Theory and applications of ion-selective electrodes Part III

This review of ion-selective electrodes is arranged in the same way as Parts I and II. The continuous growth of the whole subject should be noted. Theory has particularly progressed through mechanistic studies. Among new types of electrodes, ISFET systems have become important. Among new applications of both solid and liquid membrane electrodes, the fluoride electrode still predominates, closely followed by potassium electrodes. In the field of biological and medical applications, the steady growth is significant. More than 800 papers published between mid-1976 and the end of 1978 are mentioned in the review.     

Studies on antiulcer drugs. III. Synthesis and antiulcer activities of imidazo[1,2-a]pyridinylethylbenzoxazoles and related compounds. A novel class of histamine H2-receptor antagonists.

A series of imidazo[1,2-a]pyridinylalkylbenzoxazole derivatives was synthesized and tested for histamine H2-receptor antagonist, gastric antisecretory and antiulcer activities. Some of 2-amino-6-[2-(imidazo[1,2-a]pyridin-2-yl)ethyl]benzoxazole derivatives were found to have good pharmacological activities. Among them, 2-amino-6-[2-(7-methoxy-3-methylimidazo[1,2-a]pyridin-2-yl)ethyl] benzoxazole (II-11) and 2-acetamido-6-[2-(7-methylimidazo[1,2-a]pyridin-2-yl)ethyl] benzoxazole (II-38) showed potent antisecretory and cytoprotective activity. The structure-activity relationships of these compounds are discussed.     

Detection of NAD+-dependent alcohol dehydrogenase activities in YR-1 strain of Mucor circinelloides, a potential bioremediator of petroleum contaminated soils

Different soluble NAD⁺-dependent alcohol dehydrogenase (ADH) isozymes were detected in cell-free homogenates from aerobically grown mycelia of YR-1 strain of Mucor circinelloides isolated from petroleumcontaminated soil samples. Depending on the carbon source present in the growth media, multiple NAD⁺-dependent ADHs were detected when hexadecane or decane was used as the sole carbon source in the culture media. ADH activities from aerobically or anaerobically grown mycelium or yeast cells, respectively, were detected when growth medium with glucose added was the sole carbon source; the enzyme activity exhibited optimum pH for the oxidation of different alcohols (methanol, ethanol, and hexadecanol) similar to that of the corresponding aldehyde (≈7.0). Zymogram analysis conducted with partially purified fractions of extracts from aerobic mycelium or anaerobic yeast cells of the YR-1 strain grown in glucose as the sole carbon source indicated the presence of a single NAD⁺-dependent ADH enzyme in each case, and the activity level was higher in the yeast cells. ADH enzyme from mycelium grown in different carbon sources showed high activity using ethanol as substrate, although higher activity was displayed when the cells were grown in hexadecane as the sole carbon source. Zymogram analysis with these extracts showed that this particular strain of M. circinelloides has four different isozymes with ADH activity and, interestingly, one of them, ADH4, was identified also as phenanthrene-diol-dehydrogenase, an enzyme that possibly participates in the aromatic hydrocarbon biodegradation pathway.     

Surface-functionalized latex particles as controlling agents for the mineralization of zinc oxide in aqueous medium

Polystyrene latex particles modified at the surface with different hydrophilic functional groups were prepared by miniemulsion polymerization and used as controlling agents in the crystallization of zinc oxide from aqueous medium. The effects of the chemical nature of the surface functionalization and the latex concentration on the crystal growth, morphology, and crystalline structure of the resulting zinc oxide were analyzed. Micro- and submicrosized crystals with a broad variety of morphologies depending on the functionalization were obtained. Among the different latexes studied, the acrylic-acid-derived particles were shown to be a convenient system for further quantitative investigations. In this case, as the additive concentration increases, the length-to-width ratio (aspect ratio) of the crystals decreases systematically. Preferential adsorption of the latex particles onto the fast-growing faces {001} of ZnO is assumed to follow a Langmuir-type isotherm, and interaction of the adsorbed particles with the growth centers will reduce the growth rate in [001]. This leads to a quantitative relationship linking the aspect ratio to the latex concentration at constant diameter and surface chemistry of the latex. The dependence of the aspect ratio on charge density of the latex can also be modeled by an algorithm in which attractive forces between the latex particle and the ZnO surface are balanced against repulsive forces of an osmotic nature. The latter are associated with the confined volume between the crystal and latex particle surfaces.     

