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1

Digitale Medien

Vibrational modes of A-DNA, B-DNA, and A-RNA backbones: An application of a green-function refinement procedure (1977)

Lu, K. C. ; Prohofsky, E. W. ; Van Zandt, L. L.

New York : Wiley-Blackwell

Biopolymers 16 (1977), S. 2491-2506

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ISSN: 0006-3525

Schlagwort(e): Chemistry ; Polymer and Materials Science

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie

Notizen: Normal vibrational analysis was carried out for DNA molecules in both A and B conformations as well as for A-RNA. A simplified backbone model was examined and expanded to include the backbone phosphate-group and the ribose ring. We applied the new force-constant refinement procedure discussed in the preceeding paper [Van Zandt, L. L., Lu, K.-C. & Prohofsky, E. W. (1977) Biopolymers, 16, 2481-90] to fit some observed frequencies in the Raman spectra for all three nucleic acids with the same set of force constants. The results indicate that the observed frequency shift can be attributed to the conformational change solely. We ignored the second-order differences in force constants for the different geometries. The agreement between the observed and calculated frequencies derived from the final refined set of force constants is good and apparently justifies this assumption. Two modes previously assigned to the symmetric diester O-P-O stretch and the symmetric dioxy O‥P‥O stretch are actually fitted. They are mainly backbone phosphate-group modes. The refined ribose-ring force-constants were transferred to the calculation of the vibrational spectrum of tetrahydrofuran. The overall agreement is again good. We discuss these calculations and the resulting normal modes. We also discuss the application of the Green-function refinement scheme and several strategies adopted to bias the convergence of the procedure.

Zusätzliches Material: 2 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/bip.1977.360161112

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2

Digitale Medien

Helix coil transitions of d (A)n·d(T)n, d(A-T)n·d(A-T)n, and d(A-A-T)n·d(A-T-T)n; evaluation of parameters governing DNA stability (1977)

Oliver, Adrian L. ; Wartell, Roger M. ; Ratliff, Robert L.

New York : Wiley-Blackwell

Biopolymers 16 (1977), S. 1115-1137

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ISSN: 0006-3525

Schlagwort(e): Chemistry ; Polymer and Materials Science

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie

Notizen: The thermally induced helix-coil transitions of three A-T DNAs, d(A)n·d(T)n, d(A-T)n·d(A-T)n, and d(A-A-T)n·d(A-T-T)n, were studied. Experimental transition curves of the DNAs were analyzed using the loop entropy model of DNA melting. The calculation of the melting curve of d(A-A-T)n·d(A-T-T)n is presented using the integral equation formalism of Goel and Montroll. The aim of this work was to evaluate thermodynamic parameters which govern DNA stability and to test the theoretical model employed in the analysis. Our results show (1) an excellent over-all agreement between theory and experiment, (2) a loop entropy exponent k = 1.55 ± 0.05 provided the best fit to all the polymer transition curves, (3) the evaluated stacking free energies reflect the relative stability of the DNAs, and (4) the stacking energies of the ApA·TpT dimer evaluated from d(A)n·d(T)n and d(A-A-T)n·d(A-T-T)n differ. The last result is consistent with different conformations for the dimer in these two polymers.

Zusätzliches Material: 4 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/bip.1977.360160512

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3

Digitale Medien

Branching and molecular weight distribution of polyethylene SRM 1476 (1977)

Wagner, Herman L. ; McCrackin, Frank L.

New York, NY [u.a.] : Wiley-Blackwell

Journal of Applied Polymer Science 21 (1977), S. 2833-2845

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ISSN: 0021-8995

Schlagwort(e): Chemistry ; Polymer and Materials Science

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie , Maschinenbau , Physik

Notizen: A method of determining the distribution of branching in a polymer is developed employing limiting viscosity numbers (intrinsic viscosity), gel permeation chromatography (GPC), and absolute molecular weight determinations of fractions of the whole polymer. A molecular weight calibration of the GPC column set is first determined empolying these fractions. From the limiting viscosity number measurements of these fractions and their molecular weight distribution determined from the GPC chromatogram, the viscosity-molecular weight relationship is determined by a nonlinear least-squares fitting procedure. For the same molecular weight, the limiting viscosity number of the branched polymer is less than the limiting viscosity number of the linear polymer. From the ratio of the two, the number of branches per unit molecular weight of the branched polymer is calculated. The method was applied to SRM 1476, the standard reference branched polyethylene issued by the National Bureau of Standards. The branching density for the constituents of SRM 1476 rise from zero at molecular weights less than 10,000 to about 6 to 8×10-5 at molecular weights of 50,000 and above. The branching of SRM 1476 was also determined by the method of Drott and Mendelson, giving a result in fair agreement with the above method.

