Acidity, basicity and catalytic activity of La−Zn mixed oxides

Surface acidity/Basicity of mixed oxides of La and Zn activated at three different temperatures were determined. The data have been correlated with the catalytic activity for liquid phase reduction of cyclohexanone in isopropanol.

Catalytic oxidation of cyclohexane over Cu-Zn-Cr ternary spinel systems

Spinel systems with the composition of Cu 1−x Zn x Cr 2 O 4 [x = 0 CCr, x = 0.25 CZCr-1, x = 0.5 CZCr-2, x = 0.75 CZCr-3 and x = 1 ZCr] were prepared by homogeneous co-precipitation method and were characterized by X-ray diffraction (XRD) and FT-IR spectroscopy. Elemental analysis was done by EDX, and surface area measurements by the BET method. The redox behavior of these catalysts in cyclohexane oxidation at 243 K using TBHP as oxidant was examined. Cyclohexanone was the major product over all catalysts with some cyclohexanol. 69.2% selectivity to cyclohexanol and cyclohexanone at 23% conversion of cyclohexane was realized over zinc chromite spinels in 10 h.

Hysteresis in a system driven by either generalized force or displacement variables: martensitic phase transition in single-crystalline Cu-Zn-Al

We report on experiments aimed at comparing the hysteretic response of a Cu-Zn-Al single crystal undergoing a martensitic transition under strain-driven and stress-driven conditions. Strain-driven experiments were performed using a conventional tensile machine while a special device was designed to perform stress-driven experiments. Significant differences in the hysteresis loops were found. The strain-driven curves show reentrant behavior yield point which is not observed in the stress-driven case. The dissipated energy in the stress-driven curves is larger than in the strain-driven ones. Results from recently proposed models qualitatively agree with experiments.

Effect of preparation on magnetic properties of Mn-Zn ferrite

Mixed ferrites belonging to the type Mn0.9Zn0.1Fe2O4 have been prepared by the double sintering method and by the chemical co-precipitation for comparing their magnetic properties. Sintered and precipitated ferrites exhibit different characteristics, especially in their magnetic properties like magnetization (Ms), coercive field (Hc) and Curie temperature (Tc). The sintered particles were size reduced in order to compare with the nanosized co-precipitated particles. The effect of grinding has also been studied. Particles have been collected at regular intervals of grinding and their properties have been studied. The increase in the coercive field has been recorded by a hysteresis curve tracer confirming size reduction. X-ray diffraction studies confirmed the structure and consequent size reduction

Characterization and FTIR spectral studies of human urinary stones from Southern India

Urinary stones resected from urinary bladders of patients hailing from Kollam district of Kerala State, India were analyzed by SEM, XRD and by thermal analysis techniques. The analytical results indicate that, stones have different composition, i.e., calcium phosphate, calcium phosphate hydroxide and sodium calcium carbonate. Infrared spectral studies also reveal the presence of phosphates or carbonates in these samples. Further, IR spectral investigations have revealed that amorphous carbonated species are occupied in PO4 sites in calcium phosphate type stone and OH sites in calcium phosphate hydroxide sample. Thermal studies of these samples also reveal that, carbon dioxide is released from carbonated samples upon heating which is related to amount of carbon content and bond strength. Crystals with defects and irregular morphology are grown inside the urinary bladder due to variation in crystal growth conditions

Analytical Characterization, Thermal And Ftir Studies Of Urinary Calculi

Urolithiasis is identified to be a major urological disorder affecting people all over the world irrespective of their age, sex and race. Urinary stone samples resected from the urinary bladders of two patients belonging to tropical region, Kollam District of Kerala State, India are investigated by using XRD,SEM, EDAX, TGA, DSC and FTIR to understand its chemical structure. Uric acid shows exothermic peak around 432°C is due to the decomposition with the evolution of CO and cracking of the remaining products. Results of analytical studies reveal that samples under investigation consist mainly in uric acid and hydrated uric acid. Hydrogen bonding exists in hydrated uric acid samples

Effects of Different Feeding Regimes on the Digestibility and Faecal Excretion of Nitrogen, Soluble Carbohydrates and Fibre Fractions in Water Buffaloes kept under Subtropical Conditions

