Search results for "Absorbance"
showing 10 items of 192 documents
Effect of the Alkaline Cations on the Stability of the Model Polynucleotide Poly(dG-dC)·Poly(dG-dC)
2011
When the model polynucleotide poly(dG-dC)∙poly(dG-dC) [polyGC] is titrated with a strong acid (HCl) in unbuffered aqueous solutions containing the chlorides of the alkali metals in the concentration range 0.010 M-0.600 M, two transitions in the absorbance vs. pH plots are evidenced, characterized by the constants pK(a(₁)) and pK(a(₂)). The limiting values at infinite saline concentrations of these two constants, namely pK(∞)(a(₁)) and pK(∞)(a(₂)) obtained making use of the "one site saturation constant" equation or, in turn, of the double logarithmic plot: pK(a) vs. log([salt]⁻¹), exhibit a clear dependence on the nature of the cations. The effects of the different alkali cations on the pK(…
Untargeted screening of the bound / free phenolic composition in tomato cultivars for industrial transformation
2019
BACKGROUND Tomato is one of the most important agricultural crops and it is characterized by a wide bioactive compound profile. However, little information is reported on its comprehensive polyphenol profile. In this work, 13 commercial tomato cultivars for industrial transformation were screened by ultra-high-pressure liquid chromatography coupled to quadrupole-time-of-flight mass spectrometry (UHPLC-QTOF-MS) for both free and bound phenolic profiles. Thereafter, the in vitro antioxidant activity of each cultivar was assessed by ferric reducing antioxidant power (FRAP) and oxygen radical absorbance activity (ORAC) assays. Multivariate statistics, i.e. orthogonal projection to latent struct…
A passive solid sensor for in-situ colorimetric estimation of the presence of ketamine in illicit drug samples
2017
Abstract A colorimetric sensor has been developed for the presumptive detection of ketamine in illicit drug samples. The sensor has been prepared by immobilized the reagent Co(SCN) 2 into polydimethylsiloxane (PDMS). When exposed to solutions of ketamine at a basic pH, the sensor color changes from brown to blue-purple due to the diffusion of the analyte molecules to the polymeric matrix and subsequent interaction with the reagent particles. The sensor enables the visual identification of amounts of drug as low as 30 μg in a few minutes. Quantification of ketamine is also possible through the measurement of the absorbance in diffuse reflectance mode. Under the proposed conditions, linear re…
Calibration of in situ chlorophyll fluorometers for organic matter
2019
AbstractOrganic matter (OM) other than living phytoplankton is known to affect fluorometric in situ assessments of chlorophyll in lakes. For this reason, calibrating fluorometric measurements for OM error is important. In this study, chlorophyll (Chl) fluorescence was measured in situ in multiple Finnish lakes using two sondes equipped with Chl fluorometers (ex.470/em.650–700 nm). OM absorbance (A420) was measured from water samples, and one of the two sondes was also equipped with in situ fluorometer for OM (ex.350/em.430 nm). The sonde with Chl and OM fluorometers was also deployed continuously on an automated water quality monitoring station on Lake Konnevesi. For data from multiple lake…
H-Point standard additions method for resolution of binary mixtures with simultaneous addition of both analytes
1995
Abstract The basis of the H-point standard additions method, HPSAM, with simultaneous addition of both analytes is proposed for the resolution of binary mixtures. It is a modification of the previously described H-point standard additions method that permits the resolution of both species from a unique calibration set by making the simultaneous addition of the two analytes. The method uses as analytical signals the absorbances at pairs of wavelengths where each species shows the same absorbance. The required data to apply the method are the absorbance values at the previously selected wavelengths for the sample alone and spiked with both species at known concentrations. Linear relations bet…
The Determination of the Reaction Rate for the First Step in a Consecutive Reaction A → B → C by Absorbance Measurements Using the Wavelength of the …
1977
Kinetic experiments are often followed by spectroscopic measurements in the visible or near ultraviolet region. The advantage is not only that the results can be recorded continuously, which makes very fast reactions accessible, but also that very low concentrations of substrates can be used. This means that only very small amounts are required and, more important perhaps, that reagents can be used in excess. Thus pseudomonomolecular conditions and first-order kinetics often can be achieved easily.
Spectral and microscopic study of self-assembly of novel cationic spermine amides of betulinic acid
2016
Supramolecular characteristics of two spermine amides of betulinic acid (1 and 2) were studied by measuring and evaluating their UV-VIS-NIR spectra in aqueous acetonitrile and DOSY-NMR spectra in tetradeuteromethanol, accompanied by atomic force microscopy (AFM) images, scanning electron microscopy (SEM) micrographs, and transmission electron microscopy (TEM) micrographs. Fibrous supramolecular self-assembly of 1 and 2 was observed by AFM images, as well as by the SEM and TEM micrographs. Bathochromic shifts of the absorbance maximum at 870nm to 1015-970nm in the UV-VIS-NIR spectra were observed with increasing water content in the acetonitrile/water systems, indicating formation of fibrous…
Effect of nitrite on microsomal cytochrome P-450.
1978
1. Addition of nitrite to anaerobic rat liver microsomes leads to the appearance of a difference spectrum similar to the spectrum of the ferrous cytochrome P-450-NO complex. A Soret band is found at 444 nm in phenobarbital-stimulated microsomes but at 442 nm in 3-methylcholanthrene-stimulated microsomes. An alpha-band is located at 583 nm in both types of microsome. 2. The initial nitrite-induced difference spectrum is converted into a spectrum lacking a Soret band but with a prominent absorbance minimum at 417 nm. This is more rapid in microsomes from phenobarbital-treated animals where it is completed in 8 min than in microsomes from 3-methylcholanthrene-treated animals. A similar spectru…
Evaluation of an automated chromogenic substrate assay for the rapid determination of hirudin in plasma.
1995
Abstract A fully mechanized chromogenic substrate assay method for the rapid and specific determination of recombinant hirudin (r-hirudin) in citrated plasma on clinical chemistry analyzers (Hitachi 911 and Cobas Mira) is described. In a first step, 12 μl sample volume is mixed with the chromogenic substrate. Due to the almost immediate action of hirudin the inhibitory reaction and the cleavage of the substrate is started simultaneously when bovine thrombin is added in excess. This excludes interferences by antithrombin III or heparin cofactor II. The change in absorbance/min is recorded at 405 nm. The measuring range is about 0.2 – 4.0 mg/l r-hirudin on both analyzers. Precision is charact…
Effect of Dietaryn-3Polyunsaturated Fatty Acids on Oxidant/Antioxidant Status in Macrosomic Offspring of Diabetic Rats
2014
The aim of this work was to determine the effect of dietaryn-3PUFA on oxidant/antioxidant status,in vitrovery low and low density lipoprotein (VLDL-LDL), and VLDL-LDL-fatty acid composition in macrosomic pups of diabetic mothers. We hypothesized thatn-3PUFA would improve oxidative stress in macrosomia. Diabetes was induced in female Wistar rats fed with the ISIO diet (control) or with the EPAX diet (enriched inn-3PUFAs), by streptozotocin. The macrosomic pups were killed at birth (day 0) and at adulthood (day 90). Lipid parameters and VLDL-LDL-fatty acid composition were investigated. The oxidant/antioxidant status was determined by measuring plasma oxygen radical absorbance capacity (ORAC)…