•The set of 29 flavonoids was optimized using PM6 method in water.•Influence of O-glycosyl, galloyl and ortho-methoxy substituents on Ep1.•Regression model based on the sum of atomic orbital spin ...populations on C atoms.•Regression model based on the sum of differences in net atomic charges on C atoms.
In continuation of our investigation of the dependence of the first electrochemical oxidation potential, Ep1, on the electronic structures of flavonoids, the potentials of nine additional flavonoids (hesperetin, daidzein, kaempferol, acacetin, naringin, neohesperidin, hesperidin, quercitrin, and gossypin) were assessed using square-wave voltammetry on a glassy-carbon electrode in aqueous buffer solutions with a pH of 3 and 7. Our standard model for the estimation of the Ep1, based on the sum of atomic orbital spin populations over the carbon atoms in the skeleton of the radical molecule, Σs(C)AOSPRad, yielded S.E. = 0.063 and S.E.cv = 0.072 on this enlarged set of 29 flavonoids. We also introduced a new complementary model that yielded similar statistics, S.E. = 0.055 and S.E.cv = 0.059. This model was based on the differences in the net atomic charges between cations and neutral flavonoids also summed over the carbon atoms in their skeleton (Σs(C)ΔNACCat-Neut). Such an excellent agreement between Σs(C)ΔNACCat-Neut and Ep1 may be proof that the electrochemical oxidation of all 29 flavonoids starts with ionization, i.e. abstraction of an electron, at both of the pHs indicated.
Amino-substituted benzamide derivatives are very attractive compounds due to their capacity to act as powerful antioxidants by scavenging free radicals. Knowledge on electrochemical oxidation ...mechanisms plays an important role in understanding the free radical scavenging activity of antioxidants. In this paper, the electrochemical oxidation of four amino-substituted derivatives N-(4-aminophenyl)-2-hydroxybenzamide (1), N-(4-aminophenyl)-2-hydroxy-4-methoxybenzamide (2), N-(4-aminophenyl)-2-methoxybenzamide (3), N-(4-aminophenyl)-3,4,5-trihydroxybenzamide (4) in an aqueous buffer solution was studied by means of cyclic and square-wave voltammetry, and probable reaction mechanisms have been proposed. In compounds 1–3, the primary amino group was found to be the main electroactive centre undergoing a complex, pH-dependent oxidation process with the transfer of two electrons and two protons. This reaction occurs in one step or in two separate steps, depending on the pH of the medium. A possible explanation for this electrochemical behaviour is discussed. The final products of initial electrochemical oxidation of amino-substituted benzamides 1–3 are quinonediimine derivatives that undergo further chemical transformation into electroactive forms. Oxidation of compound 4 proceeds through two sequential reactions; the first anodic reaction is the oxidation of the trihydroxyphenyl group to the corresponding o-quinone, followed by the oxidation of a primary amino group. Considering the oxidation potentials, and bearing in mind that lower/less positive potential implies better radical scavenging activity, the order of antioxidant activity of the here studied amino-substituted benzamides is: 4 >2 >1 >3.
•The first report on the electrochemical behaviour of hydroxy and methoxy substituted N-arylbenzamides.•Mechanism of the oxidation was proposed.•Oxidation potentials were used to evaluate antioxidant activity.
Filament-induced ablation represents an attractive scheme for long-range material identification via optical spectroscopy. However, the delivery of laser energy to the target can be severely hindered ...by the stochastic nature of multiple-filamentation, ionization of ambient gas, and atmospheric turbulence. In order to mitigate some of these adverse effects, we examine the utility of beam shaping for femtosecond filament-induced breakdown spectroscopy with Gaussian and structured (Laguerre-Gaussian, Airy, and Bessel-Gaussian) beams in the nonlinear regime. Interaction of filaments with copper, zinc, and brass targets was studied by recording axially-resolved broadband emission from the filament-induced plasma. The laser-solid coupling efficacy was assessed by inferring thermodynamic parameters such as excitation temperature and electron density. While under our experimental conditions the ablation rate with Gaussian- and Laguerre-Gaussian beams is found to be similar, the Airy and Bessel-Gaussian beams offer the advantage of longitudinally extended working zones. These results provide insights into potential benefits of structuring ultrafast laser beams for standoff sensing applications.
