Development of a new sequential injection in-line cloud point extraction system for flame atomic absorption spectrometric determination of manganese in food samples

A preconcentration method for manganese determination by sequential injection cloud point extraction with subsequent detection by flame atomic absorption spectrometry (FAAS) has been developed. The enrichment of Mn was performed after a preliminary on-line cloud point extraction and entrapment of manganese-containing surfactant aggregated within a minicolumn packed with cotton. The laboratory-made reagent 4-(5′-bromo-2′-thiazolylazo)orcinol (Br-TAO) and the surfactant Triton X-114 were used for cloud point extraction. The manganese ions were eluted with sulphuric acid solution and directly introduced into the FAAS. Chemical and flow variables affecting the preconcentration were studied. Using a sample volume of 2.80 mL the limit of detection and enrichment factor were calculated to be 0.5 μg L⁻¹ and 14, respectively. The sample frequency is 48 h⁻¹, considering a total run cycle of 75 s. The accuracy of the proposed method has been demonstrated by the analysis of the certified reference biological materials rice flour and tomato leaves. The method has been applied to determination of manganese in food samples.     

Structure determination of protein-protein complexes using NMR chemical shifts: case of an endonuclease colicin-immunity protein complex

Nuclear magnetic resonance (NMR) spectroscopy provides a range of powerful techniques for determining the structures and the dynamics of proteins. The high-resolution determination of the structures of protein-protein complexes, however, is still a challenging problem for this approach, since it can normally provide only a limited amount of structural information at protein-protein interfaces. We present here the determination using NMR chemical shifts of the structure (PDB code 2K5X) of the cytotoxic endonuclease domain from bacterial toxin colicin (E9) in complex with its cognate immunity protein (Im9). In order to achieve this result, we introduce the CamDock method, which combines a flexible docking procedure with a refinement that exploits the structural information provided by chemical shifts. The results that we report thus indicate that chemical shifts can be used as structural restraints for the determination of the conformations of protein complexes that are difficult to obtain by more standard NMR approaches.     

Photoelectro-Enzymatic Glucose Reusable Biosensor by Using Dithienylethene Mediators

In the development of colorimetric biosensors, the use of electrochromic mediators has been accepted and widely used during decades. The main drawback of these types of enzymatic substrates is the difficult recovery of the initial redox state of the molecule, which can be done electrochemically or by antioxidants addition, complicating the initially simple structure of the biosensor. those strategies are rarely followed Actually, being the disposable biosensor configuration the most extended for this detection mechanisms. Alternatively, we propose the first reported use of a diacid dithienylethene 1,2-bis(5-carboxy-2-methylthien-3-yl)cyclopentene (DTE) photoelectrochromic compound as a substrate of the horseradish peroxidase (HRP). The photoisomerization between the open (DTEo) and closed (DTEc) forms of the molecule and the respective shift in the redox potential allowed the light-induced enzymatic detection of glucose in the glucose oxidase [(GOx)]–HRP cascade system. This fast and easy control over the enzymatic substrate availability by light pulses permits a gradually consumption and the light-regeneration of the biosensor for a number of cycles. We consider the presented results transcendent in the development of reusable and light-controlled photonic biosensing systems.     

New thermosets obtained from DGEBA and Meldrum acid with lanthanum and ytterbium triflates as cationic initiators

Ytterbium and lanthanum triflates were used as cationic initiators to cure mixtures of diglycidylether of bisphenol A (DGEBA) and Meldrum acid (MA) in several proportions of comonomers and initiators. The evolution of epoxy and lactone groups during curing, and of linear ester formed in the final materials were evaluated by Fourier transform infrared in the attenuated-total-reflection mode (FTIR/ATR).

The global evolution of the curing process was investigated by calorimetric analysis and the activation energy was calculated by isoconversional procedures.

Shrinkage on curing and thermal degradability of the final materials on varying the initiator and the proportion of Meldrum acid in the mixtures were evaluated. The expandable character of MA was confirmed. The materials obtained were more degradable than conventional epoxy resins due to the tertiary ester groups incorporated into the network by copolymerization, especially those obtained with ytterbium triflate. On increasing the proportion of initiator the degradability was also increased.     

Click approaches to functional water-sensitive organotriethoxysilanes

The derivatization of functional organic fragments with triethoxysilyl groups to afford hydrolyzable organosilanes with targeted properties using the copper-catalyzed alkyne azide cycloaddition reaction under strictly anhydrous conditions is described according to two approaches, starting from five silylated substrates. This high yield, fast, and selective method is applicable to a wide range of substrates and is expected to lead to important achievements in the field of functional hybrid silica.     

