Onset of Chiral Adenine Surface Growth

The structure and stability of adenine crystals and thin layers has been studied by using scanning tunneling microscopy, X‐ray diffraction, and density functional theory calculations. We have found that adenine crystals can be grown in two phases that are energetically quasi‐degenerate, the structure of which can be described as a pile‐up of 2D adenine planes. In each plane, the structure can be described as an aggregation of adenine dimers. Under certain conditions, kinetic effects can favor the growth of the less stable phase. These results have been used to understand the growth of adenine thin films on gold under ultra‐high vacuum conditions. We have found that the grown phase corresponds to the α‐phase, which is composed of stacked prochiral planes. In this way, the adenine nanocrystals exhibit a surface that is enantiopure. These results could open new insight into the applications of adenine in biological, medical, and enantioselective or pharmaceutical fields.     

Tailoring the morphology and properties of waterborne polyurethanes by the procedure of cellulose nanocrystal incorporation

Polyurethane waterborne synthesis was performed using a two-step method, commonly referred to as a prepolymer method. Nanocomposites based on waterborne polyurethane and cellulose nanocrystals were prepared by the prepolymer method by altering the mode and step in which the nanofillers were incorporated during the polyurethane formation. The morphology, structural, thermal, and mechanical properties of the resulting nanocomposite films were evaluated by Fourier transform infrared spectroscopy (FTIR), small angle X-ray scattering (SAXS), scanning electron microscopy (SEM), and tensile tests. FTIR results indicated that the degree of interaction between the nanofillers and the WPU through hydrogen bonds could be controlled by the method of cellulose nanocrystal incorporation. Data obtained from SAXS experiments showed that the cellulose nanocrystals as well as the step of the reaction in which they are added influenced the morphology of the polyurethane. The reinforcing effect of CNCs on the nanocomposites depends on their morphology.     

Synthesis of New Five Membered Nitrogen Containing Heterocycles Bearing D-Galactose Side Chains

The synthesis of 5-[6′-deoxy-(1′,2′:3′,4′-di-O-isopropylidene-α-D-galactopyranos-6′-yl)]tetrazole and its reaction with acetic anhydride and 1,2:3,4-di-O-isopropylidene-6-O-(4-toluenesulfonyl)-α-D-galactopyranose are described.     

Selective Sulfenylative Desulfonylation or Decarbalkoxylation of α-Sulfonyl Malonates with DABCO or Bu3N: Reactivity and Conformational Analysis

The study on reactivity of several α-substituted α-sulfonyl malonates toward 1,4-diazabicyclo[2.2.2]octane (DABCO) and Bu₃N is described. The reactivity with DABCO revealed the possible competition between decarbalkoxylation and unexpected desulfonylation, depending on the α-substituent, because of sterical hindrance around the electrophilic centers (SO₂ and CO₂R). The derivatives with crowded α-substituents suffer selective desulfonylation, and a novel and efficient desulfonylation method can be proposed. The dependence of the reactivity of α-sulfonyl malonates on the sterical hindrance around the electrophilic centers is confirmed by conformational analysis (Macromodel/MM2? and Mopac/MP3). The carbanionic mechanism is proved because the corresponding protonated, deuterated, and sulfenylated products were obtained by addition of the corresponding electrophilic agents. Bu₃N showed itself to be a novel selective decarbalkoxylation agent for any α-substituted α-sulfonyl malonate.     

Radiolabeling of low molecular weight d-galactose-based glycodendrimer with technetium-99m and biodistribution studies

Glycodendrimers are neoglycoconjugates that can be considered as bioisosters of glycoproteins, since they can mimic the multivalent interactions of lectin-carbohydrate. The ability of glycodendrimers to present multivalent interactions with lectins as compared to a monovalent ligand is referred to as “cluster effect”. It is expected that, because of the cluster effect, glycodendrimers would result in a better association with lectins than mono-carbohydrate anchored systems. Radioisotopes are useful to evaluate biodistribution of molecules. This study is important to obtain information about molecule–receptor interactions. Indeed, such study can provide an exquisite tool to evaluate the affinity of certain molecules to specific areas in the body, leading to the development of new radiopharmaceuticals and/or drug delivery systems. Herein, we describe a d-galactose coated low molecular weight PAMAM G0 dendrimer that was successfully radiolabeled with technetium-99m. Biodistribution studies and scintigraphic images were performed in healthy mice. It was observed high liver uptake which was significantly reduced in blocking studies, indicating hepatic specificity. Therefore, low molecular weight glycodendrimer can be considered as useful platform for selective targeting of drugs to the liver and to assess hepatic function.     

