Die quantitative chemische Bestimmung von Vitamin D

Zusammenfassung Es werden die Bedingungen zur photometrischen Bestimmung von Vitamin D mit Antimontrichlorid und Guajakol festgelegt. Die von der Vitamin D-Konzentration abhängige, beständige Grünfärbung wird durch Sterine nicht gestört, es sei denn, daß sie in 100fachem Überschuß vorhanden sind. Fette und deren Spaltprodukte stören durch eine gelbbraune Färbung, wodurch eine Verseifung natürlicher Fette notwendig wird.Die Absorptionskurven von Vitamin D₂ und D₃ zeigen völlige Übereinstimmung. Der Vitamin D₂-Gehalt wird unter dem Einfluß von Licht und Luft vermindert, wobei sich der Luftsauerstoff ungünstiger auswirkt als Licht. Kurzzeitiges Erhitzen auf 80–100° C schädigt das Vitamin D₂ nicht, eine längere Einwirkung höherer Temperaturen bedingt einen Abfall, der in einer Stickstoff-Atmosphäre geringer ist als unter SauerstoffAtmosphäre.Durch U.V.-Bestrahlung wird das Vitamin D₂ ebenso wie durch Sonnenlicht geschädigt, wobei die Verminderung durch 3stündige Sonnenbestrahlung etwa derjenigen einer 3 Minuten langen U.V.-Bestrahlung entspricht. Der Einfluß von Suprasterin und Toxisterin auf die Vitamin D-Reaktion ist nur gering, was für die Vitamin D-Bestimmung in bestrahlten Hefen von Bedeutung ist.     

NMR Relaxivities of Paramagnetic Lanthanide-Containing Polyoxometalates

The current trend for ultra-high-field magnetic resonance imaging (MRI) technologies opens up new routes in clinical diagnostic imaging as well as in material imaging applications. MRI selectivity is further improved by using contrast agents (CAs), which enhance the image contrast and improve specificity by the paramagnetic relaxation enhancement (PRE) mechanism. Generally, the efficacy of a CA at a given magnetic field is measured by its longitudinal and transverse relaxivities r₁ and r₂, i.e., the longitudinal and transverse relaxation rates T₁⁻¹ and T₂⁻¹ normalized to CA concentration. However, even though basic NMR sensitivity and resolution become better in stronger fields, r₁ of classic CA generally decreases, which often causes a reduction of the image contrast. In this regard, there is a growing interest in the development of new contrast agents that would be suitable to work at higher magnetic fields. One of the strategies to increase imaging contrast at high magnetic field is to inspect other paramagnetic ions than the commonly used Gd(III)-based CAs. For lanthanides, the magnetic moment can be higher than that of the isotropic Gd(III) ion. In addition, the symmetry of electronic ground state influences the PRE properties of a compound apart from diverse correlation times. In this work, PRE of water ¹H has been investigated over a wide range of magnetic fields for aqueous solutions of the lanthanide containing polyoxometalates [Dy^III(H₂O)₄GeW₁₁O₃₉]^5– (Dy-W₁₁), [Er^III(H₂O)₃GeW₁₁O₃₉]^5– (Er-W₁₁) and [{Er^III(H₂O)(CH₃COO)(P₂W₁₇O₆₁)}₂]¹⁶⁻ (Er₂-W₃₄) over a wide range of frequencies from 20 MHz to 1.4 GHz. Their relaxivities r₁ and r₂ increase with increasing applied fields. These results indicate that the three chosen POM systems are potential candidates for contrast agents, especially at high magnetic fields.     

Adsorptive Stripping Voltammetric Determination of 2,4-Dichlorophenol by Laponite Modified Carbon Paste Electrode

