Sodium in liquid ammonia—a versatile tool in modifications of arylphosphine oxides

A simple and practical method for modifications of tertiary arylphosphine oxides based on their reaction with sodium in liquid ammonia is presented. Depending on the structure of the starting compounds, either dearomatisation of the phenyl substituent or cleavage of a P-aryl bond from phosphorus atom can be selectively performed and the corresponding (1,4-cyclohexadien-3-yl)phosphine oxides or secondary phosphine oxides were obtained in good to excellent yields.     

Investigation of {1,2-bis(diphenylphosphino)ethane-P,P′}-(dithiocarbonato-S,S′)-nickel(II)

Summary The reaction of bis(iso-propylxanthato)nickel(II) with 1,2-bis(diphenylphosphino)ethane (dppe) in a 11 molar ratio affords [Ni(S₂CO)(dppe)], which, on the basis of its magneto-chemical and spectral properties, has been characterized as a square-planar Ni complex. The complex was one-electron irreversibly oxidized at a potential of 0.673 V versus s.c.e. The crystal and molecular structure of a twinned crystal of the complex has been elucidated, and consists of two crystallographically independent molecules in which each Ni atom is coordinated by two S atoms from the dithiocarbonate ligand and two P atoms from the dppe ligand in an approximately square-planar arrangement.     

Ground- and excited-state double proton transfer in lumichrome/acetic acid system: theoretical and experimental approach

Experimental time-resolved spectral and photon counting kinetic results confirm formation of an isoalloxazinic excited state via excited-state double proton transfer (ESDPT) catalyzed by a carboxylic acid molecule that forms a hydrogen-bond complex with the parent alloxazine molecule. This isoalloxazinic tautomer manifests itself as a distinct long-lived emissive species formed only in such alloxazine derivatives that were not substituted at the N1 nitrogen atom, being a product of the excited-state reaction occurring from the alloxazinic excited state. Theoretical calculations support the idea that the ESDPT occurs by the concerted mechanism. The calculated activation barrier in the excited state is much lower than the same barrier in the ground state and even disappears for the HOMO-1 to LUMO excitation, which explains the fact that the reaction takes place in the excited-state only. The reaction rate estimated from the emission kinetics is ca. 1.4 x 10(8) dm3 mol(-1) s(-1) in ethanolic solutions of lumichrome with added acetic acid.     

Determination of adrenolytic drugs by SPME–LC–MS

Five adrenolytic drugs have been analyzed by liquid chromatography–mass spectrometry (LC–MS). Samples were prepared by solid-phase microextraction (SPME) using polypyrrole fibers coated on stainless steel support as an adsorbent for the drugs. Adsorption efficiencies were 95% and were close for all the drugs investigated. Relative standard deviations (RSD), calculated for samples prepared in standard solutions, were in the range 2.5–13%, however RSD values for the drugs in human plasma were 2.5–4.5%. Using LC–MS the limit of detection (LOD) and the limit of quantification (LOQ) were in the ranges 0.11–0.18 and 0.39–0.54 ng mL⁻¹, respectively, for the five drugs.     

Calorimetry in the studies of cement hydration

Calorimetry was applied to an investigation of the early hydration of Portland cement (PC)–calcium aluminate cement (CAC) pastes. The heat evolution measurements were related to the strength tests on small cylindrical samples and standard mortar bars. Different heat-evolution profiles were observed, depending on the calcium aluminate cement/Portland cement ratio. The significant modification of Portland cement heat evolution profile within a few hours after mixing with water was observed generally in pastes containing up to 25% CAC. On the other hand the CAC hydration acceleration effect was also obtained with the 10% and 20% addition of Portland cement. As one could expect the compressive and flexural strength development was more or less changed—reduced in the presence of larger amount of the second component in the mixture, presumably because of the internal cracks generated by expansive calcium sulfoaluminate formation.     

Evidence for two forms, double hydrogen tunneling, and proximity of excited states in bridge-substituted porphycenes: supersonic jet studies

Laser-induced fluorescence and dispersed fluorescence spectra measured in supersonic jets for 9,10,19,20-tetra-n-methylporphycene and 9,10,19,20-tetra-n-propylporphycene reveal, for both compounds, the presence of two different species which are assigned to trans and cis tautomeric forms. Doublet splitting of lines is observed, disappearing upon deuteration of the inner nitrogen atoms. This finding is interpreted as an indication of double hydrogen tunneling. The values of tunneling splitting are obtained for both ground and lowest singlet excited states. The splitting is similar for cis and trans forms, and the barrier for tautomerization is larger in the excited state. Due to the coupling of hydrogen motion with rotation of alkyl substituents, tautomerization occurs in an asymmetric double minimum potential, with the ordering of energy minima reversed upon excitation. The second singlet excited state is found to lie very close to S(1), thus facilitating an efficient radiationless depopulation.     

High ionic strength electrokinetics

The electrokinetic potentials at high ionic strengths can be measured by means of electroacoustic method. The reported values are surprisingly high: up to 25 mV in 1 mol dm(-3) 1:1 electrolyte solution. The IEP of metal oxides in concentrated solutions of 1:1 electrolytes shifts to substantially higher pH values with respect to the pristine value, although these electrolytes are inert at low concentration. The shift in the IEP is salt-specific, and it is correlated with the hard-soft character of the anion and of the cation.     

Mechanistic information on the copper-catalysed autoxidation of mercaptosuccinic acid in aqueous solution

Copper(II) ions react rapidly with sulfur from thiol groups, forming two distinct, intensely absorbing, short-lived intermediates, which decompose in a subsequent redox reaction to produce reduced copper and disulfides. In this study we report the results of a mechanistic study on the reaction between mercaptosuccinic acid, HO(2)CCH(2)CH(SH)CO(2)H, and Cu(2+)(aq) and [Cu(tren)H(2)O](2+), tren = tris(2-aminoethyl)amine. Spectroscopic and kinetic data indicate that in the presence of an excess of thiol, at least two distinct complexes are formed, with very different decomposition rate constants and an absorption maximum at 346 nm. Upon addition of thiol to [Cu(tren)H(2)O](2+)(1:1), a transient with a maximum at 380 nm appears, whereas in an excess of thiol this complex decomposes and again the 346 nm band is observed. The use of [Cu(tren)H(2)O](2+) enables to study the reaction of thiol with copper also in alkaline solution, where the rate of the overall process is slowed down greatly. The reactions were studied in detail, including the effect of dioxygen, and a possible reaction mechanism for the catalysed autoxidation process is proposed and discussed in reference to available literature data.