Optimization of performance and minimization of silicate interference in continuous flow phosphate analysis

Specific reaction conditions for automated continuous flow analysis of phosphate are optimized in regard to minimizing coating and silicate interference, while maintaining high sensitivity. Use of Sb in the reagent increases sensitivity and yields absorbances with little temperature dependence. Coating can be minimized by using a final solution at a pH>0.5. At final pH of 0.78 there is maximum interference from silicate in the sample. We recommend therefore as an optimal reaction condition with minimal silicate interference, the use of Sb, a final solution pH of 1.00, room temperature for the reaction and a [H(+)]/[Mo] ratio of 70. An equation is provided to correct silicate interference in high precision phosphate determination.     

The role of rigid unit modes in negative thermal expansion

The rigid unit mode (RUM) model provides a valuable computational method to investigate correlations of transverse thermal motions of atoms important in negative thermal expansion (NTE) materials. We report here detailed RUM calculations of ten framework oxide structures that have been studied for their negative (or ultra low) thermal expansion properties. The results negate any simple and direct correlation between presence or absence of RUMs in a structure and its NTE property. All the structures considered can be viewed as networks of polyhedral connected by corners only. All evidence supports the importance the transverse motion of the atoms at the corners, but NTE does not correlate well with the presence RUMs for the polyhedra.     

A potassium-selective electrode with solid internal contact

The performance characteristics of potassium-selective electrodes made with valinomycin membranes plasticized with dioctyl adipate or sebacate, and with a solid silver contact or an internal solution, have been critically examined. The choice of electrode depends on a number of factors, including the interfering ion(s) present. The electrodes can be used for determination of potassium in natural waters.     

Synthesis and some reactions of 3-cyanopyridine-2-thiones

New methods for the synthesis of 3-cyanopyridine-2-thiones by the reaction of -keto nitroles with sulfur and by condensation of chalcones or benzylideneacetone with cyanothioacetamide are given. The compounds obtained were used in various reactions for the preparation of alkylated products, disulfides, and condensed heterocycles, viz., thieno[2,3-b]pyridines and pyrido[2,3:2,3]thieno[4,5-d]-pyrimidines.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 377–382, March, 1981.     

5-[(p-Methyl-phenyl)azo]-8-aminoquinoline as a new reagent for trace determination of nickel by adsorptive cathodic stripping voltammetry

The synthesis of p-MPAQ and the electroanalytical chemical properties of the nickel(II)-p-MPAQ complex are reported in this paper. A sensitive adsorptive cathodic stripping procedure for trace nickel determination was developed. For a 3-min preconcentration time the detection limit is 3.0 × 10⁻¹¹M.     

Phage-display selection of a human single-chain fv antibody highly specific for melanoma and breast cancer cells using a chemoenzymatically synthesized G(M3)-carbohydrate antigen

Overexpression of the cell-surface glycosphingolipid G(M3) is associated with a number of different cancers, including those of the skin, colon, breast, and lung. Antibodies against the G(M3) epitope have potential application as therapeutic agents in the treatment of these cancers. We describe the chemoenzymatic synthesis of two G(M3)-derived reagents and their use in the panning of a phage-displayed human single-chain Fv (scFv) antibody library derived from the blood of cancer patients. Three scFv-phage clones, GM3A6, GM3A8, and GM3A15, were selected for recombinant expression and were characterized using BIAcore and flow cytometry. BIAcore measurements using the purified, soluble scFvs yielded dissociation constants (K(d)) ranging from 4.2 x 10(-7) to 2.1 x 10(-5) M. Flow cytometry was used to evaluate the ability of each scFv to discriminate between normal human cells (human dermal fibroblast, HDFa), melanoma cells (HMV-1, M21, and C-8161), and breast cancer cells (BCM-1, BCM-2, and BMS). GM3A6 displayed cross-reactivity with normal cells, as well as tumor cells, and GM3A15 possessed little or no binding activity toward any of the cell lines tested. However, GM3A8 bound to five of the six tumor cell lines and showed no measurable reactivity against the HDFa cells. Hence, we have demonstrated that a synthetic G(M3) panning reagent can be used to isolate a fully human scFv that is highly specific for native G(M3) on the surface of tumor cells. The result is a significant step toward effective immunotherapies for the treatment of cancer.     

