Synthesis and structure determination of Co(HNCN)2 and Ni(HNCN)2

Well-crystallized cobalt and nickel hydrogencyanamide, Co(HNCN)₂ and Ni(HNCN)₂, were synthesized from the corresponding ammonia complexes [M(NH₃)₆]²⁺ under aqueous cyanamide conditions. The X-ray and neutron powder data evidence the orthorhombic system and space group Pnnm. The cell parameters for Co(HNCN)₂ are a=6.572(1), b=8.805(2), c=3.267(1) Å, and Z=2; for the isotypic Ni(HNCN)₂, the cell parameters arrive at a=6.457(1), b=8.768(2), c=3.230(1) Å. The octahedral coordinations of the metal ions are marginally squeezed, with interatomic distances of 4×Co-N=2.134(5) Å, 2×Co-N=2.122(9) Å, and 4×Ni-N=2.133(6) Å, 2×Ni-N=2.035(11) Å. The HNCN⁻ units appear as slightly bent (177.5(2)° for Co(HNCN)₂ and 175.7(2)° for Ni(HNCN)₂) and exhibit cyanamide shape character due to triple- and single-bond C-N distances (1.20(2) vs. 1.33(2) Å for Co(HNCN)₂ and 1.15(2) vs. 1.38(2) Å for Ni(HNCN)₂). The infrared vibration data compare well with those of the three existing alkali-metal hydrogencyanamides.     

A LASER FLASH SPECTROSCOPY STUDY OF THE KINETICS OF ELECTRON TRANSFER FROM SPINACH PHOTOSYSTEM I TO SPINACH AND ALGAL FERREDOXINS

Laser flash absorption spectroscopy has been used to investigate the kinetics of electron transfer from P700 in Photosystem I (PSI)-enriched particles from spinach to the ferredoxins from spinach and the green alga Monoraphidium braunii. Very similar behavior for the interaction of both ferredoxins with the PSI complex was observed, although the algal ferredoxin appears to be slightly more effective as an electron acceptor. For both proteins, a non-linear protein concentration dependence of the rate constant for reduction was obtained, indicating complex formation preceding electron transfer. Estimates of 3 times 10⁷M^?1 s^?1 and 140–180 s^?l were obtained from these data for the second order rate constants for complex formation, and the limiting first order rate constants for electron transfer, respectively. At neutral pH, a biphasic dependence of the rate constant for ferredoxin reduction on the concentration of NaCl or MgCl₂ was observed. This was interpreted in terms of the electrostatic interactions which occur between ferredoxin and the PSI membrane. In addition, magnesium cations appear to play a specific role in the interaction between PSI and ferredoxin. Thus, the addition of these ions under optimal conditions induces a 6-f-old increase in the electron transfer reaction rate constant, compared with a 2-f-old increase in the presence of an optimal amount of NaCI. This cannot be explained as arising from ionic strength effects. To our knowledge, this is the first time that a direct measurement of the rate constant for the reduction of ferredoxin by the PSI complex has been reported.     

Polymer-silica nanocomposites prepared by sol-gel technique: Nanoindentation and tapping mode AFM studies

Polymer-silica nanocomposites based on poly(2-hydroxyethyl acrylate) (PHEA) have been prepared by the simultaneous polymerization of the organic and the silica phases in a sol-gel process with the silica precursor tetraethyl orthosilicate (TEOS). The structure of this system is investigated using atomic force microscopy (AFM) in the tapping mode and in nanoindentation experiments. The structure of the PHEA/silica hybrids strongly depends on the ratio of both components in the system. For silica weight fractions lower than 0.15, the system consists of aggregated silica particles dispersed in the organic matrix; above that concentration of silica the structure is co-continuous with that of the organic matrix, similarly to two interpenetrated networks.     

Optimized determination of calcium in grape juice,wines, and other alcoholic beverages by atomic absorption spectrometry

