Layered Group(IV) Metal Phosphates as Catalysts for MTBE Synthesis

Layered group(IV) metal phosphates and their phenylsulfonic acid derivatives were used as catalysts for the synthesis of methyl tert-butyl ether (MTBE) from methanol and isobutene. Because zirconium and titanium phosphates have only moderate acidic strength, relatively high temperatures are required to activate their Brønsted acidic sites. The optimal activity was obtained at ca. 443 K. Their phenylsulfonic acid derivatives, however, demonstrated higher acidic strength by giving much higher activity toward MTBE formation at relatively low temperaures. The catalysts were characterized in terms of their structure, thermal stability, surface area and acidic strength.     

Hypothetical transformation of Ca(OH)<Subscript>2</Subscript> into CaCO<Subscript>3</Subscript> in solid-state reactions of portland cement

Summary Previous study of the hydration and ageing products of two cement pastes created the basis for the postulate of the course of solid-state reactions between the portlandite Ca(OH)₂ and the CO₂ from air in the hydrated and air dry cement. XRD basal spacing d(001) of portlandite exceeded the nominal value and increased with ageing, with the wetting and drying procedure and with carbonate content of the paste, indicating that a part of OH^- ions was gradually substituted by CO₃^2- ions, which are about twice bigger. IR spectroscopy showed a considerable content of portlandite, of CO₃^2- of water and silicates. Also HCO₃^- H₂O and CO₂ in cavities between hexagonal rings and hexagonal hydrates were indicated. By MS (mass spectrometry) in vacuum the evaporation of sorbed water was detected at 100-120°C, of gel water at 350°C of portlandite water at 400°C and of high temperature water between 500 and 700°C, simultaneously with CO₂ escape. Slightly higher peak temperatures were found by the TG test either in air or in argon. From these results and from geometric considerations it is postulated that the solid-state reactions take place on ageing of the cement paste and on its heating: hexagonal portlanditecalcium carbonate hydroxy hydratecalcium carbonate hydratehexagonal vaterite and/or orthorhombic aragoniterhombohedral calcite The analysis of the standard files of the calcium carbonate hydroxy hydrates supports this postulate and indicates a gradual transformation.     

A biphasic displacement of [60]fullerene from fac-(dihapto-[60]fullerene)(dihapto-1,10-phenanthroline) tricarbonyl molybdenum (0)

The Lewis bases (=L) triphenylphosphine (PPh₃) and tricyclohexyl phosphine (P(Cy)₃) displace [60]fullerene (C₆₀) from the complex fac-(η²-C₆₀)(η²-phen)Mo(CO)₃ (phen = 1,10-phenanthroline). The progress of the reactions was followed observing the decrease of the absorbance values at 440 nm and by monitoring the stretching carbonyl region from 1700 to 2100 cm⁻¹. The plots of absorbance vs. time were biexponential, indicative of a biphasic behavior, for reactions under flooding conditions where [L] ? [fac-(η²-C₆₀)(η²-phen)Mo(CO)₃]. The plot of absorbance vs. time consisted of two consecutive segments: the first segment of the plot was a decrease of absorbance with time followed by a second segment where the absorbance increased with time. The first segment of the biphasic plot was ascribed to the solvent-assisted displacement of C₆₀ from fac-(η²-C₆₀)(η²-phen)Mo(CO)₃ and the second segment to decomposition of the complex fac-(η¹-L)(η²-phen)Mo(CO)₃ produced in the first of the two consecutive reactions. The rate constant values corresponding to the first segment of the biphasic plot are independent of the chemical nature of L, the molar concentration of L, and the molar concentration of C₆₀ but dependent on the chemical nature of the solvent.     

Intercalation of N, N-dimethyl-1-phenylethylamine into α-Zirconium Phosphate

The intercalation and deintercalation of N, N-dimethyl-1-phenylethylamine (N,N-amine) into -zirconium phosphate was investigated by pH titration. N,N-amine was taken up easily in one step to give a new phaseZr(HPO⁴)(HPO₄·N,N-amine) · H₂O, which was characterized by X-ray diffractometry, IR spectroscopy, and thermal analysis. Therelease of N,N-amine from the solid was found to be irreversible due to structural changes in both the intercalation and deintercalation reactions.     

Design and synthesis of type-III mimetics of omega-conotoxin GVIA

Our interest lies in the rational design and synthesis of type-III mimetics of protein and polypeptide structure and function. Our approach involves interactive design of conformationally defined molecular scaffolds that project certain functional groups in a way that mimics the projection of important binding residues as determined in the parent structure. These design principles are discussed and applied to the structurally defined polypeptide, -conotoxin GVIA, which blocks voltage-gated, neuronal N-type calcium channels. These ion channels represent therapeutic targets for the development of new analgesics that can treat chronic pain. It is shown how a discontinuous, 3-residue pharmacophore of GVIA can be mimicked by different molecular scaffolds. It is illustrated how such 1^st generation leads must necessarily be weak and that optimisability must therefore be built-in during the design process.     