In the course of the ‘Livestock Revolution’, extension and intensification of, among others, ruminant livestock production systems are current phenomena, with all their positive and negative side effects. Manure, one of the inevitable secondary products of livestock rearing, is a valuable source of plant nutrients and its skillful recycling to the soil-plant interface is essential for soil fertility, nutrient - and especially phosphorus - uses efficiency and the preservation or re-establishment of environmentally sustainable farming systems, for which organic farming systems are exemplarily. Against this background, the PhD research project presented here, which was embedded in the DFG-funded Research Training Group 1397 ‘Regulation of soil organic matter and nutrient turnover in organic agriculture ’ investigated possibilities to manipulate the diets of water buffalo (Bubalus bubalis L.) so as to produce manure of desired quality for organic vegetable production, without affecting the productivity of the animals used. Consisting of two major parts, the first study (chapter 2) tested the effects of diets differing in their ratios of carbon (C) to nitrogen (N) and of structural to non-structural carbohydrates on the quality of buffalo manure under subtropical conditions in Sohar, Sultanate of Oman. To this end, two trials were conducted with twelve water buffalo heifers each, using a full Latin Square design. One control and four tests diets were examined during three subsequent 7 day experimental periods preceded each by 21 days adaptation. Diets consisted of varying proportions of Rhodes grass hay, soybean meal, wheat bran, maize, dates, and a commercial concentrate to achieve a (1) high C/N and high NDF (neutral detergent fibre)/SC (soluble carbohydrate) ratio (HH), (2) low C/N and low NDF/SC ratio (LL); (3) high C/N and low NDF/SC ratio (HL) and (4) low C/N and high NDF/SC (LH) ratio. Effects of these diets, which were offered at 1.45 times maintenance requirements of metabolizable energy, and of individual diet characteristics, respectively, on the amount and quality of faeces excreted were determined and statistically analysed. The faeces produced from diets HH and LL were further tested in a companion PhD study (Mr. K. Siegfried) concerning their nutrient release in field experiments with radish and cabbage. The second study (chapter 3) focused on the effects of the above-described experimental diets on the rate of passage of feed particles through the gastrointestinal tract of four randomly chosen animals per treatment. To this end, an oral pulse dose of 683 mg fibre particles per kg live weight marked with Ytterbium (Yb; 14.5 mg Yb g-1 organic matter) was dosed at the start of the 7 day experimental period which followed 21 days of adaptation. During the first two days a sample for Yb determination was kept from each faecal excretion, during days 3 – 7 faecal samples were kept from the first morning and the first evening defecation only. Particle passage was modelled using a one-compartment age-dependent Gamma-2 model. In both studies individual feed intake and faecal excretion were quantified throughout the experimental periods and representative samples of feeds and faeces were subjected to proximate analysis following standard protocols. In the first study the organic matter (OM) intake and excretion of LL and LH buffaloes were significantly lower than of HH and HL animals, respectively. Digestibility of N was highest in LH (88%) and lowest in HH (74%). While NDF digestibility was also highest in LH (85%) it was lowest in LL (78%). Faecal N concentration was positively correlated (P≤0.001) with N intake, and was significantly higher in faeces excreted by LL than by HH animals. Concentrations of fibre and starch in faecal OM were positively affected by the respective dietary concentrations, with NDF being highest in HH (77%) and lowest in LL (63%). The faecal C/N ratio was positively related (P≤0.001) to NDF intake; C/N ratios were 12 and 7 for HH and LL (P≤0.001), while values for HL and LH were 11.5 and 10.6 (P>0.05). The results from the second study showed that dietary N concentration was positively affecting faecal N concentration (P≤0.001), while there was a negative correlation with the faecal concentration of NDF (P≤0.05) and the faecal ratios of NDF/N and C/N (P≤0.001). Particle passage through the mixing compartment was lower (P≤0.05) for HL (0.033 h-1) than for LL (0.043 h-1) animals, while values of 0.034 h-1 and 0.038 h-1 were obtained for groups LH and HH. At 55.4 h, total tract mean retention time was significantly (P≤0.05) lower in group LL that in all other groups where these values varied between 71 h (HH) and 79 h (HL); this was probably due to the high dietary N concentration of diet LL which was negatively correlated with time of first marker appearance in faeces (r= 0.84, P≤0.001), while the dietary C concentration was negatively correlated with particle passage through the mixing compartment (r= 0.57, P≤0.05). The results suggest that manure quality of river buffalo heifers can be considerably influenced by diet composition. Despite the reportedly high fibre digestion capacity of buffalo, digestive processes did not suppress the expression of diet characteristics in the faeces. This is important when aiming at producing a specific manure quality for fertilization purposes in (organic) crop cultivation. Although there was a strong correlation between the ingestion and the faecal excretion of nitrogen, the correlation between diet and faecal C/N ratio was weak. To impact on manure mineralization, the dietary NDF and N concentrations seem to be the key control points, but modulating effects are achieved by the inclusion of starch into the diet. Within the boundaries defined by the animals’ metabolic and (re)productive requirements for energy and nutrients, diet formulation may thus take into account the abiotically and biotically determined manure turnover processes in the soil and the nutrient requirements of the crops to which the manure is applied, so as to increase nutrient use efficiency along the continuum of the feed, the animal, the soil and the crop in (organic) farming systems.

