TOSAR – A Topological Method for the Representation of Synthetic and Analytical Relations of Concepts

In mechanized systems used for searching in literature stores there is a steadily growing necessity not only to be able to formulate concepts as a search condition but also the characteristic connections under which these concepts appear in the inquiry. In this way the precision of the mechanized literature search is considerably increased. TOSAR has been developed in order to improve computerized literature searching in this respect.     

A new route to achiral and chiral 1,2-bis(phosphino)ethanes, 1-arsino-2-phosphinoethanes, and 1,3-bis(phosphino)propanes and the molecular structure and catalytic activity of some rhodium(I) complexes derived thereof

A series of unsymmetrical 1,2-bis(phosphino)ethanes R(2)PCH(2)CH(2)PR'(2) and 1-arsino-2-phosphinoethanes R(2)AsCH(2)CH(2)PR'(2) mainly with bulky substituents R and R' were prepared from the cyclic sulfate by stepwise cleavage of the carbon-oxygen bonds by LiPR(2) and LiPR'(2) or LiAsR(2) and LiPR'(2), respectively. Analogously, racemic mixtures of R(2)PCH(2)CH(Me)PPh(2)(R =iPr, Cy ) as well as the enantiomers (R)-, (R)- and (R)-tBu(2)PCH(2)CH(Me)PPh(2)(R)- were obtained from the corresponding unsymmetrical cyclic sulfates and (S)-. On a similar route, the racemates of the 1,3-bis(phosphino)propanes R(2)PCH(2)CH(2)CH(Me)PPh(2)(R =iPr, tBu ), optically pure (R)- and (S,S)-iPr(2)PCH(Me)CH(2)CH(Me)PPh(2)(S,S)- were prepared. The reaction of [[RhCl([small eta](4)-C(8)H(12))](2)] with chelating ligands L-L, where L-L is R(2)PCH(2)P(men)(2)(R =iPr, Ph; men =(1S,2R,5S)-menthyl), Cy(2)AsCH(2)P(men)(2), or (R)-, (R)-, (R)-, (R)- and (S,S)-, in the presence of AgPF(6), gave the complexes [Rh(eta(4)-C(8)H(12))(L-L)]PF(6) which were used as pre-catalysts in the hydrogenation of the methyl ester of alpha-acetamidocinnamic acid (ACM). Depending on L-L, the solvent, the temperature and the pressure of H(2), optical yields of up to 69% ee were achieved. For two of the rhodium complexes, and, the molecular structures were determined by X-ray crystallography.     

Mesomorphism,isomerization, and dynamics in a new series of pyramidic liquid crystals

Nona-alkanoyloxy tribenzocyclononene (CTV-n, where n is the number of carbons in the side chains) were prepared for n = 2 to 14. The homologues of this series appear in two stable isomeric forms, rigid crown and flexible saddle. We report on their isomerization equilibria and dynamics in solution and on their mesomorphic properties in the neat state. The crown-saddle equilibrium and interconversion kinetics of the CTV-8 isomers were studied in dimethyl formamide solutions using high-resolution (1)H NMR in the temperature range from 50 to 130 degrees C. At lower temperatures, the isomerization is too slow to measure. In this range the equilibrium saddle fraction increases from approximately 0.40 to approximately 0.65, whereas the isomerization rate increases from approximately 10(-)(4) to approximately 1 s(-)(1). The saddle isomer undergoes fast pseudorotation at room temperature, but below about -50 degrees C, it becomes slow enough to affect the NMR line width. The rate parameters for this process were estimated from the carbon-13 spectra in methylene chloride solutions to be, k(p)(-100 degrees C) approximately 1.7 x 10(3) s(-)(1) and E(a) approximately 9.6 kJ/mol. The slow crown-saddle isomerization at room temperature (half-life of about one year) allows quantitative separation (by chromatography) of the two isomers and their separate investigation. When the alkanoyloxy side chains are sufficiently long both isomers are mesogenic (n >or= 4 for the saddle and n >or= 5 for the crown), exhibiting hexagonal columnar mesophases. The structure, dynamics, and mesomorphic properties of these mesophase were investigated by X-ray diffraction, optical polarizing microscopy, differential scanning calorimetry, and NMR. The lattice parameters of the crown and saddle mesophases of corresponding homologues are almost identical and increase monotonically with increasing length of the side chains. The clearing temperatures of the saddle isomers are consistently lower than those of the corresponding crowns. Within each series, the clearing temperatures are almost independent of the length of the side chains (156 to 170 degrees C for the crown and 115 to 148 degrees C for the saddle). The thermal and kinetic properties of the neat compounds lead to peculiar phase sequences, as observed in the polarizing microscope and in the DSC thermogram, involving repeated, back and forth, interconversion between the two isomers. Carbon-13 MAS NMR measurements of the crown and saddle mesophases of several homologues were carried out. The spectra of the crown mesophase exhibit dynamic features consistent with planar 3-fold molecular jumps about the column axes. A quantitative analysis for the CTV-8 crown homologue yielded the following Arrhenius parameters, A = 3.1 x 10(22)s(-)(1) and E(a) = 130.1kJ/mol. These unusually high values suggest that the barrier to the jump process is temperature dependent, decreasing with increasing temperature. The rate of this 3-fold jump process is slower for the lower homologues and faster for the higher ones. In contrast, the saddle isomers in the mesophase do not show dynamic effects in their carbon-13 MAS spectra. They do not undergo pseudorotation, and it appears that the molecules remain locked within the columns in a saddle conformation, up to the clearing temperature. However, on (super-)cooling to room temperature and below, selective line broadening is observed in their carbon-13 MAS spectra. This suggests that the saddle conformation is twisted in the mesophase and undergoes fast high-amplitude jumps between the twisted forms. On cooling, these high-amplitude librations freeze out to give an orientationally disordered state. On a very long time scale (of the order of days at 100 degrees C), the saddle mesophase transforms into that of the crown, apparently by sublimation.     

