Phase diagrams of urea inclusion compounds

The stearic acid-urea binary system exhibits an unusual phase diagram, which, on the one hand, indicates an incongruently melting inclusion compound and on the other hand a miscibility gap in the liquid phases. The peritectic point lies near the melting point of urea and the unstable congruent melting point of the inclusion compound coincides with the melting point of urea. In addition to the processing of the phase diagram, the pure inclusion compound was prepared and its DSC curve, FTIR spectrum and X-ray diffractogram were recorded.     

Mössbauer and NMR study of the N-d-gluconylglycine complex of dimethyltin(IV) and the ascorbic acid–chloride mixed complex of iron(II) in solutions fixed as nanosize droplets in solid matrixes

Combined NMR and Mössbauer investigations were performed on two coordination chemical models of biological interest: an aqueous solution of the N-d-gluconylglycine complex of dimethyltin(IV), and methanolic and aqueous solutions of the ascorbic acid–chloride mixed complex of iron(II). When these solutions were fixed as nanosize droplets in solid matrixes, significant changes occurred in both the structure and the composition of the coordination spheres of the central atoms in the complexes situated in the bulk positions with no direct connection to the surfaces of the holes in the matrix. The phenomenon was attributed to the significant decrease in solvent activity in the pores of the matrix due to the appreciable amount of surface-bound solvent in the system. The model mimics coordination chemical systems in cell tissues.     

Precision estimates produced by specially-designed ruggedness tests compared with those derived from collaborative trials,in relation to estimation of measurement uncertainty

We have compared the reproducibility precisions provided by collaborative trials with precisions obtained from ruggedness tests specially designed to try to simulate between-laboratory variation. We found that the ruggedness tests underestimated the reproducibility variability consistently for those analytical methods requiring empirical calibration. The ruggedness tests provided on average a precision merely comparable with repeatability precision. This finding has implications for the estimation of uncertainty.     

Synthese und Kristallstruktur von dimerem Dipyrazoldipyrazolato-platin(II), [Pt(pz)2(Hpz)2]2

Synthesis and Crystal Structure of Dimeric Dipyrazole Dipyrazolato Platinum(II), [Pt(pz)₂(Hpz)₂]₂ The dimeric complex [Pt(pz)₂(Hpz)₂]₂ (Hpz = pyrazole) is obtained in water from [Pt(Hpz)₄]²⁺ and OH^? or pz^?. The colorless compound is insoluble in water. It decomposes at 191°C to form Pt(pz)₂. [Pt(pz)₂(Hpz)₂]₂ crystallizes in the monoclinic space group C2/c with the lattice constants a = 2 165.5, b = 972,0, c = 1 648.4 pm, β = 123.09°, Z = 4. Each Pt²⁺ ion is coordinated in a square-planar arrangement by two Hpz molecules and two pz^? anions. The dimeric complex is formed by four symmetrical N? H? N bridges between the Hpz and pz^? ligands of both Pt atoms causing a complete charge delocalization between the ligands. The complex has the symmetry C₂ with two of the bridging H atoms lying on the symmetry axis. The Pt? N distances of 200 pm correspond to covalent single bonds. v(NH) is observed as broad absorption at 2 400 cm^?1.     

Synthesis of Bridged Bicyclic Molecules using Halocarbenes. Derivatives of bicyclo[4.2.1]nonane

The addition of dichlorocarbene (generated by the interaction of sodium methoxide and ethyl trichloroacetate) to bicyclo[3.2.1]oct-2-ene, its 3-chloro and exo-3,4-dichloro derivatives gives the exo 1 : 1 adducts in yields of 94, 89 and 48%. By suitable chemical reactions of these adducts, convenient syntheses of bicyclo[4.2.1]nona-2,4-diene and bicyclo[4.2.1]non-3-ene, together with their monochloro, dichloro and trichloro derivatives are obtained. Bicyclo[4.2.1]-nonan-3-one is also obtained from bicyclo[4.2.1]non-3-ene in a synthesis starting from the readily available 5-hydroxymethylnorborn-2-ene in an overall yield of 20%.     

Mössbauer spectroscopy of liquid SnCl4 solutions trapped in a rigid microemulsion

A rigid microemulsion was prepared containing submicroscopic droplets of liquid aqueous tin tetrachloride solution. Recoilless-ray resonance absorption (the Mössbauer effect] was achieved in this system, indicating that the organic dispersion medium of the microemulsion behaved as a carrier, enhancing the Debye-Waller factor for the quasiliquid phase of the system. The Mössbauer spectra reflected the presence of two types of tin(IV) in the cavities of the microemulsion: SnCl₄ species situated in the bulk solution and on the cavity wall, respectively.     

