Mesoporous carbon-containing voltammetric biosensor for determination of tyramine in food products

A voltammetric biosensor based on tyrosinase (TYR) was developed for determination of tyramine. Carbon material (multi-walled carbon nanotubes or mesoporous carbon CMK-3-type), polycationic polymer—i.e., poly(diallyldimethylammonium chloride) (PDDA), and Nafion were incorporated into titania dioxide sol (TiO(2)) to create an immobilization matrix. The features of the formed matrix were studied by scanning electron microscopy (SEM) and cyclic voltammetry (CV). The analytical performance of the developed biosensor was evaluated with respect to linear range, sensitivity, limit of detection, long-term stability, repeatability, and reproducibility. The biosensor exhibited electrocatalytic activity toward tyramine oxidation within a linear range from 6 to 130 μM, high sensitivity of 486 μA mM(−1) cm(−2), and limit of detection of 1.5 μM. The apparent Michaelis–Menten constant was calculated to be 66.0 μM indicating a high biological affinity of the developed biosensor for tyramine. Furthermore, its usefulness in determination of tyramine in food product samples was also verified. [Figure: see text] ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s00216-016-9612-y) contains supplementary material, which is available to authorized users

Preferential binding of K+ ions in the selectivity filter at equilibrium explains high selectivity of K+ channels

K(+) channels exhibit strong selectivity for K(+) ions over Na(+) ions based on electrophysiology experiments that measure ions competing for passage through the channel. During this conduction process, multiple ions interact within the region of the channel called the selectivity filter. Ion selectivity may arise from an equilibrium preference for K(+) ions within the selectivity filter or from a kinetic mechanism whereby Na(+) ions are precluded from entering the selectivity filter. Here, we measure the equilibrium affinity and selectivity of K(+) and Na(+) ions binding to two different K(+) channels, KcsA and MthK, using isothermal titration calorimetry. Both channels exhibit a large preference for K(+) over Na(+) ions at equilibrium, in line with electrophysiology recordings of reversal potentials and Ba(2+) block experiments used to measure the selectivity of the external-most ion-binding sites. These results suggest that the high selectivity observed during ion conduction can originate from a strong equilibrium preference for K(+) ions in the selectivity filter, and that K(+) selectivity is an intrinsic property of the filter. We hypothesize that the equilibrium preference for K(+) ions originates in part through the optimal spacing between sites to accommodate multiple K(+) ions within the selectivity filter

Determinants of cation transport selectivity: Equilibrium binding and transport kinetics

The crystal structures of channels and transporters reveal the chemical nature of ion-binding sites and, thereby, constrain mechanistic models for their transport processes. However, these structures, in and of themselves, do not reveal equilibrium selectivity or transport preferences, which can be discerned only from various functional assays. In this Review, I explore the relationship between cation transport protein structures, equilibrium binding measurements, and ion transport selectivity. The primary focus is on K(+)-selective channels and nonselective cation channels because they have been extensively studied both functionally and structurally, but the principles discussed are relevant to other transport proteins and molecules

Physical properties responsible for the durability of high-grade concretes made from blast-furnance cement

Artykuł dotyczy badań właściwości fizycznych odpowiedzialnych za trwałość - przepuszczalności, nasiąkliwości i wytrzymałości - betonów wysokowartościowych (BWW). Badane betony o stosunku w/c=O,32 zostały wykonane z cementów hutniczych (zawierających 46, 57 i 75% żużla) i z cementu portlandzkiego. Betony były badane po 3, 28 dniach i 1 roku dojrzewania w wodzie. W badaniach stwierdzono po jednym roku dojrzewania duże zmniejszenie przepuszczalności i nasiąkliwości (poniżej 3%) betonów z cementów hutniczych oraz bardzo istotny wzrost ich wytrzymałości na ściskanie. Wszystkie betony z cementów hutniczych osiągnęły wytrzymałość większą niż 100 MPa, natomiast wytrzymałość betonu z cementu portlandzkiego wynosiła 88 MPa.This paper concerns research into the physical properties responsible for durability of high-grade concretes - permeability, absorbability and strength. The types of concrete investigated, with a water-cement ratio of 0.32, were made from blast-furnace cement (containing 46%, 57% and 75% slag) and from Portland cement. The concretes were analysed after 3 days, 28 days and one year of maturing in water. The tests showed that after a year's maturing there was a large reduction in permeability and absorbability (below 3%) for concretes made of blast-furnace cement, and a very significant increase in their compression strength. The strength value for all concretes made of blast-furnace cement was greater than 100 MPa, while that for concrete made from Portland cement was 88 MPa

