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- de Santos, A, et al.
(författare)
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Electrocatalytic NADH oxidation using an electrode based on Meldola blue immobilized on silica coated with niobium oxide
- 2002
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Ingår i: Electroanalysis. - 1040-0397. ; 14:12, s. 805-812
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Tidskriftsartikel (refereegranskat)abstract
- The immobilization of meldola blue (MB) on silica gel coated with niobium oxide (SN) and electrochemical investigation of its behavior as well as the electrocatalytical oxidation of nicotinamide adenine dinucleotide in reduced form (NADH) by this modified electrode are described. The modified silica containing 1.4 mmol g(-1) of niobium oxide dispersed on its surface adsorbed 55 mumol g(-1) of MB. SN containing MB adsorbed on its surface (SNMB) was mixed with carbon paste to prepare modified electrodes. Cyclic voltammetry of this modified electrode showed a quite reversible redox couple with a formal potential of -60 mV (vs. SCE) at pH 7.0. assigned to the immobilized MB. This formal potential is 60 mV more positive than that observed for MB in solution and this shift was attributed to the acidity of SN. The formal potential was independent of the solution pH in the range between 4 and S. A linear response range between 1.0 x 10(-5) and 7.50 x 10(-4) mol L-1 NADH concentration at pH 7.0 was observed. The electrocatalytical properties of the electrode to oxidize NADH was investigated and showed an interesting behavior. The heterogeneous electron transfer rate. k(cbp) was 1852 M(-1)s(-1) and the Michaelis-Menten constant, was 0.27 mM at pH 7,0 with the electrode coverage of about 4.4 x 10(-9) mol cm(-2), evaluated from the rotating disk electrode (RDE) experiments. The slight increase in the reaction rate with the solution pH was assigned to the thermodynamic driving force. This behavior can confirm a possible formation of a charge transfer complex between meldola blue and coenzyme.
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- de Santos, A, et al.
(författare)
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Nile blue adsorbed onto silica gel modified with niobium oxide for electrocatalytic oxidation of NADH
- 2002
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Ingår i: Electrochimica Acta. - 0013-4686. ; 47:20, s. 3351-3360
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Tidskriftsartikel (refereegranskat)abstract
- A study of modified carbon paste electrode employing Nile blue (NB) adsorbed on silica gel modified with niobium oxide (SN) for electrocatalytic oxidation of reduced nicotinamide adenine dinucleotide (NADH) is described. The adsorbed organic dye on SN was used to prepare a modified carbon paste electrode to investigate its electrochemical properties. The formal potential (E-o') of the adsorbed NB (-230 mV vs. saturated calomel electrode, SCE) showed a shift of 70 mV towards a more positive potential value, compared to NB dissolved in aqueous solution. In solutions with pH between 6.0 and 8.0 did stability and E-o' remained almost constant. However, for a solution pH lower than 6.0 the E-o' was affected by the acidity of the contacting solution, shifting the E-o' towards more positive values. For the solution pHs between 6.0 and 8.0 the electrocatalytic activity remained almost constant. A linear response range for NADH between 1.0 x 10(-5) and 5.2 x 10(-4) mol 1-1, at pH 7.0, was observed for the electrode, with an applied potential of -200 mV versus SCE. The formation of an intermediate charge transfer (CT) complex was proposed to the CT reaction between NADH and adsorbed NB. The heterogeneous electron transfer rate, k(obs), was 1400 M-1 s(-1) and the apparent Michaelis-Menten constant, was 0.21 mM at pH 7.0 evaluated from rotating disk electrode (RDE) experiments with an electrode coverage of about 5.2 x 10(-9) mol cm(-2). The increase in the reaction rate between NADH and the immobilized NB compared to those obtained with dissolved NB was assigned to the shift of the E-o' towards more positive values. (C) 2002 Elsevier Science Ltd. All rights reserved.
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- Mishra, A, et al.
(författare)
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Diminishing benefits of urban living for children and adolescents' growth and development
- 2023
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 1476-4687 .- 0028-0836. ; 615:7954, s. 874-883
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Tidskriftsartikel (refereegranskat)abstract
- Optimal growth and development in childhood and adolescence is crucial for lifelong health and well-being1–6. Here we used data from 2,325 population-based studies, with measurements of height and weight from 71 million participants, to report the height and body-mass index (BMI) of children and adolescents aged 5–19 years on the basis of rural and urban place of residence in 200 countries and territories from 1990 to 2020. In 1990, children and adolescents residing in cities were taller than their rural counterparts in all but a few high-income countries. By 2020, the urban height advantage became smaller in most countries, and in many high-income western countries it reversed into a small urban-based disadvantage. The exception was for boys in most countries in sub-Saharan Africa and in some countries in Oceania, south Asia and the region of central Asia, Middle East and north Africa. In these countries, successive cohorts of boys from rural places either did not gain height or possibly became shorter, and hence fell further behind their urban peers. The difference between the age-standardized mean BMI of children in urban and rural areas was <1.1 kg m–2 in the vast majority of countries. Within this small range, BMI increased slightly more in cities than in rural areas, except in south Asia, sub-Saharan Africa and some countries in central and eastern Europe. Our results show that in much of the world, the growth and developmental advantages of living in cities have diminished in the twenty-first century, whereas in much of sub-Saharan Africa they have amplified.
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