pH-sensitive modulation of the second hydration sphere in lanthanide(III) tetraamide-DOTA complexes: a novel approach to smart MR contrast media

The lanthanide(III) complexes of three tetraamide DOTA bearing pyridyl, phenolic and hydroxypyridyl substituents have been studied by NMR, luminescence and cyclic voltammetry. The relaxivity profiles of the gadolinium complexes of the pyridyl and phenolic ligands were flat and essentially the same between pH 2 and 8. The hydroxypyridyl ligand, however, exhibited two regions of enhanced relaxivity. The small relaxivity enhancement (25 %) at lower pH (pH 2-4) has been attributed to an increase in the prototropic exchange of the coordinated water molecule while the slightly larger enhancement (84 %) at higher pH (pH 6-9) reflects deprotonation of the ligand amide protons. Deprotonation of the amides results in the formation of an intramolecular acid-base pair interaction with the phenolic protons and this, in turn, causes a highly organized second hydration sphere to come into effect, thereby increasing the relaxivity. The water relaxivity of the Gd(3+)-hydroxypyridyl complex is further enhanced upon binding to serum albumin.     

Total synthesis and biological evaluation of (-)apicularen A and analogues thereof

Apicularen A (1) and related benzolactone acylenamines belong to a growing class of novel natural products possessing highly cytotoxic properties. The challenging structure of 1 includes a 10-membered macrolactone ring, a tetrahydropyran system, an o,m-substituted phenol and a doubly unsaturated acyl group attached on the side chain enamine functionality. The total synthesis of apicularen A described herein involves a strategy equivalent to its proposed biosynthesis and entails a reiterative two-step procedure featuring allylation and ozonolytic cleavage to grow the molecule's chain by one acetate unit at a time. The developed synthetic technology was applied to the construction of a series of apicularen A analogues whose biological evaluation established a set of structure-activity relationships in this new area of potential importance in cancer chemotherapy.     

Synthesis, binding affinity, and relaxivity of target-specific MRI contrast agents

Although magnetic resonance imaging (MRI) is one of the most important imaging modalities of the central nervous system (CNS), one of the main drawbacks of MRI is its limited specificity. This can potentially be partially alleviated by target-specific contrast agents. In the present paper we describe a simple high yield synthesis of two such gadolinium-based spiperone targeted MRI contrast agents, 1a and 1b. The R₁ relaxivities of 1a and 1b were evaluated and found to be 5.94 and 8.31 mM⁻¹ s⁻¹, respectively at 9.4T, while their R₂ relaxivities at the same magnetic field were found to be 18.05 and 22.60 mM⁻¹ s⁻¹, respectively. In addition and very importantly compound 1a, which is a gadolinium-based, spiperone-targeted MRI contrast agent, was found to preserve some of the spiperone affinity toward the dopamine D2 receptor. Compounds 1a and 1b thus represent potential agents for in vitro dopamine receptor imaging using MRI in experimental models. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

New Cisplatin Analogues—On the Way to Better Antitumor Agents

The clinical success of cisplatin (cis -diamminedichloroplatinum(II )) in antitumor chemotherapy has encouraged an all-out search for analogues with lower toxicity, improved therapeutic index and increased activity. Literally thousands of analogues, obtained by replacement of the ammine- and chloro-ligands by other amines and anionic ligands, respectively, have been systematically screened for activity in experimental tumor models. Some of these analogues have been selected for clinical evaluation, but only very few of them appear to be promising antitumor agents. More recently, cisplatin analogues have been designed and synthesized on the basis of, inter alia, the following considerations: 1) platinum complexes with carrier molecules as ligands should prove useful for achieving increasing drug concentration in tumor tissues; 2) platinum complexes with chemotherapeutic agents as ligands could afford polyfunctional drugs with synergistic action; 3) complexes containing more than one platinum atom might be more effective than complexes containing only one platinum atom; 4) platinum complexes could be used as sensitizers in radiation therapy. In this paper, we shall give a brief account of the “traditional” analogues, and then critically discuss what we believe could be the new trends in the design of cisplatin analogues.     

Evaluation of dithiocarbamates and beta-diketones as chelating agents in supercritical fluid extraction of Cd, Pb, and Hg from solid samples

