Weeks In Solution Research Articles

Hydrolysis of Zirconium and Hafnium Siloxide Complexes. Isolation and Characterization of the Intermediate Aqua Complexes M[OSi(OtBu)3]4(H2O)n (M = Zr, Hf; n = 1, 2)

Hydrolysis of the tris(tert-butoxy)siloxy complexes M[OSi(OtBu)3]4 (1, M = Zr; 2, M = Hf) was studied. Careful addition of 1 or 2 equiv of water to THF solutions of 1 and 2 produced the isolable aqua complexes M[OSi(OtBu)3]4(H2O) (3, M = Zr; 4, M = Hf) and M[OSi(OtBu)3]4(H2O)2 (5, M = Zr; 6, M = Hf). These complexes are stable for weeks in solution and are stable indefinitely in the solid state. In solution, the aqua ligands in 3−6 are labile. Crystals of 4 are monoclinic (C2/c) with a = 62.2352(4) Å, b = 13.3362(2) Å, c = 27.0940(4) Å, β = 103.535(1)°, V = 21836.0(4) Å3, and Z = 4. Addition of excess water to solutions of 5 and 6 at room temperature results in rapid hydrolysis to form a MOx(OH)y(OH2)z gel and HOSi(OtBu)3. Below 10 °C in tetrahydrofuran-d8, however, hydrolysis does not occur at an appreciable rate. At low temperatures, the rate of exchange between the aqua ligands of 5 and excess free water was found to depend on the water concentration. This indicates that the aqua ligand exchange occurs by an associative mechanism involving a seven-coordinate intermediate. On the basis of this observation, we postulate that the hydrolysis of 5 also proceeds via the tris(aqua) intermediate Zr[OSi(OtBu)3]4(H2O)3. Compounds 3−6 are more thermally stable than 1 and 2, indicating that the elimination of isobutene from the latter complexes is facilitated by a free coordination site on the Lewis acidic metal center.

The effect of dissolution on plasma sprayed hydroxylapatite coatings on titanium

Plasma sprayed hydroxylapatite (HA) coated titanium specimens were immersed into Ca-free Hank's balanced salt solution for periods of l, 2, 4, and 6 weeks. At each of the respective time intervals the HA coatings were analyzed with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy to determine the effect of dissolution on the structure and composition of the coatings. At the 2- and 6-week intervals, additional samples were removed from solution and shear tested to evaluate the effect of dissolution on the coating-to-substrate interfacial bond strength. XRD results revealed that the plasma sprayed coatings retained their basic apatitic structure throughout the 6-week period in solution. There was, however, a trend towards a more definitive baseline, suggesting a loss of amorphous material by dissolution. FTIR and Raman analyses of the as-sprayed and dissolution specimens showed that the phosphate groups were not lost during the time in solution; however, there was a decrease in hydroxyl content as a result of dissolution mechanisms. FTIR also revealed an increase in carbonate content within the coating during immersion in the simulated physiological balanced salt solution. The average shear bond strengths for the as-sprayed, 2-, and 6-week dissolution specimens were 14·82 ± 3·52 MPa, 12·51 ± 3·41 MPa, and 12·54 ± 2·02 MPa, respectively. Duncan's multiple range test confirmed that the shear bond strength was not significantly reduced after 6 weeks in solution, but there was evidence that suggested a decrease in interfacial bond strength as a result of dissolution mechanisms.

Adhesion between LDPE and hydrated aluminium in extrusion-coated laminates

Untreated aluminium and aluminium hydrated for 60 s in boiling water have been extrusion-coated with low-density polyethylene (LDPE). The hydration transforms the oxide surface into a porous oxyhydroxide, known as pseudoboehmite. LDPE samples with different melt indices (4.5, 7.5, and 15) were used, which influence the ability to penetrate into the pores. Compared with untreated aluminium, a superior peel strength was obtained for the laminates with hydrated aluminium. In almost all cases, the peel strength for the laminates with hydrated aluminium could not be measured, due to rupture in the polymer film. This improvement is suggested to be due to stronger acid-base interactions, increased contact surface, and mechanical keying into the porous surface. The obtained peel strength and analysis by means of scanning electron microscopy indicated that the polymer with the highest melt index or lowest melt viscosity had the greatest ability to penetrate into the formed pores. After ageing up to 12 weeks in solutions with 1% and 3% acetic acid, the peel strength dropped rapidly for the untreated Al laminates, but remained constant for the hydrated Al laminates. This is explained by the fact that, besides the improved adhesion, the hydrated oxide prevents corrosive attack.