Nanomanipulation using near field photonics

In this article we review the use of near-field photonics for trapping, transport and handling of nanomaterials. While the advantages of traditional optical tweezing are well known at the microscale, direct application of these techniques to the handling of nanoscale materials has proven difficult due to unfavourable scaling of the fundamental physics. Recently a number of research groups have demonstrated how the evanescent fields surrounding photonic structures like photonic waveguides, optical resonators, and plasmonic nanoparticles can be used to greatly enhance optical forces. Here, we introduce some of the most common implementations of these techniques, focusing on those which have relevance to microfluidic or optofluidic applications. Since the field is still relatively nascent, we spend much of the article laying out the fundamental and practical advantages that near field optical manipulation offers over both traditional optical tweezing and other particle handling techniques. In addition we highlight three application areas where these techniques namely could be of interest to the lab-on-a-chip community, namely: single molecule analysis, nanoassembly, and optical chromatography.     

Flavonoids from Praxelis clematidea R.M. King and Robinson modulate bacterial drug resistance

Chemical studies of Praxelis clematidea R.M. King & Robinson resulted in the isolation of six flavones: Apigenine, genkwanine, 7,4'-dimethylapigenin, trimethylapigenin, cirsimaritin and tetramethylscutellarein, which were tested for their toxicity against Staphylococcus aureus SA-1199B, a strain possessing the NorA efflux pump. Efflux pumps are integral proteins of the bacterial membrane and are recognized as one of the main causes of bacterial drug resistance, since they expel antibiotics from the cell. The inhibition of this transporter is one form of modulating bacterial resistance to antimicrobial drugs. The flavones tested did not show any significant antibacterial activity against the Staphylococcus aureus strain used, but were able to modulate bacterial drug resistance. This property might be related to the degree of lipophilicity of the flavones conferred by the methoxyl groups, since 4',5,6,7 tetramethoxyflavone the most methoxylated compound, reduced the minimal inhibitory concentration of the drug 16-fold.     

Ligand influence over the formation of dinuclear [2+2] versus trinuclear [3+3] Cu(I) Schiff base macrocyclic complexes

The preparation and characterization of three new macrocyclic ligands with pendant arms based on the [2+2] condensation of isophthalaldehyde and the corresponding triamine substituted at the central N-atom is reported. None of these new macrocyclic ligands undergo any equilibrium reaction, based on imine hydrolysis to generate [1+1] macrocyclic formation or higher oligomeric compounds, such as [3+3], [4+4], etc., at least within the time scale of days. This indicates the stability of the newly generated imine bond. In sharp contrast, the reaction of the [2+2] macrocyclic Schiff bases with Cu(I) generates the corresponding dinuclear Cu(I) complexes [Cu(2)(L(1))](2+), 1(2+); [Cu(2)(L(2))(CH(3)CN)(2)](2+), 2(2+); and [Cu(2)(L(3))(CH(3)CN)(2)](2+), 3(2+), together with their trinuclear Cu(I) homologues [Cu(3)(L(4))](3+), 4(3+); [Cu(3)(L(5))(CH(3)CN)(3)](3+), 5(3+); and [Cu(3)(L(6))(CH(3)CN)(3)](3+), 6(3+), where the [2+2] ligand has undergone an expansion to the corresponding [3+3] Schiff base that is denoted as L(4), L(5), or L(6). The conditions under which the dinuclear and trinuclear complexes are formed were analyzed in terms of solvent dependence and synthetic pathways. The new complexes are characterized in solution by NMR, UV-vis, and MS spectroscopy and in the solid state by X-ray diffraction analysis and IR spectroscopy. For the particular case of the L(2) ligand, MS spectroscopy is also used to monitor the metal assisted transformation where the dinuclear complex 2(2+) is transformed into the trinuclear complex 5(3+). The Cu(I) complexes described here, in general, react slowly (within the time scale of days) with molecular oxygen, except for the ones containing the phenolic ligands 2(2+) and 5(3+) that react a bit faster.     

Separation profile of model water-in-oil emulsions followed by nuclear magnetic resonance (NMR) measurements: application range and comparison with a multiple-light scattering based apparatus

The application range and validity of two new NMR sequences (hereafter called sequence 1 and sequence 2) for the study of water-in-oil emulsions (w/o) has been assessed using model emulsions and comparison with results obtained by a commercial apparatus (Turbiscan). These new NMR sequences allow to determine the brine profile i.e. the vertical variations of the dispersed phase content (brine) in the NMR tube. Measuring these parameters as a function of time allows to monitor the separation (sedimentation and coalescence rate) between oil and water. The results obtained on model water-in-oil emulsions with both NMR sequences are consistent and meaningful for both stable and coalescing emulsions and are similar, even if not strictly identical, to the ones obtained with the Turbiscan. It also appears that the second NMR sequence is faster (30s to obtain a profile compared with 3 min for the 1st one in the conditions used in this article) and has a broader application range. Indeed, for these two methods, the oil phase must have a viscosity higher or equal than values which is around 5 mPas for the sequence 2 and 20-25 mPas for the method 1.