Synthesis and properties of niobia films derived from niobium pentaethoxide

The hydrolysis of niobium pentaethoxide precursor in the presence of triethylamine (TEA) is discussed. Three precursors with TEA/Nb(OEt)₅ mole ratios of 0.25, 0.4 and 0.8 were prepared. Niobia colloids with different appearance were obtained after autoclaving the above precursors at 250°C during 12 h. The surface roughness and microstructure of niobia films prepared with the colloids by spread coating method are strongly dependent on the TEA/Nb(OEt)₅ mole ratio. At a value of 0.4 TEA/Nb(OEt)₅ mole ratio, a niobia film with large surface roughness can be achieved. It is opaque and mechanically stable and has differently ordered needle microstructure. The crystalline structure and photoelectrochemical property of niobia film with the largest surface roughness were examined. The effect of CO₂ gas bubbling, reflux and addition of 2-methoxyethanol on the hydrolysis of Nb(OEt)₅ and the nature of the Nb₂O₅ films is also discussed.     

Global activities in the world of reference materials including the needs of developing countries

Proceedings of previous BERM meetings have been used to assess emerging trends in the development of RMs to meet AQC requirements of clinical, food, nutrition, and environmental health areas. BRM-1 reflected a strong need to initiate and expand RM activities for certifying organic nutrients in foods. BRM-2 highlighted the distinction between primary (certified) and secondary (e.g. check samples for proficiency testing) RMs¹. BRM-3 identified the need for producing different levels of an analyte in a given matrix (spiked standards) to address matrix related measurement problems in foods. BERM-4 highlighted the need for a global vision in dealing with standards, illustrated by the activities of GESREM. Also, the logistics required for setting up intercomparison programs related to food safety monitoring programs were outlined. BERM-5 presented the changing outlook of the AOAC International in recognizing the usefulness of incorporating RMs for use in conjunction with their methods validation protocol. BERM-6 brought to the forefront the concern for traceability of chemical measurements to internationally recognized standards. BERM-7 recognized the need for multidisciplinary approaches for preparing certain types of CRMs, partly in response to the measurement needs arising from governmental regulations dealing with food safety and environmental health criteria. Finally, BERM symposia have promoted a meaningful dialogue on the RM needs of African, Asian and South American countries and provided the developing countries opportunities to discuss their problems with the international analytical community. The issue of health safety is involved in movement of foodstuffs between countries, and therefore, international efforts as voiced by the World Health Organization to provide guidance and assistance in AQC matters to the needy countries deserve consideration.     

Thermochemical Investigations of Calcium Carbonate Phase Transitions I. Thermal activated vaterite—calcite transition

The vaterite—calcite transition above 630 K has been studied by isothermal and non-isothermal differential scanning calorimetry. Vaterite samples prepared under different conditions were investigated. The transition temperature is strongly dependent on the sample preparation. The observed transition enthalpy H_tr is nearly equal for different samples and experimental conditions. From 28 measurements a value of H_tr–(3.12±0.11) kJ mol^–1 was obtained. The activation energy for the polymorphic transition was calculated from the Arrhenius plot and by use of isoconversional methods, as a function of the degree of conversion. The influence of the kinetic model distortion and experimental uncertainties on the obtained data was discussed. The actual value of the activation energy was assessed at E_a=(250±10) kJ mol^–1 for nearly all examined samples. Functions, corresponded to the model mechanism of nuclei formation and growth, provide the unambiguous consideration of the transition kinetic for the investigated vaterite samples. Differences in the dynamic behaviour of several samples at the transition are established.This revised version was published online in November 2005 with corrections to the Cover Date.     

