Experimental anomalies and the conformational theory of polymers

The influence of the size and shape of the torsional potential upon the theoretical temperature coefficient (T? ln 〈r₀²〉/?T) of a polymeric chain was studied. The uncorrelated end-to-end distance equations for isotactic, syndiotactic, and completely atactic chains were differentiated with respect to temperature and the integrals in the resulting equations were evaluated by the method of Gaussian quadrature. The calculated coefficients were found to be nonlinear functions of the energy ratio U_max/KT, where U_max is the maximum potential barrier and possess real roots which critically depend upon the size and shape of the potential. Qualitative anomalies between experiment and theory disappeared when the entire torsional potential was used in the conformational theory. It appears that quantitative agreement between theory and experiment can be established for polymeric materials if the entire potential is used, rotations within bulky side groups are included, and the potential is determined by the method of minimum conformational energy.     

Nitration of pentaerythritol by HNO3-H2SO4-H2O system

Conclusions It was shown experimentally that the nitrating agent in the O-nitration of pentaerythritol by HNO₃-H₂SO₄-H₂O nitrating mixtures is not the nitronium cation but evidently the free unionized nitric acid molecule.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 134–140, January, 1970.     

Viskoelastische Eigenschaften von Polyisobutylenen in verdünnten Lösungen

Zusammenfassung Die Speicher- und VerlustmodulnG undG verdünnter Lösungen (2–4%) dreier Isobutylenpolymerisate mit den Molekulargewichten 0,63, 1,29 und 11×10⁵ wurden in der Apparatur vonBirnboim undFerry über einen Frequenzbereich von 0,4–400 Hz und einen Temperaturbereich von –17,5 bis 25,0° bestimmt. Für die scharf fraktionierten Polymerisate von niederem Molekulargewicht ergab die Frequenzabhängigkeit der Moduln eine ausgezeichnete Übereinstimmung mit der Theorie vonZimm. Die aus den experimentell erhaltenen Kurven ermittelten Molekulargewichte und größten Relaxationszeiten waren von der erwarteten Größenordnung. Für das Polymerisat mit höherem Molekulargewicht entsprach die Frequenzabhängigkeit vonG undG – _s jedoch der Theorie vonRouse. Der Einfluß der hydrodynamischen Wechselwirkung in der Bewegung der Knäuelsegmente, in welchem der Unterschied zwischen den beiden Theorien besteht, erscheint als von der Größe des Molekulargewichts abhängig.

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Summary The storage and loss moduliG andG of dilute (2–4%) solutions of three polyisobutylenes of molecular weight 0.63, 1.29, and 11×10⁵ were determined in the apparatus ofBirnboim andFerry over a frequency range of 0.4 to 400 cps, and a temperature range of –17.0 to 25.0°. The sharply fractionated polymers of low molecular weight showed a frequency dependence in excellent agreement with the theory ofZimm. The experimentally determined molecular weights and terminal relaxation times were of the expected order of magnitude. The frequency dependence of the polymer of highest molecular weight, however, conformed more closely to the theory ofRouse. The influence of the hydrodynamic interaction on the motion of the coil segments, which constitutes the difference in the two theories, appears to depend on the magnitude of the molecular weight.

     

Fluorimetric determination of boron with resacetophenone as a reagent

Summary A method has been developed for the fluorimetric determination of boric acid, which gives a blue fluorescence with resacetophenone in sulphuric acid or phosphoric acid medium. The method has the advantage that the reaction does not require much time, because the fluorescence intensity reaches its maximum immediately after mixing the reagents and does not also decrease with time. The intensity of fluorescence can be measured with a fluorimeter and the amount of boric acid determined from a calibration curve.     

Some observations on the synthesis and HPLC of tris-(acetylacetonato)technetium(III) and (IV) complexes

[⁹⁹Tc(III) (acac)₃] was synthesized by published procedure, but recovered by extraction into CH₂Cl₂. The product was purified by preparative HPLC over a reversed phase column, RP18, using a mobile phase of 11 CH₃OHH₂O. The cationic complex [⁹⁹Tc(IV) (acac)₃]⁺ prepared by the oxidation of the purified neutral Tc(III) complex was unstable in methanol/methanol-water medium, being reduced back to the Tc(III) complex.     

The mechanism of bacteriorhodopsin functioning. I. The light-induced proton throw-over by retinal

The path of proton motion in protein bacteriorhodopsin is constructed: Tyr 43 → Tyr 26 → Asp 212 → Tyr 83 → Tyr 57 → Tyr 79 → Glu 204 → Tyr 64 → Glu 74. From the position of quantum theory the light-induced isomerization of retinal, the process carrying out the proton and throw-over from the inlet H-bond chain (Tyr 43 → Tyr 26 → Lys 216) to the outlet one (Lys 216 → Asp 212 → … → Glu 74) are investigated. The kinetics of the transition of the excitation from the π-electron subsystem to the vibrational one is studied; the function of the nonequilibrial excitation distribution of the collective intramolecular retinal vibrations is found. The mechanism of deprotonation of Schiff base (transmission of proton to the outlet channel) is considered. The correspondence between the theoretically estimated states and spectroscopically identified forms of bacteriorhodosin (initial form bR, intermediates J, K) is proposed.     

Analytical applications of crown ethers : III. Extraction and determination of nitrophenol isomers

The oxidation of aldehydes by dicyclohexyl-18-crown-6-potassium permangante complex is presented. Results obtained by this procedure showed that the presence of crown ether (DCC) and the catalyst play an important role in the oxidation of the aldehydes. The stoichiometry found corresponds to 2 μeq of permanganate per 1 μmol of aldehydes in all cases. Alcohols and ketones are not oxidized. Finally, a method for quantitative evaluation of aldehydes is proposed.     

Isothermal degradation of poly-2,2′-(m-phenylene)-5,5′-bibenzimidazole

The isothermal degradation of poly-2,2′-(m-phenylene)-5,5′-bibenzimidazole in vacuo has been studied. Measurement of the increase in pressure with time, coupled with infrared analysis, was used to determine the distribution of the degradation products. Processes A and B with different second-order rate laws were determined to be significant in the temperature range of 550–700°C. Process A leads to the formation of equimolar quantities of hydrogen and ammonia and has an activation energy of 68 kcal/mole. Process B leads to the production of HCN, NH₃, and H₂ in the ratio of 1:1:2.5 and has an activation energy of 77 kcal/mole. The activation energies and the rate laws are consistent with a mechanism in which the initial degradation step is the bimolecular reaction of two aromatic rings.     

Interaction of heavy metal ions with ammonium humates

Sorption properties of ammonium humates with respect to Fe(III), Cu(II), Al(III), Ni(II), Pb(II), and Zn(II) are studied. The effect of the metal ion concentration on the ammonium humate consumption is examined and the corresponding dependences are analyzed using regression equations. The IR spectra of brown coal humic acids, ammonium humates, as well as Fe, Cu, Ni, Zn, Pb, and Al humates are presented.     

Alkaline hydrolysis of the natural lignin of cottonplant stems in the presence of anthraquinone

The study of a three-stage alkaline hydrolysis of the natural lignin of cottonplant stems has shown that the bulk of the lignin undergoes fragmentation during stage I. The addition of anthraquinone leads to an appreciable increase in the yield of low-molecular-mass hydrolysis products.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (3712) 89 14 75. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 743–748, September–October, 1996. Original article submitted March 1, 1993.