Competitive adsorption of Ca2+ and Zn(II) ions at monodispersed SiO2/electrolyte solution interface

A study of competitive adsorption of Ca(2+) and Zn(II) ions at the monodispersed SiO(2)/electrolyte solution interface is presented. Influence of ionic strength, pH, and presence of other ions on adsorption of Ca(2+) and Zn(II) in the mentioned system are investigated. zeta potential, surface charge density, adsorption density, pH(50%), and DeltapH(10-90%) parameters for different concentrations of carrying electrolyte and adsorbed ions are also presented. A high concentration of zinc ions shifts the adsorption edge of Ca(2+) ions adsorbed from solutions with a low initial concentration at the SiO(2)/NaClO(4) solution interface to the higher pH values. This effect disappears with a concentration increase of calcium ions. The presence of Ca(2+) ions in the system slightly affects the adsorption of zinc ions on SiO(2), shifting the adsorption edge toward lower pH values and thereby increasing the adsorption slope.     

What can positronium tell us about adsorption?

The condensation and evaporation of n-heptane at 298 K in mesopores of silica material obtained by the polymer templating method have been studied by PALS measurements. It is demonstrated that the ortho-positronium lifetimes and intensities provide valuable information on pore filling and emptying which are not accessible from a conventional adsorption experiment. The results confirm the specific adsorption mechanism of n-heptane in pores with narrow openings (ink-bottle shape) which is different from that known for other pore geometries. The results from PALS experiment are compared to those derived from the conventional n-heptane and nitrogen adsorption data.     

Tabu search algorithm for DNA sequencing by hybridization with isothermic libraries

In this paper, a problem of isothermic DNA sequencing by hybridization (SBH) is considered. In isothermic SBH a new type of oligonucleotide libraries is used. The library consists of oligonucleotides of different lengths depending on an oligonucleotide content. It is assumed that every oligonucleotide in such a library has an equal melting temperature. Each nucleotide adds its increment to the oligonucleotide temperature and it is assumed that A and T add 2 degrees C and C and G add 4 degrees C. The hybridization experiment using isothermic libraries should provide data with a lower number of errors due to an expected similarity of melting temperatures. From the computational point of view the problem of isothermic DNA sequencing with errors is hard, similarly like its classical counterpart. Hence, there is a need for developing heuristic algorithms that construct good suboptimal solutions. The aim of the paper is to propose a heuristic algorithm based on tabu search approach. The algorithm solves the problem with both positive and negative errors. Results of an extensive computational experiment are presented, which prove the high quality of the proposed method.     

Molecular dynamics simulations of matrix deposition. III. Site structure analysis for porphycene in argon and xenon

Porphycene (1) and porphyrin (2), two constitutional isomers, reveal completely different electronic spectral patterns in argon and xenon matrices. For the former the spectra recorded in the two solidified gases resemble each other, whereas for the latter they are completely different. This difference can be rationalized by molecular-dynamics simulations of the structure of the microenvironment carried out for the two chromophores embedded in argon and xenon hosts. For 1, the structure of the main substitutional site is the same for Ar and Xe and consists of a hexagonal cavity obtained by removing seven host atoms from the [111] crystallographic plane. An analogous structure is obtained for 2 in xenon. However, in argon the porphyrin chromophore environment is shared between several different sites, with the number of replaced host atoms ranging from seven to ten. These results demonstrate that a relatively minor structural alternation may lead to major changes in the spectral pattern of molecules embedded in rare-gas cryogenic matrices.     

Addition of Organolithium and Grignard Reagents to Pyrimidine-2(1H)-thione: Easy Access to 4-Substituted 3,4-Dihydropyrimidine-2(1H)-thiones

Organolithium and Grignard reagents are added to pyrimidine-2(1H)-thione, yielding 4-substituted 3,4-dihydropyrimidine-2-(1H)-thiones. Since the synthetic procedure can be performed on a multigram scale, and since pyrimidine-2(1H)-thione as well as the majority of organometallic reagents are readily available, the process described provides an easy access and complementary to other methods to 4-substituted 3,4-dihydropyrimidine-2-(1H)-thiones.     

Oxidative Conversion of Aldoximes into Carboxylic Acid Esters

Aromatic and aliphatic aldoximes or their O-methyl ethers can be efficiently converted into the corresponding carboxylic acid esters by treatment with an alcoholic solution of 30% hydrogen peroxide in the presence of catalytic amounts of 2-nitrobenzeneseleninic acid. Primary alcohols give excellent to good yields, secondary ones - good to moderate, but with tertiary alcohols no esterification is obserwed.     

