Pronounced pH effects on the kinetics of cucurbit[7]uril-based pseudorotaxane formation and dissociation

Deprotonation of the two terminal COOH groups on a 4,4'-bipyridinium linear derivative leads to a pronounced slow down on the kinetics of threading and unthreading by the cucurbit[7]uril host.     

Characterization of a coherent upper conditional prevision as the Choquet integral with respect to its associated Hausdorff outer measure

A model of coherent upper conditional prevision for bounded random variables is proposed in a metric space. It is defined by the Choquet integral with respect to Hausdorff outer measure if the conditioning event has positive and finite Hausdorff outer measure in its Hausdorff dimension. Otherwise, when the conditioning event has Hausdorff outer measure equal to zero or infinity in its Hausdorff dimension, it is defined by a 0–1 valued finitely, but not countably, additive probability. If the conditioning event has positive and finite Hausdorff outer measure in its Hausdorff dimension it is proven that a coherent upper conditional prevision is uniquely represented by the Choquet integral with respect to the upper conditional probability defined by Hausdorff outer measure if and only if it is monotone, comonotonically additive, submodular and continuous from below.     

Nonperturbative calculation of the two-loop lamb shift in Li-like ions

A calculation valid to all orders in the nuclear-strength parameter is presented for the two-loop Lamb shift, notably for the two-loop self-energy correction, to the 2p-2s transition energies in heavy Li-like ions. The calculation removes the largest theoretical uncertainty for these transitions and yields the first experimental identification of two-loop QED effects in the region of the strong binding field.     

Synthesis, structure, and magnetic properties of Li-doped manganese-phthalocyanine, Li(x)[MnPc] (0 < or = x < or = 4)

We report on the first synthesis of Li-intercalated manganese-phthalocyanine (MnPc) in the bulk form and on the evolution of the structural and magnetic properties as a function of Li concentration, x. We find that solid beta-MnPc, which comprises rodlike assemblies of individual planar molecules, is best described as a glassy one-dimensional ferromagnet without three-dimensional ordering and that it can be quasi-continuously intercalated with Li up to x = 4, forming an isosymmetrical series of Li(x)[MnPc] phases. Inserted Li+ ions strongly bond to pyrrole-bridging nitrogen atoms of the Pc rings, thereby disrupting the ferromagnetic Mn-N(a)...Mn superexchange pathways. This gradually induces a crossover of the intrachain exchange interactions from ferromagnetic to antiferromagnetic as the doping level, x, increases coupled with a spin-state transition of the Mn2+ ions from intermediate spin, S = 3/2, to high spin, S = 5/2.     

Switching a molecular shuttle on and off: simple, pH-controlled pseudorotaxanes based on cucurbit[7]uril

Cucurbit[7[uril, the wheel component in two new and structurally simple pseudorotaxanes, shuttles between the two axle termini at low pH, whereas the shuttling motion stops at higher pH, as the wheel is bound to the center of the axle.     

Operating molecular elevators

Inspired by the concept of multivalency in living systems, two mechanically interlocked molecules have been conceived that incorporate not once or twice but thrice the features of a pH-switchable [2]rotaxane with two orthogonal recognition sites for dibenzo[24]crown-8 (DB24C8), and 2,3-dinaphtho[24]crown-8 (DN24C8)-one a dialkylammonium ion (CH(2)NH(2)(+)CH(2)) and the other a bipyridinium dication (BIPY(2+)). Whereas at low pH, the CH(2)NH(2)(+)CH(2) sites bind the DB24C8/DN24C8 macrocycles preferentially, at high pH, deprotonation occurs with loss of hydrogen bonding and the macrocycles will move to the BIPY(2+) sites, where they can acquire some stabilizing [pi-pi] stacking interactions. Such mechanically interlocked molecules have been assembled from a trifurcated rig-like component wherein the dumbbell-like components of three [2]rotaxanes have one of their ends fused onto alternate positions (1,3,5) around a benzenoid core. The rig is mechanically interlocked by a platform based on a tritopic receptor, wherein either three benzo[24]crown-8 or three 2,3-naphtho[24]crown-8 macrocycles are fused onto a hexaoxatriphenylene core. The synthesis of these molecular elevators involves 1:1 complexation, followed by stoppering, i.e., feet are added to the rig. (1)H NMR spectroscopy and cyclic voltammetry, aided and abetted by absorption spectroscopy, have been employed to unravel the details of the mechanism by which the rig and platform components move on the alternate addition of base and acid. For each molecular elevator, the platform operates by taking three distinct steps associated with each of the three deprotonation/reprotonation processes. Thus, molecular elevators are more reminiscent of a legged animal than they are of passengers on freight elevators.     

