The liquid-crystalline properties of bis[N-[[4-[4-(alkoxy)benzoyloxy]2-hydroxyphenyl]methylene]alkanamino] complexes of Cu(II), Pd(II) and Ni(II). A general view

The thermotropic liquid-crystalline phase behaviour of a homologous set of bis[N-[[4-[4-(alkoxy)benzoyloxy]2-hydroxyphenyl]methylene]alkanamino] copper(II) complexes is examined. New data are reported and taken into account in addition to those previously reported in this Journal. The influence of alkoxy and alkanamine groups on the nature and stability of the mesophase is underlined. As a general trend, with some notable exception, smectic (C type) mesomorphism is favoured by longer alkoxy and alkanamine chains. Data concerning some Pd(II) and Ni(II) homologous complexes are also reported. The mesophase stability (nematic phase) is higher for palladium and nickel complexes than for the copper containing homologues.     

Conductance behavior of electrolytes in 1,3-dimethylethyleneurea and 1,3-dimethylpropyleneurea at 25°C

1,3-Dimethylethyleneurea (DMEU) and 1,3-dimethylpropyleneurea (DMPU) were investigated as electrolytic media for a number of alkali metal and triisoamylbutylammonium salts via conductivity measurements over a concentration range of 1–100×10^–4 M at 25°C. The data were analyzed by the Fuoss-Shedlovsky, Fuoss-Onsager, and expanded Pitts equations. The limiting equivalent conductivities were about 1.5 times greater in DMEU than in DMPU, which is exactly the ratio of the viscosities. From the Fuoss-Onsager analysis, all salts studied were found to be essentially unassociated in both solvents. From the expanded Pitts equation the extent of association was small, but within a salt series the equation indicated that association decreased in the order iodides, thiocyanates > perchlorate > tetraphenylborates. Neither solvent differentiated between sodium and potassium ion mobilities, indicating a type of solvation behavior different from that in acyclic urea solvents such as tetramethyl- and tetraethylurea.     

Titrations of weak acids in 1,1,3,3-tetramethylguanidine

The use of 1,1,3,3-tetramethylguamdine (TMG) as a medium for the titrations of weak acids has been investigated. The hydrogen electrode behaves reversibly in this solvent and can serve as an indicator electrode in titration reactions. The titrant was a o.1 M solution of tetrabutylammonium hydroxide in a 90-10% mixture of TMG and methanol. A hydrogen electrode dipping into a TMG solution saturated with benzoic acid served as reference electrode. Potentiometric titrations of a number of weak acids gave results accurate to at least ±0.5%. It was found that in most cases curcumin could be used as an end-point indicator with an accuracy comparable to that of the potentiometric titration.     

Ester Elimination: A General Solvent Dependent Non-Hydrolytic Route to Metal and Mixed-Metal Oxides

Molecular routes to metal oxides has become an area of intensescientific interest due to the technological relevance of thesematerials. Molecular routes are proving important as a result ofthe possibility to control the physical and chemical propertiesof the final materials.We have chosen to study non-hydrolytic methods, namely esterelimination reactions between two prototypical molecularprecursors metal alkoxides, M(OR)_n, and metal carboxylates, M(O₂CR)_n, to synthesize metal oxides: This method allows for the synthesis of pure metal oxides bycomplete elimination of the organic supporting ligands withconcomitant formation of M-O-M bridges.Furthermore, incomplete esterelimination can lead to isolation of molecular clusters asintermediates which can also be used as building blocks for theformation of metal oxides with controlled microstructure.Here we report a series of reactions between Sn and Si alkoxidesand carboxylates designed to gain further insight into thefactors governing ester elimination reactions. By choosingcompounds with varying coordination environments and stericaccessibility we have devised a set of criteria which shouldallow for successful ester elimination between metal alkoxide andcarboxylate compounds. Furthermore we have also shown theability of ester elimination derived molecular clusters withspecific microstructure to be used in the synthesis of bulkmaterials retaining the structural attributes of the precursor cluster.     

