Moisture sorption, transport, and hydrolytic degradation in polylactide

Management of moisture penetration and hydrolytic degradation of polylactide (PLA) is extremely important during the manufacturing, shipping, storage, and end-use of PLA products. Moisture transport, crystallization, and degradation, in PLA have been measured through a variety of experimental techniques including size-exclusion chromatography, differential scanning calorimetry, and X-ray diffraction. Quartz crystal microbalance and dynamic vapor sorption experiments have also been used to measure moisture sorption isotherms in PLA films with varying crystallinity. A surprising result is that, within the accuracy of the experiments, crystalline and amorphous PLA films exhibit identical sorption isotherms.     

CONFLICT AND COOPERATION IN UTILIZING A COMMON PROPERTY RESOURCE

Noncooperative games are used to demonstrate that, while free riding is always an option, the “tragedy of the commons” is not inevitable. When the decision to cooperate or free ride is considered in a dynamic setting, there is no intermediate case where some cooperate and others free ride. The game is only stabilized in either full cooperation or full defection. The important factor in obtaining a cooperative outcome is the critical number of players that decide to cooperate. The concept of commitment is used to demonstrate the necessary and sufficient conditions for full cooperation. Although the analysis is based on a shared water resource, it can be extended to other natural resources with common costs and private benefits, especially in the cases where there are no international authorities or treaties that internalize the externalities involved in privatizing the resource.     

Direkte fluorimetrische Bestimmung von 3,4-Benzpyren im w?\rigen Medium

Zusammenfassung Es wurde eine direkte Bestimmung des 3,4-Benzpyrens in wä\riger Lösung beschrieben, die auf der Löslichkeitserhöhung beruht, die das in Wasser schwer lösliche 3,4-Benzpyren durch Coffein erfährt. Es können so noch 4 ng/ml bei der angegebenen Standardisierung bestimmt werden. Bei der Direktbestimmung des 3,4-Benzpyrens im System Coffein-Wasser ist ein p_H >6,0 einzuhalten, da bei höheren Wasserstoffionenkonzentrationen die Fluorescenzintensität stark abnimmt.

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Direct fluorimetric determination of benzo(a)pyrene in aqueous medium

A method for the direct determination of benzo(a)pyrene in aqueous solution is based on the increase of its solubility by coffeine. 4 ng of benzo(a)pyrene/ml can be determined by the procedure described. In this direct determination in the system coffeine-water the p_H has to be adjusted to >6.0, as the fluorescence intensity considerably decreases with higher H⁺ concentrations.

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Eine ausführliche Darstellung findet sich in der Dissertation von G. Becker, Univ. Karlsruhe 1968.

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Die Messungen zu dieser Arbeit -wurden an dem Chemischen Untersuchungsamt für das Saarland, Saarbrücken, mit einem Spektralphotometer der Deutschen Forschungsgemeinschaft ausgeführt. Beiden Institutionen sind wir zu Dank verpflichtet.     

Electrode processes in the oxidation of tetrahydroisoquinoline derivatives

The electrochemical oxidation of the alkaloid laudanosine (Ia) to O-methylflavinantine (II) has been studied in acetonitrile solvent. Using cyclic voltammetry, rotating disc voltammetry and preparative electrolyses on several alkaloids, simple aliphatic amines and aromatic compounds, some aspects of the mechanism of this coupling reaction are elucidated. The first anodic wave for laudanosine at platinum has E_p=0.55 V vs. Ag/Ag⁺. The electrode rapidly becomes partially passivated at potentials above 0.5 V. This is due to a film which “dissolves” below 0.5 V, at a rate independent of the potential. It is shown that the reaction (Ia)→(II) proceeds at 0.5 V by initial oxidation of the amine moiety. If acids such as sodium bicarbonate are added to the anolyte the amine is protonated causing the first wave to disappear. Oxidation at 1.1 V under these acidic conditions produces the same product, but more rapidly and in significantly higher yield because electrode filming and side reactions resulting from the amine oxidation are abrogated.     