Factores asociados al desarrollo de formas sintomáticas de hipercalciuria idiopática en niños de la Fundación Cardioinfantil

La hipercalciuria idiopática (HI) es un trastorno metabólico frecuente, con curso clínico, la mayoría de las veces asintomático. Sin embargo, en algunos pacientes se manifiesta clínicamente con hematuria, polaquiuria, disuria, incontinencia urinaria, enuresis y dolor abdominal o lumbar, los cuales afectan las actividades diarias de los niños y motivan consultas médicas repetitivas, con los costos que esto genera. Se requiere de la sospecha clínica y el conocimiento de la enfermedad para su diagnóstico y tratamiento oportunos. Objetivo. Determinar los factores relacionados con el desarrollo de la forma sintomática de HI, para lo cual se estudiaron: la magnitud de la calciuria, el antecedente familiar de urolitiasis, el género, la edad y la excreción de oxalato de calcio. El propósito final fue ampliar y difundir el conocimiento de la enfermedad dentro de la comunidad médica. Materiales y métodos. Se realizó un estudio analítico de casos y controles para determinar la relación existente entre los factores mencionados y la presencia de síntomas de HI. La población de estudio estuvo compuesta por 60 pacientes con diagnóstico establecido de HI, de la consulta de Nefropediatría de la Fundación Cardioinfantil, con edades entre los 2 y los 13 años. La metodología consistió en un estudio no pareado con 1,4 casos por cada control. Para el análisis estadístico de las asociaciones entre los factores en estudio y la HI sintomática se utilizó la prueba exacta de Fisher y el Ji cuadrado de Pearson con un nivel de significancia del 5% (p<0,05). Para establecer la fuerza de la asociación se calculó la razón de disparidad (OR) y el intervalo de confianza del 95%. Además, se determinaron las variables que explican en conjunto la HI sintomática, controlando las variables de confusión con un modelo de regresión logística incondicional a un nivel de significancia del 5% (p<0,05). Resultados. Se establecieron asociaciones entre los siguientes factores y la presencia de síntomas de HI en niños: el género masculino (p = 0,006; OR = 6,2; IC = 1,6-24,5) y la magnitud de la calciuria (p = 0,003). Con menor diferencia estadística se encontraron el antecedente familiar positivo de urolitiasis (p = 0,018; OR = 4,889; IC = 1,26-19,48) y el incremento en la edad (p = 0,044). La presencia de oxalato de calcio en el uroanálisis no se relacionó con los síntomas de HI (p = 0,2; OR = 0,59; IC = 0,17-1,49). Conclusiones. Los valores elevados de calciuria M(mayor a 6 mg/kg/día) y el género masculino, se asocian con la presencia de síntomas de HI en niños. Adicionalmente, se observaron, con frecuencia, en el grupo de pacientes sintomáticos, la presencia de niños de edades mayores y el antecedente familiar positivo de litiasis renal, aunque no se evidencian diferencias significativas para estos dos factores. El hallazgo de cristales de oxalato de calcio en el uroanálisis no se relacionó con los síntomas de HI.