A laponite modified carbon paste electrode was prepared, characterized and applied for the 2,4-dichlorophenol (2,4-DCP) voltammetric determination. It takes advantage of the ability of laponite to adsorb phenols, as well as of its availability and very low cost. Kinetic and equilibrium data for 2,4-DCP adsorption by laponite in aqueous dispersions demonstrated that the adsorption process obeyed a pseudo first order kinetic model and was consistent with the formation of adsorbed multilayers on a surface with heterogeneous pore distribution. The composite paste electrode exhibited a heterogeneous surface with 65 % increased surface area and 27 % enhanced catalytic activity compared to the unmodified one. The adsorptive stripping voltammetric determination of 2,4-DCP at an electrode with an optimized graphite:laponite ratio of 55 : 15 w% using a 3 min accumulation time at pH 5.5 was found to be suitable for its quantification in the linear concentration range extended up to 50 μmol L⁻¹ with a sensitivity of 0.56 μA L μmol⁻¹ and a LOD of 0.2 μmol L⁻¹ (S/N=3).The 2,4-DCP electrochemical response was not affected by the presence of some structurally similar phenols, like catechol and p-nitrophenol, while resorcinol, 2-chlorophenol, and 4-chlorophenol presented interferences. The results were validated by 2,4-DCP determination in spiked tap water.     

Zur Oxidation von 1,2-Thiazolen: Ein einfacher Zugang zu 1,2-Thiazol-3(2H)-on-1,1-dioxiden

Oxidation of 1,2-Thiazoles; A Convenient Approach to 1,2-Thiazol-3(2H)-one 1,1-Dioxides The 1,2-thiazoles obtained from 3-chloroalk-2-enals and ammonium thiocyanate ( 7 → 9 , Scheme 1) are easily transformed to 1,2-thiazol-3(2H)-one 1,1-dioxidcs 10 on treatment with H₂O₂ in AcOH at 80°. Hydrogenation of 10 in AcOH yields the corresponding saturated 1,2-thiazolidin-3-one 1,1-dioxides 16 (Scheme 3). Cycloalka[c]-1,2-thiazoles 18 are prepared from 2-[(thiocyanato)methyliden]cycloalkan-1-ones and ammonia (Scheme 4). Surprisingly, oxidation of 18a with H₂O₂ in AcOH yields the tricyclic oxaziridine 19.     

Synthesis,crystal structure,and NMR spectroscopy of a 1,3,2λ5,4λ5-oxathiadiphosphetane

From the crude product of the synthesis of the dithiadiphosphetane [RP(S)S]₂ (with R = 2,4,6-iPr₃C₆H₂), the trans-oxathiadiphosphetane has been isolated, C₃₀H₄₀OP₂S₃. X-ray structure analysis and mass spectroscopic investigations give unequivocal evidence for this structure: monoclinic, C2/c (no. 15), a = 13.066(8), b = 21.726(8), c = 12.070(6) Å, β = 103.54(10)°, V = 3331 ų, Z = 4, and D_c = 1.158 g/cm³. The asymmetric unit consists of half the formula unit. Solid-state ³¹P NMR spectra give information about the chemical shift anisotropy. Results of IGLO calculations of the ³¹P nuclear magnetic shielding tensor agree satisfactorily with the experimental data. Monitoring the reaction of several dithiadiphosphetanes with benzophenone in solution by ³¹P NMR spectroscopy indicates that additional oxathiadiphosphetanes as well as thiotrimetaphosphonates are present. © 1996 John Wiley & Sons, Inc.     

Two‐step synthesis of new 1,2,4,5‐tetrahydrospiro‐[3H‐2‐benzazepine‐3,4′‐piperidines] from 4‐iminopiperidines

New spiro[3H‐2‐benzazepine‐3,4′‐piperidines] and their precursors, N‐substituted 4‐allyl‐4‐N‐benzyl‐aminopiperidines, have been prepared as potential psychotic agents from readily available 4‐iminopiperidines, by a sequence of reactions that included nucleophilic addition of Grignard reagents and Bronsted acid‐mediated intramolecular cyclisation. Some of the compounds prepared have been tested in albine mice for spontaneous motor activity. All compounds prepared were characterized by ir and ¹H nmr spectroscopies and cg‐ms spectrometry.     

Sorption of galactose by zeolite Y

The sorption of galactose by Na-Y, K-Y and Ba-Y zeolites has been investigated by isopiestic equilibration at 25°C. The equilibrium galactose and water contents of the zeolites were determined for water activitiesa _w in the range 0.111 <a _w < 0.98. It was found that the maximum uptake of galactose U ₀ ^G (observed fora _W 0) was highest for Na-Y and least for Ba-Y. In contrast at high water activities the galactose uptake was highest for Ba-Y and least for Na-Y.