Lead speciation by HPLC-ICP-AES and HPLC-ICP-MS

Speciation of inorganic lead (Pb2+) and several trialkyllead species (trimethyllead chloride [TML], triethyllead chloride [TEL], and triphenyllead chloride [TPhL]) is investigated using high-performance liquid chromatography (HPLC) with detection by both inductively coupled plasma emission spectroscopy (ICP-AES), and inductively coupled plasma mass spectrometry (ICP-MS). Reversed-phase, ion-pairing, and ion-exchange HPLC modes are studied. Optimal chromatographic conditions for ICP-AES detection include a reversed-phase separation utilizing a step gradient from 10 to 70% methanol. However, the gradient has been found to destabilize the plasma when using ICP-MS detection. An isocratic separation with a 30% methanol mobile phase has been found to be the best compromise between plasma stability and chromatographic resolution. Detection limits using ICP-MS detection are 3 orders of magnitude improved over ICP-AES detection.     

Identification of Folding Intermediates of Streblin,The Most Stable Serine Protease: Biophysical Analysis

Streblin, a serine proteinase from plant Streblus asper, has been used to investigate the conformational changes induced by pH, temperature, and chaotropes. The near/far UV circular dichroism activities under fluorescence emission spectroscopy and 8-aniline-1-naphthalene sulfonate (ANS) binding have been carried out to understand the unfolding of the protein in the presence of denaturants. Spectroscopic studies reveal that streblin belongs to the α+β class of proteins and exhibits stability towards chemical denaturants, guanidine hydrochloride (GuHCl). The pH-induced transition of this protein is noncooperative for transition phases between pH 0.5 and 2.5 (midpoint, 1.5) and pH 2.5 and 10.0 (midpoint, 6.5). At pH 1.0 or lower, the protein unfolds to form acid-unfolded state, and for pH 7.5 and above, protein turns into an alkaline denatured state characterized by the absence of ANS binding. At pH 2.0 (1 M GuHCl), streblin exists in a partially unfolded state with characteristics of a molten globule state. The protein is found to exhibit strong and predominant ANS binding. In total, six different intermediate states has been identified to show protein folding pathways.     

ICP-MS for elemental speciation studies

The use of inductively coupled plasma mass spectrometry (ICP-MS) coupled with separation techniques for the purpose of elemental speciation has recently gained a lot of attention. Much of this is due to ever improving separation capabilities of Chromatographic techniques, the high sensitivity of ICP-MS, and the continuing development of better interface techniques. Additionally, there is a growing awareness of the need to monitor various species of an analyte, rather than just total analyte concentrations, due to their often varying natures. For the sake of learning from different elemental speciation approaches, this review brings together some selected types of elemental speciation which have been recently seen in literature. These include separations using various forms of liquid chromatography, such as reversed phase, reversed phase ion pairing, micelle, ion exchange, and size exclusion. Elemental speciation employing gas Chromatographie separations and supercritical fluid separations are discussed as well as elemental speciation using capillary electrophoresis.     

Liquid chromatography-inductively coupled plasma mass spectrometry.

The technique of coupling liquid chromatography to inductively plasma mass spectrometry (ICP-MS) is reviewed. A brief introduction to the ICP-MS instrument is given as well as methods to couple the two analytical instruments together. The various types of LC that have been used with ICP-MS detection are discussed and advantages over traditional methods of detection are highlighted, such as the improvements in sensitivity and selectivity. Several applications that have been described in the literature are reviewed. An outlook for the future of LC-ICP-MS, particularly with regard to elemental speciation is given.     

Sulpholane as a solvent for titration of barbiturates and sulpha drugs

Sulpholane (tetramethylenesulphone) has been used as the medium for non-aqueous potentiometric titration of barbiturates and sulpha drugs with tetrabutylammonium hydroxide. Recoveries for 0.1-0.3 mmole of barbituric acid, phenobarbital, amobarbital, barbital, secobarbital, sulphapyridine, sulphadiazine and sulphamerazine were generally in the range 99-101%. A glass-calomel electrode system was used: common acid-base indicators give no colour change in the medium used.