Automated method for the determination of vitamin D3 hydroxymetabolites in serum

An almost automated method for the determination of hydroxymetabolites of vitamin D₃ (cholecalciferol) in human serum is reported. The method consists of three steps: 1) a batch liquid–liquid extraction step with 2-propanol and hexane, and drying of the extract and reconstitution with phosphate buffer. 2) A cleanup and preconcentration step based on solid-phase extraction using Prospekt equipment, with CN group cartridges and elution with the chromatographic mobile phase. 3) A chromatographic step for individual separation of the target analytes starting with a 90:10 methanol–water mixture, then a linear gradient to obtain 100% methanol; followed by photometric detection. The method provides a linear range between 1.0 and 100 ng mL^–1 for 24,25-(OH)₂ vitamin D₃ and for 25-(OH)₂ vitamin D₃, and between 1.5 and 100 ng mL^–1 for 1,25-(OH) vitamin D₃, with correlation coefficients ranging between 0.993 and 0.987, repeatability between 1.9% and 4.8% and within-laboratory reproducibility between 2.8% and 8.8%.     

Determination of vitamins D2, D3, K1 and K3 and some hydroxy metabolites of vitamin D3 in plasma using a continuous clean-up-preconcentration procedure coupled on-line with liquid chromatography-UV detection

A semi-automatic procedure for the continuous clean-up and concentration of several fat-soluble vitamins prior to their separation by HPLC and UV detection is reported. The procedure is based on the use of a minicolumn packed with aminopropylsilica as sorbent located prior to the chromatographic detection system. The overall process was developed and applied to the main liposoluble vitamins (A, D2, D3, E, K1, K3) and several hydroxy metabolites of vitamin D3 [25-(OH)-D3,24,25-(OH)2-D3 and 1,25-(OH)2-D3]. All the analytes were monitored at a compromise wavelength of 270 nm. Calibration graphs were constructed between 0.01 and 100 ng ml-1 for vitamin D2 and D3 and their hydroxy metabolites, between 0.1 and 100 ng ml-1 for vitamin A, K1 and K3 and between 1 and 100 ng ml-1 for vitamin E, with excellent regression coefficients (> or = 0.9901) in all cases. The precision was established at two concentration levels with acceptable RSDs in all instances (between 3.6 and 8.7%). The method was appropriate for the determination of vitamin D2, D3, K1 and K3 and the 24,25-dihydroxy and 25-hydroxy metabolites of vitamin D3 in human plasma. The method was applied to plasma samples spiked with the target analytes and the recoveries ranged between 78 and 109%.     

Chromium(VI) transport through the Raipore 1030 anion exchange membrane

The flat sheet Raipore R1030 anion exchange membrane has been evaluated as a sample interface in an optical sensor for Cr(VI) monitoring. The R1030 is an anion exchange membrane containing quaternary ammonium groups. The Donnan dialysis (DD) that takes place has been enhanced with facilitated transport of Cr(VI) anions by using a 1,5-diphenylcarbazide (DPC) solution as stripping phase. The DPC acts as a reducing reagent for Cr(VI), and as a complexing reagent for the generated Cr(III). The Cr(III) complex is a strongly absorbing species, and this is the basis of the optical detection. The effect of chemical parameters on Cr(VI) transport has been evaluated. Experiments with UV-VIS detection have shown that the membrane R1030-DPC system exhibits features suitable for Cr(VI) optical sensing. A simplified model based on a kinetic approach is reported describing the transport mechanism of the chemically facilitated DD process.     

2‐Amino‐5‐nitro‐4,6‐dipiperidinopyrimidinium hydrogen­sulfate monohydrate: hydrogen‐bonded sheets containing highly distorted cations

In the title compound, C₁₄H₂₃N₆O₂⁺·HSO₄⁻·H₂O, the pyrimidinium ring of the cation adopts a twist‐boat conformation, induced by steric clashes between adjacent ring substituents; the anions and the water mol­ecules are linked by three O—H⃛O hydrogen bonds [H⃛O = 1.70–1.78 Å, O⃛O = 2.548 (2)–2.761 (2) Å and O—H⃛O = 161–168°] into chains of edge‐fused R(12) rings, which are linked into sheets by the cations, via three N—H⃛O hydrogen bonds [H⃛O = 1.96–2.17 Å, N⃛O = 2.820 (2)–2.935 (2) Å and N—H⃛O = 145–173°].     