Selective modification of the 2-position of pyridoxol

Pyridoxol, protected by acetylation of the hydroxyl groups, has been converted to its N-oxide which upon reaction with perfluoroacetie anhydride yields a 2-nor-2-hydroxymethylpyridoxol derivative as an intermediate. This compound undergoes acyl migration from the 3-position. Protection of the pyridoxol hydroxyls by benzylalion followed by the same treatment yields the unrearranged α²-hydroxy derivative. This compound has been converted to a series of α²-substituted pyridoxols (X = -Cl, -Br, -OCOCH₃, -OCH₃, -OC₂H₅).     

Laser desorption of DNA oligomers larger than one kilobase from cooled 4-nitrophenol

A unique matrix system consisting mostly of 4-nitrophenol has shown to be very effective for matrix-assisted laser desorption/ionization time-of-flight mass spectrometric analysis of large DNA oligomers when a cooled sample stage was used to prevent the sublimation of this matrix under vacuum. Using this 4-nitrophenol matrix with UV laser desorption, detection of picomole quantities of DNA oligomers containing up to approximately 800 nucleotides was routinely achieved. The effectiveness of this matrix was further demonstrated by the observation of a double-stranded DNA oligomer larger than 1000 base pairs, seen as a denatured single-stranded species, with a molecular ion mass exceeding 300 000 Da. The potential applications of 4-nitrophenol as a matrix for DNA sizing are discussed.     

Emissionsspektrometrische Analyse von Roheisen

Zusammenfassung Die spektrometrische Analyse von weiß erstarrtem Roheisen (auf C, Si, Mn, P, S, Cu) ist mit der gleichen Anregung und in der gleichen Funkzeit wie diejenige von Stahl möglich. Eine spezielle Kalibriertechnik mit Stahlproben garantiert ein ausreichend reproduzierbares und richtiges Resultat in relativ kurzer Zeit (20 sec).

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Emission-spectrometrical analysis of pig iron

The conditions of pig iron analysis by using a direct reading spectrometer for routine determination of C, Si, Mn, P, S and Cu, the influence of sampling and a new calibration technique of the instrument are described. The whole time needed for complete spectrometrical analysis is about 20 sec.

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Wir sind Herrn T. Nientiedt für zahlreiche Anregungen und Diskussionen zu Dank verpflichtet.     

Trimethylsilylverbindungen der Vb-Elemente. VI. Synthese,Molekül- und Kristallstruktur des Tetrakis(trimethylsilyl)distibans im Vergleich mit Tetraphenyldistiban

Trimethylsilyl Derivatives of Vb-Elements. VI. Synthesis, Molecular and Crystal Structure of Tetrakis(trimethylsilyl)distibine Compared with Tetraphenyldistibine Tetrakis(trimethylsilyl)distibine already isolated by Breunig et al. [9] from cleavage reactions of tris(trimethylsilyl)stibine may also be obtained in high yields from lithium bis(trimethylsilyl)antimonide · 2THF and 1,2-dibromoethane in n-pentane. This compound intensely red in the solid state, but only slightly yellow in solution or in the melt crystallizes in the monoclinic space group P2₁/c with a = 680.6(1); b = 1672.8(2); c = 1190.0(1) pm; β = 119.01(5)°; Z = 2 at +20°C. An X-ray structure determination (R = 0.017) shows the bis(trimethylsilyl)-stibino groups to be arranged in a transoid position. Characteristic bond lengths and angles are: Sb? Sb 286.7(1); Sb? Si 259.4 pm; Si? Sb? Si 94.46(3); Sb? Sb? Si 98.68(3) and 94.43(3)°. As in similiar 2,2′,5,5′-tetramethyldistibolyl published recently by Ashe III et al. [8] this crystal structure, too, is characterized by a nearly linear sequence of Sb? Sb groups. Compared with the sum of van-der-Waals radii the intermolecular Sb-Sb contact in such a chain is shortened from 440 to 399 pm. This probably allows electronic interactions of unknown type responsible for the colour of the crystals. In keeping with this assumption an analogous formation of chains is not found in solid, only yellow tetraphenyldistibine 5 the structure of which has already been studied by Rehder et al. [44].