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Biomedical subjects

H Schott

Publications and source records attributed to H Schott.

At least 127 records · Page 7Linked to original sources
PubMed1977

Conformation affinity of cross-linked polyacrylic gels towards nucleobases, nucleosides and nucleotides.

By radical copolymerisation of monofunctional acrylic derivatives with 1,4-tetramethylene dimethacrylate, cross-linked polyacrylic gels which show a high affinity towards nucleic acid residues have been synthesised. Using these polyacrlic gels, mixtures of nucleobases, nucleosides and nucleotides can be chromatographically separated to differing extents, in some cases quantitatively. The elution of nucleobases and nucleosides from the gel in the order Cyt, Gua, Thy, Ade (or dC, dG, dT, dA and C, G, U, A, respectively) shows that Ade (dA, A) is retarded to the highest degree from the gel matrix, Cyt (dC, C) to the lowest degree. Further, the results of the separations prove that the affinity of the polyacrylic gels is much stronger towards deoxyribonucleosides than towards ribonucleosides and nucleobases. The affinity of the polyacrylic gels towards nucleobases and nucleosides depends mainly upon their tertiary structure whereas the functional side groups of the polyacrylate matrix do not contribute significantly to the interaction of the gels.

Acrylic Resins↗
PubMed1977

Effect of symmetrical tetraalkylammonium salts on cloud point on nonionic surfactants.

The salting in and salting out of the nonionic surfactant octoxynol NF by halides of ammonium and the four lowest symmetrical tetraalkylammonium cations were investigated by measuring their effect on the cloud point at various salt concentrations. The chloride anion tended to salt the surfactant out, lowering its cloud point. The iodide anion tended to salt it in, raising the cloud point, while the bromide ion had no pronounced effect. The ammonium and tetramethylammonium cations tended to lower the cloud point, the latter more extensively than the former. The tetraethylammonium cation had no pronounced effect, while the tetra-n-propylammonium and tetra-n-butylammonium cations tended to raise the cloud point, the latter more extensively than the former. The salt effect on the cloud point generally increased with increasing salt concentration. Tetramethylammonium chloride was the most efficient salt in lowering the cloud point (by 4 degrees at the 0.10-molal level and by 20 degrees at the 1.00-molal level), while tetrabutylammonium halides were the most efficient salts in raising the cloud point (by 18-19 degrees at the 0.10-molal level for chloride and bromide). Cloud point increased were attributed to the formation of mixed micelles or to hydrotropy. The salting-out efficiency of tetramethylammonium chloride and bromide was ascribed to their ability to increase the structure of water.

Bromides↗
PubMed1977

Relationship between zero point of charge and solubility product for hydroxides of polyvalent cations.

The zero point of charge (ZPC) of slightly soluble compounds is the pH at which their particles suspended in water have zero charge. The ZPC values of slightly soluble hydroxides were compared with their solubility product in the form of its negative logarithm, pKSP, and with th pH of their suspensions in pure water, pHSP, which is a function of pKSP. The ZPC-pKSP relation was nonlinear while the ZPC-pHSP relation was linear. Either equation can used to estimate the ZPC value of a hydroxide from its solubility product. The ZPC of a given hydroxide was higher than its pHSP because polyvalent cations are more extensively adsorbed and less extensively desorbed from the particle surface than the monovalent hydroxide ion. At the pHSP, there are equivalent amounts of the cation and of the hydroxide anion in solution, but the surface layer of the hydroxide particle contains an excess cation on an equivalent basis. This imbalance confers a positive charge to the particle. The solubility product of aluminum hydroxide, redetermined at 25 degrees by means of pH measurements, was 8 X 10(-33). Its ZPC, redetermined by microelectrophoresis, was 8.5 +/- 0.1.

Chemical Phenomena↗
PubMed1977

[Preparative isolation of mono- and di-pyrimidine nucleotides from depurinated herring sperm DNA (author's transl)].

The preparative isolation of DNA fragments with defined sequences from hydrolysates of naturally occuring DNA is proposed as an alternative to their complicated synthesis and has been partially realised. Starting with herring sperm DNA which was depurinated in 100 g batches, one obtains 35-40 g of a pyrimidine-oligonucleotide mixture which is separated into high and low molecular weight fragments via column chromatography on DEAE cellulose. The low molecular weight pyrimidine-nucleotide mixture thus obtained is then selectively separated on a preparative scale into fragments with one and two monomer units by means of a three-step separation procedure on QAE-Sephadex.

