Cluster matter: the transition of optical elastic scattering to regular reflection

The optical response of many-cluster systems (cluster matter) depends strongly on the mean filling factor and on its local variations. This is shown from Au clusters of various sizes which form coagulation systems. Measured spectra of the extinction, the absorbance, the integral scattering, the angle resolved scattering, the regular reflection and corresponding TEM micrographs are presented. It is demonstrated that by varyingf from 10^?6 to 0.5 the incoherent Mie scattering is transformed into regular geometric-optical transmission and reflection (“Oseen-transition”) while the spectral features even of the most densely packed samples still differ strongly from those of a bulk Au film.     

The atomic emission detector in gas chromatographic trace analysis

Summary The atomic emission detector for element-selective detection in gas chromatography shows high selectivities for many elements vs. carbon, coupled with a large dynamic range and relatively low limits of detection. In this work we report on our experience with the detector with respect to the response in dependence on the chemical form of the element monitored, the limit of detection, the selectivity vs. carbon and efforts to improve the limit of detection by varying the flow rate of the make-up gas. Applications discussed include the quantification of a dibenzodioxin/dibenzofuran standard solution, dual-isotope monitoring and the determination of elemental ratios in organic compounds. The work centers on the elements carbon, sulphur, chlorine, bromine and oxygen.Dedicated to Prof. Dr. V. Krivan on the occasion of his 60th birthdayIn part presented at the 20th International Symposium on Environmental Analytical Chemistry, Strasbourg, France, April 1990.     

Digital nets and sequences constructed over finite rings and their application to quasi-Monte Carlo integration

A detailed study of digital (t, m, s)-nets and digital (T,s)-sequences constructed over finite rings is carried out. We present general existence theorems for digital nets and sequences and also explicit constructions. Special attention is devoted to the case where the finite ring is a residue class ring of the integers. This study is motivated by the problem of numerical integration of multivariate Walsh series by quasi-Monte Carlo methods, for which we also provide a general error bound.The third author was supported by the CEI Project PACT, WP5.1.2.1.3.     

Nonlinear “brightening” of a film of nonabsorbing chiral nematic under selective reflection conditions

A strong decrease in the reflection coefficient of a film of a nonabsorbing chiral nematic (cholesteric) is observed experimentally in the region of selective reflection under the action of a powerful beam of circularly polarized light. The independence of the effect from the average power density (and its dependence only on the peak power density) allow it to be attributed to an increase in the pitch of the cholesteric helix to such a degree that it is completely unwound, an effect previously observed only in static and low-frequency electric and magnetic fields, in the strong field of the light wave. These are the first experiments in which, on account of the specially chosen irradiation conditions, the changes produced in the pitch of the helix by the field of the light wave can accumulate over time, so that a nonthermal mechanism can be invoked to explain the nonlinear brightening of a mirror made of a chiral nematic. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 6, 403–407 (25 March 1996)     

Carbohydrate-functionalized oligothiophenes for concanavalin A recognition

Versatile synthesis of fluorescent, carbohydrate-functionalized oligothiophene hybrids via Sonogashira-type cross coupling reactions is reported. The mannose derivatives reveal specific binding with the model lectin from Canavalia enisformis (Concanavalin A).     

Contribution of liquid-phase and gas-phase ionization in extractive electrospray ionization mass spectrometry of primary amines

In this study, we investigated how binary mixtures of compounds influence each other's signal intensity in electrospray ionization (ESI), extractive electrospray ionization (EESI) and secondary electrospray ionization (SESI) experiments. The experiments were conducted using a series of homologous primary amines (from 1-butyl to 1- decylamine). In every experiment, two of the amines were present, and all 21 possible combinations were measured with EESI, ESI and SESI as ionization sources. Except for the volatility, which decreases with increasing molecular weight, the physico-chemical properties of the amines are very similar, so that the intensity ratio obtained in each experiment provides information about discrimination effects occurring during the ionization process. The results show that for the relatively volatile compounds investigated, the EESI ionization mechanism resembles the SESI-like gas-phase charge transfer more than ESI-like analyte ionization in solution. In addition, almost no discrimination effects were observed in the spectra obtained in EESI experiments. Quantitative EESI experiments with nonylamine as internal standard showed that EESI is capable of providing both more accurate and more precise results than SESI and ESI.     

Control of metal-directed self-assembly by metal-amine interactions

The complexation of a tweezers ligand with zinc perchlorate in the absence and presence of amines in methanol solution was explored. L(2)Zn(2)(ClO(4))(4) was a thermodynamic product of the reaction in the absence of an amine. The complex was shown to interact with aliphatic amines resulting in the formation of a Zn-N(amine) bond. If metal-ligand complexation was carried out in the presence of an amine the formation of a trinuclear zinc complex L(3)Zn(3)(6+) was observed. Moreover the transformation of complex L(2)Zn(2)(4+) to L(3)Zn(3)(6+) occurred, when the former was subjected to an amine in the amount, which is sufficient to coordinate more than one amino group on each zinc atom. Complexes ligand-zinc-amine were shown to be kinetically stable, and the method of their preparation was crucial to the purity of the final complexes. L(3)Zn(3)(6+) was favored under kinetic control: reagent concentration 10(-5)M, slow addition of zinc perchlorate to the mixture of an amine and the ligand. Under thermodynamic control (fast mixing of reagents, concentration 10(-2)-10(-3) M) formation of a mixture of complexes was observed. All pure complexes and their mixtures were characterized using UV-Vis, ROESY, PFGSE NMR and ESI-MS techniques. On the basis of DFT calculations the mechanism of influence of an amine on self-assembly was suggested.