Über einige Eigenschaften von Zinkphosphiten mit Berücksichtigung ihrer Wasserstoffbrückenbindung

Zinc phosphites ZnPHO₃·2.5 H₂O, Zn₂H₂P₃H₃O₉·H₂O, Zn₃H₄P₅H₅O₁₅·1.5 H₂O, ZnH₂H₂P₂H₂O₆ have been studied at higher temperatures and by X-rays and molecular spectroscopy. Hydrates ZnPHO₃·2.5 H₂O and Zn₂H₂P₃H₃O₉·H₂O, when heated, yield an anhydrous salt. Thermal decomposition of dihydrogen triorthophosphite and tetrahydrogen pentaorthophosphite leads, before oxidation of the anion, to a mixture of zinc phosphite ZnPHO₃ and dihydrogen diorthophosphite ZnH₂P₂H₂O₆ and then after loss of water of constitution dihydrogen diorthophosphite converts to zinc diphosphite ZnP₂H₂O₅. The results of the thermal decomposition study were confirmed by X-ray investigation. Anhydrous zinc dihydrogen triorthophosphite Zn₂H₂P₃H₃O₉ and zinc diphosphite ZnP₂H₂O₅ were hitherto unknown. Infrared spectra confirmed the existence of hydrogen bonding in all the phosphites studied and in the case of zinc phosphite ZnPHO₃·2.5 H₂O exhibited a symmetry decrease of the anion PHO₃ ^2– from the point group C_3v to C_s. In the crystal lattice of ZnPHO₃·2.5 H₂O hydrogen bonding by water molecules participates, with polyorthophosphites hydrogen bonding shares in the production of anions and in the case of their hydrates there is in addition hydrogen bonding by water molecules.

---

---

Mit 3 Abbildungen     

Hydroxybromierung und Methoxybromierung von (Z)-Cycloocten

In addition totrans-2-bromocyclooctanol andtrans-1,2-dibromocyclooctane,cis-4-bromocyclooctanol,cis-1,4-dibromocyclooctane,trans-1,4-dibromocyclooctane, and (Z)-5-bromocyclooctene are obtained, when (Z)-cyclooctene is treated with N-bromosuccinimide in the presence of water. Similarly the methoxybromination of (Z)-cyclooctene gives transanular products.     

Interaction of dextran sulfates with positively and negatively charged silver bromide hydrosols

Summary The effects of dextran sulfates of different molecular weights and charge densities on the stability of positively and negatively charged silver bromide solsin statu nascendi have been studied by means of light scattering.The plots of scattering intensities of a positively charged sol against the concentration of the added dextran sulfates show one pronounced maximum, the position which is independent on the molecular weight of the polyelectrolyte used. The maximum shifts to lower polyion concentrations with dilution of the sol.The effect of polyanions on the stability of silver bromide sols of the same sign of charge were investigated as a function of molecular weight of the polymers, the sol concentration, the charge and the concentration of counterions, and the addition of methanol. Destabilization only occurred if sufficient amount of indifferent electrolyte was present in the system. However, the concentration of counterions necessary to produce a flocculation maximum was lower in the presence of the polyelectrolytes than in their absence. The results obtained were compared with the data on sols containing nonionic dextrans reported earlier.

---

Zusammenfassung Der Einfluß der Dextransulfate von verschiedenen Molekulargewichten und Ladungsdichten auf die Stabilität der positiv und negativ geladenen Silberbromid-Solein statu nascendi wurden durch Lichtstreuung untersucht. Wenn die Intensitäten der Lichtstreuung eines positiv geladenen Silberbromid-Sols gegen die Konzentration der zugesetzten DextranSulfate aufgetragen werden, tritt ein ausgeprägtes Maximum auf, dessen Lage von dem Molekulargewicht des angewandten Polyelektrolyten unabhängig ist. Bei Verdünnung des Sols wird das Maximum zur niedrigeren Konzentration des Polyanions verschoben.Der Einfluß der Polyanionen auf die Stabilität der Silberbromid-Sole mit gleichem Ladungsvorzeichen wurde in Abhängigkeit von dem Molekulargewicht des zugesetzten Dextransulfats, der Solkonzentration, der Ladung und Konzentration der Gegenionen und dem Zusatz von Methylalkohol untersucht. Destabilisierung wird nur in Anwesenheit einer genügenden Menge von Neutralelektrolyten in den untersuchten Systemen beobachtet. Die Konzentration der Gegenionen, die ein Flockungsmaximum verursachen, ist immer niedriger als die kritische Koagulationsmenge derselben Ionen für das gleiche Sol in Abwesenheit von Makroionen. Die Resultate wurden mit den Wechselwirkungen der Silberbromid-Sole mit nichtionogenen Dextranen verglichen, und der Mechanismus der Flockung durch Polyelektrolyte wurde diskutiert.

