Effect Of Substitution Site Research Articles

Partial substitution of magnesium in lanthanum manganite perovskite for nitric oxide oxidation: The effect of substitution sites

Lanthanum manganite (LaMnO3) with magnesium (Mg) substituted the A- and B-sites were reported for the first time in this work. The Mg substituted LaMnO3 catalysts were prepared by means of citric acid sol–gel method. The impact of partial substitution of Mg and its substitution site on the catalytic performance of LaMnO3 in nitric oxide (NO) oxidation was investigated. Through series of characterizations, it was found that Mg substitution at both A- and B-sites improves the specific surface area, Mn4+ content, reactivity of surface oxygen species, redox property and NO adsorption capacity of LaMnO3. However, Mg substitution at the A-site of LaMnO3 can cause the total charge imbalance of B-site, which significantly improves the amount and reactivity of surface active oxygen species. Therefore, the catalytic activity of the samples decreases in the order: La0.9Mg0.1MnO3 > LaMn0.9Mg0.1O3 > LaMnO3. This study will shed more light on the fundamental understanding and designing of perovskite catalyst.

Effect of substitution site on two-photon absorption and excited States properties of lipid droplets detection NAPBr dyes: A theoretical perspective

Two-photon fluorescence dyes have shown promising applications in biomedical imaging. However, the substitution site effect on geometric structures and photophysical properties of fluorescence dyes is rarely illustrated in detail. In this work, a series of new lipid droplets detection dyes are designed and studied, molecular optical properties and non-radiative transitions are analyzed. The intramolecular weak interaction and electron-hole analysis reveal its inner mechanisms. All dyes are proven to possess excellent photophysical properties with high fluorescence quantum efficiency and large stokes shift as well as remarkable two-photon absorption cross section. Our work reasonably elucidates the experimental measurements and the effects of substitution site on two-photon absorption and excited states properties of lipid droplets detection NAPBr dyes are highlighted, which could provide a theoretical perspective for designing efficient organic dyes for lipid droplets detection in biology and medicine fields.

Design of birefringence and its wavelength dispersion for cellulose derivatives using substitution, low-mass additives, and porous structures

Birefringence and its wavelength dependence are important properties for optical applications, such as liquid crystal displays and pick-up lenses. Cellulose esters, which are eco-friendly materials from biomass resources, have been used in optical materials due to their transparency and heat resistance. This review summarized our recent works on birefringence control of cellulose esters by substitution of multiple ester groups, addition of low-mass molecules, and formation of a porous structure. Cellulose acetate propionate (CAP), which has acetyl and propionyl groups in a pyranose unit, exhibited positive birefringence with extraordinary wavelength dispersion owing to contributions from its two esters, while cellulose triacetate (CTA) showed negative birefringence with ordinary dispersion. Moreover, the effect of substitution sites (C-2, C-3, and C-6) on birefringence and its wavelength dependence was investigated by comparing birefringence data of CTA and xylan acetate. The addition of low-mass molecules improved the value of birefringence due to the intermolecular orientation correlation with the matrix cellulose esters. The anisotropic porous structure in CTA films, which was prepared by thermoinduced phase separation, generated extraordinary wavelength dispersion of birefringence. We successfully controlled birefringence and its wavelength dispersion of cellulose esters by choosing different ester substitution groups and sites, controlling the orientation of the crystal, adding low-mass molecules, and forming microscale porous structures. The substitution of two ester groups could provide extraordinary wavelength dispersion of birefringence, which is important for wide-range retardation films. The low-mass additives enhance birefringence values due to the intermolecular orientation correlation with matrix cellulose esters. The anisotropic microporous structure produced by thermoinduced phase separation generates form birefringence, which improves the total birefringence of cellulose esters.

Around the macrolide – Impact of 3D structure of macrocycles on lipophilicity and cellular accumulation

The aim of this study was to investigate lipophilicity and cellular accumulation of rationally designed azithromycin and clarithromycin derivatives at the molecular level. The effect of substitution site and substituent properties on a global physico-chemical profile and cellular accumulation of investigated compounds was studied using calculated structural parameters as well as experimentally determined lipophilicity. In silico models based on the 3D structure of molecules were generated to investigate conformational effect on studied properties and to enable prediction of lipophilicity and cellular accumulation for this class of molecules based on non-empirical parameters. The applicability of developed models was explored on a validation and test sets and compared with previously developed empirical models.

Multichromic polymers of benzotriazole derivatives: Effect of benzyl substitution

Two electroactive monomers 1-benzyl-4,7-di(thiophen-2-yl))-2H-benzo[d][1,2,3]triazole (BBTA) and 2-benzyl-4,7-di(thiophen-2-yl))-2H-benzo[d][1,2,3]triazole (BBTS) were synthesized with satisfactory yields. The effect of substitution site on electrochemical and optical properties was investigated with cyclic voltammetry and spectroelectrochemical studies. Results showed that position of pendant group alters the electronic structure of the resulting polymer causing different optical and electrochemical behaviors. Symmetrically positioned benzyl unit on benzotriazole moiety resulted in a neutral state red polymer, PBBTS, having multi-colored property in its different oxidized and reduced states. Its analogue PBBTA exhibited maximum absorption at 390nm in its neutral state and also revealed multicolored electrochromic property upon stepwise oxidation. Very different optical band gap values were calculated: 1.55eV and 2.25eV for PBBTS and PBBTA, respectively.

