Urease adsorption and activity on magnetite nanoparticles functionalized with monofunctional and bifunctional surface layers

The surface of magnetite nanoparticles was coated with functional polysiloxane layers using reaction of hydrolytic copolycondensation of tetraethoxysilane and 3-aminopropyltriethoxysilane (or N-[3-trimethoxysilylpropyl]ethylendiamine), and also that of tetraethoxysilane, 3-aminopropyltriethoxysilane and methyltriethoxysilane (or n-propyltriethoxysilane). It was shown that these functionalized magnetically controllable particles (about 60–150 nm in size as aggregates), as opposed to magnetite, adsorb urease well from aqueous solutions (up to 1 g/g), and that the level of residual activity of adsorbed layers is up to 84 % in the case of a bifunctional sample. It was established that the activity of immobilized urease is normally gradually reduced during storage of the samples, but in the case of ethylenediamine functional group is not decreased for 45 days. The synthesized samples are promising for use as magnetically directed biocatalysts.     

Inequalities for the Hadamard Weighted Geometric Mean of Positive Kernel Operators on Banach Function Spaces

Let K₁, . . . , K_n be positive kernel operators on a Banach function space. We prove that the Hadamard weighted geometric mean of K₁, . . . , K_n, the operator K, satisfies the following inequalities where || · ||and r(·) denote the operator norm and the spectral radius, respectively. In the case of completely atomic measure space we show some additional results. In particular, we prove an infinite-dimensional extension of the known characterization of those functions satisfying for all non-negative matrices A₁, . . . , A_n of the same order.     

A generalization of Kakutani’s splitting procedure

In this paper, we will study uniformly distributed sequences of partitions of [0, 1], a concept which has been introduced by Kakutani (Measure Theory 541:369–375, 1976). We will construct new families of u.d. sequences of partitions and study relations with the classical concept of uniformly distributed sequences of points.     

His6-OPH enzyme-based bio-hybrid material for organophosphate detection

In this work, we report on the development of a bio-sensing film for the detection of organophosphorous compounds using sol–gel technology. A novel sol–gel immobilization method employing tetraethoxysilane/3-glycidoxypropyltrimethoxysilane/water hybrid material was developed and used to immobilize the hexahistidine-tagged organophosphorous hydrolase enzyme (His₆-OPH). Bio-sensing layers with encapsulated His₆-OPH of various structures (water/silane, precursor ratios) have been prepared. The optimal (P = 5:1, R = 188) bio-sensing layers retained 90% of the initial enzyme activity. Furthermore, the bio-sensing layer prepared by this method was able to maintain its activity at or above 80% of its initial activity for 2 weeks. The bio-hybrid film also showed excellent reusability and improved activity at neutral pH in comparison to the same enzyme in solution.     

Removal of Pb(II) ions from aqueous systems using thiol-functionalized cobalt-ferrite magnetic nanoparticles

We have investigated the removal of Pb²⁺ ions from water using thiol-functionalized, cobalt-ferrite, magnetic nanoparticles. These magnetic nanoparticles were prepared using the co-precipitation method and their surfaces were modified with tetraethoxy silane and 3-mercaptopropyl trimethoxysilane in order to provide a sufficient surface concentration of the thiol (–SH) functional groups. The adsorption of the Pb²⁺ ions from the aqueous solutions onto the thiol-functionalized, cobalt-ferrite, magnetic nanoparticles was studied. The investigated parameters include the pH value of the model water, the concentration of the adsorbent, the contact time and the temperature of adsorption. The removal of the Pb²⁺ was found to be greater at the higher pH values and increasing the temperature was also found to increase the removal of Pb²⁺ ions.     

On Gruber’s problem concerning uniform distribution on the sphere

In this note we give a partial answer to a problem posed by Peter Gruber on the determination of uniform distribution of a sequence of points on the three-dimensional sphere from its appropriate behavior on caps.