Síntesi i estructura de lligands hexaazamacrocíclics i dels seus complexos de Zn. Estudis de catàlisi i de fenòmens de reconeixement molecular amb substrats aniònics

Es realitza una breu introducció a la Química Supramolecular, la qual estudia les estructures i funcions de les associacions que resulten de la unió d'espècies moleculars a través d'enllaços intermoleculars, no covalents. El reconeixement molecular, reactivitat i transport són les funcions bàsiques de les espècies supramoleculars. El present treball tracta de la química supramolecular d'anions i del potential efecte catalític de complexos de Zinc amb lligands hexaazamacrocilics en reaccions de hidròlisis d'esters de fosfat. Els lligands descrits en aquest treball són lligands macrocíclics hexadentats formats per amines secundàries o terciàries enllaçades a cadenes alquíliques de dos o tres àtoms de carbonis formant dos braços, que estan unides per un espaiador, El conjunt de lligands que s'estudien permeten estudiar els diferents factors, geomètrics, electrònics i estèrics que controlen els fenòmens de reconeixement molecular. El treball descriu en detall els procediments de síntesi i la caracterització d'aquest conjunt de lligands. S'ha realitzat un estudi sistemàtic dels diferents factors que afecten als fenòmens de reconeixement molecular entre lligands macrocíclics (L), descrits anteriorment i substrats aniònics (S): fosfats, polifosfats i dicarboxilats. Els estudis s'han realitzat tant en dissolució aquosa, a partir de mesures potenciomètriques, com en estat sòlid per difracció de Raig-X a partir de la obtenció de les estructures cristal·lines dels complexos. La força de l'enllaç en els complexos ternaris H:L:S es racionalitza en termes d'enllaç per pont d'hidrogen, interaccions electrostàtiques i interaccions per -Stacking. Així mateix es racionalitza la importància de les dimensions i forma de la cavitat en el grau d'interacció. Actualment hi ha un gran interès en l'estudi del paper que juguen els ions metàl·lics en el centre actiu dels metal·loenzims hidrolítics tal com la carboxipeptidasa, que catalitza la hidròlisi d'aminoàcids C-terminals de substrats polipeptídics, l'anhidrasa carbònica, que catalitza la reacció d'hidratació del CO2 per donar hidrogencarbonat, la fosfatasa alcalina, que actua catalitzant la hidròlisi no específica de monoesters de fosfats a pH alcalí. El Zn(II) és un metall que es troba sovint formant part dels centres actius dels metal·loenzims i és el segon element de transició més abundant en els organismes vius. Per aquest motiu són útils els models sintètics que puguin actuar com a mimetitzadors de reaccions bioinorgàniques en les que els metal·loenzims juguen un paper com a catalitzadors. Els models sintètics són complexos de metalls de transició formats per un lligand o lligands en el seu entorn de coordinació més immediat que tinguin efectes electrònics i estèrics els més similar possible als que es produeixen en el centre actiu dels enzims. Donat la importància dels complexos de Zn(II) com a models biomimètics de metal·loenzims hidrolítics, s'han sintetitzat i caracteritzat complexos dinuclears de Zn(II) amb lligands hexaazamacrocíclics descrits anteriorment. S'ha realitzat un estudi de la seva activitat catalítica en la hidròlisi d'un ester activat, l'acetat de p-nitrofenil, un substrat característic que s'utilitza per analitzar l'activitat catalítica dels models biomimètics.

Genotypic variations in the accumulation of Cd, Cu, Pb and Zn exhibited by six commonly grown vegetables

Metal contaminants in garden and allotment soils could possibly affect human health through a variety of pathways. This study focused on the potential pathway of consumption of vegetables grown on contaminated soil. Five cultivars each of six common vegetables were grown in a control and in a soil spiked with Cd, Cu, Pb and Zn. Highly significant differences in metal content were evident between cultivars of a number of vegetables for several of the contaminants. Carrot and pea cultivars exhibited significant differences in accumulated concentrations of Cd and Cu with carrot cultivars also exhibiting significant differences in Zn. Distinctive differences were also identified when comparing one vegetable to another, legumes (Leguminosae) tending to be low accumulators, root vegetables (Umbelliferae and Liliaceae) tending to be moderate accumulators and leafy vegetables (Compositae and Chenopodiaceae) being high accumulators. (c) 2006 Elsevier Ltd. All rights reserved.

