Taraban Marc B, Weerasekare Mahika, Trewhella Jill, Shi Xianfeng, Jeong Eun-Kee, Yu Yihua Bruce
Fischell Department of Bioengineering, University of Maryland, College Park, MD 20742.
Biopolymers. 2012;98(1):50-8. doi: 10.1002/bip.21689. Epub 2011 Jun 23.
Small-angle X-ray scattering (SAXS) was used to monitor peptide hydrogelation with and without the MRI contrast agent gadolinium chelate (Gd(III)-chelate). The gelators are a pair of decapeptides that are self-repulsive but mutually attractive. Gd(III)-chelate was either free or covalently bound to one of the decapeptides. Free and conjugated Gd(III)-chelate have the opposite effects on peptide gelation: free Gd(III)-chelate slows down gelation while having little effect on the cross-sectional area of peptide fibers; covalently conjugated Gd(III)-chelate speeds up gelation and results in peptide fibers with significantly greater cross-sectional area. After 24 h of gelation, the cross-sectional areas of hydrogels with no Gd(III)-chelate, with free Gd(III)-chelate and with conjugated Gd(III) chelate are 3700, 3800, and 6300 Å(2), respectively. Free Gd(III)-chelate is not incorporated into peptide fibers and remains in solution with little effect on MRI intensity upon gelation. In contrast, covalently conjugated Gd(III)-chelate is not only incorporated into peptide fibers, but further aggregates toward the center of the peptide fibers. In conclusion, to visualize hydrogelation using (1)H MRI, it is necessary to conjugate Gd(III)-chelate to the material covalently and use T(2)-weighted imaging.
小角X射线散射（SAXS）用于监测有无磁共振成像造影剂钆螯合物（Gd(III)-螯合物）时肽的凝胶化过程。凝胶剂是一对具有自排斥但相互吸引特性的十肽。Gd(III)-螯合物可以是游离的，也可以共价结合到其中一种十肽上。游离和共轭的Gd(III)-螯合物对肽的凝胶化有相反的影响：游离的Gd(III)-螯合物会减缓凝胶化，而对肽纤维的横截面积影响很小；共价共轭的Gd(III)-螯合物会加速凝胶化，并导致肽纤维的横截面积显著增大。凝胶化24小时后，不含Gd(III)-螯合物、含游离Gd(III)-螯合物和含共轭Gd(III)螯合物的水凝胶的横截面积分别为3700、3800和6300 Å(2)。游离的Gd(III)-螯合物不会掺入肽纤维中，而是留在溶液中，凝胶化时对磁共振成像强度影响很小。相比之下，共价共轭的Gd(III)-螯合物不仅会掺入肽纤维中，还会进一步向肽纤维中心聚集。总之，要使用(1)H磁共振成像来观察水凝胶化过程，有必要将Gd(III)-螯合物共价连接到材料上，并使用T(2)加权成像。
