C‐5 Propynyl Modifications Enhance the Mechanical Stability of DNA

Increased thermal or mechanical stability of DNA duplexes is desired for many applications in nanotechnology or ‐medicine where DNA is used as a programmable building block. Modifications of pyrimidine bases are known to enhance thermal stability and have the advantage of standard base‐pairing and easy integration during chemical DNA synthesis. Through single‐molecule force spectroscopy experiments with atomic force microscopy and the molecular force assay we investigated the effect of pyrimidines harboring C‐5 propynyl modifications on the mechanical stability of double‐stranded DNA. Utilizing these complementary techniques, we show that propynyl bases significantly increase the mechanical stability if the DNA is annealed at high temperature. In contrast, modified DNA complexes formed at room temperature and short incubation times display the same stability as non‐modified DNA duplexes.     

Electrochemical Treatment of Glassy Carbon for Label‐Free Detection of DNA Bases and Neurotransmitters

Electrochemically reduced glassy carbon (r‐GC) showed a superior electrochemical sensing performance, compared to oxidized GC (ox‐GC) and untreated GC for the oxidation of 4 DNA bases and neurotransmitters (epinephrine, norepinephrine and serotonin). r‐GC exhibited not only the largest current intensities of all redox biomolecules, but also displayed an excellent selectivity in detecting coexisting redox biomolecules. The enhanced performance of r‐GC was attributed to the improved surface cleanliness of electrode and its catalytic surface functional groups. The results presented herein imply that simple electrochemical treatments are a viable method to produce sensitive and selective electrodes for label‐free biosensing.     

Hydrophilic interaction chromatography: A promising alternative to reversed‐phase liquid chromatography systems for the purification of small protonated bases

The overloaded band profiles of the protonated species of propranolol and amitriptyline were recorded under acidic conditions on four classes of stationary phases including a conventional silica/organic hybrid material in reversed‐phase liquid chromatography mode (BEH‐C₁₈), an electrostatic repulsion reversed‐phase liquid chromatography C₁₈ column (BEH‐C₁₈+), a poly(styrene‐divinylbenzene) monolithic column, and a hydrophilic interaction chromatography stationary phase (underivatized BEH). The same amounts of protonated bases per unit volume of stationary phase were injected in each column (16, 47, and 141 μg/cm³). The performance of the propranolol/amitriptyline purification was assessed on the basis of the asymmetry of the recorded band profiles and on the selectivity factor achieved. The results show that the separation performed under reversed‐phase liquid chromatography like conditions (with BEH‐C₁₈, BEH‐C₁₈+, and polymer monolith materials) provide the largest selectivity factors due to the difference in the hydrophobic character of the two compounds. However, they also provide the most distorted overloaded band profiles due to a too small loading capacity. Remarkably, symmetric band profiles were observed with the hydrophilic interaction chromatography column. The larger loading capacity of the hydrophilic interaction chromatography column is due to the accumulation of the protonated bases into the diffuse water layer formed at the surface of the polar adsorbent. This work encourages purifying ionizable compounds on hydrophilic interaction chromatography columns rather than on reversed‐phase liquid chromatography columns.     

Supramolecular Stabilization of Metastable Tautomers in Solution and the Solid State

This work presents a successful application of a recently reported supramolecular strategy for stabilization of metastable tautomers in cocrystals to monocomponent, non‐heterocyclic, tautomeric solids. Quantum‐chemical computations and solution studies show that the investigated Schiff base molecule, derived from 3‐methoxysalicylaldehyde and 2‐amino‐3‐hydroxypyridine ( ap ), is far more stable as the enol tautomer. In the solid state, however, in all three obtained polymorphic forms it exists solely as the keto tautomer, in each case stabilized by an unexpected hydrogen‐bonding pattern. Computations have shown that hydrogen bonding of the investigated Schiff base with suitable molecules shifts the tautomeric equilibrium to the less stable keto form. The extremes to which supramolecular stabilization can lead are demonstrated by the two polymorphs of molecular complexes of the Schiff base with ap . The molecules of both constituents of molecular complexes are present as metastable tautomers (keto anion and protonated pyridine, respectively), which stabilize each other through a very strong hydrogen bond. All the obtained solid forms proved stable in various solid‐state and solvent‐mediated methods used to establish their relative thermodynamic stabilities and possible interconversion conditions.     