Efficiency calibration, i. e. determination of detection efficiency, ?p, is a crucial issue in gamma spectrometry (quantification of gamma spectroscopic measurements) with semiconductor and ...scintillation detectors. Comparing three possible ways to addressing the problem ? relative, absolute and semi empirical ? advantages of the latter are emphasized. Among semi empirical models, efficiency transfer using effective solid angles, ??, is sorted out and briefly elaborated. This approach reduces the problem of efficiency calibration to the determination of ??. It proved reliable and has been broadly used in practice, mainly in the form of the long existing ANGLE software. Progressing further, a generalized mathematical formula for calcu- lations is developed ? first of the kind ? offering an opportunity for advanced applications of gamma spectrometry. The formula enables unlimited flexibility in application, as it conveniently separates the source data from the detector data during the integration procedures ?? calculations). Its practicality is demonstrated for a number of typically encountered counting arrangements, as well as for some exotic ones. The relevant formulae are used in PC calculations and numerical testing is further performed so as to check the validity of the mathematical method and the computer code. Care was taken of the optimization of complex numerical procedures employed (involving fivefold numerical integration), so as to keep computation times as low as possible (in order of minutes or even seconds on ordinary PC). Results obtained are affirmative for both the method and the code. The model will be gradually incorporated into ANGLE software, thus making it readily available for routine use by gamma spectrometry community.
nema
This paper studies the electronic structures of the 14 flavonoids and their cation and radical forms involved in the first electrochemical oxidation step, associated with the oxidation peak appearing ...at potential Ep1. The sum of differences in Net atomic charges on atoms in skeleton of cations and neutral flavonoids (Σs(C)ΔNACCat.-Neut.) and the sum of Atomic orbital electron and spin populations on atoms in skeleton of radicals (Σs(C)AOEP and Σs(C)AOSP) revealed that electron distribution between skeleton atoms and active OH oxygen is more evenly distributed in cations and radicals of flavonoids that are more prone to oxidation. Those less susceptible to oxidation are more polarized, i.e. the skeleton becomes more positively charged. Also, Σs(C)AOSP proved to be an excellent descriptor for modelling the first oxidation potential, especially in combination with Σs(C)pzAOEP (common model for pH = 3 and 7 yielded R2 = 0.978 and S.E. = 0.43).
ANGLE software for semiconductor detector efficiency calculations - long
existing and widely accepted tool in quantitative gamma spectrometry - has
been recently extended to scintillation NaI ...detectors. The extension features
in the latest edition (ANGLE 4) and it is briefly outlined. Discretization of
reference efficiency curve, meaning possibility of using ANGLE 4 for
particular gamma energies without constructing the complete reference
efficiency curve, is particularly emphasized. This yields both in enhanced
practicality and higher accuracy, while reducing the potential for systematic
errors. The present work is primarily focussed on experimental verification
of ANGLE 4 for NaI detectors. Two detectors (2 ? 2 and 3 x 3 inches) were
employed in the experiment. Commercially calibrated gamma sources (in the
forms of quasi point and cylinder) and homemade solutions (diluted from
calibrated ones) were measured at various distances from the detector(s),
ranging 0 cm to 50 cm. Energy range observed was 59 keV to 1408 keV.
Versatility of counting conditions, in terms of detectors and sources used,
gamma energies observed, source detector separations, etc., was aimed at
creating as large experimental evidence as possible for verification
purposes. Experimentally obtained efficiencies are compared with those
calculated by ANGLE 4. Very good agreement is obtained - well within the
experimental uncertainties - thus proving the reliability of the software.
nema
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