实验性铅染毒对大鼠体内锌,钙的影响

以0、200×10-6、500×10-6、1000×10-6含铅饮用水染毒大鼠，在4、8、12周分批处死动物，取血、尿及组织分别测定铅、锌、钙等元素。结果表明，染毒200×10－6动物在4周时即出现全身症状；血铅浓度随染毒剂量增加而增高；尿铅、锌、钙的排出三者呈平行关系，排出高峰在4周。高尿锌导致脑、睾丸、骨、胰腺等组织锌含量降低，说明锌在铅中毒的发生机制中起重要作用，实验为应用锌制剂预防和治疗铅中毒提供依据。高尿钙所致机体影响有待进一步研究。     

Calix[4] crowns with Methoxynaphthoylmethyl Pendant Groups

The novel calix [4] crowns with two pendant groups were prepared by the alkylation of calix 141 crowns with 6-methoxy-2-bromoacetylnaphthalene. ^1H NMR titration and picrate extraction experiments indicated that they exhibit higher complexing efficiency than their parent compounds and possess obvious selectivity for Na^ or K^ , respetively, and that the cation is encapsulated inside the preorganized ionophoric cavity defined by carbonyl oxygens, the crown ether and the phenoxy oxygens.From UV and fluorescent spectra it is revealed that calix [4]crown-4 3a with 6-methoxy-2-naphthoylmethyl pedant groups exhibits remarkable cation-induced photophysical effects and it could be utilized as a selective fluorescent sensor for Ca^2 .     

Crystals of New Ferric Acid Phosphate, Fe 3 H 3 (PO 4 ) 4 ·6H 2 O, Performed by Inorganic Sol-Gel Process

Crystals of Fe₃H₃(PO₄)₄·6H₂O are obtained at room temperature and 50 °C from phosphate gel prepared by evaporation of H₃PO₄ and FeX₃ (X = NO₃ ^-, Cl^-). Optimal experimental conditions of crystal formation are defined. X-ray powder diffraction, IR absorption spectroscopy and TGA analysis are undertaken to investigate the effect of starting solution compositions on the nature and the growth of crystals.Formulation of synthesised phosphate is proposed on the basis of the composition comparison with the iron phosphate compounds formerly studied. A relation between OH group, phosphorus (or phosphate) and iron contents of the examined phosphates is found. The unit cell parameters are obtained from powder X-ray diffraction data. It is hexagonal with unit cell dimensions a = 9.114(7) Å, c = 16.715(3) Å and V = 1202.62 ų. The BET surface area of this phosphate is measured and a value of 5.0 m²/g is obtained.     

Metal ion interaction with dimethyl phosphate anion

The influence of metal ions on the conformation of dimethyl phosphate anion around its O-P bonds, has been studied theoretically. The perturbation caused due to metal ions like Na⁺ and Mg²⁺ seems to affect the free dimethyl phosphate anion conformation to a considerable extent. In particular, the fully extended conformation becomes much more favourable in the metal ion dimethyl phosphate complex.     

PVC membrane based potentiometric sensors for uranium determination

Two novel uranyl PVC matrix membrane sensors responsive to uranyl ion are described. The first sensor incorporates tris(2-ethylhexyl)phosphate (TEHP) as both electroactive material and plasticizer and sodium tetraphenylborate (NaTPB) as an ion discriminator. The sensor displays a rapid and linear response for UO₂²⁺ ions over the concentration range 1×10⁻¹–2×10⁻⁵ mol l⁻¹ UO₂²⁺ with a cationic slope of 25.0±0.2 mV decade⁻¹. The working pH range is 2.8–3.6 and the life span is 4 weeks. The second sensor contains O-(1,2-dihydro-2-oxo-1-pyridyl)-N,N,N′,N′-bis(tetra-methylene)uronium hexafluorophosphate (TPTU) as a sensing material, sodium tetraphenylborate as an ion discriminator and dioctyl phenylphosphonate (DOPP) as a plasticizer. Linear and stable response for 1×10⁻¹–5×10⁻⁵ mol l⁻¹ UO₂²⁺ with near-Nernstian slope of 27.5±0.2 mV decade⁻¹ are obtained. The working pH range is 2.5–3.5 and the life span of the sensor is 6 weeks. Interference from many inorganic cations is negligible for both sensors. However, interference caused by some ions (e.g. Th⁴⁺, Cu²⁺, Fe³⁺) is eliminated by a prior ion exchange or solvent extraction step. Direct potentiometric determination of as little as 5 μg ml⁻¹ uranium in aqueous solutions shows an average recovery of 97.2±1.3%. Application for the determination of uranium at levels of 0.01–1 wt.% in naturally occurring and certified ores gives results with good correlation with data obtained by X-ray fluorescence.