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That reversing-pulse electric birefringence (RPEB) is an important technique in the study of microspheres was demonstrated with two polystyrene latexes with particle diameters of 430 and 81 nm and a styrene-glycidyl methacrylate copolymer latex with a diameter of 48 nm. RPEB signals were measured at 7°C and at a wavelength of 633 nm in the low electric field region in the presence of and in the absence of added salts (Na + or Ca 2+ ions). The instrument, measurements, and analysis of RPEB signals were described in detail. Well-defined signals were observed for all samples that are electron-microscopically spherical and uniform in the dry state. The particles, dispersed in aqueous media, probably form a solution phase on the outer layer of the spherical core. The charged sulfate groups at the polymeric chain terminal behave as the polyelectrolyte in this solution phase, giving rise to the electro-optic effect. The sign of birefringence is either positive or negative, reflecting a subtle difference in the electric and optical properties of the solution phase. The field-off relaxation time was evaluated from the decay curve of the RPEB signal, and the hydrodynamic diameters of the spherical particles were estimated.

The ultrasonic scission was studied for deoxyribonucleic acid (DNA) and five polyribonucleotide duplexes; three antiparallel-stranded helices (Poly(G)·Poly(C), Poly(A)·Poly(U), Poly(I)·Poly(C)) and two parallel-stranded helices (Poly(C)·Poly(C+) and Poly(A)·Poly(A+)). The sonication was carried out in 0.1—0.2 M NaCl solutions at 0°C and 200 watts for totally 20 minutes under helium gas atmosphere. The sonicated sample was fractionated by successive precipitation with acetone as the precipitant. For each duplex, several fractions were obtained in large quantities. The weight-average molecular weight Mw, the degree of polydispersity Mw/Mn, and the molecular weight distribution were determined for unsonicated, sonicated, and fractionated samples by the gel-permeation-chromatography/low-angle-laser-light-scattering method. The Mw values were reduced to a limit of 105 and the Mw/Mn values were narrowed to a 2—1.5 range by sonication. These values were further refined by fractionation. The molecular weight distribution profiles of well-defined fractions could be fitted by the logarithmic-normal function. The relationship between intrinsic viscosity and Mw was evaluated for each duplex. The result showed that the rigidity or flexibility of polymer chain depends on the molecular weight of fractionated samples and the kind of duplex examined.

The circular dichroic (CD) spectra of calf thymus deoxyribonucleic acid (hDNA) and the sonicated fragment (sDNA) with weight-average molecular weights of 580×104 and 14.2×104, respectively, were measured in the 220–320 nm wavelength region at 15°C in water-alcohol mixed solvents with an ionic strength of 0.4×10−3. The effect of ionic valence on CD spectra was examined with sodium or magnesium ions as the counterion and NaH2PO4/Na2HPO4 or Mg(CH3COO)2/CH3COOH as the buffer reagent. The CD spectra of both hDNA and sDNA with the Na+ counterion showed a B-form pattern in 0–70 vol% ethanol and transformed to an A-form profile in 72–90 vol%, the spectral change of hDNA being more cooperative than that of sDNA. Trifluoroethanol (TFE) induced changes in the CD spectra of sDNA as ethanol. In the case of the Mg2+ counterion, the CD spectra of h- and sDNA revealed the B-form pattern between 0 and 40% ethanol. A further addition of ethanol induced another spectral change, but fibrous precipitates appeared above 56% ethanol. From circular dichroic point of view, both hDNA and sDNA behave identically toward counterion, ethanol and TFE, their secondary structure probably remaining much the same.

Adsorption of native and heat-denatured calf thymus DNA (Mw = 2.5 × 105 and 4.5 × 106) and poly(cytidylic acid) · poly(inosinic acid) ((C)n · (I)n, Mw = 1.5 × 105, and 7.7 × 105) duplex onto the negatively charged poly(styrene) latex was examined at 4°C with emphasis on the effect of the molecular chain length, the species of added salts (NaCl, CaCl2, and MgCl2), and their ionic strengths ((1–10) × 10−3). The amount of adsorbed nucleic acids was determined photometrically from teh difference in the concentrations before and after mixing with the latex (average diameter, 471 nm; surface charge density, −3.52 μC/cm2). For native DNA, the higher the molecular weights and ionic strengths were, the more was adsorbed, the effect of the added ions being Mg2+ > Ca2+ ⩾ Na+. For denaturated DNA, the adsorption behavior was qualitatively the same but the adsorbed amount was less. These trends were reversed for (C)n · (l)n, but the effect of added ions remained the same as that for DNA. The divalent cations play a role of a binder between two types of negative charges on nucleic acids and on latex.

To clarify the electric field orientation of rodlike DNA and to correctly estimate the limiting high-field value, we measured the electric birefringence over a wide range of field strength up to 22.4 kV/cm at 7 o C and 535 nm in two aqueous solutions containing 0.2 and 1.0 mM Tris/HCl/NaCl (Tris=tris(hydroxymethyl)aminoethane). The dependence of the steady-state optical phase retardation δ on field strength E was examined with a particular emphasis on the extremely low-field (E