- Formation of interim by-products in methanogenic degradation of butyrate
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The formation of interim by-products during the methanogenic degradation of butyrate was monitored and analyzed in this study. Two series of experiments were conducted at various butyrate concentrations and under the influence of increased partial pressur
- Fang, Herbert H. P.,Jia, Xiao-Shan
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p. 1791 - 1798
(2007/10/03)
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- The Kinetics of Basic Cleavage of Nitrophenyl Alkanoate Esters by 'Hydroxypropyl-β-cyclodextrin' in Aqueous Solution
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The kinetics of cleavage of m- and p-nitrophenyl alakanoates by 'hydroxypropyl-β-cyclodextrin' (Hp-β-CD) in basic aqueous solution vary significantly with the chain length of the esters (C2 to C10).For both series of esters with short chains (C2 to C6) simple saturation kinetics are observed, indicative of 1:1 (ester:CD) binding and reaction of one molecule of ester with one molecule of Hp-β-CD.For longer chains, there is also a cleavage process involving two molecules of Hp-β-CD.This type of behaviour was not found previously for the same esters reacting with α-CD and with β-CD but it has been observed for some carboxynitrophenyl alkanoates.With the longest esters there is also evidence of productive 1:2 (ester:CD) binding.For the 1:1 binding, there is a linear dependence of the strength on acyl chain length and the close similarity of the dissociation constants for the two series of esters implicate inclusion of the alkyl chains of the esters acyl groups.Transition-state binding is more complex: for the meta-nitro isomers aryl-group inclusion appears dominant whereas for the para isomers there seems to be a switch from aryl-group inclusion to acyl-group inclusion, occurring at a chain length of C6-C7.
- Gadosy, Timothy A.,Tee, Oswald S.
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p. 715 - 722
(2007/10/02)
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- Lactones. 2. Enthalpies of hydrolysis, reduction, and formation of the C4-C13 monocyclic lactones. Strain energies and conformations
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The enthalpies of hydrolysis of the monocyclic lactones from γ-butyrolactone to tridecanolactone were determined calorimetrically, and the acyclic ethyl having the number of atoms were studied in the fashion. The enthalpies of reduction of the lactones to the corresponding α,ω-alkanediols with lithium triethylborohydride also were determined. The enthalpies of formation of the lactones and the ethyl esters were derived from these data. They were converted to values for the gas phase by measuring the enthalpies of vaporization of ethyl esters and of lactones. In the of γ-butyrolactone and δ-valerolactone, the enthalpies of formation were in good accord with the previously reported values determined via combustion calorimetry. The strain energies of the lactones were obtained via isodesmic reactions. Valerolactone had a strain energy of 11 kcal/mol, and the largest strain energy was found with octanolactone (13 kcal/mol). The conformations of γ-butyrolactone and δ-valerolactone were studied via MP2/6-31G* geometry optimizations, and the conformations of the other lactones were studied with use of the molecular mechanics program MM3. The energies of the lactones estimated via molecular mechanics were compared with the experimental results.
- Wiberg, Kenneth B.,Waldron, Roy F.
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p. 7697 - 7705
(2007/10/02)
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- Contrasting Behaviors in the Cleavage of Aryl Alkanoates by α- and β-Cyclodextrins in Basic Aqueous Solution
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The kinetics of ester cleavage of 4-carboxy-2-nitrophenyl alkanoates (C2, C4, C6, C7, C8) in aqueous base containing α- or β-cyclodextrin (α- or β-CD) indicate that for the three longer esters there are processes involving two CD molecules which are quite distinct: with α-CD a 2:1 binding leads to inhibition; with β-CD a second-order process provides catalysis.
- Tee, Oswald S.,Du, Xian-xian
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p. 1837 - 1839
(2007/10/02)
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- CYCLODEXTRIN-CATALYZED HYDROLYSIS OF ESTERS BEARING A HYDROPHOBIC TAIL
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γ-Cyclodextrin-catalyzed hydrolysis of p-nitrophenyl esters bearing a long alkyl chain proceeded with larger rate acceleration than those with a short alkyl chain.Such rate acceleration behavior was not observed with β-cyclodextrin.The results suggest that the esters with a long alkyl chain take a folded structure (Type A) in the γ-cyclodextrin cavity.
- Ueno, Akihiko,Suzuki, Iwao,Hino, Yoshihiro,Suzuki, Atsuko,Osa, Tetsuo
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p. 159 - 162
(2007/10/02)
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