Zusätzliches Material: 6 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/app.1977.070211019

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4

Digitale Medien

Pressure drop, gas hold-up, and oxygen transfer in tower systems (1977)

Hsu, K. H. ; Erickson, L. E. ; Fan, L. T.

New York, NY [u.a.] : Wiley-Blackwell

Biotechnology and Bioengineering 19 (1977), S. 247-265

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ISSN: 0006-3592

Schlagwort(e): Chemistry ; Biochemistry and Biotechnology

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung

Notizen: Pressure drop, gas hold-up, and oxygen transfer were investigated in a sieve tray column, a column with Koch motionless mixers, and a bubble column. The oxygen transfer experiments were conducted using cocurrent flow of gas and liquid under steady-state conditions with oxygen transfer from the gas to the liquid phase. The oxygen transfer rates and efficiencies of the sieve tray column and the column with Koch mixers were found to be superior to those of the conventional bubble column. Gas hold-up was also greater when sieve trays or Koch mixers were inserted in the tower. The pressure drop was found to be primarily due to the liquid head in all three columns.

Zusätzliches Material: 18 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/bit.260190208

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5

Digitale Medien

Oxygen transfer and axial dispersion in an aeration tower containing static mixers (1977)

Maclean, G. T. ; Erickson, L. E. ; Hsu, K. H. ; [weitere]

New York, NY [u.a.] : Wiley-Blackwell

Biotechnology and Bioengineering 19 (1977), S. 493-505

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ISSN: 0006-3592

Schlagwort(e): Chemistry ; Biochemistry and Biotechnology

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung

Notizen: Oxygen transfer from gas to liquid under steady-state cocurrent flow conditions was modeled using the dispersion model, and the oxygen transfer coefficients were estimated from available data for a column with Koch motionless mixers. The dispersion in the column was estimated for several different gas and liquid flow rates using steady-state tracer experiments. The estimated oxygen transfer coefficients were compared with those estimated using complete mixing and plug flow models. The results indicate that the dispersion model is the most appropriate model for estimating the mass transfer coefficient from the available data.

Zusätzliches Material: 8 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/bit.260190405

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6

Digitale Medien

Inhibitoren der Korrosion 20(1)-Über die zeitliche Abhängigkeit der analytischen Zusammensetzung der Korrosionsprodukte des Eisens von der Menge an verbrauchtem Sauerstoff (1977)

Horner, L. ; Gammel, D. ; Doms, G. ; [weitere]

Weinheim [u.a.] : Wiley-Blackwell

Materials and Corrosion/Werkstoffe und Korrosion 28 (1977), S. 478-480

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ISSN: 0947-5117

Schlagwort(e): Chemistry ; Polymer and Materials Science

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Maschinenbau

Beschreibung / Inhaltsverzeichnis: Analytical composition of the corrosion products of iron as a function of time and of the oxygen consumedUsing a modified standard method of analysis it is possible to analyze mixtures containing Fe0, Fe2+ and Fe3+. This method is used to study corrosion systems catalyzed by chlorides. According to the results obtained the amount of Fe2+ is approx constant at pH 7, irrespective of the oxygen quantityt consumed, Fe0 being oxidized to give Fe2+ and the latter being oxidized, at a comparable rate, to give Fe3+. At pH 3, however, Fe2+ is obtained almost exclusively, and beyond pH Fe3+ becomes predominating.

Notizen: Mit einer modifizierten Analysenmethode ist es möglich, Gemische mit Fe0, Fe2+ und Fe3+ zu analysieren. Diese Methode wird zur Untersuchung von Systemen mit chloridkatalysierter Korrosion benutzt. Nach den Ergebnissen ist die Fe2+-Menge bei Ph 7 unabhängig von der verbrauchten Sauerstoffmenge annähernd konstant, da Fe0 zu Fe2+ und dieses weiter zu Fe3+ oxidiert wird. Die Geschwindigkeiten dieser Reaktionen sind vergleichbar. Bei pH 3 erhält man nur Fe2 und ab pH 4 wird Fe3+ vorherrschen.

Zusätzliches Material: 3 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/maco.19770280705

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7

Digitale Medien

On phase equilibrium at the gas-liquid interface during absorption (1958)

Scriven, L. E. ; Pigford, R. L.

