Synthesis of 4-aryl-2,3,6,7-tetrahydro-1H-pyrimido[4,5-b][1,4]-diazepin-6-ones from 4,5-diamino-1H-pyrimidin-6-ones and 1-aryl-3-(dimethylamino)-1-propanones

The reaction of 1-aryl-3-(dimethylamino)-1-propanones 1 with one equivalent of 4,5-diamino-1H-pyrimidin-6-ones 2 , in acidic medium, leads to the formation of 4-aryl-2,3,6,7-tetrahydro-1H-pyrimido[4,5-b]-[1,4]diazepin-6-ones 3 . The structure elucidation of the products is based on detail nmr analysis of experiments such as ¹³C, ¹H and DEPT including selective ¹³C{¹H} decoupling experiments.     

Preparation and properties of dinitrogen complexes of molybdenum and tungsten with trimethylphosphine as coligand : III. Synthesis and properties of cis-[W(N2)2(PMe3)4], trans-[W(C2H4)2(PMe3)4] and [M(N2)(PMe3)5] (M = Mo,W). The crystal and molecular structure of [Mo(N2)(PMe3)5]

The reduction of [WCl₄(PMe₃)₃] with dispersed sodium, under dinitrogen, gives cis-[W(N₂)₂(PMe₃)₄], while under ethylene trans-[W(C₂H₄)₂(PMe₃)₄] is obtained. The ethylene complex can also be prepared by displacement of the dinitrogen molecules in cis-[W(N₂)₂(PMe₃)₄] by ethylene at room temperature and pressure. Interaction of cis-[M(N₂)₂(PMe₃)₄] complexes (M = Mo, W), with PMe₃, under helium or argon, yields [M(N₂)(PMe₃)₅]. The molybdenum complex crystallizes in the orthorhombic space group Pnma, with a 22.063(6), b 12.106(4), c 9.745(4) Å. The Mo—P distance trans to the dinitrogen ligand (2.483(7) Å) is slightly longer than the average of the other four Mo—P bonds (2.460(5) Å).     

Reaction of 6-aminopyrimidin-4-ones with diethyl ethoxymethylenemalonate in several media: Synthesis of pyrido[2,3-d]pyrimidines

Reactions of 6-amino-3,4-dihydro-2-methoxy-4-oxopyrimidine 1 and its 3-methyl derivative 2 , with diethyl ethoxymethylenemalonate (EMME) are discussed in this paper. These reactions have been carried out in the following media: under fusion, ethanol, sodium methoxide/methanol, sodium ethoxide:ethanol and acetic acid media. In acetic medium, mixtures of products proceeding from C-alkylation and N-alkylation were obtained, while in the remaining conditions only products of N-alkylation were obtained.     

Simultaneous Determination of Ascorbic Acid and Uric Acid by Using a PVC/TTF‐TCNQ Composite Electrode as Detector in a FIA System

A PVC/TTF‐TCNQ composite electrode has been employed as detector in a flow injection system. The proposed method allows the simultaneous detection of ascorbic acid (AA) and uric acid (UA) in mixtures by using a FIA system in a simple manner, without pre‐treatment or modified electrode. This method is based on the amperometric determination of (a) ascorbic acid at 0.15 V and (b) both analytes at 0.35 V, being the response linear in the range 1×10^?2–4×10^?4 M for both analytes with detection limits (S/N=3) of 1.2×10^?4 M and 8.1×10^?5 M for AA and UA, respectively.     

The Role of Intramolecular Hydrogen Bonds vs. Other Weak Interactions on the Conformation of Hyponitrous Acid and Its Mono- and Dithio-Derivatives

High level ab initio and density functional theory calculations have been carried out to investigate the relative stability of the different conformers of hyponitrous acid and its mono- and dithio-derivatives. Geometries and vibrational frequencies were obtained at the B3LYP/6-311+G(d,p) level and final energies through B3LYP/6-311++G(3df,2pd) single point calculations. The reliability of this theoretical scheme has been assessed by comparing these DFT results with those obtained at the G3 level of theory, for some suitable cases. The cis conformers of hyponitrous acid and its mono- and dithio-derivatives are systematically more stable than the trans ones because in the cis conformation a dative interaction between the nitrogen-lone pairs and the σ_NX^* antibonding orbital is significantly favored. Quite interestingly, in general, the conformers presenting an intramolecular hydrogen bond (IHB) are not the global minima of the corresponding potential energy surfaces and only for hyponitrous acid the conformer with a OH ⋅s O IHB is slightly more stable than the cis conformer without IHB. The low stability of the tautomers with IHB is closely related with another weak intramolecular interaction which involves the lone-pairs of the chalcogen atoms and the π_NN^* antibondig orbital, and which is significantly perturbed when the IHB is formed.     