Gas chromatography of amino acids: Use of a fused-silica capillary column in the determination of plasma amino acids

A capillary chromatographic procedure using a fused silica column is described which can be used to quantitatively determine amino acids in plasma following the pre-chromatographic “clean-up” described in a recent paper [1]. In substituting this procedure for that involving a packed column, advantage has been taken of the greater resolving power to separate amino acids from background component peaks. In order to extend this advantage and provide a sound basis for quantitative analysis, the technique of cold on-column injection was employed. As a result, good precision of standard analysis was obtained with relative standard deviation (RSD) values for all amino acids of less than 4%. Application of the entire procedure to plasma samples yields RSD values of better than 10% for all amino acids with recoveries ranging from 72% to 104%. Simultaneous determination of plasma amino acid levels by gas chromatography (GC) using capillary columns and by classical ion exchange (CIE) showed reasonable agreement. Statistical evaluation showed no significant difference between twelve amino acids. Values for the remaining two, namely, phenylalanine and histidine are significantly different (p < 0.005). Comparison of the values obtained from GC capillary and packed columns reveals no significant difference between fourteen amino acids. Significant differences exist between results for phenylalanine and tyrosine (p < 0.001). It is concluded that there is good agreement between data obtained by GC capillary and CIE techniques and that differences between results for phenylalanine and histidine are method related.     

Carbonyl-carboxylato-ruthenium complexes incorporating diimine ligands and unexpected cyclometalation of carboxylate ligands

We report two new synthetic routes to the dinuclear Ru(I) complexes, [Ru(I)(2)(RCO(2))(CO)(4)(N( wedge )N)(2)](+) (N( wedge )N = 2,2'-bipyridine or 1,10-phenanthroline derivatives) that use RuCl(3).3H(2)O as a starting material. Direct addition of the bidentate diimine ligand to a methanolic solution of [Ru(CO)(2)Cl(2)](n) and sodium acetate yielded a mixture of [Ru(I)(2)(MeCO(2))(CO)(4)(N( wedge )N)(2)](+) (N( wedge )N = 4,4'-dmbpy, and 5,6-dmphen), and [Ru(II)(MeCO(2))(2)(CO)(2)(N( wedge )N)] (N( wedge )N = 4,4'-dmbpy and 5,5'-dmbpy). Single-crystal X-ray studies confirmed that the Ru(II) complexes had a trans-acetate-cis-carbonyl arrangement of the ligands. In contrast, the use of sodium benzoate resulted in the unexpected formation of a Ru-C bond producing ortho-cyclometalated complexes, [Ru(II)(O(2)CC(6)H(4))(CO)(2)(N( wedge )N)], where N( wedge )N = bpy or phen. A second approach used ligand exchange between a bidentate ligand (N( wedge )N) and the pyridine ligands of [Ru(I)(RCO(2))(CO)(2)(py)](2) to convert these neutral complexes into [Ru(I)(2)(RCO(2))(CO)(4)(N( wedge )N)(2)](+). This method, although it involved more steps, was applicable for a wider variety of diimine ligands (R = Me and N( wedge )N = 4,4'-dmbpy, 5,5'-dmbpy, 5,6-dmphen; R = Ph and N( wedge )N = bpy, phen, 5,6-dmphen).     

Synthesis,Mössbauer,and IP spectroscopic studies and thermal behavior of diorganotin(IV) complexes with carbohydrate ligands

A series of diethyltin(IV) complexes with carbohydrate ligands (aldoses, polyalcohols, sugar acids, sugar amines, and di- and trisaccharides] was prepared. The compositions of the complexes were determined by standard analytical methods. The results showed that complexes formed containing the diethyltin moiety and the carbohydrate ligand in 11 ratio. The IR spectra were consistent with the presence of tin—carbohydrate oxygen vibrations in the compounds. The comparison of experimental quadrupole splitting values with those calculated on the basis of the partial quadrupole splitting (PQS) concept revealed the compounds to be of three types: complexes in with the central tin(IV) atoms are present in purely trigonal bipyramidal surroundings, ones with the tin(IV) atoms present in purely octahedral surroundings, or ones with both octahedral and trigonal bipyramidal arrangements in approximately 11 ratio. The thermal decompositions showed that some of the complexes decompose via the reduction of tin(IV) to SnO as the final tin-containing product, some of them decompose without reduction, to give SnO₂, and some decompose to give indefinite final tin-containing products.