Spontaneous Formation of Stable Phosphino(silyl)‐carbenes from Unstable Diazo Compounds

The carbene‐like compounds 1, which are formed almost quantitatively from phosphanyldiazomethanes already at T ≤ 35°C if the tetramethylpiperidine(tmp)‐R residue is one of the substituents on the phosphorus, are stable for several weeks in solution. With the exception of 1a, the compounds 1 react with BuNC to give the ketenimines 2. a, R  NiPr2, R′  Me; b, R  NMe2, R′  Me; c, R  NMe2, R′  iPr; d, R  Ph, R′  Me. equation image

Tolerances of 20 Rice Cultivars to Excess Al and Mn1

AbstractManganese toxicity is a rare occurrence in flooded or paddy rice (Oryza saliva L.); however, this is not the case for upland rice grown on aerobic soils. Although acid upland soils may contain toxic levels of both Al and Mn, cultivar tolerances to excess Al and Mn do not necessarily coincide. These studies were to determine whether a procedure could be devised for rapid screening of rice cultivars for tolerances to excess Mn and to correlate tolerances between excess Al and excess Mn. Nine rice cultivars were grown in a greenhouse for 4 weeks in nutrient solutions containing 1 µg·cm−3 and 80 µg·cm−3 Mn. The relative tolerance was expressed as a ratio of the excess Mn treatment to the optimum or control treatment using weights of plant parts, height, root length, and tiller number. These expressions of relative tolerance to excess Mn were used to rank the nine cultivars. These rankings were then compared to a ranking based on previous results obtained at IRRI when the cultivars were grown on an acid soil. Significant Spearman's rank correlation coefficients were observed between rankings for tolerance to acid soil toxicity and relative root weight (r8 = −0.93**, significant at the 0.01 level) and relative tiller number (r8 = −0.68*, significant at the 0.05 level). Other rank correlations with acid soil toxicity were not significant. Subsequently, 20 cultivars were screened for tolerance to excess Mn by growing them in a greenhouse for 4 weeks in solutions containing 0.5 and 80 µg·cm−3 Mn. These cultivars were also screened for tolerance to excess Al by growing them for 3 weeks at 3 and 30 µg·cm−3 Al. The correlation between tolerances to excess Al and Mn was tested using relative root length for Al and relative shoot weight for Mn. The correlations were not significant. Large differences in tolerance to excess Mn were observed among rice cultivars; however, it was not established that screening trials using soils containing excess amounts of available Mn can be replaced by short‐term screening in nutrient solutions. The results of this study clearly indicate that tolerance to excess Al is not necessarily correlated with tolerance to excess Mn.

Isolation and partial purification of phthalate ester hydrolyzing enzyme(s) from the brine shrimp, Artemia

Isolation and 30-fold purification of a di- n-butyl phthalate (DNBP) hydrolyzing enzyme from synchronously hatched larvae of the brine shrimp, Artemia, are reported. The activity of the enzyme increases during larval development simultaneously with the acute toxic action of DNBP on the larvae. The enzyme is not stimulated by 10 mM sodium cholate, is stable for days to weeks in solution at 4°C, indefinitely stable at −70°C and is distinct from the previously reported trypsin- and chymotrypsin-like proteases [1].

Uptake and Transport of Calcium and Phosphorus in Lolium perenne in Response to N Supplied to Halves of a Divided Root System