This paper describes a study of the different methods of sample preparation for the determination of calcium in grape juice, wines, and other alcoholic beverages by flame atomic absorption spectrometry; results are also reported for the practical application of these methods to the analysis of commercial samples produced in Spain. The methods tested included dealcoholization, dry mineralization, and wet mineralization with heating by using different acids and/or mixtures of acids. The sensitivity, detection limit, accuracy, precision, and selectiviy of each method were established. Such research is necessary because of the better analytical indexes obtained after acid digestion of the sample, as recommended by the European Union, which advocates the direct method. In addition, although high-temperature mineralization with an HNO3-HCIO4 mixture gave the best analytical results, mineralization with nitric acid at 80 degrees C for 15 min gave the most satisfactory results in all cases, including those for wines with high levels of sugar and beverages with high alcoholic content. The results for table wines subjected to the latter treatment had an accuracy of 98.70-99.90%, a relative standard deviation of 2.46%, a detection limit of 19.0 microg/L, and a determination limit of 31.7 microg/L. The method was found to be sufficiently sensitive and selective. It was applied to the determination of Ca in grape juice, different types of wines, and beverages with high alcoholic content, all of which are produced and widely consumed in Spain. The values obtained for Ca were 90.00 +/- 20.40 mg/L in the grape juices, 82.30 +/- 23.80 mg/L in the white wines, 85.00 +/- 30.25 mg/L in the sweet wines, 84.92 +/- 23.11 mg/L in the red wines, 85.75 +/- 27.65 mg/L in the rosé wines, 9.51 +/- 6.65 mg/L in the brandies, 11.53 +/- 6.55 mg/L in the gin, 7.3 +/- 6.32 mg/L in the pacharán, and 8.41 +/- 4.85 mg/L in the anisettes. The method is therefore useful for routine analysis in the quality control of these beverages.     

Reaction of bis(phosphine)(hydrotris(3,5-dimethylpyrazolyl)borato)rhodium(I) with phenylacetylene,p-nitrobenzaldehyde,and triphenyltin hydride: structures of [Rh(Tp)(PPh(3))(2)], [Rh(Tp)(H)(C(2)Ph)(P(4-C(6)H(4)F)(3))], [Rh(Tp)(H)(COC(6)H(4)-4-NO(2))(PPh(3))], and [Rh(Tp)(H)(SnPh(3))(PPh(3))

The complexes [Rh(Tp)(PPh(3))(2)] (1a) and [Rh(Tp)(P(4-C(6)H(4)F)(3))(2)] (1b) combine with PhC(2)H, 4-NO(2)-C(6)H(4)CHO and Ph(3)SnH to give [Rh(Tp)(H)(C(2)Ph)(PR(3))] (R = Ph, 2a; R = 4-C(6)H(4)F, 2b), [Rh(Tp)(H)(COC(6)H(4)-4-NO(2))(PR(3))] (R = Ph, 3a), and [Rh(Tp)(H)(SnPh(3))(PR(3))] (R = Ph, 4a; R = 4-C(6)H(4)F, 4b) in moderate to good yield. Complexes 1a, 2b, 3a, and 4a have been structurally characterized. In 1a the Tp ligand is bidentate, in 2b, 3a, and 4a it is tridentate. Crystal data for 1a: space group P2(1)/c; a = 11.9664(19), b = 21.355(3), c = 20.685(3) A; beta = 112.576(7) degrees; V = 4880.8(12) A(3); Z = 4; R = 0.0441. Data for 2b: space group P(-)1; a = 10.130(3), b = 12.869(4), c = 17.038(5) A; alpha = 78.641(6), beta = 76.040(5), gamma = 81.210(6) degrees; V = 2100.3(11) A(3); Z = 2; R = 0.0493. Data for 3a: space group P(-)1; a = 10.0073(11), b = 10.5116(12), c = 19.874(2) A; alpha = 83.728(2), beta = 88.759(2), gamma = 65.756(2) degrees; V =1894.2(4) A(3); Z = 2; R = 0.0253. Data for 4a: space group P2(1)/c; a = 15.545(2), b = 18.110(2), c = 17.810(2) A; beta = 95.094(3) degrees; V = 4994.1(10) A(3); Z = 4; R = 0.0256. NMR data ((1)H, (31)P, (103)Rh, (119)Sn) are also reported.     

Determination of non-ionic polyethoxylated surfactants in wastewater and river water by mixed hemimicelle extraction and liquid chromatography-ion trap mass spectrometry

The capability of hemimicelles-based solid phase extraction (SPE)/liquid chromatography/atmospheric pressure chemical ionisation in positive mode, ion trap mass spectrometry (LC/(APCl+-IT)-MS) for the concentration, separation and quantitation of non-ionic surfactants has been investigated. Concentration was based on the formation of mixed aggregates of analytes [alkylphenol ethoxylates (APE, octyl and nonyl) and alkyl ethoxylates (AE, C12-C16)] with the anionic surfactant sodium dodecyl sulphate (SDS) that is adsorbed on alumina. Parameters affecting SPE were investigated on the basis that hemimicelles are dynamic entities in equilibrium with the aqueous phase. The performance of ion trap mass spectrometry for MS and MS/MS quantitation of non-ionic homologues was assessed. Recoveries of analytes from wastewater influent and effluent and river water samples ranged between 91 and 98% and were found independent on the length of the alkyl chain under the optimised conditions. Anionic surfactants did not interfere to the levels found in environmental samples. The detection limits ranged between 14 and 111 ng/l for wastewater influent, 10 and 40 for wastewater effluent and 4 and 35 for river water, after concentration of 250, 500 and 750 ml of sample, respectively. The approach was applied to the determination of AE and APE in influent and effluent samples from four wastewater treatment plants and four river samples. The concentrations of individual non-ionic surfactants found ranged between 0.3 and 373 microg/l.     