A solvent-controlled switch of manganese complex assemblies with a beta-diketonate-based ligand

The coordination properties of the new polynucleating ligand H(3)L1 (1,3-bis(3-oxo-3-phenylpropionyl)-2-hydroxy-5-methylbenzene) with Mn(II/III) are described. Depending on the solvent used, the reaction of H(3)L1 with Mn(OAc)(2) yields either of the two new multinuclear assemblies [Mn(2)(HL1)(2)(py)(4)] (1) and [Mn(3)(HL1)(3)] (2), as revealed by X-ray crystallography. The structure of 2 is remarkable in that it shows a unique asymmetric triple-stranded helicate. Complexes 1 and 2 can be interconverted by controlling the solvent of the reaction system, and therefore, this ensemble constitutes an interesting externally addressable switch. In the presence of Mn(III)/pyridine, partial degradation of H(3)L1 occurs via oxidative cleavage, and the new complex [Mn(2)(L2)(2)(py)(4)] (3) is formed. The crystal structure of this complex has shown the fully deprotonated form of the new donor H(3)L2 (3-(3-oxo-3-phenylpropionyl)-5-methylsalicylic acid). From the same reaction, the Mn(II) complex 1 is also obtained. A rational synthesis of H(3)L2 is reported, and this has been used to prepare 3 in high yields, directly from its components. Variable-temperature magnetic susceptibility (chi(m)) measurements were performed on complexes 1-3 under a magnetic field of 1 kG. The data for each complex were fit to the appropriate chi(m) vs T theoretical equation, respectively. In 1, the Mn(II) ions are uncoupled, with g = 2.01. The data from 2 were fit by assuming the presence of an exchange coupled Mn(II)...Mn(II) pair next to a magnetically isolated Mn(II) center. The fit gave J = -2.75 cm(-1), g(12) = 1.97, and g(3) = 1.92, respectively. In 3, two models fit the experimental data. In the most satisfactory, the Mn(III) ions are coupled antiferromagnetically with J = -1.48 cm(-1) and g = 1.98 and a term for weak ferromagnetic intermolecular exchange is included with zJ' = 0.39 cm(-1). The other model contemplates the presence of two uncoupled zero field split Mn(III) ions.     

Magnetic and spectral properties of the coligand isomer pair: Cu{N(CN)2}2(pyrazole)2 and Cu{pyrazole · N(CN)2}2

Summary New coligand isomers of composition Cu{N(CN)₂}₂(pz)₂ and Cu{pz · N(CN)₂}₂ (pz = pyrazole) were prepared and studied by measuring their magnetic susceptibilities up to 4.2K and by aid of their e.s.r., ligand field and i.r. spectra. The susceptibility data have been analysed with various models for the exchange-coupled copper(II) polymers. It is shown that the resultant exchange coupling is ferromagnetic for Cu{N(CN)₂}₂(pz)₂ (J 1.1 - 1.4 cm^–1) but antiferromagnetic for Cu{pz · N(CN)₂}₂ (J –0.4 cm^–1). A polymeric chain structure is proposed for Cu{N(CN)₂}₂(pz)₂ havingpseudo-octahedrally coordinated copper(II) and CN-bridging dicyanamide ligands. Its coligand isomer contains anionic chelate ligands, formed by nucleophilic addition between N(CN)₂ and pz in the copper(II) coordination sphere, and giving with this central atom a square-planar system. Definite, but slight axial interaction takes place between these structure units.     

