Xi:Irritant;
99-96-7Relevant articles and documents
Cyclic voltammetry and computational chemistry studies on the evaluation of the redox behavior of parabens and other analogues
Gil, Eric De S.,Andrade, Carolina H.,Barbosa, Nu?sia L.,Braga, Rodolpho,Serrano, Si?lvia H. P.
, p. 565 - 572 (2012)
Parabens are antimicrobial preservatives widely used in pharmaceutical, cosmetic and food industries. The alkyl chain connected to the ester group defines some important physicochemical characteristics of these compounds, including the partition coefficient and redox properties. The voltammetric and computational analyses were carried out in order to evaluate the redox behavior of these compounds and other phenolic analogues. A strong correlation between chemical substituents inductive effects of parabens with redox potentials was observed. Using cyclic voltammetry and glassy carbon working electrode, only one irreversible anodic peak was observed around 0.8 V for methylparaben (MP), ethylparaben (EP), propylparaben (PP), butylparaben (BP), benzylparaben (BzP) and p-substituted phenolic analogues. The electrodonating inductive effect of alkyl groups was demonstrated by the anodic oxidation potential shift to lower values as the carbon number increases and, therefore the parabens (and other phenolic analogues) oxidation processes to the quinonoidic forms showed great dependence on the substituent pattern.
FONTANESIOSIDE AND 5-HYDROXYSECOLOGANOL FROM FONTANESIA PHILLYREODES
Damtoft, Soeren,Franzyk, Henrik,Jensen, Soeren Rosendal
, p. 705 - 712 (1994)
The iridoid content of Fontanesia phillyreoides was investigated by reverse phase chromotography of the ethanolic extract of the aerial parts.Five known iridoid compounds, i.e. loganic acid, secologanoside, secologanic acide, secologanol and swertiamarin, besides verbascoside were isolated.In addition, two novel secoiridoids, named 5-hydroxysecologanol and fontanesioside, were isolated and characterized.Their structures were determined by NMR spectroscopy and by chemical evidence.
Improved performance of titanate nanostructures for manganese adsorption and posterior pollutants photocatalytic degradation
Sousa, Sara C.A.,Cardoso,Monteiro
, p. 9 - 16 (2019)
In this work, the synthesis of novel manganese-modified titanate nanowires, with enhanced photocatalytic activity for pollutants degradation, is described. Distinct modified titanate nanowires samples were produced by manganese doping (Mn-TNT) and by Mn ion-exchange (TNW/Mn). The characterization of the samples was performed by XRD, DRS, TEM, PL and XPS. The structural characterisation indicates that Mn can be incorporated in the crystalline structure in two distinct positions: replacing some Ti4+ in the TiO6 octahedra and/or replacing Na+ in the interlayers. For the TNW/Mn sample, the Mn was found only in the interlayers. However, for Mn-TNW the metal was present in both possible positions. The produced materials demonstrate to be photo-active in a wider range of radiation then pristine TNW, even starting to absorb in the visible range. The PL and XPS results indicate a decrease on the photogenerated charge carriers recombination for the metal-containing samples. The photocatalytic performance of the modified samples was tested for the hydroxyl radical production. Both Mn modified samples (Mn-TNW and TNW/Mn) demonstrated to be catalytic for this reaction. The photocatalytic degradation of the preservative methyl-paraben, considered an emergent pollutant was also studied. For this process, the results indicate that the mechanism of degradation is dependent on the photocatalyst surface ionic character. The best photocatalytic performance was achieved by the doped Mn-TNW sample, with 62% of removal of a 10 ppm methyl-paraben aqueous solution (0.13 g catalyst/L solution), after 90 min of irradiation.
Amethystin, the coloring principle of Stentor amethystinus
H?fle, Gerhard,Reinecke, Silke,Laude, Uwe,Spitzner, Dietrich
, p. 1383 - 1389 (2014)
Among the ciliates, Stentor amethystinus stands out for its conspicuous red-violet color compared to its blue- and red-colored relatives Stentor coeruleus and Blepharisma japonicum. Rich blooms in German lakes allowed us to collect sufficient organisms to isolate the pigments and elucidate the structure of the main component amethystin (4) by spectroscopic methods as a carboxy derivative of blepharismin. Depending on conditions, the carboxy group appears as an orthoester or as a mixture of the orthoester and small amounts of a hydroxylactone. Derivatives of both isomeric forms were obtained by acetylation and methylation supporting the proposed structures. On reaction of amethystin with base in the presence of oxygen, oxyamethystin and, under vigorous conditions, p-hydroxybenzoic acid were formed. In addition to 4, two homologues, an isomer of amethystin, and stentorin F (1b) were identified in the primary extract. Further, a biosynthetic scheme is proposed linking stentorin, blepharismin, and amethystin type compounds to the hypothetical protostentorin as a common intermediate.
