Hydrogen-bonding contributions to the lattice energy of salts for second harmonic generation

The lattice energies of a series of organic dihydrogenphosphate salts capable of second harmonic generation (SHG) have been calculated. These calculations, coupled with empirical data, indicate that a minimum of 20–25% of the lattice energy arises from hydrogen-bond interactions. Hydrogen bonding is shown to be a strong enough force to have a profound effect on the overall packing and crystal geometry of such ionic materials, and is thus an important factor to consider for crystal engineering.     

Functionalized Self-Assembled Monolayers on Gold as Binding Matrices for the Screening of Antibody-Antigen Interactions

Two different types of -substituted alkanethiol/disulfide compounds have been used to prepare monolayer architectures on gold serving as platforms for the immobilization of receptor probe molecules – antibodies. These are: (i) carboxylic acid alkanethiols post-reacted with amino biotin to generate streptavidin surfaces, and (ii) N-hydroxysuccinimide-terminated disulfide surfaces. The properties of the monolayers, with and without attached receptor probe molecules, were analysed using infrared spectroscopy, ellipsometry, fluorescence scanning and atomic force microscopy. Several experimental parameters, such as condensation reagents, additives, probe and target concentrations and immobilization time, were systematically varied to determine the dynamic range and to optimize the sensitivity and signal-to-noise ratio of the biochip platforms. Fluorescence screening using Cy5-labelled antigens finally demonstrated that both surfaces could be successfully employed to immobilize the antibodies. The pros and cons of the two approaches are also discussed.Received November 15, 2002; accepted March 25, 2003 Published online July 28, 2003     

Temperature-induced structural transitions and vibrational properties of microclusters: ab-initio molecular dynamics studies

We present the results of ab-initio molecular dynamics studies of selected microclusters of sodium, silicon and magnesium at finite temperatures, and especially discuss those obtained around room temperature. In particular, from the analysis of the atomic trajectories we can identify in some cases the existence of different isomers and the isomerization pathways. We have also calculated vibrational spectra at low temperatures and find that they can be used as a very sensitive structural probe also in sodium clusters, where the electronic properties are quite insensitive to the geometry.     

Untersuchungen zurFriesschen Verschiebung von Estern derortho- undpara-Methoxybenzoesäure

TheFries rearrangement of different methoxy benzoates has been investigated. Frompara-methoxy benzoates the corresponding hydroxy-4-methoxy benzophenones could be obtained in good yields by treatment withLewis acids (especially TiCl₄) in nitromethane at 20°C (4-hydroxy derivatives) or without solvent at 120°C (2-hydroxy derivatives). Under the same conditions only demethylation occurs withortho-methoxy benzoates leading to the corresponding salicylates. Small amounts of hydroxy-2-methoxy benzophenones were obtained by treatment with polyphosphoric acid.

     

Eine neue photometrische Eisenbestimmung mit Äthylendiamintetraessigsäure

Zusammenfassung Es wird gezeigt, daß man mit Hilfe von Komplexon-III Eisen-III-Verbindungen nach Überführung in gelbgefärbte Komplexverbindungen, deren Absorptionsmaximum unterhalb 366 m liegt, photometrisch bestimmen kann. Die Extinktion ist bei gleicher Eisenkonzentration vomph-Wert abhängig und in denph-Bereichen zwischen 0,80 und 2,80 sowie zwischen 3,92 und 5,10 konstant, so daß beide Bereiche zur Bestimmung geeignet sind. Es ist beachtlich, daß die komplexe Bindung erst oberhalbph 10,5 zerfällt und Eisenhydroxyd ausflockt. DasLambert-Beersche Gesetz ist in dem Konzentrationsbereich zwischen 4g und 500g Eisen/ml streng erfüllt. Die Bestimmung ist vielen anderen bisher bekannten photometrischen Eisenbestimmungsverfahren überlegen, da schwächere Komplexbildner (z. B. Weinsäure) und sonstige Lösungspartner nicht stören.