Notiz über Li2PdO2

Note on Li₂PdO₂ For the first time we prepared ruby-red single crystals of Li₂PdO₂ by reaction with the wall 3 Na₂O + Li₂O₂ + ?Tb₄O₇”?(+ Pd) = 3 Na₂TbO₃ + Li₂PdO₂ + ?TbO₂”?, Pd-tube, 1100°C, 7 d. Single crystal data confirm the Li₂CuO₂-type of structure [a = 375.34(5), b = 298.18(4), c = 931.58(10) pm; spacegroup Immm; d_x = 4.85 g · cm^?3; 144 I₀(hkl); R = 3.54%, Rw = 3.19%; MoKα ; four-circle diffractometer Philips PW 1100] and reveal clearly different parameters compared with those deduced by powder data. The Madelung Part of Lattice Energy, MAPLE, corresponds now to the sum of the MAPLE values of the binary oxides.     

Carbonyl‐Komplexe von Chrom,Molybdän und Wolfram mit Isocyanacetat. Reaktionen am koordinierten Isocyanacetat. Stabilisierung von Isocyanessigsäure und Isocyanacetylchlorid am Metall. Isocyanopeptide [1]

Carbonyl Complexes of Chromium, Molybdenum and Tungsten with Isocyano Acetate. Reactions of Coordinated Isocyanoacetate. Stabilization of Isocyanoacetic Acid and Isocyanoacetyl Chloride at the Metal Atom. Isocyanopeptides The reactions of [(OC)₅MCNCH₂CO₂Et] (M = Cr, W) with Na[N(SiMe₃)₂] or with KOH afford the isocyanoacetate complexes [(OC)₅MCNCH₂CO₂]^? ( 1,2 ). Similarly, the complex [(OC)₃Mo(CNCH₂CO₂^?Li⁺)₃] ( 4 ) was obtained from [(OC)₃Mo(CNCH₂CO₂Et)₃] ( 3 ) and LiOH. Protonation of 1 and 2 affords the sublimable isocyanoacetic acid complexes [(OC)₅MCNCH₂CO₂H] ( 5 , 6 ; M = Cr, W) in which the functional isocyanide is stabilized at the metal atom. Reactions of [(OC)₅WCNCH₂CO₂^?K⁺] and of [(OC)₃Mo(CNCH₂CO₂^?Li⁺)₃] with oxalyl dichloride give the isocyanoacetyl chloride compounds [(OC)₅WCNCH₂COCl] ( 9 ) (sublimable) and [(OC)₃Mo(CNCH₂COCl)₃] ( 10 ); the latter ( 10 ) was not isolated. Complexes 9 and 10 were reacted in situ with β‐alanine, glycine, phenylalanine and methionine esters as well as the peptide esters GlyGlyOEt, PhePheOMe, Phe‐β‐AlaOMe, and GlyGlyGlyOMe to form the isocyanoacetyl amino acid esters ( 11 ‐ 14 ) and the isocyanoacetyl peptide esters ( 15 ‐ 18 ) which are stabilized at the molybdenum atom.     

Stabilization of p-block organoelement terminal hydroxides, thiols, and selenols requires newer synthetic strategies

Metal hydroxides represent a very interesting and highly useful class of compounds that have been known to chemists for a very long time. While alkali and alkaline earth metal hydroxides (s‐block) are commonplace chemicals in terms of their abundance and their use in a chemical laboratory as bases, the interest in Brønsted acidic molecular terminal hydroxides of p‐block elements, such as aluminum and silicon, has been of recent origin, with respect to the variety of applications these compounds can offer both in materials science and catalysis. Moreover, these systems are environmentally friendly, relative to the metal halides, owing to their ‐OH functionality (resembling that of water). Design and conceptualization of the corresponding terminal thiols, selenols, and tellurols (M? SH, M? SeH, and M? TeH) offer even more challenging problems to synthetic inorganic chemists. This concept summarizes some of the recent strategies developed to stabilize these otherwise very unstable species. The successful preparation of a number of silicon trihydroxides a few years back resulted in the generation of several model compounds for metal–silicates. The recent synthesis of unusual aluminum compounds such as RAl(OH)₂, RAl(SH)₂, and RAl(SeH)₂ with terminal EH (E=O, Se, or Se) groups is likely to change the ways in which some of the well‐known catalytic conversions are being carried out. The need for very flexible and innovative synthetic strategies to achieve these unusual compounds is emphasized in this concept.     

Recent applications of the ring-oven technique : A brief review

The ring-oven technique is a special type of spot analysis. In this review, papers published since 1976 are discussed. The aspects dealt with include developments in the technique and its use, the identification and determination of inorganic ions, organic substances, enzymatic analysis, applications to air and water samples, and combinations with other techniques.