The study on Zn and Ni substituted GdBaSrCu 3O 7−δ superconductor

The effects of Zn and Ni substitution are interesting because of the contrast in magnetic properties of these elements. In this study, GdBaSr(Cu 3− x M x )O 7− δ samples (M = Zn and Ni; 0 ⩽ x ⩽ 0.1) were prepared via solid-state reaction. Four point probes were used for resistance versus temperature measurement. Results show decrease in T c with increase of x contents for both dopants. This variation is assumed to be irrelevant to the different of phases or impurity effects since X-ray patterns show all samples are in tetragonal single-phase. Decrease of T c is related to the disruption of spin correlation of the CuO 2 planes. The doping only affects the T c without changes the transition width for both dopants. It was suggested that Zn and Ni substitution do not affect the magnitude of the spin gap in the ladder but change the number of spin-singlet pairs. However, Zn doping depresses the T c more obviously than Ni doping. It is suggested that Zn as a non-magnetic dopant might induce more unpaired hole carriers. Moreover, the effect of substitution site by both dopants will also be discussed.

Gas transport in modified polysulfones with trimethylsilyl groups: effect of substitution site

Trimethylsilyl (TMS) groups were chemically introduced on to the phenylene group of bisphenol-A polysulfone (PSf) at sites ortho to ether (EM3) or to sulfone (SM3) linkages. Gas permeabilities increased by substitution of TMS and especially oxygen permeability increased from 1.1 barrer for PSf to 4.2 barrer for SM3 and to 7.1 barrer for EM3. Perm-selectivity of oxygen to nitrogen decreased from 5.8 to 5.5 and therefore substitution of TMS on polysulfone resulted in improved gas transport properties. In addition, it was found that EM3 is more effective in enhancing the gas transport properties than SM3. In order to interpret the effect substitution site on gas transport, d-spacing was investigated in terms of interchain packing. Furthermore, the effect of substitution site on chain motion was investigated through dynamic mechanical analyzer (DMA), dielectric analyzer (DEA), and solid-state NMR. DMA and DEA experiments showed that motions of unsubstituted phenylene and sulfonyl linkage are much more hindered in SM3 than in EM3. NMR experiments showed that motion of TMS is more mobile in EM3 than in SM3. These results revealed that chain motions of SM3 are more hindered than those of EM3 and substitution site affects chain motions. Therefore, we can conclude that these changes in chain motion also gas transport in modified polysulfones with silyl side group.

Effect of substitution site upon the oxidation potentials of alkylanilines, the mutagenicities of N-hydroxyalkylanilines, and the conformations of alkylaniline-DNA adducts.

Carcinogenic arylamines typically undergo metabolic activation via N-hydroxylation followed in most instances by O-esterification. In this study, the ability of methyl-, dimethyl-, and ethylaniline constituents of tobacco smoke to undergo oxidation at the nitrogen atom was analyzed. In addition, the mutagenicity of the corresponding N-hydroxyalkylanilines and the conformational properties of the DNA adducts generated from their N-acyloxy derivatives were investigated. All the arylamines underwent irreversible electrochemical N-oxidation at potentials higher than those observed for the oxidation of carcinogenic polynuclear aromatic amines. There were minor differences in the oxidation potentials, which were consistent with the position and electron-donating abilities of the alkyl substituents; however, the differences appeared to be too small to account for the range of genotoxic effects among the alkylanilines. N-Hydroxyarylamines containing p-alkyl substituents had increased mutagenicities in Salmonella typhimurium TA100, which was attributed to their higher efficiencies of adduct formation. Increased mutagenicities were also observed upon o-alkyl substitution; however, this property was not related to a greater ability of the ortho-substituted species to form DNA adducts, which suggested that adducts from ortho-substituted alkylanilines may be intrinsically more mutagenic than their meta- and para-substituted analogues. In all instances, N-(acyloxy)-arylamines generated from the N-hydroxyarylamines reacted with dG, dG nucleotides, and DNA to yield C8-substituted dG derivatives as the major adducts. The alkylaniline-dG adducts displayed distinct conformational trends that were determined by the location of the alkyl substituents. Spectroscopic data indicated higher percentages of low-energy syn conformers in the adducts that contained alkyl groups ortho to the arylamine nitrogen as opposed to adducts not bearing ortho substituents. The data strongly suggest that the conformational properties of the DNA adducts, in particular their ability to adopt syn conformations, may be determinant factors for the genotoxic responses elicited by certain alkylanilines (e.g., 2-methylaniline and 2,6-dimethylaniline).