The use of four dithiocarbamates and three fluorinated β-diketones as potential chelating agents for three transition metal ions (Cd²⁺, Pb²⁺, and Hg²⁺) extracted from spiked sand and filter paper samples by supercritical fluid extraction (SFE) was investigated. The extractions were performed at 45°C and 250 atm for spiked sand samples and at 60°C and 200 atm for filter paper samples using supercritical carbon dioxide modified with 5% methanol. At 250 atm and using carbon dioxide modified with 5% methanol, the recoveries of Cd²⁺, Pb²⁺, and Hg²⁺ ions from spiked sand samples were 95% with lithium bis(trifluoroethyl)dithiocarbamate (LiFDDC) as the chelating agent; they ranged from 83–97% with diethylammonium diethyldithiocarbamate and from 87–97% with sodium di-ethyldithiocarbamate as chelating agents, and from 68–96% with trifluoracetylacetone, hexafluoroacetylacetone, and thenoylfluoroacetone as chelating agents. Ammonium pyrrolidinedithiocarbamate was not effective in the chelation SFE of Cd²⁺, Pb²⁺, and Hg²⁺ ions from either spiked sand or spiked filter paper samples under the extraction conditions used. Supercritical carbon dioxide alone gave consistently lower analyte recoveries than supercritical carbon dioxide modified with 5% methanol. The results suggest that the solubility of the metal chelate in the supercritical fluid plays a more important role than the solubility of the chelating agent in the supercritical fluid, as long as sufficient chelating agent is present in the fluid phase. Fluorination of the chelating agent, as in the case of LiFDDC, increases the solubility of the metal chelate, and subsequently enhances the extraction efficiency for the metal ions.     

Development and Validation of a High Performance Liquid Chromatographic Method for the Determination of Voriconazole Content in Tablets

This paper describes the validation of an isocratic HPLC method for the assay of voriconazole in tablets. The method employs a Merck LiChrospher^? 100 RP-8 (125 × 4.6 mm I.D., 5 μm particle size) column, with a mobile phase of methanol : triethylamine solutions 0.6 %, pH 6.0 (50:50, v/v) and UV detection at 255 nm. A linear response (r > 0.9999) was observed in the range of 20.0–100.0 μg mL⁻¹. The method showed good recoveries (average 100.4%) and the relative standard deviation intra and inter-day were ≤ 1.0 %. Validation parameters as specificity and robustness were also determined. The method can be used for both quality control assay of voriconazole in tablets and for stability studies as the method separates voriconazole from its degradation products and tablet excipients.     

Preparation of 5-diaminomethylenebarbiturates by barbituric acid addition to carbodiimides

Through NMR spectroscopic monitoring of barbituric acid addition to carbodiimide, a general synthetic procedure for the preparation of 5-diaminomethylenebarbiturates (DABA) was developed. This procedure is very simple and applicable to the preparation of large quantities of DABA derivatives. Through an X-ray structural study of one of the DABA derivatives, it was established that these compounds have an ylide-type structure with strong charge separation within the molecule.     

锂离子电池用纳米Sn/SnSb合金三维复合负极的制备及性能

采用多步电沉积法制备的三维多孔铜箔作为集流体、低温液相化学还原法制备的纳米Sn/SnSb 合金作为负极材料, 制备出一种新型三维多孔结构的纳米Sn/SnSb合金复合负极. 通过与普通负极电化学性能的对比实验发现, 这种新型三维复合负极具有如下优点: 三维多孔网络结构提高了负极活性材料与集流体之间的结合力, 使不含粘结剂电极的制备成为可能; 有效缓解了高容量负极活性材料在充放电过程中的体积膨胀, 提高了负极活性材料的循环性能, 当循环到第30周时, 普通负极剩余容量为初始容量的33%, 而三维复合负极剩余容量为初始容量的41%; 三维铜箔集流体的特殊结构为高容量负极活性材料提供了一个良好的导电环境, 使电极反应进行得更加完全, 从而获得了更高的电极比容量, 普通负极初始容量为480 mAh·g-1, 而三维复合负极达到了800 mAh·g-1. 纳米Sn/SnSb合金三维复合负极良好的电化学性能为锂离子电池负极结构的设计开发提供了新的思路.     

Obtainment of chelating agents through the enzymatic oxidation of lignins by phenol oxidase

Oxidation of lignin obtained from acetosolv and ethanol/water pulping of sugarcane bagasse was performed by phenol oxidases: tyrosinase (TYR) and laccase (LAC), to increase the number of carbonyl and hydroxyl groups in lignin, and to improve its chelating capacity. The chelating properties of the original and oxidized lignins were compared by monitoring the amount of Cu²⁺ bound to lignin by gel permeation chromatography. The Acetosolv lignin oxidized with TYR was 16.8% and with LAC 21% higher than that of the original lignin. For ethanol/water lignin oxidized with TYR was 17.2% and with LAC 18% higher than that of the original lignin.     

Impregnated silica-based layers in thin layer chromatography

Abstract

Impregnated thin-layer chromatography (TLC) layers based on silica gel are presented. Impregnating agents such as metal cations, inorganic ions, chelating agents, chiral selectors, surfactants, ion-pairing reagents, and ionic liquids are discussed. The role of impregnated TLC layers in medicinal chemistry is highlighted. The historical overview of TLC separations on physically coated layers is given and some future prospects ahead of this technique are discussed.