Bestimmung von Absorption und Brechungsindex extrem hochabsorbierender Lösungen im Mikromaßstab

Zusammenfassung Eine Methode für die Messung der Absorption in extrem hochabsorbierenden Lösungen wird beschrieben. Die Küvette besteht aus einer plankonvexen Linse auf einer ebenen Platte. Die Messungen können entweder Punkt für Punkt in einem Mikroskop oder durch Registrierung, z. B. im Mikrospektrophotometer dieses Institutes, ausgeführt werden. Es kann sowohl im UV wie im sichtbaren Licht gemessen werden. Die optische Dichte kann innerhalb eines Bereiches von ca. 0,01 bis 5 per bestimmt werden. Die Genauigkeit ist besser als ± 1 % und die Substanzmenge kann kleiner als 0,1l sein.Der Brechungsindex der Lösungen wird mit Hilfe derNewtonschen Ringe bestimmt, die in der Linsenküvette sichtbar sind, falls diese aluminisiert oder versilbert ist. Die Durchmesser der Ringe werden entweder manuell in einem Mikroskop oder durch Registrierung im Mikrospektrophotometer gemessen. Es kann sowohl im UV wie im sichtbaren Licht gemessen werden. Die Genauigkeit des Brechungsindex ist besser als 0,005 und die notwendige Substanzmenge kleiner als 0,01l.

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Summary A method is described for measuring the absorption and refractive index of extremely highly absorbing solutions. A cuvette consisting of a planeconvex lens on a plane plate is used. Measurements of absorption can be carried out either point by point in a microscope or by continuous recording in e. g. the microspectrophotometer of this Institute. Measurements can be made in ultraviolet as well as in visible light. It is possible to determine the extinction within an approximate range of 0.01 to 5 per micron. The accuracy is better than ± 1% and the amount of substance to be examined can be less than 0.1l.The refractive index of a solution can be determined fromNewton's rings which are visible in the lens-cuvette coated with aluminum or silver. The diameters of the rings are measured either manually in a microscope or by recording in the microspectrophotometer. Measurements can be made in ultraviolet as well as in visible light. The accuracy is better than ± 0.005 and the necessary amount of substance is less than 0.011.

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Résumé L'auteur décrit une méthode de mesure de l'absorption et de l'indice de réfraction de solutions de très haut pouvoir absorbant. On emploie une cuvette comportant une lentille plan-convexe sur une plaque plane. Il est possible d'effectuer les mesures d'absorption point par point, à l'aide d'un microscope ou bien par enregistrement continu sur un spectrophotomètre tel que celui de l'institut où ont été effectuées les recherches. Les mesures peuvent être réalisées en lumière ultraviolette ou visible. Il est possible de déterminer l'extinction dans le domaine approximatif 0,01 à 5 par micron. L'exactitude est meilleure que ± 1% et le volume de substance peut être inférieur à 0,1l.L'indice de réfraction de la solution peut être déterminé à l'aide des anneaux de Newton qui sont visibles dans la cuvette à lentille si elle est recouverte d'un dépôt d'aluminium ou d'argent. Les diamètres des anneaux sont mesurés manuellement à l'aide d'un microscope ou par enregistrement dans un microspectrophotomètre. Les mesures peuvent être effectuées soit en lumière ultraviolette soit en lumière visible. L'exactitude de la détermination de l'indice de réfraction est supérieure à ± 0,005 et le volume de substance nécessaire est inférieur à 0,01l.

     

Effects of surface-active substances on polarographic waves of some complexes

The effect of the charge type of surface-active substances on the polarographic waves of various complexes has been investigated. The results indicate that the polarograms are practically unaffected by the presence of a aurfactant, provided that the adsorbed layer has a charge opposite to that of the depolariser. Polarographic waves of depolarisers with the same charge as the adsorbed layer are, however, shifted to more negative values or greatly distorted. The distorting effect is qualitatively interpreted in terms of an electrostatic repulsion between the adsorbed layer and the depolariser. The charge type of a surfactant seems to be important for the appropriate choice of a nondistorting maximum suppressor.     

Antiferroelectric behavior in a liquid crystalline polymer

Electro-optic and polarization reversal measurements were performed on a side-chain polymer exhibiting a chiral smectic phase. Based on the observed electro-optic and current responses, we discuss the possibility of an antiferroelectric structure in the polymer. In order to establish a model for the observed behavior, a detailed comparison with the properties of the low molar mass antiferroelectric substance MHPOBC was made. The birefringence modulation in the chiral smectic polymer, originating from the field-induced antiferroelectric-to-ferroelectric transition, is analyzed for the case of a randomly oriented sample. The result shows that the coincidence of birefringence modulation and polarization current peaks is strong evidence for the existence of antiferroelectric order in the smectic layers. Such coincidence was observed both for MHPOBC and the chiral side-chain polyacrylate.     

Analysis of reduced density matrices in the coordinate representation. I. Definitions and basic formulas

The probability interpretation of density matrics is reviewed and certain quantities suggested for study by means of diagrams. The case of a “spin-symmetric ensemble” is further discussed.     

Self-assembling peptide nanotubes from enantiomeric pairs of cyclic peptides with alternating D and L amino acid residues

Cyclic peptides with alternating d- and l-amino acid residues containing tert-leucine residues in every second position can form peptide nanotubes only when both enantiomers of the peptide are present in the solution. These results strongly indicate the formation of peptide nanotubes that assemble with one enantiomer in every second position, thereby forming a lamellar structure.     

