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)
Cleavage of Carboxylic Esters by Aluminum and Iodine
Sang, Dayong,Yue, Huaxin,Fu, Yang,Tian, Juan
, p. 4254 - 4261 (2021/03/09)
A one-pot procedure for deprotecting carboxylic esters under nonhydrolytic conditions is described. Typical alkyl carboxylates are readily deblocked to the carboxylic acids by the action of aluminum powder and iodine in anhydrous acetonitrile. Cleavage of lactones affords the corresponding ω-iodoalkylcarboxylic acids. Aryl acetylates undergo deacetylation with the participation of the neighboring group. This method enables the selective cleavage of alkyl carboxylic esters in the presence of aryl esters.
Biocatalytic Cross-Coupling of Aryl Halides with a Genetically Engineered Photosensitizer Artificial Dehalogenase
Fu, Yu,Huang, Jian,Wu, Yuzhou,Liu, Xiaohong,Zhong, Fangrui,Wang, Jiangyun
supporting information, p. 617 - 622 (2021/02/03)
Devising artificial photoenzymes for abiological bond-forming reactions is of high synthetic value but also a tremendous challenge. Disclosed herein is the first photobiocatalytic cross-coupling of aryl halides enabled by a designer artificial dehalogenase, which features a genetically encoded benzophenone chromophore and site-specifically modified synthetic NiII(bpy) cofactor with tunable proximity to streamline the dual catalysis. Transient absorption studies suggest the likelihood of energy transfer activation in the elementary organometallic event. This design strategy is viable to significantly expand the catalytic repertoire of artificial photoenzymes for useful organic transformations.
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