A very sensitive flow system for the direct determination of copper in natural waters based on spectrophotometric detection

A very sensitive flow injection method with spectrophotometric detection has been developed for the on-line determination of copper in natural waters. The method exhibits a limit of detection three times lower than the most sensitive direct spectrophotometric method previously described and then allows the direct and simple in situ determination of copper in most natural waters.The method was based on the measurement of the absorbance of the coloured complex formed by copper with the chromogenic reagent di-2-pyridyl ketone benzoylhydrazone (dPKBH) in an alkaline medium. This complex presents stoichiometry 1:2 (Cu:dPKBH), and exhibits maximum absorbance at 370 nm. The manifold used was very simple, and consisted of two channels. The first one contained the sample while the second one contained the colorimetric reagent (3.3×10⁻⁴ M dPKBH in 10% ethanol), in a 1.6×10⁻² M phosphate buffer solution at pH 8. The performance of the system was optimised by using both univariate and modified simplex methodologies. When modified simplex was used, the best signal was obtained for a sample injection volume of 529 μl, a reaction coil length of 1.29 m, and a reagent flow rate of 4.8 ml min⁻¹. Under optimum conditions, the response was linear up to 3 mg l⁻¹ copper, the equation of the straight line being y=0.314x+5.2×10⁻⁴ (r²=0.998). The method allowed a sampling frequency of 40 samples per hour and exhibited a precision of 2.11% (as R.S.D., n=11). The limit of detection was 4.6 μg l⁻¹ (calculated as 3s_b/m, where s_b is the standard deviation of the y-intercept and m represents the slope of the straight line), and was therefore more sensitive than all the direct continuous methods reported previously.The method was successfully applied to the analysis of real water samples, with an average relative error of 5.32%.     

BLEACHING OF PURPLE MEMBRANE WITH O-SUBSTITUTED HYDROXYLAMINES

Abstract The retinal Schiff base of bacteriorhodopsin, in the purple membrane from Halobacterium halobium , can be cleaved by hydroxylamine in the presence of light. We have further investigated this reaction with a series of O -substituted hydroxylamines, RONH₂, where R = -H (HA), -CH₃ (MHA), -SO₃− (HAS), benzyl- (BHA), p -nitrobenzyl- (NBHA), and pentafluorobenzyl- (FBHA). All except MHA caused light-induced bleaching of the purple membrane and the chromophore could be regenerated from apomembrane and all- trans retinal. Relative bleaching rate constants were obtained from V = QI _a k ₀ X /( k _r+ k ₀ X ), where V = bleaching rate, Q = quantum yield, I a = absorbed light intensity, X = hydroxylamine concentration, k ₀= rate constant for bleaching and k _r= rate constant for return of photoexcited bacteriorhodopsin to the initial state. This equation fits the time-, concentration- and intensity-dependences of the bleaching reactions in 0.02 M phosphate, pH 7.0. The rate constants k ₀ relative to HA were: MHA: 0; HAS: 0.3; HA: 1.0; BHA: 1.8; FBHA: 10.1; NBHA: 10.8. The relative rate constants do not correlate with the basicity of the derivatives. Instead, the results suggest that the retinal Schiff base is near a non-polar cavity into which an aromatic group can be inserted.     

Carbocyclic analogues of nucleosides from bis-(Hydroxymethyl)-cyclopentane: synthesis,antiviral and cytostatic activities of adenosine,inosine and uridine analogues

Six new carbocyclic nucleosides were prepared by constructing a purine base (in compounds 9-11) or pyrimidine base (in 6-8) on the amino groups of (+/-)-(1 beta,2 alpha,4 beta)-4-amino-1,2-cyclopentanedimethanol (4) and (+/-)-(1 beta,3 alpha,4 beta)-4-amino-1,3-cyclopentanedimethanol (5), and their activities against a variety of viruses and tumour cell lines were determined.     

Estimating the PDMS-Coated, SPME-Fibre/Water- and Fibre/Gas-Partition Coefficients of Chlorinated Ethenes by Headspace-SPME

In this work, a simple, fast and reproducible method is presented for the determination of fibre/liquid-phase and fibre/gas-phase partition coefficients of five chlorinated ethenes on a poly-(dimethylsiloxane), PDMS-coated, solid-phase microextraction fibre, by employing a headspace HS-SPME coupled with gas chromatography. The partition coefficients were estimated by a numerical method using a Level-I fugacity method coupled with parameter-estimation software. Dimensionless partition coefficients between SPME fibre and liquid as well as gas phases were obtained at temperatures of 10 °C, 25 °C and 30 °C. The partition coefficients of the fibre and the gas phase, K _fg, increase with decreasing temperature by a factor of ≈2 to 6, and they are directly proportional to the linear slope of the regression line. The same tendency is observed for the partition coefficient of the fibre and liquid phase, K _fw, in a factor ≈1.2 to 2.0. The sorption enthalpy is higher in the gas phase; therefore, the sorption onto the fibre is favoured at lower temperatures. The correlation of the log K _ow versus log K _fw and log K _oa versus log K _fg shows a linear relationship with the number of chlorine atoms in the C = C molecule. Long-term experiments resulted in sorption to Teflon surfaces and possible losses in 43 mL vials, not observed in 250 mL Boston bottles.