A HYDROXYBUTENOLIDE FROM SPHAGNUM SPECIES
Wilschke, Juergen,Sprengel, Birgit,Wolff, Christian,Rudolph, Hansjoerg
, p. 1725 - 1728 (1989)
One of the main products formed by peroxidative degredation of sphagnum acid in vitro is identified as (-)2,5-dihydro-5-hydroxy-4--furan-2-one, abbreviated as hydroxybutenolide.It seems to be the first report of the isolation of this compound.Peroxidase isozymes isolated from Sphagnum magellanicum have specific preferences in degrading sphagnum acid.Hydroxybutenolide is a naturally occurring component in Sphagnum spp.Occurrin g mainly bound to the cell wall.In contrast to sphagnum acid, hydroxybutenolide is not excreted into the surrounding medium by living Sphagnum plantlets. Key Word Index- Sphagnum magellanicum; Sphagnaceae; bryophyta; sphagnum acid; Degradation; peroxidase; isoenzymes; hydroxybutenoide; cell wall.
The catalytic mechanism of the hotdog-fold enzyme superfamily 4-hydroxybenzoyl-coa thioesterase from arthrobacter sp. Strain SU
Song, Feng,Zhuang, Zhihao,Latham, John,Dunaway-Mariano, Debra,Thoden, James B.,Holden, Hazel M.,Trujillo, Michael
, p. 7000 - 7016,17 (2012)
The hotdog-fold enzyme 4-hydroxybenzoyl-coenzyme A (4-HB-CoA) thioesterase from Arthrobacter sp. strain AU catalyzes the hydrolysis of 4-HB-CoA to form 4-hydroxybenzoate (4-HB) and coenzyme A (CoA) in the final step of the 4-chlorobenzoate dehalogenation pathway. Guided by the published X-ray structures of the liganded enzyme (Thoden, J. B., Zhuang, Z., Dunaway-Mariano, D., and Holden H. M. (2003) J.Biol. Chem. 278, 43709-43716), a series of site-directed mutants were prepared for testing the roles of active site residues in substrate binding and catalysis. The mutant thioesterases were subjected to X-ray structure determination to confirm retention of the native fold, and in some cases, to reveal changes in the active site configuration. In parallel, the wild-type and mutant thioesterases were subjected to transient and steady-state kinetic analysis, and to 18O-solvent labeling experiments. Evidence is provided that suggests that Glu73 functions in nucleophilic catalysis, that Gly65 and Gln58 contribute to transition-state stabilization via hydrogen bond formation with the thioester moiety and that Thr77 orients the water nucleophile for attack at the 4-hydroxybenzoyl carbon of the enzyme-anhydride intermediate. The replacement of Glu73 with Asp was shown to switch the function of the carboxylate residue from nucleophilic catalysis to base catalysis and thus, the reaction from a two-step process involving a covalent enzyme intermediate to a single-step hydrolysis reaction. The E73D/T77A double mutant regained most of the catalytic efficiency lost in the E73D single mutant. The results from 31P NMR experiments indicate that the substrate nucleotide unit is bound to the enzyme surface. Kinetic analysis of site-directed mutants was carried out to determine the contributions made by Arg102, Arg150, Ser120, and Thr121 in binding the nucleotide unit. Lastly, we show by kinetic and X-ray analyses of Asp31, His64, and Glu78 site-directed mutants that these three active site residues are important for productive binding of the substrate 4-hydroxybenzoyl ring.
Controlling structure and porosity in catalytic nanoparticle superlattices with DNA
Auyeung, Evelyn,Morris, William,Mondloch, Joseph E.,Hupp, Joseph T.,Farha, Omar K.,Mirkin, Chad A.
