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.
Structure of samferine
Eshbakova,Saidkhodzhaev
, p. 194 - 195 (2004)
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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.
Bavachromanol: A new chalcone from the seeds of Psoralea corylifolia
Suri,Gupta,Dhar,Atal
, p. 336 - 337 (1980)
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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.
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.
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.
Carboxylation of phenol with potassium ethyl carbonate. A new method of synthesis of p-hydroxybenzoic acid
Suerbaev,Akhmetova,Shalmagambetov
, p. 1498 - 1499 (2005)
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Serkerov
, (1973)
Ho et al.
, p. 1059 (1973)
Rostron,Spivey
, p. 3092,3096 (1964)
An Anionic, Chelating C(sp3)/NHC ligand from the Combination of an N-heterobicyclic Carbene and Barbituric Heterocycle
Benaissa, Idir,Gajda, Katarzyna,Vendier, Laure,Lugan, No?l,Kajetanowicz, Anna,Grela, Karol,Michelet, Véronique,César, Vincent,Bastin, Stéphanie
, p. 3223 - 3234 (2021/09/30)
The coordination chemistry of the anionic NHC1-based on an imidazo[1,5-a]pyridin-3-ylidene (IPy) platform substituted at the C5 position by an anionic barbituric heterocycle was studied with d6(Ru(II), Mn(I)) and d8(Pd(II), Rh(I), Ir(I), Au(III)) transition-metal centers. While the anionic barbituric heterocycle is planar in the zwitterionic NHC precursor 1·H, NMR spectroscopic analyses supplemented by X-ray diffraction studies evidenced the chelating behavior of ligand 1-through the carbenic and the malonic carbon atoms in all of the complexes, resulting from a deformation of the lateral barbituric heterocycle. The complexes were obtained by reaction of the free carbene with the appropriate metal precursor, except for the Au(III) complex 10, which was obtained by oxidation of the antecedent gold(I) complex [AuCl(1)]?with PhICl2as an external oxidant. During the course of the process, the kinetic gold(I) intermediate 9 resulting from the oxidation of the malonic carbon of the barbituric moiety was isolated upon crystallization from the reaction mixture. The νCOstretching frequencies recorded for complex [Rh(1)(CO)2] (5) demonstrated the strong donating character of the malonate-C(sp3)/NHC ligand 1-. The ruthenium complex [Ru(1)Cl(p-cymene)] (11) was implemented as a precatalyst in the dehydrogenative synthesis of carboxylic acid derivatives from primary alcohols and exhibited high activities at low catalyst loadings (25-250 ppm) and a large tolerance toward functional groups.
Rapid biosynthesis of phenolic glycosides and their derivatives from biomass-derived hydroxycinnamates
Zhao, Mingtao,Hong, Xulin,Abdullah,Yao, Ruilian,Xiao, Yi
, p. 838 - 847 (2021/02/09)
Biomass-derived hydroxycinnamates (mainly includingp-coumaric acid and ferulic acid), which are natural sources of aromatic compounds, are highly underutilized resources. There is a need to upgrade them to make them economically feasible. Value-added phenolic glycosides and their derivatives, both belonging to a class of plant aromatic natural products, are widely used in the nutraceutical, pharmaceutical, and cosmetic industries. However, their complex aromatic structures make their efficient biosynthesis a challenging process. To overcome this issue, we created three novel synthetic cascades for the biosynthesis of phenolic glycosides (gastrodin, arbutin, and salidroside) and their derivatives (hydroquinone, tyrosol, hydroxytyrosol, and homovanillyl alcohol) fromp-coumaric acid and ferulic acid. Moreover, because the biomass-derived hydroxycinnamates directly provided aromatic units, the cascades enabled efficient biosynthesis. We achieved substantially high production rates (up to or above 100-fold enhancement) relative to the glucose-based biosynthesis. Given the ubiquity of the aromatic structure in natural products, the use of biomass-derived aromatics should facilitate the rapid biosynthesis of numerous aromatic natural products.
MOF-Zn-NHC as an efficient N-heterocyclic carbene catalyst for aerobic oxidation of aldehydes to their corresponding carboxylic acids: Via a cooperative geminal anomeric based oxidation
Babaee, Saeed,Zarei, Mahmoud,Zolfigol, Mohammad Ali
, p. 36230 - 36236 (2021/12/02)
As an efficient heterogenous N-heterocyclic carbene (NHC) catalyst, MOF-Zn-NHC was used in the aerobic oxidation of aryl aldehydes to their corresponding carbocyclic acids via an anomeric based oxidation. Features such as mild reaction conditions and no need for a co-catalyst or oxidative reagent can be considered as the major advantages of the presented method in this study. This journal is