- Binding and catalytic properties of 2-0-and 3-o-permethylated cyclodextrins
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Hexakis(3-0-methyl)-α,-cyclodextrin (3α) bound tom-and p-nitrophenolate ions more strongly, whereas hexakis(2-0-methy1)-α- cyclodextrin (2α) bound less strongly than native α-cyclodextrin. ROESY spectra showed that the 3-0-mefhyl groups of 3a interact with the guest protons, whereas 2-0-methyl groups of 2a do not. 3a accelerated and 2a decelerated the cleavage of m-nitrophenyl acetate in an alkaline solution, suggesting that the C(2)-OH of α-cyclodextrin is more catalytic than the C(3)-OH. However, the catalytic effect of 3a was much smaller than that of native a-cyclodextrin. Loss of hydrogen bonding between the C(3)-OH and C(2)-OH by 3-O-permethylation is responsible for the small catalytic effects of 3α. Similar results were obtained for β-cyclodextrin analogs.
- Nagata, Takuya,Yoshikiyo, Keisuke,Matsui, Yoshihisa,Yamamoto, Tatsuyuki
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- Catalytic applications of β-cyclodextrin/palladium nanoparticle thin film obtained from oil/water interface in the reduction of toxic nitrophenol compounds and the degradation of azo dyes
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A supramolecular catalyst of Pd/β-cyclodextrin thin film is synthesized via a facile and one-pot procedure at an oil-water interface. Macrocyclic oligosaccharides of cyclodextrins with glucose units have a wide range of applications due to their hydrophobic and chiral interior. Due to the ability of this supramolecular catalyst to form inclusion complexes with small organic molecules, the as-synthesized catalyst was applied for the reduction of toxic nitroaromatic compounds (p, o, m-nitrophenol and 4-Cl-2-nitrophenol) and the degradation of harmful azo dyes (methyl orange and bismarck brown) with considerable results. This investigation illustrates the change of the catalyst properties in the presence of molecular receptors attached to the catalyst surface.
- Zare Asadabadi, Azam,Hoseini, S. Jafar,Bahrami, Mehrangiz,Nabavizadeh, S. Masoud
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p. 6513 - 6522
(2019/05/10)
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- Synthesis and isolation of non-chromophore cage-rearranged silsesquioxanes from base-catalyzed reactions
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The nucleophilicity of both ortho- and meta-nitrophenolate anions is strong enough to give substituted products, but their basicity also facilitates cage-rearrangement reactions in polyhedral oligomeric silsesquioxanes (POSS). Anions having a stronger basicity, but weaker nucleophilicity, such as CO32-, gave products only from cage-rearrangement, with the cage expansion products being isolable in multi-gram quantities using conventional column chromatography.
- Hanprasit, Sasikarn,Tungkijanansin, Nuttanee,Prompawilai, Arisa,Eangpayung, Supattra,Ervithayasuporn, Vuthichai
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supporting information
p. 16117 - 16120
(2016/10/31)
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- Mechanistic study of Protein Phosphatase-1 (PP1), a catalytically promiscuous enzyme
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The reaction catalyzed by the protein phosphatase-1 (PP1) has been examined by linear free energy relationships and kinetic isotope effects. With the substrate 4-nitrophenyl phosphate (4NPP), the reaction exhibits a bell-shaped pH-rate profile for kcat/KM indicative of catalysis by both acidic and basic residues, with kinetic pKa values of 6.0 and 7.2. The enzymatic hydrolysis of a series of aryl monoester substrates yields a Bronsted βlg of -0.32, considerably less negative than that of the uncatalyzed hydrolysis of monoester dianions (-1.23). Kinetic isotope effects in the leaving group with the substrate 4NPP are 18(V/K)bridge = 1.0170 and 15(V/K) = 1.0010, which, compared against other enzymatic KIEs with and without general acid catalysis, are consistent with a loose transition state with partial neutralization of the leaving group. PP1 also efficiently catalyzes the hydrolysis of 4-nitrophenyl methylphosphonate (4NPMP). The enzymatic hydrolysis of a series of aryl methylphosphonate substrates yields a Bronsted βlg of -0.30, smaller than the alkaline hydrolysis (-0.69) and similar to the βlg measured for monoester substrates, indicative of similar transition states. The KIEs and the βlg data point to a transition state for the alkaline hydrolysis of 4NPMP that is similar to that of diesters with the same leaving group. For the enzymatic reaction of 4NPMP, the KIEs are indicative of a transition state that is somewhat looser than the alkaline hydrolysis reaction and similar to the PP1-catalyzed monoester reaction. The data cumulatively point to enzymatic transition states for aryl phosphate monoester and aryl methylphosphonate hydrolysis reactions that are much more similar to one another than the nonenzymatic hydrolysis reactions of the two substrates.
- McWhirter, Claire,Lund, Elizabeth A.,Tanifum, Eric A.,Feng, Guoqiang,Sheikh, Qaiser I.,Hengge, Alvan C.,Williams, Nicholas H.
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scheme or table
p. 13673 - 13682
(2009/02/06)
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- Do electrostatic interactions with positively charged active site groups tighten the transition state for enzymatic phosphoryl transfer?