A new gravity-driven microfluidic-based electrochemical assay coupled to magnetic beads for nucleic acid detection

In this work, the characterisation and the optimisation of hybridisation assays based on a novel, rapid and sensitive micro-analytical, gravity-driven, flow device is reported. This device combines a special chip containing eight polymer microchannels, with a portable, computer-controlled instrument. The device is used as a platform for affinity experiments using oligonucleotide-modified paramagnetic particles. In our approach, both hybridisation and labelling events are performed on streptavidin-coated paramagnetic microparticles functionalized with a biotinylated capture probe. Modified particles, introduced in the microchannel inlet of the chip, accumulate near the electrode surface by virtue of a magnetic holder. After hybridisation with the complementary sequence, the hybrid is labelled with an alkaline phosphatase conjugate. The electrochemical substrate for alkaline phosphatase revelation is p-aminophenyl phosphate. Solutions and reagents are sequentially passed through the microchannels, until enzyme substrate is added for in situ signal detection. Upon readout, the magnet array is flipped away, beads are removed by addition of regeneration buffer, and the so-regenerated chip is ready for further analysis. This protocol has been applied to the analytical detection of specific DNA sequences of Legionella pneumophila, with an RSD=8.5% and a detection limit of 0.33 nM.     

Determination of levamisole in feeds by liquid chromatography coupled to electrospray mass spectrometry on an ion trap

Test methods have to be developed by laboratories for official control to monitor possible misuse of veterinary drugs in animal productions, also through feeding stuff. A novel method for identification and quantification of levamisole in feeds by liquid chromatography coupled to electrospray mass spectrometry in an ion trap (LC/ESI‐MS/MS) is herein described; after a single‐step cleanup by liquid‐liquid extraction from the feed and separation by reversed‐phase liquid chromatography, levamisole was determined and unambiguously confirmed by tandem mass spectrometry, on the basis of two product ions. The method was in‐house validated, according to the Regulation 882/2004/EC, evaluating trueness, repeatability, within‐laboratory reproducibility, ruggedness, specificity, and the limit of quantification (LOQ). The method is reliable and specific for complete and complementary feeds for pigs, cattle, rabbits and poultry; very good mean recoveries (higher than 92 %) and precision (RSD values < 15.2%) were attained. The LOQ at 2.0 mg/kg was verified. Moreover, we describe how the method was developed to support Italian Police investigations regarding illegal treatments of pigs; in this case, since the drug(s) added to the feed were unknown, a preliminary untargeted analysis was performed by full scan mass spectrometry on an ion trap, from 50 up to 2000 m/z; the presence of levamisole was hypothesised, on the basis of the most abundant ion and its fragmentation pattern. Then, levamisole was unambiguously confirmed by the ion trap LC/ESI‐MS/MS method. Copyright © 2012 John Wiley & Sons, Ltd.     

A Study on the Stability and Enzymatic Activity of Yeast Alcohol Dehydrogenase in Presence of the Self-Assembling Block Copolymer Poloxamer 407

Yeast alcohol dehydrogenase (ADH) is an enzyme widely studied for biotechnological applications due to its involvement in fermentation industry, and various attempts to improve its catalytic properties and its thermal stability have been carried out. In this paper, the influence of a block copolymer (Poloxamer 407) on ADH enzymatic activity and thermal behaviour has been studied in order to get new insights about the use of poloxamers in formulation of sustained release systems for therapeutic proteins. Poloxamer 407 has the ability to form micelles and gel due to its self-assembling and thermoresponsive properties. The effect of the copolymer towards thermal stress and pH changes, which often reduce enzymes activity it has been investigated by means of enzymatic assays and differential scanning calorimetry. Results showed that at pH?9.1 and 7.3, the Poloxamer in the form of unimeric, micellar and gel state is able to effectively preserve the enzyme from thermoinactivation. In addition by calorimetric data Poloxamer 407 has showed an effect in preserving ADH from aggregation at pH?7.3. In conclusion, Poloxamer 407 seems to be very effective in protecting ADH from stress related events, like alkaline inactivation and aggregation.