Crystal structure and magnetic properties of two new antiferromagnetic spin dimer compounds; FeTe3O7X (X = Cl, Br)

Two new isostructural layered oxohalides FeTe(3)O(7)X (X = Cl, Br) were synthesized by chemical vapor transport reactions, and their crystal structures and magnetic properties were characterized by single-crystal X-ray diffraction, Raman spectroscopy, magnetic susceptibility and magnetization measurements, and also by density functional theory (DFT) calculations of the electronic structure and the spin exchange parameters. FeTe(3)O(7)X crystallizes in the monoclinic space group P2(1)/c with the unit cell parameters a = 10.7938(5), b = 7.3586(4), c = 10.8714(6) ?, β = 111.041(5)°, Z = 4 for FeTe(3)O(7)Cl, and a = 11.0339(10), b = 7.3643(10), c = 10.8892(10) ?, β = 109.598(10)°, Z = 4 for FeTe(3)O(7)Br. Each compound has one unique Fe(3+) ion coordinating a distorted [FeO(5)] trigonal bipyramid. Two such groups share edges to form [Fe(2)O(8)] dimers that are isolated from each other by Te(4+) ions. The high-temperature magnetic properties of the compounds as well as spectroscopic investigations are consistent with an isolated antiferromagnetic spin dimer model with almost similar spin gaps of ~35 K for X = Cl and Br, respectively. However, deviations at low temperatures in the magnetic susceptibility and the magnetization data indicate that the dimers couple via an interdimer coupling. This interpretation is also supported by DFT calculations which indicate an interdimer exchange which amounts to 25% and 10% of the intradimer exchange for X = Cl and Br, respectively. The magnetic properties support the counterion character and a weak integration of halide ions into the covalent network similar to that in many other oxohalides.     

Development and validation of a sensitive and fast solid-phase spectrophotometric procedure for phenol determination in pharmaceuticals

A very sensitive, simple, and fast solid-phase spectrophotometric procedure for the determination of phenol using the p-nitrobenzenediazonium reagent (DAR reagent) was developed. This procedure is based on the simultaneous concentration of the orange product on a Dowex 1-X2 anion exchanger within 15 min, and a direct absorbance measurement of the sorbed species at both 530 nm (the absorption maximum of the phenol-DAR in the resin phase) and 700 nm (the range where only the resin absorbs light). Quality control and evaluation of the analytical parameters was carried out using a comprehensive prevalidation strategy. The linearity of the method was confirmed within an analyte working range from 0.01 to 0.10 μmol (0.2 to 2.0 nmol mL(-1)). The precision ranged from ±1.17 to ±9.61%; the accuracy ranged from -17.50 to +17.81%. The evaluated limiting values were L(D) = 0.0013 μmol and L(Q) = 0.0082 μmol. The DAR-SPS method was successfully applied to the determination of phenol in a pharmaceutical sample of salicylic acid (98.0-100.0%) and vaccines (98.0-103.4%).     

Analysis of lysergic acid amide in human serum and urine after ingestion of Argyreia nervosa seeds

The ergot alkaloid lysergic acid amide (LSA) is a secondary plant constituent in a number of plants, but it is mainly present in considerable amounts in Convolvulaceae, like Argyreia nervosa. Due to its close structural similarity to lysergic acid diethylamide, LSA is considered as psychedelic and therefore promoted as so-called “legal high” in various internet forums. During a human behavioral study with orally administered seeds of A. nervosa, blood and urine samples were obtained. The present study describes the validation of a sensitive and robust high performance liquid chromatography method with fluorescence detection, which was applied to the study samples. The limit of detection (LOD) and lower limit of quantification in human serum were 0.05 and 0.17 ng/mL, respectively, and in urine, the LOD was 0.15 ng/mL. Intra- and interday precision and accuracy were below 15 % relative standard deviation with a bias better than ±15 %. No conversion of LSA to its epimer iso-LSA was noted during analyses. The LSA concentrations in the authentic human serum samples were in the range of 0.66 to 3.15 ng/mL approximately 2 h after ingestion. In urine, LSA could be found 1–24 h after ingestion; after 48 h, no LSA could be detected. The LSA epimer iso-LSA was also detected in serum and urine in varying ratios. In conclusion, LSA serum levels in the low nanogram per milliliter range correlated with severe vegetative adverse effects (nausea, weakness, fatigue, tremor, blood pressure elevation) and a psychosis-like state, which led to study termination.     

