Finikova Olga, Galkin Alexander, Rozhkov Vladimir, Cordero Maria, Hägerhäll Cecilia, Vinogradov Sergei
Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
J Am Chem Soc. 2003 Apr 23;125(16):4882-93. doi: 10.1021/ja0341687.
The pH dependencies of the UV-vis and fluorescent spectra of new water-soluble dendritic porphyrins and tetrabenzoporphyrins were studied. Because of extended pi-conjugation and nonplanar distortion, the absorption and the emission bands of tetraaryltetrabenzoporphyrins (Ar(4)TBP) are red-shifted and do not overlap with those of regular tetraarylporphyrins (Ar(4)P). When encapsulated inside dendrimers with hydrophilic outer layers, Ar(4)Ps and Ar(4)TBPs become water soluble and can serve as pH indicators, with pK's adjustable by the peripheral charges on the dendrimers. Two new dendritic porphyrins, Gen 4 polyglutamic porphyrin dendrimer H(2)P-Glu(4)OH (1) with 64 peripheral carboxylates and Gen 1 poly(ester amide) Newkome-type tetrabenzoporphyrin dendrimer H(2)TBP-Nw(1)OH (2) with 36 peripheral carboxylates, were synthesized and characterized. The pK's of the encapsulated porphyrins (pK(H)()2(P)(-)(Glu)()4(OH) = 6.2 and pK(H)()2(TBP)(-)(Nw)()1(OH) = 6.3) were found to be strongly influenced by the dendrimers, revealing significant electrostatic shielding of the cores by the peripheral charges. The titration curves obtained by differential excitation using the mixtures of the dendrimers were shown to be identical to those determined for the dendrimers individually. Due to their peripheral carboxylates and nanometric molecular size, porphyrin dendrimers cannot penetrate through phospholipid membranes. Dendrimer 1 was captured inside phospholipid liposomes, which were suspended in a solution containing dendrimer 2. No response from 1 was detected upon pH changes in the bulk solution, while the response from 2 was predictably strong. When proton channels were created in the liposome walls, both compounds responded equally to the bulk pH changes. These results suggest that porphyrin dendrimers can be used as fluorescent pH indicators for proton gradient measurements.
研究了新型水溶性树枝状卟啉和四苯并卟啉的紫外可见光谱和荧光光谱的pH依赖性。由于π共轭的扩展和非平面畸变，四芳基四苯并卟啉（Ar(4)TBP）的吸收带和发射带发生红移，且与常规四芳基卟啉（Ar(4)P）的吸收带和发射带不重叠。当被封装在具有亲水性外层的树枝状大分子内部时，Ar(4)P和Ar(4)TBP变得可溶于水，并可作为pH指示剂，其pK值可通过树枝状大分子上的外围电荷进行调节。合成并表征了两种新型树枝状卟啉，即具有64个外围羧酸盐的第4代聚谷氨酸卟啉树枝状大分子H(2)P-Glu(4)OH（1）和具有36个外围羧酸盐的第1代聚（酯酰胺）Newkome型四苯并卟啉树枝状大分子H(2)TBP-Nw(1)OH（2）。发现被封装卟啉的pK值（pK(H)()2(P)(-)(Glu)()4(OH) = 6.2和pK(H)()2(TBP)(-)(Nw)()1(OH) = 6.3）受到树枝状大分子的强烈影响，表明外围电荷对核心有显著的静电屏蔽作用。使用树枝状大分子混合物通过差分激发获得的滴定曲线与单独测定的树枝状大分子的滴定曲线相同。由于其外围羧酸盐和纳米级分子尺寸，卟啉树枝状大分子无法穿透磷脂膜。树枝状大分子1被捕获在磷脂脂质体内，脂质体悬浮在含有树枝状大分子2的溶液中。在本体溶液pH变化时未检测到1的响应，而2的响应如预期的那样强烈。当在脂质体壁上形成质子通道时，两种化合物对本体pH变化的响应相同。这些结果表明，卟啉树枝状大分子可作为用于质子梯度测量的荧光pH指示剂。
