Surface morphology of polyethylene glycol films produced by matrix-assisted pulsed laser evaporation (MAPLE): Dependence on substrate temperature

The dependence of the surface morphology on the substrate temperature during film deposition was investigated for polyethylene glycol (PEG) films by matrix-assisted pulsed laser evaporation (MAPLE). The surface structure was studied with a combined technique of optical imaging and AFM measurements. There was a clear difference between the films produced below and above the melting point of PEG. For temperatures above the melting point, the polymer material was distributed non-uniformly over the substrate with growths areas, where cluster-like structures merge into large islands of micrometer size. At these temperatures, the islands in the investigated growth areas cover most of the bottom layer which has a typical height of 50-150 nm.     

Complexation of lanthanide nitrates

Summary The change of the stability constantsK ⁰ ₁ of the lanthanide nitrato complexes in the lanthanide series is presented and discussed from the viewpoint of the interaction between the first and second hydration sheath of lanthanide ions.

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Komplexierung bei Lanthaniden-Nitraten

Zusammenfassung Es wird der Verlauf der StabilitätskonstantenK ⁰ ₁ von Nitrato-Komplexen in der Lanthanidenreihe vorgestellt und auf Basis von Wechselwirkungen zwischen der ersten und zweiten Hydrat-Schicht der Lanthaniden-Ionen diskutiert.

     

In Vitro Screening of Bioactive Compounds in some Gluten-Free Plants

Electrophoretic, antioxidant, and FTIR profiles of some varieties of amaranth, quinoa, and buckwheat seeds and their by products were compared. Water extracts of these products were evaluated by the Folin–Ciocalteau method in order to determine total phenolic content. The antioxidant activities were determined by 2,2′-azobis-2-methyl-propanimidamide, ferric-reducing/antioxidant power, and cupric reducing antioxidant capacity radical scavenging assays. FTIR spectra showed the secondary structure of pseudocereals in the ranges of amides I, II, and III shifts. Results of evaluated methods could be used to control several products (seeds, flours, extracts, flakes, roasting) with high phenolic content and antioxidant activity suitable for supplementation in food applications.

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On the ground state eigenfunction of a convex domain in Euclidean space

We study the first eigenfunction ₁ of the Dirichlet Laplacian on a convex domain in Euclidean space. Elementary properties of Bessel functions yield that if D is a sector in Euclidean plane with area 1 and the angle tends to 0. We aim to characterize those domains D such that is large in terms of the ratio of the first eigenvalue of D and the infimum of the first eigenvalues of all subdomains D of D with given volume.Research supported by the Deutsche Forschungsgemeinschaft     

Scintillators for Alpha and Neutron Radiations Synthesized by Room Temperature Sol–Gel Processing

Solid-state scintillating materials were synthesized by the co-doping of sol–gel components with neutron absorbers [⁶Li and ¹⁰B], organic fluorescence sensitizers such as salicylic acid and 2,5-diphenyloxazole (PPO) and activator 1,4-bis-2-(5-phenyloxazolyl)-benzene (POPOP). The room-temperature sol–gel process through the addition of organic polymers is the key to the successful entrapment of the organic sensitizers and activator in inorganic matrixes. These transparent or translucent sol–gel scintillators were evaluated for alpha radiation and neutron detections.     

3-pyridylcarbene and 3-pyridylnitrene: ring opening to nitrile ylides

Photolysis of 3-pyridyldiazomethane in an Ar matrix at 7-10 K gives 3-pyridylcarbene. Further photolysis causes ring opening to nitrile ylide 26 (formonitrile pent-2-en-4-ynylide) as the major reaction together with a minor amount of ring expansion to 1-azacyclohepta-1,3,4,6-tetraene, 27. Matrix photolysis of 3-azidopyridine leads to ring opening to formonitrile N-cyanovinylmethylide, 33.     

A combined density functional theory and molecular mechanics study of the relationship between the structure of coenzyme B12 and its binding to methylmalonyl-CoA mutase

A combined density functional theory (DFT) and molecular mechanics (MM) approach was applied to investigate the relationship between the structure of a free coenzyme B12, and bound to methylmalonyl-CoA mutase. It was found that, upon coenzyme binding to apoenzyme, the Co-C bond remains intact, while the C-Naxial bond becomes slightly elongated and labilized. The labilization of the Co-Naxial bond that takes place in coenzyme B12-dependent enzymes is most likely necessary for fine-tuning of the cobalt-nitrogen (axial base) distance. The controlling of this distance is important to inhibit abiological site reaction involving heterolysis of the Co-C bond but is not important for biologically relevant Co-C bond homolysis.     

Different behavior of nitrenes and carbenes on photolysis and thermolysis: formation of azirine, ylidic cumulene, and cyclic ketenimine and the rearrangement of 6-phenanthridylcarbene to 9-phenanthrylnitrene

Flash vacuum thermolysis (FVT) of 9-azidophenanthrene 8, 6-(5-tetrazolyl)phenanthridine 18, and [1,2,3]triazolo[1,5-f]phenanthridine 19 yields 9-cyanofluorene 12 as the principal product and 4-cyanofluorene as a minor product. In all cases, when the product is condensed at or below 77 K, the seven-membered ring ketenimine 24 is detectable by IR spectroscopy (1932 cm(-1)) up to 200 K. Photolysis of Ar matrix isolated 8 at lambda = 308 or 313 nm generates at first the azirine 26, rapidly followed by the ylidic cumulene 27. The latter reverts to azirine 26 at lambda > 405 nm, and the azirine reverts to the ylidic cumulene at 313 nm. Nitrene 9 is observed by ESR spectroscopy following FVT of either azide 8, tetrazole 18, or triazole 19 with Ar matrix isolation of the products. Nitrene 9 and carbene 21 are observed by ESR spectroscopy in the Ar matrix photolyses of azide 8 and triazole 19, respectively.     

An ESCA study of chemical reactions on the surfaces of cellulose fibers

Cellulose fibers in the form of paper sheets were chemically modified with different functional groups using trichloro-s-triazine as coupling moiety. The treatments made the paper surfaces hydrophobic, as was indicated by an increase in contact angle against water. ESCA was used for the chemical characterization of the paper surfaces. The shape of the carbon 1s peak depended on the chemical functionality of the triazine derivatives. As a reference, ESCA spectra were also recorded for the triazine derivatives precipitated on aluminum plates. The chemical composition of modified cellulose surfaces could then be determined using a computer program for the peak separation and peak area measurement.     

Application of explicitly correlated Gaussian functions for calculations of the ground state of the beryllium atom

The electronic energy of atoms and molecules may be evaluated accurately by the use of wave functions where the interelectronic distances are explicitly present. In particular, explicitly correlated Gaussian-type functions make these types of calculations feasible and computationally tractable even for more extended systems. The resulting multielectron integrals may be reduced to standard one- and two-electron integrals that are readily evaluated. Initial calculations have been made for the Be atom where all four electrons were correlated at the same time. The preliminary results show that accurate results may be obtained. © 1993 John Wiley & Sons, Inc.