Synthesis,antimicrobial and cytotoxic activity of novel azetidine-2-one derivatives of 1H-benzimidazole

A series of 1-methyl-N-[(substituted-phenylmethylidene)-1H-benzimidazol-2-amines (4a–4g) were prepared via the formation of 1-methyl-1H-benzimidazol-2-amine (3), which was prepared by the cycloaddition of o-phenylenediamine (1) with cyanogen bromide in the presence of aqueous base followed by N-methylation with methyl iodide in the presence of anhydrous potassium carbonate in dry acetonitrile. Moreover, the four-membered β-lactam ring was introduced by the cycloaddition of 4a–4g and chloroacetyl chloride in the presence of triethylamine catalyst to give 3-chloro-1-(1-methyl-1H-benzimidazol-2-yl)-(4′-substituted)-phenylazetidin-2-one 5a–5g. A total of 14 compounds were synthesized and characterized by IR, ¹H NMR, ¹³C NMR and Mass spectral technique, in addition they were evaluated for anti-bacterial and cytotoxic properties. Among the chemicals tested 4a, 4b, 5a, 5b, 5g exhibited good antibacterial activity and 5f, 5g shown good cytotoxic activity in vitro.     

MCM-41固载不对称席夫碱Cu(Ⅱ)配合物的制备及催化性能

用多步接枝法将不对称席夫碱Cu(Ⅱ)配合物Cu(CBP-PHEN-Sal)共价联接到介孔分子筛MCM-41的表面。对得到的材料用XRD、FTIR、DR UV-Vis、氮气吸附、元素分析和ICP进行了表征。结果表明,不对称席夫碱Cu(Ⅱ)配合物被成功地固载于MCM-41的孔道中,而且固载后MCM-41的结构特征保持不变。考察了固载催化剂在烯烃液相氧化中的催化活性。以叔丁基过氧化氢为氧化剂,在苯乙烯氧化中,固载催化剂比配合物表现出更高的催化活性。同时,研究了反应条件,例如溶剂、催化剂用量、温度和反应时间对固载催化剂催化性能的影响。     

Continua of interactions between pairs of atoms in molecular crystals

The electron density distributions in crystals of five previously studied DMAN complexes and five Schiff bases (two new ones) have been analysed in terms of various properties of bond critical points (BCPs) found in the pair-wise interactions in their lattices. We analysed the continua of interactions including covalent/ionic bonds as well as hydrogen bonds and all other types of weak interactions for all pairs of interacting atoms. The charge density at BCPs and local kinetic and potential energy densities vary exponentially with internuclear distance (or other measures of separation). The parameters of the dependences appear to be characteristics of particular pairs of atom types. The Laplacian and the total (sum of kinetic and potential) energy density at BCPs show similar behaviour with the dependence being of the Morse type. The components lambda1, lambda2, lambda3 of the Laplacian at BCPs vary systematically with internuclear distance according to the type of atom pair. For lambda1 and lambda2 the distribution is of the exponential type, whereas lambda3 does not seem to follow any simple functional form, consistent with previous theoretical findings. Analytical nonlinear dependences of Laplacian on charge density have been found. They agree reasonably well with those obtained by least square fit of the Laplacian to charge density data. There are four distinct regions of the [symbol: see text]2rho(BCP)/rho(BCP) space, generated by E(BCP) = 0 and G(BCP)/rho(BCP) = 1 conditions. Two regions clearly correspond to the shared-shell and closed-shell interactions and the other two to some intermediate situation.     

微波无溶剂法合成香草醛氨基酸席夫碱

氨基酸席夫碱是制备特殊生物活性物质的重要中间体。氨基酸席夫碱中的亚胺(C=N)结构与亚磷酸烷基酯加成的化合物具有良好的抗植物病毒,除草,杀菌等性能[1-3]。氨基酸席夫碱中的羟基,羧基和亚胺等多个活性基团,可以与多种金属离子配位,其配合物具有抗菌,抗病毒,抗癌等性能[4-9],     

Biological Properties of New Chiral 2-Methyl-5,6,7,8-tetrahydroquinolin-8-amine-based Compounds

The synthesis of a small library of 8-substituted 2-methyl-5,6,7,8-tetrahydroquinoline derivatives is presented. All the compounds were tested for their antiproliferative activity in non-cancer human dermal microvascular endothelial cells (HMEC-1) and cancer cells: human T-lymphocyte cells (CEM), human cervix carcinoma cells (HeLa), human dermal microvascular endothelial cells (HMEC-1), colorectal adenocarcinoma (HT-29), ovarian carcinoma (A2780), and biphasic mesothelioma (MSTO-211H). Compounds 3a, 5a, and 2b, showing significant IC₅₀ values against the whole panel of the selected cells, were further synthesized and tested as pure enantiomers in order to shed light on how their stereochemistry might impact on the related biological effect. The most active compound (R)-5a was able to affect cell cycle phases and to induce mitochondrial membrane depolarization and cellular ROS production in A2780 cells.