Determination of acidity constants of curcumin in aqueous solution and apparent rate constant of its decomposition

The stability of curcumin (H3Cur) in aqueous media is improved when the systems in which it is present are at high pH values (higher than 11.7), fitting a model describable by a pseudo-zero order with a rate constant k' for the disappearance of the Cur3- species of 1.39 (10(-9)) Mmin(-1). There were three acidity constants measured for the curcumin as follows: pKA3 = 10.51 +/- 0.01 corresponding to the equilibrium HCur2- = Cur3- + H+, a pKA2 = 9.88 +/- 0.02 corresponding to the equilibrium H2Cur- = HCur-(2) + H+. These pKA values were attributed to the hydrogen of the phenol part of the curcumin, while the pKA1 = 8.38 +/- 0.04 corresponds to the equilibrium H3Cur = H2Cur- + H+ and is attributed the acetylacetone type group. Formation of quinoid structures play an important role in the tautomeric forms of the curcumin in aqueous media, which makes the experimental values differ from the theoretically calculated ones, depending on the conditions adopted in the study.     

Vibrational and 57Fe-Mössbauer spectra of some mixed cation diphosphates of the type M(II)Fe2(III)(P2O7)2

The infrared (IR), Raman and 57Fe-M?ssbauer spectra of SrFe2(P2O7)2, BaFe2(P2O7)2 and PbFe2(P2O7)2 were recorded and discussed on the basis of the structural peculiarities of the compounds.     

Null controllability of a system of viscoelasticity with a moving control

In this paper, we consider the wave equation with both viscous Kelvin–Voigt and frictional damping as a model of viscoelasticity in which we incorporate an internal control with a moving support. We prove the null controllability when the control region, driven by the flow of an ODE, covers all the domain. The proof is based upon the interpretation of the system as, roughly, the coupling of a heat equation with an ordinary differential equation (ODE). The presence of the ODE for which there is no propagation along the space variable makes the controllability of the system impossible when the control is confined into a subset in space that does not move. The null controllability of the system with a moving control is established in using the observability of the adjoint system and some Carleman estimates for a coupled system of a parabolic equation and an ODE with the same singular weight, adapted to the geometry of the moving support of the control. This extends to the multi-dimensional case the results by P. Martin et al. in the one-dimensional case, employing 1-d Fourier analysis techniques.     

Lower previsions induced by filter maps

We investigate under which conditions a transformation of an imprecise probability model of a certain type (coherent lower previsions, n  -monotone capacities, minitive measures) produces a model of the same type. We give a number of necessary and sufficient conditions, and study in detail a particular class of such transformations, called filter maps. These maps include as particular models multi-valued mappings as well as other models of interest within imprecise probability theory, and can be linked to filters of sets and {0,1}$\{0,1\}$-valued lower probabilities.     

Numerical Exact Controllability of the 1D Heat Equation: Duality and Carleman Weights

This article is devoted to the numerical computation of distributed null controls for the 1D heat equation. The goal is to compute a control that drives (a numerical approximation of) the solution from a prescribed initial state exactly to zero. We extend the earlier contribution of Carthel, Glowinski, and Lions, which is devoted to the computation of controls of minimal square-integrable norm. We start from some constrained extremal problems (involving unbounded weights in time), introduced by Fursikov and Imanuvilov, and we apply appropriate duality techniques. Then, we provide numerical approximations of the associated dual problems, and apply conjugate gradient algorithms. Finally, several experiments are presented, and we highlight the influence of the weights and analyze this approach in terms of robustness and efficiency. Also, the results are compared with others in a previous article of the authors, where primal methods were considered.     

Harmonic analysis on the Sierpiński gasket and singular functions

We study the restriction on [0,1] of harmonic functions on the Sierpiński gasket, proving they are singular functions whenever they are monotone. We show that their derivatives are zero or infinity on certain non-denumerable sets. Finally, we show they are among a wider class of functions that contains some already known and studied functions.     

Biogenic Silver Nanoparticles from Iris tuberosa as Potential Preservative in Cosmetic Products

Biogenic-silver nanoparticles emerge as new nanosilver platforms that allow us to obtain silver nanoparticles via “green chemistry”. In our study, biogenic-silver nanoparticles were obtained from Iris tuberosa leaf extract. Nanoparticles were characterized by a UV-vis spectroscopy, dynamical light scattering technique. The transmission electron microscope revealed spheric and irregular nanoparticles with 5 to 50 nm in diameter. Antimicrobial properties were evaluated against typical microbial contaminants found in cosmetic products, showing high antimicrobial properties. Furthermore, natural moisturizing cream was formulated with biogenic-silver nanoparticles to evaluate the preservative efficiency through a challenge test, indicating its promising use as preservative in cosmetics.     

Study of the ferrocene-lithium cation interaction by DFT calculations: an in-depth analysis of the existence of a planetary system

Irigoras et al. found two isomers of the ferrocene-lithium cation complex by DFT calculations [Irigoras, A.; Mercero, J. M.; Silanes, I.; Ugalde, J. J. Am. Chem. Soc.2001, 123, 5040-5043]. The most stable isomer (I) of this complex has Li⁺ on top of one of the cyclopentadienyls, while in the least stable isomer (II) Li⁺ binds to the central iron metal. The latter isomer has been characterized as a planetary system in the sense that Li⁺ has one thermally accessible planar orbit around the central ferrocene moiety. Afterwards, Scheibitz et al. have provided experimental indication for the existence of structure II [Scheibitz, M.; Winter, R. F.; Bolte, M.; Lerner, H.-W.; Wagner, M. Angew. Chem., Int. Ed.2003, 42, 924-927]. However, their experimental proof is indirect, since it is only based on the synthesis of [3-Li]Li([12]crown-4)₂, a crystalline solid, which anion (structure A) has a lithium cation bound to the iron atoms. As these authors have indicated, the existence of structure A could not represent a conclusive proof, because the Li⁺ placement in this structure could be due to different effects to those of complex II (specifically, the electrostatic field originating from the two anionic dimethylborate bridges). To analyze this subject we have carried out a comprehensive DFT study of the ferrocene-Li⁺ interaction in this kind of compounds.     

Synthesis and nonlinear optical properties of chromophores for photorefractive polymer materials

The synthesis and nonlinear optical (NLO) properties of a series of nitrostilbene-, dinitrostilbene-, and dicyanomethylenedihydrofuran-based chromophores potentially useful in photorefractive multifunctional polymers are reported. Electronic absorption spectra have been measured in different solvents. Electric field induced second harmonic (EFISH) generation results show that the 2-dicyanomethylen-3-cyano-5,5-dimethyl-2,5-dihydrofuran moieties lead to the best NLO performances. Dinitrophenyl-based chromophores have shown a reduced nonlinear response as compared with the mononitro analogues. Nonlinear optical properties of a selected nitro-dinitro couple have been also determined theoretically.