactions of DNA and DNA complexes using linear dichroism spectroscopy, with emphasis on the technique of orientation by flow. The theoretical and experimental background to be given may serve, in addition, as a general introduction into the state of the art of linear dichroism spectroscopy, particularly as it is applied to biophysical problems.

LINEAR DICHROISM(250–700 nm) OF CHLOROPHYLL a AND PHEOPHYTIN a ORIENTED IN A LAMELLAR PHASE OF GLYCERYLMONOOCTANOATE/H2O. CHARACTERIZATION OF ELECTRONIC TRANSITIONS

Abstract— We determined the polarized and isotropic visible/UV absorption spectra of chlorophyll a (Chi a) and pheophytin a (Pheo a) oriented in the lamellar phase of glycerylmonooctanoate/H2O. Resolution into mutually perpendicular X‐ and Y‐polarized absorption spectra of the pigments was achieved assuming that the transition moments of Chi a and Pheo a are located in the plane of the chromophores. The polarized spectra were deconvoluted into harmonic progressions and the resultant assignment of band positions in the long‐wavelength region was found to correlate well with independent spectral measurements, such as the polarisation of fluorescence. However, the correlation of the experimentally determined transitions with the results of theoretical calculations is not straightforward. The overall conclusions are of fundamental interest in the determination of orientations of the tetrapyrrole macrocycle in lipid lamellae and pigment‐protein structures of photosynthetic membranes.

The binding of 9-aminoacridine to calf thymus DNA in aqueous solution electronic spectral studies

Absorption, circular dichroism and steady-state fluorescence spectra were determined of 9-aminoacridine solutions in the presence of DNA at an ionic strength of 0.001 mol dm-3. Up to a dye/DNA phosphorus ratio of about 0.2 the results are fully consistent with the requirements and predictions of a binding model already shown to apply to the binding of other aminoacridines to DNA. The apparently anomalous spectroscopic behaviour of the 9-aminoacridine/DNA system compared with proflavine/DNA, for example, can be satisfactorily explained from a consideration of the magnitudes of exciton interactions between dyes bound to DNA.

Effect of 2.45 GHz microwave radiation on permeability of unilamellar liposomes to 5(6)-carboxyfluorescein. Evidence of non-thermal leakage

The influence of 2.45 GHz microwave radiation on the membrane permeability of unilamellar liposomes was studied using the marker 5(6)-carboxyfluorescein trapped in phosphatidylcholine liposomes. The release of the fluorescent marker was followed by spectrofluorimetry after an exposure of 10 minutes to either microwave radiation or to heat alone of the liposome solutions. A significant increase of the permeability of carboxyfluorescein through the membrane was observed for the microwave-exposed samples compared to those exposed to normal heating only. Exposure to 2.45 GHz microwave radiation of liposomes has been previously found to produce increased membrane permeability as compared with heating. However, in contrast to previous studies, the observations reported here were made above the phase transition temperature of the lipid membrane. The experimental setup included monitoring of the temperature during microwave exposure simultaneously at several points in the solution volume using a fiberoptic thermometer. Possible mechanisms to explain the observations are discussed.

Analysis of the visible-near-ultraviolet spectrum of 9-aminoacridine using dichroic spectra in stretched polymer films

Abstract We have achieved a deconvolution of the absorption spectrum of 9-aminoacridine dispersed in polyvinyl alcohol films into 11 separate harmonic vibronic progressions of which 5 are polarised along the long axis and 6 along the short axis of the dye. The correlation between the experimental electronic transitions in this range and the calculated (π * , π) transitions is very satisfactory.

Hydrodynamic properties of polyelectrolytes: VI. Viscosity studies on dilute solutions of poly-4-vinylpyridinium chloride☆

Abstract The concentration dependence of the relative viscosity of partially neutralized poly-4-vinylpyridine is discontinuous both in aqueous solutions and in the presence of sodium chloride. The discontinuity is shown not to be an artifact of the technique of measurements. Possible explanations of the phenomenon are discussed. A tentative hypothesis involving aggregation of the poly-ions in solution is presented.

Determination of transition moment directions by means of dichroic spectra in stretched polymer films. Part 1.—Orientation of solutes

The dichroic ultraviolet spectra of naphthalene, anthracene, quinoline and acridine have been determined in stretched polyethylene and poly(vinyl alcohol) films. The molecules studied all tend to orient with their long axes along the direction of stretch. However, molecules of essentially identical shape do not necessarily orient to the same extent, nor is the orientation behaviour of a given molecule necessarily identical in the two polymer matrices.

Hydrodynamic properties of polyelectrolytes: V. Viscosity studies on dilute solutions of 4-vinylpyridine-methacrylic acid copolymers

Abstract The concentration dependence of the reduced viscosity of aqueous polyampholyte solutions has a maximum at low concentrations. Previous explanations of this behaviour are discussed. The concentration dependence of the relative viscosity of the solutions studied is shown to be discontinuous.

X-ray structure and UV spectroscopic studies of (adenmato-N9)triethylphosphinegold(I)

The preparation, characterization, and X-ray structure analysis of (adeninatoN9)triethylphosphinegold(I) is reported. The crystal structure consists of discrete molecules, the adeninate anion coordinates via the N(9) atom with a Au-N(9) bond distance of 2.057(5) Å and the linear geometry about the Au atom is completed by the P atom of a disordered Et3P ligand; the Au-P(1) bond distance is 2.238(2) Å and the N(9)-Au-P(1) bond angle is 178.8(2)°. The crystals are orthorhombic, space groupPbca, with unit cell dimensionsa=8.528(1),b=17.797(3),c=18.526(2) Å andZ=8. The structure was refined by a full-matrix least-squares procedure to finalR=0.030 andRw=0.033 for 1749 reflections withI>2.5a(I). The electronic spectrum of the complex dissolved in water in the near ultraviolet is consistent with essentially separate π-electron systems of the adenine and phosphinegold moieties; a conclusion which corroborates the X-ray structural results.

Nucleic acid-metal interactions. III. Complexes of Ag(I) with adenine and 1-methyladenine from studies of UV and IR dichroic spectra

Attempts to characterize nucleic acid-silver interactions raise questions about how the free nucleic acid bases interact with silver ions in dilute aqueous solution. Studies of ultraviolet and infrared dichroism lead to the conclusion that with silver(I) ions in dilute solution adenine forms linear polymers, whereas 1-methyladenine forms dimers. The composition and structure of the complexes are further discussed against the background of the spectroscopic results.