Spin-labeled pH-sensitive phospholipids for interfacial pKa determination: synthesis and characterization in aqueous and micellar solutions.
Spin-labeled pH-sensitive phospholipids for interfacial pKa determination: synthesis and characterization in aqueous and micellar solutions.
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用于界面 pKa 测定的自旋标记 pH 敏感磷脂：水溶液和胶束溶液中的合成和表征。
DOI：
10.1021/jp810993s
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发表时间：
2009
期刊：
影响因子：
--
通讯作者：
Smirnov,AlexI
中科院分区：
文献类型：
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作者：
Voinov,MaximA;Kirilyuk,IgorA;Smirnov,AlexI
自旋标记磷脂 (SLP) 的合成和表征 - 1,2-二棕榈酰基-sn-甘油-3-磷酸硫代乙醇 (PTE) 的衍生物 - 以及共价连接到脂质极性头基上的 pH 报告氮氧化合物正在被报道。通过 PTE 与硫醇特异性、pH 敏感的甲硫基磺酸盐自旋标记甲硫基磺酸 S-(1-氧基-2,2,3,5,5-五甲基咪唑烷-4-基甲基)酯 (IMTSL) 反应合成两种脂质和S-4-(4-(二甲基氨基)-2-乙基-5,5-二甲基-1-氧基-2,5-二氢-1H-咪唑-2-基)甲硫代磺酸苄酯(IKMTSL)。通过 EPR 滴定在不同成分的水性缓冲液/异丙醇溶液中测量的 IMTSL-PTE 脂质的 pKa 值基本相同 (pKa ≈ 2.35)，表明在混合的水性/有机溶剂中，两亲性脂质分子可以通过溶剂分子的局部外壳来保护其免受本体条件变化的影响。为了克服这个问题，通过合成 IMTSL-和 IKMTSL−2-巯基乙醇加合物来模拟自旋标记的脂质。这些模型化合物在水性缓冲液中产生的 IMTSL−PTE 和 IKMTSL−PTE 的固有 pKa0 分别为 3.33 ± 0.03 和 5.98 ± 0.03。在水/异丙醇混合溶液中对 IMTSL−PTE 进行一系列 EPR 滴定，可以校准极性引起的 pKashifts、ΔpKapol 与本体溶剂介电常数的关系。这些校准数据可以估计掺入非离子 Triton X-100 胶束中的 IMTSL−PTE 脂质的报告氮氧自由基的局部介电常数 εeff，在 23 °C 和 48 °C 下分别为 60 ± 5 和 57 ± 5。对于由阴离子表面活性剂十二烷基硫酸钠 (SDS) 形成的胶束，静电诱导的 pKa 偏移，ΔpKael= 2.06 ± 0.04 pH 单位，通过减去极性诱导的贡献获得。这种转变产生了 SDS 胶束表面的 Ψ = -121 mV 电势。
The synthesis and characterization of spin-labeled phospholipids (SLP)derivatives of 1,2-dipalmitoyl-sn-glycero-3-phosphothioethanol (PTE)with pH-reporting nitroxides that are covalently attached to the lipid’s polar headgroup are being reported. Two lipids were synthesized by reactions of PTE with thiol-specific, pH-sensitive methanethiosulfonate spin labels methanethiosulfonic acidS-(1-oxyl-2,2,3,5,5-pentamethylimidazolidin-4-ylmethyl) ester (IMTSL) andS-4-(4-(dimethylamino)-2-ethyl-5,5-dimethyl-1-oxyl-2,5-dihydro-1H-imidazol-2-yl)benzyl methanethiosulfonate (IKMTSL). The pKavalues of the IMTSL−PTE lipid measured by EPR titration in aqueous buffer/isopropyl alcohol solutions of various compositions were found to be essentially the same (pKa≈ 2.35), indicating that in mixed aqueous/organic solvents, the amphiphilic lipid molecules could be shielded from changing bulk conditions by a local shell of solvent molecules. To overcome this problem, the spin-labeled lipids were modeled by synthesizing IMTSL- and IKMTSL−2-mercaptoethanol adducts. These model compounds yielded the intrinsic pKa0’s for IMTSL−PTE and IKMTSL−PTE in aqueous buffers as 3.33 ± 0.03 and 5.98 ± 0.03, respectively. A series of EPR titrations of IMTSL−PTE in mixed water/isopropyl alcohol solution allowed for calibrating the polarity-induced pKashifts, ΔpKapol, vs bulk solvent dielectric permittivity. These calibration data allowed for estimating the local dielectric constant, εeff, experienced by the reporter nitroxide of the IMTSL−PTE lipid incorporated into the nonionic Triton X-100 micelles as 60 ± 5 and 57 ± 5 at 23 and 48 °C, respectively. For micelles formed from an anionic surfactant sodium dodecyl sulfate (SDS) the electrostatic-induced pKashift, ΔpKael= 2.06 ± 0.04 units of pH, was obtained by subtracting the polarity-induced contribution. This shift yields Ψ = −121 mV electric potential of the SDS micelle surface.