Bemerkungen zur colorimetrischen Bestimmung von Vanadium mit Phosphorwolframs?ure

Zusammenfassung Die colorimetrische Bestimmungsmethode von Vanadium mit Phosphorwolframsäure wurde in bezug auf den Einfluß der Reagenskonzentrationen untersucht. Außerdem wurde die Bestimmungsmöglichkeit in Gegenwart von Eisen geprüft. Es zeigte sich, daß die Konzentrationen an Phosphorsäure und Wolframat in weiten Grenzen geändert werden können, ohne die Bestimmungsgenauigkeit zu beeinflussen. Zu große Mengen Salpetersäure bewirken negative Fehler, indem die Extinktionen mit zunehmender HNO₃-Konzentration linear abnehmen. Nach der angegebenen Vorschrift kann Vanadium in Gegenwart von bis zu 150 mg Eisen(III)-ionen in einem Volumen von 25 ml bestimmt werden.     

Optimization of stepwise gradient elution in reversed-phase chromatography

Summary Equations describing multi-step gradient elution with a mobile phase of constant composition in each step were derived. These equations useful for calculating the retention volumes in both gradient HPLC and TLC were derived on the basis of the relationship between the isocratic capacity factor and the volume fraction of the organic modifier. The validity of the equations was experimentally verified in a LiChrosorbRP-18-water/methanol system for 11 methyl- and chlorobenzenes and phenols. A satisfactory agreement between the theoretical and experimental k′ values was found.     

Synthesis and structure of a new rhodium(I) complex [Rh{P(OPh)3}3CN]

Summary The [Rh(acac){P(OPh)₃)}₂] complex (Hacac = 2,4-pentadione) reacts in solution with gaseous HCN in the presence of P(OPh)₃ to give [Rh{P(OPh)₃}₃CN]. Structural investigations of this complex including its³¹P n.m.r. spectra are reported.     

Thiyl radical interaction with pyrimidine C5-C6 double bond

Addition and elimination interaction of thiyl radicals with the C5-C6 double bond in pyrimidines was studied by the pulse radiolysis technique in aqueous solution with the use of different monitoring systems. For this purpose, p-thiocresol, cysteamine hydrochloride, and mercaptoethanol were used. The rate constants of addition and elimination of thiyl radicals were determined by applying the modified version of ACUCHEM (computer program for modeling complex reaction systems). Aliphatic thiyl radicals add to the pyrimidine C5-C6 double bond with k = 1.0-3.0 x 10(7) dm3 mol(-1) s(-1), whereas elimination takes place with k = 0.7-2.0 x 10(5) s(-1). Quantum chemical calculations at the B3LYP/6-31G(d)/PCM level show that the addition should occur at the C6 position of the pyrimidine ring and that the energy of interaction between thiyl radicals and the pyrimidine double bond C5-C6 is low.     

Thin-Layer Chromatography with an Isolated Support and Forced Flow of the Mobile Phase

JPC – Journal of Planar Chromatography – Modern TLC -     

Amino-Modified Silicate Xerogels Complexed with Cu(II) as Catalyst Precursors. Coordination State and Thermal Decomposition

The sol-gel process is a useful method for preparing two series of organically and co-ordinately modified xerogels of the types [CuN _n ]·N _5–n ·5xSiO_4/2 (n < 4) and [Cu(N–N)_n]·(N–N)_2–n ·2x SiO_4/2(n 2), where N = NH₂(CH₂)₃ SiO_3/2, N–N = NH₂(CH₂)₂NH·(CH₂)₃SiO_3/2 and x = [SiO_4/2]/[N] or [SiO_4/2]/[N–N]. The amino groups in the materials are coordinately active and participate partly in the coordination sphere of Cu(II) ions. The composition of the coordination sphere can be varied with the SiO_4/2 content and also as a result of the thermal decomposition of the organic residues at higher temperatures.Because the xerogel materials are considered to be catalyst precursors, this study is focused on their coordination and thermal properties. The prepared xerogels, such as silica, aminated silicates with N and N–N, as well as those entities complexed with Cu(II), were characterised by FT-IR spectroscopy. During gelation and thermal decomposition the materials were analysed by electron paramagnetic resonance (EPR) spectroscopy. The xerogels were additionally studied by UV-Vis absorption spectroscopy. The gaseous products of the thermal decomposition of these materials in an Ar atmosphere were investigated by the use of FT-IR spectroscopy coupled with TG and DTG thermal analysis. These data were complemented by temperature-programmed decomposition (TPDec) in a 2% O₂ + 98% Ar stream coupled with quadrupole mass spectroscopy.     

