Electrodeposition of mercury on gold from very dilute mercury(II) solution

Flameless atomic absorption spectrometry (flameless a.a.s.) was applied to study the state of mercury deposited on a gold plate electrode from very dilute mercury(II) solution by controlled-potential electrolysis. A stable monolayer is formed on the gold electrode by the electrolysis at a potential about 200 mV more positive than the reversible Nernst potential for the reduction of mercury(II) to mercury(0). After the monolayer formation, bulk mercury is deposited on the monolayer at the reversible potential and an adatom layer is also found. The difference of activation free energies between the evaporation of mercury from the monolayer and that from bulk mercury corresponds to the underpotential shift for the electrodeposition of mercury on the gold electrode.     

Ion chromatography of nitrite and carbonate in inorganic matrices on an octadecyl—poly(vinyl alcohol) gel column using acidic eluents

Low levels of carbonate and nitrite contained in inorganic matrices were determined by ion chromatography on an Asahipak ODP-50 poly(vinyl alcohol) gel-based reversed-phase column. With an acidic mobile phase, inorganic matrix anions and cations eluted near the void volume of the column, whereas carbonate and nitrite were retained and separated completely from the matrix ions. After the separation column, the peak response was enhanced using a cation-exchange hollow fibre and 25 mM sodium sulphate or alkaline enhancers. Sea-water samples can be applied directly for the determination of carbonate and added nitrite at ppm levels. The maximum sample volume that can be loaded on the column without peak deformation depended on the pH of the sample solution and the sulphuric acid concentration in the eluent. A 50 μl sea-water sample was applicable with a 2.5 mM acid eluent.     

Stereoselective adduct formation of α-acylcamphorato-copper(II) chelates with some chiral Lewis bases

The formation constants of the mono-adducts of α-acylcamphorato-copper(II) chelates such as (+)-Cu(facam)₂, (?)-Cu(facam)₂, (+)-Cu(hfbc)₂ and (?)-Cu(hfbc)₂ with some chiral Lewis bases were determined spectrophotometrically in benzene. In order to compare the adduct formation constants obtained with the (+)- and (?)-forms, some pairs of chiral Lewis bases such as 1-amino-2-propanol [(R)(?), (S)(+)], 1-(α-naphthyl)ethylamine [(R)(+), (S)(?)], α-phenyl ethylamine [(R)(+), (S)(?)] and also quinine and quinidine were examined as neutral ligands. Although not very pronounced, the effects of combinations obtained for (+)- or (?)-Cu(II) chelates and (+)- or (?)-ligands indicate that formation constants obtained by the formation of adducts with the ligands having different directions of the optical rotation seems to be superior to those with the same direction.     

Determination of glutamate-pyruvate transaminase activity in blood serum with a pyruvate oxidase/poly(vinyl chloride) membrane sensor

Pyruvate oxidase (E.C. 1.2.3.3.) is immobilized by adsorption on a wet PVC membrane. Glutamate-pyruvate transaminase activity (5–1600 IU l^?1) in serum is determined by a pyruvate oxidase sensor consisting of the immobilized pyruvate oxidase coupled to a platinum electrode for measuring hydrogen peroxide, after an l-alanine—α-ketoglutarate reaction. The assay requires ?60 s, and has a precision of 2–3%. Endogenous pyruvate should not interfere if measurements are made > 30 s after starting the reaction.     

C-H to N substitution dramatically alters the sequence-specific DNA alkylation, cytotoxicity, and expression of human cancer cell lines

We designed and synthesized sequence-specific alkylating conjugates 1 and 2, which selectively alkylate matched sequences at nanomolar concentrations. Conjugates 1 and 2 differ only in that the C-H is substituted by an N in the second ring, which precisely recognizes and effectively alkylates DNA according to the recognition rule of Py-Im polyamides. We investigated sequence-specific DNA alkylation, cytotoxicity in 39 human cancer cell lines, and the effect on expression levels in cancer cell lines by Py-Im conjugates 1 and 2. The COMPARE analysis of the mean graphs showed that conjugates 1 and 2 did not correlate well with each other (r = 0.65) despite having a common DNA alkylating mechanism (purine N3 alkylation). Array-based gene expression analysis demonstrated that there are several oppositely regulated genes. The results suggest the intriguing possibility that DNA alkylating agents recognizing longer base-pair sequences may provide a promising approach for developing new types of antigene agents.     

Dynamic covalent approach to [2]- and [3]roxtanes by utilizing a reversible thiol-disulfide interchange reaction

A dynamic covalent approach to disulfide-containing [2]- and [3]rotaxanes is described. Symmetrical dumbbell-shaped compounds with two secondary ammonium centers and a central located disulfide bond were synthesized as components of rotaxanes. The rotaxanes were synthesized from the dumbbell-shaped compounds and dibenzo-[24]crown-8 (DB24C8) with catalysis by benzenethiol. The yields of isolated rotaxanes reached about 90 % under optimized conditions. A kinetic study on the reaction forming [2]rotaxane 2 a and [3]rotaxane 3 a suggested a plausible reaction mechanism comprising several steps, including 1) initiation, 2) [2]rotaxane formation, and 3) [3]rotaxane formation. The whole reaction was found to be reversible in the presence of thiols, and thermodynamic control over product distribution was thus possible by varying the temperature, solvent, initial ratio of substrates, and concentration. The steric bulk of the end-capping groups had almost no influence on rotaxane yields, but the structure of the thiol was crucial for reaction rates. Amines and phosphines were also effective as catalysts. The structural characterization of the rotaxanes included an X-ray crystallographic study on [3]rotaxane 3 a.     