Effect of viscosity of a liquid membrane containing oleyl alcohol on the pertraction of butyric acid

Solvent formulation is important in the optimization of the mass-transfer through supported liquid membranes (SLM) in pertraction and membrane extraction. Oleyl alcohol (OA) is frequently used as the solvent or diluent in the extraction of carboxylic acids. A disadvantage of OA is its relatively high viscosity of 28.32 mPa s at 25°C. This can be decreased by the application of a less viscous OA diluent, e.g. dodecane. The relationship between the ratio of the distribution coefficient of butyric acid (BA), D _F, and the viscosity of OA-dodecane solvents, µ, as extraction and transport characteristics, and the overall mass-transfer coefficient, K _p, through SLMs was analyzed. Dependence of the D _F/µ ratio on the OA concentration showed a maximum at the OA concentration of 15 mass % to 30 mass %. The OA concentration dependence of K _p for SLMs exhibited also a maximum at about 30 mass % and 20 mass % of OA at the BA concentration driving force of 0.12 kmol m^?3 and 0.3 kmol m^?3, respectively. Shifting of the maximum in K _p dependences towards lower OA concentrations by increasing the BA concentration driving force is in agreement with the D _F/µ ratio dependence. Using pure OA as the solvent or diluent is not preferable and a mixture of a low viscosity diluent with the OA concentration below 40 mass % should be used. The presented results show the potential of the D _F/µ ratio in the screening and formulation of solvents in extraction and SLM optimization.     

Trapped modes along a periodic array of freely floating obstacles

We consider the coupled problem describing the motion of a linear array of three‐dimensional obstacles floating freely in a homogeneous fluid layer of finite depth. The interaction of time‐harmonic waves with the floating objects is analyzed under the usual assumptions of linear water‐wave theory. Quasi‐periodic boundary conditions and a simplified reduction scheme turn the system into a linear spectral problem for a self‐adjoint operator in Hilbert space. Based upon the operator formulation, we derive a sufficient condition for the nonemptiness of its discrete spectrum. Various examples of obstacles that generate trapped modes are given. Copyright © 2014 John Wiley & Sons, Ltd.     

Penultimate Approximations in Statistics of Extremes and Reliability of Large Coherent Systems

In reliability theory any coherent system can be represented as either a series-parallel or a parallel-series system. Its lifetime can thus be written as the minimum of maxima or the maximum of minima. For large-scale coherent systems it is sensible to assume that the number of system components goes to infinity. Then, the possible non-degenerate extreme value laws either for maxima or for minima are eligible candidates for the system reliability or at least for the finding of adequate lower and upper bounds for the reliability. The identification of the possible limit laws for the system reliability of homogeneous series-parallel (or parallel-series) systems has already been done under different frameworks. However, it is well-known that in most situations such non-degenerate limit laws are better approximated by an adequate penultimate distribution. Dealing with regular and homogeneous parallel-series systems, we assess both theoretically and through Monte-Carlo simulations the gain in accuracy when a penultimate approximation is used instead of the ultimate one.     

Bovine lactoferrin purification from whey using Yellow HE‐4R as the chromatographic affinity ligand

The worldwide production of whey increases by around 186 million tons each year and it is generally considered as a waste, even when several whey proteins have important economic relevance. For its valorization, inexpensive ligands and integrated chromatography methods need to be developed for specific and low‐cost protein purification. Here, we describe a novel affinity process with the dye Yellow HE‐4R immobilized on Sepharose for bovine lactoferrin purification. This approach based on a low‐cost ligand showed an efficient performance for the recovery and purification of bovine lactoferrin directly from whey, with a yield of 71% and a purification factor of 61.