---

---

5 figures and 1 table

---

Supported by the NSF Grant GP 42331 X.

---

A part of the Ph.D. Thesis by David Lindsay.     

Further explorations on bridged 1,2,4-trioxanes

Three new bicyclo[3.2.1]-type 1,2,4-trioxanes have been designed and synthesized. One of them demonstrates better tolerance of the intramolecular hemiketals to steric crowding in hydroperoxidation. The other represents a prototype for possible manipulation of the transient radicals generated in cleavage reactions. A new substitution pattern in the bridged system is explored through synthesis of the third molecule. The configurations of all stereogenic centers in the bridged system can be effectively controlled by the chirality of the allyl alcohol as illustrated by the enantioselective synthesis of the fourth molecule. Finally, similar bicyclo[3.3.1]-type 1,2,4-trioxanes are shown very difficult to be synthesized because of the involvement of a conformer with two substituents at axial positions at the same time.     

Spektrophotometrische Bestimmung von L-Askorbinsäure mit 2,2',5,5'-Tetra-(4-nitrophenyl)-3,3'-(3,3'-dimethoxy-4, 4'-biphenyl)-ditetrazoliumchlorid (TNBT)

Zusammenfassung Die Optimalbedingungen für die spektrophotometrische Bestimmung der L-Askorbinsäure mit TNBT wurden ermittelt. Die L-As-korbinsäure wurde in Anwesenheit eines 100fachen Überschusses folgender Stoffe bestimmt: Glukose, Fruktose, Saccharose, Wein-, Zitronen-, Oxal-, Äpfel- und Bernsteinsäure. 0,5g/ml ist die minimale Askorbinsäurekonzentration, die sich bestimmen läßt. Die rel. Standardabweichung beträgt 2,1%, der rel. Fehler 0,875%.

---

Spectrophotometric assay of L. ascorbic acid with 2,2,5,5-tetra-(4-nitro-phenyl)-3, 3-(3,3-dimethoxy-4,4-biphenyl)-ditetrazolium chloride (TNBT)

Summary The optimal conditions for spectrophotometric assay of L-ascorbic acid with TNBT were determined. L-ascorbic acid was assayed in the presence of a 100 fold excess of the following substances: glucose, fructose, sucrose, tartaric acid, citric acid, oxalic acid, malic acid and succinic acid. 0.5g/ml is the minimum concentration of ascorbic acid which can be assayed. The relative standard deviation is 2.1%, the relative error 0.875%.

     

Anwendung mikroanalytischer Methoden zur Lösung kunst- und kulturgeschichtlicher Probleme

Zusammenfassung Mit bekannten mikroanalytischen Arbeitsmethoden — Oberflächenreaktionen, Abstrichuntersuchungen mit dem Korundstäbchen, Schutzschichtreaktionen sowie dem Abdruckverfahren — lassen sich archaeometrische Probleme einer Lösung näherbringen. Die Art der Korrosion kupferhaltiger Oberflächen wurde diskutiert.

---

Application of microanalytical methods to the solution of artistic- and cultural historical problems

Summary Archeometrical problems are brought closer to a solution by means of known microanalytical procedures-surface reactions, surface scraping studies with the corundum rod, protective layer reactions as well as the imprint method. A discussion of the corrosion of copper-bearing surfaces is included.

---

---

Vortrag anläßlich der Tagung Chemische Analysen — Kunst- und Kulturwissenschaften im Reiß-Museum in Mannheim, 19.–21. September 1974.     

