Apparent Specific Volume Measurements of Poly(ethylene oxide), Poly(butylene oxide), Poly(propylene oxide), and Octadecyl Chains in the Micellar State as a Function of Temperature

Apparent specific densities of aqueous solutions of the diblock copolymers C18(EO)100, C18(EO)20, and (EO)92(BO)18 and the triblock copolymers (EO)25(PO)40(EO)25 and (EO)21(PO)47(EO)21 in the micellar state have been measured over a temperature range from 10 to 90 degrees C at concentrations between 1% and 5%, using an oscillating tube densitometer. From these measurements, apparent specific volumes of poly(ethylene oxide) (PEO), poly(propylene oxide) (PPO), poly(butylene oxide) (PBO), and octadecane in the micellar state have been determined. The composition of the block copolymers was checked by NMR spectroscopy. Results were compared with published data for the polymers and bulk values for octadecane, respectively. The apparent specific density of PEO chains in the dissolved state was also measured for PEG4600 solutions at different concentrations and compared with results in the micellar state. The results presented in the paper are crucial in connection with analysis and modeling of small-angle X-ray scattering (SAXS) data from polymer and block copolymer micellar systems. PEO and PPO have a relatively low apparent partial specific volume in water at low temperatures. It is associated with water molecules making strong hydrogen bonds with the oxygen atoms on the polymer backbone. These water molecules gradually become disordered when the temperature is increased and the polymer apparent specific volume increases. For PBO in the micellar cores of PBO-PEO block copolymer micelles and in PNiPAM microgels, pronounced temperature dependence with the same origin is also found. The application of the derived results for the apparent specific volume of PEO for deriving contrast factors is demonstrated and the results are used in the analysis of SAXS data for semidilute solutions of PEG4600 in a broad temperature range.     

Complexation of aluminium, yttrium, lanthanum and lanthanides with 4-(2-pyridylazo)resorcinol (par)

The sensitive reactions between 4-(2-pyridylazo)resorcinol (PAR) and yttrium, lanthanum and the lanthanides can be used for the spectrophotometric determination of these elements. The method has no advantage over other methods for the determination of aluminium and lanthanum. Only M(PAR)H and M(PAR) complexes are formed in solutions where the molarity of the metal ion is greater than or nearly equal to the molarity of the ligand at pH < 7-5. If there is molar excess of PAR, 1:2 complexes may be formed but this is certain only for the yttrium-PAR system. Errors in analysis may result from the simultaneous occurrence of optically different complexes; close control of pH and reagent concentration is essential. Optical and equilibrium data are given for the systems investigated.     

Construction of orbital angular momentum eigenfunctions for many-particle systems by harmonic projection

Formulas are derived which allow the direct construction of total orbital angular momentum eigenfunctions for many-particle systems without the use of Clebsch–Gordan coefficients. One of the equations is closely analogous to Dirac' identity for the total spin operator. This equation describes the action of L² on a function of the particle coordinates in terms of a class operator of the symmetric group and a "contraction operator." A general projection operator for constructing symmetric eigenfunctions of L² is presented.     

Tellur (IV)

Ohne Zusammenfassung     

Bimetallic reactivity. One-site addition two-metal oxidation reaction of dioxygen with a bimetallic dicobalt(II) complex bearing five- and six-coordinate sites

The di-Co(2+) complex, [Co(2+)(mu-OH)(oxapyme)Co(2+)(H(2)O)](+), contains an unsymmetrical binucleating ligand (oxapyme) which provides five- and six-coordinate metal sites when a hydroxide bridge is introduced. This complex absorbs 1 equiv of O(2) irreversibly in solution, producing an unstable di-Co(3+) oxygenated product. The oxygenated product has been studied at low temperatures, where its electronic absorption and (1)H NMR spectra were recorded. It is probable that the oxygenation reaction involves a one-site addition two-metal oxidation reaction to produce an end-on-bonded peroxide ligand at the available coordination site, giving the complex [Co(3+)(mu-OH)(oxapyme)Co(3+)(mu(1)-O(2))](+). Addition of 1 equiv of HClO(4) to this oxygenation product gives a stable peroxide complex, [Co(3+)(mu,eta(1):eta(2)-O(2))(oxapyme)Co(3+)](2+), where one of the oxygen atoms bridges the two metals and is sideways bonded to one of the metals. The formation of this stable complex involves expulsion of the OH(-) bridge. Addition of NO(2)(-) to the sideways-bonded peroxide complex leads to the formation of another stable complex, [Co(3+)(mu,eta(1):eta(1)-O(2))(oxapyme)Co(3+)(NO(2))](+), where the peroxide forms a classic di-end-on bridge to the two metals. Both of these complexes have been fully characterized. Addition of acid to this second stable dioxygen complex leads to the release of HNO(2) and the formation of the mu,eta(1):eta(2) sideways-bonded peroxide complex.     

