A disposable biosensor for the determination of alpha-amylase in human saliva

A disposable tri-enzymatic biosensor is presented for the determination of α-amylase in human saliva. It is based on the quantity of maltose generated by hydrolysis of maltopentose in the presence of salivary α-amylase. The biosensor is fabricated by co-immobilization of the enzymes α-glucosidase, glucose oxidase, and mutarotase on screen-printed electrodes modified with Prussian Blue. The assay can be performed with a “drop” of sample, this allowing for ease and simplicity. A linear relationship is found for the range from 5 to 250 units per mL, with an LOD of 5 units per mL. The biosensor is stable for at least one month and over this time retains 80% of its original activity. The system was then evaluated for matrix effects of human saliva and compared to a spectrometric method using a commercially available kit.     

A Refined Schwarz Lemma for the Spectral Nevanlinna-Pick Problem

The spectral Nevanlinna–Pick problem asks for necessary and sufficient conditions for the existence of a holomorphic map from the unit disc to the set of $n\times n$ complex matrices with spectral radius less than 1, that interpolates given data. Some versions of the Schwarz lemma, obtained by Ransford and Nokrane, and by Bharali, provide necessary conditions. We prove a refined version of their results, which makes it possible to treat problems with more than two interpolation points.     

Elasticity of ion stuffing in chemically strengthened glass

The chemical strengthening of glass involves the stuffing of large ions into network sites previously occupied by smaller ions. Typically this involves an exchange of Li⁺ or Na⁺ ions in the glass for larger K⁺ ions from a molten salt bath. This swapping of ions creates compressive stress in the surface of the glass, significantly increasing the strength of the final glass product. The magnitude of this compressive stress is governed by the linear network dilation coefficient (LNDC), which defines the amount of linear strain per unit of ion substitution. However, the amount of strain attainable through ion exchange is much smaller compared to what is expected from as-melted versions of the same final glass composition. This effect, which we have termed the “network dilation anomaly,” is a result of the different local environment around the invading ion species in as-melted versus ion-exchanged glasses. A remaining question concerns the nature of the network strain due to ion stuffing. Using molecular dynamics simulations, we show that the strain induced by ion stuffing is entirely elastic. In other words, when a reverse ion exchange is performed to swap the original ions back into the glass, the initial volume of the as-melted glasses is entirely recovered. Moreover, we show that the local structural environment around the alkali ions is restored to the as-melted conditions. The elastic nature of ion stuffing demonstrates that the network dilation anomaly is not a result of plasticity, but rather a failure to achieve the full amount of expected elastic strain during ion exchange. The elasticity itself consists of both instantaneous and delayed contributions.     

Bioactive glycosides from the African medicinal plant Boerhavia erecta L.

Phytochemical studies of the previously unexplored stem of Boerhavia erecta from Burkina Faso, resulted in the isolation of an unreported glycoside 4, 2,3-dihydroxypropylbenzoate-3-O-β-[4″-methoxy] glucuronide as well as seven known glycosides (1–3, 5–8). The major isolate 5 and 8 indicated a significant inhibition against HIV integrase (IC₅₀ 10 and 22 μg/mL, respectively). The extracts and isolates were also tested for anti-malarial activity, but insignificant activity was observed.     

Topology on the Spaces Of Orderings of Groups

A natural topology on the space of left orderings of an arbitrarysemi-group is introduced here. This space is proved to be compact,and for free abelian groups it is shown to be homeomorphic tothe Cantor set. An application of this result is a new proofof the existence of universal Gröbner bases. 2000 MathematicsSubject Classification 06F15, 13P10 (primary), 06F05, 20F60(secondary).     

Using Microfluidic Set-Up to Determine the Adsorption Rate of Sporosarcina pasteurii Bacteria on Sandstone

Transport in Porous Media - Microbial-induced carbonate precipitation (MICP) in porous media is a two-step procedure: First, the suspension of bacteria is injected and some of the bacteria get...     

Synthesis of α-Functionalized Allenes

It is known, since the work of Landor et al, that α-allenic alcohols can be specifically obtained by treating the monotetrahydropyranyl ether of a butyn-1,4-diol with lithium aluminium hydride (1). In this reaction, which can be also realized with another leaving group (halogen, ammonium) (2), the allenic linkage is formed by an S_N ^2′ process where the nucleophilic hydride is transferred from the initially formed alcoholate (scheme 1).     

NMR and AM1 Study of the Tautomeric Equilibrium of Isochroman-1,2-diones

Reaction of homophtalic anhydrid with aliphatic or aryl anhydrids (or acid chlorides) and an appropriate base gives 4-acyl and 4-aroylisochroman-1,3-diones. The structure of these isochroman-1,3-diones was determined by ¹H, ¹³C and ¹⁷O NMR spectrometry. In solution, among the three possible tautomers, only the enolic one with exocyclic double bond was observed. These results are in good agreements with AMI calculations ones.     

Atomistic understanding of the network dilation anomaly in ion-exchanged glass

Chemically strengthened glasses are of increasing technological importance for personal electronic devices, tablet computers, and a variety of other applications. However, there are many unexplained phenomena associated with the physics of the ion exchange process used for strengthening. One of the most puzzling of these is the anomalous behavior of the network dilation coefficient, i.e., the parameter governing the amount of linear strain of the glass per unit of alkali ions exchanged, which is inevitably a factor of 2–4 higher for as-melted glasses as compared to chemically strengthened versions of the same glass compositions prepared via ion exchange. In this paper, we investigate the atomistic origin of this discrepancy between as-melted and ion-exchanged glasses based on molecular dynamics simulations of a series of alkali tetrasilicate glasses, viz., xNa₂O·(20 ? x)K₂O·80SiO₂ (mol%). The network dilation coefficient of the ion-exchanged glasses is dependent on composition and ranges from 30% to 54% of the ideal value obtained from the as-melted glasses. This anomalous behavior of the network dilation coefficient is explained in terms of different local environments between sodium and potassium sites in the glass network and a two-stage relaxation process of the local potassium environment after ion exchange.