Synthesis in the phenothiazine series

Quaternary salts of imidazo[4,5,1-k,l]phenothiazine were reduced with potassium borohydride to 1,2-dihydro-2-methylimidazo[4,5,1-k,l]phenothiazine, which was converted to 1,2 dihydro-2-methylimidazo[4,5,1-k,l]phenothiazine-1-thione and 1-methylamino-10-formylphenothiazine. The latter was hydrolyzed to 1-methylaminophenothiazine, which was also obtained by reduction of methyl phenothiazine-1-carbamate. The PMR and IR spectra of some of the derivatives are discussed.See [1] for communication XXXV.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 372–374, March, 1974.     

Determination of Arsenic by Electrothermal Atomic Absorption Spectrometry Using Arsine Preconcentration on Palladium-Containing Adsorbents

A procedure was developed for the preconcentration of arsine on palladium-containing adsorbents followed by the determination of arsenic by electrothermal atomic absorption spectrometry. Aqueous suspensions of the adsorbent were placed in a graphite furnace at the determination step. The selection of the adsorbent was substantiated; adsorption properties of palladium-containing adsorbents were studied to validate their modifying properties. The absolute and concentration limits of detection for arsenic were 28 pg and 12 ng/L, respectively (sample volume of 100 mL).     

Mössbauer study of (Bi,Pb)-2223 superconductors irradiated with 86Kr ions

⁵⁷Fe Mössbauer spectroscopy was used to study the effects of heavy ion irradiation on (Bi_0.93Pb_0.17)Sr_1.9Ca_2.05(Cu_1.02Fe_0.01)₃O_y superconductors. The Mössbauer spectra of the irradiated superconductor showed significant changes in the subspectra belonging to different Cu microenvironments into which Fe ions were substituted. The relative occurrence of Fe occupying the square pyramidal fivefold oxygen coordinated Cu sites decreased while Fe^{3 +} substituting the square planar fourfold oxygen coordinated Cu sites increased upon bombardment by 246 MeV ⁸⁶Kr⁸⁺ ions. This observation was interpreted on the basis of partial replacement of the apical oxygen atoms in the square pyramids surrounding one of the Cu sites. Such oxygen vacancies create additional square planar coordination sites for Cu. These results also support the covalent character of Cu-O bonds in the superconducting layer as well as the ionic character of bond of apical oxygen to Cu.     

Mechanism of formation of organic carbonates from aliphatic alcohols and carbon dioxide under mild conditions promoted by carbodiimides. DFT calculation and experimental study

Dicyclohexylcarbodiimide (CyN=C=NCy, DCC) promotes the facile formation of organic carbonates from aliphatic alcohols and carbon dioxide at temperatures as low as 310 K and moderate pressure of CO2 (from 0.1 MPa) with an acceptable rate. The conversion yield of DCC is quantitative, and the reaction has a very high selectivity toward carbonates at 330 K; increasing the temperature increases the conversion rate, but lowers the selectivity. A detailed study has allowed us to isolate or identify the intermediates formed in the reaction of an alcohol with DCC in the presence or absence of carbon dioxide. The first step is the addition of alcohol to the cumulene (a known reaction) with formation of an O-alkyl isourea [RHNC(OR')=NR] that may interact with a second alcohol molecule via H-bond (a reaction never described thus far). Such an adduct can be detected by NMR. In alcohol, in absence of CO2, it converts into a carbamate and a secondary amine, while in the presence of CO2, the dialkyl carbonate, (RO)2CO, is formed together with urea [CyHN-CO-NHCy]. The reaction has been tested with various aliphatic alcohols such as methanol, ethanol, and allyl alcohol. It results in being a convenient route to the synthesis of diallyl carbonate, in particular. O-Methyl-N,N'-dicyclohexyl isourea also reacts with phenol in the presence of CO2 to directly afford for the very first time a mixed aliphatic-aromatic carbonate, (MeO)(PhO)CO. A DFT study has allowed us to estimate the energy of each intermediate and the relevant kinetic barriers in the described reactions, providing reasonable mechanistic details. Calculated data match very well the experimental results. The driving force of the reaction is the conversion of carbodiimide into the relevant urea, which is some 35 kcal/mol downhill with respect to the parent compound. The best operative conditions have been defined for achieving a quantitative yield of carbonate from carbodiimide. The role of temperature, pressure, and catalysts (Lewis acids and bases) has been established. As the urea can be reconverted into DCC, the reaction described in this article may further be developed for application to the synthesis of organic carbonates under selective and mild conditions.