Torsionsabhängige Beiträge zur Spin-Bahn-Kopplung in organischen Molekülen

Zusammenfassung Die Spin-Bahn-Kopplung der niedrigen elektronischen Anregungszustände von organischen Molekülen wird untersucht. Es wird gezeigt, daß die Zerstörung der aromatischen Ebene durch Torsionen oder Schwingungen zu nicht-verschwindenden Zweizentrenbeiträgen führt. Am Beispiel des Triphenylmethyl-Kations wird mit Hilfe der LCAO MO SCF-Methode die Größenordnung der auftretenden Wechselwirkungen ermittelt. Diese haben wahrscheinlich großen Einfluß auf die strahlungslosen Prozesse in Molekülen mit leicht beweglichen Gruppen.

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Spin-orbit coupling of the lower excited electronic states of organic molecules has been investigated. It is shown that any destruction of the aromatic plane through torsions or vibrations leads to non-vanishing contributions from two-centre integrals. The order of magnitude of this type of interactions is determined for the triphenylmethyl-cation with the aid of the LCAO MO SCF method. These interactions probably have much influence on radiationless transitions in molecules containing mobile groups.

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Résumé Etude du couplage spin-orbite dans les états électroniques exités les plus bas des molécules organiques. Toute non planéité aromatique créée par torsions ou vibrations entraîne une contribution non nulle de la part des intégrales bicentriques. L'ordre de grandeur de ce type d'interaction est detérminé, à l'aide de la méthode L.C.A.O. M.O. SCF, pour le cation triphenylméthyle. Ces interactions ont probablement beaucoup d'influence sur les transitions non radiatives dans les molécules contenant des groupements mobiles.

     

Auf eine Eichkurve bezogene emissionsspektrographische 15N-Bestimmung mit dem Spektrographen Q24-Zeiss

Zusammenfassung Zur spektrographischen ¹⁵N-Bestimmung wird für ¹⁵N-Konzentrationen von 0,38–20,0 At-% ¹⁵N ein Verfahren beschrieben, das mit UV-Spektrographen mit normaler Ausstattung ausgeführt werden kann. Die relative IsotopenhÄufigkeit wird mittels einer Eichkurve in leitprobengebundener oder leitprobenfreier Spektralanalyse bestimmt. Das Verfahren weist eine relative Standardabweichung der Analysenergebnisse zwischen 2,0 und 3,0% auf.

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Summary A method for a spectrographic ¹⁵N determination in the atomconcentration range from 0.38 to 20.0% ¹⁵N is described. The method can be used with normal spectrographic equipment. The relative isotopic abundance is determined by means of a calibration curve. The relative standard deviation of the isotope determinations is between 2.0 and 3.0% for the method described.

     

Dynamical scaling of single chains on adsorbing substrates: diffusion processes

We study the dynamics of tethered chains of length N on adsorbing surfaces, considering the dilute case; for this we use the bond fluctuation model and scaling concepts. In particular, we focus on the mean-square displacement of single monomers and of the center of mass of the chains. The characteristic time tau of the fluctuations of a free chain in a good solvent grows as tau approximately N(a), where the coefficient a obeys a=2nu+1. We show that the same coefficient also holds at the critical point of adsorption. At intermediate time scales single monomers show subdiffusive behavior; this concurs with the behavior calculated from scaling arguments based on the dynamical exponent a. In the adsorbed state tau(perpendicular), the time scale for the relaxation in the direction perpendicular to the surface, becomes independent of N; tau(perpendicular) is then the relaxation time of an adsorption blob. In the direction parallel to the surface the motion is similar to that of a two-dimensional chain and is controlled by a time scale given by tau(parallel) approximately N(2nu(2)+1)L(-2Delta(nu/nu)), where nu(2) is the Flory exponent in two dimensions, nu is the Flory exponent in three dimensions, and Deltanu=nu(2)-nu. For the motion parallel to the surface we find dynamical scaling over a range of about four decades in time.