Synthesis, characterization and X-ray structure of hexahydrazinium diuranyl pentaoxalate dihydrate, (N2H5)6(UO2)2(C2O4)5·2H2O

A new hydrazinium uranyl oxalate complex (N2H5)6[(UO2)2(C2O4)5]·2H2O has been prepared and characterized by chemical analysis, infrared, visible spectra and TG-DTA. The single crystal X-ray structure of the complex shows the presence of discrete N2H5+ cations, water molecules and [(UO2)2(C2O4)5]6− anions. In the anion, the linear uranyl groups are coordinated by two chelating bidentate oxalates and one bridging oxalate which lies on the center of symmetry between the two uranyl groups. The coordination polyhedron around each uranium atom is approximately a pentagonal bipyramid.

Thermal reactivity of metal oxalate hydrazinates

Metl oxalate hydrazinates MC2O4·2 N2H4 where M=Mg, Mn, Fe, Co, Ni, Cu, Zn and Cd have been prepared and characterised by chemical analysis and infrared spectra. Thermal reactivity and decomposition of these oxalato complexes have been studied using thermogravimetry and differential thermal analysis. Hydrazinates of Mn, Fe, Co, Ni and Cu oxalates exhibit autocatalytic decomposition behaviour whereas the others do not. This phenomenon can be attributed to the presence of a bridged hydrazine as well as the thermal stability of the anhydrous metal oxalates.

Thermal reactivity of metal oxalate hydrazinates

Metal oxalate hydrazinates MC2O4·2 N2H4 where M=Mg, Mn, Fe, Co, Ni, Cu, Zn and Cd have been prepared and characterised by chemical analysis and infrared spectra. Thermal reactivity and decomposition of these oxalato complexes have been studied using thermogravimetry and differential thermal analysis. Hydrazinates of Mn, Fe, Co, Ni and Cu oxalates exhibit autocatalytic decomposition behaviour whereas the others do not. This phenomenon can be attributed to the presence of a bridged hydrazine as well as the thermal stability of the anhydrous metal oxalates.

Thermal decomposition of rare-earth trioxalatocobaltates

The thermal decomposition of rare-earth trioxalatocobaltates LnCo(C2O4)3 · x H2O, where Ln = La, Pr, Nd, has been studied in flowing atmospheres of air/oxygen, argon/ nitrogen, carbon dioxide and a vacuum. The compounds decompose through three major steps, viz. dehydration, decomposition of the oxalate to an intermediate carbonate, which further decomposes to yield rare-earth cobaltite as the final product. The formation of the final product is influenced by the surrounding gas atmosphere. Studies on the thermal decomposition of photodecomposed lanthanum trioxalatocobaltate and a mechanical mixture of lanthanum oxalate and cobalt oxalate in 1 : 2 molar ratio reveal that the decomposition behaviour of the two samples is different. The drawbacks of the decomposition scheme proposed earlier have been pointed out, and logical schemes based on results obtained by TG, DTA, DTG, supplemented by various physico-chemical techniques such as gas and chemical analyses, IR and mass spectroscopy, surface area and magnetic susceptibility measurements and X-ray powder diffraction methods, have been proposed for the decomposition in air of rare-earth trioxalatocobaltates as well as for the photoreduced lanthanum salt and a mechanical mixture of lanthanum and cobalt oxalates.

Oxalato complexes of oxovanadium (IV)

Oxalato oxovanadium (IV) complexes with neutral ligand molecules like dimethyl sulphoxide (DMSO) and antipyrine (Apy), VOOX·2DMSO and VOOX·2Apy and complex oxalates of oxovanadium (IV)-(NH4)2[VOOX2]·2H2O, (NH4)2[(VO)2OX3]·6H2O and (NH4)2[(VO)2OX3] have been prepared and characterized by different methods. In the divanadyl complexes, V-V and V-O-V-O types of bonding are shown to be absent by magnetic and spectral data and a bridged oxalato group co-ordinated to the two vanadium atoms is shown to be present, in addition to the usual bidentate oxalate groups. The possible stereochemical arrangements are indicated for the complexes.

