Synthesis, Crystal Structure, and IR Spectroscopic Characterization of 1,6-Hexanediammonium Dihydrogendecavanadate

Summary.  Anhydrous 1,6-hexanediammonium dihydrogendecavanadate ((HdaH₂)₂H₂V₁₀O₂₈, 1) was prepared by reaction of V₂O₅ with 1,6-hexanediamine in aqueous solution. The crystal structure of 1 was determined, and the proton positions in the H₂V₁₀O₂₈ ⁴⁻ anion were calculated by the bond length/bond number method. The protons are bound to the centrosymmetrically oriented μ–OV₃ groups of the decavanadate anion. Based on the analysis of IR spectra of 1 prepared from H₂O and D₂O, the absorption band at 871 cm⁻¹ can be attributed to δ(V–O_b–H) vibrations. Received August 3, 2001. Accepted (revised) October 8, 2001     

Planar Chromatography of Some 1-Arylpiperazines Behaving as Dopaminergic Ligands

JPC – Journal of Planar Chromatography – Modern TLC - The chromatographic behavior of fourteen 1-arylpiperazine derivatives has been studied by thin-layer chromatography on both silica...     

Thin-Layer Chromatographic Analysis of Flavonoids,Phenolic Acids,and Amino Acids in Some Croatian Hypericum Taxa

JPC – Journal of Planar Chromatography – Modern TLC - The flowering tops of Hypericum hirsutum, H. montanum, H. perforatum subsp. angustifolium, H. perforatum subsp. perforatum, and H....     

Chemometrically Assisted Development and Validation of LC for Simultaneous Determination of Carbamazepine and Its Impurities Iminostilbene and Iminodibenzyl in Solid Dosage Form

A chemometrical approach was applied to develop a reversed-phase liquid chromatographic method for simultaneous determination of carbamazepine and its impurities iminostilbene and iminodibenzyl in solid dosage form. According to contemporary literature, no method was developed for simultaneous determination of carbamazepine and these impurities by chemometrical approach. The fractional factorial design was used for selection of variables significantly influencing the chromatographic separation of the investigated substances. The investigated variables were: temperature of the column, the percentage of organic modifier, the acetate buffer concentration and pH of water phase. The first three variables were proved to be significant and were optimized by face centered, central composite design. Investigation was performed using C18 XBridge Shield analytical column (50 mm × 4.6 mm i.d., particle size 3.5 µm). The optimal conditions for the separation were established with the mobile phase composition of methanol–10 mM acetate buffer (pH adjusted to 2.21 with glacial acetic acid) (50:50, v/v) at a flow rate of 1.5 mL min^?1, 25 °C column temperature and detection at 260 nm. Total analysis time was shortened to about 8 min. Finally, the method was successfully validated and subsequently applied to the analysis of commercially available carbamazepine tablets.     

Surface-induced dissociation and chemical reactions of C2D 4 + on stainless steel, carbon (HOPG), and two different diamond surfaces

Surface-induced interactions of the projectile ion C₂D₄⁺ with room-temperature (hydrocarbon covered) stainless steel, carbon highly oriented pyrolytic graphite (HOPG), and two different types of diamond surfaces (O-terminated and H-terminated) were investigated over the range of incident energies from a few eV up to 50 eV. The relative abundance of the product ions in dependence on the incident energy of the projectile ion [collision-energy resolved mass spectra, (CERMS) curves] was determined. The product ion mass spectra contained ions resulting from direct dissociation of the projectile ions, from chemical reactions with the hydrocarbons on the surface, and (to a small extent) from sputtering of the surface material. Sputtering of the surface layer by low-energy Ar⁺ ions (5–400 eV) indicated the presence of hydrocarbons on all studied surfaces. The CERMS curves of the product ions were analyzed to obtain both CERMS curves for the products of direct surface-induced dissociation of the projectile ion and CERMS curves of products of surface reactions. From the former, the fraction of energy converted in the surface collision into the internal excitation of the projectile ion was estimated as 10% of the incident energy. The internal energy of the surface-excited projectile ions was very similar for all studied surfaces. The H-terminated room-temperature diamond surface differed from the other surfaces only in the fraction of product ions formed in H-atom transfer surface reactions (45% of all product ions formed versus 70% on the other surfaces).     