Influence of time on the plant availability of Cd, Ni and Zn after sewage sludge has been applied to soils

A pot experiment was conducted to test the hypothesis that decomposition of organic matter in sewage sludge and the consequent formation of dissolved organic compounds (DOC) would lead to an increase in the bioavailability of the heavy metals. Two Brown Earth soils, one with clayey loam texture (CL) and the other a loamy sand (LS) were mixed with sewage sludge at rates equivalent to 0, 10 and 50 1 dry sludge ha(-1) and the pots were sown with ryegrass (Lolium perenne L.). The organic matter content and heavy metal availability assessed with soil extractions with 0.05 M CaCl2 were monitored over a residual time of two years, while plant uptake over one year, after addition of the sludge. It was found that the concentrations of Cd and Ni in both the ryegrass and the soil extracts increased slightly but significantly during the first year. In most cases, this increase was most evident especially at the higher sludge application rate (50 t ha(-1)). However, in the second year metal availability reached a plateau. Zinc concentrations in the ryegrass did not show an increase but the CaCl2 extracts increased during the first year. In contrast, organic matter content decreased rapidly in the first months of the first year and much more slowly in the second (total decrease of 16%). The concentrations of DOC increased significantly in the more organic rich CL soil in the course of two years. The pattern followed by the decomposition of organic matter with time and the production of DOC may provide at least a partial explanation for trend towards increased metal availability.

Displacement of Zn through acidic light-textured soils

In order to gain understanding of the movement of pollutant metals in soil. the chemical mechanisms involved in the transport of zinc were studied. The displacement of zinc through mixtures of sand and cation exchange resin was measured to validate the methods used for soil. With cation exchange capacities of 2.5 and 5.0 cmol(c) kg(-1). 5.6 and 8.4 pore volumes of 10 mM CaCl2, respectively, were required to displace a pulse of ZnCl2. A simple Burns-type model (Wineglass) using an adsorption coefficient (K-d) determined by fitting a straight line relationship to an adsorption isotherm gave a good fit to the data (K-d=0.73 and 1.29 ml g(-1), respectively). Surface and subsurface samples of an acidic sandy loam (organic matter 4.7 and 1.0%. cation exchange capacity (CEC) 11.8 and 6.1 cmol(c) kg(-1) respectively) were leached with 10 mM calcium chloride. nitrate and perchlorate. With chloride. the zinc pulse was displaced after 25 and 5 pore volumes, respectively. The Kd values were 6.1 and 2.0 ml g(-1). but are based on linear relationships fitted to isotherms which are both curved and show hysteresis. Thus. a simple model has limited value although it does give a general indication of rate of displacement. Leaching with chloride and perchlorate gave similar displacement and Kd values, but slower movement occurred with nitrate in both soil samples (35 and 7 pore volumes, respectively) which reflected higher Kd values when the isotherms were measured using this anion (7.7 and 2.8 ml g(-1) respectively). Although pH values were a little hi-her with nitrate in the leachates, the differences were insufficient to suggest that this increased the CEC enough to cause the delay. No increases in pH occurred with nitrate in the isotherm experiments. Geochem was used to calculate the proportions of Zn complexed with the three anions and with fulvic acid determined from measurements of dissolved organic matter. In all cases, more than 91% of the Zn was present as Zn2+ and there were only minor differences between the anions. Thus, there is an unexplained factor associated with the greater adsorption of Zn in the presence of nitrate. Because as little as five pore volumes of solution displaced Zn through the subsurface soil, contamination of ground waters may be a hazard where Zn is entering a light-textured soil, particularly where soil salinity is increased. Reductions in organic matter content due to cultivation will increase the hazard. (C) 2004 Elsevier B.V. All rights reserved.