Improved syntheses of bis(beta-cyclodextrin) derivatives, new carriers for gadolinium complexes

In the last decade a number of reports have been published on the synthesis and characterization of bridged cyclodextrin dimers (bis-CDs) connected with linkers of different lengths and structures. These dimers, having two hydrophobic cavities in close proximity, display much higher binding affinities and molecular selectivities than parent CDs, forming stable supramolecular adducts. We describe new synthetic protocols for the preparation of bis(beta-CDs) bearing 2-2', 3-3' and 6-6' bridges. Some of the critical steps were carried out either under high-intensity ultrasound (US) or microwave (MW) irradiation. Bis(beta-CDs) containing 6-6' ureido- and thioureido-bridges were prepared in high yields by a MW-promoted aza-Wittig reaction using polymer-bound triphenylphosphine, while those containing 2,2' and 3,3' bridges were prepared from mono-alkenyl beta-CDs by the cross-metathesis reaction (homodimerization) in the presence of 2(nd)-generation Grubbs catalyst under sonochemical conditions. By these improved protocols CD dimers could be obtained in gram amounts to prepare stable adducts of bis-CDs with contrast agents (CAs) containing gadolinium(iii) chelates. In the case of Gd(iii) chleate "G-1" the inclusion complexes were found to be 2 to 3 orders of magnitude more stable than that formed by beta-CD (K(ass) = 4.3 x 10(4) M(-1)vs 8.0 x 10(2) M(-1)). Relaxivity increased as well by factors of 3 and 4, viz. from 9.1 mM(-1) s(-1) (beta-CD) to 27.7 and 35 mM(-1) s(-1).     

Solution of the mixed Dirichlet–Neumann problem for molecular orientation in liquid crystals

The orientation of the nematic director field under the action of an external time‐dependent field is theoretically investigated as a mixed Dirichlet–Neumann boundary‐value problem. This mathematical problem represents the situation in which a nematic liquid crystal sample is limited by two inhomogeneous flat surfaces, separated by a distance d, on which the anchoring is weak. By considering the one‐constant approximation and a parabolic approximation for the surface energy, the initial conditions and boundary‐value problem for the profile of the tilt angle can be analytically solved even in the case in which the surfaces are not identical, which represents the more general situation. The results are valid for small deviations from the homeotropic orientation and for θ?Θ?1, where θ is the actual tilt angle and Θ characterizes the easy direction imposed by the surface, and can be relevant to investigation of the molecular orientation in a nematic cell submitted to a small external voltage.     

Catalytic properties of a mixed calcium-cobalt orthophosphate, II. Determination of the active sites in propan-2-OL dehydrogenation

The effect of acidic (phenol) and basic (pyridine) poisons as well as that of water on propan-2-ol dehydrogenation were used to determine the nature of the active sites in the most active catalyst found in the mixed calcium-cobalt orthophosphate system, Ca_3−xCo_x(PO₄)₂, with x=0.32. A mechanism for catalyst action is discussed in light of the results obtained.     

94Mo高自旋态能级纲图

通过重离子融合蒸发反应^16O(^82Se 4n)^94Mo布局了^94Mo核的高自旋态．利用多探头探测器阵列GASP进行了在束γ测量，从而重新研究了^94Mo核的高自旋态能级结构．基于新发现的一些重要的连接跃迁，对^94Mo核的高自旋态能级纲图做了重要修改．将新的能级结构与壳模型计算进行了比较和讨论．结果表明要正确的描述^94Mo核的高自旋态(自旋值大于14)能级结构，应考虑价中子在d5／2，g7／2和h11/2轨道上的激发．     

A facile one-step synthesis of chromeno[4,3-b]pyridine derivatives promoted by niobium pentachloride

Chromenes are part of an important class of heterocyclic compounds, natural or synthetic, and have many biological and chemical applications. Among them, chromenopyridines has arisen as a promising material for pharmacological applications. In this work is described a simple and cost-effective method to synthesize chromeno[4,3-b]pyridine derivatives from multicomponent reaction between 4-aminocoumarin, benzaldehyde derivatives, and ethyl benzoylacetates catalyzed by niobium pentachloride. The new method provides good yields with reasonable reaction times, under mild reaction conditions.     

Switchable Biosensor Controlled by Biocatalytic Process

The poly(dimethylamino methacrylate) (PDMAEMA) brush‐modified indium tin oxide (ITO) electrode was used to test the switch properties of interfacial activity caused by bioelectrochemical signals. The swelling of the polymer brushes increased when the medium’s pH changed from alkaline to acid after glucose was added to the system. A pH change generated in situ by means of biocatalytic reactions enabled bioelectrocatalytic interface’s reversible activation.     

Supramolecular compounds of azo dyes derived from 1-phenylazo-2-naphthol and their nickel and copper complexes

In this study, experimental techniques including Raman, infrared and X-ray crystal diffraction, as well as quantum chemistry calculations, are used to investigate two new azo dyes supramolecular complexes: 1-phenylazo-2-naphthol (Sudan I) with nickel(II) ion and 1-(2,4-xylylazo)-2-naphthol (Sudan II) with copper(II) ion. The crystallographic structures have been solved for bis-1-(pheny-l-azo)-2-naphtholatenickel(II) and bis-1-(2,4-xylylazo)-2-naphtholatecopper(II) complexes, revealing the presence of supramolecular interactions, such as the centroid–centroid π-stacking interactions and CH…π hydrogen interactions. These weak intermolecular interactions appear to play an important role on the crystal structure stability for both compounds. Density functional theory calculations at B3LYP/6-311++G(d,p) level were performed in order to help understanding such molecular interactions and to assign the vibrational spectra. The experimental and theoretical data have allowed the analysis of the packing forces, revealing charge accumulation at key molecular regions.     

Chemical analysis of the semipurified extract of Paullinia cupana and evaluation of in vitro inhibitory effects against Helicobacter pylori

Abstract

Paullinia cupana Kunth, commonly known as guarana, is a native Brazilian plant species from the Amazon area that presents various biological effects, including antimicrobial action. The aim of this study was to chemically analyse the semipurified aqueous extract (AqF) of the plant and to evaluate the activity of crude (CE), ethyl-acetate (EAF), and AqF extracts against Helicobacter pylori. The chemical profile of AqF was determined based on solid analysis ¹³C-NMR, direct infusion mass spectrometry (ESI-MS), and MALDI-TOF. The ¹³C-NMR spectrum showed characteristics of flavan-3-ol and oligomeric proanthocyanidins. ESI-MS revealed the presence of procyanidin, caffeic acid and its derivatives. MALDI-TOF analysis detected procyanidins of up to 6 units and profisetinidins of up to 5 units. Whereas CE and EAF showed inhibitory activity against H. pylori, CE, EAF, and AqF presented not high inhibitory activity against urease. The results demonstrate the potential of P. cupana to control and prevent H. pylori infection.     

Isoxazoline-carbocyclic aminols for nucleoside synthesis through aza-Diels-Alder reactions

A novel approach to useful aminols for the synthesis of carbocyclic nucleosides is reported starting from a convenient source, the 2-azanorborn-5-enes. These are readily available through the Grieco cycloaddition of cyclopentadiene with iminium salts and are reactive dipolarophiles toward nitrile oxides. The prolific elaboration of the isoxazoline cycloadducts allowed preparation of the target aminols through the unmasking of the hydroxymethylene group at the C3 level of the azanorbornene structure.