Conformational dependence of pyranoid rings 1,2-cis-fused to dioxolane rings on the configuration of the dioxolane rings in acetylated derivati

X-Ray and ¹H N.M.R. studies on pyranoid rings 1,2-$\text{cis}$-fused to dioxolane rings in acetylated $\text{D}$-gluco- and $\text{D}$--galactopyranose derivatives demonstrate that the configuration of the dioxolane ring influences the conformation of the pyranoid ring in the $\text{D}$-gluco but not in the $\text{D}$-galactopyranose series. The crystal structure of 3,4,6-tri-$\text{O}$-acetyl-1,2-$\text{O}$-(R)--(l-cyano-ethylidene)-α-$\text{D}$-glucopyranose ($\text{1}$) and 3,4,6-tri-$\text{O}$-acetyl-1,2-$\text{O}$-($\text{R}$)-(1-cyano-ethylidene)-α-$\text{D}$-galactopyranose ($\text{2}$)have been determined by X-ray analysis. Lattice parameters for $\text{1}$ are a=20.6021 (11), b=8.0438 (2), c=5.5541 (1) Å and β= 95.588 (3)° for a cell with P21 symmetry. These parameters for $\text{2}$ are a=20.3361 (7), b=10.0907 (2), c=18.9115 (5) Å, β =112.399 (2)°, C2, with two crystallographycally independent molecules. The conformation of the pyranoid ring in both compounds can be described as flattened ⁴C₁ and that of the dioxolane ring as distorted E₁. The importance of the torsion angles for describing problems of configuration is remarked and the use of relative configurational angles is stressed. The ¹H N.M.R. spectra of $\text{1}$ and $\text{2}$ and 3,4,6-tri-$\text{O}$-acetyl-1,2-O-(S)- and (R)-ethylidene-α-$\text{D}$-glucopyranose ($\text{5}$ and $\text{7}$), 3,4,6-tri-O-acetyl--1,2-O-(S)- and ($\text{R}$)-ethylidene-α-$\text{D}$-galactopyranose ($\text{6}$ and $\text{8}$), and 3,4,6-tri-$\text{O}$-acetyl-1,2-$\text{O}$-($\text{S}$)-and ($\text{R}$)-benzylidene-α-$\text{D}$-glucopyranose ($\text{9}$ and $\text{10}$) have been analyzed by using iterative computer methods and N.O.E. measurements. The results indicate that the major solution conformation of the pyranoid ring of the derivatives in the $\text{D}$-gluco series $\text{1}$, $\text{5}$ and $\text{9}$ may be described as flattened ⁴C₁ and that of $\text{7}$ and $\text{10}$ as ²$\text{S}$₅. The major solution conformation of the pyranoid ring in all compounds in the $\text{D}$-galacto series ($\text{2}$,$\text{4}$,$\text{6}$,$\text{8}$) may be described as flattened ⁴$\text{C}$₁.     

Energetics of hydroxybenzoic acids and of the corresponding carboxyphenoxyl radicals. Intramolecular hydrogen bonding in 2-hydroxybenzoic acid