Simulation of Industrial Processes Involving Concentrated Aqueous Solutions

The Pitzer model is applied to simulate various single- and multistage modifications of the industrial conversion process

Time-resolved electrophoretic analysis of mobility shifts for dissociating DNA ligands

Intercalative binding of ligands to DNA can be demonstrated by helix unwinding, monitored by gel electrophoresis of supercoiled DNA, as electrophoretic mobility is sensitive to the topological DNA state. However, we show that an apparent lack of unwinding in an electrophoretic assay could be due to dissociation of the (intercalated) ligand during the analysis, rather than evidence for a nonintercalative mode of binding to DNA. Repetitive scanning during the electrophoresis ensures that release of the ligand during electrophoresis does not affect the measured degree of unwinding, based on the electrophoretic velocity being determined as a function of time. We use this assay to establish intercalation as a mode of binding to DNA for the cyanine dyes YO, YO-PRO as well as two enantiomeric forms of the ruthenium complexes [(phen)2 Ru(tatpp)Ru(phen)2]4+, and to support groove-binding for the new unsymmetrical cyanine dyes BOXTO and BOXTO-PRO. Groove-binding could be concluded from a lack of unwinding, because we could rule out that it is caused by release of the dye during the electrophoresis. The gel electrophoresis has the advantage over hydrodynamic techniques that much smaller sample amounts are required, and our time-resolved approach can be employed in all mobility-shift assays when applied to dissociating complexes.     

Local properties of quantum chemical systems: the LoProp approach

A new method is presented, which makes it possible to partition molecular properties like multipole moments and polarizabilities, into atomic and interatomic contributions. The method requires a subdivision of the atomic basis set into occupied and virtual basis functions for each atom in the molecular system. The localization procedure is organized into a series of orthogonalizations of the original basis set, which will have as a final result a localized orthonormal basis set. The new localization procedure is demonstrated to be stable with various basis sets, and to provide physically meaningful localized properties. Transferability of the methyl properties for the alkane series and of the carbon and hydrogen properties for the benzene, naphtalene, and anthracene series is demonstrated.     

Intrinsic acid-base properties of purine derivatives in aqueous solution and comparison of the acidifying effects of platinum(II) coordinated to N1 or N7: acidifying effects are reciprocal and the proton "outruns" divalent metal ions

The effect of Pt(2+) coordination, in particular of (dien)Pt(2+) or cis-(NH(3))(2)Pt(2+), on the acid-base properties of the purine ligands 9-ethylguanine (9EtG), 9-methylhypoxanthine (9MeHx), inosine (Ino), 9-methyladenine (9MeA), and N6',N6',N9-trimethyladenine (TriMeA) is quantitatively evaluated. The corresponding acidity constants of the complexes are calculated by curve-fitting procedures using previously published (1)H NMR shift data which had been measured in aqueous solution (D(2)O) in dependence on pH (pD). Comparison of the pK(a) values of the ligands with those of the Pt(2+) complexes reveals the expected behavior for the (N7)-platinated complexes; i.e., the (N1)H(0/+) sites are acidified due to charge repulsion. However, Pt(2+) coordination at (N1)(-)(/0) sites leads to an (already previously observed) apparent increase in the basicity of the N7 sites for the guanine, hypoxanthine, and adenine residues; this is also the case if Pt(2+) is bound to N3. Coordination of Pt(2+) to both the (N1)(-) and N7 sites of 9EtG results apparently in an enhanced basicity of N3 if compared with the release of the proton from the (N3)H(+) site in H(2)(9EtG)(2+). For the former cases in aqueous solution (H(2)O) it is now proven for a comprehensive set of data (seven examples), by taking into account the intrinsic basicities of the various N7 sites via micro acidity constants, that the acidifications are reciprocal and identical. This means Pt(2+) coordinated to (N1)(-)(/0) sites in guanine, hypoxanthine, or adenine residues acidifies the (N7)H(+) unit to the same extent as (N7)-coordinated Pt(2+) acidifies the (N1)H(0/+) site. In other words, the apparently increased basicity of N7 upon Pt(2+) coordination at (N1)(-)(/0) sites disappears if the micro acidity constants of the appropriate isocharged tautomers of the ligand are properly taken into account. It is further proven, on the basis of the evaluations of the nucleotide analogue 9-[2-(phosphonomethoxy)ethyl]adenine (PMEA), that these given conclusions are also valid for nucleotides. In addition, it is shown that the mentioned apparent basicity increase, which results from the use of macro acidity constants, has its origin in the fact that the proton-metal ion (Pt(2+)) interaction (the extent of which depends on the kind of metal ion involved) is less pronounced than the proton-proton interaction. Finally, the proven reciprocal behavior will now allow one to determine micro acidity constants of ligands by studying complexes formed with kinetically inert metal ions. A further result of interest is the proof that the competition of Pt(2+) (or Pd(2+)) with the proton for the (N1)(-) and N7 binding sites of inosinate results in the isomer where the metal ion is at N7 with the proton relegated to (N1)(-); this isomer is favored by a factor of about 2000 compared with the one having the metal ion at (N1)(-) and the proton at N7.