Hydro­gen bonding in substituted nitro­anilines: isolated nets in 1,3‐­diamino‐4‐nitrobenzene and continuously interwoven nets in 3,5‐­dinitro­aniline

Molecules of 1,3‐diamino‐4‐nitrobenzene, C₆H₇N₃O₂, are linked by N—H?O hydrogen bonds [N?O 2.964 (2) and 3.021 (2) Å; N—H?O 155 and 149°] into (4,4) nets. In 3,5‐di­nitro­aniline, C₆H₅N₃O₄, where Z′ = 2, the mol­ecules are linked by three N—H?O hydrogen bonds [N?O 3.344 (2)–3.433 (2) Å and N—H?O 150–167°] into deeply puckered nets, each of which is interwoven with its two immediate neighbours.     

N‐(2‐Amino‐1,6‐di­hydro‐5‐nitro­so‐6‐oxopyrimidin‐4‐yl)‐l‐isoleucine–water (4/1): interplay of molecular and supramolecular structures

In the title compound, 2C₁₀H₁₅N₅O₄·0.5H₂O, there are two independent mol­ecules of the pyrimidinyl­isoleucine in general positions and a water mol­ecule lying on a twofold rotation axis. The bond lengths within the organic moieties demonstrate significant polarization of the electronic structure. Each of the organic mol­ecules participates in 12 intermolecular hydrogen bonds, of O—H?O and N—H?O types, while the water mol­ecule acts as a double donor and as a double acceptor of O—H?O hydrogen bonds. The organic components are linked by the hydrogen bonds into a single three‐dimensional framework, reinforced by the water mol­ecules.     

Amperometric Detection and Quantification of 8‐Hydroxy‐2′‐deoxyguanosine (8‐OHdG) Using Dendrimer Modified Electrodes

8‐Hydroxy‐2′‐deoxyguanosine (8‐OHdG) detection by high performance liquid chromatography (HPLC) with amperometric detection was studied using a Au electrode modified with different dendrimer based thin films. Gold electrode is thiol‐modified, forming self‐assembled monolayers on which different generation PAMAM dendrimers with terminal functional groups ? COOH and ? NH₂ have been attached using peptidic bonds. Results obtained in synthetic samples show low limits of detection and quantification for 8‐OHdG (1.2×10^?9 and 3.7×10^?9 M respectively), with matrix interference elimination, thus avoiding sample pretreatment. Best results are obtained with electrodes modified with aliphatic amino thiols and 3.5 and 4.5 generation carboxylated dendrimers (Au/AET/DG^3.5 and Au/AET/DG^4.5), demonstrating that these materials constitute a good alternative for 8‐OHdG determination in biological fluids.     

Pressure-induced structural transformations of the Zintl phase sodium silicide

The high-pressure behaviour of NaSi has been studied using Raman spectroscopy and angle-dispersive synchrotron X-ray diffraction to observe the onset of structural phase transformations and potential oligomerisation into anionic Si nanoclusters with extended dimensionality. Our studies reveal a first structural transformation occurring at 8–10 GPa, followed by irreversible amorphisation above 15 GPa, suggesting the formation of Si–Si bonds with oxidation of the Si⁻ species and reduction of Na⁺ to metallic sodium. We have combined our experimental studies with DFT calculations to assist in the analysis of the structural behaviour of NaSi at high pressure.     

Benzomorphan related compounds. XIII. Syntheses of 2,6-methanopyrrolo[1,2-d] [1,4]diazocines

Two alternative syntheses of 2,6-methanopyrrolo[1,2-d][1,4]diazocines (I) based in the acidic cyclization of 2-(1-pyrrolylmethyl)tetrahydropyridines are described. In the first synthetic route, lithium aluminum hydride reduction of 2-cyano-1,4-dimethyl-1,2,3,6-tetrahydropyridine (IIa) followed by reaction of the resulting primary amine with 2,5-diethoxytetrahydrofuran affords the requisite tetrahydropyridine IVa. An analogous sequence from 2-cyano-4,6-di-methylpyridine (V) leads to the corresponding 2-(1-pyrrolylmethyl)pyridine VII which by quaternization and borohydride reduction yields a mixture of isomeric tetrahydropyridines, precursors of the pyrrolodiazocine systems Ib and Ic. Structural and stereochemical assignment of the synthesized compounds are discussed.