The energetics of the phenolic O-H bond in the three hydroxybenzoic acid isomers and of the intramolecular hydrogen O-H- - -O-C bond in 2-hydroxybenzoic acid, 2-OHBA, were investigated by using a combination of experimental and theoretical methods. The standard molar enthalpies of formation of monoclinic 3- and 4-hydroxybenzoic acids, at 298.15 K, were determined as Delta(f)(3-OHBA, cr) = -593.9 +/- 2.0 kJ x mol(-1) and Delta(f)(4-OHBA, cr) = -597.2 +/- 1.4 kJ x mol(-1), by combustion calorimetry. Calvet drop-sublimation calorimetric measurements on monoclinic samples of 2-, 3-, and 4-OHBA, led to the following enthalpy of sublimation values at 298.15 K: Delta(sub)(2-OHBA) = 94.4 +/- 0.4 kJ x mol(-1), Delta(sub)(3-OHBA) = 118.3 +/- 1.1 kJ x mol(-1), and Delta(sub)(4-OHBA) = 117.0 +/- 0.5 kJ x mol(-1). From the obtained Delta(f)(cr) and Delta(sub) values and the previously reported enthalpy of formation of monoclinic 2-OHBA (-591.7 +/- 1.3 kJ x mol(-1)), it was possible to derive Delta(f)(2-OHBA, g) = -497.3 +/- 1.4 kJ x mol(-1), Delta(f)(3-OHBA, g) = -475.6 +/- 2.3 kJ x mol(-1), and Delta(f)(4-OHBA, cr) = -480.2 +/- 1.5 kJ x mol(-1). These values, together with the enthalpies of isodesmic and isogyric gas-phase reactions predicted by density functional theory (B3PW91/aug-cc-pVDZ, MPW1PW91/aug-cc-pVDZ, and MPW1PW91/aug-cc-pVTZ) and the CBS-QMPW1 methods, were used to derive the enthalpies of formation of the gaseous 2-, 3-, and 4-carboxyphenoxyl radicals as (2-HOOCC(6)H(4)O(*), g) = -322.5 +/- 3.0 kJ.mol(-1) Delta(f)(3-HOOCC(6)H(4)O(*), g) = -310.0 +/- 3.0 kJ x mol(-1), and Delta(f)(4-HOOCC(6)H(4)O(*), g) = -318.2 +/- 3.0 kJ x mol(-1). The O-H bond dissociation enthalpies in 2-OHBA, 3-OHBA, and 4-OHBA were 392.8 +/- 3.3, 383.6 +/- 3.8, and 380.0 +/- 3.4 kJ x mol(-1), respectively. Finally, by using the ortho-para method, it was found that the H- - -O intramolecular hydrogen bond in the 2-carboxyphenoxyl radical is 25.7 kJ x mol(-1), which is ca. 6-9 kJ x mol(-1) above the one estimated in its parent (2-OHBA), viz. 20.2 kJ x mol(-1) (theoretical) or 17.1 +/- 2.1 kJ x mol(-1) (experimental).     

Characterization of the pores in hydrous ferric oxide aggregates formed by freezing and thawing

Hydrous ferric oxides (HFO) are efficient sorbents for inorganic and organic pollutants and therefore have great potentials in environmental science and engineering applications. Freezing and thawing of HFO suspensions leads to the formation of dense HFO aggregates. It facilitates the handling and increases the drying rate of HFO. In this study, we used a combination of pycnometry, gas adsorption (N(2) gas, water vapor), and small-angle neutron scattering (SANS) to characterize the porosity and pore size distribution of dense HFO aggregates formed by freezing dialyzed HFO suspensions at -25 degrees C and thawing them at room temperature. The crystallinity of the HFO, which was a 2-line ferrihydrite, was not affected by this treatment. Wet sieving and laser diffraction analysis showed that the dense HFO aggregates had a unimodal size distribution with an average diameter of 235+/-35 microm. Increasing the freezing rate by cooling with liquid N(2) (-196 degrees C) resulted in much smaller aggregates with an average diameter of 20 microm. Adding NaNO(3) electrolyte to the HFO suspensions prior to freezing also resulted in the formation of smaller aggregates. The dense HFO aggregates formed at -25 degrees C had a porosity of 0.73+/-0.02 ll(-1). SANS revealed a unimodal size distribution of pores, with an average pore diameter of 2.0 nm. The diameter of the HFO crystallites was estimated by transmission electron microscopy to be 1.9+/-0.5 nm. Geometrical considerations taking into account the unit particle and average pore size suggest that the crystallites retain 1-2 layers of hydration water during the coagulation induced by freezing. Analysis by N(2) gas adsorption showed that drying the dense HFO aggregates induced a reduction in porosity by about 25% and shifted the pore size distribution to smaller diameters. Rewetting during water vapor adsorption did not induce significant changes of the aggregate structure. The specific surface area of the dry HFO aggregates was between 320 and 380 m(2)g(-1).     

Two New Spermidine Alkaloids from Chisocheton weinlandii

The investigation of the MeOH extract of the leaves of Chisocheton weinlandii Harms (Meliaceae) revealed two new open‐chain spermidine alkaloids, chisitine 1 ( 1 ) and chisitine 2 ( 2 ). Their structures were elucidated by NMR spectroscopy, tandem‐mass spectrometry, and independant syntheses (Scheme 3). Detailed MS/MS fragmentation pathways are discussed for both compounds based on H/D exchange and ¹⁸O‐labeling experiments (Schemes 1 and 2).