Facultad de Química, Universidad Nacional Autónoma de México, 04510 México D.F., Mexico.
Facultad de Química, Universidad Nacional Autónoma de México, 04510 México D.F., Mexico.
Bioorg Chem. 2021 Aug;113:104993. doi: 10.1016/j.bioorg.2021.104993. Epub 2021 May 18.
Phenylboronic acid (PBA) forms neutral tetrahedral N,O-coordinated 6-membered cyclic complexes with stability constants reaching the values as large as 1.3 × 10 M at pH 7.4 in water with amino phenolic compounds including 2-(2'-hydroxyphenyl)-1H-benzimidazole (HPBI) often used for protein probing and labeling. The crystal structures of isolated complexes demonstrate unusually high for boronate adducts degree of the tetrahedral character of the boron atom with short B-N bonds in agreement with their high solution stability. The complexation of PBA with HPBI, causes a strong enhancement of the fluorescence of the "enol" form of the ligand, increases the affinity of the dye to a protein (bovine serum albumin) and makes more pronounced the shift in emission maximum induced by the protein binding. Similar, but larger effects are observed with an amino HPBI derivative and with a stronger boronic acid benzoxaborole. Thus, the binding constant to the protein about 2 × 10 M for free HPBI increases to 1.2 × 10 M for the complex of 5-amino-HPBI with benzoxaborole making it suitable for an efficient non-covalent protein labeling or bioconjugation.
苯硼酸（PBA）与包括 2-(2'-羟基苯基）-1H-苯并咪唑（HPBI）在内的氨基酚类化合物在 pH 7.4 的水中形成稳定常数高达 1.3×10 M 的中性四面体 N,O 配位六元环配合物，常用于蛋白质探测和标记。分离配合物的晶体结构表明，硼原子的四面体特征程度异常高，硼-氮键较短，这与其在溶液中的高稳定性一致。PBA 与 HPBI 的络合作用导致配体“烯醇”形式的荧光强度大大增强，增加了染料与蛋白质（牛血清白蛋白）的亲和力，并使由蛋白质结合引起的发射最大值的位移更加明显。类似的，但更大的影响也观察到与一个氨基 HPBI 衍生物和一个更强的硼酸苯并恶唑。因此，对于游离的 HPBI，与蛋白质的结合常数约为 2×10 M，对于 5-氨基-HPBI 与苯并恶唑的配合物，其结合常数增加到 1.2×10 M，使其适合用于高效的非共价蛋白质标记或生物偶联。
