Sessler Jonathan L, Král Vladimír, Shishkanova Tatiana V, Gale Philip A
Department of Chemistry and Biochemistry and Institute for Cellular and Molecular Biology, University of Texas, Austin, TX 78712-1167, USA.
Proc Natl Acad Sci U S A. 2002 Apr 16;99(8):4848-53. doi: 10.1073/pnas.062633799. Epub 2002 Apr 2.
The synthesis and characterization of two cytosine-substituted calix[4]pyrrole conjugates, bearing the appended cytosine attached at either a beta- or meso-pyrrolic position, is described. These systems were tested as nucleotide-selective carriers and as active components of nucleotide-sensing ion-selective electrodes at pH 6.6. Studies of carrier selectivity were made using a Pressman-type model membrane system consisting of an initial pH 6.0 aqueous phase, an intervening dichloromethane barrier containing the calix[4]pyrrole conjugate, and a receiving basic aqueous phase. Good selectivity for the Watson-Crick complementary nucleotide, 5'-guanosine monophosphate (5'-GMP), was seen in the case of the meso-linked conjugate with the relative rates of through-membrane transport being 7.7:4.1:1 for 5'-GMP, 5'-AMP, and 5'-CMP, respectively. By contrast, the beta-substituted conjugate, while showing a selectivity for 5'-GMP that was enhanced relative to unsubstituted calix[4]pyrrole, was found to transport 5'-CMP roughly 4.5 times more quickly than 5'-GMP. Higher selectivities were also found for 5'-CMP when both the beta- and meso-substituted conjugates were incorporated into polyvinyl chloride membranes and tested as ion selective electrodes at pH 6.6, whereas near-equal selectivities were observed for 5'-CMP and 5'-GMP in the case of unsubstituted calix[4]pyrroles. These seemingly disparate results are consistent with a picture wherein the meso-substituted cytosine calix[4]pyrrole conjugate, but not its beta-linked congener, is capable of acting as a ditopic receptor, binding concurrently both the phosphate anion and nucleobase portions of 5'-GMP to the calixpyrrole core and cytosine "tails" of the molecule, respectively, with the effect of this binding being most apparent under the conditions of the transport experiments.
本文描述了两种胞嘧啶取代的杯[4]吡咯共轭物的合成与表征，其中附加的胞嘧啶连接在β-或中位吡咯位置。这些体系在pH 6.6条件下作为核苷酸选择性载体以及核苷酸传感离子选择性电极的活性成分进行了测试。使用Pressman型模型膜系统进行载体选择性研究，该系统由初始pH 6.0的水相、含有杯[4]吡咯共轭物的中间二氯甲烷屏障以及接收碱性水相组成。对于中位连接的共轭物，观察到对沃森-克里克互补核苷酸5'-鸟苷单磷酸（5'-GMP）具有良好的选择性，5'-GMP、5'-AMP和5'-CMP的跨膜运输相对速率分别为7.7:4.1:1。相比之下，β-取代的共轭物虽然对5'-GMP的选择性相对于未取代的杯[4]吡咯有所增强，但发现其运输5'-CMP的速度比5'-GMP快约4.5倍。当β-和中位取代的共轭物都掺入聚氯乙烯膜中并在pH 6.6条件下作为离子选择性电极进行测试时，对5'-CMP也发现了更高的选择性，而在未取代的杯[4]吡咯情况下，5'-CMP和5'-GMP的选择性几乎相等。这些看似不同的结果与一种情况相符，即中位取代的胞嘧啶杯[4]吡咯共轭物而非其β-连接的同系物能够作为双位点受体，分别将5'-GMP的磷酸阴离子和核碱基部分同时结合到杯吡咯核心和分子的胞嘧啶“尾部”，这种结合的效果在运输实验条件下最为明显。