Synthesis of polyfunctionalized furans from 3-acetyl-1-aryl-2-pentene-1,4-diones

The BF₃-catalyzed cyclization of 3-acetyl-1-aryl-2-pentene-1,4-diones 1a-e in the presence of water in boiling tetrahydrofuran gave bis(3-acetyl-5-aryl-2-furyl)methanes 2a-e in 26-79% yields along with a small amount of 3-acetyl-5-aryl-2-methylfurans 3a-e. The exact structure of 2a was determined by X-ray crystallography. The use of a half volume of the solvent for the reaction of 1a resulted in the formation of 2,4-bis(3-acetyl-5-phenyl-2-furfuryl)-3-acetyl-5-phenylfuran (4) together with 2a and 3a. A similar reaction of 1a was carried out in the presence of 3-acetyl-5-(4-methylphenyl)-2-methylfuran (3d) to afford 4-(3-acetyl-5-phenyl-2-furfuryl)-3-acetyl-5-(4-methylphenyl)-2-methylfuran (5) in 49% yield. The BF₃-catalyzed reaction of 1a with 2,4-pentanedione in dry tetrahydrofuran at 23°C gave 3-(3-acetyl-5-phenyl-2-furfuryl)-4-hydroxy-3-penten-2-one (6a) and 3-(3-acetyl-2-methyl-4-phenyl-5-furyl)-4-hydroxy-3-penten-2-one (7a) in 66 and 24% yields, respectively. The product distribution depended on the reaction temperature. A similar reaction of 1b-e also yielded the corresponding trisubstituted furans 6b-e and tetrasubstituted furans 7b-e in good yields. These results suggested the presence of the furfuryl carbocation intermediate A during the reaction. The one-pot synthesis of 6a and 7a was also achieved by a similar reaction using phenylglyoxal. The deoxygenation of 1a with triphenylphosphine gave 3a in 88% yield, while 1a was treated with concentrated hydrochloric acid to yield 3-acetyl-2-chloromethyl-5-phenylfuran (8) which was quantitatively transformed in ethanol into 3-acetyl-2-ethoxymethyl-5-phenylfuran (9) and in water into 3-acetyl-5-phenylfurfuryl alcohol (10), respectively. In addition, the Diels-Alder reaction of cyclopantadiene with 1a gave the corresponding [4+2] cycloaddition products 11 and 12.     

Chromatographic analysis of phenethylamine-antihistamine combinations using C8, C18 or cyano columns and micellar sodium dodecyl sulfate-pentanol mixtures

The chromatographic behaviour of binary and ternary mixtures of several phenethylamines (phenylephrine, phenylpropanolamine, ephedrine, pseudoephedrine and methoxyphenamine) and antihistamines (pheniramine, carbinoxamine, doxylamine, chlorpheniramine, dexchlorpheniramine, dexbrompheniramine, diphenhydramine, tripolidine, azatadine and phenyltoloxamine), found in cough-cold pharmaceutical preparations, was studied using C8, C18 and cyano columns, micellar mobile phases of sodium dodecyl sulfate (SDS) and pentanol and UV detection. Using a C8 column and mobile phases of 0.05 mol l-1 SDS-6% v/v pentanol or 0.15 mol l-1 SDS-2% v/v pentanol at pH 7, more than 30 different phenethylamine-antihistamine combinations can be resolved in < 15 min. Intra- and inter-day repeatabilities and reproducibilities evaluated at three different drug concentrations (0.5, 5 and 25 micrograms ml-1, n = 10) were below 1.6, 2.5 and 2.4%, respectively. The drug amounts found in 18 formulations agreed with those declared by the manufacturers within the tolerance limits, and with those obtained using a mobile phase of 55% v/v methanol at pH 7. No interference was observed from other accompanying drugs such as acetylsalicylic acid, ascorbic acid, betamethasone, bromhexine, caffeine, codeine, dextromethorphan, paracetamol, prednisolone, salicylamide and tartrazine. The proposed procedure has the advantage over the conventional aqueous-organic procedure of using a small amount of organic solvent, which is highly retained in the SDS solution. The efficiencies are also greater. On the other hand, in the micellar system, the retentions of phenethylamines and antihistamines are similar, although the compounds can be easily resolved. In contrast, using the methanol-water mobile phase, the phenethylamines are weakly retained, whereas the antihistamines usually show a high retention.