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Summary It was found that iron (III) compounds can be determined photometrically by the aid of complexone III. The yellow complex compound has an absorption maximum below 366 m. The extinction, at equal iron concentration, is dependent on theph value. It is constant inph ranges between 0.80 and 2.80 and also between 3.92 and 5.10, so that either of these ranges is suitable for this determination. It should be noted that the complex decomposes only aboveph = 10.5; iron hydroxide separates. TheLambert-Beer law is strictly followed in the concentration range 4g and 500g iron/ml. This method of determination is far superior to many familiar photometric procedures for iron because weaker complex-formers (e. g. tartaric acid) and other cosolutes do not interfere.

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Résumé On montre que les composés du fer-III peuvent être dosés photométriquement à l'aide de la complexone-III après transformation en un complexe coloré en jaune dont l'absorption maximum se trouve au-dessous de 366 m. L'extinction dépend duph pour des concentrations égales en fer et se montre constante entre 0,80 et 2,80, de même qu'entre 3,92 et 5,10, de sorte que ces deux domaines conviennent pour le dosage. Il faut remarquer que le complexe ne se détruit qu'au-dessus deph 10,5 et l'hydroxyde ferrique flocule. La loi deLambert-Beer est satisfaite dans le domaine de concentration entre 4 g et 500 g de fer/ml. La méthode de dosage est de beaucoup supérieure aux méthodes connues jusqu'ici pour la détermination colorimétrique du fer du fait que les complexants les plus faibles, comme l'acide tartrique, ne gênent pas.

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Jetzt: Riedel De Haën A.-G., Chemische Fabriken Seelze bei Hannover.     

The Adsorption of Polyvinylpyrrolidone on Kaolinite Saturated with Sodium Chloride

The adsorption of two different molecular weights of polyvinylpyrrolidone (PVP) (M(w)=44,000 and M(w)=360,000 g mol(-1)) from water on kaolinite saturated with sodium chloride has been studied. The adsorption of PVP increases slowly as temperature increases. The adsorption of PVP on the kaolinite was studied by considering Fourier transform infrared (FTIR) spectra, X-ray diffraction patterns, and dielectric constants. During the adsorption process, PVP interacts with saturating sodium cations and possibly forces some of them onto the edges of the kaolinite; thus, the dielectric constant of saturated kaolinite is reduced after PVP adsorption. Copyright 2001 Academic Press.     

Radioanalytical quality control of11C,18F and123I-labelled compounds and radiopharmaceuticals

Radiochemical quality control using high performance high pressure liquid chromatography and, to some extent, gas chromatography is described for a variety of carrier-free¹¹C-,¹⁸F-and¹²³I-labelled compounds and radiopharmaceuticals. The particular problems associated with the handling of carrier-free compounds labelled with short-lived radionuclides are outlined, and chromatographic data are given for the separation and purification of such products.     

Simple spectrophotometric determination of Fe in oxalate and HCl soil extracts

We describe a spectrophotometric method to determine the sum of Fe(II) plus Fe(III) in HCl and oxalate extracts. The principle of the method is to reduce Fe(III) by ascorbate in near-neutral solution and to sequester the Fe(II) formed as a tri-ferrozine complex, which is then determined photometrically at 562 nm. Because the complex is stable, the reaction is irreversible and complete. Fe(III) in HCl solution reacted very rapidly, whereas oxalate decelerated the overall reaction so that pseudo first-order kinetics with respect to Fe(III) was detected. However, when extractions were conducted at the recommended soil:solution ratio, the absorption reached 98% of its final value within a few minutes. To test the method, four soils differing considerably in texture and carbonate, organic matter, and Fe(III)(hydr)oxide contents were extracted with oxalate in the dark for amorphous (Fe(o)), and with boiling oxalate for total Fe(III)(hydr)oxide (Fe(bo)). This newly developed spectrophotometric method showed excellent correspondence with the conventional atomic absorption spectroscopy (AAS) method. The method presented here can therefore be used as an alternative method to determine the Fe content of oxalate and hydrochloric acid extracts if AAS is not available. Oxalate extracts low in Fe content, which cannot be diluted, are easier to determine by the photometric method than by AAS.