Infra-red absorption bands of co-ordinated water in titanium complexes

ORANGE red and amorphous peroxy-titanium complexes of oxalic, malonic and maleic acids1-3, when vacuum-dried, have co-ordinated water molecules firmly bonded to the central titanium atom as shown in formula (I). The peroxy-oxygen from these compounds is slowly lost even at room temperature because of the strained peroxy-group3,4. The compounds, when kept at 95°-100°C. for about three days, give deperoxygenated compounds of the type (II). However, a sample of peroxy-titanium oxalate sealed in a glass tube lost all its peroxy-oxygen in about four years and gave a white crystalline basic oxalate (II). The amorphous nature of the compounds may be due to random hydrogen bonding in the complexes. The crystallinity observed in one of the deperoxygenated titanyl oxalates may be due to the rearrangement of the molecules during ageing for more than four years. The infra-red absorption of these compounds was studied to find out the effect of co-ordination and hydrogen bonding on the infra-red bands of the free water.

Crystal packing and melting temperatures of small oxalate esters: the role of C-H center dot center dot center dot O hydrogen bonding

The simple dialkyl oxalates are generally liquids at room temperature except for dimethyl and di-tert-butyl oxalate which melt at 327 and 343 K. The crystal structures of diethyl, di-iso-propyl, di-n-butyl, di-tert-butyl and methyl ethyl oxalates were determined. The liquid esters were crystallized using the cryocrystallization technique. A comparison of the intermolecular interactions and packing features in these crystal structures was carried out. The crystal structure of dimethyl oxalate was redetermined at various temperatures. The other compounds were also studied at several temperatures in order to assess the attractive nature of the hydrogen bonds therein. A number of moderate to well defined C-H center dot center dot center dot O interactions account for the higher melting points of the two solid esters. Additionally, a diminished entropic contribution Delta S(m) in di-tert-butyl oxalate possibly increases the melting point of this compound further.

Succinate esters: odd-even effects in melting points

Dialkyl succinates show a pattern of alternating behavior in their melting points, as the number of C atoms in the alkane side chain increases, unlike in the dialkyl oxalates Joseph et al. (2011). Acta Cryst. B67, 525-534]. Dialkyl succinates with odd numbers of C atoms in the alkyl side chain show higher melting points than the immediately adjacent analogues with even numbers. The crystal structures and their molecular packing have been analyzed for a series of dialkyl succinates with 1 - 4 C atoms in the alkyl side chain. The energy difference (Delta E) between the optimized and observed molecular conformations, density, Kitaigorodskii packing index (KPI) and C-H center dot center dot center dot O interactions are considered to rationalize this behavior. In contrast to the dialkyl oxalates where a larger number of moderately strong C-H center dot center dot center dot O interactions were characteristic of oxalates with elevated melting points, here the molecular packing and the density play a major role in raising the melting point. On moving from oxalate to succinate esters the introduction of the C2 spacer adds two activated H atoms to the asymmetric unit, resulting in the formation of stronger C-H center dot center dot center dot O hydrogen bonds in all succinates. As a result the crystallinity of long-chain alkyl substituted esters improves enormously in the presence of hydrogen bonds from activated donors.

Biological colonization on majolica glazed tiles: biodeterioration, bioreceptivity and mitigation strategies

The impact of microbial activity on the deterioration of cultural heritage is a well-recognized global problem. Glazed wall tiles constitute an important part of the worldwide cultural heritage. When exposed outdoors, biological colonization and consequently biodeterioration may occur. Few studies have dealt with this issue, as shown in the literature review on biodiversity, biodeterioration and bioreceptivity of architectural ceramic materials. Due to the lack of knowledge on the biodeteriogens affecting these assets, the characterization of microbial communities growing on Portuguese majolica glazed tiles, from Pena National Palace (Sintra, Portugal) and another from Casa da Pesca (Oeiras, Portugal) was carried out by culture and molecular biology techniques. Microbial communities were composed of microalgae, cyanobacteria, bacteria and fungi, including a new fungal species (Devriesia imbrexigena) described for the first time. Laboratory-based colonization experiments were performed to assess the biodeterioration patterns and bioreceptivity of glazed wall tiles produced in laboratory. Microorganisms previously identified on glazed tiles were inoculated on pristine and artificially aged tile models and incubated under laboratory conditions for 12 months. Phototrophic microorganisms were able to grow into glaze fissures and the tested fungus was able to form oxalates over the glaze. The bioreceptivity of artificially aged tiles was higher for phototrophic microorganisms than pristine tile models. A preliminary approach on mitigation strategies based on in situ application of commercial biocides and titanium dioxide (TiO2) nanoparticles on glazed tiles demonstrated that commercial biocides did not provide long term protection. In contrast, TiO2 treatment caused biofilm detachment. In addition, the use of TiO2 thin films on glazed wall tiles as a protective coating to prevent biological colonization was analysed under laboratorial conditions. Finally, conservation notes on tiles exposed to biological colonization were presented.