Hoboken, NJ : Wiley-Blackwell

AIChE Journal 4 (1958), S. 439-444

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ISSN: 0001-1541

Schlagwort(e): Chemistry ; Chemical Engineering

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung

Notizen: That phase equilibrium exists at the gas-liquid interface during gas absorption is usually assumed in the analysis and design of absorption equipment, but the validity of this assumption has been in doubt since Higbie's pioneering gas-absorption studies. Accurate measurements are reported herein of the absorption rates at 25°C. of carbon dioxide into short water jets in which the liquid was in laminar flow. The jets issued from circular nozzles of about 1.5-mm. diam., flowed intact downward through an atmosphere of carbon dioxide at average velocities of from 75 to 550 cm./sec. over distances of 1 to 15 cm., and were collected in a receiver slightly larger in diameter than the nozzles. The measured absorption rates are in excellent agreement with predictions based on unsteady state diffusion theory, when one assumes interfacial equilibrium. It is concluded from these results and those of other investigators that equilibrium prevails at a freshly formed, relatively clean, carbon dioxide-water interface and that the same statement probably applies to the absorption of other slightly soluble gases in water.Evidence is discussed which indicates that an accumulation of minute quantitities of surface-active materials may seriously reduce the rate of gas absorption, either by affecting the hydrodynamic characteristics of the system or perhaps by offering resistance to the transfer of solute molecules across the interface.

Zusätzliches Material: 8 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/aic.690040412

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8

Digitale Medien

Absorption into an accelerating film (1958)

Scriven, L. E. ; Pigford, R. L.

Hoboken, NJ : Wiley-Blackwell

AIChE Journal 4 (1958), S. 382

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ISSN: 0001-1541

Schlagwort(e): Chemistry ; Chemical Engineering

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung

Zusätzliches Material: 2 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/aic.690040330

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9

Digitale Medien

A new procedure for refining force constants in normal coordinate calculations on large molecules (1977)

Van Zandt, L. L. ; Lu, K.-C. ; Prohofsky, E. W.

New York : Wiley-Blackwell

Biopolymers 16 (1977), S. 2481-2490

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ISSN: 0006-3525

Schlagwort(e): Chemistry ; Polymer and Materials Science

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie

Notizen: We develop a force-constant refinement procedure which we believe capable of being used in problems of large molecules and biopolymers. The procedure is based on a Green-function expression which relates changes in frequency to changes in force constants. The method does not require that assignments be made before refinment (although they may be). An expansion of this expression gives rise to a set of linear algebraic equations for the force-constant corrections, rather than an equation involving residuals to minimize. The resulting calculations are considerably simpler. This approximate is iterated to find the final refined force-constants. We discuss several methods of improving the convergence of the procedure which take into account the experimental information which may be available. Of particular interest is a scheme to select the force constants to be refined by imposing a criterion for selecting those which will fit the experimental data with the smallest changes of the force constants from their expected values. We discuss some limitations which occur for all methods of refinement applied to large molecules.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/bip.1977.360161111

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10

Digitale Medien

Antioxidants and stabilizers. LXVI. Oxidation and photooxidation of methyl- and octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionates. quenching of singlet oxygenPart LXV: L. Taimr and J. Pospíšil, this journal 52 (1976) 31. (1977)

Samsonova, L. V. ; Taimr, L. ; Pospíšil, J.

Weinheim : Wiley-Blackwell

Angewandte Makromolekulare Chemie 65 (1977), S. 197-210

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ISSN: 0003-3146

Schlagwort(e): Chemistry ; Polymer and Materials Science

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie , Physik

Beschreibung / Inhaltsverzeichnis: Die Cyclohexadienonhydroperoxide IIIb und IIIc entstehen durch methylenblau-sensibilisierte Photooxidation von Methyl-(IB) und Octadecylester (Ic) der 3-(3,5-Di-tert-butyl-4-hydroxyphenyl)propionsäure. Die Reaktion verläuft über den Singulett-Sauerstoff. Es wurde die photochemische Stabilität der beiden Hydroperoxide in Anwesenheit und Abwesenheit des Sensibilisators verfolgt. Beide Hydroperoxide spalten sich thermisch unter Bildung der Ausgangsphenole Ib bzw. Ic. Die verbindung IV, die einen wirksamen Quencher (Löscher) von Singulett-Sauerstoff darstellt, entsteht durch die Oxidation von Ib mittels Bleidioxid. Sie nähert sich in ihrer Wirkung dem β-Karotin. Die Verbindung IV ist gegen weitere Oxidation im neutralen Milieu beständig. E wurden die Umwand-lungen von Ib und Ic im Hinblick auf die Prozesse, die während der Alterung von stabilisierten Polyolefinen verlaufen, verfolgt.

Notizen: Photooxidation of the methyl ester (Ib) and octadecyl ester of 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionic acid (Ic) sensitized with methylene blue gives rise to cyclohexadienone hydroperoxides IIIb or IIIc. The reaction proceeds via singlet oxygen. The photochemical stability of both hydroperoxides was examined in the presence and absence of sensitizer. The thermal decomposition of both hydroperoxides leads to the respective starting phenols Ib or Ic. Oxidation of Ib with lead dioxide yields IV, an effective quencher of singlet oxygen, the effect of which approaches that of β-carotene. In a neutral medium Iv is stable against oxidation. The transformations are investigated with respect to the system of processes occurring in the aging of stabilized polyolefins.

Zusätzliches Material: 2 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/apmc.1977.050650114

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