Magneto-structural studies on heterobimetallic malonate-bridged M(II)Re(IV) complexes (M = Mn, Co, Ni and Cu)

The mononuclear Re(IV) compound of formula (PPh(4))(2)[ReBr(4)(mal)] (1) was used as a ligand to obtain the heterobimetallic species [ReBr(4)(μ-mal)Co(dmphen)(2)]· MeCN (2), [ReBr(4)(μ-mal)Ni(dmphen)(2)] (3), [ReBr(4)(μ-mal)Mn(dmphen)(2)] (4a), [ReBr(4)(μ-mal)Mn(dmphen)(H(2)O)(2)]·dmphen·MeCN·H(2)O (4b), [ReBr(4)(μ-mal)Cu(phen)(2)]·1/4H(2)O (5) and [ReBr(4)(μ-mal)Cu(bipy)(2)] (6) (mal = malonate dianion, dmphen = 2,9-dimethyl-1,10-phenanthroline, phen = 1,10-phenanthroline and bipy = 2,2'-bipyridine). The structures of 2 and 5 (single-crystal X-ray diffraction) are made up of neutral [ReBr(4)(μ-mal)M(AA)] dinuclear units [AA = dmphen with M = Co (2) and AA = phen with M = Cu (5)] where the metal ions are connected through a malonate ligand which exhibits simultaneously the bidentate [at the Re(IV)] and monodentate [at the M(II)] coordination modes. The carboxylate-malonate group in them adopts the anti-syn conformation with intramolecular ReM separation of 5.098(8) (2) and 4.947(2) ? (5). The magnetic properties of 1-6 were investigated in the temperature range 1.9-295 K. The magnetic behaviour of 1 is the expected for a magnetically isolated Re(IV) complex with a large value of the zero-field splitting (2D ca. -70 cm(-1)) whereas weak antiferromagnetic interactions between Re(IV) and M(II) are observed in the heterobimetallic compounds 2 (J = -0.63 cm(-1)), 3 (J = -1.37 cm(-1)), 4a (J = -1.29 cm(-1)), 5 (J = -1.83 cm(-1)) and 6 (J = -0.26 cm(-1)). Remarkably, 4b behaves as a ferrimagnetic chain with regular alternating Re(IV) and Mn(II) cations (J = -2.64 cm(-1)).     

Communication: On the locality of hydrogen bond networks at hydrophobic interfaces

The formation of structured hydrogen bond networks in the solvation shells immediate to hydrophobic solutes is crucial for a large number of water mediated processes. A long lasting debate in this context regards the mutual influence of the hydrophobic solute into the bulk water and the role of the hydrogen bond network of the bulk in supporting the solvation structure around a hydrophobic molecule. In this context we present a molecular dynamics study of the solvation of various hydrophobic molecules where the effect of different regions around the solvent can be analyzed by employing an adaptive resolution method, which can systematically separate local and nonlocal factors in the structure of water around a hydrophobic molecule. A number of hydrophobic solutes of different sizes and two different model potential interactions between the water and the solute are investigated.     

Structure-based coarse-graining in liquid slabs

Structure-based coarse-graining relies on matching the pair correlation functions of a reference (atomistic) and a coarse-grained system. As such, it is designed for systems with uniform density distributions. Here, we demonstrate how it can be generalized for inhomogeneous systems by coarse-graining slabs of liquid water and methanol in vacuum, as well as a single benzene molecule at the water-vacuum interface. Our conclusion is that coarse-graining performed in inhomogeneous systems improves thermodynamic properties and the structure of interfaces without significant alterations to the local structure of the bulk liquid.     

Measurements of the heat capacity of diamond with different isotopic compositions

We report measurements of the heat capacity C_p of diamond with several isotopic compositions (¹²C_1−x¹³C_x) in the 20-280 K temperature range. The results, in particular the derivative of the specific heat with respect to the average isotopic mass, are compared with recent ab initio calculations. Agreement is good for T>150 K. At lower temperatures, the samples with isotopic compositions different from the natural one display an anomalous increase in C_p/T³ with decreasing temperature which is attributed to the presence of metallic inclusions stemming from the metal used as a solvent in the high-pressure high-temperature growth process.     

Charge-order-driven spin-peierls transition in alpha(')-NaxV2O5

We conclude from 23Na and 51V NMR measurements in alpha(')-NaxV2O5 (x = 0.996) (i) a charge-ordering transition starting at T相似文献   

High-sensitivity sapphire cells for high pressure NMR spectroscopy on proteins

High pressure NMR spectroscopy is a most exciting method for studying the structural anisotropy and conformational dynamics of proteins. The restricted volume of the high pressure glass cells causes a poor signal to noise ratio which up to now renders the application of most of the multidimensional NMR experiments impossible. The method presented here using high strength single crystal sapphire cells doubles the signal-to-noise ratio and allows to perform high pressure NMR measurements more easily. As a first application the difference of partial molar volumes caused by cis-trans-isomerisation of a prolyl peptide bond in the tetrapeptide Gly-Gly-Pro-Ala could be determined as 0.25 ml mol(-1) at 305 K.