Solution of the Spinless Salpeter Equation with a Time-Dependent Linear Potential

We derive the general solution of the semi-relativistic spinless Salpeter equation in the presence of a time-dependent linear potential via the Lewis–Riesenfeld framework and using two forms of the invariant. For comparison, we reobtain the solution in the momentum-space directly by applying a time-momentum transformation to the involved partial differential equation. We also investigate the classical-quantum correspondence for the model in the case of time-periodic force using a momentum-space Gaussian wave-packet.     

Solid-phase intermolecular radical reactions 2: synthesis of C-glycopeptide mimetics via a novel acrylate acceptor

[reaction: see text] A novel tetrafluorophenol-linked acrylate is reported as an activated acceptor for intermolecular radical reactions. Addition of alkyl radicals led to pure products in good yields. We include here the first syntheses of C1- and C6-linked glycosides using a solid-phase radical methodology.     

Kinetic and mechanistic study on the reaction of alkylcobaloximes with azoles

The kinetics of axial water substitution by azoles (pyrazole and 1,2,4-triazole) in three different cobaloximes, viz.trans-[Co(Hdmg)(2)(R)H(2)O] where Hdmg = dimethylglyoximate, R = PhCH(2), Et and CF(3)CH(2), were studied as a function of azole concentration, temperature and pressure in aqueous solution. The second order rate constants for the substitution of water in trans-[Co(Hdmg)(2)(R)H(2)O] for R = Et at pH 6.0, 25 degrees C and I= 0.1 M (NaClO(4)), were found to be 1309 and 1200 M(-1) s(-1) for pyrazole (Pz) and 1,2,4-triazole (Tz), respectively, and those obtained for R = PhCH(2) were found to be 755 and 691 M(-1) s(-1), respectively. The second order rate constants in the case of R = CF(3)CH(2) were found to be 0.358 and 0.348 M(-1) s(-1) for Pz and Tz, respectively. The relative order of reactivity for the different alkyls being Et > PhCH(2) > CF(3)CH(2). The activation parameters (DeltaH([not equal]), DeltaS([not equal]) and DeltaV([not equal])) obtained for these reactions were found to be in the range of 65-87 kJ mol(-1), 24-47 J mol(-1) K(-1) and 2.5-7.7 cm(3) mol(-1), respectively. These data suggest that an I(d) substitution mechanism operates where the azoles participate in the transition state.     

Cholinesterase inhibitory constituents from Onosma hispida

Hispidone, a new flavanone, has been isolated from Onosma hispida and assigned the structure (2S)-5,2'-dihydroxy-7,4',5'-trimethoxyflavanone (1) by spectroscopic methods. In addition, (2S)-5,2'-dihydroxy-7,5'-dimethoxyflavanone (2), benzoic acid (3), and 4-hydroxy benzoic acid (4) are also reported for the first time from this species.     

Heck vinylation of aryl iodides by a silica sol-gel entrapped Pd(II) catalyst and its combination with a photocyclization process

[reaction: see text] Silica sol-gel encaged PdCl(2)(PPh(3))(2) is a recyclable catalyst for the Heck vinylation of aryl iodides. It is possible to couple the Heck reaction with photocyclization in a one-pot process.     

A novel spectrophotometric method for batch and flow injection determination of cyanide in electroplating wastewater

A sensitive and highly selective spectrophotometric method is described for the determination of cyanide. It is based on a reaction of cyanide with aquacyanocobyrinic acid heptamethyl ester (ACCbs) reagent (orange color) at pH 9.5 to give dicyanocobester (DCCbs) (violet color). The increase of the absorption bands of the reaction product at 368 and 580 nm and the decrease of the reagent band at 353 nm are linearly proportional to the cyanide concentration. The method is used in static mode for determining cyanide over the concentration range 0.04-1.20 μg ml⁻¹ with a detection limit of 0.02 μg ml⁻¹ and for hydrodynamic analysis of 0.4-5.2 μg ml⁻¹ cyanide. Application for batch and flow injection monitoring of cyanide in electroplating wastewater samples gives results agree within ± 1.2% with those obtained by the standard potentiometry using the cyanide ion selective electrode. The method is practically free from interferences by PO₄³⁻, NO₃⁻, NO₂⁻, SO₄²⁻, F⁻, Cl⁻, Br⁻, I⁻, S²⁻ and SCN⁻ ions and gives results with average recoveries of 97.6-99.2%. Advantages offered by using ACCbs as a chromogen for cyanide assay are: (i) high selectivity and sensitivity of the coordination site of the reagent towards cyanide ion; (ii) fast reaction, since legation takes place at the axial position of the reagent; (iii) good solubility and stability of the reagent in aqueous solutions over a wide pH range; (iv) high stability of the reagent (ACCbs) and the colored complex product (DCCbs) and (v) possible absorbance measurements at three different wavelengths.     

Pyrimidine derivatives and related compounds. A novel synthesis of pyrimidines,pyrazolo[4,3-d]pyrimidines and isoxazolo[4,3-d] pyrimidine

Benzoylacetonitrile (II) reacted with trichloroacetonitrile (III) to yield the β-amino-β-trichloromethylacrylonitrile IV. Compound IV reacted with hydrazine hydrate to yield 5-amino-4-cyano-3-phenylpyrazole (V) and with 2-aminopyridine to yield the aminopyridine derivative VIII (cf., Chart I). Compound IV reacted with III to yield 2,4-bis(trichloromethyl)-5-cyano-6-phenylpyrimidine (I) which could be converted into a variety of pyrazolo[4,3-d]pyrimidine derivatives by treatment with hydrazine hydrate under a variety of different experimental conditions (cf., Chart II).