Anticancer drugs based on alkenyl and boryl substituted titanocene complexes

The alkenyl-substituted titanocene complex [Ti(η⁵-C₅H₅)(η⁵-C₅H₄{CMe₂(CH₂CH₂CHCH₂)})Cl₂] (1) has been synthesized and characterized using traditional methods. The reaction of 1 with 9-BBN gave the boryl substituted complex [Ti(η⁵-C₅H₅)(η⁵-C₅H₄{CMe₂(CH₂CH₂CH₂CH₂BC₈H₁₄)})Cl₂] (2). The cytotoxic activity of 1 and 2 was tested against tumour cell lines human adenocarcinoma HeLa, human myelogenous leukemia K562, human malignant melanoma Fem-x, human breast carcinoma MDA-MB-361 and normal immunocompetent cells peripheral blood mononuclear cells PBMC and compared with those of the reference complexes [Ti(η⁵-C₅H₅)₂Cl₂] (R1), [Ti(η⁵-C₅H₄Me)₂Cl₂] (R2) and [Ti(η⁵-C₅H₅)(η⁵-C₅H₄SiMe₃)Cl₂] (R3). Complex 1 showed higher cytotoxic activities on HeLa, Fem-x and K562 (IC₅₀ values from 96.6 ± 3.4 to 149.2 ± 2.9 μM) than the reference complexes R1, R2 and R3 which presented IC₅₀ values from 173.3 ± 6.0 to >200 μM. On the other hand, boryl substituted complex 2, present slightly lower cytotoxic activities than 1 on HeLa, Fem-x and K562 (IC₅₀ values from 155.6 ± 5.5 to 167.9 ± 4.2 μM). However, 2 was the most active of the studied complexes against MDA-MB-361 (IC₅₀ value of 161.1 ± 0.1 μM). Structural studies based on DFT calculations of 1 and 2 have also been carried out in order to gain a possible insight into the relationship between metal complex structure and cytotoxicity.     

Utilization of W/Mg(NO3)2 modifiers for the direct determination of As and Sb in soils,sewage sludge and sediments by solid sampling electrothermal atomic absorption spectrometry

A simple method has been developed for the determination of arsenic and antimony in environmental samples by solid sampling electrothermal atomic absorption spectrometry, which was validated using certified reference materials of soils (S-VM — Soil Eutric Cambisol; S-MS — Soil Orthic Luvisols; S-SP — Soil Rendzina), sewage sludge (WT-L; WT-M) and sediments (NIES2; GBW07906). The analytical procedure combines solid sampling with utilization of a matrix modifier admixture containing 5 µg of W and 5 µg of Mg. The tungsten in the admixture serves to stabilize the solid matrix during atomisation, which results in dramatically reduced non-specific absorption compared with the conventional palladium modifier. Magnesium was efficient in reducing the accumulation of the matrix residue on the platform. An alternative resonance line of 197.2 nm for arsenic and 206.8 nm for Sb was used in order to eliminate the spectral interferences caused by aluminum compounds, and silicon and iron compounds, respectively. Under optimized experimental conditions, the effective in situ analyte/matrix separation was achieved so that the use of aqueous standards for calibration became possible. With the modifier, a 3 SD detection limit of 0.5 µg g⁻¹ As and 0.1 µg g⁻¹ Sb and 10 SD quantification limit of 1.7 µg g⁻¹As and 0.3 µg g⁻¹ Sb and a characteristic mass of 65 pg As and 53 pg Sb were obtained. For all the matrices under scrutiny, a good agreement with certified values was achieved with RSD values less than 10%.     

Correlation between proton transfer and 35Cl NQR frequency as well as molecular geometry of chloranilic acid in co‐crystals with some organic bases

Proton transfer in hydrogen‐bonded organic co‐crystals of chloranilic acid with some organic bases was investigated by nuclear quadrupole resonance (NQR) spectroscopy. The ³⁵Cl NQR frequencies of chloranilic acid molecule as well as ¹⁴N NQR frequencies of the organic base molecule were measured with the conventional pulse methods as well as double‐resonance methods, respectively. The extent of proton transfer in the O···H···N hydrogen bond was estimated from Townes–Dailey analysis of the ¹⁴N NQR parameters. The ³⁵Cl NQR frequency and molecular geometry of chloranilic acid are correlated to the extent of proton transfer in the protonation process of the organic base molecule. It is shown that the hydrogen bond affects the π‐electron system of chloranilic acid. Geometry dependence of the O···H···N hydrogen bond, i.e. the H? N valence bond order versus the hydrogen‐bond geometry correlation is also discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

Thermal electrocyclization reactions II: benzooctatetraenes and benzodecapentaenes

Thermal electrocyclization reactions of benzooctatetraenes and benzodecapentaenes substituted with R=H, Cl, and methyl were studied experimentally and computationally. Methyl and unsubstituted benzooctatetraenes and benzodecapentaenes give the [4.2.0]bicyclooctadiene products by 8π,6π-electrocyclization. Chlorine substitution led to thermal rearrangement of the initially formed 8π,6π-electrocyclization intermediates to give unprecedented products.