Rheology of air entrained concretes and cements with mineral additives

W pracy podjęto próbę wyjaśnienia wpływu napowietrzenia oraz cementów zawierających dodatki mineralne na odkształcenia reologiczne betonów. Betony wykonano z następujących cementów: cement portlandzki i dwa cementy portlandzkie z dodatkami zawierającymi żużel wielkopiecowy, krzemionkowy popiół lotny oraz mielony kamień wapienny. W wyniku przeprowadzonych badań stwierdzono, że napowietrzenie betonów powoduje spadek skurczu i pęcznienia betonów zawierających cementy portlandzki i żużlowo-popiołowy, natomiast zwiększa skurcz betonów z cementów zawierających mączkę wapienną. Badania odkształceń prowadzono za pomocą aparatu Amslera, stosując po 6 próbek każdego betonu o wymiarach 10×10×50 cm.The studies were carried out to find the effect of air entrainment and blended cements on rheological deformations of concretes. The cements used were ordinary Portland cement and two blended Portland cements containing: blast furnace granulated slag-fly ash blend and limestone powder. It was stated that air entrainment results in lowering of shrinkage and swelling of concretes made of OPC and blast furnace granulated slag-fly ash blend cement. The increase in both deformations of air entrained concrete occurs when the limestone cement is used. The linear dimension changes was measured with Amsler’s apparatus, according to the Polish standard PN-B-06714-23:1984, using 6 samples of each concrete with dimensions 10×10×50 cm, equipped with steel pins cemented in the both ends of the beams. The first measurement was made after 24 hours from concrete beams preparation

Wpływ domieszki napowietrzającej i rodzaju cementu na właściwości świeżej zaprawy

In order to explain the effect of air entraining admixture (AEA) and the type of cement on the properties of fresh mortar, the following tests were carried: bulk density, flaw and air content of 20 air entrained mortars and 20 nan air entrained mortars made of ordinary Portland cement (OPC) and blended Portland cements: blast furnace slag (BSF) - limestone powder (LP), fly ash - limestone, fly ash (FA) and (BFS) cement. It has been found that the modern anionic AEAs from the group of alkyl sulfates are much more efficient and active than traditional ones i.e. sodium abietate. It is difficult to entrain air into mortars with cement of various types to the same content of air. This requires to carry out a number of tests to determine the appropriate amounts of AEA. The air entrainment of LP cement mortar does not significantly change its flow. The air entrainment of BSF and FA cement mortars increases their workability. The lowest content of air was stated in non-air-entrained mortars with FA cement, the highest air content was observed in BFS cement mortars. According to the results the bulk density of mortars is inversely proportional to the amount of air entrained

The effect of coarse aggregate on the deformation properties of normal concretes

W artykule przedstawiono wyniki badań betonów zwykłych o wartościach w/c wynoszących 0,70 i 0,58. Badano odkształcalność doraźną betonów w zakresie modułu sprężystości, współczynnika odkształcenia poprzecznego oraz wartości odkształceń granicznych przy maksymalnym naprężeniu. Ponadto przedstawiono przebieg krzywych sigma-epsilon w pełnym zakresie obciążenia. Czynnikiem zmiennym w badaniach było kruszywo grube (grys bazaltowy, granitowy, dolomitowy oraz dla porównania kruszywo naturalne otoczakowe). W obydwu grupach betonów (o tym samym w/c) stwierdzono istotny wpływ rodzaju kruszywa grubego na badane cechy odkształceniowe betonów zwykłych.The test results presented concern normal concretes of the w/c-ratio 0.58 and 0.70. There have been examined a modulus of elasticity, transverse strain coefficient and the strain at the highest compressive stress. There are presented the curves sigma-epsilon for the whole range of loading. The variable factor in the studies is the kind of coarse aggregate (crushed basalt, granite and dolomite compared with the natural gravel). There is stated a significant influence of aggregate on the deformation properties for both concrete groups of the same w/c-ratio

Self-deformations of aerated concretes

Praca przedstawia dotychczas nieznane w literaturze wyniki badań odkształceń własnych (skurczu i pęcznienia) betonu napowietrzonego. Badaniom poddano betony napowietrzone i nienapowietrzone o stosunku w/c=0,60 i w/c=0,50 wykonane z cementu portlandzkiego. Wyniki badań wykazują, że skurcz betonu napowietrzonego, mimo jego większej porowatości i niższej wytrzymałości, jest wyraźnie mniejszy niż betonu nienapowietrzonego o odpowiednim stosunku w/c. Również pęcznienie dojrzałego betonu napowietrzonego jest mniejsze niż betonu nienapowietrzonego o tym samym stosunku w/c. Odkształcenia były mierzone za pomocq tensometru Demec 8" na próbkach 8 x 8 x 32 cm i aparatu Amslera na próbkach 10 x 10 x 50 cm. Autorzy kontynuują badania odkształceń własnych betonów o różnym składzie, dla których wybrano zdecydowanie lepszą metodę pomiaru, tj. aparatem Amslera.This paper presents the results, not previously reported in the literature, of investigations of the self-deformations (shrinkage and swelling) of aerated concrete. The tests used aerated and non-aerated concretes with w/c ratios of 0.60 and 0.50, made from Portland cement. The results show that the shrinkage of aerated concrete, in spite of its greater porosity and lower strength, is markedly smaller than that of non-aerated concrete with a corresponding w/c ratio. The swelling of mature aerated concrete is also smaller than that of non-aerated concrete with the same w/c ratio. Deformations were measured using a Demec 8" extensometer on 8 x 8 x 32 cm samples, and an Amsler apparatus on 10x10x 50 cm samples. The authors are continuing tests on the self-deformations of concretes of various compositions, for which the decisively superior method for measurement - the Amsler apparatus - has been chosen