Studies on the interaction between Se,Te, Cd,As and Zn and the distribution of Fe,Co, Rb and Hg in mice by instrumental neutron activation analysis

The incorporation of Se and Te into liver, kidneys, heart, spleen, lung and small intestine after i.p. injections of Balby mice with seleno-cystine (CySe)₂ and Na₂TeO₃ in the presence of Cd (as CdCl₂), As (as As₂O₃) and Zn (as ZnSO₄) has been studied. The change of contents of Co, Fe, Rb and Hg were determined in all investigated organs after injections with the above compounds. Instrumental neutron activation analysis was applied as the analytical method. It was found that a competitive interaction occurs between As and Se or Te. Similarly, this interaction has been observed between Se and Cd. The data obtained suggest that Cd has a higher competitive ability to displace Te than Zn and Se. Injection with the above compounds affects the contents of Fe, Co, Rb and Hg in all mice organs.     

Electron-transfer reduction of selected alcohols with alkalide K, K(15-crown-5)2 via organometallic intermediates

The course of the reaction of alkalide K⁻, K⁺(15-crown-5)₂1 with selected alcohols depends on the kind of alcohol and the mode of substrate delivery. In the case of methanol, potassium methoxide formed initially undergoes destruction at the excess of 1. It results in potassium oxide and methylpotassium. The latter opens the crown ether ring giving potassium tetraethylene glycoxide vinyl ether and methane. A similar course of the process is observed for propanol. Potassium glycidoxide is the main product formed in the reaction of 1 with glycidol. Its oxirane ring is opened at the excess of 1. Organopotassium alkoxides, i.e., potassium potassiomethoxide and dipotassium potassiopropane-1,2-dioxide are intermediate products of this reaction. They react then with the crown ether. Potassium methoxide, potassium enolate of acetaldehyde, dipotassium propane-1,2-dioxide and potassium tetraethylene glycoxide vinyl ether are the final products of this process.     

Determination of dipole moment in the ground and excited state by experimental and theoretical methods of N-nonyl acridine orange

The absorption and fluorescence spectra of N-nonyl acridine orange are determined at room temperature (298 K) in cyclohexane, benzene, carbon tetrachloride, chloroform, chlorobenzene and dichloromethane. The ground state of dipole moment was obtained by impedance measurements using Guggenheim-Debeye's method. The experimental excited state dipole moment of N-nonyl acridine orange was determined using Bakhshiev's and Kawski-Chamma-Viallet's formulae and solvent polarity parameter proposed by Reichardt. These experimental results were completed with theoretical results using quantum chemical methods. The experimental (muexp=10.76 D) and theoretical (mucal=9.9 D) dipole moments in the ground and excited state (muexp*=14.56 D) were compared.     

Primary and secondary relaxations in bis-5-hydroxypentylphthalate revisited

The molecular structure of bis-5-hydroxypentylphthalate (BHPP) is like dihexyl phthalate but having appended to it two hydroxyl end groups, which contribute additional dipole moments and capacity for hydrogen-bond formation. In a previously published dielectric study of the primary and secondary relaxations of BHPP, it was found that all the dynamic properties are normal except for the anomalously large width of the primary relaxation loss peak. There are two secondary relaxations, the relaxation time of the slower one increases with increasing pressure, whereas that of the faster one is practically insensitive to pressure. Hence, the slower secondary relaxation is the "universal" Johari-Goldstein (JG) [J. Chem. Phys. 53, 2372 (1970); 55, 4245 (1971)] relaxation in BHPP. All is well except if the observed large width of the primary relaxation were an indication of a corresponding large coupling parameter n=0.45 in the coupling model. Then the predicted relations between the primary relaxation time tau(alpha) and the JG relaxation time tau(JG) found previously to hold in many glass formers would be violated. It was recognized that this singular behavior of BHPP is likely due to broadening of the primary loss peak by the overlapping contributions of two independent dipole moments present in BHPP, and the actual coupling parameter is smaller. However, at the time of publication of the previous work there were not enough data to support this explanation. By making broadband dielectric measurements of dibutyl phthalate (DBP) and dioctyl phthalate (DOP) that have chemical structures closely related to BHPP but with only one dipole moment, we show that all their dynamic properties are almost the same as BHPP but the widths of their primary relaxation loss peaks are significantly narrower corresponding to a smaller coupling parameter n=0.34. The new data presented here indicate that the coupling parameter of BHPP is about the same as DBP and DOP, and the predicted relations between tau(alpha) and tau(JG) of BHPP are brought back in agreement with the experimental data.