Fractionation of histones on a metal ion equilibrated cation exchanger. I. Chromatographic profiles on an Amberlite IR-120 (A1 3+) column

Amberlite IR-120, a polystyrene sulphonate type of cation exchanger, equilibrated with A1 3+ ions, has been employed for the fractionation of whole histone. This adsorbent permits the quantitative and reproducible recovery of whole histone in six fractions.     

Some aspects of the DNA hypochromic effect theory

The expressions for the polymer absorption band hypochromism and oscillator strength are studied in frames of the first-order perturbation theory. The physically justified approximations for a polymer hypochromism calculation are indicated. The uniform interpretation of the effect origin is given independently on the approximation used. In frames of the perturbation theory the DNA hypochromism formula is obtained, from which the known experimental dependences of hypochromism on chain length and polymer helicity degree follows directly. The analytic expression of the DNA hypochromism dependence on AT pairs content is obtained. It is established that in most cases for natural DNA the nucleotide sequence does not influence in practice the value of the hypochromic effect.     

Measurement of the axial and radial temperature profiles of a chromatographic column. Influence of thermal insulation on column efficiency

The temperatures of the metal wall along a chromatographic column (longitudinal temperature gradients) and of the liquid phase across the outlet section of the column (radial temperature gradients) were measured at different flow rates with the same chromatographic column (250 mm x 4.6 mm). The column was packed with 5 microm C18-bonded silica particles. The measurements were carried out with surface and immersion thermocouples (all junction Type T, +/-0.1 K) that measure the local temperature. The column was either left in a still-air bath (ambient temperature, T(ext) = 295-296 K) or insulated in a packing foam to avoid air convection around its surface. The temperature profiles were measured at several values of the inlet pressure (approximately = 100, 200, 300 and 350 bar) and with two mobile phases, pure methanol and a 2.5:97.5 (v/v, %) methanol:water solution. The experimental results show that the longitudinal temperature gradients never exceeded 8 K for a pressure drop of 350 bars. In the presence of the insulating foam, the longitudinal temperature gradients become quasi-linear and the column temperature increases by +1 and +3 K with a water-rich (heat conductivity approximately = 0.6 W/m/K) and pure methanol (heat conductivity approximately = 0.2 W/m/K), respectively. The radial temperature gradients are maximum with methanol (+1.5 K at 290 bar inlet pressure) and minimum with water (+0.8 K at 290 bar), as predicted by the solution of the heat transfer balance in a chromatographic column. The profile remains parabolic all along the column. Combining the results of these measurements (determination of the boundary conditions on the wall, at column inlet and at column outlet) with calculations using a realistic model of heat dispersion in a porous medium, the temperature inside the column could be assessed for any radial and axial position.     

Influence of the column hold-up time measurement accuracy on the prediction of chromatographic band profiles

The influence of the column hold-up time measurement accuracy on the determination of equilibrium isotherms by classical frontal analysis and the prediction of overloaded elution band profiles were investigated. The ideal model of chromatography in combination with a Langmuir isotherm was used. Breakthrough curves and overloaded elution profiles were computer generated with a known hold-up time value (true hold-up time). Then these data were evaluated the same way as it is done with experimental chromatographic data where the true hold-up time is unknown, i.e. to determine the equilibrium isotherm by the frontal analysis procedure, to fit the isotherm data to the Langmuir model and then to predict chromatographic band profiles using, e.g. the ideal model of chromatography. A comparison of overloaded elution profiles obtained with different deviations of the hold-up time from its true value shows that the effect of its measurement error is significant in preparative liquid chromatography because the isotherm is usually strongly nonlinear in this case.     