Chemiluminescence: liquid-phase

Article Outline
• Introduction
• Acidic Potassium Permanganate
• Acridinium Esters
• Diaryl Oxalates and Oxamides
• Dioxetanes
• Hypohalites
• Luminol and Its Analogs
• Tris(2,2′-bipyridyl)ruthenium(II)
• Practical Considerations
• HPLC and Flow Analysis
• Capillary Electrophoresis
• Enzyme Reaction Products
• Immunoassay and DNA Assays
• Further Reading

Aqueous/micellar peroxyoxalate chemiluminescent detection for ion chromatography

This thesis covers the development of the traditionally fluorescent bis(8-quinolinol-5-sulfonic acid) magnesium (II) fluorophore as a chemiluminescent emitter. A brief description of luminescence spectroscopy and its application to analytical chemistry lays the foundation to the discussion of the results obtained herein. This includes the synthesis and identification of two so called ‘water soluble’ aryl oxamides 2,2’-oxalyl-bis(trifluoromethanesulfonyl) imino] ethylene-bis(N- methylpyridinium) trifluoromethane sulfonate (PETQ) and 2,2’-oxalyl-bis(trifluoromethanesulfonyl) imino]ethylene-bis(N-pyridinium) chloride (PETH), previously developed for the US navy as a possible emergency light source, yet the synthetic methodology were incomplete. The inconsistencies of the synthetic methods for PETQ and PETH were overcome with yields satisfactory for their preliminary analytical evaluation. The evaluation of these aryl oxamides, including 4,4’-oxalyI- bis[(trifluoromethanesulfonyl) imino]ethylene-bis(l-methyM-benzylpiperidinium) trifluoromethanesulfonate (BPTQ), 4,4’-oxalyl-bis [(trifluoromethylsulfonyl)imino] ethylene-bis(N-methylmorpholinium)trifluoromethanesulfonate (METQ) and the oxalate bis(2,4,6-trichlorophenyl) oxalate (TCPO) were performed with the peroxyoxalate chemiluminescent reaction using bis(8-quinolinol-5-sulfonic acid) magnesium (II) as the fluorophore. A univariate optimisation of this system resulted in 0,0082 mol 1-1 the detection limit of magnesium in the absence of cationic surfactants and 0.0041 mol 1-1 in their presence for the majority of these compounds. The oxamides were found to be insoluble in water with long ulrasonication periods required to dissolve the compound, with solvents such as acetonitrile preferred. The determination of other chemiluminescent metal-8HQS chelates to replace magnesium -8HQS in the peroxyoxalate were limited to Al (III), Cd (II), Ca (II), In (II) and Zn (II), unfortunately these metals all possessed poorer detection limits than those obtained using magnesium The base reaction conditions used for the flow injection system with chemiluminescent detection were transferred to an ion chromatographic configuration for the separation of magnesium from other cations on an exchange column. After a univariate and simplex optimisation of these conditions, the detection limit of magnesium was found to be 0.0411 mol 1-1 which was less than the limits that could be achieved with fluorescent detection, The further development of this reaction to incorporate the displacement of magnesium from Mg-EDTA by other metals that possessed a higher conditional stability constant than magnesium also proved to be problematic with interferences from not only EDTA but from the eluant (lactic acid) from the cation column. Using this system the detection limits of the displacing metals were found to be in the order of 10 mg 1-1 which was substantially less that what was observed when exactly the same configuration was used with fluorescent detection. The final component of the thesis entails the discussion of the background emission that results from the reaction of oxamides/oxalates with hydrogen peroxide. A detailed investigation into the reaction of TCPO and hydrogen peroxide in the presence of various additives, such as imidazole , heavy atoms and triethylamine illustrated the existence of a further intermediate in fee mechanism for this reaction. The species responsible for this emission was attributed to the degradation product 2,4,6-trichlorophenyi of TCPO, which was supported by the non-existent background present with the oxamides that do not contain this degradation product.

