Calculations of chemical structures and photofading of parabens (PHB—4 hydroxybenzoic acid), which are p-hydroxybenzoic acid alkyl esters were performed. These compounds are used as preservatives for the substances u...Calculations of chemical structures and photofading of parabens (PHB—4 hydroxybenzoic acid), which are p-hydroxybenzoic acid alkyl esters were performed. These compounds are used as preservatives for the substances used in cosmetics. The reactivity of these derivatives with an oxidant—singlet oxygen—have been tested with a theoretical method of frontier orbitals. All-valence molecular orbital methods, AM1 and PM3, have been used to calculate frontier electron density for higher occupied HOMO and lower unoccupied LUMO orbitals, which might be sensitive to an electrophilic (with singleton oxygen atom 1O2) or nucleophilic ( superoxide anion radical) attack at a particular atom in a molecule. Using AM1 and PM3, we calculated the reactivity , superdelocalisability and electron density distributions. The obtained superdelocalisability rates allow you to explain the fastness values in different chemical molecules. The structure of parabens (PHB) was optimized by MM+, DM, AM1 or PM3, to achieve constant energy values at a convergence criterion of 0.01 kcal/mol. The performed calculations indicate that the electrophilic oxidation reaction should take place in the aromatic ring in the 2-position to the hydroxyl residue of PHB, whereas the superoxide radical reaction occurs mainly on the alkyl residues of the ester group. The reaction may take place according to superoxide mechanism or 1,2-addition, where the higher superdelocalisability values SN are located on neighboring atoms in aromatic systems.展开更多
The effect of simulated silk compounds- amino acids and their yellowing substances onphotofading of ary1methane dyes.and the influence of external factors such as oxygen.pH-value.the wave band of light source and nick...The effect of simulated silk compounds- amino acids and their yellowing substances onphotofading of ary1methane dyes.and the influence of external factors such as oxygen.pH-value.the wave band of light source and nickel salt on phototfading of the dyes on real silkare investigated. The results show that tryptophan and tyrosine well as their yellowing sub-stances accelerate photofading of arylmethane dyes;the photofading process of arylmethandyes on real silk is a photooxidation process and external factors exert different influences onit.展开更多
文摘Calculations of chemical structures and photofading of parabens (PHB—4 hydroxybenzoic acid), which are p-hydroxybenzoic acid alkyl esters were performed. These compounds are used as preservatives for the substances used in cosmetics. The reactivity of these derivatives with an oxidant—singlet oxygen—have been tested with a theoretical method of frontier orbitals. All-valence molecular orbital methods, AM1 and PM3, have been used to calculate frontier electron density for higher occupied HOMO and lower unoccupied LUMO orbitals, which might be sensitive to an electrophilic (with singleton oxygen atom 1O2) or nucleophilic ( superoxide anion radical) attack at a particular atom in a molecule. Using AM1 and PM3, we calculated the reactivity , superdelocalisability and electron density distributions. The obtained superdelocalisability rates allow you to explain the fastness values in different chemical molecules. The structure of parabens (PHB) was optimized by MM+, DM, AM1 or PM3, to achieve constant energy values at a convergence criterion of 0.01 kcal/mol. The performed calculations indicate that the electrophilic oxidation reaction should take place in the aromatic ring in the 2-position to the hydroxyl residue of PHB, whereas the superoxide radical reaction occurs mainly on the alkyl residues of the ester group. The reaction may take place according to superoxide mechanism or 1,2-addition, where the higher superdelocalisability values SN are located on neighboring atoms in aromatic systems.
文摘The effect of simulated silk compounds- amino acids and their yellowing substances onphotofading of ary1methane dyes.and the influence of external factors such as oxygen.pH-value.the wave band of light source and nickel salt on phototfading of the dyes on real silkare investigated. The results show that tryptophan and tyrosine well as their yellowing sub-stances accelerate photofading of arylmethane dyes;the photofading process of arylmethandyes on real silk is a photooxidation process and external factors exert different influences onit.
