Determination of arsenic(III) and arsenic(V) by electrothermal atomic absorption spectrometry after complexation and sorption on a C-18 bonded silica column

A flow injection procedure for the separation and pre-concentration of inorganic arsenic based on the complexation with ammonium diethyl dithiophosphate (DDTP) and sorption on a C-18 bonded silica gel minicolumn is proposed. During the sample injection by a time-based fashion, the As³⁺-DDTP complex is stripped from the solution and retained in the column. Arsenic(V) and other ions that do not form complexes are discarded. After reduction to the trivalent state by using potassium iodide plus ascorbic acid, total arsenic is determined by electrothermal atomic absorption spectrometry (ETAAS). Arsenic(V) concentration can be calculated by difference. After processing 6 ml sample volume, the As³⁺-DDTP complexes were eluted directly into the autosampler cup (120 μl). Ethanol was used for column rinsing. Influence of pH, reagent concentration, pre-concentration and elution time and column size were investigated. When 30 μl of eluate plus 10 μl of 0.1% (w/v) Pd(NO₃)₂ were dispensed into the graphite tube, analytical curve in the 0.3–3 μg As l⁻¹ range was obtained (r=0.9991). The accuracy was checked for arsenic determination in a certified water, spiked tap water and synthetic mixtures of arsenite and arsenate. Good recoveries (97–108%) of spiked samples were found. Results are precise (RSD 7.5 and 6% for 0.5 and 2.5 μg l⁻¹, n=10) and in agreement with the certified value of reference material at 95% confidence level.     

二肽和三肽甜味剂的结构性能关系

本文用作者(1980)提出的多点接触U-型诱导适应甜苦味受体模型说明与Asparta-me类似的二肽三肽甜味剂中结构与性能相互关系。其中生甜基(Glucophore)G=~-O_2C(CH_2)_(0-1)·CHNH_2R~ ,R=H;助味基(Auxogluc)A~N=R,R为N-端酰胺基;C-端助味基A~C=CONHC·R~1R~2R~3,此处R~3>R~2>R~1。A~N和A~C的主干链均以其能达到味受体膜的外层中部C-9位时化合物最甜。G的定味位置和方向不同,A~N和A~C主干链可到达的膜层深浅也将不同,然而总以能到达受体膜的C-9位时才能产生最强微扰。故最有利的助味基常以其约相当于一脂肪酸酰基C_9的链长为最好,且过犹不及。若以不对称碳原子上取代基R~1R~2R~3的体积大小(而不是以原子序数大小)作我们称之为“拓朴”构型的准则,则并联三肽A~N-G-A_2~C的三个氨基酸都必需是“拓朴”-D-型才能产生高甜度。而串联三肽G-A_1~C-A_2~C中仅需A_2~C是“拓朴”-L-型。二肽G-A~C中A~C的主干链宽度R~1-C-R~2以≤(CH_2)_4为度;三肽G-A_1~C-A_2~C中A_2~C宽度以≤(CH_2)_5为度。除其他指标外,R,R_2和R_3本身或其取代基所具有极性效应、空间效应,疏水效应对这些甜味剂所产生的甜强度及稳定性的影响都是容易理解的。     

Strukturelle und spektroskopische Charakterisierung sechsfach koordinierter Vanadium(V)-Komplexe: Ein Strukturmodell für das aktive Zentrum Vanadium-abhängiger Haloperoxidasen

Structural and Spectroscopic Characterization of Six-Coordinate Vanadium(V) Complexes: A Structural Model for the Active Site of Vanadium-Dependent Haloperoxidases A series of vanadium(V) complexes has been synthesized from ammonium metavanadate and trivalent, pentadentate Schiff base ligands. These aliphatic as well as aromatic hydroxyl groups containing ligands are stabilizing the VO³⁺ unit. The complexes 1–5 are characterized by ¹H-, ¹³C- and ⁵¹V-NMR, virbrational (IR, Raman and resonance Raman) and electronic spectroscopy as well as EHMO calculations. The X-ray crystal structure analysis of 1 (monoclinic space group P2₁/n: a = 1 073.3(2); b = 1 201.1(3); c = 1 165.7(3) pm; β = 101.89(2)°; Z = 4) shows that the vanadium(V) center has a distorded octahedral environment. The LMCT transition of the complexes 1–5 in the electronic spectra has been observed at comparatively high energies (21.8 ? 25.8 × 10³ cm^?1) and are assigned based on resonance Raman spectra and EHMO calculations. The implications of the observed physical properties of the complexes 1–5 to the structural model proposed for the active site of vanadat(V)-dependent haloperoxidases are discussed.     