Influence of pressure on the properties of chromatographic columns. II. The column hold-up volume

The effect of the local pressure and of the average column pressure on the hold-up column volume was investigated between 1 and 400 bar, from a theoretical and an experimental point of view. Calculations based upon the elasticity of the solids involved (column wall and packing material) and the compressibility of the liquid phase show that the increase of the column hold-up volume with increasing pressure that is observed is correlated with (in order of decreasing importance): (1) the compressibility of the mobile phase (+1 to 5%); (2) in RPLC, the compressibility of the C18-bonded layer on the surface of the silica (+0.5 to 1%); and (3) the expansion of the column tube (<0.001%). These predictions agree well with the results of experimental measurements that were performed on columns packed with the pure Resolve silica (0% carbon), the derivatized Resolve-C18 (10% carbon) and the Symmetry-C18 (20% carbon) adsorbents, using water, methanol, or n-pentane as the mobile phase. These solvents have different compressibilities. However, 1% of the relative increase of the column hold-up volume that was observed when the pressure was raised is not accounted for by the compressibilities of either the solvent or the C18-bonded phase. It is due to the influence of the pressure on the retention behavior of thiourea, the compound used as tracer to measure the hold-up volume.     

Use of an amino-silica column for the high-performance liquid chromatographic analysis of synthetic oligodeoxy-nucleotides.

The use of an amino-silica column in the chromatographic analysis of synthetic oligodeoxyribonucleotides and their derivatives from different stages of oligonucleotide synthesis has been investigated. By eluting with 0.10 M potassium phosphate solution of pH 3.30, the nucleotide composition of oligonucleotides can be established within 15 min. In a linear gradient of phosphate buffer (0.10-0.75 M) at neutral pH, the separation of oligonucleotides by length and in an acidic medium pH 3.30-4.30) by composition is possible; the oligonucleotides may be in the free form or modified by the various protecting groups used in synthetic oligonucleotide chemistry. The analysis of some reaction mixtures from different stages of oligonucleotide synthesis and of a number of synthetic oligodeoxyribonucleotides and their derivatives has been performed.     

Electrochromatography—a preliminary study of the effect of applied potential on a carbonaceous chromatographic column

The preparation of a trimethylchlorosilane-modified carbon support material and the construction of a three-electrode high-performance liquid chromatographic column are described. The effects of applied potential on the capacity factors are described. The capacity factors decrease by factors of 8 for toluene, 2 for phenol, and 1.1 for pyridine as the applied potential is changed from +0.8 to ?0.8 V vs. Ag.     

Mechanistic aspects of the Wolff-Kishner reaction. V. The cation effect on the reaction of benzophenone hydrazone in butyl carbitol and decyl alcohol

The rate of the Wolff-Kishner reaction of benzophenone hydrazone in butyl carbitol increases as the cation of the alkoxide base is varied in the order K>Na>Li>Mg. The replacement of butyl carbitol by 1-decanol also accelerates the reaction, and an additional increase is caused by the presence of crown ether. On the basis of changes in the activation parameters, it is concluded that the reactivity of the hydrazone anion increases as the contact ion pair becomes more fully solvated and dissociated.     

The effects of third elements on the kinetics of order change in Ni3Al under H.V.E.M. irradiation

The effects of boron, cobalt or titanium additions on the kinetics of order changes in Ni₃Al under irradiation were investigated in a HVEM. The long-range order (LRO) parameter was determined by measuring the intensities of superlattice spots on the diffraction patterns. Order-variation kinetics was investigated by using a previously proposed theoretical model. The number of replacements per displacement ɛ and the steady-state LRO parameter S^∞ were directly deduced by fitting a kinetic law to experimental data ; a good agreement was generally found. A weak effects of the above third elements on the disordering efficiency was observed whereas the effect of stoichiometry appeared to be more important. Reordering was found to be controlled by long-range vacancy migration with a migration enthalpy of 0.9 to 1.0 eV ; this was deduced from a comparison between the experimental temperature dependence of the steady — state LRO parameter with calculated curves. The effects of third elements on the reordering kinetics is clearly revealed : compared to binary alloys, a decrease of the effective reordering rate is generally observed.