Hydrolysis of lipophilic esters catalyzed by a Zinc(II) complex of a long alkyl-pendant macrocyclic tetraamine in Micellar solution
Hydrolysis of lipophilic esters catalyzed by a Zinc(II) complex of a long alkyl-pendant macrocyclic tetraamine in Micellar solution
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DOI：
10.1021/ja961789
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发表时间：
1996-11-13
影响因子：
15
通讯作者：
Koike, T
中科院分区：
文献类型：
--
作者：
Kimura, E;Hashimoto, H;Koike, T
合成了一种亲脂性的1-十六烷基-1，4，7，10-四氮杂环十二烷锌配合物，该配合物几乎不溶于水，但在Triton X-100表面活性剂存在下变得可溶。在Triton X-100（10 mM）存在下Zn-II-十六烷基大环烯（1 mM）的电位pH滴定分析揭示了Zn-II-结合的H2O的单去质子化，得到OH-桥连络合物（ZnL）（2）OH-（pK（d）= -log（[（ZnL）（2）OH-]a（H+）/[ZnL]（2））= 3.92 +/-0.05）和单体Zn-II-OH-络合物ZnL-OH-（pK（a））= -log（[ZnL-OH-]a（H+）/[ZnL]）= 7.56 +/- 0.05），25 ℃，I = 0.10（NaNO3）。在含有10 mM Triton X-100的共胶束水溶液中，锌（II）配合物（ZnL）对4-硝基苯乙酸酯（NA）、双（4-硝基苯）磷酸酯（BNP-）和三（4-硝基苯）磷酸酯（TNP）的水解具有比母体1，4，7，10-四氮杂环十二烷（cyclen，L '）锌（II）配合物更高的催化活性。Zn-II-十六烷基大环草烯的NA水解活性随着pH增加而增加，并且在pH > 10和25 ℃时趋于平稳，由此估计活性物质是ZnL-OH-络合物。在10 mM Triton X-100存在下，NA水解的二级速率（[NA]和[ZnL-OH-]中的一级速率）（k（NA）= 5.0 +/-0.2 M（-1）s（-1））比在10%（v/v）CH_3CN水溶液中的参比ZnL ′-OH-大50倍。在25 ℃下，在10%（v/v）MeOH水溶液中，用ZnL-OH-和10 mM Triton X-100（k（TNP）=（11 +/- 0.1）x 10（3）M（-1）s（-1））水解TNP的效率是用ZnL '-OH-（3.8 +/- 0.2 M（-1）s（-1））水解的效率的290倍。胶束中亲脂性底物与ZnL-OH-共存时的有效摩尔浓度较高，这是其具有优异催化活性的原因。从与以前报道的金属催化剂相比，本亲脂性锌（II）配合物与十六烷基大环烯可能是最好的候选催化剂有毒的磷酸三酯解毒之一。
A novel lipophilic zinc(II) complex with 1-hexadecyl-1,4,7,10-tetrazacyclododecan (hexadecylcyclen, L) has been synthesized, which is almost insoluble in water, but becomes soluble in the presence of Triton X-100 surfactant. Analysis of the potentiometric pH titration of Zn-II-hexadecylcyclen (1 mM) in the presence of Triton X-100 (10 mM) disclosed monodeprotonation of the Zn-II-bound H2O, yielding an OH--bridged complex (ZnL)(2)OH- (pK(d) = -log([(ZnL)(2)OH-]a(H+)/[ZnL](2)) = 3.92 +/- 0.05) and a monomeric Zn-II-OH- complex ZnL-OH- (pK(a) = -log([ZnL-OH-]a(H+)/[ZnL]) = 7.56 +/- 0.05) at 25 degrees C with I = 0.10(NaNO3). The zinc(II) complex (ZnL) possesses higher catalytic activity than the parent zinc(II) complex of 1,4,7,10-tetrazacyclododecane (cyclen, L') in hydrolysis of 4-nitrophenyl acetate (NA), bis(4-nitrophenyl) phosphate (BNP-), and tris(4-nitrophenyl) phosphate (TNP) in aqueous comicellar solution with 10 mM Triton X-100. The NA hydrolysis activity of Zn-II-hexadecylcyclen increased with the pH and leveled off at pH > 10 and 25 degrees C, from which the active species was estimated to be a ZnL-OH- complex. The second-order rate (first-order in [NA] and [ZnL-OH-]) of NA hydrolysis (k(NA) = 5.0 +/- 0.2 M(-1) s(-1)) in the presence of 10 mM Triton X-100 is 50 times greater than that with a reference ZnL'-OH- in 10% (v/v) CH3CN aqueous solution. Hydrolysis of TNP in 10% (v/v) MeOH aqueous solution with ZnL-OH- and 10 mM Triton X-100 (k(TNP) = (11 +/- 0.1) x 10(3) M(-1) s(-1)) is 290 times more efficient than with ZnL'-OH- (3.8 +/- 0.2 M(-1) s(-1)) at 25 degrees C. The higher effective molarity of the lipophilic substrate coexisting with ZnL-OH- in the micelles accounts for the extraordinary catalytic activity. From comparison with previously reported metal catalysts, the present lipophilic zinc(II) complex with hexadecylcyclen is probably one of the best candidate catalyst for detoxification of poisonous phosphotriesters.