Animals↗
PubMed1976

Controlled flocculation of coarse suspensions by colloidally dispersed solids I: Interaction of bismuth subnitrate with bentonite.

Deflocculated suspensions of coarse powders tend to cake as the individual particles settle out and form compact, cohesive sediments. Limited flocculation results in looser sediments because the settled-out flocs incorporate large amounts of the liquid suspending medium. Controlled flocculation of bismuth subnitrate suspensions was achieved by the addition of small amounts of bentonite. The interaction of the coarse, positively charge bismuth subnitrate particles in aqueous suspension with negatively charged, colloidally dispersed bentonite was investigated by measuring electrophoretic mobility, sedimentation volume, and viscosity. Gradual addition of bentonite dispersion to bismuth subnitrate suspensions first reduced the zeta-potential of the bismuth subnitrate particles from +28 mv to zero, then inverted it, and finally caused it to level off at -20 mv for bismuth subnitrate-bentonite weight ratios below 200. Owing to the much greater specific surface area of bentonite, the surface of the bismuth subnitrate lath-shaped crystals was completely covered by 0.5% of its weight in clay platelets. Adhesion was promoted by electrovalences between surface bismuthyl ions and cation-exchange sites of the clay and by secondary valences. The charge neutralization of bismuth subnitrate by bentonite was a heterocoagulation process: the addition of small amounts of the clay flocculated the bismuth subnitrate suspensions and eliminated caking. While the zeta-potential of the bismuth subnitrate particles leveled off when their surface was saturated with bentonite platelets, sedimentation volume and viscosity continued to increase when the clay concentration was increased further while maintaining the bismuth subnitrate concentration constant. The excess, nonadsorbed bentonite formed the characteristic house-of-cards structure, incorporating the bentonite-coated bismuth subnitrate particles as cornerstones.

Bentonite↗
PubMed1976

Effect of inorganic additives on solutions of nonionic surfactants III: CMC's and surface properties.

Continuing work on the interaction of inorganic additives with nonionic surfactants in aqueous solution dealt with their effect on the CMC and surface tension. The surfactants were octoxynol and polyoxyethylated oleyl alcohol, containing an average of 9.5 and 10 ethylene oxide units, respectively. Their CMC values were lowered by most electrolytes studied, representing salting out of the surfactants. The steepest reductions in the CMC were produced by the nitrates of sodium and potassium, which had been found to lower the cloud points of nonionic surfactants, salting them out because of the inability of their cations to form complexes with the ether oxygen linkages of the polyoxyethylene moieties. However, even electrolytes with cations such as hydrogen, lithium, calcium, nickel, lead, and aluminum capable of forming complexes with the ether oxygens, thereby increasing the cloud points of the surfactants, lowered their CMC values. In the presence of increasing concentrations of the latter electrolytes, the CMC values frequently went through minima and approached the CMC of the surfactant in the absence of additives. Increases in the CMC over the entire range of additive concentrations investigated were produced by cadmium nitrate for octoxynol, urea for polyoxyethylated oleyl alcohol, and magnesium nitrate for both. Net increases in the plateau or micellar surface tension of polyoxyethylated oleyl alcohol, i.e., in the constant surface tension of surfactant solutions above the CMC, were brought about by the nitrates of cadmium, aluminum, and magnesium at low concentrations only and by urea at all concentrations. This increase is interpreted as salting in. The area per surfactant molecule adsorbed at the air-water interface was reduced by all added electrolytes. Urea caused no such reduction.

Adsorption↗
PubMed1976

Effect of inorganic additives on solutions of nonionic surfactants IV: Krafft points.

Two polydisperse polyoxyethylated nonionic surfactants were found to possess Krafft points as well as cloud points. The significance of the Krafft point and the reason why it is rarely observed in nonionic surfactants are discussed. The values of the Krafft and cloud points of the two surfactants underwent only small changes as a function of surfactant concentration in the range of 0.5-7.5% (w/w). All electrolytes investigated, as well as urea, raised the Krafft points by between 1 and 4 degrees in the concentration range of 0.5-4 molal. Included were salting-in electrolytes, which raised the cloud points, as well as salting-out electrolytes, which lowered them. Electrolytes that salt out nonionic surfactants strongly may depress the cloud point to the Krafft point temperature, rendering a water-soluble surfactant insoluble in salt solutions at all temperatures.

Chemical Phenomena↗
PubMed1975

The investigation of peptide-oligodeoxythymidylic acid interactions using template chromatography.