Phase behavior of sucrose monoalkanoate in a water-long-chain alcohol system

Phase diagram of a water/sucrose monododecanoate (SE)/hexanol system was determined at 30°C. Aqueous micellar, reverse micellar, normal hexagonal liquid crystalline, and lamellar liquid crystalline phases appear in the phase diagram. The change in interlayer spacing and interfacial section area of surfactant in the liquid crystalline phases was investigated by small-angle x-ray scattering. Upon addition of water, the section area and the radius of cylindrical aggregates are almost constant in a hexagonal liquid crystal, whereas the distance between each cylinder is separated on the water-SE axis. The interlayer spacing slightly decreases or is almost unchanged on the surfactant-hexanol axis, because alcohol molecules penetrate into the palisade of bilayers. Although the average section area decreases with increasing alcohol content, each section area of SE and alcohol molecules are kept constant. Since the interfacial section area of alcohol is less than the section area of hydrocarbon chain, the phase transition from lamellar liquid crystal to reverse micelle occurs in an alcohol-rich region.     

Influence of the Coordination of Donor Solvent Molecules to 1,4,7,10-Tetramethyl-1,4,7,10- tetraazacyclododecanenickel(II) and Analogous Nickel(II) Complexes on Their Steric Factors

Coordination equilibrium constants (K _NiS) of some donor solvent molecules to 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecanenickel(II) ([Ni(Me₄[12]aneN₄)]²⁺) were determined in nitrobenzene (a noncoordinating bulk solvent). The first (K _NiS1) and second stepwise coordination equilibrium constants (K _NiS2) for 1,4,7,10-tetraazacyclododecanenickel(II) ([Ni([12]aneN₄)]²⁺), 1,4,8,11-tetraazac yclotetradecane- nickel(II) ([Ni([14] aneN₄)]²⁺), 1,4,8,11-tetrathiacyclotetra-decanenickel(II) ([Ni([14]aneS₄)]²⁺) were also reinvestigated. The K _NiS values for [Ni(Me₄[12]aneN₄)]²⁺ were compared to those of [Ni([12]aneN₄)]²⁺, (1R,4S, 8R,11S)-1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecanenickel(II) (R,S,R,S-[Ni(Me₄[14]aneN₄)]²⁺), R,R,S,S-[Ni(Me₄[14]aneN₄)]²⁺, [Ni([14]aneN₄)]²⁺, and [Ni([14]aneS₄)]²⁺. Coordination of pyridine (Py), N,N,N′,N′-tetramethylurea (TMU), and N,N-dimethylacetamide (DMA) to [Ni(Me₄[12]aneN₄)]²⁺ was observed, although these donor solvent molecules did not coordinate to R,S,R,S-[Ni(Me₄[14]aneN₄)]²⁺. The K _NiS values for Py, TMU, and DMA are 7.9, 2.8, and 9.0 dm³⋅mol⁻¹, respectively. Some hydrogen-bonding waters were coordinated to R,S,R,S-[Ni(Me₄[14]aneN₄)]²⁺, but such waters did not coordinate to [Ni(Me₄[12] aneN₄)]²⁺. Also, the K _NiS2 values were larger than the corresponding K _NiS1 values for [Ni([14]aneS₄)]²⁺. Furthermore, the K _NiS1 values for [Ni([12]aneN₄)]²⁺ were the largest among these nickel(II) complex cations. The K _NiS, K _NiS1, and K _NiS2 values are discussed in terms of properties of the donor solvents and steric strains of these nickel(II) complex cations.     

Synthesis and photoinduced electron transfer processes of rotaxanes bearing [60]fullerene and zinc porphyrin: effects of interlocked structure and length of axle with porphyrins

Three rotaxanes, with axles with two zinc porphyrins (ZnPs) at both ends penetrating into a necklace pending a C60 moiety, were synthesized with varying interlocked structures and axle lengths. The intra-rotaxane photoinduced electron transfer processes between the spatially positioned C60 and ZnP in rotaxanes were investigated. Charge-separated (CS) states (ZnP*+, C60*-)rotaxane are formed via the excited singlet state of ZnP (1ZnP*) to the C60 moiety in solvents such as benzonitrile, THF, and toluene. The rate constants and quantum yields of charge separation via 1ZnP decrease with axle length, but they are insensitive to solvent polarity. When the axle becomes long, charge separation takes place via the excited triplet state of ZnP (3ZnP*). The lifetime of the CS state increases with axle length from 180 to 650 ns at room temperature. The small activation energies of charge recombination were evaluated by temperature dependence of electron-transfer rate constants, probably reflecting through-space electron transfer in the rotaxane structures.