A Reduced-Symmetry Heterobimetallic [PdPtL4]4+ Cage: Assembly,Guest Binding,and Stimulus-Induced Switching

A strategy is presented that enables the quantitative assembly of a heterobimetallic [PdPtL₄]⁴⁺ cage. The presence of two different metal ions (Pd^II and Pt^II) with differing labilities enables the cage to be opened and closed selectively at one end upon treatment with suitable stimuli. Combining an inert Pt^II tetrapyridylaldehyde complex with a suitably substituted pyridylamine and Pd^II ions led to the assembly of the cage. ¹H and DOSY NMR spectroscopy and ESI mass spectrometry data were consistent with the quantitative formation of the cage, and the heterobimetallic structure was confirmed using single-crystal X-ray crystallography. The structure of the host–guest adduct with a 2,6-diaminoanthraquinone guest molecule was determined. Addition of N,N′-dimethylaminopyridine (DMAP) resulted in the formation of the open-cage [PtL₄]²⁺ compound and [Pd(DMAP)₄]²⁺ complex. This process could then be reversed, with the reformation of the cage, upon addition of p-toluenesulfonic acid (TsOH).     

Chemically‐reduced Graphene Oxide Sensor for Dipyrone Quantification in Pharmaceutical Samples Using Amperometric Detection

Dipyrone (metamizole sodium) is one of the most consumed drugs in the world. In this work a novel analytical method was developed for dipyrone sensing. This method involves the amperometric detection on a chemically‐reduced graphene‐oxide (CRGO)‐modified glassy carbon electrode. Raman spectroscopy and scanning electron microscopy revealed the presence of multilayer graphene layers that contributed to the electrocatalytic oxidation of dipyrone and increase in the electroactive area. Advantages of this sensor include elimination of previous separations, solvent extraction, or sample filtration, low detection limit (0.13 μmol L^?1) with a linear range from 48 to 246 μmol L^?1 and adequate recovery values (97–103 %). Applied to commercial pharmaceutical samples, this method showed results ranging from 451 to 541 mg of dipyrone per tablet, which agreed with the expected values. The results obtained by amperometry were compared statistically with the official method recommended by the Brazilian Pharmacopoeia (iodometric method), with no significant differences between them at 95 % confidence level. The proposed method is accurate for the monitoring of sodium dipyrone in pharmaceutical formulations, highlighting the lower reagent consumption and interferences in the analytical process.     

Regioselective Synthesis of 2-Functionalized Thiophenes by Condensation of α-Mercapto Compounds with β-Aminoenone Derivatives

2-Acylthiophenes and ethyl 2-thiophene-carboxylates are prepared regioselectively by reaction of 3-ctil oroenones and 2-acylenammoni urn chlorides with α-mercapto derivatives in good to moderate yields.     

Role of rational surfaces on fluctuations and transport in the plasma edge of the TJ-II stellarator

It has been shown that transport barriers in toroidal magnetically confined plasmas tend to be linked to regions of unique magnetic topology such as the location of a minimum in the safety factor, rational surfaces or the boundary between closed and open flux surfaces. In the absence ofE×B sheared flows, fluctuations are expected to show maximum amplitude near rational surfaces, and plasma confinement might tend to deteriorate. On the other hand, if the generation ofE×B sheared flows were linked to low order rational surfaces, these would be beneficial for confinement. Experimental evidence ofE×B sheared flows linked to rational surfaces has been obtained in the plasma edge region of the TJ-II stellarator. Presented at the Workshop on the Role of Electric Fields in Plasma Confinement and Exhaust, Budapest, 18–19 June, 2000.     

Electrochemical properties of interface formed by interlaced layers of DNA- and lysozyme-coated single-walled carbon nanotubes

Multifunctional coatings were produced by the layer by layer assembly of single-walled carbon nanotubes (SWNT) dispersed in DNA and lysozyme (LSZ) on an insulating glass substrate. The electrochemical properties of these mechanically robust biocoatings were characterized for the first time using scanning electrochemical microscopy (SECM) and impedance spectroscopy (IS). SECM surface analysis demonstrated an increase in tip current with a corresponding increase in the number of oppositely polarized interlaced layers, indicating that subsequent layers were not electrically insulated from each other and a direct correlation exists between SECM feedback response and the number of layers. The rate of charge transport was also dependent on the chemical composition/polarity of the outermost surface layer. Coatings terminating in SWNT-DNA resulted in more positive feedback than those terminating in SWNT-LSZ. IS analysis demonstrated that the SWNT-DNA had a low charge transfer resistance in comparison with SWNT-LSZ, which is consistent with the results obtained by SECM. These results enable enhanced fundamental understanding and prediction of the electrical properties of SWNT-biopolymer layers with controlled interlaced polarities and orientation. Furthermore, these finding highlight the potential for SWNT-biopolymers in electronic and sensing applications.     

Immobilization of antibodies on biosensing devices by nanoarrayed self-assembled monolayers

This work presents an original and straightforward technique for antibody immobilization onto a surface, keeping the antibody in a biologically reactive configuration. Self-assembly of molecular monolayers and plasma-based colloidal lithography were combined to create chemical nanopatterns on the surface of a biosensing device. This technique was employed to create an array of 100 nm wide motifs having a hexagonal 2-D crystalline structure, characterized by COOH-terminated nanospots in a CH3-terminated matrix. The quality control of the chemical nanopattern was carried out by combining atomic force microscopy, ellipsometry, and contact angle measurements. Enzyme-linked immunosorbent assay experiments were set up showing that the COOH/CH3 nanopatterned surface constrains the immobilization of the antibodies in a biologically reactive configuration, thus significantly improving the device performances as compared to those of more conventional nonpatterned COOH-terminated or CH3-terminated surfaces.     

An efficient synthesis of enantiomerically enriched trifluoromethylated 1,2-diols and 1,2-amino alcohols with quaternary stereocenters by diastereoselective addition of TMSCF3 to chiral 2-acyl-1,3-perhydrobenzoxazines

TMSCF3 adds to chiral 2-acyl-1,3-perhydrobenzoxazines with total diastereoselectivity leading to quaternary trifluoromethyl alcohols. Further transformation of the addition products yields enantiomerically enriched trifluoromethylated 1,2-diols and 1,2-amino alcohols.     

Solid-state single and triple-quantum 93Nb MAS NMR studies of ferroelectric Pb(Mg1/3Nb2/3)O3 and a related pyrochlore

Pb(Mg1/3Nb2/3)O3 (PMN), a well-known relaxor ferroelectric material, and a related pyrochlore phase have been studied by single- and triple-quantum 93Nb MAS NMR spectroscopy. The assignment of the NMR resonances has been attempted.     

Gel chromatography of steroid oestrogens on sephadex LH-20.

The behavior of 23 steroid oestrogens Sephadex LH-20 using six solvent systems was investigated. The fractions eluted by gel column chromatography were analysed by thin-layer chromatography and spectrometry. The method was used for the radiochemical purity of labelled compounds by isotopic dilution.