Selenium(IV) Oxide Catalyzed Oxidation of Aldehydes to Carboxylic Acids with Hydrogen Peroxide

A convenient method for oxidative transformation of aromatic, hetero-aromatic and aliphatic aldehydes into carboxylic acids is presented. It is based on the oxidation of aldehydes in THF using 30% hydrogen peroxide in the presence of 5 molar % of selenium(IV) oxide. The scope and limitation of the method are discussed.     

Acid-base equilibriums of lumichrome and its 1-methyl, 3-methyl, and 1,3-dimethyl derivatives

Lumichrome photophysical properties at different pH were characterized by UV-vis spectroscopy and steady-state and time-resolved fluorescence techniques, in four forms of protonation/deprotonation: neutral form, two monoanions, and dianion. The excited-state lifetimes of these forms of lumichrome were measured and discussed. The results were compared to those obtained for similar forms of alloxazine and/or isoalloxazine, and also to those of 1-methyl- and 3-methyllumichrome and 1,3-dimethyllumichrome. The absorption, emission, and synchronous spectra of lumichrome, 1-methyl- and 3-methyllumichrome, and 1,3-dimethyllumichrome at different pH were measured and used in discussion of fluorescence of neutral and deprotonated forms of lumichrome. The analysis of steady-state and time-resolved spectra and the DFT calculations both predict that the N(1) monoanion and the N(1,3) dianion of lumichrome have predominantly isoalloxazinic structures. Additionally, we confirmed that neutral lumichrome exists in its alloxazinic form only, in both the ground and the excited state. We also confirmed the existence and the alloxazinic structure of a second N(3) monoanion. The estimated values of pK(a) = 8.2 are for the equilibrium between neutral lumichrome and alloxazinic and isoalloxazinic monoanions, with proton dissociation from N(1)-H and N(3)-H groups proceeding at the almost the same pH, while the second value pK(a) = 11.4 refers to the formation of the isoalloxazinic dianion in the ground state.     

New findings regarding the NO angular momentum orientation in Ar-NO(2Π(1/2)) collisions

This article reports a theoretical study of the stereodynamics of Ar + NO(X(2)Π, v = 0, j = 1/2, Ω = 1/2, ε = ±1) rotationally inelastic collisions. First, quantum scattering data are used to calculate all differential polarisation moments of the reagent and product molecules; this leads to the observation that the orientations of the reagent and product angular momenta are very strongly correlated. Next, canonical collision mechanisms theory [Aldegunde et al., Phys. Chem. Chem. Phys., 2008, 10, 1139] is used to separate and characterise the stereodynamics of the two independent collision mechanisms that contribute to the collision dynamics; this leads to the observation that the average product orientation is determined by the relative contributions of the two canonical mechanisms, which have comparable importance but are associated with starkly contrasting angular momentum orientations. These observations lead to a new and rigorous explanation of the experimental results reported a decade ago by Lorenz et al. [Science, 2001, 293, 2063]. The central fact of the new explanation is the incoherent, interference-free superposition of two independent collision mechanisms. This makes the new explanation radically different from the only one previously suggested, namely that the experimental observations might be due to quantum interference in a single collision mechanism.     

Chemical Composition, Antioxidant and Anticancer Effects of the Seeds and Leaves of Indigo (Polygonum tinctorium Ait.) Plant

Seeds and leaves of indigo (Polygonum tinctorium Ait.) plant were investigated and compared with another medicinal plant named prolipid for their properties such as chemical composition, antioxidant, and anticancer effects by Fourier transform infrared, three-dimensional fluorescence spectroscopy, and electrospray ionization-MS in negative mode. It was found that polyphenols, flavonoids, and flavanols were significantly higher in prolipid (P?<?0.05), following by indigo mature leaves, immature leaves, and seeds. Methanol extract of mature indigo leaves in comparison with the ethyl acetate extract showed higher inhibition of proliferation. The interaction between polyphenol extracts of indigo mature leaves and BSA showed that indigo has a strong ability, as other widely used medicinal plants, to quench the intrinsic fluorescence of BSA by forming complexes. In conclusion, indigo mature leaves were compared with prolipid. High content of bioactive compounds, antioxidant, fluorescence, and antiproliferative properties of indigo justifies the use of this plant as a medicinal plant and a new source of antioxidants.