Determination of sodium oxalate in Bayer process liquors using flow analysis with tris(2,2'-bipyridyl)ruthenium(II) chemiluminescence detection

The research was a detailed investigation into a challenging analytical chemistry problem for the alumina industry. The successful outcomes were derived through innovative reagent chemistry and novel instrumental development. The resultant methodology and instrumentation deployed on this most demanding sample matrix is more robust, reliable and less expensive than anything currently used in this industry worldwide.

Biodisponibilidade do cálcio dietético

O cálcio (Ca) dietético é fundamental para a saúde óssea. Tanto o teor como a biodisponibilidade do elemento nos alimentos devem ser considerados. Este artigo objetiva sumarizar os fatores envolvidos na absorção e destacar os alimentos com melhor disponibilidade do Ca. Este é absorvido principalmente no jejuno e o pH baixo parece favorecer sua absorção, que é maior no crescimento, na gestação/lactação e na carência de Ca ou fósforo (P), e menor no envelhecimento. As maiores fontes, e com melhor absorção, são os laticínios bovinos. Outros alimentos apresentam concentrações elevadas de Ca, mas com biodisponibilidade variável: os ricos em ácidos oxálico e fítico apresentariam uma menor absorção, enquanto que os ricos em carboidratos teriam uma absorção maior. Por apresentarem uma biodisponibilidade do Ca mais próxima da do leite bovino, o leite de outros animais, o de soja enriquecido e alguns vegetais, em quantidades adequadas, poderiam ser usados como alternativas a este.

Thermal decomposition and rehydration of strontium oxalate: morphological evolution

Undoped and Eu3+ doped monohydrate strontium oxalate samples were precipitated under ultrasound and conventional stirring and were heated at different temperatures. All samples were characterized by X-ray powder diffraction (XDR), infrared spectra (IR) and scanning electron microscopy (SEM). Monohydrate, dehydrate oxalates and carbonate particles are ellipsoids indicating a topotatic process. Particle size decrease is observed when ultrasound stirring and europium. doping are used and rehydration of strontium oxalate results in uniform hexagonal particle shape. An oxide and carbonate mixture is obtained from oxalates treated at 1050 degreesC and its suspension in water undergoes incomplete hydrolysis. The products from this incomplete hydrolysis present dendrite shape particles only when the former is precipitated under ultrasound stirring. In this process, surface energy is important for particle dispersion and ultrasound supplies activation energy to oxalate precursor. (C) 2001 Elsevier B.V. Ltd. All rights reserved.

High sinterability of Ca-PZT, synthesized by polymeric and partial oxalate process

This study includes Ca-PZT in the morphotropic phase boundary, MPB process combining the Pechini method, (ZT) and the Partial oxalate method (Ca-PZT) by obtaining single phase particles of ZT phase with a high specific surface area (similar to 110 m(2)/g at 550 degrees C) and narrow particle size distribution. Lead and calcium oxalates were precipitated onto the ZT particle surface and reacted to a solid state interface ZT/Ca-PZT/PbO-CaO. A deviation of a coexistence region from F-T- and F-R-phases to F-R-phase (Zr rich region) was observed. Strong surface area reduction occurs by Ca-PZT crystallization at about 700 degreesC, and demonstrated high sinterability (2.40 m(2)/g - 350 nm) with apparent densities near to 99.9%. Different processing methods did not demonstrate superior results. Studies of calcined powder shows a high sinterability of powder calcined 3 h at 700 degrees C and sintered 3 h at 1000 degreesC coming up to 99.8% of relative density. (C) 2001 Kluwer Academic Publishers.