Poly(vinyl alcohol) has been substituted with oligodeoxythymidylic acid and the resulting polyanion irreversibly attached to DEAE-cellulose via ionic bonding. Peptide-oligonucleotide interactions have been studied using a column chromatography technique with the PV(pT)n-DEAE-cellulose as stationary phase. Of all the naturally occurring amino acids, only tryptophan and to a lesser extent tyrosine intreact significantly with the immobilized oligodeoxythymidylic acid residues under the conditions for base pairing. The homopolymers of tryptophan and tyrosine undergo greater retardation than the monomers, such that the effect is not additive but multiplicative. Thus Tyr-Tyr-Tyr shows an eightfold and Trp-Trp-Trp an approximately 30-fold larger retardation than tyrosine and tryptophan, respectively. The peptide-oligonucleotide interaction decreases considerably when nonaromatic amino acids are present in the peptide. Consequently, naturally occurring peptides and proteins which contain relatively small amounts of tryptophan and tyrosine compared with the nonaromatic amino acids undergo at the most only slight retardation on the PV(pT)n-DEAE-cellulose. The retention of oligonucleotides and peptides containing these aromatic amino acids is due in both cases mainly to base stacking (roughly 67% of the total interaction) but involves different mechanisms. Thus, the peptides interact preferably with the cellulose matrix whereas the oligonucleotides with the immobilized oligonucleotides. Interaction via hydrogen-bond formation makes up the remaining 33% of the total interaction. The oligonucleotides and peptides of the mobile phase interact with each other also via this mechanism. The strength of the d(pA-A-A) interaction is roughly that of Trp-Trp whereas d(pA-A-A-A) is weaker than Trp-Trp-Trp.

Binding Sites↗
PubMed1975

[Template chromatography on immobilized oligonucleotides. Synthesis and application of oligodeoxyadenosine-5'-phosphate--DEAE-cellulose (author's transl)].

Oligomers of deoxyadenylic acid, obtained by polycondensation, were covalently attached to polyvinyl alcohol. These polymer-bound oligonucleotides undergo very strong adsorption on DEAE-cellulose such that at neutral pH and with 1 M NaCl, partial desorbtion occurs only above 60 degrees. The use of this PV(pA)n-DEAE-cellulose for the column chromatographic separation of deoxythymidylic acid oligomers obtained by polycondensation, according to the principle of base-pairing, is discussed. Linear oligomers and also pyrophosphate derivatives of thymidylic acid which contain more than five monomer units undergo strong retardation under the conditions of base-pairing. Cyclic oligonucleotides do not show any noticeable interaction with the stationary phase. Thus, through the use of a temperature gradient, it is possible to fractionally separate the polycondensate, giving an average degree of polymerisation of 6--10.

Adsorption↗
PubMed1975

Effect of inorganic additives on solutions of nonionic surfactants II.

The effect of electrolytes and urea on the cloud points of the following three nonionic polyoxyethylated surfactants was studied: cetyl, stearyl, and oleyl alcohol adducts containing 10 ethylene oxide units. The results were similar to those obtained previously with polyethylene oxide and with a polyoxyethylated alkylphenol. Nitrates of cations capable of forming stable solid complexes with model ethers like dioxane raised the cloud points in proportion to their concentrations by up to 35 degrees. They salted the surfactants in through complexation with the ether oxygens. The order of effectiveness in raising the cloud points was lead nitrate greater than hydrochloric acid greater than cadmium nitrate greater than sulfuric acid approximately equal to to magnesium nitrate greater than aluminum nitrate greater than nickel nitrate greater than lithium nitrate greater than calcium nitrate. Only the nitrates of sodium, potassium, ammonium, and cesium lowered the cloud points, salting the surfactants out. These cations do not form complexes with ether oxygens. Urea, sodium perchlorate, and sodium iodide, which break the structure of water, raised the cloud points. This salting-in process is ascribed to increased hydration of the ether groups of the polyoxyethylated surfactants due to depolymerization of water by urea and the perchlorate and iodide anions. The bromide, chloride, and sulfate of sodium lowered the cloud points. The surfactant with the alkylaryl moiety was salted in more extensively but salted out only slightly more than the three surfactants with the linear hydrocarbon chain. The data indicate the need for revising the theories of the effects of salts on the solubility of nonelectrolytes in water. None of the theories takes into account the interaction between electrolytes and nonelectrolytes, even though many nonelectrolytes compete with water as ligands for the cations.

Chemical Phenomena↗