The surface activity of the lower homologues of n-alkylammonium chlorides in aqueous solutions. Effect of hydrophobic hydration

Summary The surface tensions of aqueous solutions ofn-alkylammonium chlorides (methyl to hexyl) have been measured at 25 °C. With methylammonium chloride the surface tension increased with concentration, whereas with ethylammonium chloride and higher homologues, the surface tension decreased with concentration. The results suggest that this transition is attributed to the effect of hydrophobic hydration. For propylammonium chloride and higher homologues, the relation between the surface tension lowering da and the concentrationC in the range of 0–10 dyne/cm, can be expressed by the equation; = AC + BC, whereA andB are constants. The surface tension coefficientB has been found to increase approximately twofold for each additional CH₂ group of alkyl chain.

---

Zusammenfassung Es wurden die Oberflächenspannungen wäßriger Lösungen vonn-Alkylammoniumchloriden (Methyl- bis Hexylammoniumchloride) bei 25 °C gemessen. Für Methylammoniumchlorid nimmt die Oberflächenspannung mit der Konzentration zu, aber bei allen höheren Homologen mit der Konzentration ab. Die Ergebnisse deuten darauf hin, daß dieser Übergang durch die hydrophobe Hydration bedingt wird. Für Propylammonium-chlorid und die höheren Homologen wird die Beziehung zwischen der Erniedrigung der Oberflächenspannung und der KonzentrationC in dem Bereich von 1 bis 10 dyn/cm durch die folgende Gleichung ausgedrückt: = AC + BC (A undB sind Konstanten). Es wurde gefunden, daß B für jede zusätzliche CH₂-Gruppe etwa um den Faktor 2 größer wird.

     

Organic phase conversion of bulk (wurtzite) ZnO to nanophase (wurtzite and zinc blende) ZnO

We describe the all-organic phase conversion of bulk commercial ZnO in the wurtzite modification to sub-30 nm ZnO that we find to be partially in the zinc blende [, a=4.568(3) Å] modification. The conversion involves refluxing ZnO in 2,4-pentanedione (acetylacetone) at 413 K to form the zinc 2,4-pentanedionate, which is decomposed by heating at 573 K in an appropriate high-temperature solvent such as dibenzylether to form nanophase ZnO. This nanophase, partially zinc blende ZnO can also be obtained in a single step by heating commercial zinc 2,4-pentanedionate in refluxing dibenzylether. Thermodiffractometry suggests that the conversion of zinc blende ZnO to wurtzite ZnO commences near 650 K.     

Unusually sharp dependence of water exchange rate versus lanthanide ionic radii for a series of tetraamide complexes

The tetraamide ligand, DOTA-tetra(glycine ethyl ester), forms complexes with the lanthanide(III) cations that exist in solution predominantly as the square antiprism structure with single, slowly exchanging inner-sphere water molecule. Variable-temperature 1H and 17O NMR studies revealed that the bound water lifetimes in these complexes were sharply dependent upon the ionic radius of Ln3+ cation. A novel lanthanide-induced shift technique was used to unmask the bound water 17O resonance of SmL3+ and YL3+ complexes from the bulk water resonance. The bound water lifetime (tauM298) was approximately 800 mus in the EuL3+ complex but became much shorter (several microseconds) for Ln3+ cations with larger and smaller ionic radii. This demonstrates that water exchange is exquisitely fine-tuned in this macrocyclic tetraamide system and that a variety of Ln3+ complexes meet with the exchange requirement, Deltaomega*tauM >/= 1, necessary for an efficient MT agent.     

A Novel pH-Sensitive MRI Contrast Agent

A tetrasubstituted derivative of 1,4,7,10-tetraazacyclododecane with amide coordinating groups and extended noncoordinating phosphonate groups forms a complex with gadolinium(III) (shown in the picture) which contains one slowly exchanging inner-sphere water molecule (tau(M)=21 μs). The 20-MHz water proton relaxivity of the complex was found to be highly pH dependent. Protonation of the noncoordinating phosphonate groups appears to catalyze prototropic exchange of the bound water protons, thereby providing a mechanism for enhanced water contrast below pH 7.