A Solution and Solid State Study on 2-Hydroxypropyl-β-Cyclodextrin Complexation with Hyodeoxycholic Acid

Hyodeoxycholic acid (HDCA) isa 6- dihydroxylated natural bile acid capable ofpreventing gallstone formation by reducing the bilecholesterol saturation. However, any attempt to enrichthe bile acid pool with HDCA have failed owing to thepoor solubility of the molecule. To resolve thebioavailability problems, the complexation of HDCAinto the HPCD cavity was studied in solution(solubility methods, ¹³C- and ¹H-NMRspectroscopy and circular dichroism) and in the solidstate (IR spectroscopy, X-ray diffractometry andthermal analysis). According to the results, the HDCAinclusion took place with 1 : 1 stoichiometry. Theinfluence of different preparation methods of thesolid complex was evaluated for its potential use inappropriate pharmaceutical formulations to improve thebioavailability of HDCA.     

Thermoelectric effect on charged colloids in the Hückel limit

We study the thermophoretic coefficient D_T of a charged colloid. The non-uniform electrolyte is characterized in terms of densities and diffusion currents of mobile ions. The hydrodynamic treatment in the vicinity of a solute particle relies on the Hückel approximation, which is valid for particles smaller than the Debye length, a ≪ . To leading order in the parameter a/ , we find that the coefficient D_T consists of two contributions, a dielectrophoretic term proportional to the permittivity derivative d/dT , and a Seebeck term, i.e., the macroscopic electric field induced by the thermal gradient in the electrolyte solution. Depending on the particle valency, these terms may take opposite signs, and their temperature dependence may result in a change of sign of thermophoresis, as observed in several recent experiments.     

Stereoselective total synthesis of the (Z)-isomer of a novel phytotoxic nonenolide from Phomopsis sp. HCCB03520 and its C-6 epimer

The (Z)-isomer of a phytotoxic nonenolide, (6S,7R,9R)-6,7-dihydroxy-9-propylnon-4-eno-9-lactone isolated from Phomopsis sp. HCCB03520 and its C-6 epimer have been synthesized through a common route starting from butyraldehyde. The synthesis involves enantioselective Maruoka allylation, Sharpless asymmetric epoxidation and intramolecular ring closing metathesis as the important steps.     

Two ring opened oxetane taxoids containing a C-20 benzoyloxy group from the roots of Taxus wallichiana Zucc.

Two new taxanes, named wallitaxane G (1) and H (2), were isolated from the roots of Taxus wallichiana (Taxaceae), together with nine known compounds (3?11). Their structures were elucidated on the basis of NMR spectroscopic analysis and the relative configurations of 1 and 2 were determined based on NOESY data. Wallitaxane H (2) showed the most potent α-glucosidase inhibitory activity, with an IC₅₀ value of 16.1 μM. Plausible biosynthetic pathways for the formation of 1 and 2 were proposed based on oxetane ring-opening and benzoyl migration.     

Perfusion and diffusion sensitive C stimulated-echo MRSI for metabolic imaging of cancer

Metabolic imaging with hyperpolarized [1-¹³C]-pyruvate can rapidly probe tissue metabolic profiles in vivo and has been shown to provide cancer imaging biomarkers for tumor detection, progression, and response to therapy. This technique uses a bolus injection followed by imaging within 1–2 minutes. The observed metabolites include vascular components and their generation is also influenced by cellular transport. These factors complicate image interpretation, especially since [1-¹³C]lactate, a metabolic product that is a biomarker of cancer, is also produced by red blood cells. It would be valuable to understand the distribution of metabolites between the vasculature, interstitial space, and intracellular compartments. The purpose of this study was to better understand this compartmentalization by using a perfusion and diffusion-sensitive stimulated-echo acquisition mode (STEAM) MRSI acquisition method tailored to hyperpolarized substrates. Our results in mouse models showed that among metabolites, the injected substrate ¹³C-pyruvate had the largest vascular fraction overall while ¹³C-alanine had the smallest vascular fraction. We observed a larger vascular fraction of pyruvate and lactate in the kidneys and liver when compared to back muscle and prostate tumor tissue. Our data suggests that ¹³C-lactate in prostate tumor tissue voxels was the most abundant labeled metabolite intracellularly. This was shown in STEAM images that highlighted abnormal cancer cell metabolism and suppressed vascular ¹³C metabolite signals.     

Tris(polymethoxyphenyl)bismuth derivatives: Synthesis and reactivity

Tris-(polymethoxyphenyl)bismuth diacetate and dichloride derivatives react with C-nucleophiles in basic medium, as well as with N- and O-nucleophiles under copper catalysis to give good to high yields of the corresponding C-, N- and O-arylation products.     

Dynamics of spatial Fourier modes in turbulence

We present the results of an experimental study of the spatial Fourier modes of the vorticity in a turbulent jet flow. By means of an acoustic scattering setup we have recorded the evolution in time of Fourier modes of the vorticity field, characterized by well defined wavevectors k. By computing the auto-correlation of the amplitude of the Fourier modes we evidence that, whatever the length scale (or equivalently k), the dynamic evolution of the vorticity field involves two well separated time scales. We have also performed the simultaneous acquisitions of pairs of Fourier modes with two wavevectors k and k'. Whatever the spectral gap k- k', any pair of Fourier modes exhibits a significant cross-correlation over long time delays, indicating a strong statistical dependence between scales.