, p. 1658 - 1662 (2015)
Herein, we describe a strategy for converting catalytically inactive, highly crystalline nanoparticle superlattices embedded in silica into catalytically active, porous structures through superlattice assembly and calcination. First, a body-centered cubic (bcc) superlattice is synthesized through the assembly of two sets of 5 nm gold nanoparticles chemically modified with DNA bearing complementary sticky end sequences. These superlattices are embedded in silica and calcined at 350 °C to provide access to the catalytic nanoparticle surface sites. The calcined superlattice maintains its bcc ordering and has a surface area of 210 m2/g. The loading of catalytically active nanoparticles within the superlattice was determined by inductively coupled plasma mass spectrometry, which revealed that the calcined superlattice contained approximately 10% Au by weight. We subsequently investigate the ability of supported Au nanoparticle superlattices to catalyze alcohol oxidation. In addition to demonstrating that calcined superlattices are effective catalysts for alcohol oxidation, electron microscopy reveals preservation of the crystalline structure of the bcc superlattice following calcination and catalysis. Unlike many bulk nanoparticle catalysts, which are difficult to characterize and susceptible to aggregation, nanoparticle superlattices synthesized using DNA interactions offer an attractive bottom-up route to structurally defined heterogeneous catalysts, where one has the potential to independently control nanoparticle size, nanoparticle compositions, and interparticle spacings.
Transesterification reactions of parabens (alkyl 4-hydroxybenzoates) with polyols in aqueous solution
Hensel,Leisenheimer,Muller,Busker,Wolf-Heuss,Engel
, p. 115 - 118 (1995)
Accelerated stability tests of aqueous solutions containing parabens and polyols were performed using concentrations similar to pharmaceutical and cosmetic formulations. Reaction products were detected in these solutions by HPLC and identified by chromatographic and spectroscopic means. Using xylitol and methylparaben as model reactants, three unknown peaks having the relation 1:2:4 were obtained together with the hydrolysis product 4-hydroxybenzoic acid. Diode array detection gave identical UV spectra for each peak with a maximum at 255 nm. The structures of the isomeric 1-, 2-, and 3-xylityl 4- hydroxy-benzoic acid esters were proved by means of LC-MS, GC-MS, and NMR and correlated to the peaks in the HPLC chromatograms. The rate of the transesterification was shown to be highest in strongly alkaline medium (ph 10-11), whereas equilibration of the reaction was optimally balanced at pH 8- 9. An increase of polyol concentration enhanced the formation of the esters. The reactivity of different substituted parabens was higher in the case of parabens with a short alkyl ester function. Similar reaction profiles were observed with C3-C6 polyols, but no transesterification took place when aldoses were used.
Efficient catalytic oxidation of alcohol to carbonyl compounds over CoFe hydrotalcites
Zhou,Pan,Wu,Qian,He,Chen
, p. 84106 - 84112 (2016)
A series of CO32--CoxFe-LDHs (x = 2, 3, 4 and 5) compounds with different Co/Fe ratios have been prepared, characterized and introduced into the selective oxidation of alcohols by tert-butylhydroperoxide. The characterization including XRD, SEM, FTIR, TG/DTG, DR UV-vis, N2 adsorption and XPS showed that the hydrotalcite structure was well formed with different Co/Fe ratios, and the ratio has significant influence on the materials' morphologies, physical properties and the composition of Co2+/Co3+/Fe3+. The effects of varied reaction conditions on the catalytic oxidation have been investigated, and the results indicate that the co-existence of Co2+ and Co3+ is beneficial to the catalytic activity. Comparison experiments showed that substitution of Al with Fe could markedly increase the surface area of the material, and a synergistic effect might exist between Co and Fe in the CoFe hydrotalcites for the alcohol oxidation. In addition, the catalyst also exhibited excellent stability and catalytic performance in the oxidation of varied alcohols.
Evidence from Activation Volumes for an Eliminative Mechanism in the Hydrolysis of 2,4-Dinitrophenyl 4-Hydroxybenzoate
Isaacs, Neil S.,Najem, Tariq
, p. 1361 - 1362 (1984)
A positive volume of activation is found for the hydrolysis of 2,4-dinitrophenyl 4-hydroxybenzoate, differentiating its mechanism from the BAc2 route used by other esters, all of which have been negative values.