AbstractThe uptake and transport of Ca2+ and HPO42− from roots of Lolium perenne L. was studied using variable N nutrition supplied to halves of a divided root system. Plants were grown for 4 weeks in solution containing 0.11 mM NO3−–N; then one‐half of the root system was supplied with either 4.0 mM NO3−–N or 0.28 mM NH4+–N while the other half of the root system remained in low‐N solution.Uptake and transport of Ca2+ increased and uptake of HPO42− declined in root halves supplied with high NO3−–N for 16 h. After supply of high NO3−–N or NH4+–N to half the root system for 6 days, the roots supplied with high‐N exhibited significantly higher rates of uptake and percentage transport to shoots of both Ca2+ and HPO42−–. However, in neither the 16‐h nor 6‐day treatment did Ca2+ or HPO42− uptake of the root half supplied with low N differ significantly from the control (low N supplied to both halves of the root).Significantly higher N concentrations were found in low‐N supplied roots (compared to the control) as a result of internal translocation of N from high‐N supplied roots to low‐N supplied roots. Although N concentration in the low‐N supplied roots increased, uptake rates of Ca2+ or HPO42− did not change implying that external N concentration may be the important factor which influences or governs N mediated uptake responses. This would further suggest that the site of uptake regulation for Ca2+ and HPO42− exists on the outer plasma membrane which is in direct contact with the external solution.Transport of Ca2+ and HPO42− to the shoot was generally increased in low‐N root halves after 6 days of high‐N supply to the other half of the root. This implies that plant growth demand may be a major factor in regulating rates of Ca2+ and HPO42− transport from roots to the shoot. It also reinforces the hypothesis that uptake and transport of ions out of the root are separately controlled or regulated in the plant.

Induction of transporting sites in a sodium transporting epithelium.

1. Frogs (Rana temporaria) were bathed for 1 week in solutions containing 1-1 mM sodium chloride and either one or both of amiloride (10(-4)M) and spironolactone (10(-5r both of amiloride (10(-4) M) and spironolactone (10(-5) M). This procedure was designed to deplete the sodium transporting compartment of the skin epithelium of sodium, while at the same time antagonizing the effects of endogenous aldosterone. 2. After 1 week the skins were used in vitro to measure the level of sodium transport (short-circuit current) and the density of sodium entry sites in the mucosal surface of the epithelium ([14C]amiloride binding). 3. Sodium deprivation for 1 week caused approximately a doubling of both sodium transport and the density of sodium entry sites in the mucosal surface of the epithelium compared to control skins. 4. When the results for sodium deprived and control skins were pooled there was a highly significant correlation between the density of sodium entry sites and sodium transport. 5. Mechanisms by which sodium deprivation leads to an increase in the density of sodium entry sites are discussed.

Plant Growth in Polyethylene Glycol Solutions in Relation to the Osmotic Potential of the Root Medium and the Leaf Water Balance

The changes in leaf extension, plant dry weight, leaf area, net assimilation rate (E), relative growth-rate and relative leaf growth-rate (R£), have been studied for four species grown for 2 weeks in solutions of polyethylene glycol 4000 of controlled osmotic potentials. All aspects of growth were decreased by decreasing the osmotic potential (■sol) °f the root medium and the leaf water potential ( p from the values in the control plants decreased growth during the first week but partial recovery was apparent during the second week's growth in solution culture, when leaf extension, E, Ri, and Riiincreased in plants subjected to stress. Examination of the water balance, water potential, osmotic potential, and turgor of the leaf in relation to relative water content suggests that recovery was related to increased turgor and that the ability of the plants to grow at reduced values of the osmotic potential of the root medium and of the leaf water potential depended on the maintenance of turgor.

Some Effects of a Synthetic Detergent on Estuarine Fishes

Acute toxicity of an alkyl benzene sulfonate (ABS) surfactant detergent to five species of juvenile estuarine fishes was determined at 20‰ salinity and 20° C. Concentrations of detergent that will kill 50 per cent of the test organisms in 96 hours ranged from 7.0 parts per million (ppm) for silversides, Menidia menidia, to 22.5 ppm for mummichogs, Fundulus heteroclitus. Intermediate in susceptibility were mullet, Mugil cephalus (10.1 ppm), winter flounder, Pseudopleuronectes americanus (8.2 ppm), and eels, Anguilla rostrata (7.5 ppm). After 12 weeks in solution, the synthetic detergent (syndet) retained most of its toxicity. The stock syndet contained 30.3 per cent ABS at week zero as determined by the methylene blue method. Salinity of the medium affects toxicity of the syndet. Eels which were exposed to 10 ppm syndet for 96 hours and mummichogs exposed to 20 ppm syndet for 120 hours were relatively unaffected at salinities below 15‰ but died at salinities approaching ocean strength. Prolonged exposure of 150 days of juvenile mummichogs to syndet concentrations of 1, 2, 5, 8, or 10 ppm at salinities of 10, 20, 30, or 40‰, when compared to controls, did not significantly affect any biological variable measured (mortality, growth in length and weight, red blood cell number, gonadosomatic index, liver condition).