The biotin-streptavidin interaction can be reversibly broken using water at elevated temperatures

The biotin-streptavidin system is the strongest noncovalent biological interaction known, having a dissociation constant, K(d), in the order of 4x10(-14) M. The strength and specificity of the interaction has led it to be one of the most widely used affinity pairs in molecular, immunological, and cellular assays. However, it has previously been impossible to re-use any streptavidin solid support, since the conditions needed to break the interaction with biotin has led to the denaturation of the streptavidin. Here, we show that a short incubation in nonionic aqueous solutions at temperatures above 70 degrees C can efficiently break the interaction without denaturing the streptavidin tetramer. Both biotin and the streptavidin remain active after dissociation and both molecules can therefore be re-used. The efficiency of the regeneration allowed solid supports with streptavidin to be used many times, here exemplified with the multiple re-use of streptavidin beads used for sample preparation prior to automated DNA sequencing. The results suggest that streptavidin regeneration can be introduced as an improvement in existing methods and assays based on the streptavidin system as well as emerging solid phase applications in fields, such as microfluidics and nanotechnology.     

Can time-homogeneous diffusions produce any distribution?

Given a centred distribution, can one find a time-homogeneous martingale diffusion starting at zero which has the given law at time 1? We answer the question affirmatively if generalized diffusions are allowed.     

Synthesis and identifications of potential metabolites as biomarkers of the synthetic cannabinoid AKB-48

AKB-48 belongs to the family of synthetic cannabinoids. It has strong binding affinity to CB₁ receptor and is psychoactive. It is banned in many countries including USA, Japan, Germany, New Zealand, Singapore and China etc. But the difficulty in detecting the parent compound in urine samples highlights the importance of studies of its metabolites. Here we report the synthesis of 19 potential metabolites of AKB-48, among which, compounds 2, 9, 10, 30 and 31, together with the commercially available substance 5 were identified as metabolites of AKB-48 by comparison with one authentic human urine sample and human liver microsomal data. Compounds 10 and 30 could be of use as biomarkers in detecting AKB-48 in human urine samples.     

An electronic signature of hydrolysation in the X-ray absorption spectrum of aqueous formaldehyde

Formaldehyde in aqueous solution is hydrolysed and forms methanediol. Using X-ray absorption spectroscopy we show that the hydrolysation product can be identified by a distinct electronic signature in the spectra. This is manifested by the disappearance of the oxygen 1s → π* absorption line. The X-ray absorption spectrum of aqueous formaldehyde is compared with those of the structurally similar formamide and urea, which are in contrast not hydrolysed in aqueous solution. We thereby demonstrate the exceptional sensitivity and simplicity of the technique to monitor this fundamental process in the aqueous phase.     

Competition in growth and urns

We study survival among two competing types in two settings: a planar growth model related to two‐neighbor bootstrap percolation, and a system of urns with graph‐based interactions. In the planar growth model, uncolored sites are given a color at rate 0, 1 or , depending on whether they have zero, one, or at least two neighbors of that color. In the urn scheme, each vertex of a graph G has an associated urn containing some number of either blue or red balls (but not both). At each time step, a ball is chosen uniformly at random from all those currently present in the system, a ball of the same color is added to each neighboring urn, and balls in the same urn but of different colors annihilate on a one‐for‐one basis. We show that, for every connected graph G and every initial configuration, only one color survives almost surely. As a corollary, we deduce that in the two‐type growth model on , one of the colors only infects a finite number of sites with probability one. We also discuss generalizations to higher dimensions and multi‐type processes, and list a number of open problems and conjectures.     

A quantitative criterion validating coupling power proportionality in statistical energy analysis

The response of two general spring-coupled elements is investigated to develop a unifying approach to the weak coupling criterion in Statistical Energy Analysis (SEA). First, the coupled deterministic equations of motion are expressed in the bases given by the uncoupled elements’ eigenmodes. Then, an iterative solution is expressed as a succession of exchanges between elements, where uncoupled motion provides the start approximation, converging if the ‘coupling eigenvalue’ is less than unity, in which case coupling is said to be weak. This definition is related to whether response is ‘local’ or ‘global’, encompassing a number of previously defined coupling strength definitions, applying for deterministically described structures. A stochastic ensemble is defined by that its members are equal to the investigated structure but the elements have random frequencies. It is required that the coupling eigenvalue be less than unity for all members of the ensemble. This requirement generates the title subject of the article: ‘the modal interaction strength’. It is similar to the previously defined coupling strength criterion characterising the ensemble average energy flow in uni-dimensional waveguides. Finally, SEA models are formulated in terms of the uncoupled elements’ modal data.     

Size control and growth process of alkylamine-stabilized platinum nanocrystals: a comparison between the phase transfer and reverse micelles methods

Alkylamine-stabilized platinum nanoparticles are synthesized either by the phase-transfer method or in reverse micelles. The phase-transfer method produces nanocrystals that are quite spherical whereas the synthesis in reverse micelles generates a large number of wormlike structures. An alkylamine is used as a stabilizing agent to prevent nanoparticle coalescence, and it is shown that there is an inverse relationship between the alkylamine chain length and the platinum nanoparticle diameter. By comparing alkylamine and alkylthiol analogues, it is found that the integrity of the different crystallites depends on the strength of the interaction between the stabilizing agent and the platinum nanocrystals. The results obtained and the comparison made between the two synthesis methods improve the understanding of the growth mechanisms of platinum nanocrystals in disperse media.     

Lipase-catalyzed reactions at different surfaces

Starting from gold chips, we have tailor-made three surfaces by the self-assembly monolayer technique: one entirely hydrophobic, one hydrophobic with dispersed carboxyl groups, and one hydrophilic, containing hydroxyl groups. Rhizomucor miehei lipase has been adsorbed to the hydrophobic and the hydrophilic surfaces and covalently bound to the surface containing carboxyl groups. The adsorption of two substrates-capric acid (decanoic acid) and monocaprin-on the lipase-covered surfaces was monitored by the surface plasmon resonance (SPR) technique. Biocatalysis was also performed in the SPR instrument by circulating a solution of the substrate, dissolved in an 85:15 water-glycerol mixture at a(w) = 0.81, through the instrument, thus exposing the capric acid or the monocaprin to the lipase-covered surfaces. The product composition was found to depend on the type of surface used. Lipase adsorbed at the hydrophilic surface favored hydrolysis, and capric acid was the main product formed when monocaprin was used as substrate. Lipase adsorbed at a hydrophobic surface and, in particular, lipase covalently bound to a hydrophobic surface favored condensation. More dicaprin than capric acid was formed in experiments with monocaprin as the substrate. Reactions performed outside the SPR instrument showed that small amounts of triglyceride were also formed under these conditions. We believe that this work constitutes the first example of the SPR instrument being used for in-situ biotransformation.