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The effect of electrostatic interactions on the transition-state character for enzymatic phosphoryl transfer has been a subject of much debate. In this work, we investigate the transition state for alkaline phosphatase (AP) using linear free-energy relationships (LFERs). We determined fcat/K M for a series of aryl sulfate ester monoanions to obtain the Bronsted coefficient, βIg, and compared the value to that obtained previously for a series of aryl phosphorothioate ester dianion substrates. Despite the difference in substrate charge, the observed Bronsted coefficients for AP-catalyzed aryl sulfate and aryl phosphorothioate hydrolysis (-0.76 ± 0.14 and -0.77 ± 0.10, respectively) are strikingly similar, with steric effects being responsible for the uncertainties in these values. Aryl sulfates and aryl phosphates react via similar loose transition states in solution. These observations suggest an apparent equivalency of the transition states for phosphorothioate and sulfate hydrolysis reactions at the AP active site and, thus, negligible effects of active site electrostatic interactions on charge distribution in the transition state.
- Nikolic-Hughes, Ivana,Rees, Douglas C.,Herschlag, Daniel
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p. 11814 - 11819
(2007/10/03)
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- Kinetics and mechanism of alkaline hydrolysis of aryl carbazates
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Hydrlysis of aryl carbazates (H2NNHCO2Ar with Ar=phenyl, 3- or 4-chlorophenyl, 3- or 4-nitrophenyl, 4-methylphenyl and 4-methoxyphenyl) and/or their 2- or 3-methyl derivatives in aqueous buffers or sodium hydroxide solutions gives phenolate and sodium carbazate. the kinetics and acidity constants and thermodynamic parameters are given.By analysing the pH profiles, the activation entropy, and effects of the substituent on the aromatic ring it was found that aryl carbazates containing a methyl group in the 2 position are hydrolysed by a BAc2 mechanism and the others by an E2cB mechanism.The pH profiles of nitrophenyl carbazates show a maximum.The rate of decarboxylation of carbazic acid decreases with increasing pH value.
- Vlasak, Petr,Mindl, Jaromir
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p. 1401 - 1404
(2007/10/03)
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- SYNTHESIS OF BAPTA-AM ANALOGUES CAPABLE OF ENHANCING THE VASCULAR PRODUCTION OF PROSTACYCLIN
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About 30 analogues of BAPTA-AM, a potential antithrombotic agent, have been synthesized and tested for their effect on the production of prostacyclin.None of them was found to be a better enhancher of the production of prostacyclin by aortic endothelial cells than BAPTA-AM itself.The enhancing effect can be produced by compounds unable to chelate Ca2+, thus confirming that it is not related to their buffering capacity for free Ca2+.
- Heilporn, S.,Broeders, F.,Daloze, D.,Braekman, J. C.,Boeynaems, J. M.
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p. 309 - 320
(2007/10/02)
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- REACTIONS OF IMIDIC ACID DERIVATIVES WITH NUCLEOPHILIC REAGENTS. MECHANISM OF THE ALKALINE HYDROLISIS OF ARYL N-ARYLARENECARBOXIMIDATES
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In the kinetics of the alkaline hydrolysis of aryl-N-phenylbenzimidates PhC(OArX) =NPh(I) in a water-dioxane mixture (1:1 by volume) and with a constant ionic strength in 0.2 M sodium perchlorate first order is observed in each of the reagents.The Hammett ρ and Bronsted β parameters with variation of the substituent in the leaving group are 1.6 and -0.35 respectively.The products from the hydrolysis of compounds (I) (X = 2,4-(NO2)2, 2-NO2-4-COCH3) are benzoic acid and substituted diphenylamines and, in the case of the derivatives of (I) benzanilide and the corresponding phenol.In spite of the different qualitative composition of the hydrolysis products the data for all the substituents (including the ortho substituents) satisfy the Hammett and Bronsted equations.The results are explained in terms of an addition-elimination stage mechanism with the formation of a tetrahedral intermediate product in the rate-determining stage.
- Prudchenko, A. P.,Drizhd, L. P.,Savelova, V. A.
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p. 1715 - 1719
(2007/10/02)
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- The Stereoselective Retardation of the Alkaline Hydrolysis of Organic Esters by Binuclear Cu(II) Complexes with Cyclodextrins
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The alkaline hydrolysis of p-nitrophenyl acetate (p-NPA) in 1.0 mol dm-3 NaOH at 25 deg C was almost completely retarded by the addition of a binuclear Cu(II) complex with α-cyclodextrin Cu2α-CD).The dissociation constant for an inclusion complex of Cu2α-CD with p-NPA was determined to be 0.059 mmol dm-3, which is about one 200th that for an inclusion complex of α-CD with p-NPA.The alkaline hydrolysis of o- and m-nitrophenyl acetates was also retarded by Cu2α-CD, though the extent of retardation was much less than that for p-NPA.A binuclear Cu(II) complex with β-cyclodextrin (Cu2β-CD) also caused a stereoselective deceleration of the alkaline hydrolysis of the esters.However, the stereoselectivity of Cu2β-CD was not so remarkable as that of Cu2α-CD.Dissociation constants for inclusion complexes of Cu2α-CD with several alcohols and other organic substrates were determined by the kinetic examination of the competitive inhibition effect of the substrates on the association of Cu2α-CD with p-NPA.Cu2α-CD formed stable inclusion complexes with such disk-like molecules as cyclohexanol, cycloheptanol, and p-nitrobenzyl alcohol.The geometry of a Cu2α-CD-p-NPA inclusion complex was presumed on the basis of these results.
- Matsui, Yoshihisa,Suemitsu, Daisuke
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p. 1658 - 1662
(2007/10/02)
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